2

following the use scenario on loamy sand soil in NC eastern coastal plain with two single 

bensulide maximum granular applications at 16 lb ai per acre each at 4-month interval

(Table 1).

Table 1. Recommended Surface water and Groundwater EDWCs (μg/L) for 

Bensulide Oxon

Surface Water Model: Tier II SWCC (v 1.106)

1 in 10 yr

Peak

1 in 10 yr

Annual Average

30 yr Annual 

Average

Ground Spray - CA Lettuce scenario (W23273.dvf)

(6 lbs ai/acre for 3 applications (2/1, 6/1, 10/1)

979 494 305

Groundwater Model: Tier 1 PRZM-GW

Peak

Values

Post Breakthrough 

Average

Breakthrough 

Time (Days)

NC Eastern Coastal Plain - (w13722Extended.dvf)

2.12 lbs ai/acre for 2 applications (3/1 and 7/1)

1,250 1,200 7,106

The main uncertainties with the bensulide oxon exposure estimate are lack of aerobic soil 

metabolism and aerobic aquatic studies for bensulide and bensulide oxon. In addition, 

bensulide oxon hydrolysis study is not submitted.

Previous Drinking Water Assessment

Two previous drinking water exposure assessments were conducted for parent bensulide

only (USEPA 1997, and USEPA 2000). The EDWCs from surface water sources were 

modeled using the Tier I model GENEEC, with two applications at 12.5 lb /A each and a 

120-day application interval. The previous recommended EDWCs for bensulide from 

surface water sources were 979 μg/L for acute (peak) and 947 μg/L for chronic (annual 

mean) (USEPA 1997). The EDWC from groundwater sources was not expected to 

exceed 1.0 μg/L based on the Tier I model SCI-GROW (USEPA 2000).

Use and Usage

Bensulide is a pre-emergence organophosphate herbicide currently registered for use on a 

variety of agriculture field and vegetable crops, and non-agricultural ornamentals, golf 

course turf, residential lawns and turf. According to an updated Screening Level Usage 

Analysis (SLUA) of national agricultural pesticide usage data (2004 – 2013) by the 

Agency’s Biological and Economic Analysis Division (BEAD), an average of 587,000 lb 

ai bensulide is applied in the United States and of this, about 51% of the total usage was 

on lettuce (300,000 lb ai), 14% was on cantaloupes (80,000 lb ai), and 10% was on 

broccoli (60,000 lb ai) (USEPA 2015).

Bensulide may be applied up to three times per year and with a 120-day minimum 

retreatment interval based on a LUIS report by BEAD (USEPA, 2012a), and a recent 

label summary provided by the registrant for the current federally registered agricultural 

and non-agricultural uses (Table 2). No aerial application was specified in any of the 

labels and therefore, the EDWCs were not modeled for aerial application. There are some 
3

missing use directions on the labels that are marked as “NA” or “NS” on the registrant’s 

use summary table. These use directions should be clarified on the labels, especially the 

maximum annual application rates. For this drinking water assessment, we have 

calculated the maximum annual application rate (ai) based on best available information 

on labels for the application of the formulated products. In addition, we did not assess the 

label with the vague language, for example, the label (EPA10163-205) specified “two or 

more applications per year may be necessary...” because of the uncertainty.

Table 2. Maximum Labeled Application Rates for Bensulide

Use

Ground 

Application 

Method1

Maximum 

Single 

Application 

Rate

(lb a.i./A)

Maximum

Number of 

Applications 

per Year

Maximum 

Yearly 

Application 

Rate

(lb a.i./A)

Application 

Interval

(days) and 

Date (M/D)

Golf course turf

EPA9198-176

Broadcast –

granular 16 2 32 120(4/1, 8/1)

Golf course turf, turf 

Ornamental lawns 

EPA10163-196

EPA10163-198

EPA10163-199

EPA10163-204

EPA2217-778

EPA9198-172

EPA 2217-696

Broadcast –

granular 

Broadcast 

spray –

Emulsifiable 

Concentrate

12.5 2 25 120

(4/1, 8/1)

Ornamental lawns and turf

Residential lawns

EPA10163-205

Hand spray

Disposable 

container 

(16oz)

8.65 2 or more NS2 120

Ornamental lawns and turf

Residential lawns

EPA 2217-838

Broadcast -

Granular 7.5-12.5 2 15-25 120(4/1, 8/1)
4

Use

Ground 

Application 

Method1

Maximum 

Single 

Application 

Rate

(lb a.i./A)

Maximum

Number of 

Applications 

per Year

Maximum 

Yearly 

Application 

Rate

(lb a.i./A)

Application 

Interval

(days) and 

Date (M/D)

Artichokes, beans, beet, bell 

pepper, Brassica (head and 

stem) vegetables, broccoli, 

broccoli raab, Brussels 

sprouts, cabbage, cardoon,

carrot, cauliflower, celery, 

celtuce, chervil, 

chicory/radicchio, 

chrysanthemum (garland), cole 

crops, collards, corn salad, 

cress (garden, upland), 

dandelion, dock (sorrel), 

eggplant, endive, fennel, 

garlic, greens, groundcherry 

(strawberry tomato/tomatillo), 

kale, kohlrabi, leafy 

vegetables, lettuce (head, leaf), 

mustard, mustard cabbage, 

okra, onion (dry bulb and 

green), orach (mountain 

spinach), parsley, peas, 

pepper, pepper (chili), 

pimento, radish, roquette 

(arugula), shallot, spinach, 

Swiss chard

EPA10163-200

Broadcast 

spray –

Emulsifiable 

Concentrate

5 (carrot)

6

1, 2, or 3 6, 12, or 18

120

(2/1, 6/1, 

10/1)

Cantaloupe, chayote, 

cucumber, cucurbit vegetables, 

cucuzzi, gherkin, gourds, 

gourd (wax), melons (bitter, 

honeydew, citron, mango, 

musk, water, winter melons), 

pepino, pumpkin, squash 

(butternut, summer, zucchini 

squash)

CA960003

NJ070001

Broadcast

spray –

Emulsifiable 

Concentrate

8.94 1 or 2 9 or 18 120

(4/1, 8/1)

1When there are several application methods (because of different types of formulation), the chosen method 

would either result in the highest environmental exposure or was labeled for a higher maximum rate than other 

application methods.

2NS – not specified. This information should be clarified on the labels. This spot treatment use pattern is 

considered to result in negligible exposure on the watershed-scale basis of this assessment. Therefore, it was 

not evaluated with exposure models.

Physical, Chemical and Environmental Fate Properties

Information from acceptable and supplemental laboratory studies indicates bensulide is 

persistent. Neither abiotic hydrolysis nor photolysis are major degradation processes in 

water or on soil surfaces. An aerobic aquatic metabolism study was not available for this 
5

assessment. The aerobic soil metabolism study was classified as supplemental as only 

one soil type was used. The main route of dissipation of bensulide appears to be aerobic 

soil metabolism. Under aerobic conditions, bensulide oxon (up to 13.8% of the applied) 

and carbon dioxide (up to 21% of the applied) are the major degradates in the soil (MRID 

40460301). Under anaerobic soil conditions in the laboratory, bensulide is considered 

stable (MRID 40460302). The physical, chemical, and environmental fate properties of 

bensulide and bensulide oxon are summarized in Table 3. 

Table 3. Physical, Chemical and Environmental Fate Properties of Bensulide and Its 

Major Degradate Bensulide Oxon

Parameter Bensulide (Parent) Bensulide Oxon (Major Degradate)

Value Reference Value Reference

Chemical Name O,O-diisopropyl-S-2-

phenylsulfonylaminoet

hylphosphorodithioate

MRID 45761801 O,O-diisopropyl-S-2-

phenylsulfonylaminoethyl

phosphorothioate

MRID 45761801

CAS Number 741-58-2 MRID 45761801 20243-81-6 MRID 47660403

Empirical Formula C14 H24 NO4 PS3 MRID 45761801 C14 H24 NO5 PS2 EPI Suite (v 

4.10)

Molecular Weight

(g/mole)

397.54 MRID 45761801 381.44 EPI Suite (v 

4.10)

Chemical Structure EPI Suite (v 

4.10)

EPI Suite (v 

4.10)

SMILES Code CC(C)OP(=S)(OC(C)C

)SCCNS(=O)(=O)c1cc

ccc1

EPI Suite v4.10 CC(C)OP(=O)(OC(C)C)S

CCNS(=O)(=O)c1ccccc1

EPI Suite (v 

4.10)

Melting Point (oC) 36 MRID 41532001 89.97 EPI Suite (v 

4.10)

Boiling Point (oC) 424.96 EPI Suite (v 

4.10)

476.9 EPI Suite (v 

4.10)

Vapor pressure (mm 

Hg @ 25oC)

8.2 x 10-7 MRID 41532001 2.48 10-8 EPI Suite (v 

4.10)

Henry’s Constant

(atm m3 mole-1)

7.7 x 10-8 MRID 41532001 7.10 x 10-12 EPI Suite (v 

4.10)

Solubility (mg//L @ 

25oC)

5.6 MRID 41532001 461.24 EPI Suite (v 

4.10)

Kow 4.20 EPI Suite (v 

4.10)

2.35 EPI Suite (v 

4.10)

Kd (mL/g) 10.9 Sand 

30.5 Sandy Loam Soil

34.0 Clay Loam Soil 1

96.8 Clay Loam Soil 2

MRID 42826701 1.96 Sand 

4.23 Sandy Loam Soil

6.05 Clay Loam Soil 1

26.5 Clay Loam Soil 2

MRID 43180701
6

Parameter Bensulide (Parent) Bensulide Oxon (Major Degradate)

Value Reference Value Reference

Koc (mL/g) 3480 Sand 

1348 Sandy Loam Soil

4379 Clay Loam Soil 1

2328 Clay Loam Soil 2

MRID 42826701 626 Sand 

187 Sandy Loam Soil

779 Clay Loam Soil 1

637 Clay Loam Soil 2

MRID 43180701 

Hydrolysis t1/2(day) 

@ 25 0C

230 (pH 5)

220 (pH 7 & 9)

MRID 00160074 -

(Not Available)

-

Aerobic soil met. 

t1/2(day)

Bensulide Oxon 

13.8%@270 days

Benzenesulfonamide 

<0.5%

Bond residues 

18%@360 days

CO2 21%@360

days

363 MRID 40460301 749

(Bensulide + Oxon)

MRID 40460301

Aquatic photolysis 

t1/2 (day)

Bensulide Oxon 

4.8%@41 days

132

MRID 40513401

173

(Bensulide + Oxon)

MRID 40513401

Anaerobic Soil met. Stable MRID 40460302 - -

Field Dissipation,

California

15 – 34 days MRID 40534902

MRID 40534904

MRID 40534905

- -

Field Dissipation,

Mississippi

30-210 days MRID 40534901

MRID 40534903

MRID 40534906

- -

Bioconcentration 

factor (BCF)

550 MRID 41931001 - -

Environmental Transport, Field Dissipation and Bioconcentration

The degradate bensulide oxon is more soluble in water (461 mg/L, EPISuite v. 4.10) than 

bensulide (5.6 mg/L, MRID 41532001). Bensulide is slightly mobile in the four soils 

tested (Koc's ranged from 1,433 to 4,326 mL/g) based on an acceptable study (MRID 

42826701); however, its major degradate bensulide oxon (average Koc = 557, MRID 

43180701) and the minor degradate benzenesulphonamide (average Koc = 17.72, MRID 

43180702) ranged from moderately mobile to highly mobile in the same four test soils. 

Ground spray applications may potentially result in transport and loading of bensulide to 

off-field soil, and foliage, and water bodies via spray drift. Granular ground application 

methods are not expected to result in granules being distributed to off-field soil; however 

on-field bensulide soil residues, from either ground spray or granular application 

methods, have the potential to be transported both dissolved in water and on suspended 

soil in runoff to off-field terrestrial areas and to adjacent surface waters. Once in the 

aquatic system, bensulide is expected to partition primarily to sediment where it will be 

relatively stable. Bensulide is not expected to leach to groundwater, but bensulide oxon
7

may leach to groundwater due to its higher solubility and mobility.

There are six submitted field dissipation studies classified as supplemental. Three were

conducted in California with reported half-lives ranging from 15-34 days (MRID 

40534902, 40534904 and 40534905). Three were conducted in Mississippi with halflives ranging from 30-210 days (MRID 40534901, 40534903 and 40534906). The field 

dissipation data confirmed the laboratory findings that bensulide is a persistent herbicide. 

Bensulide and bensulide oxon were detected 6-12 inches deep in soil in both California 

(MRID 40534902, 40534904 and 40534905) and Mississippi (MRID 40534901,

40534903 and 40534906).

Bensulide may bioconcentrate in fish with a whole body bioconcentration factor (BCF) of 

550. However, 98% of the compound is eliminated after 14 days depuration, once 

residues are removed from the water. Therefore, bensulide may bioaccumulate in fish but 

not at levels of concern (MRID 41931001). Biomagnification up through the food web is 

not expected to be a significant transport pathway.

Mode of Action and Residues of Concern

Bensulide, (O,O-diisopropyl S-2-phenylsulfonylaminoethyl phosphorodithioate), is a preemergence non-systemic, organophosphate herbicide, which acts on conjugation of plant 

acetyl co-enzyme A by inhibiting meristematic root tissues and preventing cell division in 

root tips (Ware, 1978; Martin, 2000). The mode of toxic action to non-target organisms 

(e.g., mammals) is via the inhibition of cholinesterase and accumulation of acetylcholine 

at the nerve synapses, resulting in classic symptoms of organophosphate poisoning.

Both bensulide and bensulide oxon (up to 13.8% in aerobic soil) are the residues of 

concerns in drinking water (USEPA 2009).

Surface Water Modeling

Drinking water from surface water sources is often subjected to water treatment via 

chlorination. During chlorination, the parent bensulide may be totally converted into 

bensulide oxon during the process (Kamel et al., 2009). Therefore, a total toxic residue 

(TTR) approach was used in this assessment for surface water exposure, in which all 

residues of bensulide are assumed to be converted to the oxon. Therefore, bensulide and 

its oxon are summed in this assessment as oxon equivalents.

Table 4 shows the modeling input parameters based on TTRs. The EDWCs in surface 

water sources were generated using the Tier II Surface Water Concentration Calculator 

(SWCC v 1.106, USEPA 2014), which is a graphical user interface that runs the Pesticide 

Root Zone Model and the Variable Volume Water Body Model. The default percentage 

crop area (PCA) of 1.0 was used due to the use of bensulide on non-agricultural settings

(USEPA 2012b).
8

Table 4. SWCC Inputs for Bensulide Total Toxic Residues

Input variable (Units) Input value and 

calculations

Source Justification

Crop name See Table 2

Product labels

Application method Ground 

Application rate (lb a.i./acre) See Table 2

Application Date (M/D) 4/1 and 8/1

or

2/1, 6/1 and 10/1

Application interval (days) >120 days

Application efficiency

Ground spray

0.99

EFED input parameters

and spray drift

guidances

(USEPA 2009a, 2013)

Spray drift fraction

Ground spray

0.066

Application efficiency

Granular ground broadcast

1

Spray drift fraction

Granular ground broadcast

0

Molecular Weight (g/mole) 397.5 MRID 45761801 

(Value for parent)

Vapor pressure @ 25oC (mm Hg) 2.48 10-8 EPI Suite (v 4.10)

Solubility in Water (mg/L) 461 EPI Suite (v 4.10) (Maximum value for 

bensulide oxon)

Aquatic photolysis t1/2 (day) 173 (40°N latitude) TTR half-life for parent 

and oxon (MRID 

40513401) calculated 

using PestDF

Aerobic soil met. t1/2 (day) 2,247 (25°C) 749 (TTR half-life for 

parent and oxon; MRID 

40460301) x 3 to 

account for potential 

variability across soils

EFED guidance, USEPA 

2009a

Hydrolysis t1/2 (day) @ 25°C, pH 7 220 MRID 00160074 

(Value for parent -

bensulide oxon not 

formed)

Aerobic aquatic met. t1/2 (day) 4,494 (25°C) No data; (soil aerobic 

met. half-life x 2 

EFED guidance; USEPA 

2009a)
9

Input variable (Units) Input value and 

calculations

Source Justification

Anaerobic aquatic met. t1/2 (day) 0 MRID 40460302 “0” indicates stability, 

based on the anaerobic 

soil metabolism study 

results

Koc (ml/g) 557 MRID 43180701 Average of 4 values for 

bensulide oxon

Table 5 shows the EDWCs of TTRs as bensulide oxon equivalent. The recommended

EDWCs from surface water sources are not expected to exceed 979 μg/L for the 1 in 10 

year daily peak concentration, 494 μg/L for the 1 in 10 year annual concentration, and 

305 μg/L for the 30 year annual average concentration based on the California lettuce use 

scenario. The peak value (979 μg/L) of the TTRs (bensulide oxon equivalents) is the 

same as the previous recommended bensulide peak value (979 μg/L) (USEPA 2000). An 

example SWCC output summary is shown in Appendix I.

Table 5. Surface Water EDWCs for Bensulide TTRs A

Scenario Application 

Method

Single 

Application 

Rate

(lbs ai/acre)

No. and 

Date(mm/dd) 

of 

Applications

Concentration (μg/L)

1 in 10 

yr

Peak

1 in 10 yr

Annual Average

30 year 

annual 

average

FL Turf

(W12834.dvf)

Granular 

Broadcast

16 2 and

(4/1, 8/1)

554 256 166

PA Turf

(W12834.dvf)

Granular 

Broadcast

16 2 and

(4/1, 8/1)

946 409 244

TurfBSS

(W13958.dvf)

Granular 

Broadcast

16 2 and 

(4/1, 8/1)

605 267 170

CA TurfRLF

(W23234.dvf)

Granular 

Broadcas

16 2 and 

(4/1, 8/1)

697 372 208

FL Turf

(W12834.dvf)

Ground Spray 12.5 2 and 

(4/1, 8/1)

195 104 80

PA Turf

(W14751.dvf)

Ground Spray 12.5 2 and 

(4/1, 8/1)

280 133 95

TurfBSS

(W13958.dvf)

Ground Spray 12.5 2 and (4/1,

8/1)

213 105 79

CA TurfRLF

(W23234.dvf)

Ground Spray 12.5 2 and (4/1, 

8/1)

205 129 87

FL Peppers

(W12844.dvf)

Ground Spray 6 3 and (2/1, 

6/1, 10/1)

532 173 113

FL Cabbage

(W12842.dvf)

Ground Spray 6 3 and (2/1, 

6/1, 10/1)

494 164 123

CA Lettuce

(W23273.dvf)

Ground Spray 6 3 and (2/1, 

6/1, 10/1)

979 494 305

CA Avocado

(W23188.dvf)

Ground Spray 6 3 and (2/1, 

6/1, 10/1)

179 100 73

A Maximum values in bold.
10

Groundwater Modeling

The maximum amount of bensulide oxon formation is 13.8% in a submitted aerobic soil 

metabolism study (MRID 40460301). This percentage and the molecular weight ratio of 

bensulide to its oxon were used to calculate the bensulide oxon conversion rate for 

modeling groundwater exposure to the oxon. For example, for the maximum single 

application rate of bensulide, 16 lbs ai/acre, the equivalent application rate for the 

bensulide oxon is 2.12 lbs ai/acre (16 × 13.8% × 381.44/397.54). The maximum annual 

application rates for bensulide and bensulide oxon represent the above single maximum 

rates times 2 applications that occur four months apart (Table 6).

The EDWCs from groundwater sources for bensulide and bensulide oxon were simulated 

separately using the Tier 1 PRZM-GW model (USEPA, 2012c,d). PRZM-GW is a onedimensional, finite-difference model that estimates the concentrations of pesticides in 

groundwater. It accounts for pesticide fate in the crop root zone by simulating pesticide 

soil transport and degradation after a pesticide is applied to an agricultural field. PRZMGW permits the assessment of multiple years of pesticide application (up to 100 years) on 

a single site. Six standard scenarios, each representing a different region known to be 

vulnerable to groundwater contamination, are available for PRZM-GW simulations. 

PRZM-GW output values represent pesticide concentrations in a vulnerable groundwater 

supply that is located directly beneath a rural agricultural field. The breakthrough time 

(i.e., the number of days that it takes for the applied chemical to reach the aquifer) is 

simulated for 30 years or for 100 years (using extended weather files) to determine

EDWCs. PCAs are not applicable to the PRZM-GW model. The fate input parameters 

used for bensulide and bensulide oxon PRZM-GW modeling are listed in Table 6.

Table 6. PRZM-GW Inputs for Bensulide and Its Oxon Degradate

Data Units Value Source Comments

Bensulide

The maximum 

application rate of 

bensulide

16 lbs ai/acre for 2 applications on 3/1 and 7/1 (4-month interval)

Aerobic Soil 

Metabolism

Days 1,089 MRID 40460301

bensulide (363 × 3)

(USEPA, 2009a)

Soil:Water Coefficient 

(Koc) L/g 2,884 MRID 43180701 

Average of 4 values 

for bensulide 

(USEPA 2009a)

Hydrolysis t1/2(day) @ 25 

°C and (pH 7)

220 MRID 00160074

Bensulide Oxon

The maximum 

application rate of 

bensulide oxon through 

aerobic soil 

transformation

2.12 lbs ai/acre for 2 applications on 3/1 and 7/1 (4-month interval)*

*16 × 13.8% (application rate conversion based on aerobic soil metabolism) × 

96% (molecular wt conversion) = 2.12 lbs ai/acre

Aerobic Soil 

Metabolism

Days 2,247 MRID 40460301

Bensulide oxon (749

× 3) (USEPA, 2009a)

Soil:Water Coefficient MRID 43180701 Average of 4 values
11

(Koc) L/g 557 for bensulide, (EFED 

Guideline 2009a) 

Hydrolysis t1/2(day) 0 No data Stable is assumed

The EDWCs of bensulide and bensulide oxon from groundwater sources in six vulnerable 

sites are shown in Table 7. Since the oxon concentrations peak much higher and earlier 

than the bensulide concentrations, the oxon concentrations are recommended for use in 

dietary risk assessment. The recommended EDWCs for oxon are not expected to exceed 

the highest daily values of 1,250 μg/L and the post-breakthrough averages of 1,200 μg/L

with average simulation breakthrough time of 7,106 days for North Carolina Coastal 

Plain scenario. The above oxon peak EDWC at 1,250 μg/L supersedes the previous 

recommended bensulide EDWC at 1 μg/L by SCI-GROW model (USEPA 2000). 

Examples of PRZM-GW modeling analysis are shown in Appendix II.

Table 7. Groundwater EDWCs Derived by PRZM-GW for Bensulide and Bensulide 

Oxon in Six Vulnerable Sites A

Crop/Scenario Highest Daily Value 

μg/L

Post Breakthrough 

Average 

μg/L

Average Simulation 

Breakthrough Time 

Days

Bensulide Oxon Bensulide Oxon Bensulide Oxon

DELMARVA sweet 

corn - Evesboro loamy 

sand

Met File 

(w13781Extended.dvf)

216 864 211 728 35733 7630

Florida Citrus - FL 

Central Ridge, Polk 

County Astatula sand, 

hrgb A. Met File 

(w12842Extended.dvf) 

374 943 360 898 29632 6321

Florida - potato 

Jacksonville

Met File 

(w13889Extended.dvf) 

1.28 348 Incomplete

breakthrough

326 Incomplete

breakthrough

12730

GA - Southern Coastal 

Plain, Tifton loamy 

sand – PEANUTS

Met File 

(w93805Extended.dvf)

7.69 234 Incomplete

breakthrough

219 Incomplete

breakthrough

10448

NC Eastern Coastal 

Plain - Norfolk loamy 

sand – Cotton 

Met File 

(w13722Extended.dvf)

48.8 1,250 46 1,200 29084 7106

Wisconsin Corn - WI 

Central Sands

Met File 

(w14920Extended.dvf)

173 915 Incomplete

breakthrough

815 Incomplete

breakthrough

9830

A The recommended EDWC values are in bold.
12

Monitoring Data

No monitoring data were found for bensulide and bensulide oxon in the U.S. Geological 

Survey (USGS) National Water Quality Assessment (NAWQA) surface and groundwater 

databases. In an ambient monitoring report by California Department of Pesticide 

Regulation, bensulide had a detection frequency of 55% out of 51 samples in surface 

water with the highest value at 14 ppb (Starner, K. 2013).

Assumptions, Uncertainties, and Limitations

1. The aerobic soil metabolism study for bensulide evaluated only one soil, with a 

half-life of 363 days. The TTR half-life was 749 days with the inclusion of 

bensulide oxon. Because the registrant only submitted data for one soil type, 

model inputs were conservatively multiplied by three to account for potential 

variability across soils, following EFED guidance (USEPA, 2009a). If the data for 

more soil types were available, the modeled aerobic soil metabolism half-life 

could be reduced.

2. The modeled aerobic aquatic metabolism half-life was calculated by multiplying 

the aerobic soil metabolism half-life by 2 (t1/2 = 2,247 × 2 = 4,494 days) due to the 

absence of data, following EFED guidance (USEPA, 2009a).

3. Bensulide oxon hydrolysis is assumed to be stable because of no data.

4. The current labels do not fully specify the application rates, number of 

applications, and minimum retreatment intervals. Label clarifications for some of 

the uses are necessary to reduce the uncertainty. As such, any application rate 

exceeded the label rates listed in Table 1 is beyond the scope of this assessment.

5. Groundwater sourced drinking water is seldom chlorinated. Therefore, bensulide 

was not assumed to convert 100% to the oxon but only the portion from the 

aerobic soil metabolism (13.8%). However, when chlorinated, high-end 

groundwater EDWCs should be similar regardless of whether bensulide is 

assumed to convert to the oxon during potential drinking water treatment based on 

the current bensulide peak concentration at 374 μg/L in groundwater.

References

Kamel, A., C. Byrne, C. Vigo, J. Ferrario, C. Stafford, G. Verdin, F. Siegelman, S. 

Knizner, and J. Hetrick. 2003. Oxidation of selected organophosphate pesticides 

during chlorination of simulated drinking water. Water Research 43:522 – 534.

Starner, Keith, 2013. Study 282. Surface Water Monitoring for Pesticides in Agricultural 

Areas of California, 2013, Department of Pesticide Regulation Environmental 

Monitoring Branch 1001 I Street Sacramento, California 95812. 77pp.

USEPA. 1997. Drinking Water Assessment for Bensulide. EFED, 11/21/1997. PC Code: 

009801). DP Barcode: None. 11pp.
13

USEPA. 2000. Revised Estimated Environmental Concentrations in Ground and Surface 

Water for Bensulide used on Golf Course Fairways. EFED, 2/10/2000. PC Code 

009801. DP Barcode: None. 6pp.

USEPA. 2009. Guidance for Registration Review Data Requests for Oxon Degradates of

Organophosphate Insecticides (OP). U.S. Environmental Protection Agency, Office 

of Pesticide Programs, Environmental Fate and Effects Division. Internal 

memorandum. Mar. 10, 2009.

USEPA. 2009a. Guidance for Selecting Input Parameters in Modeling the Environmental 

Fate and Transport of Pesticides. Version 2.1. U.S. Environmental Protection 

Agency, Office of Pesticide Programs, Environmental Fate and Effects Division. 

Oct. 22, 2009.

USEPA. 2012a. Bensulide label Data Report as of 1/11/2012, also called label use 

information system (LUIS) report by Biological and Economic Analysis Division 

(BEAD).

USEPA. 2012b. Guidance on Development and Use of Percent Cropped Area and 

Percent Turf Area Adjustment Factors in Drinking Water Exposure Assessments: 

2012 Update. March 16, 2012 Memo. 50pp.

USEPA. 2012c. Approval of PRZM-GW for Use in Drinking Water Exposure 

Assessment. EFED Memo 12/11/2012. Pp. 1.

USEPA. 2012d. Guidance for PRZM-GW in Drinking Water Exposure Assessment. 

October 15, 2012. Pp. 20

USEPA. 2013. Guidance on Modeling Offsite Deposition of Pesticides via Spray Drift 

for Ecological and Drinking Water Assessments. EFED Memo 12/20/2013. 40pp.

USEPA. 2014. Surface Water Concentration Calculator User Manual. OPP 734F14001, 

July 1, 2014.

USEPA. 2015. Updated Screening Level Usage Analysis (SLUA) Report for Bensulide, 

PC Code (009801). July 10, 2015. Biological and Economic Analysis Division. 

3pp. 
14

APPENDIX I. Examples of SWCC Modeling

Summary of Water Modeling of Bensulide and Bensulide Oxon 

and the USEPA Standard Reservoir

Estimated Environmental Concentrations for Bensulide and Bensulide Oxon are 

presented in Table 1 for the USEPA standard reservoir with the CAlettuceSTD 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 2.8% of Bensulide and Bensulide Oxon applied to the 

field eventually reaches the water body. The main mechanism of transport from the field 

to the water body is by runoff (91.5% of the total transport), followed by spray drift 

(7.08%) and erosion (1.39%).

In the water body, pesticide dissipates with an effective water column half-life of 114.1 

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 hydrolysis (effective average halflife = 220.3 days) followed by washout (245.1 days), metabolism (9953.9 days), 

photolysis (22176.9 days), and volatilization (1.26054E+07 days).

In the benthic region, pesticide dissipation is negligible (13454.8 days). The main source 

of dissipation in the benthic region is hydrolysis (effective average half-life = 13454.8 

days). The vast majority of the pesticide in the benthic region (98.36%) is sorbed to 

sediment rather than in the pore water.

Table 1. Estimated Environmental Concentrations (ppb) for Bensulide and 

Bensulide Oxon.

Peak (1-in-10 yr) 979.

4-day Avg (1-in-10 yr) 966.

21-day Avg (1-in-10 yr) 907.

60-day Avg (1-in-10 yr) 801.

365-day Avg (1-in-10 yr) 494.

Entire Simulation Mean 305.

Table 2. Summary of Model Inputs for Bensulide and Bensulide Oxon.

Scenario CAlettuceSTD

Cropped Area Fraction 1.0

Koc (ml/g) 557

Water Half-Life (days) @ 25 °C 4494

Benthic Half-Life (days) @ 25 °C 0
15

Photolysis Half-Life (days) @ 40 

°Lat

173

Hydrolysis Half-Life (days) 220

Soil Half-Life (days) @ 25 °C 2247

Foliar Half-Life (days)

Molecular Wt 397.5

Vapor Pressure (torr) 2.48e-8

Solubility (mg/l) 461

Table 3. Application Schedule for Bensulide and Bensulide Oxon.

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

2/1 Foliar 6.72 .99 .066

6/1 Foliar 6.72 .99 .066

10/1 Foliar 6.72 .99 .066

Figure 1. Yearly Peak Concentrations
16

Summary of Water Modeling of Bensulide and Bensulide Oxon 

and the USEPA Standard Reservoir

Estimated Environmental Concentrations for Bensulide and Bensulide Oxon are 

presented in Table 1 for the USEPA standard reservoir with the PAturfSTD 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 0.98% of Bensulide and Bensulide Oxon applied to the 

field eventually reaches the water body. The main mechanism of transport from the field 

to the water body is by runoff (92.3% of the total transport) followed by erosion (7.66%).

In the water body, pesticide dissipates with an effective water column half-life of 152.1 

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 hydrolysis (effective average halflife = 220.3 days) followed by washout (527.8 days), metabolism (9449.1 days), 

photolysis (27435.1 days), and volatilization (1.651258E+07 days).

In the benthic region, pesticide dissipation is negligible (13454.8 days). The main source 

of dissipation in the benthic region is hydrolysis (effective average half-life = 13454.8 

days). The vast majority of the pesticide in the benthic region (98.36%) is sorbed to 

sediment rather than in the pore water.

Table 1. Estimated Environmental Concentrations (ppb) for Bensulide and 

Bensulide Oxon.

Peak (1-in-10 yr) 946.

4-day Avg (1-in-10 yr) 925.

21-day Avg (1-in-10 yr) 850.

60-day Avg (1-in-10 yr) 735.

365-day Avg (1-in-10 yr) 409.

Entire Simulation Mean 244.

Table 2. Summary of Model Inputs for Bensulide and Bensulide Oxon.

Scenario PAturfSTD

Cropped Area Fraction 1.0

Koc (ml/g) 557

Water Half-Life (days) @ 25 °C 4494

Benthic Half-Life (days) @ 25 °C 0

Photolysis Half-Life (days) @ 40 

°Lat

173
17

Hydrolysis Half-Life (days) 220

Soil Half-Life (days) @ 25 °C 2247

Foliar Half-Life (days)

Molecular Wt 397.5

Vapor Pressure (torr) 2.48e-8

Solubility (mg/l) 461

Table 3. Application Schedule for Bensulide and Bensulide Oxon.

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

4/1 Incorporated to 0 

cm

17.92 1 0

8/1 Incorporated to 0 

cm

17.92 1 0

Figure 1. Yearly Peak Concentrations
18

APPENDIX II. Examples of PRZM-GW Modeling

Groundwater Analysis for Bensulide Oxon and the NC Eastern 

Coastal Plain - Norfolk Loamy Sand - Cotton Scenario

Estimated groundwater concentrations and breakthrough times for Bensulide Oxon 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 Bensulide Oxon and the NC Eastern Coastal 

Plain - Norfolk loamy sand - Cotton Scenario.

Peak Concentration (ppb) 1.25E+03

Post-Breakthrough Mean 

Concentration (ppb)

1.2E+03

Entire Simulation Mean 

Concentration (ppb)

 541

Average Breakthrough 

Time (days)

7106.488

Throughputs 1.542253

Table 2. Chemical Properties for Groundwater Modeling of Bensulide Oxon .

Koc (ml/g) 557

Surface Soil Half Life (days) 2247

Hydrolysis Half Life (days) 0

Diffusion Coefficint Air (cm2/day) 0

Henry's Constant 0

Enthalpy (kcal/mol) 0.0

Table 3. Pesticide application scheme used for Bensulide Oxon . This application 

scheme was applied every year of the simulation.

Application Date

(Month/Day)

Application Method Application Rate

(kg/ha)

3/1 Ground application with mass 

distribution increasing 

proportionally with depth to 4 cm

2.3744
19

7/1 Ground application with mass 

distribution increasing 

proportionally with depth to 4 cm

2.3744

Figure 1. Aquifer Breakthrough Curve for Bensulide Oxon and the NC Eastern 

Coastal Plain - Norfolk Loamy Sand - Cotton Scenario