### Page **1** of **28** OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION **UN ITED ST**  **AT ES ENVIRONMENT** **AL PROTECTION A** **GENCY**

**WA SHINGTON D.C., 20460** 



### PC Code: 053001 DP Barcode s : 404861 **MEMORANDUM** July 17 , 201 3 **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 . No s . 6836 - 107 (technical) and 71096 - 13) . **TO:** B arbara 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 Chi ef

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 (I R - 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)  Soy bean (regional registration)  Caneberry

subgroup 13 - 07A  Bushberry

subgroup 1307 - B  Berry , low growing, subgroup 13 - 07G

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When considering this request, the Environmental Fate and Effects D ivision (EFED) determined that W etland 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 W etland Taro, EFED determined that W etland Taro is not appropriate for inclusion in a national drinking water assessment beca use its use is likely limited to the Hawaii an i sland of Kauai . EFED also determined that W etland Taro is not appropriate for inclusion in a regional drinking water assessment, as is applied to submerged fields that release to surface water s ys tems . D rinking 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 generall y (b ased on the Safe Drinking Water Information Sy stem ( SDWI S ) , accessed at http://www.epa.gov/enviro/facts/sdwis/search.html ) . When reviewing the metaldehyde label s , EFED determined that th e 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 metaldehyd e 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 an d 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 Fo rmula” (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 a ssessment 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 be cause this is maximum number of site ye ars for use according to APHI S . 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 - ye ar annual average (cancer) concentrations of metaldehyde in surface water sources of drinking water are 205, 136, and 83 μg/L, respectivel y . For ground water sources of drinking water, the estimat ed peak and po st - breakthrough average concentrations were 1,740 and 635 μg/L, respectivel y ( **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 hydrol ysis half - life data, there is uncertainty in the ground water simulation results . Refinement options in this regard are limited, as an additional

### Page **3** of **28**

hydrol ys is study

is not likely

to provide sufficient data to narrow the metaldehyde hydrol ys is half - life, which may

range from to 10 to 24 2 ye ars . **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 halflives range from 10 to 240 years (MRID 41114701 ). Because the longest hydrol ys is studies are generall y carried out over the course of one year, an additional hydrolysis study is not likely

to provide sufficient data to narrow the metaldehyde hydrol ys is half - life . This uncertainty has important implications for ground water simulation results, as PRZM - GW is highl y sensitive to hydrol ys is 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 max imum 1 - in - 10 year peak EDWC was 110 μg/L (Florida cole crops scenario) , the maximum 1 - in - 10 - year annual average EDWC was 55.8 μg/L (California leafy vegetable scenario) , and the maximum overall average EDWC was 31.9 μg/L (California leafy vegetable scenario) . For ground water, EDWCs were generated from a Tier ISCI - GROW analy sis. The maximum EDWC for ground water was 62.5 μg/L (based on ornamental use rates) . It should be noted that the DWA for the RED included an EDW C for the watercress use . The watercress EDWC in the RED DWA was 1,500 μg/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.

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Monitoring data for metaldehyde are limited. Metaldehyde was only an analy te in the 2010 and 2011 USDA Pesticide Data Program (PDP). There were no detections o f 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 polic y 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 1 

### , 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 ye ars of metaldehyde use .

1 Brady, Donald. 2012. Memorandum: Approval of PRZM - GW for Use in Drinking Water Exposure Assessment.

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**Uses Assessed** The uses evaluated in this assessment are described in the following paragraphs, as well as in **Table 2**  2 . ”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 an d 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. , broadcas t) applications are allowed for this use . The maximum single application rate for all exotic mollusk eradication u ses 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 ins tructions 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

conser vative with respect to) the use sites listed above . Use of a P ercent C ropped Area (PCA) adjustment when calculating turf EDWCs is not appropriate given the presence of non - agricultural and non - turf pesticide use s on the metaldehyde label 2



### . 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 ye ar) . The “Slug - Fest All Weather Formula” (EPA Reg. No. 71096 - 4) label states that no more than two applications may

2 Brady, Donald. 2012. Memorandum: Guidance on Development and Use of Percent Cropped Area and Percent Turf Area Adjustment Factors in Drinking Water Exposure Assessments: 2012 Update. http://www.epa.gov/oppefed1/models/water/pca_adjustment_dwa.html .

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be made p er 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 canop y  The watercress field must be drained for a minimum period of 24 hours prior to metaldehyde applic ation 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**  **. Metal**  **dehyde Use**  **s 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 route s of dissipation for metaldehyde are through runoff, leaching and aerobic degradation. Based on data submitted for one soil ty p e, metaldehyde degrades under aerobic conditions with a half - life of approximately

two months, eventuall y breaking down to acetaldehyde, which readil y mineralizes to carbon dioxide. Metaldehyde appears to be persistent in anaerobic environments, with a half

- life of over 200 day s 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.

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Metaldehyde is not susceptible to either hydrolysis or photolysis under typi cal environmental conditions. Therefore, hydrol ys is and photol ys is 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 (K Foc ) 36.25 mL/g MRIDs 41228001, 41675101 Average K Foc (41.2, 55.7, 14.6, 33.5) Soil Adsorption Coefficient (K F ) 0.234 mL/g MRIDs 41228001, 41675101; Average K F (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

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**Invasive Mollusk Eradication Use**  Models and Scenarios Used Detailed description s , 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 (vers ion 3.12 .2 compiled 05/ 11/05 , Carsel, 1997 ) and EXAMS (vers ion 2.98.04 .06 compiled 0 4 /24 /0 5 , 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 surfa ce water body. The EDWCs ass essment for surface water uses single or multiple sites which ty picall y represent a high - end exposure scenario from pesticide use on a particular crop or non crop use site. PRZM and EXAMS were linked b y the program (PE 5 , vers io n 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 ye ars. During this time, pesticide is washed- off of the field into the water - body by twenty to forty ra infall/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 use d for drinking water assessments. The in dex 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 - ye ar exceedance probability at the site can be estimated. The simulation i s generated using 30 years of meteorological data, encompassing the ye ars 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 scenari o metadata. For turf, EDWCs were calculated for the 15 th 

### day of each m onth 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 com ponent of the drinking water exposure assessment using PRZM/EXAMS with the index reservoir . When appropriate, the

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EDWCs generated b y the linked PRZM/EXAMS models are multiplied by the maximum percent of crop area (PCA) in any watershed (expressed as a dec imal) 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 . Inthis 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 rule d out. Ground W

ater Modeling Tier I and II groundwater EDWCs for metaldehyde resulting from its exotic mollusk eradication use were derived with PRZM - GW (Pe sticide 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. Itaccounts 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 suppl y that is located directl y beneath a rural agricultural field. Note that, unlike in surface water modeling, PCAs are not u sed 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 residue s that might be expe cted 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 3 , 4



### . In contrast to surface water EDWCs calculated using PRZM - EXAMS, PRZM - GW EDWCs are highl y impacted b y hydrolysis half - li fe inputs . This is because hydrol ys is is generall y the onl y 3 Parameters are selected as per Guidance for Selecting Input Parameters in Modeling the Environmental Fate and Transport of Pesticides; Version 2.1, October 22, 2009. 4 Baris, R.; Barrett, M.; Bohaty, R.; Echeverria, M.; Kennedy, I.; Malis, G.; Wolf, J.; Young, D. PRZM - GW Input Parameter Guidance ; Health Canada, U.S. Environmental Protection Agency, October 12, 2012.

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transformation pathway

considered at soi l depths greater than one meter . Even if a chemical is considered stable to hydrolysis, PRZM - GW input parameter guidance recommends using a hydrol ys is half

- life calculated from the guideline hydrol ys is 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 metaldehyd e, the calculated hydrol ytic half

- lives range from 10 to 242 years based on data from a 32 - day hydrol ys is 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 hydrol ys is half - life, Because of th e imprecision in the hydrol ytic half - lives calculated, as well as the uncertainty associated with extrapolating half - lives so far beyond the 32 - day study duration, a hydroly tic half - life calculated for a pH of 7 using log - linear regression anal ys is was use d as the PRZM - GW hydrol ys is input parameter. This half - life is 4,716 days, as indicated in **Table 4**  . For comparison purposes, upper - bound PRZM - GW EDWC s resulting from the assumption that no hydrol ytic 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)

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**Model Input Parameter Input Value and Unit**  **Used as a PRZM**  **- GW**  **Input? Source/Comments**  Minimum Interval between Applications Turf: 0 - 14 days, depending on label interpretation; used 14 days in model √ Label Soil Partition Coefficient K F 0.234 ml/g √ MRID 41228001; Average K F (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 Halflife stable MRID 41337401

Vapor pressure (25 o C) 0 .00001 1 torr Product Chemistry Solubility in water (25 o C) 45,360 mg/L EpiSuite Molecular Wt. 176.2 g/mole Epi Suite

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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 E DWCs in surface water ranged from 115 to 205 μg/L . The maximum 1 - in - 10 year annual surface water EDWCs ranged from 69 to 136 μg/L . The maximum 30 - ye ar average surface water EDWCs ranged from 47 to 8 3 μg/L . The California RLF Turf scenario resulted in th e 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**  **μg/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 Wa ter For each PRZM - GW scenario, EDWCs were calculated for each ye ar in a 30 - ye ar simulation where metaldehyde was applied for the first 6 years only at the maximum annual rate of 12 lb a.i./acre per ye ar . 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 ye ar 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 day s apart based on the minimum re - application interval for

### Page **13** of **28**

grass (se ed crop), forage and hay specified on the label instructions for “OR - CALSlug - 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 use d for 6 consecutive ye ars at the application site is based on information on the maximum number of application site - ye ars submitted by the United States Department of Agriculture (USDA) Animal and P lant H ealth Inspection S ervice (APHIS) as part of its comments on the 2006 Reregistration Eligibility Decision 5 

### . There are no restrictions on the metaldehyde label concerning how many ye ars metaldehyde may be used at a particular site targeted for invasive mollusk eradication . Second, selection of the within - ye ar application window influences the EDWCs. For example, selecting an application window that starts at plant emergence versus one that starts 60 day s after plant emergence can vary peak groundwater EDWCs by

approximately ± 50 μg/L . T hird, 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 calculat ed for the 30 - ye ar simulation for each PRZM - GW ( i.e. , ground water) scenario. The peak EDWCs in the 30 - ye ar simulation ranged from 731 to 1,740 μg/L. The simulation average EDWCs ranged from 181 to 557 μg/L , and the post - breakthrough average EDWCs ranged from 205 to 635 μg/L. The Wisconsin Corn scenario resulted in the maximum EDWCs for the invasive mollusk eradication use. **Figure 1**  

### shows the modeled increas e and decline of metaldehyde concentrations in groundwater from this use over 30 ye ars for the Wisconsin Corn scenario. Itshould 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 calcul ated using SCI - GROW, which resulted in an acute and chronic EDWC of 149 μg/L . The SCI - GROW output data are available in **Appendix 1** .

5 Seeley, Kenneth R. October 4, 2006. USDA APHIS Comments on Metaldehyde RED. May be found at www.regulations.gov in docket ID number EPA - HQ - OPP - 2005 - 0231.

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**Table 6**  **. Tier I and II e stimated 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 i**  **nterval of 14 days. Application**  **Method PCA**  **Scenario 30**  **- Year Simulation** * **Peak Simulation** 

**Average Post**  ****

**Breakthrough Average**  **μg/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 = μg/L)***

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

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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 hydrol ys is half

- life data . For comparison purposes, **Table 7**  **.** includes the PRZM - GW results using a hydrol ys is half - life of 4,719 as well as the PRZM - GW results using the assumption that no hydroly tic 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 (μg/L) 1720 1730 1180 731 1260 1740 Simulation Average Value (μg/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 (μg/L) 377 296 231 205 322 635 No Degradation as a Result of Hydrolysis Highest Daily Value (μg/L) 1780 1770 1220 802 1380 1820 Simulation Average Value (μg/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 (μg/L) 392 302 239 226 353 666

### Page **16** of **28**

**Watercress Use** Models and Scenarios Used Detailed description s , 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 (v ersion 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 Mod el v1.0 is as follows: C w 

### = m ai 

### 0.00105 + 0.00013Kd 

### and, if appropriate: Kd = 

### 0.01Koc 

### where : C w 

### = 

### water concentration (μg/L) m ai 

### = 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 p esticide regulatory

work. This model has been developed under USEPA Guidance 6 

### , and e xternal independent evaluations have been positive 7



### . 6 USEPA 2009. Guidance on the Development, Evaluation, and Application of Environmental Models. EPA/100/K09/003 March 2009. US Environmental Protection Agency, Washington, DC. 7 Luo, Y. 2011. Report 263: Review and Evaluation of Pesticide Modeling Approaches in Rice Paddies. California Department of Pesticide Regulation, Environmental Monitoring Branch. Jun e 29, 2011. http://www.cdpr.ca.gov/docs/emon!surfwtr/protocols/study263protocol.pdf

### Page **17** of **28**

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 e quilibrium within each region follows a linear isotherm 8 

### . The two regions are coupled b y 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, hydrol ys is, photoly sis, 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 - ye ar cycles for the length of the simulation. For instance, a ty pical 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

fl ows 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 especiall y 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 pon d model 9 

### . 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 W

ater Modeling Ground w ater 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 bog s 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 (m ai 

### =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 10



### . The PFAM output file is shown in **Appendix 3** . 8 USEPA. 2004. Exposure Analysis Modeling System (EXAMS): User Manual and System Documentation. EPA/600/R- 00/81 - 023. May 2004. Ecosystems Research Division. United States Environmental Protection Agency. 9 FIFRA SAP. 2004. Refined (Level II) Terrestrial and Aquatic Models for Probabilistic and Ecological Assessment of Pes ticides. March 30 - April2, 2004. http://www.epa.gov/scipoly/sap/meetings/2004/033004 mtg.htm 10 USEPA 201 3 . Dirk Young , Office of Pesticide Programs Environmental Fate and Effects Division . Pesticides in Flooded Applications Model (PFAM) User Guidance Version 1.00 (Jan 23, 2013). Washington, DC.

### Page **18** of **28**

**Table 8**  **. P FAM 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/g oc ) (K oc ) 23.4 Calculated K oc from K d based on Input Parameter Guidance; Average K d 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 11

. 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 12

.

11 Smith, Erika N. 2007. Watercress (Nasturtium officinale) Production Utilizing Brook Trout (Salvelinus fontinalis) Flow - through Aquaculture Effluent. Thesis submitted to the Davis College of Agriculture, Forestry, and Consumer Sciences at West Virginia University. Morgantown, West Virginia. 12 IFAS, 1999. Univ ersity of Florida Institute of Flood and Agricultural Sciences (IFAS) Extension document FPS 590 (Originally published 1999, revised in 2007, reviewed in 2011).

### Page **19** of **28**

6. Input Parameter **7. Value**  **8. Source and Comments**  Days from Zero Height to Full Height 19 Estimated based on information from Smith 2007 13

. 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

13 Smith, Erika N. 2007. Watercress (Nasturtium officinale) Production Utilizing Brook Trout ( Salvelinus fontinalis) Flow - through Aquaculture Effluent. Thesis submitted to the Davis College of Agriculture, Forestry, and Consumer Sciences at West Virginia University. Morgantown, West Virginia.

### Page **20** of **28**

**Table 9**  **. Planting, Flooding, Drainage, Application, and Harvest Ev**  **ent Inputs for Florida**  **Watercress PFAM Modeling** (shaded events are flood events used in the PFAM “Flood s ” 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**  μg/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 watercre ss. 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.

### Page **21** of **28**

**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 col lection 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 b y 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 anal yt e in this program. USGS National W

ater- Quality Assessment (NAWQA) Program Data

**–** Metaldehyde is not anal yt e 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.g ov/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 s urface water samples were tested for metaldehyde and there were no detections. PDP data are available at http://www.ams.usda.gov/AMSv1.0/pdp

### Page **22** of **28**

**Appendix 1. SCI -**  **GROW Outputs for Invasive Mollusk Eradicati**  **on Use**

SCI GROW VERSI ON 2.3 ENVIRONMENTALFATE AND EFFECTS DIVI SI ON OFFICE OF PESTI CIDE PROGRAMS U.S. ENVIRONMENTAL PROTECTION AGENCY SCREENING MODEL FOR AQUATIC PESTI CIDE EXPOSURE SciGrow version 2.3 chemical:Metaldehyd e 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 ************************************************************************

### Page **23** of **28**

**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 environmen t: 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 8 7.28 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 9 4.5 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

### Page **24** of **28**

0.67741935483871 90.58 90.11 88.07 85.22 83.59 62.4 0.709677419354839 89.69 89.23 87.28 83.52 8 0.95 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: 8 2.994 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 Applic ation 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 apprat e 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. R un 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

### Page **25** of **28**

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 86.1 7 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 9 4.27 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

### Page **26** of **28**

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 Na me 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 Metaboli sm 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. r ate 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 t o 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)

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**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, Ve rsion 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 av g 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+0 2 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

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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 me tab 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 ***********************************************************************