### 1 OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION **UNITED ST AT**  **ES ENVIRONMENT AL**  **PROTECTION A GENCY** 

WA SHINGTON, D.C. 20460



### PC Code: 108800 DP Barcode: 420047 **Date:** December 1 6 , 2014 **MEMORANDUM Subject:**  Tier II Drinking Water Asses sment for the Proposed S - Metolachlor Use on

Lettuce (Head and Leaf), Low - Growing Berry Subgroup 13 - 07G (excluding Cranberry), Cucurbit Vegetable Group 9, Sunflower Subgroup 20B and Fruiting Vegetabl e Group 8 - 10. **To:** Bethany Benbow , Risk Manager Reviewer

Kathry n Montague , Product Manager Team 23 Dan Kenny, Branch Chief Herbicide Branch Registration Division (7505P) **From:** Christopher M. Koper , M.S. , Chemist

Sujatha Sankula , Ph.D., Branch Chief Meghan Radtke, Ph.D. , Risk Assessment Process L eader (RAPL), Acting Environmental Risk Branch 1 Environmental Fate and Effects Division (7507P) This drinking water assessment was conducted for a petition submitted by the Interregional Research Project Number 4 (IR- 4) to establish S - metolachlor tolerances for lettuce (head and leaf), low - growing berry

subgroup 13 - 07G (excluding cranberry), cucurbit vegetable group 9, sunflower subgroup 20B and fruiting vegetable group 8 - 10. S - Metolachlor is a broad spectrum herbicide that acts to inhibit seedling development. It can be applied to the proposed crops as a pre -plant, pre - emergent or post - emergent broadcast application up to a yearly maximum application rate of 3.7 lb a.i./A (single maximum application rate varies according to crop) according to the Dual Magnum  

### (EPA Reg. No. 100 - 816) label . Dual Magnum may be applied to direct seeded or transplanted crops for residual control or suppression of annual grasses, ye llow nutsedge and small seeded broadleaf weeds. Previous drinking water assessments provided separate estimated drinking water concentrations (EDWCs) for parent metolachlor/S - metolachlor and their degradates metolachlor ESA ( CGA 354743) and metolachlor OA (CGA - 51202) . Following the recent recommendation of the Residues of Concern Knowledgebase Subcommittee (D424250 ), parent metolachlor , CGA 51202 (metolachlor- OA), CGA - 40172, and CGA - 50720 will be assessed together in the drinking

### 2

water assessment using a total toxic residues (T TR ; USEPA 2009 a) approach where half - lives were recalculated (PestD F ; USEPA, 2009b) to collectively account for the parent and the combined residues of concern. These values will be utilized in surface and ground water modeling to generate aquatic exposure estimates. The highest annual application rate for the prop osed IR - 4 label (3.7 lbs a.i./A ; note that sunf lower maximum annual application rate is unspecified) is less than what EFED believes is the highest previously

registered application rates (4 lbs a.i./A to corn or cotton). Therefore, EFED is providing new EDWCs based on the scenario/annual application rate combination that will produc e the highest EDWCs because degradates of concern and the calculation method have changed . Recommended EDWCs of S - metolachlor in surface water and ground water are reported in **Table 1 .**  **Table 1. Recommended**  **EDWCs for**  **S -**  **Metolachlor Use**  **on Various Crops Drinking Water**  **Source Crop Scenario**  **1 -**  **in -**  **10 year acute**  **(** 

### μg/L **) 1**  **- in**  **- 10 year** 

**chronic (**  

### μg/L **) 30**  **- year average** 

**cancer chronic (**  

### μg/L **)** Surface Water MS Corn 1 (aerial) 371 -- --

CA Lettuce 2 (aerial ) -- 43.70 21.80 Ground Water NC Cotton 3 (aerial) 1060 NA --

WI Corn 3 (aerial) -- NA 978 1 EDWC calculated from the maximum rate (2 apps x 2.0 lb s a.i./A) registered on corn and cotton generated using SWCC mo del (aerial application; TTR approach) with a PCA factor of 0.91. 2 Current proposed use on lettuce (2 apps x 0.95 lb s a.i./A x 2 seasons). 3 Highest EDWCs generated using PRZM - GW model based on a 3 0 year simulation of 2 foliar applications of 2.0 lb s a.i./A for a maximum annual rate of 4.0 lbs a.i/A for corn/cotton ( Metolachlor RED; D 185152, 172022 ) . 

### For surface water, the acute, chronic, and cancer chronic EDWCs generated in this assessment ( **Table 2** ) exceeded the ED WCs in the previous drinking water assessment (D368735) dated 22 April 2010 . As mentioned, th e current assessment followed the total toxic residue approach with a revised tolerance expression based on the recent ROCKS meeting. For reference, the Health Effect Division’s (HED) toleranc e expression for **acute** dietary assessment is **219 μg/L** for surface water [77.60 μg/L (S - metolachlor) + 47.61 μg/L (degradate E SA) + 93.57 μg/L (degradate OA)] and the tolerance expression for **chronic** dietary assessment is **126 μg/L**  for ground water [32.8 μg/L (S - metolachlor) + 63.7 μg/L (degradate ESA) + 29.7 μg/L (degradate OA)]. Therefore, the acute and chronic EDWC values for surface water are superseded in this assessment. For ground water, the PRZM - GW (USEPA, 2012a) and SCI - GROW models were employed to model the highest appli cation rate of all metolachlor/ S - metolachlor uses (2 applications at 2.0 lb a.i./A for a maximum yearly application rat e of 4.0 lbs a.i/A on corn and cotton) in addition to the proposed uses to determine drinking water exposure in ground water ( **Table 2** ). The recommended EDWCs for ground water include the acute concentration of **1060 μg/L**  and 3 0 - ye ar average (chronic) concentration of **978 μg/L**  .

### 3

**Table 2. S**  **- Metolachlor**  **Estimated Drinking Water Concentrations (E**  **DW Cs) for**  **Surface and Ground**  **Water based on Selected Crop Scenarios Drinking Water**  **Source Proposed** 

**Label Use Model** 

**Scenario A** **pplication Rate**

**(interval betwee n**  **applications ; # seasons**  **) Acute**  **(** 

### μg/L **) Chronic** 

**(** 

### μg/L **) Cancer** 

**Chronic (**  

### μg/L **)** Surface Water (SWCC) Corn 1 KS Corn 2 app. x 2.0 lbs ai/acre (5 days) 122.00 19.80 13.20 MS Corn 2 app. x 2.0 lbs ai/acre (5 days) **371.00** 40.60 15.20 Cotton 1 MS Cotton 2 app. x 2.0 lbs ai/acre (5 days) 189.00 20.40 10.30 Curcurbit FL Cucumber 2 app. x 0.635 lbs ai/acre (14 days; 3 seasons) 136.00 17.90 10.10 MI Melon 2 app. x 0.635 lbs ai/acre

(14 days; 3 seasons) 38.30 10.30 7.67 MO Melon 2 app. x 0.635 lbs ai/acre

(14 days; 3 seasons) 52.40 9.00 6.05 NJ Melon 2 app. X 0.635 lbs ai/acre

(14 days; 3 seasons) 87.40 14.20 7.58 Lo w - Growing Berry 13 - 07G FL Straw berry 3 app. X 1.27 lbs ai/acre

(14 days) 99.30 12.90 6.64 Lettuce (Leaf) CA Lettuce 1 app. X 0.95 lbs ai/acre 1 app. X 0.32 lbs ai/acre (14 days; 3 seasons) 105.00 39.30 21.80 Lettuce (Head) CA Lettuce 2 app. X 0.95 lbs ai/acre (14 days; 2 seasons) 129.00 **43.70 21.80**  Fruiting Vegetables (Group 8 - 10) FL Pepper 1 app. X 1.60 lbs ai/acre 1 app. X 1.60 lbs ai/acre 1 app. X 0.5 lbs ai/acre (14 days) 111.00 11.10 7.74 CA Tomato 1 app. x 1.60 lbs ai/acre

1 app. x 1.60 lbs ai/acre 1 app. x 0.50 lbs ai/acre (14 days) 40.80 10.30 6.67 FL Tomato 1 app. X 1.60 lbs ai/acre

1 app. X 1.60 lbs ai/acre 1 app. X 0.50 lbs ai/acre (14 days) 123.00 12.60 6.67 PA Tomato 1 app. X 1.60 lbs ai/acre

1 app. X 1.60 lbs ai/acre 1 app. X 0.50 lbs ai/acre (14 days) 56.80 12.20 7.35

### 4

**Table 2. S**  **- Metolachlor**  **Estimated Drinking Water Concentrations (E**  **DW Cs) for**  **Surface and Ground**  **Water based on Selected Crop Scenarios Drinking Water**  **Source Proposed** 

**Label Use Model** 

**Scenario A** **pplication Rate**

**(interval betwee n**  **applications ; # seasons**  **) Acute**  **(** 

### μg/L **) Chronic** 

**(** 

### μg/L **) Cancer** 

**Chronic (**  

### μg/L **)** Sunflower (20B) ND Canola 1 app. x 1.90 lbs ai/acre 1 app. x 1.80 lbs ai/acre (14 days) 65.20 17.40 11.60 Ground Water Cotton 1 NC Cotton (PRZM - GW) 2 app. x 2.0 lbs ai/acre (5 days) **1060** NA 865 Corn 1 WI Corn

(PRZM - GW) 2 app. x 2.0 lbs ai/acre (5 days) **--** NA **978** Proposed Use 2 (Sunflower) NC Cotton

(PRZM - GW) 1 app. x 1.9 lbs ai/acre

1 app. x 1.8 lbs ai/acre (14 days) 979 NA 801 Proposed Use 2 (Sunflower) WI Corn

(PRZM - GW) 1 app. x 1.9 lbs ai/acre

1 app. x 1.8 lbs ai/acre (14 days) 974 NA 906 Corn, Cotton 1,3 SCI - GROW 2 app. x 2.0 lbs ai/acre 14.3 14.3 14.3 Various Crops (sunflower) 2,3 SCI - GROW Various apps not exceeding 3.7 lbs ai/acre 13.2 13.2 13.2 Bold values denote maximum EEC values. 1 Since HED’s tolerance expression has changed and the assessment is now following the total toxic residue (TTR) approach, corn and cotton were modeled in addition to the proposed application rates since they have the highest application rates. 2 EDW Cs generated for proposed uses represented by sunflower by applying 1 app. at 1.9 lbs a.i/A followed by 1 app. 1.8 lbs a.i./A (14 day interval). 3 EDWCs generated from SCI - GROW mo del represent both acute and chronic values. 

### Environmental Fate and Transport Metolachlor is a racemic mixture of R- and S - enantiomers (stereo isomers that are mirror images). Metolachlor is composed of approximately equal proportions of the R and S enantiomers, whereas S - metolachlor is an enrichment comprised almost solely of the S enantiomer (88% S - isomer) . Enantiomers have the same chemical and physical properties except for the direction they

rotate plane polarized light. The Agency has concluded that environmental behavior of metolachlor and S - metolachlor is expected to be similar. Therefore, the environmental fate data were bridged from metolachlor to S - metolachlor (USEPA, 2002 a). Environmental fate data indicate that parent metolachl or/S - metolachlor appear to be moderatel y persistent to persistent. Metolachlor/S - metolachlor degradation appear s to be dependent of microbially- mediated (aerobic soil metabolism t 1/2 

### = 13.9 to 67 days ; anaerobic soil metabolism t 1/2 

### =81 days) and abiotic processes (photodegradation in water t 1/2 

### = 70 days under natural sunlight and photodegradation on soil t 1/2 

### = 8 days under natural sunlight).

### 5

Depending on the soil (i.e. organic matter content), metolachlor/S - metolachlor has the potential to be mobile to moderately mobile with Koc values ranging from 21.6 to 369 mL/goc and have been detected extensively in surface water and ground water. The Agency concluded that there is no difference in soil sorption affinity between metolachlor and S - metolachlor as there were similar Koc coefficients in the batch equilibrium studies conducted on both active ingredients independentl y [mean Koc=135 (racemic) and 219 (S - enriched)] (USEPA 2002 a). Field dissipation studies indicate that metolachlor/S - metolachlor is persi stent in surface soil with half - lives ranging from 3 to 292 days in the upper six inch soil layer depending on geographic location. Metolachlor/S - metolachlor was reportedly detected as deep as 36 to 48 inches in some of the studies. The Metolachlor Task Force (MTF) has conducted a small scale prospective groundwater study (MRIDs 47017401 - 04) for metolachlor to compl y with the request of groundwater monitoring data for the conditional registration of technical metolachlor. The residue sample collection was initiated in June 2003 continuing through 939 days after application. The objective was to determine the potential for the active ingredient metolachlor and its degradates (CGA - 37735, CGA - 51202, CGA - 67125, CGA - 41638, and CGA - 354743) to reach groundwater when used in a vulnerable hydrogeologic setting. The study results show that metolachlor and two of its degradation products CGA - 51202 and CGA - 354743 can leach through the vadose zone into groundwater when applied in a vulnerable hydrogeologic setting. The detected peak concentrations of the degradation products CGA - 51202 and CGA - 354743 are higher than the detected peak metalochlor concentrations. 

### Metolachlor appears to have a low potential to bioaccumulate in fish with a reported whole body bioconcentration factor of 69X and a whole body elimination of 93% after 14 days depuration. **Total Toxic Residues (TTR) Approach**  Following the recent recommendation of the Residues of Concern Knowledgebase Subcommittee (D424250), parent metolachlor, CGA - 51202 (metolachlor- OA), CGA - 40172, and CGA - 50720 will be assessed together in the drinking water assessment using a total toxic residues (TTR; USEPA 2009a) approach where half - lives were recalculated (**Appendix A** ; PestDF; USEPA, 2009b) to collectively account for the parent and the combined residues of concern. To follow the total toxic residue (TTR) approach, half - lives were recalculated to collectively

account for the parent and the combined residues of concern. These valu es will be utilized in surface and ground water modeling to generate aquatic exposure estimates. TTR halflives for aerobic soil metabolism , aerobic aquatic metabolism , anaerobic aquatic metabolism, and aqueous photolysis, correspond to 447 days, 38.9 days, 217 days and 115.8 days, respectively . The hydrolysis half

- life was considered stable since a half - life could not be calculated due to the lack of degradation needed to fit a degradation curve. In addition, the average Koc value of 181 mL/go.c., was selected among parent b atch equilibrium studies.

### 6



### Drinking Water Exposure Modeling **Surface Water** The Surface Water Concentration Calculator (SWCC v 1.106) model 1 

### was used to generate E DW Cs for the Tier II aquatic exposure assessment. The SWCC is a graphical user interface that runs the Pesticide Root Zone Model (PRZM, v 5, November 15, 2006) and the Variable Volume Water Body Model (VVWM, 3/6/2014) . Simulations are run for multiple (usually 30) ye ars and the E DW Cs represent peak values that are expected once every t en years based on the thirty years of dail y values generated during the simulation. The national default PCA of 0.91 was used for the proposed agricultural uses (USEPA 2012a). The SWCC input parameters are shown in **Table 3**  below . EDWCs are provided in **Table 2**  above, and a representative SWCC output is provided in **Appendix B**  . **Table 3. SWCC**  **Input Param eters for S**  **- Metolachlor**  **. Input Parameter:**  **Value: Comment:**  **Source:** Scenario(s): Corn : KS, MS Corn Cotton: MS Cotton Cucurbit: FL Cucumber; MI, MO, NJ Melon Low- Growing Berry: FL Strawberry Lettuce (leaf): CA Lettuce Lettuce (head): CA Lettuce Fruiting Vegetables: FL Pepper; CA, FL, PA Tomato Sunflower: ND Canola representative scenarios for each use N/A

Maximum Single Application Rate lbs a.i./A (kg a.i./ha) Corn: 2.0 (2.25) Cotton: 2.0 (2.25) Cucurbit: 0.635 (0.713) L ow- Growing Berry: 1.27 (1.43) Lettuce (leaf): 1 st 0.95 (1.07) 2 nd 0.32 (0.36) Lettuce (head): 0.95 (1.07) Fruiting Veg s: 2 app. at 1.60 (1.80) 3 rd app at 0.5 (0.562) Sunfl ower: 1 st 1.90 (2.13) 2 nd 1.80 (2.02) proposed rates proposed label

Applications per Year Corn: 2 Cotton: 2 Cucurbit: 2 (3 seasons) Low- Growing Berry: 3 Lettuce (leaf): 2 (rate varies) Lettuce (head): 2 Fruiting Vegs: 3 (rate varies) Sunflower: 2 (rate varies) label directions. Label specifies rates per season. If crops are rotated with those on which s - metolachlor is used, yearly rates may be higher. proposed label

Application Interval (days) Corn: 5 Cotton: 5 Cucurbit: 14 Low- Growing Berry: 14 Lettuce (leaf): 14 Lettuce (head): 14 Fruiting Vegs: 14 Sunflower: 14 intervals selected to refle ct labeled application patterns proposed label

1 http://www.epa.gov/oppefed1/models/water /index.htm

### 7 **Table 3. SWCC**  **Input Param eters for S**  **- Metolachlor**  **. Input Parameter:**  **Value: Comment:**  **Source:** Date of Initial Application (relative application date ) Corn

- 3 +2 Cotton

- 3 +2 Cucurbit

- 7 +7 +21 +35 +49 +63 Berry

- 7 +7 +21 Leaf L.

- 7 +7 +21 +35 +49 +63 Head L

- 7 +7 +21 +35

. Fruit.Veg

.

- 7 +7 +21 Sunflower

- 7 +7 f

or corn and cotton, 3 days before crop emergence was selected for pre - emergent applications and 2 days after crop emergence was selected for post - emergent applications. f or proposed uses, 7 days before crop emergence was selected for pre - emergent applications and 7 days after crop emergence was selected for post - emergent applications. Crop Scenarios

Application Method Foliar : for pre - and post - emergent applications label directions proposed label CAM Input 2 foliar

– aerial proposed label IPSCND Input 3 remaining pesticide on foliage is retained as surface residue and continues to undergo decay. US EPA, 2005 Spray Drift Fraction 0.135 foliar - aerial Input parameter guidance (USEPA, 2013b ) Application Efficiency 0.95 foliar - aerial Input parameter guidance (USEPA, 2013b ) Molecular Mass (g/mol) 283.8 product chemistry data US EPA, 2002b TRED Vapor Pressure at 25°C (torr) 2.8 x 10 - 5 product chemistry data US EPA, 2002 b TRED Henry’s Law Constant (atm- m3/mol) 2.2 x 10 - 8 calculated from volatility and solubility data registrant submitted data Solubility in Water at 25oC (mg/L) 480 product chemistry data US EPA, 2002 b TRED Organic Carbon Partition Coefficient (Koc) (L/kg oc) 181 represents the average KOC represents the average value from all non -paired adsorption data Aerobic Soil Metabolism Half - life (days) 447 represents the upper 90th percentile of TTR (332 days, 39 days) values 1 US EPA, 2002 b TRED MRID 41309801 MRID 45499606 Aerobic Aquatic Metabolism Half

- life (days) 38.9 TTR based on the aerobic (first 30 days) of the anaerobic aquatic metabolism study 1 M RID 41185701 Anaerobic Aquatic Metabolism Half

- life (days) 217 TTR value 1 MRID 41185701 Hydrolysis Half

- lives (days) 0 stable US EPA, 2002 b TRED M RID 00015662 M RID 40430201 Aqueous Photolysis Half - life (days) 115.8 TTR value 1 US EPA, 2002 b TRED MRID 40430202

### 8 **Table 3. SWCC**  **Input Param eters for S**  **- Metolachlor**  **. Input Parameter:**  **Value: Comment:**  **Source:**

-N/A = Not Applicable 1 Where the TTR approach was identified, half lives were recalculated to account for the parent including the identified residu es of concern. Draft Guidance for Modeling Pesticides Total Toxic Residues (TTR; USEPA, 2009a) in addition to the NAFTA Guidance for Evaluating and Calculating Degradation Kinetics in Environmental Media (USEPA 2009b) were utilized. Recalculated half - lives (PestDF outputs) are listed in Appendix A. 

### Ground **W ater**  Screening Concentration in Ground Water (SCI - GROW v2.3, Jul. 29, 2003) is a regression model used as a screening tool to estimate pesticide concentrations found in ground water used as drinking water. The SCI - GROW model and user’s manual may also be downloaded from the EPA Water Models web - page (http://www.epa.gov/oppefed1/models/water/#scigrow ). A summary of the model input parameter values used in SCI - GROW is listed in **Table 4**  , below . SCI - GROW EDWCs are presented in **Table 2** ( above ) and a representative output is provided in **Appendix C**  . **Table 4. SCI -**  **GROW Input**  **Parameters for S**  **- Metolachlor**  **Input Parameter Value**  **Comment Source**  Maximum Application Rate per growing season (lbs a.i./A) 2.0 (corn, cotton) 3.7 (sunflower) maximum rate from all registered uses

maximum rate from proposed label EPA Reg. No. 100 - 816 Applications per Year 2 (corn, cotton) 1 (sunflower) based on maximum rate and yearly total applied EPA Reg. No. 100 - 816 Organic Carbon Partition Coefficient (KOC ) (L/kg OC ) 181 represents the average KOC value from all non paired adsorption data MRID 43928937 MRID 40494604 Aerobic Soil Metabolism Half - life (days) 447 represents the upper 90th percentile of TTR (332 days, 39 days) values US EPA, 2002 b TRED MRID 41309801 MRID 45499606 

### S ince the new ground water model (PRZM - GW) has been implemented (USEPA, 2012 a), the highest app li cation rate of all metolachlor/S - metolachlor uses ( 2 apps. at 2.0 lbs a.i/A for a ye arl y maximum application rate of 4.0 lb a.i./A on corn and cotton) in addition to the proposed uses for S - metolachlor were modeled to determine drinking water exposure in ground water. PRZM - GW is a one - dimensional, finite - difference model that estimates the concentrations of pesticides in ground water. It accounts for pesticide fate in the crop root zone b y 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 ye ars) on a single site. Six standard scenarios, each representing a different region known to be vulnerable to ground water contamination, are available for us e with PRZM - GW for risk assessment purposes. In the PRZM - GW simulations, each of the standard scenarios was used. PRZM - GW output values represent pesticide concentrations in a vulnerable ground water suppl y that is located directl y beneath a rural agricultural field following many ye ars of pesticide application. A summary

of the model input parameter values used in the PRZM - GW m odel is

### 9

listed in **Table 5**  **.** PRZM - GW result s are presented in **Table 6**  . A representative output of the PRZM - GW model can be found in **Appendix D**  . **Table 5. PRZM -**  **GW (v1.0) Input Parameter**  1 **Values for**  **S -**  **Metolachlor Parameters**  **Value Data Source**  **Comments** Application Method Aerial (Corn, Cotton) Aerial (Sunflower) EPA Reg . No. 100 - 816 --- Application Rate (lbs. a.i./acre) [kg/ha] 2.0 [2.25] (Corn, Cotton) 1 st app.1.90 [2.13] (Sunflower) 2 nd app.1.80 [2.02] (Sunflower) EPA Reg. No. 100 - 816 --- Application Number 2 (Corn, C otton) 1 (S unflower) EPA Reg. No. 100 - 816

--- Application Interval (days) 5 (Corn, Cotton) 14 (Sunflower) EPA Reg. No. 100 - 816 --- Days since Emergence Corn/Cotton:

- 3 +2 Sunflower :

- 7 + 7 Crop Scenarios and

proposed label info For corn and cotton, 3 days before crop emergence was selected for pre - emergent applications and 2 days after crop emergence was selected for post - emergent applications. For proposed uses, 7 days before crop emergence was selected for pre - emergent applications and 7 days after crop emergence was selected for post - emergent applications. Hydrolysis Half

- Life (days) 0 stable US EPA, 2002b TRED M RID 00015662 M RID 40430201 Aerobic Soil Metabolism Half

- life (days) 447 represents the upper 90th percentile of TTR (332 days, 39 days) values US EPA, 2002b TRED MRID 41309801 MRID 45499606

Koc (mL/g oc ) 181 represents the average KOC value from all non paired adsorption data MRID 43928937 MRID 40494604 1 PRZM - GW Input Guidance : http://www.epa.gov/oppefed1/mod el s/water/prz m_ gw/wqtt_przm_gw_input_guidance.pdf

### 10

**Monitoring Data** Metolachlor/ S - m etolachlor and its degradates ESA and OA have been detected extensively in surface water and groundwater . A search of the available NAWQA monito ring data was performed on December 10, 2014 to ensure that the most current monitoring data were considered in this assessment. For parent metolachlo r, 23,089 detects (16.6% were classified as estimated values) were obtained within the monitoring data with a maximum concentration of 9.84 μg/L in surface water. For ground water, 1,634 detects (33.5% were classified as estimated values) were obtained wi thin the monitoring data with a maximum concentration of 9.54 μg/L. For the degradate ESA, 1,245 detects were obtained within the monitoring data with a maximum concentration of 8.42 μg/L in surface water. For ground water, 548 detects were obtained within the monitoring data with a maximum concentration of 9. 81 μg/L. For the degradate OA, 1,122 detects were obtained within the monitoring data with a maximum concentration of 4.95 μg/L in surface water. For ground water, 298 detects were obtained within the monitoring data with a maximum concentration of 7.92 μg/L. In addition, the maximum metolachlor concentration from the 2012 Atrazine Ecological Monitoring Program (AEMP) was 59.09 ppb. **Uncertainties** For PRZM - GW modeling, the values generated are for vulnerable ground water supplies such as a rural drinking water well that exist s below or is directly influenced by

an agricultural field treated ye arl y at the maximum proposed s - metolachlor labeled rates . The EDWCs generated were from a 30 ye ar simulation with a 13 ye ar breakthrough period. 

### Conclusions Following the recent recommendation of the Residues of Concern Knowledgebase Subcommittee (D424250), parent metolachlor, CGA - 51202 (metolachlor- OA), CGA - 40172, and C GA - 50720 were assessed together using a total toxic residues (TTR) approach. Since the **Table 6. PRZM -**  **GW Estimated Drinking Water Concentrations in Ground Water Resu lting from**  **the Use of S -**  **Metolachlor Application Rate and**  **Frequency Scenario**  **1 Simulation**  **Duration (years)**  **Highest Daily**

**Value (**  **μ g/L)**  **Post**

**Breakthrough Average**  **( μ**  **g/L) Average** 

**Simulation Breakthrough**  **Time (days)** Corn/Cotton : 2 app. X 2.0 lbs a.i./acre Florida Citrus 30 843 742 2537

Florida Potato 30 182 173 4514 Georgia Peanut 30 315 289 4214 North Carolina Cotton 30 **1060** 865 3627 Delmarva Sweet Corn 30 835 734 3206 Wisconsin Corn 30 1050 **978** 4795 Sunflower: 1 st app.1.90 lbs a.i./acre 2 nd app.1.80 lbs a.i./acre Florida Citrus 30 782 684 2537 Florida Potato 30 169 161 4514 Georgia Peanut 30 290 267 4214 North Carolina Cotton 30 979 801 3627 Delmarva Sweet Corn 30 769 678 3206 Wisconsin Corn 30 974 906 4795 1 These scenarios are regional vulnerable sites for groundwater evaluation.

### 11

approach and the tolerance expression was revised since the previous drinking water assessment, the highest application rate of all metolachlor/S - metolachlor uses (2 applications at 2.0 lb a.i./A for a maximum yearly

application rate of 4.0 lbs a.i/A on corn and cotton) was modeled in addition to the proposed uses to determine drinking water exposure in surface and ground water. The recommended EDWCs for surface water include the acute concentration of **371 μg/L**  (corn ; registered) , the annual mean (chronic) concentration of **43.7 0**  **μg/L** (lettuce ; proposed) and the 30 ye ar annual average conc entration of **21.80 μg/L**  (lettuce; proposed). For ground water, the recommended EDWCs include the acute concentration of **1060 μg/L**  and 3 0 - ye ar average (chronic) concentration of **978 μg/L**  **,** based on the highest application rate (ye arl y maximum rate of 4.0 lbs a.i/A on corn, cotton) of all metolachlor/s - metolachlor uses. Extensive monitoring data was available for metolachlor and its degradation products ESA and OA. **References** USEPA. 1995. Reregistration Eligibility Decision (RED). Data Package Barcode: 185152, 172022 Metolachlor. April 1995. USEPA. 2002 a . Review of Documents Related to the Equivalency of Racemic Metolachlor (Metolachlor) and S - Metolachlor for Environmental Fate and Ecotoxicity . Environmental Fate and Effects Division, Office of Pesticide Programs. February 28, 2002. US EPA. 2002 b . Revised Metolachlor/S - Metolachlor Tolerance Reassessment Document (TRED), D248805, D228814, D258817, D258824, D258822, D258812, D259119, D259037, D259034). USEPA. 2005. PRZM - 3, A Model for Predicting Pesticide and Nitrogen Fate in the Crop Root and Unsaturated Soil Zones: User ’ s Manual for Release 3.0. May 2005. USEPA . 2009 a . DRAFT Guidance for Modeling Pesticides Total Toxic Residues (TTR) May 20, 2009. U.S. Environmental Protection Agency, Office of Pesticide Programs, Environmental Fate and Effects Division. Arlington, VA. USEPA, 2009b. DRAFT NAFTA Guidance for Evaluating and Calculating Degradation Kinetics in Environmental Media, U.S. Environmental Protection Agency, Office of Pesticide Programs, Environmental Fate and Effects Divis ion. Arlington, VA. USEPA. 2010 . Guidance for Selecting Input Parameters in Modeling the Environmental Fate and Transport of Pesticides http://www.epa.gov/oppefed1/mod els/water/input_parameter_guidance.htm US EPA. 2012a. Memorandum: Approval of PRZM - GW for use of Drinking Water Exposure Assessment. Environmental Fate and Effects Division, Office of Chemical Safety and Pollution Prevention. U. S. Environmental Protectio n Agency .

### 12

USEPA. 2012b. Guidance on Development and Use of Percent Cropped Area Adjustment Factors in Drinking W

ater Exposure Assessments . Environmental Fate and Effects Division, Office of Pesticide Programs, United States Environmental Protection Agency . Available at http://www.epa.gov/oppefed1/models/water/pca_adjustment_dwa.pdf. US EPA. 2013b. Guidance on Modeling offsite deposition of pesticides via spray drift for Ecological and Drinking Water Assessments. Environmental Fate and Effects Divisi on, Office of Chemical Safety and Pollution Prevention. U. S. Environmental Protection Agency . December 20, 2013.

**APPENDIX A: PestDF Outputs Aerobic Soil Metabolism (322 days and 39 days**  **; 90 th**  

### percentile = 447 days **) MRID 41309801** 

**MRID 45499606**

### 13

**Aqueous Photolysis (115.7 days) MRID 40430202** 

**Aerobic Aquatic Metabolism (38.9 days) MRID 41185701** 

### 14

**Anaerobic Aquatic Metabolism (217 days) MRID 41185701** 

### 15 **APPENDIX B**  **SWCC Ou**  **tput: Mississippi Corn –**  **Aerial Application**

### 16 **APPENDIX C**  **SCI -**  **GROW Model**  **Output : Corn/Cotton and Sunflower** 

### 17

**1.) Corn/Cotton (maximum rate)**  SciGrow version 2.3 chemical:S - Metolachlor use on Corn and Cotton time is 12/11/2014 15:27:32

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

------------------------------------- ----------------------------------- 2.000 2.0 4.000 1.81E+02 447.4

------------------------------------------------------------------------ groundwater screening cond (ppb) = 1.43E+01 or 14.3 ppb ******************* ***************************************************** 

### 2.) **Sunflower (representing various crops )**  SciGrow version 2.3 chemical:S - Metolachlor use on Sunflower time is 12/ 5/2014 14:13: 7

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

------------------------------------- ----------------------------------- 3.700 1.0 3.700 1.81E+02 447.4

------------------------------------------------------------------------ groundwater screening cond (ppb) = 1.32E+01 or 13.2 ppb ******************* *****************************************************



### APPENDIX **D PRZM**  **- GW**  **Output: North Carolina Cotton Scenario (Corn/Cotton**  **)**

### 18