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


                                                                PC Code: 053001
                                                            DP Barcodes: 404861


MEMORANDUM	July 17, 2013


SUBJECT:	Metaldehyde: Tier II Drinking Water Exposure Assessment for the Existing Watercress Use, the Existing Special Use for Invasive Mollusk Eradication, and the Proposed Wetland Taro Use (Reg. Nos. 6836-107 (technical) and 71096-13).

TO:			Barbara Madden, Risk Manager
            Laura Nollen, Risk Manager Reviewer
         Risk Integration, Minor Use, and Emergency Response Branch
         Registration Division
		
FROM:	James Hetrick, Ph.D., Senior Science Advisor
                              Melanie Biscoe, Physical Scientist
               Environmental Fate and Effects Division

THROUGH:	Dana Spatz, Branch Chief
               Environmental Risk Branch 3
         Environmental Fate and Effects Division (7507P)


Executive Summary & Background

Metaldehyde (2,4,6,8-tetramethyl-1,3,5,7-tetraoxacyclooctane) is a molluscicide used to control slugs and snails.  Interregional Research Project #4 (IR-4) requested new or expanded uses of metaldehyde for the following crops/crop groups:
   * Grass (grown for seed)
   * Leaf petioles subgroup 4B
   * Mint
   * Taro (wetland)
   * Corn (field)
   * Soybean (regional registration)
   * Caneberry subgroup 13-07A
   * Bushberry subgroup 1307-B
   * Berry, low growing, subgroup 13-07G
When considering this request, the Environmental Fate and Effects Division (EFED) determined that Wetland Taro would have the highest annual use rate of all the proposed new or expanded uses, as well as the highest annual rates for all existing uses.  Although EFED estimated preliminary drinking water exposures for Wetland Taro, EFED determined that Wetland Taro is not appropriate for inclusion in a national drinking water assessment because its use is likely limited to the Hawaiian island of Kauai.  EFED also determined that Wetland Taro is not appropriate for inclusion in a regional drinking water assessment, as is applied to submerged fields that release to surface water systems.  Drinking water estimates for such an aquatic application would not be reflective of actual drinking water concentrations, because ground water is the source of drinking water in Hawaii's Taro-producing areas and the majority of the Hawaiian Islands generally (based on the Safe Drinking Water Information System (SDWIS), accessed at http://www.epa.gov/enviro/facts/sdwis/search.html).
When reviewing the metaldehyde labels, EFED determined that the existing Watercress use had a higher application rate than the remaining proposed uses, as well as a higher application rate than the other agricultural uses on the metaldehyde label.  With regard to non-agricultural uses, EFED determined that the Special Use for Exotic Mollusk Eradication had the highest application rate.  EFED has therefore prepared a drinking water assessment for the existing watercress use and the existing "Special Use" for exotic mollusk eradication.  The "Special Use" use pattern and application rate are based on information in IR-4's amended label submission for "OR-CAL Slug-Fest 4.0" (EPA Reg. No. 71096 - -13). The watercress use pattern and application rate used in this assessment are based on the label for "Slug-Fest All Weather Formula" (EPA Reg. No. 71096 - -4) approved on September 11, 2012, as watercress is not included on the label for "OR-CAL Slug-Fest 4.0" (EPA Reg. No. 71096 - -13).  

The recommended Estimated Drinking Water Concentrations (EDWCs) for use in human health risk assessment are based on the exotic mollusk eradication use rate of 2 lbs a.i./acre applied in 6 broadcast (ground) applications for a total maximum annual application of 12 lb a.i./acre.   Although there is no specific re-application interval stated in the "Special Use" box on the metaldehyde label, EFED assumed there would be a minimum 14-day interval based on label directions for applications to grass (seed crop), forage and hay.  EFED also assumed that applications would occur for six consecutive years because this is maximum number of site-years for use according to APHIS.  The computer models PRZM/EXAMS (surface water) and PRZM-GW (ground water) were used to develop the EDWCs for use in the human health risk assessment.  

The highest estimated 1-in-10-year annual peak (acute), annual average (chronic) and 30-year annual average (cancer) concentrations of metaldehyde in surface water sources of drinking water are 205, 136, and 83 μg/L, respectively.  For ground water sources of drinking water, the estimated peak and post-breakthrough average concentrations were 1,740 and 635 μg/L, respectively (Table 1).  

EFED recommends using the maximum concentrations from the ground water simulation for human health risk assessment (i.e., 1,740 and 635 μg/L).   EFED recognizes that, due to substantial uncertainty in the metaldehyde hydrolysis half-life data, there is uncertainty in the ground water simulation results.  Refinement options in this regard are limited, as an additional hydrolysis study is not likely to provide sufficient data to narrow the metaldehyde hydrolysis half-life, which may range from to 10 to 242 years. 

Table 1. Maximum Tier II estimated drinking water concentrations (EDWCs) in parts per billion (μg/L) resulting from applications of metaldehyde at an annual application rate of 12 lb a.i./acre.
Drinking water source (model)
                                 1-in-10 year 
                              30-year simulation

                                     Acute
                                    Chronic
                                     Acute
                                    Chronic
Surface water    
(PRZM-EXAMS)
                                      205
                                      136
                                       -
                                      83
Ground water     
(PRZM-GW)
                                       -
                                       -
                                     1740
                                      635

Data Uncertainties

The EPA Office of Pesticide Programs published the metaldehyde Reregistration Eligibility Decision (RED) on July 27, 2006 and issued the associated Data Call-In on September 3, 2008.  No additional environmental fate data were required for metaldehyde as part of the reregistration process, and EFED considers the environmental fate database for metaldehyde to be fulfilled.

There is substantial uncertainty in the metaldehyde hydrolysis half-life data, as calculated half-lives range from 10 to 240 years (MRID 41114701).   Because the longest hydrolysis studies are generally carried out over the course of one year, an additional hydrolysis study is not likely to provide sufficient data to narrow the metaldehyde hydrolysis half-life.  This uncertainty has important implications for ground water simulation results, as PRZM-GW is highly sensitive to hydrolysis half-life inputs.  These implications are discussed in more detail in the Drinking Water Modeling section.


Previous Drinking Water Assessments

The residue of concern in drinking water for human health risk assessment is metaldehyde parent. The most recent drinking water assessment was conducted for the 2006 metaldehyde RED.  For surface water, EDWCs were generated using the Tier II PRZM-EXAMS model.  The maximum 1-in-10 year peak EDWC was 110 ug/L (Florida cole crops scenario), the maximum 1-in-10-year annual average EDWC was 55.8 ug/L (California leafy vegetable scenario), and the maximum overall average EDWC was 31.9 ug/L (California leafy vegetable scenario).  For ground water, EDWCs were generated from a Tier I SCI-GROW analysis.  The maximum EDWC for ground water was 62.5ug/L (based on ornamental use rates).  

It should be noted that the DWA for the RED included an EDWC for the watercress use.  The watercress EDWC in the RED DWA was 1,500 ug/L, and was calculated by diluting the application rate in the volume of a 1-acre paddy with a water depth of 6 inches. This EDWC did not consider degradation, sorption, or distance from drinking water intake, and was therefore not used in the dietary assessment for the RED.

Monitoring data for metaldehyde are limited.  Metaldehyde was only an analyte in the 2010 and 2011 USDA Pesticide Data Program (PDP).  There were no detections of metaldehyde in surface water.

Current Assessment

The current assessment:
   * Estimates drinking water concentrations expected from ground spray applications of metaldehyde on turf for the purposes of exotic mollusk eradication
   * Estimates drinking water concentrations expected from application to watercress fields 
   * Estimates drinking water concentrations consistent with recent EFED policy changes concerning
Ground water modeling - EFED is implementing the use of PRZM-GW for Tier 1 and Tier 2 modeling for residues in ground water, while SCI-GROW model is being used as a Tier 1 screen. Therefore both PRZM-GW and SCI-GROW estimates are reported in this assessment.  PRZM-GW allows for the estimation of pesticide concentrations with multiple years of applications and the consideration of different scenarios. The SCI-GROW model represents a generic vulnerable site where one or multiple application(s) may be made within a single year. The ground water EDWCs for metaldehyde are higher with PRZM-GW. The increase is due in part to the consideration of multiple years of application. The simulated average concentration and post-breakthrough averages from PRZM-GW are greater than the value estimated by SCI-GROW because they represent multiple years of metaldehyde use. 
         o 
Uses Assessed

The uses evaluated in this assessment are described in the following paragraphs, as well as in Table 22.

"Special Use" for Exotic Mollusk Eradication

The existing use sites for exotic mollusk eradication include the following:
   * Fallow land
   * Barrier strips
   * Uncultivated non-agricultural areas
   * Recreational areas
   * Non-food or non-feed brush
   * Weed or dense vegetative areas
   * Railroad, pipeline, highway, power and telephone rights of way and roadsides
   * Guardrails and fences
   * Lumberyards
   * Storage areas
   * Seaports
   * Industrial facility sites, including yards and walkways around industrial buildings, parking areas, parks, golf courses, other public areas
   * Airports and similar industrial non-crop areas

This use is limited to State and/or Federal invasive mollusk eradication operations.  Only ground (i.e., broadcast) applications are allowed for this use.  The maximum single application rate for all exotic mollusk eradication uses is 2 lb a.i/acre, and the maximum annual application rate is 12 lb a.i./acre (i.e., 6 applications of 2 lb a.i/acre per year).  Although the label does not specify a minimum reapplication interval, EFED assumes that a 14-day reapplication interval is used.  This assumption is based on the 14-day minimum re-application interval for grass (seed crop), forage and hay specified on the label instructions for "OR-CAL Slug-Fest 4.0" (EPA Reg. No. 71096 - -13) submitted by IR-4.  With regard to surface water EDWCs, this assessment calculates EDWCs for application to turf, as the turf scenario is expected to be representative of (or sufficiently conservative with respect to) the use sites listed above.  Use of a Percent Cropped Area (PCA) adjustment when calculating turf EDWCs is not appropriate given the presence of non-agricultural and non-turf pesticide uses on the metaldehyde label. 

Watercress

Only ground (i.e., broadcast) applications are allowed for the watercress use (Table 3).  The maximum single application rate for watercress is 2 lb a.i/acre, and the maximum annual application rate is 8 lb a.i./acre (i.e., 4 applications of 2 lb a.i/acre per year).  The "Slug-Fest All Weather Formula" (EPA Reg. No. 71096 - -4) label states that no more than two applications may be made per harvested crop, and that the second application can be made no closer than three days prior to harvest.  The label also states that:
   * The average depth of water in the watercress beds must be between 1 to 15 inches
   * Metaldehyde applications are to be made to the watercress canopy
   * The watercress field must be drained for a minimum period of 24 hours prior to metaldehyde application and must remain drained for 24 hours following the application
   * When the flow-through irrigation cycle is resumed, the effluent from the first hour from metaldehyde-treated beds must be held or recirculated on-site for five days or longer

Although the label does not specify a minimum reapplication interval, EFED assumed a 20-day reapplication interval based on growth and harvest patterns of watercress in Florida, a major watercress production state.  

Table 2. Metaldehyde Uses and Rates Assessed 
                                      Use
 Single Application Rate                            lb a.i./acre              
                           Re-application Interval 
                Maximum Annual Rate lb a.i./acre              
                              Application Method
                  Percent Crop Area (PCA)  Adjustment Factor*
                                   Existing
"Special Use" for Invasive Mollusk Eradication
                                       2
                                    14 days
                                      12
                                    Ground
                                      n/a
Watercress
                                       2
                                    20 days
                                       8
                                    Ground
                                      n/a
*Only applicable for surface water modeling using PRZM-EXAMS.


Environmental Fate and Transport Characterization


Based on submitted laboratory data, metaldehyde is expected to be moderately persistent and mobile in the environment (Table 4).  The major routes of dissipation for metaldehyde are through runoff, leaching and aerobic degradation.  

Based on data submitted for one soil type, metaldehyde degrades under aerobic conditions with a half-life of approximately two months, eventually breaking down to acetaldehyde, which readily mineralizes to carbon dioxide.  Metaldehyde appears to be persistent in anaerobic environments, with a half-life of over 200 days reported for a soil maintained under anaerobic conditions. A Henry's Law constant of 2.43x10[-8] atm-m[3]/mol and vapor pressure of 1.1x10[-5] torr suggest that volatility is not a major route of transport in the environment.

Metaldehyde is not susceptible to either hydrolysis or photolysis under typical environmental conditions.  Therefore, hydrolysis and photolysis are not expected to be major routes of dissipation in the environment.  

Metaldehyde is very mobile in soil, with adsorption coefficients (KF values) ranging from 0.10 to 0.44 in four soils, and corresponding Koc values between 14.6 and 55.7.  These relatively low values indicate potential for leaching and runoff in the open environment.  

Table 3. Physical/chemical properties and environmental fate source data for metaldehyde
Drinking Water Modeling
                                   Property
                                     Value
                            Source and/or Comments
Chemical Name
               2,4,6,8-tetramethyl-1,3,5,7-tetraoxacyclooctane 
                                       
Molecular Weight
                                 176.2 g/mole
                                   Epi Suite
Solubility in Water
                               200 mg/L (17°C)
          Product Chemistry, supported by Epi Suite results at 20°C

                              45,360 mg/L (25°C)
                                   Epi Suite
Vapor Pressure (25°C)
                                 0.000011 torr
                               Product Chemistry
Hydrolysis Half-life (25°C)
                              pH 5: 3,649-88,455
                                 MRID 41114701

                              pH 7: 4,308-66,092


                                 pH 9: stable 

Aqueous Photolysis Half-life (pH 7)
                                    stable
                                 MRID 41337401
Soil Photolysis Half-life
                                    stable
                                 MRID 41507701
Aerobic Soil Metabolism Half-life 
                                   67.2 days
          half-life for one soil                       MRID 41546001
Anaerobic Soil Metabolism Half-life
                                   222 days
          half-life for one soil                        MRID 41507701
Organic Carbon-Normalized Soil Partition Coefficient (KFoc)
                                  36.25 mL/g
       MRIDs 41228001, 41675101   Average KFoc (41.2, 55.7, 14.6, 33.5)
Soil Adsorption Coefficient (KF)
                                  0.234 mL/g
      MRIDs 41228001, 41675101; Average KF (0.103, 0.223, 0.175, 0.436) 
Henry's Law Constant
                           2.43x10[-8] atm-m[3]/mol
Calculated from vapor pressure, solubility, and molecular weight per input parameter guidance

Invasive Mollusk Eradication Use

Models and Scenarios Used

Detailed descriptions, documentation, and links for running the models discussed in the paragraphs below may found at http://www.epa.gov/oppefed1/models/water/index.htm.  

Surface Water Modeling

The estimated drinking water concentrations (EDWCs) for the invasive mollusk eradication  use of metaldehyde were generated using PRZM3 (version 3.12.2 compiled 05/11/05, Carsel, 1997) and EXAMS (version 2.98.04.06 compiled 04/24/05, Burns, 2002).  PRZM simulates pesticide fate and transport as a result of leaching, direct spray drift, runoff and erosion from an agricultural field and EXAMS estimates environmental fate and transport of pesticides in surface water body. The EDWCs assessment for surface water uses single or multiple sites which typically represent a high-end exposure scenario from pesticide use on a particular crop or non-crop use site.  PRZM and EXAMS were linked by the program (PE5, version 01 compiled 07/23/07). The linked PRZM and EXAMS models simulate the impact of daily weather on the treated agricultural field over a period of thirty years. During this time, pesticide is washed-off of the field into the water-body by twenty to forty rainfall/runoff events per year. Each new addition of pesticide to the water-body adds to the pesticide which has arrived earlier either through previous runoff events or through spray-drift and begins degrading on the day it reaches the water. Longer-term, multiple-day average concentration values are calculated based on the peak day value and subsequent values considering degradation processes.  
	
Within the linked PRZM and EXAMS models, the "index reservoir" is used for drinking water assessments.  The index reservoir is used in a manner similar to the "standard pond" used in ecological exposure modeling, except that flow rates have been modified to reflect local weather conditions.  The index reservoir is approximately 82 m wide and 640 m long, with an area of 5.3 ha.  The area of the entire watershed is 172.8 ha.  Weather and agricultural practices are simulated for 30 years so that the 1-in-10-year exceedance probability at the site can be estimated. The simulation is generated using 30 years of meteorological data, encompassing the years from 1961 to 1990. 

In this assessment, EFED's Standard and California Red-Legged Frog (RLF) scenarios were used within the linked PRZM/EXAMS.  For turf, the FL and PA Standard Turf scenarios were used, as well as the CA Red-Legged Frog (RLF) Turf scenario.  The metadata for each scenario identifies the growing season for the crop of concern in that scenario.  In this assessment, EDWCs were calculated for each month of the growing season identified in the scenario metadata.  For turf, EDWCs were calculated for the 15[th] day of each month of the growing season.  

The Percent Crop Area (PCA) is a generic watershed-based adjustment factor that is applied to pesticide concentrations estimated for the surface water component of the drinking water exposure assessment using PRZM/EXAMS with the index reservoir.  When appropriate, the EDWCs generated by the linked PRZM/EXAMS models are multiplied by the maximum percent of crop area (PCA) in any watershed (expressed as a decimal) generated for the crop or crops of interest.  Guidance for using PCAs and a thorough discussion of this method and comparisons of monitoring and modeling results for selected pesticide/crop/site combinations is located at http://www.epa.gov/oppefed1/models/water/pca_adjustment_dwa.html.  In this assessment, PCA adjustment factors were not used because the label includes numerous agricultural and non-agricultural use sites for metaldehyde, and the co-occurrence of metaldehyde uses within a watershed cannot be ruled out.     

Ground Water Modeling

Tier I and II groundwater EDWCs for metaldehyde resulting from its exotic mollusk eradication use were derived with PRZM-GW (Pesticide Root Zone Model for Groundwater, version 1.0, August 31, 2012), using the GW-GUI (Graphical User Interface, version 1.0, August 31, 2012).  PRZM-GW is a one-dimensional, finite-difference model that estimates the concentrations of pesticides in groundwater.  It accounts for pesticide fate in the crop root zone by simulating pesticide transport and degradation through the soil profile after a pesticide is applied to an agricultural field. PRZM-GW permits the assessment of multiple years of pesticide application (up to 100 years) on a single site. Six standard scenarios, each representing a different region known to be vulnerable to groundwater contaminations, are available for use with PRZM-GW for risk assessment purposes. In the PRZM-GW simulations, each of these standard scenarios was used.  PRZM-GW output values represent pesticide concentrations in a vulnerable groundwater supply that is located directly beneath a rural agricultural field. Note that, unlike in surface water modeling, PCAs are not used with PRZM-GW per EFED guidance.  

For comparison purposes, EDWCs were also calculated using the Screening Concentration in Ground Water model (SCI-GROW v2.3, compiled 08/08/03).  SCI-GROW was developed by fitting a linear model to ground water concentrations with the Relative Index of Leaching Potential (RILP) as the independent variable.  Ground water concentrations were taken from 90-day average high concentrations from Prospective Ground Water studies.  The RILP is a function of aerobic soil metabolism and the soil-water partition coefficient.  There is no PCA adjustment for SCI-GROW.  The output of SCI-GROW represents the concentrations of metaldehyde residues that might be expected in shallow unconfined aquifers under sandy soils. 

Modeling Input Parameters

The model input parameters for PRZM-EXAMS and PRZM-GW are summarized in Table 4.  Model input values were prepared following EFED input guidance[,].  

In contrast to surface water EDWCs calculated using PRZM-EXAMS, PRZM-GW EDWCs are highly impacted by hydrolysis half-life inputs.  This is because hydrolysis is generally the only transformation pathway considered at soil depths greater than one meter.  Even if a chemical is considered stable to hydrolysis, PRZM-GW input parameter guidance recommends using a hydrolysis half-life calculated from the guideline hydrolysis study (OCSPP 835.2120) for better estimates of groundwater concentrations (this is supported by EFED's comparison of PRZM-GW results to groundwater monitoring data).  In the case of metaldehyde, the calculated hydrolytic half-lives range from 10 to 242 years based on data from a 32-day hydrolysis study.  This wide range of half-lives cannot be refined, as an additional hydrolysis study is not likely to provide sufficient data to narrow the metaldehyde hydrolysis half-life, 

Because of the imprecision in the hydrolytic half-lives calculated, as well as the uncertainty associated with extrapolating half-lives so far beyond the 32-day study duration, a hydrolytic half-life calculated for a pH of 7 using log-linear regression analysis was used as the PRZM-GW hydrolysis input parameter.  This half-life is 4,716 days, as indicated in Table 4.  For comparison purposes, upper-bound PRZM-GW EDWCs resulting from the assumption that no hydrolytic degradation of metaldehyde occurs are also reported in the Modeling Results section.  SCI-GROW input parameters include the maximum single application rate , the maximum number of applications, and the aerobic soil metabolism half-life as well as the Koc (36.25 ml/g).

Table 4. Input values used for modeling the metaldehyde mollusk eradication use on turf with PRZM-EXAMS and PRZM-GW.
Model Input Parameter
                             Input Value and Unit
                           Used as a PRZM-GW Input?
                                Source/Comments
Maximum Application Rate
                                  Turf: 2.24
                                      √
kg/ha Labeled Use, Per 2006 RED Addendum
Maximum Number of Applications
                                       6
                                      √
Maximum yearly application rate stated on label (equivalent to 13.44 kg/ha)
Method of Application
    Surface applied, not incorporated (In PRZM-EXAMS, CAM = 1, IPSCND = 1 )
                                       v
Label
Application Efficiency
                              0.99 (ground spray)
                                       
Input parameter guidance
Spray Drift Fraction
                             0.064 (ground spray)
                                       
Input parameter guidance
Type of Application
                                    Ground
                                       
PRZM/EXAMS manual
Date of Application
                            15th day of each month.
         √ (30 days after post-emergence date in PRZM-GW scenario)

Minimum Interval between Applications
   Turf: 0-14 days, depending on label interpretation; used 14 days in model
                                      √
Label
Soil Partition Coefficient  KF
                                  0.234 ml/g
                                      √
MRID 41228001; Average KF (0.103, 0.223, 0.175, 0.436) 
Henry's Law Constant
                                 2.43 x 10[-8]
                                       
 
Hydrolysis
                                    stable
                                √ (4716 days)
MRID 41114701; although metaldehyde is stable, a specific half-life is used for PRZM-GW, as the model is sensitive to hydrolysis half-life values.
Aerobic Soil Metabolism Half-life
                                   201 days
                                      √
MRID 41546001 (67-day half-life times 3 for single value)
Aerobic Aquatic Metabolism Half-life (25[o]C)
                                   402 days
                                       
MRID 41546001  (201-day aerobic soil half-life times 2)
Anaerobic Aquatic Metabolism Half-life
                                   666 days
                                       
MRID 41507701 (222-day anaerobic soil half-life times 3)
Aqueous Photolysis Half-life
                                    stable
                                       
MRID 41337401
Vapor pressure (25[o]C)
                                 0.000011 torr
                                       
Product Chemistry


                                       
 
Solubility in water  (25[o]C)
                                  45,360 mg/L
                                       
EpiSuite


                                       
 
Molecular Wt.
                                 176.2 g/mole
                                       
Epi Suite


                                       
 



Modeling Results

Surface Water

For each PRZM-EXAMS scenario, EDWCs were calculated for each month of the growing season described in the scenario metadata.  Table 5 reports the maximum EDWCs calculated for each PRZM-EXAMS (i.e., surface water) scenario.  The maximum 1-in-10 year acute EDWCs in surface water ranged from 115 to 205 ug/L.  The maximum 1-in-10 year annual surface water EDWCs ranged from 69 to 136 ug/L.  The maximum 30-year average surface water EDWCs ranged from 47 to 83 ug/L.  The California RLF Turf scenario resulted in the maximum EDWCs.  The PRZM-EXAMS output data for the surface water EDWCs for the California RLF Turf scenario are attached in Appendix 2.   

Table 5. Maximum (Per Scenario) Tier II Surface Water EDWCs for Existing Invasive Mollusk Eradication (6 applications of 2 lb a.i./acre metaldehyde applied to turf each year with a reapplication interval of 14 days). 
                              1. Use Assumptions
                            2. PRZM-EXAMS Scenario
                           3. First Application Date
                             4. 1-in-10 year EDWC
                              5. 30-Year Average



                                     Peak
                                    Annual
                                    Overall


                                   month-day
                                     ug/L
                              Ground Application
                                  CA RLF Turf
                                     15-01
                                      193
                                      136
                                      83


                                     15-10
                                      205
                                      130
                                      77

                                    FL Turf
                                     15-08
                                      111
                                      62
                                      47


                                     15-09
                                      115
                                      60
                                      43


                                     15-10
                                      109
                                      69
                                      42

                                    PA Turf
                                     15-08
                                      190
                                      119
                                      63


Ground Water

For each PRZM-GW scenario, EDWCs were calculated for each year in a 30-year simulation where metaldehyde was applied for the first 6 years only at the maximum annual rate of 12 lb a.i./acre per year.  In each of the 6 years of application, it was assumed that there were 6 applications of 2 lb a.i./acre.  The first application in each year was assumed to be 30 days after the plant emergence date described in the scenario metadata.  Each of the five subsequent applications is assumed to be 14 days apart based on the minimum re-application interval for grass (seed crop), forage and hay specified on the label instructions for "OR-CAL Slug-Fest 4.0" (EPA Reg. No. 71096 - -13) submitted by IR-4.  

There is substantial uncertainty in the PRZM-GW modeling assumptions.  First, the assumption that metaldehyde is only used for 6 consecutive years at the application site is based on information on the maximum number of application site-years submitted by the United States Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) as part of its comments on the 2006 Reregistration Eligibility Decision.  There are no restrictions on the metaldehyde label concerning how many years metaldehyde may be used at a particular site targeted for invasive mollusk eradication.  Second, selection of the within-year application window influences the EDWCs.   For example, selecting an application window that starts at plant emergence versus one that starts 60 days after plant emergence can vary peak groundwater EDWCs by approximately +-50 ug/L.  Third, there is uncertainty in calculating EDWCs using of a 14-day re-application interval, as a re-application interval not specified in the "Special Use" box describing the directions for invasive mollusk eradication.  

Table 4 reports the EDWCs calculated for the 30-year simulation for each PRZM-GW (i.e., ground water) scenario.  The peak EDWCs in the 30-year simulation ranged from 731 to 1,740 ug/L.  The simulation average EDWCs ranged from 181 to 557 ug/L, and the post-breakthrough average EDWCs ranged from 205 to 635 ug/L.  The Wisconsin Corn scenario resulted in the maximum EDWCs for the invasive mollusk eradication use.  Figure 1 shows the modeled increase and decline of metaldehyde concentrations in groundwater from this use over 30 years for the Wisconsin Corn scenario.  It should be noted that the DelMarVa Corn and Florida Citrus scenarios resulted in EDWCs similar to those calculated for the Wisconsin Corn scenario.

For comparison purposes, EDWCs for the mollusk eradication use were also calculated using SCI-GROW, which resulted in an acute and chronic EDWC of 149 ug/L.  The SCI-GROW output data are available in Appendix 1.  

Table 6. Tier I and II estimated drinking water concentrations (EDWCs) in parts per billion (μg/L) resulting from 6 consecutive years of metaldehyde use in an invasive mollusk eradication program where 6 applications of  2 lb a.i./acre are applied each year with a reapplication interval of 14 days.

                              Application Method
                                      PCA
                                   Scenario
                              30-Year Simulation*



                                     Peak
                              Simulation Average
                           Post-Breakthrough Average



                                     ug/L
                                   SCI-GROW
                                    Ground
                                      n/a
                                      n/a
                                      149
                                    PRZM-GW
                                    Ground
                                      n/a
                                   FL Citrus
                                     1720
                                      365
                                      377


                                 DELMARVA Corn
                                     1730
                                      291
                                      296


                                   FL Potato
                                     1180
                                      220
                                      231


                                  GA Peanuts
                                      731
                                      181
                                      205


                                   NC Cotton
                                     1260
                                      290
                                      322


                                    WI Corn
                                     1740
                                      557
                                      635
*Note that while this is a 30-year simulation, the EDWCs are a result of only 6 years of consecutive use.


Figure 1. Estimated Groundwater Concentrations of Metaldehyde from 6 years of use in a 30-Year Simulation using PRZM-GW Wisconsin Corn Scenario (ppb = ug/L)*

*Maximum Single Application rate 2 lb a.i./acre;  Maximum Annual Application rate 12 lb a.i./acre; Minimum Re-Application Interval 14 days; Initial application modeled is 30 days post-emergence, based on emergence date in the scenario


As discussed in the Modeling Input Parameters section, there is additional uncertainty in the PRZM-GW EDWCs presented in for the invasive mollusk eradication use due to the uncertainty in the hydrolysis half-life data.  For comparison purposes, Table 7. includes the PRZM-GW results using a hydrolysis half-life of 4,719 as well as the PRZM-GW results using the assumption that no hydrolytic degradation of metaldehyde occurs. 



Table 7. PRZM-GW 30-year simulation outputs resulting from 6 consecutive years of metaldehyde use in an invasive mollusk eradication program where 6 applications of 2 lb a.i./acre are applied each year with a reapplication interval of 14 days.
 
                                   FL Citrus
                                 DELMARVA Corn
                                   FL Potato
                                  GA Peanuts
                                   NC Cotton
                                    WI Corn
                      Hydrolysis Half-Life of 4,716 Days
Highest Daily Value (ug/L)
                                     1720
                                     1730
                                     1180
                                      731
                                     1260
                                     1740
Simulation Average Value (ug/L)
                                      365
                                      291
                                      220
                                      181
                                      290
                                      557
Average Breakthrough Time (days)
                                      239
                                      217
                                      247
                                      993
                                     1055
                                      874
Throughputs
                                      46
                                      50
                                      44
                                      11
                                      10
                                      13
Post Breakthrough Average (ug/L)
                                      377
                                      296
                                      231
                                      205
                                      322
                                      635
                   No Degradation as a Result of Hydrolysis
Highest Daily Value (ug/L)
                                     1780
                                     1770
                                     1220
                                      802
                                     1380
                                     1820
Simulation Average Value (ug/L)
                                      380
                                      297
                                      228
                                      200
                                      318
                                      584
Average Breakthrough Time (days)
                                      239
                                      217
                                      247
                                      993
                                     1055
                                      874
Throughputs
                                      46
                                      50
                                      44
                                      11
                                      10
                                      13
Post Breakthrough Average (ug/L)
                                      392
                                      302
                                      239
                                      226
                                      353
                                      666





Watercress Use

Models and Scenarios Used

Detailed descriptions, documentation, and links for running the models discussed in the paragraphs below may found at http://www.epa.gov/oppefed1/models/water/index.htm.  

Surface Water Modeling

The Tier I EDWCs for the watercress use of metaldehyde were generated using the Tier 1 Rice Model (version 1.0, May 8, 2007).  The Tier I Rice Model is used to estimate aquatic exposures for applications directly to water. The model estimates exposure in a water body holding a 10 cm water depth. When a pesticide is applied to a water body, the model assumes that it will instantaneously partition between a water phase and a sediment phase based on the partition coefficient of the chemical. The formula of the Tier I Rice Model v1.0 is as follows:

                                 Cw = 		mai 		
                                  0.00105 + 0.00013Kd
and, if appropriate:
                                 Kd = 0.01Koc

where:

Cw = water concentration (ug/L)
mai = mass applied per unit area (kg/ha)
Kd = water-sediment partitioning coefficient (L/kg)
Koc = organic carbon partitioning coefficient (L/kg)

The Tier I Rice Model was calibrated to generate estimates that are similar to or greater than dissolved concentrations measured within flooded paddies and in discharged paddy water. The calibration involved determination of the sediment interaction depth by calibrating the model to exceed residues measured in paddy water in the vast majority of dissipation studies. The model does not account for pesticide degradation, volatilization, dilution, or other dissipation processes.
The model was not evaluated or calibrated for concentrations measured in sediment. 

Based on the results of the Tier I modeling (see the Modeling Results section below), refined Tier II EDWCs for watercress were generated using the Pesticide Flooded Application Model (PFAM) (version 0.70).  PFAM was developed as a flooded agriculture model for use in pesticide regulatory work. This model has been developed under USEPA Guidance, and external independent evaluations have been positive.    

PFAM includes both hydrological processes and chemical processes. The water body depth may change due to precipitation, refill, drainage, evaporation, and weir-height changes. The model consists of two regions: a water column and a benthic region. Each individual region is completely mixed and at equilibrium with all phases within the individual region, and equilibrium within each region follows a linear isotherm. The two regions are coupled by a first-order mass transfer process.  Equations for chemical processes (i.e., hydrolysis, bacterial metabolism, photolysis, and sorption) within each region are similar to the EXAMS model described earlier in this assessment. The model accounts for plant growth, metabolism, hydrolysis, photolysis, and metabolism in water, sediment, and soil (when no water is present), sorption, and volatilization.  Water, sediment, and pesticide may flow out of the field. Changes in water body conditions (temperature, water levels, wind speed, etc.) and the resulting changes in degradation rates occur on a daily time step. Pesticide application and flooding sequences are mapped onto the time series in 1-year cycles for the length of the simulation.  For instance, a typical exposure assessment assumes the pesticide is used every year for 30 years (the length of most EFED meteorological files). Output is delivered as released mass of pesticide as well as a daily time series of concentrations.

PFAM estimates exposure in the paddy effluent, which is eventually mixed with surface water which potentially flows to a drinking water intake.  Mixing of paddy water with other surface water will result in dilution of the paddy water and reductions in the drinking water concentrations; this is especially true for estimated chronic concentrations. In order to account for this, PFAM was set up to flow (mass and volume) into the index reservoir, the standard drinking water body used by EFED to estimate surface water source drinking water concentrations using the varying volume pond model. This portion of the model is still under development and evaluation, so the derived estimates using PFAM with the index reservoir are considered provisional. 

Ground Water Modeling

Ground water modeling was not conducted for watercress because PRZM-GW or SCI-GROW models are not appropriate to represent saturated flow condition with a constant head pressure from watercress bogs or rice paddies.     

Modeling Input Parameters

The model input parameters for the Tier I Rice Model were the average Kd (0.234 L/kg, MRID 41228001) and the maximum single application rate (mai =4.65 kg/ha).  The model input parameters for PFAM are summarized in Table 8 and 9.  Model input values were prepared following EFED input parameter guidance.   The PFAM output file is shown in Appendix 3.

Table 8.  PFAM Input Parameters for Metaldehyde Use on Watercress
6. Input Parameter
                                   7. Value
                            8. Source and Comments
                       Chemical Property and Fate Inputs
Water Column Half-life (days) at 25°C
                                      402
MRID 41546001 (201 day aerobic soil half-life times 2)
Benthic Compartment Half-Life (days) at 25°C
                                      666
MRID 41507701 (222 day half-life times 3 for single value)
Unflooded Soil Half-life (days) at 25°C
                                      201
MRID 41546001 (67 day half-life times 3 for single value)
Aqueous Near Surface Half-life (days) at 40° Latitude
                                    Stable
MRID 41337401
Hydrolysis Half-life (days)
                                    Stable
MRID 41114701 
Organic Carbon Partition Coefficient (mL/goc) (Koc)
                                     23.4
Calculated Koc from Kd based on Input Parameter Guidance; Average Kd of 0.234 from four soils (0.103, 0.223,0.175, 0.436) MRID 41228001
Molecular Weight (g/mol)
                                     176.2
Product Chemistry
Vapor Pressure (torr) at 25°C
                                    0.00002
Product Chemistry
Solubility (mg/L) at 25°C
                                    45,360
EPISuite
Heat of Henry (J/mol)
                                    37,413
Estimated using HENR YWIN program in EPISuite 
Henry Reference Temperature (°C)
                                      25
Product Chemistry/EPISuite
                              Application Inputs
Number of Applications
                                       2
Label (EPA Reg. No. 71096-4)
Applied Mass (kg/ha)
                                     2.352
Label (EPA Reg. No. 71096-4)
Application Dates
                               21-Oct and 10-Nov
Based on information from MRID 45718601 and Smith 2007.
Slow Release
                                      No
Label indicates that the product is slow-release.  Because the release rate is not specified, it is assumed that the a.i. is immediately released upon application.
                                Location Inputs
Meteorological files
                                  w12834.dvf
Meteorological data available in PRZM-EXAMS 5 installation. Station corresponds to Daytona Beach, FL.
                                  Crop Inputs
Zero Height Reference
                                     1-Oct
Based on information from IFAS 1999.
Days from Zero Height to Full Height
                                      19
Estimated based on information from Smith 2007.
Days from Zero Height to Removal
                                      60
Estimated based on information from Smith 2007[13].
Maximum Fractional Areal Coverage
                                       1
Conservative assumption
                                Physical Inputs
Reference depth (m)
                                    0.1524
Corresponds to a water depth of 6 inches.
                               Watershed Inputs
Area of Application (m[2])
                                    362,880
21% of the watershed drainage acreage (1,728,000 m[2]), based on the PCA for rice as a conservative assumption.
Area of Surrounding Watershed (m[2])
                                   1,365,120
Difference in watershed drainage acreage (1,728,000 m[2]) and area of application
Curve Number of Surrounding Watershed
                                      83
Curve number for a contoured pasture with Fair hydrologic conditions and a Soil Group of D




Table 9. Planting, Flooding, Drainage, Application, and Harvest Event Inputs for Florida Watercress PFAM Modeling (shaded events are flood events used in the PFAM "Floods" Tab)
Event 
Day
Date
Water Height (m)
Fill Level (m)
Wier Level   (m) 
Min Level
Turn Over 






(m) 
 (per day)
Plant Seedlings
0
1-Oct
0
0
0
0
0
First Flood
1
2-Oct
0.1524
0.1524
0.1524
0.1524
14.2
Drain
19
20-Oct
0
0
0
0
0
Application
20
21-Oct
0
0
0
0
0
Flood with Retention
21
22-Oct
0.1524
0.1524
0.1524
0.1524
0
Flood with Turnover
26
27-Oct
0.1524
0.1524
0.1524
0.1524
14.2
Drain
39
9-Nov
0
0
0
0
0
Application
40
10-Nov
0
0
0
0
0
Flood with Retention
41
11-Nov
0.1524
0.1524
0.1524
0.1524
0
Flood with Turnover
46
16-Nov
0.1524
0.1524
0.1524
0.1524
14.2
Harvest 1
60
30-Nov
0.1524
0.1524
0.1524
0.1524
14.2


Modeling Results

EFED conducted Tier 1 and PFAM model simulations for metaldehyde use on watercress (Table 10). 

Table 10. Maximum Tier I (Single Application) and Tier II estimated drinking water concentrations (EDWCs) in parts per billion (μg/L) 
                                   Scenario
                                     Peak
                                    Chronic
                                       
                                     ug/L
                                    Tier 1
                                     4,303
                                    Tier 1 
                              PCA correction[1] 
                                      904
                                    PFAM[1]
                                     1,120
                                      665
                  1- Rice PCA was used as a surrogate for watercress.
                  2- 
EFED estimated acute and chronic EDWCs for metaldehyde using the refined Tier I Rice Model and Pesticide Flooded Application Model (PFAM) without the index reservoir. These estimated concentrations result in conservative estimates of drinking water concentrations and reflect possible concentrations that may occur when a drinking water intake is near the location where paddy water is released, and mixing with uncontaminated water is minimal.  The Tier I Rice Model output has been shown to generate concentrations that are similar to measured concentrations in paddy waters, and is conservative when compared with surface water concentrations downstream of paddy discharges. The percent crop area for rice (PCA=0.21) was used as surrogate PCA for watercress. 

Monitoring Data

Surface water data from one state and three nationwide pesticide monitoring programs were reviewed to provide additional context concerning the potential presence of metaldehyde in ambient water resources.  These water monitoring programs do not target sample collection to peak use locations or application times for particular pesticides, nor do they target sample collection to high precipitation events (i.e., high-runoff events).  Additionally, the sampling frequency in these monitoring programs was not designed to capture peak concentrations.  Therefore, the monitoring data reported by these programs may not represent the highest concentrations in ambient surface water, and are considered qualitative information for the purposes of this ecological risk assessment.

USGS-EPA Pilot Reservoir Monitoring Program  -  Metaldehyde is not an analyte in this program.

USGS National Water-Quality Assessment (NAWQA) Program Data  -  Metaldehyde is not analyte in the USGS NAWQA monitoring program.  NAWQA program data are available at http://infotrek.er.usgs.gov/nawqa_queries/index.jsp.

California Surface Water Monitoring Program Data -  Metaldehyde is not analyte in the California surface water monitoring program.  California Surface Water Monitoring Program data are available at http://www.cdpr.ca.gov/docs/emon/surfwtr/surfdata.htm.

Pesticide Data Program (PDP) Data - The PDP drinking water monitoring project provides non-targeted pesticide occurrence data in raw, finished (treated/tap), and ground water in the United States.  In 2010 and 2011 PDP surface water samples were tested for metaldehyde and there were no detections.  PDP data are available at http://www.ams.usda.gov/AMSv1.0/pdp

Appendix 1.  SCI-GROW Outputs for Invasive Mollusk Eradication Use

                           SCIGROW
                          VERSION 2.3
            ENVIRONMENTAL FATE AND EFFECTS DIVISION
                 OFFICE OF PESTICIDE PROGRAMS
             U.S. ENVIRONMENTAL PROTECTION AGENCY
                        SCREENING MODEL
                FOR AQUATIC PESTICIDE EXPOSURE
 
 SciGrow version 2.3
 chemical:Metaldehyde
 time is  5/21/2013  13:17:48
 ------------------------------------------------------------------------
  Application      Number of       Total Use    Koc      Soil Aerobic
  rate (lb/acre)  applications   (lb/acre/yr)  (ml/g)   metabolism (days)
 ------------------------------------------------------------------------
      2.000           6.0          12.000      3.62E+01      201.0
 ------------------------------------------------------------------------
 groundwater screening cond (ppb) =   1.49E+02 
 ************************************************************************
Appendix 2.  PRZM-EXAMS Output for Invasive Mollusk Eradication Use  -  California RLF Turf Scenario

Initial Application on January 15
stored as FINALCAdwTurf14_15-01.out
Chemical: Metaldehyde
PRZM environment: CATurfRLF.txt	modified Tueday, 20 February 2007 at 12:03:48
EXAMS environment: ir298.exv	modified Thuday, 29 August 2002 at 15:34:12
Metfile: w23234.dvf	modified Wedday, 3 July 2002 at 09:04:22
Water segment concentrations (ppb)

Year	Peak	96 hr	21 Day	60 Day	90 Day	Yearly
1961	48.05	47.79	46.7	44.72	43.28	30.17
1962	89.69	89.23	87.28	85.22	83.59	62.4
1963	172	171	168	159	153	110
1964	98.54	98.03	95.9	94.33	92.98	73.46
1965	68.99	68.64	67.55	65.35	63.94	50.49
1966	109	108	106	105	103	76.8
1967	194	193	189	182	177	137
1968	221	220	217	209	201	154
1969	225	224	221	217	212	161
1970	125	124	122	120	118	92.95
1971	135	134	131	127	123	89.59
1972	80.45	80.03	78.28	76.35	74.95	59.36
1973	154	153	151	149	144	109
1974	109	109	107	102	99.8	78.46
1975	168	167	165	159	154	117
1976	140	140	138	136	132	98.12
1977	113	112	110	106	102	77.82
1978	94.5	94.01	91.95	90.28	88.71	67.85
1979	186	185	182	176	173	125
1980	141	140	138	136	132	100
1981	108	108	106	104	101	78.96
1982	95.15	94.81	93.06	89.68	87.54	67.16
1983	96.14	95.63	93.88	91.02	88.02	66.61
1984	66.74	66.51	65.14	62.95	61.55	47.97
1985	90.58	90.11	88.07	83.52	80.2	58.05
1986	88.64	88.16	86.16	83.38	80.95	61.88
1987	121	121	119	117	115	83.04
1988	79.94	79.51	77.8	75.84	74.43	58.38
1989	61.94	61.61	60.2	57.83	56.1	43.64
1990	78.9	78.48	76.71	74.73	73.16	53.66

Sorted results
Prob.	Peak	96 hr	21 Day	60 Day	90 Day	Yearly
0.032258064516129	225	224	221	217	212	161
0.0645161290322581	221	220	217	209	201	154
0.0967741935483871	194	193	189	182	177	137
0.129032258064516	186	185	182	176	173	125
0.161290322580645	172	171	168	159	154	117
0.193548387096774	168	167	165	159	153	110
0.225806451612903	154	153	151	149	144	109
0.258064516129032	141	140	138	136	132	100
0.290322580645161	140	140	138	136	132	98.12
0.32258064516129	135	134	131	127	123	92.95
0.354838709677419	125	124	122	120	118	89.59
0.387096774193548	121	121	119	117	115	83.04
0.419354838709677	113	112	110	106	103	78.96
0.451612903225806	109	109	107	105	102	78.46
0.483870967741936	109	108	106	104	101	77.82
0.516129032258065	108	108	106	102	99.8	76.8
0.548387096774194	98.54	98.03	95.9	94.33	92.98	73.46
0.580645161290323	96.14	95.63	93.88	91.02	88.71	67.85
0.612903225806452	95.15	94.81	93.06	90.28	88.02	67.16
0.645161290322581	94.5	94.01	91.95	89.68	87.54	66.61
0.67741935483871	90.58	90.11	88.07	85.22	83.59	62.4
0.709677419354839	89.69	89.23	87.28	83.52	80.95	61.88
0.741935483870968	88.64	88.16	86.16	83.38	80.2	59.36
0.774193548387097	80.45	80.03	78.28	76.35	74.95	58.38
0.806451612903226	79.94	79.51	77.8	75.84	74.43	58.05
0.838709677419355	78.9	78.48	76.71	74.73	73.16	53.66
0.870967741935484	68.99	68.64	67.55	65.35	63.94	50.49
0.903225806451613	66.74	66.51	65.14	62.95	61.55	47.97
0.935483870967742	61.94	61.61	60.2	57.83	56.1	43.64
0.967741935483871	48.05	47.79	46.7	44.72	43.28	30.17

0.1	193.2	192.2	188.3	181.4	176.6	135.8
					Average of yearly averages:	82.994

Inputs generated by pe5.pl - Novemeber 2006

Data used for this run:
Output File: FINALCAdwTurf14_15-01
Metfile:	w23234.dvf
PRZM scenario:	CATurfRLF.txt
EXAMS environment file:	ir298.exv
Chemical Name:	Metaldehyde
Description	Variable Name	Value	Units	Comments
Molecular weight	mwt	176.2	g/mol
Henry's Law Const.	henry	2.43e-8	atm-m^3/mol
Vapor Pressure	vapr	.000011	torr
Solubility	sol	45360	mg/L
Kd	Kd	.234	mg/L
Koc	Koc		mg/L
Photolysis half-life	kdp		days	Half-life
Aerobic Aquatic Metabolism	kbacw	402	days	Halfife
Anaerobic Aquatic Metabolism	kbacs	666	days	Halfife
Aerobic Soil Metabolism	asm	201	days	Halfife
Hydrolysis:	pH 7	0	days	Half-life
Method:	CAM	1	integer	See PRZM manual
Incorporation Depth:	DEPI		cm
Application Rate:	TAPP	2.24	kg/ha
Application Efficiency:	APPEFF	0.99	fraction
Spray Drift	DRFT	0.064	fraction of application rate applied to pond
Application Date	Date	15-01	dd/mm or dd/mmm or dd-mm or dd-mmm
Interval 1	interval	14	days	Set to 0 or delete line for single app.
app. rate 1	apprate	2.24	kg/ha
Interval 2	interval	14	days	Set to 0 or delete line for single app.
app. rate 2	apprate	2.24	kg/ha
Interval 3	interval	14	days	Set to 0 or delete line for single app.
app. rate 3	apprate	2.24	kg/ha
Interval 4	interval	14	days	Set to 0 or delete line for single app.
app. rate 4	apprate	2.24	kg/ha
Interval 5	interval	14	days	Set to 0 or delete line for single app.
app. rate 5	apprate	2.24	kg/ha
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	total	none, monthly or total(average of entire run)


Initial Application on October 15
stored as FINALCAdwTurf14_15-10.out
Chemical: Metaldehyde
PRZM environment: CATurfRLF.txt	modified Tueday, 20 February 2007 at 12:03:48
EXAMS environment: ir298.exv	modified Thuday, 29 August 2002 at 15:34:12
Metfile: w23234.dvf	modified Wedday, 3 July 2002 at 09:04:22
Water segment concentrations (ppb)

Year	Peak	96 hr	21 Day	60 Day	90 Day	Yearly
1961	50.42	50.17	47.45	31.68	22.38	5.518
1962	55.79	55.5	51.46	48.2	46.77	37.66
1963	60.71	60.41	57.8	51.46	49.76	40.84
1964	63.69	63.36	60.66	55.76	53.81	44.22
1965	168	167	104	72.02	58.92	48.28
1966	166	165	162	154	149	115
1967	170	170	166	158	153	116
1968	115	115	102	94.27	90.96	72.98
1969	119	118	114	111	103	86.17
1970	121	121	118	107	103	82.15
1971	120	119	117	111	107	80.9
1972	122	121	118	102	82.48	65.31
1973	239	238	201	143	117	97.58
1974	236	235	230	219	211	155
1975	150	150	147	140	135	101
1976	85.91	85.49	83.75	79.9	77.06	58.98
1977	75.88	75.48	72.86	65.99	63.6	51.34
1978	74.31	74.03	72.67	69.17	66.59	51.09
1979	150	149	89.63	61.23	53.95	45.15
1980	147	146	143	136	131	99.13
1981	148	141	119	103	99.51	81.49
1982	159	158	150	137	132	106
1983	193	192	152	145	139	106
1984	206	205	202	178	169	137
1985	199	198	194	185	178	132
1986	116	116	113	108	104	77.64
1987	91.58	91.12	89.2	84.96	81.81	62.06
1988	91.91	91.44	67.14	59.73	57.52	45.45
1989	90.03	89.58	87.69	83.58	80.53	63.09
1990	79.81	79.54	77.91	75.57	73.07	55.97

Sorted results
Prob.	Peak	96 hr	21 Day	60 Day	90 Day	Yearly
0.032258064516129	239	238	230	219	211	155
0.0645161290322581	236	235	202	185	178	137
0.0967741935483871	206	205	201	178	169	132
0.129032258064516	199	198	194	158	153	116
0.161290322580645	193	192	166	154	149	115
0.193548387096774	170	170	162	145	139	106
0.225806451612903	168	167	152	143	135	106
0.258064516129032	166	165	150	140	132	101
0.290322580645161	159	158	147	137	131	99.13
0.32258064516129	150	150	143	136	117	97.58
0.354838709677419	150	149	119	111	107	86.17
0.387096774193548	148	146	118	111	104	82.15
0.419354838709677	147	141	118	108	103	81.49
0.451612903225806	122	121	117	107	103	80.9
0.483870967741936	121	121	114	103	99.51	77.64
0.516129032258065	120	119	113	102	90.96	72.98
0.548387096774194	119	118	104	94.27	82.48	65.31
0.580645161290323	116	116	102	84.96	81.81	63.09
0.612903225806452	115	115	89.63	83.58	80.53	62.06
0.645161290322581	91.91	91.44	89.2	79.9	77.06	58.98
0.67741935483871	91.58	91.12	87.69	75.57	73.07	55.97
0.709677419354839	90.03	89.58	83.75	72.02	66.59	51.34
0.741935483870968	85.91	85.49	77.91	69.17	63.6	51.09
0.774193548387097	79.81	79.54	72.86	65.99	58.92	48.28
0.806451612903226	75.88	75.48	72.67	61.23	57.52	45.45
0.838709677419355	74.31	74.03	67.14	59.73	53.95	45.15
0.870967741935484	63.69	63.36	60.66	55.76	53.81	44.22
0.903225806451613	60.71	60.41	57.8	51.46	49.76	40.84
0.935483870967742	55.79	55.5	51.46	48.2	46.77	37.66
0.967741935483871	50.42	50.17	47.45	31.68	22.38	5.518

0.1	205.3	204.3	200.3	176	167.4	130.4
					Average of yearly averages:	77.3666

Inputs generated by pe5.pl - Novemeber 2006

Data used for this run:
Output File: FINALCAdwTurf14_15-10
Metfile:	w23234.dvf
PRZM scenario:	CATurfRLF.txt
EXAMS environment file:	ir298.exv
Chemical Name:	Metaldehyde
Description	Variable Name	Value	Units	Comments
Molecular weight	mwt	176.2	g/mol
Henry's Law Const.	henry	2.43e-8	atm-m^3/mol
Vapor Pressure	vapr	.000011	torr
Solubility	sol	45360	mg/L
Kd	Kd	.234	mg/L
Koc	Koc		mg/L
Photolysis half-life	kdp		days	Half-life
Aerobic Aquatic Metabolism	kbacw	402	days	Halfife
Anaerobic Aquatic Metabolism	kbacs	666	days	Halfife
Aerobic Soil Metabolism	asm	201	days	Halfife
Hydrolysis:	pH 7	0	days	Half-life
Method:	CAM	1	integer	See PRZM manual
Incorporation Depth:	DEPI		cm
Application Rate:	TAPP	2.24	kg/ha
Application Efficiency:	APPEFF	0.99	fraction
Spray Drift	DRFT	0.064	fraction of application rate applied to pond
Application Date	Date	15-10	dd/mm or dd/mmm or dd-mm or dd-mmm
Interval 1	interval	14	days	Set to 0 or delete line for single app.
app. rate 1	apprate	2.24	kg/ha
Interval 2	interval	14	days	Set to 0 or delete line for single app.
app. rate 2	apprate	2.24	kg/ha
Interval 3	interval	14	days	Set to 0 or delete line for single app.
app. rate 3	apprate	2.24	kg/ha
Interval 4	interval	14	days	Set to 0 or delete line for single app.
app. rate 4	apprate	2.24	kg/ha
Interval 5	interval	14	days	Set to 0 or delete line for single app.
app. rate 5	apprate	2.24	kg/ha
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	total	none, monthly or total(average of entire run)


















Appendix 3.  PFAM Output for Watercress Use 
***********************************************************************
 **************** Inputs *******************
 Chemical #            1
   402.000000000000      
 Water Column System Halflife(except photo & hydrolysis = 
   666.000000000000      Benthic Compartment Halflife (except hydrolysis) = 
   1000000.00000000      Photolysis Halflife =        
   1000000.00000000      Hydrolysis Halflife =        
   176.200000000000      Molecular Wieght =           
  2.000000000000000E-005 Vapor Pressure =             
   45360.0000000000      Solubility =                 
   23.4000000000000      Koc =                        
   25.0000000000000      Aerobic Reference Temper =   
   25.0000000000000      Anaerobic Reference Temper = 
   40.0000000000000      Reference Latitude =         
   37413.0000000000      Enthalpy of Henry =          
   25.0000000000000      Henry Reference Temperature  
 ****************** End of Run ************************
 ******************************************************
 
 Variable Volume Water Model, Version 0.0
 
 *******************************************
Performed on:  7/17/2013  at  7:58
 Standard Reservoir, Area = 52555 m2,  Depth = 2.73 m 
 Chemical #            1
 
Peak 1-in-10       =   1.12E+03 ppb
Chronic 1-in-10    =   6.65E+02 ppb
 
4-day avg 1-in-10  =   1.12E+03 ppb
21-day avg 1-in-10 =   1.11E+03 ppb
60-day avg 1-in-10 =   1.07E+03 ppb
90-day avg 1-in-10 =   1.07E+03 ppb
 
 YEAR    Peak      4-day      21-day     60-day     90-day   Yearly Avg
  1    9.00E+02   8.99E+02   8.99E+02   8.94E+02   8.89E+02   5.92E+02
  2    9.29E+02   9.26E+02   9.18E+02   8.87E+02   8.71E+02   5.75E+02
  3    6.51E+02   6.50E+02   6.45E+02   6.30E+02   6.20E+02   4.02E+02
  4    8.49E+02   8.47E+02   8.45E+02   8.29E+02   8.15E+02   5.85E+02
  5    1.13E+03   1.12E+03   1.12E+03   1.09E+03   1.06E+03   6.05E+02
  6    9.00E+02   8.99E+02   8.99E+02   8.95E+02   8.93E+02   6.31E+02
  7    1.08E+03   1.08E+03   1.08E+03   1.07E+03   1.07E+03   6.56E+02
  8    8.66E+02   8.65E+02   8.65E+02   8.62E+02   8.60E+02   5.58E+02
  9    6.11E+02   6.07E+02   6.03E+02   5.90E+02   5.86E+02   4.79E+02
 10    1.15E+03   1.14E+03   1.12E+03   1.06E+03   1.00E+03   6.57E+02
 11    8.99E+02   8.96E+02   8.93E+02   8.78E+02   8.59E+02   5.19E+02
 12    6.02E+02   6.02E+02   6.01E+02   5.90E+02   5.83E+02   4.51E+02
 13    1.05E+03   1.05E+03   1.05E+03   1.04E+03   1.02E+03   7.06E+02
 14    9.67E+02   9.66E+02   9.66E+02   9.56E+02   9.40E+02   6.69E+02
 15    1.12E+03   1.12E+03   1.12E+03   1.11E+03   1.08E+03   5.83E+02
 16    6.62E+02   6.57E+02   6.54E+02   6.02E+02   5.85E+02   4.68E+02
 17    8.85E+02   8.83E+02   8.78E+02   8.47E+02   8.16E+02   5.19E+02
 18    6.98E+02   6.94E+02   6.87E+02   6.27E+02   5.92E+02   3.49E+02
 19    7.28E+02   7.27E+02   7.26E+02   7.14E+02   7.09E+02   5.06E+02
 20    1.04E+03   1.04E+03   1.03E+03   9.86E+02   9.45E+02   6.57E+02
 21    8.52E+02   8.48E+02   8.44E+02   8.14E+02   8.06E+02   4.72E+02
 22    8.82E+02   8.78E+02   8.68E+02   8.26E+02   7.91E+02   4.22E+02
 23    5.34E+02   5.27E+02   5.09E+02   4.66E+02   4.48E+02   2.94E+02
 24    8.87E+02   8.85E+02   8.81E+02   8.68E+02   8.51E+02   5.87E+02
 25    8.81E+02   8.71E+02   8.38E+02   7.50E+02   6.87E+02   5.04E+02
 26    8.38E+02   8.32E+02   8.18E+02   7.79E+02   7.36E+02   4.85E+02
 27    9.37E+02   9.31E+02   9.15E+02   8.72E+02   8.54E+02   6.66E+02
 28    7.35E+02   7.26E+02   6.95E+02   6.39E+02   6.17E+02   4.23E+02
 29    8.32E+02   8.29E+02   8.21E+02   7.82E+02   7.47E+02   5.40E+02
 30    9.05E+02   8.95E+02   8.34E+02   6.32E+02   5.22E+02   5.78E+02
 
 
 ***********************************************************************
 Effective compartment halflives averaged over simulation duration:
 
 washout halflife (days) =              117.9621    
 water col metab halflife (days) =      502.1136    
 hydrolysis halflife (days)  =          1000042.    
 photolysis halflife (days)  =         1.3676309E+08
 volatile halflife (days)  =            2446864.    
 total water col halflife (days) =      95.50826    
 
 zero burial
 benthic metab halflife (days) =        831.8600    
 benthic hydrolysis halflife (days) =   3527164.    
 total benthic halflife (days) =        831.6638    
 ***********************************************************************
