2 

EXECUTIVE SUMMARY

The subject chemical addressed in this drinking water assessment is identified by the chemical 

name nicosulfuron (DPX-V9630) with the chemical synthesis (IUPAC) name of 2-[[[[(4,6-

dimethoxy-2- pyrimidinyl)amino]carbonyl]amino]sulfonyl]-N,Ndimethyl- 3-

pyridinecarboxamide. Figure 1 below shows the chemical composition of nicosulfuron. 

Nicosulfuron is composed of molecular structures attached to pyrimide and pyridine rings 

bonded together by a sulfonylurea bridge (-NH-CO-NH-SO2-). 

Figure 1. Chemical structure of nicosulfuron. 

Nicosulfuron is proposed to be used in conventional ground and aerial foliar applications on the 

ALS inhibition tolerant sorghum crops. Table 1 in the Use Characterization section shows the 

complete proposed use information for nicosulfuron on ALS inhibition tolerant sorghum crops. 

Proposed maximum application rates range between 0.031 to0.061 lbs. a.i./A with seasonal 

application rates ranging between 0.057 – 0.084 lbs. a.i./A with a minimum of 7 seven days 

between applications specified on the draft product label. The most recent drinking water 

assessment for nicosulfuron (DP Barcode Nos. 301842, 302623, and 302624, dated August 3, 

2004) was conducted for corn new uses with maximum single application rates of up to 0.0625 

lbs. a.i./A. Although this maximum single application rate is higher than the proposed ALS 

inhibition tolerant sorghum crops (0.061 lbs. a.i./A), the maximum seasonal application rate of 

0.0625 lbs. a.i./A for the existing corn use is lower than the new ALS inhibition tolerant soybean 

crop new use (0.084 lbs. a.i./A). Therefore, exposure in surface water and ground water is 

expected to be higher for the proposed sorghum use. 

Nicosulfuron is a sulfonylurea herbicide currently used on crops other than corn including 

Bermuda grass, switch grass, fodder, rights of way, and fields (within construction sites, flood 

plains, swamps, and sewage disposal areas). Nicosulfuron is applied to crop foliage and grass 

via ground (broadcast and banded applications) and aerial applications. In addition, spot 

treatments are allowed in uses for Bermuda grass, fields, and rights of way. Nicosulfuron 

products are available as an emulsifiable concentrate or dispersible granules. Maximum single 

application rates for existing uses range between 0.00023 – 0.0703 lbs. a.i./A. The number of 

applications per year and the minimum time interval between treatments are not specified on 

many labels for current uses. 

Nicosulfuron belongs to the sulfonyl urea class of herbicides, which acts by inhibiting the plant 

enzyme acetolactate synthetase (ALS). The inhibition of this enzyme blocks the production of 

amino acids, valine and isoleucine, which are important in the production of plant proteins and 
3 

other components. This leads to the disruption of cell division and elongation in the plant. It is 

intended to control a variety of annual and perennial broadleaf and grass weeds in both 

agricultural and non-agricultural settings such as barnyardgrass, crabgrass, foxtail, panicum, 

volunteer wheat, Johnson grass and shattercane. The application of nicosulfuron to ALS 

inhibition tolerant sorghum crops will enable for nicosulfuron to treat these crops without 

damage while killing other target weeds. The new use for ALS inhibition tolerant soybean crops 

is proposed for DuPontTM Accent® and DuPontTM Steadfast® which possess 75 and 55 percent 

of the active ingredient nicosulfuron, respectively. Both products are water soluble granule 

formulations. Details on the nicosulfuron products which the new use encompasses are provided 

in Table 1 of the Use Characterization section. 

This Tier I Drinking Water Assessment for the proposed new use of nicosulfuron on ALS 

inhibition tolerant sorghum crops provides estimates of the upper bound residue concentration of 

nicosulfuron in surface and ground water drinking water sources resulting from its proposed 

uses. In addition, the proposed uses and fate properties of nicosulfuron are evaluated to identify 

the exposure pathways to drinking water. Both modeling tools and monitoring data are measures 

of exposure used to evaluate the impact of the new proposed nicosulfuron uses on drinking water 

resources. The tier 2 model PRZM/EXAMS (PRZM version 3.12.2, May 2005 and EXAMS 

version 2.98.4.6, April 2005) will be used to evaluate surface water exposure. The tier 1 model 

PRZM-GW (version 1.0, December 2012) will be used to evaluate ground water exposure. 

Nicosulfuron existing monitoring data found from stream water, spring water, and ground water 

sources from the United States Geological Survey National Water Quality Assessment (USGS 

NAWQA) program will also be presented to verify modeled exposures for drinking water. 

Nicosulfuron foliar applications using ground and aerial sprays both may impact both surface 

and ground water drinking water sources given that it possesses similar physical chemical 

properties and persistence to other chemicals which are known to translocate to these media. 

Nicosulfuron mainly degrades in soil and water to the following degradates: IN-HYY21 and IN37740 which maintain the sulfonylurea bridge, and pyridine sulfonamide (IN-V9367) and 

pyrimidine amine (IN-J0290). Since IN-HYY21 and IN-37740 are expected to possess similar 

environmental fate and toxicity to parent nicosulfuron due to similarities in molecular structure, 

these degradates are included in the drinking water assessment. Please refer to the Problem 

Formulation section of this drinking water assessment for the full discussion on how degradates 

were considered in this drinking water assessment. Acute exposure of nicosulfuron total residues 

(including parent, IN-HYY21 and IN-37740) in surface drinking water sources is represented by 

annual peak concentrations and chronic exposure represents annual average concentrations. In 

this Tier I analysis, 1-in-10 year peak concentrations are representative of acute levels of 

exposure, the 1-in-10 year annual average concentration are representative of noncancer chronic 

levels of exposure, and the 30-year mean concentration is assumed to represent cancer drinking 

water exposure from surface drinking water sources. In ground water, estimated peak 

concentrations are assumed to represent acute exposure concentrations and the post-breakthrough 

average estimated concentrations are assumed to represent chronic and cancer concentrations. 

It appears that the modeling estimates indicates that ground water exposure will drive the 

drinking water assessment. The PRZM-GW model estimates upper-bound concentrations of 
4 

nicosulfuron, IN-HYY21, and IN-37740 in ground drinking water sources not likely to exceed 

26.3 g/L (26.3 ppb) for acute exposure and 19.2 g/L (19.2 ppb) for chronic and cancer 

exposure. Upper-bound Tier I modeling using PRZM/EXAMS predicts generally lower 

concentrations of 9.67 μg/L (9.67 ppb) for the acute peak concentration, 2.80 μg/L (2.80 ppb)

for the chronic concentration, and 2.15 μg/L (2.15 ppb) for the cancer concentration. 

The EDWCs reported above for the ALS inhibition tolerant sorghum uses represent the 

maximum exposure with nicosulfuron uses that have a maximum annual application rate 

specified on the label since this proposed use possesses the highest annual application rate 

specified out of all uses. However, it is important to note that there are other uses that have 

unspecified annual application rates including Bermuda grass, switch grass, fodder, and rights of 

way. 

USE CHARACTERIZATION

Nicosulfuron water soluble granular products are proposed to be used in conventional ground 

and aerial foliar applications on ALS inhibition tolerant sorghum crops. This new use is 

proposed for DuPontTM Accent® (75 percent nicosulfuron) and DuPontTM Steadfast® (55 

percent nicosulfuron) products. Proposed maximum application rates range between 0.031 lbs. 

a.i./A – 0.061 lbs. a.i./A with seasonal application rates ranging between 0.057 – 0.084 lbs. a.i./A 

with a minimum of 7 seven days between applications specified on the draft product label. 

Table 1 in the Use Characterization section shows the complete proposed use information for 

nicosulfuron on ALS inhibition tolerant sorghum crops. Data from the USDA National 

Agricultural Statistics Service (NASS) indicate that sorghum crop production is highly 

concentrated over an area of the country confined to mainly the Southern Great Plains region 

including Central and West Texas, the Panhandle of and Central Oklahoma, Central and Western 

Kansas, South Central Nebraska, and South Central South Dakota1

. 

Table 1. Summary of application information based on labels provided by DuPontTM for 

nicosulufuron related to the proposed Section 3 new use for ALS inhibition tolerant 

sorghum crops. 

PRODUCT % A.I. FORMULATION 

APPLICATION 

METHOD 

SINGLE APP. 

RATE 

(lbs. a.i./A) 

MAX. 

SEASONAL 

APP. RATE 

(lbs. a.i./A)

MIN. 

RETREATMENT 

INTERVAL 

(days) 

DuPontTM 

Accent® 75 SG G, A 0.031 - 0.061 0.084 7 

DuPontTM 

Steadfast® 55 SG G, A 0.043 - 0.057 0.057 7 

1. Formulation identifier: SG = Water soluble granule 2. Application method identifiers: G = foliar ground application; A = foliar aerial application

 

1 Citation: http://www.nass.usda.gov/Charts_and_Maps/Crops_County/pdf/AS-PL12-RGBChor.pdf
5 

ENVIRONMENTAL FATE AND TRANSPORT CHARACTERIZATION

Physical and chemical properties of nicosulfuron are shown in Table 2 below. Environmental 

fate and transport properties of nicosulfuron based upon registrant submitted studies or other 

references are shown in Table 3 below. 

Table 2. Physical and chemical properties of nicosulfuron.

Property Value and units MRID or Source 

Chemical Name 

2-[(4,6-Dimethoxypyrimidin-2-

ylcarbamoyl)sulfamoyl]-N,Ndimethylnicotinamide. 

Product chemistry 

(MRID 47006001) 

Structure EpiSuite 

Chemical 

Formula C15H18N6O6S 

Product chemistry 

(MRID 47006001) 

Molecular 

Weight 410.4 g/mol Product chemistry (MRID 47006001) 

Vapor Pressure 

(25°C) 2.17 x 10-10 torr Product chemistry 

(MRID 48399916) 

Water Solubility 

(pH 7, 20°C) 8,070 mg/L 

Product chemistry 

(MRID 47006001) 

Henry’s Law 

Constant 3.51 x 10-12 atm·m3

/mol 

Calculated value from 

vapor pressure and water 

solubility 

Octanol – water 

partition 

coefficient 

(log KOW)

0.14 

Product chemistry 

(MRID 47006001) 

Table 3. Summary of nicosulfuron environmental fate properties.

Study/ 

OCSPP 

Guideline 

No. 

Value and unit MRID # 

or 

Citation 

Study 

Classification, 

Comment 

Abiotic 

Hydrolysis 

(835.2120) 

pH 5, 25°C: 14.7 days 

pH 7; 25°C: 606 days 

pH 9, 25°C: 635 days 

40924220, 

47083601 

Supplemental (All 

Studies)

 Sulfonylurea 
6 

Table 3. Summary of nicosulfuron environmental fate properties.

Study/ 

OCSPP 

Guideline 

No. 

Value and unit MRID # 

or 

Citation 

Study 

Classification, 

Comment 

bridge contraction 

in the degradation 

pathway not well 

understood 

Aqueous 

Photolysis 

(835.2240) 

t 1⁄2 = Stable 41082620 Acceptable

Soil 

Photolysis 

(835.2410) 

t 1⁄2 = 67 days 41082621 Acceptable

Degradation 

in air 

(835.2370) 

Reaction with Hydroxyl Radicals

t 1⁄2 = 0.587 hours 

EpiSuite 

AopWin v. 

1.92 

NA 

Aerobic Soil 

Metabolism 

(835.4100) 

SiL Soil (Neutral, pH 7.06, OC = 1.39 %): 

 t1/2 = 35.9 days 

SiCL Soil (Acidic, pH 6.10, OC = 2.96 %): 

t1/2 = 26 days 

Denmark SaL Soil (Acidic, pH 6.14, OC = 1.04 %): 

t1/2 = 88.4 days 

France SaL Soil (Acidic, pH 5.35, OC = 1.62 %): 

t1/2 = 27.7 days 

Germany L Soil (Neutral, pH 7.48, OC = 1.04 %): 

t1/2 = 25 days 

41082622, 

46240901, 

49169703 

Supplemental (All 

Studies)

All studies were 

conducted for durations 

between 120 – 240 days. 

The overall pattern of 

degradation for residues 

could not be determined 

over the study durations. 

Calculated half-lives 

extrapolated of the data 

provided within the 

study durations. 

Anaerobic 

Soil 

Metabolism 

(835.4200) 

SiCL Soil (Acidic, pH 6.10, OC = 2.95%): 

 t1/2 = 63 days 41082623 

Supplemental

Only one soil was 

evaluated in the study. 

Aerobic 

Aquatic 

Metabolism 

(835.4300) 

Spain Water - Silt Loam Sediment, (pH 7.33 – 7.80) 

t1/2 = 83 days 

North Dakota Water – Sand Sediment, (pH 6.96 – 8.20) 

t1/2 = 101 days 

48354304 

Supplemental (All 

Studies)

All studies were 

conducted for a duration 

of 102 days. The overall 

pattern of degradation 

for residues could not be 

determined over the 

study durations. 

Calculated half-lives 
7 

Table 3. Summary of nicosulfuron environmental fate properties.

Study/ 

OCSPP 

Guideline 

No. 

Value and unit MRID # 

or 

Citation 

Study 

Classification, 

Comment 

extrapolated of the data 

provided within the 

study durations. 

Anaerobic 

Aquatic 

Metabolism 

(835.4400) 

Missouri Silt Loam Sediment, (pH 7.13 – 7.80) 

 t 1⁄2 = 92.3 days 

Georgia Sand Sediment, (pH 7.09 – 7.6) 

t 1⁄2 = 98.8 days 

48790905 

Supplemental (All 

Studies)

All studies were 

conducted for a duration 

of 102 days. The overall 

pattern of degradation 

for residues could not be 

determined over the 

study durations. 

Calculated half-lives 

extrapolated of the data 

provided within the 

study durations. 

Mobility, 

unaged 

leaching, 

adsorption/ 

desorption 

(Koc) 

(835.1220) 

Dover, DE SaL: 25.07 mL/g; OC = 0.64 % 

Raleigh, NC SaL: 22.99 mL/g; OC = 1.22 % 

Rochelle, IL SiL: 69.36 mL/g; OC = 2.49 % 

Newark, DE SiL: 22.38 mL/g; OC = 2.73 % 

40924222 Acceptable

Terrestrial 

Field 

Dissipation 

(835.6100) 

Illinois SiCL Soil (Acidic, pH 6.00, OC = 2.30 %): 

t1/2 = 108 – 120 days 

California SaL Soil, (Alkaline, pH 8.24, OC = 0.43 %) 

t1/2 = 114 – 120 days 

43483901 Acceptable

Fish 

Bioconcen 

-tration 

Factor 

(BCF) 

(850.1730) 

No Data N/A No Data 

1 NA means not applicable. 
8 

2 Soil textural classifications: 

 SaL: Sandy Loam 

 SiL: Silt Loam 

 SiCL: Silty Clay Loam 

 L: Loam 

Mobility and Transport to Drinking Water Sources 

Nicosulfuron appears to be very mobile in mineral soils with an average Koc value of 34.95 mL/g 

with a range of between 22.38 mL/g – 69.36 mL/g in sandy loam and silt loam soils. In addition, 

Nicosulfuron high water solubility at 8,070 mg/L suggests that residues will dissolve readily and 

be subject to transport in runoff and drainage water. Nicosulfuron is not expected to volatilize 

under dry or moist environmental conditions as its vapor pressure is 5.25 x 10-8 torr and Henry’s 

Law Constant is 3.51 x 10-12 atm•m3/mol. Therefore, it appears that nicosulfuron can reach 

nearby water bodies, ground water, and terrestrial habitats adjacent to application sites primarily 

via dissolved residues within leaching and runoff water. Nicosulfuron is expected to remain in 

the water column once reaching surface water bodies and ground water given its low soil-water 

partition coefficient value (average Koc of 34.95 mL/g). It is also noted that the chemical is 

expected to reach surface water bodies by drift. 

 
9 

Degradation of Nicosulfuron and Identification of Transformation Products in Soil and Water 

Environmental laboratory and field data suggest that in general, nicosulfuron is moderately 

persistent to persistent in the environment. The predominant degradation mechanism appears to 

be hydrolysis in acidic environments and soil biodegradation in aerobic soil environments. 

Nicosulfuron appears to hydrolyze to some extent under acidic conditions with a half-life of 15 

days. Otherwise, nicosulfuron is practically stable to hydrolysis in neutral and alkaline 

environments. In addition, for aerobic soil metabolism, the variation of half-lives is limited, 

ranging between 25 – 36 days over a variety of soils with different properties with one exception. 

The aerobic soil half-life in Denmark sandy loam soil is longer at 88.4 days, and one reason for 

this is possibly due to the low organic matter content of the soil relative to the other soils. 

Otherwise, nicosulfuron tends to be relatively persistent to soil and aquatic photodegradation 

with half lives of 67 and 250 days, respectively. In addition, nicosulfuron appears to biodegrade 

slowly in aerobic aquatic environments with half-lives ranging between 83 – 100 days. Field 

dissipation half-lives of between 108 – 120 days confirm nicosulfuron’s relatively high 

persistence in the field as these half-lives were generally higher than laboratory fate studies. In 

the field, nicosulfuron tended to exhibit bi-phasic degradation behavior possibly contributing to 

the higher half-lives. 

Several sulfonylurea degradates form at major quantities (>10 percent of the applied) including 

AUSN (IN-HYY21) in the soil system as well as IN-37740 in the water/sediment system, both of 

which possess the sulfonylurea bridge (-NH-CO-NH-SO2-) entact forming as a result of 

molecular contraction on either side of the sulfonylurea bridge. In addition, pyridine 

sulfonamide (IN-V9367) and pyrimidine amine (IN-J0290), degradates which form resulting 

from cleavage of the sulfonyl urea bridge, are observed in significant quantities in both soil and 

water. The percent formation of these degradates which form in each fate laboratory study are 

described in Table C-1 in Appendix C.

 
10 

Figure 1. Biodegradation pathway of nicosulfuron in soil system.
11 

Figure 2. Biodegradation pathway of nicosulfuron in water

It should be noted that Figures 1 and 2 above depict that nicosulfuron and degradates are all 

expected to all terminally mineralize to carbon dioxide or be embedded within soil and sediment 

particles. However, the pattern of formation and decline of the degradates from nicosulfuron 

applications is not fully established in many cases since the environmental degradation studies 

were conducted for an insufficient amount of time to determine the terminal fate of nicosulfuron. 

This is the case for all of the hydrolysis, aerobic soil metabolism, anaerobic soil metabolism, and 

the aerobic aquatic metabolism studies for nicosulfuron. This is evident in Table C-1 in 

Appendix C as it shows that in numerous cases, the maximum formation amount of the 

degradates occur at the last sample period of these studies.

Bioconcentration of Nicosulfuron and Degradate Residues in Fish 

Bioaccumulation occurring from nicosulfuron applications is not expected in tissues of fish, 

aquatic, or terrestrial organisms due to its low octanol-water partition coefficient of Log Kow = 

0.14 (Kow= 1.38). 

Fate and Transport Characteristics of Transformation Products 

+

Major 
12 

Metabolites which form in the environmental fate laboratory and field studies described above 

along with the maximum levels that they form at is summarized in Table C-1 of Appendix C. 

There are no physical-chemical or environmental fate data which have been submitted by 

registrants or available from the open literature for the degradates discussed above including 

AUSN (IN-HYY21), pyridine sulfonamide (IN-V9367), pyrimidine amine (IN-J0290), and IN37740. However, physical chemical property values for these metabolites were estimated from 

EPISuite2

.

. Table 4 shows the comparison of physical chemical properties of selected degradates 

estimated by EPISuite to the physical chemical properties of nicosulfuron that have been 

measured and resulting values submitted to the Agency. In general, physical chemical properties 

between nicosulfuron and the degradates are similar. All constituents are highly soluble in 

water, are highly mobile in soil as indicated by Koc values less than 100 mL/g, and would not 

likely bind to tissue from biota as indicated by very low Log Kow values. The only notable 

exception is for pyrimidine amine with estimates of vapor pressure and Henry’s Law Constant 

values that are much greater than parent nicosulfuron. However, the existing aerobic soil, 

anaerobic soil, and aerobic aquatic metabolism studies do not indicate the presence of volatile 

elements of pyrimidine amine. This suggests that the estimated values of vapor pressure and 

Henry’s Law Constant for pyrimidine amine may not be accurate. 

Table 4. Comparison of physical chemical properties of nicosulfuron degradation 

products to parent nicosulfuron.

Property/ 

EPISuite 

Estimator 

Program 

Value from 

Existing 

Database EPISuite Value 

Nicosulfuron IN-HYY21 1 IN-37740 1

Pyridine 

Sulfonamide 

(IN-V9367) 

Pyrimidine 

Amine 

(IN-J0290) 

Solubility in Water 

(25 °C) 

(WSKOW v. 1.41) 

8,070 mg/L 37,280 mg/L 5,064 mg/L 90,380 mg/L 11,080 mg/L 

Vapor Pressure 

(25 °C) 

(MPBPVP v. 1.43) 

5.25 x 10-8 

torr 

7.87 x 10-12

torr 

2.05 x 10-15

torr 

4.01 x 10-7 

torr 1.74 x 10-3 torr 

Henry’s Law 

Constant (25 °C) 

(HENRYWIN v. 

3.20) 

3.51 x 10-12

atm·m3

/mol 

3.05 x 10-23 

atm·m3/mol 

2.68 x 10-22 

atm·m3/mol 

4.24 x 10-14

atm·m3

/mol 

1.07 x 10-6 

atm·m3/mol 

Octanol-Water 

Partition 

Coefficient 

0.14 -2.20 -1.76 -2.08 0.95 

 

2 EPISuite (Estimation Programs Interface Suite) version 4.0 was used. EPISuite is a software developed by the 

EPA Office of Chemical Safety and Pollution Prevention in collaboration with the Syracuse Research Corporation 

(SRC). EPISuite is a collection of programs which estimate physical chemical and environmental fate properties for 

mainly organic compounds. 
13 

Table 4. Comparison of physical chemical properties of nicosulfuron degradation 

products to parent nicosulfuron.

Property/ 

EPISuite 

Estimator 

Program 

Value from 

Existing 

Database EPISuite Value 

Nicosulfuron IN-HYY21 1 IN-37740 1

Pyridine 

Sulfonamide 

(IN-V9367) 

Pyrimidine 

Amine 

(IN-J0290) 

(Log Kow) 

(WSKOW v. 1.41) 

Soil-Water Partition 

Coefficient (Koc) 

(KOCWIN v. 2.00) 

22.4 – 69.4 

mL/g 0.5241 mL/g 4.036 mL/g 0.6911 mL/g 86.94 mL/g 

1

 Degradates maintained sulfonylurea bridge. 

2

 Other identified degradates including DPX-V9360 Ipso Precursor, IN-77799, IN-GDC42, IN-R5Q09, 

and IN-37740 are not likely to form at major levels in the environment, as they formed at less than 10 percent 

of applied in laboratory fate studies. 3

 Nicosulfuron physical chemical property values generally agreed well with estimates from EPISuite. 

PROBLEM FORMULATION

The environmental fate properties of nicosulfuron indicate that drinking water exposure 

potentially may occur in surface reservoir water or in drinking water wells. Application of 

nicosulfuron granules from aerial and ground applications and subsequent washoff from crop 

foliage, runoff, leaching, and the drift of granules to water bodies are potential transport 

mechanisms to surface and ground water. The potential for nicosulfuron exposure in surface and 

ground drinking waters also exists based on the nicosulfuron’s moderate persistence, high water 

solubility, and high mobility in the environment. Therefore, this drinking water assessment will 

address scenarios which depict the potential for nicosulfuron to be transported off-site to 

drinking water sources. 

As per meeting with the Health Effects Division’s Risk Assessment Branch 3 (meeting dated 

December 17, 2013) the residues of concern for drinking water include parent nicosulfuron and 

all major degradates which maintain the sulfonylurea bridge. These include degradates 

identified as IN-HYY21 and IN-37740. Table C-1 in Appendix C indicates that these 

degradates were detected at significant levels (greater than 10 percent of applied) in soil, 

sediment, and water. 

These degradates possess similar physical chemical properties. Furthermore, each of these 

degradates possess similar structures to parent nicosulfuron. Therefore, the total residue method 

will be used to estimate exposure in drinking water sources. In estimated drinking water 

concentrations (EDWCs) using the total residue method, degradate residues from environmental 

fate laboratory studies were added to the parent nicosulfuron to calculate the total residue halflife. This approach assumes that degradates possess equivalent toxicity and fate properties to the 

parent active ingredient. An overview of the total residue method is provided in the white paper 

on the FIFRA SAP Meeting on, “Selected Issues Associated with the Risk Assessment Process 
14 

for Pesticides with Persistent, Bioaccumulative, and Toxic Characteristics” held in October 2008 

(EPA, 2008). 

EXPOSURE ANALYSIS

Estimated drinking water concentrations (EDWCs) in surface waters are estimated using the Tier 

2 model PRZM/EXAMS (PRZM version 3.12.2, May 2005 and EXAMS version 2.98.4.6, April 

2005). PRZM/EXAMS is publically available on-line at 

http://www.epa.gov/oppefed1/models/water/#przmexamsshell. The index reservoir scenario 

simulating inflow and pesticide transport from streams into a reservoir intake is simulated for the 

drinking water assessment. Crop and regional specific percent crop areas (PCAs) are accounted 

for in EDWCs specific to each crop to factor in the portion of watersheds that are typically 

subject to pesticide loadings and subsequent transport to water bodies. The guidance, 

“Development and Use of Percent Cropped Area and Percent Turf Area Adjustment Factors in 

Drinking Water Exposure Assessments: 2012 Update”, are used to determine PCA values for 

each crop (EPA, 2012). 

Ground water estimates of concentrations are estimated using the PRZM-GW (version 1.0, 

December 2012) will be used to evaluate ground water exposure. PRZM-GW is publically 

available on-line at http://www.epa.gov/oppefed1/models/water/#przm_gw. Results from the 

long-standing tier I SCI-GROW model (Screening Concentration in GRound Water model, 

Version 2.3, May 16, 2006) will also be shown in comparison with the PRZM-GW modeling 

results according to EFED guidance related to the evaluation period for the recent release of 

PRZM-GW. SCI-GROW is publically available on-line at 

http://www.epa.gov/oppefed1/models/water/#scigrow. The SCI-GROW model inputs and 

results are shown in Appendix B.

Nicosulfuron existing monitoring data found from stream water, spring water, and ground water 

sources from the United States Geological Survey National Water Quality Assessment (USGS 

NAWQA) program will also be presented to verify modeled exposures for drinking water. 

Monitoring data from NAWQA are available on-line at: 

http://infotrek.er.usgs.gov/traverse/f?p=NAWQA:HOME:1405517206944567

 Surface Water

The fate parameters and use-specific input parameters for the PRZM/EXAMS surface water 

modeling are shown in Table 5. The EDWCs of nicosulfuron in surface water are shown for 

aerial applications in Table 6. Aerial applications are only evaluated in this Tier 1 drinking 

water assessment since this is considered to be the application method resulting in the most 

conservative exposure scenario. The PRZM/EXAMS output files are provided in Appendix A. 
15 

Table 5. PRZM/EXAMS input parameter values for physical chemical and fate 

properties used for nicosulfuron and total toxic residues (including IN-HYY21 and 

IN-37740) surface water aquatic exposure estimation. 

PRZM/EXAMS Input 

Parameter 

Input Value and Unit Source 

Physical Chemical Properties

Molecular Weight (g/mol) 410.4 MRID 47006001 

Vapor Pressure (torr) 2.17 x 10-10 MRID 48399916 

Solubility in Water (mg/L) 8,070 MRID 48399916 

Henry’s Law Constant 

(atm∙m3

/mol) 

3.51 x 10-12 Calculated value from vapor 

pressure and water solubility 

Soil-Water Partition Coefficient 

(Koc) 

(mL/g) 

34.95 MRID 40924222 

EFED Input Parameter Guidance

Mean value between: 

DE Sandy Loam – 25.07 mL/g 

NC Sandy Loam – 22.99 mL/g 

IL Silt Loam – 69.36 mL/g 

DE Silt Loam – 22.38 mL/g 

Environmental Fate Properties

Hydrolysis at pH7 (t1/2) 606 days MRID 409242201

Aerobic soil metabolism (t1/2) 253.37 days MRID 41082622, 46240901, and 

49169703 

EFED Input Parameter Guidance

Upper 90TH percentile 

confidence interval between2,4: 

Silt Loam Soil: 175 days 

Silty Clay Loam Soil: 31.1 days 

Denmark Sandy Loam: 142 

days 

France Sandy Loam: 33.6 days 

Germany Loam: 387 days 

Aerobic aquatic metabolism 

(t1/2) 

260.62 days MRID 48354304 

EFED Input Parameter Guidance

Upper 90th percentile confidence 

interval between2,4: 

Water - Silt Loam Sed.: 244 

days 

Water – Sand Sed.: 228 days 

Anaerobic aquatic metabolism 

(t1/2) 

177.78 days MRID 48790905 

EFED Input Parameter Guidance

Upper 90th percentile confidence 

interval between2,4: 
16 

Table 5. PRZM/EXAMS input parameter values for physical chemical and fate 

properties used for nicosulfuron and total toxic residues (including IN-HYY21 and 

IN-37740) surface water aquatic exposure estimation. 

PRZM/EXAMS Input 

Parameter 

Input Value and Unit Source 

Water - Silt Loam Sed.: 137 

days 

Water – Sand Sed.: 157 days 

Aqueous Photolysis (t1/2) Stable MRID 410826201

Application Methods and Crop Management Input Parameters

Crop Scenario and Weather KS Sorghum 

w13996 (Topeka, KS) 

Representative scenario for ALS 

inhibition tolerant sorghum 

crops 

Application Rate 1rst App.: 0.0683 kg/ha 

2nd App.: 0.0265 kg/ha 

Maximum single application rate 

(0.061 lbs. a.i./A) and maximum 

seasonal application rate (0.084 

lbs. a.i./A) specified on Product 

Labels3

Application Date June 25 Conservatively selected based on 

maximum rainfall climatological 

date at meteorological station 

after crop emergence date 

specified in PRZM crop scenario 

Number of Applications and 

Retreatment Interval 

2 applications every 7 

days 

Product Labels 

Regional PCA 0.87 Region 10 (Missouri) All 

Agriculture PCA from Table 7 

of EPA, 2012, “Development 

and Use of Percent Cropped 

Area and Percent Turf Are 

Adjustment Factors in Drinking 

Water Exposure Assessments: 

2012 Update” 

Application Methods CAM = 2, linearly 

applied to crop canopy 

Most conservative application 

method from product label 

Application Efficiency 0.95 EFED input parameter guidance 

for aerial applications 

Spray Drift Fraction 0.20 Spray drift fraction for aerial 

applications, fine to medium 

drop size distribution for 

windspeed of 15 mph from 

Table C1 of EPA, 2013, 

“Guidance on Modeling Offsite 

Deposition of Pesticides via 

Spray Drift”. 

Foliar Extraction FEXTRC = 0.5 Default assumption for foliar 

applications 

Pesticide Removal After 

Harvest 

ISPCND = 1.0, 

pesticide remaining on 

Conservative default assumption 
17 

Table 5. PRZM/EXAMS input parameter values for physical chemical and fate 

properties used for nicosulfuron and total toxic residues (including IN-HYY21 and 

IN-37740) surface water aquatic exposure estimation. 

PRZM/EXAMS Input 

Parameter 

Input Value and Unit Source 

foliage is converted to 

surface application to 

the top soil layer 1

 Half-lives for parent nicosulfuron only as IN-HYY21 and IN-37740 did not form in hydrolysis or aqueous 

photolysis studies. 2

 Half-lives based on total residues including parent nicosulfuron, IN-HYY21, and IN-37740. 

3

 Identified from proposed label DuPontTM Accent® label. 4

 The upper 90th percentile half life calculated as follows: t1/2 input = ݐଵ/ଶ തതതതത + (t90, n-1 x σ)

 n1/2 

where ݐଵ/ଶ തതതതത is the mean of the set of half lives from each study, t90, n-1 is the one-sided t value for the 90th percentile 

level, σ is the standard deviation of the set of half lives determined from each study, and n is the sample size of the 

set of half lives determined from each study. 

Table 6. PRZM/EXAMS estimated upper bound concentrations in surface water (ppb) 

of nicosulfuron and degradates of concern including IN-HYY21 and IN-37740. 

PRZM Crop 

Scenario 

PCA 

1-in-10 yr. 

Annual Peak 

(Acute) 

1-in-10 yr. 

Annual Mean 

(Chronic) 

30-year Mean 

(Cancer) 

KS Sorghum 0.87 9.67 2.80 2.15 

 Ground Water

Tables 7 and 8 show the input parameter values used in PRZM-GW and its predicted 

concentrations of nicosulfuron and degradates IN-HYY21 and IN-37740 in ground water, 

respectively. Tier I scenarios are run in this assessment to capture upper-bound screening 

exposure based on vulnerable environmental conditions. The PRZM-GW output files for both 

scenarios are provided in Appendix B. 

Table 7. PRZM-GW input parameter values for physical chemical and fate 

properties used for nicosulfuron and total toxic residues (including IN-HYY21 and 

IN-37740) surface water aquatic exposure estimation. 

PRZM/EXAMS Input 

Parameter 

Input Value and Unit Source 

Pesticide Properties

Hydrolysis at pH7 (t1/2) 606 days MRID 409242201

Surface soil metabolism (t1/2) 253.37 days MRID 41082622, 46240901, and 

49169703 

EFED Input Parameter Guidance

Upper 90TH percentile 

confidence interval between2,4: 
18 

Table 7. PRZM-GW input parameter values for physical chemical and fate 

properties used for nicosulfuron and total toxic residues (including IN-HYY21 and 

IN-37740) surface water aquatic exposure estimation. 

PRZM/EXAMS Input 

Parameter 

Input Value and Unit Source 

Silt Loam Soil: 175 days 

Silty Clay Loam Soil: 31.1 days 

Denmark Sandy Loam: 142 

days 

France Sandy Loam: 33.6 days 

Germany Loam: 387 days 

Soil-Water Partition Coefficient 

(Koc) 

(mL/g) 

34.95 MRID 40924222 

EFED Input Parameter Guidance

Mean value between: 

DE Sandy Loam – 25.07 mL/g 

NC Sandy Loam – 22.99 mL/g 

IL Silt Loam – 69.36 mL/g 

DE Silt Loam – 22.38 mL/g 

Application Methods and Crop Management Input Parameters

Crop Scenarios, Application 

Date5, and Weather 

WI Sands: Sept. 15, w14920 (La Crosse, WI) 

NC Coastal: May 25, w13722 (Raleigh, NC) 

GA Coastal: June 10, w93805 (Tallahasse, FL) 

Delmarva Peninsula: May 7, w13781 (Wilmington, 

 DE) 

FL Citrus: August 5, w12842 (Tampa, FL) 

FL Potato: Sept. 5, w13889 (Jacksonville, FL) 

Application Rate 1rst App.: 0.0683 kg/ha 

2nd App.: 0.0265 kg/ha 

Maximum single application rate 

(0.061 lbs. a.i./A) and maximum 

seasonal application rate (0.084 

lbs. a.i./A) specified on Product 

Labels3

Application Date September 15 Conservatively selected based on 

maximum rainfall climatological 

date at meteorological station 

after crop emergence date 

specified in PRZM crop scenario 

Number of Applications and 

Retreatment Interval 

2 applications with a 

7- day interval 

Product Labels 

Application Methods Ground application Most conservative application 

method from product label 1

 Half-lives for parent nicosulfuron only as IN-HYY21 and IN-37740 did not form in hydrolysis or aqueous 

photolysis studies. 2

 Half-lives based on total residues including parent nicosulfuron, IN-HYY21, and IN-37740. 

3

 Identified from proposed label DuPontTM Accent® label. 4

 The upper 90th percentile half life calculated as follows: t1/2 input = ݐଵ/ଶ തതതതത + (t90, n-1 x σ)

 n1/2 
19 

where ݐଵ/ଶ തതതതത is the mean of the set of half lives from each study, t90, n-1 is the one-sided t value for the 90th percentile 

level, σ is the standard deviation of the set of half lives determined from each study, and n is the sample size of the 

set of half lives determined from each study. 5

 Conservatively selected based on maximum rainfall climatological date at meteorological station after crop 

emergence date specified in PRZM crop scenario. 

Table 8. PRZM-GW estimated upper bound concentrations in ground water 

(ppb) for nicosulfuron and degradates of concern including IN-HYY21 and 

IN-37740. 

Tier I Scenario 

Highest Daily Value 

(Acute) 

Post-Breakthrough 

Average 

(Chronic and Cancer) 

WI Sands 26.3 19.2 

NC Coastal 9.53 7.10 

GA Coastal 4.70 3.39 

FL Citrus 14.5 10.2 

FL Potato 6.95 5.46 

Delmarva Peninsula 17.1 11.6 

*Bolded values show the highest ground water EDWC. 

EXPOSURE CHARACTERIZATION

The comparison between the PRZM/EXAMS surface water modeling and PRZM-GW ground 

water modeling, shown in Tables 4 and 6, respectively, suggest that nicosulfuron applications 

will predominately impact ground water resources. Estimated peak ground water concentrations 

of nicosulfuron and degradates IN-HYY21 and IN-37740 are approximately three times higher 

the estimated surface water concentration. Longer term ground water concentrations are 

approximately a magnitude of six higher than surface water. This is expected for nicosulfuron 

due to its high mobility and resulting ability to leach through the top soil to the water table. 

Considering this, the predicted ground water concentration in PRZM-GW should be 

conservative, consistent with the high porosity of the sandy soil of the Wisconsin scenario 

modeled and relatively shallow water table representative of the scenario (30 feet). However, it 

is important to note that these results based on Tier 1 vulnerable scenarios are intended to 

be a screening upper-bound estimate of the impact of nicosulfuron applications to ground 

water. Further consideration of additional refinements or scenario development 

representative of nicosulfuron applications to sorghum crops is possible, if needed. 

One significant contributing factor to the relatively large concentrations of nicosulfuron, INHYY21, and IN-37740 in estimated ground water is due to the assumption that the ground water 

possesses a neutral pH. Nicosulfuron is practically hydrolytically stable in neutral and alkaline 

environments. However, in more acidic environments, nicosulfuron can degrade much more 

rapidly with a hydrolysis half-life of 14.7 days. Therefore, in acidic ground water, concentrations 

of nicosulfuron would be drastically reduced. Estimated peak concentrations in PRZM-GW at 

0.128 ppb are calculated, and only trace long-term average ground concentrations amounting to 
20 

<0.01 ppb are expected in acidic environments. These concentrations could be more 

representative of conditions mostly in the eastern part of the area where sorghum is grown. 

However, in the western part of the sorghum growing area, calcareous soil and more alkaline 

environments are generally more likely to dominate in the drier climate (citation: 

http://www.fao.org/soils-portal/soil-management/management-of-some-problemsoils/calcareous-soils/en/). Therefore, the screening ground water concentrations shown in 

Table 9 may more represent nicosulfuron applications occurring in this region. The growing 

region of sorghum crops is shown in the map in Figure 1. 

At this time, nicosulfuron monitoring data is only available through the USGS NAWQA 

program. Despite the results of the modeling analysis in this drinking water assessment 

suggesting that nicosulfuron would be predominate in ground water, nicosulfuron was only 

detected in surface water (in streams) but not in ground water. 88 wells were sampled, and 2 

springs were sampled as well. Nicosulfuron may have not been found at these sites for a number 

of reasons including the possibility that monitoring was random and non-targeted to pesticide 

applications or that conditions were dry during the observing period. For surface water, 5 out of 

23 stream water sites (23 percent) contained detections of nicosulfuron, mainly in Alabama. 

PRZM/EXAMS peak nicosulfuron estimated surface water concentrations were over an order of 

magnitude higher than the monitoring data (9.67 ppb3

/0.2161 ppb = 44.7X). The main reason for 

the large departure of monitoring detections versus the modeling results is due to that screening 

modeled concentrations are based on a static pond, and lower concentrations in stream water 

would be expected in a flowing water body such as the stream as monitored at the site of 

nicosulfuron detections. Furthermore, the monitoring retrievals do not measure composite 

residues including IN-HYY21 and IN-37740 such as the modeling calculations reflect. 

UNCERTAINTIES AND LIMITATIONS

The main uncertainty in this drinking water assessment is the degradation of the fate of 

degradates IN-HYY21 and IN-37740 in soil and water are uncertain in most cases. Aerobic soil 

metabolism, aerobic aquatic, and anaerobic aquatic metabolism studies were all terminated 

before substantial decline was observed with these degradates. However, in all cases, levels of 

these degradates were observed to level off several sampling period before study termination 

coincident with continued nicosulfuron degradation. This suggests that the degradates were 

biodegrading at the same rate that they were forming due to nicosulfuron biodegradation. 

Therefore, the total toxic residue half-life between nicosulfuron, IN-HYY21, and IN-37740 

would not likely change given that the degradates would not be stable, and eventually degrade at 

a rate similar to the total toxic residue half-life as parameterized in the models used in this 

drinking water assessment. 

REFERENCES

FIFRA SAP Final Meeting Minutes 2008. Transmittal of Meeting Minutes of the FIFRA 

 

3 Since parent nicosulfuron alone is moderately persistent in soil and water, it is not anticipated that peak 

concentrations in surface water including IN-HYY21 and IN-37740 would be much different from just parent 

nicosulfuron alone. 
21 

Scientific Advisory Panel Meeting Held October 28 - 31, 2008 on Selected Issues Associated 

with the Risk Assessment Process for Pesticides with Persistent, Bioaccumulative, and Toxic 

Characteristics. http://www.epa.gov/scipoly/sap/meetings/2008/october/minutes.pdf 

USEPA. 2002. Guidance for Selecting Input Parameters in Modeling the Environmental Fate 

and Transport of Pesticides. U.S. Environmental Protection Agency, Office of Prevention, 

Pesticides and Toxic Substances, Office of Pesticide Programs, Environmental Fate and Effects 

Division. Feb. 28, 2002. Online at: 

http://www.epa.gov/oppefed1/models/water/input_guidance2_28_02.htm. 

U.S. Environmental Protection Agency 2012.. Development and Use of Percent Cropped Area 

and Percent Turf Area Adjustment Factors in Drinking Water Exposure Assessments: 2012 

Update. EPA Office of Pesticide Programs. Washington, DC. 

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

Environmental Protection Agency, Office of Prevention, Pesticides and Toxic Substances, Office 

of Pesticide Programs, Environmental Fate and Effects Division. Dec. 20, 2013. 
22 

Appendix A – Surface Water Modeling Supporting Documentation 

PRZM/EXAMS Modeling File 

stored as Nico_Sorgm.out 

Chemical: Nicosulfuron 

PRZM environment: KSsorghumSTD.txt modified Tueday, 26 August 2008 at 05:16:38 

EXAMS environment: ir298.exv modified Tueday, 26 August 2008 at 05:14:08 

Metfile: w13996.dvf modified Tueday, 26 August 2008 at 05:14:52 

Water segment concentrations (ppb) 

Year Peak 96 hr 21 Day 60 Day 90 Day Yearly 

1961 7.555 7.417 6.962 5.929 5.334 1.962 

1962 6.367 6.249 5.991 5.325 4.763 2.19 

1963 15.1 14.78 13.51 11.2 9.825 3.962 

1964 5.925 5.798 5.449 4.629 4.157 2.341 

1965 8.108 7.941 7.326 6.222 5.485 2.349 

1966 6.885 6.734 6.144 5.158 4.587 2.123 

1967 5.562 5.45 5.005 4.715 4.261 1.952 

1968 11.8 11.55 10.78 9.021 7.95 3.332 

1969 6.734 6.594 6.322 5.375 4.737 2.439 

1970 5.565 5.448 4.99 4.675 4.247 1.963 

1971 7.207 7.079 6.555 5.516 4.849 2.112 

1972 8.112 7.949 7.399 6.274 5.583 2.402 

1973 10.09 9.906 9.322 8.077 7.137 3.029 

1974 7.645 7.48 6.832 6.452 5.824 2.713 

1975 5.664 5.547 5.083 4.322 3.895 1.939 

1976 7.187 7.093 6.54 5.635 5.059 2.19 

1977 6.472 6.35 5.876 5.556 5.144 2.364 

1978 5.637 5.52 5.066 4.515 4.046 1.947 

1979 11.17 11.02 10.23 8.619 7.584 3.1 

1980 6.658 6.517 5.967 5.211 4.938 2.491 

1981 7.524 7.383 7.005 6.514 5.836 2.63 

1982 10.62 10.39 9.518 8.074 7.213 3.122 

1983 7.393 7.235 6.611 5.434 4.755 2.332 

1984 6.995 6.85 6.443 5.364 4.713 2.086 

1985 5.882 5.758 5.548 5.144 4.714 2.134 

1986 7.675 7.512 7.037 6.025 5.328 2.344 

1987 6.654 6.515 6.144 5.235 4.624 2.095 

1988 8.301 8.131 7.75 6.611 5.848 2.498 

1989 8.733 8.562 7.879 6.843 6.165 2.756 

1990 10.45 10.24 9.503 8.003 7.14 3.23 

Sorted results 

Prob. Peak 96 hr 21 Day 60 Day 90 Day Yearly 

0.032258064516129 15.1 14.78 13.51 11.2 9.825 3.962 

0.0645161290322581 11.8 11.55 10.78 9.021 7.95 3.332 

0.0967741935483871 11.17 11.02 10.23 8.619 7.584 3.23 

0.129032258064516 10.62 10.39 9.518 8.077 7.213 3.122 

0.161290322580645 10.45 10.24 9.503 8.074 7.14 3.1 

0.193548387096774 10.09 9.906 9.322 8.003 7.137 3.029 

0.225806451612903 8.733 8.562 7.879 6.843 6.165 2.756 

0.258064516129032 8.301 8.131 7.75 6.611 5.848 2.713 

0.290322580645161 8.112 7.949 7.399 6.514 5.836 2.63 
23 

0.32258064516129 8.108 7.941 7.326 6.452 5.824 2.498 

0.354838709677419 7.675 7.512 7.037 6.274 5.583 2.491 

0.387096774193548 7.645 7.48 7.005 6.222 5.485 2.439 

0.419354838709677 7.555 7.417 6.962 6.025 5.334 2.402 

0.451612903225806 7.524 7.383 6.832 5.929 5.328 2.364 

0.483870967741936 7.393 7.235 6.611 5.635 5.144 2.349 

0.516129032258065 7.207 7.093 6.555 5.556 5.059 2.344 

0.548387096774194 7.187 7.079 6.54 5.516 4.938 2.341 

0.580645161290323 6.995 6.85 6.443 5.434 4.849 2.332 

0.612903225806452 6.885 6.734 6.322 5.375 4.763 2.19 

0.645161290322581 6.734 6.594 6.144 5.364 4.755 2.19 

0.67741935483871 6.658 6.517 6.144 5.325 4.737 2.134 

0.709677419354839 6.654 6.515 5.991 5.235 4.714 2.123 

0.741935483870968 6.472 6.35 5.967 5.211 4.713 2.112 

0.774193548387097 6.367 6.249 5.876 5.158 4.624 2.095 

0.806451612903226 5.925 5.798 5.548 5.144 4.587 2.086 

0.838709677419355 5.882 5.758 5.449 4.715 4.261 1.963 

0.870967741935484 5.664 5.547 5.083 4.675 4.247 1.962 

0.903225806451613 5.637 5.52 5.066 4.629 4.157 1.952 

0.935483870967742 5.565 5.45 5.005 4.515 4.046 1.947 

0.967741935483871 5.562 5.448 4.99 4.322 3.895 1.939 

0.1 11.115 10.957 10.1588 8.5648 7.5469 3.2192 

 Average of yearly averages: 2.4709 

Inputs generated by pe5.pl - Novemeber 2006 

Data used for this run: 

Output File: Nico_Sorgm 

Metfile: w13996.dvf 

PRZM scenario: KSsorghumSTD.txt 

EXAMS environment file: ir298.exv 

Chemical Name: Nicosulfuron 

Description Variable Name Value Units Comments 

Molecular weight mwt 410.4 g/mol 

Henry's Law Const. henry 3.51e-12 atm-m^3/mol 

Vapor Pressure vapr 5.25e-8 torr 

Solubility sol 8070 mg/L 

Kd Kd mg/L 

Koc Koc 34.95 mg/L 

Photolysis half-life kdp 0 days Half-life 

Aerobic Aquatic Metabolism kbacw 260.62 days Halfife 

Anaerobic Aquatic Metabolism kbacs 177.78 days Halfife 

Aerobic Soil Metabolism asm 253.37 days Halfife 

Hydrolysis: pH 7 606 days Half-life 

Method: CAM 2 integer See PRZM manual 

Incorporation Depth: DEPI cm 

Application Rate: TAPP 0.0683 kg/ha 

Application Efficiency: APPEFF 0.95 fraction 

Spray Drift DRFT 0.2 fraction of application rate applied to pond 

Application Date Date 25-06 dd/mm or dd/mmm or dd-mm or dd-mmm 

Interval 1 interval 7 days Set to 0 or delete line for single app. 

app. rate 1 apprate 0.02625 kg/ha 

Record 17: FILTRA 
24 

 IPSCND 1 

 UPTKF 

Record 18: PLVKRT 

 PLDKRT 

 FEXTRC 0.5 

Flag for Index Res. Run IR Reservoir 

Flag for runoff calc. RUNOFF total none, monthly or total(average of entire run) 
25 

Appendix B – Ground Water Modeling Supporting Documentation 

PRZM-GW Modeling Output File

Figure B-1. PRZM-GW daily aquifer nicosulfuron, IN-HYY21, and IN-37740 

concentration time series chemograph (30-years) for WI Sands scenario. 

SCI-GROW Modeling Input Parameter Values and Output File

Table B-1. SCI-GROW input parameter values for physical chemical and fate 

properties used for nicosulfuron and total toxic residues (IN-HYY21 and IN-37740) 

ground water exposure estimation. 

SCI-GROW Input Parameter Input Value and Unit Source 

Application Methods and Crop Management Input Parameters 

Maximum Application Rate 0.061 lbs. a.i./A Product Label1

Number of Applications 2 Conservative input value based 

on maximum seasonal 

application rate (0.084 lbs. 

a.i./A) 1
26 

Table B-1. SCI-GROW input parameter values for physical chemical and fate 

properties used for nicosulfuron and total toxic residues (IN-HYY21 and IN-37740) 

ground water exposure estimation. 

SCI-GROW Input Parameter Input Value and Unit Source 

Physical Chemical Properties

Soil-Water Partition Coefficient 

(Koc) 

24.0 mL/g MRID 40924222 

EFED Input Parameter Guidance

Median value between: 

DE Sandy Loam – 25.07 mL/g 

NC Sandy Loam – 22.99 mL/g 

IL Silt Loam – 69.36 mL/g 

DE Silt Loam – 22.38 mL/g 

Environmental Fate Properties

Aerobic soil metabolism (t1/2) 142 days MRID 48399928 

EFED Input Parameter Guidance

Median value between2: 

Silt Loam Soil: 175 days 

Silty Clay Loam Soil: 31.1 days 

Denmark Sandy Loam: 142 

days 

France Sandy Loam: 33.6 days 

Germany Loam: 387 days 1

 Identified from proposed label DuPontTM Accent® label. 2

 Half-lives based on total residues including parent nicosulfuron, IN-HYY21, and IN-37740. 

Figure B-2. SCI-GROW output file for nicosulfuron applications to ALS inhibition 

tolerant sorghum. 

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

 

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:nicosulfuron 

 time is 1/13/2014 14:28:45 

 ------------------------------------------------------------------------ 

 Application Number of Total Use Koc Soil Aerobic 

 rate (lb/acre) applications (lb/acre/yr) (ml/g) metabolism (days) 

 ------------------------------------------------------------------------ 

 0.061 2.0 0.122 2.40E+01 142.0 

 ------------------------------------------------------------------------ 

 groundwater screening cond (ppb) = 1.42E+00 

 ************************************************************************ 
27 

Comparison of PRZM-GW Modeling Results to SCI-GROW Modeling Results

Table B-2. Comparison of PRZM-GW and SCI-GROW estimated upper bound 

concentrations in ground water (ppb) for nicosulfuron and degradates of concern 

including IN-HYY21 and IN-37740. 

Exposure Duration 

PRZM-GW 

(ppb) 

SCI-GROW 

(ppb)1

PRZM-GW Magnitude 

Departure from SCIGROW Results2,3

Highest Daily Conc. 

(Acute) 26.3 

1.42 

18.5X 

Post-Breakthrough 

Average Conc. 

(Chronic and Cancer) 

19.2 13.5X 

1 SCI-GROW modeling conservatively assumes that ground water concentrations are uniform over time and 

therefore, acute, chronic, and cancer concentration are the same. 2

 SCI-GROW magnitude departure from PRZM-GW Results = PRZM-GW Conc./SCI-GROW Conc. 

3 PRZM-GW results greater than SCI-GROW results if value >0. PRZM-GW results less than SCI-GROW results 

if value<0. 

 
28 

Appendix C – Formation and Decline of Environmental Degradates of Nicosulfuron 

Table C-1. Nicosulfuron degradation products identified in environmental fate studies.

Degradate 

Identity Structure

Max% of 

Applied 

and Days 

Post 

Application

Comments

Hydrolysis (pH 5 only; Nicosulfuron stable at pH 7 and pH 9) – MRID No. 40924220 

IN-V9367 

or Pyridine Sulfonamide 

2-(aminosulfonyl)-N,Ndimethyl-3-

pyridinecarboxamide 

31.4% at 30 

days 

Detected with 

[Pyridine-2-

14C]Nicosulfuron 

Radiolabel. 

Study was 

terminated at 30 

days. 

IN-J0290 

or Pyrimidine Amine 

4,6-dimethoxy-2-

pyrimidinamine 

32.1% at 30 

days 

Detected with 

[Pyrimidine-2-

14C]Nicosulfuron 

Radiolabel. 

Study was 

terminated at 30 

days. 

DPX-V9360 Ipso Precursor 

2-[(Aminocarbcnyl)(4,6-

dimethoxy-pyrimidin-2-yl)-

amino]-N,N-dimethyl-3-

pyridinecarboxamide 

6.05% at 30 

days 

Detected with 

[Pyrimidine-2-

14C]Nicosulfuron 

Radiolabel. 

Study was 

terminated at 30 

days. 
29 

Table C-1. Nicosulfuron degradation products identified in environmental fate studies.

Degradate 

Identity Structure

Max% of 

Applied 

and Days 

Post 

Application

Comments

Aerobic Aquatic Metabolism (MRID No. 4854304) 

IN-37740 

2-[[(3,4-dihydro-6-methoxy-4-

oxopyrimidin-2-

yl]aminocarbonyl]aminosulfon

yl]-N, Ndimethyl-3-

pyridinecarboxamide 

29.1% at 102 

days 

Detected with 

[Pyridine-2-

14C]Nicosulfuron 

Radiolabel. 

Studies were 

terminated at 102 

days. 

IN-HYY21 or AUSN 

2-[[[[(Aminoiminomethyl) 

amino]carbonyl]amino]sulfony

l]-N,N-dimethyl-3-

pyridinecarboxamide 

6.6% at 102 

days 

Detected with 

[Pyrimidine-2-

14C]Nicosulfuron 

Radiolabel. 

Studies were 

terminated at 102 

days. 

IN-77799 

2-[(Aminocarbonyl) [4-

methoxy-6-(methyldioxy)-2-

pyrimidinyl] amino]-N, N -

dimethyl-3-

pyridinecarboxamide 

3.0% at 102 

days 

Detected with 

[Pyrimidine-2-

14C]Nicosulfuron 

Radiolabel. 

Studies were 

terminated at 102 

days. 

IN-V9367 

or Pyridine Sulfonamide 

2-(aminosulfonyl)-N,Ndimethyl-3-

pyridinecarboxamide 

4.8% at 102 

days 

Detected with 

[Pyridine-2-

14C]Nicosulfuron 

Radiolabel. 

Studies were 

terminated at 102 

days. 
30 

Table C-1. Nicosulfuron degradation products identified in environmental fate studies.

Degradate 

Identity Structure

Max% of 

Applied 

and Days 

Post 

Application

Comments

Anaerobic Aquatic Metabolism (MRID No. 48790905)

IN-37740 

2-[[(3,4-dihydro-6-methoxy-4-

oxopyrimidin-2-

yl]aminocarbonyl]aminosulfon

yl]-N, Ndimethyl-3-

pyridinecarboxamide 

13.9% at 102 

days 

Detected with 

[Pyridine-2-

14C]Nicosulfuron 

Radiolabel. 

Studies were 

terminated at 102 

days. 

IN-V9367 

or Pyridine Sulfonamide 

2-(aminosulfonyl)-N,Ndimethyl-3-

pyridinecarboxamide 

4.8% at 102 

days 

Detected with 

[Pyridine-2-

14C]Nicosulfuron 

Radiolabel. 

Studies were 

terminated at 102 

days. 

IN-R5Q09 

2-[[[[(l,6-Dihydro-4-hydroxy-6-

oxo2-pyrimidinyl)amino]carbonyl] 

amino]sulfonyl]-N-N-dimethyl-3 - 

pyridinecarboxamide) 

6.6% at 102 

days 

Detected with 

[Pyridine-2-

14C]Nicosulfuron 

Radiolabel. 

Studies were 

terminated at 102 

days. 
31 

Table C-1. Nicosulfuron degradation products identified in environmental fate studies.

Degradate 

Identity Structure

Max% of 

Applied 

and Days 

Post 

Application

Comments

Aerobic Soil Metabolism (MRID Nos. 41082622, 46240901, and 49169703)

IN-HYY21 or AUSN 

2-[[[[(Aminoiminomethyl) 

amino]carbonyl]amino]sulfony

l]-N,N-dimethyl-3-

pyridinecarboxamide 

34.6 % at 120 

days in 

neutral soil 

Detected with 

[Pyrimidine-2-

14C]Nicosulfuron 

Radiolabel. 

Study was 

terminated at 120 

days. 

IN-V9367 

or Pyridine Sulfonamide 

2-(aminosulfonyl)-N,Ndimethyl-3-

pyridinecarboxamide 

72.4% at 120 

days in acidic 

soil 

Detected with 

[Pyridine-2-

14C]Nicosulfuron 

Radiolabel. 

Study was 

terminated at 120 

days. 

IN-J0290 

or Pyrimidine Amine 

4,6-dimethoxy-2-

pyrimidinamine 

48.8% at 62 

days in acidic 

soil 

Detected with 

[Pyrimidine-2-

14C]Nicosulfuron 

Radiolabel. 

Study in acidic 

soil was 

terminated at 120 

days. 

IN-GDC42 

2-[[[(Aminocarbonyl) 

amino]carbonylamino] 

sulfonyl]-N,N-dimethyl-3-

pyridinecarboxamide 

7.0% at 90 

and 120 days 

in neutral soil 

Detected with 

[Pyrimidine-2-

14C]Nicosulfuron 

Radiolabel. 

Study in alkaline 

soil was 

terminated at 120 

days. 
32 

Table C-1. Nicosulfuron degradation products identified in environmental fate studies.

Degradate 

Identity Structure

Max% of 

Applied 

and Days 

Post 

Application

Comments

IN-37740 

2-[[(3,4-dihydro-6-methoxy-4-

oxopyrimidin-2-

yl]aminocarbonyl]aminosulfon

yl]-N, Ndimethyl-3-

pyridinecarboxamide 

5.5% at 14 

days in acidic 

soil 

Detected with 

[Pyrimidine-2-

14C]Nicosulfuron 

Radiolabel. 

Study in alkaline 

soils was 

terminated at 120 

days. 

IN-77799 

2-[(Aminocarbonyl) [4-

methoxy-6-(methyldioxy)-2-

pyrimidinyl] amino]-N, N -

dimethyl-3-

pyridinecarboxamide 

3.1% at 30 

days in acidic 

soil 

Detected with 

[Pyrimidine-2-

14C]Nicosulfuron 

Radiolabel. 

Study was 

terminated at 120 

days. 

Anaerobic Soil Metabolism (MRID No. 41082623)

IN-V9367 

or Pyridine Sulfonamide 

2-(aminosulfonyl)-N,Ndimethyl-3-

pyridinecarboxamide 

29.5% at 90 

days in acidic 

soil 

Detected with 

[Pyridine-2-

14C]Nicosulfuron 

Radiolabel. 

Study was 

terminated at 90 

days 

IN-J0290 

or Pyrimidine Amine 

4,6-dimethoxy-2-

pyrimidinamine 

25% at 61 

days in acidic 

soil 

Detected with 

[Pyrimidine-2-

14C]Nicosulfuron 

Radiolabel. 

Study was 

terminated at 90 

days 
33 

Table C-1. Nicosulfuron degradation products identified in environmental fate studies.

Degradate 

Identity Structure

Max% of 

Applied 

and Days 

Post 

Application

Comments

Terrestrial Field Dissipation (MRID No. 43483901) 

IN-V9367 

or Pyridine Sulfonamide 

2-(aminosulfonyl)-N,Ndimethyl-3-

pyridinecarboxamide 

15.85% in 0 -

6 inch soil 

depth at 61 

days in 

Illinois Silty 

Clay Loam 

Soil (acidic) 

5.15% in 0 -6 

inch soil 

depth at 121 

days in 

California 

Sandy Loam 

Soil 

(alkaline) 

Detected with 

[Pyridine-2-

14C]Nicosulfuron 

Radiolabel. 

Studies were 

terminated at 545 

days 

IN-J0290 

or Pyrimidine Amine 

4,6-dimethoxy-2-

pyrimidinamine 

13.4% in 0 - 

6 inch soil 

depth at 61 

days in 

Illinois Silty 

Clay Loam 

Soil (acidic) 

Detected with 

[Pyrimidine-2-

14C]Nicosulfuron 

Radiolabel. 

Study was 

terminated at 545 

days 

*NA means half life unavailable.