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

September 16, 2015

PC Code: 128712 MEMORANDUM DP Barcode: 425572
SUBJECT: Carfentrazone-ethyl: Drinking Water Exposure Assessment of Section 3 Proposed Label Amendments for New Uses, Expansi ons from Representative Crops and Crop Group Conversions.

FROM: Richard Shamblen, Biologist ERB2/EFED (7507P)

THRU: Brian Anderson, Chief Elyssa Arnold, Risk Assessment Process Leader James Lin, PhD, Environmental Engineer, Secondary Reviewer ERB2/EFED (7507P)

TO: Driss Benmhend, Risk Reviewer Manager Shaja Joyner, Product Manager PM Team 20 Fungicide Herbicide Branch Registration Division (7505P)

Barbara Madden, Minor Use Team Leader Minor Use and Emergency Response Branch Registration Division (7505P)
Thomas Bloem, Dietary Assessor Thurston Morton, Acting Branch Chief Health Effects Division (7509P)

The Environmental Fate and Effects Divi sion (EFED) conducted a drinking water exposure assessment for three proposed Section 3 label amendments for carfentrazone-ethyl. These proposed amendments include: 1) new use on Artichoke, Asparagus, Mint and Teff; 2) expansion from representative crops to subgr oups for Oil seed Group 20, Low Growing Berry Subgroup 13-07G, Small Fruit Vine Climb ing Subgroup 13-07F; and, 3) crop group conversions for Bulb Group 3-07, Fruiting Vegetable Group 8-10, Citrus Fruit Group 10-10, Pome Fruit Group 11-10, Stone Fruit Group 12- 12, Caneberry subgroup 13-07A, Bushberry subgroup 13-07B and Tree Nut Group 14-12. 

## RICHARD SHAMBLEN Digitally signed by RICHARD SHAMBLEN DN: c=US, o=U.S. Government, ou=USEPA, ou=Staff, cn=RICHARD SHAMBLEN, dnQualifier=0000051207 Date: 2015.09.17 14:38:11 -04'00'



## JAMES LIN Digitally signed by JAMES LIN DN: c=US, o=U.S. Government, ou=USEPA, ou=Staff, cn=JAMES LIN, dnQualifier=0000014809 Date: 2015.09.17 14:41:37 -04'00' 2015.09.17 14:59:33 -04'00' For2 Table 1 summarizes results of the three mode ls used to assess current and proposed use scenarios. Results of the drinking water exposure assessment indicate that the use of carfentrazone-ethyl on rice in California yields the highest total residue estimated drinking water concentrations (EDWC). The revised percent cropped area (PCA) of 100% adjusted peak and annual average exposure estimates are 224 μ g/L and 86 μ g/L, respectively.
The current rice use scenario with the previous adjusted PCA value of 56% yields a peak and annual average exposure estimates are 126 μ g/L and 48 μ g/L, respectively (DP Barcode 384371, 2011). Results of the provisional cranbe rry model v2.0 at the maximum single application rate of 0.4 lbs a.i./A yields a peak and annual average exposure estimates are 131 μ g/L and 53 μ g/L, respectively. These lower EDWCs can be directly attributed to the minimum cranberry bog water column depth of 0.305 m (12 in ches), versus the 0.1 meters (4 inches) in the rice paddy model.
Groundwater EDWC for current use on Crop Group 13 crops at 0.4 lbs a.i./A resulted in highest daily (peak exposure) and post-breakthrou gh (annual mean exposure) concentrations of 48.9 μ g/L and 43.9 μ g/L, respectively.

Table 1: Screening-Level Total Residue EDWCs for Current and Proposed Carfentrazoneethyl Uses. Drinking Water Source (Model) Maximum Single Application Rate (lbs a.i./A) Current or Proposed/ Use Peak Exposure

ȝJ/ Annual Mean Exposure

ȝJ/ Surface water (Tier I Rice Model) 0.188, 0.10 (14-d interval) Current/ Rice 126 48

Surface water (Tier I Rice Model) 0.188, 0.10 (14-d interval) Revised/ Rice 224 86

Surface water (Provisional Cranberry Model) 0.4 Proposed/ Cranberry in Crop

Group 13-07G 131 53

Ground water (PRZM-GW) 0.4 Current/ Crop Group 13 48.9 43.9

Label Uncertainties
A large source of uncertainty arises from current and proposed label language. For example, the use of carfentraz one-ethyl on rice in California yielded the highest EDWCs. The maximum annual application rate is 0.3 lbs a.i./A; however , the label limits the maximum application rates in California are 0.188 lbs a.i. /A for early post-seeding applications to submerged weeds and 0.10 lbs a.i./A for applicati ons to emerged weeds above the water surface. Pursuant to the label use directions, this a ssessment assesses only the direct application of carfentrazone-ethyl to a flooded rice paddy. Th e current label enables pre-plant burn-down programs for rice, but does not specify, nor limit, the application rate. Thus this assessment does not account for the pre-plant, pre-flood applicatio n of up to 0.012 lbs a.i./A, or 4% of the total annual application rate.3 1. Background
EFED completed a preliminary problem formul ation and conducted two drinking water exposure assessments for carfentrazone-e thyl in 2011 (DP Barcode 382665, 384371 and 389087). Both drinking water exposure assessments included the residues of concern and total toxic residues (TTR) of carfentrazone-ethyl (F 8426 parent plus its chloropropionic acid, its cinnamic acid, its propionic acid, its benzoic acid, and its 3-hydoxymethyl benzoic acid). EFED relied upon these documents for information and data to conduct this drinking water exposure assessment.
For surface water systems, EFED identified the use of carfentrazone-ethyl on cranberry and rice crops as likely to produce conservative ( i.e. higher) screening-level Tier I drinking water exposure estimates. The previous drinki ng water assessment (DP Barcode 384371, 2011) revealed that carfentrazone-ethyl applied to inte ntionally flooded rice fields in California resulted the highest estimated drinking water concentrations (EDWCs). Therefore, EFED used the Tier 1 Rice model to assess carfentrazone-ethyl use on flooded rice in California. Under the proposed label expansion from representative crops to include subgroups, the Low Growing Berry Subgroup 13-07G includes the crop cranberry. EFED used the provisional cranberry model to assess the proposed cranberry use site. Lastly , to assess screening-le vel Tier I groundwater exposure, EFED used the PRZM-GW model. Th e Low Growing Berry Subgroup 13-07 includes the highest annual application rate of 0.4 lbs a.i./A.

Unless otherwise noted, all m odel input parameterization values selected in the 2011 drinking water exposure assessments were usedfor this assessment. Only changes to EFED guidance affected differences in mode ls used and parameter input values.

2. Exposure Analysis
EFED conducted an exposure analysis for surface and groundwater drinking water systems using the Tier 1 Rice, provi sional Cranberry and PRZM-GW models.

2.1 Surface Water: Tier 1 Rice Model
The previous drinking water assessment for rice (DP Barcode 384371, 2011) evaluated the use of carfentrazone-ethyl on rice produ ction in California and Southern States. The California scenario yielded the highest estimated drinking water concentrations (EDWC) at 126 μ g/L and 48 μ g/L for peak and annual mean exposures, respectively. Since then, however, EFED has modified the percent cropped area (PCA) adjus tment factors. A PCA fo r rice is not reported and, thus, has increased from 56% to 100% (Bohaty et al ., 2014). For these reasons, the California rice production scenario was re-assess ed and compiled in the Tier 1 Rice model.

2.1.1 Model Inputs

Table 2 summarizes input parameters for the Tier I Rice Model, which were selected from the previous drinking water assessments (DP Barcodes 384371, 2001; and, 389087, 2011). The maximum application rates in California are 0.188 lbs a.i./A for early post-seeding4 applications to submerged weeds and 0.10 lbs a.i. /A for applications to emerged weeds above the water surface. These rates were modeled with a 14-day reapplication interval although the minimum reapplication interval is not specified on the labels. The soil-water partition coefficient (Kd ) input (0.89 L/kg) reflects the mean value for car fentrazone acid in five soils. The aerobic aquatic metabolism half-lif e input (106 d) is the upper 90% confidence bound on the mean of two half-lives for residues of concern (64 and 84 days). Derived model input values are fully discussed in the previous drinkingwater assessment (DP Barcode 384371, 2011).
Standard percent cropped area (PCA) values, represent of the extent of watershed in which agricultural crops are grown, were used to modify estimated drinking water concentrations (EDWC). The previous drinking water exposur e assessment for use on rice (DP Barcode 384371, 2011), a regional PCA for California of 56% was us ed to adjust the EDWC. However, in 2014, a PCA for rice is not reported and, thus, has increased from 56% to 100% (Bohaty et al ., 2014).

Table 2: Tier I Rice Model Input Parameters for Residues of Concern. Input Parameter (units) Value Source
Application Rates (lbs a.i./A) 0.188 0.10 Existing and Proposed labels Soil-water Partition Coefficient (K d) (L/kg) 0.89 DP Barcode 384371 389087 Aerobic Aquatic Metabolism Half-life (days) 106 DP Barcode 384371 389087 Percent Cropped Area (%) 100 USEPA, 2014

2.1.2: Modeling Results
Total residue exposure estimates from the Ti er I Rice Model v2.0 are presented below in Table 3. These estimates represent peak and annual average exposure concentrations in the rice paddy tail water following the proposed 23-day holding period after the second application. The table compares the differences between the results of the previous drinking water assessment for rice and, results of the updated PCAs for rice (100%). The label directions for use on rice in California result in the highest estimated exposure. The peak estimated drinking water concentration (EDWC) 23 days af ter the second application is 224 μ g/L. The annual mean EDWC is 86 μ g/L.5 Table 3: Total Residue Estimated Drinking Water Concentrations in Surface Water from Split Applications of Carf entrazone-ethyl on Rice.

Regional Basin: Reference State Application Rate (lbs a.i./A) Percent Cropped

Area (%) Peak EDWC (ppb) Annual Mean EDWC (ppb)

18: California 0.188, 0.10 (14-d interval) 56 126 48

18: California 0.188, 0.10 (14-d interval) 100 224 86

Abbreviations: EDWC = estimated drinking water concentration

2.2 Surface Water: Provisional Cranberry Model v2.0

EFED used the Provisional Cr anberry Model v2.0 because the registrant is seeking a label expansion from representative crops to subgroups for, among others, the Low Growing Berry Subgroup 13-07G, which includes cranberry.

2.2.1 Model Inputs
Input parameters (listed in Table 4 ) for the Provisional Cr anberry Model v2.0 were selected from the previous drinking water assessments (DP Barcodes 384371, 2011; and, 389087, 2011). The soil-water partition coefficient (Kd ) input (0.89 L/kg) reflects the mean value for carfentrazone acid in five soils. The aerobic aquatic metabolism half-life input (106 d) is the upper 90% confidence bound on the mean of two half-lives for residues of concern (64 and 84 days). The aerobic soil metabolism half-life i nput (193 d) is the upper 90% confidence bound on the mean of four half-lives for residues of concern (149, 203, 184 and 156 days).Because the label does not identify application timing intervals at rates lower than the maximum seasonal rate, EFED modeled the maximum proposed annual application rate as the maximum single application rate of 0.4 lbs a.i./A.

Table 4: Provisional Cranberry Model v2.0 InputParameters for Re sidues of Concern. Input Parameter Value Source Application Rates (lbs a.i./A) 0.4 Proposed labels

Soil-water Partition Coefficient (K d) (L/kg) 0.89 DP Barcode 384371 389087
Aerobic Aquatic Metabolism Half-life (days) 106 DP Barcode 384371 389087

Aerobic Soil Metabolism Half-life (days) 193 DP Barcode 38437 3890876 2.2.2 Modeling Results
Total residue drinking water exposure estimates from the Provisional Cranberry Model v2.0 are summarized below in Table 5 . These estimates represent peak and annual average exposure estimates in bog tail water based on 0, 3 and 21-day holding periods after application.

Table 5: Total Residue Estimated Drinking Water Exposure (EDWC) in Surface Water from Single Application of Carfentrazone-ethyl on Cranberry. Maximum Application Rate (lbs a.i./A) Holding Period (days) Peak EDWC (ppb) Annual Mean EDWC (ppb)

0.4 0 130.7 53.2 0.4 3 128.1 52.2 0.4 21 113.9 46.4

2.3 Ground Water: PRZM-GW

EFED uses the Pesticide Root Zone M odel for Ground Water (PRZM-GW) to conduct screening-level (Tier 1) and refined (Tier II) drinking water exposure assessments for groundwater systems (Brady, 2012).

2.3.1 Model Inputs
Input parameters for the PRZM-GW model are summarized in Table 3.4 (USEPA, 2012). From the proposed label amendments, th e maximum total seasona l (annual) application rate of 0.4 lbs a.i./A is proposed for Canebe rry (Subgroup 13-07A), Bushberry (Subgroup 13- 07B), Fruit, small vine climbing, except fuzzy kiwi fruit (Subgroup 13-07F), and Berry low growing (Subgroup 13-07G). Similar to the cranberr y model, since the label does not identify application timing intervals at rates lower than the maximum seasonal rate, EFED modeled the maximum proposed annual applicati on rate as the maximum single application rate of 0.4 lbs a.i./A. Application method is gr ound applied without incorporation.
From the previous drinking water ex posure assessments (DP Barcodes 384371, 2011; and, 389087, 2011), the following summarize the pestic ide degradation properties. Hydrolysis of the carfentrazone acid, a residue of concern, show ed no evidence of degradation at the three tested pH levels (DP Barcode 384371). The maximum hydrolysis hal f-life value, or in this case “stable” with a value of 0, was selected (USEPA, 2012).
The aerobic soil metabolism half-life input(193 d) is the upper 90% confidence bound on the mean of four half-lives for residues of concern (149, 203, 184 and 156 days) (DP Barcode 389087, 2011). Batch equilibrium data for the predominant and most mobile residue, carfentrazone acid, were used to represent the residues of concern (MRID 43189233). Partitioning to soil was not correlated with the soil’s fraction of organic matter (DP Barcode 382665, 2011). The soil-water partition coefficient (Kd ) input (0.89 L/kg) reflects the mean value for carfentrazone acid in five so ils (DP Barcodes 384371, 2011; and, 389087, 2011).7 Table 6: PRZM-GW Model Input Parameters. Input Parameter Value Source Application Rates (lbs a.i./A) 0.4 Proposed labels

Hydrolysis (days) 0 DP Barcode 384371 389087

Aerobic Soil Metabolism half-life (days) 193 DP Barcode 384371 389087
Soil-water Partition Coefficient (K d) (L/kg) 0.89 DP Barcode 384371 389087
Application Method 2 (Above canopy application) Proposed labels
Incorporation Depth (cm) 0 Proposed labels

2.3.2 Modeling Results
Total residue exposure estimates from the PRZM-GW model follow below in Table 3.5

. These estimates represent highest daily and post breakthrough average exposure estimates in ground water. The Wisconsin sands corn scenar io yielded the highest daily, average postbreakthrough time and post breakthrough average.

Table 7: Total Residue Drinking Water Exposure Estimates in Ground Water from Single Maximum Annual Applications of Carfentrazone-ethyl on Rice.

Scenario Highest Daily (ppb) Average PostBreakthrough Time (days) Post Breakthrough Average

(ppb) DELMARVA_STD.SCN 25.4 8092.9 20.1 FLCITRUS_STD.SCN 48.5 4522.1 43.7 FLPOTATO_STD.SCN 20.5 3807.8 18.7 GACOASTAL_STD.SCN 15.7 6775 13.3 NCCOASTAL_STD.SCN 22 12139.3 20 WISANDS_STD.SCN 48.9 17015 43.98 3. Uncertainties
The exposure values in this assessment are conservative for a number of reasons. The actual fraction of drinking wate r basins cropped to rice is likely to be less than 100% of the watershed area. Also, there are a number of factor s inherent in the modeling that can affect the accuracy of these analyses including: the availabil ity and quality of the model input data; the use of maximum labeled practices that may be greater than actual agricultural practices; and the neglect, due in part to lack of data, of dissipation processes such as dilution, flow, and adsorption to downstream sediment that may attenuate dissolv ed concentrations in surface water. Further, the metabolism half-lives used to model expos ure estimates reflect hi gh-end confidence bounds based on limited data.
A large source of uncertainty arises from current and proposed label language. More specifically for rice, holdingperiods on the labels do not appear to restrict releases of paddy water following all applications. For example, current and proposed labe ls contain statements that holding periods apply in California “when ap plications are made to flooded fields.” If applications are made prior to flooding ( i.e . pre-plant, pre-flood), it appears that fields may be subsequently flushed with immediate release, which may result in substantially higher exposure than is estimated. Also, label statements to “hold the floodwater static for at least five days after application” appear to allow for release of paddy water prior to the end of the holding period. Label language that disallows the release of any paddy water for a period of time following any application would reduce uncertainty in these assessments.
The use of carfentrazone-ethyl on rice in California yielded the highest EDWCs. The maximum annual application rate is 0.3 lbs a.i./A; however , the label limits the maximum application rates in California are 0.188 lbs a.i. /A for early post-seeding applications to submerged weeds and 0.10 lbs a.i./A for applicati ons to emerged weeds above the water surface. Pursuant to the label use direc tions, this assessmentassesses only the dire ct application of carfentrazone-ethyl to a flooded rice paddy. The current label enables pre-plant burn-down programs for rice, but does not specify, nor limit, the application rate. Thus this assessment does not account for the pre-plant, pre-flood applicatio n of up to 0.012 lbs a.i./A, or 4% of the total annual application rate.
Lastly, the variance between modeled and actual depths of rice paddy water between application and release of the water is a source of uncertainty. Proposed and current labels stipulate that “floodwater must be 3 to 6 inches deep” for post-seeding applications to submerged weeds. The Tier I Rice Model is parameterized w ith a 4-inch water depth. If actual flood depths are higher, exposure may be lower than estimated. If actual flood depths are less than 4 inches (such as 3 inches), than exposure may be substantially (26-27%) higher than estimated.9 4. Literature Citations
Bohaty, R.F.H., Carleton, J.N. Crk, T., Echeverri a, M., Ruhman, M., Thawley, M. Thurman, N., Villanueva, P., White, K. 2014. Development and Use of Percent Cropped Area Adjustment Factors in Drinking Water Exposure Assessments. U.S. Environmental Protection Agency, Office of Pe sticide Programs. September 9, 2014.
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, Envi ronmental Fate and Effects Division, Oct. 22, 2009. Online at: http://www.epa.gov/oppefed1/models/w ater/input_parameter_guidance.htm
Orrick, Greg. 2011. Carfentrazone -ethyl: Assessment of Proposed Label Amendments for Use on Rice. DP barcode 384371 . U.S. Environmental Protection Agency, Office of Chemical Safety and Pollution Prevention, Environmental Fate and Effects Division. February 9, 2011
Orrick, Greg. 2011. Carfentrazone-ethyl: Drinki ng Water Exposure Assessment for Proposed Use on Crop Group 18 (Non-grass Animal F eed) Crops. DP barcode 389087. U.S. Environmental Protection Agency, Office of Chemical Safety and Pollution Prevention, Environmental Fate and Effects Division. Memorandum to the Health Effects Division and Registration Division.
USEPA. 2011. Registration Review: Preliminary Problem Formulation for Environmental Fate, Ecological Risk, Endangered Species, and Drinking Water Exposure Assessments for Carfentrazone-ethyl. DP barc ode 382665. U.S. Environmental Protection Agency, Office of Chemical Safety and Pollution Prevention, Environmental Fate and Effects Division. Memorandum to the Pesticid e Re-evaluation Division.
USEPA. 2012. Guidance for Selecting Input Parameters for Modeling Pest icide Concentrations in Groundwater Using the Pesticide Root Z one Model Version 1.0. U.S. Environmental Protection Agency, Office of Chemical Sa fety and Pollution Prevention, Environmental Fate and Effects Division. Health Canada, Pes ticide Management Regulatory Agency, Environmental Assessment Directorate. October 15, 2012