UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON D.C., 20460 

OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION 

April 9, 2013 

MEMORANDUM 

PC Code: 12200 1 

DP Barcode: 0409662 

SUBJECT: Response to DuPont Crop Protection Comments regarding EFED Problem 

Formulation on the Registration Review of Sulfometuron Methyl (D409662) 

TO: Russell Wasem, Chemical Review Manager 

Neil Anderson, Branch Chief 

Risk Management and Implementation Branch 1 

Pesticide Re-evaluation Division 508 

FROM: Michael Barrett, Senior Che 'st \.f,~ /LJ> 

Environmental Risk Branch V 7 ~ { " 

Environmental Fate and Effects Division (7507P) ~ 

THROUGH~h Shamim, Ph.D., Branch Chief ~ /);· t/. o~ f 11 ~t{t ""\ 

"}/ E~"~ironmental Risk Branch V 

Environmental Fate and Effects Division (7507P) 

The Environmental Fate and Effects Division (EFED) previously completed the preliminary 

problem formulation for the environmental fate, ecological risk, endangered species, arid human 

health drinking water exposure assessments to be conducted as part of the Registration Review 

of Sulfometuron methyl , a sulfonyl urea herbicide registered for use on forest plantings, rightsof way, and other non-cropped lands (review dated 12/5/2012, DP Barcode D402497). Comments 

have been received from the registrant, DuPont Crop Protection, . A summary of the comments and 

EFED's response follows. 

List of Comments and EFED Responses 

DuPont has separately submitted comments on ecological effects data needs in a letter from 

Bridget O'Neill, Global Regulatory Ecotoxicologist dated 2/12/2013 and on environmental fate 

data needs in a letter from Daniel M. Tessier dated 2/13/2013; the full text of these submissions 

is provided in Appendix 1. DuPont's comments and EFED's response to these comments is 

1 2-[[[[(4,6-Dimethyl-2-pyrimidinyl) amino] carbonyl] amino] sulfonyl] benzoic acid, methyl ester. 
2

provided below, first for the environmental fate related comments and then for the ecological 

effects related comments. 

Environmental Fate Comments

DuPont has commented on partial data deficiencies identified in the Preliminary Problem 

Formulation with regard to the 835.4100 and the 835.6100 /835.6300 data requirements, both of 

which refer to specific Environmental Fate data requirements elucidated in the Preliminary

Problem Formulation. Each section below begins with DuPont’s quote of the EPA document 

followed by the DuPont response, and then by EFED’s current response.

1. Guideline 835.4100 Aerobic Soil Metabolism.

The Preliminary Problem Formulation states on page 35, "Guideline requirements are partially 

fulfilled ... results from at least four relevant soils of different organic carbon content, pH, clay 

content and with active microbial biomass must be submitted in order to characterize the 

variability of aerobic biodegradation ... studies must be conducted on three additional soils." This 

data requirement appears on page 4 of the Preliminary Work Plan, GDLN 835.4100 and 

proposes testing of both the Technical Grade Active Ingredient (TGAI), and Typical End-Use 

Product (TEP).

DuPont Response:

Laboratory data has been submitted for the degradation of sulfometuron methyl in Keyport silty 

loam, pH 6.4, 1.6% organic carbon content {%0C), showing degradation half-lives (DegT50) of 

23 and 29 days in separate trials [MRID 42091401, 43174102, 245375]. Data has also been 

provided from bare soil field studies which demonstrated DT50 values of 12 days in a silty clay 

loam with soil pH 6.7 and 0.6% OC; 14 days in a silty clay loam with soil pH 6.8 and 1.0% OC; 

13 days in a clay soil with soil pH 7.9 and 1.3% OC; and 23 days in a sandy loam with soil pH 

7.8 and 0.7% OC [MRID 43212101, 43637101]. Additional field testing returned DT50 values 

of 14 to 21 days in a silt loam soil with pH 5.5 and 0.8% OC, a sand soil with pH 4.9 and 0.2% 

OC and a silt loam with pH 6.4 and 0.6% OC [MRID94840].

These data provide a robust characterization of the variability of sulfometuron biodegradation, in 

eight soils of different pH, %0C and soil texture classification. The degradation pathway of 

sulfometuron methyl has been well established in these laboratory and field studies, and the 

degradation rate data shown in the lab and field studies is consistent. Therefore, DuPont is of the 

opinion that another laboratory study on additional soils is not warranted, as it will not 

significantly alter the quantitative or qualitative understanding of degradation of sulfometuron 

methyl in aerobic soil. Laboratory studies of degradation in soil are routinely conducted with 

either radiolabeled forms of the pesticide active ingredient or technical grade active ingredient 

(TGAI). Laboratory studies are not routinely conducted with typical end use product (TEP or

formulated material) as formulation components have no impact on behavior of the active 

ingredient in soil and therefore such a study would add no meaningful information to that 

obtained with TGAI. 
3

If it is still deemed necessary to augment the already robust data set on the degradation of 

sulfometuron methyl in aerobic soil, DuPont proposes the option of a laboratory study in aerobic 

soils with non-radiolabeled test material to provide additional degradation rate data. 

EFED Reply:

EFED has reviewed the studies referenced by DuPont as possibly providing sufficient 

information on sulfometuron methyl aerobic soil metabolism to justify a full or partial waiver of 

the requirement to submit the 835.4100 a total of four (two additional to the two already 

accepted) soils / sites. EFED agrees that the cited field dissipation studies do provide extremely 

useful information relevant to the aerobic soil metabolism of sulfometuron methyl and the 

formation and decline patterns of degradates at each site. However, ultimately these studies were 

not under sufficiently controlled conditions to fully isolate the role of degradation in the 

dissipation process. If some of these field studies had been conducted to more fully isolate 

degradation and dissipation processes (with e.g., use of field lysimeters to facilitate a more 

complete recovery of applied residues and tracking of losses due to drift, volatilization, runoff) it 

might be plausible to along with tracking of cumulative average soil temperature and moisture 

overtime, to closely estimate degradation half-lives in the field and adjust them for standard 

conditions as are used in the laboratory. It appears that only some of these characteristics are 

present in the studies submitted under Guideline 835.6100 (Field Dissipation), for example; daily 

soil temperature and precipitation data are available, but daily soil moisture measurements are 

apparently not available and confirmation of recovery within controlled lysimeters or similar 

devices was not attempted. 

A second alternative proposed by DuPont would be to submit these studies under all 835.4100 

guideline requirements with the proposed exception that sulfometuron methyl would not be 

radiolabeled to facilitate a mass balance accounting. EFED agrees to review, if submitted a 

formal proposal to fulfill the data requirement without radiolabeling of sulfometuron methyl. 

Such a submission would need to demonstrate that the major degradates in aerobic soil are all 

well-established such that an accounting of difficult to extract or volatilized residues (which is 

more easily accomplished with the use of a radiolabel on the test compound) could be waived in 

this case only for the two additional aerobic soil metabolism studies.

EFED concurs with DuPont’s comment regarding the use of TGAI versus TEP.

2. Guideline 835.6100 /835.6300 (Supporting) Environmental Chemistry Methods;

Independent Laboratory Validation.

The Preliminary Problem Formulation states on page 35, "State of the art ECMs in soil and water 

and ILVs used in sulfometuron methyl environmental fate studies are requested at this time."

DuPont response:

DuPont concurs with this statement. New soil and water analytical methods can be made

available for sulfometuron methyl and metabolitesiN-X0993, IN-D5803 and IN-581, and will be 

provided upon request along with independent laboratory validation.

EFED Reply:
4

These data needs have been communicated to the Pesticide Re-Evaluation Division for 

appropriate action.

Ecological Effects Comments

There were six issues related to the available ecological effects data in the Preliminary Problem 

formulation that DuPont commented on (see below), in each case DuPont has concurred with 

EFED conclusions regarding the use of these data. EFED thanks DuPont for carefully reviewing 

the document and responding in detail. The context for each of these issues in the Problem 

Formulation is included in Appendix 1. 

Issue 1: section 7, page 37, Guideline 850.1025.

DuPont Comment 1: DuPont agrees with the agency that repeating these studies would not 

likely affect the risk assessment conclusions.

Issue 2: section 7, page 38; Guideline 850.1350.

DuPont Comment 2: DuPont agrees with the agency’s decision to use toxicity data for 

freshwater invertebrates to characterize toxicity for estuarine/marine invertebrates.

Issue 3: section 7, page 38; Guideline 850.1400.

DuPont Comment 3: DuPont agrees with the agency’s decision to use chronic exposure toxicity 

data for freshwater and estuarine/marine fish for another sulfonylurea with a similar toxicity

profile to characterize chronic exposure toxicity for freshwater and estuarine/marine fish for 

Sulfometuron Methyl.

Issue 4: section 7, page 38; Guideline 850.2100.

DuPont Comment 4: DuPont agrees with the agency’s decision to characterize toxicity to 

passerines from acute exposure to Sulfometuron Methyl by using all acute toxicity data for 

passerines for other sulfonylureas with a similar toxicity profile and the same mode of action.

Issue 5: section 7, page 39; Guideline 850.2300.

DuPont Comment 5: DuPont agrees with the agency’s decision to characterize toxicity to birds 

from chronic exposure to Sulfometuron Methyl by using data from other sulfonylureas with a 

similar toxicity profile and the same mode of action.

Issue 6: section 7, page 38; Non-Guideline (Special study for non-target plant reproductive 

toxicity with TEP).

DuPont Comment 6: DuPont agrees

Issue 6: section 7, page 39; Agency comment on the use of Guideline 850.4150.
5

DuPont Comment 6: DuPont agrees with the agency that reproductive toxicity effects are likely 

to occur at similar concentrations as those observed in vegetative vigor studies, which have 

already been conducted for Sulfometuron Methyl and submitted to the agency for review.

Appendix 1: DuPont Crop Protection Letters commenting on 

the EFED Preliminary Problem Formulation for Sulfometuron 

Methyl
February 13, 2013 

United States Environmental Protection Agency 

Office of Prevention, Pesticides and Toxic Substances 

Risk Management and Implementation Branch II 

Pesticide Re-evaluation Division 

Subject: DuPont Response to: 

Sulfometuron Methyl PC Code 122201 Case Number 3136 

DuPont Crop Protection 

Stine-Haskell Research Center 

1090 Elkton Road 

Newark, Delaware 19711 

• USEPA Registration Review: Pesticide Dockets Opened For Review and Comment 

-December 14, 2012; HQ-OPP-2012-0433-0001 

• Preliminary Problem Formulation For Environmental Fate, Ecological Risk, 

Endangered Species, and Human Health Drinking Water exposure Assessments 

for Sulfometuron Methyl- December 5, 2012; HQ-OPP-2012-0433-0002 

• Sulfometuron Methyl Preliminary Work Plan, Registration Review Initial Docket 

Case Number 3136- December, 2012; HQ-OPP-2012-0433-0011 

Submitted by: 

Daniel M. Tessier, PhD 

Principal Investigator 

DuPont Crop Protection 

Stine Haskell Research Center 

1090 Elkton Rd 

Newark, DE 19711 

DuPont appreciates the opportunity to submit comment in response to the opening of 

the Registration Review process for sulfometuron methyl. These comments are in 

specific response to EPA's careful review of the existing Environmental Fate data for 

sulfometuron methyl and the proposed data requirements specific to Environmental 

Fate. 

1. 835.4100 [162-1] Aerobic Soil Metabolism 

The Preliminary Problem Formulation states on page 35, "Guideline requirements are 

partially fulfilled ... results from at least four relevant soils of different organic carbon 

H du Pont de Neroours and Company 
content, pH, clay content and with active microbial biomass must be submitted in order 

to characterize the variability of aerobic biodegradation ... studies must be conducted on 

three additional soils." This data requirement appears on page 4 of the Preliminary Work 

Plan, GDLN 835.4100 and proposes testing of both the Technical Grade Active Ingredient 

(TGAI), and Typical End-Use Product (TEP). 

DuPont Response: 

Laboratory data has been submitted for the degradation of sulfometuron methyl in 

Keyport silty loam, pH 6.4, 1.6% organic carbon content {%0C), showing degradation 

half-lives (DegT50) of 23 and 29 days in separate trials [MRID 42091401, 43174102, 

245375]. Data has also been provided from bare soil field studies which demonstrated 

DTso values of 12 days in a silty clay loam with soil pH 6.7 and 0.6% OC; 14 days in a silty 

clay loam with soil pH 6.8 and 1.0% OC; 13 days in a clay soil with soil pH 7.9 and 1.3% 

OC; and 23 days in a sandy loam with soil pH 7.8 and 0.7% OC [MRID 43212101, 

43637101]. Additional field testing returned DT50 values of 14 to 21 days in a silt loam 

soil with pH 5.5 and 0.8% OC, a sand soil with pH 4.9 and 0.2% OC and a silt loam with pH 

6.4 and 0.6% OC [MRID94840]. 

These data provide a robust characterization of the variability of sulfometuron 

biodegradation, in eight soils of different pH, %0C and soil texture classification. The 

degradation pathway of sulfometuron methyl has been well established in these 

laboratory and field studies, and the degradation rate data shown in the lab and field 

studies is consistent. Therefore, DuPont is of the opinion that another laboratory study 

on additional soils is not warranted, as it will not significantly alter the quantitative or 

qualitative understanding of degradation of sulfometuron methyl in aerobic soil. 

Laboratory studies of degradation in soil are routinely conducted with either radiolabeled 

forms of the pesticide active ingredient or technical grade active ingredient (TGAI). 

Laboratory studies are not routinely conducted with typical end use product (TEP or 

formulated material) as formulation components have no impact on behavior of the 

active ingredient in soil and therefore such a study would add no meaningful information 

to that obtained with TGAI. 

If it is still deemed necessary to augment the already robust data set on the degradation 

of sulfometuron methyl in aerobic soil, DuPont proposes the option of a laboratory study 

in aerobic soils with non-radiolabelled test material to provide additional degradation 

rate data. 
2. 835.6100/835.6300 (Supporting) Environmental Chemistry Methods; 

Independent Laboratory Validation 

The Preliminary Problem Formulation states on page 35, "State of the art ECMs in soil 

and water and ILVs used in sulfometuron methyl environmental fate studies are 

requested at this time." 

DuPont response: 

DuPont concurs with this statement. New soil and water analytical methods can be made 

available for sulfometuron methyl and metabolitesiN-X0993, IN-D5803 and IN-581, and 

will be provided upon request along with independent laboratory validation 

In summary, DuPont asserts that the degradation route and rate of sulfometuron methyl 

in aerobic soil is well established and well understood, based on data generated in 

numerous and varied soils, and further that an additional laboratory study would not 

offer any meaningful improvement to a qualitative or quantitative understanding of 

sulfometuron methyl degradation or substantively alter the conclusions of environmental 

fate risk assessment. 

DuPont will provide an updated ECM and ILV for sulfometuron methyl analysis in soil and 

water upon request. 

Respectfully, 

~A~~ Daniel M. Tessier 
DuPont Crop Protection

Stine-Haskell Research Center

P.O. Box 30

Newark, DE 19714-0030

February 12, 2013

United States Environmental Protection Agency

Office of Prevention, Pesticides and Toxic Substances

Risk Management and Implementation Branch II

Pesticide Re-Evaluation Division

Subject: DuPont Response to: 

Sulfometuron Methyl PC Code 122201 Case Number 3136

USEPA Registration Review: Pesticide Dockets Opened For Review and Comment –

December 14, 2012; HQ-OPP-2012-0433-0001

Preliminary Problem Formulation For Environmental Fate, Ecological Risk, Endangered 

Species, and Human Health Drinking Water exposure Assessments for Sulfometuron 

Methyl – December 5, 2012; HQ-OPP-2012-0433-0002

Sulfometuron Methyl Preliminary Work Plan, Registration Review Initial Docket Case 

Number 3136 – December, 2012; HQ-OPP-2012-0433-0011

Submitted by:

Bridget O’Neill, Global Regulatory Ecotoxicologist

E.I. du Pont de Nemours & Company

1007 Market Street

Wilmington, DE 19898

E.I. du Pont de Nemours & Company is supporting the Registration Review of the herbicide 

active ingredient Sulfometuron Methyl. As part of that effort DuPont is herein submitting 

comments to the Agency in response to December 12, 2012 Federal Register Notice, via the 

docket as designated: Docket ID Number EPA-HQ-OPP-2012-0433.

DuPont warmly welcomes the opportunity to comment on the data gaps listed in the registration 

review document. The following comments are applicable to Environmental Effects as 

discussed in the EFED Reregistration Review, section 7, page 37. Each subject is characterized 

as an issue, followed by a comment. 

Issue 1: section 7, page 37, the preliminary problem formulation document states:

Guideline 850.1025 – Acute toxicity estuarine/marine invertebrate (bivalve); Guideline

850.1035 – Acute toxicity estuarine/marine invertebrate (mysid); Guideline 850.1075 –

Acute toxicity estuarine/marine fish: Acceptable acute toxicity data for an estuarine/marine

bivalve, mysid, and fish are not available. Submitted studies for these data requirements with a

48-hr IC50 > 38.2 mg a.i./L (MRID 41672805), a 48-hr LC50 > 44.8 mg a.i./L (MRID 

41672803), and a 48-hr LC50 > 45 mg a.i./L (MRID 41672804), respectively, are classified as 

supplemental due to high variability in measured test concentrations and uncertainty in exposure 

to dissolved sulfometuron methyl (i.e., test samples were not centrifuged prior to analysis). 

Although these deficiencies could have rendered the study classifications as invalid, the studies 

are considered to provide some useful information for the Registration Review ecological risk 

assessment (i.e., an indication of a lack of toxicity at or near solubility limits in test solutions). 
DuPont Crop Protection

Stine-Haskell Research Center

P.O. Box 30

Newark, DE 19714-0030

Furthermore, when viewed in the context of predicted EECs (i.e., a maximum peak concentration 

of 0.0315 mg/L in water, see Table 5), the bioavailable (dissolved) portion sulfometuron methyl 

would have to be approximately 1200-1400 fold lower than the highest measured test 

concentrations (~ 38-45 mg/L) for risks to be evident. Therefore, repeating these studies would 

not likely affect the risk assessment conclusions, and new studies are not required.

DuPont Comment 1: DuPont agrees with the agency that repeating these studies would not 

likely affect the risk assessment conclusions. 

Issue 2: section 7, page 38, the preliminary problem formulation document states:

Guideline 850.1350 – Estuarine/marine invertebrate life cycle: Aquatic invertebrate life cycle

toxicity data for an estuarine/marine invertebrate are required under 40 CFR Part 158 if the

product is expected to enter the environment in significant concentrations because of its expected

use or mobility patterns. No studies have been submitted for this data requirement. Given that

the acute toxicity of sulfometuron methyl to aquatic animals is very low (slightly to practically

non-toxic), the NOEC for the freshwater invertebrate life cycle study (MRID 41672806) was set

at the highest test concentration, and there is no evidence to indicate that estuarine/marine

animals are substantially more sensitive to sulfometuron methyl than freshwater animals,

fulfilling this data requirement has a low potential to add value to the Registration Review risk

assessment. In the absence of this data, toxicity to estuarine/marine invertebrates from chronic

exposure to sulfometuron methyl will be characterized using toxicity data for freshwater

invertebrates. New study is not required.

DuPont Comment 2: DuPont agrees with the agency’s decision to use toxicity data for 

freshwater invertebrates to characterize toxicity for estuarine/marine invertebrates.

Issue 3: section 7, page 38, the preliminary problem formulation document states:

Guideline 850.1400 – Estuarine/marine and freshwater fish early-life stage: Early-life stage

toxicity data for a freshwater fish are required under 40 CFR Part 158. Early-life stage toxicity

data for an estuarine/marine fish are required under 40 CFR Part 158 if the product is expected 

to enter the environment in significant concentrations because of its expected use or mobility

patterns. No studies have been submitted for this data requirement. Given that the acute toxicity

of sulfometuron methyl to aquatic animals is very low (slightly to practically non-toxic), the

NOEC for the freshwater invertebrate life cycle study (MRID 41672806) was set at the highest

test concentration, and there is no evidence to indicate that estuarine/marine animals are

substantially more sensitive to sulfometuron methyl than freshwater animals, fulfilling these data

requirements has a low potential to add value to the Registration Review risk assessment. In the

absence of this data, toxicity to freshwater fish from chronic exposure to sulfometuron methyl

will be estimated using a freshwater fish ACR for another sulfonylurea with a similar toxicity

profile and the same mode of action (e.g., flazasulfuron, PC code 119011; see 2008 RED,

USEPA, 2008) to extrapolate from existing acute toxicity data for freshwater fish. For

estuarine/marine fish, a similar approach may be taken. A new study is not required.

DuPont Comment 3: DuPont agrees with the agency’s decision to use chronic exposure toxicity 

data for freshwater and estuarine/marine fish for another sulfonylurea with a similar toxicity 
DuPont Crop Protection

Stine-Haskell Research Center

P.O. Box 30

Newark, DE 19714-0030

profile to characterize chronic exposure toxicity for freshwater and estuarine/marine fish for 

Sulformeturon Methyl.

Issue 4: section 7, page 38, the preliminary problem formulation document states:

Guideline 850.2100 – Avian oral toxicity, passerine species: Acute oral toxicity data for a

passerine species are required under the new 40 CFR Part 158. No studies have been submitted

for this data requirement. The acute toxicity of sulfometuron methyl to birds and mammals is

very low (practically non-toxic). In addition, acute toxicity data for a passerine species is

available for flazasulfuron (PC code 119011), a sulfonylurea with a similar toxicity profile and

the same mode of action as sulfometuron methyl. This study (MRID 47939912) indicates that

flazasulfuron is practically non-toxic to the zebra finch (Taeniopygia guttata) on an acute oral

basis (LD50 > 2000 mg a.i./kg-bw). Therefore, fulfilling this data requirement has a low 

potential to add value to the Registration Review risk assessment. In the absence of this data,

toxicity to passerines from acute exposure to sulfometuron methyl will be characterized using all

acute toxicity data for other sulfonylureas with a similar toxicity profile and the same mode of

action that are available at the time of the Registration Review risk assessment. A passerine 

acute study with SMM is not required.

DuPont Comment 4: DuPont agrees with the agency’s decision to characterize toxicity to 

passerines from acute exposure to Sulfometuron Methyl by using all acute toxicity data for 

passerines for other sulfonylureas with a similar toxicity profile and the same mode of action.

Issue 5: section 7, page 39, the preliminary problem formulation document states:

Guideline 850.2300 – Avian reproduction, upland game and waterfowl species: Avian

reproductive toxicity data for water fowl and upland game species are required under 40 CFR

Part 158. No studies have been submitted for this data requirement. The acute toxicity of

sulfometuron methyl to birds and mammals is very low (practically non-toxic). In addition, there

is ample avian reproductive toxicity data available for other sulfonylureas with a similar toxicity

profile and the same mode of action (e.g., halosulfuron, PC code 128721, NOAEC = 1010 mg

a.i./kg-diet, MRIDs 47792801 and 47792802; primisulfuron, PC code 128973, NOAEC = 500

mg a.i./kg-diet, MRID 40512004; rimsulfuron, PC code 129009, NOAEC = 1250 ppm,

D358867, D358872; flazasulfuron, PC code 119011, NOAEC = 484 mg a.i./kg-diet, MRID

46220975). Avian reproductive NOECs for these sulfonylureas are 1 to 2 orders of magnitude

greater than the peak sulfometuron methyl EEC of 90 mg/kg-diet (for birds consuming short

grass) as calculated for the 2008 ecological risk assessment for the reregistration of 

sulfometuron methyl (USEPA, 2008) suggesting there is little concern for risk to birds from 

chronic exposure to sulfometuron methyl. Therefore, fulfilling this data requirement has a low 

potential to add value to the Registration Review risk assessment. In the absence of this data, 

toxicity to birds from chronic exposure to sulfometuron methyl will be characterized using 

chronic toxicity data for other sulfonylureas with a similar toxicity profile and the same mode of 

action. New studies are not required.

DuPont Comment 5: DuPont agrees with the agency’s decision to characterize toxicity to birds 

from chronic exposure to Sulfometuron Methyl by using data from other sulfonylureas with a 

similar toxicity profile and the same mode of action.
DuPont Crop Protection

Stine-Haskell Research Center

P.O. Box 30

Newark, DE 19714-0030

Issue 6: section 7, page 39, the preliminary problem formulation document states:

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

this study, previously published as a result of the 2008 RED for sulfometuron methyl, has not

been fulfilled. 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 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 Registration Review risk

assessment, and a study is not required.

DuPont Comment 6: DuPont agrees with the agency that reproductive toxicity effects are likely 

to occur at similar concentrations as those observed in vegetative vigor studies, which have 

already been conducted for Sulfometuron Methyl and submitted to the agency for review.

DuPont would like to thank the Agency for this opportunity to comment in response to the 

opening of the preliminary problem formulation document of Sufometuron Methyl.

Sincerely

Bridget O’Neill, PhD

Global Regulatory Ecotoxicologist