2

Problem Formulation for the Environmental Fate, 

Ecological Risk, Endangered Species, and Drinking 

Water Exposure Assessments in Support of the 

Registration Review of Mesosulfuron-methyl

CAS: 208465-21-8

PC Code: 122009

Environmental Fate and Effects Division

Prepared by:

Michael Lowit, Ph.D., Ecologist

He Zhong, Ph.D., Biologist

U.S. Environmental Protection Agency

Office of Pesticide Programs

Environmental Fate and Effects Division

Environmental Risk Branch I

1200 Pennsylvania Ave., NW

Mail Code 7507P

Washington, DC 20460

Reviewed by:

Sujatha Sankula, Ph.D., Lead Biologist

Faruque Khan, Ph.D., Senior Fate Scientist
3

Table of Contents

1. Purpose........................................................................................................................................ 4

2. Problem Formulation .................................................................................................................. 4

2.1. Nature of Regulatory Action................................................................................................ 4

2.2. Previous Assessments.......................................................................................................... 4

2.2.1. Ecological Risk Assessments........................................................................................ 4

2.2.2. Drinking Water Exposure Assessments........................................................................ 4

3. Stressor Source and Distribution ................................................................................................ 5

3.1. Mechanism of Action.......................................................................................................... 5

3.2. Overview of Pesticide Use and Usage ................................................................................ 5

3.3. Environmental Fate and Transport...................................................................................... 6

3.4. Clean Water Act................................................................................................................ 13

4. Receptors.................................................................................................................................. 13

4.1. Effects to Aquatic Organisms........................................................................................... 14

4.2. Effects to Terrestrial Organisms....................................................................................... 16

4.3. Incident Databases Review............................................................................................... 19

5. Risk Hypothesis....................................................................................................................... 20

6. Analysis Plan ........................................................................................................................... 20

6.1. Stressors of Concern .......................................................................................................... 20

6.2. Measures of Exposure........................................................................................................ 24

6.3. Measures of Effect ............................................................................................................. 26

6.4. Integration of Exposure and Effects .................................................................................. 26

6.5. Endangered Species Assessments...................................................................................... 26

6.6. Endocrine Disruptor Screening.......................................................................................... 26

6.7. Drinking Water Assessment .............................................................................................. 26

6.8. Preliminary Identification of Data Gaps............................................................................ 27

6.8.1. Environmental Fate Data ............................................................................................ 27

6.8.2. Ecological Effects Data............................................................................................... 29

7. References................................................................................................................................ 34

APPENDIX A. Submitted Environmental Fate and Effects Studies........................................... 35

APPENDIX B. SIP v.1.0 Inputs and Outputs.............................................................................. 40

APPENDIX C. STIR v.1.0 Inputs and Outputs........................................................................... 41
4

1. Purpose

The purpose of this problem formulation is to provide an understanding of what is known about 

the environmental fate, ecological effects, and currently registered uses of mesosulfuron-methyl. 

This document provides a plan for analyzing data relevant to mesosulfuron-methyl and for 

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

assessments for its registered uses. Additionally, this problem formulation identifies data gaps, 

uncertainties, and potential assumptions used to address those uncertainties relative to 

characterizing the potential ecological risk associated with the registered uses of mesosulfuronmethyl.

2. Problem Formulation

2.1. Nature of Regulatory Action

As part of the implementation of the new Registration Review program1 pursuant to Section 3(g) 

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

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

standard for registration. This problem formulation in support of the registration review of 

mesosulfuron-methyl will be posted in the initial docket which will open the public phase of the 

review process.

2.2. Previous Assessments

2.2.1. Ecological Risk Assessments

Mesosulfuron-methyl (methyl-2-[3-(4,6-dimethoxypyrimidin-2-yl) ureido-sulfonyl]-4-

methanesulfonamido-methylbenzoate), a sulfonylurea herbicide, was first registered in the US in 

2004 for use as postemergent control and suppression of several types of weeds. Wheat and 

triticale are the only registered uses of mesosulfuron-methyl. EFED has conducted one 

ecological risk assessment (wheat use).

The previous risk assessment identified a risk concern for non-target terrestrial plants (listed and 

non-listed) and aquatic vascular plants (listed) (USEPA, 2004b). 

2.2.2. Drinking Water Exposure Assessments

The drinking water assessment (DWA) for wheat use was conducted using the Tier 1 FQPA 

Index Reservoir Screening Tool (FIRST) and the Screening Concentration in Ground Water 

model (SCIGROW) (USEPA, 2004a). Three bridge-intact major degradates (AE F154851, AE 

F160459, and AE F160460) were modeled along with mesosulfuron-methyl per request of the 

Health Effect Division (HED) Metabolism Committee Meeting (MARC). The findings from the 

DWA are summarized in Table 1. 

Table 1. Previous Estimated Drinking Water Concentrations

Product

Use

Peak (μg/L, Acute)1 Annual Average (μg/L ,Chronic)1

Parent Only Total Residues Parent Only Total Residues

Surface Water Sources using Tier I FIRST model

OSPREY

Winter Wheat

0.7 0.9 0.1 0.2

 1 http://www.epa.gov/oppsrrd1/registration_review/
5

Product

Use

Peak (μg/L, Acute)1 Annual Average (μg/L ,Chronic)1

Parent Only Total Residues Parent Only Total Residues

SILVERADO

Spring Wheat (including durum)

0.3 0.4 0.05 0.06

Ground Water Sources using Tier I SCIGROW model

OSPREY

Winter Wheat

0.01 0.02 0.01 0.02

SILVERADO 

Spring Wheat (including durum)

0.01 0.007 0.005 0.007

1

A PCA of0.56 was used for the surface water EDWC

3. Stressor Source and Distribution

Mesosulfuron-methyl is a sulfonylurea herbicide used to control and suppress several types of 

weeds. The formulated water dispersible granules are applied as a post-emergence ground or 

aerial spray. Several mesosulfuron-methyl degradates were identified from the submitted 

studies; some are common to other sulfonylurea herbicides. The major (formed ≥ 10%) 

degradates are AE F154851, AE F160459, AE F160460, AE F140584, AE F147447, AE 

F099095, and AE F092944. 

3.1. Mechanism of Action

Mesosulfuron-methyl belongs to the sulfonylurea herbicide family and more specifically to the 

pyrimidinylsulfonylurea group. Like all of the sulfonylurea herbicides, it is an acetolactate 

synthase inhibitor (ALS- inhibitor). Inhibition of this enzyme curtails the synthesis of branchedchain amino acids (valine, leucine, and isovaline), thus disrupting plant development and causing 

subsequent death. Valine, leucine, and isovaline are essential amino acids but they are not 

synthesized by higher animals. Sulfonylurea herbicides or other ALS-inhibitors are not expected 

to have any direct acute effects on animals because the ALS enzyme is not present in higher 

animals. Nevertheless, chronic effects cannot be ruled out.

3.2. Overview of Pesticide Use and Usage

There are currently eight registered end-use products containing mesosulfuron-methyl. All 

products are post-emergence herbicides formulated as water dispersible granules. About 

6000 lb mesosulfuron-methyl is applied annually (Screening Level Usage Analysis, 

1/18/2012) according to the Biological and Economic Analysis Division (BEAD). Uses and 

application rates are based on the most recent label use information system report (LUIS report), 

provided by BEAD (11/8/2012). The maximum application rates and application methods are 

listed in Table 2, although it should be noted that some labels do not indicate a maximum annual 

rate. To reduce uncertainty in the risk assessment, the Agency requests that the registrant provide 

additional label information where necessary on the number of applications per year, the total 

amount applied per year, and the application interval if applicable. The registration review risk 

assessment will be based on current label information at the time of assessment.
6

Table 2. Maximum Rates for Registered Uses of Mesosulfuron-methyl

Use Method of 

Application

Single Maximum 

Application Rate 

(lb ai/A)

Maximum Number 

of Applications per 

Year1

Annual Maximum

(lb ai/A)1

Winter Triticale Ground/Air 0.0134 NS NS

Winter Wheat Ground/Air 0.0134 1 0.0134

Spring Wheat Ground/Air 0.0036 1 0.003

1 Assumes one season/crop of winter or spring wheat per acre per year

NS – not stated on label

3.3. Environmental Fate and Transport

The physical, chemical, and environmental fate properties of mesosulfuron-methyl and its 

degradation products are summarized in Table 3. Mesosulfuron-methyl, like other sulfonylurea 

herbicides, has pH-dependent water solubility (e.g., medium (483 ppm) at pH 7 to very high 

(15,390 ppm) at pH 9) and exhibits weak binding to soils (Koc = 26-345). Mesosulfuron-methyl

has the potential to reach surface water by runoff and leaching to ground water but has low 

potential to bioaccumulate in fish or volatilize from soil and water.

Mesosulfuron-methyl will enter the environment through direct application onto soil and foliage. 

It may move off-site via spray drift, runoff, and leaching. Biotransformation is the major route 

of degradation in the environment (e.g., aerobic soil metabolism t1/2 = 20-199 days; anaerobic

aquatic metabolism t1/2 = 6-36 days, and aerobic aquatic metabolism t1/2 = 25-100 days). 

Mesosulfuron-methyl breaks down to unique degradates and degradates common to other 

sulfonylurea herbicides. Bridge-intact degradates (AE F154851, AE F160459, and AE F160460)

were found more frequently than bridge-cleavage degradates (AE F140584, AE F147477, AE 

F099095, AE F119094, and AE F092944) although the relative ratios among degradates appear 

to vary. There is no evidence from the environmental fate studies that the 4-methanesulfonamide 

group in the phenyl ring undergoes transformation for bridge-intact metabolites and phenyl ring 

bridge-cleavage metabolites.

Terrestrial field dissipation of mesosulfuron-methyl was conducted using the highest labeled 

application rate in bare plots in Florida, Illinois, and California (MRID 45386501). Rainfall was 

supplemented with irrigation to exceed the 10-year average rainfall at the Florida and California 

test sites; total water input during the study period was approximately 83% of the 10-year 

average at the Illinois test site. Under the field conditions, mesosulfuron-methyl exhibited a 

biphasic dissipation pattern, with an initial rapid dissipation phase occurring through 

approximately 30-50 days post treatment. The calculated half-life values of mesosulfuronmethyl were 58 days (r2 = 0.62), 136 days (r2 = 0.59), and 80 days (r2 = 0.75) at the Florida, 

Illinois, and California sites, respectively. In the study, soil samples were not analyzed for 

transformation products of mesosulfuron-methyl. However, in a laboratory aerobic soil 

metabolism study (MRID 45386425), three major and four minor nonvolatile transformation 

products of mesosulfuron-methyl were identified as AE F099095 (29.2%), AE F092944 (10.9%), 

AE F154851(16.2%), AE F160459 (8.9%), AE F160460 (8.6%), AE F147447 (7.2%), and AE 

F140584 (7.1%). Volatilized 14CO2 totaled 49.2% of the applied mesosulfuron-methyl at 

termination; volatile [14C] organic compounds were <0.1% at all intervals.

Aerobic aquatic biotransformation of mesosulfuron-methyl was studied in a gravel pit watersand sediment system and a river water-silt loam sediment system. AE F160459 (21.6%) was a 

major transformation product in both systems. AE F147447 (16.1%) was a major product only in 
7

the water-sand sediment systems. Minor products (< 10%) were AE F160460, AE F154851, AE 

F092944, AE F140584, AE F099095, and AE F119094. In addition, there were two major 

unidentified products (A (Ul, 6.9-22%) and D (U3, 6.2-13.1%)) and three minor unidentified 

products (C (U2, ≤4.2%), E (U4, ≤1.9%), and G (U5, ≤1.9%)). In the anaerobic aquatic 

metabolism study, there were two major products (AE F160459 (25.9%) and AE F160460 

(12.6%)) and six minor products (AE F140584, AE F147447, AE F154851, AE F099095, AE 

F092944, and AE F119772). 

Table 3. Physical, Chemical, and Environmental Fate Properties of Mesosulfuron-methyl

and Degradation Products

Parameter Value Reference Comments

Chemical Mesosulfuron-methyl

(AE F130060)

Chemical Name (IUPAC) methyl-2-[3-(4,6-

dimethoxypyrimidin-2-yl) ureidosulfonyl]-4-methanesulfonamidomethylbenzoate

MRID 45386202

Chemical Family sulfonylurea herbicide

Empirical Formula C17H21N5O9S2 MRID 45386202 Product Chemistry

SMILES c1(ccc(cc1S(=O)(=O)NC(=O)Nc1nc

(cc(OC)n1)OC)CNS(=O)(=O)C)C(=

O)OC

EPI V4.101

CAS Number 208465-21-8 MRID 45386202 Product Chemistry

Structure http://www.chemsp

ider.com/Structure

Search.aspx

Product Chemistry

Select Physical/Chemical Parameters

Molecular mass 503.55 MRID 45386202 Product Chemistry

Solubility (20oC), mg/L 7.2 (pH 5)

483 (pH 7)

15,390 (pH 9)

MRID 45386215 Product Chemistry

Log Kow 1.39 (pH 5)

-0.48 (pH 7)

-2.06 (pH 9)

MRID 45386219 Product Chemistry

Vapor pressure in Pascals (Pa) 3.5 x 10-12 (20°C)

1.1 x 10-11 (25°C)

3.3 x 10-11 (30°C) MRID 45386217 Product Chemistry

Henry’s law constant (25°C, pH 7) 6.17 x10-18 atm·m3/mol EPI 4.1

Persistence
8

Parameter Value Reference Comments

Hydrolysis (25oC) pH 4 

 pH 7 

pH 9

Major Degradates:

AE F092944 (38.4%, pH 4)

AE F140584 (50.3%, pH 4)

AE F092944 (37.4&32.1%, pH 7&9)

AE F147447 (45.2&46.8%, pH 7&9)

Minor Degradate: 

AE F154851 (3.8%, pH9)

3.5 days 

253.1 days

318.5 days 

MRID 45386418 Acceptable

Aqueous Photolysis (t 1⁄2 ) 

Minor Degradates (≤3.7%): 

AE F 147447

AE F 160459

AE F 140584

197 days

385 days

MRID 45386419

MRID 45386420

Supplemental

Supplemental

Soil Photolysis (t 1⁄2 ) Stable MRID 45386421 Supplemental

Aerobic Soil Metabolism (t 1⁄2 )

Major Degradates:

AE F092944(10.9%,MRID 45386425)

AE F154851(16.2%,MRID 45386425)

AE F099095(29.2%, MRID 45386425)

Minor Degradates:

AE F160459 (8.9%,MRID 45386424)

AE F160460 (8.6%,MRID 45386424)

AE F099095 (3.1%,MRID 45386422)

AE F147447 (7.2%,MRID 45386423)

AE F140584 (7.1%,MRID 45386423)

74 days (German loamy sand)

76 days (German loamy sand)

32 days (Illinois sandy loam)

86 days (German sandy loam)

100 days (German loamy sand) 

20 days (German silt loam)

29 days (France loam)

82 days (UK loam)

199 days (North Dakota Clay)

MRID 45386422

MRID 45386423

MRID 45386424

MRID 45386425

Acceptable

Acceptable

Acceptable

Acceptable

Anaerobic Aquatic Metabolism (t 1⁄2 )

Major Degradates:

AE F160459(25.9%,MRID 45386427)

AE F160460 (12.6%,MRID 45386429)

Minor Degradates:

AE F140584 (2.5%,MRID 45386427)

AE F147447 (6.8%,MRID 45386427)

AE F154851 (6.6%,MRID 45386429)

AE F099095 (0.7%,MRID 45386427)

AE F092944 (5.7%,MRID 45386429)

AE F119772 (5.7%,MRID 45386429)

23-29 days (Water)

32-48 days (Sediment)

27-36 days (Total system)

5.4 days (Water)

8.0 days (Sediment)

6.2 days (Total system)

MRID 45386427

MRID 45386429

Supplemental

Supplemental
9

Parameter Value Reference Comments

Aerobic Aquatic Metabolism (t 1⁄2 )

Major Degradates:

AE F160459 (21.6%)

AE F147447 (16.1%)

Unknown A (U1) (6.9-22%)

Unknown D (U3) (6.2-13.1%)

Minor Degradates:

AE F160460 (8.4%)

AE F154851 (4.9%)

AE F092944 (4.4%)

AE F140584 (1.9%)

AE F099095 (≤ 0.9%)

AE F119094 (1.5%)

Unknown C (U2) (≤4.2%)

Unknown E (U4) (≤1.9%)

Unknown G (U5) (≤1.9%)

Gravel pit water-sand sediment 

from Germany

[Phenyl-U14C]-label

97.2 days (Water)

108.7 days (Sediment)

99.8 days (Total system)

[Pyrimidyl-2-

14C]-label

82.3 days (Water)

84.0 days (Sediment)

83.6 days (Total system)

River water-silt loam sediment 

from Germany

Phenyl-U14C]-label

26.2 days (Water)

70.0 days (Sediment)

35.7 days (Total system)

[Pyrimidyl-2-

14C]-label

14.9 days (Water)

42.3 days (Sediment)

24.9 days (Total system)

MRID 45386430

MRID 45386431

Supplemental

Supplemental

(Kinetic Evaluation 

of MRID 45386430)

Bioconcentration/Depuration (t 1⁄2 ) N/A N/A N/A

Mobility

Koc (mL/g) 345 (Sand, pH 5.8)

137 (Sandy clay loam, pH7.9)

37 (Münster loamy sand, pH 6.3)

31 (Speyer loamy sand, pH 6.6)

92 (Millington sandy loam, pH 7.6)

26 (Schwanheim sandy loam, pH 

7.1)

36 (Clay loam, pH 7.9)

85 (Loam, pH 8.0)

48 (Silt loam, pH 7.9)

MRID 45386432 Acceptable

Field Dissipation

Terrestrial Field Dissipation (t 1⁄2 ) 58days (Florida)

136 days (Illinois)

80 days (California)

MRID 45386501 Supplemental

Mesosulfuron-methyl Degradates

Parameter Value Reference Comments

Bridge-intact Metabolites of Mesosulfuron-methyl

(Unique to Mesosulfuron-methyl)

Company Code AE F154851 MRID 45386425 Mesosulfuron

Chemical Name 2-[3-(4,6-dimethoxypyrimidine-2-

yl)ureidosulfonyl]-4-

methanesulfonamidomethyl benzoic 

acid

MRID 45386425

Empirical Formula C16H19N5O9S2 EPI 4.1
10

Parameter Value Reference Comments

SMILES O=C(Nc1nc(OC)cc(OC)n1)NS(=O)(

=O)c2cc(ccc2C(=O)O)CNS(=O)(=O

)C

EPI 4.1

CAS Number 400852-66-6

Molecular mass 489.48 EPI 4.1

Structure http://www.chemsp

ider.com/Structure

Search.aspx

Koc (mL/g) 119 (Minnesota clay loam)

66 (Hattersheim silt loam)

50 (Münster sandy loam)

MRID 45386433

(Acceptable)

Company Code AE F160459 MRID 45386427

MRID 45386429

Chemical Name Methyl 2-[3-(4-hydroxy-6-

methoxypyrimidine-2-

yl)ureidosulfonyl]-4-

methanesulfonamido-methyl 

benzoate

MRID 45386427

MRID 45386429

Empirical Formula C16H19N5O9S2 EPI 4.1

SMILES C(=O)(c1c(S(=O)(=O)NC(=O)Nc2n

c(O)cc(OC)n2)cc(CNS(C)(=O)=O)c

c1)OC

EPI 4.1

Molecular mass 489.48 EPI 4.1

Structure http://www.chemsp

ider.com/Structure

Search.aspx

Company Code AE F160460 MRID 45386429

Chemical Name 2-[3-(4-hydroxy-6-

methoxypyrimidin-2-yl) 

ureidosulfonyl]-4-

methanesulfonamidomethyl-benzoic 

acid

MRID 45386429

Empirical Formula C15H17N5O9S2 EPI 4.1

SMILES C(=O)(O)c1c(S(=O)(=O)NC(=O)Nc

2nc(O)cc(OC)n2)cc(CNS(C)(=O)=O

)cc1

EPI 4.1
11

Parameter Value Reference Comments

Molecular mass 475.45 EPI 4.1

Structure http://www.chemsp

ider.com/Structure

Search.aspx

Phenyl Ring Bridge-cleavage Metabolites of Mesosulfuron-methyl

(Unique to Mesosulfuron-methyl)

Company Code AE F140584 MRID 45386418

Chemical Name Methyl 4-

methanesulfonamidomethyl-2-

sulfamoylbenzoate

MRID 45386418

Empirical Formula C10 H14 N2 O6 S2 EPI 4.1

SMILES C(=O)(c1c(S(N)(=O)=O)cc(CNS(C)(

=O)=O)cc1)OC

EPI 4.1

Molecular mass 322.35 EPI 4.1

Structure http://www.chemsp

ider.com/Structure

Search.aspx

Company Code AE F147447 MRID 45386418

Chemical Name 6-Methanesulfonamidomethyl- 1,2-

benzisothiazol-3(2H)-one 1,l dioxide

MRID 45386418

Empirical Formula C9 H10 N2 O5 S2 EPI 4.1

SMILES C1(=O)c2c(cc(CNS(C)(=O)=O)cc2)

S(=O)(=O)N1

EPI 4.1

Molecular mass 290.31 EPI 4.1

Structure http://www.chemsp

ider.com/Structure

Search.aspx

Pyrimidine Ring Bridge-cleavage Metabolites of Mesosulfuron-methyl

(Common to Other Sulfonylurea Herbicides)

Company Code AE F099095 MRID 45386434

Chemical Name (CAS) 4,6-dimethoxypyrimidin-2-yl-urea MRID 45386434

Empirical Formula C7 H10 N4 O3 EPI 4.1

SMILES c1(OC)cc(OC)nc(NC(N)=O)n1 EPI 4.1
12

Parameter Value Reference Comments

Molecular mass 198.18 EPI 4.1

Structure http://www.chemsp

ider.com/Structure

Search.aspx

Koc (mL/g) 3856 (Minnesota clay loam)

365 (Hattersheim silt loam)

206 (Münster sandy loam)

MRID 45386434

(Acceptable)

Company Code AE F119094

Chemical Name (CAS) 4-Hydroxy-6-methoxypyrimidin-2-

yl-urea

Empirical Formula C6 H8 N4 O3 EPI 4.1

SMILES c1(O)cc(OC)nc(NC(N)=O)n1 EPI 4.1

Molecular mass 184.16 EPI 4.1

Structure http://www.chemsp

ider.com/Structure

Search.aspx

Company Code AE F092944 MRID 45386418

MRID 45386425

Chemical Name (CAS) 2-Amino-4,6-dimethoxypyrimidine MRID 45386418

MRID 45386425

Empirical Formula C6 H9 N3 O2 EPI 4.1

SMILES c1(OC)cc(OC)nc(N)n1 EPI 4.1

CAS Number 36315-01-2 CSID:106290

Molecular mass 155.16 EPI 4.1
13

Parameter Value Reference Comments

Structure http://www.chemsp

ider.com/Structure

Search.aspx

1

http://www.epa.gov/oppt/exposure/pubs/episuite.htm

3.4. Clean Water Act

Mesosulfuron-methyl is not identified as a cause of impairment for any water bodies listed as 

impaired under section 303(d) of the Clean Water Act2. In addition, no Total Maximum Daily 

Loads (TMDL) have been developed3

. The Impaired Waters and Total Maximum Daily Loads 

website can be consulted for more information4. The Agency invites submission of water quality 

data for mesosulfuron-methyl. To the extent possible, data should conform to the quality 

standards in the OPP Standard Operating Procedure: Inclusion of Impaired Water Body and 

Other Water Quality Data in OPP’s Registration Review Risk Assessment and Management 

Process5

, in order to ensure they can be used quantitatively or qualitatively in pesticide risk 

assessments.

4. Receptors

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

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

generated from surrogate test species, which are intended to be representative of broad 

taxonomic groups, are used to extrapolate the potential effects on a variety of species (receptors) 

included under these taxonomic groupings.

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

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

mesosulfuron-methyl to aquatic and terrestrial receptors. This includes toxicity on the technical 

grade active ingredient, degradates, and when available, formulated products (e.g., “Six-Pack” 

studies). Open literature studies will be identified through EPA’s ECOTOXicology (ECOTOX) 

database6

, which uses a literature search engine for locating chemical toxicity data. 

A summary of data representing non-target organisms exposed to mesosulfuron-methyl and its 

degradation products in aquatic and terrestrial habitats is provided in Sections 4.1 and 4.2. A

summary of ecological incidents associated with mesosulfuron-methyl is provided in Section 

4.3. Studies submitted by the registrant are listed in Appendix A. The ECOTOX database will 

be searched when the risk assessment for mesosulfuron-methyl is prepared. At that time, 

 2 http://iaspub.epa.gov/tmdl_waters10/attains_nation_cy.cause_detail_303d?p_cause_group_id=885

3

http://iaspub.epa.gov/tmdl_waters10/attains_nation.tmdl_pollutant_detail?p_pollutant_group_id=885&p_pollutant_

group_name=PESTICIDES

4 http://www.epa.gov/owow/tmdl/

5 http://www.epa.gov/oppfead1/cb/ppdc/2006/november06/session1-sop.pdf 6 http://cfpub.epa.gov/ecotox/
14

endpoints more sensitive than available guideline studies will be reviewed from the open 

literature studies.

4.1. Effects to Aquatic Organisms

Table 4. Summary of Toxicity of Mesosulfuron-methyl (TGAI) to Aquatic Animals 

Species Exposure 

Scenario

% AI Toxicity MRID Toxicity 

Category

Classification

Rainbow Trout 

(Oncorhynchus 

mykiss)

96 hr 94.6

LC50 > 91.5 mg total 

ai/L

NOAEC ≥ 91.5 mg 

total ai/L

45386231 NA Supplemental

Bluegill sunfish 

(Lepomis 

macrochirus) 96 hr 94.6

LC50 > 96.4 mg total 

ai/L

NOAEC ≥ 96.4 mg 

total ai/L

45386230 NA Supplemental

Rainbow Trout 

(Oncorhynchus 

mykiss)

28 day1 94.6

NOAEC ≥ 29.6 mg ai/L

LOAEC > 29.6

45386232 NA Supplemental

Waterflea

(Daphnia magna) 48 hr 94.6

EC50 > 90.2 mg ai/L

NOAEC ≥ 90.2 mg ai/L 

45386233 NA Acceptable 

(“Core”)

Waterflea

(Daphnia magna)

LifeCycle 94.6

NOAEC = 1.7 mg ai/L

LOAEC = 3.0 mg ai/L 

based on dry weight

45386305 NA Acceptable 

(“Core”)

Sheepshead 

minnow 

(Cyprinodon 

variegatus)

96 hr 95.7

LC50 > 105 mg ai/L

NOAEC ≥ 105 mg ai/L 

45386301 Practically 

non-toxic Supplemental

Mysid shrimp

(Americamysis 

bahia)

96 hr 95.7

LC50 > 111 mg ai/L

NOAEC ≥ 111mg ai/L

45386303 Practically 

non-toxic

Acceptable 

(“Core”)

Eastern oyster

(Crassostrea 

virginica)

96 hr 95.6

EC50 > 100 mg ai/L

NOAEC ≥ 100mg ai/L

45386302 Practically 

non-toxic

Acceptable 

(“Core”)

1 OECD 28-day sub-chronic study with 2 month old fish.

NA = not applicable

Table 5. Summary of Toxicity of Mesosulfuron-methyl Degradation Products (TGAI) to 

Aquatic Animals 

Species Exposure 

Scenario

% AI Toxicity MRID Toxicity 

Category

Classification

Rainbow Trout 

(Oncorhynchus 

mykiss)

96 hr Unknown

AE F092944 LC50 = 97 mg ai/L IUPAC 

footprint1

Slightly 

toxic NA

Waterflea

(Daphnia magna) 48 hr Unknown

AE F092944

EC50 > 100 mg 

ai/L

IUPAC 

footprint1

Practically 

non-toxic NA
15

Species Exposure 

Scenario

% AI Toxicity MRID Toxicity 

Category

Classification

Waterflea

(Daphnia magna) 21 day Unknown

AE F092944

NOAEC = 24 mg 

ai/L

IUPAC 

footprint1 NA NA

1 IUPAC footprint database studies are not reviewed by the Agency and the toxicity endpoints are used at face value. 

http://sitem.herts.ac.uk/aeru/iupac/441.htm

NA = not applicable

Table 6. Summary of Toxicity of Mesosulfuron-methyl (TGAI) to Aquatic Plants 

Species Exposure 

Scenario

% AI Toxicity MRID Toxicity 

Category

Classification

Marine Diatom

(Skeletonema 

costatum)

96 hr 95.7

IC50 = 98000 (91000-

110000) 1 μg ai/L

NOAEC = 37800 μg ai/L

Based on reduced 

biomass (area under the 

growth curve)

45386314 NA Acceptable 

(“Core”)

Cyanobacteria

(Anabaena 

flosaquae

96 hr 95.7

IC50 = 2400 (1700-3300) 1

μg ai/L

NOAEC = 1100 μg ai/L

Based on reduced cell 

density

45386315 NA Acceptable 

(“Core”)

Freshwater 

Diatom

(Navicula 

pelliculosa)

96 hr 94.6

IC50 > 70800 μg ai/L

NOAEC ≥ 70.8 μg ai/L

45386307 NA Acceptable 

(“Core”)

Duckweed

(Lemma gibba) 7 day 95.3

IC50 = 0.64 (0.56-0.73) 1 

μg ai/L

NOAEC = 0.19 μg ai/L

Based on reduced number 

of fronds

45386310 NA Acceptable 

(“Core”)

1

Range is 95% confidence interval. 

NA = not applicable

Table 7. Summary of Toxicity of Mesosulfuron-methyl Degradation Products (TGAI) to 

Aquatic Plants 

Species Exposure 

Scenario

% AI Toxicity MRID Toxicity 

Category

Classification

Freshwater Green 

Algae

(Pseudokirchneriella 

subcapitata)

96 hr

93.1

AE 

F147447

IC50 > 92000 μg 

ai/L

NOAEC ≥ 92000 μg 

ai/L

45386308 NA Acceptable 

(“Core”)
16

Species Exposure 

Scenario

% AI Toxicity MRID Toxicity 

Category

Classification

Freshwater Green 

Algae

(Pseudokirchneriella 

subcapitata)

96 hr

96.8

AE 

F160459

IC50 = 98000 μg 

ai/L

NOAEC = 54600 μg 

ai/L

Based on reduced 

biomass (area under 

the growth curve)

45386309 NA Acceptable 

(“Core”)

Freshwater Green 

Algae

(Pseudokirchneriella 

subcapitata)

72 hr

Unknown

AE 

F092944

IC50 = 120000 μg 

ai/L

IUPAC 

footprint2 NA NA

Duckweed

(Lemma gibba) 7 day

93.1

AE 

F147447

IC50 > 90900 μg 

ai/L

NOAEC ≥ 90900 μg 

ai/L

45386313 NA Acceptable 

(“Core”)

Duckweed

(Lemma gibba) 7 day

96.8

AE 

F160459

IC50 = 1500 (1100-

2000)1 μg ai/L

NOAEC = 290 μg 

ai/L

Based on reduced 

number of fronds

45386311 NA Acceptable 

(“Core”)

Duckweed

(Lemma gibba) 7 day

96.1

AE 

F160460

IC50 > 94710 μg 

ai/L

NOAEC ≥ 94710 μg 

ai/L

45386312 NA Acceptable 

(“Core”)

Duckweed

(Lemma gibba) 7 day

Unknown

AE 

F092944

IC50 > 100000 μg 

ai/L

IUPAC 

footprint2 NA NA

1

Range is 95% confidence interval. 

2 IUPAC footprint database studies are not reviewed by the Agency and the toxicity endpoints are used at face value.

http://sitem.herts.ac.uk/aeru/iupac/441.htm

NA = not applicable

4.2. Effects to Terrestrial Organisms

Table 8. Summary of Toxicity of Mesosulfuron-methyl (TGAI) to Terrestrial Animals

Species Exposure 

Scenario

% 

AI

Toxicity MRID Toxicity 

Category

Classification

Northern 

Bobwhite Quail 

(Colinus 

virginianus)

Single oral 

dose, birds 

observed for 

14 days

94.6

LD50 >2000 mg/kg

NOAEL < 2000 mg/kg

LOAEL ≤ 2000 based 

on reduced 

consumption

No mortality

45386224 Practically 

non-toxic Acceptable 

(“Core”)
17

Species Exposure 

Scenario

% 

AI

Toxicity MRID Toxicity 

Category

Classification

Mallard Duck 

(Anas 

platyrhynchos)

Single oral 

dose, birds 

observed for 

14 days

94.6

LD50 >2000 mg/kg

No mortality or 

sublethal effects 

observed

45386225 Practically 

non-toxic Acceptable 

(“Core”)

Northern 

Bobwhite Quail 

(Colinus 

virginianus)

8 days (5 

days 

treatment and 

3 days 

observation)

94.6

LC50 >4800 ppm ai

NOAEC < 297 ppm ai 

LOAEC ≤ 297 based on 

reduced consumption

No mortality

45386226 NA Acceptable 

(“Core”)

Mallard Duck 

(Anas 

platyrhynchos)

8 days (5 

days 

treatment and 

3 days 

observation)

94.6

LC50 >4750 ppm ai

NOAEC < 309 ppm ai 

LOAEC ≤ 309 based on 

reduced consumption

No mortality

45386227 NA Acceptable 

(“Core”)

Northern 

Bobwhite Quail 

(Colinus

virginianus)

Onegeneration 

Reproduction 

Study

94.6 NOAEC ≥ 1000 ppm ai 45386228 NA Supplemental

Mallard Duck 

(Anas 

platyrhynchos)

Onegeneration 

Reproduction 

Study

94.6 NOAEC ≥ 990 ppm ai 45386229 NA Supplemental

Honeybee 

(Apis mellifera) Acute contact 95.9 LD50 > 13 μg ai/bee 45386319 Practically nontoxic

Acceptable 

(“Core”)

Rat Acute Oral 95.6 LD50 > 5000 mg/kg 45386321 Practically 

nontoxic Acceptable

Rat 2-year 

chronic 94.6

NOAEL ≥ 16,000 ppm 

(1175 mg/kg bw/day –

males; 1388 mg/kg 

bw/day – females)

Parental systemic, 

offspring, and 

reproductive

45430405 NA Acceptable

NA = not applicable
18

Table 9. Summary of Toxicity of Mesosulfuron-methyl Degradation Products (TGAI) to 

Terrestrial Animals

Species Exposure 

Scenario

% AI Toxicity MRID Toxicity 

Category

Classification

Rat Acute 

Oral

Unknown

AE F099095

LD50 = 677 

mg/kg (males) 47305223 Slightly toxic NA

Rat Acute 

Oral

Unknown

AE F092944

LD50 = 737 

mg/kg (males)

IUPAC 

footprint1

Slightly 

toxic NA

1 IUPAC footprint database studies are not reviewed by the Agency and the toxicity endpoints are used at face 

value. http://sitem.herts.ac.uk/aeru/iupac/441.htm

NA = not applicable

Table 10. Summary of Toxicity of Mesosulfuron-methyl Formulations to Terrestrial 

Animals

Species Exposure 

Scenario

% AI Toxicity MRID Toxicity 

Category

Classification

Rat Acute 

Oral

2.26

Silverado Wild 

Oat Herbicide

LD50 > 2000 

mg/kg 46034702 Practically 

nontoxic1 Acceptable

Rat Acute 

Oral

4.84

Osprey

LD50 > 2000 

mg/kg 46034602 Practically nontoxic1 Acceptable

Rat Acute 

Oral

4.5

Olympus Flex 

(plus 6.8% 

propoxycarbazone

-sodium)

LD50 > 2000 

mg/kg 46038502 Practically 

nontoxic1 Acceptable

Rat Acute 

Oral

3.08

(plus 0.61% 

iodosulfuron)

LD50 > 2000 

mg/kg 47756302 Practically 

nontoxic1 Acceptable

1 On a formulation basis

Table 11. Summary of Toxicity of Mesosulfuron-methyl Formulations to Terrestrial Plants

Species Exposure 

Scenario

% AI Toxicity MRID Toxicity 

Category

Classification

Terrestrial 

Plants

Vegetative 

Vigor, 

21-day

4.81 

Osprey 4.5 

WG

Most sensitive monocot

46688201 NA Under Review

Oat (dry weight)

IC25 = 0.42 (0.36-0.49)1

g ai/ha

NOAEC = 0.33 g ai/ha

LOAEC = 1 g ai/ha

Most sensitive dicot

Soybean (dry weight)

IC25 = 0.16 (0.14-0.19)1

g ai/ha

NOAEC = 0.04 g ai/ha

LOAEC = 0.11 g ai/ha
19

Species Exposure 

Scenario

% AI Toxicity MRID Toxicity 

Category

Classification

Seedling 

Emergence, 

14-day

74.73

(TGAI plus 

adjuvant)

Most sensitive monocot

45745702

NA Supplemental

Onion (shoot length)

IC25 = 8.4 (5.4-13)1 g 

ai/ha

NOAEC = 7.5 g ai/ha

LOAEC = 15 g ai/ha

50% 

(TGAI plus 

iodosulfuron 

and 

adjuvant)

Most sensitive dicot

45386316

Lettuce (shoot length)

IC25 = 0.92 (0.34-2.5)1 g 

ai/ha

NOAEC = 0.81 g ai/ha

LOAEC = 1.63 g ai/ha 1

Range is 95% confidence interval. 

NA = not applicable

Table 12. Summary of Toxicity of Mesosulfuron-methyl Degradation Products (TGAI) to 

Terrestrial Plants

Species Exposure 

Scenario

% AI Toxicity MRID Toxicity 

Category

Classification

Variable Flatsedge

(Cyperus difformis)

Barnyard Grass

(Echinochloa crusgalli)

Kidneyleaf 

Mudplantain

(Heteranthera 

reniformis)

Vegetative 

Vigor, 

21-day1

Unknown

AE F099095

NOAEC ≥ 350

g ai/ha 46588504 NA Unreviewed

Japonica Rice

(Oryza sativa)

Unknown

AE F099095

NOAEC ≥ 750

g ai/ha 46588501 NA Unreviewed

1 EPPO guideline no 135 studies on rice and rice weeds

NA = not applicable

4.3. Incident Databases Review

Incidents involving mesosulfuron-methyl were reported in the Ecological Incident Information 

System (EIIS, v 2.1.1) and the Aggregate Incident Data System as of November 8, 2012. No 

incidents were reported in the Avian Incident Monitoring System (AIMS)7.

All 29 reported incidents (2004-2011) reported in EIIS involved damage to wheat and all but one 

were considered possibly or probably caused by direct application of mesosulfuron-methyl. 

Thirty-seven incidents, all of minor plant-damage attributed to mesosulfuron-methyl products, 

were reported in the Aggregate Incident Data System. 

 7 http://www.abcbirds.org/abcprograms/policy/toxins/aims/aims/index.cfm
20

The total number of actual incidents associated with the use of mesosulfuron-methyl may be 

higher than what is reported to the Agency. Incidents may go unreported since effects may not 

be immediately apparent or readily attributed to the use of a chemical. As such, the absence of 

incident reports cannot be construed as the absence of incidents.

5. Risk Hypothesis

Mesosulfuron-methyl, when used in accordance with current labels, can result in offsite 

movement of the compound via spray drift, runoff, and leaching to ground water, leading to 

exposure of non-target plants and animals. Application of mesosulfuron-methyl to wheat and 

triticale fields may serve as a major source of mesosulfuron-methyl exposure to wildlife. When 

used in accordance with the labels, mesosulfuron-methyl use will cause adverse effects upon the 

survival, growth, and reproduction of non-target terrestrial and aquatic organisms. These nontarget organisms include federally-listed threatened and endangered species. 

6. Analysis Plan

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

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

characterized and integrated to assess risk. 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 or magnitude of an adverse effect. However, as 

outlined in the Overview Document (USEPA, 2004c), the likelihood of effects to individual 

organisms from particular uses of mesosulfuron-methyl will be estimated using the probit doseresponse slope and either the level of concern or actual calculated risk quotient value.

This analysis plan will be revisited and may be revised depending upon a full review of the data 

available in the open literature and the information submitted by the public in response to the 

opening of the Registration Review docket.

6.1. Stressors of Concern

The stressors of concern will be mesosulfuron-methyl and in some cases the major degradation

products (Table 13). 

The Agency is seeking clarification on two unknown degradates from the submitted aerobic 

metabolism study (MRID 45386430 and 45386431) and requesting an ECM/ILV method that is

capable of identifying the major degradates (see Section 6.8). 

Table 13. Summary of the Major and Minor Mesosulfuron-methyl Degradates

Company Code

(Maximum % 

Formation)

Chemical Name Mechanism of Formation Comments

AE F154851

(16.2%)

MRID 45386425

2-[3-(4,6-dimethoxypyrimidine-2-

yl)ureidosulfonyl]-4-

methanesulfonamidomethyl benzoic acid

Methyl ester hydrolysis Bridge-intact 

degradates

(unique to 

mesosulfuronmethyl)

AE F160459

(25.9%)

MRID 45386427

Methyl 2-[3-(4-hydroxy-6-

methoxypyrimidine-2-

yl)ureidosulfonyl]-4-

methanesulfonamido-methyl benzoate

Demethoxyfication at the 4-

position of the pyrimidinyl 

group
21

AE F160460

(12.6%)

MRID 45386429

2-[3-(4-hydroxy-6-methoxypyrimidin-2-

yl) ureidosulfonyl]-4-

methanesulfonamidomethyl-benzoic acid

Demethoxyfication at the 4-

position of the pyrimidinyl 

group, Methyl ester 

hydrolysis

AE F140584

(50.3%, pH 4)

MRID 45386418

Methyl 4-methanesulfonamidomethyl-2-

sulfamoylbenzoate

Cleavage of the sulfonylurea 

bridge

Phenyl ring 

bridge-cleaved

(unique to 

mesosulfuronmethyl)

AE F147447

(45.2 at pH 7, 

46.8% at pH 9)

MRID 45386418

6-Methanesulfonamidomethyl- 1,2-

benzisothiazol-3(2H)-one 1,l dioxide

Cleavage of the sulfonylurea 

bridge, Methyl ester 

hydrolysis,

Isothiazole ring formation

AE F099095

(29.2%)

MRID 45386425

4,6-dimethoxypyrimidin-2-yl-urea Cleavage of the sulfonylurea 

bridge

Pyrimidine ring 

bridge-cleaved

(common to 

other 

sulfonylurea 

herbicides)

AE F119094

(1.5%)

MRID 45386430

4-Hydroxy-6-methoxypyrimdin-2-yl-urea Cleavage of the sulfonylurea

bridge, Demethoxyfication at 

the 4-position

AE F092944

(38.4% at pH 4, 

37.4% at pH 7,

32.1% at pH 9)

MRID 45386418

2-Amino-4,6-dimethoxypyrimidine Cleavage of the sulfonylurea 

bridge, Elimination of the –

NH2 CO- group

Residues of Concern for Drinking Water Consumed by Humans

The only drinking water assessment for mesosulfuron-methyl was completed in 2004 (USEPA,

2004a). Mesosulfuron-methyl and three bridge-intact major degradates (AE F154851, AE 

F160459, and AE F160460) were modeled per request of the HED’s MARC (01/28/2004

meeting). Residues of concern for human health drinking water may be revisited.

Residues of Concern for Ecological Risk Assessment

In the absence of degradate data, the major degradates will be considered stressors of concern 

when assessing risk to aquatic organisms; however, data are more likely to impact the 

assessment of aquatic vascular plants.

Limited aquatic toxicity data were available for the major degradation products; however, for 

most endpoints information was available from Ecological Structure Activity Relationship 

(ECOSAR) methods8 or the IUPAC footprint database9 (Table 14). The most toxic value was 

selected for this screening unless indicated otherwise. Some degradates may be more toxic than 

mesosulfuron-methyl to fish and invertebrates. For aquatic plants, available information 

suggests that some degradates are equal in toxicity to mesosulfuron-methyl and others are much 

less toxic.

Although some degradates may be more toxic than mesosulfuron-methyl to fish and 

invertebrates, preliminary estimates of exposure are much lower than would trigger a risk 

concern (Table 15). Exposure for this analysis was based on the highest application rate and 

mesosulfuron-methyl EECs assuming no degradation.

 8 ECOSAR predictive software is available publically though the Epi SuiteTM program. 

http://www.epa.gov/oppt/exposure/pubs/episuite.htm

9 http://sitem.herts.ac.uk/aeru/iupac/577.htm
22

The lack of information on toxicity of two degradates (AE F154851 and AE F140584) to 

vascular plants could impact risk conclusions. Listed plants are anticipated to be a risk concern 

based on mesosulfuron-methyl alone. Non-listed plants may be a risk concern as well if a total 

toxic residue (TTR) approach is used (preliminary EEC = 2.69 μg/L, as reported in Table 15); 

however, this may not be the case if all degradates are clearly less toxic than mesosulfuronmethyl and EECs are based on mesosulfuron-methyl alone (preliminary EEC = 0.31 μg/L as 

reported in USEPA, 2004b). One of the degradates, AE F154851, is a SU bridge-intact 

compound; thus it will be assumed equal in toxicity to mesosulfuron-methyl in the absence of 

data and a TTR approach will be used to estimate EECs. The other degradate, AE F140584,

would only need to be slightly more toxic than mesosulfuron-methyl to trigger a risk concern 

(listed and non-listed species) based on its own preliminary EECs10. On the other hand, 

ECOSAR estimates suggest that AE F140584 is not more toxic than mesosulfuron-methyl to 

non-vascular plants which may or may not be representative of the potential toxicity to vascular 

plants (Table 14). AE F140584 toxicity will be assumed equal to mesosulfuron-methyl in the 

absence of data and a TTR approach will be used to estimate EECs. 

 10 Preliminary EEC for AE F140584 (0.18 μg/L) was calculated by adjusting the maximum application rate of 

mesosulfuron-methyl (lb AE F140584/A = lb ai/A * maximum percent formation of AE F140584 in fate studies * 

(MW AE F140584/MW ai) and assuming that AE F140584 is stable to degradation.
23

Table 14. Comparative Aquatic Toxicity of Mesosulfuron-methyl and Major Degradation Products

Compound FW fish 

96-hr 

acute 

LC50

(mg/L)

FW fish 

chronic 

NOAEC

(mg/L)1

FW 

invertebrate 

48-hr acute 

EC50

(mg/L)

FW 

invertebrate 

chronic 

NOAEC

(mg/L)1

ME fish 

96-hr 

acute 

LC50

(mg/L)

ME 

invertebrate 

96-hr acute 

LC50

(mg/L)

Vascular 

plant 7-

day EC50

(μg/L)

Nonvascular 

plant 96-

hr EC50

(μg/L)

Mesosulfuronmethyl > 91.5 ≥ 29.62 > 90.2 1.7 > 105.0 > 111.0 0.64 56.0

AE F154851 20367.73 155.04 7284.63 96.04,5 - - - 547.0

AE F160459 97.04 0.02 5.5 6.85 1314.13 2739.43 1500.0 98000.0

AE F160460 2023.23 0.15 73.6 101.8 235000.03 - > 94700.0 532.0

AE F140584 731.04 12.0 548.2 7.25 1360.94 3249.34 - 2792.0

AE F147447 6.1 0.545 7.6 0.75 - - > 90900.0 > 92000.0

AE F099095 337.6 1.9 116.5 1.55 - - 2.5-200.06 147.0

AE F092944 97.0 89.67 > 100.0 24.0 - - >100000.0 120000.0 1 ECOSAR estimated chronic value is defined as the geometric mean of the no observed effect concentration (NOEC) and the lowest observed effect 

concentration (LOEC).

2 OECD 28-day sub chronic study 3 Endpoint exceeds predicted water solubility of compound by 10x – no effects at saturation are predicted if the compound is solid. 4 Endpoint exceeds predicted water solubility of compound.

5 Value is based on acute-to-chronic ratio. Other ECOSAR classes predict lower toxicity (i.e., higher values). 6 AE F099095 is a urea-type compound. Urea herbicides (e.g., linuron) are less toxic than mesosulfuron-methyl to vascular plants (EC50 = 2.5 - 200 

μg/L). Data are reported in the problem formulation for orthosulfamuron (DP 390068). 7 Neutral organic estimates are reported because N-substituted anilines are less toxic than estimated by the aniline ECOSAR class.

BOLD values are ECOSAR (v1.00) toxicity estimates (lowest toxicity value of multiple ECOSAR classes is shown, i.e., the most toxic). BOLD

Italic values are from the footprint database (reported when toxicity value is lower than ECOSAR estimate). Non-bolded values are toxicity values 

from available studies.

FW = freshwater and ME = marine/estuarine
24

Table 15. Preliminary Aquatic RQs for Mesosulfuron-methyl and Major Degradation 

Products1,2

Compound FW fish 

96-hr 

acute 

LC50 

(mg/l)

RQ FW fish 

chronic 

NOAEC 

(mg/l)

RQ FW 

invertebrate 

48-hr acute 

EC50 

(mg/l)

RQ FW 

invertebrate 

chronic 

NOAEC 

(mg/l)

RQ

Mesosulfuron

-methyl 91.5 0.000029 29.6 0.000091 90.2 0.000030 1.7 0.001582

AE F154851 20367.7 0.000000 155.0 0.000017 7284.6 0.000000 96.0 0.000028

AE F160459 97.0 0.000028 0.02 0.134000 5.5 0.000489 6.8 0.000396

AE F160460 2023.2 0.000001 0.15 0.017867 73.6 0.000037 101.8 0.000026

AE F140584 731.0 0.000004 12.0 0.000223 548.2 0.000005 7.2 0.000374

AE F147447 6.1 0.000441 0.54 0.004926 7.6 0.000354 0.7 0.003843

AE F099095 337.6 0.000008 1.9 0.001411 116.5 0.000023 1.5 0.001793

AE F092944 97 0.000028 89.6 0.000030 100.0 0.000027 24 0.000112 1 Toxicity based on data in Table 14 (marine-estuarine fish/invertebrates RQs are not presented because available 

toxicity data suggests that they are not more sensitive than freshwater fish/invertebrates). RQs are not typically 

calculated for non-definitive endpoints; however, they are presented here for comparative purposes only. RQs based 

on non-definitive endpoints are higher (overestimate risk) than if based on actual toxicity. RQs based on toxicity 

endpoints greater than the predicted solubility limit (i.e., ECOSAR estimates of some of the degradates) have limited 

meaning. Nonetheless, risk is low in these cases given that (1) the preliminary EECs are ≥ 11,000 X lower than the 

ECOSAR-estimated solubility limit(s) of the pertinent degradate(s) and (2) ECOSAR-estimated toxicity suggests

that there is less than a 50% acute effect and no adverse chronic effect at the solubility limit(s) of the pertinent 

degradate(s). 2

 RQs calculated using mesosulfuron-methyl EECs based on the highest application rate and assuming no 

degradation (Peak, 21-day, and 60-day EEC = 2.69 μg/l).

Limited terrestrial toxicity data were available for the major degradation products (Table 9 and 

12). However, the degradation products are not likely a risk concern for birds or mammals given 

that they would need to be at least two to three orders of magnitude more toxic than 

mesosulfuron-methyl to exceed levels of concern (LOC). Preliminary degradate EECs were 

calculated based on the highest acute (3.66 mg/kg bw) and subacute/chronic (3.22 mg/kg diet)

mesosulfuron-methyl EEC calculated in T-REX. Each degradate EEC was calculated as follows: 

EEC = mesosulfuron-methyl EEC * max % of degradate formed in fate studies * (MW degradate 

/ MW mesosulfuron-methyl)

There are limited degradate toxicity data for terrestrial plants. SU bridge-intact degradates (AE 

F154851, AE F160459, and AE F160460) and mesosulfuron-methyl will be assumed equal in 

toxicity to terrestrial plants in the absence of data. AE F099095, a urea-type compound, is a 

potentially herbicidally-active non-SU degradate. Limited data for AE F099095 suggests that it 

is not more toxic than mesosulfuron-methyl. Furthermore, mesosulfuron-methyl is more toxic 

than urea herbicides (see orthosulfamuron problem formulation for toxicity comparison; DP 

390068); thus, AE F099095 is likely not more toxic than mesosulfuron-methyl assuming its 

toxicity is similar to that of the urea herbicides. 

6.2. Measures of Exposure

Mesosulfuron-methyl concentrations in aquatic and terrestrial environments will be modeled 

using the maximum labeled application rates and numbers of applications, the minimum 
25

application intervals, and application methods that have the greatest potential for off-site 

transport. 

Spray Drift

The AgDRIFT spray drift model (v2.01; May, 2001) or AgDISP model11 will be used to assess 

exposure of non-target organisms to mesosulfuron-methyl through off-site spray drift. The

models also function as tools for evaluating potential buffer zones. 

Aquatic Exposure 

Tier II models PRZM (Pesticide Root Zone Model, v3.12.2; May, 2005) and EXAMS (EXposure 

Analysis Modeling System, version 2.98.04.06, April 2005) in the PE5 shell12 will be used to 

estimate environmental concentrations (EECs) of mesosulfuron-methyl and degradation products 

(as appropriate) in surface waters.

If available, monitoring data will be evaluated and used for characterizing the distribution of 

mesosulfuron-methyl and degradation products. 

Terrestrial Exposure

There is potential exposure to non-target organisms through consumption of contaminated food 

items (e.g., insects or vegetation), drinking water, direct application, inhalation, runoff, and spray 

drift. 

T-REX (v 1.5)13 will be used to estimate exposure of birds and mammal to mesosulfuron-methyl. 

For input into T-REX, the default foliar dissipation half-life of 35 days will be used in the 

absence of acceptable foliar dissipation rate data (if labels allow multiple applications).

TerrPlant (v 1.2.2)13 will be used to calculate EECs for characterizing exposure to terrestrial and 

semi-aquatic plants. 

Screening Imbibition Program

The Screening Imbibition Program (SIP v.1.0)

13 was used to calculate an upper bound estimate 

of bird and mammal exposure to mesosulfuron-methyl in drinking water. 

Although the model identifies a potential concern for birds (acute and chronic) and mammals 

(acute and chronic), the model prediction has limited meaning because toxicity was based on 

non-definitive endpoints from studies with no observed mortality (Table 8). That is, the 

potential concern is unquantifiable and less than suggested by the model.

Although conclusions about risk from drinking water exposure alone are uncertain, drinking 

water may contribute to a total exposure (dietary food sources, dermal, and inhalation) that has 

 11 http://www.epa.gov/pesticides/science/models_pg.htm#atmospheric 12 http://www.epa.gov/oppefed1/models/water 13 http://www.epa.gov/oppefed1/models/terrestrial
26

potential for effects on non-target animals and should be explored further. Appendix B provides 

model results.

Screening Tool for Inhalation Risk 

The Screening Tool for Inhalation Risk (STIR v. 1.0)13 was used to provide an upper bound 

estimate of exposure of birds and mammals to pesticides through inhalation of spray drift or 

vapor. 

The screening suggests that mesosulfuron-methyl exposure is not likely significant enough for an 

inhalation risk concern. Appendix C provides model results.

6.3. Measures of Effect

Toxicity effects data will be used as measures of direct and indirect effects to biological 

receptors (USEPA, 2004c). As discussed previously, data will be obtained from registrantsubmitted studies and from literature studies identified in ECOTOX. 

Quantitative assessment of risks will be based on study endpoints that can be directly linked to 

the Agency’s assessment endpoints of impaired survival, growth, and reproduction. Sub-lethal 

effects (e.g., lethargy and changes in coloration) will be evaluated qualitatively. Available 

incident data will be used to further characterize risk.

6.4. Integration of Exposure and Effects

The exposure and effects data will be integrated in order to evaluate potential adverse ecological 

effects on non-target species. The risk quotient (RQ) method will be used to compare exposure 

and measured toxicity values. EECs will be divided by acute and chronic toxicity values. The 

resulting RQs will be compared to the Agency’s LOC (USEPA, 2004c). 

6.5. Endangered Species Assessments

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

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

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

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

Species Consultation Handbook (USFWS and NMFS, 1998).

6.6. Endocrine Disruptor Screening

As required by Federal Food, Drug and Cosmetic Act (FFDCA) section 408(p), mesosulfuronmethyl is subject to the endocrine screening part of the Endocrine Disruptor Screening Program 

(EDSP)14. Mesosulfuron-methyl is not in the first or second group of pesticide active 

ingredients to be screened under the EDSP. 

6.7. Drinking Water Assessment

A new DWA may be conducted for mesosulfuron-methyl based on new or revised label 

information at the time of risk assessment. Three bridge-intact major degradates (AE F154851, 

AE F160459, and AE F160460) will be included based on the past HED MARC meeting 

 14 http://www.epa.gov/endo/
27

(01/28/2004). Residues in surface waters will be estimated using PRZM/EXAMS and residues 

in ground water will be estimated using the Tier I SCI-GROW model and the Tier II 

PRZM/EXAM ground water model.

15 EECs will be adjusted by percent cropped area (PCA) 

factors to account for the maximum fractional area within a watershed that may be planted.

16

6.8. Preliminary Identification of Data Gaps

Available studies submitted to fulfill environmental fate and ecological effects guideline 

requirements are presented in Sections 6.8.1 and 6.8.2, respectively. Data gaps are identified 

and discussed in regard to impacts on risk assessment.

6.8.1. Environmental Fate Data

Data gaps for mesosulfuron-methyl remain (Table 16). The following data are recommended to 

reduce uncertainty in the ecological risk assessment.

• Aerobic Aquatic Metabolism (OPPTS Guideline 835.4300) – (mesosulfuron-methyl)

• Aquatic Field Dissipation Study (OPPTS Guideline 835.6200) – (mesosulfuron-methyl)

• Environmental Chemistry Methods for Soil and Plant Material (OCSPP Guideline

850.6100) - (mesosulfuron-methyl and major degradates AE F160459, AE F160460, AE 

F154851, AE F140458, AE F147447, AE F099095, and AE F092944)

Aerobic Aquatic Metabolism (mesosulfuron-methyl)

Two major metabolites (“unknown A and D”) were not identified in the submitted studies

(MRID 45386430 and 45385431). Data are needed that identifies all major transformation 

products (i.e., formed >10%). 

Aquatic field dissipation (mesosulfuron-methyl)

No aquatic field dissipation data are available. Mesosulfuron-methyl is a very water soluble and 

persistent chemical in aquatic environments. It is very likely that the compound will be 

introduced into the aquatic environment via run-off and leaching. 

ECM/ILV method for plant and soil (mesosulfuron-methyl and major degradates)

Studies are needed for mesosulfuron-methyl and major degradation products. Mesosulfuronmethyl, like most sulfonylureas, exhibits long term phytotoxicity. Whether this is due to 

sorption on soil or toxicity of degradates cannot be resolved with available information. It leaves 

open the possibility of soil mediated transport due to windborne dust or other pathways. The 

lack of analytical methods with a limit of quantitation (LOQ) at levels of ecological concern for 

plants will leave this question unresolved. ECM/ILV for soil will be used to confirm the 

submitted terrestrial field dissipation data. Therefore, the ECM/ILV methods are required for 

soil and plants to mediate the uncertainties.

 15 http://www.epa.gov/oppefed1/models/water 16 http://www.epa.gov/oppefed1/models/water/pca_adjustment_dwa.html
28

Other data gaps, “Yes” without bold font in Table 16, are not likely to change risk conclusions; 

therefore, studies are not recommended at this time.

Table 16. Environmental Fate Data Gaps for Mesosulfuron-methyl

Guideline Description MRID Classification Data 

Gap Comments

835.2120 Hydrolysis 45386418 Acceptable No

1 Data gaps exist for 

aquatic photolysis at pH 

5 and 9; however, 

available data at pH 7 

will be sufficient for 

modeling purposes.

2

Study is not required 

because of low vapor 

pressure. 

3

Study can be 

substituted by 

Anaerobic Aquatic 

Metabolism (835.4400)

4

Addtional data are 

needed to identify two 

major unknown 

metabolites

5

Study waiver was 

granted DP Barcode(s): 

297232, 12/08/03

6

The terrestrial field 

dissipation study was 

not conducted with the 

typical end use products 

nor does it appear that 

attempts were made to 

identify degradates.

7 Additional data will 

not be needed if the 

available data are 

deemed acceptable. 

835.2240 Photodegradation in 

Water

45386419

45386420

Supplemental

Supplemental Yes1

835.2410 Soil Photolysis 45386421 Supplemental No

835.2370 Photodegradation in Air -- -- Yes2

835.4100 Aerobic Soil Metabolism

45386422

45386423

45386424

45386425

Acceptable

Acceptable

Acceptable

Acceptable

No

835.4200 Anaerobic Soil 

Metabolism -- -- Yes3

835.4300 Aerobic Aquatic 

Metabolism

45386430

45385431

Supplemental

Supplemental Yes4

835.4400 Anaerobic Aquatic 

Metabolism

45386427

45386428

Supplemental

Supplemental No

835.1230

835.1240

Leaching

Adsorption/Desorption

45386432

45386433

45386434

Acceptable

Acceptable

Acceptable

No

835.1410 Laboratory Volatility -- -- Yes 5

835.8100 Field Volatility -- -- No2 

835.6100 Terrestrial Field 

Dissipation

45386501

45386502

46948901

Supplemental

In Review

Yes6,7

835.6200 Aquatic Field Dissipation -- -- Yes

850.6100 ECM/ILV

(Water)

45386522

45386523

46451701

46451702

In Review

In Review

In Review

In Review

Yes7

850.6100 ECM/ILV 

(Soil) -- -- Yes

850.1730 Bioaccumulation in Fish -- -- Yes5
29

6.8.2. Ecological Effects Data

Several data gaps for mesosulfuron-methyl remain (Tables 17, 18, and 19). After review, some 

studies have been reclassified and no longer meet a given data requirement. Studies are not 

recommended at this time for some data gaps (“Yes” without bold font in Tables 17, 18, and 19) 

because risk conclusions are unlikely to change.

The following studies are recommended:

• Aquatic plant growth (850.4500) - freshwater green alga (Mesosulfuron-methyl)

• Aquatic plant growth (850.4400) - vascular plant (AE F154851 and AE F140584)

Mesosulfuron-methyl

Acute freshwater fish toxicity 

Available data for freshwater fish are supplemental in part because samples were not filtered or 

centrifuged prior to analysis given the presence of precipitate in the test chambers. The amount 

of mesosulfuron-methyl that was freely dissolved and bioavailable cannot be determined without 

centrifugation or filtration. As such, toxicity may be underestimated. However, uncertainty is 

minimal in regard to the risk conclusions. Effects were not observed (mortality or sublethal) and 

there is no risk concern as long as about 0.05% of the mesosulfuron-methyl was in solution (i.e., 

dissolved)17. Furthermore, there is no risk concern based on the lowest ECOSAR estimate (LC50

= 332 mg ai/L). Repeat testing is unlikely to change risk conclusions unless aquatic EECs are 

substantially higher in the future (e.g., higher application rates are requested).

Freshwater fish early life stage

Data are available for sub-chronic (28 day) toxicity to rainbow trout (two months of age) but not 

for early life stage (ELS) toxicity. No effects (mortality or growth) were observed in the 28-day 

study (NOAEC ≥ 29.6 mg ai/L). The potential for chronic effects on fish reproduction remains 

uncertain without an early life stage study. However, there is a large margin of safety based on 

the current application rates and available toxicity information. ELS toxicity would need to be ≥ 

four orders of magnitude more toxic than the sub-chronic NOAEC (29.6 mg ai/L) to have a risk 

concern. Additionally, ELS toxicity would need to be ≥ three orders of magnitude greater than 

the lowest ECOSAR estimate (most toxic, NOEC = 3.4 mg ai/L) to have a chronic risk concern. 

An ELS study is unlikely to change risk conclusions at this time given the margin of safety. 

However, additional data could be important in the future if aquatic EECs approach the 

ECOSAR estimate (e.g., higher application rates are requested) or new information suggests 

reproductive effects at environmentally relevant concentrations of mesosulfuron-methyl.

Passerine acute oral toxicity

Data are not available for a passerine species, which are potentially more sensitive than larger 

birds due to their smaller size and higher metabolic rates. The available acute oral studies with 

 17 Percentage not precise and would be lower because EECs were calculated using a TTR approach and toxicity 

endpoints are non-definitive.
30

bobwhite quail and mallard duck showed no mortality at a concentration of 2000 mg/kg. A 

passerine species (ca. 25 g) would need to be > 50 X more sensitive than the quail and duck to 

exceed the listed species LOC at the highest registered application rate. Additionally, no 

mortality was observed at 4800 ppm in the available avian acute dietary studies. At the current 

application rates, the value of a passerine study would be confirmatory in nature.

Avian reproduction

A non-definitive NOAEC was established in the available studies (MRID 45386228 and 

45386229) based on no adverse effects at the highest dose tested. Requesting additional data to 

establish a definitive NOAEC has little value at this time because terrestrial EECs for currently 

registered uses are more than 300 X lower than the non-definitive NOAEC. However, additional 

data could be important in the future if terrestrial EECs approach the highest concentration tested 

in the available studies (e.g., higher application rates are requested).

Terrestrial plants – seedling emergence

Available data are supplemental because the observation period was 14 days post-application 

instead of 21 days post-emergence of control plants. Additionally, the test material was TGAI 

plus adjuvant instead of a TEP (including inert materials) plus adjuvant. Available data suggest 

that repeat testing would likely result in minimal impact on risk conclusions. 

Risk from spray drift is likely to be impacted more by foliar applications. Toxicity was greater 

for foliar application (vegetative vigor) than for application to seeds (seedling emergence) in 

studies conducted with the same test material and duration. The value of repeat testing would be 

confirmatory in this regard.

 

Seedling emergence data will have a greater impact on assessing risk from runoff. However, 

little may be gained from repeat testing considering the results of the available vegetative vigor 

studies. Vegetative vigor data show little difference in toxicity for studies conducted for 21 days 

using a TEP (MRID 46688201, under review) and 14 days using TGAI plus adjuvant (MRID 

45386317 and 45745701). The general risk picture would change little if effects to seedling 

emergence, like vegetative vigor, are minimally impacted by extending the study duration and 

testing with a TEP.

Aquatic plant growth - freshwater green alga

Acceptable data are available for three of four recommended test species. Green alga data are 

needed to assess risk to non-vascular plants because different species are likely to show a range 

of sensitivity to mesosulfuron-methyl. The most sensitive species will be used to assess risk. 

Data are of value in reducing uncertainty of risk to non-vascular plants. Other means of 

addressing risk will be used to reduce uncertainty in the absence of a study. For instance, 

toxicity may be estimated based on the lowest ECOSAR estimate (IC50 = 56 μg ai/L) or data 

from other SU herbicides. 

Non-Guideline – Special study for non-target plant reproductive toxicity with TEP

EFED's Plant Technical Team (PTT) conducted an analysis of available SU plant reproduction 

data from the open literature and the registrant-submitted data for chlorsulfuron and concluded 
31

that data from the 850.4150 vegetative vigor guideline study are sufficiently protective of 

potential impacts to plant reproduction. Acetolactate synthase (ALS) inhibitors primarily affect 

metabolically-active meristem tissues. When plants are exposed at a young, vigorously growing 

life-stage, effects are expressed primarily as inhibition of vegetative growth (i.e. biomass, shoot 

length). As plants mature these effects are less pronounced. However, as plants enter their 

reproductive life-stage, the metabolically-active tissue will include flower and seed production. 

Plants exposed to SU herbicides during the reproductive life stage are likely to exhibit adverse 

effects on reproduction, generally expressed as reduced seed number or reduced seed weight. 

Based on the latest data analysis, these effects are expected to occur at similar concentrations to 

those effects determined in the guideline vegetative vigor studies (850.4150). Therefore, 

fulfilling this DCI has a low potential to add value to the risk assessment and a study is not 

recommended.

Degradation Products

Fish and aquatic invertebrates (acute and chronic toxicity)

Data are not requested at this time because risk conclusions are unlikely to change based on the 

currently labeled rates (see Section 6.1). ECOSAR estimates suggest that some degradates may 

be more acutely or chronically toxic than mesosulfuron-methyl to fish and invertebrates. 

However, LOCs are not exceeded even when the lowest ECOSAR estimates (i.e., most toxic for 

each degradate) are compared to preliminary mesosulfuron-methyl EECs (maximum application 

rate) calculated with the assumption of no degradation. EECs of individual degradates would be 

lower. Other means of addressing risk will be used to reduce uncertainty in the absence of 

studies. A TTR approach will be used to calculate EECs and toxicity may be based on 

ECOSAR estimates or analogous compounds. However, studies could be important in the future 

if aquatic EECs are expected to be higher (e.g., higher application rates are requested).

Avian (acute and chronic toxicity)

Data are not requested at this time because risk conclusions are unlikely to change based on the 

currently labeled rates (see Section 6.1). Degradates would need to be at least two to three 

orders of magnitude more toxic than mesosulfuron-methyl to be a risk concern. However, data 

could be important in the future if EECs are expected to be higher (e.g., higher application rates 

are requested).

Aquatic plant growth – vascular plant (AE F154851 and AE F140584)

Data are recommended to reduce potential uncertainty in risk conclusions for non-listed species 

(see Section 6.1). AE F154851 (SU bridge-intact compound ) and AE F140584 toxicity will be 

assumed equal to mesosulfuron-methyl in the absence of data and a TTR approach will be used 

to calculate EECs.

Aquatic plant growth – non-vascular plants

Data are not requested at this time because available information suggests that the degradation 

products are not more toxic than mesosulfuron-methyl (see Section 6.1). In the absence of 

submitted data, those degradates will be assumed as toxic as mesosulfuron-methyl and a TTR 
32

approach will be used to calculate EECs. However, as discussed above, an acceptable study is 

needed to establish mesosulfuron-methyl toxicity to green algae. 

Terrestrial plants

Data are not requested at this time; however, SU bridge-intact degradates will be assumed equal 

in toxicity to mesosulfuron-methyl in the absence of data (see Section 6.1). 

Table 17. Ecological Effects Data (TGAI) for Aquatic Animals Exposed to Mesosulfuronmethyl and Data Gaps

Guideline Description MRID Classification Data 

Gap? Comments

850.1075

Acute freshwater fish 

toxicity

(cold water species)

45386231 Supplemental Yes1,2

1

EFED does not recommend 

requesting a new study because 

little will be gained from 

submission of a new study.

2 See text above Table 17.

Acute freshwater fish 

toxicity

(warm water species)

45386230 Supplemental Yes1,2

Acute estuarine/

marine fish toxicity 45386301 Supplemental Yes1

850.1010

Acute toxicity to 

freshwater 

invertebrates

45386233 Acceptable 

(“Core”) No

850.1025

Acute estuarine/

marine mollusk 

toxicity

45386302 Acceptable 

(“Core”) No

850.1035

Acute estuarine/

marine invertebrate 

toxicity

45386303 Acceptable 

(“Core”) No

850.1300 Freshwater 

invertebrate life cycle 45386305 Acceptable 

(“Core”) No

850.1400 Freshwater fish early 

life stage 45386232 Supplemental Yes1,2
33

Table 18. Ecological Effects Data (TGAI) for Terrestrial Animals Exposed to 

Mesosulfuron-methyl and Data Gaps

Guideline Description MRID Classification Data 

Gap?

Comments

850.2100

Avian acute oral toxicity

(upland game or 

waterfowl species)

45386224

45386225

Acceptable 

(“Core”) No

1

These data are required under 

40 CFR part 158 for terrestrial 

outdoor uses. However, 

EFED does not recommend 

requesting a study at this time.

2 See text above Table 17

3

EFED does not recommend 

requesting a new study 

because little will be gained 

from submission of a new 

study.

Avian acute oral toxicity 

(passerine species) None Not applicable Yes1,2

850.2200

Avian dietary toxicity 

(upland game species) 45386226 Acceptable (“Core”) No

Avian dietary toxicity 

(waterfowl species) 45386227 Acceptable 

(“Core”) No

850.2300

Avian reproduction 

(upland game species) 45386228 Supplemental Yes2,3

Avian reproduction 

(waterfowl species) 45386229 Supplemental Yes2,3

850.3020 Honeybee acute contact 

toxicity 45386319 Acceptable (“Core”) No

Table 19. Ecological Effects Data for Plants Exposed to Mesosulfuron-methyl and Data 

Gaps

Guideline Description MRID Classification Data 

Gap? Comments

850.4100A

Terrestrial plant 

toxicity (Tier I&II 

seedling emergence)

45745702

45386316

Supplemental

Supplemental Yes1,2

1

EFED does not recommend 

requesting a new study because 

little will be gained from 

submission of a new study.

2 See text above Table 17

3 These data are required under 40 

CFR part 158 for terrestrial outdoor 

uses. Data are of value in reducing 

uncertainty of risk to non-vascular 

plants.

4 No data gap for mesosulfuronmethyl; however, data are 

recommended for two 

degradation products (AE 

F154851 and AE F140584).

850.4150B

Terrestrial plant 

toxicity (Tier I&II 

vegetative vigor)

46688201 Under Review TBD

850.4500C

Aquatic plant growth

(freshwater green 

alga)

45386306 Invalid Yes3

Aquatic plant growth 

(freshwater diatom) 45386307 Acceptable (“Core”) No

Aquatic plant growth 

(saltwater diatom) 45386314 Acceptable (“Core”) No

850.4550 C Aquatic plant growth 

(Cyanobacteria) 45386315 Acceptable (“Core”) No

850.4400 Aquatic plant growth 

(vascular plants) 45386310 Acceptable 

(“Core”) No2,4

A As of July 2012 the Final Guideline 850.4100 contains both Tier I and Tier II test guidance (formerly 850.4100

and 850.4225, respectively). B As of July 2012 the Final Guideline 850.4150 contains both Tier I and Tier II test guidance (formerly 850.4150 

and 850.4250, respectively). C Formerly 850.5400
34

7. References

USEPA. 2004a. Drinking Water Assessment for Mesosulfuron-methyl and Its Major Metabolites New 

Chemical- Uses on Winter Wheat (OSPREY; 4.5% mesosulfuron-methyl) and Spring Wheat, 

Including Dumm (SILVERADO, 2.0% mesosulfuron-methyl). DP Barcode: D295662

USEPA. 2004b. Mesosulfuron Methyl Section 3 - Uses on Winter Wheat (OSPREY; 4.5% 

mesosulfuron-methyl) and Spring Wheat, Including Durum (SILVERADO, 2.0% mesosulfuronmethyl). DP Barcodes: D284053, D284719, D295614, D295656, D296 120, D297232

USEPA. 2004c. 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.

USFWS and 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.
35

APPENDIX A. Submitted Environmental Fate and Effects Studies

MRID Citation Reference

Fate 

Studies

45386418 Burri, R. (2000) Hydrolysis of (Carbon 14)-AE F130060 at Different pH Values: Lab Project Number: 

738090: C008110. Unpublished study prepared by RCC Ltd. 70 p. {OPPTS 835.2110 and 835.2130} 

45386419 Schmidt, W.; Buerkle, W. (2000) Aqueous Photolysis Under Laboratory Conditions: (U-(Carbon 14)-

AE F130060: Lab Project Number: CP97/040: C008008. Unpublished study prepared by Aventis 

CropScience. 58 p. 

45386420 Buerkle, W. (2000) Real Half-Lives of the Aqueous Photolysis: AE F130060: Lab Project Number: 

C009998: OE00/118. Unpublished study prepared by Aventis CropScience. 6 p. {OPPTS 835.2210} 

45386421 Burri, R. (2000) Photolysis of (Carbon 14)-AE F130060 on Soil Surface Under Laboratory Conditions: 

Lab Project Number: 738088: C006911. Unpublished study prepared by RCC Ltd. 51 p. 

45386422 Tarara, G. (2000) Kinetics and Metabolism in Soil LS 2.2 at 10C and 20C Under Aerobic Conditions: 

(2-(Carbon 14)-Pyrimidyl)AE F130060: Lab Project Number: CB96/011: C009871. Unpublished study 

prepared by Aventis CropScience. 82 p. 

45386423 Tarara, G. (2000) Kinetics and Metabolism in Soil LS 2.2 at 10C and 20C Under Aerobic Conditions: 

(2-(Carbon 14)-Phenyl)AE F130060: Lab Project Number: CB97/053: C009873. Unpublished study 

prepared by Aventis CropScience. 60 p. 

45386424 Tarara, G. (2000) Degradation in Three Soils at 20C Under Aerobic Conditions: AE F130060: Lab 

Project Number: CB96/056: C009874. Unpublished study prepared by Aventis CropScience. 80 p. 

45386425 Tarara, G. (2000) Degradation in Four Soils at 20C Under Aerobic Conditions: (2-(Carbon 14)-

Pyrimidinyl)AE F130060: Lab Project Number: CB96/140: C009870. Unpublished study prepared by 

Aventis CropScience. 96 p. 

45386426 Schafer, D. (2000) Kinetic Evaluation of AE F130060 Aerobic Soil Degradation Studies Using TopFit 

2.0: Lab Project Number: C009951: OE00/105. Unpublished study prepared by Aventis CropScience 

GmbH. 121 p. {OPPTS 835.4100} 

45386427 Tarara, G. (2000) Kinetics and Metabolism in Soil LS 2.2 at 20C Under Anaerobic Soil Conditions: 

(U-(Carbon 14)AE F130060 and (2-(Carbon 14)-Pryrimidinyl)AE F130060: Lab Project Number: 

CB98/136: C009872. Unpublished study prepared by Aventis CropScience GmbH. 71 p. 

45386428

Schafer, D. (2000) Kinetic Evaluation of AE F130060 Anaerobic Soil Degradation Studies Using 

TopFit 2.0: Lab Project Number: C010057: OE00/122. Unpublished study prepared by Aventis 

CropScience GmbH. 33 p. {OPPTS 835.4200} 

45386429 Gildemeister, H. (2001) Degradation in a Water/Sediment-System at Different Temperatures Under 

Anaerobic Conditions in the Laboratory (2-(Carbon 14)-Pyrimidinyl)-and (U-(Carbon 14)-Phenyl)-AE 

F130060: Lab Project Number: CB97/143: C011868. Unpublished study prepared by Aventis 

CropScience. 76 p. 

45386430 Steinfuhrer, T.; Zumdick, A. (2000) Aerobic Degradation in Two Water/Sediment-System at 20C 

(Carbon 14)-AE F130060: Lab Project Number: CB97/082: C009416. Unpublished study prepared 

by Aventis CropScience. 218 p. {OPPTS 835.4300} 

45386431 Schafer, D. (2000) Kinetic Evaluation of AE F130060 Aerobic Water/Sediment-System Using TopFit 
36

2.0: Lab Project Number: C009952: OE00/115. Unpublished study prepared by Aventis CropScience 

GmbH. 97 p. {OPPTS 835.4300} 

45386432 Allan, J.; Pate, M. (2000) The Adsorption/Desorption of (Carbon 14)-AE F130060 on Nine Soils: Lab 

Project Number: 500CK: C003710: CK96E500. Unpublished study prepared by Aventis CropScience. 

84 p. 

45386433 Rosenwald, J. (2000) AE F154851: Adsorption in Three Soils: Final Report: Lab Project Number: 

1490-017: C007785. Unpublished study prepared by Covance Labs., GmbH. 79 p. 

45386434 Rosenwald, J. (2000) AE F099095: Adsorption in Three Soils: Final Report: Lab Project Number: 

1490-016: C007786. Unpublished study prepared by Covance Labs., GmbH. 79 p. 

45386501 Cole, M. (2001) Dissipation of AE F115008 and AE F130060 in Soil Following Application of AE 

F115008 WDG and AE F122006 WDG or AE F130060 WDG and AE F107982 WDG to a Bare Plot 

at the Maximum Proposed Rates, USA, 1998: Lab Project Number: BY98R004: B003218. 

Unpublished study prepared by Aventis CropScience. 256 p. 

46948901 Lenz, M. (2006) Terrestrial Field Dissipation of Mesosulfuron-methyl in North Dakota Soil, 2004. 

Project Number: MEMMY002. Unpublished study prepared by Agvise Inc and Bayer Corp. 109 p.

45386502 Wrede, A. (2000) Stability of AE F130060 in Soil During Deep Freeze Storage of 24 Months. 

Unpublished Study Performed and Submitted by Aventis CropScienceGmbH, Frankfurt, Federal 

Republic of Germany. Study ID. CR 97/037. Experiment Imitation August 12, 1997 and Completion 

August 12, 1999 p. 10. Final Report Issued August 21, 2000.

45386504 Frey, J.; Harrison, C.; Buerkle, L. (2000) Residues in Rotated Crops Sown 31 Days after Application to 

Bare Soil at a Rate of 15 g a.s./ha: (2-(Carbon-14)-Pyrimidyl)-AE F130060: Lab Project Number: 

CM97/044: C008238. Unpublished study prepared by Aventis CropScience. 32 p. 

45386505 Frey, J.; Harrison, C.; Buerkle, L. (2000) Residues in Rotated Crops Sown 32 Days after Application to 

Bare Soil at a Rate of 15 g a.s./ha: (U-(Carbon-14)-Phenyl)-AE F130060: Lab Project Number: 

CM97/046: C008240. Unpublished study prepared by Aventis CropScience. 32 p. 

45386506 Frey, J.; Harrison, C. (2000) Residues in Rotated Crops Sown 4 Months after Application to Bare Soil at 

a Rate of 15 g a.s./ha: (2-(Carbon-14)-Pyrimidyl)-AE F130060: Lab Project Number: CM97/163: 

C008242. Unpublished study prepared by Aventis CropScience. 26 p. 

45386507 Frey, J.; Harrison, C. (2000) Residues in Rotated Crops Sown 4 Months after Application to Bare Soil at 

a Rate of 15 g a.s./ha: (U-(Carbon-14)-Phenyl)-AE F130060: Lab Project Number: CM97/164: 

C008243. Unpublished study prepared by Aventis CropScience. 26 p. 

45386508 Frey, J.; Harrison, C. (2000) Residues in Rotated Crops Sown 1 Year after Application to Bare Soil at a 

Rate of 15 g a.s./ha: (2-(Carbon-14)-Pyrimidyl)-AE F130060: Lab Project Number: CM97/045: 

C008239. Unpublished study prepared by Aventis CropScience. 26 p. 

45386509 Frey, J.; Harrison, C. (2000) Residues in Rotated Crops Sown 1 Year after Application to Bare Soil at a 

Rate of 15 g a.s./ha: (U-(Carbon-14)-Phenyl)-AE F130060: Lab Project Number: CM97/047: C008241. 

Unpublished study prepared by Aventis CropScience. 26 p. 

45386522 Wrede, A. (2000) Enforcement Method for Surface and Drinking Water by HPLC-UV: AE F130060: 

Lab Project Number: EM F15/99-0: C008689. Unpublished study prepared by Aventis CropScience 

GmbH. 35 p. {OPPTS 860.1340} 

45386523 Wrede, A. (2000) Validation of the Enforcement Method EM F15/99-0 for Surface and Drinking 

Water by HPLC-UV: AE F130060: Lab Project Number: CR 00/008: C008686: EM F15/99-0. 

Unpublished study prepared by Aventis CropScience GmbH. 68 p. {OPPTS 860.1340} 

45386532 Phillips, J.; Ramanarayanan, T. (2001) Tier One Chronic Dietary Exposure Analysis for 

Mesosulfuron-Methyl Including Drinking Water Estimated Concentration (DWEC) Comparison to 

Drinking Water Level of Comparison (DWLOC): Lab Project Number: MESOSULFURON-01-01: 

B003220. Unpublished study prepared by Aventis CropScience. 25 p. 
37

46451701 Wrede, A. (2002) Validation of the Enforcement Method EM F04/00-0 for Surface Water by LCMS/MS: Amidosulfuron, Mesosulfuron-Methyl and Foramsulfuron. Project Number: 02F026, 

C024802. Unpublished study prepared by Bayer Cropscience Gmbh. 56 p.

46451702 Reichert, N.; Klimmek, S. (2003) Independent Laboratory Validation of the Analytical Method for the 

Residue Analysis of Amidosulfuron, Mesosulfuron-Methyl and Foramsulfuron in Surface Water. 

Project Number: IF/02/000105070, C/030823. Unpublished study prepared by Institut Fresenius 

Chemische und Biologische. 47 p.

Effects 

Studies

45386224 Ebert, E. (1998) Bobwhite Quail Acute Oral Toxicity Test: AE F130060; Substance, Technical: Lab 

Project Number: 98.0450: C0002332. Unpublished study prepared by Hoechst Marion Roussel 

Deutschland GmbH. 34 p. 

45386225 Ebert, E. (1998) Mallard Duck Acute Oral Toxicity Test: AE F130060; Substance, Technical: Lab 

Project Number: A67403: 98.0047. Unpublished study prepared by Hoechst Marion Roussel 

Deutschland GmbH. 33 p. 

45386226 Ebert, E. (1999) Bobwhite Quail Dietary LC(50) Study: AE F130060; Substance, Technical: Lab 

Project Number: 98.0964: C002392. Unpublished study prepared by Hoechst Marion Roussel 

Deutschland GmbH. 36 p. 

45386227 Ebert, E. (1998) Mallard Duck Dietary LC(50) Study: AE F130060; Substance, Technical: Lab 

Project Number: 98.0436: C000841. Unpublished study prepared by Hoechst Marion Roussel 

Deutschland GmbH. 37 p. 

45386228 Ebert, E. (2000) Bobwhite Quail Dietary Reproduction Study: AE F130060; Substance, Technical: 

Lab Project Number: 2000.0138: C009084: 97.0745. Unpublished study prepared by Aventis Pharma 

Deutschland GmbH. 186 p. 

45386229 Frey, L.; Beavers, J.; Jaber, M. (1999) Mallard Duck Dietary Reproduction Toxicity Study: AE 

F130060; Substance, Technical: Lab Project Number: C005103: 312-115. Unpublished study prepared 

by Wildlife International Ltd. 152 p. 

46392501 Ortego, L. (2004) Proposed NOEC and LOEC for the Avian Reproduction Study: "Mallard Duck 

Dietary Reproduction Toxicity Study AE F130060; Substance Technical (Code: AE F130060 00 1C95 

0001)". Project Number: C005103, B004809. Unpublished study prepared by Bayer Cropscience LP. 

8 p.

45386230 Heusel, R.; Weller, O.; Gosch, H. (1999) Acute Toxicity to Bluegill Sunfish (Lepomis macrochirus): 

AE F130060; Substance, Technical: Lab Project Number: CE97/025. Unpublished study prepared by 

Hoechst Schering AgrEvo GmbH. 26 p. 

45386231 Sowig, P.; Weller, O.; Gosch, H. (1999) Acute Toxicity to Rainbow Trout (Oncorhynchus mykiss): 

AE F130060; Substance, Technical: Lab Project Number: CE97/026: C003718. Unpublished study 

prepared by Hoechst Schering AgrEvo GmbH. 27 p. 

45386233 Sowig, P.; Weller, O.; Gosch, H. (1999) Acute Toxicity to Waterflea (Daphnia magna): AE F130060; 

Substance, Technical: Lab Project Number: CE97/027: C003741. Unpublished study prepared by 

Hoechst Schering AgrEvo GmbH. 29 p. 

45386301 Abedi, J.; Stachura, B.; Young, B. (2001) 96 Hour Acute Toxicity to the Sheepshead Minnow, 

Cyprinodon variegatus, in Static System: AE F130060 Technical 95.7% w/w: Lab Project Number: 

CK99W506: B003157. Unpublished study prepared by Aventis CropScience. 39 p. 

45386302 Dionne, E. (2000) AE 130060 00 1C96 0004: Acute Toxicity to Eastern Oysters (Crassostrea 

virginica) Under Flow-Through Conditions: Lab Project Number: B003104: CK 99W508: 13726. 

6125. Unpublished study prepared by Springborn Labs., Inc. 60 p. {OPPTS 850.1025} 

45386303 Abedi, J.; Stachura, B.; Young, B. (2001) 96 Hour Acute Toxicity to the Mysid Shrimp, Mysidopsis 

bahia, in a Static System: AE F130060 Technical 95.7% w/w: Lab Project Number: CK99W507: 
38

B003158. Unpublished study prepared by Aventis CropScience. 36 p. 

45386232 Sowig, P.; Weller, O.; Gosch, H. (2000) Effects on Juvenile Growth of Rainbow Trout (Oncorhynchus 

mykiss) in a 28 Days Static Renewal System: AE F130060; Substance, Technical: Lab Project Number: 

CE97/097: C004237. Unpublished study prepared by Aventis CropScience GmbH. 62 p. {OPPTS 

850.1075} 

45386304 Sowig, P.; Gosch, H.; Weller, O. (2000) Effects on Growth and Reproduction of Daphnia magna 

(Waterflea): AE F130060; Substance, Technical: Lab Project Number: CE97/098: C008780: 

CE97/098-1. Unpublished study prepared by Aventis CropScience GmbH. 62 p. 

45386305 Sowig, P.; Gosch, H.; Weller, O. (2000) First Amendment to Report CE97/098-1; C008780: Effects on 

Growth and Reproduction of Daphnia magna (Waterflea): AE F130060; Substance, Technical: Lab 

Project Number: CE97/098: C009791: CE97/098-2. Unpublished study prepared by Aventis 

CropScience GmbH. 64 p. 

45386316 Christ, M.; Abedi, J. (2001) Effect on Seedling Emergence of Non-Targeting Terrestrial Plants (Tier II) 

AE F130060 + AE F115008: Water Dispersible Granule 50 + 10% w/w: Including a Representative 

Adjuvant: Lab Project Number: 01CK27636: B003211. Unpublished study prepared by Aventis 

CropScience GmbH. 170 p. 

45386317 Christ, M.; Abedi, J. (2001) Effect on Vegetative Vigor of Non-Target Terrestrial Plants (Tier II) AE 

F130060 + AE F115008: Water Dispersible Granule 50 + 10% w/w: Including a Representative 

Adjuvant: Lab Project Number: 01CK27635: B003212. Unpublished study prepared by Aventis 

CropScience GmbH. 170 p. 

45745701 Christ, M.; Abedi, J. (2002) Effect on Vegetative Vigor of Non-Target Terrestrial Plants (Tier 2) AE 

F130060+ (Inert Ingredient); Water Dispersible Granule (75.3% w/w) Including a Representative 

Adjuvant: Lab Project Number: CK99W504: B003969. Unpublished study prepared by Aventis 

CropScience. 112 p. 

45745702 Christ, M.; Abedi, J. (2002) Effect on Seedling Emergence of Non-Target Terrestrial Plants (Tier 2) AE 

F130060+ (Inert Ingredient); Water Dispersible Granule (75.3% w/w) Including a Representative 

Adjuvant: Lab Project Number: CK99W505: B003970. Unpublished study prepared by Aventis 

CropScience. 114 p. 

46688201 Christ, M.; Lam, C. (2005) Vegetative Vigor Nontarget Terrestrial Plant Study Using Osprey. Project 

Number: EBMMY002. Unpublished study prepared by Bayer Corp. 66 p.

45386306 Heusel, R.; Weller, O.; Gosch, H. (1998) AE F130060; Substance, Technical 94.6%: Algal Growth 

Inhibition--Pseudokirchneriella: Lab Project Number: CE97/024: A59843. Unpublished study prepared 

by Hoechst Schering AgrEvo GmbH. 46 p. 

45386307 Sowig, P.; Weller, O.; Gosch, H. (2000) Algal Growth Inhibition--Navicula pelliculosa: AE F130060; 

Substance, Technical: Lab Project Number: CE98/090: C004457. Unpublished study prepared by 

Aventis CropScience GmbH. 34 p. 

45386308 Sowig, P.; Weller, O.; Gosch, H. (2000) Algal Growth Inhibition--Pseudokirchneriella subcapitata: AE 

F147447; Substance, Technical (Metabolite of AE F130060): Lab Project Number: CE00/082: 

C009927. Unpublished study prepared by Aventis CropScience GmbH. 38 p. 

45386309 Sowig, P.; Weller, O.; Gosch, H. (2000) Algal Growth Inhibition--Pseudokirchneriella subcapitata: AE 

F160459; Substance, Pure (Metabolite of AE F130060): Lab Project Number: CE00/081: C010060. 

Unpublished study prepared by Aventis CropScience GmbH. 38 p. 

45386310 Sowig, P.; Weller, O. (2000) Duckweed (Lemna gibba G3) Growth Inhibition Test Substance, 

Technical, 95.3%: Lab Project Number: CE97/029: C007190. Unpublished study prepared by Aventis 

CropScience GmbH. 42 p. 

45386311 Sowig, P.; Weller, O. (2000) Duckweed (Lemna gibba G3) Growth Inhibition Test AE F160459, 

Substance, Pure (Metabolite of AE F130060): Lab Project Number: CE00/058: C009078. Unpublished 

study prepared by Aventis CropScience GmbH. 41 p. 
39

45386312 Sowig, P.; Weller, O. (2000) Duckweed (Lemna gibba G3) Growth Inhibition Test AE F160460, 

Substance, Pure (Metabolite of AE F130060): Lab Project Number: CE00/059: C009792. Unpublished 

study prepared by Aventis CropScience GmbH. 41 p. 

45386313 Sowig, P.; Weller, O. (2000) Duckweed (Lemna gibba G3) Growth Inhibition Test AE F147447, 

Substance, Technical (Metabolite of AE F130060): Lab Project Number: CE00/057: C009245. 

Unpublished study prepared by Aventis CropScience GmbH. 41 p. 

45386314 Young, B.; Abedi, J. (2001) Effect to Skeletonema costatum (Marine Diatom)in a Growth Inhibition 

Test AE F130060 Technical 95.7% w/w: Lab Project Number: CK99W502: B003156. Unpublished 

study prepared by Aventis CropScience GmbH. 59 p. 

45386315 Abedi, J.; Christ, M.; Young, B. (2000) Effect to Anabaena flos-aqua (Blue-Green Alga) in a Growth 

Inhibition Test AE F130060 Technical 95.7% w/w: Lab Project Number: CK99W503: B003222. 

Unpublished study prepared by Aventis CropScience GmbH. 57 p. 

45386318 Waltersdorfer, A. (1996) Oral Toxicity (LD 50) to Honey Bees (Apis mellifera L.): AE F130060: Lab 

Project Number: CW 96/032: A58014. Unpublished study prepared by Hoechst Schering AgrEvo 

GmbH. 13 p. 

45386319 Waltersdorfer, A. (1997) Contact Toxicity (LD 50) to Honey Bees (Apis mellifera L.): AE F13006 00 

1C96 0002: Lab Project Number: CW97/129: A59434. Unpublished study prepared by Hoechst 

Schering AgrEvo GmbH. 14 p. {OPPTS 850.3020} 

45386331 Rosinger, C. (1999) Evaluation of Herbicidal Potential of Metabolites of AE F130060: Lab Project 

Number: C002929. Unpublished study prepared by Hoechst Schering AgrEvo GmbH. 11 p. {OPPTS 

850.4250} 

46767101 Ortego, L.; Priester, T.; Kemman, R.; et. al. (2006) Mesosulfuron: An Assessment of Possible Risk to 

Endangered Species Associated with Wheat. Project Number: CS1/06704. Unpublished study 

prepared by Compliance Services International. 51 p.
40

APPENDIX B. SIP v.1.0 Inputs and Outputs

Table 1. Inputs

Parameter Value

Chemical name Mesosulfuron

Solubility (in water at 25oC; mg/L) 15390

Mammalian LD50 (mg/kg-bw) 5000

Mammalian test species laboratory rat

Body weight (g) of "other" mammalian 

species

Mammalian NOAEL (mg/kg-bw) 1175

Mammalian test species laboratory rat

Body weight (g) of "other" mammalian 

species

Avian LD50 (mg/kg-bw) 2000

Avian test species northern bobwhite quail

Body weight (g) of "other" avian species

Mineau scaling factor 1.15

Mallard NOAEC (mg/kg-diet) 990

Bobwhite quail NOAEC (mg/kg-diet) 1000

NOAEC (mg/kg-diet) for other bird species 0

Body weight (g) of other avian species 0

NOAEC (mg/kg-diet) for 2nd other bird 

species 0

Body weight (g) of 2nd other avian species 0

Table 2. Mammalian Results

Parameter Acute Chronic

Upper bound exposure (mg/kg-bw) 2647.0800 2647.0800

Adjusted toxicity value (mg/kg-bw) 3845.8028 903.7637

Ratio of exposure to toxicity 0.6883 2.9290

Conclusion*

Exposure through 

drinking water alone is a 

potential concern for 

mammals

Exposure through 

drinking water alone is a 

potential concern for 

mammals

Table 3. Avian Results

Parameter Acute Chronic

Upper bound exposure (mg/kg-bw) 12465.9000 12465.9000

Adjusted toxicity value (mg/kg-bw) 1440.8590 49.1164

Ratio of exposure to acute toxicity 8.6517 253.8030

Conclusion*

Exposure through 

drinking water alone is a 

potential concern for 

birds

Exposure through 

drinking water alone is a 

potential concern for 

birds
41

APPENDIX C. STIR v.1.0 Inputs and Outputs

Input

Application and Chemical Information

Enter Chemical Name Mesosulfuron

Enter Chemical Use Outdoor

Is the Application a Spray? (enter y or n) y

If Spray What Type (enter ground or air) air

Enter Chemical Molecular Weight (g/mole) 503.5

Enter Chemical Vapor Pressure (mmHg) 8.25E-14

Enter Application Rate (lb ai/acre) 0.013

Toxicity Properties

Bird

Enter Lowest Bird Oral LD50 (mg/kg bw) 10

Enter Mineau Scaling Factor 1.15

Enter Tested Bird Weight (kg) 0.025

Mammal

Enter Lowest Rat Oral LD50 (mg/kg bw) 5000

Enter Lowest Rat Inhalation LC50 (mg/L) 1.33

Duration of Rat Inhalation Study (hrs) 4

Enter Rat Weight (kg) 0.35

Output

Results Avian (0.020 kg )

Maximum Vapor Concentration in Air at Saturation 

(mg/m3) 2.24E-09

Maximum 1-hour Vapor Inhalation Dose (mg/kg) 2.81E-10

Adjusted Inhalation LD50 1.99E-02

Ratio of Vapor Dose to Adjusted Inhalation LD50 1.41E-08

Exposure not Likely 

Significant

Maximum Post-treatment Spray Inhalation Dose (mg/kg) 1.25E-03

Ratio of Droplet Inhalation Dose to Adjusted Inhalation 

LD50 6.27E-02

Exposure not Likely 

Significant

Results Mammalian (0.015 kg )

Maximum Vapor Concentration in Air at Saturation 

(mg/m3) 2.24E-09

Maximum 1-hour Vapor Inhalation Dose (mg/kg) 3.53E-10

Adjusted Inhalation LD50 7.92E+01

Ratio of Vapor Dose to Adjusted Inhalation LD50 4.46E-12

Exposure not Likely 

Significant

Maximum Post-treatment Spray Inhalation Dose (mg/kg) 1.57E-03

Ratio of Droplet Inhalation Dose to Adjusted Inhalation 

LD50 1.98E-05

Exposure not Likely 

Significant