-2 of 75

• Aerobic soil metabolism (OPPTS guideline # 835.4100) – guideline requirements are 

partially fulfilled; additional data with supplemental study are needed. 

• Hydrolysis (OPPTS guideline #835.2120) – Existing study remains valid, but additional 

hydrolysis data are being requested. 

The available ecological effects data are considered incomplete for the purposes of risk 

assessment. The following data gaps exist:

• Terrestrial plant reproduction study (non-guideline)

• Fish acute toxicity test, freshwater (850.1075) – typical end-use product

• Aquatic invertebrate acute toxicity test, freshwater daphnids (850.1010) – typical 

end-use product

See the attached assessment for additional details on the current data gaps for environmental fate 

and ecological effects.
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Problem Formulation for the Environmental Fate and 

Ecological Risk, Endangered Species, and Drinking 

Water Assessments in Support of the Registration 

Review of Halosulfuron-methyl

methyl 5-{[(dimethoxy-2-pyrimidinyl) amino] carbonylaminosulfonyl -3-chloro -1-methyl-1-Hpyrazole-4-carboxylate

PC Code: 128721

Prepared by:

Michael Barrett, Senior Chemist, ERB5

Amanda Solliday, Biologist, ERB5 U. S. Environmental Protection Agency

Office of Pesticide Programs

Environmental Fate and Effects Division

Environmental Risk Branch IV

1200 Pennsylvania Ave., NW

Mail Code 7507P

Washington, DC 20460

Reviewed by:

Keith Sappington, Senior Advisor, ERB5

Mohammed Ruhman, Senior Fate Scientist, ERB5

Bill Shaughnessy Environmental Scientist, ERB 2

Brian Kiernan, Biologist, ERB 6

Mah Shamim, Branch Chief, ERB 5
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Table of Contents

1. Purpose........................................................................................................................................ 5

2. Problem Formulation .................................................................................................................. 6

2.1. Nature of Regulatory Action................................................................................................ 6

2.2. Previous Risk Assessments.................................................................................................. 7

3. Stressor Source and Distribution ................................................................................................ 8

3.1. Mechanism of Action....................................................................................................... 8

3.2. Overview of Pesticide Use and Usage ............................................................................. 8

3.3. Environmental Fate and Transport..................................................................................... 12

3.4. Bioaccumulation ............................................................................................................ 17

4. Receptors................................................................................................................................... 17

4.1. Effects to Aquatic Organisms............................................................................................ 18

4.2. Effects to Terrestrial Organisms........................................................................................ 22

4.3. Incident Database Review.................................................................................................. 26

4.4. Ecosystems Potentially at Risk .......................................................................................... 27

5. Assessment Endpoints .............................................................................................................. 28

6. Conceptual Model..................................................................................................................... 28

6.1. Risk Hypothesis................................................................................................................. 29

6.2. Conceptual Diagram .......................................................................................................... 29

7. Analysis Plan ............................................................................................................................ 31

7.1. Stressors of Concern .......................................................................................................... 32

7.2. Measures of Exposure........................................................................................................ 33

7.3. Measures of Effect ............................................................................................................. 36

7.4. Integration of Exposure and Effects .................................................................................. 36

7.5. Deterministic and Probabilistic Assessment Methods....................................................... 37

7.7. Endangered Species Assessment ....................................................................................... 38

7.8. Drinking Water Assessment .............................................................................................. 39

7.9. Environmental Monitoring Data ........................................................................................ 39

8.0. Preliminary Identification of Data Gaps............................................................................ 40

8.1. Environmental Fate........................................................................................................ 40

8.2. Ecological Effects.......................................................................................................... 42

9. References................................................................................................................................. 46

Appendix A. Justification for Special Studies............................................................................. 55

Appendix B. Chemical structures of halosulfuron-methyl and selected environmental degradates

....................................................................................................................................................... 58

Appendix C. Aquatic Toxicity Predictions of Halosulfuron-Methyl and Major Degradates from 

Structure-Activity Relationships (SARs) using the ECOSAR Class Program and Review of 

Available Data .............................................................................................................................. 62
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1. Purpose

The purpose of this problem formulation is to provide an understanding of the environmental fate 

and ecological effects of the registered uses of halosulfuron-methyl (PC Code 128721). 

Halosulfuron-methyl belongs to the sulfonylurea (SU) class of herbicides and is applied for 

selective control of annual and perennial broadleaf weeds and sedges at a variety of crop and 

non-crop sites. Crop registration sites include corn, cotton, nuts, rice, sorghum, soybeans, 

squash, sugarcane, and fruiting vegetables. In addition to the agricultural food uses, 

halosulfuron-methyl is also registered for use on turfgrass, ornamentals, and a variety of noncrop areas including, but not limited to, airports, cemeteries, fallow non-crop areas, golf courses, 

landscaped areas, public recreation areas, residential and commercial lawns, sod or turf farms, 

sports fields, tennis courts, race tracks, fairgrounds, and rights-of-way. This herbicide can be 

applied as a pre-and post-emergence treatment, and tank-mixed with other compatible herbicides

to increase the weed control spectrum. 

Halosulfuron-methyl is an acetolactate synthase (ALS) inhibitor. ALS is an important enzyme 

for the synthesis of branched chain amino acids, and this metabolic pathway is present only in 

plants. Halosulfuron-methyl is absorbed by the foliage and roots in plants.

Halosulfuron methyl is a sulfonylurea herbicide in which the sufonylurea moiety serves as a 

“bridge” between aminopyrimidine (the “R2” moiety on the -NH- side of bridge) and pyrazole 

(“R1” on the -SO2- side of bridge) ring structures in the molecule as shown below. 

R1-SO2-NH-CO-NH-R2 

Generic Molecular Structure for Sulfonylurea Herbicides

Halosulfuron Structure

This document will provide a plan for analyzing data relevant to halosulfuron-methyl and for 

conducting environmental fate and ecological risk, endangered species, and drinking water 

assessments for its registered uses. Additionally, this problem formulation is intended to identify 
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data gaps, uncertainties, and potential assumptions used to address those uncertainties relative to 

characterizing the ecological risk associated with the registered uses of halosulfuron-methyl. 

2. Problem Formulation

2.1. Nature of Regulatory Action

Under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), all pesticides distributed 

or sold in the United States generally must be registered by the Environmental Protection 

Agency (EPA). As part of determining whether a pesticide can be registered in the U.S., the 

Agency evaluates its safety to non-target species based on a wide range of environmental and 

health effects studies. In 1996, FIFRA was amended by the Food Quality Protection Act, and the 

Agency was mandated to implement a new program for the periodic review of pesticides, i.e., 

Registration Review (http://www.epa.gov/oppsrrd1/registration_review/). The Registration 

Review program is intended to ensure that, as the ability to assess risk evolves and as policies 

and practices change, all registered pesticides continue to meet the statutory standard of no 

unreasonable adverse effects to human health and the environment. Changes in science, public 

policy, and pesticide use practices occur over time. Through the Registration Review program, 

the Agency periodically reevaluates pesticides to make sure that as change occurs, products in 

the marketplace can be used safely. 

As part of the implementation of the Registration Review program pursuant to Section 3(g) of 

the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA), the Agency is beginning its 

evaluation of halosulfuron-methyl to determine whether it continues to meet the FIFRA standard 

for registration. This problem formulation for the environmental fate, ecological risk, 

endangered species, and drinking water assessment chapter in support of the Registration Review 

will be posted in the initial docket, which will open the public phase of the review process.
-7 of 75

2.2. Previous Risk Assessments

Halosulfuron-methyl was first registered in 1994 for use on various crops including: corn, cotton, 

nuts, rice, sorghum, soybean, squash, sugarcane, and fruiting vegetables. Non-crop uses are 

registered on turf, grasses grown for seed ornamentals, residential and commercial lawns, rightsof-way and commercial premises and equipment. Like most sulfonylurea herbicides, 

halosulfuron-methyl has a high potential to move off-site by spray drift, runoff and via windblown soil particles. 

Because halosulfuron-methyl was not registered until 1994, the Agency did not prepare a 

Reregistration Eligibility Decision for this chemical. The latest full ecological risk assessment

for halosulfuron-methyl was conducted in 2002 for a Section 3 new use on alfalfa within the 

states of California, Arizona, Oklahoma, Texas, New Mexico, Kansas, Arkansas and Colorado 

with a maximum single application rate of 0.047 lbs a.i./A (D313402). In that assessment, use of 

halosulfuron-methyl did not result in acute or chronic risk for mammals, freshwater fish, aquatic 

invertebrates, or estuarine/marine invertebrates that exceeded Agency levels-of-concern. 

Although chronic risk to birds could not be assessed at the time because avian reproduction 

studies had not been submitted, direct acute risk to avian species was not expected to be a 

concern. Halosulfuron-methyl is classified as non-toxic to terrestrial invertebrates on an acute 

contact basis. In the 2002 assessment, the primary ecological concern for halosulfuron is the

direct acute risk to terrestrial and aquatic plants and the potential for indirect effects to aquatic 

and terrestrial animals through possible habitat alteration.

In December 2009, EFED conducted an ecological risk assessment for new use on soybeans 

(DP358030 and DP358032). Because of demonstrated concerns for effects on plants well 

outside treatment areas from spray drift for similar sulfonylurea herbicides, this assessment 

provided new risk estimations for terrestrial and aquatic plants. Based on the single maximum 

application rate for soybeans (0.0625 lbs ai/A) for aerial and ground applications, the risk 

quotients (RQs) ranged from 13-520 for terrestrial plants, 110-2900 for semi-aquatic plants, 85-

160 for aquatic vascular plants and 0.87-6.0 for algal species. Aerial application resulted in the 

higher RQs. Levels-of-concern were exceeded for listed and non-listed terrestrial and aquatic 

plants. All risk conclusions for other taxa relied upon the 2002 assessment.

In May 2010, EFED completed the most recent Section 3 new use assessment of halosulfuronmethyl on dried shelled peas & beans (except soybean), succulent shelled peas & beans, apples, 

rhubarb, bushberry, fruiting vegetables and tuberous & corm vegetables (D366537). No changes 

were made to conclusions from the 2009 assessment because the application rate, number of 

applications and interval between applications were each similar to or less than currently 

registered uses.
-8 of 75

For drinking water, the latest exposure assessment was conducted in August 2010 (DP Barcode: 

D366411); estimated concentrations for this assessment remained the same as in the previous 

assessment in June 2009 (DP Barcode: D358032). The acute exposure concentrations estimated 

with the FIRST model ranged up to 8.3 ppb or ug/L for halosulfuron-methyl on corn and 

sugarcane. Chronic exposure (annual average EDWC) estimates were also calculated for the 

corn and sugarcane use pattern and ranged up to 1.7 ppb. Tier 1 EDWCs for ground-water (using 

the SCI-GROW model) were significantly lower (0.065 ppb or less).

3. Stressor Source and Distribution

3.1. Mechanism of Action

Halosulfuron-methyl belongs to the sulfonylurea herbicide family. The common mode of action 

for these herbicides is acetolactate synthase (ALS) enzyme inhibition in affected plant species. 

The ALS enzyme is important for the synthesis of branched chain amino acids (leucine, 

isoleucine, and valine). ALS inhibition in plants adversely affects plant growth and 

reproduction, most intensely in meristematically-active tissues. Although acetolactate is present 

in mammals, the biosynthesis of branch chain amino acids occurs only in plants and, in general, 

SU herbicides are far less toxic to animals than plants.

3.2. Overview of Pesticide Use and Usage

Labeled Use

Halosulfuron-methyl is a pre- or post-emergence herbicide and it is applied after emergence of 

target weeds. This herbicide selectively controls many weed species at very low rates including 

a variety of large- and small-seeded broadleaf weeds and annual and perennial sedges. 

Halosulfuron-methyl is formulated as water dispersible granules and emulsifiable, flowable and 

soluble concentrates. 

The maximum annual application rate for any of the current uses is 0.125 lb ai/A, and single 

applications may be made at a rate as high as 0.094 lb ai/A (i.e., use on apple west of the 

Rockies). Table 1 provides a synopsis of the current use patterns, noting that the registrant is 

asked to review the table and correct the assumed numbers and clarify labels where factors such 

as minimum application intervals are not explicitly stated on the label.
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Table 1. Registered uses of halosulfuron-methyl

Crop Use Pattern

Single Application Rate (lbs 

a.i/A) Number 

Of Applic./ 

season

Total Application Rate 

(lbs a.i/A)

d

Minimum Application 

Intervals (days)

PHI

c, d Minimum Maximum Season Year Days

Alfalfa (CA & AZ only) 0.031 0.047 2 0.094 0.094 NS NS

Apples (east of the Rockies)3 0.023 0.047 2 0.094 0.094 NS 14

Apples (west of the Rockies) 0.023 0.047 2 0.094 0.094 NS 14

Apples (west of the Rockies) 0.023 0.094 1 0.094 0.094 NS 14

Asparagus 0.023 0.07 2 0.094 0.094 NS 1

Beans (dry) 0.023 0.047 2 0.047 0.094 NS NS

Beans (Succulent snap beans incl. lima 

beans) 0.031 0.063 2 0.063 0.125 NA NS

Beans and pea Dry shelled (east of the 

Rockies) 0.023 0.031 3 0.047 e 0.094 NS e 30

Beans and pea Dry shelled (West of the 

Rockies) 0.023 0.047 2 0.047 0.094 NS 30

Bushberry 0.023 0.047 2 0.094 0.094 45 60

Corn (Field for seed; non-IR) 0.031 0.063 2 0.125 0.125 NS 30

Corn (Pioneer Hybrid IR for seed) 0.063 0.094 2 0.125 0.125 NS 30

Corn (Sweet and Pop) 0.031 0.047 2 0.078 0.078 NS 30

Cotton 0.031 0.063 1 0.063 0.063 NS 28

Cucurbits (Cucumbers) 0.023 0.047 2 0.047 0.094 NS 30

Cucurbits (Cantaloupes, Honeydews, 

Crenshaw & Melons) 0.023 0.047 2 0.047 0.094 NS 57

Cucurbits (Pumpkins, Winter Squash) 1) 0.023 0.047 2 0.047 0.094 NS 30

Cucurbits (Watermelons) h 0.023 0.047 2 0.047 0.094 NS 57

Fallow ground 0.031 0.063 2 0.125 0.125 NS NA

Pea and bean, succulent shelled, subgroup 6B 0.023 0.023 1 0.023 0.023 NA NS

Rhubarb 0.023 0.047 2 0.047 0.047 NA 60
-10 of 75

Crop Use Pattern

Single Application Rate (lbs 

a.i/A) Number 

Of Applic./ 

season

Total Application Rate 

(lbs a.i/A)

d

Minimum Application 

Intervals (days)

PHI

c, d Minimum Maximum Season Year Days

Rice NS 0.063 2 0.063 a 0.063 NS

48 (69 in 

CA)

Sorghum (Grain) NS 0.047 1 0.047 0.047 NA 30

Soybeans 0.031 0.063 2 0.125 b 0.125 NS NS

Soybeans NS 0.063 2 0.125 0.125 150 NS

Sugarcane 0.031 0.063 3 0.125 0.125 NS 30

Tree nuts 0.031 0.063 2 0.125 0.125 NS 1

Turf grass sod and seed farms 0.031 0.063 2 0.125 0.125 42 NA g

Vegetable (tuberous and corm, subgroup l C) 0.023 0.047 2 0.047 0.047 NA 45 f

Vegetables, Fruiting (Chile And Bell 

Peppers) 0.023 0.047 2 0.094 0.094 NS 30

Vegetables, Fruiting (including eggplant, 

tomatoes, peppers, & Okra) 0.023 0.047 2 0.094 0.094 NS 30 a This is the apparent intent of the label but it is not explicitly mandated on the label. b This is the apparent intent of the label but it is not explicitly mandated on the label.

c NA = not applicable.

d NS = not specified.

e Although these are the limits stated on the label, the label also states “Make only one Sandea application per crop cycle”. It does not appear to be possible to 

have more than 2 crops per year. 

f The label states “If needed, make a second post-emergence foliar application 45 days before harvest” without any further elaboration. g The label states “A second treatment may be required 6 to 10 weeks after the Initial treatment.”

h Only: AL, AR, AZ, CT, DE, FL, GA, IL, IN, KS, KY, LA,MA, MD, ME, MI, MO, MS, NC, NH, NJ, NY, OH, OK, PA, RI, SC, TN,TX, VA, VT, WV, WI
-11 of 75-

Label information requests

Label information that would help inform the risk assessment include: specific maximum 

application rate (per application and per year); maximum number of applications allowed; 

defined application intervals; ASABE S-572 droplet size spectra; and other drift management 

language.

Usage

From 1998-2010, the crops with the most usage in terms of total pounds of active ingredient 

applied were corn and rice accounting for about 83% of usage during this period1

Figure 1

 With the 

addition of several new uses in recent years, it is possible that other crop uses sites will increase 

in importance in the future. Other registered uses include a large number of grain, fruit, and 

vegetable row crops, apples, and turf, fallow, and landscape uses. Possible geographic 

distribution and intensity of usage may be indicated from the acreage distribution of the two 

crops with the highest usage: corn and rice. and Figure 2 2show the distribution of 

planted acres for corn and rice crops, respectively, in the United States (2010 data in 

acres/county).

Figure 1. Corn for all purposes acres planted in the US in 2010 (USDA-NASS).

 1 BEAD Chemical Profile for Registration Review: Halosulfuron-methyl (128721); memorandum dated 9/2/2011. 2 Source: http://www.nass.usda.gov/Charts_and_Maps/Crops_County/index.asp#cs .
-12 of 75-

Figure 2. Rice acres planted in the US in 2010 (USDA-NASS).

3.3. Environmental Fate and Transport

The Agency has completed a review of all available data submitted by the registrant as part of 

registration review; the guidelines noted below are considered data gaps. At this time, the 

following environmental fate guidelines are not fulfilled for halosulfuron-methyl and are 

considered data gaps. The fate data gaps are: 

• Aerobic soil metabolism (OPPTS guideline # 835.4100) – additional data with 

supplemental study are needed to further investigate the change in soil metabolism rate 

with study conditions. 

• Hydrolysis (OPPTS guideline #835.2120) – current study acceptable, but additional 

data are needed with a supplemental study to further investigate the change in rate with 

study conditions. 

A rationale for and details of these requirements are provided in Section 8.1. In general, as 

discussed below, the behavior of parent halosulfuron methyl is highly variable from site to site, 

as evidenced by the variance in results regarding its persistence and mobility between laboratory 

and field data and consequently data in addition to the minimum guidelines are requested under 

Guidelines 835.4100 and 835.2120.

Halosulfuron-methyl has properties with regards to persistence and sorptivity that allow for a 

potential for residues to occur in ground and surface waters at some sites where conditions favor 
-13 of 75-

greater persistence and mobility of the parent molecule. Some degradates of halosulfuronmethyl may be present in the environment for months or longer (see Appendix A for chemical 

structures and see Table 3 for a summary of conditions under which the degradates have been 

observed in significant amounts). The identified degradates are also not included in the residues 

of concern for drinking or ecological exposure. A more complete environmental fate picture is 

provided below.

The environmental fate profile for halosulfuron-methyl is complex, indicating highly variable 

persistence, significant mobility in many soils, and/or the presence of a number of degradation 

products in the environment. A summary of halosulfuron-methyl chemical and environmental 

fate properties is provided in Table 2. Additionally, a summary of the formation and decline of 

halosulfuron-methyl degradation products is provided in Table 3. Furthermore, direct studies 

with the degradates (available only for adsorption/desorption characteristics) are summarized in 

Table 4. 

Table 2. Chemical and Physical Properties and Environmental Fate Properties of 

Halosulfuron-methyl.

Parameter Value Reference (MRID #) 

/Comment

Physical/Chemical Parameters

CAS Registry Number 100184-20-1 47442201

Molecular mass 434.81 42139402

42139403

42139404

42661401

42661402

43237101

47442201

47442203

Vapor pressure (25°C) 0.0000001 (1 x 10E-7)

Henry’s Law Constant (dimensionless, 

calculated) 1.08 X 10-09

Water solubility (25°C) (mg/L)

15 pH 5

1650 pH 7

Octanol-water partition coefficient (Log KOW) -0.0186 (Kow= 1)

Dissociation Constant (pKa) 3.44

Mobility

Soil Partitioning Coefficient (Koc) mL/g 31 to 199 in 4 soils:

Drummer silt loam(Mollisol)

= 94

Sarpy sandy loam (Entisol)

= 114

Spinks loamy sand (Alfisol)

= 199

Sable silty clay loam (unknown)= 

31

42139411

41356336

Soil Partitioning Coefficient (Kd) 0.32 to 3.6 42139411

41356336

Persistence in Water

Hydrolysis half-life (25°C, pH 5, 7, & 9); days pH 5 = 27

pH 7 = 14

pH 9 = 0.75

42139409

42846801 (Follow-up)
-14 of 75-

Parameter Value Reference (MRID #) 

/Comment

Aqueous photolysis half-life (25°C); days Stable 42661409

Aerobic aquatic metabolism half-life; days ND (study is currently in review) 45671701

Anaerobic aquatic metabolism half-life; days 29 42661411

Persistence in Soil

Aerobic soil metabolism half-life (25°C); days 11 to 16 (2 soils); 

DT90 values were 63 and 110 

days.

42139410

42846802 (Follow-up)

Soil photolysis 16.2 (may be due to non-photolytic 

degradation)

42661410

Field Dissipation

Field dissipation half-life; days 4 to 64 (7 sites) 42661412

42661413

42661414

42661415 (Stor. Stabil.)

42976302

42976303

42976304

43699801

Field dissipation half-life; days (pipe lysimeter 

studies)

15-81 (2 sites with 4 treatment 

types per site)

42976303 and 

42661414

Aquatic field dissipation total water and soil halflife in days (dry- and wet-field applied, 

respectively, for the LA and CA test sites.)

Registrant used a non-linear model 

to calculate as follows:

LA: DT50 = 1.30, DT90 = 6.48

CA: DT50 = 1.87, DT90 = 12

Half-life 7.2 to 14.5 days using 

pseudo 1st

44437304

order model.

Aquatic Bioconcentration

Bioconcentration Factor (BCF) in fish No Data None

Bioconcentration Factor (BCF) in crayfish No Data None

Table 3. Summary of formation and decline information on halosulfuron methyl 

degradates from environmental fate studies.

Degradate: > 10% for 3 months or more?

(Maximum % of applied in parenthesis; time periods are in days or months after the 

application of halosulfuron-methyl to the soil or water)

Study 3-chlorosulfonamide 

ester

3-chlorosulfonamide 

acid

Aminopyrimidine halosulfuronmethyl 

guanidine

halosulfuronmethyl 

rearrangement 

ester

Hydrolysis 

(1-month 

study)

Persistent, low pH -- Persistent low pH -- Persistent, high 

pH
-15 of 75-

Degradate: > 10% for 3 months or more?

(Maximum % of applied in parenthesis; time periods are in days or months after the 

application of halosulfuron-methyl to the soil or water)

Study 3-chlorosulfonamide 

ester

3-chlorosulfonamide 

acid

Aminopyrimidine halosulfuronmethyl 

guanidine

halosulfuronmethyl 

rearrangement 

ester

Aerobic 

soil

Yes, 1 of 2 soils (up to 

29%) 

Yes, 1 of 2 soils (up to 

32%)

Yes, 1 of 2 soils (up 

to 27%)

Yes, 1 of 2 

soils (up to 

15%)

No (up to 11%)

Anaerobic 

aquatic 

soil

Yes (up to 92%) No Yes (up to 78%) No No

Field 

"pipe" 

lysimeter, 

IA 

Yes (up to 19%, & up to 

11% at 4 months)

No. (always <8%) No (usually <5% 

max.)

No No (but up to 

28% as late as 4 

months)1

Field 

"pipe" 

lysimeter, 

NC 

No (but up to 24% in 1st No (but up to 18% in 1

30 days).

st No (but up to 18% 

30 days) in 1st

No

30 days)

No

Traditiona

l field 

dissipation 

(164-1)

Residues of each of the degradates were below the quantification limit of 5 ppb; field persistence cannot be 

evaluated from these studies. 

Soil 

photolysis

2

(1-month 

study)

Persistent, up to 37% No Persistent, up to 

36%

No No

Aqueous 

photolysis

(1-month 

study)

5

Persistent, up to 31% No Persistent, up to 

28%

No No

 1

Substantial amounts of rearrangement acid were found (Up to 21% in one treatment), total amounts of rearrangement acid plus rearrangement 

ester were often 20 to 30% of the applied halosulfuron-methyl from columns analyzed over the first 4 months.

2

Most of the degradation did not appear to be due to photolysis.
-16 of 75-

Table 4. Summary of direct environmental fate studies with halosulfuron-methyl 

degradates.

Parameter Value Reference (MRID #) 

/Comment

Soil Partitioning Coefficient (Kd

(degradation products)

) chlorosulfonamide acid, -0.03 to 0.16 

chlorosulfonamide ester: 0.75 to 6.85

aminopyrimidine: 2.32 to 165.6

42139411

In the two available aerobic soil metabolism studies, there was relatively rapid degradation of 

halosulfuron-methyl. Both aerobic soil metabolism half-lives and hydrolysis rates were only a 

few weeks under the conditions tested (Table 2). Hydrolysis rates may be significantly slower at 

lower pH and lower temperatures than tested and may also be affected by the complex soil 

matrix under field conditions. At least one published study suggests that the hydrolysis rate for 

this molecule may be slower than under either mildly acidic or mildy alkaline conditions.3 In the 

field dissipation studies there are clear indications of very long (i.e., up to two or three years) 

persistence of halosulfuron residues at some sites. First, in some of the field studies a significant 

portion of the applied halosulfuron-methyl persisted for several months or longer. Here a pseudo 

first-order kinetic model poorly described the data and severely under predicted the residue 

levels remaining several months to a year or more after application. Additionally, possible 

recognition of the danger of residues persisting at phytotoxic levels for an extended period is 

captured in label restrictions that prohibit rotation into many crops for up to 3 years after the last 

application of halosulfuron-methyl.

Halosulfuron-methyl is quite mobile in most soils. Soil organic carbon partition coefficients 

(Kocs) for halosulfuron-methyl parent were 31 to 199 in four soils; the median value was 104. If 

the median mobility and persistence values in these studies are representative of the behavior of 

halosulfuron-methyl in the majority of the prospective use area, then halosulfuron-methyl would 

only have a modest leaching potential in the majority of the use area. It is important to note that 

the degree of adsorption in soils may have a correlation with soil pH (i.e., tendency for lower Kd

or other sorption coefficients with increasing pH) similar to the behavior of other sulfonylureas 

that are weak acids. However, soil organic carbon content also appears to be an important factor 

in determining the degree of adsorption/desorption4. 

Halosulfuron-methyl can apparently be both mobile and highly persistent in at least some soils 

and is probably more likely to be both in more alkaline soils. Field dissipation rates at some 

study sites were slower than the metabolism rates measured in laboratory studies (Table 2). 

Dissipation rates may be faster than degradation rates because some loss of pesticide from the 

 3 Zheng, W., S.R. Yates, and S.K. Papiernik. Transformation Kinetics and Mechanism of the Sulfonylurea 

Herbicides Pyrazosulfuron Ethyl and Halosulfuron Methyl in Aqueous Solutions J. Agric. Food Chem. 2008, 56, 

7367–7372. 4 Among the published references on this subject is a study specifically directed at this variability for halosulfuronmethyl: 

Kuwatsuka, D.S. and I. Yamamoto. 1997. Journal of Pesticide Science Vol.22(4):288-292.- Relationships between 

Soil Properties and Sorption Behavior of the Herbicide Halosulfuron-methyl in Selected Japanese Soils.
-17 of 75-

treated zone of soil may be by mechanisms other than degradation (leaching, volatilization, 

irreversible adsorption, runoff, and lateral movement). However, the dissipation rate cannot be 

more rapid than the degradation rate in the field, because degradation is one of the dissipation 

processes.

Of several environmental degradates all are fragments of the parent molecule (i.e., containing 

either the pyrimidine or pyrazole moieties, but not both due to cleavage of the sulfonylurea 

bridge) with the exception of the "halosulfuron-methyl rearrangement ester", sometimes referred 

to as "RRE" or "MON 5781." This product results from the abstraction of the S02NHCO moiety 

between the rings, such that the pyrimidine and pyrazole rings are then joined together only by 

an NH group. These degradates are not included in the ecological or drinking water residues of 

concern. 

For additional details on the environmental fate, the reader is referred to the most comprehensive 

previous review of halosulfuron as provided in an August 13, 2002 Risk Assessment (including 

drinking water) by EFED (DP Barcode D2784495

); subsequent assessments rely upon this 

environmental fate review.

 3.4. Bioaccumulation

There are no bioconcentration or bioaccumulation studies for halosulfuron-methyl in fish or 

other aquatic animals. However, the chemical properties of halosulfuron-methyl (e.g., soil Koc 

less than 200, Kow= 1) imply a low bioconcentration potential. Therefore, these studies are not 

required.

4. Receptors

Consistent with the process described in the Overview Document (USEPA 2004), the risk 

assessment for halosulfuron-methyl relies on a surrogate species approach. Toxicological data 

generated from surrogate test species are used to extrapolate the potential effects on a variety of 

species (receptors) included under these taxonomic groupings. Available studies are classified as 

acceptable, supplemental or invalid, depending upon the suitability of the data for risk 

assessment purposes.

Acute and chronic toxicity data from studies submitted by the pesticide registrant, along with the 

available open literature, will be used to evaluate the potential direct and indirect effects of 

halosulfuron-methyl to aquatic and terrestrial receptors. Open literature studies are primarily 

identified through EPA’s ECOTOX database, which employs a literature search engine for 

locating chemical toxicity data for aquatic and terrestrial plants and wildlife. This includes 

toxicity on the technical grade active ingredient, degradates, and when available, formulated 

products. The evaluation of both sources of data may also provide insight into the direct and 

indirect effects of halosulfuron-methyl usage on biotic communities from loss of species that are 

 5 DP Barcodes: D278449; D273885; D261707; D271575. Expanded Section 3 and IR-4 Uses To Add Asparagus, 

Flowering Vegetables and Beans to Halosulfuron-methyl Label (August 14, 2002).
-18 of 75-

sensitive to the chemical and from changes in structure and functional characteristics of the 

affected communities.

A summary of the aquatic and terrestrial toxicity data available for the species most sensitive to 

halosulfuron-methyl is provided in Sections 4.1 and 4.2, respectively. In addition, a summary of 

ecological incidents associated with halosulfuron-methyl and a description of ecosystems 

potentially at risk are provided in Sections 4.3 and 4.4, respectively. 

Toxicity to fish, aquatic-phase amphibians and aquatic invertebrates is categorized using the 

system shown in Table 5 (US EPA, 2004). Toxicity to terrestrial fauna (birds, reptiles, 

terrestrial-phase amphibians and mammals) is categorized using the system shown in Table 6. 

Toxicity categories for plants have not been defined.

Table 5. Categories of Acute Toxicity for Aquatic Animals

LC50 (ppm) Toxicity Category

< 0.1 Very highly toxic

> 0.1 - 1 Highly toxic

> 1 - 10 Moderately toxic

> 10 - 100 Slightly toxic

> 100 Practically nontoxic

Table 6. Categories of Acute Toxicity for Terrestrial Animals

LD50 (mg/kg) LC50 (ppm) Toxicity Category

<10 <50 Very highly toxic

10-50 50-500 Highly toxic

51-500 501 - 1000 Moderately toxic

501-2000 1001 - 5000 Slightly toxic

>2000 >5000 Practically nontoxic

If open literature toxicity studies for halosulfuron-methyl are identified through ECOTOX, they 

will be reviewed for the risk assessment. 

4.1. Effects to Aquatic Organisms

The most sensitive of the available aquatic toxicity data from registrant-submitted studies are 

provided in Table 7. 

Based on the available information, halosulfuron-methyl technical is classified as no more than 

slightly toxic to fish and invertebrates on an acute exposure basis. No aquatic toxicity data is 

available for halosulfuron-methyl typical end-use products on fish or aquatic invertebrates. 

Available data indicate both vascular and nonvascular aquatic plants are affected by 

halosulfuron-methyl at low levels of exposure.
-19 of 75-

Table 7. Aquatic Toxicity Profile for Halosulfuron-methyl

Taxonomic Group Species Endpoint Acute Toxicity 

Classification

MRID Reference

and 

Study 

Classification

Freshwater fish

Lepomis 

macrochirus

(Bluegill sunfish)

96-hour LC50 > 

118 mg a.i./L Practically nontoxic 42661422

Acceptable

Oncorhynchus

mykiss

(rainbow trout)

NOAEC = 34 

mg a.i./L

LOAEC = 106 

mg a.i./L 

---a 43493001

Acceptable

Freshwater 

invertebrates

Daphnia magna

(Water flea)

EC50 > 107 mg 

a.i./L Practically nontoxic 42661423

Acceptable

NOAEC = 0.98 

mg a.i./L

LOAEC = 1.8 

mg a.i./L

---a 43493003

Acceptable

Estuarine/marine fish

Cyprinodon 

variegatus

(Sheepshead 

minnow)

LC50 Practically nontoxic >125 mg 

a.i./L

42773001

Supplemental

Estuarine/marine 

invertebrates

Crassostrea 

virginica

(Eastern oyster) and

Americamysis bahia

(Mysid shrimp)

EC50= 94 mg 

a.i./L (oyster)

EC50= 109 mg 

a.i./L (shrimp)

Slightly toxic to 

practically nontoxic

42773003, 

Acceptable 

and 

42773002, 

Acceptable

Vascular aquatic 

plants

Lemna gibba

(duckweed)

EC50

NOAEC = 

0.023 μg a.i./L

= 0.042 μg 

a.i./L

---b 43330701

Acceptable

Nonvascular aquatic 

plants

Pseudokirchneriella 

subcapitata

(Green algae)

EC50

NOAEC = 0.63 

μg a.i./L

= 4.1 μg 

a.i./L ---b 43330702

Acceptable

a Chronic toxicity categories have not been defined.

b Toxicity categories for plants have not been defined.

On an acute basis, halosulfuron-methyl is practically non-toxic to freshwater and 

estuarine/marine fish. The 96-hour LC

Fish

50 > 118 mg a.i./L for bluegill sunfish and 96-hour LC50 > 

131 mg a.i./L for rainbow trout (MRIDs 42661422 and 42661423). For both acute studies with 

freshwater fish, no effects were observed at any treatment level. For the estuarine/marine test 

species, sheepshead minnow, the 96-hour LC50 > 125 mg a.i./L (MRID 42773001). However, 

this study was classified as supplemental information because a precipitate formed at in the test 

solution and it is unclear from the study report if the solids were included in the analytical 

samples. No treatment-related effects were observed at any test concentration. An additional 

study is not requested at this time, because the bioavailable fraction of halosulfuron-methyl in 
-20 of 75-

this study would have to be approximately 5 orders of magnitude lower than the measured 

concentrations to approach the maximum peak expected exposure concentration of 5.68 μg a.i./L 

estimated in the previous risk assessments (DP358030 and DP358032). 

In addition, the registrant submitted two additional acute fish studies, one with rainbow trout and 

one with bluegill sunfish. These studies were determined to be supplemental information only, 

due to lack of confidence in the measured chemical concentrations as a result of the poor 

solubility of the test material. 

Based on a submitted early-life stage study with rainbow trout, chronic effects to freshwater fish, 

such as reductions in post-hatch length and weight, were observed at higher levels of exposure to 

halosulfuron-methyl. In this study, the NOAEC is 34 mg a.i./L and a LOAEC is 106 mg a.i./L 

(43493001).

No data have been submitted that examine the chronic effects of halosulfuron-methyl to 

estuarine/marine fish. However, there is no indication of increased a sensitivity of 

estuarine/marine fish compared to freshwater fish, as halosulfuron-methyl was practically 

nontoxic to both taxa on an acute basis. Therefore, the available data does not suggest that a 

greater sensitivity to halosulfuron-methyl for estuarine/marine fish species on a chronic basis

would exist.

On an acute basis, halosulfuron-methyl is practically non-toxic to freshwater and 

estuarine/marine invertebrates. In a study with freshwater daphnids, the 48-hour EC

Aquatic Invertebrates

50 was 

greater than 107 mg a.i./L (MRID 42661423). In studies with estuarine/marine invertebrates, the 

48-hour EC50 was 109 mg a.i./L for mysid and the 48-hour EC50 was 94 mg a.i./L for the eastern 

oyster (MRIDs 42773002 and 42773003).

In a chronic study with freshwater daphnids, the NOAEC was 0.98 mg a.i./L and LOAEC was

1.8 mg a.i./L, based on reduced length of the test organisms (43493003). In another chronic 

study with daphnids, the NOAEC could not be determined due to the adverse effects observed at 

all treatment levels. The LOAEC was 6.9 mg a.i./L, the lowest concentration tested, based on 

effects to growth and offspring production (MRID 43493002).

No data have been submitted that examine the chronic effects of halosulfuron-methyl on 

estuarine/marine invertebrates. However, there is no indication of increased sensitivity of 

estuarine/marine invertebrates compared to freshwater invertebrates, as halosulfuron-methyl was 

practically nontoxic to both taxa on an acute basis. The level at which no adverse effects were

observed in the chronic freshwater study with aquatic invertebrates, 0.98 mg a.i./L, is over 2 

orders of magnitude higher than the maximum 21-day expected exposure concentration of 5.43 

μg a.i./L estimated in the previous risk assessments (DP358030 and DP358032). Therefore, 

additional chronic data for estuarine/marine invertebrates is not requested at this time.

Vascular and Nonvascular Aquatic Plants
-21 of 75-

Halosulfuron-methyl exhibits phytotoxic activity towards aquatic vascular and nonvascular 

plants. In a study with halosulfuron-methyl technical, the EC50 was 0.042 μg a.i./L for 

duckweed (Lemna gibba), based on frond counts and nominal concentrations at a pH of 6.4 

(MRID 43330701). The registrant submitted another study examining the effects of 

halosulfuron-methyl technical on Lemna gibba and this study is in review (MRID 46004101). 

Four algal toxicity studies are available for the chemical, with an EC50 range from 4.1 μg a.i./L

for freshwater algae (Selenastrum capricornutum), 110 μg a.i./L for the freshwater algae 

(Anabaena flos-aquae), >350 μg a.i./L for the freshwater diatom (Navicula pelliculosa) to >400 

μg a.i./L for the marine diatom (Skeletonema costatum) (MRIDs 43330702, 43330703, 

43330704 and 43330705).

Various degradates of parent halosulfuron have been identified from the various fate studies, as 

previously highlighted in Table 3. From the list of degradates that have been identified, only 

five of them are considered major degradates with formation rates at or above 10% of the applied 

parent compound. The structures of these four halosulfuron methyl metabolites with 

demonstrated environmental persistence were entered into the ECOSAR v.1.0 model. These 

metabolites are halosulfuron aminopyrimidine (CP 17477), 3-chlorosulfonamide ester (CP 

147925), 3-chlorosulfonamide acid (CP 147924) and the halosulfuron rearrangement ester (CP 

151790). For context, the parent model is also included in the predicted toxicity analysis. The 

ECOSAR output and parameterization with available toxicity information are included in 

Appendix C.

Degradate Toxicity to Aquatic Organisms

Cleavage of the sulfonylurea bridge (-NH-CO-NH-SO2-) between the two ring structures in the 

parent compound is predicted to result in degradates that are either not phytotoxic or require 

relatively higher residues to affect plant growth. This assumption is supported by the predicted 

toxicity results, which indicate lower degradate toxicity to algae, as compared to the parent 

compound. The halosulfuron rearrangement ester (CP 147925 or CP 151790) contains a 

contracted sulfonylurea bridge, but this compound is also predicted to be substantially less toxic 

than the parent compound to aquatic taxa.

Based on the results of this analysis, the degradates of halosulfuron-methyl have lower predicted 

toxicity to other aquatic organisms than the parent compound. One exception is the predicted 

toxicity of the degradate halosulfuron aminopyrimidine to daphnids. The predicted toxicity for 

the aniline structure in this compound is 2.4 mg/L, compared to 20 mg/L predicted toxicity for 

the pyrazole structure of halosulfuron methyl. These are the lowest (most sensitive) ECOSARpredicted values for each compound. However, this toxicity estimate for halosulfuron 

aminopyrimidine is still substantially lower than the predicted exposure aquatic estimates for the 

parent compound in previous assessments, and the formation of halosulfuron aminopyrimidine is 

expected to form at even lower concentrations than the parent compound.

See Section 7.1 Stressors of Concern of this document for more information on how the 

degradate compounds will be analyzed in the upcoming risk assessment.
-22 of 75-

4.2. Effects to Terrestrial Organisms

Table 8 summarizes the most sensitive terrestrial toxicity endpoints for halosulfuron-methyl, 

based on an evaluation of the submitted data. 

Summary

Halosulfuron-methyl is classified as practically nontoxic to terrestrial birds based on the 

available acute oral and subacute dietary exposure studies. An acute oral study with a passerine 

species is not requested at this time for the upcoming ecological risk assessment. The submitted 

reproductive studies for this chemical also indicate low chronic toxicity to birds. Halosulfuronmethyl is classified as practically nontoxic to mammals on an acute oral exposure basis. Chronic 

effects were observed in submitted developmental toxicity studies with rats and rabbits, but at 

levels that were higher than predicted exposure concentrations. Halosulfuron-methyl is 

classified as practically nontoxic to honey bees (Apis mellifera) on an acute contact exposure 

basis. Halosulfuron-methyl causes adverse effects on terrestrial plants at low levels of exposure.

Table 8. Terrestrial Toxicity Profile for Halosulfuron-methyl.

Taxonomic 

Group

Surrogate Species

(Common Name) Endpoint Acute Toxicity Classification

MRID Reference 

and

Study Classification

Birds Colinus 

virginianus

(Bobwhite quail)

LD50 Practically nontoxic > 2210 mg 

ai/kg bw

42139434

Acceptable

Colinus 

virginianus

(Bobwhite quail)

and 

Anas 

platyrhynchos

(mallard duck)

LC50 Practically nontoxic >5620 mg 

ai/kg diet

42139435, Acceptable 

and 

42139436, Acceptable

Colinus 

virginianus

(Bobwhite quail)

and 

Anas 

platyrhynchos

(mallard duck)

NOAEC = 1010 

mg a.i./kg diet

LOAEC > 1010 

mg a.i./kg diet

---a

47792801, Acceptable

and 

47792802, Acceptable

Mammals Rattus norvegicus

(Laboratory rat)

LD50

(males)

= 3170 

mg/kg Practically non toxic 42139414

Acceptable

(rabbit)

Oryctolagus 

cuniculus

NOAEL = 50 mg 

ai/kg/day ---a 42139426

Acceptable
-23 of 75-

Taxonomic 

Group

Surrogate Species

(Common Name) Endpoint Acute Toxicity Classification

MRID Reference 

and

Study Classification

LOAEL = 150 mg 

ai/kg/day

Terrestrial 

Invertebrates Apis mellifera

(Honey bee)

LD50 Practically nontoxic (contact) > 

98.2 μg a.i./bee

42139440

Acceptable

Terrestrial Plants 

Monocots –

ryegrass, corn, oat, 

onion (most 

sensitive in 

seedling 

emergence and 

vegetative vigor)

Dicots – soybean, 

tomato, cucumber, 

cabbage, lettuce 

(most sensitive in 

seedling 

emergence)

and radish (most 

sensitive in 

vegetative vigor) 

Seedling 

emergence

Monocots

EC25

NOAEC = 

0.000094 lbs 

a.i./A 

= 0.00063 

lbs a.i./A

Dicots

EC25

NOAEC = 

0.000012 lbs 

a.i./A

= 0.000020 

lbs a.i./A

---

42661424 (addendum 

43195501), 

Acceptable

b

Monocots

Vegetative vigor

EC25

NOAEC = 

0.000035 lbs 

a.i./A

= 0.00075 

lbs a.i./A

Dicots

EC25

NOAEC = 

0.000018 lbs 

a.i./A

= 0.000057 

lbs a.i./A

---

42661425 (addendum 

43195502), 

Acceptable

b

a Chronic toxicity categories have not been defined.

b Toxicity categories for plants have not been defined.

The results of the single acute oral toxicity study available for halosulfuron-methyl indicate that 

the chemical is practically non-toxic to avian species on an acute oral basis. The acute oral LD

Birds

50

value for bobwhite quail (Colinus virginianus) is >2210 mg a.i./kg bw, based on nominal 

concentrations and corrected for percent active ingredient of the test substance (MRID 

42139434, acceptable). No mortality was observed at any treatment level. At the lowest and the 

second highest dose (287 and 1326 mg ai/kg bw) of five treatment levels, observations of 

toxicity effects included lethargy, depression, reduced reaction to external stimuli, 
-24 of 75-

submissiveness, wing droop, loss of coordination, lower limb weakness, prostrate posture, 

shallow and rapid respiration and convulsions on Day 0 following dosing. No weight loss or 

feed consumption was observed in any treatment level, compared to the control birds. 

No acute avian oral study with halosulfuron-methyl has been submitted for passerine species.

However, additional acute oral data with a passerine species is not requested at this time. Due to 

the low application rates for halosulfuron-methyl, the modeled peak dose-based exposure 

concentrations for birds (36 mg a.i./kg bw based on 2 application at the maximum rate of 0.125 

lbs a.i./A) is two orders of magnitude lower than the levels at which no mortality was observed 

in the submitted acute oral study with bobwhite quail (2210 mg a.i./kg bw). Therefore, 

information on the toxicity of halosulfuron-methyl to additional avian species is unlikely to 

influence the upcoming ecological risk assessment conclusions.

The results of the two sub-acute dietary toxicity studies available for halosulfuron-methyl 

indicate that it can be classified as practically non-toxic to avian species on a short-term dietary 

basis. The LC50 is greater than 5620 mg a.i./kg bw for bobwhite quail (Colinus virginianus) 

(MRID 42139436). In a dietary study conducted with mallard ducks (Anas platyrhynchos), the 

LC50 is also greater than 5620 mg a.i./kg bw (MRID 42139435). In both submitted avian dietary 

studies, the NOAEC was 5620 mg a.i./kg body weight, based on no observations of mortality or 

other sublethal effects. 

No treatment-related effects were observed in the submitted reproduction studies with either 

bobwhite quail (Colinus virginianus) or mallard ducks (Anas platyrhynchos) at measured test 

concentrations up to 1010 mg a.i./kg diet (MRIDs 47792801 and 47792802).

A number of mammalian toxicity studies have been submitted for halosulfuron-methyl. Two 

acute oral studies are available, conducted with the laboratory rat. In the submitted study with 

halosulfuron-methyl technical, the LD

Mammals

50 > 10,435 mg a.i./kg bw in males, LD50 > 7758 mg 

a.i./kg bw in females and LD50 > 8866 mg a.i./kg bw for both sexes combined (MRID 

42139413). In another submitted acute oral study, rats were exposed to the halosulfuron-methyl 

product MON 12051 (50% active ingredient), resulting in an LD50 = 3170 mg a.i./kg bw in 

males, LD50 > 6000 mg a.i./kg bw in females and LD50 > 4704 mg a.i./kg bw for both sexes 

combined (MRID 42139414).

Inhalation and dermal toxicity studies were also submitted for laboratory rats. Two acute dermal 

studies were conducted on the laboratory rat. In the submitted study with halosulfuron-methyl 

technical, the LD50 >2000 mg ai/kg bw for each sex (MRID 42139415). In another submitted 

dermal study with the product MON 12051, the LD50 >5000 mg a.i./kg bw for each sex 

(42139416). Two inhalation studies with halosulfuron-methyl are also available. In the 

submitted inhalation study with halosulfuron-methyl technical, the LD50 was greater than 6.0 mg 

ai/L for each sex (MRID 42139417). In another submitted inhalation study with the product 

MON 12051, the LD50 >4.8 mg a.i./kg bw for each sex (42139418).
-25 of 75-

Based on the available submitted studies examining the acute effects of halosulfuron-methyl and 

the product MON 12051 to rats, the chemical shows low toxicity via oral, dermal and inhalation 

routes of exposure.

Several chronic mammalian studies have also been submitted for halosulfuron-methyl. In two 

developmental toxicity studies, halosulfuron-methyl technical was administered orally by gavage 

to two different species –laboratory rats (dose administered on gestation days 6 though 15) and 

rabbits (dose administered on gestation days 6 through 19). In the rat study, the NOAEL = 250 

mg a.i./kg/day and LOAEL = 750 mg a.i./kg/day based on decreases in maternal body weight 

gain, maternal food consumption, litter size and fetal body weight (MRID 42139425). Rabbits 

appear to be more sensitive than rats to chronic exposures of halosulfuron-methyl, with a 

NOAEL = 50 mg a.i./kg/day and a LOAEL = 150 mg a.i./kg/day based on decreases in maternal 

body weight gain, maternal food consumption and litter size (MRID 42139426). When the 

results of these toxicity studies are adjusted for the weight of the typically-modeled mammals 

(15 g, 35 g and 1000 g), the adjusted NOAELs are 110, 89 and 38 mg a.i./kg bw, respectively. 

These adjusted NOAELs are higher than the modeled peak dose-based exposure concentrations 

for mammals, 54, 37 and 9 mg a.i./kg bw for the 15 g, 35 g and 1000 g mammals, respectively 

(based on 2 application at the maximum rate of 0.125 lbs a.i./A). Therefore, chronic dietary risk 

concerns for mammals are not expected based on this preliminary screen, using the maximum 

application rate of halosulfuron-methyl and most sensitive chronic mammalian toxicity endpoint 

available.

In a multigenerational reproductive study with rats, dietary exposure of halosulfuron-methyl 

technical resulted in a NOAEL = 800 mg a.i./kg diet and a LOAEL = 3600 mg a.i./kg diet, based 

on decreases in body weight and food consumption of both parental sexes (MRID 42139427). 

No reproductive effects (effects to offspring) were observed at the highest test concentration of 

3600 mg a.i./kg diet.

A single study examining the effects of halosulfuron-methyl on terrestrial invertebrates has been 

submitted. In an acute contact study with honey bees, the LD

Terrestrial Invertebrates

50 >98.2 μg a.i./bee, corrected for 

percent active ingredient of the test substance (MRID 42139440). Mortality of bees did not 

exceed 4% in either the negative or solvent control, or any treatment level.

Phytotoxic effects to terrestrial plants are observed at exposure levels of halosulfuron-methyl 

several orders of magnitude lower than label rates. In a submitted seedling emergence study, the 

most sensitive EC

Terrestrial Plants

25 = 0.00002 lbs ai/A, based on effects to lettuce dry weight (MRIDs 42661424 

and 43195501). Both monocots and dicots were affected by low levels of exposure to 

halosulfuron-methyl. For the most sensitive monocot species, onion, the EC25 is 0.00063 lbs 

a.i./A and the NOAEC is 0.000094 lbs a.i./A based on reductions in plant dry weight.

In vegetative vigor toxicity studies, radish was the most sensitive species, with an EC25 = 

0.000057 lbs ai/A and NOAEC of 0.000018 lbs a.i./A, based on adverse effects to plant dry 
-26 of 75-

weight (MRIDs 42661425 and 43195502). For the most sensitive monocot species, onion, the 

EC25 is 0.00075 lbs a.i./A and the NOAEC is 0.000035 lbs a.i./A based on reductions in plant 

dry weight. The overall toxicological sensitivity of the tested plant species indicates that many 

nontarget plant species may be susceptible if exposed to halosulfuron-methyl. 

4.3. Incident Database Review

A review of the Ecological Incident Information System (EIIS, v. 2.1) and Aggregate Incident 

databases for ecological incidents involving halosulfuron-methyl was completed on September 6, 

2011. This database consists of exposure incident reports submitted to the EPA from 1994 to 

present. A search for halosulfuron-methyl was also conducted in the American Bird 

Conservancy’s Avian Incident Monitoring System (AIMS), which contains publicly available 

data on reported avian incidents involving pesticides:

(http://www.abcbirds.org/abcprograms/policy/toxins/aims/aims/index.cfm). 

No incidents for halosulfuron-methyl were reported in either the EIIS or the AIMS database. 

The number of reports listed in the EIIS database is believed to be only a small fraction of the 

total incidents involving organism mortality and damage caused by pesticides. Few resources 

are assigned to incident reporting. Reporting by states is only voluntary, and individuals 

discovering incidents may not be informed on the procedure of reporting these occurrences. 

Much of the database is generated from registrant-submitted incident reports. In addition, 

incident reports for non-target organisms typically provide information only on mortality events 

and plant damage incidents. Except for phytotoxic effects in terrestrial plants, sublethal effects 

for organisms such as reduced growth or impaired reproduction are rarely reported. Because of 

these logistical difficulties, EIIS is most likely a minimal representation of all pesticide-related 

ecological incidents.

Registrants are legally required to provide detailed reports of only “major” ecological incidents 

involving pesticides, while “minor” incidents are reported aggregately. Based on 40 CFR 

§159.184, an ecological incident is considered major and must be submitted to the Agency by the 

registrant if any of the following criteria are met:

Fish or wildlife:

(A) Involves any incident caused by a pesticide currently in Formal Review6

(B) Fish: Affected 1,000 or more individuals of a schooling species or 50 or more 

individuals of a non-schooling species. 

for 

ecological concerns. 

 6 Formal Review means Special Review, Rebuttable Presumption Against Registration (RPAR), FIFRA 

section 6(c) suspension proceeding, or FIFRA section 6(b) cancellation proceeding, whether completed or 

not.
-27 of 75-

(C) Birds: Affected 200 or more individuals of a flocking species, or 50 or more 

individuals of a songbird species, or 5 or more individuals of a predatory species. 

(D) Mammals, reptiles, amphibians: Affected 50 or more individuals of a 

relatively common or herding species or 5 or more individuals of a rare or solitary 

species. 

(E) Involves effects to, or illegal pesticide treatment (misuse) of a substantial tract 

of habitat (greater than or equal to 10 acres, terrestrial or aquatic). 

Plants: 

(A) The effect is alleged to have occurred on more than 45 percent of the acreage 

exposed to the pesticide.

All ecological incidents classified as ‘minor’ only need to be aggregately reported as quarterly 

counts of incidents by the registrant(s). Ecological incidents reported in aggregate reports 

include those categorized as ‘minor fish and wildlife’ (W-B), ‘minor plant’ (P-B), and ‘other 

non-target’ (ONT) incidents. ‘Other non-target’ incidents include reports of adverse effects to 

insects and other terrestrial invertebrates. 

For halosulfuron-methyl, two minor plant incidents have been reported. The first reported 

incident occurred in 1999, and involved the product Permit. The second reported incident 

involved Manage Turf Herbicide, and occurred in 2000. Unless additional information on these 

aggregated incidents becomes available, they will be assumed to be representative of registered 

uses of halosulfuron-methyl in the risk assessment.

4.4. Ecosystems Potentially at Risk

The ecosystems at risk are often extensive in scope; therefore, it may not be possible to identify 

specific ecosystems during the development of a nation-wide ecological risk assessment. 

However, in general terms, terrestrial ecosystems potentially at risk could include the treated 

field and immediately adjacent areas that may receive drift or runoff. Areas adjacent to the 

treated field could include cultivated fields, fencerows and hedgerows, meadows, fallow fields or 

grasslands, woodlands, riparian habitats and other uncultivated areas. 

Aquatic ecosystems potentially at risk include water bodies adjacent to or downstream from the 

treated field and could include impounded bodies such as ponds, lakes and reservoirs, or flowing 

waterways such as streams or rivers. For uses in coastal areas, aquatic habitat also includes 

marine ecosystems, including estuaries. 
-28 of 75-

5. Assessment Endpoints

Assessment endpoints are defined as “explicit expressions of the actual environmental value that 

is to be protected.”7

 Selection of the assessment endpoints is based on valued entities (fish, 

birds, etc.), the ecosystems potentially at risk (such as water bodies, riparian vegetation, and 

upland habitats), the migration pathways of halosulfuron-methyl (runoff, drift, etc.), and the 

routes by which ecological receptors are exposed to halosulfuron-methyl (direct contact, dietary 

exposure, inhalation, etc.).

Assessment endpoints for halosulfuron-methyl include direct toxic effects on the survival, 

reproduction, and growth of the receptors, as well as indirect effects, such as reduction of the 

prey base or modification of habitat. Each assessment endpoint requires one or more “measures 

of ecological effect,” defined as changes in the attributes of an assessment endpoint or changes in 

a surrogate entity or attribute in response to exposure to a pesticide. Specific measures of 

ecological effect are generally evaluated based on acute and chronic toxicity information from 

registrant-submitted guideline tests that are performed on a limited number of organisms. 

Additional ecological effects data from the open literature will also be considered.

6. Conceptual Model

For a pesticide to pose an ecological risk, it must reach ecological receptors in biologically 

significant concentrations. An exposure pathway is the means by which a pesticide moves in the 

environment from a source to an ecological receptor. For an ecological pathway to be complete, 

it must have a source, a release mechanism, an environmental transport medium, a point of 

exposure for ecological receptors, and a feasible route of exposure.

The conceptual model for halosulfuron-methyl provides a written description (risk hypothesis) 

and visual representation (conceptual diagram) of the predicted relationships between 

halosulfuron-methyl, potential routes of exposure, and the predicted effects for the assessment 

endpoint. A conceptual model consists of two major components: risk hypothesis and a 

conceptual diagram (USEPA 1998b).

Based on the available data (including those from valid but limited studies, and considering 

existing data gaps), the persistence of halosulfuron-methyl in the environment is highly variable. 

Laboratory and field studies showed that persistence in some soil environments was significantly 

greater than would be predicted from the hydrolysis rates measured in laboratory studies. 

Although the measured hydrolysis rates were more rapid at higher pH levels (e.g., 0.5 day halflife at pH 9), there was no consistent correlation between the measured soil pH and the 

degradation rate in aerobic soil or the dissipation rate in field studies. Also as noted previously 

at least one published study suggests that the hydrolysis rate may not consistently increase with 

increasing pH. Although the submitted hydrolysis study has been previously accepted, it is 

recommended that a more detailed follow-up study be conducted to more fully assess the 

hydrolysis rate of halosulfuron-methyl at different temperatures and pH levels and the formation 

 7 From U.S. EPA (1992). Framework for Ecological Risk Assessment. EPA/630/R-92/001.
-29 of 75-

of hydrolysis products. These data can be used to more accurately parameter many exposure 

prediction models. Halosulfuron-methyl is highly mobile (Koc range 31 to 199) and has 

significant potential for runoff at sites where it is more persistent and may leach significantly at 

sites where hydrolysis is a relatively insignificant route of dissipation in topsoil and subsoil. 

Halosulfuron-methyl is not expected to bioaccumulate in aquatic or terrestrial food chains.

6.1. Risk Hypothesis

A risk hypothesis describes the predicted relationship among the stressor, exposure, and 

assessment endpoint response along with the rationale for their selection. For halosulfuronmethyl, the following ecological risk hypothesis will be employed for the national-level 

ecological risk assessment:

Given the uses of halosulfuron-methyl and its environmental fate properties, there is a likelihood 

of exposure to non-target terrestrial and aquatic plants. When used in accordance with the label, 

halosulfuron-methyl may result in potential adverse effects upon the survival, growth, and 

reproduction of non-target terrestrial and aquatic plants. 

6.2. Conceptual Diagram

The conceptual model used to depict the potential ecological risk associated with the use of 

halosulfuron-methyl (the stressor) assumes that as a pesticide, halosulfuron-methyl can adversely 

affect terrestrial and aquatic organisms (the receptors) if environmental concentrations exceed 

toxic thresholds as a result of application according to the label directions (Figures 3 and 4). 

Ecological receptors that may potentially be exposed to halosulfuron-methyl include: terrestrial 

and semi-aquatic wildlife (such as mammals, birds, terrestrial-phase amphibians and reptiles);

terrestrial and semi-aquatic plants; and terrestrial invertebrates. Additionally, given the mobility 

of halosulfuron-methyl, aquatic organisms (freshwater and estuarine/marine fish and 

invertebrates, aquatic-phase amphibians, and aquatic plants) are potential receptors in adjacent 

water bodies through off-site transport of halosulfuron-methyl from the application site through 

runoff, erosion, and spray drift.
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Figure 3. Conceptual model for halosulfuron-methyl exposure to aquatic organisms. 

Dashed lines indicate route of exposure considered of lower likelihood for halosulfuron-methyl.

Stressor

Source

Receptors

Attribute

Change

Ground or Aerial Applications of Halosulfuron-methyl 

Spray drift

Fish/aquatic-phase 

amphibians

Eggs 

Larvae 

Juveniles / Adults

Individual organisms

Reduced survival

Reduced growth

Reduced reproduction

Food chain

Reduction in algae

Reduction in prey

Habitat integrity

Reduction in primary productivity

Reduced cover

Community change

Surface water

Runoff

Aquatic Animals

Invertebrates

Vertebrates

Exposure

Media

Uptake/gills 

or integument

Ingestion Ingestion

Atmospheric 

transport

Wet/dry deposition

Soil Ground water

Uptake/gills 

or integument

Aquatic Plants

Non-vascular

Vascular

Uptake/cell, 

roots, leaves Riparian plant

terrestrial 

exposure 

pathways see 

Figure 2
-31 of 75-

Figure 4. Conceptual model for halosulfuron-methyl exposure to terrestrial organisms. 

Dashed lines indicate route of exposure considered of lower importance for halosulfuron-methyl.

7. Analysis Plan

In order to address the risk hypothesis, the potential for adverse effects on the environment will 

be estimated. The use, environmental fate, and ecological effects of halosulfuron-methyl will be 

characterized and integrated to assess the risks. This will be accomplished using a risk quotient 

(ratio of exposure concentration to effects concentration) approach. Although risk is often 

defined as the likelihood and magnitude of adverse ecological effects, the risk quotient-based 

approach does not provide a quantitative estimate of likelihood and/or magnitude of an adverse 

effect. However, as outlined in the Overview Document (USEPA 2004), the likelihood of 

effects to individual organisms from particular uses of halosulfuron-methyl may be estimated 

using the probit dose-response slope and either the level-of-concern (discussed below) or the 

actual calculated risk quotient value.

This analysis plan will be revisited and may be revised depending upon the information 

submitted by the public in response to the opening of the Registration Review docket for 

halosulfuron-methyl.

Stressor

Source

Receptors

Attribute

Change

Applications of Halosulfuron-methyl

Direct

application Spray drift

Birds / Terrestrialphase amphibians / 

reptiles / mammals/ 

Insects

il

Terrestrial 

inverts

Individual organisms

Reduced survival

Reduced growth

Reduced reproduction

Food chain

Reduction in 

prey

Habitat integrity

Reduction in primary 

productivity

Reduced cover

Community change

Terrestrial/riparian plants

grasses/forbs, fruit, seeds 

(trees, shrubs)

Runoff

Mammals

Exposure

Media

Soil

Ingestion

Ingestion

Ingestion

Ingestion

Dermal uptake/Ingestion

Atmospheric 

transport

Root uptake

Wet/dry 

deposition

Birds / 

Amphibians

Ingestion
-32 of 75-

7.1. Stressors of Concern

The stressor of concern in the assessment is the parent compound halosulfuron-methyl. 

Cleavage of the sulfonylurea bridge (-NH-CO-NH-SO2-) between the two ring structures in the 

parent compound is predicted to result in degradates that are either not phytotoxic or require 

relatively higher residues to affect plant growth. Therefore, the long-term phytotoxicity of 

halosulfuron-methyl observed under some field conditions is likely due to the very high 

persistence of the parent compound.

Terrestrial exposure

Exposures in terrestrial habitats will model the parent compound alone due to its high persistence 

and limitations in the models to incorporate the fate of the degradates. 

Aquatic exposure

The metabolite desmethyl halosulfuron (CP 147922) retains the sulfonylurea bridge and could 

potentially contribute to the overall total toxic residues for aquatic exposure. However, based 

upon currently available fate information, desmethyl halosulfuron does not contribute 

significantly to the environmental exposure in aquatic environments. This conclusion may be 

modified, depending on the results of the additional fate studies that are requested in this 

problem formulation.

In addition, the halosulfuron rearrangement ester (CP 147925 or CP 151790) contains a 

contracted sulfonylurea bridge. However, this compound is predicted to be substantially less 

toxic than the parent compound to aquatic taxa (see Appendix C). Therefore, the halosulfuron 

rearrangement ester will not be included as a stressor of concern.

Based on these lines of evidence, evaluation of parent compound alone is expected to accurately 

represent the potential aquatic exposure that may result in risk concerns following halosulfuronmethyl application.

Residues from application of multiple sulfonylurea active ingredients

Additionally it should be noted that the aminopyrimidine degradate of halosulfuron methyl is 

identical to fractional degradates of several other sulfonylurea herbicides such as amidosulfuron, 

bensulfuron, flazasulfuron, flucetosulfuron, flupyrsulfuron, formasulfuron, imazosulfuron, 

mesosulfuron, nicosulfuron, orthosulfamuron, pyrazosulfuron, rimsulfuron, sulfometuronmethyl, sulfosulfuron, and trifloxysulfuron. Available evidence from environmental fate 

guideline studies submitted to the Agency for halosulfuron methyl shows that this metabolite can 

be quite persistent in the environment. To the extent that multiple sulfonylureas with the 

aminopyrimidine moiety present may be included in the same regions the level of exposure to 

this metabolite may be increased beyond the level anticipated for this individual chemical 

assessment.
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In some cases halosulfuron methyl is applied with other herbicides and exposure to multiple 

active ingredients at the same time might occur. There are several products of specific mixtures 

of halosulfuron-methyl and other herbicides:

• Yukon: a mixture with dicamba.

• Permit Plus: a mixture with thifensulfuron-methyl. 

• Priority: a mixture with carfenthrazone-ethyl

• RiceEdge (Registration # 71085-31 and -32) with propanil (used on rice; fields may be 

flooded; rate for halosulfuron methyl is only 0.0465 lb ai and 0.062 lb ai / acre / season)

• NC-398: a mixture with dicamba.

• Gwn-9889: a mixture with tribenuron methyl and metribuzin

In its ecological risk assessments, the Agency does not routinely include an evaluation of 

mixtures of active ingredients, either those mixtures of multiple active ingredients in product 

formulations or those in the applicator’s tank. In the case of registered product formulations of 

multiple active ingredients, each active ingredient is subject to an individual risk assessment for 

regulatory decision regarding the active ingredient on a particular use site. If effects data are 

available for a formulated product containing more than one active ingredient, the data may be 

used qualitatively or quantitatively in accordance with the Agency’s Overview Document and 

the Services’ Evaluation Memorandum (USEPA, 2004; Williams and Hogarth, 2004). 

7.2. Measures of Exposure

In order to estimate risks of halosulfuron-methyl exposures in aquatic and terrestrial 

environments, exposure modeling will be based on application rates and methods cited in Table 

1. Measures of exposure are based on aquatic and terrestrial models that predict estimated 

environmental concentrations (EECs) of halosulfuron-methyl. For the rice use, the Tier I Rice 

Model is used to assess ecological exposure in surface water from released paddy water 

following use on rice (for drinking water exposure in human dietary exposure risk assessments a 

model is currently in development and may or may not be approved for use in time for 

Registration Review). For other uses it might be necessary to complete an aquatic ecological 

risk assessment of halosulfuron including the following:

Environmental concentrations will be modeled using PRZM-EXAMS. When there are multiple 

crop use scenarios for halosulfuron modeling using PRZM-EXAMS, EFED will choose 

conservative surrogate scenarios that are likely to generate high-end EECs. In addition, the 

potential for contaminated irrigation water to adversely affect sensitive agricultural crops will be 

assessed. 

Exposure estimates for terrestrial organisms assumed to be in the target area or in an area 

exposed to off-site deposition are derived using the T-REX model (version 1.4.1, 10/09/2008). 

This model incorporates the Kenaga nomograph, as modified by Fletcher et al. (1994), which is 

based on a large set of field residue data. The upper limit values from the nomograph represent 

the upper bound of residue values from actual field measurements (Hoerger and Kenaga 1972). 

The Fletcher et al. (1994) modifications to the Kenaga nomograph are based on measured field 

residues from 249 published research papers, including information on 118 species of plants, 121 
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pesticides, and 17 chemical classes. Based on these data, T-REX assumes a 35-day foliar 

dissipation half-life in the absence of other data.

The model used to derive EECs relevant to terrestrial plants is TerrPlant. Since risks to 

terrestrial plants from spray drift of halosulfuron-methyl, terrestrial plant exposure assessment is 

appropriately further refined with the spray drift model AgDRIFT. These models are 

parameterized using relevant reviewed environmental fate data from registrant submissions and 

the literature. Model input values will be consistent with the most recent version of the input 

parameter guidance (Version 2.1, USEPA 2009).

The Environmental Fate and Effects Division (EFED) most recently conducted a drinking water 

assessment for soybeans and other previously registered uses in June 2009 (DP Barcode 

D3580328

). Estimated drinking water concentrations (EDWCs) for surface and ground water 

were derived from the EFED Tier 1 screening models, FIRST and SCI-GROW, respectively. 

This document presented a Tier 1 drinking water assessment (DWA) which was prepared for the 

Health Effects Division (HED). All previous drinking water assessments have resulted in 

estimated drinking water concentrations (EDWCs) which were below the HED level of concern 

(LOC).

Two screening tools were utilized to assess the potential for halosulfuron-methyl exposure to 

terrestrial organisms via inhalation and drinking water exposure. The Screening Tool for 

Inhalation Risk (STIR v.1.0) was used to calculate an upper bound estimate of exposure using 

vapor pressure and molecular weight of halosulfuron-methyl for vapor phase exposure, as well as 

the maximum application rate and method of application for spray drift. The screening analysis 

considers results from several toxicity studies including acute oral and inhalation rat toxicity 

(oral LD50 = 3170 mg/kg bw and LC50 >4.8 mg/L, respectively) as well as the most sensitive 

acute oral avian toxicity endpoint (bobwhite quail, LD50 > 2210 mg ai/kg bw). Based on the 

results of the STIR model, inhalation exposure alone was determined not to be a potential 

pathway of concern for avian and mammalian species on an acute basis. 

The Screening Imbibition Program (SIP v.1.0) was used to calculate an upper bound estimate of 

exposure using halosulfuron-methyl’s range of solubility in water (15 mg/L at pH 5, 1650 mg/L 

at pH 7 and 7470 mg/L at pH 9), the most sensitive acute oral and chronic avian toxicity 

endpoints (LD50 > 2210 mg ai/kg bw and NOAEL = 1010 mg a.i./diet, respectively) and the 

most sensitive acute and chronic mammalian toxicity endpoints (oral LD50 = 3170 mg/kg bw and 

NOAEL = 50 mg a.i./kg/day, respectively). At pH 5, drinking water exposure of halosulfuronmethyl is not expected to be a concern for birds and mammals. However, drinking water 

exposure was determined to be a potential pathway of concern for avian and mammalian species 

on an acute basis and chronic basis within the range of solubility for halosulfuron-methyl at pH 7 

and 9. Based on the results of the SIP screen, drinking water theoretically cannot be ruled out as 

a potential route of exposure to birds and mammals, based solely on the solubility of the 

chemical. 

 8 Halosulfuron methyl Drinking Water Assessment for Additional food uses (including proposed use on soybean); 

6/4/2009.
-35 of 75-

To further explore the potential for drinking water exposure to birds and mammals, a 

conservative exposure scenario was created that incorporates the application rate of the chemical. 

The maximum registered application rate of halosulfuron-methyl (0.94 lbs a.i./A) was assumed 

to be applied directly to a puddle with 2.54 cm depth (1 inch), 1 meter width and 1 meter length

(area = 1 m2, volume = 0.0254 m3). Based on these assumptions, direct application to water 

would only result in a halosulfuron-methyl concentration of 0.41 mg a.i./L (0.94 lbs a.i./A = 10.5 

mg/m2, assuming the hypothetical dimensions of a small puddle, 0.0254 m3 or 25.4 L).

In comparison, SIP was used to estimate the level of exposure that may result in drinking water 

concerns for birds and mammals. The chemical concentrations in SIP are represented by the 

solubility of the chemical in the tool, as one assumption for the screen is that the chemical is 

present at its solubility limit in water. Based on the avian and mammalian toxicity endpoints for 

halosulfuron-methyl, a concentration of 62 mg a.i./L would need to be achieved before chronic 

drinking water concerns occur for avian species. Chronic concerns to birds are indicated at a 

lower level than either acute risk concerns to birds and mammals or chronic risk concerns to 

mammals, based on the toxicity endpoints for the chemical and the water intake rates for each 

taxon. Therefore, upon further analysis, the drinking water exposure pathway to birds and 

mammals is not likely result in risk concerns, due to the low application rate of the chemical in 

relation to the concentration that would need to be achieved before drinking water would be a 

concern. In addition, the acute estimates provided in the screen likely overestimate the likelihood 

of importance of the drinking water pathway on an acute basis, as the acute toxicity values are 

based on the highest halosulfuron-methyl treatment concentration in the submitted avian and 

mammalian acute oral tests, at which no mortality occurred.

The analysis of the individual dietary, inhalation and drinking water routes of exposure in these 

screening level tools does not consider that aggregation with other exposure pathways.

However, the Agency does consider the relative importance of other routes of exposure in 

situations where data indicate that pesticide exposures through other routes may be potentially

significant contributors to wildlife risk (US EPA, 2004). More information about the models and 

tools used for pesticide ecological risk assessments can be found on the EPA’s website at

http://www.epa.gov/pesticides/science/models_pg.htm#terrestrial.

Although not available at this time, the Agency is actively pursuing modeling techniques to 

account for dermal exposure via direct application of spray and by incidental contact with 

contaminated vegetation, soil and water.

Exposure concentrations for terrestrial plants are derived using TerrPlant (v.1.2.2). This model 

uses estimates of pesticides in runoff and in spray drift to calculate EECs. EECs are based upon 

solubility, application rate and minimum incorporation depth. 

The AgDRIFT (v2.01; May 2001) or AgDISP (v. 8.15) spray drift model may be used to assess 

exposures of organisms to halosulfuron-methyl deposited on terrestrial habitats by spray drift.
-36 of 75-

7.3. Measures of Effect

Ecological effects data are used as measures of direct and indirect effects to biological receptors. 

Data are typically obtained from registrant-submitted studies or from literature studies identified 

by ECOTOX. The ECOTOX database provides more ecological effects data in an attempt to 

bridge existing data gaps. ECOTOX is a source for locating single chemical toxicity data and 

potential chemical mixture toxicity data for aquatic life, terrestrial plants, and wildlife.

ECOTOX was created and is maintained by the USEPA, Office of Research and Development, 

and the National Health and Environmental Effects Research Laboratory's Mid-Continent 

Ecology Division.

The acute measures of effect used for animals in this assessment are the LD50, LC50 and EC50. 

LD stands for "Lethal Dose", and LD50 is the amount of a material, given all at once, that is 

estimated to cause the death of 50% of the test organisms. LC stands for “Lethal Concentration” 

and LC50 is the concentration of a chemical that is estimated to kill 50% of the test organisms. 

EC stands for “Effective Concentration” and the EC50 is the concentration of a chemical that is 

estimated to produce a specific effect in 50% of the test organisms. Endpoints for chronic 

measures of exposure for listed and non-listed animals are the NOAEL/NOAEC and NOEC. 

NOAEL stands for “No Observed-Adverse-Effect-Level” and refers to the highest tested dose of 

a substance that has been reported to have no harmful (adverse) effects on test organisms. The 

NOAEC (i.e., “No-Observed-Adverse-Effect-Concentration”) is the highest test concentration at 

which none of the observed effects were statistically different from the control. For non-listed 

plants, only acute exposures are assessed (i.e., EC25 for terrestrial plants and EC50 for aquatic 

plants); for listed plants either the NOAEC or EC05 is used.

At the time of the risk assessment, updated information on the potential effects of halosulfuronmethyl to non-target organisms will be collected from the Ecological Incident Information 

System (EIIS), Aggregrate Incident Reports and the Avian Monitoring Information System 

(AIMS). 

Where available, sub-lethal effects observed in both registrant-submitted and open literature 

studies will be evaluated qualitatively. Such effects may include behavioral changes (e.g., 

lethargy and changes in coloration). Quantitative assessments of risks, though, are limited to 

those endpoints that can be directly linked to the Agency’s assessment endpoints of impaired 

survival, growth and reproduction.

In the absence of taxon-specific data, the assessment of risk for direct effects to non-target 

organisms makes the assumption that toxicity of halosulfuron-methyl to birds is similar to 

terrestrial-phase amphibians and reptiles. The same assumption is made for fish and aquaticphase amphibians. In the absence of data for either acute or chronic effects, the conservative 

assumption will be to presume that halosulfuron-methyl is toxic. 

7.4. Integration of Exposure and Effects
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Risk characterization is the integration of exposure and ecological effects characterization to 

determine the potential ecological risk from the registered uses of halosulfuron-methyl and the 

likelihood of direct and indirect effects to non-target organisms in aquatic and terrestrial habitats. 

The exposure and toxicity effects data are integrated in order to evaluate the risks of adverse 

ecological effects on non-target species. For the assessment of halosulfuron-methyl risks, the 

risk quotient (RQ) method is used to compare exposure and measured toxicity values. EECs are 

divided by acute and chronic toxicity values. The resulting RQs are then compared to the 

Agency’s Levels of Concern (LOCs) (USEPA 2004). These criteria are used to indicate when 

halosulfuron-methyl use, as directed on the labels, has the potential to cause adverse direct or 

indirect effects to non-target organisms. In addition, halosulfuron-methyl incident data will be 

considered as part of the risk characterization. 

7.5. Deterministic and Probabilistic Assessment Methods

The quantitative assessment of risk will primarily depend on the deterministic point-estimate 

(RQ) based approach described in the risk assessment. An effort will be made to further 

qualitatively describe risk using probabilistic tools that the Agency has developed. These tools 

have been reviewed by FIFRA Scientific Advisory Panels and have been deemed as appropriate 

means of refining assessments where deterministic approaches have identified risks

(http://www.epa.gov/scipoly/sap/index.htm). Newer tools may be available to assess the routes 

of exposure and will be applied as appropriate in Registration Review.

7.6. Endocrine Disruptor Screening Program

As required by FIFRA and the Federal Food, Drug, and Cosmetic Act (FFDCA), EPA reviews 

numerous studies to assess potential adverse outcomes from exposure to chemicals. 

Collectively, these studies include acute, subchronic and chronic toxicity, including assessments 

of carcinogenicity, neurotoxicity, developmental, reproductive, and general or systemic toxicity. 

These studies include endpoints which may be susceptible to endocrine influence, including 

effects on endocrine target organ histopathology, organ weights, estrus cyclicity, sexual 

maturation, fertility, pregnancy rates, reproductive loss, and sex ratios in offspring. For 

ecological hazard assessments, EPA evaluates acute tests and chronic studies that assess growth, 

developmental and reproductive effects in different taxonomic groups. As part of its most recent 

registration decision, EPA reviewed these data and selected the most sensitive endpoints for 

relevant risk assessment scenarios from the existing hazard database. However, as required by 

FFDCA section 408(p), halosulfuron-methyl is subject to the endocrine screening part of the 

Endocrine Disruptor Screening Program (EDSP). 

EPA has developed the EDSP to determine whether certain substances, including pesticide active 

and other ingredients, may have an effect in humans or wildlife similar to an effect produced by 

a naturally occurring estrogen, or other such endocrine effects as the Administrator may 

designate. The EDSP employs a two-tiered approach to making the statutorily required 

determinations. Tier 1 consists of a battery of 11 screening assays to identify the potential of a 

chemical substance to interact with the estrogen, androgen, or thyroid (E, A, or T) hormonal 
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systems. Chemicals that go through Tier 1 screening and are found to have the potential to 

interact with E, A, or T hormonal systems will proceed to the next stage of the EDSP where EPA 

will determine which, if any, of the Tier 2 tests are necessary based on the available data. Tier 2 

testing is designed to identify any adverse endocrine-related effects caused by the substance, and 

establish a dose-response relationship between the dose and the E, A, or T effect. 

Under FFDCA section 408(p), the Agency must screen all pesticide chemicals. Between 

October 2009 and February 2010, EPA issued test orders/data call-ins for the first group of 67 

chemicals, which contains 58 pesticide active ingredients and 9 inert ingredients. Halosulfuronmethyl is not among the group of 58 pesticide active ingredients on the initial list to be screened 

under the EDSP. Accordingly, as part of registration review, EPA will issue future EDSP 

orders/data call-ins, requiring the submission of EDSP screening assays for halosulfuron-methyl. 

For further information on the status of the EDSP, the policies and procedures, the list of 67 

chemicals, future lists, the test guidelines and the Tier 1 screening battery, please visit our 

website: http://www.epa.gov/endo/.

7.7. Endangered Species Assessment

Consistent with the Agency’s responsibility under the Endangered Species Act (ESA), the 

Agency will evaluate risks to Federally-listed threatened and/or endangered (listed) species from 

registered uses of halosulfuron-methyl. This assessment will be conducted in accordance with 

the Overview Document (USEPA 2004), provisions of the ESA, and the Services’ Endangered 

Species Consultation Handbook (USFWS/NMFS, 1998).

The assessment of effects associated with the registration of halosulfuron-methyl is based on an 

action area. The action area is considered to be the area directly or indirectly affected by the 

federal action, as indicated by the exceedance of Agency Levels of Concern (LOCs) used to 

evaluate direct or indirect effects. The Agency’s approach to defining the action area under the 

provisions of the Overview Document (USEPA 2004) considers the results of the risk 

assessment process to establish boundaries for that action area with the understanding that 

exposures below the Agency’s defined LOCs constitute a no-effect threshold. For the purposes 

of this assessment, attention will be focused on the footprint of the action (the area where 

halosulfuron-methyl application occurs), plus all areas where offsite transport (spray drift, 

runoff, etc.) may result in potential exposure that exceeds the Agency’s LOCs. Specific measures 

of ecological effect that define the action area for listed species include any direct and indirect 

effects and/or potential modification of its critical habitat, including reduction in survival, 

growth, and reproduction as well as the full suite of sublethal effects available in the effects 

literature. Therefore, the action area extends to a point where environmental exposures are below 

any measured lethal or sublethal effect threshold for any biological entity at the whole organism, 

organ, tissue, and cellular level of organization. In situations where it is not possible to determine 

the threshold for an observed effect, the action area will initially be assumed to include all 

counties where halosulfuron-methyl is used in the United States. 
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7.8. Drinking Water Assessment

A drinking water assessment will be conducted to support future human health risk assessments 

of halosulfuron methyl should it be required, based on all the available environmental fate 

information. The drinking water assessment will incorporate model estimates of halosulfuron 

methyl in surface and ground waters. Concentrations in surface waters will be estimated using 

FQPA Index Reservoir Screening Tool (FIRST, v.1.1.1, 12/18/07) (or subsequently using 

PRZM/ EXAMS, with the Index Reservoir – for description see above – if refinements are 

required). Ground water estimates of concentrations will be obtained using the Screening 

Concentration In GRound Water (SCI-GROW) model (v.2.3, July 2003). The drinking water 

assessment will also include a summary of available surface and ground water monitoring data.

7.9. Environmental Monitoring Data

Halosulfuron-methyl has not been included in the United States Geological Survey’s (USGS) 

National Water Quality Assessment Program (NAWQA) list of analytes nor was it included in 

the pilot reservoir monitoring study conducted by USGS with EPA Support (USGS Open file 

report 01-456 ). The most extensive study of halosulfuron-methyl residues in surface water 

from Battaglin et al. (1999, 2000)9 who screened reservoir, river, and ground water samples for a 

variety of low-rate herbicides, including halosulfuron. Out of 129 water samples from 

Midwestern streams and rivers, halosulfuron was detected in 7 samples at concentrations above 

0.01 ug/L (ppb), with a maximum concentration of 0.067 ppb. No sampling for halosulfuron 

was reported in the 1992 Pesticides in Ground Water Database (Jacoby et al., 1992)10. 

Previously, a prospective Ground-Water Monitoring Study (see EFED Review of DP Barcode 

D226451 dated 2/14/97) was requested, but that requirement has been deferred by the Agency. 

During the risk assessment process, the following databases and sources will be searched for 

monitoring information on halosulfuron:

• The United States Environmental Protection Agency (USEPA) STORET Database 

(http://www.epa.gov/storet/dbtop.html)

 9

Battaglin, W.A., Furlong, E.T., Burkhardt, M.R., and Peter, J.C. 1999. Occurrence of Sulfonylurea, Sulfonamide, 

Imidazolinone, and other herbicides in Midwestern rivers, reservoirs, and ground water, 1998 in U.S. Geological 

Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting, Charleston, South Carolina, 

March 8-12, 1999: U.S. Geological Survey Water-Resources Investigations Report 99-4018B, Volume 2, pp. 215-

225. 

Battaglin, W.A., Furlong, E.T., Burkhardt, M.R., and Peter, J.C. 2000. Occurrence of Sulfonylurea, 

Sulfonamide, Imidazolinone, and other herbicides in rivers, reservoirs, and ground water in the Midwestern United 

States, 1998. Science Total Environ. Vol. 248, Issues 2-3, 5 April 2000, Pages 123-133. 10Jacoby, H.J. et al. U.S. EPA. 1992. Pesticides in Ground Water Database -A Compilation of Monitoring Studies: 

1971-199, EPA 734-12-92-001.
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• The United States Geological Survey (USGS) National Water-Quality Assessment 

(NAWQA) Program Data Warehouse 

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

• The USGS National Stream Quality Accounting Network (NASQAN) program 

(http://water.usgs.gov/nasqan/)

• Sampling for Pesticides Residues in California Well Water Cumulative Report; EEH03-

08; December 2003 (http://www.cdpr.ca.gov/docs/emon/pubs/ehapreps/eh0308.pdf) 

• California Department of Pesticide Regulation (DPR) Surface Water Database 

(http://www.cdpr.ca.gov/docs/emon/surfwtr/surfdata.htm)

8.0. Preliminary Identification of Data Gaps

8.1. Environmental Fate

The studies submitted to fulfill environmental fate data requirements for halosulfuron-methyl are 

not complete by current standards. The requirements have not been met as stipulated in 40 CFR 

part 158 Subpart N §158.1300 for all pesticides with use patterns for aquatic food and nonfood 

applications: 

• Guideline 835.4100. There are acceptable data from only two sites for aerobic 

soil metabolism. The guideline stipulates that results from at least four relevant 

soils of different organic carbon content, pH, clay content, and microbial biomass 

must be submitted in order to characterize the variability in the aerobic 

biodegradation of halosulfuron-methyl in the environment. Due to the high 

variability in halosulfuron-methyl persistence by site additional tests will also be 

required (see below.)

• Guideline 835.2120. The submitted hydrolysis study is acceptable; but given the 

apparent critical importance of the change in hydrolysis rate of halosulfuronmethyl with pH and temperature, an additional study will be required. Suggested 

parameters include testing at pH 5, 7, and 9 and at 10, 15, 20, and 25 C for 60 

days (and additionaly at pH 4, 6 and 8 at 15 C) and analysis for halosulfuronmethyl and potentially major hydrolysis products.

• Non-Guideline Study. Environmental Chemistry Analytic Methods 

(ECMs)/Independent Laboratory Validation (ILV). ECMs in soil and water and 

ILVs used in halosulfuron environmental fate studies are requested at this time. 

Environmental chemistry methods for analysis of halosulfuron methyl and its 

major degradates in soil and water were submitted as part of the aquatic field 

dissipation study (MRID 444373-04) but no ILVs have been submitted to the 

Agency. Therefore, ECMs should be resubmitted and ILVs should be conducted 

for parent halosulfuron and its major degradates in water and soil.

For the 835.4100 additional tests, prior to providing complete guideline studies in at least 2 

additional soils, the registrant shall conduct limited studies for parent decline (analysis for 

degradate formation in these preliminary studies is optional) for at least ten soil types 

representative of the spectrum of major halosulfuron-methyl use areas. Particular attention 
-41 of 75-

should be paid to selecting representative low pH soils and a variety of organic matter amounts 

and type and mineral compositions should be included in the selected test soils. These 

preliminary studies should be conducted with sampling and analysis out to 180 days after 

application or until parent halosulfuron-methyl has declined below 1% of the applied amount 

(whichever comes first). The objective of the preliminary studies is to provide a baseline for the 

range of metabolism rates likely to occur in the field for halosulfuron-methyl; the registrant may 

choose to also choose at least two of the soils where halosulfuron-methyl was most persistent to 

conduct the required two addition guideline 835.4100 studies (which require full characterization 

of the formation and decline of major degradates.) Note, as previously described the preliminary 

studies are needed because discrepancies between field and laboratory results confirm that 

halosulfuron can be significantly more persistent at some sites than shown in the currently 

available aerobic soil metabolism studies.

Table 9 identifies studies by MRID that offer data for each guideline requirement, as well as 

study classifications and whether or not further data are needed in order to support risk 

assessment (i.e., whether there is a data gap).

Table 9. Summary of available environmental fate data.

Guideline Study Title MRID / 

ACC No. Classification Data Gap? Comments

835.2120 Hydrolysis

42139409

,

42846801

Acceptable No

835.2240 Photodegradatio

n in Water

42661409 Supplemental No

835.2410 Photodegradatio

n on Soil 42661410 Supplemental No

835.4100 Aerobic Soil 

Metabolism

42139410,

42846802 Supplemental Yes Submitted studies in two soils are acceptable but tests in additional soils are required.

835.4200 Anaerobic Soil 

Metabolism None Not required No

835.4300

Aerobic 

Aquatic 

Metabolism

45671701 Not reviewed TD Review of this study is in progress.

835.4400

Anaerobic 

Aquatic 

Metabolism

42661411 Acceptable No

835.1240,

835.1230

Mobility - 

Adsorption / 

Desorption

42139411 Acceptable

No

Also includes study with degradates.

835.6100 Terrestrial Field 

Dissipation1

42661412

42661413

42661414

42976302

42976303

42976304

43699801

Acceptable No 42976303 and 42661414 are “pipe lysimeter” 

studies.
-42 of 75-

Guideline Study Title MRID / 

ACC No. Classification Data Gap? Comments

835.6200 Aquatic Field 

Dissipation1 44437304 Conditionally 

acceptable TBD

Acceptance was made conditional upon 

submission of an acceptable aerobic aquatic 

metabolism study.

850.1730 Fish 

Accumulation NA Not required Halosulfuron-methyl is not expected to bioaccumulate.

1

8.2. Ecological Effects

Environmental chemistry methods used to generate data associated with this study must include results of a 

successful confirmatory method trial by an independent laboratory. Test standards and procedures for independent 

laboratory validation are available as addenda to the guideline for this test requirement.

The available ecological effects data for halosulfuron-methyl is incomplete. The full list of 

ecological toxicity data requirements and available studies are listed in Tables 10-12.

The following additional study is requested for halosulfuron:

• Terrestrial plant reproduction study (non-guideline)

Terrestrial plants are typically very sensitive to sulfonylurea urea herbicide exposure. There is 

evidence11 to suggest plant reproduction may be affected by sulfonylurea herbicides at levels 

below effects on vegetative growth or visual injury (Fletcher et al., 1993). Uncertainty regarding 

the potentially greater sensitivity of terrestrial plant reproduction has been discussed extensively 

in the environmental fate and effects Reregistration Eligibility Decision assessment for 

chlorsulfuron (D330621). Therefore, to the extent that terrestrial plant reproduction is more 

sensitive to halosulfuron-methyl than growth endpoints, risks to terrestrial plants may be 

underestimated in this risk assessment. Additional information on the reproductive toxicity of 

halosulfuron-methyl to terrestrial plants is necessary to address this uncertainty.

Note: The guideline numbers for terrestrial plants in the 40 CFR Part 158 were updated to 

reflect final 850 guidelines and do not reflect the numbers of the Public Draft 850 guidelines. 

Part 158 lists 850.4100 and 850.4150 (seedling emergence and vegetative vigor, respectively) for 

both Tier 1 and Tier 2 studies. The Public Draft guidelines 850.4100 and 850.4150 are for Tier 1 

and 850.4225 and 850.4250 are for Tier 2.

• Non-guideline. Terrestrial Plant Reproduction Study (special study, see justification 

in Appendix A).

• Fish acute toxicity test, freshwater (850.1075) – typical end-use product

• Aquatic invertebrate acute toxicity test, freshwater daphnids (850.1010) – typical 

end-use product

 11 Snipes et al. 1992, Bansal et al. 1999; Fletcher et al. 1993, 1995,1996; Bhatti et al. 1995; Al-Khatib et al. 1992; 

Boutin et al. 2000; Asghari and Evans 1992
-43 of 75-

TABLE 10. Available ecological effects data for terrestrial animals exposed to halosulfuron-methyl

Guideline Description MRID Classification

Study 

available

?

Data 

requested

?

Comments

850.2100 Avian oral 

toxicity 42139434 Acceptable Yes Yes Avian acute oral toxicity:Data are not available for 

passerine species, which 

are required under 40 CFR 

Part 158. However, due to 

the low maximum expected 

exposure concentrations 

for avian species, as well 

as the low toxicity in the 

available acute oral study 

with bobwhite quail, no 

additional data are 

requested at this time.

850.2200

Avian 

dietary 

toxicity 

42139435 Acceptable

No No

42139436 Acceptable

850.2300 Avian 

reproduction

47792801 Acceptable No No

47792802 Acceptable

850.3020

Honeybee 

acute contact 

toxicity

42139440 Acceptable No No

TABLE 11. Available ecological effects data for aquatic animals exposed to halosulfuron-methyl.

Guideline Description MRID Classification

Study 

available

?

Data 

requested

?

Comments

850.1075

Freshwater 

fish –

Acute 

toxicity 

42661421 Acceptable

Yes Yes

Freshwater fish acute 

toxicity and freshwater 

invertebrate acute toxicity: 

No information is available

on the aquatic toxicity of a 

typical end-use product 

containing halosulfuron 

methyl. Because 

halosulfuron-methyl can be 

directly applied to water 

when used on rice, more 

toxicity information on

freshwater fish and 

invertebrates is requested 

for applicable products.

Saltwater fish acute 

toxicity: Solubility issues 

occurred in the submitted 

acute test with saltwater 

fish. However, due to the 

low expected aquatic 

exposure concentrations and 

low overall toxicity of 

halosulfuron-methyl 

technical to aquatic 

organisms, no additional 

42139438 Supplemental

42661422 Acceptable

42139437 Supplemental

850.1075

Saltwater 

fish –

Acute 

toxicity 

42773001 Supplemental Yes No

850.1010

Freshwater 

invertebrates 

–

Acute 

toxicity

42139439 Acceptable Yes Yes

850.1025

850.1035

Saltwater 

invertebrates 42773002 Acceptable Yes No
-44 of 75-

Guideline Description MRID Classification

Study 

available

?

Data 

requested

?

Comments

–Acute 

toxicity 42773003 Acceptable data are requested at this time.

Saltwater invertebrate life 

cycle test and saltwater fish 

early life stage test: No 

chronic studies have been 

submitted for 

estuarine/marine fish or 

invertebrates. For 

estuarine/marine chronic 

endpoints, acute-to-chronic 

ratios will be calculated in 

the absence of additional 

taxa-specific data. Based on 

the currently available 

information, saltwater 

organisms do not appear to 

have increased sensitivity to 

this chemical compared to 

the sensitivity of freshwater 

organisms.

850.1300

Freshwater 

invertebrate 

–

life cycle 

test

43493003 Acceptable

Yes No

43493002 Supplemental

850.1350

Saltwater 

invertebrates 

–

life cycle test

None --- No No

850.1400

Freshwater 

fish –

early life 

stage test

43493002 Acceptable Yes No

850.1400

Saltwater 

fish –

early life 

stage test

None --- No No
-45 of 75-

TABLE 12. Available ecological effects data for plants exposed to halosulfuron-methyl.

Guideline Description MRID Classification

Study 

available

?

Data 

requested

?

Comments

850.4225

Terrestrial Plant 

toxicity: Tier II 

seedling 

emergence

42661424 

and 

43195501 

(addendum)

Acceptable Yes No

850.4250

Terrestrial Plant 

toxicity: Tier II 

vegetative vigor

42661425 

and 

43195502 

(addendum)

Acceptable Yes No

850. 5400 Aquatic Plant 

Growth: algae

43330702 Acceptable

Yes No

43330703 Acceptable

43330704 Acceptable

43330705 Acceptable

850.4400

Aquatic Plant 

Growth: vascular 

plants

43330701 Acceptable Yes No

Non 

guideline

Terrestrial Plant 

Reproduction 

Study

None --- No Yes

Special study, see 

justification in 

Appendix A
-46 of 75-

9. References

Fletcher, J.S., J.E. Nellessen, and T.G. Pfleeger. 1994. Literature review and evaluation of the 

EPA food-chain (Kenaga) nomogram, an instrument for estimating pesticide residues on 

plants. Environ. Tox. Chem. 13:1383-1391.

Hoerger, F., and E.E. Kenaga. 1972. Pesticide residues on plants: Correlation of representative 

data as a basis for estimation of their magnitude in the environment. In F. Coulston and 

F. Korte, eds., Environmental Quality and Safety: Chemistry, Toxicology, and 

Technology, Georg Thieme Publ, Stuttgart, West Germany, pp. 9-28.

U.S. Fish and Wildlife Service (USFWS) and National Marine Fisheries Service (NMFS). 1998. 

Endangered Species Consultation Handbook: Procedures for Conducting Consultation 

and Conference Activities Under Section 7 of the Endangered Species Act. Final Draft. 

March 1998.

USEPA. 2007. Bradbury, S. Guidance for Tier I Estimation of Aqueous Pesticide 

Concentrations in Rice Paddies. U.S. Environmental Protection Agency, Office of 

Prevention, Pesticides and Toxic Substance, Environmental Fate and Effects Division. 

Internal Memorandum. May 8, 2007.

USEPA. 2004. Overview of the Ecological Risk Assessment Process in the Office of Pesticide 

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

Toxic Substances, Office of Pesticide Programs, Washington DC. January 23, 2004.

USEPA. 1998. Guidelines for Ecological Risk Assessment. Risk Assessment Forum, Office of 

Research and Development, Washington, D.C. EPA/630/R-95/002F. April 1998. 

http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=30759

Willis, G.H. and L.L. McDowell. 1987. Pesticide Persistence on Foliage in Reviews of 

Environmental Contamination and Toxicology. 100:23-73.

Submitted Fate Studies

62-3 Analytical Method

MRID Citation Reference
-47 of 75-

45473503 Comb, A. (2001) NC-398 WG: Method Validation: Lab Project Number: RD 

1549: NAS/337: NAS337/012433. Unpublished study prepared by Huntingdon 

Life Sciences Ltd. 60 p. {OPPTS 830.1800} 

161-1 Hydrolysis

MRID Citation Reference

42139409 Kesterson, A.; Lawrence, B.; Lawrence, L. (1991) Hydrolysis of ?carbon 14| 

MON 12000 at pH 5,7 and 9: Lab Project Number: MSL- 11505: PTRL 1288: 

PTRL 454. Unpublished study prepared by PTRL East, Inc. 97 p. 

42846801 Moran, S. (1993) Response to EPA Comments on the Hydrolysis of (carbon 

14)-MON 12000 at pH 5, 7 and 9: Lab Project Number: R. D. 1181. 

Unpublished study prepared by Monsanto Co. The Agriculture Group. 26 p. 

161-2 Photodegradation-water

MRID Citation Reference

42661409 Kesterson, A.; Lawrence, B. (1993) Solution Photolysis of (carbon 14)-MON 

12000 in Natural Sunlight: Lab Project Number: MSL 12097: 512: 1153. 

Unpublished study prepared by PTRL East, Inc. 151 p. 

161-3 Photodegradation-soil

MRID Citation Reference

42661410 Kesterson, A.; Lawrence, B. (1992) Soil Surface Photolysis of (carbon 14)-

MON 12000 in Natural Sunlight: Lab Project Number: MSL 12096: 561: 1153. 

Unpublished study prepared by PTRL East, Inc. 66 p. 

162-1 Aerobic soil metabolism

MRID Citation Reference

42139410 Chott, K.; Mehrsheikh, M. (1991) Aerobic Soil Metabolism of MON 12000: 

Lab Project Number: MSL-10663: RD 1061. Unpublished study prepared by 

Monsanto Ag Co. 248 p. 
-48 of 75-

42846802 Mehrsheikh, M. (1993) Response to EPA Comments on the Aerobic Soil 

Metabolism of MON 12000: Lab Project Number: RD 1181. Unpublished study 

prepared by Monsanto Co. The Agriculture Group. 14 p. 

162-3 Anaerobic aquatic metab.

MRID Citation Reference

42661411 Kesterson, A.; Lawrence, B.; Mobley, S.; et al. (1993) Anaerobic Aquatic 

Metabolism of (carbon 14)-MON 12000: Lab Project Number: MSL 12568: 

491: 1153. Unpublished study prepared by PTRL East, Inc. 141 p. 

162-4 Aerobic aquatic metab.

MRID Citation Reference

45671701 Volkl, S. (2002) Aerobic Aquatic Metabolism of (Carbon-14)-HalosulfuronMethyl: Lab Project Number: RD 1579: 823555: 01-42-M1. Unpublished study 

prepared by RCC Ltd. 164 p. 

163-1 Leach/adsorp/desorption

MRID Citation Reference

42139411 Nadeau, R.; Sidhu, R. (1991) Adsorption/Desorption Studies of MON 12000 

and Three Aerobic Soil Metabolites: Lab Project Number: MSL-11288: RD 

1061. Unpublished study prepared by Monsanto Ag Co. 198 p. 

164-1 Terrestrial field dissipation

MRID Citation Reference

42139412 Mehrsheikh, M.; Allan, J. (1991) Confined Rotational Crop Study of MON 

12000: Quantitation, Characterization and Identification of MON 12000 and its 

Metabolites in Rotational Crops: Lab Project Number: MSL-11156: RD 1061. 

Unpublished study prepared by Monsanto Ag Co. 230 p. 

42661412 Beasley, R. (1993) Dissipation of MON 12000 and MON 12000 Metabolites in 

Field Soil: Lab Project Number: MSL 12356: 9200520: 12356. Unpublished 

study prepared by Harris Labs, Inc., Monsanto, and Stewart Agricultural 

Services, Inc. 660 p. 
-49 of 75-

42661413 Beasley, R. (1993) Dissipation of MON 12000 and MON 12000 Metabolites in 

Field Soil: Lab Project Number: MSL 12357: 6103-156: 90-42-R-4. 

Unpublished study prepared by Hazleton Wisconsin, Inc., Monsanto, and 

Stewart Agricultural Research Services, Inc. 588 p. 

42661414 White, R.; Schlicher, M. (1993) Dissipation of Radiolabeled MON 12000 and 

MON 12000 Metabolites in Field Soil: Interim Report: Lab Project Number: 

MSL 12463: 91-42-R-3: 1153. Unpublished study prepared by Hazleton 

Wisconsin, Inc., Monsanto, and American Agricultural Services, Inc. 635 p. 

42661415 Beasley, R. (1993) Storage Stability of MON 12000 and its Metabolites in or on 

Soil: Interim Report: Lab Project Number: MSL 12358: 1153: 12358. 

Unpublished study prepared by Monsanto. 97 p. 

42976302 Beasley, R. (1993) Dissipation of MON 12000 and MON 12000 Metabolites in 

Field Soil: Lab Project Number: 12892: 90-42-R-2: 9200520. Unpublished 

study prepared by Monsanto Co., the Agric. Group; Stewart Agric. Research 

Services, Inc.; and Harris Laboratories, Inc. 943 p. 

42976303 White, R.; Schlicher, M. (1993) Dissipation of Radiolabeled MON 12000 and 

MON 12000 Metabolites in Field Soil: Lab Project Number: MSL 12891: HWI 

6103-157: 0642-91-3. Unpublished study prepared by Monsanto Co., the Agric. 

Group; Hazleton Wisconsin, Inc.; and American Agric. Services, Inc. 731 p. 

42976304 Beasley, R. (1993) Dissipation on MON 12000 and MON 12000 Metabolites in 

Turf Soil: Lab Project Number: MSL 12893: 90-42-R-4: HWI-6103-156. 

Unpublished study prepared by Monsanto Co., the Agric. Group; Stewart Agric. 

Research Services, Inc.; Hazleton Wisconsin, Inc.; Harris Laboratories, Inc. 764 

p. 

43699801 Beasley, R. (1995) MON 12000 Soil Dissipation Study: Lab Project Number: 

MSL 14062: 93-42-R-3: RD 1310. Unpublished study prepared by Monsanto 

Co. and American Agricultural Services, Inc. 554 p. 

44408101 Mehrsheikh, M. (1997) Storage Stability of MON-12000 and its Metabolites in 

Water: Lab Project Number: 91-42-R-11: MSL-14354: 1382. Unpublished study 

prepared by Monsanto Company. 85 p. 

164-2 Aquatic field dissipation

MRID Citation Reference

44437304 Allan, J. (1997) Aquatic Sediment Dissipation Study of MON 12000 in Rice: 

Lab Project Number: 96-42-R-4: MSL-14689: RD 1388. Unpublished study 

prepared by Monsanto Co. 432 p. 
-50 of 75-

840.1200 Spray drift field deposition

MRID Citation Reference

48421801 Wright, J. (2011) Drift Study for Halomax 75 (Halosulfuron-methyl) in 

California Rice Country. Project Number: 11/PRA/ACETO/064. Unpublished 

study prepared by Helena R&D, LLC and Environmental Micro Analysts, Inc. 

84 p.

165-4 Bioaccumulation in fish

No Studies Submitted.

165-5 Bioaccum-aquatic non-target

No Studies Submitted.

71-1 Avian Single Dose Oral Toxicity

Submitted Ecological Effects Studies

MRID Citation Reference

42139434 Campbell, S.; Grimes, J.; Smith, G. (1991) MON 12000: An 

Acute Oral Toxicity Study with the Northern Bobwhite Quail: 

Lab Project Number: WL-90-153: 139-268: RD 1061. 

Unpublished study prepared by Wildlife International, Ltd. 24 p. 

71-2 Avian Dietary Toxicity

MRID Citation Reference

42139435 Foster, J.; Driscoll, C.; Hoxter, K. et al. (1991) MON 12000: A 

Dietary LC50 Study with the Mallard Duck: Lab Project Number: 

WL-90-155: 139-267: RD 1061. Unpublished study prepared by 

Wild life International, Ltd. 21 p. 
-51 of 75-

42139436 Foster, J.; Driscoll, C.; Hoxter, K. et al. (1991) MON 12000: A 

Dietary Study with the Northern Bobwhite Quail: Lab Project 

Number: WL-90-154: 139-266: RD 1061. Unpublished study 

prepared by Wildlife International, Ltd. 21 p. 

42396213 Schermes, S. (1992) Results of the Analyses of Avian Diet 

Samples for MON 12000: Lab Project Number: MSL 10305: EHL 

90065. Unpublished study prepared by Monsanto Co. 24 p. 

850.2300 Avian reproduction test

MRID Citation Reference

47792801 Temple, D.; Martin, K.; Beavers, J.; et al. (2009) Halosulfuron: A 

Reproduction Study with the Northern Bobwhite: Final Report. 

Project Number: 334/117. Unpublished study prepared by 

Wildlife International, Ltd. 159 p.

47792802 Temple, D.; Martin, K.; Beavers, J.; et al. (2009) Halosulfuron: A 

Reproduction Study with the Mallard: Final Report. Project 

Number: 334/118. Unpublished study prepared by Wildlife 

International, Ltd. 158 p.

72-1 Acute Toxicity to Freshwater Fish

MRID Citation Reference

42139437 Murphy, D. ; Smith, G. (1991) MON 12000: A 96-Hour Static 

Renewal Acute Toxicity Test with the Bluegill Sunfish (Lepomis 

macro- chirus): Lab Project Number: WL-90-550: WL 139A-118: 

RD 1061. Unpublished study prepared by Wildlife International, 

Ltd. 52 p. 

42139438 Murphy, D.; Smith, G. (1991) MON 12000: A 96-Hour Static 

Renewal Acute Toxicity Test with the Rainbow Trout 

(Oncorhynchus mykiss) Lab Project Number: WL-90-549: WL 

139A-117: RD 1061. Unpublished study prepared by Wildlife 

International, Ltd. 52 p. 

42661421 Holmes, C.; Swigert, J. (1993) A 96-hour Flow-through Acute 

Toxicity Test with the Rainbow Trout (Oncorhynchus mykiss): 

MON 12000: Lab Project Number: WL-92-123: 139A-148: 1153. 

Unpublished study prepared by Wildlife International, Ltd. 46 p. 

42661422 Holmes, C.; Swigert, J. (1993) A 96-hour Flow-through Acute 
-52 of 75-

Toxicity Test with the Bluegill (Lepomis macrochirus): MON 

12000: Lab Project Number: WL-92-124: 139A-147: 1153. 

Unpublished study prepared by Wildlife International, Ltd. 46 p. 

42661423 Holmes, C.; Swigert, J. (1993) A 48-hour Flow-through Acute 

Toxicity Test with the Cladoceran (Daphnia magna): MON 

12000: Lab Project Number: WL-92-125: 139A-146: 1153. 

Unpublished study prepared by Wildlife International, Ltd. 47 p. 

72-2 Acute Toxicity to Freshwater Invertebrates

MRID Citation Reference

42139439 Murphy, D.; Smith, G. (1991) MON 12000: A 48-Hour Static 

Renewal Acute Toxicity Test with the Cladoceran (Daphnia 

magna): Lab Project Number: WL-90-551: WL 139A-119: RD 

1061. Unpublished study prepared by Wildlife International, Ltd. 

51 p. 

72-3 Acute Toxicity to Estuarine/Marine Organisms

MRID Citation Reference

42773001 Swigert, J.; Smith, G. (1993) MON 12000: A 96 Hour FlowThrough Acute Toxicity Test with the Sheepshead Minnow 

(Cyprinodon variegatus): Lab Project Number: WL-92-16: 139A142: RD 1170. Unpublished study prepared by Wildlife 

International Ltd. 40 p. 

42773002 Swigert, J.; Smith, G. (1993) MON 12000: A 96 Hour FlowThrough Acute Toxicity Test with the Saltwater Mysid 

(Mysidopsis bahia): Lab Project Number: WL-92-17: 139A-141B: 

RD 1170. Unpublished study prepared by Wildlife International 

Ltd. 41 p. 

42773003 Swigert, J.; Smith, G. (1993) MON 12000: A 96 Hour Shell 

Deposition Test with the Eastern Oyster (Crassostrea virginica): 

Lab Project Number: WL-92-18: 139A-143: RD 1170. 

Unpublished study prepared by Wildlife International Ltd. 45 p. 

72-4 Fish Early Life Stage/Aquatic Invertebrate Life Cycle Study

MRID Citation Reference
-53 of 75-

43493001 Graves, W.; Mank, M.; Swigert, J. (1993) MON 12000: An Early 

Life-stage Toxicity Test With the Rainbow Trout (Oncorhynchus 

mykiss): Lab Project Numbers: WL-92-132: 139A-150: RD 1288. 

Unpublished study prepared by Wildlife Int'l. Ltd. 89 p. 

43493002 Zelinka, E.; Martin, K.; Swigert, J. (1993) MON 12000: A Flowthrough Life-Cycle Toxicity Test With the Cladoceran (Daphnia 

magna): Lab Project Numbers: WL-92-133: 139A-149A: RD 

1288. Unpublished study prepared by Wildlife Int'l. Ltd. 56 p. 

43493003 Zelinka, E.; Martin, K.; Swigert, J. (1993) MON 12000: A Flowthrough Life-Cycle Toxicity Test With the Cladoceran (Daphnia 

magna): Lab Project Numbers: WL-93-192: 139A-158: RD 1288. 

Unpublished study prepared by Wildlife Int'l. Ltd. 56 p. 

123-1 Seed germination/seedling emergence and vegetative vigor

MRID Citation Reference

42661424 Chetram, R. (1992) Tier 2 Seed Germination/Seedling Emergence 

Nontarget Phytotoxicity Study using MON 12000: Lab Project 

Number: MSL 12510: BL91-464: 1153. Unpublished study 

prepared by Pan Agricultural Labs, Inc. 314 p. 

42661425 Chetram, R. (1992) Tier 2 Vegetative Vigor Nontarget 

Phytotoxicity Study using MON 12000: Lab Project Number: 

MSL 12511: BL91-463: 1153. Unpublished study prepared by 

Pan Agricultural Labs, Inc. 323 p. 

43195501 Chetram, R. (1994) Tier 2 Seed Germination/Seedling Emergence 

NonTarget Phytotoxicity Study Using MON 12000: Addendum: 

Lab Project Number: MSL 13302: 93320: 1234. Unpublished 

study prepared by Pan-Agricultural labs, Inc. 119 p. 

43195502 Chetram, R. (1994) Tier 2 Vegetative Vigor Nontarget 

Phytotoxicity Study Using MON 12000: Addendum: Lab Project 

Number: MSL 13301: 93314: 1234. Unpublished study prepared 

by Pan-Agricultural Labs, Inc. 122 p. 

123-2 Aquatic plant growth

MRID Citation Reference
-54 of 75-

43330701 Thompson, S.; Swigert, J. (1994) MON 12000: A 14-Day 

Toxicity Test with Duckweed (Lemna gibba G3): Lab Project 

Number: RD 1241: WL-93-149: 139A-156. Unpublished study 

prepared by Wildlife International Ltd. 48 p. 

46004101 Sutherland, C.; Kendall, T.; Krueger, H. (2002) A 14-Day 

Toxicity Test with Duckweed (Lemna gibba G3) with Subsequent 

Recovery Phase: MON 12000: Final Report. Project Number: 

WL/199/284, 139A/255A, R/D/1614. Unpublished study prepared 

by Wildlife International, Ltd. 81 p.

43330702 Thompson, S.; Swigert, J. (1993) MON 12000: A 5-Day Toxicity 

Test with the Freshwater Algae (Selenastrum capricornutum): Lab 

Project Number: RD 1241: WL-92-178: 139A-151A. 

Unpublished study prepared by Wildlife International Ltd. 48 p. 

43330703 Thompson, S.; Swigert, J. (1994) MON 12000: A 5-Day Toxicity 

Test with the Freshwater Algae (Anabaena flos-aquae): Lab 

Project Number: RD 1241: WL-93-274: 139A-164A. 

Unpublished study prepared by Wildlife International Ltd. 42 p. 

43330704 Thompson, S.; Swigert, J. (1994) MON 12000: A 5-Day Toxicity 

Test with the Marine Diatom (Skeletonema costatum): Lab 

Project Number: RD 1241: WL-93-276: 139A-162. Unpublished 

study prepared by Wildlife International Ltd. 41 p. 

43330705 Thompson, S.; Swigert, J. (1994) MON 12000: A 5-Day Toxicity 

Test with the Freshwater Diatom (Navicula pelliculosa): Lab 

Project Number: RD 1241: WL-93-275: 139A-163. Unpublished 

study prepared by Wildlife International Ltd. 42 p. 

141-1 Honey bee acute contact

MRID Citation Reference

42139440 Winter, P.; Hoxter, K.; Smith, G. (1990) MON 12000: An Acute 

Con- tact Study with the Honey Bee: Lab Project Number: WL-90-

183: 139-265: RD 1061. Unpublished study prepared by Wildlife 

Inter- national Ltd. 17 p.
-55 of 75-

Appendix A. Justification for Special Studies

Guideline Number: none

Study Titles: Special Study for Non-Target Plant Reproductive Toxicity

Rationale for Requiring the Data

As stated in the Problem Formulation, investigations/studies have indicated a small percentage 

of the label application rate of low dose high potency herbicides such as sulfonylureas, such as 

halosulfuron-methyl, may impact the reproduction of non-target terrestrial plants. However, 

there are no available data on adverse reproductive impacts to terrestrial plants from 

halosulfuron-methyl residues due to spray drift. Terrestrial plant reproductive toxicity data 

would help to screen for potential plant risks associated with halosulfuron-methyl use. Plants 

form the basis of most habitats and contribute significantly to overall environmental quality. The 

loss of plant reproductive output could potentially have an adverse effect on animals, both 

invertebrates and vertebrates, as many are dependent on plant reproduction for a food source and 

for habitat quality and structure. A solid understanding of the potential risks to plants is 

therefore essential for sound environmental management. A study protocol must be submitted 

for review and approved by the Agency prior to initiation of the study.

Practical Utility of the Data

How will the data be used? 

The data will be used to estimate potential reproductive risks to non-target terrestrial plants, 

including the likelihood of potential risks to endangered species, either by direct effects or by 

indirect effects, and to reduce uncertainties associated with the current ecological risk 

assessment. By refining the assessment, the Agency will be able to determine whether current 

labeling is appropriate and whether further mitigation is necessary. In the absence of this data, 

risks to terrestrial plants will be presumed.

How could the data impact the Agency’s future decision-making?

These data, once submitted, should allow the Agency to characterize the risk posed to plant 

reproductive processes from halosulfuron-methyl in terrestrial ecosystems. Primary producers 

(i.e. plants) provide food and habitat vital to ecological processes. Therefore, a solid 

understanding of the potential risks to non-target plants is essential in order to assess the 

environmental risks the use of halosulfuron-methyl may pose. If the data indicate that 

halosulfuron-methyl poses significant risks to these non-target plant species, the Agency may 

explore additional decision options to minimize the risks to these species. The lack of these data

will limit the flexibility the Agency and registrants have in complying with the Endangered 

Species Act and could result in use restrictions for halosulfuron-methyl which may otherwise be 

avoided, or which are unnecessarily severe. 
-56 of 75-

Guideline Number: 835.4100 (Enhanced Study Requested)

Study Title: Aerobic Soil Metabolism

Rationale for Requiring the Data

Acceptable data on the aerobic soil metabolism of halosulfuron-methyl in four soils are required 

under 40 CFR Part 158, Subpart N (revised July 1, 2009) for labeling that includes terrestrial 

uses. Submitted aerobic soil metabolism data were conducted at an insufficient number of sites 

to meet current guidelines. The Agency has a limited understanding of how halosulfuron-methyl 

behaves in aerobic soil environments once applied. There are acceptable data from only two sites 

for aerobic soil metabolism. The guideline specifically stipulates that results from at least four 

relevant soils of different organic carbon content, pH, clay content, and microbial biomass must 

be submitted in order to characterize the variability in the aerobic biodegradation of 

halosulfuron-methyl in the environment. Furthermore, due to the high variability in 

halosulfuron-methyl persistence by site additional tests will also be required, as outlined below.

 

The behavior of parent halosulfuron methyl is highly variable from site to site, as evidenced by 

the variance in results regarding its persistence and mobility between laboratory and field data. 

Therefore, data above the minimum guidelines are being required under Guidelines 835.4100 

and 835.2120 (rationale for the additional data requirements to supplement the minimum data 

requirements for the latter guideline is discussed separately).

For the 835.4100 additional tests, prior to providing complete guideline studies in at least 2 

additional soils, the registrant shall conduct limited studies for parent decline (analysis for 

degradate formation in these preliminary studies is optional) for at least ten soil types 

representative of the spectrum of major halosulfuron-methyl use areas (note, that the preliminary 

studies may track, but are not required to track the formulation and decline of degradation 

products). Particular attention should be paid to selecting a representative range of soil types / 

classifications representing a range of pH values and a variety of organic matter amounts and 

type and mineral compositions for the test soils. These preliminary studies should be conducted 

with sampling and analysis out to 180 days after application or until parent halosulfuron-methyl 

has declined below 1% of the applied amount (whichever comes first). The objective of the 

preliminary studies is to provide a baseline for the range of metabolism rates likely to occur in 

the field for halosulfuron-methyl; the registrant may choose soils where halosulfuron-methyl was 

most persistent to conduct at least the minimum required two addition guideline 835.4100 

studies (which always require full characterization of the formation and decline of major 

degradates.) Note that the preliminary studies are needed because discrepancies between field 

and laboratory results confirm that halosulfuron can be significantly more persistent at some 

sites than shown in the currently available aerobic soil metabolism studies.
-57 of 75-

Practical Utility of the Data

How will the data be used?

The aerobic soil metabolism data from multiple soil types will facilitate a better understanding of 

the fate of halosulfuron-methyl residues in soil. For example, if data indicate that degradation in 

aerobic conditions occurs rapidly in neutral and acidic soils to nontoxic transformation products, 

then the Agency could potentially determine that halosulfuron-methyl residues of concern do not 

persist in these systems. The studies may potentially reveal that halosulfuron-methyl 

degradation is relatively slow in certain types of soil systems which might justify certain 

restrictions on its use in these areas.

How could the data change the Agency’s decision or impact the Agency’s future decisionmaking? 

In the absence of the requested data, halosulfuron-methyl aerobic soil metabolism half-lives will 

be conservatively assumed to be higher than shown in the limited available studies (which are 

not representative of all field conditions). If the required data indicate that halosulfuron-methyl

in aerobic soil environments is rapidly biodegraded to nontoxic degradation products, then risk 

assessment conclusions and associated labeled use precautions and/or restrictions could be made 

less restrictive.

Guideline Number: 835.2120 (Enhanced Study Requested)

Study Title: Hydrolysis

Rationale for Requiring the Data

The submitted hydrolysis study is acceptable; but given the apparent critical importance of the 

change in hydrolysis rate of halosulfuron-methyl with pH and temperature, an additional study 

will be required. Suggested parameters include testing at pH 5, 7, and 9 and at 10, 15, 20, and 

25 C for 60 days and analysis for halosulfuron-methyl and potentially major hydrolysis products

(with additional evaluations at pH 4, 6, and 8 for the 15 C studies.)

Practical Utility of the Data

How will the data be used?

The hydrolysis rate data from multiple soil types will facilitate a better understanding of the fate 

of halosulfuron-methyl residues in soil and water and more accurate predictions of surface and 

groundwater exposure. 

How could the data change the Agency’s decision or impact the Agency’s future decisionmaking? 

In the absence of the requested data, halosulfuron-methyl hydrolysis half-lives will be 

conservatively assumed to be higher than shown in the limited available studies (which are not 

representative of all field conditions). 
-58 of 75-

Appendix B. Chemical structures of halosulfuron-methyl and selected 

environmental degradates

Halosulfuron-methyl

CHEMICAL NAME:methyl 5-{[(dimethoxy-2-pyrimidinyl) amino] carbonylaminosulfonyl -3-

chloro -1-methyl-1-H- pyrazole-4-carboxylate

Halosulfuron rearrangement ester or CP-151790 or PZ-SP-2

CHEMICAL NAME:

3-Chloro-5-[(4,6-dimethoxy-2-pyrimidinyl)amino]-1-methyl-1H-pyrazole4-carboxylic acid, methyl ester

1H-Pyrazole-4-carboxylic acid, 3-chloro-5- [(4,6-dimethoxy-2-pyrimidinyl)amino]-1-methyl, 

methyl ester

OR

Methyl 3-Chloro-5-(4,6-dimethoxypyrimidin-2-ylamino)-

OR

1-methylpyrazole-4-carboxylate
-59 of 75-

Halosulfuron aminopyrimidine or CP 17477

CHEMICAL NAME:4,6-Dimethoxy-2-pyrimidinamine

Halosulfuron guanidine or PZ-SP-12

IH-Pyrazole-4-carboxylic acid. S-[([[(aminoiminomethyl)amino]carbonyl]amino]sulfonyl]-

3-chloro-l-melhyl

Halosulfuron acid or CP-147921

CHEMICAL NAME:

3-Chloro-5-[[[[(4,6-dimethoxy-2-pyrimidinyl) amino] carbonyl]amino] sulfonyl]-l-methyl-1Hpyrazole-4-carboxylic acid
-60 of 75-

3-Chlorosulfonamide acid (pyrazole) or CP-147924 or PZ-SP-8

CHEMICAL NAME:

5-(Aminosulfonyl)-3-chloro-l-methyl-1H-pyrazole-4-carboxylic acid

IH-Pyrazole-4-carboxylic acid. 5-(aminosulfonyl)-3-chloro-l-melhyl

OR

Desmethyl halosulfuron or CP 147922

CHEMICAL NAME:

3-Chloro-5-[[[[(4-hydroxy-6-methoxy-2-pyrimidinyl) amino]

carbonyl] amino] sulfonyl]-1-methyl-1H-pyrazole-4-carboxy!ic acid,

methyl ester
-61 of 75-

3-Chlorosulfonamide ester or CP 147925

CHEMICAL NAME:

5-(Aminosulfonyl)-3-chloro-l-methyl-1H-pyrazole-4-carboxylic acid,

methyl ester

OR

IH-Pyrazole-4-carboxylic acid. S-(aminosulfonyl)-3-chloro-l-melhyl-. methyl ester

S NH2

O

O

N N

O O

Cl
-62 of 75-

Appendix C. Aquatic Toxicity Predictions of Halosulfuron-Methyl and Major 

Degradates from Structure-Activity Relationships (SARs) using the ECOSAR 

Class Program and Review of Available Data

The structures of four halosulfuron methyl metabolites with demonstrated environmental 

persistence (as well as the parent molecule, for context) were entered into the ECOSAR v.1.0 

model as SMILES strings. 

One of the major persistent metabolites of halosulfuron-methyl, CP 17477 or 4,6-Dimethoxy-2-

pyrimidinamine, is common to several other sulfonylurea pesticides with registrations in the US 

and/or other countries. This is the only metabolite of halosulfuron-methyl with some measured 

toxicological data currently available. Both predicted and observed toxicological endpoint data 

for aquatic species are summarized in Table C1. CP17477 was classified as a neutral organic 

and an aromatic amine. Table C1 shows the observed values recorded in the Pesticide Properties 

database (PPDB) maintained by the FOOTPRINT Project12 and predicted toxicity using either 

neutral organic or aromatic amine structure-activity relationships. Based on the data available in 

the PPDB database, the measured values are within the range of the predicted values by 

ECOSAR and more closely related to the toxicity values predicted for the neutral organic 

structure-activity relationship for this compound. 

Table C1. Toxicity Data for Analog Chemical And QSAR Analysis for the aminopyrimidine 

metabolite of halosulfuron methyl (CP 17477).

Endpoint CP 17477 (PPDB 

data1

CP 17477

) (ECOSAR – aromatic 

amine SAR)

CP 17477

(ECOSAR – neutral 

organic SAR)

Fish 96-h LC50 97 mg/L

(rainbow trout) 

79 mg/L 920 mg/L

Fish chronic toxicity 

value

No data

2

0.38 mg/L 90 mg/L 

Algae 96h EC50 120 mg/L 

(P. subcapitata)

9.2 mg/L 130 mg/L

Lemna 7-d EC50 > 100 mg/L No prediction No prediction

Daphnid 48-h EC50 > 100 mg/L 2.4 mg/L 469 mg/L

Daphnid chronic

toxicity value

24 mg/L (21-d NOEC)

2

0.05 mg/L 36 mg/L 

1 Other company chemical codes for this metabolite include INJV0290, AE-F092944, and 

HOE092944. Aquatic toxicity data were retrieved from PPDB through a search for the string “2-

amino-4,6-dimethoxypyrimidine” or for “AE-F092944” (duplicate entries for this compound in 

the database may not contain this information). The Pesticide Properties Database (aka. 

Footprint) may be accessed at: http://sitem.herts.ac.uk/aeru/footprint/en/index.htm

2

 ChV = ECOSAR chronic toxicity value

 12 More information accessible at: http://sitem.herts.ac.uk/aeru/footprint/.
-63 of 75-

The ECOSAR results for the parent compound, halosulfuron-methyl, and four degradates are 

presented below.

AMINOPYRIMINDINE ECOSAR OUTPUT:

Halosulfuron aminopyrimidine or CP 17477 

CHEMICAL NAME:4,6-Dimethoxy-2-pyrimidinamine

SMILES: N1=C(C=C(OC)N=C1N)OC

Molecular Weight 155.16

Molecular Formula C6 H9 N3 O2

SMILES : n1c(cc(OC)nc1N)OC

CHEM : 

CAS Num: 

ChemID1: 

ChemID2: 

ChemID3: 

MOL FOR: C6 H9 N3 O2 

MOL WT : 155.16

Log Kow: 0.95 (KowWin estimate)

Melt Pt: 

Wat Sol: 1.108E+004 mg/L (WskowWin estimate)

ECOSAR v1.00 Class(es) Found

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

Anilines (Aromatic Amines)

 Predicted

ECOSAR Class Organism Duration End Pt mg/L (ppm)

=========================== ================== ======== ====== ==========

Anilines (Aromatic Amines) : Fish 96-hr LC50 78.845

Anilines (Aromatic Amines) : Fish 14-day LC50 225.619

Anilines (Aromatic Amines) : Daphnid 48-hr LC50 2.376

Anilines (Aromatic Amines) : Green Algae 96-hr EC50 9.172

Anilines (Aromatic Amines) : Fish ChV 0.380

Anilines (Aromatic Amines) : Daphnid ChV 0.050

Anilines (Aromatic Amines) : Green Algae ChV 6.078

=========================== ================== ======== ====== ==========

Neutral Organic SAR : Fish 96-hr LC50 922.143

(Baseline Toxicity) : Daphnid 48-hr LC50 468.756

 : Green Algae 96-hr EC50 131.427

: Fish ChV 89.591

: Daphnid ChV 35.968

: Green Algae ChV 39.276
-64 of 75-

Note: * = asterisk designates: Chemical may not be soluble

 enough to measure this predicted effect.

Anilines (Aromatic Amines):

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

 For Fish Acute Toxicity Values: 2,3,5,6-Tetrachloroaniline is 19 times

more toxic than predicted by this SAR. Tetrabromoaniline may be more toxic

than predicted by this SAR as well.

 For Daphnid and Green Algae Toxicity Values: Tetrachloro- and tetrabromaniline may be 20 times toxic than predicted by this SAR.

 N-Substituted anilines are less toxic than predicted by these SARs;

for these compounds, Neutral Organic SARs are used.

ECOSAR v1.00 SAR Limitations:

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

Maximum LogKow: >7.8 (Fish 96-hr LC50, Daphnid 48-h LC50)

Maximum LogKow: >3.7 (Fish 14-day LC50)

Maximum LogKow: >4 (Green Algae 96-hr EC50 and ChV)

Maximum LogKow: >4.3 (Fish ChV)

Maximum LogKow: >2.4 (Daphnid ChV)

Maximum Mol Wt: 1000

Baseline Toxicity SAR Limitations:

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

Maximum LogKow: 5.0 (Fish 96-hr LC50; Daphnid LC50)

Maximum LogKow: 6.4 (Green Algae EC50)

Maximum LogKow: 8.0 (ChV)

Maximum Mol Wt: 1000

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

3-Chlorosulfonamide ester or CP 147925 ECOSAR OUTPUT:

3-Chlorosulfonamide ester or CP 147925

CHEMICAL NAME:

5-(Aminosulfonyl)-3-chloro-l-methyl-1H-pyrazole-4-carboxylic acid, methyl ester

OR

IH-Pyrazole-4-carboxylic acid. S-(aminosulfonyl)-3-chloro-l-melhyl-. methyl ester

NS(=O)(C1=C(C(OC)=O)C(Cl)=NN1C)=O

SMILES : NS(=O)(c1c(C(=O)(OC))c(CL)nn1C)=O

CHEM : 

CAS Num: 

ChemID1: 

S NH2

O

O

N N

O O

Cl
-65 of 75-

ChemID2: 

ChemID3: 

MOL FOR: C6 H8 CL1 N3 O4 S1 

MOL WT : 253.66

Log Kow: -0.54 (KowWin estimate)

Melt Pt: 

Wat Sol: 6.491E+004 mg/L (WskowWin estimate)

ECOSAR v1.00 Class(es) Found

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

Esters

Amides 

Pyrazoles/Pyrroles 

 Predicted

ECOSAR Class Organism Duration End Pt mg/L (ppm)

=========================== ================== ======== ====== ==========

Esters : Fish 96-hr LC50 973.003

Esters : Fish 14-day LC50 6.3e+006 *

Esters : Daphnid 48-hr LC50 2773.907

Esters : Green Algae 96-hr EC50 1553.011

Esters : Fish 32/33-d ChV 160.932

Esters : Daphnid 21-day ChV 3363.099

Esters : Green Algae ChV 171.468

Esters : Fish (SW) 96-hr LC50 1886.022

Esters : Mysid Shrimp 96-hr LC50 5335.749

Esters : Fish (SW) ChV 170.435 !

Esters : Mysid Shrimp (SW) ChV 8.13e+007 *

Esters : Earthworm 14-day LC50 21747.797

Amides : Fish 96-hr LC50 3316.245

Amides : Daphnid 48-hr LC50 777.645

Amides : Green Algae 96-hr EC50 2.838

Amides : Fish ChV 19.604

Amides : Daphnid ChV 10.258 !

Amides : Green Algae ChV 0.424

Pyrazoles/Pyrroles : Fish 96-hr LC50 44.265

Pyrazoles/Pyrroles : Daphnid 48-hr LC50 26.196

Pyrazoles/Pyrroles : Fish ChV 4.280 !

Pyrazoles/Pyrroles : Daphnid ChV 2.814 !

=========================== ================== ======== ====== ==========

Neutral Organic SAR : Fish 96-hr LC50 27406.164

(Baseline Toxicity) : Daphnid 48-hr LC50 11637.252

 : Green Algae 96-hr EC50 1771.492

: Fish ChV 2751.721

: Daphnid ChV 686.280

 : Green Algae ChV 403.411

Note: * = asterisk designates: Chemical may not be soluble

 enough to measure this predicted effect.

Note: ! = exclamation designates: The toxicity value was determined from

 a predicted SAR using established acute-to-chronic ratios and ECOSAR

 regression techniques which are documented in the supporting Technical

 Reference Manual. When possible, this toxicity value should be

 considered in a weight of evidence approach.

Esters:

------

 For Fish LC50 (96-h), Daphnid LC50, Mysid: If the log Kow is greater

than 5.0, or if the compound is solid and the LC50 exceeds the water

solubility by 10X, no effects at saturation are predicted.
-66 of 75-

 For Fish LC50 (14-day) and Earthworm LC50: If the log Kow is greater

than 6.0, or if the compound is solid and the LC50 exceeds the water

solubility by 10X, no effects at saturation are predicted.

 For Green Algae Acute Toxicity Values: If the log Kow of the chemical is

greater than 6.4, or if the compound is solid and the EC50 exceeds the water

solubility by 10X, no effects at saturation are predicted for these endpoints.

 For All Chronic Toxicity Values: If the log Kow of the chemical is greater

than 8.0, or if the compound is solid and the ChV exceeds the water solubility

by 10X, no effects at saturation are predicted for these endpoints.

ECOSAR v1.00 SAR Limitations:

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

Maximum LogKow: 5.0 (Fish 96-hr LC50; Daphnid LC50, Mysid LC50)

Maximum LogKow: 6.0 (Fish 14-day LC50; Earthworm LC50)

Maximum LogKow: 6.4 (Green Algae EC50)

Maximum LogKow: 8.0 (ChV)

Maximum Mol Wt: 1000

Amides :

-------

No limitations known at this time.

ECOSAR v1.00 SAR Limitations:

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

Maximum LogKow: >8.5 (LC50)

Maximum LogKow: >8.0 (EC50,ChV)

Maximum Mol Wt: 1000

Pyrazoles/Pyrroles :

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

 For Fish and Daphnid Acute Toxicity Values: If the log Kow of the chemical

is greater than 5.0, or if the compound is solid and the LC50 exceeds the

water solubility by 10X, no effects at saturation are predicted for these

endpoints.

 For Green Algae Acute Toxicity Values: If the log Kow of the chemical is

greater than 6.4, or if the compound is solid and the EC50 exceeds the water

solubility by 10X, no effects at saturation are predicted for these endpoints.

 For All Chronic Toxicity Values: If the log Kow of the chemical is greater

than 8.0, or if the compound is solid and the ChV exceeds the water solubility

by 10X, no effects at saturation are predicted for these endpoints.

ECOSAR v1.00 SAR Limitations:

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

Maximum LogKow: 5.0 (LC50)

Maximum LogKow: 6.4 (EC50)

Maximum LogKow: 8.0 (ChV)

Maximum Mol Wt: 1000

Baseline Toxicity SAR Limitations:

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

Maximum LogKow: 5.0 (Fish 96-hr LC50; Daphnid LC50)

Maximum LogKow: 6.4 (Green Algae EC50)

Maximum LogKow: 8.0 (ChV)

Maximum Mol Wt: 1000

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-67 of 75-

3-Chlorosulfonamide acid or CP 147924 ECOSAR OUTPUT:

3-Chlorosulfonamide acid (pyrazole) or CP-147924 or PZ-SP-8

CHEMICAL NAME:

5-(Aminosulfonyl)-3-chloro-l-methyl-1H-pyrazole-4-carboxylic acid

IH-Pyrazole-4-carboxylic acid. 5-(aminosulfonyl)-3-chloro-l-melhyl

OR

SMILES: NS(=O)(C1=C(C(O)=O)C(Cl)=NN1C)=O

SMILES : NS(=O)(c1c(C(=O)(O))c(CL)nn1C)=O

CHEM : 

CAS Num: 

ChemID1: 

ChemID2: 

ChemID3: 

MOL FOR: C5 H6 CL1 N3 O4 S1 

MOL WT : 239.63

Log Kow: -0.49 (KowWin estimate)

Melt Pt: 

Wat Sol: 7.083E+004 mg/L (WskowWin estimate)

ECOSAR v1.00 Class(es) Found

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

Amides -acid

Pyrazoles/Pyrroles -acid

 Predicted

ECOSAR Class Organism Duration End Pt mg/L (ppm)

=========================== ================== ======== ====== ==========

--> Acid moeity found: Predicted values multiplied by 10

Amides -acid : Fish 96-hr LC50 28800.607

Amides -acid : Daphnid 48-hr LC50 6862.251

Amides -acid : Green Algae 96-hr EC50 26.026

Amides -acid : Fish ChV 170.256

Amides -acid : Daphnid ChV 90.525 !

Amides -acid : Green Algae ChV 4.004

Pyrazoles/Pyrroles -acid : Fish 96-hr LC50 394.236

Pyrazoles/Pyrroles -acid : Daphnid 48-hr LC50 237.681

Pyrazoles/Pyrroles -acid : Fish ChV 38.226 !

Pyrazoles/Pyrroles -acid : Daphnid ChV 25.376 !

=========================== ================== ======== ====== ==========

Neutral Organic SAR : Fish 96-hr LC50 23661.834

(Baseline Toxicity) : Daphnid 48-hr LC50 10103.599

 : Green Algae 96-hr EC50 1567.464

 : Fish ChV 2373.346

: Daphnid ChV 600.724
-68 of 75-

 : Green Algae ChV 359.973

Note: * = asterisk designates: Chemical may not be soluble

 enough to measure this predicted effect.

Note: ! = exclamation designates: The toxicity value was determined from

 a predicted SAR using established acute-to-chronic ratios and ECOSAR

 regression techniques which are documented in the supporting Technical

 Reference Manual. When possible, this toxicity value should be

 considered in a weight of evidence approach.

Amides :

-------

No limitations known at this time.

ECOSAR v1.00 SAR Limitations:

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

Maximum LogKow: >8.5 (LC50)

Maximum LogKow: >8.0 (EC50,ChV)

Maximum Mol Wt: 1000

Pyrazoles/Pyrroles :

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

 For Fish and Daphnid Acute Toxicity Values: If the log Kow of the chemical

is greater than 5.0, or if the compound is solid and the LC50 exceeds the

water solubility by 10X, no effects at saturation are predicted for these

endpoints.

 For Green Algae Acute Toxicity Values: If the log Kow of the chemical is

greater than 6.4, or if the compound is solid and the EC50 exceeds the water

solubility by 10X, no effects at saturation are predicted for these endpoints.

 For All Chronic Toxicity Values: If the log Kow of the chemical is greater

than 8.0, or if the compound is solid and the ChV exceeds the water solubility

by 10X, no effects at saturation are predicted for these endpoints.

ECOSAR v1.00 SAR Limitations:

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

Maximum LogKow: 5.0 (LC50)

Maximum LogKow: 6.4 (EC50)

Maximum LogKow: 8.0 (ChV)

Maximum Mol Wt: 1000

Baseline Toxicity SAR Limitations:

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

Maximum LogKow: 5.0 (Fish 96-hr LC50; Daphnid LC50)

Maximum LogKow: 6.4 (Green Algae EC50)

Maximum LogKow: 8.0 (ChV)

Maximum Mol Wt: 1000

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Halosulfuron rearrangement ester (CP-151790 CP 147924) ECOSAR OUTPUT:
-69 of 75-

Halosulfuron rearrangement ester or CP 147925 or CP-151790 or PZ-SP-2

CHEMICAL NAME:

3-Chloro-5-[(4,6-dimethoxy-2-pyrimidinyl)amino]-1-methyl-1H-pyrazole-4-carboxylic acid, 

methyl ester

1H-Pyrazole-4-carboxylic acid, 3-chloro-5- [(4,6-dimethoxy-2-pyrimidinyl)amino]-1-methyl, 

methyl ester

OR

Methyl 3-Chloro-5-(4,6-dimethoxypyrimidin-2-ylamino)-1-methylpyrazole-4-carboxylate

OR

SMILES : COc1nc(Nc2c(C(=O)(OC))c(CL)nn2C)nc(OC)c1

CHEM : 

CAS Num: 

ChemID1: 

ChemID2: 

ChemID3: 

MOL FOR: C12 H14 CL1 N5 O4 

MOL WT : 327.73

Log Kow: 2.01 (KowWin estimate)

Melt Pt: 

Wat Sol: 162.1 mg/L (WskowWin estimate)

ECOSAR v1.00 Class(es) Found

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

Esters

Pyrazoles/Pyrroles 

 Predicted

ECOSAR Class Organism Duration End Pt mg/L (ppm)

=========================== ================== ======== ====== ==========

Esters : Fish 96-hr LC50 44.015

Esters : Fish 14-day LC50 6252.322 *

Esters : Daphnid 48-hr LC50 90.360

Esters : Green Algae 96-hr EC50 38.472

Esters : Fish 32/33-d ChV 3.945

Esters : Daphnid 21-day ChV 56.877

Esters : Green Algae ChV 9.727

Esters : Fish (SW) 96-hr LC50 65.916

Esters : Mysid Shrimp 96-hr LC50 63.179

Esters : Fish (SW) ChV 9.628 !

Esters : Mysid Shrimp (SW) ChV 4650.664 *

Esters : Earthworm 14-day LC50 4243.429 *

Pyrazoles/Pyrroles : Fish 96-hr LC50 2.220

Pyrazoles/Pyrroles : Daphnid 48-hr LC50 3.655
-70 of 75-

Pyrazoles/Pyrroles : Fish ChV 0.252 !

Pyrazoles/Pyrroles : Daphnid ChV 0.280 !

=========================== ================== ======== ====== ==========

Neutral Organic SAR : Fish 96-hr LC50 247.939 *

(Baseline Toxicity) : Daphnid 48-hr LC50 143.230

 : Green Algae 96-hr EC50 61.986

 : Fish ChV 23.532

: Daphnid ChV 13.251

: Green Algae ChV 22.471

Note: * = asterisk designates: Chemical may not be soluble

 enough to measure this predicted effect.

Note: ! = exclamation designates: The toxicity value was determined from

 a predicted SAR using established acute-to-chronic ratios and ECOSAR

 regression techniques which are documented in the supporting Technical

 Reference Manual. When possible, this toxicity value should be

 considered in a weight of evidence approach.

Esters:

------

 For Fish LC50 (96-h), Daphnid LC50, Mysid: If the log Kow is greater

than 5.0, or if the compound is solid and the LC50 exceeds the water

solubility by 10X, no effects at saturation are predicted.

 For Fish LC50 (14-day) and Earthworm LC50: If the log Kow is greater

than 6.0, or if the compound is solid and the LC50 exceeds the water

solubility by 10X, no effects at saturation are predicted.

 For Green Algae Acute Toxicity Values: If the log Kow of the chemical is

greater than 6.4, or if the compound is solid and the EC50 exceeds the water

solubility by 10X, no effects at saturation are predicted for these endpoints.

 For All Chronic Toxicity Values: If the log Kow of the chemical is greater

than 8.0, or if the compound is solid and the ChV exceeds the water solubility

by 10X, no effects at saturation are predicted for these endpoints.

ECOSAR v1.00 SAR Limitations:

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

Maximum LogKow: 5.0 (Fish 96-hr LC50; Daphnid LC50, Mysid LC50)

Maximum LogKow: 6.0 (Fish 14-day LC50; Earthworm LC50)

Maximum LogKow: 6.4 (Green Algae EC50)

Maximum LogKow: 8.0 (ChV)

Maximum Mol Wt: 1000

Pyrazoles/Pyrroles :

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

 For Fish and Daphnid Acute Toxicity Values: If the log Kow of the chemical

is greater than 5.0, or if the compound is solid and the LC50 exceeds the

water solubility by 10X, no effects at saturation are predicted for these

endpoints.

 For Green Algae Acute Toxicity Values: If the log Kow of the chemical is

greater than 6.4, or if the compound is solid and the EC50 exceeds the water

solubility by 10X, no effects at saturation are predicted for these endpoints.

 For All Chronic Toxicity Values: If the log Kow of the chemical is greater

than 8.0, or if the compound is solid and the ChV exceeds the water solubility

by 10X, no effects at saturation are predicted for these endpoints.

ECOSAR v1.00 SAR Limitations:

----------------------------
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Maximum LogKow: 5.0 (LC50)

Maximum LogKow: 6.4 (EC50)

Maximum LogKow: 8.0 (ChV)

Maximum Mol Wt: 1000

Baseline Toxicity SAR Limitations:

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

Maximum LogKow: 5.0 (Fish 96-hr LC50; Daphnid LC50)

Maximum LogKow: 6.4 (Green Algae EC50)

Maximum LogKow: 8.0 (ChV)

Maximum Mol Wt: 1000
-72 of 75-

PARENT HALOSULFURON METHYL ECOSAR OUTPUT:

Halosulfuron-methyl

CHEMICAL NAME:methyl 5-{[(dimethoxy-2-pyrimidinyl) amino] carbonylaminosulfonyl -3-

chloro -1-methyl-1-H- pyrazole-4-carboxylate

Molecular Formula: C13H15ClN6O7

Smiles Code:

S

O=S(=O)(c1c(C(=O)OC)c(Cl)nn1C)NC(=O)Nc2nc(OC)cc(OC)n2

SMILES : O=S(=O)(c1c(C(=O)OC)c(CL)nn1C)NC(=O)Nc2nc(OC)cc(OC)n2

CHEM : 

CAS Num: 

ChemID1: 

ChemID2: 

ChemID3: 

MOL FOR: C13 H15 CL1 N6 O7 S1 

MOL WT : 434.81

Log Kow: 0.40 (KowWin estimate)

Melt Pt: 

Wat Sol: 15 mg/L (experimental database)

ECOSAR v1.00 Class(es) Found

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

Esters

Amides 

Sulfonyl Ureas 

Pyrazoles/Pyrroles 

 Predicted

ECOSAR Class Organism Duration End Pt mg/L (ppm)

=========================== ================== ======== ====== ==========

Esters : Fish 96-hr LC50 486.273 *

Esters : Fish 14-day LC50 7.73e+005 *

Esters : Daphnid 48-hr LC50 1228.641 *

Esters : Green Algae 96-hr EC50 621.988 *

Esters : Fish 32/33-d ChV 64.204 *

Esters : Daphnid 21-day ChV 1170.562 *

Esters : Green Algae ChV 93.130 *

Esters : Fish (SW) 96-hr LC50 857.266 *

Esters : Mysid Shrimp 96-hr LC50 1629.007 *

Esters : Fish (SW) ChV 92.429 *!

Esters : Mysid Shrimp (SW) ChV 3.49e+006 *

Esters : Earthworm 14-day LC50 18603.760 *

Amides : Fish 96-hr LC50 1033.179 *

Amides : Daphnid 48-hr LC50 334.777 *

Amides : Green Algae 96-hr EC50 2.668

Amides : Fish ChV 6.108

Amides : Daphnid ChV 4.416 !

Amides : Green Algae ChV 0.726
-73 of 75-

Sulfonyl Ureas : Daphnid 48-hr LC50 1323.615 *

Sulfonyl Ureas : Green Algae 96-hr EC50 0.049

Sulfonyl Ureas : Daphnid ChV 118.392 *!

Sulfonyl Ureas : Green Algae ChV 0.012 !

Pyrazoles/Pyrroles : Fish 96-hr LC50 22.978 *

Pyrazoles/Pyrroles : Daphnid 48-hr LC50 19.809 *

Pyrazoles/Pyrroles : Fish ChV 2.356 !

Pyrazoles/Pyrroles : Daphnid ChV 1.878 !

=========================== ================== ======== ====== ==========

Neutral Organic SAR : Fish 96-hr LC50 7578.789 *

(Baseline Toxicity) : Daphnid 48-hr LC50 3603.776 *

 : Green Algae 96-hr EC50 805.555 *

: Fish ChV 745.362 *

: Daphnid ChV 250.794 *

: Green Algae ChV 217.647 *

Note: * = asterisk designates: Chemical may not be soluble

 enough to measure this predicted effect.

Note: ! = exclamation designates: The toxicity value was determined from

 a predicted SAR using established acute-to-chronic ratios and ECOSAR

 regression techniques which are documented in the supporting Technical

 Reference Manual. When possible, this toxicity value should be

 considered in a weight of evidence approach.

Esters:

------

 For Fish LC50 (96-h), Daphnid LC50, Mysid: If the log Kow is greater

than 5.0, or if the compound is solid and the LC50 exceeds the water

solubility by 10X, no effects at saturation are predicted.

 For Fish LC50 (14-day) and Earthworm LC50: If the log Kow is greater

than 6.0, or if the compound is solid and the LC50 exceeds the water

solubility by 10X, no effects at saturation are predicted.

 For Green Algae Acute Toxicity Values: If the log Kow of the chemical is

greater than 6.4, or if the compound is solid and the EC50 exceeds the water

solubility by 10X, no effects at saturation are predicted for these endpoints.

 For All Chronic Toxicity Values: If the log Kow of the chemical is greater

than 8.0, or if the compound is solid and the ChV exceeds the water solubility

by 10X, no effects at saturation are predicted for these endpoints.

ECOSAR v1.00 SAR Limitations:

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

Maximum LogKow: 5.0 (Fish 96-hr LC50; Daphnid LC50, Mysid LC50)

Maximum LogKow: 6.0 (Fish 14-day LC50; Earthworm LC50)

Maximum LogKow: 6.4 (Green Algae EC50)

Maximum LogKow: 8.0 (ChV)

Maximum Mol Wt: 1000

Amides :

-------

No limitations known at this time.

ECOSAR v1.00 SAR Limitations:

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

Maximum LogKow: >8.5 (LC50)

Maximum LogKow: >8.0 (EC50,ChV)

Maximum Mol Wt: 1000
-74 of 75-

Sulfonyl Ureas :

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

 For Fish and Daphnid Acute Toxicity Values: If the log Kow of the chemical

is greater than 5.0, or if the compound is solid and the LC50 exceeds the

water solubility by 10X, no effects at saturation are predicted for these

endpoints.

 For Green Algae Acute Toxicity Values: If the log Kow of the chemical is

greater than 6.4, or if the compound is solid and the EC50 exceeds the water

solubility by 10X, no effects at saturation are predicted for these endpoints.

 For All Chronic Toxicity Values: If the log Kow of the chemical is greater

than 8.0, or if the compound is solid and the ChV exceeds the water solubility

by 10X, no effects at saturation are predicted for these endpoints.

ECOSAR v1.00 SAR Limitations:

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

Maximum LogKow: 5.0 (LC50)

Maximum LogKow: 6.4 (EC50)

Maximum LogKow: 8.0 (ChV)

Maximum Mol Wt: 1000

Pyrazoles/Pyrroles :

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

 For Fish and Daphnid Acute Toxicity Values: If the log Kow of the chemical

is greater than 5.0, or if the compound is solid and the LC50 exceeds the

water solubility by 10X, no effects at saturation are predicted for these

endpoints.

 For Green Algae Acute Toxicity Values: If the log Kow of the chemical is

greater than 6.4, or if the compound is solid and the EC50 exceeds the water

solubility by 10X, no effects at saturation are predicted for these endpoints.

 For All Chronic Toxicity Values: If the log Kow of the chemical is greater

than 8.0, or if the compound is solid and the ChV exceeds the water solubility

by 10X, no effects at saturation are predicted for these endpoints.

ECOSAR v1.00 SAR Limitations:

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

Maximum LogKow: 5.0 (LC50)

Maximum LogKow: 6.4 (EC50)

Maximum LogKow: 8.0 (ChV)

Maximum Mol Wt: 1000

Baseline Toxicity SAR Limitations:

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

Maximum LogKow: 5.0 (Fish 96-hr LC50; Daphnid LC50)

Maximum LogKow: 6.4 (Green Algae EC50)

Maximum LogKow: 8.0 (ChV)

Maximum Mol Wt: 1000
-75 of 75-