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EPA REGISTRATION DIVISION COMPANY NOTICE OF FILING FOR 

PESTICIDE PETITIONS PUBLISHED IN THE FEDERAL REGISTER 

EPA Registration Division contact: Susan Lewis 

Monsanto Company

4F8339

 EPA has received a pesticide petition (4F8339) from [Monsanto Company], [1300 

I Street NW, Suite 450 East, Washington, D.C. 20005] requesting, pursuant to section 

408(d) of the Federal Food, Drug, and Cosmetic Act (FFDCA), 21 U.S.C. 346a(d), to 

amend 40 CFR part 180 by establishing a tolerance for residues of [tioxazafen (MON 

102100): (3-phenyl-5-(2-thienyl)-1,2,4-oxadiazole) and its metabolite, benzamidine 

(benzenecarboximidamide)] in or on the following raw agricultural and processed 

commodities [Corn, field, forage] at [0.01] parts per million (ppm), [Corn, field, grain] at 

[0.01] ppm, [Corn, field, stover] at [0.02] ppm, [Cotton, gin byproducts] at [0.02] ppm, 

[Cotton, undelinted seed] at [0.01] ppm, [Soybean, forage] at [0.15] ppm, [Soybean, hay] 

at [0.3] ppm, [Soybean, meal] at [0.05] ppm, [Soybean, seed] at [0.04] ppm; and in or on 

the following food commodities [Cattle, fat] at [0.01] ppm, [Cattle, meat] at [0.01] ppm, 

[Cattle, meat byproducts] at [0.01] ppm, [Goat, fat] at [0.01] ppm, [Goat, meat] at [0.01] 

ppm, [Goat, meat byproducts] at [0.01] ppm, [Horse, fat] at [0.01] ppm, [Horse, meat] at 

[0.01] ppm, [Horse, meat byproducts] at [0.01] ppm, [Milk] at [0.01] ppm, [Sheep, fat] at 

[0.01] ppm, [Sheep, meat] at [0.01] ppm, and [Sheep, meat byproducts] at [0.01] ppm. 

EPA has determined that the petition contains data or information regarding the elements 

set forth in section 408 (d)(2) of FDDCA; however, EPA has not fully evaluated the 

sufficiency of the submitted data at this time or whether the data supports granting of the 

petition. Additional data may be needed before EPA rules on the petition. 

A. Residue Chemistry

 1. Plant metabolism. [Nature of the residue studies were conducted with 

tioxazafen applied as a seed treatment in corn, cotton, and soybean. Two radiolabeled 

forms of the parent molecule, [phenyl-U-14C] tioxazafen and [thiophene-2-14C] 

tioxazafen, were studied in each crop. Parent tioxazafen was a significant residue only in 

soybean forage and hay. Benzamidine was found in all three crops, and was the only 

identified metabolite found at or above approximately 10% of the TRR (total radioactive 

residues), and greater than or equal to 0.01 ppm, in any of the crop matrices. In a 

confined rotational crop study conducted as a seed treatment on corn as a primary crop, 

residues were low in rotational crop commodities of lettuce, radish and wheat with no 

single metabolite residue exceeding 0.01 ppm. Small amounts of MON 102100 and 

benzamidine were observed in rotational crop matrices. 
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Based on the results of these metabolism studies, the crop tolerance expression is 

proposed to be: 

“The sum of tioxazafen (3-phenyl-5-(2-thienyl)-1,2,4-oxadiazole) and its metabolite 

benzamidine (benzenecarboximidamide), expressed as tioxazafen.”] 

 2. Analytical method. [An independently validated analytical method has been 

submitted for the residue analysis of parent tioxazafen and its metabolite, benzamidine, in 

crop and processed commodities for corn, cotton, and soybean. Additionally, an 

independently validated method has been used in cattle and hen feeding studies for the 

analysis of residues in the food commodities animal meat, fat, liver, kidney, cream, and 

milk, and poultry meat, fat, liver and eggs, and is proposed for enforcement of requested 

tolerances in animal food commodities.] 

 3. Magnitude of residues. [Field trials were conducted to determine the magnitude 

of the residue in or on corn, cotton, and soybean. The number and locations of field trials 

were in accordance with OPPTS Guideline 860.1500, with minor adjustments in location 

distribution for cotton to better reflect current planted acreage. Seed was treated using 

the maximum label rates, planted in the field, and commodities grown from the treated 

seed were harvested per OPPTS Residue Guidelines. 

The magnitude of the residues (tioxazafen plus benzamidine) in field corn forage and 

grain was <0.01 ppm. Residues in field corn stover ranged from <0.01 to 0.01 ppm, with 

a median value of <0.01 ppm. In the processing study, there were no quantifiable residues 

in corn grain or in any processed fraction. 

The magnitude of the residues (tioxazafen plus benzamidine) in undelinted cotton seed 

was <0.01 ppm. Residues in cotton gin byproducts ranged from <0.01 to 0.01 ppm, with 

a median value of <0.01 ppm. 

The magnitude of the residues (tioxazafen plus benzamidine) in soybean forage samples 

ranged from <0.01 ppm to 0.11 ppm, with a median value of 0.03 ppm. Residues in 

soybean hay ranged from 0.02 to 0.24 ppm, with a median value of 0.07 ppm. Residues 

in soybean seed ranged from <0.01 to 0.04 ppm, with a median value of <0.01 ppm.  In 

the processing study, benzamidine residues in soybean seed concentrated in the meal and 

toasted meal, with concentration factors of about 1.5. Benzamidine levels were reduced 

in hulls (average concentration factor of 0.41) and significantly reduced in all the oil and 

lecithin fractions (concentration factor <0.1). 

In a limited field rotation crop study, conducted as a seed treatment on soybean as a 

primary crop, residues (tioxazafen plus benzamidine) were <0.01 ppm in rotational crop 

commodities of lettuce, radish and grain sorghum at a 30-day plant-back interval, and 

were <0.01 ppm in lettuce, radish, and wheat commodities at a 120-day plant-back 

interval.] 

B. Toxicological Profile
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 1. Acute toxicity. [Tioxazafen displayed low acute toxicity via the oral, dermal 

and inhalation routes of exposure. It was mildly irritating to the eye, non-irritating to the 

skin, and is not a dermal sensitizer. The acute toxicity studies place technical tioxazafen 

in toxicity Category IV for acute oral, dermal, inhalation, and eye and skin irritation. 

Tioxazafen is not a dermal sensitizer.] 

 2. Genotoxicty. [Tioxazafen was not genotoxic in a battery of assays. It was 

negative for inducing mutations in bacterial and mammalian cell assays. No clastogenic 

effect was observed in vitro human lymphocytes or in vivo mouse bone marrow 

micronucleus.] 

 3. Reproductive and developmental toxicity. [The reproductive and developmental 

toxicity of tioxazafen was investigated in a two-generation rat reproduction study and in 

rat and rabbit developmental toxicity studies. In the reproduction study, the reproductive 

and developmental no-observed-adverse-effect level (NOAEL) was the highest dose 

tested (HDT), 60 mg/kg bw/day, based on no effects on reproduction or pup growth and 

development. The parental systemic NOAEL was 60 mg/kg bw/day (HDT) for females 

and 20 mg/kg bw/day for males, based on lower body weight gains, body weights, food 

consumption, or food efficiency in the 60 mg/kg bw/day males. !!

In the rat developmental toxicity study, the maternal NOAEL was 10 mg/kg bw/day, 

based on lower food consumption that resulted in mean body weight losses or reduced 

body weight gains at 50 and 200 mg/kg bw/day. No evidence of developmental toxicity 

was observed in the rat up to the HDT of 200 mg/kg bw/day. 

In the rabbit teratology study, the maternal NOAEL was 5 mg/kg bw/day, based on lower 

mean body weight gains, food consumption, and food efficiency with the corresponding 

clinical finding of decreased defecation at dose levels greater than, or equal to, 20 mg/kg 

bw/day. The developmental NOAEL was 100 mg/kg bw/day (HDT), based on the 

absence of effects on intrauterine growth, survival, and fetal morphology.] 

 4. Subchronic toxicity. [The adrenal gland and bone were the primary target 

organs in subchronic toxicity studies in rats, whereas the liver was the primary target 

organ in mice. No target organs were identified in dogs, where toxicity was manifested 

primarily through clinical signs and decreased body weight. The lowest NOAEL in 90-

day subchronic oral toxicity studies was approximately 16 mg/kg bw/day in the rat. 

In the 28-day repeat dose dermal toxicity study, the NOAEL was 100 mg/kg bw/day, 

based on lower mean cumulative body weight gains in the 300 and 1000 mg/kg bw/day 

males and females, and adrenal cortical cytoplasmic vacuolation in the ≥300 mg/kg 

bw/day males. 

In a 13-week rat inhalation toxicity study, the lowest no-observed-adverse-effect 

concentration (NOAEC) of MON 102100 was 15 mg/m3

, based on adrenal cortical 

vacuolation, with or without adrenal cortical atrophy, in the 50 mg/m3 and 275 mg/m3 

males. 
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 No evidence of a direct or specific effect on the nervous system was observed in the 

acute and subchronic neurotoxicity studies conducted in the rat. Although a NOAEL was 

not determined in the acute neurotoxicity study, a decrease in motor activity at the time of 

peak effect was noted at ≥250 mg/kg/day. The NOAEL for the subchronic study was the 

HDT, 1000 ppm (equivalent to 67 mg/kg bw/day and 75 mg/kg bw/day for males and 

females, respectively).] 

 5. Chronic toxicity. [In the two-year oral toxicity and carcinogenicity study in the 

rat, no clinical findings resulted from exposure to tioxazafen. Additionally, no test 

substance-related effects on survival, incidence of palpable masses, hematology and 

coagulation parameters, ophthalmic findings, macroscopic findings, microscopically 

noted tumors, or organ weights were noted. The NOAEL was 75 ppm (3.9 mg/kg 

bw/day) in males and 250 ppm (16.0 mg/kg bw/day) in females, based on mean 

cumulative body weight gain differences of 10% or more in the 250 and 750 ppm males 

and 750 ppm females during the early phases of the study. No oncogenic findings were 

observed at any dose level in the rat. 

In the 18-month oral toxicity and carcinogenicity study in the mouse, there were no test 

substance-related effects on body weights, food consumption, food efficiency, incidence 

of palpable masses, or macroscopic findings. There was a statistically significant 

decreased trend in survival of females, indicating a possible test substance-related effect 

on survival in the high dose. Based on clinical signs and hepatocellular damage, the 

lowest-observed-adverse-effect levels (LOAELs) were 750 ppm (120 mg/kg bw/day) and 

250 ppm (50 mg/kg bw/day), for males and females, respectively, and the NOAEL were 

250 ppm (41 mg/kg bw/day) and 50 ppm (10 mg/kg bw/day), for males and females, 

respectively.

Chronic administration of tioxazafen at cytotoxic doses is associated with a marginal 

increase in hepatocellular carcinomas in male mice and hepatocellular adenomas in 

female mice at the highest doses tested. Additional data demonstrated that the mouse 

liver tumors were caused by a non-genotoxic, cytotoxic mode of action at doses above 

the maximum tolerated dose. Therefore, no onocogenic effects that are relevant to 

humans were observed in the mouse.] 

 6. Animal metabolism. [Metabolism studies were conducted in rats, lactating goats 

and laying hens to determine metabolism pathways and the nature of tioxazafen residues 

in animals. The metabolism of two radiolabeled forms of the parent molecule, 

[phenyl-U-14C] tioxazafen and [thiophene-2-14C] tioxazafen, was investigated in each 

species. In rats, tioxazafen is rapidly and almost completely absorbed (>88% in a bile 

cannulation experiment) following administration by oral gavage. Tioxazafen is 

extensively metabolized and the metabolites are readily eliminated, primarily in the feces 

via biliary excretion, with little retention in tissues. No unchanged parent is observed in 

excreta. Tioxazafen is also extensively metabolized in goats and hens to metabolites that 

are readily excreted with very little or no unchanged parent observed in excreta and 

minimal accumulation in edible tissues, milk or eggs. The primary pathways of 

metabolism of tioxazafen were consistent across the three species. Major pathways were 

1) reductive opening (N-O bond reduction) and hydrolytic cleavage of the oxadiazole 
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ring affording benzamidine and 2-thiophenecarboxylic acid, and 2) hydroxylation of the 

thiophene ring and conjugation as the glucuronide or sulfate. Benzamidine was a 

principal residue in livestock edible tissues, milk and eggs. The glycine conjugate of 2-

thiophenecarboxylic acid, 2-thenoylglycine, was a significant residue in goat milk and 

kidney. Sulfate and glucuronic acid conjugates of hydroxylated tioxazafen were 

significant residues only in milk. Only in fat, however at low levels, was unchanged 

tioxazafen observed as a significant residue.] 

 7. Metabolite toxicology. [Metabolism of tioxazafen in plants and animals 

proceeds through a number of competing pathways. The primary pathways of 

metabolism (oxadiazole ring cleavage and thiophene ring hydroxylation and conjugation) 

are observed in crops, livestock and the rat. The most significant metabolites identified 

in crops and livestock are also observed as metabolites in the rat. Benzamidine is 

consistently observed in crop and poultry matrices, and is a major metabolite in 

ruminants. In the rat metabolism study, benzamidine was the major excreted metabolite 

and was present in both urine and feces. In rat urine, benzamidine constituted up to 13% 

of the administered dose. The glucuronic acid conjugate of hydroxylated tioxazafen, 

analogous to the glucuronic acid and sulfate conjugates in goat milk, was the major 

metabolite excreted in rat bile (up to 27% of the administered dose) and also was present 

in rat urine (up to 5% of administered dose). The goat milk and kidney metabolite, 

2-thenoylglycine was a significant rat metabolite and was excreted in the urine in 

amounts up to 6% of the administered dose. Thus, systemic exposure to the principal 

crop and livestock metabolites, benzamidine, 2-thenoylglycine and the conjugates of 

hydroxylated tioxazafen was significant in the rodent toxicology studies of tioxazafen.] 

 8. Endocrine disruption. [Tioxazafen does not belong to a class of chemicals 

known for having adverse effects on the endocrine system. There were no significant 

findings in other relevant toxicity studies (subchronic, chronic, reproductive or 

developmental toxicity studies) that would suggest that tioxazafen produces any 

endocrine disruption.] 

C. Aggregate Exposure 

 1. Dietary exposure. [Based on the results of crop field trials, animal transfer 

studies, and exposure analysis, Monsanto is proposing a tolerance expression of parent 

tioxazafen plus its metabolite, benzamidine (expressed as tioxazafen equivalents).] 

i. Food. [Acute Dietary Exposure Assessment 

Acute dietary exposure estimates are well within acceptable limits for all population 

subgroups. Exposure estimates from the proposed uses of tioxazafen as a seed treatment 

on corn, soybean, and cotton seed were based on the proposed tolerances for the 

combined residues of tioxazafen plus its metabolite, benzamidine. The acute module of 

the Dietary Exposure Evaluation Model software with the Food Commodity Intake 

Database (DEEM-FCIDTM, version 3.16, 03-08-d) was used to conduct the assessment 

with the acute Population Adjusted Dose (aPAD) of 0.05 mg/kg bw/day for females 13-

49 in age and the aPAD of 0.8 mg/kg/day for all other population groups. This model 
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incorporates nation-wide food consumption data as reported by respondents in the US 

Department of Agriculture (USDA) 2003-2008 two-day National Health and Nutrition 

Examination Survey (NHANES). Food translations (i.e., between surveyed “as 

consumed” foods and EPA-defined food commodities) are based on the EPA/USDA 

FCID recipe set as of February 2012. Food residues associated with the proposed uses of 

tioxazafen on corn, cotton, and soybean were set at tolerance levels adjusted with 

processing factors where applicable. The percentage of crop treated was assumed to be 

100% for all crops. Acute dietary modeling results for the general population and for the 

most highly exposed subpopulations are summarized in Table 1. 

Table 1. Acute Dietary Analysis of Tioxazafen + Benzamidine (Food Only) 

Population Subgroup 

Acute Dietary 

Food Only (95 percentile) 

Exposure 

(mg/kg/day) 

% of aPAD 

General population 0.000333 0.04 

Non-nursing infants 0.000761 0.10 

Children 1-2 years 0.001087 0.14 

Females 13-49 0.000167 0.33 

Chronic Dietary Exposure Assessment 

Chronic dietary exposure estimates are well within acceptable limits for all population 

subgroups. Exposure estimates from the proposed uses of tioxazafen as a seed treatment 

on corn, soybean, and cotton seed were based on the proposed tolerances for the 

combined residues of tioxazafen plus its metabolite, benzamidine. The chronic module 

of the Dietary Exposure Evaluation Model software with the Food Commodity Intake 

Database (DEEM-FCID version 3.16, 03-08-d) was used to conduct the assessment with 

the chronic Population Adjusted Dose (cPAD) of 0.04 mg/kg bw/day for all population 

groups. This model incorporates nationwide food consumption data as reported by 

respondents in the U.S. Department of Agriculture (USDA) 2003-2008 two-day National 

Health and Nutrition Examination Survey (NHANES). Food translations (i.e., between 

surveyed “as consumed” foods and EPA-defined food commodities) are based on the 

EPA/USDA FCID recipe set as of February 2012. Food residues associated with the 

proposed uses of tioxazafen on corn, cotton, and soybean were set at tolerance levels 

adjusted with processing factors where applicable. The percentage of crop treated was 

assumed to be 100% for all crops. Chronic dietary modeling results for the general 

population and for the most highly exposed subpopulations are summarized in Table 2. 

Table 2. Chronic Dietary Analysis of Tioxazafen + Benzamidine (Food Only) 
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Population Subgroup 

Chronic Dietary 

Food Only 

Exposure 

(mg/kg/day) 

% of cPAD 

General population 0.000101 0.3 

Non-nursing infants 0.000226 0.6 

Children 1-2 years 0.000516 1.3 

Females 13-49 0.000065 0.2 

] 

ii. Drinking water. 

[All proposed uses of tioxazafen were evaluated at maximum application rates using the 

SWCC v.1.106, PRZM-GW v.1.07, and SCI-GROW v.2.3 to estimate surface water and 

groundwater concentrations of tioxazafen. The highest acute Estimated Drinking Water 

Concentration (EDWC) was 0.283 ppb, and the highest chronic EDWC was 0.013 ppb. 

These EDWCs do not contribute significantly to the total dietary exposure estimates 

(food and water) presented below. 

Acute Aggregate Exposure Assessment: Food and Water 

Acute aggregate (food and water) dietary exposure was evaluated using the DEEM-FCID 

as described above (tolerance-level food residues, processing factors, and 100% of crop 

treated) and with the inclusion of the acute EDWC of 0.283 ppb. The acute dietary 

exposure of the US population to tioxazafen and benzamidine from cotton, corn, and 

soybean application utilizes <1% of the aPAD for the overall U.S. population. No 

population subgroup had an exposure that utilized more than 1% of the aPAD. Based on 

these results, there is reasonable certainty that no acute effects would result from dietary 

exposure to tioxazafen. Acute dietary modeling results for the general population and for 

the most highly exposed subpopulations are summarized in Table 3. 

 
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Table 3. Acute Dietary Analysis of Tioxazafen and Benzamidine (Food and Water)

Population Subgroup 

Acute Dietary 

Food and Water (95 percentile) 

Exposure 

(mg/kg/day) 

% of aPAD 

General population 0.000340 0.04 

Non-nursing infants 0.000768 0.10 

Children 1-2 years 0.001094 0.14 

Females 13-49 0.000175 0.35 

Chronic Aggregate Exposure Assessment: Food and Water 

Chronic aggregate (food and water) dietary exposure was evaluated using the DEEMFCID as described above (tolerance-level food residues, processing factors, and 100% of 

crop treated) and with the inclusion of the chronic EDWC of 0.013 ppb. The chronic 

dietary exposure of the US population to tioxazafen and benzamidine from cotton, corn, 

and soybean application utilizes <1% of the cPAD for the overall U.S. population. No 

population subgroup had an exposure that utilized more than 2% of the cPAD. Based on 

these results, there is reasonable certainty that no chronic effects would result from 

dietary exposure to tioxazafen and benzamidine. Chronic dietary modeling results for the 

general population and for the most highly exposed subpopulations are summarized in 

Table 4. 

Table 4. Chronic Dietary Risk (DEEMTM) Analyses of Tioxazafen 

Population Subgroup 

Chronic Dietary 

Food and Water 

Exposure 

(mg/kg/day) 

% of cPAD 

General population 0.000101 0.3 

Non-nursing infants 0.000227 0.6 

Children 1-2 years 0.000516 1.3 

Females 13-49 0.000066 0.2 

] 

 2. Non-dietary exposure. [There are no current or proposed residential uses for 
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tioxazafen. Therefore, a residential exposure and risk evaluation was not conducted.] 

D. Cumulative Effects

 ["Section 408(b){2){D){v) of the Federal Food, Drug, and Cosmetic Act 

(FFDCA) requires that, when considering whether to 

establish, modify, or revoke a tolerance, the Agency consider "available information" 

concerning the cumulative effects of a particular pesticide's residues and "other 

substances that have a common mechanism of toxicity." Unlike other pesticides for 

which EPA has followed a cumulative risk approach based on a common mechanism of 

toxicity, EPA has not made a common mechanism of toxicity finding for tioxazafen. For 

the purposes of this tolerance action, therefore, Monsanto has not assumed that tioxazafen 

has a common mechanism of toxicity with other substances.] 

E. Safety Determination

 1. U.S. population. [Based on this risk assessment, Monsanto concludes that there 

is a reasonable certainty that no harm will result to the general population from the 

aggregate exposure to tioxazafen from the proposed uses.] 

 2. Infants and children. [Based on this risk assessment, Monsanto concludes that 

there is a reasonable certainty that no harm will result to infants or children from the 

aggregate exposure to tioxazafen from the proposed uses.] 

F. International Tolerances

[No CODEX or European Union (EU) Maximum Residue Levels (MRL) have 

been established for tioxazafen in any agricultural commodity. Tioxazafen is submitted 

for registration as a joint review between Canada PMRA and US EPA, and thus any 

MRL based on tioxazafen should coincide between the two countries.]