UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

January 12, 2012

PC Code: 128845

MEMORANDUM DP Barcode: 391089

SUBJECT: Tier I Drinking Water Assessment for New Use of Thifensulfuron-methyl

on Chicory

FROM: Wm. J. Shaughnessy, Ph.D., Environmental Scientist

Environmental Fate and Effects Division/ERB II (7507P)

THRU: Brian Anderson, Branch Chief

Greg Orrick, Environmental Scientist

Environmental Fate and Effects Division/ERB II (7507P)

TO: Barbara Madden, Risk Manager

Andrew Ertman, Risk Reviewer

Registration Division/RIMUERB (7505P)

The Environmental Fate and Effects Division (EFED) has conducted a Tier I 

Drinking Water Assessment (DWA) of the herbicide thifensulfuron-methyl, also known 

as DPX-M6316 (3-(4-methoxy-6-methyl-1,3,5-triazin-2-

ylcarbamoylsulfamoyl)thiophene-2-carboxylic acid; CAS Reg. No. 79277-67-1) for an 

IR-4 petition (1E7885) for use on chicory. This assessment contains estimated drinking 

water concentrations (EDWCs) for both surface and ground water. Since the predicted 

EDWCs for use of thifensulfuron-methyl on chicory do not exceed those of the maximum 

use pattern on barley, EFED recommends using for dietary assessment the highest 

EDWCs for the use on barley: 4.429 μg/L (acute) and 0.9 μg/L (chronic) for surface 

water and 0.0972 μg/L (acute and chronic) for groundwater.

PREVIOUS ASSESSMENT

In September 2009, EFED completed a drinking water assessment for the proposed 

new use of thifensulfuron-methyl to control broadleaf weeds on safflower1

. In this 

assessment, EFED compared EDWCs for a proposed use on safflower with those 

predicted for an existing use on barley (see attached). 

The maximum application rate and maximum amount applied per season were the 

same in the 2009 assessment, at 0.0188 lbs a.i./A for safflower. Current uses on barley 

allow a maximum single application rate of 0.028 lbs a.i./A with up to two applications 

per season for a seasonal total of 0.056 lbs a.i./A per year. Table 1 contains summary 

information used for comparing EDWCs for thifensulfuron-methyl use on safflower and 

barley.

 

1 Memorandum from Andrew Shelby and Nelson Thurman, ERB2, EFED to Tobi Colvin-Snyder, RD, subj: Tier I 

Drinking Water Assessment for Proposed New Use of Thifensulfuron methyl on safflower, DP Barcode 363089, 

dtd: September 29, 2009.

OFFICE OF CHEMICAL SAFETY

AND POLLUTION PREVENTION
Table 1: Summary of maximum use information for thifensulfuron, based on 

Harmony SG Herbicide labels

USE SINGLE 

APP. RATE 

(lbs a.i./A)

NUMBER 

OF APPS.

SEASONAL 

APP. RATE 

(lbs a.i./A)

INTERVAL 

BETWEEN 

APPS. (days)

APP. 

METHOD

INCORP. 

DEPTH 

(inches)

Safflower 0.0188 1* 0.0188 Not 

Specified*

Aerial or 

Ground 

Spray

0

Barley, 

Fallow**

0.028 2 0.056 14 Aerial or 

Ground 

Spray

0

Source: 2009 DWA

* Given a single application of 0.0188 lbs a.i./A, the seasonal application rate is achieved and only one 

application can occur. Subsequent applications can occur if the maximum application rate is not used. The 

interval between these applications is not specified.

** Thifensulfuron-methyl is currently registered for use on barley through an existing label.

The acute EDWCs in surface water, as predicted by the tier 1 FIRST model, ranged 

from 1.66 (safflower) to 4.43 (barley) μg/L. The chronic EDWCs in surface water 

ranged from 0.34 (safflower) to 0.90 (barley) μg/L. The groundwater EDWC as 

predicted by the SCI-GROW model ranged from 0.03 (safflower) to 0.09 (barley) μg/L. 

Table 2 provides a summary of EDWCs predicted by the FIRST and SCIGROW models 

in the 2009 assessment. The EDWCs for the proposed new use of thifensulfuron-methyl

on safflower were less than the EDWCs for the existing use on barley.

Table 2: Maximum Tier I Estimated Drinking Water Concentrations (EDWCs) for 

drinking water risk assessment based on ground application of thifensulfuron. 

DRINKING WATER 

SOURCE (MODEL 

USED)

USE (rate modeled) MAXIMUM ESTIMATED 

DRINKING WATER 

CONCENTRATION (EDWC) (μg/L)

Groundwater (SCIGROW) Safflower (0.0188 lbs a.i./A; 1 

application)

Acute and Chronic 0.0326

Barley, Fallow (0.028 lbs a.i./A; 

2 applications)

Acute and Chronic 0.0972

Surface water (FIRST) Safflower (0.0188 lbs a.i./A; 1 

application)

Acute 1.656

Safflower (0.0188 lbs a.i./A; 1 

application)

Chronic 0.336

Barley, Fallow (0.028 lbs a.i./A; 

2 applications)

Acute 4.429

Barley, Fallow (0.028 lbs a.i./A; 

2 applications)

Chronic 0.900

EFED concluded that thifensulfuron-methyl is a somewhat persistent chemical that 

partitions readily to water. Acid hydrolysis and photodegradation in water are the 

primary routes of degradation. Rapid leaching is not unlikely because of the low sorption 

coefficients. In soils, hydrolysis under acidic conditions and metabolism will likely be 

the dominant routes of degradation. As a result, while collectively these data suggest that 

some attenuation in the aquatic environment may occur, these data indicate that surface 

and ground drinking water supplies may be impacted by this herbicide. Further, the 

highest surface water EDWC (as predicted by the FIRST model) was from the barley use: 

4.429 ppb (acute) and 0.9 ppb (chronic). The SCI-GROW estimated groundwater EDWC

from the barley use was 0.0972 ppb (acute and chronic).
ANALYSIS

In the current assessment, EFED is assessing the potential for exposure to drinking 

water supplies from the proposed new use of thifensulfuron-methyl on chicory. 

According to the proposed supplemental label2

, the maximum seasonal application rate is 

0.3 oz a.i./A or 0.0187 lbs. a.i./A. This is the same application rate that was proposed for 

use on safflower and assessed in the September 2009 DWA; and is one-third the 

approved rate for use on barley. The supplemental label for use on chicory does not 

specify the method of application; however, EFED assumes that the herbicide can be 

applied in the same manner as described on the labels for use on barely and safflower; 

either through ground or aerial applications. Since the application rate and method 

proposed for chicory are the same as those for safflower, and there have been no changes 

to the environmental fate model input values, EFED expects that model output EDWCs 

will be the same for these proposed uses.

Monitoring Data

EPA’s STORET database reports 82 non-targeted water analyses for thifensulfuronmethyl conducted in Iowa from June to July, 2005 and 26 analyses of aquatic organisms 

in North Dakota from April to August, 1994 (as of Dec. 29, 2011). There were no 

detections in these analyses. Thifensulfuron-methyl is not an analyte in the United States 

Geological Survey’s (USGS) National Water Quality Assessment Program (NAWQA)

program (as of Dec. 29, 2011).

Drinking Water Treatment

No data are available to indicate the effectiveness of drinking water treatment on the 

degradation of thifensulfuron. 

CONCLUSIONS

Since the predicted EDWCs for use of thifensulfuron-methyl on chicory are expected 

to be the same as those predicted in the September 2009 DWA for use on safflower and 

do not exceed those of the maximum use pattern on barley, EFED recommends using for 

dietary assessment the highest EDWCs for the use on barley: 4.429 μg/L (acute) and 0.9 

μg/L (chronic) for surface water and 0.0972 μg/L (acute and chronic) for groundwater.

 

2 DuPont BASIS Herbicide, EPA Reg. No. 352-571; supplemental label.
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C., 20460

MEMORANDUM DATE: 29 September 2009

PC code: 128845

DP #: 363089

SUBJECT: Tier I Drinking Water Assessment for New Use of Thifensulfuron on 

Safflower

FROM: Andrew Shelby, Physical Scientist

Nelson Thurman, Senior Scientist

Environmental Fate and Effects Division/ERB II (MC 7507P)

THRU: Tom Bailey, Branch Chief

Environmental Fate and Effects Division/ERB II (MC 7507P)

TO: Tobi Colvin-Snyder

Registration Division (7505C)

This assessment contains estimated drinking water concentrations (EDWCs) for both surface and 

ground water for thifensulfuron, also known as DPX-M6316 (3-(4-methoxy-6-methyl-1,3,5-

triazin-2-ylcarbamoylsulfamoyl)thiophene-2-carboxylic acid; CAS Reg. No. 79277-67-1) on 

safflower. Assessed here is the parent thifensulfuron compound. Contact Andrew Shelby at 

703-347-0119 if there are any questions. 

EXECUTIVE SUMMARY

Thifensulfuron is an herbicide of the triazinylsulfonylura family. The chemical’s mode of action 

is systemic and inhibits synthesis of amino acids. Current uses of thifensulfuron include wheat, 

barley, oats, soybeans, fallow land, field corn, flax and canola. The pesticide can be applied by 

air or ground. The proposed new use is for broadleaf weed control on safflower. This new use 

assessment is in response to a proposed Section 3 new use of Harmony SG Herbicide in North 

Dakota, South Dakota, Nebraska, Montana (East of Route 87 or East of I-15), and Wyoming 

(East of I-25 or North of I-90).

Screening Concentration in Ground Water (SCIGROW) and FQPA Index Reservoir Screening 

Tool (FIRST) models were parameterized for maximum application rates and used to determine 

Estimated Drinking Water Concentrations (EDWCs). The following table summarizes results 

for hazard maximizing modeling scenarios. 

OFFICE OF CHEMICAL SAFETY

AND POLLUTION PREVENTION
Table 1: Maximum Tier I Estimated Drinking Water Concentrations (EDWCs) for 

drinking water risk assessment based on ground application of thifensulfuron.

DRINKING WATER 

SOURCE (MODEL 

USED)

USE (rate modeled) MAXIMUM ESTIMATED 

DRINKING WATER 

CONCENTRATION (EDWC) 

(ppb)

Groundwater 

(SCIGROW)

Safflower (0.0188 lbs 

a.i./A; 1 application)

Acute and Chronic 0.0326

Barley, Fallow (0.028 lbs 

a.i./A; 2 applications)

Acute and Chronic 0.0972

Surface water (FIRST) Safflower (0.0188 lbs 

a.i./A; 1 application)

Acute 1.656

Safflower (0.0188 lbs 

a.i./A; 1 application)

Chronic 0.336

Barley, Fallow (0.028 lbs 

a.i./A; 2 applications)

Acute 4.429

Barley, Fallow (0.028 lbs 

a.i./A; 2 applications)

Chronic 0.900

The EDWCs for the proposed new safflower use are less than the EDWCs for the highest 

applications for existing uses on barley (Table 1).

Thifensulfuron degrades primarily into two amines: thiophene and triazine. Other common 

degradation routes involve demethylation, hydroxyl substitution or formyl group substitution. 

This drinking water assessment does not take into account the potential toxicity of the primary 

degradates. The extent to which EPA could assess potential contributions of these degradates, if 

necessary, depends on how much information is available on the fate and transport properties of 

the chemicals. However, estimated concentrations of the degradates would be lower than the 

EDWCs for the parent reported in Table 1. 

Though thifensulfuron has many chemical characteristics that would indicate potential concerns 

in groundwater (i.e. low sorption coefficients and degradation half-lives on the order of weeks), 

the low application rate results in low EDWCs in shallow groundwater. The only significant 

data gap for determining EDWCs of thifensulfuron is the determination of an aerobic aquatic 

metabolism half-life. In the absence of this study, EPA derived an estimated rate from the 

aerobic soil metabolism study. This Tier I assessment provides conservative EDWCs. A Tier II 

assessment can take into account specific crop scenarios, refine application methods and account 

for time of application. Better characterization of these parameters would allow for a more 

accurate determination of EDWCs if needed.

PROBLEM FORMULATION

This is a Tier I drinking water assessment that uses modeling and available monitoring data to 

estimate the ground water and surface water concentrations of pesticides in drinking water 

source water (pre-treatment) resulting from pesticide use on sites that are highly vulnerable. 

This initial tier screens out chemicals with low potential risk and provides estimated exposure 

concentrations for the human health dietary risk assessment.
ANALYSIS

Use Characterization

The new use assessed here calls for a maximum application rate and maximum amount applied 

per season of 0.0188 lbs a.i./A for safflower. Applications can occur up to 81 days prior to 

harvest. This new use, like current uses, can be applied aerially or by ground spray. Current 

uses allow application rates up to 0.028 lbs a.i./A and 0.056 lbs a.i./A per year. 

Table 2: Summary of maximum use information for thifensulfuron, based on Harmony SG 

Herbicide labels

USE SINGLE 

APP. 

RATE 

(lbs 

a.i./A)

NUMBER 

OF APPS.

SEASONAL 

APP. RATE 

(lbs a.i./A)

INTERVAL 

BETWEEN 

APPS. 

(days)

APP. 

METHOD

INCORPORATION 

DEPTH (inches)

Safflower 0.0188 1* 0.0188 Not 

Specified*

Aerial or 

Ground 

Spray

0

Barley, 

Fallow

0.028 2 0.056 14 Aerial or 

Ground 

Spray

0

* - Given a single application of 0.0188 lbs a.i./A, the seasonal application rate is achieved and 

only one application can occur. Subsequent applications can occur if maximum application rate 

is not used. The interval between these applications is not specified.

Fate and Transport Characteristics

The primary routes of dissipation for thifensulfuron methyl are acid hydrolysis, photodegradation 

in water and aerobic soil metabolism, with half-lives of 5 to 36 days. The aerobic soil 

metabolism half-lives were 27 days and 36 days. The field dissipation half-lives (based on 

lysimeters) range from 3 to 21 days, and are consistent with the laboratory half-lives. Longer 

half-lives in the field may be associated with cooler temperatures used in the studies. 

Thifensulfuron methyl is also very mobile, and thus may move laterally to surface water or 

downward to ground water.

The rate of degradation due to chemical processes varies widely. The rate of degradation in pH 

5, 7 and 9 aqueous buffered solutions were 5.5, 184, and 145 days, respectively. This indicates 

acid hydrolysis readily occurs. The major degradate was the thiophene portion of the molecule, 

2-ester-3-sulfonamide, which increased until the end of the study. However, the pH did not 

affect the rate of degradation in aqueous photolysis studies, based on dark-control adjusted halflives of 4.9-5.3 days at pH values of 5,7 and 9. The half-lives due to soil photolysis were 41-54 

days, with the major degradates being the intact thiophene (2-ester-3-sulfonamide) and triazine 

(triazine amine) rings of the molecule.

Microbial degradation also appears to degrade parent thifensulfuron methyl. The major 

metabolites were parent compound with hydroxyl and formyl group ring substitutions, the 

thiophene portion of the molecule (cyclized and non-cyclized), and aminotriazine (the triazine 

portion of the molecule). The linear half-lives of the parent compound in aerobic soil were 27 

and 36 days. These aerobic soil half-life estimates were determined from a slightly acidic soil 

and a slightly alkaline soil. A more alkaline soil would provide a more conservative estimate of 

aerobic soil metabolism by assuring that an acid hydrolysis effect is not occurring. There is 

some indication that an acid hydrolysis effect is occurring in the referenced soils as empirical 

DT50 and DT90 values are substantially smaller for the slightly acidic soil when compared to the 
slightly alkaline soil. Further, an alkaline soil would be more representative of upper great plains 

soils relevant to this assessment. Thus, it is possible persistence in some areas relevant to this 

assessment may be greater than that predicted by the referenced studies. 

In anaerobic aquatic conditions, the half-lives ranged from 19 to 29 days, forming 2-ester-3-

sulfonamide. Triazine amine was also formed and increased until the end of the study (365 

days). In the field, the degradates O-demethyl DPX-M6316 and 2-ester-3-sulfonamide were 

present in all four test sites, and remained in the top 5 inches of soil primarily. In stainless steel 

cylinders of silt loam soil, triazine amine (from applied chlorsulfuron) reached 23.5-24.9% of 

applied by 4-8 weeks after treatment, and mostly occurred in the top 10 cm.

Sorption of thifensulfuron methyl was studied in four soils using the batch equilibrium method. 

The chemical was very mobile in soils with Kd values of 0.08 to 1.38 mL/g. Desorption values 

were similar, ranging from 0.27 to 1.69 mL/g. Adsorption was related to soil organic carbon 

content (r2 = 0.71). KOC values ranged from 7.4 to 32 mL/g o.c. In soil columns, the mobility of 

thifensulfuron was studied in five soils. In sandy loam, silt, loamy sand, and silt loam soils, 72-

96% of applied thiophene-labeled thifensulfuron was present in the leachate of soil columns, 

while only 3-28% was present in soils. In silt loam soil, 69% of triazine-labeled thifensulfuron 

was present in the leachate and 31% was present in the soils columns. Virtually all radioactivity 

in leachate was present as parent compound, while 29% was parent-acid in the silt loam soil. No 

other metabolites reached significant levels.

Table 3: Summary of physical/chemical and environmental fate and transport properties of 

thifensulfuron.

PARAMETER VALUE(S) (units) SOURCE COMMENT

Chemical Name 3-(4-methoxy-6-methyl-1,3,5-

triazin-2-

ylcarbamoylsulfamoyl)thiophen

e-2-carboxylic acid

Molecular Weight 373.36

Solubility (250C) 2.24 g/L at pH 7

Vapor Pressure 

(250C)

5.6 x 1011 mm Hg MRID 

47141802

pKa 4.0 MRID 

47141802

Octanol-Water 

Partition 

Coefficient (KOW)

0.018 MRID 

47141802

Hydrolysis HalflifepH 5 5.5 days

pH 7 184 days

pH 9 145 days

MRID 

00145151

MRID 

00161284

Aqueous 

Photolysis Halflife

5.3 days

5.7 days

MRID 

00161285

pH 7

Soil Photolysis 

Half-life

41 days

55 days

MRID 

00161286

Thiopene label

Triazine label

Aerobic Soil 

Metabolism Halflife

t1/2: 27.3 days; 36.1 days

DT50: 7-14 days; <3.5 days

DT90: 28-42 days; 3.5-7 days

tinput = 41.3

MRID 

00145154

Flanagan silt loam (pH 7.5); 

Keyport silt loam (pH 6.4)

n

t s

t t 90,n-1

input = 1/2 + per 

2002 Input Parameter 

Guidance
Anaerobic 

Aquatic 

Metabolism Halflife

29 days

21 days

19 days

MRID 

00161288

Loamy sand (pH 4.9)

Sandy loam (pH 7.5)

Silt loam (pH 6.5)

Aerobic Aquatic 

Metabolism Halflife

2 x 41.3 = 82.6 days Data gap 2 x aerobic soil metabolism 

half-life parameter per 2002 

Input Parameter Guidance

Organic Carbon 

Partition 

Coefficient (KOC)

7.4 ml/g o.c.

9.1 ml/g o.c.

32 ml/g o.c.

17 ml/g o.c.

MRID 

00161290

Sandy loam (pH 6.6)

Sandy loam (pH 6.5)

Silt loam (pH 5.4)

Silt loam (pH 5.2)

Terrestrial Field 

Dissipation Halflife

linear

<1 day

2.8 days

2.0 days

0.8 day

MRID 

00161291 Loam (pH 6.5)

Silt loam (pH 6.4)

Silty clay loam (pH 7.3)

Silty clay loam (pH 7.9)

Drinking Water Exposure Modeling

SCIGROW (Screening Concentration in Ground Water) is a regression model used as a 

screening tool to estimate pesticide concentrations found in ground water used as drinking water. 

SCIGROW 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 Ground 

Water studies; the RILP is a function of aerobic soil metabolism and the soil-water partition 

coefficient. The output of SCIGROW represents the concentrations that might be expected in 

shallow unconfined aquifers under sandy soils, which is representative of the ground water most 

vulnerable to pesticide contamination likely to serve as a drinking water source.

FIRST (FQPA Index Reservoir Screening Tool) is a metamodel of PRZM and EXAMS used as a 

screening tool to estimate pesticide concentrations found in surface water used as drinking water. 

FIRST was developed by making multiple runs of PRZM using varying sorption coefficients and 

determining the concentration in the EXAMS index reservoir scenario after a two-inch single 

storm event. (The Index Reservoir is a standard water body used by the Office of Pesticide 

Programs to assess drinking water exposure (Office of Pesticide Programs, 2002). It is based on 

a real reservoir (albeit not currently in active use as a drinking water supply), Shipman City Lake 

in Illinois, that is known to be vulnerable to pesticide contamination.) The single runoff event 

moves a maximum of 8% of the applied pesticide into the reservoir. This amount can be reduced 

by degradation or effects of binding to soil in the field. Additionally, FIRST can account for 

spray drift and adjusts for the area within a watershed that is planted with the modeled crop 

(Percent Crop Area). Spray drift (modeled as direct deposition of the pesticide into the reservoir) 

is assumed to be 16% of the applied active ingredient for aerial application, 6.3% for orchard air 

blast application, and 6.4% for other group spray application. Despite being a single event 

model, FIRST can account for spray drift from multiple applications. The default agricultural 

Percent Cropped Area (PCA) is 87%. The PRZM scenario used for FIRST development was 

among the most vulnerable, and thus resulting surface water concentrations represent the upper 

bound values on the concentrations that might be found in drinking water from the use of a 

pesticide.

Modeling Approach and Input Parameters

Input parameters were determined based on “Guidance for Selecting Input Parameters in 

Modeling the Environmental Fate and Transport of Pesticides” (Version II, February 28, 2002). 

The following tables display input parameters for SCIGROW and FIRST models respectively 
and provide explanation for the determination of the parameter. 

Table 4: SCIGROW (v2.3) input parameters for thifensulfuron use on safflower

PARAMETER (units) VALUE(s) SOURCE/RATIONALE

Maximum Application Rate (lbs 

a.i./A)

0.0188 Proposed label

Number of Applications per 

Year

1 Maximum application rate matches 

maximum application per season

Organic Carbon Partition 

Coefficient (KOC;mL/g o.c.)

9.1 MRID 00161290 ; Median non-sand value

Aerobic Soil Metabolism Halflife (days)31.7 MRID 00145154; 1st Order Degradation

Table 5: FIRST (v1.1.0) input parameters for thifensulfuron use on safflower

PARAMETER (units) VALUE(s) SOURCE/RATIONALE

Application rate (pounds 

a.i. acre-1)

0.0188 Proposed label

Number of applications 

(per year)

1 Maximum application rate matches maximum 

application per season

Application interval 

(days)

N/A

Percent Crop Area 0.87 Since no PCA has been determined, 0.87 is the 

recommended value from Guidance

KOC 7.4 MRID 00161290; Minimum non-sand value, 

2002 Input Parameter Guidance

Aerobic soil t1/2 (days) 41.3 MRID 00145154;

1st Order Degradation

n

t s

t t 90,n-1

input = 1/2 +

per 2002 Input Parameter Guidance

Is the pesticide wettedin?No

Method of application A Aerial application

Depth of incorporation 

(inches)

0 Section 3 label?

Solubility (mg/L) 2,240 MRID 47141802

Aerobic aquatic t1/2

(days)

82.6 2 x (aerobic soil metabolism parameter) per 

2002 Input Parameter Guidance

Photolysis half-life 

(days)

5.7 pH 7, MRID 00161285

Modeling Results

SCIGROW concentration (ppb) represents the groundwater concentration that might be expected 

in shallow unconfined aquifers under sandy soils. Output is used for both acute and chronic 

endpoints.

FIRST concentrations (ppb) represent untreated surface water concentrations. The one-in-10-

year peak day concentration is used for acute endpoints and the one-in-10-year average 

concentration is used for chronic endpoints.
The estimated concentrations provided in this assessment are conservative estimates of 

concentrations in drinking water. If dietary risks require refinement, higher tiered crop-specific 

models and modeling scenarios can be used.

Table 6: Maximum Tier I Estimated Drinking Water Concentrations (EDWCs) for 

drinking water risk assessment based on ground application of thifensulfuron.

DRINKING WATER 

SOURCE (MODEL 

USED)

USE (rate modeled) MAXIMUM ESTIMATED 

DRINKING WATER 

CONCENTRATION (EDWC) (ppb)

Groundwater 

(SCIGROW)

Safflower (0.0188 lbs a.i./A; 

1 application)

Acute and Chronic 0.0326

Barley, Fallow (0.028 lbs 

a.i./A; 2 applications)

Acute and Chronic 0.0972

Surface water (FIRST) Safflower (0.0188 lbs a.i./A; 

1 application)

Acute 1.656

Safflower (0.0188 lbs a.i./A; 

1 application)

Chronic 0.336

Barley, Fallow (0.028 lbs 

a.i./A; 2 applications)

Acute 4.429

Barley, Fallow (0.028 lbs 

a.i./A; 2 applications)

Chronic 0.900

Monitoring Data

For most compounds, modeled concentrations in surface water and ground water are generally 

higher than monitored concentrations because the frequency of sampling is inadequate to catch 

high concentrations and samples may not be taken in high use areas. Comparison of monitoring 

and modeling is not possible for thifensulfuron because EFED is not aware of any monitoring 

data.

Drinking Water Treatment

No data are available to indicate the effectiveness of drinking water treatment on the degradation 

of thifensulfuron. 

CONCLUSIONS

Thifensulfuron is a somewhat persistent chemical that partitions readily to water. Though it 

degrades through many processes, acid hydrolysis and photodegradation in water appear to be 

the primary routes of degradation. Photolysis can be short-circuited if leaching to groundwater is 

rapid or where the surface water bodies limit light penetration. Rapid leaching is not unlikely 

given the indicated low sorption coefficients. These concerns, however, are allayed given the 

low application rate considered in this assessment. In soils, hydrolysis in acidic conditions and 

metabolism will likely be dominant routes of degradation.