## Drinkin **g Water Exposure Assessment for Proposed New**  **Uses of**

**Abam ectin on**  **Chives, Dried Beans, and Bulb Onion**  **s (Crop** 

**Subgroup 3**  **- 07A** **)**

**Abam ectin**  **CAS# 71751**  **- 41**  **- 2**  **PC Code 122804 Prepared by:**  Greg Orrick, Environmental Scientist U.S. Environmental Protection Agency Office of Pesticide Programs Environmental Fate and Effects Division Environmental Risk Branch II 1200 Pennsylvania Ave., NW Mail Code 7507P Washington, DC 20460 **Reviewed by:** Nelson Thurman, Senior Science Advisor Brian Anderson , Branch ChiefPage 2 of 21 

## Table of Contents 1. EXECUTIVE SUMMARY ................................ ................................ ................................ .... 3 2. PROBLEM FORMULATION ................................ ................................ ................................ 4 2.1. U se Characterization ................................ ................................ ................................ ........ 4 2.1.1. Usage Summary ................................ ................................ ................................ ........ 7 3. ANALYSIS ................................ ................................ ................................ ............................. 8 3.1. Fate and Transport Characterization ................................ ................................ ................ 8 3.1.1. Residues of Concern ................................ ................................ ............................... 11 3.2. Drinking Water Exposure Modeling ................................ ................................ .............. 11 3.2.1. Exposure Modeling Approach ................................ ................................ ................ 11 3.2.2. Input Parameters ................................ ................................ ................................ ..... 12 3.2. 3. Modeling Results ................................ ................................ ................................ .... 14 3.2.4. Monitoring Data ................................ ................................ ................................ ...... 16 3.2.5. Drinking Water Treatment ................................ ................................ ...................... 16 4. CONCLUSIONS ................................ ................................ ................................ ................... 16 5. REFERENCES ................................ ................................ ................................ ..................... 17 Appendix A. SCI - GROW Input/Output Data. ................................ ................................ ............. 20 Appendix B. PE Input Files. ................................ ................................ ................................ ........ 21Page 3 of 21

**1. EXECUTIVE SUMMARY**  This assessment provides Estimated Drinking Water Concentrations (EDWC) in surface water and in ground water from the use patterns of maximum abamectin exposure in support of the Health Effects Division’s (HED) human health risk assessment ( **Table 1.1** ). EDWCs of abamectin were modeled for the proposed uses on dried beans, fresh and dried chives, and the bulb onions crop sub group ( 3 - 07A) and current use s on cotton and tomatoes . The proposed u se on dry beans is the use pattern of maximum exposure used to represent potential drinking water exposure for the dietary

assessment of the proposed uses. Exposure estimates reflect all residues of abamectin because the comp ound is stable to abiotic hydrol ys is and acceptable data are not available to estimate the formation and decline of residues of concern via other degradation routes . For characterization, exposure estimates are also provided that reflect the degradation rates used in the previous assessment that are based on studies currentl y determined to be unacceptable . Surface water exposure estimates are adjusted b y the national default percent cropped area (PCA) adjustment factor (87%). This default PCA does not ne cessarily mean that dry beans will occupy

87% of the watershed, but reflects the likelihood that abamectin may be used on multiple crops in the same watershed. Water resource monitoring data for abamectin are not available. Therefore, exposure estimates cannot be evaluated with monitoring data. **Table 1.1. Abamectin**  **Total Residue EDWCs in Surface Water and Ground Water for Use in Dietary Risk Assessment Based on the Use Pattern of Maximum Exposure,**  **Dry Beans .**  **A Use (maximum rate)**  **Source PCA**  **(%) 1**  **- in**  **- 10**  **- y**  **ear Peak Exposure**  **(ppb) 1**  **- in**  **- 10**  **- year** 

**Annual Mean Exposure (ppb)**  **30 -**  **year Mean**

**Exposure (ppb)** Dry Beans (0.056 lbs a.i./A/year) Surface water 87 2.3 [1.1] A 1.3 [0.41] A 0.94 [0.27] A Tomatoes, cucurbits (0.18 lbs a.i./A/year) Ground water N/A 1.6 × 10 - 3 A ED W Cs assume persistence in degradation processes. Values based on (currently unacceptable) degradation inputs used in previous assessments are in brackets for characterization purposes . The surface water EDWCs in **Table 1.1** are 5x to 6 x higher than those reported in the previous assessment ( DP barcode 335118; USEPA, 2007 ). This increase is due to modeling different model scenarios and application dates in this assessment as well as the assumption in this assessment that the abamectin is stable to de gradation in the absence of acceptable data . The environmental fate of abamectin is uncertain because submitted environmental fate data are not acceptable oth er than submitted hydroly sis, batch equilibrium , and terrestrial field dissipation studies. The compound mixture appears to readil y photolyze, biodegrade moderatel y slowly in aerobic soil, and persist in anaerobic soil . However , the studies supporting that characterization are considered unacceptable and new data need to be submitted . Abamectin does not hydrol yz e and data have not been submitted on its bio degradation in water . The residues of concern of abamectin are unclear due to uncertainty in the environmental fate data . Abamectin is nonvolatile , has a wide range of low mobility in soil, and is expected to be transported off of agricultural fields mainly via spray drift and runoff of residues sorbed to suspended solids . Field studies indicate that abamectin moderatel y dissipates with a field dissipation half

- life of 31 day s.Page 4 of 21

E xposure estimates for the proposed uses of abamectin l ikely exceed actual values that occur in drinking water reservoirs and ground water due to the screening design of the exposure models and variability and uncertainty in the subm itted environmental fate data. **2. PROBLEM FORMULATION**  Abamectin was first registered in 1985 for fire ant control on turf, lawns, and non agricultural areas, followed by registrations in 1987 for use on ornamentals and in 1989 for use on cotton and citrus, the first agricultural uses . A variety of uses have been registered since. The Interregional Research Project No. 4 (IR - 4) is now proposing use on dry beans, fresh and dried chives, and bulb onions ( i.e. , crop sub group 3 - 07A). The bulb onions include “daylily , bulb; fritillaria , bulb; garlic, bulb; garlic, great - headed, bulb; garlic, serpent, bulb; lily, bulb; onion, bulb; onion, Chinese, bulb; onion, pearl; onion, potato, bulb; shallot, bulb; cultivars, varieties, and/or hy brids of these” (40 CFR Part 180.41; Jul. 1, 2010 ). Th is drinking water assessment uses modeling to provide estimates of surface water and ground water concentrations of residues in drinking water source water (pre - treatment) resulting from abamectin use on vulnerable sites according to current and proposed l abels. EDWCs reflect drinking water exposure to residues of concern for abamectin , which the Health Effects Division’s 2008 dietary

risk assessment reported is the parent compound and a mixture of 8 - α hydrox y and ring - opened aldehyde derivative s (“Compoun d 7” ; DP 359583; USEPA, 200 8 ). Primary routes of transport to source water include runoff, including erosion, and spray drift to surface water. Leaching of the residues of concern to ground water is not expected due to the compounds’ affinity for soil particles. The models PRZM and EXAMS, coupled with the PE interface, were used to assess exposure in surface water due to runoff, erosion, and spray drift from the proposed and current abamectin uses. Exposure in ground water due to leaching was assessed with the screening model SCI - GROW. **2.1. Use Characterization**  Abamectin is a mixture of avermectins containing at least 80% avermectin B 1a (5 - 0 - demethyl avermectin A 1a) and up to 20% avermectin B 1b (5 - 0 - demethyl - 25 - de(1 - methylprop yl ) - 25 - (1 - methylethyl) avermectin A 1a). The avermectins are natural fermentation product s of the soil bacterium Streptomyces avermitilis . The active ingredient, a bamectin , is used as an insecticide (and miticide ) and as a seed protectant nematocide . The compound acts as a chl orine channel agonist in invertebrates (Fritz, et al ., 1979, Mellin et al ., 1983 and Arena et al ., 1991 in Sherma and Cairns, 1993), and may function as a gamma - aminobuty ric acid (GABAergic) agonist (Kass et al. , 1980, 1984 in Sherma and Cairns, 1993). It acts b y stimulating the release of gamma - aminobutyric acid, an inhibitory neurotransmitter, thus causing paral ys is (Tomlin, 1994). The difference in toxicity between invertebrates and mammals may be partiall y due to different distribution of the GABAergic neurons (Turner and Schaeffer, 1989 in Sherma and Cairns, 1993).Page 5 of 21

The compound is currently registered on dozens of Section 3 end - use labels with uses on numerous fruit, vegetable, and other agricultural crops, including seed treatment uses on cotton, corn, cucurbit, and tomato seeds , cattle ear - tag uses, and non - agricultural uses including ornamental uses, bait uses, and use in residential, commercial, industrial and other non - crop areas for fire ant - and related ant - control and fo r crack and crevice treatments . Proposed uses are for control of leafminers and thrips in bulb onions and control of leafminers and spider mites in dry beans and fresh and dried chives. This assessment anal yz es the proposed uses as well as currentl y la beled uses of abamectin . **Table 2.1** display s the maximum labeled use patterns for each proposed use (dry beans, bulb onions, and chives) and the current use s of maximum exposure ( cotton , tomatoes, and cucurbits) . Exposure estimates generated from these maximum use patterns were used to characterize drinking water exposure from abamectin use, both in surface water and in ground water. **Table 2.1. Maximum Use Patterns for Proposed and**  **Selected Current Abamectin**  **U ses.**  **A Use Pattern**  **Current/**

**Proposed Single App.** 

**Rate (lbs a.i./A)**  **Max. N**  **o. of** 

**App. B**  **Seasonal App. Rate (lbs a.i./A)**  **C App.** 

**Interval (days)**  **B Application** 

**Type** Dry beans Proposed 0.019 Sets of 2 in sequence 0.056 6 Aerial/ ground Bulb onions Proposed 0.019 Sets of 2 in sequence 0.056 7 Aerial/ground Chives Proposed 0.019 2 per cutting 0.056 7 Ground Cotton Current 0.019 2 0.038 21 Aerial/ground Tomatoes, cucurbits Current 0.019 Sets of 2 in sequence 0.056 7 Aerial/ground 0.12 1 0.12 N/A Seed treatment A Current uses selected for this table are those that result in maximum exposure. B Applications to chives are limited to two per cutting or harvest (which occur approximately six weeks apart , five to nine times per year ; USEPA, 2010 a ) . Applications to dry beans and bulb onions are limited to two sequential applications , with additional sets of two sequential applications allowed if a different insecticide is applied (twice in the case of bulb onions) in between sets of abamectin applications . C One crop season occurs per year for the proposed and current crops. Seasonal application rates are equivalent to annual application rates for the proposed and current uses because only one crop season occurs per year. The current uses on tomatoes and cucurbits, which were the uses of maximum exposure in previous drinking wat er exposure modeling (USEPA, 2007 ) , have seed treatm ent uses as well as foliar uses. When the uses are evaluated collectivel y, this makes them the use patterns of highest ground water exposure. The current use on cotton has a seed treatment use as well. However, the application rate per seed (0.15 mg) is 25% less than that for tomatoes and cucurbits (0.60 mg), resulting in an insubstantial increase in exposure. The proposed use on dry beans (with no seed treatments) is the use pattern of highest surface water exposure . The maximum application rate for dry beans is 0.019 pounds of active ingredient per acre (lbs a.i./A), limited to sets of two sequential applications six days apart that are separated by application of a different insecticide (interval not provided) up to a total seasonal (or annual) application rate limit of 0. 0 5 6 lbs a.i./A.Page 6 of 21

The proposed uses may

be applied by

aerial or ground application e quipment, with the exceptions that 1) use on chives is limited to ground equipment and 2) aerial application is prohibited in New York State for the other proposed uses on dry beans and bulb onions. **Figures 2.1 and**  **2.2** display Census of Agriculture maps of harvested acres of dry beans and dry onions, respectively , in 2007 (USDA, 2010). Maps of harvested acres for chives or other more specific proposed uses are not available from the Census.

**Figure 2.1. Harvested Ac res of Dry Edible Beans Other Than Limas in 2007 (USDA, 2010).** Page 7 of 21

**Figure 2.2. Harvested Acres of Dry Onions in 2007 (USDA, 2010). 2.1.1.**  **Usage Summary Figure 2.**  **3** presents the national agricultural usage pattern of abamectin in 2002 (USGS, 2010). At that time , 21% of the national agricultural usage was on citrus fruits , followed by 19% on cotton, 13% on almonds, 9% on pears, and <6 % on each of the remaining crops, grapes, tomatoes, strawberries, lettuce, avocados, and apples . These data are relatively consistent with BEAD’s Screening Level Usage Analy sis (SLUA) of abamectin (dated October 6, 2010 ) based on source data from 2001 to 2008 (USEPA, 2010 ) . However, usage on most crops is reportedl y higher than USGS estimates , with amounts used on cotton and almonds surpassing that on citrus . The SLUA reports that cotton ( 1 0,000 lbs a.i.), almonds (6 ,000 lbs a.i. ), and citrus ( grapefruit, lemons, oranges, tangelos, and tangerines; collectively 3,000 - 4,5 00 lbs a.i. ) account for the greatest amount of usage, followed b y avocados, grapes, pears, strawberries, and tomatoes ( accounting for 1,000 lbs a.i. of usage each ) .Page 8 of 21

**Figure 2.3 .**  **National Agricultural Usage of Abamectin in 2002 (USGS, 2010). 3.**  **ANALYSIS 3.1.**  **Fate and Transport Characterization**  Abamectin ( CAS No. 71751 - 41 - 2; PC code 122804 ; chemical structure in **Figure 3.1** ) is a mixture of avermectins containing at least 80% avermectin B 1a (5 - 0 - demethyl avermectin A 1a ; CAS No. 65195 - 55 - 3 ) and up to 20% avermectin B 1b (5 - 0 - demethyl - 25 - de(1 - methylpropyl) - 25 - (1 - methylethyl) avermectin A 1a ; CAS No. 65195 - 56 - 4) . The environmental fate of this compound mixture is uncertain because submitted environmental fate data are not acceptable other than the submitted hydrol ys is, bat ch equilibrium , and terrestrial field dissipation studies. Based on submitte d data, including the currentl y un acceptable data used in recent assessments, abamectin moderatel y degrades in aerobic soil (with half - lives of 15 to 47 day s) and persists in anaerobic soil (half

- life of 26 7 day s). Data have not been submitted on the biodegradation of abamectin in water ; however, its close derivative ivermectin has an aerobic aquatic DT 50 of 15 day s according to Lo ffler et al. (2005). The compound mixture is stable to hydrol ys is. Illuminated, abamectin photoly zes readil y (half

- life of <1 day) on soil surfaces and in clear, shallow waters . However, there is uncertainty in the photolysis data because the studies arePage 9 of 21

unacceptable. Photol ys is is not likely to be substantial where abamectin is incorporated or under canop y . Because the submitted photolysis and biodegradation studies of abamectin are not acc eptable, the compound mixture will be conservatively assumed stable to these routes o f degradation, which includes the assumption that any observed degradation results in structurally similar degradates of similar toxicity and environmental fate to the parent compound mixture, until acceptable data are submitted to refine this assumption.

**Figure 3.1. Chemical structure of abamectin (mixture of avermectins B 1a**  **and B 1b**  **; MRID 46877502**  **).** Abamectin is soluble in water onl y up to 0 .010 mg/L (at 21 °C ) and is non - volatile under field conditions (vapor pressure of 1.5 × 10 - 9 torr at 25°C) . Insoil, abamectin display s a wide range of low mobility (K d range of 18 to 132 L/kg) , with no correlation between absorption to soils and the ir organic carbon content . Therefore, the compound mixture is not expected to be a ground water concern. Important means of transport off of agricultural fields following application will include spray drift and runoff of residues sorbed to suspended solids. Field dissipation data appear to be consistent with the laboratory data, indicating that abamectin dis sipation on the field is moderate (dissipation half - life of 31 day s). However, leaching of abamectin and its delta - 8,9 - isomers to the 12 - 18 - inch depth was observed by 28 day s after application, indicating that abamectin residues may have increased mobilit y in some soils. A summary of the environmental fate characteristics of abamectin from registrant - submitted studies is presented in **Table 3.1** .Page 10 of 21

**Table 3.1.**  **General Physicoc hemical Properties and Environmental Fate Parameters of**  **Abamectin .**  **Parameter Value**  **Reference Physical/Chemical Parameters**  Molecular mass avermectin B 1a : 873.1 g/mol avermectin B 1b : 859.1 g/mol Calculated Vapor pressure (25°C) 1.5 x 10 - 9 torr MRID 4 7436204 Henry’s Law constant (25 °C) 1 .7 x 10 - 7 atm·m3 /mol Calculated Water solubility (21 °C) 0.010 mg/L MRID 47436204 Octanol -water partition coefficient (K OW); (log KOW) (25 °C) avermectin B 1a : 300,000 ; ( 5.5 ) avermectin B 1b : 100,000; (5.0) MRID 46877502 Dissociation constant (pKa) 7.22 MRID 46877502 **Persistence in Water** Hydrolysis half

- life (pH 5, 7, and 9) No evidence of degradation MRID 131083 Aqueous photolysis DT 50 [ 3.5, 12 hrs (0.29, 1.0 solar day) ] A [ MRID 159163 ] A Aerobic and anaerobic a quatic metabolism half

- lives (No submitted data) -- **Persistence in Soil** Soil photolysis DT 50 [ 21 hrs (1.7 solar days) ] A [ MRID 159163 ] A Aerobic soil metabolism half - li ves [ 15, 20, 20, 28, 40, 47 d] A [ MRID 159163 ] A Anaerobic soil metabolism half - life [ 267 d] A [ MRID 159163 ] A

**Mobility** Soil -water partitioning coefficient (Kd) 77 ± 58 L/kg (range: 9.7 - 161 L/kg; 3 soils) MRID 4 0856301 **Field Dissipation** Field dissipation half

- life 31±6 d (leaching to 12 - 18” depth at 28 days) MRID 42627601 ; 41191501 A Data in brackets are unacceptable and provided for characterization . The major abamectin degradates in soil include d a mixture of 8 - α - hydroxy and ring opened aldehyd e derivatives of the parent compound mixture (“Compound 7”; maximum of 20% of the applied 56 day s after treatment) and two other unidentified compounds or mixtures (“Compound 4”, maximum of 12% of the applie d at 84 day s, and “Compound 12”, maximum of 12% of the applied at 28, 56, 112 day s). These major degradates appeared to be more persistent in soil than the parent compound mixture. Their mobility in soil i s not determined. The major abamectin photodegradates were not identified. However, three chromatographic fractions representing degradates were described, including a major non - polar fraction consistent with the delta - 8,9 - isomers of abamectin, a major “moderatel y polar” fraction, and a major polar fraction that consisted of multiple components.Page 11 of 21

**3.1.1. Residues of Concern**  The Health Effects Division’s 2008 dietary risk assessment i nclud ed abamectin and its soil degradate mixture “Compound 7” as residues of concern in drinking water (DP barcode 359583 ; USEPA, 200 8 ). Compound 7 wa s considered as toxic as the parent compound due to structural similarity

and because its toxicity

is unknown. O ther major environmental degradate s may meet these criteria as well pending their identification. Because submitted photolysis and biodegradation studies are not acceptable due to failure to identify major degradates among other deficiencies , abamectin is conservativel y assumed stable to th ese routes of degradation, as stated above, which includes the assumption that any observed degradation results in structurally similar degradates of similar toxicity and environmental fate to the parent compound mixture. Due to this assumption of no degradation , only abamectin is modeled in this assessment as the residue of concern. Once acceptable environmental fate data for abamectin are submitted, a total residues approach will be used to estimate exposure to the abamectin residues of concern. This a pproach involves the use of total - residues degradation half - lives based on the sum of residues of concern at each sampling interval in submitted laboratory degradation studies. Also, the chemical properties and soil mobility of the residue of concern most vulnerable to environmental transport are typicall y used to represent the chemical properties and soil mobility of all residues. **3.2. Drinking Water Exposure**  **Modeling 3.2.1.**  **Exposure Modeling Approach** The Tier II models, Pesticide Root Zone Model (PRZM v3.12.2, May 12, 2005) linked with EXposure Anal ys is Modeling S ys tem (EXAMS v2.98.04.06, Apr. 25, 2005) via the PE model shell (PE v5.0, Nov. 15, 2006, i.e. , PRZM/EXAMS) were run to estimate screening - lev el exposure of surface water drinking water sources to abamectin following the proposed and current uses. Ground water drinking water sources were assessed with the Tier I model, Screening Concentration in Ground Water (SCI - GROW v2.3, Jul. 29, 2003). The PE model generates estimated drinking water concentrations (EDWC) of abamectin residues that may

occur in surface water used as drinking water down gradient from applications on terrestrial crops. The PRZM model simulates pesticide movement and transform ation from crop application through soil residue processes. The EXAMS model simulates pesticide loading via runoff, erosion, and spray drift assuming a standard watershed of 172.8 ha that drains into an adjacent standard drinking water index reservoir of 5.26 ha and an average depth of 2.74 m. A more detailed description of the index reservoir watershed can be found in Jones et al. , 2010. SCI - GROW estimates a single screening - level ground water concentration that might be expected in shallow unconfined aquifers under highly permeable soils, for use as both an acute and chronic drinking water endpoint. SCI - GROW was developed by fitting a linear model to ground water concentrations with the Relative Index of L eaching 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 soilPage 12 of 21

metabolism and the soil - water partition coefficient. The output of SCI - GROW represents th e concentrations of abamectin residue s that might be expected in shallow unconfined aquifers under sandy soils, which is representative of the ground water most vulnerable to pesticide contamination and likely

to serve as a drinking water source. The coup led PRZM/EXAMS (PE) model, SCI - GROW model, and associated users manuals may

be downloaded from the U.S. Environmental Protection Agency (EPA) Water Models web - page (USEPA, 2010 a ). **3.2.2. Input Parameters** 

**Ground Water Exposure** Input parameters for the SCI - GROW model appear in **Table 3. 2**  . The selected application inputs represent the maximum proposed or current use pattern, which is for the current use s on tomatoes and cucurbits ( one seed treatment per year at 0.12 lbs a.i ./A and three foliar applications per year at 0.019 lbs a.i./A). The seed treatment application rate of 0.12 lbs a.i./A was multiplied by

6%, producing 0.0072 lbs a.i./A, to account for the availability of abamectin on treated seeds (MRID 47000503). Beca use SCI - GROW cannot accept multiple applications at different rates (and abamectin is persistent below the soil surface), all applications were summed and input a s one total application of 0.064 lbs a.i./A. **Table 3.2 . SCI**  **- GROW Input Parameters for**  **Abamec tin**  **Residues. A**  **Input Parameter Value**  **Source** Application Rate 0.064 lbs a.i./A B Current labels Applications per Year 1 B Current labels Organic Carbon Partition Coefficient (KOC ) 4700 L/kg OC MRID 4 0856301 Aerobic Soil Metabolism Half - life ( f rom previously assessments ) C 10,000 d ( 101 d) No acceptable data available (USEPA, 2007 ) A Source data are in **Tables 2.1** and **3. 1**  . B Input is annual sum of applications [(0.019 lbs a.i./A × 3) + 0.0072 lbs a.i./A = 0.064 lbs a.i./A] because SCI GROW does not accept different application rates per year. C For characterization (in parentheses) , the total residue half - life used in previous assessments (USEPA, 2007) wa s also mo deled . The lowest measured mean organic carbon partition coefficient (4700 L/kg OC ) from the submitted batch equilibrium study of abamectin (MRID 40856301) was input into SCI - GROW , in accordance with current input parameter guidance (USEPA, 2009) , because of the greater than three - fold variation in measured values . Because acceptable a erobic soil metabolism data have not been submitted, the compound was assumed stable for the aerobic soil metabolism half - life input (represented as 10,000 day s). For characterization, the total residues half - life value (101 day s) used in previous assessm ents (USEPA, 2007 ) was modeled as well , although the data represented b y the half

- life (MRID 159163) have since been reclassified as unacceptable. Input and output data for SCI - GROW are attached in **Appendix A** .Page 13 of 21 **Surface Water Exposure** The model input parameters used in PE to simulate the scenarios and application practices for the proposed and current uses of abamectin are provided in **Table 3. 3**  . Input files used for modeling results are listed in **Appendix B**  . **Table 3.3 .**  **PRZM Scenarios and Input Parameters Describing Proposed and Current Maximum Use Patterns of**  **Abamectin .**  **Use Scenario**  **Date of Initial**  **App. App. Rate in lbs** 

**a.i./A (kg a.i./ha)**  **App.**

**per Year**  **App. Interval**  **(days) CAM** 

**Input IPSCND** 

**Input Application** 

**Efficiency/ Spray Drift**  Dry beans MI beans Aug. 1 0.019 (0. 021 ) 3 6, 12 A 2 1 0.95/0.16 Bulb onions GA onion Apr. 24 0.019 (0. 021 ) 3 7, 21 B 2 1 0.95/0.16 Chives OR mint Jul. 1 0.019 (0. 021 ) 3 7 2 1 0.99/0.064 Cotton MS cotton Jun. 15 0.019 (0. 021 ) 2 21 2 1 0.95/0.16 Tomatoes FL tomato Mar. 5 0.019 (0. 021 ) 3 14, 7 C 2 1 0.95/0.16 Jan. 18 0.0072 (0.0081) D 1 -- 8 E 1 1.0/0.0 A The second application occurs after 6 days. The third application was assumed to occur after 12 days, allowing for an application of an alternative insecticide after the second application . B The second application occurs after 7 days. The third application was assumed to occur after 21 days, allowing for two applications of an alternative insecti cide after the second application . C The second application was assumed to occur after 14 days, following an application of an alternative insecticide. The third application occurs 7 days after the second application . D The application rate of 0.12 lbs a.i./A was multiplied by 6%, producing 0.0072 lbs a.i./A, to account for the availability of abamectin on treated seeds (MRID 47000503). E Treated seeds are planted at a 0.5 - inch (1.3 - cm) depth . However, a 2.0 - cm incorporation depth was modeled due to li mitations with PRZM. Applicable scenarios were modeled for each proposed use. The Oregon mint scenario was used as a surrogate for chives in the absence of a scenario specific to chives and because mint is an herb as well. Scenarios listed in **Table 3.3** are th ose that are most vulnerable to exposure for each use. Dates of initial application were selected that were within the application window and characterized by vulnerability

to runoff. Runoff vulnerability was explored by modeling a range of initial application dates approximately 14 day s apart within the labeled application timing and scenario crop season , and selecting the date for which exposure estimates were highest. This was expected to produce high - end exposure estimates that are conservativ e but that may

not represent the highest possible exposure. Use on cucurbits was not modeled , as was done in previous assessments, because use on tomatoes produces higher exposure. All foliar uses were modeled as aerially applied , with the exception that use on chives was modeled as a ground application per labeled directions . For seed treatment of tomatoes, the application rate of 0.12 lbs a.i./A was multiplied by 6% (producing 0.0072 lbs a.i./A) to account for the availability of abamectin on treated s eeds (MRID 47000503). The entire application (100% efficiency) was modeled with a 2.0 - cm incorporation depth (chemical application method 8) due to limitations with PRZM, although treated seed may

be planted at a 0.5 - inch (1.3 - cm) depth ( DP 335118; USEPA, 2007) .Page 14 of 21

The chemical and environmental fate data for abamectin listed in **Table 3.1**  were used for generating model input parameters for PE (listed in **Table 3. 4**  ). The chemical inputs were based on abamectin parent and reflect stability to degradation due to a lack of acceptable degradation data , with the exception that hydrol ys is data indicate that abamectin is stable to abiotic hydrol ys is . This results in exposure estimates that are conservative unless abamectin degrades into persistent residues of simil ar or greater toxicity and mobility . The soil - water partition coefficient (Kd) input (77 L/kg) is the mean of three mean value s for abamectin. **Table 3.4 . PE Chemical Input Parameters for**  **Abamectin .**  **A Input Parameter**  **Value Justification**  **Source** Molecular Mass (g/mol) 873.1 MW of ≥80% of avermectins in abamectin (Calculated) Henry’s Law Constant (atm m3 /mol) 1 .7 x 10 - 7 Ratio of vapor pressure to water solubility (Calculated from MRID 47436204 ) Solubility in Water (mg/L) 0.010 Study value MRID 47436204 Soil -water Partition Coefficient (Kd) (L/kg) 77 Mean of three mean value s MRID 4 0856301 Aerobic Soil Metabolism Half - life (days) 0 [150] Assumed stable in absence of acceptable data [value from previous assessments] No acceptable data [USEPA, 2007] Aerobic Aquatic Metabolism Half

- life (days) 0 [300] Assumed stable in absence of acceptable data [value from previous assessments] No acceptable data [USEPA, 2007] Anaerobic Aquatic Metabolism Half

- life (days) 0 Assumed stable in absence of acceptable data No acceptable data Hydrolysis Half

- life at pH 7 (days) 0 Study value MRID 131083 Aqueous Photolysis Half - life (days) 0 [0.5] Assumed stable in absence of acceptable data [value from previous assessments] No acceptable data [USEPA, 2007] A For characterization, v alues in brackets represent total residue half - lives used in previous assessments (USEPA, 2007). **3.2.3. Modeling Results** 

**Ground Water Results** The single exposure estimate from the SCI - GROW model is used as a conservative peak and annual mean value in ground water leachate. The exposure estimate for the maximum use pattern s (tomatoes and cucurbits) is 1.6 × 10 - 3 μg/L (1.6 ng/L) assuming residues do not degrade . Using the mean total residue aerobic soil degradation half - life value used in previous assessments , for charact erization, the m aximum exposure estimate is 9.1 × 10 - 4 μg/L (0.91 ng/L) ; however, the degradation data used to calculate this v alue have been downgraded to unacceptable. These values support the expectation that abamectin residues will not produce appreciable exposure in ground water due to low mobility in soil and low application rates .Page 15 of 21 **Surface Water Results** Proposed and current use patterns were modeled to estimate exposure in surface water, as described above. Maximum abamectin EDWCs in surface water per use are listed in **Table 3. 5**  . Exposure estimates were adjusted by the default national percent cropped area (PCA) value (87%) that accounts for the maximum area within any watershed that may

be in agriculture (Jones et al. , 2010 a ). Modeled dail y EDWCs for foliar and seed - treatment uses on tomatoes were combined in an Excel spreadsheet prior to adjusting for the PCA and calculating the EDWCs reported in **Table 3.5** . **Table 3.5 .**  **Abamectin EDWCs in Surface Water f**  **rom Proposed and Current Uses .**  **A Use**  **PRZM Scenario 1**  **- in**  **- 10**  **- year Peak**  **Exposure (ppb) 1**  **- in**  **- 10**  **- year Annual** 

**Mean Exposure (ppb) 30**  **- year Mean**  **Exposure (ppb) Proposed Uses**  Dry beans MI beans **2.3 [**  **1.1 ]**  **1.3 [**  **0.41 ]**  **0.94 [0.27]** Bulb onions GA onion 1.4 [0.81] 0.63 [0.26] 0.49 [0.19] Chives OR mint 0.91 [0.27] 0.67 [0.15] 0.54 [0.12] **Current Uses** Cotton MS cotton 1.2 [0.74] 0.58 [0.22] 0.42 [0.15] Tomatoes FL tomato 1.5 [0.67] 0.63 [0.22] 0.53 [0.18] A Maximum values are in bold. Values based on degradation inputs used in previous assessments are in brackets . Exposure estimates from the proposed maximum use pattern for dry beans are greater in this national screen than those from other proposed and currently labeled uses . This use pattern of maximum exposure results in a 1 - in - 10 - ye ar peak EDWC (2.3 μg/L) that is 5x higher than that reported in the previous assessments for use on cucurbits (0.46 μg/L ; USEPA, 2007 ) . The 1 - in 10 - ye ar annual mean EDWC (1.3 μg/L) for use on dry beans is 6x higher than that reported in the previous assessments for use on tomatoes (0.21 μg/L) . However, these 1 - in - 10 - year peak and annual mean exposure estimates for use on dry beans are onl y 2x and 3x higher, respectivel y, than the exposure estimates based on the degradation inputs used in the previous assessments for characterization (listed in brackets in **Table 3.5** ). Addition of seed treatment to the foliar use on tomatoes did not change 1 - in - 10 - ye ar peak exposure estimates for foliar use and increased 30 - ye ar mean exposure estimates by only 15%. Values provided for characterization should not be used quantitativel y in exposure assessment because they are based on unacceptable data. They indicate that the current version of PE , with most of the same inputs (dates of initial application used in previous modeling are unknown), results in 1 - in - 10 - year peak and annual mean values for use of abamectin on tomatoes that are similar ( 1.0 - 1.5x) to those resulting from the previous version of PE . There are a number of factors inherent in the modeling that can affect the accuracy of this anal ys is; these include the availability and quality

of the model input dat a and the use of maximum labeled practices and environmental conditions that may differ from ac tual practices and conditions. The exposure values listed above are conservative for a number of reasons. The actual application area of these uses in drinking water basins is likely to be less than the totalPage 16 of 21

cropped area of the watershed. Also, degradation rates for abamectin residues of concern were assumed stable in the absence of acceptable photoly sis and biodegradation data . **3.2.4. Monitoring Data**  This assessment contains a cursory review of available surface water and ground water monitoring data sources for data on abamectin . Abamectin is not a regulated chemical under the Safe Water Drinking Act (SWDA) or related statutes. The compound is not an anal yt e listed in the USEPA STORET database (USEPA, 2010 b ), the California Department of Pesticide Regulation (DPR) Surface Water Database (C DPR, 2010), or the USGS NAWQA program (USGS, 2010 a ). Therefore, water monitoring data on abamectin have not been located. **3.2.5. Drinking Water Treatment**  Because direct data regarding the effects of drinking water treatment on abamectin residues of concern hav e not been provided to the Agency and could not be located in the public literature, drinking water treatment effects on abamectin have been considered onl y qualitativel y based on the phys icochemical properties of the compound. Carbon filtering is expecte d to reduce abamectin residue concentrations due to the compound’s affinity to organic carbon. Flocculation and sedimentation removal may be effective at reducing abamectin residue concentrations, especially if residues are bound to suspended sediment. L ime softening is not expected to reduce concentrations of abamectin residues because the compound mixture do es not indicate susceptibility

to abiotic hydrol ys is. **4. CONCLUSIONS**  Drinking water exposure estimates for the proposed uses of abamectin on dry beans, chives, and bulb onions are represented by the use pattern of maximum abamectin exposure, dry beans ( **Tables 1.1** and **3. 5**  ). Maximum acute, chronic, and cancer EDWCs in surface water are 2 .3, 1.3 , and 0.94 μg/L , respectivel y . The maximum exposure estimate for ground water (from use on tomatoes and/or cucurbits) is only 1.6 × 10 - 3 μg/L . Monitoring and drinking water treatment data on abamectin are not available . Abamectin was modeled in this assessment as stable to degradati on because it is stable to hydrol ys is and submitted photoly sis and biodegradation data are not acceptable. It could not be concluded, based on the unacceptable data, that any observed degradation of abamectin resulted in degradates of much less toxicity . Assessment modeling relied on maximum labeled use patterns and a default national PCA value. Where actual use patterns are less than the labeled maximums and location - specific PCAs are less than assumed in this assessment, actual environmental exposures may be lower.Page 17 of 21

**5. REFERENCES**  California Department of Pesticide Regulation (CDPR). 2010. Surface Water Database. California Environmental Protection Agency , Department of Pesticide Regulation, Surface Water Protection Program. Data available through June, 2008. Online at: http://www.cdpr.ca.gov/docs/sw/surfdata.htm Jones, R. D., K. Costello, J. Hetrick, J. L in, R. Parker, N. Thurman, C. Peck. 2010. Development and Use of the Index Reservoir in Drinking Water Exposure Assessments. U.S. Environmental Protection Agency , Office of Pesticide Programs. April 15, 2010. Online at: http://www.epa.gov/oppefed1/models/water/index_reservoir_dwa.html Jones, R. D., K. Costello, J. Hetrick, J. L in, R. Parker, N. Thurman, C. Peck, G. Orrick. 2010 a . Development and Use of Percent Cropped Area Adjustment Factors in Drinking Water Exposure Assessments. U.S. Environmental Protection Agency , Office of Pesticide Programs. September 9, 2010. Online at: http://www.epa.gov/oppefed1/models/water/pca_adjustment_dwa.html Loffler D., J. Rombke, M. Mell er, and T. Ternes. 2005. Environmental Fate of Pharmaceuticals in Water/Sediment Systems. Environ. Sci. Technol. , **39** , 5209 - 5218. Sherma, J. and Cairns, T. Comprehensive anal ytical profiles of important pesticides. 1993. CRC Press, Inc. Boca Raton, Fl. p 75. Tomlin, C.D.S. (ed.). 1994. The Pesticide Manual - Wo rld Compendium . 10th ed. Surrey , UK. The British Crop Protection Council, p. 4. U.S. Department of Agriculture (USDA). 2010. 2007 Census of Agriculture: United States: Summary and State Data. U.S. Department of Agriculture, National Agricultural Statistics Service. I ssued February , 2009; updated December, 2009. Online at: http://www.agcensus.usda.gov/Publications/2007/index.asp USEPA. 2007. Abdel - Saheb, I. Revised Drinking Water Assessment for Abamectin as a Seed Treatment and as a Foliar Application on Cucurbits and Tomato Based on New Seed Leaching Study

Submitted to EFED. DP Barcode 335118. U.S. Environmental Protection Agency , Office of Prevention, Pesticides, and Toxic Substances, Environmental Fate and Effects Division. Memorandum to the Registration Division. Mar. 20, 2007. USEPA. 2008. P iper, S. Abamectin: (Acute and Chronic Aggregate Dietary Exposure and Risk Assessments for the Section 3 on Stone Fruit Crop Group 12, Tree Nut Crop Group 14, Pistachio, Tuberous and Corm Vegetables Subgroup 1C and Cattle Ear Tag Use. DP Barcode 359583. U.S. Environmental Protection Agency , Office of Prevention, Pesticides, and Toxic Substances, Health Effects Division. Memorandum to the Health Effects Division and Registration Division. Dec. 13, 2008.Page 18 of 21

USEPA. 2009. Guidance for Selecting Input Parameters in Modeling the Environmental Fate and Transport of Pesticides. Version 2.1. U.S. Environmental Protection Agency , Office of Pesticide Programs, Environmental Fate and Effects Division, Oct. 22, 2009. Onl ine at: http://www.epa.gov/oppefed1/models/water/input_parameter_guidance.htm USEPA. 2010. Screening Level Usage Anal ys is (SLUA) of Abamectin (122804). U.S. Environmental Protection Agency , Office of Chemical Safety and Pollution Prevention, Biological an d Economic Analy sis Division. Oct. 6, 2010. USEPA. 2010 a . Water Models. U.S. Environmental Protection Agency , Pesticides: Science and Policy . Last updated: Dec. 8 , 2010. Online at: http://www.epa.gov/oppefed1/models/water/ USEPA. 2010 b . STORET. U.S. Environmental Protection Agency, Office of Water. Online at: http://www.epa.gov/STORET/ United States Geological Survey (USGS ). 2010. 2002 Pesticide Use Maps . United States Geological Survey , National Water- Quality Assessment (NAWQA) Program, Pesticide National Sy

nthesis Project. Online at: http://water.usgs.gov/nawqa/pnsp/usage/maps/ USGS. 2010 a . National Water- Quality Assessment (NAWQA) Program. United States Geological Survey . Data available through Sep. 30, 2007. Last update d: Dec. 14 , 2010. Online at: http://infotrek.er.usgs.gov/apex/f?p=NAWQA:HOME:3966441777962223 **Submitted Environmental Fate and Product Chemistry**  **Data** MRID 131083 . May

nard, M.; Ku, C.; Gruber, V.; et al. (1982) Hydroly sis of Aver mectin B1a (MK- 0936). (Unpublished study received Jan 3, 1983 under 618 - EX - 10; submitted by Merck & Co., Inc., Rahway , NJ; CDL :249152 - F) MRID 159163 . MSD AGVET, Inc. (19??) Chemical and Phy sical Pro perties of Techni cal MK936 (Avermectin B1) and Avid 0.15 EC Miticide/Insecticide for Experimental Use on Citrus. (Compilation; unpublished study received Dec 29, 1983 under 50658 - EX - 1; CDL :252113 - A) MRID 40856301 . Wislocki, P. (1988) Position Paper: Abamectin -- Soil Dissipation and Crop Rotation: Supplemental: P roject ID: 618 - 936 - SD - CR. Unpublished study prepared by Merck Sharp & Dohme Research Labora - tories. 47 p. MRID 41191501. Wehner, T. (1989) Additional Soil Residue Data in Support of Applications for Registration of Abamectin Soil L eaching and Dissipation Study : Project ID: Merck No. 001 - 87 - 6045R; ADC No. 992. Unpublished study prepared by

Merck Sharp & Dohme Research Laboratories and Anal ytical Development Corp. 18 p.Page 19 of 21

MRID 42627601. Wertz, P. (19 93) Soil Residue Data in Support of an Application for Registrations of Abamectin: Soil L eaching and Dissipation Study 001 - 87 - 6045R: A Supplement: L ab Project Number: 618 - 936 - 6045. Unpublished study prepared by Analy tical Development Corp. 603 p. MRID 468 77502 . Friis, M. (2006) Product Chemistry - Abamectin Technical (CHA 204) - EPA Reg. No. 4787 - (none ye t) Group B - Phy sical /Chemical Properties. Project Number: MVF/060500/ABA/204/B/USA, PYC/170, PYC/171. Unpublished study prepared by Cheminova Agro A/S . 399 p. MRID 47436204 . Wagner, J. (2008) Abamectin Technical Herbicide: Stability to Normal and Elevated Temperatures, Metals, and Metal Ions: Oxidation/Reduction: Flammability : Explodability : Storage Stability : Miscibility : Corrosion Characteristics: Di electric Breakdown Voltage: Viscosity : Boiling Point: Dissociation Constants in Water: Particle Size, Fiber Length, and Diameter Distribution: Partition Coefficient: Water Solubility : Vapor Pressure. Unpublished study prepared by

Wagner Regulatory

Associat es, Inc. 6 p. MRID 47000503. Clark, A. (2005) Abamectin FS 400 Pre - Treated Tomato Seeds and Abamectin FS 500 Pre - Treated Corn Seeds: Desorption of (Carbon 14) Abamectin Following Applications of Pre - Treated Corn and Tomato Seeds to Various Soils: Final Report. Project Number: T005067/05. Unpublished study prepared by

Sy ngenta Crop Protection. 63 p.Page 20 of 21

**Appendix A . SCI**  **- GROW Input/Output Data.**  **SCI -**  **GROW Input/Output File.**  SciGrow version 2.3 chemical:Abamectin time is 1/10/2011 13:47:22

------------------------------------------------------------------------ Application Number of Total Use Koc Soil Aerobic rate (lb/acre) applications (lb/acre/yr) (ml/g) metabolism (day s)

------------------------------------------------------------------------ 0.064 1.0 0.064 4.70E+03 10000.0

------------------------------------------------------------------------ groundwater screening cond (ppb) = 1.58E - 03 ************************************************************************ SciGrow version 2.3 chemical:Abamectin time is 1/10/2011 15:22:12

------------------------------------------------------------ ------------ Application Number of Total Use Koc Soil Aerobic rate (lb/acre) applications (lb/acre/yr) (ml/g) metabolism (day s)

------------------------------------------------------------------------ 0.064 1.0 0.064 4.70E+03 101.0

------------------------------------------------------------------------ groundwater screening cond (ppb) = 9.14E - 04 ****************************************************************** ******Page 21 of 21

**Appendix B . PE Input Files.**  **Table B .1. Summary of PE Input File Names.**  **Use File name**  **s Date**  Dry beans Aba_

bean .out Aba_ bean_char .out Jan. 11 , 2010 Bulb onions Aba_onio .out Aba_onio_char .out Chives Aba_

mint .out Aba_ mint_char .out Cotton Aba

_cott.out Aba _cott _char .out Tomatoes Aba

_toma .out Aba

_toma_char .out Aba

_toma_seed .out Aba

_toma_seed_char .out **Example Input File (Use on Dry Beans**  **)** Output File: Aba_

bean Metfile: w14826.dvf PRZM scenario: MIbeansSTD.txt EXAMS environment file: ir298.exv Chemical Name: Abamectin Description Variable Name Value Units Comments Molecular weight mwt 873.1 g/mol Henry's La w Const. henry 1.7e - 7 atm - m^3/mol Vapor Pressure vapr torr Solubility sol 0.010 mg/L Kd Kd 77 mg/L Koc Koc mg/L Photolysis half

- life kdp 0 days Half - life Aerobic Aquatic Metabolism kbacw 0 days Halfife Anaerobic Aquatic Metabolism kbacs 0 days Halfife Aerobic Soil Metabolism asm 0 days Halfife Hydroly sis: pH 7 0 days Half - life Method: CAM 2 integer See PRZM manual Incorporati on Depth: DEPI cm Application Rate: TAPP 0.021 kg/ha Application Efficiency: APPEFF 0.95 fraction Spray Drift DRFT 0.16 fraction of application rate applied to pond Application Date Date 01 - 08 dd/mm or dd/mmm or dd - mm or dd - mmm Interval 1 interval 6 days Set to 0 or delete line for single app. app. rate 1 apprate kg/ha Interval 2 interval 12 days Set to 0 or delete line for single app. app. rate 2 apprate kg/ha Record 17: FILTRA IPSCND 1 UPTKF Record 18: PLVKRT PLDKRT FEXTRC 0.5 Flag for Index Re s. Run IR Reservoir Flag for runoff calc. RUNOFF total none, monthly or total(average of entire run)