
                 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
                           WASHINGTON, D. C.  20460
                                       
              OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION
                                       
                         ENVIRONMENTAL RISK BRANCH III
                   ENVIRONMENTAL FATE & EFFECTS DIVISION
                         OFFICE OF PESTICIDE PROGRAMS


                                                   PC CODE: 060101
                                                             DP BARCODE: 410836     
MEMORANDUM 						       DATE:  April 10, 2014


SUBJECT: 	EFED Risk Assessment for the Proposed New Uses of Thiabendazole as a Seed Treatment for Several Crop Groups, and an Increased Application Rate for Soybean Seed Treatment

TO:		Tony Kish, Product Manager (RM 23)
		Rosemary Kearns, Reviewer
		Fungicide Branch
		Registration Division (7505P)

FROM: 	Nick Mastrota, Ph.D., Wildlife Biologist 
		James K. Wolf, Ph.D., Environmental Scientist
		Environmental Risk Branch III
		Environmental Fate and Effects Division (7507P)	
		
THRU:	Dana Spatz, Branch Chief
		James Hetrick, Ph.D., Senior Science Advisor
		Melissa Panger, Ph.D., Senior Biologist
      Rosanna Louie-Juzwiak, RAPL
            Environmental Risk Branch III
      Environmental Fate and Effects Division (7507P)

			
EFED has completed an assessment of the ecological exposure and potential risks associated with the proposed additional seed treatment uses of thiabendazole on root vegetables (except sugar beet) (Subgroup1B); onion, bulb (Subgroup 3-07A); brassica, head and stem (Subgroup 5A); cucurbit (Group 9); alfalfa; spinach (including baby), and small grains cereals (wheat, barley, oats, rye, and triticale), as well as an increase in the maximum seed treatment rate for soybean. 

The ecological risk assessment concluded that all of the proposed new uses could pose a risk to mammals because of potential chronic toxic effects resulting from consumption of treated seeds (risk quotients (RQ) of 1.1 to 44.2). All of the proposed new uses except soybean and some root vegetables (e.g., radish) may also pose a risk to birds because of chronic toxic effects (RQs 1.43 to 11.5), although these RQs may overestimate risk because they were based on NOAECs from chronic avian tests that were conducted at dietary residue levels less than those predicted on many of the treated seeds. These chronic avian studies set the NOAEC at the highest dietary concentration tested, but testing at higher levels could establish higher NOAECs, which would decrease the RQ values. A few cucurbit uses (e.g., cucumbers and muskmelons) also may pose an acute risk to birds. For many of the new uses, RQs for acute toxicity exceed the endangered species level of concern for birds, but not for mammals. These conclusions are based on exposure through direct consumption of treated seeds. Species that do not consume seeds would have much less exposure and may not be at risk.

The proposed seed treatment uses are expected to result in very little exposure to aquatic organisms and nontarget terrestrial plants. Risk to all aquatic organisms and all terrestrial plants is expected to be minimal.

Available ecotoxicity data were adequate to assess the ecological risks associated with the proposed new seed treatment uses.  However, it should be noted that information about avian acute oral toxicity to passerines (850.2100) and effects on avian reproduction (850.2300) at dietary concentrations above 400 mg a.i./kg is not available from the current thiabendazole ecotoxicity database.

                      ECOLOGICAL RISK ASSESSMENT FOR THE

                  Registration of New Uses for Thiabendazole
                                       
                                PC Code: 060101


                     Proposed New Seed  - Treatment Use: 

   *                       Root vegetables (except sugar beet), Subgroup1B
   *                       Onion, bulb; Subgroup 3-07A
   *                       Brassica, head and stem; Subgroup 5A
   *                       Cucurbit, Group 9
   *                       Alfalfa
   *                       Spinach (including baby)
   *                       Small grains cereals (wheat, barley, oats, rye, and triticale)
   *                       Soybean (increased application rate)
                                       
                                       
                                       
                      End Use Product: 
Mertect[(R)] 340-F
                                       
                                       
   
Table of Contents

I.	Problem Formulation	3
A.	Nature of Chemical Stressor	3
B.	Mode of Action	3
C.	Structure and Physical-Chemical Characteristics	3
D.	Overview of Pesticide Usage	3
E.	Uncertainties	3
II.	Environmental Fate and Transport	3
A.	Transformation Products	3
B.	Bioaccumulation	3
III.	Estimation of Exposure	3
A.	Aquatic Exposure Modeling	3
B.	Water Monitoring Data	3
C.	Terrestrial Exposure Modeling	3
1.	Oral Exposure from Consumption of Treated Seed	3
2.	LD50 per Square Foot Analysis	3
3.	Exposure Modeling for Non-Target Plants	3
IV.	Ecological Effects Characterization	3
V.	Risk Characterization	3
A.	Aquatic Organisms	3
B.	Terrestrial Organisms	3
1.	Oral Exposure from  Consumption of Treated Seeds	3
2.	LD50 per Square Foot Analysis	3
3.	Terrestrial Plants	3
VI.	Risk Discussion and Conclusions	3
VII.	References	3
Appendix A.  Thiabendazole degradates identified in Environmental Fate Studies	3
Appendix B.  Thiabendazole and Its Environmental Degradates	3
Appendix C.  GENEEC2 Model Outputs	3
Appendix D.  Output from Terrestrial Exposure Model (T-REX)	3
Appendix E.  Output from Terrestrial Plant Risk Model (TerrPlant)	3
Appendix F.  Ecotoxicity Data	3



Problem Formulation

Nature of Chemical Stressor

Thiabendazole is a fungicide used to control fungal diseases in germinating seeds.  It is currently registered for treatment of seeds of clover, corn, garbanzo (including chickpea), lentil, peas, and soybean, and treatment of seed pieces of potato and sweet potato.  This ecological risk assessment evaluates expanding the crop group uses registered for the product Mertect[(R)] 340-F Fungicide (EPA Reg. No. 100-889) to include the following crops and crop groups:

   * Root vegetables (except sugar beet), Subgroup1B
   * Onion, bulb; Subgroup 3-07A
   * Brassica, head and stem; Subgroup 5A
   * Cucurbit, Group 9
   * Alfalfa
   * Spinach (including baby)
   * Small grains cereals (wheat, barley, oats, rye, and triticale)

In addition, the risk assessment evaluates the proposed increase of the maximum seed treatment application rate for soybean from 0.005 lb a.i./100 lb seed to 0.020 lb a.i./100 lb seed (or 0.0087 lb a.i./A to 0.033 lb a.i./A).


Mode of Action

Thiabendazole is a systemic fungicide. The mode of action of thiabendazole inhibits the mitosis of plant pathogenic fungi species by preventing the polymerization of beta-tubulins. Because dimers of beta-tubulin and alpha-tubulin polymerize to form microtubule structures inside the cells, thiabendazole acts as an inhibitor of microtubuline polymerization, terminating cell division.


Structure and Physical-Chemical Characteristics

The CAS name for thiabendazole is 2-(4-Thiazolyl)-1H-benzimidazole, the CAS No. 148-79-8. The IUPAC name is 4-(1H-benzimidazol-2-yl)-1,3-thiazole.  Figure 1 shows the chemical structure of thiabendazole.  Select physical-chemical characteristics are provided for thiabendazole in Table 1.




                                       

Figure 1.  Chemical Structure of Thiabendazole


Table 1.  Physical and Chemical Properties of Thiabendazole
Parameter
                                     Value
                                  Description
                                    Source
                                   (MRID #)
                     Selected Physical/Chemical Parameters
Molecular mass 
201.1 g/mol 
                                      --
                                 (Calculated)
Molecular formula
C10H7N3S
                                      --
                                       
Vapor pressure (25°C)
3.45 x 10[-9] mm Hg 
4.0 x 10[-9]  mm Hg
                                      --
                                   48354601
                           Thiabendazole RED (2002)
Henry's Law Constant (25°C)
 3.26 x10[-11] atm-m[3]/mol
                                      --
                                 (Calculated)
Dissociation Constants
pKa1 = 4.5
pKa2 = 12.01
                                      --
                                   48354604
                                   40947302
Aqueous solubility 
Buffered solution (25C) at   pH 5:  30 mg/L
pH 7:  28 mg/L
pH 9:  28 mg/L

Water:  22.74 mg/L
Buffer solution (20C) at:
pH4:     79.82 mg/L
pH7:     22.77 mg/L
pH10:   23.75 mg/L
                                      --
                                    40947301
                                       
                                       
                                       
                                       
                                   48354601
                                   48354604
                                       
Log octanol-to-water partition coefficient (log KOW)
1.61
@ Room temperature = 16.6°C
                                   48254601
                                   48354604
[a] Transformation rates of thiabendazole: pH 5 (-0.0019 days[-1]); pH 7 (-0.0035 days[-1]); pH 9 (-0.0026 days[-1])


Overview of Pesticide Usage

Mertect[(R)] 340-F (42.3% thiabendazole) is applied to crop seeds as a water-based slurry using standard seed treatment equipment. Treated seeds may be planted at any time of the year. Only one application (i.e., one planting of treated seed) may be made per crop cycle; however, in some regions, more than one may occur per year. The maximum seed treatment rates defined on the label are given in Table 2. 

Table 2.  Maximum Application Rates for Proposed New Seed Treatment Uses of Thiabendazole
Crop or Crop Group
Crop Group ID
                           Max. Seed Treatment Rate


                                 mg a.i./seed
                         fl oz product per 100 lb seed
                                  lb a.i. per
                                  100 lb seed
Alfalfa
NA
                                     0.004
                                      5.8
                                    0.18578
Cereals, Small Grain[a]
    Barley
NA
                                     0.03
                                      2.6
                                    0.08328
    Oat
NA
                                     0.03
                                      3.4
                                    0.10891
    Rye
NA
                                     0.03
                                      3.2
                                    0.1025
    Triticale
NA
                                     0.03
                                      2.6
                                    0.08328
    Wheat
NA
                                     0.03
                                      3.1
                                    0.09930
Brassica, head and stem
Subgroup 5A
                                     0.002
                                     ND[b]
                                      ND
Cucurbit
Group 9
                                      0.1
                                      ND
                                      ND
Onion, bulb
Subgroup 3-07A
                                     0.002
                                      ND
                                      ND
Root vegetables 
(except sugar beet)
Subgroup 1B
                                     0.002
                                      ND
                                      ND
Spinach
NA
                                     0.006
                                      ND
                                      ND
[a] "Small grains" is not designated as an EPA crop group.
[b]  "ND" designates that the value is not defined by the product label.

In addition to adding these new uses, the proposed label for Mertect[(R)] 340-F Fungicide would increase the maximum seed treatment rate for soybean (for control of Fusarium spp. fungal diseases) by approximately four times. The maximum seed treatment rate for soybeans would increase from 0.0052 lb a.i./100 lb seed to 0.020 lb a.i./100 lb seed. Assuming a maximum seeding rate of 166.7 soybean seeds per acre (USEPA, 2011), the maximum rate for soybean seed treatment would change from 0.0087 lb a.i./A to 0.033 lb a.i./A.

The seed treatment rates provided on the label define the maximum amount of active ingredient that can be applied per seed. To convert this to rates in terms of pounds of active ingredient per acre, these seed treatment rates need to be multiplied by the seeding rates (number of seeds per acre). Maximum seeding rates for a variety of crops were defined by the Biological and Economical Analysis Division (USEPA, 2011). These values are used in the conversion calculations and the resulting application rates (in lb a.i./A) are shown in Table 3. It is EFED's understanding that the registrant of Mertect[(R)] 340-F (Syngenta Crop Protection) has agreed to put on the label a statement which would restrict the maximum allowable annual application rate for any seed treatment to 0.15 lb a.i./A per year. This is similar to the maximum single application rate on the current label for wheat (assuming the maximum seeding rate for wheat proposed by Syngenta), whereas the maximum single rates for other seed treatment crops is expected to be less than this. Therefore, this risk assessment will use the calculated rates shown in Table 3 as the maximum single application rate, and 0.15 lb a.i./A as the maximum annual rate for all crops. 

Table 3.  Conversion of Proposed Seed Treatment Rates to Pounds of Active Ingredient per Acre
Crop Group
                           Max. Seed Treatment Rate
Representative Crops
                                 Seeding Rates
                               (# seeds/acre)[b]
                                Max. Appl. Rate
                              (lbs a.i./acre)[c]

                               fl. oz. product/
                                100 lb seed[a]
                                mg a.i./seed[a]

                                       
                                       
Alfalfa
5.8
0.004 
Alfalfa
                                   3,405,000
                                     0.030
Cereals (small grains)
2.6
0.03
Barley
                            1,222,000 to 1,300,000
                                     0.086

3.4
0.03
Oats
                                   1,305,000
                                    0.0863

3.2
0.03
Rye
                                   1,962,000
                                     0.130

2.6
0.03
Triticale
                                   1,744,000
                                     0.115

3.1

0.03

Wheat
Wheat, winter
                                 2,250,000[d]
                             600,000 to 1,350,000 
                                     0.149
                                     0.089
Brassica, head and stem
-
0.002
Broccoli
                               8,297 to 210,845
                                    0.00093



Cabbage
                                7,260 to 98,010
                                    0.00043
Bulb Vegetables
-
0.002
Onion
                              87,120 to 1,254,528
                                    0.0055



Garlic
                                261,360-392,040
                                    0.0017
Cucurbit Vegetables
-
0.1
Cucumber
                               4,840 to 139,392
                                     0.031



Muskmelon
                                2,420 to 34,848
                                    0.0077



Pumpkin
                                 908 to 7,260
                                    0.0016



Squash, summer
                                1,452 to 15,374
                                    0.0034



Squash, winter
                                2,723 to 7,260
                                    0.0016



Watermelon
                                 605 to 4,356
                                    0.00096
Spinach
-
0.006

                              196,020 to 653,400
                                    0.0086
Root Vegetables 
(except sugarbeet)
-
0.002
Beet, garden

                             261,360 to 2,090,880
                                       
                                    0.0092



Carrot
                             104,544 to 2,090,880
                                    0.0092



Horseradish
                                9,680 to 10,249
                                    0.00005



Radish
                             418,176 to 1,045,440 
                                    0.0046



Parsley
                              52,272 to 1,568,160
                                    0.0069



Parsnip
                               87,120 to 435,600
                                    0.0019



Turnip
                               29,040 to 261,360
                                    0.0012
Soybeans
1.05
0.0302
Soybean
                               50,000 to 250,000
                                     0.017
a  Proposed label MERTEC 340-F  889 MAS 0313 HILITE  - dt/df 3/15/13 (Density = 4.1 lb a.i./gallon of product; 42.3 % active ingredient (a.i.).[e-submission #4085; MRID 4907800]
[b] USEPA, 2011.
[c] The maximum application rates were calculated based on the maximum expected seeding rates as follows:  mg a.i./seed * seeds/acre * (1 lb/453.59 g) * 1 g/1000 mg = lb a.i./acre.
[d] Conservative maximum seeding rate proposed by Syngenta.

Uncertainties

The assessment assumes that 100 percent of the a.i. comes off the seed and is available for runoff or leaching (EFED, 1999).  Thus, the amount of "a.i." in runoff and leachate are expected to be conservative.  

The avian acute toxicity studies yielded non-definitive "greater than" values for the acute oral LC50 and the dietary LC50. These data were adequate for concluding that the acute risk is below the LOC for risk to nonlisted species, but in some cases are not adequate for concluding that the acute risk is below the LOC for endangered species. 

For chronic risk, the avian reproduction studies with the bobwhite (MRID 00123327) and the mallard (MRID 00123328) tested only up to 400 mg/kg-diet. No statistically significant effects were observed at the highest test concentration. The concentrations of thiabendazole on treated seeds of some crops are expected to be much greater than this amount, up to 4590 mg/kg-diet for muskmelon seeds. Therefore, these results are not adequate for assessing chronic risk to seed-eating birds. Without additional testing at higher test levels, the assessment must calculate RQ's based on the NOAEC equal to the highest concentration tested (400 mg a.i./kg-diet), which yield chronic avian RQs that exceed the LOC.

Tier 1 terrestrial plant toxicity data for thiabendazole failed to establish an NOAEL for some plant species. However, the data do show that thiabendazole has relatively low toxicity to terrestrial plants. Exposure to the relatively high rate of 0.23 lb a.i./A (which is higher than the maximum allowable seasonal application rate of 0.15 lb ai/A) resulted in growth inhibition of no more than 25%. Likewise, aquatic plant tests with thiabendazole are supplemental, but are adequate to show that it has low toxicity. Considering that seed treatment uses result in very little exposure to nontarget terrestrial and aquatic plants, additional testing with plants is not warranted.

Toxicity data are not available for saltwater animals except for one acute test with the saltwater mysid. However, seed treatment use of thiabendazole is expected to result in little exposure to aquatic habitats, and based on toxicity data for freshwater species, risk to aquatic species is expected to be minimal. Furthermore, the mysid study indicates that the toxicity of thiabendazole to saltwater species is similar to that of freshwater species. Therefore, additional testing with saltwater species is not needed to assess these proposed uses.

Environmental Fate and Transport 		

There have been no additional environmental fate data submitted since the previous assessments.  
The environmental fate studies show that thiabendazole is persistent and immobile (Table 4). Thiabendazole is stable to hydrolysis and soil photolysis and degrades slowly in aerobic (half-life ~ 700 days) and anaerobic soil environments (>200 days). Aquatic photolysis, with a half life of 1.2 days in clear water, appears to be the only significant degradation pathway. Under anaerobic aquatic conditions thiabendazole showed no evidence of abiotic or biotic degradation but moved rapidly from water phase to the sediment phase. Thiabendazole binds tightly to soil due to its high soil/water partitioning coefficients (Kocs > 1,000 mL/goc), thus limiting the amount available for leaching into ground water and for solution phase runoff into surface water. With the high sorption capacity, thiabendazole would be transported on eroded sediment. Sorption was weakly correlated to organic carbon. Terrestrial field dissipation studies showed thiabendazole to be extremely persistent with no leaching. Vapor pressure and Henry's Constant indicate that there is a low potential for thiabendazole to volatilize from soil and water. These studies are discussed in more detail in the most recent Reregistration Eligibility Decision (RED) (DP Barcode D245780).  There are no degradation products that are expected to form at levels that are of ecological concern.

Table 4.  Environmental Fate Parameters of Thiabendazole
Parameter
                                     Value
                                  Description
                                    Source
                                   (MRID #)
                                  Persistence
Hydrolysis half-life (22C)
Stable @ pHs 5, 7, 9
Rates[a] of transformation were extrapolated resulting in t(1/2)s (200 days) far beyond the length of the study (30 days)
                                   41265301
                              (D245780; 02/04/99)
Aqueous photolysis half-life (22.5 to 23.2C)
 1.2 days
96 hour study @ pH5
                                   43328305
Soil photolysis half-life (25C)
Stable
--
                                   41297301
                                   41397302
Aerobic soil metabolism half-life  (25°C)
688 days
EFED Registration Document D245780
                                   41791201
Anaerobic soil metabolism half-life  (25°C)
211 day
Only degradate detected was benzimidazole in a 90 day study.
(max 13.7 % AR;).
                                   41559601 
Anaerobic aquatic metabolism half-life 
No evidence of biotic or abiotic degradation.
 Rapidly moved from water phase to the sediment phase.
                                    122888
                                    070753
Aerobic aquatic metabolism half-life [dissipation half-life A] (25C)
                                      --
Study requirement waived
                                   41559601 
                              (D169687; 12/30/92)
                                   Mobility
Freundlich soil-water partition coefficients (KF); organic carbon-normalized Freundlich coefficients (KFOC)
KF (mL/g)/ Koc(mL/goc):
(soil textural class)

2.49/1,104: (sand)
15.97/3,992: (sandy loam)
21.75/1,812: (silt loam)
269.6/22,467: (clay)
Mean = 7,343 mL/goc
Median = 2,902 mL/goc


                                   41170102
                               Field Dissipation
Terrestrial field dissipation half-life in upper 6 inch soil layer; (max. depth of observed leaching)
1100 days; (6 inches). 
 990 and 1444 days; (12 inches)
833 and 1093 days: (6 inches).
Winter wheat/loamy sand/WA
Soybean and bare ground/sandy loam/IL
Soybean and bare ground/sandy loam/GA
                                   43187201
                                   43187202
                                   43187201
                 Octanol/Water Partition Coefficient (logPow)
 1.61
                                      --
                                   48354604
[a] Transformation rates of thiabendazole: pH 5 (-0.0019 days[-1]); pH 7 (-0.0035 days[-1]); pH 9 (-0.0026 days[-1])


 Transformation Products

Three degradates were identified in the aqueous photolysis study (benzimidazole-2-carboxamide as a major degradate; benzimidazole and benzimidazole-2-carboxylic acid as minor degradates), two minor degradates were identified in the aerobic soil metabolism study (benzimidazole and 5-hydroxythiabendazole), and one major degradate was identified in the anaerobic soil metabolism study (benzimidazole) (Appendix A).  The metabolite 5-hydroxythiabendazle and benzimidazole are included in the tolerance dietary exposure for food (40 CFR 180.242), but not included in drinking water. The common name, chemical names, CAS No., molecular formula and mass, chemical structure, and maximum and final percent of applied radioactivity (AR) of the major degradates are summarized in Appendix B.  

Bioaccumulation  

A BCF study with the rainbow trout measured a BCF value 86.5 (whole); 19.7 (fillet), 747 (viscera). Three-day depuration was 96% in viscera and 50% in edible tissue (MRIDs 41631801; 42022701).  These results indicate that the potential of thiabendazole to bioconcentrate is low.
Estimation of Exposure 

Aquatic Exposure Modeling 

This exposure assessment was completed using the GENEEC model.  Exposure was estimated for a seed treatment application at 0.15 lb ai/A, which is to be the maximum annual application rate allowed on the Mertect[(R)] 340-F label for any seed treatment use. Model input parameters used are given in Table 4.  A description of this model can be found on the EPA's website at: http://www.epa.gov/pesticides/science/models_pg.htm

Table 4.  Summary of Input Parameter Values for Modeling Aquatic Exposure of Thiabendazole Using the GENEEC Model
 Environmental Fate Parameter
                                    Value[a]
                                 Justification
                                     Source
                                  Solubility
                                 28 ppm (mg/L)
                                       -
                                 MRID 40947301
                         Adsorption Coefficient (Koc) 
                                 7,343 mL/goc
                                  Average Koc
                                 MRID 41170102
                        Aerobic Soil Metabolism (ASM)  
                                   2064 days
                           3 x single ASM half-life
                                 MRID 41791201
                          Aerobic Aquatic Metabolism
                                    (Days)
                                  Stable (0)
                    No Data and Persistence observed in ASM
                                    No Data
                              Aqueous Photolysis
                                   1.2 days
                                       -
                                 MRID 43328305
                               Hydrolysis (@pH7)
                                  Stable (0)
                                       -
                                 MRID 41265301
                           GENEEC Management Options
                                   Wetted-In
                                      No
                            Not specified on label
                                     Label
                             Method of Application
                                   Granular
It is assumed there is no spray drift for treated seed and granular is the non-drift option in GENEEC   
                                       -
                              Incorporation Depth
                                 1 and 2 inch
             Range of planting depths for a variety of crops[b,c].
                                       -
  [a] http://www.epa.gov/oppefed1/models/water/input_parameter_guidance.htm
  b http://www.channel.com/Agronomics/Pages/Plant-Soybeans-to-the-Right-Depth.aspx
  c http://www.omafra.gov.on.ca/english/crops/pub811/4planting.htm
      

Maximum generic estimated environmental concentrations (EECs) for seed-treatment use at 0.15 lb a.i./A are given in Table 5. These values represent the upper bound of concentrations expected for the proposed new use on the label. This modeling indicates that peak EECs for all uses are expected to be less than 1.0 ug a.i./L (1 ppb). A representative GENEEC model output is listed in Appendix C.

Table 5. Generic aquatic estimated environmental concentrations (EECs) of thiabendazole for proposed maximum annual application rate of 0.15 lb a.i./A and two seeding depths. 
                                     Crop
                                   Scenario
                           Aquatic EECs (ug a.i./L)
                                       
                                       
                                     Peak
                                  21-Day Mean
                                  60-Day Mean
All crops, 
0.15 lb a.i./A
    Generic granular/seed treatment scenario with 1-inch soil incorporation
                                     0.88
                                     0.73
                                     0.53

    Generic granular/seed treatment scenario with 2-inch soil incorporation
                                     0.44
                                     0.37
                                     0.27


Water Monitoring Data 

There are no detections of thiabendazole reported in the California Department of Pesticide Regulation (CDPR) Surface Water Monitoring Database available and it is not included in CDPR Groundwater Protection List.  Thiabendazole is not included in the surface water database collected in the USGS National Water Quality Assessment (NAWQA) Program. There were no detections of thiabendazole reported in groundwater (49 samples from CA, DE, FL,MD, NJ) in USGS NAWQA data warehouse with limits of detection <0.06 ug/L.  

Terrestrial Exposure Modeling
Oral Exposure from Consumption of Treated Seed

Oral exposure from use of thiabendazole as seed treatment was estimated by modeling the dose to birds and mammals that feed directly on the treated seeds or seed pieces. EPA's T-REX program (version 5.1) was used to predict the dose of pesticide that would be ingested by birds and mammals of various sizes. A sample of the T-REX model output is provided in Appendix D. These predictions are calculated based on average daily food intake and the concentration of active ingredient on a treated seed. The model makes the assumption that 100% of the animal's diet is comprised of treated seed. Maximum concentrations on seeds were calculated by dividing the maximum seed treatment rate (mg a.i./seed) by the minimum seed weights (mg/seed). The minimum seed weights were derived from the maximum seeds per pound counts reported by the Biological and Economical Analysis Division (BEAD) (USEPA, 2011).  Input values for this analysis are presented in Table 6.


Table 6. Input values for the analysis of risk to terrestrial animals from consumption of thiabendazole-treated seeds.
Crop Group
                              Seed Treatment Rate
                             Representative Crops
                          Max. No. of Seeds per Pound
                            Max Seed Concentration
                                (mg a.i./seed)

                          fl. oz. product/100 lb seed
                                 mg a.i./seed
                                       
                                       
                                       
Alfalfa
                                      5.8
                                    0.004 
Alfalfa
                                    227,000
                                     2,002
Cereals (small grains)
                                      2.6
                                     0.03
Barley
                                    14,000
                                      926

                                      3.4
                                     0.03
Oats
                                    18,144
                                     1,200

                                      3.2
                                     0.03
Rye
                                    18,000
                                     1,190

                                      2.6
                                     0.03
Triticale
                                    22,680
                                     1,500

                                      3.1
                                     0.03
Wheat
                                    18,000
                                     1,190
Brassica, head and stem
                                       -
                                     0.002
Broccoli
                                    150,000
                                      661

                                       
                                       
Cabbage
                                    165,000
                                      728
Bulb Vegetables
                                       -
                                     0.002
Onion
                                    130,000
                                      573
Cucurbit Vegetables
                                       -
                                      0.1

Cucumber

                                     18144
                                       
                                     4,000

                                       
                                       
Muskmelon
                                    20,800
                                     4,586

                                       
                                       
Pumpkin
                                     6,400
                                     1,411

                                       
                                       
Squash, summer
                                     6,400
                                     1,411

                                       
                                       
Squash, winter
                                     6,400
                                     1,411

                                       
                                       
Watermelon
                                     9,600
                                     2,116
Spinach
                                       -
                                     0.006
Spinach
                                    45,360
                                      600
Root Vegetables 
(except sugarbeet)
                                       -
                                     0.002
Carrot
                                    400,000
                                     1,764

                                       
                                       
Radish
                                    50,000
                                      220

                                       
                                       
Parsley
                                    296,500
                                     1,307

                                       
                                       
Turnip
                                    167,000
                                      736
Soybeans
                                     0.624
                                    0.0302
Soybean
                                     3,600
                                      240

LD50 per Square Foot Analysis

In addition to exposure through a dietary route, risk to terrestrial animals was assessed using the LD50-per-square-foot risk index.  This analysis does not assume any explicit exposure route, but rather relates the amount of active ingredient available to an animal within one square foot of treated habitat to the acute oral LD50.  The LD50-per-square-foot is considered a proxy for an RQ. For seed treatment uses of thiabendazole, the maximum application rate in terms of lb a.i./A were calculated by multiplying the maximum allowable seed treatment rate (i.e., amount of a.i. per seed) by the maximum expected seeding rates (seeds per acre) expected for each crop (Table 3).  Seeding rates were assumed to be at the maximum of the range of seeding rates provided by the BEAD (USEPA, 2011). As a conservative screen, this analysis assumed no soil incorporation of the seed. It is recognize, however, that most seeds will be soil incorporated, which would reduce the exposure to terrestrial animals. The amount of AI available on one square foot of ground planted with treated seeds were then divided by the body-weight adjusted LD50 for small, medium, and large birds and mammals. Equations for these calculations are given in the User Manual for the T-REX Mode (USEPA, 2012).

Exposure Modeling for Non-Target Plants

Exposure to terrestrial and semi-aquatic plants was estimated using the OPP's TerrPlant model (version 1.2.2). Sample output from the TerrPlant model is provided in Appendix E. The application rate was assumed to be 0.15 lb a.i./A, the maximum annual application rate allowed on the proposed Mertect[(R)] 340-F label. Seeds were assumed to be planted at a depth of 1 inch. Because the new uses are seed treatments, the spray drift fraction was set at zero. The predicted terrestrial plant EECs for the new seed treatment uses are summarized in Table 7.  

Table 7.  EECs for Thiabendazole Seed Treatment Uses with an Application Rate of 0.15 lb a.i./A
Exposure Description
                                EEC (lb a.i./A)
Runoff to dry areas
                                    0.0075
Runoff to semi-aquatic areas
                                     0.075
Spray drift
                                       0
Total for dry areas
                                    0.0075
Total for semi-aquatic areas
                                     0.075

Ecological Effects Characterization


Table 8 provides a summary of the toxicity of thiabendazole to aquatic organisms. Thiabendazole is highly toxic to fish and aquatic invertebrates on an acute basis (LC50s 0.1-1.0 mg a.i./L). With chronic exposure, the Daphnia magna was the most sensitive species, with chronic effects observed at concentrations as low as 87 ug a.i./L (NOAEL: 42 ug a.i./L). Table 9 provides a summary of the toxicity of thiabendazole to terrestrial animals.  On an acute basis, thiabendazole is classified as practically nontoxic to birds, mammals, and the honey bee. While the avian acute oral tests with the bobwhite and mallard determined the LD50s were greater than the highest test dose of 4640 mg ai/kg-bw, one mortality and some sublethal toxic effects were observed in the test with the mallard. One duck died on day 2 at 4640 mg ai/kg-bw, and lethargy, lower limb weakness, and loss of coordination was observed in ducks at this level during the first 5 days after exposure (MRID 00123313). In the avian dietary tests with the bobwhite and mallard, no mortality was observed at any test level, but reduced food consumption and reduced body weight gain were observed in the bobwhite test at 5620 mg ai/kg-bw (MRID 41025003) and in the mallard test at 3160-5620 mg ai/kg-bw (MRID 41025004). No reproductive or developmental effects were observed in chronic toxicity studies with birds at a concentration of 400 mg a.i./kg-diet. For chronic toxicity to mammals, a two-generation rat reproductive study established the NOAEL at 10 mg a.i./kg/day based on reduction in body weight gain and food consumption at the next higher concentration of  30 mg a.i./kg/day (MRID 43190301). This NOAEL is roughly equivalent to a dietary dose of approximately 200 mg a.i./kg-diet. Previous ecological risk assessments used a higher NOAEC of 1800 mg ai/kg-diet, but that was based only on the lack of reproductive effects observed in this study. Other studies also have noted sublethal toxic effects at dietary exposures at or near 600 mg a.i./kg-diet, including liver hypertrophy (MRID 43593201) and histopathological changes in bone marrow, liver, and thyroid (MRID 42942802). In a developmental rat study, a growth effect was also observed in developing young (decreased fetal body weight) at the slightly higher dietary concentration of 800 mg ai/kg-diet (MRID 42942803).  

Table 8. Toxicity of Thiabendazole to Aquatic Organisms
Taxonomic Group
                                 Test Species
                       Principal Acute Toxicity Endpoint
                           Acute Toxicity Categories
                      Principal Chronic Toxicity Endpoint
Freshwater Fish

Rainbow Trout
(Oncorhynchus mykiss)
	96-hr 	LC50 =  0.56 ppm a.i.
Highly toxic
NOAEC:  0.11 ppm a.i.
LOAEC:  0.23 ppm a.i.
(Reduced weight)
Freshwater Invertebrates

Water Flea 
(Daphnia magna)
                                       
                          48-hr EC50 = 0.31 ppm a.i.
                                       
Highly toxic
NOAEL: 0.042 ppm a.i.
LOAEL: 0.087 ppm a.i.
(Reduced survival and number of young per female)
Marine/ 
Estuarine Invertebrates
                          Mysid (Americamysis bahia)
                          96-hr EC50 = 0.34 ppm a.i.
                                 (acceptable)
Highly toxic
No Data Available
Aquatic nonvascular plants

Duckweed 
(Lemna gibba)
                          7-day EC50 = 2.32 ppm a.i.
                             NOAEC:  0.26 ppm a.i.
                                (supplemental)
NA[1]
NA [2]
Aquatic vascular plants
Freshwater Green Algae (Pseudokirchneriella subcapitata)
                             EC50 = 3.06 ppm a.i.
                            NOAEC:  0.532 ppm a.i.
(supplemental)
NA[1]	
NA [2]
1. This item is not applicable (NA) because the EPA does not assign acute toxicity characterizations to aquatic plant toxicity endpoints. 
2.  This item is not applicable (NA) because the EPA does not characterize aquatic plant toxicity tests as being "acute" or "chronic."


Table 9. Toxicity of Thiabendazole to Terrestrial Animals
Taxonomic Group
                                 Test Species
                       Principal Acute Toxicity Endpoint
                           Acute Toxicity Categories
                      Principal Chronic Toxicity Endpoint
Birds

Bobwhite
(Colinus virginianus)
and mallard (Anas platyrhynchos)
Acute oral LD50 > 4,460
 mg a.i./kg-bw 
(One mortality and sublethal effects, see text)

Acute dietary LC50  > 5,620 mg a.i./kg-diet 
(No mortality but sublethal effects, see text)
Practically nontoxic
NOAEC: 400 ppm a.i.
LOAEC: >400 ppm a.i.
(No observed toxic effects)
Mammals

Laboratory rat
(Mus musculus)
LD50  = 5,070 mg a.i./kg (M)
LD50  = 4,734 mg a.i./kg (F)

Practically nontoxic
NOAEC = 
      10 mg a.i./kg/day
LOAEL = 
     30 mg a.i./kg/day
(Reduced bodyweight gain and food consumption) 
Honey Bee
Honey bee 
(Apis mellifera)
Acute Contact LD50 > 34 ug a.i./bee
Practically nontoxic
NA
1. This item is not applicable (NA) because the Agency does not assign toxicity characterizations to terrestrial plant toxicity endpoints.
2.  This item is not applicable (NA) because there no guideline terrestrial plant chronic toxicity studies.

Table 10 provides a summary of the toxicity of thiabendazole to terrestrial plants. Information on the phytotoxicity of thiabendazole is limited because only tier-1 terrestrial plant toxicity tests are available. Based on these studies, the EC25 values were determined to be equal to or greater than the tested rate of 0.23 lb a.i./A, which is greater than the maximum annual application rate allowed on the label (0.23 lb a.i./A). However, statistically significant adverse effects were observed at this test level in both the seedling emergence study and the vegetative vigor study. In the seedling emergence study, cucumber exhibited significant reduction in emergence and survival (22% reduction compared to the control) at 0.23 lb a.i./A (MRID 48996306). In the vegetative vigor study, significant inhibition was observed in growth, as measured by shoot length, in ryegrass (9% inhibition), tomato (11% inhibition), and soybean (13% inhibition). Therefore, these studies did not determine NOAEL values for toxicity of thiabendazole to terrestrial plants.

The toxicity data given in these tables represent the most sensitive toxicity endpoints available from acceptable studies. A complete listing of all available toxicity data for thiabendazole can be found in Appendix F

Table 10. Toxicity of Thiabendazole to Terrestrial Plants
                                Taxonomic Group
                                  Study Type
                               Surrogate Species
                                Toxicity Value
              (all units in terms of measured active ingredient)
                                   Source  
Terrestrial plants
Seedling Emergence
Monocot*

NOAEL = 0.23 lb/A
EC25 > 0.23 lb/A
48996306 (Acceptable, except Supplemental for bean and soybean)


Dicot  -  cucumber

NOAEL < 0.23 lb/A
EC25 >= 0.23 lb/A
Endpoint: emergence and survival


Vegetative Vigor
Monocot  -  Ryegrass

NOAEL < 0.23 lb/A
EC25 > 0.23 lb/A
Endpoint: shoot length
48996307 (Acceptable)


Dicot*
NOAEL = 0.23 lb/A
EC25 > 0.23 lb/A

* Because no significant inhibition was observed in any test species, the most sensitive species was not determined in this study.

Risk Characterization

        Aquatic Organisms

For aquatic risk, a screening-level assessment was conducted by calculating risk quotients for the maximum annual application rate for all proposed seed treatment crops, which the label restricts to 0.15 lb ai/A. At this application rate, none of the acute or chronic RQs exceed the acute or chronic LOC (Table 11). While data are not available to assess acute or chronic risk to saltwater fish, or chronic risk to saltwater invertebrates, the very low aquatic RQs for freshwater species suggest that risk to saltwater species is unlikely. Therefore, all of the proposed new seed treatment uses of thiabendazole are presumed to pose minimal risk to all aquatic plants and animals.

Table 11.  RQs for Aquatic Organisms Exposed to Thiabendazole from the Proposed New Seed Treatment Uses
Risk Type
                                     Taxa
                                    EEC[a]
                                  (ug a.i./L)
                                   Toxicity
                                 (ug a.i./L)
                                      RQ
                                Aquatic Animals
Acute
Freshwater Fish
                                     0.88
                                      560
                                   <0.01

Freshwater Invertebrate
                                     0.88
                                      310
                                   <0.01

Saltwater Invertebrate
                                     0.88
                                      340
                                   <0.01
Chronic
Freshwater Fish
                                     0.53
                                      110
                                   <0.01
                                       
Freshwater Invertebrate
                                     0.73
                                      42
                                     0.017
                                       
Saltwater Invertebrate
                                     0.73
                                    No Data
                                      --
                                Aquatic Plants
Non-listed Species
Vascular Plants
                                     0.88
                                     2,320
                                   <0.01

Non-vascular Plants
                                     0.88
                                     3,060
                                   <0.01
Listed Species
Vascular Plants
                                     0.88
                                      260
                                   <0.01
                                       
Non-vascular Plants
                                     0.88
                                      532
                                   <0.01
 [a] From Table 5.


Terrestrial Organisms
Oral Exposure from  Consumption of Treated Seeds
Birds

Acute RQs for risk to birds are given in 

Table 13. The values shown were calculated using the nondefinitive "greater than" toxicity values (i.e., the highest level tested in the acute studies).  These RQs are conservative because if the actual toxicity levels were determined,  the RQs would be less than the values shown. For all crops except two cucurbit crops, cucumbers and muskmelons, the conservative RQs indicate that the acute risk is below the LOC for nonendangered species. For cucumber and muskmelons, the acute risk to nonendangered species is uncertain because the conservative RQs slightly exceed the acute risk LOC of 0.5 None of the acute dose-based RQs for non-endangered species exceed the LOC. Most of the uses had one or more conservative RQ that exceed the LOC for threatened and endangered species (0.10). Again, however, acute risk for listed species is uncertain since the actual RQs would be less than the values shown. Only radish, and soybean had RQs which were all below the endangered species LOC.

Table 12.  Avian Acute RQs for the Proposed New Uses of Thiabendazole
Crop Group
                              Seed Treatment Rate
                             Representative Crops
                            Max Seed Concentration
                                (mg a.i./seed)
                                   Dietary-
                                     Based
                                      RQ
                              Dose-Based Acute RQ
                                       
                               fl. oz. product/
                                100 lb seed[a]
                                mg a.i./seed[a]
                                       
                                       
                                       
                                     Small
                                     Med.
                                     Large
Alfalfa
                                      5.8
                                    0.004 
Alfalfa
                                     2,002
                                     0.36*
                                     0.15*
                                     0.07
                                     0.02
Cereals (small grains)
                                      2.6
                                     0.03
Barley
                                      926
                                     0.16*
                                     0.07
                                     0.03
                                     0.01

                                      3.4
                                     0.03
Oats
                                     1,200
                                     0.21*
                                     0.09
                                     0.04
                                     0.01

                                      3.2
                                     0.03
Rye
                                     1,190
                                     0.21*
                                     0.09
                                     0.04
                                     0.01

                                      2.6
                                     0.03
Triticale
                                     1,500
                                     0.27*
                                     0.11*
                                     0.05
                                     0.02

                                      3.1
                                     0.03
Wheat
                                     1,190
                                     0.21*
                                     0.09
                                     0.04
                                     0.01
Brassica, head and stem
                                       -
                                     0.002
Broccoli
                                      661
                                     0.12*
                                     0.05
                                     0.02
                                     0.01

                                       
                                       
Cabbage
                                      728
                                     0.13*
                                     0.06
                                     0.02
                                     0.01
Bulb Vegetables
                                       -
                                     0.002
Onion
                                      573
                                     0.10*
                                     0.04
                                     0.02
                                     0.01
Cucurbit Vegetables
                                       -
                                      0.1

Cucumber
                                     4,000
                                    0.71**
                                     0.30*
                                     0.14*
                                     0.04

                                       
                                       
Muskmelon
                                     4,586
                                    0.82**
                                     0.35*
                                     0.16*
                                     0.05

                                       
                                       
Pumpkin
                                     1,411
                                     0.25*
                                     0.11*
                                     0.05
                                     0.02

                                       
                                       
Squash, summer
                                     1,411
                                     0.25*
                                     0.11*
                                     0.05
                                     0.02

                                       
                                       
Squash, winter
                                     1,411
                                     0.25*
                                     0.11*
                                     0.05
                                     0.02

                                       
                                       
Watermelon
                                     2,116
                                     0.38*
                                     0.16*
                                     0.07
                                     0.02
Spinach
                                       -
                                     0.006
Spinach
                                      600
                                     0.11*
                                     0.05
                                     0.02
                                     0.01
Root Vegetables 
(except sugarbeet)
                                       -
                                     0.002
Carrot
                                     1,764
                                     0.31*
                                     0.13*
                                     0.06
                                     0.02

                                       
                                       
Radish
                                      220
                                     0.04
                                     0.02
                                     0.01
                                   <0.01

                                       
                                       
Parsley
                                     1,307
                                     0.23*
                                     0.10*
                                     0.04
                                     0.01

                                       
                                       
Turnip
                                      736
                                     0.13*
                                     0.06
                                     0.02
                                     0.01
Soybeans
                                     0.624
                                    0.0302
Soybean
                                      240
                                     0.04
                                     0.02
                                     0.01
                                   <0.01
  * RQ exceeds the LOC for presumption of acute risk to threatened and endangered species.
** RQ exceeds the LOC for presumption of acute risk to non-endangered species. 


RQs for chronic risk to birds (

Table 13) are considerably higher than the acute RQs. The chronic RQ exceeds the LOC (1.0) for chronic risk for all crops evaluated except for radish and soybean. For crops which exceeded the LOC, chronic RQs generally ranged from approximately 1.5 to 5.0, but were 10 or more for cucumber and muskmelons.


Table 13.  Avian Chronic RQs for the Proposed New Uses of Thiabendazole
Crop Group
                              Seed Treatment Rate
                             Representative Crops
                            Max Seed Concentration
                                (mg a.i./seed)
                                  Chronic RQ
                                       
                               fl. oz. product/
                                100 lb seed[a]
                                mg a.i./seed[a]
                                       
                                       
                                       
Alfalfa
                                      5.8
                                    0.004 
Alfalfa
                                     2,002
                                     5.00*
Cereals (small grains)
                                      2.6
                                     0.03
Barley
                                      926
                                     2.31*

                                      3.4
                                     0.03
Oats
                                     1,200
                                     3.00*

                                      3.2
                                     0.03
Rye
                                     1,190
                                     2.98*

                                      2.6
                                     0.03
Triticale
                                     1,500
                                     3.75*

                                      3.1
                                     0.03
Wheat
                                     1,190
                                     2.98*
Brassica, head and stem
                                       -
                                     0.002
Broccoli
                                      661
                                     1.65*

                                       
                                       
Cabbage
                                      728
                                     1.82*
Bulb Vegetables
                                       -
                                     0.002
Onion
                                      573
                                     1.43*
Cucurbit Vegetables
                                       -
                                      0.1

Cucumber
                                     4,000
                                    10.00*

                                       
                                       
Muskmelon
                                     4,586
                                    11.46*

                                       
                                       
Pumpkin
                                     1,411
                                     3.53*

                                       
                                       
Squash, summer
                                     1,411
                                     3.53*

                                       
                                       
Squash, winter
                                     1,411
                                     3.53*

                                       
                                       
Watermelon
                                     2,116
                                     5.29*
Spinach
                                       -
                                     0.006
Spinach
                                      600
                                     1.50*
Root Vegetables 
(except sugarbeet)
                                       -
                                     0.002
Carrot
                                     1,764
                                     4.41*

                                       
                                       
Radish
                                      220
                                     0.55

                                       
                                       
Parsley
                                     1,307
                                     3.27*

                                       
                                       
Turnip
                                      736
                                     1.84*
Soybeans
                                     0.624
                                    0.0302
Soybean
                                      240
                                     0.60
 * RQ exceeds the LOC for presumption of chronic risk to endangered and non-endangered species.

Mammals
Acute RQs for risk to mammals are given in Table 14. Acute RQs were all below the LOC for risk to non-endangered species (0.5), as well as the LOC for possible direct effects to listed species (0.05). Therefore, all of the proposed new seed-treatment uses of thiabendazole is presumed to pose minimal acute risk to mammals.

Table 14.  Mammalian Acute RQs for the Proposed New Uses of Thiabendazole
Crop Group
                              Seed Treatment Rate
                             Representative Crops
                            Max Seed Concentration
                                (mg a.i./seed)
                              Dose-Based Acute RQ
                                       
                               fl. oz. product/
                                100 lb seed[a]
                                mg a.i./seed[a]
                                       
                                       
                                     Small
                                     Med.
                                     Large
Alfalfa
                                      5.8
                                    0.004 
Alfalfa
                                     2,002
                                     0.04
                                     0.03
                                     0.02
Cereals (small grains)
                                      2.6
                                     0.03
Barley
                                      926
                                     0.01
                                   <0.01
                                   <0.01

                                      3.4
                                     0.03
Oats
                                     1,200
                                     0.02
                                   <0.01
                                   <0.01

                                      3.2
                                     0.03
Rye
                                     1,190
                                     0.02
                                   <0.01
                                   <0.01

                                      2.6
                                     0.03
Triticale
                                     1,500
                                     0.02
                                   <0.01
                                   <0.01

                                      3.1
                                     0.03
Wheat
                                     1,190
                                     0.01
                                   <0.01
                                   <0.01
Brassica, head and stem
                                       -
                                     0.002
Broccoli
                                      661
                                   <0.01
                                   <0.01
                                   <0.01

                                       
                                       
Cabbage
                                      728
                                   <0.01
                                   <0.01
                                   <0.01
Bulb Vegetables
                                       -
                                     0.002
Onion
                                      573
                                   <0.01
                                   <0.01
                                   <0.01
Cucurbit Vegetables
                                       -
                                      0.1

Cucumber
                                     4,000
                                     0.05
                                     0.02
                                     0.04

                                       
                                       
Muskmelon
                                     4,586
                                     0.07
                                     0.03
                                     0.04

                                       
                                       
Pumpkin
                                     1,411
                                   <0.01
                                   <0.01
                                   <0.01

                                       
                                       
Squash, summer
                                     1,411
                                   <0.01
                                   <0.01
                                   <0.01

                                       
                                       
Squash, winter
                                     1,411
                                   <0.01
                                   <0.01
                                   <0.01

                                       
                                       
Watermelon
                                     2,116
                                     0.02
                                     0.01
                                     0.02
Spinach
                                       -
                                     0.006
Spinach
                                      600
                                     0.01
                                   <0.01
                                   <0.01
Root Vegetables 
(except sugarbeet)
                                       -
                                     0.002
Carrot
                                     1,764
                                     0.02
                                     0.01
                                     0.02

                                       
                                       
Radish
                                      220
                                   <0.01
                                   <0.01
                                   <0.01

                                       
                                       
Parsley
                                     1,307
                                     0.01
                                   <0.01
                                     0.01

                                       
                                       
Turnip
                                      736
                                     0.02
                                   <0.01
                                   <0.01
Soybeans
                                     0.624
                                    0.0302
Soybean
                                      240
                                   <0.01
                                   <0.01
                                   <0.01


Chronic RQs are given in Table 15. Dose-based chronic RQs range from 0.88 for turnip to 44.2 for muskmelon. All dose-based chronic RQs exceeds the LOC (1.0) except for those for large mammals for use on turnips. Thus, the risk assessment concludes chronic risk to mammals from all of the proposed seed treatment uses.  

Table 15.  Mammalian Chronic RQs for the Proposed New Uses of Thiabendazole
Crop Group
                              Seed Treatment Rate
                             Representative Crops
                            Max Seed Concentration
                                (mg a.i./seed)
                             Dose-Based Chronic RQ
                                       
                               fl. oz. product/
                                100 lb seed[a]
                                mg a.i./seed[a]
                                       
                                       
                                     Small
                                     Med.
                                     Large
Alfalfa
                                      5.8
                                    0.004 
Alfalfa
                                     2,002
                                     19.3*
                                     16.5*
                                     8.8*
Cereals (small grains)
                                      2.6
                                     0.03
Barley
                                      926
                                     8.9*
                                     7.6*
                                     4.1*

                                      3.4
                                     0.03
Oats
                                     1,200
                                     11.6*
                                     9.9*
                                     5.3*

                                      3.2
                                     0.03
Rye
                                     1,190
                                     11.5*
                                     9.8*
                                     5.3*

                                      2.6
                                     0.03
Triticale
                                     1,500
                                     14.5*
                                     12.4*
                                     6.6*

                                      3.1
                                     0.03
Wheat
                                     1,190
                                     11.5*
                                     9.8*
                                     5.3*
Brassica, head and stem
                                       -
                                     0.002
Broccoli
                                      661
                                     6.4*
                                     5.4*
                                     2.9*

                                       
                                       
Cabbage
                                      728
                                     7.0*
                                     6.0*
                                     3.2*
Bulb Vegetables
                                       -
                                     0.002
Onion
                                      573
                                     5.5*
                                     4.7*
                                     2.5*
Cucurbit Vegetables
                                       -
                                      0.1

Cucumber
                                     4,000
                                     38.6*
                                     32.9*
                                     17.7*

                                       
                                       
Muskmelon
                                     4,586
                                     44.2*
                                     37.8*
                                     20.2*

                                       
                                       
Pumpkin
                                     1,411
                                     13.6*
                                     11.6*
                                     6.2*

                                       
                                       
Squash, summer
                                     1,411
                                     13.6*
                                     11.6*
                                     6.2*

                                       
                                       
Squash, winter
                                     1,411
                                     13.6*
                                     11.6*
                                     6.2*

                                       
                                       
Watermelon
                                     2,116
                                     20.4*
                                     17.4*
                                     9.3*
Spinach
                                       -
                                     0.006
Spinach
                                      600
                                     5.8*
                                     4.9*
                                     7.8*
Root Vegetables 
(except sugarbeet)
                                       -
                                     0.002
Carrot
                                     1,764
                                     17.0*
                                     14.5*
                                     1.0*

                                       
                                       
Radish
                                      220
                                     2.1*
                                     1.8*
                                     5.8*

                                       
                                       
Parsley
                                     1,307
                                     12.6*
                                     10.8*
                                     3.3*

                                       
                                       
Turnip
                                      736
                                     7.1*
                                     6.1*
                                     0.88
Soybeans
                                     0.624
                                    0.0302
Soybean
                                      240
                                     2.3*
                                     2.0*
                                     1.1*
* RQ exceeds the LOC for presumption of chronic risk to endangered and non-endangered species.


LD50 per Square Foot Analysis

To further evaluate the potential risk posed the proposed new seed treatment uses of thiabendazole, the LD50-per-square-foot index was calculated to compare the amount of active ingredient expected in one square foot of ground to the acute oral toxicity of thiabendazole for birds and mammals. This index was calculated for all crops shown in Table 3 based on the maximum application rates (lb a.i./A) given in that table. For all of the crops, the LD50-per-square-foot index was less than 0.01. Thus, for all proposed seed treatment crops, the index was well below all levels of concern.

Terrestrial Plants

RQs for risk to nontarget terrestrial plants are given in Table 16. In tier-1 phytotoxicity tests, plants were exposed to an application rate (0.23 lb a.i./A) which was greater than the maximum annual application rate allowed by the proposed product label for Mertect 340-F (0.15 lb a.i./A). At this rate, the observed inhibition of emergence and plant growth was less than 25% for all monocot and dicot plants. Results from the TerrPlant model indicates that the RQs for nonendangered species are well less than 1, and thus less the LOC. For threatened and endangered species, however, the conclusions are less certain. Statistically significant effects were observed in test some species in the seedling emergence and the vegetative vigor studies. As the percent inhibition was no greater than 22% with exposure at 0.23 lb a.i./A (see Section IV), and the proposed new seed-treatment uses are expected to result in nontarget plant exposure at no more than 0.075 lb a.i./A (Table 16Table 7), direct adverse effects to nontarget plants are expected to be small. Additional factors that suggest little risk to nontarget plants are that 
   1. Seed treatment uses would result in no spray drift, and thus there would be minimal foliar exposure
   2. Thiabendazole is immobile in soil, and therefore off-site movement from planted fields would be minimal
   3. The widespread use of thiabendazole as a fungicidal seed treatment and lack of plant incidents suggest that it does not have significant phytotoxicity at the application rates used.

Therefore, while limitations of the phytotoxicity data results in some uncertainty, the EPA does not expect the proposed seed treatment uses of thiabendazole to result in effects to terrestrial plants.


Table 16.  RQs for Terrestrial Plants Exposed to Thiabendazole from the Proposed Seed-Treatment Uses
                                     Taxa
                                     EECs
                                  (lb a.i./A)
                                       
                          Non-listed Species Endpoint
                              (EC25 in lb a.i./A)
                            Listed Species Endpoint
                             (NOAEC in lb a.i./A)
                             Non-Listed Species RQ
                               Listed Species RQ
                                   Monocots
                                    Uplands
                                    0.0015
                                   >0.23
                                   <0.23
                                   <0.07
                                   >0.007
                                   Wetlands
                                     0.015
                                   >0.23
                                   <0.23
                                   <0.07
                                   >0.007
                                    Dicots
                                    Uplands
                                    0.0015
                                   >0.23
                                     0.23
                                   <0.07
                                   <0.007
                                   Wetlands
                                     0.015
                                   >0.23
                                     0.23
                                   <0.07
                                   <0.07

Risk Discussion and Conclusions

The proposed seed treatment uses are expected to result in very little exposure to aquatic organisms and nontarget terrestrial plants. The application rates of the new uses in terms of pounds of active ingredient per acre is small (0.00004 to 0.15 lb a.i./A). These application rates are not higher than those of previously registered seed treatment uses. No spray drift would occur with seed treatment uses, which reduces off-site transport of the pesticide. Furthermore, because the seeds generally are buried and because thiabendazole has very little mobility in soil, off-site movement of thiabendazole in runoff is expected to be very limited. As a result, exposure to aquatic organisms and to nontarget terrestrial plants is expected to be very limited, and is not expected to reach levels which may be toxic.

The acute oral honeybee test classifies thiabendazole as practically nontoxic to the honey bee (LD50 > 34 ug a.i./bee). Therefore, no warning statement is needed on the product labels to protect bees.

In contrast, wildlife that feed on the treated seeds in fields planted with treated seeds may have significant exposure to thiabendazole. Based on an assumption of a diet comprised entirely of treated seeds, the ecological risk assessment concluded that all of the proposed new uses pose a risk to mammals due to chronic toxicity (RQs of 1.1 to 44.2). All of the proposed new uses except soybean and some root vegetables (e.g., radish) also pose a risk to birds due to chronic toxicity (RQs 1.43 to 11.5). A few cucurbit uses (e.g., cucumbers and muskmelons) also may pose a risk to birds because of acute toxicity, although this conclusion is uncertain because the avian acute toxicity endpoints are non-definitive (i.e., "greater than" values). For many of the new uses, RQ values also indicate that the endangered species acute toxicity level of concern is exceeded for birds, but not for mammals. 

The potential for acute effects to birds is uncertain because the assessment is based on non-definitive "greater than" estimates of acute toxicity endpoints. The conclusions for chronic risk are also uncertain because the available avian reproduction studies only tested up to 400 mg a.i./kg-diet, which is lower than some of the estimated exposure values. Since the chronic avian toxicity of thiabendazole is above 400 mg a.i./kg-diet, the level of risk is uncertain for all crops for which the seed concentration exceeds this amount. The chronic risk conclusions for mammals are more certain as they are based on studies in which toxic effects were observed and thus both  NOAEC and LOAEC values were established.

The conclusions of risk to terrestrial wildlife are based on exposure through direct consumption of treated seeds. Exposure would be much less for species that do not consume seeds, or for which seeds comprise only a small portion of their diet. Some thiabendazole may be absorbed by the plant and translocated to emerged portions of the plant, and thus may result in some exposure to herbivorous animals which feed on the crop soon after it emerges. Likewise, some thiabendazole could leach into the upper soil and expose soil arthropods, and thereby would expose insectivorous animals which feed on them. However, these routes of exposure are expected to be much less significant than direct consumption of treated seeds. Therefore, risk to herbivorous and insectivorous animals is uncertain. Acute RQs for birds and mammals derived from the LD50-per-square-foot analysis were very low (<0.01), which indicates that acute risk to wildlife that do not feed on seeds might be low.

Since birds serve as a surrogate for reptiles and terrestrial phases of amphibians, the conclusion that the proposed uses of thiabendazole pose risk to birds also apply to terrestrial reptiles and amphibians with terrestrial phases. However, reptiles and amphibians are generally insectivorous or herbivorous, and therefore risks to these taxa are uncertain.

To further characterize the chronic risk to seed eating mammals, an analysis was done to determine the number of seeds that small mammals of various sizes would need to eat for the chronic RQ to reach 1, the LOC for concluding chronic risk (Table 17). Since most seed-eating mammals are small rodents, the results for small to medium mammals are most relevant. The number of seeds required for mammals of these sizes range from 3.3 to 311. None of the numbers for these weight sizes appear to be so large to be considered impossible, although the numbers for Brassica, bulb vegetable, and root crops appear unlikely. The numbers for small grains, soybeans, and cucurbits would be easy for small mammals to reach. This analysis agrees with that of the previous RQ analysis in indicating that chronic mammalian risk is highest for cucurbit vegetable crops (See Table 15). This is because the seed treatment rate is higher for this crop group than for other crops and crop groups.

Table 17.  Number of Seeds that Must Be Eaten for Oral Exposure to Reach a Mammalian Chronic LOC
Crop Group
                              Seed Treatment Rate
                                (mg a.i./seed)
                                     Size
                                    BW (g)
                             Weight-Adjusted NOAEL
                               Number of Seeds 
Alfalfa
                                    0.004 
                                     Small
                                      15
                                    21.978
                                      82

                                       
                                    Medium
                                      35
                                    17.783
                                      156

                                       
                                     Large
                                     1000
                                    7.6916
                                     1923
Cereals (small grains)
                                     0.03
                                     Small
                                      15
                                    21.978
                                      11

                                       
                                    Medium
                                      35
                                    17.783
                                      21

                                       
                                     Large
                                     1000
                                    7.6916
                                      256
Brassica, head and stem
                                     0.002
                                     Small
                                      15
                                    21.978
                                      165

                                       
                                    Medium
                                      35
                                    17.783
                                      311

                                       
                                     Large
                                     1000
                                    7.6916
                                     3846
Bulb Vegetables
                                     0.002
                                     Small
                                      15
                                    21.978
                                      165

                                       
                                    Medium
                                      35
                                    17.783
                                      311

                                       
                                     Large
                                     1000
                                    7.6916
                                     3846
Cucurbit Vegetables
                                      0.1

                                     Small
                                      15
                                    21.978
                                       3


                                    Medium
                                      35
                                    17.783
                                       6


                                     Large
                                     1000
                                    7.6916
                                      77
Spinach
                                     0.006
                                     Small
                                      15
                                    21.978
                                      55

                                       
                                    Medium
                                      35
                                    17.783
                                      104

                                       
                                     Large
                                     1000
                                    7.6916
                                     1282
Root Vegetables 
(except sugarbeet)
                                     0.002
                                     Small
                                      15
                                    21.978
                                      165

                                       
                                    Medium
                                      35
                                    17.783
                                      312

                                       
                                     Large
                                     1000
                                    7.6916
                                     3846
Soybeans
                                    0.0302
                                     Small
                                      15
                                    21.978
                                      11

                                       
                                    Medium
                                      35
                                    17.783
                                      20

                                       
                                     Large
                                     1000
                                    7.6916
                                      255

The chronic mammalian RQ analysis was based on an NOAEC of 200 mg/kg-diet, which was established by observations of reduced weight gain in adult rats and reduced food consumption in the next highest treatment level of 600 mg a.i./kg (MRID 43190301). Previous ecological risk assessments used the NOAEC obtained in this study for reproductive endpoints only, which was 1800 mg ai/kg-diet. However, consistent with current EFED policy, the NOAEC used in this assessment is based on the most sensitive endpoint affecting the reproduction, survival, or growth, and effects on weights of the adults is considered a growth effect. Other studies have also noted toxic effects at dietary exposures at or near 600 mg a.i./kg-diet based on organ-level effects, such as liver hypertrophy (MRID 43593201) and histopathological changes in bone marrow, liver, and thyroid (MRID 42942802). In a developmental rat study, a growth effect was also observed in developing young (decreased fetal body weight) at the slightly higher dietary concentration of 800 mg ai/kg-diet (MRID 42942803). Taken together, these results support use of 200 mg/kg-diet as the appropriate NOAEC for chronic effects to mammals. 

The primary ecological risk from the proposed thiabendazole seed-treatment uses (as well as existing uses) is to birds and small mammals which could feed directly on the treated seeds. Exposure, and thus risk, to these animals depend on two factors, the maximum seed treatment rate (i.e., the maximum amount of active ingredient that can applied to a seed) and the size of the seed. Greater risk is associated with crops for which the seed treatment rate is higher and the seed size is smaller. The maximum seed treatment rate for cucurbit vegetables (0.1 mg a.i./seed) is far greater than for any other crop or crop group, making the risk to seed-eating animals greatest for this crop groups. Among the crops within this group, ones with relatively small seeds, such as cucumbers and melons, have the highest risk. Risk to seed-eating animals is also high for alfalfa and for certain root vegetables, such as carrots. While the seed treatment rates for these crops are fairly low, the seeds are extremely small, making the concentration on these seeds fairly high. RQs are also fairly high for small grains (barley, oat, rye, triticale, and wheat), which have the second highest seed treatment rate (0.03 mg a.i./seed) and moderately small seeds. 

References

USEPA, 2011. Acres Planted per Day and Seeding Rates of Crops Grown in the United States. Memorandum from the Biological and Economic Analysis Division to the Environmental Fate and Effects Division. Office of Pesticide Programs. U.S. Environmental Protection Agency. Washington, DC.  March 17, 2011.


 Appendix A.  Thiabendazole degradates identified in Environmental Fate Studies


Degradates

Hydrolysis

Photolysis (water)

Photolysis (soil)

Aerobic Soil

Anaerobic Soil

Terrestrial Field
Benzimidazole

X

X 
X[a]

5-hydroxy thiabendazole



X 


Benzimidazole-2-carboxamide


X[a]




Benzimidazole-2-carboxylic acid


X




Unidentified [[14]C]

X

X


Unknown 1



X


[14]CO2



X


[a] - major degradates (>10%)



 Appendix B.  Thiabendazole and Its Environmental Degradates

Name
Chemical Name CAS No.
Formula
Molecular Mass
Chemical Structure
Study Type
Maximum %AR (day)
Final %AR (study length)
PARENT
Thiabendazole
2-(4-thiazolyl)-1H-benzimidazole

CAS No.: 148-79-8

Formula: C10H7N3S
MW: 201.25 g/mol







Aerobic Soil Metabolism
Anaerobic Soil Metabolism




56.8%
78% (@ day 90)
TRANSFORMATION PRODUCTS
Thiabendazole-5-hydroxy
5-hydroxythiabendazole;
2-(4-Thiazolyl)-5-benzimidazolol

CAS No.: 948-71-0


Formula: C10H7N3S


MW:  217.25g/mol

Aerobic Soil Metabolism


Benzimidazole
1H-Benzimidazole
CAS No.: 962-28-7 
Formula: C7H6N2

MW: 118.05 g/mol
            


Aq. Photolysis (minor)
Aerobic  Soil Metabolism
Anaerobic Soil Metabolism
Terrestrial Field Dissipation
-
2.2%
13.7%
-
6.49% (avg.)
0.17%
5.5% (@ day 90
-
Benzimidazole carboxylic acid

1H-Benzimidazole-2-carboxylic acid 
CAS No.:
Formula: C8H6N2O2

MW: 162.15 g/mol
   


Aq. Photolysis (minor)

9.98% @ 96 hrs
Benzimidazole-2-carboxamide

1H-Benzimidazole-2-carboxamide

CAS NO. 5805-52-7

Formula: C8H7N3O


MW: 161.16 g/mol

Aq.  Photolysis (major)

10.2% @ 96 hrs
 
 Appendix C.  GENEEC2 Model Outputs


   RUN No.   1 FOR thiabendazole    ON   seed treat    * INPUT VALUES * 
   --------------------------------------------------------------------
    RATE (#/AC)   No.APPS &   SOIL  SOLUBIL   APPL TYPE NO-SPRAY INCORP
     ONE(MULT)    INTERVAL    Koc   (PPM )    (%DRIFT)   (FT)     (IN)
   --------------------------------------------------------------------
   .150(   .150)   1   1    7343.0   28.0   GRANUL(   .0)     .0   1.0


   FIELD AND STANDARD POND HALFLIFE VALUES (DAYS) 
   --------------------------------------------------------------------
   METABOLIC  DAYS UNTIL  HYDROLYSIS   PHOTOLYSIS   METABOLIC  COMBINED
    (FIELD)   RAIN/RUNOFF   (POND)     (POND-EFF)    (POND)     (POND) 
   --------------------------------------------------------------------
   2064.00        2          N/A      1.20-  148.80      .00    148.80


   GENERIC EECs (IN NANOGRAMS/LITER (PPTr))     Version 2.0 Aug 1, 2001
   --------------------------------------------------------------------
       PEAK      MAX 4 DAY     MAX 21 DAY    MAX 60 DAY    MAX 90 DAY
       GEEC      AVG GEEC       AVG GEEC      AVG GEEC      AVG GEEC
   --------------------------------------------------------------------
      885.85      860.43        734.13        530.42        427.70


   RUN No.   2 FOR thiabendazole    ON   seed treat    * INPUT VALUES * 
   --------------------------------------------------------------------
    RATE (#/AC)   No.APPS &   SOIL  SOLUBIL   APPL TYPE NO-SPRAY INCORP
     ONE(MULT)    INTERVAL    Koc   (PPM )    (%DRIFT)   (FT)     (IN)
   --------------------------------------------------------------------
   .150(   .150)   1   1    7343.0   28.0   GRANUL(   .0)     .0   2.0


   FIELD AND STANDARD POND HALFLIFE VALUES (DAYS) 
   --------------------------------------------------------------------
   METABOLIC  DAYS UNTIL  HYDROLYSIS   PHOTOLYSIS   METABOLIC  COMBINED
    (FIELD)   RAIN/RUNOFF   (POND)     (POND-EFF)    (POND)     (POND) 
   --------------------------------------------------------------------
   2064.00        2          N/A      1.20-  148.80      .00    148.80


   GENERIC EECs (IN NANOGRAMS/LITER (PPTr))     Version 2.0 Aug 1, 2001
   --------------------------------------------------------------------
       PEAK      MAX 4 DAY     MAX 21 DAY    MAX 60 DAY    MAX 90 DAY
       GEEC      AVG GEEC       AVG GEEC      AVG GEEC      AVG GEEC
   --------------------------------------------------------------------
      442.93      430.22        367.07        265.21        213.85



 Appendix D.  Output from Terrestrial Exposure Model (T-REX)


                                                                      Chemical:
                                 Thiabendazole
                                            Name of seed treatment formulation:
                                 Mertect 340-F
                                                     Percent AI in formulation:
                                      42%
 
                                       0
                                                  Density of product (lbs/gal):
                                  9.692670395
                                                                      Endpoints
                                   Reported
                                  Tested Body
                                 Adjusted LD50
                         Size class for adjusted LD50


                                  Weight (g)


                                                                    Avian LD50:
                                    4640.00
                                      178
                                    3342.79
Small (20g)
                                                            Avian repro. NOAEC:
                                    400.00
 
                                    4255.54
Medium (100g)
                                                                              
                                       
 
                                    6011.11
Large (1000g)
                                                                Mammalian LD50:
                                    4734.00
                                      350
                                   10404.53
Small (15g)
                                                               Mammalian NOAEL:
                                    200.00
 
                                    8418.37
Medium (35g)
                                                                              
                                       
 
                                    3641.21
Large (1000g)
                                                                              
                                       
                          Adjusted NOAEL for Mammals
                                                                              
                                       
Small (15g)
                                     21.98
                                                                              
                                       
Medium (35g)
                                     17.78
                                                                              
                                       
Large (1000g)
                                     7.69


                                  Animal Size
                                     Crop
                           Maximum Application Rate
                         Maximum Seed Application Rate
                                Avian Nagy Dose
                              Mammalian Nagy Dose
                                 Available AI

                                       
                                  (lbs ai/A)
                                (mg ai/kg seed)
                               (mg ai/kg-bw/day)
                               (mg ai/kg-bw/day)
                                 (mg ai ft-2)
                                     Small
                                   cucumber
                                     0.031
                                    2645.55
                                    669.56
                                    560.52
                                     0.32
                                    Medium



                                    381.81
                                    387.39

                                     Large



                                    170.94
                                     89.82

 
                                       
                                       
 
 
 
 
 
                                       
                                       
 
 
 
 
                                     Crop
                               Risk Quotients†

                                 Avian (20 g)
                               Mammalian (15 g)

                                  Acute (# 1)
                                  Acute (# 2)
                                    Chronic
                                  Acute (# 1)
                                  Acute (# 2)
                                    Chronic
                                   cucumber
                                    0.2003
                                    0.00480
                                     6.61
                                    0.0539
                                    0.00205
                                     25.50
                                       
                                 Avian (100 g)
                               Mammalian (35 g)

                                  Acute (# 1)
                                  Acute (# 2)
                                    Chronic
                                  Acute (# 1)
                                  Acute (# 2)
                                    Chronic
                                   cucumber
                                    0.0897
                                    0.00075
                                     6.61
                                    0.0460
                                    0.00109
                                     21.78
                                       
                                Avian (1000 g)
                              Mammalian (1000 g)

                                  Acute (# 1)
                                  Acute (# 2)
                                    Chronic
                                  Acute (# 1)
                                  Acute (# 2)
                                    Chronic
                                   cucumber
                                    0.0284
                                    0.00005
                                     6.61
                                    0.0247
                                    0.00009
                                     11.68
                                                                            †
                                                                  Acute RQ #1 =
(mg ai /kg-bw/day) / LD50
 
 
                                                                  Acute RQ #2 =
mg ai ft-2 /(LD50*bw)
 
 
                                                             Avian Chronic RQ =
mg kg-1 seed / NOAEL
 

                            Mammalian Chronic RQ =
mg a.i./kg-bw/day / adjusted NOAEL


                                                                               


 
                                       

 
                                    Animal
                                Nagy allometry
                                       
                          Food ingestion value g/day
                                                                      20 g Bird
                                                                    5.061777181
                                                                    15 g Mammal
                                                                    3.178078065
                                                                     100 g Bird
                                                                     14.4321986
                                                                    35 g Mammal
                                                                    5.125113265
                                                                    1000 g Bird
                                                                     64.6148732
                                                                  1000 g Mammal
                                                                    33.95072796



 Appendix E.  Output from Terrestrial Plant Risk Model (TerrPlant)

TerrPlant v. 1.2.2
 
 
 

 

 
 
 
 
Table 1. Chemical Identity.
                                 Chemical Name
Thiabendazole
                                    PC code
60101
                                      Use
Seed treatments
                              Application Method
Ground
                               Application Form
Seed treatments
                           Solubility in Water (ppm)
22.74
                                       
                                       
                                       
                                       
Table 2. Input parameters used to derive EECs.
                                Input Parameter
                                    Symbol
                                     Value
                                     Units
                               Application Rate
                                       A
                                     0.15
                                    lb ai.A
                                 Incorporation
                                       I
                                       1
                                     none
                                Runoff Fraction
                                       R
                                     0.05
                                     none
                                Drift Fraction
                                       D
                                       0
                                     none
 
 
 
 
Table 3. EECs for Thiabendazole.  Units in lb ai.A.
                                  Description
                                   Equation
                                      EEC
                              Runoff to dry areas
                                    (A/I)*R
                                    0.0075
                         Runoff to semi-aquatic areas
                                  (A/I)*R*10
                                     0.075
                                  Spray drift
                                      A*D
                                       0
                              Total for dry areas
                                ((A/I)*R)+(A*D)
                                    0.0075
                         Total for semi-aquatic areas
                              ((A/I)*R*10)+(A*D)
                                     0.075



 
 Appendix F.  Ecotoxicity Data

Table F.1.  Aquatic Toxicity Profile for Thiabendazole

                                     Taxon
                               Exposure Duration
                         Most Sensitive Species Tested
                                Toxicity Value
                               Toxicity Category
                                    MRID /
                                Classification 
                                     Fish
                                Freshwater Fish
                                     Acute
                                 Rainbow trout
                              Oncorhynchus mykiss
96-hr LC50 = 0.56 mg/L
Highly toxic
                             41025005 (Acceptable)
                                       
                                    Chronic
                                 Rainbow trout
NOAEC = 0.11 mg/L
LOAEC = 0.23 mg/L
Endpoint: Reduced weight
--
                                   42508901
                                 (Acceptable)
                            Estuarine/ Marine Fish
                                     Acute
                               Sheepshead minnow
                             Cyprinodon variegatus
LC50 > 10 mg/L[3]
Slightly toxic
                            41192003 (Supplemental)
                                       
                                    Chronic
                                    No data
                                    No data
--
                                      --
                             Aquatic Invertebrates
                           Freshwater Invertebrates
                                     Acute
                                  Water Flea
                                 Daphnia magna
48-hr EC50 = 0.31 mg/L[2]
Highly toxic
                             00123326 (Acceptable)
                                       
                                    Chronic
                                  Water Flea
NOAEC = 0.042 mg/L
LOAEC = 0.087 mg/L
Endpoint: survival, offspring production
--
                             00094645 (Acceptable)
                                       
                        Estuarine/ Marine Invertebrates
                                     Acute
                       Mysid shrimp (Americamysis bahia)
96-hr LC50 = 0.34 mg/L
Highly toxic
                             41192002 (Acceptable)
                                       
                                       
                    Eastern Oyster (Crassostrea virginica)
IC50 > 0.26 mg/L
(22% inhibition at 0.26 mg/L) 
Endpoint: shell growth
Not determined
                            41192004 (Supplemental)
                                       
                                    Chronic
                                    No data
                                    No data
--
                                      --
                       Freshwater Benthic Invertebrates
                                     Acute
                                    No data
                                       
                                    Chronic
                                    No data
                                Aquatic Plants
                                Vascular plant
                                     Acute
                                   Duckweed
                                  Lemna gibba
7-day EC50 = 2.32 mg/L 
NOAEC = 0.26 mg/L
Not defined
                            48996308 (Supplemental)
                              Non-vascular plant
                                     Acute
                                  Green algae
                           Selenastrum capricornutum
96-hr EC50 = 3.06 mg/L 
NOAEC = 0.532 mg/L
Not defined
                                   49146601
                                (Supplemental)



Table F.2.  Terrestrial Toxicity Profile for Thiabendazole

                                     Taxon
                               Exposure Duration
                         Most Sensitive Species Tested
                                Toxicity Value
                               Toxicity Category
                                     MRID
                                   Reference
                            Terrestrial Vertebrates
                                    Mammals
                                     Acute
                                Laboratory Rat
                               Rattus norvegicus
                         LD50 =  5,070 mg ai/kg bw (M)
                         LD50 =  4,734 mg ai/kg bw (F)
                             Practically nontoxic
                                   41258201
                                 (acceptable)
                                       
                                    Chronic
                                Laboratory Rat
                           NOAEL = 10 mg ai/kg diet
                           LOAEL = 30 mg ai/kg diet
                 (Reduced bodyweight gain and food consumption)
                                Not applicable
                                   43190301
                                 (acceptable)
                              Non-Passerine Birds
                                  Acute Oral
                                   Bobwhite
                              Colinus virginianus
                          LD50 > 2250 mg ai/kg bw
                             Practically nontoxic
                                   410250-02
                                 (acceptable)
                                       
                                       
                                   Bobwhite
                                       
                          LD50 > 4640 mg ai/kg bw
                             Practically nontoxic
                                   00123313
                                 (acceptable)
                                       
                                       
                                    Mallard
                              Anas platyrhynchos
                          LD50 > 4640 mg ai/kg bw
                             Practically nontoxic
                                   00137948
                                 (acceptable)
                                       
                                 Acute Dietary
                             Bobwhite and Mallard
                                       
                         LC50 > 5620 mg ai/kg diet
                             Practically nontoxic
                                   41025003
                                   41025004
                                 (acceptable)
                                       
                                    Chronic
                             Bobwhite and Mallard
                                       
                           NOAEC = 400 mg ai/kg diet
                          LOAEC >400 mg ai/kg diet
                                Not applicable
                                   00123327 
                             00123328 (acceptable)
                                Passerine Birds
                                     Acute
                                    No data
                            Terrestrial Arthropods
                              Terrestrial Insects
                                     Acute
                                   Honey Bee
                                Apis mellifera
                           LD50 > 34 ug a.i./bee
                             Practically nontoxic
                             48996305 (acceptable)
                              Terrestrial Plants
                    Terrestrial Plants -Seedling Emergence
                              Survival and growth
                                   Monocots
NOAEL = 0.23 lb/A
EC25 > 0.23 lb/A
                                      NA
        48996306 (Acceptable, except Supplemental for bean and soybean)
                                       
                                       
                                    Dicots
NOAEL < 0.23 lb/A
EC25 >= 0.23 lb/A
Endpoint: emergence and survival
                                      NA
                                       
                     Terrestrial Plants -Vegetative Vigor
                              Survival and growth
                                   Monocots
NOAEL < 0.23 lb/A
EC25 > 0.23 lb/A
Endpoint: shoot length
                                      NA
                             48996307 (Acceptable)
                                       
                                       
                                    Dicots
NOAEL = 0.23 lb/A
EC25 > 0.23 lb/A
                                      NA
                                       
 
