                 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
                                       
WASHINGTON, D.C.  20460                                       
                                 OFFICE OF   
                              CHEMICAL SAFETY AND
                             POLLUTION PREVENTION

 							
                                          PC Code No.:	114004
                                          DP Barcode:		D 384659
                                          Date:	September 7, 2011
MEMORANDUM				
      
SUBJECT:	Estimated Drinking Water Concentrations of Parent Amicarbazone and its Degradates for New Use on Turf and Conifers.

TO:	Kathryn Montague, Risk Manager
                  Registration Division (7505C)

AND	Christina Swartz, RAB2
                  Health Effects Division

FROM:	Andrew Shelby, Physical Scientist.
                  Environmental Risk Branch VI
                  Environmental Fate and Effects Division (7507C)

THRU:	Mark Corbin, Chief
                  Environmental Risk Branch VI
                  Environmental Fate and Effects Division (7507C)

Summary
This memo presents the Estimated Drinking Water Concentrations (EDWCs) for parent amicarbazone and its Des-amino and N-methyl Des-amino degradates for use in an FQPA human health risk assessment.  The two degradates chosen for this assessment are those expected to be present in natural/acidic or neutral environments where the parent is proposed to be applied.  Application of this herbicide is not proposed for soils with pH greater than 7.4. Parent amicarbazone and/or its degradates may reach both surface and groundwater under some conditions.  The registrant is seeking registration for use of this new chemical on turf on golf courses, sod farms, residential and commercial turf sites, park and recreation areas, school grounds and other turf areas and conifers in nurseries and field plantings (including Christmas trees).

The surface water and ground water estimates are calculated using PRZM/EXAMS and SCI-GROW, respectively.   The estimates are presented in Table 1 for surface water and groundwater for total toxic residues of amicarbazone to include the des-amino and N-methyl des-amino degradates as well as unextracted residues.



Table 1.  A list of the surface/ground water EDWC values for amicarbazone. 

                                   Chemical
                           Surface water EDWCs (ppb)
                                 Ground water 
Acute/Chronic EDWC (ppb)
                                       
                             Peak 96 hour average
                              Peak annual average
30 year average


                     Total Toxic Residues of amicarbazone
                                       
                                     33.3
                                       
                                     25.8
                                       
                                     11.1
                                       
                                      136



The above stated values for total toxic residues of amicarbazone represent upper-bound estimates that might be found in surface water and groundwater due to the use of amicarbazone on turf and conifers using one application at the maximum yearly rate (worst case scenario).  EDWCs would be reduced if degradates were not assumed equally toxic as amicarbazone or if unextracted residues were determined to be bound residues. Exclusion of degradates and bound residue results in reduction of EDWCs as much as 70%.  Exclusion of bound residue results in reduction of EDWCs as much as 20%.  


Environmental fate of amicarbazone
Environmental Persistence
Amicarbazone has a low vapor pressure (9.75 x10[-9] mm Hg at 30 [o]C) and is highly soluble in water (solubility 4,600 ppm at 20 [o]C).  Based on submitted environmental fate studies, the chemical is moderately persistent in aerobic soil (t1/2= 37-87 days determined for five soils, shorter half-lives were determined under field conditions: t1/2= 19 to 29 days).  It appears to slowly degrade into a number of degradation products under different environmental conditions.  The three major degradates for amicarbazone are Des-amino, N-methyl Des-amino, and Decarboxamide.  Amicarbazone is stable to direct photolysis (indirect photolysis in natural pond water: t1/273 days); hydrolysis (except at pH 9: t1/2= 66 days); and anaerobic aquatic metabolism (t1/2= >4 years in the solid phase and 533 days in the water phase).  With the exception of natural clear water bodies subjected to sunlight, the major route of dissipation of amicarbazone appears to be bio-transformation.  In clear water bodies subjected to sunlight, indirect photolysis may contribute to amicarbazone dissipation.  Although photolysis might occur on soil surfaces (t1/2= 54 days), label recommended incorporation of the pesticide just after application may render this process unimportant.  Photolysis on soil study suggests that the resultant major degradate is Des-amino (Max. of 15% in irradiated samples compared with 6% in the dark) with Decarboxamide being a very minor degradate (Max. Of 1% in irradiated samples compared with 3% in the dark).

Environmental Metabolites
Laboratory and field studies identified only three major degradates for amicarbazone: Des-amino, N-methyl Des-amino and Decarboxamide.  Des-amino and  N-methyl Des-amino degradates were both the result of biodegradation in aerobic soil in the laboratory and in the field while Des-amino alone resulted from indirect photolysis in aqueous systems. Decarboxamide resulted only from hydrolysis in alkaline aqueous systems.  Mobility studies were the only reviewed studies for the major three degradates of amicarbazone, however, data from the single aerobic soil study on the parent and unreviewed degradate specific studies suggest that both Des-amino and N-methyl Des-amino are highly persistent.  Table 2 is a summary of available data indicating maximum concentrations of degradation products found in submitted fate studies. 

Table 2. Maximum concentrations of various degradation products found in submitted fate studies. 




Degradate 

Max Degradate Concentration (% of applied) and Time (days) to Max Concentration


                                       
                                Hydrolysis [2]

                        Indirect Aqueous Photolysis [1]

                                       
                                 Aerobic Soil

                                  Anaerobic 
                                    Aquatic

                                    Aerobic
                                    Aquatic 

                                       
                                     TFD  

Des-amino

                                       
                                     None

                                      16%
                                   (35 days)

                                     63% 
                                  (125 days)

                                       
                                       
                                     None
                              (Parent is stable)

                                       
                                       
                                       
                                 No Acceptable
                                     Data

                                    26-27%
                                  (59-61days)

N-methyl Des-amino

                                       
                                     None

                                       
                                     None

                                      11%
                                  (360 days)



                                       
                                     None

Decarboxamide

                                     29% 
                                  (30 days) 
                                  Only @ pH 9

                                      9% 
                                  (35 days) 
                              with 2% in the dark

                                       
                                     None



                                       
                                     None
[1] In natural pond water, pH 8.4, note that parent is stable to direct aqueous photolysis.

Amicarbazone is not to be applied on soils with pH values higher than 7.4.  Therefore, the fate of the chemical in only neutral and acidic conditions is important to this assessment.  In such environments, amicarbazone and two of its major degradates (Des-amino, N-methyl Des-amino) are expected to be important.  Only in cases where amicarbazone is transported into alkaline ground water, surface water bodies and/or soils, the third degradate (Decarboxamide) is expected to become important.
 
Expected Mobility of Amicarbazone and its Metabolites
Available data suggest that amicarbazone is very highly mobile (Koc range= 16.7 to 37.0 L kg[-1], from adsorption/desorption and aged leaching studies).  Additionally, adsorption/desorption and aged leaching studies, suggest that all of the three major degradates of amicarbazone are very highly mobile (ASTM 1996).  Determined Koc values were: Des-amino (Koc range= 26.4 to 42.3 L kg[-1]), N-methyl Des-amino (Koc range= 34.3 to 56.4 L kg[-1]) and Decarboxamide (Koc range= 9.4 to 16.2 L kg[-1]). 

Given the moderate persistence/high mobility and solubility of the parent and the apparent high persistence/high mobility of its two degradates, parent is expected to dissipate slowly and at the same time be vulnerable to leaching/run-off.  The resultant Des-amino and N-methyl Des-amino degradates are expected to behave similar to their parent and become the major terminal degradates of this chemical in surface and ground water.

In the case of amicarbazone being transported into alkaline ground water, surface water bodies and/or soils, the third degradate (Decarboxamide) is expected to become important contaminant to surface and/or groundwater. This is because decarboxamide was the major hydrolysis degradate in alkaline conditions and it was determined to be highly mobile.  Possible contamination of surface and ground water with this degradate is expected to increase if it was determined to be highly persistent.  

Estimating Drinking Water Exposure from Surface Water Sources

Surface water EDWCs were estimated using PRZM/EXAMS.  Input parameters are presented and described in the following table.


Table 3. PRZM/EXAMS input parameter values for ambicarbazone use on turf and conifers
                               PARAMETER (units)
                                   VALUE(S)
                                    SOURCE
                                    COMMENT
Application Rate (kg a.i./ha)
                                 Parent: 0.490
                                       
                  Product label; MRID 45121731; MRID 48237507
Represents the maximum possible single application rate per crop season (year) for all new uses.  
Number of Applications
                                       1
                                       
       Maximum single application rate equals maximum annual application
Molecular weight (g/mol)
                                  Parent: 241
                                       
                               Product Chemistry
                                       -
Henry's Law Constant (atm-m[3]/mol)
                                 1.5 x 10[-12]
                                       
   (Vapor Pressure [torr]/760)/(Solubility [mg/L]/Molecular Weight [g/mol])
Vapor Pressure (torr)
                                 2.2 x 10[-8]
                                       
                                       -
Solubility in Water @ 20 [O]C, (mg/L or ppm)
                                    4,600 
                               Product Chemistry
                                       - 
Organic Carbon Partition Coefficient  (mL/g)
                                 Parent: 16.7
                                       
                    45121719; 45121732; 45121801; 45121733
KOC ranges from 16.7 to 37.0.  Lowest non-sand KOC used for modeling.  KOC is correlated to KD (r[2] = 0.62).
CAM (Chemical Application Method)
                                       1
                                       
                  ground spray; pre-emergence, unincorporated
Depth of Incorporation (inches)
                                       0
                                 Product label
                                       - 
Application efficiency (decimal)
                                     0.99
                                       
                                       
Spray drift fraction (decimal)
                                     0.064
                                       
                                       
Application date
                                  February 15
                                       
Multiple application dates surrounding the emergence dates for highest agricultural and non-agricultural EDWCs were modeled also
Hydrolysis Half-life (days)
                                    Stable
    45121730 (parent); 48073601 (N-methyl Des-amino); 48237506 (Des-amino)
                                       
Aqueous Photolysis Half-life @ pH 7 (days)
                                    Stable
                                   45121803
                                       
Aerobic Aquatic Metabolism Half-life (days)
                                     2816
                                       

                     2x Aerobic Soil Metabolism half-life
Anaerobic Aquatic Metabolism Half-life (days)
                                    Stable
                                       
                                       
Aerobic Soil Metabolism Half-life (days)
                                     1408

                              45121731; 48237507
90[th] percentile average of 5 total toxic residue half-life estimates: 533 days, 990 days, 1155 days, 1155 days and 1733 days.  These total toxic residue half-lives include des-amino and N-methyl des-amino degradates along with ambient unextracted residues.
Percent Crop Area
                                       1
                                       
      PCAs for turf and conifers have not been developed and/or approved
1 "Input Parameter Guidance" refers to Guidance for Selecting Input Parameters in Modeling the Environmental Fate and Transport of Pesticides; Version 2.1, October 22, 2009.

For new uses on turf and conifers, nine PRZM scenarios and two application dates were utilized with the California Nursery scenario resulting in highest EDWCs.  All available scenarios representing turf and conifers were used and two early spring application dates were used to represent label application recommendations.  Results for the all scenarios and application dates are presented below.  PRZM/EXAMS output for the highest modeled concentrations (CA Nursery/February 15) is attached as Appendix 1.

Table 4.  PRZM/EXAMS EDWCs for amicarbazone use on turf and conifers
Scenario
Application date
Peak 96 hour average (ppb)
Peak annual average (ppb)
30-year average (ppb)
CA Nursery
February 15
                                     33.3
                                     25.8
                                     11.1

March 1
                                     15.2
                                     13.9
                                      6.5
FL Turf
February 15
                                      4.3
                                      3.5
                                      2.4

March 1
                                      4.0
                                      3.1
                                      2.4
FL Nursery
February 15
                                     12.7
                                      3.3
                                      1.5

March 1
                                     22.3
                                      3.7
                                      1.5
MI Nursery
February 15
                                      7.7
                                      2.6
                                      1.5

March 1
                                      9.3
                                      3.2
                                      1.9
NJ Nursery
February 15
                                     11.3
                                      3.8
                                      1.5

March 1
                                     12.5
                                      4.6
                                      1.9
OR Christmas tree
February 15
                                      5.5
                                      4.6
                                      3.0

March 1
                                      3.8
                                      3.3
                                      2.6
OR Nursery
February 15
                                      5.7
                                      3.6
                                      2.0

March 1
                                      5.3
                                      3.3
                                      1.8
PA Turf
February 15
                                      4.4
                                      3.7
                                      2.7

March 1
                                      5.3
                                      4.4
                                      3.0
TN Nursery
February 15
                                     13.7
                                      4.0
                                      1.8

March 1
                                     14.6
                                      3.1
                                      1.4



Estimating Drinking Water Exposure from Ground Water Sources

Groundwater EDWCs were estimated using SCI-GROW.  Input parameters are presented and described in the following table.  

Table 5. Summary of SCI-GROW input parameters for total toxic residues of amicarbazone. 
Parameter
Value
Reference

Application Rate
 (lb a.i./acre)
And
(Number of Applications)

                                  0.4375 (1)

Maximum label rate for turf and conifers

Aerobic Soil Metabolism t(1/2) (days)

                                     1155

Median value from 5 studies... (451217-31)

Koc (L Kg[-1])

                                     24.2

Median of  7 values (451217-19/32)
* Fate data values are as per Guidance for Selecting Input Parameters in Modeling the Environmental Fate and Transport of Pesticides; Version 2.1 October 22, 2009



Refinements to groundwater EDWCs can be made using the provisional Tier II model, PRZM-GW.  Though mitigation of maximum application rates can be modeled through SCIGROW, PRZM-GW can allow for other mitigation options to be explored such as well set-backs and geographic restrictions. The groundwater EDWs produced by SCIGROW is 136 ppb for acute and chronic endpoints.

Appendix 1


stored as CAnursery215.out
Chemical: amicarbazone
PRZM environment: CAnurserySTD.txt	modified Tueday, 26 August 2008 at 06:16:36
EXAMS environment: ir298.exv	modified Tueday, 26 August 2008 at 06:14:08
Metfile: w23188.dvf	modified Tueday, 26 August 2008 at 06:15:38
Water segment concentrations (ppb)

Year	Peak	96 hr	21 Day	60 Day	90 Day	Yearly
1961	1.279	1.278	1.274	1.266	1.261	1.072
1962	4.07	4.051	3.964	3.924	3.906	3.442
1963	5.155	5.149	5.123	5.098	5.084	4.644
1964	5.391	5.389	5.38	5.363	5.35	5.038
1965	7.55	7.534	7.467	7.089	6.912	5.926
1966	4.056	4.041	3.975	3.889	3.665	3.025
1967	3.598	3.596	3.59	3.57	3.561	3.286
1968	12.23	12.13	11.74	11.32	11.21	9.385
1969	10.49	10.22	9.176	8.997	8.957	8.656
1970	39.93	39.56	39.28	38.83	38.64	32.47
1971	35.55	35.33	34.6	34.24	33.97	32.1
1972	27.5	27.49	27.47	27.41	27.36	26.18
1973	20.34	20.31	20.16	19.75	19.72	19.1
1974	18.04	17.83	16.99	16.16	16.14	15.6
1975	16.28	16.11	15.42	14.42	14.1	13.3
1976	12.97	12.97	12.96	12.34	12.19	11.68
1977	10.45	10.35	10.08	10.06	9.993	8.592
1978	9.111	9.025	8.729	8.203	8.071	7.254
1979	6.108	5.845	4.884	4.257	4.233	4.101
1980	4.654	4.577	4.301	4.012	3.926	3.618
1981	17.87	17.65	16.74	14.83	14.34	11.68
1982	11.18	10.99	10.75	10.44	10.32	9.156
1983	10.19	10.09	9.52	8.392	8.099	7.499
1984	7.997	7.993	7.981	7.952	7.929	7.54
1985	6.423	6.421	6.413	6.397	6.384	5.781
1986	34.54	33.9	31.57	29.46	28.31	22.18
1987	19.03	18.92	18.54	18.43	18.3	17.34
1988	12.29	12.25	12.07	11.75	11.61	9.391
1989	10.09	10.08	10.05	10.01	9.982	9.356
1990	17.31	17.26	17.08	16.96	16.89	15.37

Sorted results
Prob.	Peak	96 hr	21 Day	60 Day	90 Day	Yearly
0.032258064516129	39.93	39.56	39.28	38.83	38.64	32.47
0.0645161290322581	35.55	35.33	34.6	34.24	33.97	32.1
0.0967741935483871	34.54	33.9	31.57	29.46	28.31	26.18
0.129032258064516	27.5	27.49	27.47	27.41	27.36	22.18
0.161290322580645	20.34	20.31	20.16	19.75	19.72	19.1
0.193548387096774	19.03	18.92	18.54	18.43	18.3	17.34
0.225806451612903	18.04	17.83	17.08	16.96	16.89	15.6
0.258064516129032	17.87	17.65	16.99	16.16	16.14	15.37
0.290322580645161	17.31	17.26	16.74	14.83	14.34	13.3
0.32258064516129	16.28	16.11	15.42	14.42	14.1	11.68
0.354838709677419	12.97	12.97	12.96	12.34	12.19	11.68
0.387096774193548	12.29	12.25	12.07	11.75	11.61	9.391
0.419354838709677	12.23	12.13	11.74	11.32	11.21	9.385
0.451612903225806	11.18	10.99	10.75	10.44	10.32	9.356
0.483870967741936	10.49	10.35	10.08	10.06	9.993	9.156
0.516129032258065	10.45	10.22	10.05	10.01	9.982	8.656
0.548387096774194	10.19	10.09	9.52	8.997	8.957	8.592
0.580645161290323	10.09	10.08	9.176	8.392	8.099	7.54
0.612903225806452	9.111	9.025	8.729	8.203	8.071	7.499
0.645161290322581	7.997	7.993	7.981	7.952	7.929	7.254
0.67741935483871	7.55	7.534	7.467	7.089	6.912	5.926
0.709677419354839	6.423	6.421	6.413	6.397	6.384	5.781
0.741935483870968	6.108	5.845	5.38	5.363	5.35	5.038
0.774193548387097	5.391	5.389	5.123	5.098	5.084	4.644
0.806451612903226	5.155	5.149	4.884	4.257	4.233	4.101
0.838709677419355	4.654	4.577	4.301	4.012	3.926	3.618
0.870967741935484	4.07	4.051	3.975	3.924	3.906	3.442
0.903225806451613	4.056	4.041	3.964	3.889	3.665	3.286
0.935483870967742	3.598	3.596	3.59	3.57	3.561	3.025
0.967741935483871	1.279	1.278	1.274	1.266	1.261	1.072

0.1	33.836	33.259	31.16	29.255	28.215	25.78
					Average of yearly averages:	11.1254

Inputs generated by pe5.pl - Novemeber 2006

Data used for this run:
Output File: CAnursery215
Metfile:	w23188.dvf
PRZM scenario:	CAnurserySTD.txt
EXAMS environment file:	ir298.exv
Chemical Name:	amicarbazone
Description	Variable Name	Value	Units	Comments
Molecular weight	mwt	241	g/mol
Henry's Law Const.	henry	1.5E-12	atm-m^3/mol
Vapor Pressure	vapr	2.2E-8	torr
Solubility	sol	4600	mg/L
Kd	Kd		mg/L
Koc	Koc	16.7	mg/L
Photolysis half-life	kdp	0	days	Half-life
Aerobic Aquatic Metabolism	kbacw	2816	days	Halfife
Anaerobic Aquatic Metabolism	kbacs	0	days	Halfife
Aerobic Soil Metabolism	asm	1408	days	Halfife
Hydrolysis:	pH 7	0	days	Half-life
Method:	CAM	1	integer	See PRZM manual
Incorporation Depth:	DEPI	0	cm
Application Rate:	TAPP	0.49	kg/ha
Application Efficiency:	APPEFF	0.99	fraction
Spray Drift	DRFT	0.064	fraction of application rate applied to pond
Application Date	Date	15-02	dd/mm or dd/mmm or dd-mm or dd-mmm
Record 17:	FILTRA	
	IPSCND	1
	UPTKF	
Record 18:	PLVKRT	
	PLDKRT	
	FEXTRC	0.5
Flag for Index Res. Run	IR	Reservoir
Flag for runoff calc.	RUNOFF		none, monthly or total(average of entire run)
