UNITED STATES ENVIRONMENT AL PROTECTION AGENCY 

MEMORANDUM 

DA TE: 7109115 

WASHINGTON, DC 20460 

OFFICE OF 

CHEMICAL SAFETY AND POLLUTION 

PREVENTION 

SUBJECT: Chlorimuron-Ethyl Toxicology Data Evaluation Records. 

PC Code: 128901 

Decision No.: N/A 

Petition No.: NIA 

DP Barcode: D397470 

Registration Nos.: N/A 

Regulatory Action: N/A 

Risk Assessment Type: N/A Case No.: NA 

TXR No.: 0056215 CAS No.: 90982-32-4 

MRID No.: See table 40 CFR: N/A 

FROM: 

THRU: 

TO: 

Karlyn Middleton, Toxicologist h 

Health 

Registration 

Effects 

Action 

Division 

Branch 

(7509 

2 

P) 

~ 

Christina Swartz, Chief /'"\n ' .A~ Registration Action Branch 2 ~\)-l Health Effects Division (7509 P) 

Heather Garvie, Mindy Ondish PM Team 24 

Herbicide Branch 

Registration Division (7505P) 

ACTION REQUESTED: The Health Effects Division (HED) was asked to review toxicology 

studies submitted for chlorimuron-ethyl. The studies have been reviewed and data evaluation 

records (DERs) have been prepared for the studies (see Table I). 

BACKGROUND: Chlorimuron ethyl is an herbicide of the sulfonylurea class. Its mode of 

action is through inhibition of the plant enzyme acetolactate synthase, which is also known as 

acetohydroxy acid synthase. Inhibition of this enzyme blocks branched-chain amino acid 

biosynthesis of valine, leucine, and isoleucine (involved in plant growth) processes and leads to 

death of the plant. Chlorimuron ethyl is registered for use on soybeans, field corn, peanuts, low 

growing berries (subgroup l 3-07H, except strawberry) and non-crop areas such as fence rows and 

roadsides for the control of broadleaf weeds and grasses. 

Page 1of2 

Page 1 of 32
Page 2 of 2 

Table 1. List of Chlorimuron-ethyl Toxicology Studies with New Data Evaluation Records 

MRID Number Guideline

[OCSPP]

STUDY TITLE

48704301 870.7485 SUBCHRONIC ORAL NEUROTOXICITY STUDY IN RATS

48704302 870.6200 ACUTE ORAL NEUROTOXICITY STUDY IN RATS 

Page 2 of 32
DATA EVALUATION RECORD

Chlorimuron Ethyl 

PC Code: 128901

TXR#: 0056215 

MRID#: 48704301

Study Type: Subchronic Neurotoxicity [feeding] - 90-Day Study in Crl:CD(SD) rats

OPPTS 870.7800 

Prepared for

Health Effects Division

Office of Pesticide Programs

U.S. Environmental Protection Agency 

One Potomac Yard

2777 S. Crystal Drive 

Arlington, VA 22202 

Prepared by

Tetrahedron Incorporated

1414 Key Highway, Suite B 

Baltimore, MD 21230 

Principal Reviewer: _____________________________________ Date: 5/25/2012 

Ahmed Elnabawi, Ph.D. 

Secondary Reviewer: _____________________________________ Date: 5/29/2012 

Katherine Squibb, Ph.D.

Quality Assurance: _________________________________________ Date: 

Nasrin Begum, Ph.D. 

Contract Number: EP-W-10013 

Work Assignment No.: WA-0-01 

Task Number: 1-1-88 

EPA Reviewer//WAM: Swartz and Levy//Farwell and Brunsman

Disclaimer

This review may have been altered by the EPA subsequent to the contractors’ signature 

above.

Page 3 of 32
Subchronic Neurotoxicity Study (rats) (2011) /Page 2 of 16 

Chlorimuron Eth 1/128901 OPPTS 870.6200b/ MAFF 12 Nou . 8147/0 ECD 424 

EPA Reviewer: Karlyn Middleton Signature: --1--~----

Risk Assessment Branch 2, Health Effects Division (7509P) Date: ~~~~~~~~~ EPA Work Assignment Manager: Lori Brunsman Signature;. 

Science Info. Mgmt. Branch, Health Effects Division (7509P) Date. ---#-,'-4-+1-.~--

TXR#: 0056215 

DATA EVALUATION RECORD 

STUDY TYPE: Subchronic Neurotoxicity, (oral, feeding) :._ (rat); OPPTS 870.6200b [§82-7], 

OECD 424; MAFF 12 Nousan 8147; EEC B.43 Directive 2004/73/EC. 

PC CODE: 128901 DP BARCODE: D397470 

TEST MATERIAL (PURITY): Chlorimuron Ethyl (DPX-F6025) (97.5% a.i.). 

SYNONYMS: Ethyl 2-( 4-chloro-6-methoxypyrimidin-2-ylcarbamoylsulfamoy l)benzoate; Ethyl 

2-[[[[(4-chloro-6-methoxy-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl) benzoate; DPXF6025-258. 

CITATION: Satheesh Anand, S. (2011). Chlorimuron Ethyl (DPX-F6025) Technical: 

Subchronic Oral Neurotoxicity Study in Rats. E.I. du Pont de Nemours and 

Company, DuPont Haskell Global Centers for Health and Environmental 

Sciences, Newark, Delaware, U.S.A. Laboratory project numbers: DuPont-31864, 

December 15, 2011. MRID 48704301. Unpublished. 

SPONSOR: E.I. du Pont de Nemours and Company, Wilmington, Delaware 19898, U.S.A. 

EXECUTIVE SUMMARY: 

In a subchronic neurotoxicity study (MRID 48704301), Chlorimuron Ethyl (DPX-F6025) 

technical (97.5 % a.i., batch# MAR09MA047) was administered in the diet to young adult 

Crl:CD(SD) rats (12/sex/dose) at concentration levels of 0, 500, 1,250, or 3,750/5,000 ppm 

(equivalent to 0/0, 27/35, 71 /90, and 220/259 mg/kg/day in males and females, respectively) for 

approximately 90 days (95-97 days). At Week 9, the high dietary concentration was increased 

from 3,750 to 5,000 ppm as there were minimal or no test substance-related changes observed in 

the 3,750 ppm groups at this time. Neurobehavioral assessment (functional observational battery 

and motor activity testing) was performed on all animals prior to test substance administration 

(baseline), and during Weeks 4, 8, and 13. At study termination (Days 95 and 96), 6 

animals/sex/group were euthanized and perfused in situ for neuropathological examination. The 

brain and peripheral nervous system tissues collected from the perfused animals in the control 

and 3,750/5,000 ppm groups were subjected to histopathological evaluation. 

There were no test substance-related effects on mortality or clinical signs at any dietary 

concentration level in males and females. 

Treatment-related effects on body weights were evident at the high concentration (3,750/5,000 

ppm) in females, but not in males. Body weights were significantly reduced by 16-10% (Day 21 

through Day 91) at 3,750/5,000 ppm in females. On Day 84, lower (p:S0.05) mean body weight 

Page 4 of 32
Subchronic Neurotoxicity Study (rats) (2011) /Page 3 of 16 

Chlorimuron Ethyl/128901 OPPTS 870.6200b/ MAFF 12 Nousan 8147/OECD 424

was noted in the 1,250 ppm (↓7%) group females. No significant differences in body weights 

were observed in 500 ppm group females. Mean body weight gains were significantly lower 

during test Day 0-7 (↓34%), Day 14-21 (↓40%), and Day 0-28 (↓21%) in the 3,750/5,000 group 

of females. Overall (0-91) body weight gains were significantly lower at 1,250 ppm (↓15%) and 

3,750/5,000 ppm (↓24%) in females when compared to the control group. In males, no test 

substance-related or statistically significant effects were noted on body weight or body weight 

gain at any dietary concentration level.

Test substance-related decreases on mean daily food consumption were evident in the high 

dietary concentration (3,750/5,000 ppm) females. Mean food consumption was significantly 

reduced by 9-18% in the 3,750/5,000 ppm group females from Day 14-21 through the end of the 

treatment period. In addition, lower (p≤0.05) mean food consumption was observed at the dietary 

concentration of 1,250 ppm on Day 63-70 (↓11%) and Day 56-91 (↓8%). Overall (0-91) mean 

food consumption was significantly decreased by ↓12% at 3,750/5,000 ppm; whereas, overall (0-

91) mean daily food consumption at concentrations of 500 and 1,250 ppm was similar to the 

control. In males, no treatment-related or statistically significant effects on mean daily food 

consumption were seen at any dietary concentration level. There were no test substance-related 

effects on food efficiency in the 500, 1,250, or 3,750/5,000 ppm group males or females.

No test substance-related effects on FOB (home cage, open field, removal from the home cage 

and handling) parameters, rearing, forelimb and hindlimb grip strength, body temperature or 

motor activity (duration of movements and number of movements) were observed at any dose 

level in either sex. 

There were no test substance-related alterations in gross histopathology observations or 

microscopic neurohistopathology in the 3,750/5,000 ppm group males and females. 

It is concluded that there were no neurotoxic effects observed at any dietary concentration level, 

based on the lack of altered behavior in the FOB parameters, no significant changes observed on 

motor activity (duration of movements and number of movements), and no effects on the 

macroscopic and microscopic pathology of nervous system tissues. However, systemic toxicity 

of was observed in the 3,750/5,000 ppm group females, but not in males. This was characterized 

by treatment related decreases in body weight and body weight gains and significant reductions 

in food consumption. 

The systemic NOAEL is 1,250 ppm (equivalent to 71/90 mg/kg/day), based on decreased 

body weight and body weight gains and reduced food consumption observed in females at 

the LOAEL of 3,750/5,000 ppm (equivalent to 220/259 mg/kg/day, M/F respectively). 

The NOAEL for neurotoxicity is the highest dose tested 3,750/5,000 ppm (equivalent to 

220/259 mg/kg/day, M/F respectively) since no treatment related neurotoxic effects were 

seen in the study. 

This study is classified as acceptable/guideline and satisfies the guideline requirement (OPPTS 

870.6200b; OECD 424) for a subchronic neurotoxicity study in rats. 

COMPLIANCE: Signed and dated GLP, Quality Assurance, Flagging, and Data 

Confidentiality (no claim of confidentiality under FIFRA, but waiver does not apply to other 

regulatory agencies and information is labeled trade secret) were provided. Page 5 of 32
Subchronic Neurotoxicity Study (rats) (2011) /Page 4 of 16 

Chlorimuron Ethyl/128901 OPPTS 870.6200b/ MAFF 12 Nousan 8147/OECD 424

I. MATERIALS AND METHODS:

A. MATERIALS:

1. Test material: Chlorimuron Ethyl (DPX-F6025) Technical

Description: Crystalline, powder

Lot/Batch #: MAR09MA047

Purity: 97.5% a.i.

Compound Stability: The Sponsor stated that the test substance was considered to be stable when stored at room 

temperature for up to 24 days.

CAS # of TGAI: 90982-32-4

Structure:

 

2. Vehicle: Diet. 

3. Test animals:

Species: Rat

Strain: Crl:CD(SD) 

Age/weight at study initiation: 52 days of age. Males: 223.2-272.1 g; Females: 161.7-196.3 g.

Source: Charles River Laboratories, Inc., Raleigh, NC.

Housing: Housed in pairs in solid bottom caging with bedding mixed with enrichment 

(Shepherd’sTM Cob + PLUSTM). Each cage rack contained only animals of one sex

Diet: PMI® Nutrition International, LLC Certified Rodent LabDiet®5002, ad libitum, 

except during neurobehavioral testing.

Water: Tap water, ad libitum, except during neurobehavioral testing.

Environmental conditions: Temperature:

Humidity:

Air changes:

Photoperiod:

20-26°C

30-70% 

Not stated

12 hrs dark / 12 hrs light

Acclimation period: 7 days

B. STUDY DESIGN:

1. In life dates: Start: March 11, 2011; End: June 16, 2011. 

2. Animal assignment and dose rationale: Animals were randomly assigned to the test groups 

noted in Table 1 using a weight stratification-based computer program. The body weights of 

all animals were within ±20% of the mean weight for each sex. Test substance was 

administered orally in the diet to rats at dietary concentration levels of 0, 500, 1,250 and 

3,750/5,000 ppm for 90 days (95-97 days). 

Dose levels were chosen based on the results of a subchronic toxicity study in rats, conducted 

with the test substance at concentration levels of 0, 100, 2,500 and 7,500 ppm(1)

. In that

study, reduced body weights and nutritional parameters were observed at dietary 

concentration level of 7,500 ppm in males and at 2,500 and 7,500 ppm in females. In 

 

1 DuPont Haskell (1983). Ninety-day feeding and one-generation reproduction study in rats with benzoic acid, 2-[[[[(4-chloro-6-

methoxy-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl]-ethyl ester (INF-6025). Unpublished DuPont report, HLR-306-83.

Page 6 of 32
Subchronic Neurotoxicity Study (rats) (2011) /Page 5 of 16 

Chlorimuron Ethyl/128901 OPPTS 870.6200b/ MAFF 12 Nousan 8147/OECD 424

addition, a higher incidence of margination of hepatocyte cytoplasmic contents was observed 

in the 2,500 and 7,500 ppm males group and in the 7,500 ppm females group. No clinical 

signs were observed at any dietary concentration level. Therefore, the no-observed-adverseeffect (NOAEL) in for the subchronic toxicity was 100 ppm. 

Based on these results, the concentration levels selected for the current study were 500 ppm 

(low concentration), 1,250 ppm (mid concentration) and 3,750/5,000 ppm (high 

concentration) (Table 1). Starting from Week 9, however, the high-dietary concentration of 

3,750 ppm was increased to 5,000 ppm due to a lack of treatment-related changes observed 

in this group. 

TABLE 1. Study Design

Experimental parameter Concentration in Diet (ppm)

0 500 1,250 3,750/5,000a

Achieved dose (mg/kg/day; M/F) 0/0 27/35 71/90 220/259

Total number of animals/sex/group 12 12 12 12

Behavioral testing (FOB, Motor activity) 12/sex 12/sex 12/sex 12/sex

Neuropathology 6/sex 0/sex 0/sex 6/sex

a= The dietary concentration of test substance was increased from 3,750 to 5,000 ppm starting from Week 9.

Concentrations of test substance were adjusted for purity of active ingredient. 

Data were extracted from pages 12 and 14 of the study report. 

3. Test Substance preparation and analysis: All diet formulations were prepared by mixing 

appropriate amounts of test substance with the diet (PMI® Nutrition International, LLC 

Certified Rodent LabDiet®5002) and stored refrigerated. Homogeneity and concentration 

analyses of test substance were verified in diet samples (top, middle, and bottom) at dietary 

concentrations of 500, 1,250 and 3,750 ppm at the start of the study and at 5,000 ppm starting 

from Week 9, when the high diet concentration was increased to 5,000 ppm. Stability of test 

substance in the diet was verified at concentrations of 50 and 20,000 ppm for 10, 17, and 24 

days at room temperature storage prior to the start of the study. 

Results

Homogeneity analysis (% RSD): 1-3%.

Stability analysis: The test substance was stable in the diet at concentrations of 500 and 

20,000 ppm for up to 24 days at room temperature. 

Concentration analysis (range as % nominal): 93.2-102%. 

These analytical data indicated that the mixing procedure was adequate and that the variance 

between nominal and actual dosage to the animals was acceptable.

4. Statistics: The data were presented as mean± standard deviation (SD). Each test substance 

exposed group was compared to the control group for the parameters listed below. The data 

were analyzed using the following statistical methods and significance was defined at p≤0.05 

or p≤0.01 for all tests. 

 

Page 7 of 32
Subchronic Neurotoxicity Study (rats) (2011) /Page 6 of 16 

Chlorimuron Ethyl/128901 OPPTS 870.6200b/ MAFF 12 Nousan 8147/OECD 424

Parameters Statistical Methods

- Body weight 

- Body weight gain

- Food consumption

- Food efficiency

Levene’s test for homogeneity and Shaprio-Wilk test for normality. If 

preliminary test was not significant, one-way analysis of variance followed 

by Dunnett’s test was used to compare treated groups with control groups. 

If preliminary test was significant, transforms of the data were used. The 

rank order of transforms was log, square-root, and rank-order.

- Rearing 

- Grip strength 

- Foot splay

- Body temperature

- Motor activity

Levene’s test for homogeneity and Shaprio-Wilk test for normality. If 

preliminary test was not significant, repeated measures analysis of variance 

was followed by linear contrasts. If preliminary test was significant, a 

normalizing, variance stabilizing transformation followed by repeated 

measures analysis of variance or sequential application of the JonckheereTerpstra trend test was used.

Incidence FOB, descriptive parameters Cochran-Armitage test for trend; if the incidence was not significant, but a 

significant lack of fit occurred, Fisher’s Exact test with a Bonferroni-Holm 

correction was used.

These statistical analyses were considered to be appropriate. 

 

C. METHODS / OBSERVATIONS:

1. Mortality and Clinical Observations: Animals were observed twice daily for mortality and 

moribundity throughout the study. General clinical observations were recorded once daily 

throughout the study. 

2. Body Weight: Animals were weighed on the days of FOB assessment and weekly during 

the exposure period. 

3. Food Consumption: Food consumption was recorded weekly throughout the study and 

reported as g/animal/day. The mean daily food efficiency and mean daily intake of test 

substance were calculated from the food consumption and body weight data. 

4. Cholinesterase determination: Cholinesterase activity was not evaluated.

5. Neurobehavioral Assessment:

a. Functional Observational Battery (FOB): All animals were subjected to a FOB during

acclimation (baseline) and during Weeks 4, 8 and 13. Animals were counterbalanced by 

sex and treatment and tested in replicates over 2 days to minimize the influence of 

uncontrolled factors. The FOB was conducted by an observer who was “blind” to the 

treatment status of the animal, and the same observer performed all of the evaluations. 

The FOB evaluations were conducted in a sound-attenuated room equipped with a whitenoise-generation system to minimize variations in environmental test conditions. Animals 

were weighed on the day of the FOB assessment. The time in the open-field was at least 2 

minutes. 

The following CHECKED (X) parameters were examined. 

Page 8 of 32
Subchronic Neurotoxicity Study (rats) (2011) /Page 7 of 16 

Chlorimuron Ethyl/128901 OPPTS 870.6200b/ MAFF 12 Nousan 8147/OECD 424

HOME CAGE OBSERVATIONS REMOVAL FROM THE HOME 

CAGE AND HANDLING

OPEN FIELD OBSERVATIONS

X Posture X Ease of removal X Righting reflex

X Gait/coordination X Ease of handling X Gait/coordination

X Convulsions X Vocalization X Muscle spasms/fasciculation

X Tremors X Muscle tone X Convulsions

X Palpebral closure X Piloerection X Tremors

X Fur/skin appearance X Ease of respiration

X Mucous membranes X Rate of respiration 

X Palpebral closure X Posture

NEUROMUSCULAR 

OBSERVATIONS

X Exophthalmus X Palpebral closure

X Landing foot splay X Lacrimation X Number of rearing movements

X Forelimb grip strength X Salivation X Vocalizations

X Hindlimb grip strength X Dehydration X Arousal

X Emaciation X Approach/touch

PHYSIOLOGICAL 

OBSERVATIONS

X Papillary constriction/Polyuria / 

Diarrhea #

X Body temperature X Tail pinch

X Body weight X Sharp auditory stimulus

Parameters based on OPPTS Guideline 870.6200. 

# Papillary constriction, polyuria and diarrhea were assessed at the end of the motor activity session.

Data were obtained from pages 18-20 of the study report.

b. Motor activity: Motor activity was evaluated after the last animal completed the FOB 

pre-exposure (baseline) and during Weeks 4, 8, and 13. An automated Coulbourn®

Instruments activity monitor was used with infrared beams for motor activity data 

collection. The infrared monitoring device enabled measurements of two dependent 

variables: duration of movement and number of movements. A continuous movement, 

regardless of its duration, was counted as one movement by the activity measurement 

system. The technical characteristics of the measurement system are such that duration of 

movement was analogous to “counts” in other types of devices that employ interruption 

of light beams. Duration of movement and number of movements were evaluated in 9 

consecutive intervals of 10 minutes each as well as for the total 90-minute session. 

6. Sacrifice and Pathology: 

Animals selected for neuropathological evaluation (6 rats/sex/dose) were deeply 

anaesthetized by i.p. injection of a mixture of ketamine/xylazine and perfused in situ. 

Animals were subjected to gross necropsy. The remaining animals were sacrificed by 

isoflurane anesthesia and CO2 asphyxiation and were disposed of without any pathological 

examinations. 

The tissues from the control and high-dose animals (3,750/5,000 ppm) were processed for 

microscopic evaluation. The brain, spinal cord sections, cauda equine, eyes, optic nerve, and 

gastrocnemius muscle were embedded in paraffin, sectioned at 5μm, and stained with 

hematoxylin-eosin (H&E). The dorsal root ganglia (including dorsal and ventral root fibers) 

from the cervical and lumbar swellings, gasserian ganglia, and peripheral nerves were 

embedded in glycol methacrylate (GMA), sectioned 3 μm, and stained with hematoxylineosin (H&E). Stained histological sections were examined by light microscopy. 

 

Brain weight and measurements were not evaluated in this study. 

Page 9 of 32
Subchronic Neurotoxicity Study (rats) (2011) /Page 8 of 16 

Chlorimuron Ethyl/128901 OPPTS 870.6200b/ MAFF 12 Nousan 8147/OECD 424

The following CHECKED (X) tissues from the control and high-dose animals, as well as all 

gross lesions were evaluated. 

CENTRAL NERVOUS SYSTEM PERIPHERAL NERVOUS SYSTEM

BRAIN SCIATIC NERVE

X Forebrain Mid-thigh Region

X Cerebrum X Sciatic Nerve

X Hippocampus X Tibial Nerve

Basal ganglia X Sural Nerve

X Cerebellum

Thalamus

X Pons

X Medulla oblongata OTHER

X Midbrain X Lumbar dorsal root ganglion

Hypothalamus X Lumbar dorsal root fibers

SPINAL CORD X Lumbar ventral root fibers

X Cervical swelling X Cervical dorsal root ganglion

X Lumbar swelling X Cervical dorsal root fibers

X Thoracic swelling X Cervical ventral root fibers

OTHER

X Gasserian Ganglion

Trigeminal nerves

X Optic nerve

X Eye

X Gastrocnemius muscle

7. Positive Controls: It was stated in this report that three separate reports (MRID 44628703, 

MRID 47053501 and MRID 48710304, performed in 1997, 2002 and 2011, respectively) 

were previously performed by DuPont Haskell to generate positive control data and validate 

the procedures and the inter-observer reliability of the performing lab to conduct and assess 

neurobehavioral and neuropathology tests. The data also documents that the equipment and 

procedures are capable of detecting effects that may be seen in neurotoxicity studies. The 

positive control data is acceptable for use with the current study. Historical control data were 

not provided in the report. 

II. RESULTS:

A. OBSERVATIONS:

 

1. Mortality: There were no treatment-related mortalities. 

 

2. General Clinical Observations: There were no significant test substance-related clinical 

findings in the 500, 1,250 or 3,750/5,000 ppm group males or females. 

B. BODY WEIGHT AND BODY WEIGHT GAIN: Summary results of mean body weights 

and body weight gains are presented in Table 2 (a and b) and Table 3, respectively. There 

were no test substance-related or statistically significant effects on body weight or body 

weight gain in males at any dietary concentration level (Table 2a). The only significant 

(p≤0.05) difference from the control group was a lower mean body weight gain in the 

Page 10 of 32
Subchronic Neurotoxicity Study (rats) (2011) /Page 9 of 16 

Chlorimuron Ethyl/128901 OPPTS 870.6200b/ MAFF 12 Nousan 8147/OECD 424

3,750/5,000 ppm (↓14%) group males on Day 0-7 compared to the control (Table 2a); 

however, this finding was considered incidental and not treatment related since there was no 

dose response relationship and it occurred only at one time point. Overall (0-91) body weight 

gains were increased by 5-7% at concentrations of 500, 1,250 and 3,750/5,000 ppm in males, 

but were not statistically significantly different and did not change in a dose responsive 

manner. 

In contrast to males, treatment-related effects on body weights were evident in the high 

dietary concentration (3,750/5,000 ppm) group females (Day 21 though Day 91) (Table 2b). 

At 3,750/5,000 ppm, lower (p≤0.05) body weights ranged from ↓6-10% in females from Day 

21 though Day 91. On Days 7 and 14, body weight was reduced by ↓5% in the 3,750/5,000 

ppm females compared to the control, but not statistically significant different. No significant 

differences in body weights were noted in females at dietary concentration levels of 500 or 

1,250 ppm compared to the controls, except on Day 84, when a lower (p≤0.05) mean body 

weight was noted in the 1,250 ppm (↓7%) group females. Mean body weight gains were 

reduced by ↓34%, ↓40% and ↓21% in the 3,750/5,000 ppm group females during test Day 0-

7, Day 14-21, and Day 0-28, respectively, compared to the controls (Table 3). Overall (0-91) 

body weight gains were significantly lower at 1,250 ppm (↓15%) and 3,750/5,000 ppm 

(↓24%) in females when compared to the control group. 

It is concluded that lower body weight gains observed in females, but not in males, in the 

high concentration (3,750/5,000 ppm) groups were associated with the reductions in body 

weights observed over the entire study period and were test substance-related. Over the full 

period of the study (Day 0 to 91), lower mean body weight gains were also observed in the 

female 1,250 ppm treated group. 

TABLE 2a. Selected Mean (±SD) Body Weights and Body Weight Gains in Male Rats 

Exposure Time Concentration in Diet (ppm)

0 500 1,250 3,750/5,000

Body Weight (g)

Day 0 248.1±9.4 249.9±7.0 251.6±14.1 253.6±7.6

Day 7 308.8±12.8 307.5±9.2 311.9±20.7 305.9±12.5

Day 28 423.4±27.4 426.9±23.7 433.7±35.3 429.6±34.7

Day 63 516.2±43.0 530.7±46.3 526.4±44.2 533.3±54.6

Day 70 528.9±44.3 545.9±46.8 541.6±45.7 549.8±61.2

Day 84 556.8±46.1 578.1±54.9 571.7±51.8 573.7±64.3

Day 91 562.8±46.4 586.4±58.7 581.5±56.5 583.2±65.3

Body Weight Gains (g)

Day 0-7 60.7±7.8 57.6±6.7 60.3±7.9 52.4±8.2*

(↓14%)

Day 0-28 175.3±24.8 177.0±23.6 182.0±26.9 176.0±30.9

Day 28-56 81.7±15.0 88.8±25.7 81.6±18.3 90.7±21.3

Day 56-91 57.7±13.5 70.7±21.8 66.3±15.8 62.9±14.5

Overall (Day 0-91) 314.7±43.7 336.5±56.4 329.9±50.2 329.6±62.8

Values represent mean ±SD, n=12. 

The dietary concentration level of 3,750 ppm was increased to 5,000 ppm on Week 9. 

Percent difference from the control is included in parentheses and was calculated by the Investigators. 

* Significantly different from the control group, p≤0.05. Statistically significant results are shown in bold.

Data were obtained from Tables 3 (pages 32-33) and 5 (pages 37-39) of the study report.

Page 11 of 32
Subchronic Neurotoxicity Study (rats) (2011) /Page 10 of 16 

Chlorimuron Ethyl/128901 OPPTS 870.6200b/ MAFF 12 Nousan 8147/OECD 424

TABLE 2b. Mean (±SD) Body Weights and Body Weight Gains in Female Rats 

Exposure Time Concentration in Diet (ppm)

0 500 1,250 3,750/5,000

Body Weights (g)

Day 0 183.1±10.5 184.2±6.8 180.9±8.5 181.3±9.0

Day 7 206.6±14.4 207.8±6.8 201.9±12.3 197.0±10.7

Day 14 224.8±16.0 230.9±9.4 217.6±11.8 214.7±13.5

Day 21 238.8±15.1 245.7±11.3 230.9±12.0 223.1±13.0*

(↓7%)

Day 28 251.6±19.2 255.5±14.0 241.5±11.8 235.2±15.7*

(↓7%)

Day 35 263.6±20.9 274.0±12.5 252.4±11.9 247.0±17.5*

(↓6%)

Day 42 271.3±20.8 281.0±13.1 257.3±14.3 254.3±18.7*

(↓6%)

Day 49 282.0±20.6 286.1±14.6 266.4±15.8 259.3±20.4*

(↓8%)

Day 56 283.1±27.6 286.9±15.4 267.2±16.0 260.8±22.0*

(↓8%)

Day 63 292.8±27.8 298.7±18.6 273.4±17.6 266.8±21.1*

(↓9%)

Day 70 298.6±27.4 303.7±20.2 277.9±17.3 272.0±19.3*

(↓9%)

Day 77 304.7±26.0 309.0±19.7 285.8±15.0 276.0±19.6*

(↓9%)

Day 84 309.0±30.9 310.4±19.9 286.8±15.1*

(↓7%)

278.4±20.1*

(↓10%)

Day 91 308.9±32.0 311.8±20.4 287.7±16.3 277.6±19.7*

(↓10%)

Body Weight Gains (g)

Day 0-7 23.5±7.0 23.6±5.1 21.1±8.1 15.6±5.0*

(↓34%)

Day 7-14 18.2±7.0 23.1±5.0 15.7±7.0 17.7±5.9

Day 14-21 14.0±5.0 14.8±4.1 13.3±6.3 8.4±6.0*

(↓40%)

Day 21-28 12.8±7.2 9.8±8.2 10.6±5.0 12.1±6.6

Day 0-28 68.5±10.6 71.2±11.0 60.6±8.5 53.9±9.3*

(↓21%)

Day 28-35 12.0±6.9 18.5±14.7 10.9±10.0 11.8±8.8

Overall (Day 0-91) 125.8±25.8 127.6±19.2 106.8±13.0*

(↓15%)

96.2±14.3*

(↓24%)

Values represent mean ±SD, n=12.

The dietary concentration level of 3,750 ppm was increased to 5,000 ppm on Week 9. 

Percent difference from the control is included in parentheses and was calculated by the Investigators. 

* Significantly different from the control group, p≤0.05. Statistically significant results are shown in bold.

Data were obtained from Tables 4 (pages 34-36) and 6 (pages 40-42) of the study report.

C. FOOD CONSUMPTION: Results of mean food consumption (g/animal/day) in males and 

females are presented in Table 4. In males, no test substance-related or statistically 

significant effects on food consumption occurred at any dietary concentration level. The only 

significant (p≤0.05) difference from the control group was higher food consumption in the 

3,750/5,000 ppm (↑8%) group males on Day 63-70 compared to the controls (Table 4). 

However, this finding was considered incidental and not treatment related since there was no 

dose response relationship and it occurred only at one time point. Overall (0-91) food 

consumption was not affected.

Page 12 of 32
Subchronic Neurotoxicity Study (rats) (2011) /Page 11 of 16 

Chlorimuron Ethyl/128901 OPPTS 870.6200b/ MAFF 12 Nousan 8147/OECD 424

In females, treatment-related effects on mean daily food consumption were evident in the 

high dietary concentration (3,750/5,000 ppm). Lower (p≤0.05) mean food consumption 

ranged ↓9-18% from Day 14-21 though the end of the treatment (Table 4). In addition, lower 

(p≤0.05) mean food consumption was observed at the dietary concentration of 1,250 ppm on 

Day 63-70 (↓11%) and Day 56-91 (↓8%). Overall (0-91) mean food consumption was 

significantly decreased by ↓12% at 3,750/5,000 ppm; whereas overall (0-91) mean daily food 

consumptions at concentrations of 500 and 1,250 ppm were similar to control values. 

It was concluded that the effects on body weight and body weight gains were consistent with 

the effects observed on food consumption in the high dietary concentration (3,750/5,000 

ppm) group females. 

TABLE 3. Selected Mean (±SD) Food Consumption (g/animal/day) in Male and Female Rats 

Exposure Time Concentration in Diet (ppm)

0 500 1,250 3,750/5,000

Males

Day 0-7 24.5±0.9 23.8±0.6 25.1±1.6 24.1±1.0

Day 7-14 26.3±1.6 25.2±1.2 26.5±1.6 27.4±2.4

Day 0-28 25.5±1.3 24.9±1.1 26.4±1.4 25.8±1.5

Day 28-56 25.6±1.7 25.5±1.3 26.5±1.4 26.6±1.6

Day 63-70 24.5±1.8 25.0±1.4 25.6±1.6 26.6±1.7*

(↑8%)

Day 84-91 24.6±1.4 25.2±1.7 25.3±1.7 25.8±1.8

Overall (Day 0-91) 25.3±1.4 25.3±1.2 26.2±1.2 26.2±1.5

Females

Day 0-7 17.2±1.5 18.2±1.8 17.8±2.2 16.7±3.9

Day 7-14 18.3±1.1 19.1±1.8 17.9±1.6 17.4±1.5

Day 14-21 19.6±1.5 20.5±1.9 20.1±2.7 17.0±1.6*

(↓13%)

Day 21-28 20.1±2.5 19.6±1.5 18.3±2.0 17.1±1.1*

(↓15%)

Day 0-28 18.8±1.5 19.3±1.6 18.5±1.6 17.1±1.8*

(↓9%)

Day 28-35 19.4±2.0 19.7±1.4 17.8±2.1 16.7±0.8*

(↓14%)

Day 35-42 19.4±1.8 19.2±1.5 19.0±2.1 17.7±3.5*

(↓9%)

Day 42-49 20.8±3.0 19.1±2.0 20.3±3.1 17.0±3.1*

(↓18%)

Day 49-56 18.4±2.0 18.9±1.7 17.5±1.1 16.4±1.8*

(↓11%)

Day 28-56 19.5±1.9 19.2±1.4 18.6±1.6 16.9±2.2*

(↓13%)

Day 56-63 18.2±1.7 19.0±2.4 17.0±1.2 16.9±1.7

Day 63-70 19.0±1.9 18.3±1.2 17.0±1.4*

(↓11%)

16.9±3.2*

(↓11%)

Day 70-77 18.8±1.8 17.9±0.8 17.5±1.5 15.5±0.9*

(↓17%)

Day 77-84 18.3±1.7 18.9±1.5 16.9±1.1 16.8±2.2*

(↓8%)

Day 84-91 18.0±1.7 17.0±3.0 16.7±1.5 15.5±1.3*

(↓14%)

Page 13 of 32
Subchronic Neurotoxicity Study (rats) (2011) /Page 12 of 16 

Chlorimuron Ethyl/128901 OPPTS 870.6200b/ MAFF 12 Nousan 8147/OECD 424

TABLE 3. Selected Mean (±SD) Food Consumption (g/animal/day) in Male and Female Rats 

Exposure Time Concentration in Diet (ppm)

0 500 1,250 3,750/5,000

Day 56-91 18.5±1.7 18.2±1.6 17.0±0.9*

(↓8%)

16.3±1.7*

(↓12%)

Overall (Day 0-91) 18.9±1.6 18.9±1.4 18.1±1.4 16.7±1.9*

(↓12%)

Values represent mean ±SD, n=12.

The dietary concentration of 3,750 ppm was increased to 5,000 ppm on Week 9. 

Percent difference from the control is included in parentheses and was calculated by the Investigators. 

* Significantly different from the control group, p≤0.05. Statistically significant results are shown in bold.

Data were obtained from pages Tables 7 (pages 43-45) and 8 (pages 46-48) of the study report.

D. FOOD EFFICIENCY: There were no test substance-related effects on food efficiency in 

the 500, 1,250, or 3,750/5,000 ppm group males and females. The only significant 

differences from the control group were lower mean food efficiency in males (↓12%, p≤0.05) 

and females (↓28%, p≤0.05) at the high concentration (3,750/5,000) groups on Day 0-7 

(Table 4). Overall (0-91) mean food efficiency was not statistically significant different from 

the control group in males or females at any dietary concentration level. No test substancerelated effects on mean food efficiency were noted at 500 or 1,250 ppm in males or females. 

TABLE 4. Selected Mean (±SD) Daily Food Efficiency (g/g) in Male and Female Rats 

Exposure Time Concentration in Diet (ppm)

0 500 1,250 3,750/5,000

Males

Day 0-7 0.353±0.038 0.346±0.042 0.342±0.035 0.310±0.044*

(↓12%)

Day 0-91 0.136±0.014 0.146±0.021 0.138±0.018 0.138±0.023

Females

Day 0-7 0.193±0.048 0.185±0.036 0.171±0.066 0.140±0.053*

(↓28%)

Day 0-91 0.073±0.014 0.074±0.009 0.065±0.007 0.064±0.010

(↓13%)NS

Food efficiency was reported as average weight gain/average food consumption. 

Values represent mean ±SD, n=12.

The dietary concentration of 3,750 ppm was increased to 5,000 ppm on Week 9. 

Percent difference from the control is included in parentheses and was calculated by the Investigators. 

* Significantly different from the control group, p≤0.05. Significant results are shown in bold.

Data were obtained from pages Tables 9 (pages 49-51) and 10 (pages 52-54) of the study report.

E. TEST SUBSTANCE INTAKE: The mean daily intake (mg/kg/day) of Chlorimuron Ethyl 

over the entire study period is presented in Table 5. 

TABLE 5. Intake of Chlorimuron Ethyl in Males and Females

Test Group Concentration in Diet

(ppm)

Mean daily intake (mg/kg bw/day)

Male Female

1 500 27±16 35±2.2

2 1,250 71±4.4 90±6.2

3 3,750/5,000 220±49.9 259±37.8

Data were obtained from Tables 11 (p. 55-56) and 12 (p. 57-58) of the study report. 

F. NEUROBEHAVIORAL RESULTS:

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Chlorimuron Ethyl/128901 OPPTS 870.6200b/ MAFF 12 Nousan 8147/OECD 424

1. FOB findings: No test substance-related effects on FOB (home cage, open field, removal 

from the home cage and handling) parameters were noted at any dietary concentration level 

for either sex. In addition, there were no statistically significant differences between the 

control and the test substance-exposed groups at any time point or between any of the doses. 

2. Motor activity: No test substance-related effects were observed on motor activity (duration 

of movements and number of movements) in either sex at any dietary concentration level of 

the test substance. In addition, there were no statistically significant differences between the 

control and the test substance-exposed groups at any time point. The comparison of the 

single intervals with the control group during the assessment of the duration of movement 

resulted in some isolated significantly increased values (interval 4; at 3,750/5,000 ppm) 

during the pretest evaluation, or decreased values (interval 2; at 3,750/5,000 ppm) at Week 4 

in males, and increased values (intervals 8 and 9; at 3,750/5,000 ppm) at Week 8 in females. 

On the other hand, during the assessment of the number of movements, some increased 

individual interval values were observed during the pretest evaluation in males (interval 3; at 

3,750/5,000 ppm) and at Week 8 in females (interval 9; at 3,750/5,000 ppm). These 

deviations were considered to be incidental based on the isolated occurrence and the lack of a 

dose-response relationship. Interval motor activity was provided in Tables 17 to 20 on pages 

74-77 of the study report. 

TABLE 6. Motor Activity in Male and Female Rats 

Exposure Time Concentration in Diet (ppm)

0 500 1,250 3,750/5,000

Total Duration of Movements (sec) 

Males 

Baseline 968±289 1057±311 971±208 1043±269

Week 4 1745±555 1684±392 1612±571 1686±440

Week 8 1794±483 1742±474 1641±488 1616±407

Week13 1507±464 1486±410 1229±363 1464±305

Females

Baseline 1324±426 1259±429 1318±524 1528±700

Week 4 1730±556 1715±606 1791±492 1766±475

Week 8 1565±453 1689±499 1730±560 1823±444

Week13 1444±353 1480±409 1469±458 1548±378

Total Number of Movements

Males

Baseline 451±178 469±130 451±132 515±152

Week 4 771±280 734±204 695±263 764±195

Week 8 866±277 818±217 748±284 799±204

Week13 779±205 736±179 681±233 771±185

Females

Baseline 668±256 629±176 652±242 737±244

Week 4 821±239 789±238 870±208 840±204

Week 8 799±233 847±225 900±260 916±201

Week13 821±201 811±221 841±243 880±216

Values represent mean ±SD, n=12.

The dietary concentration of 3,750 ppm was increased to 5,000 ppm on Week 9. 

No statistically significant differences from the control group.

Data were obtained from Tables 17 to 20 on pages 74-77 of the study report.

3. Rearing: Mean number of rearing movements was unaffected by the test diet consumption at 

500, 1,250, or 3,750/5,000 ppm in males and females. There were no statistically significant 

Page 15 of 32
Subchronic Neurotoxicity Study (rats) (2011) /Page 14 of 16 

Chlorimuron Ethyl/128901 OPPTS 870.6200b/ MAFF 12 Nousan 8147/OECD 424

differences between the control and the test substance-exposed groups (by sex) at the study 

Week 4, 8, and 13 evaluations. 

4. Forelimb and Hindlimb Grip Strength: There were no test substance-related effects on 

forelimb and hindlimb grip strength in either sex at any dietary test substance concentration 

level. The only significant (p≤0.05) difference from the control group was a higher mean 

forelimb grip strength in the 1,250 ppm (↑16%) group males at Week 8 (Table 7); however, 

this finding was considered incidental and not treatment related since there was no evidence 

of a dose response relationship. 

TABLE 7. Mean (±SD) Forelimb Grip Strength (kg) for Male Rats 

Exposure Time Concentration in Diet (ppm)

0 500 1,250 3,750/5,000

Baseline (Pretest) 0.69±0.12 0.70±0.08 0.68±0.13 0.72±0.13

Week 4 1.23±0.26 1.17±0.24 1.23±0.19 1.20±0.17

Week 8 1.32±0.35 1.26±0.27 1.53±0.34*

(↑16%)

1.41±0.30

Week 13 1.25±0.25 1.14±0.22 1.20±0.15 1.16±0.31

Values represent mean±SD, n=12.

Percent difference from the control is included in parentheses and was calculated by the Reviewers. 

* Significantly different from the control group, p≤0.05. Statistically significant results are shown in bold.

Data were obtained from Table 13 on page 59 of the study report.

5. Foot Splay: No treatment-related effects on foot splay occurred at any dietary concentration 

level of the test substance in males and females. There were no statistically significant 

differences between the control and test substance-treated groups.

6. Body Temperature: Body temperature was unaffected by the administration of test 

substance at 500, 1,250, or 3,750/5,000 ppm in males and females. There were no statistically 

significant differences between the control and test substance-treated groups 

G. SACRIFICE AND PATHOLOGY: 

1. Gross Pathology: No adverse, treatment-related effects were noted during gross pathology. 

2. Neuropathology: No adverse, treatment-related histological changes were noted in the highconcentration (3,750/5,000 ppm) group males or females compared to controls. 

Page 16 of 32
Subchronic Neurotoxicity Study (rats) (2011) /Page 15 of 16 

Chlorimuron Ethyl/128901 OPPTS 870.6200b/ MAFF 12 Nousan 8147/OECD 424

III. DISCUSSION AND CONCLUSIONS:

A. INVESTIGATORS’ CONCLUSIONS:

 

The investigator concluded that under the conditions of this study, the no-observed-adverseeffect level (NOAEL) for systemic toxicity was 3,750/5,000 ppm (220 mg/kg/day), the 

highest concentration, for male rats and 500 ppm (35 mg/kg/day) for female rats. The female 

NOAEL was based on decreased body weight and nutritional parameters in females

administered 1,250 and 3,750/5,000 ppm. The NOAEL for neurotoxicity in males and 

females was greater than 3,750/5,000 ppm (220 and 259 mg/kg/day, respectively), the 

highest dietary concentration tested, based on the absence of test substance-related effects on 

the nervous system. 

B. REVIEWER COMMENTS: 

Exposure of Crl:CD(SD) male and female rats to Chlorimuron Ethyl at dietary concentration

levels of 500, 1,250 or 3,750/5,000 ppm resulted in no effect on mortality or clinical signs in 

either male or female rats. 

No test substance-related effects were observed on FOB (home cage, open field, removal 

from the home cage and handling) parameters, rearing, hindlimb grip strength, body 

temperature or motor activity (duration of movements and number of movements) at any 

dietary concentration level in either sex. Higher (p≤0.05) mean forelimb grip strength was 

noted in the 1,250 ppm (↑16%) group males at Week 8; however, this finding was considered 

incidental with no dose or time relationships that would indicate that this finding was related 

to treatment, nor were there similar trends in both males and females.

Treatment-related effects on body weights, body weight gains and food consumption were 

evident in the high dietary concentration (3,750/5,000 ppm) group females, but not in males. 

In females, mean body weight was significantly reduced by 6-10% from Day 21 though Day 

91. No significant differences in body weights were noted in females at dietary concentration 

levels of 500 or 1,250 ppm compared to the controls, except on Day 84, lower (p≤0.05) body 

weight was noted in the 1,250 ppm (↓7%) group females. However, the decrease was not 

considered adverse since the reduction was less than 10%. Mean body weight gain was 

lower (p≤0.05) during test Day 0-7 (↓34%), Day 14-21 (↓40%) and Day 0-28 (↓21%) in the 

3,750/5,000 ppm group females when compared to the control group. Overall (0-91) body 

weight gains were significantly reduced by ↓15% and ↓24% at concentrations of 1,250 and 

3,750/5,000 ppm in females, respectively. Lower (p≤0.05) mean daily food consumption 

ranged ↓9-18% from Day 14-21 though the end of the treatment in the 3,750/5,000 ppm 

group females. In addition, mean daily food consumption was significantly decreased by 

11% and 8% on Day 63-70 and Day 56-91, respectively, at the concentration of 1,250 ppm. 

However, in the absence of a treatment related effect on absolute bodyweight, the reductions 

in bodyweight gain and food consumption were not considered adverse at 1,250 ppm. 

Overall (0-91) mean food consumption was lower (p≤0.05) in the 3,750/5,000 ppm group 

females. In contrast to females, there were no treatment-related or statistically significant 

effects on body weight, body weight gain or food consumption in males at any dietary 

concentration level. There were no test substance-related effects on food efficiency in the 

500, 1,250, or 3,750/5,000 ppm group males or females. It was concluded that lower body 

weight gains observed in the high concentration (3,750/5,000 ppm) group females, but not in 

Page 17 of 32
Subchronic Neurotoxicity Study (rats) (2011) /Page 16 of 16 

Chlorimuron Ethyl/128901 OPPTS 870.6200b/ MAFF 12 Nousan 8147/OECD 424

males, were associated with the significant reduction in body weights and food consumption 

over the entire study period and were test substance-related. Overall, females were more 

sensitive than males.

No test substance-related alterations were observed in gross histopathology observations or 

microscopic neurohistopathology in the 3,750/5,000 ppm group males and females. 

It is concluded that Chlorimuron Ethyl did not exhibit neurotoxic effects on Crl:CD(SD) 

male and female rats at dietary concentration levels of 500, 1,250 and 3,750/5,000 ppm, 

based on the lack of altered behavior in the FOB parameters, no significant effects in motor 

activity (duration of movements and number of movements), and no effects on the 

macroscopic and microscopic pathology of nervous system tissues. However, systemic 

toxicity was observed in females at 3,750/5,000 ppm. This was characterized by decreased 

body weights and body weight gains and significant reductions in food consumption over the 

study period. 

The systemic NOAEL is 1,250 ppm (equivalent to 71/90 mg/kg/day), based on decreased 

body weight and body weight gains and reduced food consumption observed in females 

at the LOAEL of 3,750/5,000 ppm (equivalent to 220/259 mg/kg/day, M/F respectively). 

The NOAEL for neurotoxicity is the highest dose tested 3,750/5,000 ppm (equivalent to 

220/259 mg/kg/day, M/F respectively) since no treatment related neurotoxic effects were 

seen in the study. 

 

This study is classified as acceptable/guideline and satisfies the guideline requirement 

(OPPTS 870.6200b; OECD 424) for a subchronic neurotoxicity study in rats. 

C. STUDY DEFICIENCIES: 

 

In the study report, the highest dietary concentration was primarily reported as 3,500/5,000 

ppm (e.g. see Summary section; page 12 and Conclusion section; page 26), however the 

Study Design table on page 14 indicates that the high dietary concentration of Chlorimuron 

Ethyl was 3,750/5,000 ppm. Also, all summary and individual Tables as well as Appendix B 

indicate the high dose was 3,750/5,000 ppm. Except the aforementioned problem, there were 

no other deficiencies reported in this study. 

Page 18 of 32
DATA EVALUATION RECORD

Chlorimuron Ethyl 

PC Code: 128901

TXR#: 0056215 

MRID#: 48704302

Study Type: Acute Neurotoxicity [feeding] - 14-Day Study in Crl:CD(SD) rats

OPPTS 870.7800 

Prepared for

Health Effects Division

Office of Pesticide Programs

U.S. Environmental Protection Agency 

One Potomac Yard

2777 S. Crystal Drive 

Arlington, VA 22202 

Prepared by

Tetrahedron Incorporated

1414 Key Highway, Suite B 

Baltimore, MD 21230 

Principal Reviewer: _____________________________________ Date: 

5/16/2012 

Henry Spencer, Ph.D. 

Secondary Reviewer: _____________________________________ Date: 

5/25/2012 

William Burnam, M.S.

Quality Assurance: _________________________________________ Date: 

5/28/2012 

Nasrin Begum, Ph.D. 

Contract Number: EP-W-10013 

Work Assignment No.: WA-0-01 

Task Number: 1-1-88 

EPA Reviewer//WAM: Swartz and Levy//Farwell and Brunsman

Disclaimer

This review may have been altered by the EPA subsequent to the contractors’ signature 

above.

Page 19 of 32
Chlorimuron Ethyl/12890 I 

TXR#: 0056215 

Acute Neurotoxicity Study (rats) (20 I I) I Page 2 of I 4 

OPPTS 870.6200a/ DAC 4.5.12/ OECD 424 

DATA EVALUATION RECORD 

STUDY TYPE: Acute Neurotoxicity - Rats OPPTS 870.6200a [§81-8]; OECD 424. 

PC CODE: 128901 DP BARCODE: D397470 

TEST MATERIAL (PURITY): Chlorimuron Ethyl (chlorimuron ethyl) 97.5% a.i. 

SYNONYMS: DPX-F6025, IPAC Name: Ethyl 2-(-4-chloro-6-methoxypyrimidin-2-

ylcarbamoylsulfamoyl) benzoate; CAS Name: Ethyl 2-[[[[(4-chloro-6-methoxy2-pryrimidinyl)amino ]carbonyl]amino] sulfonyl]benzoate 

CITATION: Author: Carpenter, C. (2011), Title: Chlorimuron Ethyl (DPX-F6025) Technical: 

Acute Oral Neurotoxicity Study in rats. Laboratory: DuPont Haskell Global 

Centers for Health & Environmental Sciences P.O. Box 50, Newark, Delaware 

19714, U.S.A., Laboratory report number: DuPont- 31865, December 12, 2011. 

MRID48704 302. Unpublished. 

SPONSOR: E.I du Pont de Nemours and Company, Wilmington, Delaware, 19898. 

EXECUTIVE SUMMARY: 

In an acute neurotoxicity study (MRID 48704302), groups Crl:CD (SD) rats (12/sex/dose) were 

given a single oral dose of chlorimuron ethyl (97.5% a.i, DPX F6025-258) in 0.5% 

methylcellulose at doses of I 00, 500, or 2000 mg/kg bw and observed for 14 days. 

Neurobehavioral assessment (functional observational battery and motor activity testing) was 

performed on all animals at -7 days (pretest), 0 (approximately 2 hours after dosing), 7, and 14 

days. At study termination, 6 animals/sex in the control and high dose groups were euthanized 

and perfused in situ for histopathological evaluation of brain and peripheral nervous system 

tissues. 

Treatment related clinical signs were absent in the animals. There were no effects on mortality, 

histopathology, or neuropathology. 

No significant body weight changes were seen in male and female groups when compared to 

controls. Body weight gains were significantly reduced by 111.4% (p<0.05) in males on day 0-1 

at 2000 mg/kg bw, but these effects were not seen at later time intervals. Reductions in body 

weight gain in males at other dose levels were not significant, though there were questionable 

reductions at 500 mg/kg bw on Days 0-1. 

In females, there was a significant decrease in body weight gain for the time period of 0-7 days, 

Page 20 of 32
Acute Neurotoxicity Study (rats) (2011) / Page 3 of 14

Chlorimuron Ethyl/128901 OPPTS 870.6200a/ DACO 4.5.12/ OECD 424 

but this significance was not seen for the 9-14 day period. FOB findings on motor activity 

indicated that males at 2000 mg/kg bw preferred a curled up posture. Arousal was also reduced 

at 500 and 2000 mg/kg bw in males and females on Day 0. Palpebral closure was noted in a few 

females at 2000 mg/kg bw on day 0. No treatment-related effects were seen in the 100 mg/kg 

bw group. 

Motor activity on Day 0 was affected in a few early sessions by statistically significant 

reductions in activity in males at 500 and 2000 mg/kg bw. Sessions at 100 mg/kg bw showed 

changes, but only the #2 session at 100 mg/kg bw was statistically significantly different from 

the control. Sessions in females from #2-#6 at 500 mg/kg bw were reduced but the changes were 

not statistically significant. 

The NOAEL is 100 mg/kg/day, based on reduced arousal and reduced motor activity in male and 

female rats at the LOAEL of 500 mg/kg bw. 

This neurotoxicity study is classified as acceptable/guideline) and satisfies the guideline 

requirement for an acute neurotoxicity study in rats (870.6200a; OECD 424). 

COMPLIANCE: Signed and dated GLP, Quality Assurance, and Data Confidentiality 

statements were provided.

Page 21 of 32
Acute Neurotoxicity Study (rats) (2011) / Page 4 of 14

Chlorimuron Ethyl/128901 OPPTS 870.6200a/ DACO 4.5.12/ OECD 424 

I. MATERIALS AND METHODS:

A. MATERIALS:

1. Test material: Chlorimuron Ethyl (DPX-F6025) Technical

Description: Crystalline, powder, white

Lot/batch #: DPX-F6025-258 (Laboratory designation); Analysis No.:MAR09MA047

Purity: 97.5% a.i.

CAS # of TGAI: 90982-32-4

Structure:

 2. Vehicle and/or positive control: The vehicle was 0.5% methylcellulose. 

3. Test animals: Species: Rat

Strain:Crl:CD(SD)

Age/weight at dosing: 49 days, 200.5-256.6g males, 143.6-201.9 g 

females.

Source: Charles River Labs. Inc., Kingston, New York

Housing: One sex, in pairs in solid bottom caging

Diet: PMI Nutrition International, LLC Certified Rodent LabDiet ® 5002 ad 

libitum.

Water: Tap water was provided ad libitum.

Environmental 

conditions:

Temperature:

Humidity:

Air changes:

Photoperiod:

18-26°C

30-70% 

Thenumber of changes of air/ hour was not reported. 

12 hrs dark/12hrs light

Acclimation period: Quarantined 8 day, acclimated for additional 7 days

B. STUDY DESIGN:

1. In life dates: Start:May 17, 2011; End: June 3, 2011 

2. Animal assignment and treatment: Animals were assigned to the test groups noted in 

Table 1 by a computerized, stratified, randomization program so that body weight means for 

each group were comparable within a sex. Rats on Day 0 were given a single dose of 

chlorimuron ethyl in 0.5% methylcellulose by oral-gavage at 10 mL/kg bw based on the body 

weight taken just before dosing. Controls received only the 0.5% methylcellulose solution. 

The study animals were then observed 2X daily for daily health observations and were 

weighed on Day 0, 1, 7, and 14 for 14 days. Dose levels were chosen based on a recent acute 

oral toxicity study using 175, 550, 1750 or 5000mg/kg bw chlorimuron ethyl in distilled 

water. No significant clinical signs of toxicity were reported. There was no determination of 

a time to peak effect reported previously. The 2000 mg/kg bw dose was included in the 

present study with the 100 and 500 mg/kg bw doses as a limit range. Administration was 

staggered over a 2-day interval to facilitate neurobehavioral observations. Males and females 

were treated on the same days in 4 replicates in the 2-day period. Survivors were sacrificed 

and a necropsy was performed.

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Chlorimuron Ethyl/128901 OPPTS 870.6200a/ DACO 4.5.12/ OECD 424 

TABLE 1.Study design

Experimental parameter

Dose group (mg/kg bw)

0 mg/kg 

bw

100 mg/kg 

bw

500 mg/kg 

bw

2000 mg/kg 

bw

Total number of animals/sex/group 12/sex 12/sex 12/sex 12/sex

Behavioral testing [FOB, (Motor Activity (9)10 min 

sessions) Days 0, 7, 14] 12/sex 12/sex 12/sex 12/sex

Neuropathology 6/sex 6/sex 6/sex 6/sex

Body weights, weight gains, and food consumption on 

Days 0, 1, 7, 14 12/sex 12/sex 12/sex 12/sex

3. Test Substance preparation and analysis: The test substance was supplied as a white solid. 

It was used in the established period of stability of 5 days at ambient temperature. A 

weighed portion of the white powder corrected for purity was suspended in 0.5% methyl 

cellulose. Exact methods of formulation were not provided. The homogeneity was 

determined for each formulation by sampling a portion at levels designated as top, middle, 

and bottom for test material concentration. Homogeneity was evaluated by calculating the 

relative standard deviation (RSD) of the measured concentration of each level. 

Concentrations of the test substance in the sample analyses for each respective dose level

were determined. Stability was determined by comparing the values found at February 17, 

2011 and comparing them to the values found after a resuspension following storage for 5 

days at ambient temperature. 

Results: 

Homogeneity analysis: RSD range 2%-5% comparing initial and 5 days storage. 

Stability analysis: 99.9%-94.2% at 10 mg/mL; and 95%-90.5% at 200 mg/mL in initial and 

5 day storage, respectively.

Concentration analysis: Percent of nominal: 10mg/mL 99.9% RSD =3%; 200 mg/mL 95% 

RSD=3%. At initial formulation, the analytical data indicated that the mixing procedure was 

adequate and that the variance between nominal and actual dosage to the animals was 

acceptable.

4. Statistics: Statistical analyses noted that males and females were analyzed separately and 

that significance was set at p<0.05.

Table 2.Parameters and statistical tests used

Method of Statistical Analysis

Parameter Preliminary Test If preliminary test is 

not significant

If preliminary test is significant

Body Weight

Body Weight Gain

Food Consumption 

Food Efficiency

Levine’s test for 

homogeneity and 

Shapiro-Wilk test for 

normality

One-way analysis of 

variance followed 

by Dunnett’s test

Transforms of the data to achieve normality and 

variance homogeneity were used.The order of 

transforms attempted was log, square-root, and 

rank-order.If the log and square-roottransforms 

failed, the rank-order was used.

Grip Strength

Foot Splay

Body Temperature

Rearing

Levine’s test for 

homogeneity and 

Shapiro-Wilk test for 

normality

Repeated measures 

and analysis of 

variance followed 

by linear contrasts

(1) A normalizing variance stabilizing 

transformation followed by repeated measures 

analysis of variance or (2) sequential application 

of Jonckheere-Terpstrab

trend test.

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Chlorimuron Ethyl/128901 OPPTS 870.6200a/ DACO 4.5.12/ OECD 424 

Motor Activitya

Incidence of FOB

Descriptive 

Parameters

None Cochran-Armitage test for trend.If the incidence is not significant, but a 

significant lack of fit occurs, the Fisher’s Exact test with a BonferroniHolm correction is used.

a - Test day and 10-minute interval were used as repeated measure factors.

b - If there was a significant lack of monotonicity (i.e. Linear Trend:Dose was not significant, and Quadratic Trend:

Dose was significant), Dunn’s test was used instead of Jonckheere-Terpstra.

For each parameter analyzed with a trend test, the test was applied to the data sequentially. If 

a significant dose response was detected, data from the top dose group was excluded and the 

test repeated until no significant trend is detected. The analyses used were appropriate. 

C. METHODS / OBSERVATIONS:

1. Mortality and clinical observations: Animals were observed 2X daily for mortality and 

morbidity. Detailed clinical observations were recorded at least once daily except on the day 

of a neurobehavioral evaluation. Times in the day when each evaluation or observations 

were made were not provided. 

2. Body weight: Animals were weighed during the baseline FOB and on test day 0, and on 

Days 1, 7, and 14. 

3. Food consumption: Each animal‘s food consumption was determined on Days 0, 1, 7, and 

14. The feeders were weighed prior to adding new material and again weighed after the 

consumption period. 

4. Cholinesterase determination: Cholinesterase activity was not determined in this study. 

5. Neurobehavioral assessment:

 

a. Functional Observational Battery (FOB): Open-field behavioral observations included 

sharp auditory stimulus evaluation following the use of a clicker. Additionally, pain 

reception was evaluated by a tail pinch. Grip strengths were measured using a Chatillon® 

Digital Force gauge. Rectal body temperatures were recorded with a YSI PrecisionTM 4000 

thermometer and temperature probe. The landing foot splay was determined using 

measurements of fresh ink impressions made by the heels of the hind paws when the animals 

were dropped from about a 32 cm height. The animals were examined as a blind effort using 

the same investigators throughout the study. The studies were carried out in a soundattenuated room with white-noise-generation to minimize environmental test conditions. 

Exact time of the day the evaluations were conducted after exposure was not provided. Table 

3.shows the parameters evaluated in the FOB. 

Table 3.The CHECKED (X) parameters were examined. 

X HOME CAGE OBSERVATIONS X HANDLING OBSERVATIONS X OPEN FIELD OBSERVATIONS

X Posture* Reactivity* X Mobility

Biting X Lacrimation*/chromodacryorrhea X Rearing+

X Convulsions* X Salivation* X Arousal/ general activity level*

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Chlorimuron Ethyl/128901 OPPTS 870.6200a/ DACO 4.5.12/ OECD 424 

X HOME CAGE OBSERVATIONS X HANDLING OBSERVATIONS X OPEN FIELD OBSERVATIONS

X Tremors* X Piloerection* X Convulsions*

X Abnormal Movements* X Fur appearance X Tremors*

X Palpebral closure* X Palpebral closure* X

X

Abnormal movements*

spasms/fasciculations

Feces consistency Respiratory rate+ X Urination / defecation*

X coordination Red/crusty deposits* Grooming

SENSORY OBSERVATIONS X Mucous membranes /eye /skin 

color X Gait abnormalities / posture*

X 

Approach response+ X Eye prominence* X Gait score*

X Vocalization X Righting reflex

X Dehydration X Ease and rate of respiration

X Emaciation X vocalization

X Touch response+ X Muscle tone* Bizarre / stereotypic behaviour*

X Startle response* X Ease of removal/handling Backing

X Pain response* PHYSIOLOGICAL 

OBSERVATIONS

Time to first step

X Pupil response* X Body weight* X Palpebral closure

Eyeblink response X Body temperature+ NEUROMUSCULAR 

OBSERVATIONS

Forelimb extension Hindlimb extensor strength

Hindlimb extension OTHER OBSERVATIONS X Forelimb grip strength*

X Air righting reflex+ X Hindlimb grip strength*

Olfactory orientation X Landing foot splay*

Rotarod performance

*Required parameters; +Recommended parameters

b. Locomotor activity: Locomotor Activity was evaluated on individuals in one of thirty 

identical, automated infrared beam activity monitors (Moulbourn® Instruments). 

Measurements were of duration of movement and number of movements per animal in a 

series of 9, 10 minute consecutive intervals. There were 12 animals/sex/dose in this 

evaluation. Scoring criteria were not provided for the measured parameters. However, 

“counts” appeared to be of duration in seconds (total activity) and the number of counts 

representing the numbers of any type of movement. 

6. Sacrifice and pathology: On day 16, 6 rats/sex/dose were anesthetized by an i.p. dose of a 

mixture of ketamine/xylazine and whole-body perfused in situ.The perfusion solution was 

not described. The remaining animals not chosen for histological evaluation were terminated 

with isoflurane anesthesia and asphyxiated by carbon dioxide. Necropsy was not performed 

on the remaining animals. The perfused animals in each group were eviscerated and necropsy 

samples taken prior to emersion fixation for further processing of the appropriate tissues. 

Paraffin embedded, which were sectioned at about 5 μm and stained with hematoxylin and 

eosin tissues included: the brain (cerebrum and hippocampus, forebrain, midbrain, 

cerebellum, pons, and medulla) spinal cord (cervical, thoracic, and lumbar), eye with optic 

nerve, and gastrocnemius muscle. Tissues that were embedded in glycol methacrylate 

(GMA), sectioned at about 3 μm and stained with hematoxylin and eosin included: cervical 

and lumbar dorsal root fibers and ganglia, and ventral root fibers, sciatic, tibial and sural 

nerves and gasserian ganglia. Only the tissues from the high dose and control animals were 

processed and evaluated as reported in Table 4.

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Chlorimuron Ethyl/128901 OPPTS 870.6200a/ DACO 4.5.12/ OECD 424 

Table 4.The CHECKED (X) tissues were evaluated.

X CENTRAL NERVOUS SYSTEM X PERIPHERAL NERVOUS SYSTEM

BRAIN SCIATIC NERVE

X Forebrain

X Center of cerebrum X Sciatic Notch

X Midbrain

X Cerebellum OTHER

X Pons X Sural Nerve

X Medulla oblongata X Tibial Nerve

SPINAL CORD

X Cervical swelling X Lumbar dorsal root ganglion

X Lumbar swelling X Lumbar dorsal root fibers

X Thoracic swelling X Lumbar ventral root fibers

OTHER X Cervical dorsal root ganglion

X Gasserian Ganglion X Cervical dorsal root fibers

X Optic nerve X Cervical ventral root fibers

X Eyes

X Gastrocnemius muscle

7. Positive controls: It was stated in this report that three separate reports (MRID 44628703, 

MRID 47053501 and MRID 48710304, performed in 1997, 2002 and 2011, respectively) 

were previously performed by DuPont Haskell to generate positive control data and validate 

the procedures and the inter-observer reliability of the performing lab to conduct and assess 

neurobehavioral and neuropathology tests. The data also documents that the equipment and 

procedures are capable of detecting effects that may be seen in neurotoxicity studies. The 

positive control data is acceptable for use with the current study. Historical control data were 

not provided in the report. 

II. RESULTS:

A. OBSERVATIONS:

1. Clinical signs: There were no clinical signs considered to be treatment related in either sex. 

2. Mortality: All animals survived to termination.

B. BODY WEIGHT AND BODY WEIGHT GAIN: The body weight of the male and female 

groups did not show significant changes when compared to control. There did not appear to 

be much variability between groups. The body weight gains however, do show significant 

reduction (-111.4%) in gains in males at 2000 mg/kg bw in the day 0-1 interval. Control 

females also exhibited poor weight gains between Day 0-1 (-0.5 g). The body weight gains 

in the test groups were greater with a gain of 3.3 g seen at 500 mg/kg bw, and 2.9 g at 2000 

mg/kg bw. There was some significance at the female high dose for body weight gain for 

days 0-7, but the significance was gone at day 14. The 500 mg/kg bw females showed lower 

weight gains than the 100 mg/kg bw group on Day 0-1. 

Page 26 of 32
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Chlorimuron Ethyl/128901 OPPTS 870.6200a/ DACO 4.5.12/ OECD 424 

TABLE5.Body weight and body weight gain (g)

Observation (g ± s.d.) Dose level (mg/kg bw) N=12

0 mg/kg bw 100 mg/kg bw 500 mg/kg bw 2000 mg/kg bw

Body weight-males

-Day0 238.2 ± 14.2

Diff.-

236.1± 13.2

Diff.- 0.9%

232.3 ± 15.1

Diff.-2.5%

237.9 ± 13.9

Diff.- 0.1%

Day 1 243± 12.7

Diff.-

241.4± 12.6

Diff.- 0.7%

238.2± 15.9

Diff.-2%

237.3± 12.0

Diff.- 2.3%

Day 7 300.9 ± 21.1

Diff. -

297.5± 12.2

Diff.-1.1%

294.8± 19.5

Diff.-2%

294.5± 18.9

Dif.-2.1%

Day 14 360.6 ± 26.7

Diff. -

355.7 ± 12.0

Diff.- 1%

355.5 ± 23.9

Diff.- 1%

356.7 ± 24/9

Diff.- 1%

Body weight-females

-Day 0 180.7 ± 11.5

Diff.-

178 ± 14.2

Diff.- 1.5%

177.8 ± 16.1

Diff.- 1.6%

178.9 ± 10.3

Diff.- 1%

Day 1 180.1 ± 11.7

Diff. -

181.8 ± 14.3

Diff. - 0.9%

181.2 ± 14.8

Diff. - 0.6%

181.9 ± 10.3

Diff.-1%

Day 7 209.8 ± 11.6

Diff. -

203.2 ± 18.6

Diff.- 3.1%

207.9 ± 17.1

Diff.- 0.9%

201.4 ± 12.6

Diff.- 4%

Day 14 235.1 ± 12.2

Diff. -

228.6 ± 21.4

Diff.-2.8%

231.8 ± 18.8

Diff.- 1.4%

229.2 ± 14.3

Diff.- 2.5%

Body weight gain-males

-Day0-1 4.8 ± 2.9

Diff. -

5.3 ± 4.0

Diff.10.5%

5.9 ± 10.1

Diff. 22.5%

-0.6 ± 6.2#

Diff. -111.4%

Day 0-7 62.7 ± 7.9

Diff. -

61.4 ± 3.1

Diff. -2%

62.5 ± 16.3

Diff. -0.3%

56.6 ± 8.7

Diff. -9.7%

Day 7-14 59.8 ± 8.8

Diff.-

58.3 ± 6.3

Diff. -2.5%

60.7 ± 6.7

Diff. 1.6%

62.2 ± 8.6

Diff. 4%

Day 0-14 122.5 ± 14.4

Diff. -

119.7 ± 6.7

Diff. -2.3%

123.2 ± 22.1

Diff. 0.6%

118.8 ± 16.8

Diff. -3%

Body weight gain-females

-Day0-1 -0.5 ± 3.5

Diff.-

3.9 ± 5.5

Diff -838.1%

3.3 ± 5.7

Diff. -733.3%

2.9 ± 3.0

Diff. -657.1%

Day 0-7 29.1 ± 4.6

Diff. -

25.2 ± 6.6

Diff. -13.4%

30.1 ± 5.5

Diff. 3.4%

22.5 ± 8.0#

Diff. -22.8%

Day 7-14 25.3 ± 5.5

Diff. -

25.4 ± 9.5

Diff. 0.3%

23.9 ± 7.4

Diff. -5.6%

27.8 ± 6.3

Diff. 9.7%

Day 0-14 54.4 ± 5.8

Diff. -

50.6 ± 11.6

Diff. -7%

54 ± 10.8

Diff. -0.8%

50.3 ± 9.2

Diff. -7.7%

 #p<0.05. Data extracted from pages 32 and 33 of the study report.

C. FOOD CONSUMPTION: Significant reductions in food consumption were observed at 

Day 0-1 in both sexes (Males, -9.6% (NS) and females, -20.8% (p<0.05) at 2000 mg/kg bw. 

TABLE 6.Food consumption (g/kg/day)

Days No. Dose level (mg/kg bw)n=12

0 mg/kg bw 100 mg/kg bw 500 mg/kg bw 2000 mg/kg bw

Males

Days0-1 23.0 ± 4.2 

Diff. -

26.0 ±1.4

Diff.13.2%

25.3 ±3.0

Diff. 10.3%

20.8± 4.1

Diff. -9.6%

Days 0-7 27.4± 1.7

Diff. -

26.9 ± 0.7

Diff. -1.9%

27.4± 1.6

Diff. 0.1%

27.7 ±1.8

Diff. 1%

Females

Days 0-1 17.2± 1.4

Diff. -

19.3 ± 2.3

Diff. 12.4%

18.4± 2.6

Diff. 7.3%

13.6 ±3.5#

Diff. -20.8%

Days 0-7 19.4 ±0.7

Diff. - 

18.6± 0.9

Diff. -3.9%

19.6± 1.4

Diff. 1.2%

18.4± 0.7

Diff. -4.9%

Data were extracted from pages 35, 36 of the study report. 

Values represent mean +s.d.

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Chlorimuron Ethyl/128901 OPPTS 870.6200a/ DACO 4.5.12/ OECD 424 

n=12/ group

# p<.05, when compared to control means

Diff. = difference of group compared to control group.

D. CHOLINESTERASE ACTIVITIES: Cholinesterase activity was not measured in this 

study.

E. NEUROBEHAVIORAL RESULTS:

1. FOB findings: FOB results noted in Table 7 showed males in the 2000 mg/kg bw group 

preferred a curled-up posture (4/12 treated vs. 0/12 control) on Day 0. They were also more

difficult to arouse in the 500 and 2000 mg/kg bw groups (3/12 and 3/12 respectively, vs. 0/12 

controls) (p<0.05). The posture of females at 500 and 2000 mg/kg bw was only slightly 

affected (2/12, 2/12 respectively vs.0/12 controls) (N.S). Palpebral closure occurred in 2/12 

animals on Days 0 and 14 (p<0.05). 

TABLE 7.Functional observation battery results

Observation Dose level (mg/kg bw) n=12

0 mg/kg bw 100 mg/kg bw 500 mg/kg bw 2000 mg/kg bw

Males

Posture: curled up

-Pretest

-Day 0

-Day 7

-Day 14

1 

0 

0 

0

1 

0 

2 

0

0 

1 

0 

0

1 

4 #

3 

0

Arousal-low

-Pretest

-Day 0

-Day 7

-Day 14

0 

0 

0 

0

0 

2 

3 

1

1 

3# 

1 

1

1 

3# 

1 

1

Females

Home cage curled up

-Pretest

-Day 0

-Day 7

-Day 14

0 

1 

0 

0

0 

0 

0 

0

1 

2 

0 

0

1 

2 

1 

2#

Home cage Palpebral closure

Appears to be sleeping

-Pretest

-Day 0

-Day 7

-Day 14

0 

0 

0 

0

0 

0 

0 

0

1 

0 

0 

0

0 

2#

1 

2#

Data were extracted from pages 43, 47, 50

Values represent incidence 

n=12

# =p<.05 compared with controls

Additionally, both male and female rats at 2000 mg/kg bw on Day 0 exhibited reduced 

activity in the number of rearing incidences. The reduction in females (4/7 treated vs. 

controls) was statistically significant while the males were lower (2/5), but not statistically 

significant. Body temperatures on Day 0 at 2000 mg/kg bw were significantly lower than 

controls by 1 and 1.2 degrees in males and females, respectively. Females also exhibited 

slightly lower body temperatures at 500 mg/kg bw. 

2. Motor activity: The total activity counts in Table 8 for the sum of 9, 10 minute sessions 

suggests that on Day 0, males at 500 and 2000 mg/kg bw were more subdued than controls 

Page 28 of 32
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Chlorimuron Ethyl/128901 OPPTS 870.6200a/ DACO 4.5.12/ OECD 424 

and animals at 100 mg/kg bw. The reduced activity numbers were not statistically 

significantly different from controls. However, there were several 10 minute sessions in 

males and females at the 500 and 2000 mg/kg bw dose levels that measured a decrease in 

activity at Day 0 as indicated by the mean number of movements per session (Tables, 9, 10). 

In males on Day 0, Session # 2 showed statistically significant reductions in activity in all 

test groups. Session #3 showed statistically significant reductions in the 500 and 2000 mg/kg 

bw groups. Sessions # 4 and #5 were not statistically significant and appeared to plateau at 

lower activity levels –not unlike controls. 

 Female rats at 2000 mg/kg bw showed significantly reduced movements in sessions # 1, #2, 

#3. However, at 500 mg/kg bw, sessions #2, #3, #4, #5, #6 showed lower activity than 

controls, but were not statistically significantly different. 

The statistically significant reduced effect at 2000 mg/kg bw in females is in 1-3 sessions (30 

minutes), but sessions #4, #5 also show effects lower than controls. A statistically significant 

effect at 500 mg/kg bw did not occur, but sessions #1 - #6 show effects lowered compared to 

control. The duration in seconds/session were also statistically significantly decreased in 

sessions #2-#3 and #2-#4 in males on Day 0 at 500 and 2000 mg/kg bw respectively. The 

females at 500 and 2000 exhibited statistically significant reduction of counts in sessions #1-

#4. Changes in activity at 100 mg/kg bw were similar to controls. 

TABLE 8.Motor activity (total activity counts for 90 minute session)

Test day Dose level (mg/kg bw)n=12

0 mg/kg bw 100 mg/kg bw 500 mg/kg bw 2000 mg/kg bw

Males

Pre-test 536± 164 468± 163 532± 165 575± 240

Day 0 402± 107 365 ±84 317 ±91 319± 161

Day 7 496± 246 539± 213 456± 142 534± 267

Day 14 583± 154 568± 246 497± 127 577 ±257

Females

Pre-test 610 ±237 693 ±207 759±294 718 ±296

Day 0 412±167 487 ±243 339± 100 242± 122

Day 7 639 ±259 704± 295 670 ±242 620 ±238

Day 14 611 ±227 648± 220 632± 223 731± 218

Data were extracted from pages 58,59

Values represent mean +s.d.

n= 12

Table 9. Day 0 mean number of movements per session in Male Rats n=12 

Session @10 min 0 mg/kg bw 100 mg/kg bw 500 mg/kg bw 2000 mg/kg bw

#1 126 ± 22 126 ±16 113 ±22 113 ± 40

#2 123 ± 27 91 ±45# 48± 41# 31 ±36#

#3 56 ± 45 40 ± 43 16± 20# 18 ± 19#

#4 17 ± 15 13 ±9 39± 37 16 ± 18

#5 28 ± 37 29 ±42 19± 13 33 ± 37

#6 9± 7 21 ± 25 26± 21 23 ± 17

#7 14 ± 18 24 ± 34 28± 26 21 ± 19

#8 18 ± 32 12±8 13± 11 32 ± 29

#9 10 ± 12 10±8 16± 18 31 ± 26#

Data extracted from Page 58 of the study report.

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#=p<.05 compared with controls

Table 10. Day 0 mean number of movements per session in Female Rats n=12 

Session @ 10 min 0 mg/kg bw 100 mg/kg bw 500 mg/kg bw 2000 mg/kg bw

#1 129 ±18 134 ±16 131 ±21 103 ±34#

#2 72 ± 47 101 ± 55 42 ± 31 30 ± 24#

#3 55 ± 54 59 ± 55 15 ±15 11 ±13#

#4 47 ± 51 42 ± 55 18 ± 26 17 ± 21

#5 44 ± 52 26 ± 41 19 ± 27 14 ± 12

#6 36 ± 44 27 ±26 10 ± 11 27 ± 25

#7 6 ±7 26 ±44 33 ± 41 18 ± 23

#8 13 ± 18 35 ± 43 47 ±45 9 ± 10

#9 10±8 35 ± 47 24 ±28 12 ±18

Data extracted from Page 59 of the study report.

# = p<0.05

F. SACRIFICE AND PATHOLOGY:

1. Gross pathology: There were no treatment–related gross pathological lesions observed. 

An eye lesion was seen in 1 female at 2000 mg/kg bw. The lesion (which was graded 

minimal) is considered a normal finding resulting from the folding of the retina; it was 

not considered to be treatment related. 

 2. Brain weight: Brain weights were not measured in this study. 

3. Neuropathology: No microscopic alterations of neural fibers or tissues were observed. 

III.DISCUSSION AND CONCLUSIONS:

A. INVESTIGATORS’ CONCLUSIONS: The investigators found reduced body weight gains 

reduced by 111% in males and in females by 23% at 2000 mg/kg bw in days 0-1 and Days 0-

7 respectively, and concluded that effects on bodyweight and body weight gains were not 

affected at 100 or 500 mg/kg bw. The reported changes were transient and not considered 

adverse. Food consumption was reduced 9.6% (N.S.) in males and by 21% in females at 

2000 mg/k bw compared to controls. The changes were considered transient and not adverse 

and did not affect the body weights of the test animals. It was determined that there were no 

effects on grip strength or foot splay in either sex at any dose. Body temperatures were 

reduced statistically significantly in males at 2000 mg/kg bw and in females at 500 and 2000 

mg/kg bw on Day 0, but recovery occurred by Day 7 and the changes were not considered 

adverse.

Males at 2000 mg/kg bw had fewer rearing incidences than controls (N.S.) at Day 0. 

However, females had fewer incidences of rearing at 2000 (p<0.05) at Day 0, but were 

essentially back to control group levels at Day 7. The effect was considered to be test dose 

related and adverse. There was a reported decrease of activity as related to the home cage 

condition of a curled-up posture and low arousal in the open field. In both cases the controls 

were 0/12. The posture change included 4/12 and correlated in males at 2000 mg/kg bw with 

reduced motor activity on Day 0. The effect was considered to be test substance related and 

adverse. Changes later in the study (i.e. Day 7 and Day 14) were not considered test dose 

related in females.

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Motor activity was statistically significantly decreased in males at 500, 2000 mg/kg bw in the 

first 30 minutes (sessions 1-3) of Day 0 and in females at 2000 mg/kg bw (sessions 1-3). The 

decreases in males at 500 and above were considered to be adverse and test dose related. 

However, there was statistically positive data for 100 mg/kg bw males in the #2 session 

followed by a NS decrease in session #3, these changes were not considered adverse. 

Statistically significant decreases in duration (seconds/session) were noted in the 500 mg/kg 

bw group in sessions 1, 3, 4 and at 2000 mg/kg bw in sessions 1, 2, 3, 4. These decreases 

were considered test related and adverse. No test substance related gross lesions of neural 

tissues or microscopic pathology were observed. 

The investigators considered at the NOAEL is 100 mg/kg bw in males and females based on 

systemic toxicity (body weight gains) accompanied by associated effects on motor activity, 

rearing and/or low arousal parameters on Day 0 (dosing) at 500 mg/kg bw. A NOAEL for 

neurotoxicity is 2000 mg/kg bw based on the absence of neuropathology and neurobehavioral 

parameters. 

B. REVIEWER COMMENTS:

Body weight gains were significantly reduced by 111.4% (p<0.05) in males on day 0-1 at 

2000 mg/kg bw, but these effects were not seen at later time intervals. Reductions in body 

weight gain in males at other dose levels were not significant, though there were questionable 

reductions at 500 mg/kg bw on Days 0-1. In females there was a significant decrease in body 

weight gain for the time period of 0-7 days, but this significance was not seen for the 9-14 

day period. In the absence of decreased absolute body weights, the changes were not 

considered adverse. 

Food intake values at Day 0-1 for both sexes at 2000 mg/kg bw indicate significant 

reductions in consumption (Males, -9.6% (NS) and females, -20.8% (p<0.05). 

Body temperatures on Day 0 were statistically significantly reduced 1°C in males at 2000 

mg/kg bw and at 500 (p<0.05) and 2000 mg/kg bw 1.2°C in females. Recovery was complete 

by Day 7.

Rearing in males 2/12 vs. 5/12 (NS) and females 4/12 vs. 7/12 was significantly reduced at 

2000 mg/kg bw at Day 0. 

In FOB observations, males preferred a curled-up posture at 2000 mg/kg bw on Day 0 (4/12 

vs. 0/12, p<0.05) compared to control animals. Additionally, the males were more difficult 

to arouse in the 500 and 2000 mg/kg bw groups (3/12, 3/12 vs. 0/12), (p<0.05). Females

exhibited slightly lower body temperatures at 500 mg/kg bw (p<0.05) compared to controls. 

Motor activity total counts were lower for the sum of the 9, 10 minute sessions on Day 0 in 

males at 500 and 2000 mg/kg bw than controls or animals at 100 mg/kg bw. The reduced 

activity numbers were not statistically different from controls. However, individual 10 

minute sessions in male and female rats at 100, 500 and 2000 mg/kg bw showed a temporary 

albeit significant reduction in activity. In Session #2 (20 minutes) all three dose levels were 

significantly reduced in males. In Session #3 (30 minutes) reductions occurred at 500 and 

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Acute Neurotoxicity Study (rats) (2011) / Page 14 of 14

Chlorimuron Ethyl/128901 OPPTS 870.6200a/ DACO 4.5.12/ OECD 424 

2000 mg/kg bw in males. In Sessions #4 and #5 (40-50 minutes) (NS), reductions appeared 

to plateau to levels similar to controls in males. Females at Session #2 were statistically 

significantly reduced at 2000 mg/kg bw and NS but lower than controls at 500 mg/kg bw. In 

Sessions #4-#6 females at 500 and 2000 mg/kg bw had values lower than control, but NS. 

The NOAEL is 100 mg/kg/day, based on reduced arousal and reduced motor activity in male 

and female rats at the LOAEL of 500 mg/kg bw. 

The study is considered to be Acceptable / Guideline and satisfies the requirement for acute 

neurotoxicity. 

C. STUDY DEFICIENCIES:

• Time to peak effect information was not presented. 

 

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