OFFICE OF

CHEMICAL SAFETY AND 

POLLUTION PREVENTION

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

PC Code: 129122

DP Barcode: 426157

Date: March 19, 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: James 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 Division (7507P)

EXECUTIVE SUMMARY

The Environmental Fate and Effects Division (EFED) has completed a screeninglevel drinking water assessment (DWA) for diclosulam in support of Registration 

Review. 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 acetolactate synthase (ALS) inhibitors, which act by interfering with amino 

acid synthesis. The maximum application rates for diclosulam are 0.0315 lb a.i./acre/yr
2

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. The maximum acute, chronic and cancer surface water 

estimated drinking water concentrations (EDWCs) are associated with the soybean use. 

The computer models PRZM and EXAMS, as implemented in EFED’s Surface Water 

Concentration Calculator (SWCC, version 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, version 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 evaluated 

the results of plant (peanut and soybean) and livestock metabolism (goats and hens), 

uptake in rotational crops, analytical methodology, magnitude of the residue in peanut 

and soybean, and animal metabolism (rats) for diclosulam. The MARC concluded that 

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 include 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, the 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 EDWCs. 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.

Drinking Water Source

(Model Used)

Use (rates 

modeled)

Maximum Estimated Drinking Water

Concentration (EDWC) 

Acute (μg/L) Chronic (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 11.0
3

PROBLEM FORMULATION

This is a screening-level drinking water assessment (DWA) that uses modeling to 

estimate surface water and groundwater concentrations of pesticides in drinking water 

source water (pre-treatment), resulting from pesticide use on sites that are contaminationvulnerable. Screening-level DWAs are designed to eliminate the need for further 

scrutiny of chemicals with low potential 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 peanuts in 2000. In 

March 2000, the Agency completed a screening-level ecological risk assessment 

(USEPA, 2000) in support of the Section 3 Registration on soybeans 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 since 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 rates of application of currently registered uses 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 NS1 NS1 0.0236 

Soybeans Ground 0.0315 1 NA 0.0315

1 Not stated: for 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 ranges 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 environmentally 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 (Kow) decreases as pH 
4

increases from 5 to 9. Diclosulam’s low Kow (maximum of 263 at pH 5) suggests 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 persistent1if 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. When 

unextracted residues are included, diclosulam’s aerobic 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

surface, 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 of 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; KOC = 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 both 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 degradate 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 

diclosulam were made at near the label maximum. Registrant-calculated dissipation halflives 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 of 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 Mississippi 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 chemical properties of diclosulam.

Property Value(s) Source

Molecular weight (g/mol) 406 45441001

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 (Kow) 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 fate parameters 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 t1/2)

MRID 43441043

Aqueous photolysis half-life 

(days, 25C) 101

MRID 43441044; mean of 

pyrimidine and aniline ring label 

results; natural sunlight, 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 halflives, parent (days, 25C)

49.1 (Norfolk sandy loam), 

29.8 (Commerce silty clay), 

57.6 (Tama silt loam)

MRID 43441045

Aerobic soil metabolism halflives, parent+unextracted (days, 

25)

312 (Norfolk sandy loam), 

2520 (Commerce silty clay), 

177 (Tama silt loam)

MRID 43441045

Aerobic aquatic metabolism halflives (days, 25C) 151 MRID 44103530

Anaerobic aquatic metabolism 

half-lives, parent (days, 25C) 61 (silt loam) MRID 44192604; whole-system halflife, combined labels
6

Parameter Value(s) Source/Comments

Mobility

Soil-water sorption coefficients 

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

Organic-carbon normalized 

sorption coefficients (Koc)

(mL/gOC)

81, 144, 55, 33 MRID 43471901

Field Dissipation

Terrestrial field dissipation halflives (days)

120 (Georgia, soybean 

application pattern)

70 (Illinois, soybean 

application pattern)

MRID 44630601

Terrestrial field dissipation halflives (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 1.106; 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 implementations of the PRZM and EXAMS models) 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 concentrations in the water body.

Standard 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, and

average depth 2.74 m. Spray drift (modeled as direct deposition 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 GWGUI (Graphical User Interface, version 1.0, August 31, 2012). PRZM-GW is a onedimensional 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 potato and FL citrus. Each 
7

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 pesticide 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 Groundwater 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 representative 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 EDWCs in surface water 

and groundwater of diclosulam following diclosulam use on peanuts and soybeans. 

Surface water modeling for all crops was conducted using SWCC, based on application 

rates presented in Tables 2 and 6. Input fate parameters used in surface water modeling 

are presented in Table 5. Scenarios modeled with SWCC are indicated in Table 6, along 

with key scenario details. All scenarios employed the assumptions of ground spray (preplant) application, with no soil incorporation. In running SWCC and PRZM-GW on 

diclosulam, the mean soil sorption coefficient (KOC = 78 mL/goc) was employed. In 

accordance with EFED’s input parameter guidance 

(http://www.epa.gov/oppefed1/models/water/input_parameter_guidance.htm) the KOC

model of sorption was determined to apply rather than the Kd model, because the 

coefficient of variation was lower for the reported KOC values than for corresponding Kd

values. In running SCI-GROW on diclosulam the median KOC (68 mL/gOC) 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 for 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-life for the same aerobic soil values.
8

Table 5. Input values for the SWCC modeling of diclosulam.

Input Parameter Value Source/comment

Hydrolysis half-life (t1⁄2 in days; pH 7) stable MRID 43441043

Aqueous photolysis half-life (t1⁄2 in 

days) 101 MRID 43441044: natural sunlight, Richmond, CA, Aug-Sept, 1993

Aerobic soil metabolism half-life (t1⁄2

in days) 2435

MRID 43441045: upper 90% 

confidence limit on mean of three 

available values1for parent + 

unextracted residues

Aerobic aquatic metabolism half-life 

(t1⁄2 in days) 453

MRID 44103530: 3 x single available 

aerobic aquatic half-life to account for 

uncertainty in using a single value1

Anaerobic aquatic metabolism halflife (t1⁄2 in days) 183

MRID 44192604: 3 x single available 

anaerobic whole-system half-life1, 

Commerce silt loam

Organic carbon-normalized soil 

partition coefficient Koc (mL/gOC)

78

MRID 43471901: mean of four 

available values1. CV for KOC is lower 

than that for Kd

Application date, peanuts April 20

Preplant application. Optimal planting 

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 Model for diclosulam.

Input Parameter Value Source/comment

App. Rate (lb a.i./A/yr) 0.0315 Max label rate (soybean use)

Hydrolysis half-life (t1⁄2 in 

days; pH 7)

stable MRID 43441043

Aerobic Soil metabolism 

half-life (t1⁄2 in days) 2435

MRID 43441045: upper 90% CL 

on mean of three available values1

for parent + unextracted residues

Soil partition coefficient Koc

(mL/g) 78

MRID 43471901: mean of four 

available values. CV for KOC is 

lower than that for Kd

1 As per EFED model input parameter guidance, located at: 

http://www.epa.gov/oppefed1/models/water/input_parameter_guidance.htm
9

Table 8. Input values for the SCI-GROW model for diclosulam.

Input Parameter Value Source/comment

App. Rate (lb a.i./A/yr) 0.0315 Max value

Hydrolysis half-life (t1⁄2 in days; 

pH 7)

stable MRID 43441043

Aerobic Soil metabolism halflife (t1⁄2 in days) 1003

MRID 43441045: mean of three 

available values1for parent + 

unextracted residues

Soil partition coefficient Koc

(mL/goc)

68 MRID 43471901: median 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

Surface water EDWCs for diclosulam are presented in Table 9. Groundwater

EDWCs are presented in Table 10. Values in bold are recommended for use in the 

human health dietary risk assessment. In the case of PRZM-GW results, the postbreakthrough 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 screening level EDWCs for surface water.

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)

PostBreakthrough 

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 2674
10

PRZM-GW Results

Scenario Use

Annual 

Appl. 

Rate (lbs 

a.i./A/yr)

Max. Daily 

Conc. 

(μg/L)

PostBreakthrough 

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 concentrations

that might be expected in shallow, unconfined aquifers under sandy soils. The SWCC

model results represent concentrations that might occur in untreated 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 monitoring data are available for diclosulam. EFED conducted a 

search (February 20, 2015) of the USGS National Water Quality Assessment (NAWQA)

Program database (http://cida.usgs.gov/nawqa_queries_public/), the USGS Community 

Water System (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

No 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 

pesticide 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 the 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), might be expected to remove some 

diclosulam. However given the compound’s low KOCs 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, where 

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 half-life input from 61 to 2435 days. The drinking water assessment is a screeninglevel assessment based on conservative assumptions. The modeling assessment relies on 

maximum use patterns and national default PCAs to reflect potential surface and 

groundwater 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 EDWCs

reported herein.

CITATIONS

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. 2014. Interim Guidance for Addressing 

Unextracted Residues in Laboratory Studies. May 10, 2014.

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 Calculator (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) and 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 Concentrations (ppb) for Diclosulam.

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-10 yr) 0.874

Entire Simulation Mean 0.261
13

Table 2. Summary of Model Inputs for Diclosulam.

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 Diclosulam.

Date (Mon/Day) Type Amount (kg/ha) Eff. Drift

4/10 Ground 0.0354 .99 .066

Figure 1. Yearly Peak Concentrations
14

PRZM-GW Output

Groundwater Analysis for Diclosulam 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 Diclosulam and the NC Eastern Coastal Plain -

Norfolk loamy sand - Cotton Scenario.

Peak Concentration (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 Diclosulam.

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 0.0354
15

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 PESTICIDE 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) applications (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

************************************************************************