UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION 

MEMORANDUM 

May 22,2014 

SUBJECT: Pyroxasulfone Human Health Risk Assessment for the Amended Section 3 Use 

of Pyroxasulfone on Corn. 

DP Barcode: 417424 

Registration No.: 63588-91, -92, -93 

Regulatory Action: Section 3 Registration 

PC Code: 090099 

Decision No.: 482174 

Petition No.: 3F8196 

Risk Assessment Type: Single Chemical Aggregate Case No.: NA 

TXR.No.: NA 

MRIDNo.: NA 

CAS No.: 447399-55-5 

40 CFR: 1 .659 

FROM: 

_,4// ~ Thurston G. Morton, Chemist ~, . 

James S. Miller, Environmental Scien · 

Abdallah Khasawinah, PhD., Toxicologist /D 

Risk Assessment Branch 4 (RAB IV) · 

Health Effects Division (7509P) 

THROUGH: Elissa Reaves, PhD, Chief ~~ <;;;;;;:. 

Risk Assessment Branch 4 

Health Effects Division (7509P) 

TO: Bethany Benbow 

Herbicide Branch 

Registration Division (7505P) 

This document provides the revised Health Effects Division's (HED's) risk assessment of the 

amended Section 3 use of pyroxasulfone on com. The registrant is currently requesting to 

amend the com use pattern to include the addition of adjuvants to the products. The additional 

com field trials conducted with the addition of adjuvants resulted in a need for increased 

tolerances from those established. 

Page 1 of81 
1.0 EXECU.TI.VE SUMMARY ................................................................................................ 5 

2.0 HED RECOMME.NDATIONS .......................................................................................... 7 

2.1 Data Deficiencies/Conditions of Registration ..................................•............................. 7 

2.2 Tolerance Considerations .................................................................•.............•............... 7 

2.2.1 Enforcement Analytical Method ............................................................................. 7 

2.2.2 International Harmonization ..................................................•...........•.................... 8 

2.2.3 Recommended Tolerances ........................................................................................ 8 

2.2.4 Revisions to Petitioned-For Tolerances .................................................................. 8 

2.3 Label Recommendations ................................................................................................. 9 

3.0 INGREDIENT PROFILE .................................................................................................. 9 

3.1 Chemical Identity ............................................................................................................ 9 

3.2 Physical/Chemical Characteristics ............................................................................... 11 

3.3 Pesticide Use Pattern ..................................................................................................... 11 

3.3.1 Registered Products ................................................................................................ 11 

3.3.2 Proposed New Uses ................................................................................................. 11 

3.4 Anticipated Exposure Pathways ................................................................................... 12 

3.5 Considerations of Environmental J ustice .................................................................... 13 

4.0 HAZARD CHARACTERIZATION/ASSESSMENT ................................................... 13 

4.1 Toxicology Studies Available for Analysis .................................................................. 13 

4.2 Absorption, Distribution, Metabolism and Excretion .....................•.......................... 13 

4.3 Toxicologic.al Effe·cts ...................................................................................................... 14 

4.4 Safety Factor for Infants and Children (FQP A Safety Factor) ......•.......................... 15 

4.4.1 Completeness of the Toxicology Database .................................•.......................... 15 

4.4.2 Evidence of Neurotoxicity ...................................................................................... 16 

4.4.3 Evidence of Sensitivity/Susceptibility in the Developing or Young Animal ...... 16 

4.4.4 Residual Uncertainty in the Exposure Database .................................................. 17 

4.5 Toxicity Endpoint and Point of Departure .................................................................. 17 

4.5.1 Dose-Response Assessment .................................................................................... 17 

4.5.2 Recommendations for Combining Exposure Routes .................•......................... 19 

4.5.3 Classification of Carcinogenic Potential ............................................................... 19 

Page 2 of 81 
Page 3 of 81

4.5.4 Summary of Points of Departure Used in Risk Assessment ............................... 19

5.0 DIETARY AND DRINKING WATER EXPOSURE AND RISK ASSESSMENT.... 21

5.1 Metabolite/Degradate Residue Profile......................................................................... 21

5.1.1 Summary of Plant and Livestock Metabolism Studies........................................ 21

5.1.2 Comparison of Metabolic Pathways...................................................................... 22

5.1.3 Environmental Fate and Transport ...................................................................... 22

5.1.4 Residues of Concern Summary and Rationale..................................................... 23

5.2 Food Residue Profile ..................................................................................................... 24

5.2.1 Residues in Crops.................................................................................................... 24

5.3 Water Residue Profile ................................................................................................... 24

5.3.1 Estimated Drinking Water Concentrations.......................................................... 24

5.4.1 Acute Dietary and Drinking Water Analysis ....................................................... 25

5.4.2 Chronic Dietary and Drinking Water Analysis ................................................... 26

6.0 RESIDENTIAL EXPOSURE AND RISK ASSESSMENT .......................................... 26

6.1 Residential Bystander Post-application Inhalation Exposure................................... 26

6.2 Spray Drift...................................................................................................................... 26

7.0 AGGREGATE EXPOSURE AND RISK ASSESSMENT............................................ 27

7.1 Acute & Chronic Aggregate Risk................................................................................. 27

8.0 CUMULATIVE RISK...................................................................................................... 27

9.0 OCCUPATIONAL EXPOSURE/RISK CHARACTERIZATION.............................. 28

9.1 Exposure Scenarios....................................................................................................... 28

9.2 Handler Exposure.......................................................................................................... 28

9.2.1 Handler Exposure Scenarios.................................................................................. 28

9.2.2 Handler Exposure Data.......................................................................................... 29

9.2.3 Handler Exposure Assumptions............................................................................ 29

9.2.4 Handler Exposure and Risk Estimates................................................................. 29

9.3 Post Application Exposure............................................................................................ 31

9.3.1 Post Application Exposure Scenarios ................................................................... 31

9.3.2 Post Application Exposure Assumptions.............................................................. 32

9.3.3 Post-Application Exposure and Risk Estimates................................................... 32

9.3.4 Restricted Entry Interval ....................................................................................... 32

9.3.5 Inhalation Post-application Risk.................................................................................. 33

10. REFERENCES.................................................................................................................. 33
Page 4 of 81

A TOXICOLOGY DATA SUMMARY.............................................................................. 34

A.1 Guideline Data Requirements................................................................................ 34

A.3 Toxicological Endpoints............................................................................................. 50

APPENDIX B. Chemical Names And Structures Of Metabolites......................................... 78

APPENDIX C. Physical/Chemical Properties.......................................................................... 81

APPENDIX D. Studies Reviewed for Ethical Conduct.......................................................... 81
Page 5 of 81

1.0 EXECUTIVE SUMMARY

This assessment provides information to support an amended Section 3 registration for the use of 

the active ingredient, pyroxasulfone on corn. This document addresses the exposures and 

estimated risk associated with the proposed amended use of pyroxasulfone. It provides an 

assessment of proposed tolerances (pesticide residue limits in food) to ensure that they meet the 

safety standard established by the Food Quality Protection Act (FQPA) of 1996. 

Use Profile

Pyroxasulfone (3-[5-(difluoromethoxy)-1-methyl-3-(trifluoromethyl)pyrazol-4-yl 

methylsulfonyl]-4,5-dihydro-5,5-dimethyl-1,2-oxazole) is a new herbicide belonging to a class of 

selective herbicides identified as pyrazole herbicides. It is used to control a broad spectrum of 

broadleaf weeds and grasses, including glyphosate-resistant varieties. Pyroxasulfone is thought 

to act as an inhibitor of very-long-chain fatty acid biosynthesis. Applications may be made using 

ground or aerial equipment. There are no pyroxasulfone products registered for homeowner use 

and there are no products registered for application to residential areas. Amended tolerances are

proposed for combined residues of pyroxasulfone and its major metabolites in/on corn. 

K-I Chemical, U.S.A. Inc. is requesting an amended Section 3 registration of two pyroxasulfone 

products; Pyroxasulfone 85 WG Herbicide, an 85% water-dispersible granule (WG) formulation 

(EPA Reg. No. 63588-92), and V-10233 Herbicide, a 42.5% WG formulation (EPA Reg. No. 

63588-93) for use on corn. The addition of adjuvants to the products is requested. 

Hazard Identification

The toxicology database for pyroxasulfone is adequate for evaluating and characterizing toxicity 

and selecting endpoints for purposes of this risk assessment. Pyroxasulfone acute toxicity to 

mammals is low by all routes of exposure. Subchronic and chronic oral studies in mice, rats and 

dogs produced a variety of effects including cardiac toxicity (increased cardiomyopathy), liver 

toxicity (centrilobular hepatocellular hypertrophy, histopathological and/or clinical pathological 

indicators), kidney toxicity (nephropathy), neurotoxicity (impaired hind limb function, ataxia, 

tremors, sciatic nerve lesions, axonal/myelin degeneration in the sciatic nerve and spinal cord 

sections), skeletal muscle myopathy, urinary bladder mucosal hyperplasia, and urinary bladder 

transitional cell papillomas. Minimal to mild cardiac myofiber degeneration and local 

inflammation were also seen in a rat dermal toxicity study. Neurotoxicity was also seen in a 

developmental neurotoxicity study in rats (decreased brain weight, decreased thickness of the 

hippocampus, corpus callosum and cerebellum in offspring). Dogs appear to be the most 

sensitive species to the neurotoxic effects of pyroxasulfone. Immunotoxicity studies in rats and 

mice show no evidence of immunotoxic effects from pyroxasulfone. There is evidence of fetal 

and offspring susceptibility in the developmental neurotoxicity study in rats as effects occurred 

in the absence of maternal toxicity. There is no concern for reproductive toxicity as offspring 
Page 6 of 81

effects occurred only at maternally toxic doses in the reproduction study. The FQPA safety 

factor was reduced to 1X because all the points of departure (POD) selected for risk assessment 

are protective of offspring effects seen in the developmental neurotoxicity study, the 

fetal/offspring effects occurred at high doses of administration, and a clear dose-response has 

been well defined with NOAELs and LOAELs for all effects of concern. Thus, there are no 

residual uncertainties with regard to pre-and/or postnatal toxicity. Pyroxasulfone is classified as 

“Not Likely to be Carcinogenic to Humans” at doses that do not cause crystals with subsequent 

calculi formation resulting in cellular damage of the urinary tract. The Agency has determined 

that the quantification of risk using a non-linear approach (i.e., RfD) will adequately account for 

all chronic toxicity, including carcinogenicity, that could result from exposure to pyroxasulfone. 

Dose Response Assessment

Toxicological points of departure (PODs) were selected for dietary/drinking water and 

occupational exposure scenarios for this assessment. Acute and chronic reference doses (RfDs) 

were selected for assessment of food and drinking water exposures. The population adjusted 

dose (PAD) is equivalent to the reference dose (RfD) divided by the additional FQPA Safety 

Factor, if applied. An acute RfD/PAD for all populations was selected from a developmental 

neurotoxicity study in rats based on neurotoxicity characterized by decreased brain weights and 

morphometric brain changes in offspring in the DNT study. A chronic RfD/PAD for all 

populations was selected from a chronic feeding study in dogs based on neurotoxic effects. A 

POD for short- and intermediate-term inhalation exposure was selected from subchronic and 

chronic oral toxicity studies in dogs based on neurotoxic effects. The POD for short-and 

intermediate-term dermal exposure was chosen from a 28 day dermal toxicity study in rats based 

on mild cardiac myofiber degeneration and local inflammation. 

The POD for short- and intermediate-term inhalation exposure was chosen from a 90-day oral 

dog study based on axonal/myelin degeneration in the sciatic nerve and minimal to mild subacute 

inflammation of skeletal muscle in males and females and impaired limb function. An 

uncertainty factor of 100x was applied to endpoints selected for all exposure routes (10x for 

interspecies extrapolation, 10x for intraspecies variation). 

Exposure/Risk Assessment and Risk Characterization

A dietary (food and water) exposure and risk assessment was conducted for corn. HED assessed 

occupational exposure and risk from uses of pyroxasulfone on soybean recently. The 

occupational exposure from the use of pyroxasulfone on corn will be covered from that 

assessment. Worker exposures were assessed for handler and post-application activities. 

Screening level acute and chronic dietary and drinking water risk assessments for pyroxasulfone 

show that dietary and drinking water exposure estimates for the amended corn use are below 

HED’s level of concern for the general population and all population subgroups. The highest 

acute dietary exposure risk is for All Infants <1 year resulting in 3.6% of the aPAD. While the 

highest chronic dietary exposure risk is for All Infants <1 year resulting in 48% of the cPAD. 

Occupational exposure and risk estimates indicate that worker handler and post-application 

exposures are not of concern at the maximum allowable application rates for the majority of 

scenarios. Exposure and risk estimates indicate that for most exposure scenarios non-cancer 
Page 7 of 81

risks are not of concern for occupational handler activities for the proposed new use (MOEs > 

100). However, risks of concern exist (MOE<100) for “Inhalation” exposure during mixing and 

loading activities for aerial applications. Risks of concern exist for the “mixing and loading” of 

a water dispersible granular for aerial applications (MOE = 71) with label specific PPE (longsleeved shirt and long pants, chemical resistant gloves and shoes and socks). However, with a 

PF5 respirator, risks are not of concern (MOE = 350). 

Use of Human Studies

This risk assessment relies in part on data from studies in which adult human subjects were 

intentionally exposed to a pesticide or other chemical. These studies, listed in Appendix D, have 

been determined to require a review of their ethical conduct. Some of these studies are also 

subject to review by the Human Studies Review Board. All of the studies used have received the 

appropriate review.

2.0 HED RECOMMENDATIONS

2.1 Data Deficiencies/Conditions of Registration 

HED recommends for the amended tolerances to support the proposed amended use of 

pyroxasulfone on corn commodities provided requirements in Section 2.1 are met. 

Deficiencies are stated below. The specific tolerance recommendations are discussed in Section 

2.2, and label modifications are discussed in Section 2.3.

Note to PM:

Analytical standards for metabolite M-28 are not currently available in the EPA National 

Pesticide Standards Repository. Analytical reference standards of pyroxasulfone and 

metabolites M-1, M-3, M-25, and M-28 must be supplied and supplies replenished as 

requested by the Repository. 

2.2 Tolerance Considerations

2.2.1 Enforcement Analytical Method

The petitioner has proposed high performance liquid chromatography/triple quadrupole mass 

spectrometry (LC/MS/MS) methods for the enforcement of tolerances for pyroxasulfone residues 

in/on crop commodities. The methods are adequate to determine residues of pyroxasulfone and 

metabolites M-1, M-3, and M-25 in corn commodities. The validated limit of quantitation 

(LOQ) is 0.01 ppm for parent, M-1, M-3 and M-25 in most corn commodities. Enforcement 

methods for milk commodities have an LOQ of 0.001 ppm for parent, M-1, and M-3. 
Page 8 of 81

2.2.2 International Harmonization

There are no Codex MRLs established for residues of pyroxasulfone in any corn commodities. 

International harmonization is not an issue at this time.

2.2.3 Recommended Tolerances

HED has examined the residue chemistry database for pyroxasulfone. Pending submission of 

analytical reference standards (see requirements under Submittal of Analytical Reference 

Standards), there are no residue chemistry issues that would preclude granting an amended

Section 3 registration for the requested use of pyroxasulfone, or establishment of tolerances for 

residues of pyroxasulfone as follow:

Tolerances are established for residues of the herbicide pyroxasulfone, including its 

metabolites and degradates, in or on the commodities in the table below. Compliance 

with the tolerance levels specified below is to be determined by measuring only the sum 

of pyroxasulfone [3-[[[5-(difluoromethoxy)-1-methyl-3-(trifluoromethyl)-1H-pyrazol-4-

yl]methyl]sulfonyl]-4,5-dihydro-5,5-dimethylisoxazole] and its metabolites [5-

(difluoromethoxy)-1-methyl-3-(trifluoromethyl)-1H-pyrazol-4-yl]methanesulfonic acid 

(M-1), 5-(difluoromethoxy)-1-methyl-3-(trifluoromethyl)-1H-pyrazol-4-carboxylic acid 

(M-3), and [5-(difluoromethoxy)-3-(trifluoromethyl)-1H-pyrazol-4-yl]methanesulfonic 

acid (M-25), calculated as the stoichiometric equivalent of pyroxasulfone, in or on the 

commodity.

Corn, field, forage .......................................................................... 0.09 ppm

Tolerances are established for residues of the herbicide pyroxasulfone, including its 

metabolites and degradates, in or on the commodities in the table below. Compliance 

with the tolerance levels specified below is to be determined by measuring only the sum 

of pyroxasulfone [3-[[[5-(difluoromethoxy)-1-methyl-3-(trifluoromethyl)-1H-pyrazol-4-

yl]methyl]sulfonyl]-4,5-dihydro-5,5-dimethylisoxazole] and its metabolite [5-

(difluoromethoxy)-1-methyl-3-(trifluoromethyl)-1H-pyrazol-4-carboxylic acid (M-3) 

calculated as the stoichiometric equivalent of pyroxasulfone, in or on the commodity.

Corn, field, grain ............................................................................ 0.02 ppm

2.2.4 Revisions to Petitioned-For Tolerances

K-I Chemical proposed that tolerances for pyroxasulfone residues of concern in crop 

commodities be expressed in terms of combined residues of pyroxasulfone and its major 

metabolites M-1, M-3, and M-25, calculated as pyroxasulfone. K-I Chemical proposed 

tolerances for pyroxasulfone on corn commodities. HED has no revisions to the tolerances 

submitted by K-I Chemical for corn are listed in Table 2.2.4.
Page 9 of 81

Table 2.2.4. Tolerance Summary for Pyroxasulfone for Wheat and Cotton.

Commodity Proposed Tolerance 

(ppm)

HED 

Recommended 

Tolerance (ppm)*

Comments; Correct Commodity 

Definition

Corn, field, forage 0.09 0.09

Corn, field, grain 0.02 0.02

2.3 Label Recommendations

The following label revisions must be provided prior to the tolerance being amended.

 Risks of concern exist for the “mixing and loading” of a water dispersible granular for 

aerial applications, therefore, the PPE for this scenario must require a PF5 respirator.

3.0 INGREDIENT PROFILE 

3.1 Chemical Identity

Structure and nomenclature are reported in Table 3.1.
Page 10 of 81

Table 3.1. Pyroxasulfone Nomenclature.

Chemical structure

Common name Pyroxasulfone

Company experimental name KIH-485; AE 2196191

IUPAC name 3-[5-(difluoromethoxy)-1-methyl-3-(trifluoromethyl)pyrazol-4-ylmethylsulfonyl]-

4,5-dihydro-5,5-dimethyl-1,2-oxazole

CAS name 3-[[[5-(difluoromethoxy)-1-methyl-3-(trifluoromethyl)-1H-pyrazol-4-

yl]methyl]sulfonyl]-4,5-dihydro-5,5-dimethylisoxazole

CAS registry number 447399-55-5

End-use product (EP) Pyroxasulfone 85 WG Herbicide (85% WG; EPA File Symbol 63588-OE)

V-10233 Herbicide (42.5% WG; EPA File Symbol 63588-OG)

Chemical structure of M-1 

metabolite

[5-(difluoromethoxy)-l-methyl-3-(trifluoromethyl)-lH-pyrazol-4-

yl)]methanesulfonic acid

Chemical structure of M-3 

metabolite

5-(difluoromethoxy)-l-methyl-3-(trifluoromethyl)-lH-pyrazole-4-carboxylic acid

Chemical structure of M-25 

metabolite

[5-(difluoromethoxy)-3-(trifluoromethyl)-1H-pyrazol-4-yl)]methanesulfonic acid
Page 11 of 81

3.2 Physical/Chemical Characteristics 

A detailed description of the physicochemical properties of pyroxasulfone is provided in 

Appendix C. Pyroxasulfone exhibits relatively low solubility in water and higher solubility in 

organic solvents. It has a very low vapor pressure. Pyroxasulfone is mobile and persistent in 

terrestrial and aquatic environments. Pyroxasulfone does not present significant concerns for 

bioaccumulation based on the lipophilicity of the compound. 

3.3 Pesticide Use Pattern

3.3.1 Registered Products

Pyroxasulfone is an herbicide belonging to a new class of selective herbicides identified as 

pyrazole herbicides. Currently, Pyroxasulfone 85 WG Herbicide, an 85% water-dispersible 

granule (WG) formulation, and V-10233 Herbicide, a 42.5% WG formulation are currently 

registered on field corn, sweet corn, and pop corn without the addition of adjuvants. The 

registrant is currently requesting to amend the corn use pattern to include the addition of 

adjuvants to the products. Product registrations and proposed use patterns and formulations are 

provided in Table 3.

3.3.2 Proposed New Uses 
Page 12 of 81

Table 3.3.2. Summary of Directions for Use of Pyroxasulfone.1

Applic. Timing, 

Type, and Equip.

Formulation

[EPA File 

Symbol]

Applic. Rate 

(lb ai/A)

Max. No. 

Applic. per 

Season

Max. Seasonal 

Applic. Rate

(lb ai/A)

PHI

(days)

Use Directions and 

Limitations

Corn (Field, Pop, Sweet, and Seed)

Fall application

Broadcast

Ground

85% WG

[63588-92]

C: NA

M: 0.11-0.15

MF: 0.15-0.19

F: 0.19-0.21

NS

0.267 37 (sweet 

corn ears)

Application may be 

made in the fall to 

minimum or no tillage 

fields to be planted to 

corn the following 

spring. 

Preplant

Broadcast 

surface or 

incorporated

Ground

85% WG

[63588-92]

C: 0.08-0.11

M: 0.11-0.15

MF: 0.15-0.19

F: 0.19-0.21

NS

Surface application 

may be made up to 45 

days prior to planting, 

and soil incorporated 

application may be 

made up to 14 days 

prior to planting.

Preemergence

Broadcast

Ground

85% WG

[63588-92]

C: 0.08-0.11

M: 0.11-0.15

MF: 0.15-0.19

F: 0.19-0.21

NS

Early 

postemergence

Broadcast

Ground

85% WG

[63588-92]

C: 0.08-0.11

M: 0.11-0.15

MF: 0.15-0.19

F: 0.19-0.21

NS

Application may be 

made up to V4 stage 

(visible 4th leaf collar). 

A 7-day pregrazing 

interval (PGI) is 

proposed for corn or 

corn forage.

Corn (Field)

Fall application

Broadcast

Ground or aerial

42.5% WG

[63588-193] 0.08-0.12 NS

NS NS

Application may be 

made in the fall to 

minimum or no tillage 

fields to be planted to 

corn the following 

spring. 

Preplant

Broadcast 

Ground or aerial

42.5% WG

[63588-193] 0.08-0.12 NS

Corn must be planted 

within 7-30 days after 

application.

3.4 Anticipated Exposure Pathways

Dietary (food and water) and occupational exposures via dermal and inhalation pathways are 

expected based on proposed use of pyroxasulfone on corn. A dietary (food and water) exposure 

and risk assessment was conducted for the requested amended corn use. HED previously 

assessed occupational exposure and risk from the use of pyroxasulfone on soybean commodities

which will cover the exposures from the use of pyroxasulfone on the amended corn use. Worker 

exposures were assessed for handler and post-application activities. There are no residential uses 
Page 13 of 81

for pyroxasulfone so residential exposure to children via incidental oral activities is not 

anticipated.

3.5 Considerations of Environmental Justice

Potential areas of environmental justice concerns, to the extent possible, were considered in this 

human health risk assessment, in accordance with U.S. Executive Order 12898, “Federal Actions 

to Address Environmental Justice in Minority Populations and Low-Income Populations,” 

http://www.eh.doe.gov/oepa/guidance/justice/eo12898.pdf.

As a part of every pesticide risk assessment, OPP considers a large variety of consumer 

subgroups according to well-established procedures. In line with OPP policy, HED estimates 

risks to population subgroups from pesticide exposures that are based on patterns of that 

subgroup’s food and water consumption, and activities in and around the home that involve

pesticide use in a residential setting. Extensive data on food consumption patterns are compiled 

by the USDA under the Continuing Survey of Food Intake by Individuals (CSFII) and are used 

in pesticide risk assessments for all registered food uses of a pesticide. These data are analyzed 

and categorized by subgroups based on age, season of the year, ethnic group, and region of the 

country. Additionally, OPP is able to assess dietary exposure to smaller, specialized subgroups 

and exposure assessments are performed when conditions or circumstances warrant. Whenever 

appropriate, nondietary exposures based on home use of pesticide products and associated risks 

for adult applicators and for toddlers, youths, and adults entering or playing on treated areas 

post-application are evaluated. Further considerations are currently in development as OPP has 

committed resources and expertise to the development of specialized software and models that 

consider exposure to bystanders and farm workers as well as lifestyle and traditional dietary 

patterns among specific subgroups.

4.0 HAZARD CHARACTERIZATION/ASSESSMENT

4.1 Toxicology Studies Available for Analysis

The studies available for consideration of pyroxasulfone toxicity provide a comprehensive and 

complete database. All toxicity studies required in accordance with the new 40 CFR Part 158 

data requirements have been submitted. 

4.2 Absorption, Distribution, Metabolism and Excretion

Pyroxasulfone was shown to be quickly absorbed and excreted after oral administration to rats 

with the half-life ranging from 15 – 173 hours; the longer half life corresponded to a high orally 

administered dose (700 mg/kg). At lower administered oral doses (10 mg/kg) absorption was 

fast (tmax of 1.1-7 hours with 77-88 % absorption) while at a higher dose (700 mg/kg) absorption 

was slower (tmax 7.0-17.3 hours, with 22-26% absorption). The main excretory routes were the 

urine and feces. Biliary excretion was demonstrated. Following absorption pyroxasulfone was 

widely distributed, with high concentrations observed in the bladder, prostate, adrenals, kidney, 

liver, abdominal fat, uterus, and blood. 
Page 14 of 81

There was no significant sex difference in the metabolism of pyroxasulfone. There appeared to 

be saturation or induction of metabolism at the high dose, which resulted in an altered metabolic 

profile. The absorbed pyroxasulfone was extensively metabolized to a number of compounds. 

The major metabolite in the urine of rats dosed with [Py14C]- pyroxasulfone was M-13, 

accounting for up to 26% of the dose at the low dose and up to 4% at the high dose. M-7 and M3 were the next most abundant metabolites. Most of the metabolites in urine were produced by 

the cleavage between the pyrazole and isoxazoline ring structure. There were three major 

metabolites in urine in rats dosed with [Ix14C]- pyroxasulfone; M-13 accounting for up to 20% 

of the dose, M-16 accounting for up to 19% of the dose and M-26 accounting for up to 6.4% of 

the dose. A major portion of the radioactivity was highly polar and multi-component, containing 

5-methyl-5-isoxazoline carboxylic acid and M-30, and accounted for up to 34% of the dose.

A dermal absorption study with pyroxasulfone is not available. A dermal absorption factor can

be derived by comparing the toxicity endpoints from a dermal toxicity study and an oral toxicity 

study of comparative durations. In one 28-day oral toxicity study in rats (MRID 47889320), the 

LOAEL was 1000 ppm (75.4/84.4 mg/kg/day for M/F) based on myocardial 

degeneration/necrosis and the NOAEL is 100 ppm (7.3/8.3 mg/kg/day for M/F). In the 28-day 

dermal toxicity study, the LOAEL was 1000 mg/kg/day based on minimal to mild cardiac 

myofiber degeneration with inflammation in males and females and the NOAEL was 100 

mg/kg/day. By comparing the LOAELs from both studies a dermal absorption factor of 7.5% is 

derived.

4.3 Toxicological Effects

The toxicology database for pyroxasulfone is adequate for evaluating and characterizing 

pyroxasulfone toxicity and selecting endpoints for purposes of this risk assessment. Subchronic 

and chronic toxicity testing of pyroxasulfone technical in mice, rats and dogs produced a variety 

of adverse effects in several target organs, but the most sensitive effect is neurotoxicity in dogs. 

Effects seen in animal studies ranged from cardiac toxicity (increased cardiomyopathy in mice 

and rats), liver toxicity (centrilobular hepatocellular hypertrophy, histopathological and/or 

clinical pathological indicators), neurotoxicity characterized by axonal/myelin degeneration in 

the sciatic nerve (dog, mouse and rat) and spinal cord sections (dog), skeletal muscle myopathy, 

kidney toxicity (increased incidence of chronic progressive nephropathy in dogs and retrograde 

nephropathy in mice), urinary bladder mucosal hyperplasia, inflammation, and urinary bladder 

transitional cell papillomas (rats). Decreased body weight, enzyme changes were noted in some 

studies. Toxic adverse effects (impaired hind limb function, ataxia, hind limb twitching and 

tremors; increased creatine kinase, aspartate aminotransferase; axonal/myelin degeneration of the 

sciatic nerve and spinal cord sections) in dogs occurred at ≥10 mg/kg/day doses while in the 

mouse toxic adverse effects (degeneration of sciatic and trigeminal nerve axons and their 

associated myelin sheaths and chronic progressive nephropathy, renal tubular adenomas) 

occurred at higher doses (131 mg/kg/day and above). 

Comparing effects by route of administration, pyroxasulfone was moderately toxic to rats 

following a 4-week dermal exposure producing local inflammation and systemic effects of 
Page 15 of 81

minimal to mild cardiac myofiber degeneration at the limit dose of 1000 mg/kg/day with a 

NOAEL of 100 mg/kg/day. No adverse effects were noted in an inhalation study following 

exposure for 28 days at 200 mg/m3/day (equivalent to 52.2 mg/kg/day oral dose), the highest 

dose tested of an aerosol dust. 

In cancer studies in mice and rats, renal tubular adenomas were observed in male mice at a 

dietary dose of 0.6 and 255 mg/kg/day (but not at an intermediate dose of 18 mg/kg/day) and 

urinary bladder transitional cell papillomas were observed in male rats at 42 and 84 mg/kg/day. 

The CARC met in May, 2011 to consider studies submitted by the registrant to support a mode 

of action for bladder tumors and a re-evaluation of the kidney tumors conducted by an external 

Pathology Working Group (PWG). Based on the evidence provided by the PWG, the CARC 

concluded that that the kidney adenomas in male mice were not treatment-related. The CARC 

considered the transitional cell bladder tumors in male rats to be treatment-related based on 

statistically significant trends for urinary bladder transitional cell papillomas and combined 

papilomas and carcinomas, the occurrence of preneoplastic lesions at 42 and 84 mg/kg/day and 

the rare occurrence of bladder transitional cell tumors. The CARC concluded that the mode of 

action for bladder tumors has been adequately established based on submitted data that support 

both a dose-response and temporal concordance of the key events and bladder tumors. The 

Agency has determined that the quantification of risk using a non-linear approach (i.e., RfD) will 

adequately account for all chronic toxicity, including carcinogenicity, that could result from 

exposure to pyroxasulfone. 

Pyroxasulfone did not exhibit developmental toxicity in the rat guideline study at the limit dose 

of 1000 mg/kg/day and it exhibited slight developmental toxicity in rabbits (reduced fetal weight 

and resorptions) at the limit dose of 1000 mg/kg/day. However, developmental effects were 

noted in PND 21 offspring at 300 mg/kg/day in the rat developmental neurotoxicity (DNT) study 

characterized as decreased brain weight and morphometric changes. In a reproductive toxicity in 

rats reduced pup weight and body weight gains during lactation) occurred at similar or higher 

doses causing pronounced maternal toxicity (reduced body weight, body weight gain and food 

consumption and increased kidney weight, cardiomyopathy and urinary bladder mucosal 

hyperplasia with inflammation).

Pyroxasulfone did not produce immunotoxic effects in mice following dietary feeding for 28 

days up to 4000 ppm (633/791 mg/kg/day, M/F) or in rats at dietary concentrations of 7500 ppm 

(529/570 mg/kg/day in M/F).

Acute toxicity studies show that pyroxasulfone exhibits low acute toxicity by all exposure routes 

(EPA Toxicity Category III or IV) and is not a dermal sensitizer. 

The complete toxicity profile for pyroxasulfone is provided in Appendix A.

4.4 Safety Factor for Infants and Children (FQPA Safety Factor)

4.4.1 Completeness of the Toxicology Database
Page 16 of 81

The toxicity database for pyroxasulfone is sufficient for a full hazard evaluation and is 

considered adequate to evaluate risks to infants and children. Acceptable developmental toxicity 

studies in the rat and rabbit and acceptable multi- and single generation reproduction studies in 

the rat have been submitted. Acceptable acute, subchronic and developmental neurotoxicity 

studies in the rat are available. Acceptable immunotoxicity studies in mice and rats are 

available. 

4.4.2 Evidence of Neurotoxicity

Pyroxasulfone produced neurotoxic effects in dogs, mice and rats. Dogs appear to be the most 

sensitive species as minimal to mild axonal/myelin degeneration in the sciatic nerve occurred at 

≥ 10 mg/kg/day for 90 days. The nerve effects in dogs were also accompanied by impaired limb 

function, body and limb hypotonia at a subchronic dose of 15 mg/kg/day. Chronic administration 

of pyroxasulfone at 10 mg/kg/day to dogs resulted in similar findings of impaired hind limb 

function, ataxia, hind limb twitching and tremors and axonal/myelin degeneration of the sciatic 

nerve and spinal cord sections. 

In rats, sciatic nerve lesions (minimal to mild axon/myelin degeneration within the sciatic nerve 

sections) were observed in a reproduction study in parental females fed pyroxasulfone at 5000 

ppm (383 mg/kg/day) but not at lower doses. These lesions were also seen in female rats 

administered doses of 1000 ppm (54 mg/kg/day) and above after chronic feeding for two years, 

but not after one year of feeding. However, specific acute and subchronic neurotoxicity tests in 

rats did not reveal neurotoxic effects following an acute oral dose of 2000 mg/kg or subchronic 

dietary administration of 2500 ppm (equivalent to 161/200 mg/kg/day (M/F), the HDT. In the 

rat DNT studies, pyroxasulfone did not produce behavioral or maternal toxicity at the highest 

dose tested of 900 mg/kg/day. However, it was associated with offspring toxicity at 300 

mg/kg/day resulting in decreased brain weight in male and female offspring accompanied with a 

decrease in the thickness of the hippocampus, corpus callosum and cerebellum in PND 21 female 

offspring with a NOAEL of 100 mg/kg/day. Although the offspring are more sensitive, the doseresponse is well characterized for neurotoxicity and a NOAEL is identified. 

4.4.3 Evidence of Sensitivity/Susceptibility in the Developing or Young Animal

Evidence of increased susceptibility of fetuses and offspring was seen in a DNT study in rats and 

a developmental study in rabbits following in utero or post natal exposure to pyroxasulfone. 

However, no susceptibility was seen in the rat developmental or reproduction studies. In rabbits, 

developmental toxicity was only seen at the limit dose of 1000 mg/kg/day as reduced fetal 

weight and increased fetal resorptions with a NOAEL of 500 mg/kg/day for these effects, 

compared to no maternal toxicity at these doses. In a DNT study in rats, offspring toxicity was 

seen at 300 mg/kg/day compared to no maternal toxicity at 900 mg/kg/day. This increased 

susceptibility is occurring at high doses. NOAELs and LOAELs have been identified for all 

effects of concern and thus, a clear dose response has been well defined. Therefore, residual 

uncertainties or concerns for pre- and/or post-natal toxicity are minimal, and HED recommends 

the FQPA safety factor be reduced to 1x. 
Page 17 of 81

4.4.4 Residual Uncertainty in the Exposure Database 

Since the dietary and non-dietary exposure estimates were based on several conservative 

assumptions, HED does not believe that the exposure estimates are underestimated. The acute 

and chronic dietary assessments conducted with DEEM-FCID were screening level analyses. 

The assessments utilized tolerance values, default processing factors, and 100% crop treated was 

assumed for all commodities. The DEEM analysis also assumed that all drinking water will 

contain pyroxasulfone at the highest EDWC levels modeled by EFED for ground water or 

surface water. For these reasons it can be concluded that the DEEM-FCID analysis does not 

underestimate risk from acute or chronic exposure to pyroxasulfone. Similarly, HED does not 

believe that the non-dietary occupational exposures are underestimated because they are also 

based on conservative assumptions, including maximum application rates, labeled PPE, and 

standard values for unit exposures, acreage treated/amount handled.

4.4.5 FQPA Factor for Infants and Children

HED recommends the FQPA SF be reduced to 1x based on the following: 

- The toxicological data base is complete for FQPA assessment. 

- There are no residual uncertainties or concerns for pre- and/or post-natal toxicity.

- Although an apparent increased quantitative susceptibility was observed in fetuses 

and offspring based on toxicity at high doses of administration, a clear dose-response

has been well defined with NOAELs and LOAELS for all effects of concern and all 

points of departure (PODs) are protective of the fetal/offspring effects. 

4.5 Toxicity Endpoint and Point of Departure

4.5.1 Dose-Response Assessment

Toxicity endpoints and PODs for dietary (food and water) and occupational exposure scenarios 

are summarized below. A detailed description of the studies used as a basis for the selected 

endpoints are presented in Appendix A. PODs for incidental oral, dermal and inhalation for nonoccupational (i.e., residential) exposure are not required to assess risk for the proposed uses 

because there are no pyroxasulfone products registered for homeowner use and there are no 

products registered for application to residential areas. 

An acute POD of 100 mg/kg/day (NOAEL) was selected from a developmental neurotoxicity 

study in rats based on decreased brain weight in both sexes and decreased thickness of the 

hippocampus, corpus callosum and cerebellum in PND 21 female offspring occurring at 300 

mg/kg/day. An uncertainty factor (UF) of 100x (10x to account for interspecies extrapolation 

and 10x for intraspecies variation) was applied to the NOAEL to obtain an acute reference dose 

(aRfD) of 1.0 mg/kg/day. Since the FQPA factor has been reduced to 1X, the acute population 

adjusted dose (aPAD) is equivalent to the aRfD. The HED DNT committee considers 

morphometric changes in the hippocampus, corpus callosum and cerebellum during the first 21 

days to result from a single acute exposure. This endpoint is considered to be protective of all 

populations including women of child-bearing age and nursing infants. 
Page 18 of 81

A chronic POD of 2.0 mg/kg/day (NOAEL) was selected from the one year dog study based on 

impaired hind limb function, ataxia, hind limb twitching and tremors; clinical pathology: 

increased creatine kinase, aspartate aminotransferase; axonal/myelin degeneration of the sciatic 

nerve and spinal cord sections at 10 mg/kg/day. An UF 100x (10x to account for interspecies 

extrapolation and 10x for intraspecies variation) was applied to the dose to obtain a chronic 

reference dose (cRfD) of 0.02 mg/kg/day. Since the FQPA factor has been reduced to 1X, the 

chronic population adjusted dose (cPAD) is equivalent to the cRfD. The dog was the most 

sensitive species for the neurotoxic effects of pyroxasulfone. Also the dose ranges used in the 

dog testing were the narrowest allowing for more accurate determination of a NOAEL. The 2 

mg/kg/day NOAEL from this dog study is also protective from other adverse effects seen at 

higher doses in rats and mice such as cardiac and skeletal myopathy, liver, kidney and urinary 

bladder toxicity. 

A POD of 100 mg/kg/day (NOAEL) for short- and intermediate-term dermal exposure was 

selected from the 28-day dermal toxicity in the rat based on cardiac myofiber degeneration with 

inflammation at 1000 mg/kg/day. The target margin of exposure (MOE) for dermal toxicity is 

100. The 28-day dermal toxicity study is route specific and is considered appropriate for this 

exposure scenario. This endpoint is considered protective of developmental effects seen in the 

DNT study at 300 mg/kg/day and in the rabbit developmental study at 1000 mg/kg/day. While 

the effects aren’t seen until the limit dose of 1000 mg/kg/day, there is a 10-fold difference 

between the dermal NOAEL and LOAEL. Therefore, the true NOAEL is probably higher 

(between 100 and 1000 mg/kg/day). This POD is also protective of the neurotoxic effects seen 

in the dog following chronic oral exposure to 10 mg/kg/day. Dermal absorption is estimated to 

be 7.5%, so the relative dermally absorbed dose for the dermal NOAEL of 100 mg/kg/day is 

approximately 7.5 mg/kg/day which is less than the oral LOAEL of 10 mg/kg/day identified in 

the dog study. In addition, rats in general are a more sensitive species for the dermal exposure 

route because of higher skin permeability. 

A POD of 2.0 mg/kg/day for short- and intermediate-term inhalation exposure was selected from 

the oral 90 day dog study (MRIDs 47701696 -97) based on a LOAEL of 10 mg/kg/day for 

axonal/myelin degeneration in the sciatic nerve, minimal to mild subacute inflammation of 

skeletal muscle in males and females and impaired limb function, body and limb hypotonia, 

increase in serum creatine kinase activity. The target MOE for inhalation toxicity is 100. This 

endpoint is more protective than the findings in the 28 day rat inhalation study (MRID 

47701699) where no effects were seen at the highest dose tested for an aerosol dust of 200

mg/m3(equivalent to 52.2 mg/kg/day) (NOAEL). Since mixer/loader exposures would be to 

both dust and aerosols (with aerosol exposures typically being more sensitive than dust 

exposures), HED believes the inhalation study was not protective of the neurotoxicity findings in 

the dog study. 
Page 19 of 81

4.5.2 Recommendations for Combining Exposure Routes

Under FQPA, when there are potential residential exposures to a pesticide, HED must aggregate 

exposures from three major sources: oral, dermal and inhalation exposures. These combined 

residential exposures must then be aggregated with exposure from food and water to determine 

aggregate risk. Since there are no residential incidental oral exposures to pyroxasulfone, 

aggregate exposure from food and non-food oral exposures is not required. Although the dermal 

and inhalation scenarios are based on muscle effects, the cardiac muscle is histologically very 

different from skeletal muscle particularly as it relates to its electrophysiology. Therefore, shortterm dermal and inhalation exposures to workers should be not aggregated with dietary (food and 

water) exposures because endpoints are not based on common toxicity effects.

4.5.3 Classification of Carcinogenic Potential

In accordance with EPA’s Final Guidelines for Carcinogen Risk Assessment (March 2005), the 

CARC classified Pyroxasulfone as “Not Likely to be Carcinogenic to Humans” at doses that do 

not cause crystals with subsequent calculi formation resulting in cellular damage of the urinary 

tract (HED TXR 0055883). This classification was based on urinary bladder tumors seen in 

male rats. Crystal formation in the absence of calculi is not associated with hyperplasia or 

urinary bladder tumors; therefore, the formation of urinary bladder calculi is the prerequisite for 

subsequent hyperplasia and neoplasia. The requirement for calculi formation also supports a 

high-dose threshold phenomenon for the development of urinary bladder tumors, i.e., tumors do 

not develop at doses too low to produce calculi. There is no concern for mutagenicity. As noted 

previously, the CARC concluded that the kidney adenomas in male mice were not treatmentrelated. The Agency has determined that the quantification of risk using a non-linear approach 

(i.e., RfD) will adequately account for all chronic toxicity, including carcinogenicity, that could 

result from exposure to pyroxasulfone. There is a clear threshold of 1000 ppm (42.55 

mg/kg/day) for tumorigenesis. A point of departure (POD) of 50 ppm (2.0 mg/kg/day) is not 

expected to result in urinary bladder calculi formation which is a prerequisite for subsequent 

hyperplasia and neoplasia.

4.5.4 Summary of Points of Departure Used in Risk Assessment

Toxicological doses/endpoints selected for the pyroxasulfone risk assessment are provided in 

Tables 4.5.4.1 and 4.5.4.2.
Page 20 of 81

Table 4.5.4.1. Toxicological Doses and Endpoints for Pyroxasulfone for Use in Dietary Human Health Risk Assessments

Exposure/

Scenario

Point of 

Departure

Uncertainty/

FQPA Safety 

Factors

RfD & PAD Study and Toxicological Effects

Acute Dietary 

(General 

Population, 

including Infants 

and Children)

NOAEL= 100 

mg/kg

UFA= 10 x

UFH=10 x

FQPA SF=1x

Acute RfD = 

1.0 mg/kg

aPAD = 1.0 

mg/kg

Developmental neurotoxicity study (DNT) in 

rats, MRID 47701724.

The LOAEL of 300 mg/kg/day is based on 

decreased brain weight in both sexes, reduced 

thickness of the hippocampus, corpus callosum 

and cerebellum in PND 21 female offspring.

Chronic Dietary 

(All Populations)

NOAEL= 2 

mg/kg/day

UFA= 10 x

UFH=10 x

FQPA SF=1x

Chronic RfD 

= 0.02

mg/kg/day

cPAD = 0.02 

mg/kg/day

One- year chronic dog study, MRID 47701707

The LOAEL of 10 mg/kg/day is based on 

impaired hind limb function, ataxia, hind limb 

twitching and tremors; clinical pathology: 

increased creatine kinase, aspartate 

aminotransferase; axonal/myelin degeneration of 

the sciatic nerve and spinal cord sections.

Cancer (all routes) “Not Likely to be Carcinogenic to Humans” at doses that do not cause crystals with subsequent calculi 

formation resulting in cellular damage of the urinary tract. Risk is quantified using a non-linear (i.e., 

RfD) approach. 

Point of Departure (POD) = A data point or an estimated point that is derived from observed dose-response data and used to 

mark the beginning of extrapolation to determine risk associated with lower environmentally relevant human exposures. NOAEL 

= no observed adverse effect level. LOAEL = lowest observed adverse effect level. UF = uncertainty factor. UFA = 

extrapolation from animal to human (interspecies). UFH = potential variation in sensitivity among members of the human 

population (intraspecies). FQPA SF = FQPA Safety Factor. PAD = population adjusted dose (a = acute, c = chronic). RfD = 

reference dose. MOE = margin of exposure. LOC = level of concern. N/A = not applicable.
Page 21 of 81

Table 4.5.4.2. Toxicological Doses and Endpoints for Pyroxasulfone for Use in Occupational Human Health Risk 

Assessments

Exposure/

Scenario

Point of 

Departure

Uncertainty/

FQPA Safety 

Factors

Level of 

Concern Study and Toxicological Effects

Incidental Oral Not required. Incidental exposure not anticipated. There are no registered residential uses

Dermal Short- (1-

30 days) & 

Intermediate-Term 

(1-6 months) 

NOAEL = 100 

mg/kg/day

UFA= 10 x

UFH=10 x

Occupational

MOE = 100

28-day dermal toxicity study in rats MRID 47701698

The LOAEL of 1000 mg/kg/day was based on minimal 

to mild cardiac myofiber degeneration with in 

inflammation in males and females

Inhalation Short-

(1-30 days) & 

NOAEL = 2 

mg/kg/day

100% 

absorption

UFA= 10 x

UFH=10 x Occupational

MOE = 100

90-day toxicity study in dogs MRIDs 47701696 and 

47701697 LOAEL of 10 mg/kg/day: axonal/myelin 

degeneration in the sciatic nerve. Minimal to mild 

subacute inflammation of skeletal muscle in males 

and females. Impaired limb function, body and 

limb hypotonia, increase in serum creatine kinase 

activity.

Inhalation

Intermediate-Term 

(1-6 months)

NOAEL = 2 

mg/kg/day

100% 

absorption

UFA= 10 x

UFH=10 x Occupational

MOE = 100

One- year chronic dog study, MRID 47701707

The LOAEL of 10 mg/kg/day is based on impaired 

hind limb function, ataxia, hind limb twitching and 

tremors; clinical pathology: increased creatine 

kinase, aspartate aminotransferase; axonal/myelin 

degeneration of the sciatic nerve and spinal cord 

sections.

Cancer (all routes) “Not Likely to be Carcinogenic to Humans” at doses that do not cause crystals with subsequent calculi 

formation resulting in cellular damage of the urinary tract. Risk is quantified using a non-linear (i.e., 

RfD) approach.

Point of Departure (POD) = A data point or an estimated point that is derived from observed dose-response data and used to 

mark the beginning of extrapolation to determine risk associated with lower environmentally relevant human exposures. NOAEL 

= no observed adverse effect level. LOAEL = lowest observed adverse effect level. UF = uncertainty factor. UFA = 

extrapolation from animal to human (interspecies). UFH = potential variation in sensitivity among members of the human 

population (intraspecies). FQPA SF = FQPA Safety Factor. PAD = population adjusted dose (a = acute, c = chronic). RfD = 

reference dose. MOE = margin of exposure. LOC = level of concern. N/A = not applicable.

5.0 DIETARY AND DRINKING WATER EXPOSURE AND RISK ASSESSMENT

5.1 Metabolite/Degradate Residue Profile

5.1.1 Summary of Plant and Livestock Metabolism Studies

The metabolism studies submitted for pyroxasulfone are adequate to satisfy data requirements on 

the nature of the residue in plants. The nature of the residue in plants is adequately understood 

based on the submitted studies. The metabolic pathway of pyroxasulfone involves cleavage of 

the methyl sulfone bridge of the parent compound, oxidation and/or demethylation of the 

pyrazole cleavage product to yield metabolites M-1 and M-25, and reaction of the isoxazoline 

cleavage product with cysteine and/or glutathione; further demethylation, deamination, and/or 

conjugation of these metabolites occurs, yield additional metabolites including M3 (chemical 

structures are provided in Appendix B). 
Page 22 of 81

The submitted livestock metabolism studies with goats and hens are adequate to satisfy data 

requirements for the nature of the residue in livestock. The nature of the residue in livestock is 

adequately understood based on submitted metabolism studies. Metabolism of pyroxasulfone in 

livestock occurs primarily via cleavage between the rings, to form metabolites M-1, M-8, M-10, 

and/or M-15, followed by oxidation, to yield metabolite M-3, and/or demethylation, to yield 

metabolites M-12 and M-9. The parent compound may also undergo demethylation, 

hydroxylation followed by oxidation, or oxidation followed by ring cleavage. 

5.1.2 Comparison of Metabolic Pathways

The proposed metabolic pathway for pyroxasulfone in plants is provided in Appendix B. The 

major pyroxasulfone metabolites in plants are M-1, M-3, M-25, M-28. All of the plant 

metabolites exhibit low acute toxicity (Toxicity Category IV). The M-1 and M-3 metabolites, 

which are also found in rat, were not toxic in rats after 14 days of oral dosing at 1000 mg/kg/day. 

Structure-activity relationship (SAR) analysis (DEREK) did not reveal any alerts for any of the 

major metabolites. All of the tested metabolites were negative in the Ames test. M1, M25, and 

M-28 are potentially less toxic than the parent as they are lower molecular weight acids (i.e., 

more easily excreted). However, there are no data to demonstrate that they do not retain the 

toxic properties of the parent compound. Based on the limited testing data available, 

pyroxasulfone metabolites appear to be equal or less toxic than the parent material. 

The metabolic pathway of pyroxasulfone in plants mainly involves cleavage of the methyl 

sulfone bridge of the parent compound followed by oxidation and/or demethylation of the 

pyrazole cleavage product to yield metabolites M-1 and M-25, and reaction of the isoxazoline 

cleavage product with cysteine and/or glutathione; further demethylation, deamination, and/or 

conjugation of these metabolites occurs, yield additional metabolites including M-3. 

The metabolism of pyroxasulfone in rats appears to proceed by two main routes. One route, 

similar to the metabolic pathway seen in plants, involves cleavage of the sulfonyl group and 

subsequent sequential oxidations of this group on the pyrazole moiety or glutathione conjugation 

and subsequent hydrolysis of the isoxazoline moiety. The second route involves sequential 

oxidations of the parent compound. 

5.1.3 Environmental Fate and Transport

Pyroxasulfone is mobile (average Koc= 94.75) and persistent (t1/2= 142 to 533 days) in terrestrial 

and aquatic environments There are two major degradation products (>10% of applied 

radioactivity) and 6 minor degradation products (<10 % of applied radioactivity) detected in 

laboratory metabolism studies. Additionally, there is a high percentage of applied radioactivity 

(8-25% of applied radioactivity) identified as “bound” soil/sediment residues. Because the 

extraction of pyroxasulfone residues was conducted using only acetonitrile/water without the use 

of sequentially harsher soil extractants, there is uncertainty regarding the identity and availability 

of the “bound” soil residues. 
Page 23 of 81

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

assessment for the proposed use of pyroxasulfone on cotton which will adequately cover the 

amended use on corn. Previously they had conducted drinking water assessments of the use of 

pyroxasulfone on corn, wheat, and soybean. EFED provided modeling-based drinking water 

exposure estimates using the Tier II PRZM GW drinking water assessment from surface water 

sources for the proposed use of pyroxasulfone. Residues of concern for drinking water for risk 

assessment purposes were parent, M1, and M3. Estimated drinking water residues for peak 

concentration of 0.210 mg/L (ppm) were used in the acute assessment. Estimated 30 yr annual 

average drinking water concentrations of 0.174 mg/L (ppm) were used the chronic assessment. 

5.1.4 Residues of Concern Summary and Rationale

Previously, in order to harmonize with Canada and Australia, HED has concluded the residues of 

concern for Corn, field, grain and Corn, sweet, kernel plus cob with husks removed consist of 

pyroxasulfone and its metabolite M-3. Residues of concern for drinking water for risk 

assessment purposes were parent, M-1, and M-3. The modeling was conducted for 

pyroxasulfone and total pyroxasulfone residues (parent+M-1+M-3, and total pyroxasulfone 

residues (parent+M-1+M-3+M-5+M-6+M-8+M-9+M-10+M-11+unidentified bound soil 

residues). Another acidic metabolite, M3, was proposed as a residue of concern by the 

petitioner. Although not a major component of the total radioactive residue (TRR), ROCKS 

recommends that M3 be included in the residues of concern since it is analyzed concurrently 

with the parent compound in the proposed analytical enforcement method.

Table 5.1.4. Compounds to be Included in the Risk Assessment and Tolerance Expression.

Matrix Residues included in Risk Assessment

Residues included in Tolerance 

Expression for Compliance 

Monitoring

Plants Cereal Grains Pyroxasulfone, M1, M3, M25 Pyroxasulfone, M1, M3, M25***

Soybeans Pyroxasulfone, M1, M3, M25, M28** Pyroxasulfone, M1, M3, M25, M28*

Livestock Pyroxasulfone, M1, M3, M25, M28 Pyroxasulfone, M1, M3

Drinking Water Pyroxasulfone, M1, M3 Not Applicable

Pyroxasulfone = 3-[[[5-(difluoromethoxy)-1-methyl-3-(trifluoromethyl)-1H-pyrazol-4-yl]methyl]sulfonyl]-4,5-

dihydro-5,5-dimethylisoxazole.

M1 = [5-(difluoromethoxy)-l-methyl-3-(trifluoromethyl)-lH-pyrazol-4-yl)] methanesulfonic acid.

M3 = 5-(difluoromethoxy)-l-methyl-3-(trifluoromethyl)-lH-pyrazole-4-carboxylic acid.

M25 = [5-(difluoromethoxy)-3-(trifluoromethyl)-1H-pyrazol-4-yl)] methanesulfonic acid.

M28 = 3-[1-carboxy-2-(5,5-dimethyl-4,5-dihydroisoxazol-3-ylthio)ethylamino]-3-oxopropanoic acid.

Metabolite C = 3-[1-carboxy-2-(5,5-dimethyl-4,5-dihydroisoxazol-3-ylthio)ethenylamino]-3-oxopropanoic acid.

* reanalysis of the seed samples showed residues of M28 and therefore M28 needs to be included in both the 

tolerance expression and risk assessment as a residue of concern in soybean seed. M-1 is included for soybean 

forage and hay.

** residues of concern for soybean seed is pyroxasulfone and metabolite M-1, M-3, M-25, & M-28 for risk 

assessment and does not include M-1 for tolerance enforcement purposes.

***residues of concern for wheat grain, cotton seed, corn, field, grain and corn, sweet, kernel plus cob with 

husks removed is pyroxasulfone and metabolite M-3. 
Page 24 of 81

5.2 Food Residue Profile

5.2.1 Residues in Crops

K-I Chemical previously submitted field trial data from corn field trials conducted in the U.S. 

The purpose of this study was to obtain Raw Agricultural Commodity (RAC) residue data for 

pyroxasulfone (KIH-485) and its metabolites M-1, M-3, and M-25 on corn commodities 

following the addition of adjuvants to the registered products. The results from these field trials 

along are discussed previously (D402247, T. Morton, 1/10/13). 

For all studies, HED converted residues of metabolites to parent equivalents for calculation of 

total residues; molecular weight conversion factors of 1.262 for M-1, 1.504 for M-3, 1.321 for 

and M-25. The full LOQ value was used for residues <LOQ for calculating total residues. 

Table 5.2.1.1. Summary of Residue Data from Corn Crop Field Trials with Pyroxasulfone 85 WG.

Crop matrix Target Applic. 

Rate

(lb ai/A)

PHI 

(days)

Total Residues of Pyroxasulfone and Metabolites M-1, M-3, and 

M-25 (ppm)1

n Min. Max. HAFT2 Median Mean Std. 

Dev.3

Corn forage 0.147-0.270 59-68 36 <0.025 0.099 0.086 0.036 0.043 0.019

Corn stover 105-113 36 0.025 0.051 0.047 0.025 0.030 0.007

Corn grain 105-113 36 <0.025 <0.028 <0.026 0.025 0.025 0.001

1

 For the purposes of calculating total residues, HAFT, median, mean, and standard deviation, the LOQ was used 

for residues reported as <LOQ. Metabolite residues were converted to parent equivalents. 2 HAFT = Highest 

average field trial result.

5.3 Water Residue Profile

5.3.1 Estimated Drinking Water Concentrations 

Pyroxasulfone is mobile (average Koc= 94.75) and persistent (t1/2= 142 to 533 days) in terrestrial 

and aquatic environments There are two major degradation products (>10% of applied 

radioactivity) and 6 minor degradation products (<10 % of applied radioactivity) detected in 

laboratory metabolism studies. Additionally, there is a high percentage of applied radioactivity 

(8-25% of applied radioactivity) identified as “bound” soil/sediment residues. Because the 

extraction of pyroxasulfone residues was conducted using only acetonitrile/water without the use 

of sequentially harsher soil extractants, there is uncertainty regarding the identity and availability 

of the “bound” soil residues. 

The Environmental Fate and Effects Division (EFED) conducted a drinking water assessment for 

the proposed uses of pyroxasulfone on cotton and wheat (D402603, J. Hetrick, 01/31/13). These 

estimated drinking water concentrations (EDWCs) have identical to the EDWCs provided for the 

initial registration of pyroxasulfone. EFED provided modeling-based drinking water exposure 

estimates using the Tier II PRZM GW drinking water assessment from surface water sources for 
Page 25 of 81

the proposed uses of pyroxasulfone. Residues of concern for drinking water for risk assessment 

purposes were parent, M1, and M3. Estimated drinking water residues for peak concentration of 

0.210 mg/L (ppm) were used in the acute assessment. Estimated average drinking water 

concentrations of 0.174 mg/L (ppm) were used the chronic assessment. 

5.4 Dietary and Drinking Water Exposure and Risk

HED conducted screening-level acute and chronic dietary and drinking water exposure and risk 

assessments using the Dietary Exposure Evaluation Model with the Food Commodity Intake 

Database (DEEM-FCIDTM). Dietary risk assessment incorporates both exposure and toxicity of

a given pesticide. For acute and chronic dietary assessments, the risk is expressed as a 

percentage of a maximum acceptable dose (i.e., the dose which HED has concluded will result in 

no unreasonable adverse health effects). This dose is referred to as the population adjusted dose 

(PAD). The PAD is equivalent to the reference dose (RfD) divided by the additional FQPA 

Safety Factor, if applied. For acute and non-cancer chronic exposures, HED is concerned when 

estimated dietary risk exceeds 100% of the PAD. 

The proposed amended use on corn was assessed for dietary and drinking water exposure. 

DEEM® residue inputs for corn commodities used tolerance level residues adjusted for 

metabolites which are not in the tolerance expression from specific use patterns for the acute and 

chronic dietary exposure analyses. Percent crop treated was set at 100 %. 

5.4.1 Acute Dietary and Drinking Water Analysis

A new dietary assessment was conducted for the proposed amended use. The proposed use results 

dietary risk estimates below HED’s level of concern; see Table 5.4.1. The highest is All Infants <1

year resulting in 3.6% of the aPAD. 

Table 5.4.1. Results of Acute Dietary Exposure Analysis for Food and Drinking Water

Population Subgroup aPAD (mg/kg/day)

95th Percentile

Exposure (mg/kg/day) % aPAD

General U.S. Population

1.0

0.011740 1.2

All Infants (< 1 year old) 0.036394 3.6

Children 1-2 years old 0.018442 1.8

Children 3-5 years old 0.015013 1.5

Children 6-12 years old 0.011445 1.1

Youth 13-19 years old 0.009849 1.0

Adults 20-49 years old 0.011476 1.2

Adults 50-99 years old 0.010239 1.0

Females 13-49 years old 0.011621 1.2
Page 26 of 81

5.4.2 Chronic Dietary and Drinking Water Analysis

A new dietary assessment was conducted for the proposed amended use of pyroxasulfone and results 

in dietary risk estimates below HED’s level of concern; see Table 5.4.2.

Table 5.4.2. Results of Chronic Dietary Exposure Analysis for Food and Drinking Water

Population Subgroup cPAD (mg/kg/day) Exposure (mg/kg/day) % cPAD

General U.S. Population

0.02

0.003822 19

All Infants (< 1 year old) 0.009679 48

Children 1-2 years old 0.005829 29

Children 3-5 years old 0.004898 25

Children 6-12 years old 0.003509 18

Youth 13-19 years old 0.002843 14

Adults 20-49 years old 0.003774 19

Adults 50+ years old 0.003700 19

Females 13-49 years old 0.003757 19

6.0 RESIDENTIAL EXPOSURE AND RISK ASSESSMENT

A residential assessment is not required because there are no pyroxasulfone products registered 

for homeowner use and there are no products registered for application to residential areas. 

 

6.1 Residential Bystander Post-application Inhalation Exposure

Based on the Agency's current practices, a quantitative residential bystander post-application 

inhalation exposure assessment was not performed for pyroxasulfone at this time. However, 

volatilization of pesticides may be a potential source of post-application inhalation exposure to 

individuals nearby to pesticide applications. The Agency sought expert advice and input on 

issues related to volatilization of pesticides from its Federal Insecticide, Fungicide, and 

Rodenticide Act Scientific Advisory Panel (SAP) in December 2009. The Agency received the 

SAP’s final report on March 2, 

2010(http://www.epa.gov/scipoly/SAP/meetings/2009/120109meeting.html). The Agency is in 

the process of evaluating the SAP report and may, as appropriate, develop policies and 

procedures, to identify the need for and, subsequently, the way to incorporate post-application 

inhalation exposure into the Agency's risk assessments. If new policies or procedures are put 

into place, the Agency may revisit the need for a quantitative postapplication inhalation exposure 

assessment for pyroxasulfone.

6.2 Spray Drift

Spray drift is always a potential source of exposure to residents nearby to spraying operations. 

This is particularly the case with aerial application, but, to a lesser extent, could also be a 

potential source of exposure from the ground application method employed for pyroxasulfone. 

The Agency has been working with the Spray Drift Task Force, EPA Regional Offices and State 
Page 27 of 81

Lead Agencies for pesticide regulation and other parties to develop the best spray drift 

management practices (see the Agency’s Spray Drift website for more information at 

http://www.epa.gov/opp00001/factsheets/spraydrift.htm). On a chemical by chemical basis, the 

Agency is now requiring interim mitigation measures for aerial applications that must be placed 

on product labels/labeling. The Agency has completed its evaluation of the new database 

submitted by the Spray Drift Task Force, a membership of U.S. pesticide registrants, and is 

developing a policy on how to appropriately apply the data and the AgDRIFT computer model to 

its risk assessments for pesticides applied by air, orchard airblast and ground hydraulic methods. 

After the policy is in place, the Agency may impose further refinements in spray drift 

management practices to reduce off-target drift with specific products with significant risks 

associated with drift.

7.0 AGGREGATE EXPOSURE AND RISK ASSESSMENT 

In accordance with the FQPA, when there are potential residential exposures to a pesticide, 

aggregate risk assessment must consider exposures from three major routes: oral, dermal, and 

inhalation. There are three sources for these types of exposures: food, drinking water, and 

residential uses. In an aggregate assessment, exposures from relevant sources are added together 

and compared to quantitative estimates of hazard (e.g., a NOAEL or PAD), or the risks 

themselves can be aggregated. When aggregating exposures and risks from various sources, 

HED considers both the route and duration of exposure. The proposed/registered pyroxasulfone 

uses are not expected to result in residential exposure. Therefore, the acute and chronic exposure 

estimates provided in the Dietary Exposure Section represent aggregate exposure. 

7.1 Acute & Chronic Aggregate Risk

Acute and chronic aggregate exposures include food plus drinking water exposures. As 

demonstrated under Section 5.4, acute and chronic aggregate risks are not of concern.

8.0 CUMULATIVE RISK

Section 408(b)(2)(D)(v) of 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.”

EPA does not have, at this time, available data to determine whether pyroxasulfone has a 

common mechanism of toxicity with other substances. 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 as to pyroxasulfone and any other substances 

and, pyroxasulfone does not appear to produce a toxic metabolite produced by other substances 

which have tolerances in the U. S. For the purposes of this tolerance reassessment action, 

therefore, EPA has not assumed that pyroxasulfone has a common mechanism of toxicity with 
Page 28 of 81

other substances. For information regarding EPA’s efforts to determine which chemicals have a 

common mechanism of toxicity and to evaluate the cumulative effects of such chemicals, see the 

policy statements released by EPA’s OPP concerning common mechanism determinations and 

procedures for cumulating effects from substances found to have a common mechanism on 

EPA’s website at http://www.epa.gov/fedrgstr/EPA_PEST/2002/January/Day_16/.

9.0 OCCUPATIONAL EXPOSURE/RISK CHARACTERIZATION

9.1 Exposure Scenarios

Occupational handler and post-application exposure scenarios were assessed for the registered

use on soybeans. The proposed uses of pyroxasulfone on corn have comparable application rates 

as those assessed in the soybean assessment. Therefore, the exposure to occupational handler 

and post-application exposure will not increase from the proposed amended use. Based on the 

product labels and information provided by the registrant, short- and intermediate-term exposure 

is assessed for occupational handlers and post-application activities. Dermal and inhalation 

exposures to workers are not aggregated for pyroxasulfone because the toxicity endpoints for 

these exposure routes are not based on common toxicological effects. Labels for both 

pyroxasulfone formulations require that applicators and other handlers wear long-sleeved shirt 

and long pants, chemical resistant gloves and shoes and socks. 

9.2 Handler Exposure 

The term “handler” applies to individuals who mix, load, and apply the pesticide product. 

There is a potential for exposure to pyroxasulfone during mixing, loading, and application 

activities through the dermal and inhalation routes. Pyroxasulfone is applied in the spring at 

preplant and preemergence growth stages and in the fall to minimum or no tillage fields to be 

planted the following spring. Pyroxasulfone products are applied using aerial, right of way and 

or handgun sprayers, as well as groundboom equipment. The following handler exposure 

scenarios evaluated for this assessment are based on information provided in the proposed labels. 

9.2.1 Handler Exposure Scenarios

The term “handler” applies to individuals who mix, load, and apply the pesticide product. 

There is a potential for exposure to pyroxasulfone during mixing, loading, and application 

activities through the dermal and inhalation routes. Pyroxasulfone is applied in the spring at 

preplant and preemergence growth stages and in the fall to minimum or no tillage fields to be 

planted the following spring. Pyroxasulfone products are applied using aerial, right of way and 

or handgun sprayers, as well as groundboom equipment. The following handler exposure 

scenarios evaluated for this assessment are based on information provided in the proposed labels. 
Page 29 of 81

9.2.1.1 Mixing and Loading Scenarios

• Mixing and Loading a water-dispersible granule formulation for groundboom 

application.

• Mixing and Loading a water-dispersible granule formulation for aerial application.

9.2.1.2 Application Scenarios

• Applying a water-dispersible granule formulation with groundboom equipment.

 • Applying a water-dispersible granule formulation with aerial equipment.

• Flagging for aerial application scenarios.

9.2.2 Handler Exposure Data

No chemical-specific handler exposure data were submitted in support of this registration. It is 

HED’s policy to use data from the USEPA OPP Occupational Pesticide Handler Unit Exposure 

Surrogate Reference Table (5/4/11). http://www.epa.gov/pesticides/science/handler-exposuredata.html). 

9.2.3 Handler Exposure Assumptions

• Average body weight of an adult handler is 80 kg.

• Exposure duration short-term (1- 30 days), intermediate-term (1-6 months)

• Maximum label application rates:

- 0.21 lb ai/A for soybean 

• Area treated: 

- 1200 acres per day for aerial application

- 200 acres per day for groundboom application. 

- 350 acres for flagging during aerial application scenarios. 

-

9.2.4 Handler Exposure and Risk Estimates

A target LOC or MOE of 100 is considered adequate for dermal and inhalation exposure. All 

worker exposures are assessed as short-term based on label prescribed uses and expected 

exposure durations. Exposure and risk estimates indicate that for most exposure scenarios noncancer risks are not of concern for occupational handler activities for the proposed new use 

(MOEs > 100). However, risks of concern exist (MOE<100) for “Inhalation” exposure during 

mixing and loading activities for aerial applications A summary of occupational handler 

exposure and risk calculations, assumptions, and results is provided in Table 9.2.4. 
Page 30 of 81

Table 9.2.4. Short and Intermediate-Term Occupational Handler Exposure and Risk for Pyroxasulfone

Exposure

Scenario 1

Crop or 

Target

App 

Rate

(lb ai/A)2

Acres 

Treated 

Daily3

Unit Exposure3 Dose 

(mg/kg/Day)4,5 Risk Estimation

Dermal 

(mg/lb ai)

Inhalation 

(μg/lb ai) Dermal Inhal

MOEs6,7

Dermal

Inhal

BL Resp.

PF5

Mixer/Loader (water-dispersible granule)

Groundboom

Baseline

Soybean 0.21

200

0.227 8.96 0.119 0.0047 840 430

Groundboom

Gloves 0.052 8.96 0.0271 0.0047 3,700 430

Aerial

Baseline

1200

0.227 8.96 0.715 0.0283 140 71 350

Aerial

Gloves 0.052 8.96 0.163 0.0283 610 71 350

Applicator (water-dispersible granule)

Groundboom

Baseline Soybean 0. 21 200

0.0786 0.34 0.0413 0.0002 2,400 110,000

Groundboom

Gloves 0.0161 0.34 0.00845 0.0002 120,000 110,000

Aerial Protected by Groundboom Application

Flagging

Aerial Soybean 0.21 350 0.011 0.35 0.0101 0.0003 9,900 6,200

1. Baseline and PPE unit exposure values are reported USEPA OPP Occupational Pesticide Handler Unit Exposure Surrogate 

Reference Table

2 Application rates based on proposed label rate.

3. Amount treated based on information provided ExpoSAC Policy 9

4. Dermal dose (mg/kg/event) = [unit dermal exposure (mg/lb ai) * application rate (lb ai/A) * Amount treated / body weight (80 

kg)].

5

Inhalation dose (mg/kg/event) = [unit exposure (kg/lb ai) * (1mg/1000 kg) conversion * appl. rate (lb ai/lbs seed) * Amount 

treated / body weight (80 kg)].

6. Dermal MOE = short-term endpoint for dermal (NOAEL 100 mg/kg/day)/Dermal Dose

7. Inhalation MOE = short-term endpoint for dermal (NOAEL 2 mg/kg/day)/Inhalation Dose 

Note; Risks of concern exist for the “mixing and loading” of a water dispersible granular for 

aerial applications (MOE = 71) with label specific PPE (long-sleeved shirt and long pants, 

chemical resistant gloves and shoes and socks). However, with a PF5 respirator, risks are not of 

concern (MOE = 350).
Page 31 of 81

9.3 Post Application Exposure 

HED uses the term “post-application” to describe those individuals who can be exposed to 

pesticides after entering areas previously treated with pesticides and performing certain tasks or 

activities (also often referred to as reentry exposure). Post-application exposures are expected to 

occur primarily via the dermal route. Based on current Agency's practices, a quantitative postapplication inhalation exposure assessment was not performed. However, the Agency is in the 

process of evaluating available data and information on post-application inhalation exposure. If 

new policies or procedures are put into place based on that evaluation, the Agency may revisit 

the need for a quantitative occupational post-application inhalation exposure assessment for 

pyroxasulfone.

Minimal exposure during harvesting or other late season activities is expected for pre-emergent 

applications of pyroxasulfone for the following reasons. Preemergence herbicides are applied to 

the surface soil directly or are incorporated into the soil well before the crops mature. 

Pyroxasulfone is proposed for use on the high acreage field crop soybean. This crop is

mechanically planted early in the season which minimizes the potential for dermal contact. 

Based on these considerations, HED does not require a post-application occupational exposure 

assessment for pre-emergent herbicides used on crops that are mechanically planted (HED 

Exposure Science Advisory Council Policy No. 008). However, there is potential exposure to 

persons entering treated sites after application of pyroxasulfone as an early post-emergence 

herbicide to soybean (application up to third trifoliate leaf stage). Consequently, post-application 

exposure from early post-emergence uses is assumed to occur during minimum foliage 

development for soybean (ExpoSAC Policy No. 003.1). 

9.3.1 Post Application Exposure Scenarios

The following post-application exposure scenarios were assessed for proposed postemergence uses of pyroxasulfone. 

• Hand weeding soybean at low crop height and minimum foliage development

Note: Based on label specific directions, the application method and timing for soybeans is 

preplant and pre-emergence only. Therefore the TC of 70 for “hand weeding” was 

appropriate because the crop height is low with minimal foliage. However, since 

pyroxasulfone is used to control a broad spectrum of broadleaf weeds and grasses, therfore 

scouting will be the activity associated with this TC. 

In accordance with the Worker Protection Standard (WPS), a 12-hr restricted entry 

interval (REI) is required for chemicals classified under Toxicity Category III/IV. 
Page 32 of 81

9.3.2 Post Application Exposure Assumptions

No chemical-specific handler exposure data were submitted in support of this 

registration. Therefore, agricultural transfer coefficients used for this assessment are taken from 

HED’s Science Advisory Council for Exposure Policy on Agricultural Transfer Coefficients 

(SOP # 003.1, 8/7/00). 

• Average body weight of an adult handler is 80 kg.

• Exposure duration is short-term (1- 30 days)

• Maximum label application rates:

- 0.21 lb ai/A for soybean

• Transfer Coefficients:

- 70cm2/hour for scouting immature soybean crop

• Initial fraction of ai retained on foliage is 25% 

• Exposure is assumed to occur on the day of application (day 0) 

9.3.3 Post-Application Exposure and Risk Estimates

A target LOC or MOE of 100 is considered adequate for dermal exposure. Exposure and risk 

estimates indicate post-application risks are not of concern (MOEs > 100) as shown on Table 

9.3.3. 

Table 9.3.3. Estimated Pyroxasulfone Exposure & MOEs for Occupational Post-Application Exposure 

Exposure Scenario App Rate

(lb ai/A) 1

DFR 

(μg/cm2)

2

TC 

(cm2/hr) 3

Exposure Duration 

(hrs/day)

Dermal dose

(mg/kg/day) 4 MOE 5

Soybean - Scouting 

immature plants

0.21 0.589 70 8 0.00412 24,000

1 Application rates are based on maximum values based on proposed label.

2 DFR (mg/cm2

) = Dislodgeable Foliar Residues corresponding to day 0. Application Rate (lb ai/A) x CF (4.54E+5 mg/lb) x CF 

(2.47E-8 A/ cm2) x 25% (initial fraction of ai retained on foliage)

3 TC cm2

/hr = Transfer coefficients and associated activities (ExpoSAC Policy Memo #003.1)

4 Dermal Dose (mg/kg/day) = DFR (mg/cm2

) x TC (cm2/hr) x 8 (hrs/day) / Body weight (80 kg).

5 Dermal MOE = short-term endpoint for dermal (NOAEL 100 mg/kg/day)/Dermal Dose

9.3.4 Restricted Entry Interval

Pyroxasulfone has been classified in Toxicity Category III for acute dermal and Category IV for 

eye irritation and primary skin irritation. Per the Worker Protection Standard (WPS), a 12-hr 

restricted entry interval (REI) is required for chemicals classified under Toxicity Category III/IV. 
Page 33 of 81

9.3.5 Inhalation Post-application Risk

Based on the Agency's current practices, a quantitative occupational postapplication inhalation 

exposure assessment was not performed for pyroxasulfone at this time. However, there are 

multiple potential sources of post-application inhalation exposure to individuals performing postapplication activities in previously treated fields. These potential sources include volatilization 

of pesticides and resuspension of dusts and/or particulates that contain pesticides. The Agency 

sought expert advice and input on issues related to volatilization of pesticides from its Federal 

Insecticide, Fungicide, and Rodenticide Act Scientific Advisory Panel (SAP) in December 2009. 

The Agency received the SAP’s final report on March 2, 2010 

(http://www.epa.gov/scipoly/SAP/meetings/2009/120109meeting.html). The Agency is in the 

process of evaluating the SAP report as well as available post-application inhalation exposure 

data generated by the Agricultural Reentry Task Force and may, as appropriate, develop policies 

and procedures, to identify the need for and, subsequently, the way to incorporate occupational 

post-application inhalation exposure into the Agency's risk assessments. If new policies or 

procedures are put into place, the Agency may revisit the need for a quantitative occupational 

post-application inhalation exposure assessment for pyroxasulfone.

10. REFERENCES

Pyroxasulfone. Application for Amended Section 3 Registration for Use on Corn – T. Morton, D414667, 5/20/14

Pyroxasulfone. Acute and Chronic Aggregate Dietary Exposure and Risk Assessments for the Amended Section 3 

Registration Request for Use of Pyroxasulfone on Corn. – T. Morton, D417422, 5/20/14

Pyroxasulfone, Herbicide End-Use Product: V-10233, Fierce TM Herbicide and Pyroxasulfone 85 WG Herbicide, 

Herbicide Drinking Water Assessment of Pyroxasulfone Proposed Use on Cotton.

– J. Hetrick, D402603, 1/31/2013

Pyroxasulfone: Occupational and Residential Exposure Assessment for Proposed Uses on Cotton and Wheat.– J. S. 

Miller, D413467, 7/24/13
Page 34 of 81

APPENDICES

A TOXICOLOGY DATA SUMMARY

A.1 Guideline Data Requirements

The requirements (40 CFR 158.340) for food use for pyroxasulfone are in Table 1. 

Guideline 

No. Study Type Technical MRID No. Required Submitted

870.3100

870.3150

870.3200

870.3250

870.3465

Subchronic (Oral) Toxicity - Rodent...............................................................

Subchronic (Oral) Toxicity - Non-Rodent ......................................................

21/28-Day Dermal Toxicity ............................................................................

90-Day Dermal Toxicity

90-Day Inhalation Toxicity .............................................................................

Y

Y

N

N

N

Y

Y

Y

N

Y

47701692 

47701693

47701694

47701695

47701696

47701697

47701698

---

47701699

870.3700a

870.3700b

870.3800

Prenatal Developmental Toxicity - Rodent .....................................................

Prenatal Developmental Toxicity - Non-Rodent .............................................

Reproduction and Fertility Effects ..................................................................

Y

Y

Y

Y

Y

Y

47701701

47701702 

47701703

47701704

47746840

47701705

47701706

870.4100a

870.4100b

870.4200a

870.4200b

870.4300

Chronic (Oral) Toxicity - Rodent....................................................................

Chronic (Oral) Toxicity - Non-Rodent (Dog) .................................................

Carcinogenicity - Rat

Carcinogenicity - Mouse

Combined Chronic Toxicity /Carcinogenicity ................................................

Y

N

N

Y

Y

Y

Y

N

Y

Y

47701708 

47701707

---

47701710 

47701709

870.6100a

870.6100b

870.6200a

870.6200b

870.6300

870.7800

Neurotoxicity - Acute Delayed Neurotox.- Hen..............................................

Neurotoxicity - Subchronic - Hen ..................................................................

Neurotoxicity Screening Battery - Acute - Rat ...............................................

Neurotoxicity Screening Battery -Subchronic - Rat........................................

Developmental Neurotoxicity..................

Immunotoxicity............................. .........................................................

N

N

Y

Y

N

Y

N

N

Y

Y

Y

Y

---

---

47701721 

47701722

47701723

47701724 

47701731

47701732
Page 35 of 81

A.2 TOXICITY PROFILES 

A.2.1 Acute Toxicity

Table A.2.1.1 Acute Toxicity Profile – Pyroxasulfone

Guideline 

No.

Study Type MRID(s) Results Toxicity Category

870.1100 Acute oral – rat (females) 47701677 LD50 = >2000 mg/kg III

870.1200 Acute dermal – rat 47701684 LD50 >2000 mg/kg

M & F

III

870.1300 Acute inhalation – rat 47701685 LC50 >6.56 mg/L M & F IV

870.2400 Acute eye irritation – rabbit 47701686 Minimally irritating IV

870.2500 Acute dermal irritation – rabbit 47701687 Non-irritating IV

870.2600 Skin sensitization – local lymph 

node - mice

47701688 No sensitization -

TableA.2.1.2 Acute Toxicity Profile – Pyroxasulfone Metabolites

Guideline 

No.

Study Type MRID(s) Results Toxicity Category

870.1100 Acute oral – rat (females) M-1 47701678 LD50 = >2000 mg/kg III

870.1100 Acute oral – rat (females) M-3 47701679 LD50 = >2000 mg/kg III

870.1100 Acute oral – rat (females) M-25 47701680 LD50 = >2000 mg/kg III

870.1100 Acute oral – rat (females) M-28 47701755 LD50 = >2000 mg/kg III

870.1100 Acute oral – rat (females) I-3 47701681 LD50 = >2000 mg/kg III

870.1100 Acute oral – rat (females) I-4 47701682 LD50 = >2000 mg/kg III

870.1100 Acute oral – rat (females) I-5 47701683 LD50 = >2000 mg/kg III
Page 36 of 81

A.2.2 Subchronic, Chronic, Other Toxicity

Table A.2.2 Subchronic, Chronic and Other Toxicity Profile of Pyroxasulfone

Guideline No. Study Type MRID No. (year)/ 

Classification /Doses

Results

870.3050 28-Day Dietary 

toxicity – Han Wistar 

Rat

5 rat/sex/dose

47701689 (2003), Covance 

Labs 0, 500, 5000, 

20,000 ppm 

M: 64.3, 649.6, 2677.5 

mg/kg/day

F: 62.2, 673.9, 2584.7 

mg/kg/day

Acceptable/guideline

NOAEL = 500 ppm (64.3/62.2 mg/kg/day in 

males/females) 

LOAEL = 5000 ppm (650/674 mg/kg/day in 

males/females) based on hepatocyte and myocardial 

vacuolation; myocardial degeneration.

Non-Guideline 

Special Study

28-Day Dietary 

toxicity – Rat

Myocardial toxicity 

and enzyme markers

5 rat/sex/dose

47889320 (2004)

Covance Labs

0, 100, 1000, 5000, 20000 

ppm

M: 7.3, 75.4, 367.2, and 

1364.0 mg/kg/day

F: 8.3, 84.4, 388.0, and 

1676.1 mg/kg/day

Acceptable/Non-Guideline

Aspartate aminotransferase was increased by 138% in the 

20,000 ppm females on Day 22. On Day 29, increases in 

aspartate aminotransferase were noted in the 5000 (incr 

150%) and 20,000 (incr 93%) ppm females. On Day 29, 

increases in lactate dehydrogenase were observed in the 

5000 ppm group (incr 119-167%) and 20,000 ppm group 

(incr 57-87%). Decreases (p≤0.05) in alanine 

aminotransferase and creatinine phosphokinase were 

observed, but were not considered toxicologically 

relevant. 

hepatic lesions were noted at 1000 ppm and above and 

20,000 ppm females 

myocardial degeneration/necrosis in the 1000 ppm and 

above males and females, vacuolation in 5000 and 20,000 

ppm males and fibrosis in 20,000 ppm males and 

females.

CPK enzymes were not predictive markers of myocardial 

toxicity. 

870.3100 90-Day oral toxicity -

Han Wistar Rat

10 rats/sex/dose, 

5 rats/sex/dose for 

recovery

47701692(2005); Covance 

Labs

0, 100, 500, 2500, 5000 ppm;

M: 0, 8.9, 43.9, 221.4, 451.2 

mg/kg/day;

F: 0, 10.2, 48.9, 255.8, 514.2 

mg/kg/day

Acceptable/guideline

NOAEL 500 ppm (44/49 mg/kg/day in M/F) LOAEL = 

2500 ppm (221/256 mg/kg/day in M/F) based on either 

altered organ weights, histopathological indicators or 

clinical pathological indicators in liver, skeletal and 

cardiac muscle and the pancreas (liver centrilobular 

hepatocyte hypertrophy and eosinophilia in males, a dose 

related increased incidence of myocardial degeneration or 

necrosis in the heart of males and skeletal muscle 

myopathy in females). Full or partial recovery was 

evident in all the above effects apart from kidney weights 

in females.
Page 37 of 81

Table A.2.2 Subchronic, Chronic and Other Toxicity Profile of Pyroxasulfone

Guideline No. Study Type MRID No. (year)/ 

Classification /Doses

Results

870.3100 90-Day oral toxicity -

Crl:CD®(SD)IGS BR 

rats

10 rats/sex/dose

47701693 (2005) Haskell 

Labs

0, 25, 250, 2500 ppm

M: 0, 1.7, 16.4, 171.2 

mg/kg/day

F: 0, 2.20, 20.6, 205.4 

mg/kg/day

Acceptable/guideline

NOAEL = 250 ppm (16/21 mg/kg/day in males/females) 

LOAEL = 2500 PPM (171/205 mg/kg/day in males and 

females, based on increased liver weight, centrilobular 

hepatocellular hypertrpophy, focal/multifocal myofiber 

degeneration and inflammation, urinary bladder diffuse 

mucosal hyperplasia.

870.3100 90-Day oral toxicity 

B6C3F1 mouse

12 mice/sex/dose

47701694 (2005); Covance 

Labs

0, 500, 1000, 5000, 

10000/7500 ppm;

M: 0, 103, 206, 1424, 2494 

mg/kg/day;

F: 0, 96, 202, 1228, 

1941mg/kg/day

Acceptable/guideline

NOAEL = 1000 ppm (equivalent to 206/202 mg/kg/day, 

M/F)

LOAEL = 5000 ppm (1424/1228 mg/kg/day in 

males/females) based decreased body weight, changes in 

clinical chemistry parameters, changes in organ weights 

(including increased kidney and liver weights), and 

microscopic effects in the kidney (cortical tubular 

nephropathy) and heart (myocardial 

degeneration/fibrosis). Target organs at 5000 ppm and 

above are heart, liver, kidney.

870.3100 90-Day oral toxicity 

B6C3F1 mouse

10 mice/sex/dose

47701695 (2005); Haskell 

Labs

0, 25, 250, 2500 ppm

M: 4.0, 39.8, 394 mkd

F: 5.4, 51.2, 531.3 mkd

Acceptable/guideline

NOAEL = 250/2500 ppm in females /males (51.2/394 

mg/kg/day in females /males). 

LOAEL = 2500 ppm in females (equivalent to 531 

mg/kg/day) based on an increased incidence of chronic 

progressive nephropathy (minimal to mild), multifocal 

tubules lined by basophilic epithelium indicative of 

tubular regeneration in females. LOAEL in males is 

>2500 ppm (394 mg/kg/day).

870.3150 90- day oral toxicity –

Dog

4 dogs/sex/dose

47701696 (2004); Biosafety 

Research Center, Japan

0, 0.2, 2.0, 10.0 mg/kg/day in 

gelatin caps

Acceptable/guideline 

NOAEL = 2 mg/kg/day

LOAEL =10 mg/kg/day. Slight muscle fiber degeneration 

of the diaphragm and hyperplasia of satellite cells; nerve 

fiber degeneration, in addition to the similar adverse 

effects occurring at 15 mg/kg/day dose in a subsequent 

90-day dog study (MRID 47701697). 

870.3150 90- day oral toxicity –

Dog

4 dogs/sex/dose

47701697 (2006); Haskell

0, 15 mg/kg/day in gelatin 

caps

Acceptable/guideline

LOAEL = 15 mg/kg/day: Decreased BW gain (↓40%) in 

males; Minimal to mild axonal/myelin degeneration in the 

sciatic nerve of all males and 3⁄4 females. Minimal to mild 

subacute inflammation of skeletal muscle in males and 

females. Impaired limb function, body and limb 

hypotonia, increase in serum creatine kinase activity. 

870.4100 1-yr oral toxicity –

Dog

4/dog/sex/dose

47701707 (2008) MPI 

Research (Mattawan 

Michigan)

0, 0.2, 2.0, 10.0 mg/kg/day in 

gelatin caps

Acceptable/guideline

NOAEL = 2 mg/kg/day

LOAEL = 10 mg/kg/day based on impaired hind limb 

function, ataxia, hind limb twitching and tremors; clinical 

pathology: increased creatine kinase, aspartate 

aminotransferase; axonal/myelin degeneration of the 

sciatic nerve and spinal cord sections
Page 38 of 81

Table A.2.2 Subchronic, Chronic and Other Toxicity Profile of Pyroxasulfone

Guideline No. Study Type MRID No. (year)/ 

Classification /Doses

Results

870.3465 4- week inhalation –

Rat

10/sex/dose

47701699 (2008) – Dupont

0, 10 40, 200 mg/m3/day 

aerosol dust/nose only

Acceptable/guideline

NOAEL = 200 mg/ m3/day based on lack of adverse toxic 

effects at this HDT.

870.3200 28-Day dermal – Rat 

10/sex/dose

47701698 (2005)

Dupont

0, 20, 100, 1000 mg/kg/day

Acceptable/guideline

NOAEL = 100 mg/kg/day 

LOAEL = 1000 mg/kg/day based on minimal to mild 

cardiac myofiber degeneration with inflammation in 

males and females

870.3700a Prenatal 

developmental in (rat) 

Crj:CD(SD)IGS[SPF] 

Range finding

7/dose

47701701 (2004) Biosafety 

Res. Ctr. Japan

0, 125, 250, 1000 mg/kg GD 

5-19

Acceptable/non-guideline

NOAEL for maternal and developmental toxicity = 1000 

mg/kg/day (HDT)

unossified hyoids at 1000 mg/kg/day and this finding was 

not considered to be an unequivocally treatment-related 

effect

870.3700a Prenatal 

developmental in 

Crl:CD(SD) (rat)

22 rats/dose 

47701702 (2007) Haskell

0, 100, 50, 1000 mg/kg/day 

on GD 6-20

Acceptable/guideline

NOAEL for maternal and developmental toxicity = 1000 

mg/kg/day (HDT)

870.3700b Prenatal 

developmental in 

(rabbit) ) Range 

finding

7/dose 

47701703 (2004) Covance

0, 250, 500, 1000 mg/kg/day 

on GD 7-28

Acceptable/non-guideline

NOAEL for maternal and developmental toxicity = 1000 

mg/kg/day (HDT)

870.3700b Prenatal 

developmental in 

(rabbit) 22/dose

47701704 (2007) Haskell

0, 250, 500, 1000 mg/kg/day 

on GD 7-28

Acceptable/guideline

Maternal toxicity

NOAEL = 1000 mg/kg/day (HDT)

Developmental toxicity

NOAEL = 500 mg/kg/day

LOAEL = 1000 mg/kg/day reduced fetal weight and 

increased fetal resorptions
Page 39 of 81

Table A.2.2 Subchronic, Chronic and Other Toxicity Profile of Pyroxasulfone

Guideline No. Study Type MRID No. (year)/ 

Classification /Doses

Results

870.3800 Reproduction and 

fertility effects

(rat) 

Crl:CD®(SD)IGS BR

One-Gen Study

12/sex/dose

Range-finding

47701705 (2006)

Dupont Haskell

0, 25, 250, 5000 ppm 

P M premating 1.69,16, 339 

mg/kg/day

P F premating 1.98, 19.6, 

383 mg/kg/day

P F gestation 1.78, 18, 332 

mg/kg/day

P F lactation 3.82, 37.9, 728 

mg/kg/day

F1 M postweanling 2.73, 

27.9, 564 mg/kg/day

F1 F postweanling 2.99, 

30.4, 643 mg/kg/day

Acceptable/nonguideline

Parental toxicity

NOAEL = 250 ppm (16/20 mg/kg/day M/F)

LOAEL = 5000 ppm, (339/383 mg/kg/day) reduced body 

weight and gain and food consumption, cardiac myofiber

and sciatic nerve lesions, microscopic effects in the heart, 

liver, muscle, and sciatic nerve of males and females 

Reproductive toxicity

NOAEL = 5000 ppm (339 mg/kg/day) (HDT)

Offspring toxicity

NOAEL = 250 ppm (16/20 mg/kg/day) 

LOAEL = 5000 ppm (339 mg/kg/day) reduced pup weight 

during lactation (27%-30% lower than control mean) and 

delayed sexual maturation in both sexes.

870.3800 Reproduction and 

fertility effects

(rat) 

Crl:CD®(SD)IGS BR

2-gen study

30/sex/dose

47701706 (2008)

Dupont Haskell

0, 5, 100, 2000 ppm 

Mean substance intake 

0.4/0.4, 7.2/8.4, 144/165 

mg/kg/day for 

Males/Females

Acceptable/guideline

Parental toxicity

NOAEL = 100 ppm (7.2/8.4mg/kg/day)

LOAEL = 2000 ppm (144/165mg/kg/day) reduced body 

weight, body weight gain and food consumption and 

increased kidney weight, cardiomyopathy and urinary 

bladder mucosal hyperplasia with inflammation.

Reproductive toxicity

NOAEL = 2000 ppm (135 mg/kg/day) (HDT)

Offspring toxicity

NOAEL = 100 ppm (11 mg/kg/day)

LOAEL = 2000 ppm (144/165 mg/kg/day) reduced pup 

weights and body weight gains during lactation
Page 40 of 81

Table A.2.2 Subchronic, Chronic and Other Toxicity Profile of Pyroxasulfone

Guideline No. Study Type MRID No. (year)/ 

Classification /Doses

Results

870.4200b Carcinogenicity

(mouse)

Crl:CD1(ICR) mice 

50+10/sex/dose

47701710 (2009)

Dupont Haskell

0, 5, 150, 2000 ppm

After 14 months 2000 ppm 

reduced to 1000 ppm for M 

and 500 ppm for F.

M: 0, 0.63/0.61, 18.33/18.56, 

255.13/131.34 mg/kg/day

F: 0, 0.88/0.71, 26.33/22.44, 

371.64/76.49 mg/kg/day 

Overall mean

0, 0.62/0.84, 18.4/25.5, 

228/306, M/F

Acceptable/guideline

NOAEL = 150 ppm (18.4/25.5mg/kg/day)

(M/F)

LOAEL = 228/306 mg/kg/day M/F, based on 

degeneration of sciatic and trigeminal nerve axons and 

their associated myelin sheaths and an increase in the 

incidence of chronic progressive nephropathy (females). 

Renal tubular adenomas at this dose in 3 of 50 main study 

males, in the presence of a 17% reduction of body weight 

gain compared to control males. 

The test substance was considered initially oncogenic 

in male mice. Revaluation of the renal tubular 

adenomas of the male mice was conducted by an 

independent kidney expert pathologist (MRID 

48354403) and reviewed by a Pathology Working 

Group (MRID 48354405). The renal tubular 

adenomas observed in male mice were considered by 

the PWG to be incidental and unrelated to the 

administration of pyroxasulfone. A dose-related 

increase in retrograde nephropathy in males was also 

identified.

870.4100 One year chronic 

(Rat)

20 rats/sex/dose 

47701708 (2008)

Dupont Haskell

0, 5, 50, 1000, 2000 ppm

M: 0, 0.22, 2.22, 46.2, 91.91 

mg/kg/day

F: 0, 0.3, 3.12, 60.80, 121.33 

mg/kg/day

Acceptable/guideline

NOAEL = 50 ppm mg/kg/day. 

LOAEL = 1000 ppm or 46.2/60.8 mg/kg/day (M/F) based 

on reduced body weight parameters in males (↓ 5-10%) 

and microscopic findings in the liver (centrilobular 

hepatocellular hypertrophy (males)), heart (increased 

cardiomyopathy (females)) and urinary bladder (mucosal 

hyperplasia (males and females)). At 2000 ppm, these 

effects were accompanied by increased clinical 

observations of red discharge from the penis and 

associated red-stained cage boards as well as increased 

liver and kidney weights. 

870.4200a Carcinogenicity

(rat)

70/sex/dose

47701709 (2009)

Dupont Haskell

0, 5, 50, 1000, 2000 ppm

M: 0, 0.21, 2.05, 42.55, 

84.55 mg/kg/day

F: 0, 0.28, 2.69, 54.28, 

106.74 mg/kg/day

Acceptable/guideline

NOAEL = 50 ppm or 2.05/2.69 (M/F) mg/kg/day

LOAEL = 1000 ppm or 42.55/54.28 (M/F) mg/kg/day 

based on reduced body weight parameters (males and 

females), reduced food consumption (females), and 

increased red-stained urine on cageboards (males) at 2000 

ppm and reduced body weight and food consumption 

parameters (females) and increased red-stained urine on 

cageboards (males) at 1000 ppm. Increased 

cardiomyopathy (males and females); urinary bladder 

mucosal hyperplasia, inflammation, and transitional cell 

papillomas (males); and sciatic nerve degeneration 

(females) at 1000 ppm and above. 

Based on a low incidence in urinary bladder transitional 

cell papillomas in the 1000 ppm and 2000 ppm males, the 

test substance was considered oncogenic in male rats at 

exposures of 1000 ppm and above.
Page 41 of 81

Table A.2.2 Subchronic, Chronic and Other Toxicity Profile of Pyroxasulfone

Guideline No. Study Type MRID No. (year)/ 

Classification /Doses

Results

870.5100 Bacterial reverse 

mutation test

47701712 (2003), Covance

TA98, TA1535 and TA1537-

S typhimurium & WR2 uvrA 

of E coli

Acceptable/guideline

Test article has no reverse mutagenic potential under these 

experimental conditions either in the presence or absence 

of metabolic activities.

Precipitation of the test article was observed on all E coli

test plates treated at 1581 μg/plate, and on all S 

typhimurium test plates treated at 632.4 μg/plate and 

above.

870.5380 In vivo studies in 

germ cells -

Mammalian 

spermatogonial 

chromosomal 

aberration test 

NA Because all other genotoxicity studies are negative, no 

studies for this data point were performed with regulatory 

agency concurrence per 28 February 2009 OECD 

meeting.

870.5550 In vivo genotoxicity 

testing – Unscheduled 

DNA synthesis

NA Because all other genotoxicity studies are negative, no 

studies for this data point were performed with regulatory 

agency concurrence per 28 February 2009 OECD 

meeting.

870.5300 In vitro mammalian 

cell gene mutation 

test: Mouse 

Lymphoma L5178Y 

Cells

47889311 (2009)

Huntingdon

Acceptable/guideline

Pyroxasulfone TGAI was tested up to the limit of 

solubility and up to cytotoxic effects and was not 

mutagenic in the presence or absence of S9-activation. 

870.5375 In vitro mammalian 

cell chromosome 

aberration test, CHO 

cells

47701719 (2003) , Covance

Acceptable/guideline

Test article did not induce chromosome aberrations in 

cultured (CHO) cells when tested up to its limit of 

solubility in both the absence and presence of metabolic 

activation (S-9).

870.5395 Mammalian 

erythrocyte 

micronucleus test

47701720 (2007), Dupont

500, 1000, 2000 mg/kg 

orally to male and female 

mice

Acceptable/guideline

Under the conditions of this study, KIH-485TGAI did not 

induce biologically relevant increases in micronucleated

polychromatic erythrocytes in animal bone marrow. The 

test substance was concluded to be negative in this in vivo 

study.

870.6200a Acute neurotoxicity 

screening battery

Crl:CD(SD) rat

10/sex/dose

47701721 (2007), Dupont

0, 20, 200, 2000 mg/kg

Acceptable/guideline

NOAEL = 2000 mg/kg/day in males and females (HDT).

870.6200b Subchronic 

neurotoxicity 

screening battery

Crl:CD(SD) rat

12/sex/dose

47701722 (2007), Dupont

0, 25, 250, 2500 ppm

M: 0, 1.56, 15.85, and 

161.48 mg/kg/day

F: 0, 1.92, 19.60, and 199.59 

mg/kg/day

Acceptable/guideline

Systemic NOAEL = 2500 ppm or 161/200 mg/kg/day 

(M/F), the HDT

Neurotoxicity NOAEL = 2500 ppm or 161/200 

mg/kg/day (M/F), the HDT
Page 42 of 81

Table A.2.2 Subchronic, Chronic and Other Toxicity Profile of Pyroxasulfone

Guideline No. Study Type MRID No. (year)/ 

Classification /Doses

Results

870.6300 DNT Study

Crl:CD(SD) rat

Preliminary Range 

Finding

8 mated females/dose

47701723 (2007), 

Huntingdon

0, 100, 300, 600, 1000 

mg/kg/day GD6-LD7; 

Offspring Day 7-20 of age

Acceptable/nonguideline

There was no effect of maternal treatment, or direct 

treatment of the offspring with KIH-485, on the clinical 

condition, survival, or macropathology findings of the 

dams or the offspring. 

Treatment of adult females at 1000 mg/kg/day was 

associated with up to 16% lower mean numbers of 

implantations and litter sizes at birth and on Day 4. The 

use of a dose above 1000 mg/kg/day may be associated 

with a more marked reduction in the implantation rate and 

litter size sufficient to preclude a meaningful evaluation of 

developmental neurotoxicity in the offspring. Treatment at 

600 mg/kg/day was associated with up to 8% lower mean 

numbers of implantations and litter size at birth.

870.6300 DNT Study

Crl:CD(SD) rat

24 mated 

females/dose

47701724 (2008), 

Huntingdon

0, 100, 300, 900 mg/kg/day 

GD6-LD7; Offspring Day 7-

20 of age (EPA reviewed 

protocol)

Acceptable/guideline

Maternal NOAEL = 900 mg/kg bw/day (HDT), the 

LOAEL was >900 mg/kg/day.

Functional development NOAEL = 900 mg/kg/day.

Offspring NOAEL = 100 mg/kg/day based on decrease 

in brain weight in male and female offspring accompanied 

with a decrease in the thickness of the hippocampus, 

corpus callosum and cerebellum in PND 21 female 

offspring at 300 mg/kg/day

870.7800 Immunotoxicity 

Feeding Study in 

mice 

10/mice/sex/dose

47701732 (2008)

Dupont

0, 40, 400, 4000 ppm for 28 

days

M: 0, 6, 61, 633 mg/kg/d

F: 0, 8, 77, 791 mg/kg/d

Acceptable/guideline

Systemic toxicity

NOAEL = 61/77 (M/F) mg/kg/day

LOAEL = 633/791 (M/F) mg/kg/day based on reduction 

in body weight (-5 to -9%) and body weight gain (-32%)

Immunotoxicity:

NOAEL = 633/791 (M/F) mg/kg/day (HDT) based on 

absence of immunotoxic effects.

870.7800 Immunotoxicity 

Feeding Study in rats

10/rats/sex/dose

47701731 (2006)

Dupont

0, 25, 250, or 7500 ppm for 

28 days (0/0, 2/2, 18/19, and 

529/570 mg/kg/day in 

males/females). 

Acceptable/guideline

Systemic toxicity

NOAEL = 250 ppm (18/19 mg/kg/day M/F)

LOAEL = 7500 ppm (529/570 (M/F) mg/kg/day based on 

reduction in body weight gain (-30% to -56%) and food 

consumption (-19% to – 52%)

Immunotoxicity:

NOAEL = 529/570 (M/F) mg/kg/day (HDT) based on 

absence of immunotoxic effects.

870.7600 Dermal penetration NA Not required for US or Australia and waived for Canada 

per 28 February 2009 OECD meeting.
Page 43 of 81

Table A.2.2 Subchronic, Chronic and Other Toxicity Profile of Pyroxasulfone

Guideline No. Study Type MRID No. (year)/ 

Classification /Doses

Results

870.7485 Metabolism and 

pharmacokinetics

(beagle dog)

47701726 (2005),

Covance

One female dog: single oral 

dose of 10 mg of pyrazole14C /kg bw, urine and feces 

were collected over 120 h. 

Sequential blood samples 

were and the dog was killed 

at 120 h after dosing. The 

level of radioactive residues 

was determined in the blood, 

plasma, and selected tissues 

(heart, kidney and liver) at 

necropsy. The excreta were 

analyzed to determine the 

number and nature of any 

metabolites present using 

HPLC and HPLC/MS. 

Acceptable/nonguideline

Overall recovery of radioactivity was 98%. Oral 

absorption of radioactivity was at least 51%. The majority 

of the radioactivity (76.9%) was eliminated in the first 24 

h. The radioactivity was equally excreted in urine and 

feces. Cmax was of 3.954 and 2.116 μg equivalents/g at 8 

h in blood and plasma respectively and were still 

quantifiable at 120 h. The terminal half-life was of 89.58 

and 40.80 h in blood and plasma respectively. The levels 

of radioactivity in the tissues were highest in the liver and 

blood (0.334 and 0.327 μg equivalents/g, respectively). 

The kidney, plasma and heart contained the next highest 

concentrations. The feces contained only unchanged 

KIH-485. Urine contained no parent compound. HPLC 

chromatography showed that there were several 

metabolites, some of which were changed following 

treatment with ß-D-glucuronidase. Metabolites M-3, M-7 

and M-8 were identified in the dog, though M-3 was only 

a minor metabolite. Structures were proposed for three 

other metabolites.

870.7485 Metabolism and 

pharmacokinetics

(Mouse)

47701730 (2007)

Huntingdon

single oral dose of 10 mg 

pyrazole14C 

pyroxasulfone/kg bw,

Autoradiography: 4 ♀

Excretion/balance:3 ♀

Tissue distribution: 12 ♀

Acceptable/nonguideline

KIH-485 was rapidly absorbed, metabolized and 

eliminated. ~ 78% excreted in the urine after 120 hours 

(about 73% was excreted within the first 24 hours). The 

remainder in the feces. Only about 0.2% of the dose was 

retained in the tissues. Fifteen metabolites were resolved 

by the chromatographic and three products resulting from 

oxidative phase I processes (KIH-485-MI, KIH-485-M3 

and KIH-485-13) were identified by co-chromatography. 

One minor metabolite was identified as a glucuronide or 

sulfate conjugate. KIH-485 itself was not present in urine.

Concentrations of total radioactivity in the liver and heart 

were highest at the earliest sacrifice time of 2 hours: 3.186 

μg KIH-485 equivalents/g in the liver and 0.603 μg KIH485 equivalents/g in the heart. After 48 hours these levels 

had declined to 0.430 and 0.031 μg KIH485 

equivalents/g, respectively.

Whole-body autoradiography showed. At 2 hours after 

dosing, radioactivity had been absorbed from the GI tract 

and was distributed into the vast majority of tissues. High 

concentrations in the liver and gallbladder were consistent 

with an appreciable first-pass elimination of 14C-KIH-485 

and/or its metabolites by the liver, followed by biliary 

excretion. Low radioactivity concentrations were 

associated with the bone surfaces, brain, spinal cord and 

the lens of the eye. By 24 hours after dosing, radioactivity

concentrations in the majority of tissues (including the 

central nervous system) were close to, or indistinguishable 

from, background levels.
Page 44 of 81

Table A.2.2 Subchronic, Chronic and Other Toxicity Profile of Pyroxasulfone

Guideline No. Study Type MRID No. (year)/ 

Classification /Doses

Results

870.7485 Metabolism and 

pharmacokinetics

(rat) 4/sex/group

47701728 (2008)

Covance

Single oral dose

10, 700 mg/kg of either the 

pyrazole14C or the 

isoxzzoline14C radiolabel

Acceptable/guideline

91-104% recovery. Absorption at the low dose based on 

bile and urine >76% AD. Cmax 2 hrs at low dose, 11 hrs 

at the high dose. T1/2 longer for the IX label. Saturation of 

absorption with increasing dose; a 70-fold dose level 

increase produced a 10-fold increase in Cmax and a 20 to 

50-fold increase in AUC(0-t) with [Py14C]-KIH-485, and a 

20-fold increase in Cmax and a 10-fold increase in AUC(0-t) 

with [Ix14C]-KIH-485. Excretion rapid and complete 

within 48-72 hrs. Low dose animals’ excretion mostly in 

urine. High dose animals mostly in feces. Residual in 

carcass <7% in low dose and <0.5% in high dose. No 

significant sex differences in elimination or metabolism. 

No significant 14CO2 elimination. Liver and kidney 

highest residues. Extensive metabolism ~30 

chromatographic regions in urine, 19 in feces, 31 in bile. 

Major metabolite of [Py14C] urine was M-13 (up to 26% 

of the low dose level and up to 4% at the high dose level) 

followed by M-7 and M-3. Cleavage between the pyrazole 

and isoxazoline ring structure. Major metabolites of 

[Ix14C]-compound in the urine were M-13 (20% of the 

dose), M-16 (19% of the dose) and M-26 (6.4% of the 

dose). The major fecal radioactivity was unabsorbed 

KIH-485 (10% of the dose at the low dose level and up to 

78% at the high dose level). The next most abundant 

metabolite was M-13 (up to 3% of the dose).

In bile of the [Py14C] rats a sulphate conjugate of 

hydroxy KIH-485 and M-13 glucuronide accounted for up 

to 3.1% of the dose each plus free M-13 metabolite (~ 

1.6% of the AD).

[Ix14C]-KIH-485 bile, M-26 (10% of the AD) tentatively 

identified and was produced by the cleavage of the 

pyrazole ring and subsequent loss of the fluorine moieties. 

A sulphate conjugate of hydroxy KIH-485 (7%) and the 

other M-13 glucuronide (3%). A glutamyl cysteine 

conjugate of the isoxazoline ring (4%) was tentatively 

identified.
Page 45 of 81

Table A.2.2 Subchronic, Chronic and Other Toxicity Profile of Pyroxasulfone

Guideline No. Study Type MRID No. (year)/ 

Classification /Doses

Results

870.7485 Metabolism and 

pharmacokinetics

(rat)

47701729 (2008)

Covance

Steady State:

10mg/kg/day to 4 females of 

the pyrazole14C for 14 

days

Pharmacokinetics:

10 mg/kg/day to 4 females 

for 7days followed by 10 

mg/kg of either radiolabel

Excretion Balance:

10 mg/kg/day to 4 females 

for 7days followed by 10 

mg/kg of either radiolabel

Tissue Distribution:

10 mg/kg/day to 10 females 

for 7days followed by 10 

mg/kg of either radiolabel

Acceptable/guideline

Steady state reached after 7 doses. Recoveries ranged 

from between 92.4 to 99.6% of administered radioactivity. 

Absorption, based on urinary excretion, was >69% of the 

dose. Absorbed radioactivity was rapidly excreted, 

primarily in the urine. KIH-485 or its radiolabeled 

metabolites were associated with the cellular fraction of 

blood. For the Py14C, Cmax 1 hr. There were no 

apparent differences in the tmax in plasma and blood but 

the t1⁄2 was ca 7-fold greater in blood; the t1⁄2 was 16.8 

hours in plasma and 112 hours in blood. For the Ix14C, 

Cmax ca 1.5 hours in plasma and at ca 7.5 hours in blood. 

The tmax in blood was approximately double the levels in 

plasma and the t1⁄2 was ca 5-fold greater in blood; the t1⁄2

was 60.9 hours in plasma and 302 hours in blood.

Absorbed radioactivity was rapidly distributed throughout 

tissues and rapidly cleared without accumulation of 

radioactivity in the tissues. KIH-485 underwent extensive 

metabolism with the major metabolite being M-13. 

Excretion was rapid with 85-95% of radioactivity being 

excreted within 24 hours. There was minimal difference in 

the routes and rates of excretion between the two 

radiolabeled forms. Elimination half life in plasma was 

extended following [Ix14C]-KIH-485 administration.

Compared with single dose animals, there was saturation 

or induction of metabolism which resulted in an altered 

metabolic profile, particularly for the [Py14C] label, and 

this may also have resulted in small shift (6%) from 

urinary to fecal excretion in repeat dose animals. 

Otherwise, repeat dosing did not discernibly affect the 

overall pharmacokinetics of KIH-485. There was no 

discernible difference in the tissue distribution between 

single dose and repeat dosing.

------------- Metabolism and 

pharmacokinetics

Transfer to milk (rat)

47701727 (2006)

Covance

single oral dose of 250 mg 

[

14C]-KIH-485/kg to 18 

female lactating rats

Milk collected from 3 rats 

each interval at 0.5, 2, 8, 24, 

48, 96 hours, then sacrificed 

for blood collection

acceptable/non-guideline

The concentrations of radioactivity in the milk and plasma 

reached maximal concentrations of 23.48 and 47.89 μg 

equivalents/g respectively at 2 h post-dose before 

decreasing to 0.667 and 0.184 μg equivalents/g 

respectively at 96 h post-dose. 

The elimination half-lives of the test substance from the 

milk and plasma were similar at 21.4 h and 22.5 h, 

respectively. The milk: plasma ratio of levels of 

radioactivity increased throughout the study, from 0.189 

at 30 min after dosing, reaching near parity at 24 h, to 

3.625 at 96 h after dosing.
Page 46 of 81

Table A.2.2 Subchronic, Chronic and Other Toxicity Profile of Pyroxasulfone

Guideline No. Study Type MRID No. (year)/ 

Classification /Doses

Results

870.7485 Metabolism and 

pharmacokinetics

Transfer to offspring 

(rat)

4770125(2006)

Huntingdon

3 female rats dose at 10 

mg/kg/day of pyrazole-5-

14C]-KIH-485 from GD 6 

until Day 9 after parturition. 

Ten mated undosed rats 

provided naïve pups. Three 

naïve pups at each interval of 

3, 5, 7, 9, 10, 11, 13 days 

post parturition replaced the 

pups of the dosed mothers 

and allowed to suckle for 1 

hour, then sacrificed and 

stomach contents analyzed.

acceptable/non-guideline

During the dosing period at Days 3 - 9 after parturition, 

concentrations in maternal plasma (1.31 – 1.76 μg 

equivalents/g ) were ~ double those in pup stomach 

contents (0.672 – 1.013 μg equivalents/g).

After cessation of dosing (1 - 4 days after last dose)

concentrations dropped rapidly for both matrices (13 days 

after parturition, pup stomach contents: <0.028 μg 

equivalents/g; maternal plasma: <0.060 μg equivalents/g).

Changes in concentrations of radioactivity in both 

matrices mimicked each other. The ratio of the mean 

concentrations of pup stomach contents to maternal 

plasma remained relatively constant with an overall mean 

value, both during and after dosing, of 0.49.

Toxicity of Metabolites

870.3050 14-Day oral gavage 

toxicity – Han Wistar 

Rat

3 females/dose

47701690 (2005)

Safepharm Labs

0, 1000 mg/kg/day of 

KIH-485 M-1

acceptable/non-guideline

NOAEL = 1000 mg/kg/day no observed adverse effects.

870.3050 14-Day oral gavage 

toxicity – Han Wistar 

Rat

3 females/dose

47701691 (2008)

Safepharm Labs

0, 100, 1000 mg/kg/day of 

KIH-485 M-3

acceptable/non-guideline

NOAEL = 1000 mg/kg/day no observed adverse effects.

870.5100 Bacterial reverse 

mutation test

47701713 (2005), 

Safepharm Labs

TA98, TA1535, TA100 

and TA1537- S 

typhimurium & WP2 

uvrA of E coli

50-5000 μg/plate

KIH-485 M-1

acceptable/guideline

Test article has no reverse mutagenic potential under the 

experimental conditions either in the presence or absence 

of metabolic activities.

870.5100 Bacterial reverse 

mutation test

47701714 (2004), 

Safepharm Labs

TA98, TA1535, TA100 

and TA1537- S 

typhimurium & WP2 

uvrA of E coli

50-5000 μg/plate

KIH-485 M-3

acceptable/guideline

Test article has no reverse mutagenic potential under the 

experimental conditions either in the presence or absence 

of metabolic activities.
Page 47 of 81

Table A.2.2 Subchronic, Chronic and Other Toxicity Profile of Pyroxasulfone

Guideline No. Study Type MRID No. (year)/ 

Classification /Doses

Results

870.5100 Bacterial reverse 

mutation test

47701715 (2008), RCC 

Ltd., Germany

TA98, TA1535, TA100 

and TA1537- S 

typhimurium & WP2 

uvrA of E coli

33-5000 μg/plate

KIH-485 M-25

acceptable/guideline

Test article has no reverse mutagenic potential under the 

experimental conditions either in the presence or absence 

of metabolic activities.

870.5100 Bacterial reverse 

mutation test

47701756 (2009), 

Huntingdon

TA98, TA1535, TA100 

and TA1537- S 

typhimurium & WP2 

uvrA of E coli

50-5000 μg/plate

KIH-485 M-28

acceptable/guideline

Test article has no reverse mutagenic potential under the 

experimental conditions either in the presence or absence 

of metabolic activities.

870.5100 Bacterial reverse 

mutation test

47701716 (2007), 

Safepharm Labs

TA98, TA1535, TA100 

and TA1537- S 

typhimurium & WP2 

uvrA of E coli

15-5000 μg/plate

KIH-485 I-3

acceptable/guideline

Test article has no reverse mutagenic potential under the 

experimental conditions either in the presence or absence 

of metabolic activities.

870.5100 Bacterial reverse 

mutation test

47701717 (2007), 

Safepharm Labs

TA98, TA1535, TA100 

and TA1537- S 

typhimurium & WP2 

uvrA of E coli

50-5000 μg/plate

KIH-485 I-4

acceptable/guideline

Test article has no reverse mutagenic potential under the 

experimental conditions either in the presence or absence 

of metabolic activities.

870.5100 Bacterial reverse 

mutation test

47701718 (2007), 

Safepharm Labs

TA98, TA1535, TA100 

and TA1537- S 

typhimurium & WP2 

uvrA of E coli

50-5000 μg/plate

KIH-485 I-5

acceptable/guideline

Test article has no reverse mutagenic potential under the 

experimental conditions either in the presence or absence 

of metabolic activities.
Page 48 of 81

Table A.2.2 Subchronic, Chronic and Other Toxicity Profile of Pyroxasulfone

Guideline No. Study Type MRID No. (year)/ 

Classification /Doses

Results

NA DEREK Evaluation 47701757 (2009)

LSR Associates 

Metabolites: M-1, M-3, 

M-9, M-25, M-29 and 

parent Pyroxasulfone

All available toxicity endpoints were searched 

(carcinogenicity, chromosome damage, genotoxicity, 

hepatotoxicity, HERG channel inhibition, irritation, 

mutagenicity, reproductive toxicity, respiratory 

sensitization, thyroid toxicity and other miscellaneous 

endpoints). Toxicity to humans, mammals and bacteria 

was assessed. Neither pyroxasulfone nor the five 

metabolites evaluated fired any structural alerts for 

toxicity.

NA (Special Study: 

A Toxicological 

Mechanism Study)

Effects on motor 

systems in mice after 14-

day dietary exposure 

using a glutathione 

depletion animal model.

48046901 (2009)

Female CD1 mice 

(3/group) were 

administered 0, 4500 

ppm pyroxasulfone + 20 

mM BSO, 20000 ppm

pyroxasulfone + 20 mM

BSO and 20 mM BSO 

alone for 14 days.

acceptable/non-guideline

Gross pathological observation showed wasted body 

muscle volumes in the 20000 ppm pyroxasulfone + BSO

group animals. Histopathological examination showed

degeneration/necrosis, calcification, cellular infiltration

and the features of regenerating muscular tissue, namely 

proliferation of satellite cells in skeletal muscle in all BSO 

treated animals. Pyroxasulfone appeared to augment the 

depletion of the intracellular GSH in muscular tissues. 

NA (Special Study: 

A Toxicological 

Mechanism Study)

Heart histopathology for 

a toxicological 

mechanism study of 

Pyroxasulfone (KIH485): effects on motor 

systems in mice after 14-

days dietary exposure 

using a glutathione 

depletion animal model

48046902 (2010)

mice (3 females/group) 

were treated with 

pyroxasulfone at 0, 4500

+ 20 mM BSO, and 20000

+ 20 mM BSO or 20 mM 

BSO alone mg/kg/day for 

14 days.

acceptable/non-guideline

Hearts (2 slices/animal) of all animals in control and 

treated groups were routinely fixed, processed, embedded 

in paraffin wax, sectioned at 4 μm, stained and examined 

microscopically. Pyroxasulfone induced very mild 

myocardial toxicity in mice at the dietary level of 20000 

ppm under the GSH depleted conditions of the study

NA (Special Study: 

A Toxicological 

Mechanism Study)

Investigation for Cell 

Proliferation Activity 

and Oxidative Stress in 

Rat Urinary Bladder 

After Dietary Exposure 

for 14 Days

48046903 (2009)

Male rats at 0, 2000, and 

20000 ppm Pyroxasulfone

(160 and 1632 mg/kg/day)

acceptable/non-guideline

Both the 2000 and 20000 ppm groups showed an increase 

in Ki-67 labeling index associated with hyperplasia in the 

urinary bladder epithelium. 

NA (Special Study: 

A Toxicological 

Mechanism Study)

Investigation for Cell 

Proliferation Activity 

and Oxidative Stress in 

Mouse Kidneys After 

Dietary Exposure for 14 

Days

48046904 (2009)

Male Crlj:CD1 (ICR) 

mice (8 /group) at 2000 or

15000 ppm pyroxasulfone

(292 and 2199 mg/kg/day)

acceptable/non-guideline

The Ki-67 labeling indices, an indicator of cell 

proliferation activity, in all regions of both treatment 

groups were almost equal to those in the control groups. 

Malondialdehyde contents in the kidneys of both KIH485-treated groups from confirmation of the oxidative 

stress were comparable to that in the control group. It is 

unlikely that KIH-485 treatment is involved in cell 

proliferation activity and oxidative stress in the mouse 

kidney under the conditions of the present study.
Page 49 of 81

Table A.2.2 Subchronic, Chronic and Other Toxicity Profile of Pyroxasulfone

Guideline No. Study Type MRID No. (year)/ 

Classification /Doses

Results

NA (Special Study: 

A Toxicological 

Mechanism Study)

Electron Microscopic 

Examination of Rat 

Urinary Bladder Treated 

with Pyroxasulfone 

(KIH-485) for 14 Days

48354402 (2011)

Male Crl:CD(SD) rats (5/

group) at 0, 500, 2000 or 

20000 ppm pyroxasulfone 

(44, 177 and 1765 

mg/kg/day)

Doses of 2,000 and 20,000 ppm of KIH-485 

(pyroxasulfone) induced morphological changes 

(suggesting hyperplastic and toxic effects) in the surface 

of the bladder epithelium.

NA (Special Study) Rat In Vivo Comet Test. 48046906 (2010)

Male rats at 0, 500, 1000 

and 2000 mg/kg 

pyroxasulfone : one dose 

at 0 time, 2nd dose after 21 

hrs. Positive control 

group received ethyl 

methanesulphonate at 200 

mg/kg.

acceptable/non-guideline

A statistically significant increase in the tail intensity was 

observed in the liver of rats treated with Pyroxasulfone at 

2000 mg/kg/day (p<0.001), compared to vehicle control 

values, Statistically significant increases in the tail 

intensity were observed in the bladder of rats treated with 

Pyroxasulfone at 1000 and 2000 mg/kg/day (p<0.001),

NA (Special Study) Mouse In Vivo Comet 

Test.

48046907 (2010)

Male mice at 0, 500, 1000 

and 2000 mg/kg 

pyroxasulfone : one dose 

at 0 time, 2nd dose after 21 

hrs. Positive control 

group received ethyl 

methanesulphonate at 200 

mg/kg.

acceptable/non-guideline

A statistically significant increase in the tail intensity was 

observed in the liver of CD1 mice treated at 500, 1000 

and 2000 mg/kg/day (p<0.01), compared to vehicle 

control values. Group mean values are within historical 

control range, considered not biologically significant.

Statistically significant increases in the tail intensity were 

observed in the kidney at 1000 (p<0.05) and 2000 

mg/kg/day (p<0.001).

NA (Special Study) One week oral 

cytotoxicity study in 

male rats

48354404 (2010)

Male rats 918/group) at 0, 

50, 1000 or 2000 ppm

pyroxasulfone. 6 

rats/group sacrificed at 1, 

3 or 7 days, SEM of 

urinary bladders

acceptable/non-guideline

This study provides evidence to the cytotoxicity of 

pyroxasulfone the urinary bladder epithelium of male rats.
Page 50 of 81

A.3 Toxicological Endpoints

A.3.1 Acute Reference Dose (aRfD) – General Population

Study Selected: Developmental Neurotoxicity Study- Rats

MRID No: 47701724

Dose and Endpoint for Risk Assessment: 100 mg/kg/day based on decreased brain weight in 

both sexes and decreased thickness of the hippocampus, corpus callosum and cerebellum in 

PND 21 female offspring occurring at 300 mg/kg/day. 

Uncertainty Factor: 100x (10x interspecies extrapolation, 10x intraspecies variability. 1X 

FQPA safety factor)

aRfD =

100 mg/kg/day (NOAEL)

100 (UF)

= 1.0 mg/kg

aPAD =

1 mg/kg/day (aRfD)

1 (FQPA SF)

= 1.0 mg/kg

Comments: The HED DNT committee considers morphometric changes in the hippocampus, 

corpus callosum and cerebellum during the first 21 days to result from a single acute exposure. 

A.3.2 Chronic Reference Dose (cRfD)

Study Selected: 1-year oral toxicity study - Dog

MRID No: 47701707

Dose and Endpoint for Risk Assessment: 2 mg/kg/day based on impaired hind limb function, 

ataxia, hind limb twitching and tremors; clinical pathology: increased creatine kinase, aspartate 

aminotransferase; axonal/myelin degeneration of the sciatic nerve and spinal cord sections at 10 

mg/kg/day.

Uncertainty Factor: 100x (10x interspecies extrapolation, 10x intraspecies variability, 1X 

FQPA safety factor)

cRfD =

2 mg/kg/day (NOAEL)

100 (UF)

= 0.02 mg/kg

cPAD =

0.02 mg/kg/day (cRfD)

1 (UF)

= 0.02 mg/kg

Comments about Study/Endpoint/Uncertainty Factors: In the various species tested, the dog 

exhibited adverse toxic effects at lower doses of exposure to pyroxasulfone. Also the dose 

ranges used in the dog testing were the narrowest allowing for more accurate determination of a 
Page 51 of 81

NOAEL. The 2 mg/kg/day NOAEL from this dog study is also protective from other adverse 

effects seen at higher doses in rats and mice such as cardiac and skeletal myopathy, liver, kidney 

and urinary bladder toxicity and developmental effects in the DNT and rabbit developmental 

studies. This endpoint is considered to be protective of all populations including women of 

child-bearing age and nursing infants.

A.3.3 Incidental Oral Exposure

Pyroxasulfone has not been proposed for residential uses; therefore, selection of a 

toxicity endpoint is not necessary for this exposure scenario at this time.

A.3.4 Dermal Absorption

A dermal absorption study with pyroxasulfone is not available. 

A.3.5 Dermal Exposure (Short- & Intermediate-Term)

Critical Study Selected: 28-day Dermal -- Rat

MRID No: 47701698

Dose and Endpoint for Risk Assessment: Dermal NOAEL= 100 mg/kg/day based on cardiac 

myofiber degeneration/inflammation cutaneous myofiber degeneration/inflammation at 1000 

mg/kg/day. 

Uncertainty Factor: 100x (10x interspecies extrapolation, 10x intraspecies variability)

Comments about Study/Endpoint/Uncertainty Factors:

A 28-day dermal toxicity study was selected as for the dose and endpoint for short and 

intermediate term dermal exposure. This study is route specific and is appropriate for this 

exposure scenario. The LOAEL of 1000 mg/kg/day is based on minimal to mild cardiac 

myofiber degeneration with inflammation in males and females. This endpoint is also 

considered protective of developmental effects in DNT at 300 mg/kg/day and rabbit 

developmental study at 1000 mg/kg/day. This POD is also protective of the neurotoxic effects 

seen in the dog following chronic oral exposure to 10 mg/kg/day. Dermal absorption is 

estimated to be 7.5%, so the relative dermally absorbed dose for the dermal NOAEL of 100 

mg/kg/day is approximately 7.5 mg/kg/day which is less than the oral LOAEL of 10 mg/kg/day 

identified in the dog study. In addition, rats in general are a more sensitive species for the 

dermal exposure route because of higher skin permeability. 

A.3.6 Inhalation Exposure (Short -Term, 1-30 days)

Critical Study Selected: 90 day oral toxicity study in dogs.

MRID No: 47701696 and 47701697

Dose and Endpoint for Risk Assessment: 2 mg/kg/day based on a LOAEL of 10 mg/kg/day for 

axonal/myelin degeneration in the sciatic nerve, minimal to mild subacute inflammation of 

skeletal muscle in males and females and impaired limb function, body and limb hypotonia, 
Page 52 of 81

increase in serum creatine kinase activity. . The assumed inhalation absorption factor is 100%. 

Uncertainty Factor: 100x (10x interspecies extrapolation, 10x intraspecies variability)

Comments about Study/Endpoint/Uncertainty Factors:

A 28 day inhalation toxicity study in rats (MRID 47701699) was considered for selecting an 

endpoint of toxicity for assessing this route specific exposure. However the endpoint based on 

the 90-day dog study is more protective than the findings in the 28 day inhalation toxicity study 

in rats where the NOAEL was 200 mg/m3(equivalent to 52.2 mg/kg/day oral dose), the highest 

dose tested using an aerosol dust of pyroxasulfone, not an aerosol. Since no effects were seen at 

the highest dose tested in the inhalation study and since mixer/loader exposures would be to both 

dust and aerosols (with aerosol exposures typically being more sensitive than dust exposures), 

HED believes that a dust exposure study was not as protective. Since no effects were seen at the 

highest dose tested in the inhalation study, use of the oral dog would compensate for this 

uncertainty, and is protective of neurotoxicity. The inhalation NOAEL of 200 mg/m3/day is 

equivalent to 52.2 mg/kg/day oral dose using the following formula:

 mg/kg/day = mg/L x A x CF x D x AF

where 

A is absorption factor using 1 as a default value

CF is a conversion factor in L/hr/kg to account for respiratory volume and body weight for a 

given species and strain. For the rat strain used in this study it is 43.5

D is duration of daily exposure in hours. A 6 hour daily exposure was used.

AF is activity factor. The animal default factor of 1 was used.

MOE: 100

A.3.7 Inhalation Exposure (Intermediate-Term 1-6 months)

Critical Study Selected: 1-year toxicity study in dogs.

MRID No: 47701707

Dose and Endpoint for Risk Assessment: 2 mg /kg/day based on impaired hind limb function, ataxia, hind limb 

twitching and tremors; clinical pathology: increased creatine kinase, aspartate aminotransferase; axonal/myelin 

degeneration of the sciatic nerve and spinal cord sections at 10 mg/kg/day. The assumed inhalation absorption 

factor is 100%. 

Comments about Study/Endpoint/Uncertainty Factors:

Among the various species tested, the dog exhibited adverse toxic effects at lower doses of exposure to 

pyroxasulfone. Also the dose ranges used in the dog testing were the narrowest allowing for more accurate 

determination of a NOAEL. The 2 mg/kg/day NOAEL from this dog study is also protective from other adverse 

effect seen at higher doses in rats and mice such as cardiac and skeletal myopathy, liver, kidney and urinary bladder 

toxicity.

MOE: 100
Page 53 of 81

A.4 EXECUTIVE SUMMARIES

A.4.1 Subchronic Toxicity

870.3100 90-Day Oral Toxicity – Rat

In a subchornic oral toxicity study (MRID 47701692), Pyroxasulfone (KIH-485; 99.1% a.i.; 

Lot/Batch No. RCT301) was administered in the diet to Crl:WI(Glx/BRL/Han)BR rats 

(10/sex/dose) for up to 13 weeks at doses of 0, 100, 500, 2500, or 5000 ppm (equivalent to 0/0, 

8.9/10.2, 43.9/48.9, 221.4/255.9, and 451.2/514.2 mg/kg bw/day in males/females). In the 

control and 5000 ppm group, an additional 5 rats/sex/group were fed the test diets for 13 weeks 

followed by a 4-week recovery period. 

Assessment of toxicity was based on mortality, clinical observations, and clinical and anatomic 

pathology evaluations. There were no effects on food consumption, ophthalmoscopy, or 

functional observational battery parameters.

The target organs were liver, skeletal muscle, cardiac muscle, and the pancreas based on altered 

organ weights, histopathological indicators, and/or clinical pathological indicators. Reduced 

body weight gain was observed in the 5000 ppm group. 

At 2500 and 5000 ppm, slight decreases in overall body weight gain were noted in both sexes 

(decr 12-15%). Additionally, the following adverse findings were observed that each may 

indicate an adverse effect on muscle tissue: (i) decreased ambulation and total movement in 

males (decr 24-38%); (ii) decreased creatinine in males (decr 11-12%); (iii) increased minimal to 

slight myocardial degeneration in both sexes (8-10/10 treated vs 0-1/10 controls); (iv) increased 

minimal quadriceps myopathy in males (6/10 each treated vs 3/10 controls); and (vi) increased 

minimal to slight myopathy in skeletal muscles other than quadriceps in both sexes (4-9/10 

treated vs 1/10 controls). In the females, increased aspartate aminotransferase (AST; incr 122%, 

each dose) and increased liver weights (decr 10-23%) were also noted.

Additionally at 5000 ppm, the following adverse findings were observed: (i) pale teeth in both 

sexes; (ii) decreased body weight and body weight gain in both sexes; (iii) increased AST in 

males; (iv) increased urine volume in both sexes; (v) increased liver weights in males; (vi) gross 

changes in the liver (large, mottled, and/or pale) in both sexes; (vii) dark pancreas in females; 

(viii) microscopic changes in the liver (agonal congestion/hemorrhage, centrilobular 

hypertrophy/eosinophilia, and/or hepatocyte vacuolation) in both sexes; and (ix) degranulation in 

the pancreas of females.

After the recovery period, increased incidences in agonal congestion/hemorrhage in the liver was 

observed at 5000 ppm in males (3/5 treated vs 0/5 controls), and pale teeth was noted in 1/5 rats 
Page 54 of 81

in each sex (vs 0 controls). Decreased body weights were noted in the 5000 ppm males (decr 7-

19%) with body weights remaining decreased during the recovery period (decr 10-12%), 

although a slight increase in body weight gain was noted during the recovery period. However, 

all other microscopic findings in the liver, heart, muscle and pancreas in the 5000 ppm animals 

were comparable to control rats.

The LOAEL is 2500 ppm (equivalent to 221/256 mg/kg/day in males/females), based on the 

findings detailed above. The NOAEL is 500 ppm (equivalent to 44/49 mg/kg/day in 

males/females).

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

870.3100; OECD 408) for a subchronic oral toxicity study in the rat. 

870.3150 90-Day Oral Toxicity – Dog

The purpose of this study was to evaluate the potential toxicity of KIH-485 TGAI when 

administered via oral capsule dose administration (MRID 47701696). Four dogs per sex per dose 

level were administered the test substance via gelatin capsules at concentrations of 0.2, 2.0, and 

10.0 mg/kg/day for the 90 day (13 week) in-life test period. An additional group of four dogs per 

sex served as the control and received the empty gelatin capsules. The dogs were observed twice 

daily for signs of toxicity. Body weights and food consumption were measured weekly and a 

battery of urinalysis, hematological and clinical pathology examinations was conducted at 

initiation and at six and thirteen weeks. Ophthalmological examinations were done at initiation 

and at 13 weeks. The post-life phase of the study included organ weight measurements, gross 

and pathologic assessments. 

No deaths occurred during the study period. There were no treatment related changes in body 

weight, food consumption, hematology, blood chemistry, coagulation, ophthalmological or 

urinalysis parameters. Pathological examination (organ weight measurement and gross 

observation), found no effects attributable to the administration of the test substance. 

Slight muscle fiber degeneration of the musculature portion of the diaphragm, slight hyperplasia 

of satellite cell of the muscle, and slight nerve fiber degeneration of the sciatic nerve were 

observed in one 10 mg/kg/day male dog. In a subsequent 90-day dog toxicity study (MRID 

47701697), dogs administered pyroxasulfone at 15 mg/kg/day developed minimal to mild 

axonal/myelin degeneration in the sciatic nerve of all males (4/4) and 3⁄4 females in addition to 

minimal to mild subacute inflammation of skeletal muscle in males and females. Considering 

these two studies together, the LOAEL for these adverse effects in dogs is 10 mg/kg/day 

and the NOAEL is 2 mg/kg/day.
Page 55 of 81

When reviewed in conjunction with MRID 47701697 (concurrently reviewed), this study is 

classified acceptable/guideline and satisfies the guideline requirements (OPPTS 870.3150; 

OECD 409) for a subchronic oral toxicity study in dogs.

870.3200 21/28-Day Dermal Toxicity – Rat 

In a 29-day dermal toxicity study (MRID 47701698), Pyroxasulfone (97.2% a.i.; Lot No. L001) 

in deionized water was applied to the shaved, intact skin of male and female Crl: CD® (SD) IGS 

BR rats (10 sex/dose) at dose levels of 0, 20, 100, or 1000 mg/kg bw/day for 6 hours/day for 29 

consecutive days.

No adverse, treatment-related effects was observed on mortality, clinical signs, body weight, 

body weight gain, food consumption, food efficiency, hematology, clinical chemistry, organ 

weights, or gross pathology.

An increased incidence of minimal to mild focal/multifocal cardiac myofiber degeneration with 

inflammation was observed in the hearts of the 1000 mg/kg/day males (90% treated vs 0% 

controls) and females (40% treated vs 10% controls). An increased incidence of minimal 

focal/multifocal cutaneous myofiber degeneration with inflammation was observed in the treated 

skin of 1000 mg/kg/day male rats (60% treated vs 0% controls).

The LOAEL is 1000 mg/kg/day (the limit dose), based on cardiac myofiber 

degeneration/inflammation in both sexes and cutaneous myofiber 

degeneration/inflammation in males. The NOAEL is 100 mg/kg/day.

This 29-day dermal toxicity study is classified as acceptable/guideline and satisfies the 

guideline requirement for a 28-day dermal toxicity study (OPPTS 870.3200; OECD 410) in rats. 

870.3465 28-/90-Day Inhalation – Rat 

In a 28-day inhalation study (MRID 47701699), four groups of 10 male and 10 female rats each were 

exposed to aerosols of KIH-485TGAI dust at targeted concentrations of 10, 40, or 200 mg/m3(mean, gravimetrically 

determined concentrations were 9.4, 40, and 200 mg/m3). The mass median aerodynamic equivalent diameter of the 

aerosols ranged from 2.9 to 3.3 μm.

Rats were exposed nose-only for 6 hours per day for a total of 20 exposures for each sex over a 4-week period. A 

similar control group of 10 males and 10 female rats were simultaneously exposed to air only. On the day following 

the last exposure, blood samples were collected for clinical analyses from each rat, and all rats were sacrificed for 

anatomic pathology examination.
Page 56 of 81

There were no test substance-related adverse effects on mortality, body weights, clinical signs, or food consumption 

as a result of KIH-485TGAI exposure. Clinical pathology evaluations showed no test substance-related effects in 

hematology, coagulation, serum chemistry, or urine parameters as a result of exposure to KIH-485TGAI dust.

There were no test substance-related organ-weight effects observed in the tested animals in this study. Histologic 

evaluation showed no effects in the respiratory tract or in any other organ systems. The fact that there were no test 

particles observed in the lung in the pathologic exam, despite the very high dust concentrations, was attributed to the 

absorption or metabolism of the test substance in the respiratory tract.

The NOAEL for repeated inhalation exposure to KIH-485TGAI dust was considered to be 200 mg/m3, the 

highest concentration tested. The LOAEL was not observed.

At the request of the Agency, this study was conducted for 4 weeks, instead of the 13 weeks required by Guideline 

OPPTS 870.3465. Aside from the different study duration, this study was conducted in accordance with Guideline 

OPPTS 870.3465.

This 4-week study is classified as acceptable/guideline and satisfies the guideline requirement (OPPTS 870.3465; 

OECD 413) for a subchronic inhalation study in the rat.

A.4.2 Prenatal Developmental Toxicity

870.3700a Prenatal Developmental Toxicity Study – Rat

The purpose of this study (MRID 47701702) was to determine the potential maternal and 

developmental toxicity of KIH-485 (Pyroxasulfone; 99.1%; Lot #05TG005) in rats, when 

administered orally, by gavage. Time-mated female Crl:CD(SD) rats were assigned to 

four groups (22 animals/group). Each group received dose preparations containing the control 

article or 100, 500 or 1000 mg of test article/kg of body weight/day (mg/kg/day) at a dose 

volume of 10 ml/kg of body weight from Days 6 to 20 of gestation. All dams were observed for 

general conditions. Body weights and food consumption were recorded during the gestation 

period. On GD 21, caesarean section and necropsy were conducted on the dams, and the fetuses 

were examined for external, visceral, and skeletal malformations and variations.

There were no maternal deaths and no dose related clinical signs or necropsy findings. There was 

no adverse effect of treatment on group mean body weights or food intake.

The maternal LOAEL was not observed. The maternal NOAEL is 1000 mg/kg/day (limit 

dose).
Page 57 of 81

There were no abortions, premature deliveries, dead fetuses, late resorptions, or complete litter 

resorptions and no effects of treatment on the numbers of litters, live fetuses, or early resorptions. 

Additionally, sex ratio and mean litter weight in the treated groups were comparable to controls. 

There were no external, visceral, or skeletal defects attributable to treatment.

The developmental LOAEL was not observed. The developmental NOAEL is 1000 

mg/kg/day (limit dose).

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

870.3700a; OECD 414) for a developmental toxicity study in rats.

Rat Developmental Study 

In a rat developmental toxicity study (MRID 47701702), 22 female rats/dose group were 

administered 0, 100, 500 or 1000 mg of pyroxasulfone from gestation day (GD) 6-20. There 

were no maternal deaths and no dose related clinical signs or necropsy findings. There was no 

adverse effect of treatment on group mean body weights or food intake. The maternal LOAEL 

was not observed. The maternal NOAEL is 1000 mg/kg/day (limit dose). There were no 

abortions, premature deliveries, dead fetuses, late resorptions, or complete litter resorptions and 

no effects of treatment on the numbers of litters, live fetuses, or early resorptions. Sex ratio and 

mean litter weight in the treated groups were comparable to controls. There were no external, 

visceral, or skeletal defects attributable to treatment. The developmental LOAEL was not 

observed. The developmental NOAEL is 1000 mg/kg/day (limit dose).

870.3700b Prenatal Developmental Toxicity Study – Rabbit

In a developmental study (MRID 47701704), time mated female Hra:(NZW)SP rabbits 

(22 animals/group) were administered by oral gavage 0, 250, 500 or 1000 mg of KIH-485 TGAI 

(Pyroxasulfone; Lot/Batch #05TG005; 99.1%)/kg of body weight/day at a dose volume of 

5 ml/kg of body weight from Gestation Day (GD) 7 to 28. All dams were observed for general 

conditions. Body weights and food consumption were recorded during the gestation period. On 

GD 29, caesarean section and necropsy were conducted. Fetuses were examined for external, 

visceral, and skeletal abnormalities.

Seven females died or were euthanized prior to scheduled necropsy, 3 due to premature abortion 

and 4 because of intubation injury. One abortion occurred at 250 mg/kg/day and 2 occurred at 

1000 mg/kg/day.

There were no test substance-related deaths, clinical signs of toxicity, or gross post-mortem 

findings in dams at any dosage. There were no test-substance related reductions in body weight 
Page 58 of 81

or food consumption parameters at any level tested. The LOAEL for maternal toxicity was not 

observed. The NOAEL for maternal toxicity is 1000 mg/kg/day (limit dose).

There were test substance-related effects on fetal weights and the number of resorptions (total 

and early) at 1000 mg/kg/day; these effects were relatively slight, but statistically significant. 

The mean number of corpora lutea, implantation sites, live fetuses, and sex ratio were 

comparable across all groups. Totals of 164, 164, 170 and 125 fetuses were examined for 

abnormalities and variations at 0, 250, 500 and 1000 mg/kg/day, respectively. There were no test 

substance-related fetal external, visceral, or skeletal malformations or variations observed at any 

dosage.

The LOAEL for developmental toxicity is 1000 mg/kg/day (limit dose) based on reduced 

fetal weight and increased fetal resorptions. The NOAEL for developmental toxicity is 500 

mg/kg/day.

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

870.3700a; OECD 414) for a developmental toxicity study in rats.

A.4.3 Reproductive Toxicity

870.3800 Reproduction and Fertility Effects – Rat

The purpose of this study (MRID #47701705) was to determine the reproductive toxicity of the 

test article, KIH-485TGAI (Pyroxasulfone; 97.2%; Lot/Batch #L001), following oral (dietary) 

administration to the rat. This study was conducted as a pilot study for a multigenerational 

reproduction study. Crl:CD®(SD) IGS BR rats (12/sex/concentration) were fed diets containing 

0, 25, 250, or 5000 ppm KIH-485TGAI for at least 28 days prior to mating to produce the F1 

litters. Dams were allowed to deliver and rear their offspring until weaning (postpartum day 21). 

At weaning, 12 F1 rats/sex/group were randomly selected to continue on study until post-natal 

day (PND) 60 and were fed the same dietary concentration level as their parents.

There was a significant (p<0.05) trend for stained perineum in the P dams during lactation, with 

3/12 animals affected at 5000 ppm compared to 0/11 controls.

In P males test substance-related reductions in weight gain were observed at 250 and 5000 ppm. 

At 5000 ppm, weekly mean body weight gains were decreased throughout most of the study, 

most notably on Days 0-7 and 21-28 and resulted in reductions in overall weight gain for the premating period and the entire exposure period. At 250 ppm, weekly mean body weight gains were 

also decreased throughout the study, and, except for Days 0-7, the reductions were of similar 

magnitude as those in the 5000 ppm group, despite the 20-fold difference in dietary 
Page 59 of 81

concentration. Overall weight gains for the pre-mating period and the entire exposure period 

were decreased in this group. In P females, there were test substance-related reductions in body 

weights at 5000 ppm and weight gain at 250 and 5000 ppm. At 5000 ppm, weekly body weight 

gains were decreased during pre-mating and during the first and last week of gestation. As a 

result of these decreases in weekly weight gain, overall weight gain for the pre-mating and 

gestation periods were 36-38% lower than the control group mean. In addition, weekly mean 

body weights were decreased at the end of the pre-mating period and throughout gestation and 

lactation. At 250 ppm, body weight gain was decreased during the last week of gestation, which 

resulted in a decrease in overall weight gain during gestation.

In F1 adult males and females, test substance-related reductions in body weights and weight 

gain were observed at 5000 ppm. Overall mean body weight gain for the post-weaning period for 

this group was 20% lower than the controls in males and 18% lower in females as a result of 

decreased weekly body weight gains throughout the post-weaning period. These reductions in 

weekly weight gains were reflected in weekly mean body weights that were lower than controls 

throughout the post-weaning period. In the 5000 ppm F1 adult males and females, weekly 

decreases in food consumption throughout most of the post-weaning period resulted in decreases 

of 16-18% in overall food consumption for the post-weaning period (Days 0-39).

In P males, food efficiency was decreased during pre-mating at 5000 ppm and reflected lower 

food efficiency throughout the pre-mating period, most notably on Days 0-7 and 21-28. In P 

females, there were test-substance related effects on food efficiency at 250 and 5000 ppm. At 

5000 ppm, weekly food efficiency was decreased throughout pre-mating and gestation. At 250 

ppm, weekly food efficiency was decreased during the last week of gestation; as a result of this 

decrease, overall food efficiency during gestation in this group was 14% lower than control.

Dietary exposure to 5000 ppm of the test substance resulted in increased mean relative liver 

weights (%body wt.) in both P and F1 adult males and females. The increased liver weights

correlated with microscopic hepatocellular hypertrophy (in P adults) and were interpreted to be 

the result of non-adverse induction of hepatocellular enzymes by a xenobiotic. All other organ 

weight differences were interpreted to be the result of general body weight loss and not 

indicative of organ-specific effects.

In the 5000 ppm P adult rats, there were test substance-related microscopic findings in the liver, 

quadriceps muscle, heart, and sciatic nerve. Minimal centrilobular hepatocellular hypertrophy

was observed in the livers of five (5/12) male and three (3/12) female rats exposed to 5000 ppm 

in the P generation. Locally extensive, minimal to mild atrophy of the quadriceps muscle was 

observed in all of the 5000 ppm females in the P animals and in none of the other rats examined. 

The atrophy consisted of a minimal (10/12 rats) to mild (2/12 rats) decrease in the cross-sectional 

area of the muscle fibers, as compared to the control tissue. Minimal to mild focal and multifocal 

degeneration of heart myofibers (i.e., myocardium) was present in five (5/12) 5000 ppm P 
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females and was considered a heart-specific adverse effect. Minimal to mild axon/myelin 

degeneration within the sciatic nerve sections was observed in all (12/12) of the 5000 ppm 

female rats. The occurrence of myocardial and peripheral nerve fiber degeneration exclusively in 

females treated at 5000 ppm may be related to substantially increased food consumption, and test 

substance dose, during lactation.

The LOAEL for parental toxicity is 5000 ppm (equivalent to 339/383 mg/kg/day in 

males/females, respectively) based and microscopic effects in the heart, liver, muscle, and 

sciatic nerve of males and females, decreased body weight gains in the P males and females 

and decreased food efficiency in the P dams. The NOAEL for parental toxicity is 250 ppm 

(equivalent to 16/20 mg/kg/day in males/females, respectively). The decreased body weigh 

gains at the 250 ppm dose were transient and mostly not statistically significant, and the 

bodyweights were not affected. The effects at 250 ppm are therefore equivocal. 

There were no treatment-related effects on litter size, sex ratio, or pup survival. At 5000 ppm, 

mean pup weights were decreased by 27-30% compared to controls throughout the post-natal 

period. There were test substance-related effects on developmental landmarks at 5000 ppm. The 

mean day of achievement of preputial separation was increased by 3 days in this group compared 

to the control group, and the mean age of achievement of vaginal patency was increased by 1.8 

and 2.7 days in the 250 and 5000 ppm groups, respectively; changes that were considered due to 

reductions in body weight and weight gain in these groups.

The LOAEL for offspring toxicity is 5000 ppm (equivalent to 339/383 mg/kg/day in 

males/females, respectively) based on decreased pup weight and delayed sexual maturation 

in both sexes. The NOAEL for offspring toxicity is 250 ppm (equivalent to 16.0/19.6 

mg/kg/day in males/females, respectively). 

There were no test substance-related effects on mating, fertility, gestation duration, number of 

implantation sites, or implantation efficiency in P adult females at any concentration.

The LOAEL for reproductive toxicity was not observed. The NOAEL for reproductive 

toxicity is 5000 ppm (equivalent to 339/383 mg/kg/day in males/females, respectively), the 

highest concentration tested. 

This study is classified acceptable/non-guideline provides data for use in dose selection for the 

definitive 2-generation reproductive toxicity study in rats.

A.4.4 Chronic Toxicity

870.4100a (870.4300) Chronic Toxicity – Rat 
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In a chronic feeding toxicity study (MRID 47701708), KIH485 TGAI (pyroxasulfone), was 

administered to male and female rats Crl:CD(SD) from Charles River Lab. Twenty rats per sex 

per level were administered test material by daily feeding at concentrations of 0, 5, 50, 1000 and 

2,000 ppm for the one year. Data for body weights and food consumption clinical observations 

and ophthalmological examinations were collected. A full battery of hematological and clinical 

pathology examinations was conducted at three, six and twelve months. The post-life phase of 

the study included organ weight measurements and gross and microscopic pathologic 

assessments.

The mean daily intake of KIH-485 TGAI in males was 0, 0.22, 2.22, 46.20 and 91.91 mg/kg/day 

at 0, 5, 50, 1000 and 2000 ppm, respectively. In females, the mean daily intake of the test 

substance was 0, 0.30, 3.12, 60.80 and 121.33 mg/kg/day at the same respective dietary levels.

Test substance-related effects occurred at 1000 ppm and above that included reduced body 

weight parameters and microscopic findings. These findings were observed in the liver 

(centrilobular hepatocellular hypertrophy (males)), heart (increased cardiomyopathy (females)) 

and urinary bladder (mucosal hyperplasia (males and females)). At 2000 ppm, these effects were 

accompanied by increased clinical observations of red discharge from the penis and associated 

red-stained cageboards as well as increased liver and kidney weights. A slight increase in liver 

and kidney weights was observed in the 2000 ppm male and female dietary exposure groups.

The lowest-observed-adverse-effect level (LOAEL) of KlH-485 TGAI, given as a dietary 

mixture, was 1000 ppm (46.20 and 60.80 mg/kg/day for males and females, respectively). The 

no-observed-adverse-effect level (NOAEL) was 50 ppm (2.22 and 3.12 mg/kg/day for males and 

females, respectively). 

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

870.4100a; OECD 452) for a chronic study in rats.

870.4100b Chronic Toxicity – Dog

In a 1-year dog study (MRID: 47701707), KIH-485, (99.1%) was administered daily to 4 beagle 

dogs/sex/dose in capsules at dose levels of 0.0, 0.2, 2.0, and 10.0 mg/kg bw/day) for 364 

consecutive days.

No effects of treatment were observed on mortality, body weights, body weight gains, food 

consumption, food efficiency, ophthalmoscopic examinations, electrocardiograpic examinations, 

urinalysis, organ weights, or gross pathology.
Page 62 of 81

Toxicity was observed at 10 mg/kg/day. Impaired hind limb function and tremors was noted in 

two males, and impaired hind limb function was noted in one female. One of the males was also 

observed with hind limb twitching and ataxia. Dogs in this group (3 males and one female) also 

had abnormal, test article-related neurobehavioral observations including mild, moderate, and/or 

severe limb weakness, primarily in the hind limbs. Limb tone was sometimes noted as hypotonic. 

Abnormal gait, mobility, and limb position were noted. Clonic (quivering) or tonic (rigid limbs) 

movements were noted infrequently. Increases were observed in aspartate aminotransferase (not 

statistically significant) and creatine kinase (p < 0.05) starting during Week 13 and continuing 

throughout the treatment period. Females approached control values by Week 52. All males (4 of 

4) and females (4 of 4) had minimal to mild axonal/myelin degeneration of the sciatic nerve. 

Minimal axonal/myelin degeneration was observed in the spinal cord as follows: (i) in the 

cervical cord of two (2 of 4) males and two (2 of 4) females; (ii) in the lumbar cord of all (4 of 4) 

males and one (1 of 4) female; and (iii) in the thoracic cord of two (2 of 4) males and three (3 of 

4) females.

Additionally at 10 mg/kg/day, minimal myofiber degeneration/necrosis was observed in the 

following skeletal muscles: (i) in the biceps femoris of two (2 of 4) males; (ii) in the diaphragm 

of one (1 of 4) male; and (iii) in the quadriceps of one (1 of 4) males. Skeletal muscles of the 10 

mg/kg/day females were unremarkable. Although elevations of aspartate aminotransferase and 

creatine kinase in both sexes indicated a possible effect on skeletal muscle, the microscopic 

findings were minimal in severity, and the clinical chemistry findings appeared to be returning to 

normal levels by Week 52. These observations suggested that any test article-related effects on 

muscle were transient and/or reversible.

Beginning at Week 13 in females only, there was a mild, dose-dependent trend towards 

decreased erythrocyte mass as illustrated by sequential decreases in erythrocytes (↓8-16%) , 

hemoglobin (↓8-14%), and hematocrit (↓7-12%) relative to controls at 2.0 and 10.0 mg/kg/day. 

However, group means were within expected ranges, and statistical significance was rarely and 

sporadically attained. Therefore, these findings were considered equivocal.

The LOAEL is 10.0 mg/kg/day, based on clinical and neuromuscular observations of the 

hind limbs as described above, increased serum aspartate aminotransferase and serum 

creatine kinase, minimal to mild axonal/myelin degeneration of the sciatic nerve, and 

minimal axonal/myelin degeneration in all three levels of the spinal cord in males and 

females. The NOAEL is 2.0 mg/kg/day.

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

870.4100; OECD 452) for a chronic oral toxicity study in dogs.

A.4.5 Carcinogenicity
Page 63 of 81

870.4200a Carcinogenicity/Chronic Study – Rat

In this oncogenicity study (MRID # 47701709), Crl:CD®(SD)IGS BR rats (70/sex/group) were 

administered diets that contained 0, 5, 50, 1000 or 2000 ppm of pyroxasulfone (M: 0, 0.21, 2.05, 

42.55, 84.55 mg/kg/day; F: 0, 0.28, 2.69, 54.28, 106.74 mg/kg/day) for two years. Males were 

exposed for at least 99 weeks and females were exposed for at least 97 and surviving males and 

females were euthanized and examined for gross and microscopic pathologic alterations. The 

decision to terminate these groups prior to the intended termination at 104 weeks was 

necessitated by the expected survival of the rats. Unscheduled deaths were approaching the 

minimum deemed adequate for ensuring robust data sets and regulatory compliance. All 

surviving rats were sacrificed and subjected to gross and microscopic pathological examination. 

Assessment of toxicity was based on mortality, clinical observations, and clinical and anatomic 

pathology evaluations.

Test substance-related effects occurred at 1000 and 2000 ppm. At 2000 ppm, effects included 

reduced body weight parameters (males and females), reduced food consumption (females), and 

increased red-stained urine on cageboards (males). At 1000 ppm, effects included reduced body 

weight and food consumption parameters (females) and increased red-stained urine on 

cageboards (males). Dietary exposure of male and female rats to 1000 ppm or more of the test 

substance, for approximately two years, resulted in increased cardiomyopathy (males and 

females); urinary bladder mucosal hyperplasia, inflammation, and transitional cell papillomas 

(males); and sciatic nerve degeneration (females); and liver peribiliary fibrosis/inflammation 

(females). 

An increase in urinary bladder transitional cell papillomas was observed in males at 1000 ppm 

and above in association with a marked increase in mucosal hyperplasia. A slight increase in 

mucosal inflammation also appeared to be associated with the mucosal hyperplasia. There were

no test substance-related urinary bladder effects in females. Therefore, the test substance was 

interpreted to be oncogenic in male but not female rats. 

An increase in the background incidence and severity of cardiomyopathy occurred in both sexes 

at 1000 ppm and above. The lesion included myocardial degeneration, inflammation, and fibrosis 

and resembled naturally occurring cardiomyopathy of control rats of this age and strain. 

An increase in the background incidence of sciatic nerve degeneration was observed in female 

rats at 1000 ppm and above. The lesion was graded minimal in most cases. Test substancerelated sciatic nerve degeneration was not observed in males. 

An increase in liver peribiliary fibrosis/inflammation was observed in females at 1000 ppm and 

above. An increase in bile duct hyperplasia was observed in females at 2000 ppm.

There were no test substance related effects on causes of death, organ weights or gross 
Page 64 of 81

observations made at necropsy. There were no treatment-related changes in white blood cell 

relative differential counts at any dietary concentration tested. 

Under the conditions of the current study, test substance-related effects that were considered 

adverse were observed at 1000 and 2000 ppm. There were no test substance-related or adverse 

effects at either 5 or 50 ppm. Therefore, the no-observed-adverse-effect level (NOAEL) was 50 

ppm. Based on an increase in urinary bladder transitional cell papillomas in the 1000 ppm and 

2000 ppm males, the test substance was considered oncogenic in males at exposures of 1000 

ppm and above.

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

870.4200a; OECD 451) for a carcinogenicity study in rats.

870.4200b Carcinogenicity (feeding) – Mouse

The purpose of this study (MRID: 47701710) was to determine oncogenic potential of KIH-485 

in mice, following oral (dietary) administration to the mouse for 18 months. Four groups of 

young adult male and female Crl:CD1(ICR) mice (60/sex/group) were administered diets that 

contained 0, 5, 150, or 2000 ppm or 4000 ppm (males)/4000 ppm (females) substance 

(equivalent to 0, 0.62/0.84, 18.4/25.5, 228/306, and 465/668 mg/kg/day in males/females) of the 

test substance for up to 18 months. Treatment at 4500/4000 ppm exceeded the maximum 

tolerated dose, and this group was terminated prior to the scheduled sacrifice. After 

approximately 14 months on study, dietary concentrations for the 2000 ppm groups were reduced 

to 1000 and 500 ppm for males and females, respectively, in order to insure a satisfactory 

survival rate at the scheduled sacrifice. To provide interim data at one year, 10 mice per sex per 

group were sacrificed and given gross and microscopic pathological examinations. After 

approximately 18 months of dietary exposure, all surviving mice were sacrificed and given a 

gross and microscopic pathological examination. Assessment of toxicity was based on mortality, 

clinical observations, and clinical and anatomic pathology evaluations.

In the 4500/4000 ppm group, marked body weight losses occurred during the first 2 months of 

the study, which warranted the reduction of the dietary concentration to 3000 ppm. This 

reduction appeared to stabilize the body weights. However, after about 10 (females) or 12 

(males) months on the study, clinical observations (principally, affects on the hindlimbs) began 

to be noted with a frequency and severity that was dose-related. These effects included abnormal 

hindlimb gait, low carriage, curled toes, extended hindlimbs, and splayed limbs. The progression 

of effect on the hindlimbs began to interfere with the mice access to food and water. Therefore, 

this group was terminated before the scheduled sacrifice. 

Test substance-related adverse effects were observed in males and females at 2000/1000 and 
Page 65 of 81

2000/500 ppm, respectively. No adverse effects were observed in males or females at 150 ppm 

or lower. In males and females at 2000/1000 and 2000/500 ppm, respectively, test substancerelated effects during the in-life period included reductions in body weight parameters and 

increases in adverse clinical signs. The clinical signs consisted of hindlimb gait/stance 

abnormalities and included abnormal hindlimb gait, low carriage, curled toes, extended 

hindlimbs, and splayed limbs. These clinical observations were not overtly obvious until about 

10 months on study and correlate with the histopathologic lesions of the nervous system 

described below. 

At 2000 ppm, the one-year interim sacrifice data indicated that daily dietary exposure of male 

and female mice had adverse effects on the kidneys and nerve fibers in both sexes. Minimal to 

mild tubular nephrosis in the pars recta, and an associated decrease in kidney weight parameters, 

was observed in both sexes. Minimal to mild degeneration of nerve fiber axons and myelin was 

observed in the sciatic nerve of some mice. Minimal trigeminal nerve degeneration was observed 

in one male and one female mouse. There were no test substance-related effects on gross 

pathology. 

At 2000 ppm, the 18 month terminal sacrifice data indicated test substance-related changes in the 

kidneys, sciatic nerve, and trigeminal nerve (detailed below). Test substance-related causes of 

death were limited to five 2000 ppm female mice that were euthanized due to clinical signs 

secondary to test substance-related sciatic nerve degeneration. 

At one year, minimal to mild tubular nephrosis in the pars recta, and an associated decrease in 

kidney weight parameters, was observed in both sexes at 2000 ppm. Minimal to mild 

degeneration of nerve fiber axons and myelin was observed in the sciatic nerve of some mice, 

observed in one male and one female mouse, also at 2000 ppm. 

Minimal to mild hepatocellular hypertrophy in the 2000 ppm females was associated with a 

small increase in mean liver weight parameters. Both liver effects were consistent with 

pharmacological enzyme induction and were interpreted to be not adverse. 

Organ weight effects at 2000 ppm included lower mean kidney (both sexes), as compared to 

controls. Lower mean kidney weights in both sexes correlated with adverse microscopic changes. 

At necropsy, there was a small increase in gross kidney deformity in males. Microscopic kidney 

effects in males included the presence of an intratubular precipitate as well as increased tubular 

epithelial nephrosis (degeneration/necrosis), hyperplasia, and adenoma. An increase in the 

incidence (females) and severity (males) of chronic progressive nephropathy (CPN) was also 

observed. 

At 2000 ppm, microscopic nervous tissue effects in both sexes included degeneration of sciatic 

and trigeminal nerve axons and their associated myelin sheaths. Degeneration of axons in the 
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dorsal funiculi of the spinal cord and the trigeminal tract in the pons of the brain (females only) 

were interpreted to be an extension of the sciatic and trigeminal nerve lesions, respectively. 

The LOAEL is 2000 ppm (equivalent to 228/306 mg/kg/day in males/females, based on 

decreased body weight and body weight gain, nervous system toxicity, and renal toxicity in 

both sexes. The NOAEL was 150 ppm (equivalent to 18/25 mg/kg/day in males/females).

Three (3/50) benign tubular adenomas in the 2000/1000 ppm male kidneys were observed and 

may have been related to the test substance-related degenerative and hyperplastic changes 

observed in the 2000 ppm males. Based on this finding, the test substance was initially 

considered oncogenic in male mice. Revaluation of the renal tubular adenomas of the male mice 

was conducted by an independent kidney expert pathologist (MRID 48354403) and reviewed by 

a Pathology Working Group (MRID 48354405). The renal tubular adenomas observed in male 

mice were considered by the PWG to be incidental and unrelated to the administration of 

pyroxasulfone. HED CARC considered the evidence presented by the PWG and concluded that 

the renal tubular adenomas observed in this mouse study were not treatment related.

Dosing was considered adequate based on decreased body weight and body weight gain, nervous 

system toxicity, and renal toxicity in both sexes.

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

870.4200b; OECD 451) for a carcinogenicity study in mice.

A.4.6 Mutagenicity
Page 67 of 81

Gene Mutation

Guideline # 870.5100 Bacterial assay

Guideline #870.5300, In vitro 

mammalian cell gene mutation test

MRID 47889311

Acceptable Guideline

Not mutagenic

Not mutagenic in the presence or absence of S9-activation up to the limit 

of solubility and cytotoxic effects.

Cytogenetics

Guideline # 870.5375, 

Clastogenicity in mammalian cells

MRID 47701719

Acceptable Guideline

Guideline #870.5395 

Micronucleus test in bone marrow

MRID 47701720

Acceptable Guideline

No evidience of clastogenicity up to its limit of solubility

No evidence of genotoxicity

A.4.7 Neurotoxicity

870.6100 Delayed Neurotoxicity Study – Hen - NA

870.6200 Acute Neurotoxicity Screening Battery - Rat

In an acute neurotoxicity study (MRID # 47701721), 10 Sprague-Dawley rats/sex/dose were 

administered a single oral (gavage, 10 mL/kg) dose of KIH-485 TGAI (99.1% purity) suspended 

in 0.5% methylcellulose and Tween 80 at doses of 0, 20, 200, or 2000 mg/kg (limit dose) and 

were observed for 2 weeks. A functional observational battery (FOB) and motor activity testing 

were performed during the pretest period (baseline), and on Days 1 (approximately 2 hours postdosing, time of peak effect), 8, and 15. At termination, 6 rats/sex/dose underwent whole-body in 

situ perfusion, and tissues from the control and 2000 mg/kg groups were processed for 

neuropathology. References to 5 positive control studies were cited; however, no data were 

provided. No compound-related effects on mortality, clinical signs, body weight, body weight 

gain, food consumption, and gross or neuropathology were observed at any dose in either sex. 

No evidence of neurotoxicity was observed in the FOB or motor activity assessments.

The LOAEL was not observed. The NOAEL is 2000 mg/kg (limit dose) in rats.

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

(870.6200; OECD 424) for an acute neurotoxicity study in rats.
Page 68 of 81

870.6200 Subchronic Neurotoxicity Screening Battery

In a subchronic neurotoxicity study (MRID# 47701722), 12 Sprague-Dawley rats/sex/dose were 

administered KIH-485 TGAI (99.1% purity) in the diet at concentrations of 0, 25, 250, or 2500 

ppm (equivalent to 0/0, 1.56/1.92, 15.85/19.60, and 161.48/199.59 mg/kg/day [M/F]) for 13 

weeks. A functional observational battery (FOB) and motor activity testing were performed 

during the pretest period (baseline), and during Weeks 4, 8, and 13. At termination, 6 

rats/sex/dose underwent whole-body in situ perfusion, and tissues from the control and 2500 ppm 

groups were processed for neuropathology. References to 5 positive control studies were cited; 

however, no data were provided.

No compound-related effects on mortality, clinical signs, body weight, body weight gain, food 

consumption, food efficiency, and gross or neuropathology were observed at any dose in either 

sex. No evidence of neurotoxicity was observed in the FOB or motor activity assessments.

The LOAEL is 2500 ppm (equivalent to 161.48/199.59 mg/kg/day) based on muscular 

degeneration observed in females. The NOAEL is 250 ppm (equivalent to 15.85/19.60 

mg/kg/day).

The study is classified as acceptable/guideline and satisfies the Guideline requirements 

(870.6200b) for a subchronic neurotoxicity study in the rat.

870.6300 Developmental Neurotoxicity Study - Rat

In a developmental neurotoxicity study (MRID# 47701724), KIH-485 (Pyroxasulfone, 99.1% 

a.i., Batch# 05TG005) in 0.5% (w/v) sodium carboxymethylcellulose was administered daily by 

gavage (5 mL/kg) to groups of 24 mated female Sprague-Dawley rats/dose at dose levels of 0, 

100, 300, or 900 mg/kg/day from gestation day (GD) 6 through lactation day (LD) 7, inclusive. 

Subsequently, the pups were directly dosed via gavage at the same doses as their dams from 

post-natal day (PND) 7 to 20 or 21, inclusive. 

Dams were allowed to deliver naturally and were killed on LD 21, following weaning of their 

respective litters. On PND 4, at least twenty litters of appropriate size (≥ 8 pups/litter) were 

available. These litters were standardized to 8 pups/litter; the remaining offspring and dams were 

sacrificed and discarded without further examinations. Subsequently, 10-12 pups/sex/group were 

allocated to Subsets 1-6 for neurobehavioral testing (Subsets 2, 3, 4, and 5), neuropathological 

examination (Subsets 1 and 2). References for 7 positive control studies that provided data that 

validated the procedures and observers of the performing lab to assess motor activity, 

neurotoxicity and behavioral effects were provided; however, data from these studies were not 

provided. 
Page 69 of 81

Treatment of pregnant and lactating female rats with KIH-485 from GD 6 to LD 7 at doses up to 

900 mg/kg/day was well tolerated. There were no treatment-related effects on mortality, clinical 

signs of toxicity, body weight, body weight gain, food consumption, FOB parameters, gestation 

length, macropathology findings, or brain weights. Additionally, there was no effect of treatment 

on the mean number of implantations or litter size. 

The maternal LOAEL was not observed. The maternal NOAEL is 900 mg/kg bw/day.

No effects on offspring survival or bodyweight performance of the offspring to PND 7 

(commencement of direct treatment of the offspring) were observed at any dose. Additionally, no 

effects on clinical condition or mean bodyweight gain were observed in the offspring during 

direct administration of KIH-485 from PND 7 to 20/21. 

Sexual maturation, assessed by the time of vaginal opening or balano-preputial separation was 

unaffected by treatment at all dose levels. There was no clear effect of treatment on the FOB 

performance including all activity measures, auditory startle response habituation, pre-pulse 

inhibition, or on the learning and memory of the offspring at any dose level.

Motor activity assessments on PND 13 and 17 of age indicated several differences in the activity 

of treated offspring of both sexes relative to concurrent controls. However, reported motor 

activity measurements were very highly variable making conclusions difficult to make. 

Coefficients of variation exceeded 50% and reached above 200%. 

There were no treatment-related macroscopic findings observed at scheduled termination and no 

histopathological changes in the tissues presented for neuropathological examination on PND 21 

or 66.

The mean absolute brain weights of male offspring in the 900 mg/kg/day group and female 

offspring in the 900 and 300 mg/kg/day groups on PND 21 were significantly lower (p<0.05) 

than concurrent controls and the laboratory historical control, and this decrease was dose-related. 

There was no effect of treatment on the mean length and width of the brain of males or females 

on either PND 21 or 66.

Although the mean brain morphometric changes were stated to be within the limits of accuracy 

of the measurement, no valid positive control data were available to demonstrate that the testing 

laboratory was capable of detecting changes in brain morphometry with known positive control 

substances (e.g., methimazole). The measurements in the treated groups were less than HC, as 

were the concurrent control values; however, a consistent pattern in reduced thicknesses was 

observed. This is better seen when brain morphometric values in PND 21 males and females 

were compared to the conducting laboratory historical control data from four studies. The 

hippocampus thickness was decreased in males (-11%) and females (-8%) in the 900 mg/kg/day 
Page 70 of 81

dose groups and in females at the 300 mg/kg/day dose (-6%). In female PND21 offspring this 

was accompanied by reduction in the thickness of the cerebellum (-19 to -20%) in the 300 and 

900 mg/kg/day groups and a reduction in the thickness of the corpus callosum (-38%) in the 300 

and 900 mg/kg/day dose groups. The decrease in the cerebellum thickness at the 100 mg/kg/day 

dose in females was not considered to be treatment related since it was not accompanied by a 

decrease in the hippocampus thickness and the lack of effect on PND 66 and the absence of 

associated neurobehavioral effects. 

It is concluded that the LOAEL for offspring toxicity derived from this DNT study is 300 

mg/kg/day based on decrease in brain weight in male and female offspring accompanied with a 

decrease in the thickness of the hippocampus, corpus callosum and cerebellum in PND 21 female 

offspring. The NOAEL is 100 mg/kg/day.

With the deficiencies reported above, this study is classified acceptable/guideline and satisfies 

the guideline requirement (OPPTS 870.6300; OECD 426) for a developmental neurotoxicity 

study in rats.

A.4.8 Metabolism

870.7485 Metabolism – Rat – Single Dose

In a rat metabolism study (MRID 47701728), four Sprague Dawley [Crl:CD(SD)] rats/sex/group 

were gavaged with a single dose of one of two radiolabeled forms of KIH-485 in 0.5% aqueous 

carboxymethylcellulose: [pyrazole14C]-KIH-485 or [isoxazoline14C]-KIH-485 at doses of 

either 10 mg/kg (low dose) or 700 mg/kg (high dose) in a nominal dose volume of 10 mL/kg. 

Urine and feces were collected up to 96 hours after dosing, and expired air was collected in one 

group for up to 48 hours after dosing. For tissue distribution studies, 9 rats/sex/group were 

treated, and 3 rats/sex/group were sacrificed at 3 (10 mg/kg) or 9 (700 mg/kg), 54 (both doses), 

and 96 (both doses) hours after treatment. Upon sacrifice, selected tissue/organ samples, as well 

as the residual carcass, were collected. All these samples were radioassayed, and selected fecal 

and urine samples were pooled and analyzed to determine a metabolic profile. 

Absorption was at least 77-88% of the administered dose (AD) at 10 mg/kg, based on residues 

isolated in the urine, bile, and carcass. Absorption was at least 22-26% AD at 700 mg/kg, based 

on residues isolated in the urine, carcass, and tissues. Although bile was not collected in the 700 

mg/kg animals, the parent was isolated in feces at 61-77% AD suggesting that limited absorption 

was occurring. (Absorbed parent compound is extensively metabolized as detailed below.)

Absorption was relatively quick at 10 mg/kg, with a tmax of 1.1-7.0 h in the blood and plasma of 

both sexes; at 700 mg/kg, the tmax was 7.0-17.3 hours. A 70-fold increase in dose resulted in an 

increase in radioactivity concentrations in the whole blood and plasma (Cmax) of 9-12 fold in both 
Page 71 of 81

sexes treated with [pyrazole14C]-KIH-485 and the [isoxazoline14C]-KIH-485 treated females 

and 17-18 fold in the [isoxazoline14C]-KIH-485 treated males. One possible explanation for this 

observation is limited absorption at the high dose, an explanation that was corroborated by the 

large amount of parent compound isolated in the feces. An apparent sex-related difference was 

noted in the [isoxazoline14C]-KIH-485 animals. Half-lives were highly variable and ranged from 

15-173 hours. Half-lives were always greater in the blood than in the plasma, suggesting the 

possibility of protein binding. 

Excluding the gastrointestinal tract (GIT), the highest tissue concentrations (μg equiv/g) were 

initially found in the bladder (males: 245-227; females: 12-19 at low dose and 178 at high dose) 

at both doses and labels. Initially, very high tissue concentrations were also isolated in the 

prostate (16-47) at both doses and labels. High concentrations were also noted in the adrenals, 

kidney, liver, abdominal fat, uterus, blood, and plasma at both doses, sexes (except uterus), and 

labels. After 96 hours, the concentration (μg equiv/g) in blood was 0.08-2.49 (4.58 in the 

[isoxazoline14C]-KIH-485 treated females) and in kidney was 0.10-1.30 in each sex, dose, and 

label.

Following administration of [Ix14C]-KIH-485, it was noticeable that concentrations in the 

stomach and stomach contents were much greater than in the [pyrazole14C]-KIH-485 group. 

This suggested the possibility of active secretion of radioactivity into the stomach following 

administration of [Ix14C]-KIH-485. 

Total recovery was 91-105% AD. Most of the dose was excreted in the urine within 24 hours 

regardless of sex, dose, or radiolabel; although, excretion was slowest in the 700 mg/kg males. 

Excretion was essentially complete by 48 hours (approximately 90% AD recovered in all the 

groups). 

In the 10 and 700 mg/kg [pyrazole14C]-KIH-485 group; slightly less residues were excreted in 

the urine and more residues in the feces in males compared to females; however, no sex 

difference was noted when the other radiolabel was used. In the excretion balance groups, the 

excretion profiles were generally similar regardless of radiolabel. At 10 mg/kg, residues were 

found primarily in the urine (63-76% AD) and feces (13-29% AD). Less than 5% AD was 

isolated in the carcass and tissues, and <7% AD and was found in the cage wash and debris. Only 

negligible amounts of residues (<0.2% AD) were found in the expired air. 

The excretion profile was different at 700 mg/kg compared to 10 mg/kg. At 700 mg/kg, residues 

were found primarily in the feces (70-80% AD) and urine (22-26% AD). Less than 0.3% AD was 

isolated in the carcass and tissues, and <5% AD and was found in the cage wash and debris.

In the 10 mg/kg bile-duct cannulated animals, there was a differing metabolic profile depending 

on the radiolabel. In the [pyrazole14C]-KIH-485 group, residues were found in the urine (62-
Page 72 of 81

63% AD), bile (13-16% AD), feces (6-10% AD), cage wash (6-7% AD), and cage debris and 

carcass (<1.2% AD). In the [isoxazoline14C]-KIH-485 group, residues were found primarily in 

the urine (44-50% AD), bile (33-37% AD), feces (1-6% AD), cage wash (7-9% AD), and cage 

debris and carcass (6-8% AD).

Techniques used in the isolation and identification of the metabolites included the use of 

metabolite standards with HPLC, TLC, LC-MS, and GC-MS; enzyme deconjugation was used 

with some samples. KIH-485 underwent extensive metabolism following oral administration 

with up to 30 chromatographic regions of interest seen in the urine, up to 19 in the fecal extracts 

and up to 31 in bile. There was no significant sex difference in the metabolism of KIH-485. 

Compared with low dose animals, there appeared to be saturation or induction of metabolism at 

the high dose, which resulted in an altered metabolic profile.

The major metabolite in the urine of rats dosed with [Py14C]-KIH-485 was M-13, accounting for 

up to 26% of the dose at the low dose level and up to 4% at the high dose level. M-7 and M-3 

were the next most abundant metabolites. Most of the metabolites in urine were produced by the 

cleavage between the pyrazole and isoxazoline ring structure.

When the rats were dosed with [Ix14C]-KIH-485, there were three major metabolites in urine, 

M-13 accounting for up to 20% of the dose, M-16 accounting for up to 19% of the dose and M26 accounting for up to 6.4% of the dose. A major portion of the radioactivity was highly polar 

and multi-component, containing 5-methyl-5-isoxazoline carboxylic acid and M-30, and 

accounted for up to 34% of the dose.

The major component of the feces following dosing with both radiolabels was unabsorbed KIH485 accounting for up to 10% of the dose at the low dose level and up to 78% at the high dose 

level. The next most abundant metabolite was M-13, accounting for up to 3% of the dose.

In bile, the major metabolites of rats dosed with [Py14C]-KIH-485 were two conjugated 

compounds one of which co-eluted with a sulphate conjugate of hydroxy KIH-485 and the other 

co-eluted with M-13 glucuronide. These two regions each accounted for up to 3.1% of the dose. 

Another metabolite was M-13, accounting for up to 1.6% of the dose.

When the rats were dosed with [Ix14C]-KIH-485, the major metabolite in bile was tentatively 

identified as M-26 accounting for up to 10% of the administered dose and was produced by the 

cleavage of the pyrazole ring and subsequent loss of the fluorine moieties. There were also two 

conjugated compounds one of which co-eluted with a sulphate conjugate of hydroxy KIH-485 

and the other co-eluted with M-13 glucuronide. These two regions accounted for up to 7% and 

3% of the dose each. There was one further metabolite with a molecular weight of 347 

accounting for up to 4% of the dose, which was tentatively identified as a glutamyl cysteine 

conjugate of the isoxazoline ring.
Page 73 of 81

This metabolism study in the rat is classified acceptable/guideline and satisfies the guideline 

requirement for a metabolism study [OPPTS 870.7485, OECD 417] in rats when considered in 

conjunction with the concurrently submitted metabolism study in rats (MRID 47701729).

870.7485 Metabolism – Rat – Repeat Dose

In a rat metabolism study (MRID 47701729), non-radiolabeled KIH-485 was orally administered 

to four female Sprague Dawley (Crl:CD(SD) strain rats per group at a nominal dose level of 10 

mg/kg/day for 7 days, followed by a dose radiolabeled with 14C at either the pyrazole (Py) or 

isoxazole (Ix) ring in 0.5% aqueous carboxymethylcellulose and Tween 80 (<0.02% v/v): in a 

volume of 10 mL/kg. Additionally, one group of 4 rats were administered 10 mg/kg [pyrazole14C]-KIH-485 in an oral gavage dose for 14 consecutive days. Urine and feces were collected up 

to 96 hours after dosing. For tissue distribution studies, 12 rats/group were treated, and 3 

rats/sex/group were sacrificed at 1, 20, 48, and 72 hours after treatment with [pyrazole14C]-KIH485 or 2, 65, 168, and 288 hours after treatment with [isoxazoline14C]-KIH-485. Upon sacrifice, 

selected tissue/organ samples, as well as the residual carcass, were collected. All these samples 

were radioassayed, and selected fecal and urine samples were pooled and analyzed to determine 

a metabolic profile. 

This regime was based on an initial experiment in which four females received 14 daily doses of 

[Py14C]-KIH-485. Blood and plasma concentrations had essentially achieved steady state 

conditions after 7 repeated oral administrations of [Py14C]-KIH-485. 

Absorption was at least 69% of the administered dose (AD) in all animals, based on residues 

isolated in the urine. Absorption was relatively quick at 10 mg/kg, with a tmax of 0.9-1.5 h in the 

blood and plasma (or 7.0 h in the blood of the of [isoxazoline14C]-KIH-485 treated animals). 

Half-lives were highly variable (17-302 h) and seemed to be higher in blood and higher in the 

[isoxazoline14C]-KIH-485 treated animals. As half-lives were always greater in the blood than 

in the plasma, protein binding may be occurring. The following parameters were higher in the 

[isoxazoline14C]-KIH-485 treated animals than the [pyrazole14C]-KIH-485 treated animals in 

blood and plasma: tmax, t1/2, and AUC; Cmax was higher in the blood only.

Excluding the gastrointestinal tract (GIT), the highest tissue concentrations (μg equiv/g) were 

initially found in the bladder (20.7) and remained higher than plasma at 96 hours after dosing 

(0.04 in bladder vs 0.03 in plasma). After 96 hours post-dose, the highest residues were found in 

the erythrocytes, regardless of radiolabels. As indicated by pharmacokinetic parameters, the 

concentration of radioactivity remaining in the tissues at 96 hours after treatment were higher in 

the [isoxazoline14C]-KIH-485 treated animals than the [pyrazole14C]-KIH-485 treated animals.
Page 74 of 81

Following administration of [Ix14C]-KIH-485, it was noticeable that concentrations in the 

stomach and stomach contents were much greater than in the [pyrazole14C]-KIH-485 group. 

This suggested the possibility of active secretion of radioactivity into the stomach following 

administration of [Ix14C]-KIH-485. 

Total recovery was 92-100% AD. Most of the dose was excreted within 24 hours (>80% AD), 

predominantly in the urine (>60% AD). After 96 hours, 0.5-3.9% AD remained in the carcass 

and tissues (higher in the [isoxazoline14C]-KIH-485 treated animals). The excretion profiles 

were generally similar regardless of radiolabel in that urine was the predominant route of 

excretion, feces was a major but secondary route, and relatively little residues were isolated in 

the other samples. 

KIH-485 is extensively metabolized, and there were up to 16 regions of interests found during 

chromatography of the urine. Up to 17 proposed structures are presented in the proposed 

metabolic pathway of KIH-485. The major metabolites (structures presented in this report) 

include M-3, M-7, and M-16 in urine and M13 in the urine and feces. Thus, metabolism in the 

repeated dose animals was similar to that of the single dose animals. Differences were noted, but 

these differences typically involved minor metabolites. Overall, the metabolism of KIH-485 

appears to proceed by two main routes. One route involved the cleavage of the sulfonyl group 

and subsequent sequential oxidations of this group on the pyrazole moiety or glutathione 

conjugation and subsequent hydrolysis of the isoxazoline moiety. The second route involved 

sequential oxidations of the parent compound. 

This metabolism study in the rat is classified acceptable/guideline and satisfies the guideline 

requirement for a metabolism study [OPPTS 870.7485, OECD 417] in rats when considered in 

conjunction with the concurrently submitted metabolism study in rats (MRID 47701728).

870.7600 Dermal Absorption – Rat - NA

A.4.9 Immunotoxicity

870.7800 Immunotoxicity – Rat

The purpose of this study was to evaluate the potential of KIH-485 TGAI to suppress the primary 

humoral immune response following exposure via the diet for 28 days. Groups of 10 rats per sex 

were administered the test substance at dietary levels of 0, 25, 250, or 7500 ppm (equivalent to 

0/0, 2/2, 18/19, and 529/570 mg/kg/day in males/females). Body weights, food consumption 

measurements, and clinical observations were recorded during the in-life period. Prior to 

sacrifice, the immune system was stimulated by injecting sheep red blood cells (SRBC) on test 
Page 75 of 81

day 22 and blood samples were collected from each rat on test day 28. The serum samples were 

assayed for their concentration of SRBC-specific IgM antibodies to provide a quantitative 

assessment of humoral immune response. Serum from animals similarly challenged with a 

positive control immunosuppressive agent was analyzed concurrently to provide confirmation 

that the assay performance was acceptable for detection of immunosuppression. At sacrifice, 

each animal was examined grossly and selected organs were weighed (brain, spleen, and 

thymus).

There were no test substance-related effects observed on clinical observations, organ weights, or 

gross pathology.

Systemic toxicity was observed at 7500 ppm. Body weights and food consumption were 

decreased in the males throughout the study, resulting in an overall (Days 0-28) decrease in body 

weight gains of 30% and an overall decrease in food consumption of 13%. In the females, body 

weights were decreased on Days 21 and 28, resulting in an overall decrease in body weight gains 

of 56%, and food consumption was slightly decreased throughout the study, resulting in an 

overall decrease of 8%. Overall food efficiency was also decreased by 19% in males and by 52% 

in females.

There was no evidence of test substance-related toxicity in male or female rats at 250 ppm or 

lower.

The LOAEL for systemic toxicity is 7500 ppm (equivalent to 529/570 mg/kg/day in 

males/females), based on reduced body weights, body weight gains, food consumption, and 

food efficiency in both sexes. The NOAEL for systemic toxicity is 250 ppm (equivalent to 

18/19 mg/kg/day in males/females).

There was no test substance-related evidence of immunosuppression in either male or female rats 

at any dietary concentration tested. The IgM titers were generally comparable across all groups. 

The serum samples for the positive control groups that received 20 mg/kg/day of 

cyclophosphamide for 6 consecutive days demonstrated 60 and 68% decreases in the IgM 

antibody response to SRBC for male and female rats respectively.

The LOAEL for immunotoxicity was not observed. The NOAEL for immunotoxicity was 

7500 ppm (equivalent to 529/570 mg/kg/day in males/females).

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

870.7800) for an immunotoxicity study in rats.

870.7800 Immunotoxicity – Mouse
Page 76 of 81

The purpose of this study was to evaluate the potential of KIH-485 TGAI to suppress the primary 

humoral immune response following exposure via the diet for 28 days. Groups of 10 mice per 

sex were administered the test substance at dietary levels of 0, 40, 400, or 4000 ppm (equivalent 

to 0/0, 6/8, 61/77, and 633/791 mg/kg/day in males/females). Body weights, food consumption 

measurements, and clinical observations were recorded during the in-life period. Prior to 

sacrifice, the immune system was stimulated by injecting sheep red blood cells (sRBC) on test 

day 23 (males) and 24 (females). Blood samples collected from each mouse on test day 28 

(males) and 29 (females) were assayed for their concentration of sRBC-specific IgM antibodies 

to provide a quantitative assessment of humoral immune response. Serum from the animals 

similarly challenged with a positive control immunosuppressive agent (cyclophosphamide) was 

analyzed concurrently to provide confirmation that the assay performance was acceptable for 

detection of immunosuppression. At sacrifice, each animal was examined grossly and selected 

organs were weighed (brain, spleen, and thymus).

There were no test substance-related effects observed on clinical observations, food 

consumption, organ weights, or gross pathology.

At 4000 ppm, body weights were decreased in the males throughout the study by 7-9%, resulting 

in an overall (Days 0-28) decrease in body weight gains of 31%. Decreased (p<0.05) food 

efficiency was noted in the males on Days 0-7 (↓42%) and overall (Days 0-28; ↓31%); this was 

considered a reflection of the effects on body weight. In the females, body weights were slightly 

decreased throughout the study, resulting in an overall decrease in body weight gains of 32%.

There was no evidence of test substance-related toxicity in male or female mice at 400 ppm or 

lower.

The LOAEL for systemic toxicity is 4000 ppm (equivalent to 633/791 mg/kg/day in 

males/females), based on reduced body weights and body weight gains in both sexes, and 

decreased food efficiency in males. The NOAEL for systemic toxicity is 400 ppm 

(equivalent to 61/77 mg/kg/day in males/females).

There was no test substance-related evidence of immunosuppression in either males or females at 

any dietary concentration tested. The IgM titers were generally comparable across all groups. In 

contrast, male and female mice injected for five consecutive days with 50 mg/kg/day of the 

known immunosuppressive agent, cyclophosphamide, demonstrated 100% and 92% inhibition, 

respectively, of the IgM antibody response to SRBC.

The LOAEL for immunotoxicity was not observed. The NOAEL for immunotoxicity was 

4000 ppm (equivalent to 633/791 mg/kg/day in males/females).
Page 77 of 81

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

870.7800) for an immunotoxicity study in mice.
Page 78 of 81

APPENDIX B. Chemical Names And Structures Of Metabolites

B.1 Chemical Names and Structures of Pyroxasulfone and Metabolites. 

Code IUPAC Name Common Name Chemical Structure

KIH-485

3-[[[5-(difluoromethoxy)-1-methyl-3-

(trifluoromethyl)-1H-pyrazol-4-

yl]methyl]sulfonyl]-4,5-dihydro-5,5-

dimethylisoxazole

Pyroxasulfone

M-1

[5-(Difluoromethoxy)-1-methyl-3-

(trifluoromethyl)-1H-pyrazol-4-

yl]methanesulfonic acid 

N/A

M-3

5-(Difluoromethoxy)-1-methyl-3-

(trifluoromethyl)-1H-pyrazol-4-carboxylic acid N/A

M-5

3-(5-Difluoromethoxy-3-trifluoromethyl-1Hpyrazol4-ylmethanesulfonyl)-4,5-dihydro-5,5-

dimethylisoxazole

N/A

M-6

3-(5-Difluoromethoxy-1-methyl-3-

trifluoromethyl-1H-pyrazol-4-

ylmethanesulfonyl)-4,5-dihydro-5,5-

dimethylisoxazol-4-ol

N/A

M-8

(5-Difluoromethoxy-1-methyl-3-trifluoromethyl1H-pyrazol-4-yl)methanol N/A

M-9

5-Difluoromethoxy-3-trifluoromethyl-1Hpyrazole-4-carboxylic acid N/A

F

F

O

N

N

CF3

CH3

S

O

O

N

O

CH3

H3C

F

F

O

N

N

CF3

S

O

O

HO

CH3

F

F

O

N

N

CF3

CH3

HO

O
Page 79 of 81

B.1 Chemical Names and Structures of Pyroxasulfone and Metabolites. 

Code IUPAC Name Common Name Chemical Structure

M-9 malonyl 

glucoside 

(RT26)1

None provided NA

N-glycoside 

of M-9 

(Unknown @ 

13 mins.)1

None provided NA

M-10 5-Difluoromethoxy-1-methyl-3-trifluoromethyl1H-pyrazole-4-carbaldehyde N/A

M-11

[3-(5-Difluoromethoxy-1-methyl-3-

trifluoromethyl-1H-pyrazol-4-

ylmethanesulfonyl)-4,5-dihydro-5-

methylisoxazol-5-yl] methanol

N/A

M-12 (5-Difluoromethoxy-3-trifluoromethyl-1Hpyrazol-4-yl) methanol N/A

M-13

3-(5-Difluoromethoxy-1-methyl-3-

trifluoromethyl-1H-pyrazol-4-

ylmethanesulfonyl)-4,5-dihydro-5-

methylisoxazole-5-carboxylic acid

N/A

M-15

2-Amino-5-[1-(carboxymethylamino)-3-(5,5-

dimethyl-4,5-dihydroisoxazol-3-ylthio)-1-

oxopropan-2-ylamino]-5-oxopentanoic acid

N/A

M-16 2-Acetylamino-3-(5,5-dimethyl-4,5-

dihydroisoxazol-3-ylthio)propanoic acid N/A

H

H

H

O

HO

H

O

HO

OH

O

O

H

OH

O

N

H

N

CF3

F2HCO

O

N

N

O

F

F F

F F

H

C184

O

HO

O

OH

OH

OH

OH
Page 80 of 81

B.1 Chemical Names and Structures of Pyroxasulfone and Metabolites. 

Code IUPAC Name Common Name Chemical Structure

M-22 5,5-Dimethyl-4,5-dihydroisoxazole N/A

M-25 [5-(Difluoromethoxy)-3-(trifluoromethyl)-1Hpyrazol-4-yl]methanesulfonic acid N/A

M-28

3-[1-Carboxy-2-(5,5-dimethyl-4,5-

dihydroisoxazol-3-ylthio)ethylamino]-3-

oxopropanoic acid

N/A

M-29 3-(5,5-Dimethyl-4,5-dihydroisoxazol-3-ylthio)-2-

hydroxypropanoic acid N/A

M-302 3-cyano-2-hydroxy-2-methylpropanoic acid N/A

Metabolite A1 None provided (cysteine glucose conjugate of 

isoxazoline-ring metabolite) N/A

Metabolite B1 None provided (dimethylpropyl cysteine 

sulfoxide derivative) N/A

Metabolite C1 None provided (malonyl dehydrogenated cysteine 

derivative of isoxazoline group) N/A

Metabolite D1 None provided (cysteine conjugate of dimethyl 

acrylic acid) N/A

P11

None provided (malonyl cysteine conjugate of 

isoxazoline-ring products following reaction of 

pyroxasulfone or metabolites with glutathione)

N/A

F

F

O

N

H

N

CF3

S

O

O

HO

HO

H C3 COOH

CN

S

O

H3C

CH3

NH2

O

O-Glucose

S

NH2

O

OH

O

H3C

CH3

S

NH2

O

H3C OH

O

HO

S

O N

H3C N

H

HO O

OH

O O

OH
Page 81 of 81

APPENDIX C. Physical/Chemical Properties

Appendix C. Physicochemical Properties of Pyroxasulfone.

Parameter Value Reference1

Melting point 130.7 oC MRID 47701615

pH 5.03 at 22 oC MRID 47701613

Density 1.60 g/cM-3 MRID 47701616

Water solubility 3.49 x 10-3 g/L at 20.0 ± 0.5 oC MRID 47701619

Solvent solubility g/L at 20 oC 

Methanol: 11.4

Acetone: > 250

Ethyl acetate: 97.0

n-Hexane: 0.0721

Toluene: 11.3

Dichloromethane: 151

MRID 47701620

Vapor pressure 2.4 x 10-6 Pa at 25 oC MRID 47701621

Dissociation constant, pKa Not applicable (pyroxasulfone Ncontaining rings are not expected to be 

protonated in a practical pH range)

MRID 47701617

Octanol/water partition coefficient, 

Log(POW)

log POW = 2.39 at 25 oC, pH 8.7 MRID 47701618

UV/visible absorption spectrum at pH 1.13:

λmax = 225.5 nm; ε = 7291 Lmol-1cm-1

at pH 7.23:

λmax = 225.0 nm; ε = 7340 Lmol-1cm-1

at pH 10.91:

λmax = 225.5 nm; ε = 7334 Lmol-1cm-1

MRID 47701614

APPENDIX D. Studies Reviewed for Ethical Conduct

The PHED Task Force, 1995. The Pesticide Handlers Exposure Database, Version 1.1. Task Force members 

Health Canada, U.S. Environmental Protection Agency, and the National Agricultural Chemicals Association, 

released February, 1995.

Agricultural Re-entry Task Force (ARTF) data base (SOP #3.1)