OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON , D.C. 20460

PC Code: 1 29122 DP Barcode : 426157 Date: March 1 9 , 2015 MEMORANDUM

SUBJECT : Diclosulam Drinking Water Assessment for Registration Review

TO: Susan Bartow, Chemical Review Manager

Kevin Costello, Branch Chief Risk Management and Implementation Branch IV Pesticide Re

- Evaluation Division (7508P)

Kristin Rury

, Chemist Christine Olinger , Branch Chief Risk Assessment Branch III Health Effects Division (7509P)

FROM: J a m es N. Carleton, PhD, Senior Scientist

Environmental Risk Branch IV Environmental Fate and Effects Division (7507P )

REVIEWED Cheryl Sutton, PhD, Environmental Scientist BY: Environmental Risk Branch IV

Environmental Fate and Effects Division (7507P )

APPROVED Jean Holmes, DVM, MPH
, Branch Chief BY: Environmental Risk Branch IV

Environmental Fate and Effects Divisi on (7507P )

EXECUTIVE SUMMARY

The Environmental Fate and Effects Division (EFED) has completed a screening

level drinking water assessment (DWA) for diclosulam in support of R egistration R eview

. Diclosulam (N

- (2,6

- dichlorophenyl)

- 5

- ethoxy

- 7

- fluoro[l,2,4]triazolo

- [l,5

- c] pyrimidine

- sulfonamide) is a sulfonanilide herbicide used to control broadleaf weeds in soybeans and peanuts , and belongs to the group of low

- volume herbicides collectively known as acetolact ate synthase ( ALS ) inhibitors , which act by interfering with amino acid synthesis

. The maximum application rates for diclosulam are 0.0315 lb a.i./acre /yr2

on soybeans and 0.0236 lb a.i./acre /yr on peanuts, applied by ground spray only. The sole registered product containing diclosulam is Strongarm® herbicide (84% a.i.), marketed by Dow AgroSciences

. T he maximum acute, chronic and cancer surface water estimated drinking water concentrations ( EDWCs ) are associated with the soybean use

. The comput er model s PRZM and EXAMS , as implemented in EFED’s Surface Water Concentration Calculator (SWCC , v ersion 1.106 ; 5/22/2014 )

, were used to generate surface water EDWCs for use in the human health dietary risk assessment, while the Pesticide Root Zone Model for Groundwater (PRZM

- GW) and Screening Concentration in Ground Water (SCI

- GROW , v ersion 2.3 ; 10/23/2010 ) models were used to generate groundwater EDWCs

. According to a memorandum from Leung Cheng dated December 6

, 1999 (DP 262014 )

, an ad hoc meeting of the Health Effects Division ’s (HED) Metabolism Assessment Review Committee ( MARC ) was held on October 26, 1999 and evaluat ed the results of plant (peanut and soybean) and livestock metabolism (goats and hens), uptake in rotational crops, analytical method ology, magnitude of the residue in peanut and soybean, and animal metabolism (rats) for diclosulam

. The MARC concluded t hat only the parent compound must be included in the tolerance expression

. In accordance with EFED’s interim guidance for addressing unextracted residues (USEPA, 2013)

, EFED has chosen to includ e unextracted residues together with the parent compound in the surface and groundwater modeling conducted for this assessment

. As indicated by bold type in Table 1, t he maximum EDWC values recommended for use in the human health dietary risk assessment are 15.8 μg/L for acute EDWC and 11.0 ug/L for chronic and cancer EDWC s

. These values were generated for groundwater sources of drinking water using PRZM

- GW, and were higher than the values determined for surface water sources of drinking water. Both groundwater and surface water EDWCs are presented in the table below. Selected model results are provided in Appendix A

.

Table 1

. Maximum EDWCs of diclosulam

.
D rinking W ater S ource (M odel U sed ) U se (rates modeled) M aximum E stimated D rinking W ater C oncentration (EDWC)

A cute ( μg/L ) C hronic ( μg/L ) Cancer ( μg/L )
Surface water (SWCC : MSsoybeanSTD scenario, ground application ) 0.0315 lb a.i./ A /yr 4.44 0.874 0.261

Groundwater ( PRZM

- GW ) 0.0315 lb a.i./ A/ yr (soybeans, NC Norfolk loamy sand soil : cotton ) 15.8 11.0 11.03

PROBLEM FORMULATION

This is a screening

- level drinking water assessment (DWA) that uses modeling t o estimate surface water and groundwater concentrations of pesticides in drinking water source water (pre

- treatment)

, resulting from pesticide us e on sites that are contamination

vulnerable. Screening

- level DWAs are designed to eliminate the need for further scrutiny of chemicals with low potent ial for posing a drinking water concern. This assessment is based on available environmental fate data. There are no significant data gaps in the environmental fate database. There are no known monitoring data for diclosulam in water or sediment

.

ANALYSIS

Use Characterization

Diclosulam was initially registered for use on soybeans and pe anut s in 2000 . In March 200 0 , the Agency completed a screening

- level ecological risk assessment (USEPA

, 2000 ) in support of the Section 3 Registration on soybean s and peanuts

. There are 24(c) Special Local Needs (SLN) registrations indicating a special local need for diclosulam to control tropical spiderwort in peanut in Georgia, Florida and Mississippi. No additional uses of diclosulam have been registered sinc e completion of the Section 3 registration. According to the BEAD Chemical Profile for Registration Review ( USEPA, 2014 ), although the chemical is registered for use on both peanuts and soybeans, usage between at least 2000

- 2012 was limited to application on peanuts, with an average of 4,000 lb a.i. applied annually in the U.S., primarily in the states of Georgia and Alabama. Details regarding the two registered diclosulam uses are given in Table 2

.

Table 2 . Methods and r ates of a pplication of c urrently r egistered u ses of diclosulam

.

Use Scenario Application Type Maximum

Single Application Rate (lbs a.i./A) Maximum #

of apps/yr RTI

(days) Maximum

Annual Application Rate (lbs a.i./A) Peanuts Ground 0.0236 NS 1 NS 1 0.0236 Soybeans Ground 0.0315 1 NA 0.0315

1 Not stated: f

or peanuts no maximum number of applications or minimum retreatment interval are given on the label. For modeling, a single application per year at the maximum rate was assumed.

Environmental Fate Characterization

Diclosulam exhibits pH

- dependent aqueous solubility, which rang es from about 100 mg/L at pH 5 to greater than 4000 mg/L at pH 9. Diclosulam’s pKa is 4.09 at 20 ° C, which suggests that the chemical exists in anionic form at environmentall y relevant pH levels

. Diclosulam ’s relatively low reported vapor pressure [5 x 10

- 15 mm Hg ( at 25 ° C)] is probably influenced by this property ( i.e.
, only undissociated molecules can volatilize )

. Similarly, diclosulam’s reported octanol/water partition coefficient (K ow ) decreases as pH4

increases from 5 to 9. Diclosulam’s low K ow ( maximum of 263 at pH 5 ) suggest s that it is not likely to significantly bioconcentrate in aquatic organisms.

General physical/chemical properties are summarized in Table 3 , and submitted environmental fate data for diclosulam are summarized in Table 4. Based on these data, diclosulam is not considered to be persistent 1 if unextracted residues in the aerobic soil studies (43441045) are not considered, but persistent if these residues are included

. Aerobic soil metabolism may be an important mechanism of degradation, but uncertainty about this exists because soil extraction of most samples involved the use of only an acetone:HCl (95:5 v:v) mixture. High levels ( from 22 to 51% between DAT 56 and 140 in three soils ) of residues were unextracted and uncharacterized

, and the possibility that some of these could have consisted of parent diclosulam cannot be ruled out . W hen unextracted residues are includ ed

, diclosulam’s a erobic soil half

- lives increase substantially , from a range of 29.8

- 57.6 days to a range of 177

- 2520 days . Photolysis (44192603) may be an important contributor to diclosulam’s degradation at the soil

s urface , and anaerobic aquatic metabolism ( 441092604 ) may be important under anaerobic conditions ( e.g ., in benthic sediments) . Hydrolysis of the chemical (43441043) is rapid under alkaline conditions (pH 9) , but negligible otherwise. Major degradates include 5

- OH (hydroxyl diclosulam), 8

- Cl (8

- chloro

- 5

- OH chloro hydroxyl diclosulam) and ASTP (aminosulfonyltriazolopyrimidine), which reached maxima of 16.6% , 15% and 15.8% of applied radioactivity (AR) respectively, in the aerobic soil study . 5

- OH was also formed in the anaerobic aquatic study, at a maximum o f 34% AR, as was the additional degradate TAAA (XDE

- 564

- triazolacetic acid), which was present at a maximum of 34% AR in the aqueous phase. Based on its low sorption coefficient ( 43471901; K OC = 33 to 144 ) diclosulam is classified as moderately mobile to mobile under the FAO system of classification , and particularly in its anionic form the compound is expected to move readily through the environment

. Degradates are generally expected to be more mobile than the parent compound, and limited data (43471901) tend to confirm that this is the case, at least for 5

- OH.

In terrestrial field dissipation studies (4463061) conducted in southern Georgia and southern Illinois, diclosulam dissipated with half

- lives of 120 and 70 days, respectively. In b oth fields, diclosulam was applied at a nominal rate of 0.033 lb a.i./acre, which is slightly above the maximum label application rate. Diclosulam was quantifiable at a maximum depth of 6 to 12 inches during each of the one

- year studies. Only the degrada te ASTP was monitored

, and it was detected only in the 0

- 6 inch depth interval

. In another supplemental dissipation study (44103531), two 150

- day lysimeter tests were performed: one each in North Carolina and one in Mississippi. Applications of diclosul am were made at near the label maximum. Registrant

- calculated dissipation half

lives of diclosulam were 22 and 25 days for the NC and MS site, respectively.

1 Based on the Toxic Release Inventory classification system where half

- lives greater than 60 days in water, soil, and sediment are considered persistent and half

- life greater than 6 months are considered very persistent (USEPA, 2012a)5

Radioactivity was detected at depths of 45

- 60 cm at levels between the LOD and LOQ. The majority o f the radiolabel, however, remained in the top 15 cm of soil. Degradates observed were 5

- OH, 8

- CL, TAAA, ASTP, and TPSA (triazolopyrimidinesulfonic acid). At the North Carolina site, no single degradate exceeded 10% of applied radioactivity. At the Missi ssippi site, ASTP reached a maximum of 39 % of applied radioactivity, but no other single degradate exceeded 10% of applied radioactivity.

Table 3. General physical and c hemical p roperties of diclosulam

.

Property Value(s) Source

Molecular weight ( g/ mol ) 406 45441 0 01 Water solubility (mg/L at 25  C) 117 at pH 5 124 at pH 7 4290 at pH 9 USEPA

, 2000

pKa (20  C ) 4.09 USEPA

, 2000 Vapor Pressure (mm Hg) 5 x 10

- 15 MRID 43441004

Octanol

- water partition coefficient (K ow ) 263 at pH 5 (Log Kow = 1.42) 0.897 at pH 7 (Log Kow = - 0.047) 0.356 at pH 9 (Log Kow = - 0.448) USEPA

, 2000

Table 4

. Environmental f ate p arameters of diclosulam

. Parameter Value (s) Source /Comments

Persistence (days)

Hydrolysis half

- lives ( days, 25  C) stable at pH 5 & 7, labile at pH 9 (1.85 d t 1/2 ) MRID 43441043

Aqueous photolysis half

- life ( days, 25  C) 101 MRID 43441044 ; mean of pyrimidine and aniline ring label results ; natural sun light, Richmond, CA, Aug

- Sept, 1993

Soil photolysis half

- life (days

, 25  C) 48 MRID 44192603 ; Norfolk loamy sand, mean of pyrimidine and aniline ring label results; natural sunlight

Aerobic soil metabolism half

li v e s , parent ( days, 25  C) 49.1 (Norfolk sandy loam ), 29.8 (Commerce silty clay ), 57.6 (Tama silt loam ) MRID 43441045

Aerobic soil metabolism half

li v e s , parent+unextracted ( days,

25  ) 312 (Norfolk sandy loam ),

2520 (Commerce silty clay ), 177 (Tama silt loam ) MRID 43441045

Aerobic aquatic metabolism half

li v e s (days

, 25  C) 151 MRID 44103530

Anaerobic aquatic metabolism half

- li v e s , parent (days

, 25  C) 61 (silt loam) MRID 44192604 ; whole

- system half

life , combined labels6

Parameter Value (s) Source /Comments Mobility

S oil

- water sorption coefficients

(K d, mL/g) 0.59, 1.4, 3.79, 0.62 MRID 43471901

Organic

- carbon normalized sorption coefficients (K oc ) ( m L/g OC ) 81, 144, 55, 33 MRID 43471901

Field Dissipation

Terrestrial field dissipation half

li v e s (days) 120 (Georgia , soybean application pattern ) 70 (Illinois , soybean application pattern ) MRID 446306 0 1

Terrestrial field dissipation half

li v e s (days) 12.5 (North Carolina, soybean application pattern) 14.8 (Mississippi, soybean application pattern) MRID 44103531

Drinking Water Exposure Modeling

Models

Diclosulam EDWCs for surface water and groundwater were generated using EFED’s standard suite of models. The Surface Water Concentration Calculator (SWCC version 1.10 6 ; May 2014 ) model was used to generate EDWCs of diclosulam that may occur in surface water used as drinking water. SWCC (which essentially comprises updated implementat ions of the PRZM and EXAMS mo dels) simulates pesticide application, movement and transformation on an agricultural field and the resultant pesticide loadings to a receiving water body via runoff, erosion, and spray drift, and then simulates the fate of the pesticide and resulting conc entrations in the water body. S tandard assumptions for drinking water assessment are a watershed of 172.8 ha that drains into an adjacent drinking water “ index ” reservoir of 5.26 ha surface area , an d average depth 2.74 m. Spray drift (modeled as direct d eposition of the pesticide into the reservoir) is assumed to be 13.5 % of the applied active ingredient for aerial application

, and 6.6% of the applied for ground application

. The national default Percent Cropped Area (PCA) of 100 % was used because current labels include a crop ( i.e ., peanuts) other than soybeans, corn, wheat, cotton, orchards, vegetables, and residential turf

. Groundwater EDWCs for diclosulam were derived using the PRZM

- GW model (Pesticide Root Zone Model for Groundwater, version 1.07, Nov., 2014), with the GW

GUI (Graphical User Interface, version 1.0, August 31, 2012). PRZM

- GW is a one

dimensional leaching model that estimates potential concentrations of pesticides in vulnerable groundwater . The model simulates transport through the crop root zone and soil profile, of a pesticide following its application to an agricultural field. PRZM

- GW was used to simulate 30 to 100 years of repeated diclosulam application in six standard scenarios: Delmarva, GA coastal, NC cotton, WI corn, FL pot ato and FL citrus. Each7

scenario represents a different location known to be vulnerable to contaminant leaching ( e.g ., because of sandy soils). SCI

- GROW (version 2.3; 10/23/2010) is a regression model used as a screening tool to estimate potential pestic ide concentrations in vulnerable groundwater that might be used as drinking water. SCI

- GROW was developed by fitting a linear model to groundwater concentrations with the Relative Index of Leaching Potential (RILP) as the independent variable. Groundwater concentrations were taken from 90

- day average high concentrations from Prospective Gro undwater studies; the RILP is a function of aerobic soil metabolism and the soil

- water partition coefficient. The output of SCI

- GROW represents concentrations that might be expected to occur in shallow unconfined aquifers under sandy soils, which is repre sentative of the groundwater most vulnerable to pesticide contamination likely to serve as a drinking
water source

.

Modeling Approach and Input Parameters Screening

- level modeling was conducted to generate EDWC s in surface water and groundwater of diclo sulam following diclosulam use on peanuts and soybeans

. Surface water modeling for all crops was conducted using SWCC

, based on application rates presented in Table s 2 and 6

. Input fate parameters used in surface water modeling are presented in Table 5

. Scenarios model ed with SWCC are indicated in Table 6 , along with key scenario details

. All scenarios employed the assumptions of ground spray (pre

plant) application, with no soil incorporation. In running SWCC and PRZM

- GW on diclosulam

, the mean soil sorption coefficient (K OC = 78 mL/ g oc ) was employ ed

. I n accordance with EFED’s input parameter guidance ( http://www.epa.gov/oppefed1/models/water/input_parameter_guidanc e.htm ) t he K OC model of sorption was determined to apply rather than the K d model

, because the coefficient of variation was lower for the reported K OC values than for corresponding K d values

. I n running SCI

- GROW on diclosulam the median K OC ( 68 mL/g OC ) was used

, also in accordance with EFED’s input parameter guidance . In running SWCC to model diclosulam , an aerobic soil metabolism half

- life of 2435 days was used, which is the 90 percent upper confidence limit on the mean value fo r three aerobic soil measurements of half

- life of parent plus unextracted residues

. In running SCI

- GROW to represent diclosulam , an aerobic soil metabolism half

- life of 1003 days was used

, which is the median half

- li fe for the same aerobic soil values

.8

Table 5 . Input v alues for the SWCC m odel ing of diclosulam

.

Input Parameter Value Source/comment Hydrolysis half

- life (t 1⁄2 in days ; pH 7 ) stable MRID 43441043 Aqueous p hotolysis half

- life (t 1⁄2 in days) 101 MRID 43441044: natural sunlight, Richmond, CA, Aug

- Sept, 1993

Aerobic s oil metabolism half

- life (t 1⁄2 in days) 2435 MRID 43441045: upper 90% confidence limit on mean of three available values 1 for parent + unextracted residues

Aerobic a quatic metabolism half

- life (t 1⁄2 in days) 453 MRID 44103530: 3 x single available aerobic aquatic half

- life to account for uncertainty in using a single value 1

Anaerobic aquatic metabolism half

life (t 1⁄2 in days) 183 MRID 44192604: 3 x single available anaerobic whole

- system half

- life 1

, Commerce silt loam

Organic carbon

- normalized soil partition coefficient K oc (mL/g OC ) 78 MRID 43471901: mean of four available values 1 . CV for K OC is lower than that for K d

Application date, peanuts April 20 Preplant application. Optimal p lanting dates for peanuts are given in the NC crop profile as May 1

– May 20.

Application date, soybeans April 10 Preplant application. Planting dates for soybeans are given in the LA crop profile as mid

- April to mid

- June.

1 As per EFED model input parameter guidance

, located at: http://www.epa.gov/oppefed1/models/water/input_parameter_guidance.htm

Table 6 . SWCC scenarios and inputs for diclosulam modeling

.
Use SWCC Scenario Single Applic. Rate (lbs a.i./A) [kg/ha] Number of

Applications Peanuts NCpeanutSTD 0.0236 [0.0265] 1 Soybeans MSsoybeanSTD 0.0315 [0.0354] 1

Table 7 . Input values for the PRZM

- GW M odel for diclosulam

. Input Parameter Value Source/comment App. Rate (lb a.i./A/yr ) 0.0315 Max label rate (soybean use) Hydrolysis half

- life (t 1⁄2 in days ; pH 7 ) stable MRID 43441043

Aerobic Soil metabolism half

- life (t 1⁄2 in days) 2435 MRID 43441045: upper 90% CL on mean of three available values 1 for parent + unextracted residues

Soil partition coefficient K oc (mL/g) 78 MRID 43471901: mean of four available values . CV for K OC is lower than that for K d
1 As per EFED model input parameter guidance

, located at: http://www.epa.gov/oppefed1/models/water/input_parameter_guidance.htm9

Table 8 . Input v alues for the SCI

- GROW m odel for diclosulam

. Input Parameter Value Source/comment App. Rate (lb a.i./A/yr) 0.0315 Max value Hydrolysis half

- life (t 1⁄2 in days ; pH 7 ) stable MRID 43441043

Aerobic Soil metabolism half

life (t 1⁄2 in days) 1003 MRID 43441045: m ean of three available values 1 for parent + unextracted residues Soil partition coefficient K oc (mL/g oc ) 68 MRID 43471901: me di an of four available values

. 1 As per EFED model input parameter guidance

, located at: http://www.epa.gov/oppefed1/models/water/input_parameter_guidance.htm

Modeling Results

S urface water EDWCs for diclosulam are presented in Table 9

. Groundwater EDWCs are presented in Table 10 . V alues in bold are recommended for use in the human health dietary risk assessment. In the case of PRZM

- GW results, the post

breakthrough mean concentration is used as both the “chronic” and “cancer” exposure value. Outputs from the model runs that produced the highest EDWCs are provided in Appendix A

. Output concentrations reported in Appendix A for surface water have not been modified for percent cropped area since the PCA adjustment factor is 1.0
, as multiple uses are included in the DWA

. Output concentrations for groundwater are never adjusted using a PCA

, since PCAs represent watershed

- scale dilution effects that cannot be presumed to apply to groundwater

.

Table 9

. Diclosulam s creening l evel EDWCs for s urface w ater

. Use Scenario Application Method 1

- in

- 10 year

acute (μg/L) 1

- in

- 10 year

chronic (μg/L ) 30

- year mean

cancer (μg/L)

Peanuts NCpeanutSTD ground 0.632 0.208 0.103 Soybeans MSsoybeanSTD ground 4.44 0.874 0.261

Table 10

. PRZM

- GW and SCI

- GROW groundwater EDWCs based on diclosulam use on soybeans

. PRZM

- GW Results

Scenario Use Annual Appl. Rate (lbs a.i./A /yr ) Max. Daily

Conc. (μg/L) Post

Breakthrough Mean Conc. (μg/L) Simulation

Breakthrough Time (days)

Delmarva loamy sand soil (sweet corn) Soybeans 0.0315 11.1 8.46 1994

FL central ridge sand soil (citrus) Soybeans 0.0315 9.78 8.11 1500

FL sand soil ( potato ) Soybeans 0.0315 6.79 5.47 2251 GA loamy sand soil (peanut) Soybeans 0.0315 4.32 3.46 2506

NC loamy sand soil (cotton) Soybeans 0.0315 15.8 11.0 267410 PRZM

- GW Results

Scenario Use Annual Appl. Rate (lbs a.i./A /yr ) Max. Daily

Conc. (μg/L) Post

Breakthrough Mean Conc. (μg/L) Simulation

Breakthrough Time (days)

WI sand soil ( corn ) Soybeans 0.0315 4.53 3.87 3416 SCI

- GROW Results Application Rate (lbs a.i./A /yr ) EDWC (μg/L)

0.0315 1.47

The PRZM

- GW and SCI

- GROW results represent groundwater concentration s that might be expected in shallow

, unconfi ned aquifers under sandy soils. The SWCC model result s represent concentrations that might occur in untreate d surface water in runoff

- vulnerable locations. The simulated concentrations provided in this assessment

are expected to represent conservative estimates of concentrations in drinking water. Monitoring Data

No known m onitoring data are available for diclosulam

. EFED conducted a search ( February 2 0 , 2015) of the USGS National Water Quality Assessment ( NAWQA ) Program database ( http://cida.usgs.gov/nawqa_queries_public/ ) , the USGS Community Water S ystem ( CWS ) data (http://pubs.usgs.gov/ds/544/) , the CDPR surface water and sediment database (http://cdpr.ca.gov/docs/emon/surfwtr/surfcont.htm) , and the USEPA /USGS /

NWQMC (National Water Quality Monitoring Council) Water Quality Portal database ( http://www.waterqualitydata.us/ )

. None of these databases include any records of diclosulam as a sampled constituent.

Drinking Water Treatment Effects

N o specific information on the effects of drinking water treatment on the removal of diclosulam is currently available. The EDWCs in this assessment are representative of concentrations in drinking water source water (pre

- treatment) and are derived from daily instantaneous peak concentrations. For surface water, the conceptual model assumes that pesti cide reaches surface water via spray drift and runoff, and is then instantaneously mixed within the water column and reversibly sorbed to benthic sediments

. As diclosulam residues are stable to hydrolysis, the compound is not expected to degrade during th e time that elapses from drinking water intake through distribution to the consumer’s tap. Because organic carbon mediates the sorption of diclosulam to soils

, treatment methods such as sedimentation, flocculation, and activated carbon ( that are designed to capture contaminants via sorption )

, m ight be expected to remov e some diclosulam

. H owever given the compound’s low K OC s and low pKa it will exist in predominantly anionic form except at low pH, thus any removal via sorption is likely to be negligible

. Diclosulam does degrade via aqueous photolysis ; therefore

, w here ultraviolet light is used as a means of disinfection, degradation may be enhanced

.11

Uncertainties and Data Gaps

This assessment is based on available environmental fate data. There are no significant data gaps in the environmental fate database submitted by the registrant

, however uncertainty exists regarding the rate of aerobic soil metabolism because substantial unextracted, uncharacterized residues remained due to inadequacy of soil extraction procedures, and the possibility that some of these residues could have consisted of parent diclosulam cannot be ruled out. Modeling was conducted with unextracted residues included, which had the effect of increasing diclosulam’s aerobic soil h alf

- life input from 61 to 2435 days. The drinking water assessment is a screening

level assessment based on conservative assumptions. The modeling assessment relies on maximum use patterns and national default PCAs to reflect potential surface and ground water concentrations. To the extent that modeled inputs do not reflect the actual behavior of the compound, or that actual use patterns involve application of less a.i. than the permissible (labeled) maxima, aquatic concentrations could be lower than EDWC s reported herein

.

CITATION S

U.S. Environmental Protection Agency. 2000

. EFED Risk Assessment for Section 3 Registration of Diclosulam {N

- (2,6

- dichlorophenyl)

- 5

- ethoxy

- 7

- fluoro[1,2,4]triazolo

- [1,5

- c]pyrimidine

- 2

- sulfonamide}

. March 6

, 2000 (DP Barcode D260980 ). U.S. Environmental Protection Agency. 201 4

. Interim Guidance for Addressing Unextracted Residues in Laboratory Studies. May 10, 201 4

. U.S. Environmental Protection Agency. 2014

. BEAD Chemical Profile (BCP) for Registration Review: Diclosulam (129122)

. December 12, 2014.12 

### Appendix A SELECTED SURFACE WATER AND GROUNDWATER

MODELING OUTPUT FILES

SWCC Output


## Summary of Water Modeling of Diclosulam and the USEPA Standard Reservoir

Estimated Environmental Concentrations for diclosulam are presented in Table 1 for the USEPA standard reservoir with the MSsoybeanSTD field scenario. A graphical presentation of the year

- to

- year peaks is presented in Figure 1. These values were generated with the Surface Water Concentration Calcula tor (SWCC Version 1.106). Critical input values for the model are summarized in Tables 2 and 3. This model estimates that about 3.1% of diclosulam applied to the field eventually reaches the water body. The main mechanism of transport from the field to the water body is by runoff (93% of the total transport), followed by spray drift (6.51%) and erosion (0.51%). In the water body, pesticide dissipates with an effective water column half

- life of 52.1 days. (This value does not include dissipation by transport to the benthic region; it includes only processes that result in removal of pesticide from the complete system.) The main source of dissipation in the water column is washout (effective average half

- life = 56.7 days) followed by metabolism (666.3 days) an d photolysis (14995.9 days). In the benthic region, pesticide dissipates slowly (243.6 days). The main source of dissipation in the benthic region is metabolism (effective average half

- life = 243.6 days). Most of the pesticide in the benthic region (89%) is sorbed to sediment rather than in the pore water.

Table 1. Estimated Environmental Con centrations (ppb) for D iclosulam. Peak (1

- in

- 10 yr) 4.44

4

- day Avg (1

- in

- 10 yr) 4.32

21

- day Avg (1

- in

- 10 yr) 3.84

60

- day Avg (1

- in

- 10 yr) 3.02

365

- day Avg (1

- in

- 1 0 yr) 0.874

Entire Simulation Mean 0.26113

Table 2. Summary of Model Inputs for D iclosulam.

Scenario MSsoybeanSTD Cropped Area Fraction 1.0 Koc (ml/g) 78

Water Half

- Life (days) @ 25 °C 453

Benthic Half

- Life (days) @ 25 °C 165.6 Photolysis Half

- Life (days) @ 25 °Lat 101

Hydrolysis Half

- Life (days) 0

Soil Half

- Life (days) @ 25 °C 2435.4

Foliar Half

- Life (days) 0

Molecular Wt 406 Vapor Pressure (torr) 0 Solubility (mg/l) 100

Table 3. Application Schedule for D iclosulam. Date (Mon/Day) Type Amount (kg/ha) Eff. Drift
4/10 Ground 0.0354 .99 .066

Figure 1. Yearly Peak Concentrations14



### PRZM

- GW Output


## Groundwater Analysis for D iclosulam and the NC Eastern Coastal Plain

- Norfolk Loamy Sand

- Cotton Scenario Estimated groundwater concentrations and breakthrough times for diclosulam are presented in Table 1 for the NC Eastern Coastal Plain

- Norfolk loamy sand

- Cotton groundwater scenario. A graphical presentation of the daily concentrations in the aquifer is presented in Figure 1. These values were generated with the PRZM

- GW (Version 1.07). Critical input values for the model are summarized in Tables 2 and 3.

Table 1. Groundwater Results for D iclosulam and the NC Eastern Coastal Plain

- Norfolk loamy sand

- Cotton Scenario.

Peak C oncentration (ppb) 15.8

Post

- Breakthrough Mean Concentration (ppb) 11

Entire Simulation Mean Concentration (ppb) 8.18

Average Breakthrough Time (days) 2674.228

Throughputs 4.098379

Table 2. Chemical Properties for Groundwater Modeling of D iclosulam

. Koc (ml/g) 78 Surface Soil Half Life (days) 2435 Hydrolysis Half Life (days) 0 Diffusion Coefficint Air (cm2/day) 0.0 Henry's Constant 0.0 Enthalpy (kcal/mol) 0.0

Table 3. Pesticide application scheme used for diclosulam. This application scheme was applied every year of the simulation. Application Days Relative to Emergence Date (05/15) Application Method Application Rate (kg/ha)

10 Ground application with mass 0.035415 distribution increasing proportionally with depth to 4 cm

Figure 1. Aquifer Breakthrough Curve for diclosulam and the NC Eastern Coastal Plain

- Norfolk Loamy Sand

- Cotton Scenario

SCIGROW Output

SCIGROW VERSION 2.3
ENVIRONMENTAL FATE AND EFFECTS DIVISION OFFICE OF PESTICIDE PROGRAMS U.S. ENVIRONMENTAL PROTECTION AGENCY

SCREENING MODEL FOR AQUATIC PE STICIDE EXPOSURE

SciGrow version 2.3 chemical:diclosulam time is 2/20/2015 13:49: 2

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

------------------------------------------------------------------------ 0.032 1.0 0.032 6.80E+01 1003.0

------------------------------------------------------------- ----------- groundwater screening cond (ppb) = 1.47E+00

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