UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

MEMORANDUM 

DATE: February 23, 2015 

OFFICE OF CHEMICAL SAFETY AND 

POLLUTION PREVENTION 

SUBJECT: Trinexapac-ethyl: Human Health Risk Assessment to Support New Uses on Rice 

and Rye. 

PC Code: 112602 

Decision Nos.: 488373 

Petition Nos.: NA 

Risk Assessment Type: Single Chemical 

TXRNo.:NA 

MRIDNo.: NA 

DP Barcode: D41 965 1 

Registration Nos.: NA 

Regulatory Action: Registration Review 

Case No.: NA 

CAS No.: 95266-40-3 

40 CFR: §180.662 

FROM: Sheila Piper, Chemist/Risk Assessor ~htt1u (t.p.e,v / / / 

Nancy McCarroll, Geneticist/Toxicologist ;JI a-.- 7 /J,c ~f . \/ . . . 

Monica Hawkins, Ph.D., M.P.H., Environmental Health Scientist ~efU,UL, ~f\MY Sumitra Bose Biswas, Chemist ~ (!; Rn~· 

Risk Assessment Branch VI 

Health Effects Division (7509P) 

THROUGH: Donn

Risk 

Healt

Assessment 

h 

a Dav

Effects 

is, Branch 

Division 

Branch 

Chief 

(7509P) 

VI 

~ 

TO: Dominic Schuler, Risk Manager Reviewer 

Dan Kenny, Branch Chief 

Herbicide Branch/ Registration Division (7505P) 

The Health Effects Division (HED) of the Office of Pesticide Programs (OPP) is charged with 

estimating the risk to human health from exposure to pesticides. Registration Division (RD) of 

OPP has requested that HED evaluate the hazard and exposure data and conduct dietary, 
Trinexapac-ethyl Human Health Risk Assessment DP No.419651 ~~~ ~~~ ~~~~~--~~~· 

occupational, residential, and aggregate exposure assessments, as needed, to estimate the risk to 

human health that will result from the registered uses of trinexapac-ethyl on rice and rye. 

The HED team members contributing to this risk assessment include Monica Hawkins 

(occupational and residential assessment), Nancy McCarroll (hazard assessment), Sumitra 

Biswas (chemistry and dietary assessment), and Sheila Piper (risk assessment). Christopher 

Koper of the Environmental Fate and Effects Division (EFED) performed the drinking water 

assessment. 

Page 2 of 55 
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Table of Contents

1.0 Executive Summary.............................................................................................................5

2.0 HED Recommendations.......................................................................................................7

2.1 Data Deficiencies.................................................................................................................7

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

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

2.2.2 Recommended Tolerances...................................................................................................7

2.2.3 Revisions to Petitioned For Tolerances ..............................................................................8

2.2.4 International Harmonization ...............................................................................................8

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

3.0 Introduction..........................................................................................................................9

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

3.2 Physical/Chemical Characteristics.....................................................................................10

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

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

3.5 Consideration of Environmental Justice ............................................................................13

4.0 Hazard Characterization and Dose-Response Assessment................................................13

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

4.2 Absorption, Distribution, Metabolism, & Elimination (ADME).......................................14

4.2.1 Dermal Absorption.............................................................................................................14

4.3 Toxicological Effects.........................................................................................................15

4.3.1 Toxicology Profile .............................................................................................................15

4.4 Safety factor for Infants and Children (FQPA Safety Factor)...........................................16

4.4.1 Completeness of the Toxicology Database........................................................................16

4.4.2 Evidence of Neurotoxicity and Immunotoxicity................................................................16

4.4.3 Evidence of Sensitivity/Susceptibility in the Developing or Young Animal ..................166

4.4.4 Residual Uncertainty in the Exposure Database..............................................................166

4.5 Toxicity Endpoint and Point of Departure Selection.......................................................177

4.5.1 Dose Response Assessment .............................................................................................177

4.5.2 Recommendation for Combining Routes of Exposure for Risk Assessment ....................20

4.5.3 Cancer Classification and Risk Assessment Recommendation.........................................20

4.6 Endocrine Disruption.........................................................................................................20

5.0 Dietary Exposure and Risk Assessment ............................................................................22

5.1 Residues of Concern Summary........................................................................................231

5.2 Food Residue Profile........................................................................................................242

5.3 Water Residue Profile ......................................................................................................242

5.4 Dietary Assessment Assessment........................................................................................25

5.4.1 Description of Residue Data Used in Dietary Assessment................................................25

5.4.2 Percent Crop Treated Used in Dietary Assessment ...........................................................25

5.4.3 Acute Dietary Risk Assessment.........................................................................................25

5.4.4 Chronic Dietary Risk Assessment .....................................................................................25

5.4.5 Cancer Dietary Risk Assessment.......................................................................................25
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5.4.6 Dietary Summary Table.....................................................................................................25

6.0 Residential (Non-Occupational) Exposure/Risk Characterization ....................................26

6.1 Spray Drift .........................................................................................................................26

6.2 Residential Bystander Post-Application Inhalation Exposure...........................................26

7.0 Aggregate Exposure/Risk Characterization.....................................................................267

7.1 Acute Aggregate Risk .......................................................................................................28

7.2 Short- and Intermediate-Term Aggregate Risk..................................................................29

7.3 Cancer Aggregate Risk ......................................................................................................30

8.0 Cumulative Exposure/Risk Characterization.....................................................................30

9.0 Occupational Exposure/Risk Pathway...............................................................................30

9.1 Occupational Handler Exposure/Risk Estimates...............................................................30

10.0 References..........................................................................................................................31

Appendix A: Toxicology Profile and Executive Summaries.............................................33
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1.0 Executive Summary

HED has conducted a human health risk assessment to support requested Section 3 uses for the 

active ingredient, trinexapac-ethyl, a plant growth regulator/herbicide that is registered for uses 

on cereal grains (wheat, barley, oats, triticale), sugarcane and grasses grown for seeds. The 

requested action is to establish permanent tolerances for residues of trinexapac-ethyl on rice and 

rye. It is formulated as an emulsifiable concentrate, wettable powder packed in water-soluble 

bags, and granule. Trinexapac-ethyl is used on turf in residential and commercial lawns, golf 

courses, parks, athletic fields, cemeteries, as well as grass grown for seed (non-food) and turf 

grown for sod.

The toxicological database for trinexapac-ethyl is complete. Trinexapac-ethyl exhibits low acute 

toxicity as shown in the standard acute toxicity battery as well as in the acute neurotoxicity study 

in rats with no systemic or neurotoxic effects up to the limit dose. The dog appears to be the most 

sensitive species while no systemic adverse effects were seen in rats, rabbits, or mice up to the 

limit dose (1,000 mg/kg/day) following subchronic or chronic oral exposure. Data from the 

combined chronic toxicity/carcinogenicity study in the rat did not demonstrate an increase in any 

tumor type that would be relevant to humans. The immunotoxicity study showed no evidence of 

immunotoxicity up to the limit dose. Trinexapac-ethyl is classified as “Not likely to be 

Carcinogenic to Humans.” Therefore, aggregate cancer risk was not quantitatively assessed.

HED recommends that the 10x FQPA Safety Factor (for the protection of infants and children) 

be reduced to 1x. The toxicity database is complete and there is no evidence of neurotoxicity in 

the database. While there is evidence of increased qualitative and quantitative susceptibility in 

the rat (increased incidence of asymmetrical sternebrae at the limit dose) and rabbit (decreased 

number of live fetuses/litter and increased post-implantation loss and early resorptions) at doses 

in the absence of maternal toxicity, these effects occurred only at the highest doses tested, are 

well characterized, and there is a clear NOAEL for these effects. Therefore there is no residue 

concerns with respect to developmental and reproductive effects. Lastly, the exposure estimates 

used to assess risk are unlikely to underestimate exposure.

An endpoint for the incidental oral exposure scenario was not identified from the available 

trinexapac-ethyl toxicity studies. For short- and intermediate-term dermal and inhalation 

exposures, a rabbit developmental toxicity study was selected with a NOAEL of 60 mg/kg/day 

and a LOAEL of 360 mg/kg/day based on a decrease in mean number of fetuses/litter and an 

increase in post-implantation loss. This endpoint is only applicable to adults (females) because 

the endpoint is based on in utero effects. HED reviewed the full toxicological database for 

trinexapac-ethyl in an attempt to select endpoints for the dermal and inhalation exposure 

scenarios for children; however, no appropriate endpoint was identified. A target MOE of 100 is 

considered adequate for all exposure scenarios (10x for interspecies extrapolation, 10x for 

intraspecies variability).
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The residue chemistry database for trinexapac ethyl is complete. The nature of the residue in 

plants and livestock is adequately understood, and the residue of concern in primary crops, 

rotational crops, and livestock for both tolerance enforcement and risk assessment include free 

and conjugated residues of both parent trinexapac-ethyl and its acid metabolite, trinexapac. In 

drinking water, the degradates of concern for risk assessment are trinexapac-ethyl, trinexapac, 2-

(4-cyclopropyl-4-hydroxy-2-oxobutyl) succinic acid (CGA-313458), an open chain cyclohexane 

ring, and the unidentified hydroproduct M3. Rice field trials have been submitted which are 

adequate in number and geographic representation, generated by a validated analytical method, 

and supported by adequate storage stability data. An acceptable processing study has been 

provided which shows that residues of trinexapac-ethyl concentrate in polished rice and bran but 

do not concentrate in hulls. There are no livestock feed items associated with this petition; therefore 

a discussion of the magnitude of residues in livestock commodities, as well as the need for livestock 

tolerances and analytical methods is not pertinent to this discussion.

Highly conservative acute and chronic dietary (food and drinking water) risk assessments were 

conducted using tolerance-level residues, assuming 100% crop treated for all commodities, using 

default processing factors, and incorporating modelled drinking water estimated exposure values. 

The acute dietary food and drinking water risk estimates are 2% of the acute population-adjusted 

dose (aPAD) for females 13-49 years old and are below HED’s level of concern (<100% of the 

acute population adjusted dose (aPAD)) at the 95th percentile of exposure. An acute dietary 

endpoint was not selected for the general population or any other population subgroups except 

females 13-49 years old. The chronic dietary risk estimate for food and drinking water is 3% of 

the chronic population-adjusted dose (cPAD) for the general U.S. population and 6% for children 

1-2 years old, the population subgroup with the highest estimated chronic dietary exposure to 

trinexapac-ethyl.

No new residential uses are being proposed at this time so an updated residential exposure 

assessment is not required. There are registered residential uses for trinexapac-ethyl on turf that 

were assessed previously. The residential handler MOEs range from 240 to 21,000,000. The 

residential post-application MOEs range from 450 to 61,000. 

The acute (females 13– 49 years only) and chronic aggregate assessments are equivalent to the 

corresponding dietary (food plus water) risk estimates, which do not exceed HED’s level of 

concern (MOEs > 100). The short/intermediate-term aggregate MOE for females 13– 49 years 

old is 230 and children (11 - 16 years old) is 4,500. There are no oral, dermal or inhalation 

hazards for children associated with trinexapac-ethyl; therefore an aggregate risk assessment is 

not required for this population subgroup.

In the previous occupational exposure assessment for trinexapac-ethyl, occupational handler and 

post-application exposures were assessed for the currently registered use for each trinexapacethyl crop, including cereal grains which was assessed at a maximum application rate of 0.11 lb 

ai/A. The maximum single application rates for both rice and rye are either the same or lower 
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than crops that were previously assessed. Therefore, an updated occupational exposure 

assessment for the proposed new uses is not required at this time. The occupational handler 

assessment MOEs range from 140 to 2,100,000 with baseline attire and/or with the addition of 

gloves (as required on the labels). The occupational post-application MOEs on the day of 

application range from 87 to 43,000. Based on HED’s occupational post-application exposure 

assessment, the restricted-entry interval (REI) for hand-harvesting sugarcane was estimated to be 

2 days for short- and intermediate-term exposure. However, HED does not recommend that 

sugarcane REI’s be changed on the trinexapac-ethyl labels at this time based on two main issues. 

One, almost all sugarcane harvesting in the United States is done mechanically. Two, the 

proposed trinexapac-ethyl labels have a 28-day pre-harvest interval (PHI) for sugarcane, so hand 

harvesting should not occur until after 28 days which is protective of the estimated REIs (M. 

Hawkins, 9/18/13, D413030). 

2.0 HED Recommendations

2.1 Data Deficiencies

There are no data deficiencies relating to toxicology and residue chemistry associated with the 

current petition for uses of trinexapac-ethyl. As previously stated in the last risk assessment

(D413570), a DFR study will be required for future assessments for trinexapac-ethyl. In 

accordance with the updated Part 158 data requirements (2007), one or more DFR studies are 

required when a pesticide has residential or occupational uses that could result in postapplication dermal exposure. 

2.2 Tolerance Considerations

2.2.1 Enforcement Analytical Method

An adequate enforcement method is available for trinexapac-ethyl, Method GRM020.01A,

which utilizes high performance liquid chromatography with triple-quadrupole mass 

spectrometry (LC-MS/MS) to support cereal grain uses. The method includes a strong acid 

hydrolysis/extraction procedure to release both “free” and “conjugated” residues of trinexapac 

acid from field grown grass commodities. The reported limit of quantitation (LOQ) is 0.010 

ppm. Validated analytical methods are available for both data collection and enforcement 

purposes. 

Also, trinexapac-ethyl was evaluated using the FDA multi-residue method Protocols C and D, 

and its acid metabolite, trinexapac, was evaluated using Protocol B. These data indicate FDA 

multi-residue methods are not suitable for determining residues of trinexapac-ethyl and 

trinexapac in plant commodities. 
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2.2.2 Recommended Tolerances

Permanent tolerances are currently established for residues of the plant growth regulator 

trinexapac-ethyl, including its metabolite and degradate, in or on the commodities in the 40

§CFR 180.662. The tolerance expression listed in the 40 CFR 180.662 complies with the HED 

interim tolerance expression policy (S. Knizner, 5/27/09). Permanent tolerances for trinexapacethyl should be established under 180.662(a) for the commodities listed below at the HEDrecommended tolerance levels shown in Table 2.2.2.

Table 2.2.2. Tolerance Summary for Trinexapac-ethyl.

Commodity Proposed Tolerance 

(ppm)

HEDRecommended 

Tolerance (ppm)

Comments 

(correct commodity 

definition)

Rice, grain 0.4 0.4

Rice, straw 0.07 0.07

Rice, bran 1.5 1.5

Rice, wild, grain 0.4 0.4

Rye, bran 2.5 6.0

Rye, grain 2.0 4.0

Rye, hay 0.8 1.5

Rye, straw 0.4 0.9

2.2.3 Revisions to Petitioned-For Tolerances

There are no changes to the petitioned-for tolerances for rice commodities. However, HED 

recommends revisions to the proposed rye tolerances. For rye, the registrant proposed tolerances 

by extrapolating residue data for barley. HED concurs with translating from the existing cereal 

grains, however, since tolerances for wheat commodities are higher than tolerances for barley

commodities, and HED recommends setting tolerances for rye, based on the higher wheat 

tolerances.

2.2.4 International Harmonization

There are no established or proposed Codex, Canadian, or Mexican maximum residue limits 

(MRLs) for trinexapac-ethyl in or on any food or feed crops. However, a variety of European 

countries, as well as Argentina, Brazil, Japan, Korea, and Australia have established or proposed 

MRLs for trinexapac-ethyl on cereal grains (0.02-0.5 mg/kg), cereal grain forages and fodders 

(0.2-3 mg/kg), sugarcane (0.05-0.1 mg/kg), sugar forage and fodder (1 mg/kg), meat (0.02 

mg/kg), and/or milk (0.1-0.005 mg/kg). At this time, there are no issues with respect to 

international harmonization associated with this petition.
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2.3 Label Recommendations

Trinexapac-ethyl is classified as Toxicity Category III for acute oral, dermal, and eye irritation, 

and IV for acute inhalation and skin irritation. It is not a dermal sensitizer. Therefore, the acute 

toxicity categories for this chemical require a 12 hour restricted entry interval (REI) under 40 

CFR 156.208 (c) (2) (iii). 

3.0 Introduction

Trinexapac-ethyl is a cyclohexadione plant growth regulator currently registered for use on 

grasses grown for seed, cereal grains (barley, oats, triticale, and wheat) and sugarcane. 

Trinexapac-ethyl inhibits internodal elongation and growth in cereal grains, grasses and several 

dicotyledonous species. It is registered in numerous European countries and several Asian and 

Latin American countries for uses on cereal grains and sugarcane. Tolerances are currently 

established for residues of trinexapac-ethyl in or on food commodities under 40 CFR §180.662, 

at levels ranging from 0.02 to 40 ppm. 

The most recent risk assessment was performed for registration review on September 12, 2013 

(D413570; S. Piper, D. Smegal, M. Hawkins).

Syngenta Crop Protection has petitioned to establish a permanent tolerance for residues of 

trinexapac-ethyl in/on rice and rye. The registrant provided field trial data on the use of 

trinexapac-ethyl in/on rice commodities. The tolerances on rye was requested based on the 

November 25, 2009, ChemSAC decision that provides an allowance for extrapolating residue 

data from barley and wheat to additional small cereal grains. Since tolerance are established for 

cereals (wheat, barley, and oats), the tolerances for rye commodities can be translated from 

established tolerances on small cereal grains.

3.1 Chemical Identity

Table 3.1. Trinexapac-ethyl Compound Nomenclature

Compound

Common name Trinexapac-ethyl

Company experimental name CGA163935

IUPAC name ethyl (RS)-4-cyclopropyl(hydroxy)methylene-3,5-dioxocyclohexanecarboxylate

CAS name ethyl 4-(cyclopropylhydroxymethylene)-3,5-dioxocyclohexanecarboxylate

OH

O

O

O

O

H3C
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Table 3.1. Trinexapac-ethyl Compound Nomenclature

CAS registry number 95266-40-3

End-use product (EP) 1.0 lb/gal EC (PalisadeTM EC; EPA Reg. No. 100-949)

2.0 lb/gal EC (Palisade 2EC; EPA Reg. No. 100-1241)

Regulated Metabolite

Common Name Trinexapac

Company Experimental 

Name

CGA-179500

IUPAC name (RS)-4-cyclopropyl(hydroxy)methylene-3,5-dioxocyclohexanecarboxylic acid

CAS name 4-(cyclopropylhydroxymethylene)-3,5-dioxocyclohexanecarboxylic acid

CAS registry number 104273-73-6

3.2 Physical/Chemical Characteristics

Trinexapac-ethyl has a relatively low octanol/water partition coefficient. At pH 5.3, the log KOW

value is 2.44 (KOW = 275). Trinexapac-ethyl has a low potential to leach into groundwater and is 

not expected to be volatile because of its low vapor pressure (2.16 x 10-3 Pa at 25oC). See Table 

3.2 for a listing of trinexapac-ethyl physical and chemical properties. 

O

O

O

HO OH
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Table 3.2. Physical and Chemical Properties of Trinexapac-Ethyl.

Parameter Value Reference

Melting point/range 36.1-36.6°C Provided in MRID 

pH 3.3 46809305

Density (20oC) 1.215 g/cm3

Water solubility (g/L at 25°C) 2.8 at pH 4.9

10.2 at pH 5.5

21.1 at pH 8.2

Solvent solubility Acetone 100% Ethanol 100%

Toluene 100% n-octanol 100%

n-hexane 5%

Vapor pressure (25oC) 2.16x 10-3 Pa

Dissociation constant, pKa 4.57

Octanol/water partition coefficient, 

Log(KOW) at 25oC

2.44 at pH 5.3

UV/visible absorption spectrum Neutral: 9335 L/mol·cm @ 240.2 nm

13976 L/mol·cm @ 277.4 nm

Acidic: 11712 L/mol·cm @ 240.0 nm

12368 L/mol·cm @380.4 nm

Basic: 21320 L/mol·cm @ 270.8 nm

3.3 Pesticide Use Pattern

Trinexapac-ethyl is marketed as an emulsifiable concentrate, wettable powder packed in watersoluble bags, and granule. Syngenta Crop Protection has registered trinexapac-ethyl for multiple 

end-use products on turf areas such as sod farms, golf courses, sport fields, cemeteries, and 

similar areas, and on grasses grown for seed, sugarcane, and cereal grains (wheat, barley, oats, 

triticale). The label-required personal protective equipment (PPE) for occupational applicators 

and handlers is a long-sleeved shirt, long pants, shoes, and socks, chemical-resistant gloves, and 

protective eyewear. The currently proposed uses on rice and rye are requested only on the 1 lb 

ai/gal and 2 lb ai/gal EC formulations and are summarized in Table 3.3. HED notes that the 

requested use on rye is identical to the established uses for wheat and barley.
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Table 3.3. Summary of Directions for the Proposed Uses of Trinexapac-ethyl 

Applic. Timing, 

Type, and 

Equip.

EPA Reg. 

No.

(formulation 

type)

Max.

Single 

Application 

Rate 

(lb ai/A)

Max. No. 

Application 

per year

Max. 

Annual 

App. 

Rate 

(lb ai/A) 

RTI 

(days)

PHI 

(days)

Use Directions and 

Limitations

Rice

Post-emergent 

aerial

application to 

flooded rice 

fields

1.0 lb/gal EC 

100-949 

2.0 lb/gal EC

100-1241

0.045 1 0.045 NA 50

For best performance, 

apply a single 

application to one of 

the following growth 

stages:

Fully tillered, panicle 

initiation, or panicle 

formation. Do not 

apply once internode is 

more than 1⁄2 to 3⁄4 inch 

in length. 

Rye

(same use directions as other small grains/cereals currently on the labels)

Post-emergent 

application 

(ground or aerial)

1.0 lb/gal EC 

100-949 

2.0 lb/gal EC

100-1241

0.11 1

0.11 45

Make applications from 

the Feekes growth 

stage 4 through Feekes 

growth stage 7.

Split applications may 

be made at Feekes 

growth stage 4-5 and 

then again at Feeks 7 

and 8. Apply in a min 

of 20 gal/A.

0.05 2

Conclusion

The proposed label for trinexapac-ethyl is adequate to allow evaluation of the residue data 

relatively to the proposed use on rice. Label direction for rye are equivalent to the currently 

registered uses of cereal grains for the same formulations. 

3.4 Anticipated Exposure Pathways

Humans may be exposed to trinexapac-ethyl in food because trinexapac-ethyl may be applied 

directly to growing crops. In addition, these applications can result in trinexapac-ethyl 

reaching surface and groundwater, both of which can serve as sources of drinking water. 

Homeowners may be exposed to trinexapac-ethyl when applying to their lawns, and both adults 
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and children may be exposed when coming in contact with treated turf. In an occupational 

setting, applicators may be exposed while handling the pesticide prior to application, as well as 

during application. There is a potential for exposure for workers re-entering treated fields and 

coming in contact with treated foliage.

3.5 Consideration 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’s 

National Health and Nutrition Examination Survey, What We Eat in America, 

(NHANES/WWEIA) 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 and ethnic 

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

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

appropriate, non-dietary 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 postapplication 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 and Dose-Response Assessment

4.1 Toxicology Studies Available for Analysis

The toxicology database for trinexapac-ethyl is complete and adequate to support the proposed 

new uses. The Hazard and Science Policy Council (HASPOC) determined that the subchronic 

inhalation study is not required at this time (Dunbar, 2013, TXR # 0056699). Data requirements 

for the food uses of trinexapac-ethyl are listed in Table A.1 in Appendix A. The data from the 

following studies were used to evaluate the hazard potential of trinexapac-ethyl (see Appendix 

A: Tables A.2 and A.3): 

 Acute lethality studies (oral, dermal, inhalation, primary eye and dermal irritation, 

and dermal sensitization)
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 Acute and subchronic neurotoxicity studies (rat)

 Subchronic oral toxicity studies (rat and dog) 

 Developmental (rat and rabbits) and reproductive toxicity (rat) studies 

 Dermal toxicity (21-day dermal toxicity in rabbits)

 Chronic oral toxicity studies (rat and dog)

 Carcinogenicity study (mouse)

 Metabolism study (rat)

 Dermal penetration study (rat)

 Mutagenicity battery

 Immunotoxicity study (mouse) 

4.2 Absorption, Distribution, Metabolism, & Elimination (ADME)

The metabolism study (MRID 41563927) was available and considered acceptable\guideline. In 

this study, groups of 5 male and 5 female rats received single oral doses of 0.97 or 166 mg/kg, or 

0.91 mg/kg intravenously (i.v.) of trinexapac-ethyl. An additional group of males and females 

were pre-conditioned for 14 days with daily oral doses of ~1 mg/kg/day non-radiolabeled 

trinexapac-ethyl, followed by 7 daily doses of radiolabeled test material (~1 mg/kg/day). 

4.2.1 Dermal Absorption

A single dermal dose of 0.01, 0.1, or 1.0 mg/cm2 14C-trinexapac-ethyl administered to male rats 

was rapidly absorbed, distributed, and eliminated (MRID 42238105). The amount absorbed 

increased with duration of exposure. The average 14C-trinexapac-ethyl absorbed within 24 hours 

was 56.8, 66.7, and 33.8% of the applied dose for the low-, mid-, and high- dose groups, 

respectively. Recovery of the applied dose was 97-117% and most was recovered from the skin 

washes and urine. The current policy is to use 8-hours exposure and to assume that residues 

found on the skin are potentially absorbable, unless data are provided to demonstrate otherwise. 

This policy reflects an 8-hour work day, and ongoing exposure is expected to cease at the end of 

the workday. Likewise, the Agency’s position is to be conservative to ensure public safety, and 

this is reflected in the assumption that residues found on the skin will be absorbed, unless there 

are data which contradicts this assumption. Since absorption rates were not measured beyond 24 

hours, the percent of the dose absorbed plus the percentage of the dose remaining on the washed 

application site (potentially absorbable) at 10 hours was 56.5% and 21%, respectively. Using the 

conservative approach, HED calculates the dermal absorption factor (DAF) to be 77.5% of the 

dose (0.01mg/cm2) for trinexapac-ethyl. 
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4.3 Toxicological Effects

4.3.1 Toxicology Profile

Trinexapac-ethyl exhibits low acute toxicity as shown in the standard acute toxicity battery as 

well as in the acute neurotoxicity study in rats with no systemic or neurotoxic effects up to the 

limit dose. The dog appears to be the most sensitive species while no systemic adverse effects 

were seen in rats, rabbits, or mice up to the limit dose (1,000 mg/kg/day) following subchronic or 

chronic oral exposure. In the dogs; however, decreased body weight gain and food consumption, 

diffuse thymic atrophy, and changes in the epithelial cells of the renal tubules were seen in the 

90-day dog study at 516/582 mg/kg/day (males/females). Following chronic exposure, doserelated neuropathology of the brain characterized as focal bilateral vacuolation of the dorsal 

medial hippocampus and/or lateral midbrain was seen at ≥365/357 mg/kg/day in male and 

female dogs, respectively. The lesions remained confined to the supporting cells in the central 

nervous system and did not progress to more advanced or more extensive damage of the nervous 

tissue. These lesions were not associated with other neuropathological findings or overt 

neurological signs, so their biological significance is unknown. Similar lesions were not 

observed in the rat or mouse following subchronic or chronic dietary exposure, and there was no 

other evidence in any other species tested to indicate a neurotoxicity potential. Furthermore, the 

brain lesions observed in the chronic dog study are not likely to develop from a short-term 

exposure and were not observed in either the rat or mouse short-term studies. In support of these 

findings, no evidence of neurotoxicity in the acute or subchronic rat neurotoxicity studies was 

found. 

In the rat and rabbit developmental toxicity studies, there is evidence of increased qualitative and 

quantitative susceptibility in the rat (increased incidence of asymmetrical sternebrae at the limit 

dose) and rabbit (decreased number of live fetuses/litter and increased post-implantation loss and 

early resorption at 360 mg/kg/day) in the absence of maternal toxicity. Qualitative sensitivity 

was observed in the 2-generation reproduction study but only in excess of the limit dose (1,212 

mg/kg/day). The decreased pup survival when analyzed with sexes combined, resulted in 

statistical significance (5-7%); this finding was not significant when the data were analyzed 

separately. Further evaluation of the individual litters suggested that one or two litters were the 

cause of the reduced pup survival at the highest dose tested. Reproductive toxicity was not 

observed up to the limit dose. There was also no indication of immunotoxicity in mice up to the 

limit dose. 

Data from the combined chronic toxicity/carcinogenicity study in the rat did not demonstrate an 

increase in any tumor type that would be relevant to humans. The observation of squamous cell 

carcinomas in the non-glandular portion of the stomach of two males at 806 mg/kg/day does not 

provide reasonable evidence of a possible deleterious effect of trinexapac-ethyl on the pharynx 

and/or esophagus (non-glandular areas) of the human. This is because trinexapac-ethyl would 

not be in contact with human tissues for a significant period of time compared to the length of 
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time it was in contact with the non-glandular portion of the rat stomach. Follicular 

adenocarcinomas of the thyroid were significantly increased in males (5%) at 806 mg/kg/day but 

this value was within the historical control range. In the mouse, there was no evidence of 

carcinogenicity. The mutagenicity database is complete, with no evidence of mutagenicity. The 

cancer classification for trinexapac-ethyl is “Not Likely to be Carcinogenic to Humans.”

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

The existing use pattern for trinexapac-ethyl could potentially result in dietary (various crops) 

and residential (turf) exposure to infants and children. Thus, FQPA hazard considerations were 

addressed in HED’s evaluation of the toxicology database. HED recommends that the 10x 

FQPA Safety Factor (for the protection of infants and children) be reduced to 1x. The rationale 

for this decision is that the toxicological database for trinexapac-ethyl is complete with regard to 

pre-and postnatal toxicity, immunotoxicity, and neurotoxicity studies, and there are no residual 

uncertainties. Additionally, the dietary exposure assessment is based on conservative, healthprotective assumptions that ensure that exposures to trinexapac-ethyl are not underestimated. 

These assumptions include tolerance-level residues and 100% crop treated estimates for all 

commodities. Furthermore, conservative, upper-bound assumptions were used to determine 

exposure through drinking water and residential sources, such that these exposures have not been 

underestimated.

4.4.1 Completeness of the Toxicology Database

The toxicology database for trinexapac-ethyl is complete for the risk assessment. There are 

acceptable studies available for toxicity endpoint selection. There are acceptable/guideline acute 

and subchronic neurotoxicity studies and an immunotoxicity study. The HASPOC determined, 

based the weight of the evidence (WOE), that the subchronic inhalation study could be waived 

(Dunbar, 2014, TXR # 0056699).

4.4.2 Evidence of Neurotoxicity

There was no evidence of neurotoxicity in the acute and subchronic neurotoxicity studies in rats 

at the limit dose. Nevertheless, dose-related neuropathology characterized as focal bilateral

vacuolation of the dorsal medial hippocampus and/or lateral midbrain in both sexes was 

observed at study termination in the chronic dog study at the two highest doses tested (356 

mg/kg/day: 3/8 dogs and 727 mg/kg/day: 8/8 dogs in the mid- and high dose groups, 

respectively). The vacuolation was associated with the astrocytes and oligodendrocytes. The 

lesions remained confined to the supporting cells in the central nervous system (CNS) and did 

not progress to more advanced or more extensive damage of the nervous tissue. The lesions were 

not associated with other neuropathological findings or overt neurological signs. The biological 

significance of these lesions is not known. Similar microscopic lesions in the brain were not 
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reported in the 90-day dog study, although, there was an inconsistency in the neuropathological 

screening of the brain in the 90-day study. Furthermore, similar lesions were not observed in the 

rat or mouse following subchronic or chronic dietary exposure, and there was no other evidence 

in any species tested to indicate a neurotoxicity potential. 

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

Evidence of increased qualitative and/or quantitative susceptibility of the offspring was seen only 

at high doses in the developmental rat and rabbit studies, and in the rat reproduction study. 

Developmental toxicity in the rat was only observed at the limit dose (increased incidence of 

asymmetrical sternebrae at 1,000 mg/kg) in the absence of maternal toxicity. In the rabbit, no 

maternal toxicity was demonstrated at the highest dose tested [360 mg/kg/day], but there was a 

decrease in the mean number of fetuses/litter and an increase in post-implantation loss and early 

resorptions at this dose level. Therefore, clearly identified NOAELs were established in both the 

rat and rabbit developmental studies. Reproductive toxicity was not observed in the rat 

reproduction study, but decreased pup survival and decreased pup body weight/body weight gain 

during lactation were observed above the limit dose (1212 mg/kg/day) with only reduced body 

weight/body weight gain and food consumption observed in the parental animals at a comparable 

LOAEL (1212 mg/kg/day). The NOAEL for this study was 594 mg/kg/day for offspring and 

parental animals.

Although, there is evidence of susceptibility in the rat and rabbit developmental studies and 

qualitative susceptibility in the 2-generation rat reproduction study, these effects only occurred at 

the highest doses tested (360-1200 mg/kg/day) for each study, and there were clearly identified 

NOAELs/LOAELs for the rabbit developmental study (60/593 mg/kg/day), the rat 

developmental study (200/1000 mg/kg/day) and for the reproduction study (593/1212 

mg/kg/day) for each fetal/offspring effect. Therefore, there are no residual concerns with respect 

to developmental and reproductive effects.

4.4.4 Residual Uncertainty in the Exposure Database

There are no residual uncertainties in the exposure database. Since the dietary and non-dietary 

exposure estimates were based on several conservative assumptions, HED does not believe the 

exposure assessment underestimates risk. These assumptions include tolerance-level residues 

and 100% crop treated estimates for all commodities. Actual exposures and risks from 

trinexapac-ethyl will likely be lower. Furthermore, conservative, upper-bound assumptions were 

used to determine exposure through drinking water and residential sources, such that these 

exposures have not been underestimated. 

4. 5 Toxicity Endpoint and Point of Departure Selections

The details for selecting toxicity endpoints and points of departure (PoDs) are presented in 
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Appendix A2. Based on the existing and new use patterns proposed by the registrant for 

trinexapac-ethyl, the exposure is expected to be via the oral, dermal, and inhalation routes. 

4.5.1 Dose-Response Assessment: The summary of toxicological doses and endpoints for 

trinexapac-ethyl that were used in the human health risk assessments is shown in Table 4.4.5. 

Acute Dietary (General Population): No appropriate endpoint for the general population 

including infants and children was found since no effects attributable to a single dose were 

identified in the toxicology database.

Acute Dietary (Females 13-49 years of age): A rabbit developmental toxicity study was 

selected for the acute dietary endpoint for females 13-49 years old. The NOAEL was 60 

mg/kg/day and the LOAEL was 360 mg/kg/day based on a decrease in the mean number of 

fetuses/litter and an increase in post-implantation loss and early resorptions. An Uncertainty 

Factor (UF) of 100 was applied to account for interspecies extrapolation (10X) and intraspecies 

variability (10X). The FQPA SF was reduced to 1X. Therefore, the acute reference dose (aRfD) 

for females 13-49 was calculated to be 0.6 mg/kg/day. This endpoint will be protective of the 

fetal effects (increased incidence of asymmetrical sternebrae) observed at higher doses (1000 

mg/kg/day) in the rat. The selection of this study and the PoD is protective of the potentially 

pregnant female and the developing fetus. It is also a conservative endpoint since this is a large 

dose spread (the NOAEL is 6-fold lower than the LOAEL).

Chronic Dietary: Quantification of chronic dietary (dietary and drinking water) risks was 

performed using the chronic oral toxicity in dogs with a NOAEL of 31.6 mg/kg/day based on 

elevated serum cholesterol values in females, mucoid feces in females, bloody feces in both 

sexes, and minimal focal vacuolation of the dorsal medial hippocampus and/or lateral midbrain 

in both sexes at the LOAEL of 357 mg/kg/day. This endpoint is protective since the dog is the 

most sensitive species. Additionally, there is a large dose spread in the chronic dog study (the 

NOAEL is 10-fold lower than the LOAEL) but there is a clear NOAEL and LOAEL. 

Vacuolation was observed in all dogs at the high level (males 727 mg/kg/day; females 784 

mg/kg/day) and was associated with the astrocytes and oligodendrocytes in the hippocampus. 

The lesions remained confined to the supporting cells in the CNS and did not progress to more 

advanced or more extensive damage of the nervous system. Similar lesions were not reported in 

the 90-day dog study but there is an inconsistency in the neuropathological screening of the 

brain, which precludes a definitive determination on the occurrence of this lesion following 

subchronic exposure. Similar lesions were not observed in the rat or mouse following acute, 

subchronic or chronic dietary exposure. Because of the concern for the brain lesions and the 

uncertainty of the timing of the brain lesions, the use of the dog sturdy is warranted in this case 

to be protective of these concerns.

Incidental Oral (Short-Term): An endpoint for the incidental oral exposure scenario for 

children was not identified from the available trinexapac-ethyl toxicity studies. The rationale for 
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this conclusion is based on the following weight of evidence considerations: 1) the toxicity 

observed during the appropriate duration of concern (short/intermediate term) were observed 

only at high doses [LOAEL = 900 mg/kg/day in the dog, 1000 mg/kg/day in the rat, and 1212 

mg/kg/day in the reproduction study]; 2) the brain lesions observed in the chronic dog study are 

not appropriate for this scenario since the brain lesions were seen only at termination (i.e. after 

exposure to 1-year) and toxicity observed after chronic exposure is not appropriate for 

application to the short/intermediate term scenarios; 3) the brain lesion observed in the chronic 

study are not expected to occur after short term exposure due to the lack of similar lesions or 

associated toxicity (i.e., clinical neurologic signs) in the 90-day studies in rats or dogs; 4) the 

cause for concern for the brain lesions is low because of the minimal lesion severity, lack of 

associated changes (i.e., gliosis, myelin loss astrocyte hypertrophy, neuronal necrosis etc), and 

the non-specific nature of the lesions (i.e., focal vacuoles); 5) the overall toxicity profile of this 

chemical clearly shows that toxicity is observed only at high doses (lowest LOAEL = 360 m/k/d 

in the chronic dog study); and 6) the in utero endpoint identified in the rabbit study is not 

appropriate for this population of concern (children) (D392798, M. Hawkins, 11/23/2011). 

Dermal and Inhalation (Short- and Intermediate-Terms): The rabbit developmental toxicity 

study was selected with a NOAEL of 60 mg/kg/day and a LOAEL of 360 mg/kg/day based on a 

decrease in mean number of fetuses/litter and an increase in post-implantation loss. This selected 

endpoints are only applicable to adults (females) because the endpoint is based on in utero

effects. HED reviewed the full toxicological database for trinexapac-ethyl in an attempt to select 

endpoints for the dermal and inhalation children scenarios; however, no appropriate endpoint 

was available. Detailed rationales are described as follows.

For adults, the short- and intermediate-term dermal and inhalation scenarios are both based on 

the in utero effect observed in the rabbit developmental study (LOAEL 360 mg/kg/day). This is 

protective of female workers that may become pregnant while exposed to trinexapac-ethyl. The 

chronic dog study was also considered since it has a similar LOAEL (357 mg/kg/day). The 

NOAELs established in these two studies, however, are 2-fold different due to the dose-spread in 

the two studies. Therefore, the higher NOAEL of 60 mg/kg/day from the rabbit developmental 

study (LOAEL 360 mg/kg/day) is protective of the effects observed (LOAEL 357 mg/kg/day) in 

the chronic dog study with NOAEL of 31.6 mg/kg/day. Although the 21-day rabbit dermal study 

did not result in systemic toxicity at the limit dose and suggests a dermal assessment is not 

warranted, this study is performed only in adult animals, not pregnant animals. It is currently 

unknown if a dermal study with pregnant rabbits would result in an in utero effect similar to that 

observed in the rabbit developmental study. Therefore, the use of the rabbit developmental study 

for the short- and intermediate-term dermal and inhalation scenarios is conservative and 

protective for these routes of exposure.

For children, the short- and intermediate-term dermal and inhalation endpoints selected for adults 

are not applicable because the adult endpoints are based on in utero effects. HED reviewed the 

full toxicological database for trinexapac-ethyl in an attempt to select endpoints for children for 
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the dermal and inhalation exposure scenarios; however, no appropriate endpoints were identified 

for these scenarios based on the following reasons: 1) dermal irritation effects are mild after 

21/28 days of exposure in the rabbit study; 2) dermal irritation effects after a single exposure 

disappear after seven days; 3) there are no systemic effects up to the limit dose in the dermal 

rabbit study; 4) there are no adverse toxicological effects (at doses close to the limit dose of 1000 

mg/kg/day) in the 2-generation reproductive study in rats or in the chronic/carcinogenicity 

studies in rats and mice; 5) there is no maternal toxicity in the developmental toxicity studies in 

both rats and rabbits; 6) there are no identifiable endpoints for the oral studies in the rat or rabbit.

Table 4.4.5. Summary of Toxicological Doses and Endpoints for Trinexapac-ethyl for use in 

Human Health Risk Assessments.

Exposure/

Scenario

Point of 

Departure

Uncertainty/ 

FQPA Safety 

Factors

RfD, PAD, 

Level of 

Concern for 

Risk 

Assessment

Study and Toxicological Effects

Acute Dietary

(General 

Population, 

including Infants 

and Children)

No appropriate endpoint for the general population including infants and children was available.

Acute Dietary

(Females 13-49 

years of age)

NOAEL = 60 

mg/kg/day

UFA= 10x

UFH = 10x

FQPA SF= 1x

Acute RfD = 0.6 

mg/kg

aPAD = 0.6 

mg/kg/day

Developmental rabbit study

MRID 41869524

LOAEL = 360 mg/kg, based on a 

decrease in mean number of fetuses/litter 

and an increase in post-implantation loss

and early resorptions. 

Chronic Dietary

(All Populations)

NOAEL= 31.6 

mg/kg/day

UFA= 10x

UFH = 10x

FQPA SF= 1x

Chronic RfD = 

0.32

mg/kg/day

cPAD = 0.32 

mg/kg/day

Chronic oral toxicity study – dog

MRID 42779402/ 42779401

LOAEL = 357 mg/kg/day, based on 

elevated serum cholesterol values in 

females, mucoid feces in females and 

bloody feces in both sexes, and minimal, 

focal vacuolation of the dorsal medial 

hippocampus and/or lateral midbrain in 

both sexes

Incidental Oral 

(Short -Term) No appropriate endpoint for the incidental oral scenario for children.
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Table 4.4.5. Summary of Toxicological Doses and Endpoints for Trinexapac-ethyl for use in 

Human Health Risk Assessments.

Exposure/

Scenario

Point of 

Departure

Uncertainty/ 

FQPA Safety 

Factors

RfD, PAD, 

Level of 

Concern for 

Risk 

Assessment

Study and Toxicological Effects

Dermal & 

Inhalation

Short and 

Intermediate- Term

(Adults only)

NOAEL = 60 

mg/kg/day

Dermal 

absorption rate 

= 77.5% of oral

absorption 

Inhalation rate = 

100 % of oral 

absorption

UFA= 10x

UFH = 10x

FQPA SF= 1x

Residential LOC 

for MOE = 100

Occupational 

LOC for MOE = 

100

Developmental rabbit study 

MRID 41869524

LOAEL = 360 mg/kg, based on a 

decrease in mean number of fetuses/litter 

and an increase in post-implantation loss

and early resorptions.

Dermal & 

Inhalation

Short and 

Intermediate- Term

(Children)

No appropriate endpoint for these exposure scenario for children.

Cancer (oral, 

dermal, inhalation)

Classification: “Not likely to be Carcinogenic to Humans” 

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. 

4.5.2 Recommendation for Combining Routes of Exposure for Risk Assessment

In accordance with the requirements of the FQPA (1996), HED has considered the potential for 

concurrent exposure to trinexapac-ethyl via oral, dermal, and inhalation routes. HED combines 

exposure from different routes for each population if the same toxic effects are seen for that 

duration of exposure by each route. There are no short-term oral, dermal or inhalation endpoints 

for children; therefore a discussion of combining routes is not relevant for this population 

subgroup. Since the short-term oral, dermal and inhalation PoDs for adults (females) were 

selected from a single study, exposure from these three routes of exposure should be combined 

for aggregate risk assessment. 

4.5.3 Cancer Classification and Risk Assessment Recommendations

Trinexapac-ethyl is classified as “Not Likely to be Carcinogenic to Humans”; therefore, a cancer 

dietary exposure assessment was not conducted.
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4.6 Endocrine Disruption

As required under FFDCA section 408(p), EPA has developed the Endocrine Disruptor 

Screening Program (EDSP) to determine whether certain substances (including pesticide active 

and other ingredients) may have an effect in humans or wildlife similar to an effect produced by 

a “naturally occurring estrogen, or other such endocrine effects as the Administrator may 

designate.” The EDSP employs a two-tiered approach to making the statutorily required 

determinations. Tier 1 consists of a battery of 11 screening assays to identify the potential of a 

chemical substance to interact with the estrogen, androgen, or thyroid (E, A, or T) hormonal 

systems. Chemicals that go through Tier 1 screening and are found to have the potential to 

interact with E, A, or T hormonal systems will proceed to the next stage of the EDSP where EPA 

will determine which, if any, of the Tier 2 tests are necessary based on the available data. Tier 2 

testing is designed to identify any adverse endocrine related effects caused by the substance, and 

establish a dose-response relationship between the dose and the E, A, or T effect.

Between October 2009 and February 2010, EPA is issuing test orders/data call-ins for the first 

group of 67 chemicals, which contains 58 pesticide active ingredients and 9 inert ingredients. 

This list of chemicals was selected based on the potential for human exposure through pathways 

such as food and water, residential activity, and certain post-application agricultural scenarios. 

This list should not be construed as a list of known or likely endocrine disruptors.

Trinexapac-ethyl is not among the group of 58 pesticide active ingredients on the initial list to be 

screened under the EDSP. Under FFDCA Sec. 408(p), the Agency must screen all pesticide 

chemicals. Accordingly, EPA anticipates issuing future EDSP test orders/data call-ins for all 

pesticide active ingredients. 

For further information on the status of the EDSP, the policies and procedures, the list of 67 

chemicals, the test guidelines and the Tier 1 screening battery, please visit our website: 

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

5.0 Dietary Exposure and Risk Assessment 

5.1 Residues of Concern Summary

For plants (primary and rotational crops) and livestock commodities, the Residues of Concern 

Knowledgebase Subcommittee (ROCKS) recommends that parent trinexapac-ethyl and the free 

acid metabolite, trinexapac (CGA 179500), are the residues of concern for both the tolerance 

expression and the risk assessment. For drinking water, the residue of concern are the parent 

ester including its free acid CGA-179500, CGA-313458, an open chain cyclohexane ring and 

an unidentified hydroproduct M3 (ROCKS memo, D390121, 7/12/11).
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Table 5.1.4. Summary of Metabolites and Degradates of Trinexapac-ethyl.

Matrix Residues included in Risk 

Assessment

Residues included in Tolerance 

Expression 

Plants Primary 

Crop

Trinexapac-ethyl parent + 

Trinexapac acid (CGA 179500)

Trinexapac-ethyl parent + 

Trinexapac acid (CGA 179500)

Rotational 

Crop

Livestock Ruminant

Poultry

Drinking Water Total residues (parent + 

identified degradates)1

Not Applicable

1 A total major residue approach is recommended, including parent and major environmental degradates 

trinexapac (CGA-179500), 2-(4-cyclopropyl-4-hydroxy-2-oxobutyl)succinic acid (CGA-313458), the open chain 

cyclohexane ring, and the unidentified hydroproduct M3. 

5.2 Food Residue Profile

Available metabolism data shows that trinexapac-ethyl does translocate to the growing shoot 

when applied as a foliar application. Trinexapac-ethyl is used at relatively low application rates, 

and the submitted field trial studies demonstrate that when applied at post-emergence, 

quantifiable residues are seen in cereal grains treated up to 51-100 days before harvest. Also, 

data from the confined rotational crop study indicate that trinexapac-ethyl residues are detected 

(lettuce and wheat) at the 30-day plant back interval. Quantifiable residues were only seen in 

livestock at low levels in the animal feedstuff associated with this action. 

5.3 Water Residue Profile

The drinking water residues used in the dietary risk assessment were provided by the 

Environmental Fate and Effects Division (EFED) in the following memorandum: “Drinking 

Water Assessment for Trinexapac-Ethyl New Use on Rice and Rye” (C. Koper, D421848, 

10/01/14) and incorporated directly into the dietary assessment. A Tier I rice model for drinking 

water assessment was conducted to support the human health risk assessment for the new food 

use registration for trinexapac ethyl on rice and rye. A separate model run for rye is not required 

since application rates are the same for rye as previously assessed on cereal grains (D377936; 

08-09-11); therefore, estimated drinking water concentrations from the rye use are expected to be 

the same as from the currently registered cereal grain uses. The recommended estimated drinking 

water concentrations (EDWCs) for the human health risk assessment are based on highest 

predicted values for surface water and ground water. For surface water, application (1 

application at 0.045 lb ai/acre) to rice yielded the highest EDWCs. The acute and chronic 

concentrations were estimated to be 31.68 ppb. For ground water, based on the proposed highest 

annual use rate for turf (8 applications at 0.34 lb ai/acre), the PRZM-GW (v.1.07) model 
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estimated an acute concentration of 0.116 ppb and 30-year average (chronic) concentration of 

0.054 ppb. HED notes that the rice model estimated surface water concentration is a calculated 

water number in the rice paddy water reflecting the concentration in the rice paddy at the time of 

application. Use of this number in a chronic assessment is considered highly conservative; 

however since there is no chronic refinement for the rice water and since risks are not of concern, 

that value was used in the chronic dietary assessment. 

Water residues were incorporated in the DEEM-FCID into the food categories “water, direct, 

all sources” and “water, indirect, all sources.” Table 5.3 provides a summary of the Tier 2 

modeled drinking water concentrations. The model and its description are available at the EPA 

internet site: http://www.epa.gov/oppefed1/models/water/. 

Table 5.3. Recommended Trinexapac-Ethyl Estimated Drinking Water Concentrations

(EDWCs) for Surface Water and Ground Water based on selected Crop Scenarios

Proposed

Label Use

Model Method

1 Maximum 

Application Rate 

(interval between 

applications)

1-in-10 

year

acute

(μg/L)

1-in-10 

year

chronic

(μg/L)

30- year 

average

(μg/L)

Surface Water

Rice Tier 1 Rice Model NA 1 app @ 0.045 lb a.i./acre

31.68

(12.61)

2

31.68

(1.56)

31.68

(1.04)

Ground Water

Turf PRZM-GW G 8 app @ 0.34 lb a.i./acre

0.116

(0.009)

NA 0.054

(0.009)

1 G = foliar, ground application, NA = Not Applicable.

2

Italicized values generated from turf scenario (parent D377936; sub D395601)

Bold numbers denote maximum EDWC values. Italicized numbers denote maximum EDWC values from previous 

drinking water assessment (parent D377936; Sub D395601; 10-28-11).

5.4 Dietary Risk Assessment

5.4.1 Description of Residue Data Used in Dietary Assessment

Updated acute and chronic dietary (food and drinking water) exposure and risk assessments were 

conducting using the Dietary Exposure Evaluation Model software with the Food Commodity 

Intake Database (DEEM-FCID) Version 3.16. This software uses 2003-2008 food consumption 

data from the U.S. Department of Agriculture’s (USDA’s) National Health and Nutrition 

Examination Survey, What We Eat in America, (NHANES/WWEIA). The drinking water 

estimates provided by EFED are modeled estimates, and were generated using the most 

conservative model available for the existing uses. The unrefined acute and chronic assessment 
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using tolerance level residues for the dietary risk exposure analysis will not underestimate risk to 

the general U.S. population or any population subgroup (S. Biswas, 02/11/2015, D424893).

5.4.2 Percent Crop Treated Used in Dietary Assessment

Percent crop treated information was not used in these assessments. The acute and chronic 

assessments were both based on the assumption that 100% of all commodities with trinexapacethyl recommended tolerances will be treated.

5.4.3 Acute Dietary Risk Assessment

There were no appropriate toxicological effects attributable to a single exposure (dose) for the 

general population or any other population subgroups except females 13-49 years old; therefore,

these population subgroups were not included in this assessment. For food and drinking water, 

the acute dietary risk estimate is below HED’s level of concern (<100% of the aPAD) at the 95th

percentile of exposure. The acute dietary exposure estimate for females 13-49 years old is 

0.014667 mg/kg/day (2% of the aPAD).

5.4.4 Chronic Dietary Risk Assessment

Combined chronic dietary exposure estimates for food and drinking water are well below HED’s 

level of concern. Using the DEEM-FCID software, dietary exposure is estimated at 0.008293

mg/kg/day for the U.S. population which is equivalent to 3% of the cPAD, and 0.020596 

mg/kg/day, equivalent to 6% of the cPAD for children 1-2 years old, the population with highest 

estimated chronic dietary exposure to trinexapac-ethyl.

5.4.5 Cancer Dietary Risk Assessment

Trinexapac-ethyl is classified as “Not Likely to be Carcinogenic to Humans.” Therefore, a 

cancer dietary exposure assessment was not conducted.

5.4.6 Dietary Summary Table
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Table 5.4.6. Summary of Dietary (Food and Drinking Water) Exposure and Risk for Trinexapacethyl

Population Subgroup

Acute Dietary1

(95th% Percentile) Chronic Dietary Cancer

Dietary 

Exposure 

(mg/kg/day)

% aPAD

Dietary 

Exposure

(mg/kg/day)

% 

cPAD

Dietary 

Exposure

(mg/kg/day)

Risk

General U.S. 

Population

N/A N/A

0.008293 2.6

N/A N/A

All Infants (< 1 year 

old) 0.008387 2.6

Children 1-2 years 

old 0.020596 6.4

Children 3-5 years 

old 0.019487 6.1

Children 6-12 years 

old 0.013981 4.4

Youth 13-19 years 

old 0.008238 2.6

Adults 20-49 years 

old 0.006853 2.1

Adults 50+ years old 0.005861 1.8

Females 13-49 

years old1

0.014667 2.4 0.006466 2.0

1

aPAD=0.6 mg/kg/day for females 13-49 only (no appropriate endpoint for general US population including infants 

and children) cPAD=0.32 mg/kg/day. Not likely to be carcinogenic to humans.

6.0 Residential (Non-Occupational) Exposure/Risk Characterization

As was mentioned, no new residential uses are being proposed at this time so an updated 

residential exposure assessment is not required; however, there are registered residential uses for 

trinexapac-ethyl that were assessed previously for turf using the 2012 Residential SOPs (M. 

Hawkins, D413030, 9/18/2013). The residential handler MOEs range from 240 to 21,000,000. 
Trinexapac-ethyl Human Health Risk Assessment DP No.419651

Page 27 of 55

The residential post-application MOEs range from 450 to 61,000. Recommendations for the 

residential input of the aggregate remain unchanged from the previous memo. They are as 

follows:

• The recommended residential exposure estimate for use in the adult (female) aggregate 

assessment reflects dermal and inhalation exposure from handler exposure to sprays that 

are applied on turf with backpack sprayers (edging/banding), which resulted in a MOE of 

240.

• The recommended residential exposure estimate for use in the child (11 – 16 years old)

aggregate assessment reflects dermal exposure from mowing turf that has been treated 

with a granular formulation, which resulted in a MOE of 13,000.

• There are no endpoints for short-term oral, dermal or inhalation exposure for young 

children (< 11 years old); therefore quantitative residential exposure assessments are not 

conducted for younger children

The residential exposure/risk estimates and recommendations for the trinexapac-ethyl aggregate 

are provided below in Table 6.1.

Table 6.1. Recommendations for the Residential Exposures for the Trinexapac-ethyl Aggregate Assessment.1

Lifestage

Residential Handler Residential Post-application 

Dose (mg/kg/day)2 MOE3 Dose (mg/kg/day)4 MOE5

Dermal Inhalation Total Dermal Inhalation Total Dermal Inhalation Oral Total Dermal Inhalation Oral Total

Short-Term

Adult 

Female 0.2482 0.00034 0.249 240 170,000 2401 0.135 N/A N/A 0.135 450 N/A N/A 450

Child 11 

to 16 

years old

N/A N/A N/A N/A N/A N/A 0.005 N/A N/A 0.005 13,000 N/A N/A 13,0001

1

 Bolded risk estimates should contribute to the residential exposure portion of the aggregate assessment. 

2 Residential Handler Dose = the highest handler dose for each applicable lifestage of all scenarios assessed from 

Table 6.1.1. (D413570) Total = dermal + inhalation.

3 Residential Handler MOE = the MOEs associated with the highest doses identified in Table 6.1.1. (D413570) 

Total = 1 ÷ ((1/Dermal MOE) + (1/Inhalation MOE)).

4 Residential Post-application Dose = the highest post-application dose for each applicable lifestage of all scenarios 

assessed from Table 6.2.1. (D413570) Total = dermal + inhalation + incidental oral, where applicable.

5 Residential Post-application MOE = the MOEs associated with the highest doses identified in Table 6.2.1 

(D413570) Total = 1 ÷ (1/Dermal MOE) + (1/Inhalation MOE) + (1/Incidental oral MOE). 

6.1 Spray Drift

Spray drift is a potential source of exposure to those nearby pesticide applications. This is 

particularly the case with aerial application, but, to a lesser extent, spray drift can also be a 

potential source of exposure from the ground application methods (e.g., groundboom and 

airblast) employed for trinexapac-ethyl. The agency has been working with the Spray Drift Task 

Force (a task force composed of various registrants which was developed as a result of a Data 
Trinexapac-ethyl Human Health Risk Assessment DP No.419651

Page 28 of 55

Call-In issued by EPA), EPA Regional Offices and State 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). 1 The agency has also developed a policy on how to 

appropriately consider spray drift as a potential source of exposure in risk assessments for 

pesticides. The potential for spray drift was quantitatively evaluated for trinexapac-ethyl during 

the Registration Review process (D413030). 

HED notes that the proposed new uses on rice and rye do not impact the spray drift assessment.

6.2 Residential Bystander Post-Application Inhalation Exposure

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

individuals nearby 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, and received the SAP’s final report on 

March 2, 2010 (http://www.epa.gov/scipoly/SAP/meetings/2009/120109meeting.html). The 

Agency has evaluated the SAP report and has developed a Volatilization Screening Tool and a 

subsequent Volatilization Screening Analysis (http://www.regulations.gov/#!docketDetail;

D=EPA -HQ-OPP-2014-0219). During Registration Review, the Agency will utilize this 

analysis to determine if data (i.e., flux studies, route-specific inhalation toxicological studies) or 

further analysis is required for trinexapac-ethyl.

7.0 Aggregate Exposure/Risk Characterization

In accordance with the FQPA, HED must consider and aggregate (add) pesticide exposures and 

risks from three major sources: food, drinking water, and residential exposures. 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.

7.1 Acute Aggregate Risk

Acute aggregate risk results from exposure to residues in food and drinking water alone. The 

acute dietary exposure analysis for females 13-49 years included both food and drinking water. 

Therefore, acute aggregate risk is equivalent to the acute dietary risk, as discussed in Section 

5.4.3, above. All risk estimates are below HED’s level of concern. No appropriate endpoint for 

the general population, including infants and children was found; therefore, aggregate 

assessments are not required for these population subgroups.

 

1 Available: http://www.epa.gov/opp00001/factsheets/spraydrift.htm 
Trinexapac-ethyl Human Health Risk Assessment DP No.419651

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7.2 Short- and Intermediate-Term Aggregate Risk

The short- and intermediate-term toxicological endpoints for trinexapac-ethyl are the same for 

each route of exposure. Therefore, for residential exposure scenarios, only short-term exposures 

were assessed, and are considered to be protective of intermediate-term exposure and risk. 

Exposures from these scenarios are aggregated with average dietary exposure from food and 

water which is considered to be background exposure. The LOCs for these exposure routes are 

all 100.

For the adult short- and intermediate-term aggregate risk assessment, chronic dietary exposure 

was added directly to the adult and children (11< 16 years old) post-application exposure 

estimate. To be health protective, the post-application scenario was used in the aggregate 

because it resulted in higher exposure than the handler scenario. The chronic dietary exposure 

estimate for females 13-49 years old and youth 13-19 years old were used to determine the 

aggregate risk estimate because they best match the lifestages assessed in the residential 

assessment.

Short-term aggregate margins of exposure for adult and children exceed HED’s level of concern 

of 100 and are not of concern (MOEs > 100). Short- and intermediate-term estimated exposure 

and risks are shown below in Table 7.2. 

Table 7.2. Short-Term and/or Intermediate Term Dermal Aggregate Risk Calculation

Short- or Intermediate-Term Scenario

Population NOAEL 

mg/kg/day

LOC1 Max 

Allowable 

Exposure 

mg/kg/day2

Average 

Food and 

Water 

Exposure 

mg/kg/day3

Residential

Postapplication 

Dermal

Exposure 

mg/kg/day4

Total 

Exposure 

mg/kg/day5

Aggregate 

MOE (food, 

water, and 

residential)6

Child 11- 16 

years old 60 100 0.60

0.008283 0.005 0.013283 4500

Adult 

Female 0.006466 0.249 0.255466 230

1 An UF of 100x was applied to account for interspecies extrapolation (10x) and intraspecies variation 

(10x) and no additional uncertainty factors/safety factors are required.

2 Maximum Allowable Exposure (mg/kg/day) = NOAEL/ (60 mg/kg/day)/LOC (100)

3 Average food and water exposure from chronic dietary exposure for youth 13-19 yrs old and females 13-

49 yrs old. See Table 5.4.6 

4Residential Exposure = Dermal exposure from treated turf (See Table 6.1 and further details see Table 

6.1.1. (D413570) 

5 Total Exposure = Avg Food & Water Exposure + Residential Exposure

6 Aggregate MOE = NOAEL/Total Exposure
Trinexapac-ethyl Human Health Risk Assessment DP No.419651

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7.3 Cancer Aggregate Risk

The Cancer Assessment Review Committee (CARC) classified trinexapac-ethyl as “not likely to 

be carcinogenic to humans.” Therefore, cancer aggregate cancer risk was not quantitatively 

assessed.

8.0 Cumulative Exposure/Risk Characterization

The Food Quality Protection Act (FQPA) requires the Agency to consider the cumulative risks of 

chemicals sharing a common mechanism of toxicity. The Agency determined that there was 

insufficient evidence to suggest trinexapac-ethyl shares a common mechanism of toxicity with 

other chemical 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 Office of Pesticide Program 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/pesticides/

cumulative/.

9.0 Occupational Exposure/Risk Pathway

9.1 Occupational Handler Exposure/Risk Estimates

In the previous occupational exposure assessment for trinexapac-ethyl (D413570), occupational 

handler and post-application exposures were assessed for the currently registered use for each 

trinexapac-ethyl crop, including cereal grains which was assessed at a maximum application rate 

of 0.11 lb ai/A. The maximum single application rates for both rice (0.045 lb ai/A) and rye (0.11 

lb ai/A) are either the same or lower than crops that were previously assessed. Therefore, an 

updated occupational exposure assessment for the proposed new uses is not required at this time. 

The occupational handler assessment MOEs range from 140 to 2,100,000 with baseline attire 

and/or with the addition of gloves (as required on the labels). The occupational post-application 

MOEs on the day of application range from 87 to 43,000. Based on HED’s occupational postapplication exposure assessment, the REI for hand-harvesting sugarcane was estimated to be 2 

days for short- and intermediate-term exposure. However, HED does not recommend that 

sugarcane REI’s be changed on the trinexapac-ethyl labels at this time based on two main issues. 

One, almost all sugarcane harvesting in the United States is done mechanically. Two, the 

proposed trinexapac-ethyl labels have a 28-day PHI for sugarcane, so hand harvesting should not 

occur until after 28 days which is protective of the estimated REIs (M. Hawkins, 9/18/13, 

D413030). 
Trinexapac-ethyl Human Health Risk Assessment DP No.419651

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Trinexapac-ethyl is classified as Toxicity Category III for acute oral, dermal, and eye irritation, 

and IV for acute inhalation and skin irritation. It is not a dermal sensitizer. Therefore, the acute 

toxicity categories for this chemical require a 12 hour restricted entry interval (REI) under 40 

CFR 156.208 (c) (2) (iii) 

10.0 Review of Incident Report

Trinexapac-ethyl incidents were analyzed from January 1, 2010- January 20, 2015 (S.Recore, 

2/4/2015, D425401). There was 1 incidents identified from the Main IDS (Incident Data 

System) and 2 additional incidents reported involving more than one chemical; and 3 incidents 

identified in Aggregate IDS. Based on the low frequency and severity of incident cases reported 

for trinexapac-ethyl in both IDS and NIOSH SENSOR-Pesticides, there does not appear to be a 

concern at this time that would warrant further investigation. The Agency will continue to 

monitor the incident information and if a concern is triggered, additional analysis will be 

conducted.

11.0 References

DP#: 413570

Subject: Trinexapac-ethyl: Human Health Risk Assessment for Registration Review.

From: S. Piper, D. Smegal, and M. Hawkins

To: K. Keller

Date: 09/12/13

MRIDs: NA

DP#: 424894

Subject: Trinexapac-ethyl: Section 3 Registration Request to Add New Uses on Rice and 

Rye. Summary of Analytical Chemistry and Residue Data. 

From: S. Bose Biswas

To: B. Benbow and K. Montague

Date: 2/11/2015

MRIDs: 49282807

DP#: 424893

Subject: Trinexapac-ethyl: Acute and Chronic Aggregate Dietary (Food and Drinking 

Water) Exposure and Risk Assessments to Support New Uses on Rice and Rye.

From: S. Bose Biswas

To: B. Benbow and K. Montague

Date: 2/11/2015

MRIDs: NA
Trinexapac-ethyl Human Health Risk Assessment DP No.419651

Page 32 of 55

DP#: 421848

Subject: Drinking Water Assessment for Trinexapac-ethyl New Use on Rice and Rye.

From: C. Koper, S. Sankula, M. Radtke

To: B. Benbow and K. Montague

Date: 10/01/14

MRIDs: NA

DP#: 413030

Subject: Preliminary Occupational and Residential Exposure/Risk Assessment for 

Registration Review.

From: M. Hawkins

To: S. Piper and K. Keller

Date: 09/18/13

MRIDs: NA

DP#: 425401

Subject: Trinexapac-ethyl: Tier I Review of Human Incidents for Preliminary Risk 

Assessment

From: S. Recore and E. Evans

To: S. Piper and A. Jakob

Date: 02/04/2015

MRIDs: NA

Toxicology:

41563920 Chau, R. Y.; McCormick, G. C.; and Arthur, A. T. (1989). 13-Week Oral Feeding 

Study in Dogs.

41563921 Chau, R. Y.; McCormick, G. C.; and Arthur, A. T. (1989). 13-Week Oral Feeding 

Study in Rats.

41563922 Huber, K. R.; Batastini, G.; and Arthur, A. T. (1989). 21-Week Dermal Toxicity 

Study in Rabbits.

41563923 Schoch, M. (1988). Developmental Toxicity (Teratogenicity) Study with CGA 

163935 Technical in Rats.

41869524 Hughes, E. (1990). Developmental Toxicity (Teratogenicity) Study with CGA 

163935 Technical in Rabbits.

42238104 Giknis, M. L.; Batastini, G.; and Arthur, A. T. (1992).52/104 Week Oral Toxicity 

Study in Rats. 

42779401 Hardisty, J. F. (1992). Supplement to 52-Week Feeding Study in Dogs. 
Trinexapac-ethyl Human Health Risk Assessment DP No.419651

Page 33 of 55

42779402 Chau, R. Y.; Kirchner, F. R.; and Arthur, A. T. (1991). 52-Week Feeding Study in 

Dogs.

43128603 Rudzki, M. W.; Batastini, G., and Arthur, A. T. (1991). 78-Week Oral 

Carcinogenicity Study in Mice. 

43128604 Singh, A.; Hazelette, J.; and Yau, E. (1991). CGA-163935 Technical. A TwoGeneration Reproductive Toxicity Study in Rats.

43128605 Geleick, D. Gene Mutations Test Mouse Lymphoma Mutagenicity Assay in vitro.

46809308 Deparade, E. (2001). CGA275537 Technical (metabolite of trinexapac-ethyl).

48764506 Beck, M. (2012). Trinexapac-Ethyl- An Oral (Gavage) Acute Neurotoxicity 

Study in Rats Final Report.

48764507 Beck, M. (2012). Trinexapac-ethyl – Subchronic (13-week) Dietary

Neurotoxicity Study in Rats.

Appendix A: Toxicology Profile and Executive Summaries

A.1 Toxicology Data Requirements 

The requirements (40 CFR 158.340) for a food use for trinexapac-ethyl are in Table A.1 Use of 

the new guideline numbers does not imply that the new (1998) guideline protocols were used. The 

toxicity profiles are present below in Tables A.2.1 and A.1.2.

Table A.1. Toxicology Data Requirements

Test Technical 

Required Satisfied

870.1100 Acute Oral Toxicity ......................................................

870.1200 Acute Dermal Toxicity .................................................

870.1300 Acute Inhalation Toxicity .............................................

870.2400 Primary Eye Irritation ...................................................

870.2500 Primary Dermal Irritation .............................................

870.2600 Dermal Sensitization.....................................................

yes

yes

yes

yes

yes

yes

yes

yes

yes

yes

yes

yes

870.3100 Oral Subchronic (rodent)..............................................

870.3150 Oral Subchronic (nonrodent) ........................................

870.3200 21/28-Day Dermal ........................................................

870.3250 90-Day Dermal .............................................................

870.3465 90-Day Inhalation .........................................................

yes

yes

yes

no

yes

yes

yes

yes

---

---

a

870.3700a Developmental Toxicity (rodent)...................................

870.3700b Developmental Toxicity (nonrodent) ............................

870-3800 Reproduction...................................................................

yes

yes

yes

yes (83-3a)

yes (83-3b)

yes (83-4)

870.4100a Chronic Toxicity (rodent)..............................................

870.4100b Chronic Toxicity (nonrodent)........................................

870.4200a Oncogenicity (rat)..........................................................

870.4200b Oncogenicity (mouse) ...................................................

870.4300 Chronic/Oncogenicity...................................................

yes

yes

yes

yes

yes

yes

yes

yes

yes

yes
Trinexapac-ethyl Human Health Risk Assessment DP No.419651

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Table A.1. Toxicology Data Requirements

Test Technical 

Required Satisfied

870.5100 Mutagenicity—Gene Mutation - bacterial....................

870.5300 Mutagenicity—Gene Mutation - mammalian...............

870.5375 Mutagenicity—Structural Chromosomal Aberrations..

870.5395 Mutagenicity—Other Genotoxic Effects......................

yes

yes

yes

yes

yes

yes

yes

yes

870.6100a Acute Delayed Neurotox. (hen).....................................

870.6100b 90-Day Neurotoxicity (hen) ..........................................

870.6200a Acute Neurotox. Screening Battery (rat) .......................

870.6200b 90 Day Neurotox. Screening Battery (rat).....................

870.6300 Develop. Neurotoxicity.................................................

no

no

yes

yes

CR

---

---

yes

yes

no

870.7485 General Metabolism .....................................................

870.7600 Dermal Penetration .......................................................

870.7800 Immunotoxicity ............................................................

yes

no

yes

yes

yes

yes

Non guideline Thyroid MOA Investigation Study No ---

aData waiver granted by HASPOC, July 11, 2013 (TXR 0056699).

A.2.1 Toxicity Profiles

Table A.2.1. Acute Toxicity Profile of Trinexapac-ethyl (97%).

Guidelin

e No. Study Type MRID Results

Toxicity 

Category

870.1100 Acute oral [rat]

41563901

♂ LD50 = 4613 mg/kg

♀ LD50 = 4212 mg/kg

Combined LD50 = 4458 mg/kg

III

870.1200 Acute dermal [rabbit] 41563910 LD50 > 4000 mg/kg III

870.1300 Acute inhalation [rat] 41563912 LC50 ≥ 5.3 mg/L IV

870.2400 Acute eye irritation [rabbit] 41563914 Minimal irritant; cleared by 72 hours III

870.2500 Acute dermal irritation [rabbit] 41563916 Slightly irritating; cleared by day 7 IV

870.2600 Skin sensitization [guinea pig] 41869522 Not a dermal sensitizer N/A

Table A.2.2 Acute Toxicity Profile- – VisionTM Formulation (23% Trinexapac-ethyl)

Guideline 

No.

Study Type MRID(s) Results Toxicity 

Category

870.1100 Acute oral rat] 41563909 LD50 = 4514 mg/kg (both sexes) III

870.1200 Acute dermal [rabbit] 41563911 LD50 >2020 mg/kg III

870.1300 Acute inhalation [rat] 41563913 LC50 = > 0.912 mg/L III

870.2400 Acute eye irritation [rabbit] 41563915 severe irritant I

870.2500 Acute dermal irritation [rabbit] 41563916 moderate irritant III

870.2600 Skin sensitization [guinea pig] 41869519

41869521

not a dermal sensitizer N/A
Trinexapac-ethyl Human Health Risk Assessment DP No.419651

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Table A.2.3 Acute Toxicity Profile – PrimoTM Formulation (12% Trinexapac-ethyl)

Guideline 

No.

Study Type MRID(s) Results Toxicity 

Category

870.1100 Acute oral rat] 41869514 LD50 = 5010 mg/kg (males)

LD50 = 5730 mg/kg (females)

IV

870.1200 Acute dermal [rabbit] 41869515 LD50 >2020 mg/kg III

870.1300 Acute inhalation [rat] 41869516 LC50 = > 0.888 mg/L III

870.2400 Acute eye irritation [rabbit] 41869517 moderately irritating; corneal 

involvement, conjunctival 

irritation did not clear within 7 

days

II

870.2500 Acute dermal irritation [rabbit] 41869519 slightly irritating IV

870.2600 Skin sensitization [guinea pig] 41869522 not a dermal sensitizer N/A

Table A.2.4. Subchronic, Chronic and Other Toxicity Profile of Trinexapac-ethyl.

Guideline No./ 

Study Type

MRID No. (year)

Classification /Doses

Results

870.3100

90-Day oral 

toxicity [rat]

MRID 41563921 (1989)

0, 5, 50, 500, 5000, 20,000 ppm

[males 0, 3, 34, 346, 1350 

mg/kg/day] 

[females 0, 4, 38, 395, 1551 

mg/kg/day]acceptable/guideline

NOAEL = 20,000 ppm [males 1350/females 1551 

mg/kg/day HDT

870.3150

13-week oral 

toxicity in 

nonrodent (dog)

7-week pilot 

study

MRID 41563920 (1989)

0, 50, 100, 15,000, 30,000 ppm

[males 0, 2.0, 34.9, 515.9, 927.1 

mg/kg/day]

[females 0, 1.9, 38.8, 582.4, 890.8 

mg/kg/day]

acceptable/guideline

MRID 41869523

0, 500, 5000, 15,000-50,000 ppm

[males 0, 22, 219, (686, 956, 734)* 

mg/kg/day]

[females 0, 23, 214, (680, 1373, 

965)* mg/kg/day]

*15,000 ppm (days 1-3); 30,000 

ppm (days 4-28); 50,000 ppm 

(weeks 4-7)

NOAEL = 15,000 ppm [males 515.9/females 582.4 

mg/kg/day

LOAEL = 30,000 ppm [males 927.1/females 890.8 

mg/kg/day, based on clinical signs (few feces and 

emaciation) decreased BWG/FC/FE in both sexes 

(related to lack of palatability) and diffuse thymic 

atrophy 

Negative BWG in males HDT from week 5 on; HDT 

females from week 6 on; BW of HDT males 81% of 

control/females 74% control at week 7; severe decrease 

in food consumption HDT; tubular dilatation and 

degeneration/regeneration of epithelial cells of renal 

tubules at HDT; diffuse thymic atrophy at mid- and 

high-dose females and high-dose males.

870.3200

21/28-Day dermal 

toxicity (rabbit)

MRID 41563922 (1989)

[46809310 (2006)]

0, 10, 100, or 1000 mg/kg/day,

Systemic toxicity 

NOAEL: 1000 mg/kg/day; LOAEL: Not determined

Local dermal irritation
Trinexapac-ethyl Human Health Risk Assessment DP No.419651

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Table A.2.4. Subchronic, Chronic and Other Toxicity Profile of Trinexapac-ethyl.

Guideline No./ 

Study Type

MRID No. (year)

Classification /Doses

Results

acceptable/guideline NOAEL: 10 mg/kg/d; LOAEL: 100 mg/kg/d, based on 

hyperkeratosis and subacute lymphocytic infiltrates in 

the skin.

870.3365

28-Day inhalation 

toxicity (rat)

Data waiver granted by HASPOC July 11, 2013 TXR 0056699.

83-3a

Prenatal 

developmental in 

rodent [rat]

MRID 41563923 (1988)

0, 20, 200, 1000 mg/kg/day

gestation days 6-15

Acceptable/guideline; (does not 

fulfill 870.3700a because study 

pre-dates this 1998 guideline)

Maternal NOAEL = 1000 mg/kg/day, highest dose 

tested 

Developmental NOAEL = 200 mg/kg/day

Developmental LOAEL = 1000 mg/kg/day, based on 

increased incidence of asymmetrically-shaped 

sternebrae. 

83-3b

Prenatal 

developmental in 

nonrodent (rabbit)

MRID 41869524 (1990)

0, 10, 60, or 360 mg/kg/day

gestation days 7-19

Acceptable/guideline; 

Maternal toxicity NOAEL = 360 mg/kg/day, highest 

dose tested

Developmental toxicity NOAEL = 60 mg/kg/day

Developmental toxicity LOAEL = 360 mg//kg/day, 

based on a decrease in the mean number of fetuses/litter 

and an increase in post-implantation loss and early 

resorptionsa

83-4

Reproduction and 

fertility effects 

(rats)

MRID 43128604 (1991)

0, 10, 1000, 10,000, 20,000 ppm

[P0 males: 0, 0.59, 59.97, 595.26, 

1169.16 mg/kg/day]

[P0 females: 0, 0.75, 74.84, 

736.89, 1410.08 mg/kg/day]

F1 males: 0, 0.59, 59.10, 591.76, 

1254.96 mg/kg/day]

F1 females 0, 0.77, 77.17, 765.20, 

1559.65 mg/kg/day]

Acceptable/guideline

Parental toxicity NOAEL = 10,000 ppm [males 

593.5/females 751.1 mg/kg/day]

Parental toxicity LOAEL 20,000 ppm [males 

1212.1/females 1484.9 mg/kg/day], based on reduced 

premating and gestation body weight/body-weight gain 

and food consumption

Reproductive NOAEL = 20,000 ppm [males 

1212/females 1484 mg/kg/day]. No adverse treatmentrelated effect on reproductive parameters up to and 

including 20,000 ppm (HDT)

Offspring NOAEL = 10,000 ppm [males 

593.5/females 751.1 mg/kg/day]

Offspring LOAEL = 20,000 ppm [males 

1212.1/females 1484.9 mg/kg/day], based on decreased 

F1 postnatal survival and reduced pup body weights in 

both generations [both sexes].

870.4100a

Chronic toxicity 

rodents (rat)

MRID 42238104 (1992)

0, 10, 100, 3000, 10,000, 20,000 

ppm

M 0, 0.38, 3.87, 115.6, 392.7, 805.7 

mg/kg/day

F 0, 0.49, 4.88, 147.4, 494.0, 1054 

mg/kg/day

acceptable/guideline

Systemic toxicity NOAEL = 20,000 ppm [males 

806/females 1054 mg/kg/day, highest dose tested.
Trinexapac-ethyl Human Health Risk Assessment DP No.419651

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Table A.2.4. Subchronic, Chronic and Other Toxicity Profile of Trinexapac-ethyl.

Guideline No./ 

Study Type

MRID No. (year)

Classification /Doses

Results

870.4100b

Chronic toxicity 

nonrodent (dogs)

MRID 42779402/42779401 

(1991-92)

0, 40, 1000, 10,000, or 20,000 ppm 

[males 0, 1.56, 31.62, 356.72, or 

726.65 mg/kg/day]

[females 0, 1.37, 39.54, 357.13, 

783.83 mg/kg/day]

acceptable/guideline

Systemic toxicity NOAEL = 1000 ppm [males 

31.62/females 39.54 mg/kg/day

Systemic toxicity LOAEL = 10,000 ppm [males 

365.72/females 357.13 mg/kg/day], based on elevated 

serum cholesterol values in females, mucoid feces in 

females and bloody feces in both sexes, and minimal, 

focal vacuolation of the dorsal medial hippocampus 

and/or lateral midbrain in both sexes. 

870.4200

Carcinogenicity 

(rat)

Sprague-Dawley

MRID 42238104 (1992)

0, 10, 100, 3000, 10,000, 20,000 

ppm

M 0, 0.38, 3.87, 115.6, 392.7, 

805.7 mg/kg/day

F 0, 0.49, 4.88, 147.4, 494.0, 1054 

mg/kg/day

acceptable/guideline

See above under 870.4100a

There was a possible treatment related increased 

incidence of squamous cell carcinoma of the 

forestomach in M at 20000 ppm (HDT); however, this 

is not considered toxicologically relevant to humans. 

No treatment-related difference detected in total number

of animals with tumors or in the total number of benign 

or malignant tumors at 52 or 104 weeks. No treatmentrelated effect on the time-dependent occurrence of 

tumor-bearing animals.

Not Likely to be Carcinogenic to Humans

870.4300

Carcinogenicity 

(mouse) 

CD-1 [Crl:CD-1

(ICR)Br] 

MRID 43128603 (1991)

0, 7, 70, 1000, 3500, 7000 ppm

[males 0, 0.91, 9.01, 130.81, 

450.72, 911.77 mg/kg/day]

[females 0, 1.08, 10.66, 154.08, 

538.73, 1073.42 mg/kg/day]

acceptable/guideline

Systemic toxicity NOAEL = 7000 ppm [males 

911/females 1073 mg/kg/day], the highest dose tested.

There was no treatment-related increase in tumors of 

any type in either sex at dose levels up to an including 

7000 ppm, the HDT

No evidence of carcinogenicity

870.5100

Bacterial Reverse 

Gene Mutation 

Assay

46809308 (2001)

Salmonella typhimurium

strains TA98, TA100, TA102,

TA1535 and TA1537

Escherichia coli strain WP2uvrA

0, 312.5, 625, 1250, 2500, or 5000 

μg/plate ± S9 metabolic activation

Acceptable/guideline

Negative up to the limit concentration.

870.5300

Mouse 

Lymphoma 

Cells/Mammalian 

43128605 (1993)

Mouse lymphomaL5178Y cells (at 

the thymidine kinase locus)

0, 7.54, 30.16, 120.62, or

Negative up to a precipitating concentration (1930 

μg/mL)
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Table A.2.4. Subchronic, Chronic and Other Toxicity Profile of Trinexapac-ethyl.

Guideline No./ 

Study Type

MRID No. (year)

Classification /Doses

Results

Activation Gene 

Forward Mutation 

Assay at TK+/-

locus

1930 μg/mL for 4 hours

± S9 metabolic activation

Acceptable/guideline

870.5395

Structural 

chromosomal 

aberration test - 

Micronucleus 

Test Mouse

41563926 (1989)

42081402 (1991)

41869527 (1991)

M and F mouse bone marrow cells 

(erythrocytes)

0, 1000, 2000, or 4000 mg/kg bw 

(sacrifice at 16, 24, and 48 h)

Initial assay: 0 or 3000 mg/kg bw 

(sacrifice at 16, 24, and 48 h)

Confirmatory assay: 0, 750,

1500, or 3000 mg/kg bw

(sacrifice at 48 h)

Acceptable/guideline

Negative up to doses in excess of the limit dose. 

Significant increased frequency of micronucleated 

polychromatic erythrocytes in M and sexes combined at 

48 h in the initial assay; however, values were within 

historical control range and not observed in the 

confirmatory assay

at 3000 mg/kg bw at 48 h . In this study possible weak 

clastogen, however, weight of evidence suggestsCGA163935 not likely clastogenic.

870.5550

Other 

Genotoxicity 

In vitro UDS in 

Primary Rat 

Hepatocytes

41604205 (1987) 

41869528 (1991)

Preliminary cytotoxicity assay: 0, 

5, 10, 21, 41, 82, 164, 328, 656, 

1313, 2625, or 5250 μg/mL

Initial UDS assay: 0, 0.8, 4, 20, 

100, 200, or 400 μg/mL; 

Confirmatory UDS assay: 0, 4, 20, 

100, 150, 200, 300, 400, or 500 

μg/mL 

Acceptable/guideline

Negative up to a cytotoxic concentrations

870.6200a

Acute 

neurotoxicity 

screening battery 

(rat)

48764506 (2012)

0, 500, 1000, or 2000 mg/kg (♂♀)

Acceptable/guideline

Systemic/Neurotoxicity 

NOAEL = >2000 mg/kg (Highest dose tested, limit 

dose)

LOAEL was not established

870.6200b

90-day 

neurotoxicity 

screening battery 

(rat)

48764507 (2012)

0, 3750, 7500, or 15,000 ppm

(0, 233, 463, or 948 mg/kg/day, ♂

0, 294, 588, or 1171 mg/kg/day, 

♀)

Systemic/Neurotoxicity 

NOAEL = >15,000 ppm (Highest dose tested; near or in 

excess of the limit dose)

LOAEL was not established.

870.7485

Metabolism and 

pharmacokinetics 

(rat)

MRID 41563927 (1990)

i. v. 0.91 mg/kg [14C- CGA163935]

oral 0.97 or 166 mg/kg [14C- CGA163935]

Rapidly, extensively absorbed (both sexes) w/ >95% of 

administered dose being absorbed; little potential for 

accumulation; >85% eliminated w/in 12 hours via urine; 

2% via feces w/in 24 hours; very little or no biliary 

excretion; no sex difference; free acid derivative 
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Table A.2.4. Subchronic, Chronic and Other Toxicity Profile of Trinexapac-ethyl.

Guideline No./ 

Study Type

MRID No. (year)

Classification /Doses

Results

oral 0.97 mg/kg/day [CGA163935] for 14 days followed by 

0.97 mg/kg [14C- CGA-163935]

acceptable/guideline

resulting from hydrolysis of the ester bond of parent 

compound is major component in urine and feces; only 

other component was parent, found only in feces.

870.7600

Dermal 

penetration

(rat)

MRID 42238105 (1990)

0, 0.01, 0.1, or 1.0 mg/cm2[

14CCGA-163935]

single dermal dose

acceptable/guideline

Recovery of applied dose 97%-117%; most recovered 

in skin washes and urine; <1% in blood and feces; 

excreted in urine within 2 hours of dose

56.5% absorbed, with 21% associated with application 

site

Dermal absorption factor = 77.5% based on 10 hour 

exposure regimen. 

870.7800

Immunotoxicity 

study

(female mice)

MRID 48444101 (2011)

0, 500, 2000, and 5000 ppm

0,160.2, 613.7, 1530.5 mg/kg/day

acceptable/guideline

Systemic toxicity NOAEL = 5000 ppm (1530.5 

mg/kg/day, the highest dose tested) the LOAEL was not 

established.

The immunotoxicity NOAEL for anti-SRBC AFC 

response and NK cell activity is 5000 ppm (1530.5 

mg/kg/day), the LOAEL was not established.

Highest dose tested was in excess of the limit dose 

A.3 Hazard Identification and Endpoint Selection

A.3.1 Acute Reference Dose (aRfD) - Females age 13-49

Study Selected: Prenatal Developmental Toxicity Study– rabbit

MRID No.: 41869524

Summary: See Appendix A, Guideline 870.3700a

Dose and Endpoint for Risk Assessment: NOAEL = 60 mg/kg, based on a decrease in the 

mean number of fetus/litter and an increase in post-implantation loss and early resorptions at the 

developmental toxicity LOAEL of 360 mg/kg/day.

Uncertainty Factor(s): 100X [10 interspecies; 10X intraspecies] FQPA SF = 1X, UFDB = 1X.

Comments about Study/Endpoint/Uncertainty Factor: The route and duration of exposure are 

appropriate for selection of the acute dietary endpoint for females 13-49 years old. The toxicity 

could occur following a single exposure and is appropriate for this exposure scenario. This 

endpoint will also be protective of the rat fetal effects [increased incidence of asymmetrical 

sternebrae] observed at higher dose levels [1000 mg/kg/day]. This is a conservative endpoint 

since this is such a large dose spread (the NOAEL is 6-fold lower than LOAEL). 

aRfD = aPAD = 60 mg/kg/day = 0.60 mg/kg/day

100

A.3.2 Acute Reference Dose (aRfD) general population 

An acute reference dose was not defined; no effects attributable to a single dose were identified 
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in the toxicology database. An in utero effect from the developmental rabbit study provided an 

acute reference dose for females 13-49 years old but is not appropriate for the general 

population.

A.3.3 Chronic Reference Dose (cRfD)

Study Selected: chronic oral toxicity – dog

MRID No.: 42779402/42779401

Executive Summary: See Appendix A, Guideline 870.4100 b

Dose and Endpoint for Risk Assessment: NOAEL = 1000 ppm [males 31.6 mg/kg/day; 

females 39.5 mg/kg/day], based on elevated serum cholesterol values in females, mucoid feces in 

females and bloody feces in both sexes, and minimal, focal vacuolation of the dorsal medial 

hippocampus and/or lateral midbrain in both sexes at the LOAEL of 10000 ppm [males 

365.72/females 357.13 mg/kg/day].

Uncertainty Factor(s): 100X [10 interspecies; 10X intraspecies] FQPA SF = 1X, UFDB = 1X.

Comments about Study/Endpoint/Uncertainty Factor: The chronic toxicity study in the dog 

(MRID 42779402/42779401) was selected for the chronic dietary cRfD because the route and 

duration of exposure are appropriate for selection of the chronic dietary endpoint. This endpoint 

is protective since the dog is the most sensitive species, there is a large dose spread in the chronic 

dog study (the NOAEL is 10-fold lower than the LOAEL), and there is a clear NOAEL and 

LOAEL. The vacuolation was also observed in all of the dogs at the high dose level (males 727

mg/kg/day /females 784 mg/kg/day) and was associated with the astrocytes and oligodendrocytes

in the hippocampus. The lesions remained confined to the supporting cells in the CNS and did 

not progress to more advanced or more extensive damage of the nervous tissue. The lesions were 

not associated with other neuropathological findings or overt neurological signs. Similar 

microscopic lesions in the brain were not reported in the 90-day dog study, but there was an 

inconsistency in the neuropathological screening of the brain, which precludes a definitive 

determination on the occurrence of this lesion following subchronic exposure. Similar lesions 

were not observed in the rat (including neonates) or mouse following subchronic or chronic 

dietary exposure, and there was no other evidence in any other species tested to indicate a 

neurotoxicity potential. 

cRfD = cPAD = 31.6 mg/kg/day = 0.32 mg/kg/day

 100

A.3.4 Incidental Oral Exposure (Short- and Intermediate-Term)

An endpoint for children for the incidental oral exposure scenario was also not identified from 

the available trinexapac-ethyl toxicity studies and the rationale for this conclusion is based on the 

following weight of evidence considerations: 

 the toxicity observed during the appropriate duration of concern (short/intermediate 

term) were observed only at high doses [LOAELs = 900 mg/kg/day in the dog, 1000 

mg/kg/day in the rat, and 1212 mg/kg/day in the reproduction study],

 the brain lesions observed in the chronic dog study are not appropriate for this 

scenario since the brain lesions were seen only at termination (i.e. after exposure for 

1-year) and toxicity observed after chronic exposure is not appropriate for application 

to the short/intermediate term scenarios,
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 the brain lesions observed in the chronic study are not expected to occur after short 

term exposure due to the lack of similar lesions or associated toxicity (i.e., clinical 

neurologic signs) in the 90-day studies in rats or dogs,

 the cause for concern for the brain lesions is low because of the minimal lesion 

severity, lack of associated changes (i.e., gliosis, myelin loss astrocyte hypertrophy, 

neuronal necrosis etc.), and the non-specific nature of the lesions (i.e., focal 

vacuoles),

 the overall toxicity profile of this chemical clearly shows that toxicity is observed 

only at high doses (lowest LOAEL = 360 mg/kg/day in the chronic dog study), and

 the in utero endpoint identified in the rabbit study is not appropriate for this 

population of concern (children) (D392798, M. Hawkins, 11/23/2011).

3.5 Dermal and Inhalation Short- and Intermediate-Term: 

Study Selected: developmental rabbit study

MRID No.: 41869524

Summary: See Appendix A, Guideline 83-3

Uncertainty Factor(s): 100X [10 interspecies; 10X intraspecies] FQPA SF = 1X, UFDB = 1X.

Comments about Study/Endpoint/Uncertainty Factor: The developmental rabbit study was 

selected for both the short- and intermediate-term dermal and inhalation exposure scenarios with 

a NOAEL of 60 mg/kg/day and a LOAEL of 360 mg/kg/day. 

An appropriate dermal study, showing no adverse systemic effects up to the limit doses and an 

inhalation study were not available for these endpoints. However, the short- and intermediateterm dermal and inhalation endpoints selected for adults are not applicable to children because 

the adult endpoints are based on in utero effects. HED reviewed the full toxicological database 

for trinexapac-ethyl in an attempt to select endpoints for children for the dermal and inhalation

exposure scenarios; however, no appropriate endpoints were identified for these scenarios based 

on the following reasons:

 dermal irritation effects are mild after 21/28 days of exposure in the rabbit study,

 dermal irritation effects after a single exposure disappear after seven days,

 there are no systemic effects up to the limit dose in the dermal rabbit study,

 there are no adverse toxicological effects (at doses close to the limit dose of 1000 

mg/kg/day) in the 2-generation reproductive study in rats or in the 

chronic/carcinogenicity studies in rats and mice, 

 there is no maternal toxicity in the developmental toxicity studies in both rats and 

rabbits, and

 there are no identifiable endpoints for the oral studies in the rat or rabbit.

The DAF of 77.5% (MRID 42238105) and an inhalation absorption rate of 100% were applied to 

the NOAEL for the assessment of the dermal and inhalation risks, respectively. 

3.5 Dermal and Inhalation Short- and Intermediate-Term: Based on the use pattern, longterm exposures are not expected.
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A.4 Executive Summaries

Subchronic Rat Study

In a subchronic oral toxicity study [MRID 41563921], 15 Sprague-Dawley [Crl:VAF/Plus CD® 

rats/sex/dose were administered CGA 163935 Technical [96.9%] via the diet at concentrations of 

0 ppm, 50 ppm, 500 ppm, 5000 ppm, or 20,000 ppm for 13 consecutive weeks. The mean daily 

intakes were 3, 34, 346, or 1350 mg/kg/day for males and 4, 38, 395, or 1551 mg/kg/day for 

females, respectively. 

There was no adverse effect of treatment on survival, and no apparent treatment-related clinical 

signs of toxicity. At 20,000 ppm, both sexes displayed slight decreases in body weight 

throughout most of the study [93%-94% of control at study termination], and overall bodyweight gains were reduced in both sexes [males 93%/females 89% of control]. Both sexes at the 

20000 ppm dose level displayed decreased food consumption throughout the study, with the 

largest deficit occurring initially suggesting a palatability problem. 

There were no treatment-related ocular changes in either sex. There were no apparent, treatmentrelated effects on the hematology or clinical chemistry parameters monitored in either sex. The 

urinalysis assessment found decreased urinary pH values in both sexes at 20,000 ppm. 

There were no treatment-related effects on organ weights in either sex. There was an increased 

incidence of renal tubular changes [basophilia (3, 2, 1, 7, 13***), hyaline droplets (5, 7, 7, 11*, 

13**), casts (2, 2, 0, 2, 6), with increasing dose] in males at 5000 ppm and 20,000 ppm, which 

was said to represent a shortened time of onset of spontaneous senile nephropathy, a common 

condition in aging rats. However, based on the fact that the incidence of senile nephropathy was 

comparable among the male groups in the chronic rat study at dose levels up to 20,000 ppm for 

104 weeks indicates that these findings should not be considered adverse.

The systemic toxicity NOAEL is 20,000 ppm [males 1350 mg/kg/day; females 1551 

mg/kg/day], the highest dose tested. 

This guideline subchronic oral toxicity study is classified ACCEPTABLE, and it satisfies the 

guideline [OPPTS 870.3100; §82-1] for a subchronic oral toxicity study in the rat. 

COMMENT: The original DER identified a no observed effect level [NOEL], which was based 

on the renal tubular changes in the males at 5000 ppm [346 mg/kg/day] and 20000 ppm [1350 

mg/kg/day]. 

Subchronic Dog Study

In a subchronic oral toxicity study [MRID 41563920], 4 beagle dogs/sex/dose were administered 

CGA 163935 Technical [96.9%] via the diet at concentrations of 0 ppm, 50 ppm, 1000 ppm, 

15,000 ppm, or 30,000 ppm for 13 consecutive weeks. The mean daily intakes were 2.0, 34.9, 

515.9, or 927.1 mg/kg/day for males and 1.9, 39.8, 582.4, or 890.8 mg/kg/day for females 

receiving 50, 1000, 15,000, or 30,000 ppm, respectively.

There was no adverse effect of treatment on survival, and no apparent treatment-related clinical 

signs of toxicity other than few feces and emaciation. Both sexes at the 30000 ppm dose level 

displayed decreased food consumption throughout the study and, consequently, body weights 

[males 74%/females 88% of control at termination] and body-weight gains [negative weight gain 
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compared to control (males –0.325 kg vs 1.775 kg (control)/females –0.075 kg vs 1.225 kg 

(control)] were decreased throughout the study also. 

There were no treatment-related ocular changes in either sex. There were no apparent, treatmentrelated effects on the hematology, clinical chemistry, or urinalysis parameters monitored in either 

sex. 

The treatment-related effects on most organ weights in both sexes at the 30,000 ppm dose level 

are considered to be changes that would be expected due to decreased body weight/body-weight 

gain. Both sexes at the 30,000 ppm dose level displayed decreased popliteal lymph node weights 

[absolute and relative-to-brain]. Non-significant decreases in thymic weight were reported in 

males at 30,000 ppm. No other treatment-related organ-weight effects were reported in either 

sex. 

Diffuse thymic atrophy was observed in all dogs [both sexes] at the 30,000 ppm dose level 

compared with none of the controls [either sex]. Focal thymic atrophy was not observed at the 

30,000 ppm dose level but was observed in 3 of the 4 male controls (2-3 males in all other 

groups) and all of the female controls (2-3 females in all other groups). It was noted that the 

diffuse thymic atrophy observed at 30,000 ppm most likely occurred secondary to the nutritional 

imbalances related to reduced food consumption and body-weight loss. 

The systemic toxicity NOAEL is 15,000 ppm [males 515.9 mg/kg/day; females 582.4 

mg/kg/day], based on clinical signs (few feces and emaciation), decreased body 

weight/body-weight gain, and decreased food consumption in both sexes (related to the lack 

of palatability) and diffuse thymic atrophy at the systemic LOAEL of 30,000 ppm [males 

927.1 mg/kg/day; females 890.8 mg/kg/day]. 

This guideline subchronic oral toxicity study is classified ACCEPTABLE, and it satisfies the 

guideline [OPPTS 870.3150; §82-1] for a subchronic oral toxicity study in the dog. 

NOTE: In the original DER, the subchronic oral toxicity study in the dog was classified 

Supplementary, pending the submission of the 7-week pilot study for justification of the dose 

levels selected.

In a 7-week pilot study [MRID 41869523], beagle dogs [3/sex/group] were administered CGA 

163935 technical (96.6%) via the diet at levels of 0, 500, 5,000, 15,000, or 15,000-50,000 ppm. 

At the highest dietary level, dogs were fed 15,000 ppm for 3 days, 30000 ppm from day 4 to 28, 

and 50,000 ppm from day 29 to 49. During the first 4 weeks of the 7-week pilot study, males at 

the highest dose level gained 42% less body weight than the control, and females at this dose 

level gained 12% less than control. During the week 4 to week 5 interval, both sexes at the 

highest dose level displayed a negative body-weight gain [males -0.80 kg/females –0.76 kg] 

compared to the positive body-weight gains in the controls [males 0.3 kg/females 0.23 kg] and 

other dose groups [males 0.07 kg to 0.13 kg/females 0.03 kg to 0.13 kg]. At study termination, 

decreased body weight/negative body-weight gains were observed at the highest dose level in 

both sexes [males 82% of control/-0.54kg; females 74% of control/-0.43 kg]. Food consumption 

was decreased throughout the study in both sexes at the highest dose level [males 68% and 30% 

of control; females 89% and 34% of control during weeks 1-4 and 4-7, respectively]. No 

apparent adverse effects were observed in hematology, clinical chemistry, or urinalysis 

parameters monitored. Absolute and relative thymus weights were decreased in females at the 
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highest dose level [14.5 g vs 3.4 g] only. In the kidney, tubular dilatation and tubular

degeneration/regeneration were observed in all dogs/both sexes at the highest dose level 

compared to none in the control or other dose groups. Diffuse thymic atrophy was observed in all 

dogs/both sexes at the highest dose level and in 2 of 3 females at 15000 ppm. 

Due to the (1) lack of palatability of the test material, (2) refusal of the dogs to eat diets 

containing greater than 30000 ppm of the test material, and (3) severe weight losses at 50000 

ppm during weeks 4-7, it was concluded that 50000 ppm was too excessive for use in the 

subchronic (13 week) study. The average daily compound intake was 22.2, 218.7, 685.8, 956.2, 

and 733.6 mg/kg/day for males and 23.1, 214.3, 679.9, 1373.3, and 964.7 mg/kg/day for females 

at the 500 ppm, 5000 ppm, 15,000 ppm, 30,000 ppm, and 50000 ppm dose levels, respectively. 

The dose levels used in the subchronic study are considered adequate [30,000 ppm], based 

on the 7-week pilot study [MRID 41869523; HED Document No. 009711]. 

Comment: Microscopic evidence of minimal, focal vacuolation of the dorsal medial 

hippocampus and/or lateral midbrain in all dogs at 20,000 ppm and in one male and two female 

dogs at 10,000 ppm was observed in the one year dog study. Although similar microscopic 

lesions in the brain were not reported in this 90-day study in dogs, there was an inconsistency in 

the level of sectioning of the brain [MRID 42779401] in the subchronic study, which precludes a 

definitive determination of the occurrence of these lesions following subchronic exposure. 

However, the chronic study identifies a NOAEL for these lesions [1000 ppm [males 

31.6/females 39.5 mg/kg/day], which were observed at the LOAEL of 10000 ppm [males 

366/females 357 mg/kg/day].

21-Day Rabbit Dermal Toxicity Study

In a repeat dermal toxicity study [MRID 41563922], 5 New Zealand white rabbits/sex/dose were 

administered CGA 163935 Technical [96.6%] via dermal application at dose levels of 0 

(untreated), 0 (vehicle: dehydrated alcohol), 10, 100, or 1000 mg/kg/day for at least 21 

consecutive days. 

There was no adverse effect of treatment on survival, and no apparent treatment-related clinical 

signs of toxicity. There were no treatment-related, adverse effects on body weight, body-weight 

gain, or food consumption in either sex. 

There were no treatment-related effects on any of the hematology parameters monitored in either 

sex. There were no apparent, treatment-related, consistent, adverse effects on the clinical 

chemistry parameters monitored in either sex, although several statistically-significant trends 

were noted at 100 mg/kg/day and 1000 mg/kg/day. For example, decreased mean total bilirubin 

was observed in both sexes on day 21, but there was no dose response. Higher albumin/globulin 

ratios were observed at termination in both sexes compared to both control groups, but statistical 

significance was not attained in females and a dose response was not observed in males. 

There were no treatment-related effects on organ weights in either sexes. Microscopic evaluation 

of the liver, kidney, and lungs did not reveal any treatment-related effects in either sex. 

There was a dose-related increase in gross lesions [dark, red or tan] of the treated skin, including 

the vehicle group. Erythema was observed in females at the mid- (5 of 5) and high- (4 of 5) dose 

groups compared to none in either control of low-dose groups. No microscopic findings of the 
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skin were observed in any of the untreated controls (both sexes). Dermal microscopic 

observations included subacute lymphocytic infiltration in all high-dose females and 2 of 5 middose females compared to none in either control group or low-dose group, and acanthosis was 

observed in all rabbits at each dose level (both sexes) and in the vehicle control group (both 

sexes) compared to none in the untreated control groups. 

The systemic toxicity NOAEL is 1000 mg/kg/day, the highest dose tested. 

The dermal toxicity NOAEL is 10 mg/kg/day, based on subacute lymphocytic infiltration in 

females at the LOAEL of 100 mg/kg/day.

This guideline repeat dermal toxicity study is classified ACCEPTABLE, and it satisfies the 

guideline [OPPTS 870.3200; §82-2] for a repeat dermal toxicity study in the rabbit. 

COMMENT: In the original DER, the NOEL [10 mg/kg/day] was based on effects on various 

biochemistry parameters [decreases in total bilirubin, increase in mean albumin/globulin ratios, 

and increase in mean phosphorus] and on microscopic observations of the skin [hyperkerotosis 

and subacute lymphocytic infiltrates]. The original reviewer [1990] concluded that no adverse 

effects were noted in the clinical chemistry parameters. Since that time, NOAELs rather than 

NOELs are established. The registrant submitted a request [MRID 46809310] to establish a 

NOAEL for this study, based on arguments that the clinical chemistry findings do not constitute 

adverse effects due to dermal exposure to trinexapac-ethyl. The updated Executive Summary 

incorporates this change.

Developmental Rat Study

In a developmental oral toxicity study [MRID 41563923], 24 pregnant Tif: RAIf (SPF), hybrids 

of RII/1 x RII/2 rats/sex/dose were administered CGA 163935 Technical [96.6%] via gavage at 

dose levels of 0, 20, 200, or 1000 mg/kg/day during gestation days 6-15. 

There was no adverse effect of treatment on survival, and no apparent treatment-related clinical 

signs of toxicity. Body weight was not adversely affected at any dose level. At the high-dose 

level, the dams displayed a significant decrease in body-weight gain during GD 0-6 (prior to 

dosing; 92% of control) and GD 0-21 (overall; 94% of control). Corrected body weight and bodyweight gains were comparable among the groups. There was no treatment-related effect on food 

consumption.

Pregnancy rates were comparable among the groups (pregnant prior to dosing). There were no 

maternal deaths, no abortions, and no premature deliveries. There was a statistically-significant 

decrease (89% of control) in the mean number of corpora lutea at the high-dose level [17.0] 

compared to the control [19.1]; however, the value is stated to be within the historical control 

range. Also at the high-dose level, the mean numbers of implantations (95% of control) and live 

fetuses (94% of control) were slightly lower than the control. The number of early resorptions 

was comparable among the groups, and there were no late resorptions. There were no dead 

fetuses. Pre- and post-implantation losses were comparable among the groups. Fetal body weights 

and sex ratios were comparable among the groups. 

There were no treatment-related malformations. One fetus at 1000 mg/kg/day displayed 

hypoplasia of the testicle (no historical control data reported). There was an increase in the 

incidence of asymmetrically shaped sternebra at 1000 mg/kg/day [8 fetuses in 7 litters; litter 
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incidence: 29.2%] compared to the concurrent [2 fetuses in 2 litters; litter incidence: 9.1%] and 

historical [48 fetuses/35 litters; litter incidence: 15.1%] control groups. 

The maternal toxicity NOAEL is 1000 mg/kg/day, the highest dose tested. The 

developmental toxicity NOAEL is 200 mg/kg/day, based on an increased incidence of 

asymmetrically-shaped sternebrae at the LOAEL of 1000 mg/kg/day (limit dose). 

This guideline developmental toxicity study is classified ACCEPTABLE, and it satisfies the 

guideline [OPPTS §83-3, but not 870.3700 because it only dosed from GD 6-15] for a 

developmental toxicity study in the rat. 

Rabbit Developmental

In a developmental oral toxicity study [MRID 41869524], 16-17 pregnant New Zealand White 

rabbits/sex/dose were administered CGA 163935 Technical [96.6%] via gavage at dose levels of 

0, 10, 60, or 360 mg/kg/day during gestation days 7-19. 

On pregnant doe at the high-dose level was found dead (convulsion) on gestation day [GD] 13. A 

second high-dose doe was sacrificed on GD 24 following abortion on GD 22 and severe weight 

loss (hemorrhagic depressions in the stomach). There were no treatment-related abortions, but one 

doe in each of the control, mid-, and high-dose groups aborted. There were no apparent treatmentrelated clinical signs of toxicity in any of the surviving does. 

Body weight/body-weight gain and food consumption were not adversely affected in the 

survivors at any dose level. 

Pregnancy rates were comparable among the groups (pregnant prior to dosing). There were no 

premature deliveries. The mean number of corpora lutea was comparable among the groups. At 

the high-dose level, the mean number of implantations [7.6±2.4 vs 8.8±2.7; 86% of control] and 

mean number of live fetuses [5.7±2.7 vs 7.7±2.8; 74% of control] was reduced compared to the 

control. The mean number of live fetuses at the high-dose level was below that of the historical 

control [6.1]. Total resorptions were increased at 60 (29) and 390 (27) mg/kg/day compared to 

control (22). Similarly, the number of early resorptions (19 and 14 at 60 and 360 mg/kg/day, 

respectively) were increased compared to control (7), and there were no dead fetuses. Pre-

[24.3%] and post- [24.8%] implantation losses were significantly increased at the high-dose level 

compared to the control [14.3% and 13.2%, respectively]. Fetal body weights and sex ratios were 

comparable among the groups. 

There were no treatment-related malformations or variations [external, visceral, or skeletal]. 

The maternal toxicity NOAEL is 360 mg/kg/day, the highest dose tested. The developmental 

toxicity NOAEL is 60 mg/kg/day, based on a decrease in the mean number of fetus/litter and 

an increase in post-implantation loss, and an increase in early resorptions at the 

developmental toxicity LOAEL of 360 mg/kg/day. 

This guideline developmental toxicity study is classified ACCEPTABLE, and it satisfies the 

guideline [OPPTS §83-3, but not 870.3700 because it only dosed dams from GD 7-19] for a 

developmental toxicity study in the rabbit. 

Reproductive Toxicity Study
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In a 2-generation reproduction study (MRID 43128604), CGA 163935 Technical [96.2% a. i.] 

was administered to 30 Sprague-Dawley rats/sex/dose in the diet at concentration levels of 0, 10, 

1000, 10,000, or 20,000 ppm [equivalent to 0, 0.91, 9.01, 130.81, 450.72, or 911.77 mg/kg 

bw/day (males)/ 0, 1.08, 10.66, 154.08, 538.73, or 1073.42 mg/kg/day (females)] for 78 weeks. 

There were no adverse or compound-related effects on mortality or clinical signs for either the P 

or F1 generation. At 20,000 ppm, decreased body weight [P males 92%**/females 83%** of 

control (day 91); F1 males 82%**/females 86%** of control (day 84)], body-weight gain [P 

males 87%**/females 62%** of control (days 0-91); F1 males 83%**/females 81%* of control 

(days 0-84)], and food consumption [P males 86%**-96%*/females 81%**-87%** of control; F1 

males 87%**/females 86%**-93%** of control] were observed during the pre-mating period in 

both generations. At 10,000 ppm, there were slight decreases in body weight [P 

males94%*/females 93%* of control (day 91); F1 males 93%*/females 96% of control], bodyweight gain [P males 90%**/females 85% of control; F1 males 90%**/females 94% of control], 

and food consumption [P males 93%*-98%/females 95% of control; F1 males 90%**-

93%/females 94%-100% of control] during the pre-mating period. Although sporadic, significant, 

decreases in body weight [P males 93%-95%*/females 94%-96% of control; F1 males 92%*-

95%/females 94%*] and body-weight gain [P males 93%/females 89% of control; F1 males 

87%**/females 88% of control] were noted at 1000 ppm mainly in the males (both generations), 

there was no dose-response. Additionally, during week 4 the P 1000 ppm rats were inadvertently 

fed the 20000 ppm diet, which may have contributed to these weight changes. 

Throughout gestation, dams at the 20000 ppm displayed decreased body weights [P generation 

83%**-86%** of control; F1 generation 89%** of control] and body-weight gain [ P generation 

93%; F1 generation 89% of control (days 0-20)]. Food consumption was decreased initially also 

[P generation 90%** of control (days 0-7), 91%-92% of control (days 7-20); F1 generation 

87%** (days 0-7)/91%* (days 7-14)/94% (days 14-20) of control]. 

Throughout lactation, there was a decrease in body weight at 20,000 ppm, although the deficit 

diminished with time. The overall body-weight gain (days 0-21) at 20,000 ppm was positive [P 

dams 30.5 grams **; F1 dams 21.1 grams **] compared to negative gains in the control and lower 

dose groups. 

There was no adverse effect on reproductive performance in either generation [comparable male 

and female mating index, fertility index, gestation index, gestation duration, # and % pregnant, # 

implantation sites, # viable litters, # and % stillbirths, pre- and post-implantation losses].

There were no treatment-related adverse effects on organ weights, and no treatment-related 

differences in macroscopic and microscopic pathology for either generation. 

There were no adverse effects on the mean litter size on day 0, and the % of males was 

comparable among the groups for both generations. In each generation, pup survival (days 0-4) at 

20000 ppm was lower [F1 90.1%/F2 93.6%] than the control [F1 96.9%/F2 96.9%] and other 

dose groups [F1 96.3%, 93.4% 98.5% with increasing dose/F2 96.9%, 96.5%, 96.9%, 96.9% with 

increasing dose], although statistical significance was not attained. F1 pup survival (lactation days 

4-21) was lower at 20000 ppm [92.4%*] than the control [98.3%] and other dose groups [97.8%, 

100%, 98.3%, 98.0% with increasing dose]. F2 pup survival (lactation days 4-21) was comparable 

among the groups. Pup body weights were decreased at 20000 ppm for both generations on day 0 
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[F1 males 94%/females 95% of control; F2 males 95%/females 93%* of control] and throughout 

lactation [F1 males 76%**-82%**/females 77%**-82%** of control; F2 males 76*-

83%**/females 76**-93%* of control]. Body-weight gains were decreased in both sexes/both 

generations throughout the lactation period at 20,000 ppm, with the largest deficit being observed 

initially (days 0-4; F1 males 39%/females 41% of control; F2 males and females 59% of control). 

The magnitude of the body-weight gain deficits was 74%-89% (F1 males), 76%-87% (F1 

females), 70%-81% (F2 males), and 71%-79% (F2 females). Clinical observations of the pups 

during lactation did not demonstrate treatment-related systemic toxicity. 

The NOAEL for reproductive toxicity is 20,000 ppm [males 1212 mg/kg/day; females 1485 

mg/kg/day (highest dose tested; HDT)].

The NOAEL for parental systemic toxicity is 10,000 ppm (males 593.5 mg/kg/day; females 

751.1 mg/kg/day), based on reduced premating and gestation body weight/body-weight gain 

and food consumption at the parental systemic toxicity LOAEL of 20,000 (males1212 

mg/kg/day; females 1485 mg/kg/day).

The offspring systemic toxicity NOAEL is 10,000 ppm (males 593.5 mg/kg/day; females 

751.1 mg/kg/day), based on decreased pup survival and decreased pup body weight/bodyweight gain during lactation at the offspring systemic toxicity LOAEL of 20,000 ppm

[males 1212 mg/kg/day; females 1485 mg/kg/day).

This 2-generation reproduction study in rats is acceptable (guideline), and it satisfies the 

guideline requirement for a reproduction study [OPPTS 83-4; OECD 416] in rats.

Developmental milestone data (age of vaginal opening and preputial separation; anogenital 

distance for F2 pups); assessment of implantations sites; estrous cycle length and periodicity (F1 

weanlings); and sperm measures were not included in this study.

Chronic Dog Study

In an oral chronic toxicity study (MRID 42779402, CGA-163935 Technical [(96.2/92.2% a.i.), 

batch/lot #s FL 882373, 892178, 891417] was administered to 4 purebred beagle dogs/sex/dose 

via the diet at dose levels of 0, 40, 1000, 10,000, or 20,000 ppm (equivalent to 0, 1.56, 31.62, 

365.72, or 726.65 (males)/1.37, 39.54, 357.13, or 783.83 mg/kg bw/day) for 52 weeks. 

All dogs survived until study termination. At dose levels of 10,000 ppm and/or 20,000 ppm, 

emesis with food (earliest occurrence at week 7 in males), mucoid/bloody feces (earliest 

occurrence at week 6 in males), reduced RBC and hematocrit, elevated cholesterol and alkaline 

phosphatase were observed in both sexes. Slightly lower body weights were observed at study 

termination in males at 10,000 ppm [89% of control] and 20,000 ppm [90% of control] and in 

females at 20,000 ppm [89% of control]. Body-weight gains fluctuated throughout the study 

especially in males such that a clear dose-response was not evident. Decreased body-weight 

gains were observed initially at 20,000 ppm in both sexes [males negative gain; females 14% of 

control during first week; males 55%/females 60% of control during weeks 1-13 interval]. 

Overall, males at 10,000 ppm [66% of control] and 20,000 ppm [76% of control] displayed the 

lowest body-weight gain, although there was no dose-response. Females at 20,000 ppm 

displayed a decrease in body-weight gain overall [73% of control]. Food consumption was not 

affected. Although not statistically significant, decreased spleen weights were observed in both 

sexes at 20,000 ppm. Testes (absolute*, relative-to-body/brain) and uterus weights (absolute*, 
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relative-to-body*/brain) were significantly decreased at the three highest dose levels, but there 

was no dose-response and no histopathological lesions in either organ. There was microscopic 

evidence of minimal, focal vacuolation of the dorsal medial hippocampus and/or lateral midbrain 

in all dogs at 20,000 ppm and in one male and two female dogs at 10,000 ppm. Dose levels up to 

20000 ppm were well tolerated by both sexes and are considered adequate. 

The LOAEL is 10,000 ppm [males 365.72/females 357.13 mg/kg/day], based on elevated 

serum cholesterol values in females, mucoid feces in females and bloody feces in both 

sexes, and minimal, focal vacuolation of the dorsal medial hippocampus and/or lateral 

midbrain in both sexes. The NOAEL is 1000 ppm [males 31.62/females 39.54 mg/kg/day]. 

This chronic oral toxicity study in the dog is acceptable, and it satisfies the guideline 

requirement for a chronic oral study [OPPTS 870.4100, OECD 452] in the dog.

Combined Chronic Toxicity/Carcinogenicity Study in Rats

In a chronic toxicity/carcinogenicity study [MRID 42238104], 50 Sprague-Dawley Crl:VAF Plus 

CD(SD)BR rats/sex/dose were administered CGA 163935 Technical [96.9%/96.2%/92.2%] via

the diet at concentrations of 0 ppm, 10 ppm, 100 ppm, 3000 ppm, 10,000 ppm, or 20,000 ppm 

for 104 weeks [carcinogenicity phase]. An additional group of 20 Sprague-Dawley Crl:VAF Plus 

CD(SD)BR rats/sex/dose were administered CGA 163935 via the diet at the same concentrations 

for 104 weeks [chronic toxicity phase], and an additional group of 10 Sprague-Dawley Crl:VAF 

Plus CD(SD)BR rats/sex/dose were administered CGA 163935 via the diet at the same 

concentrations for 52 weeks [interim sacrifice]. The time-weighted mean daily intakes were 0.38, 

3.87, 115.6, 392.7 or 805.7 mg/kg/day for males and 0.49, 4.88, 147.4, 494.0, or 1054 mg/kg/day 

for females receiving 10, 100, 3000, 10,000, or 20,000 ppm, respectively. A recovery phase of 4 

weeks followed the administration of the test material to 10 rats/sex at the 20000 ppm dose level 

[compared with an additional control group of 10 rats/sex]. 

There was no adverse effect of treatment on survival, and no apparent treatment-related clinical 

signs of toxicity. There was a reduction in body weight in both sexes [males 91%-94%; females 

86%-92%] at the 20,000 ppm dose level throughout the study beginning at day 7. At 13 weeks, 

both sexes at 20,000 ppm displayed an 8% decrease in body weight. At study termination, males 

at 20,000 ppm displayed a 9% deficit in body weight compared to the control. Females at this 

dose level showed a greater gain in body weight during the last 24 weeks of the study [week 76-

104 interval] such that terminal body weight was comparable [98% of control] to the control; 

however, at week 76, females at 20,000 ppm displayed a 14% deficit in body weight compared 

to the control. Decreased body-weight gains were observed in both sexes at the high dose during 

the weeks 0-12 interval [males 93*%/females 84%** of control]. Females also showed 

decreased body-weight gain at the 1-year time point [81%**of control]. Overall body-weight 

gain was 90% of control for the males and 95% of control for the females at 20,000 ppm. Food 

consumption values were lower than the control values for the first 6 months in males and for the 

first 15.5 months for females.

There were no treatment-related ocular changes in either sex. There were no apparent, treatmentrelated effects on the hematology or clinical chemistry parameters monitored in either sex. 

Urinary pH was decreased in both sexes at the 10,000 ppm and 20,000 ppm dose levels 

throughout the study, although no histopathological correlations accompanied these findings. 
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In males, decreased absolute and relative-to-brain heart weights were observed at 20,000 ppm at 

52 weeks. There was a slight but significant increase in relative liver and lung weights in females 

at the 20,000 ppm dose level at 52 weeks. At termination [104 weeks], the increased relative 

organ weights were considered due to decreased body weight at 20,000 ppm. No treatmentrelated organ-weight effects were reported in either sex at 10,000 ppm. 

In the liver, there was a statistically-significant increase in bile duct hyperplasia in males at 

20,000 ppm at study termination [16, 11, 13, 13, 18, 35** with increasing dose]. Females at 

20,000 ppm displayed an increased incidence of acanthosis in the glandular stomach at study 

termination [7, 6, 1, 1, 8, 13* with increasing dose]. Lymphangietasis was increased at the two 

highest dose levels in males at study termination [3, 4, 8, 4, 9*, 19* with increasing dose]. 

Females displayed an increased incidence of galactocele of the mammary gland [5, 5, 4, 7, 9, 

13** with increasing dose] and stromal hyperplasia of the ovary was increased at the two highest 

dose levels [3, 1, 3, 1, 7*, 5* with increasing dose], but there was no dose response. 

Squamous cell carcinoma of the non-glandular stomach was observed in two males (2.5%) at 

20,000 ppm but in none of the control rats or other rats at any dose level in either sex. The 

normal range reported for males by the author was 0%-1.2%. Follicular adenocarcinoma of the 

thyroid was significantly increased in males (5%) at 20,000 ppm, and there was a significant 

positive trend [1, 0, 0, 1, 1, 4*]. The historical control range was 0%-5% (1.8% mean) compared 

to 1.2% in concurrent control. The incidence of combined follicular adenomas and 

adenocarcinomas of the thyroid did not show a dose-related increase [5, 2, 3, 6, 6, and 7 with 

increasing dose]. Urinary bladder papilloma incidence was significantly increased in females at 

20,000 ppm [0, 0, 0, 0, 1, 2* with increasing dose), but the increase was slight and the finding is 

considered incidental. 

The systemic toxicity NOAEL is 20,000 ppm [males 806 mg/kg/day; females 1054 

mg/kg/day], the highest dose tested. 

This guideline chronic toxicity/carcinogenicity study is classified ACCEPTABLE, and it 

satisfies the guideline [OPPTS 870.4300; §83-5] for a chronic toxicity/carcinogenicity study in 

the rat. 

Non-neoplastic lesions: There was no apparent increase in the incidence of any non-neoplastic 

lesion in either sex. 

Neoplastic lesions: Squamous cell carcinomas were observed in the non-glandular portion of the 

rat stomach in two males at the 20,000 ppm dose level. 

Discussion of Tumor Data: It was concluded that extrapolation of effects on the non-glandular 

portion of the rat stomach to possible deleterious effects of trinexapac-ethyl on the pharynx 

and/or esophagus (non-glandular areas) of the human was not appropriate. This was because 

trinexapac-ethyl would not be in contact with the human tissues for a significant period of time 

compared with how it would have been in contact with the rat stomach. 

Adequacy of the Dose Levels Tested: The highest dose [20,000 ppm] is approaching the limit 

dose in males (806 mg/kg/day) and is greater than the limit dose in females (1054 mg/kg/day). 

The dose levels are considered adequate for the assessment of carcinogenicity potential in the rat. 

Carcinogenicity Study in Mice
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In a carcinogenicity study (MRID 43128603), CGA 163935 Technical [FLs 872026, 881224, 

882373; 96.9%/96.2% a. i.] was administered to 70 CD-1 mice (Crl:CD-1(ICR)BR)/sex/dose in 

the diet at dose levels of 0, 7, 70, 1000, 3500, or 7000 ppm [equivalent to 0, 0.91, 9.01, 130.81, 

450.72, or 911.77 mg/kg bw/day (males)/ 0, 1.08, 10.66, 154.08, 538.73, or 1073.42 mg/kg/day 

(females)] for 78 weeks. 

There were no adverse or compound-related effects on mortality, clinical signs, body weight, 

food consumption, hematology, organ weights, or gross and histologic (including tumors) 

pathology. The decreased body-weight gain observed in the 7000 ppm female group initially 

was attributed to palatability. A LOAEL was not attained. The NOAEL is 911/1073 

mg/kg/day (highest dose tested; HDT).

There was no treatment-related increase in tumor incidence when compared to controls. Dosing 

was considered adequate based on a lack of adverse effect at dose levels up to and exceeding the 

limit dose.

This carcinogenicity study in mice is acceptable (guideline), and it satisfies the guideline 

requirement for a carcinogenicity study [OPPTS 870.4200; OECD 451] in mice.

Non-neoplastic lesions: There was no apparent increase in the incidence of any non-neoplastic 

lesion in either sex. 

Neoplastic lesions: There was no treatment-related increase in tumor incidence when compared 

to controls.

Discussion of Tumor Data: There was no increase in tumors of any type in either sex of mouse.

Adequacy of the Dose Levels Tested: . Dosing was considered adequate based on a lack of 

adverse effect at dose levels up to and exceeding the limit dose.

Acute Neurotoxicity Screening Battery

In an acute neurotoxicity study (MRID 48764506), groups of 10/sex Crl:CD(SD) rats (6

weeks of age) were given a single gavage dose (10 mL/kg) oftrinexapac-ethyl (95.8% a.i)

suspended in the vehicle (0.5% carboxymethylcellulose in water containing 0.1% Tween®

80), at dose levels of 0 (vehicle only), 500, 1000, or 2000 mg/kg, respectively and observed

for 15 days. The animals were observed twice daily for mortality and moribundity. 

Individual body weights were recorded on study days -7, 0, 1, 2, 7, 8, 14, and 15; individual

food consumption was recorded during study days 0-1, 1-2, and 7-8. Neurobehavioral

assessment (functional observational battery and motor activity testing) was performed in 10

animals/sex/group pretest and on days 0 (4 hours post dosing time of peak effect), 7, and 14. 

At study termination, 5 animals/sex/group were euthanized and perfused in situ for

neuropathological examination. Tissues from control and 2000 mg/kg/day animals were

subjected to histopathological evaluation of brain and peripheral nervous system tissues. Brain 

weights and brain dimensions (excluding olfactory bulbs) were recorded. Animals not selected 

for in situ perfusion were euthanized and discarded without macroscopic examination.

All animals survived to study termination. There were no treatment-related clinical signs of 

toxicity. There were statistically significant lower mean body weight gains for the 2000 mg/kg 
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males and females over the first day following dosing (study days 0-1). This effect did not 

continue for the rest of the study. There were no effects noted FOB evaluations performed at 

the time of peak effect (approximately 4 hours post-dose) and on study days 7 and 14. The FOB 

evaluations collectively involved home cage, handling, open field, sensorimotor, neuromuscular, 

and physiological parameters. There were also no treatment-related effects on mean total and 

ambulatory locomotor activity counts for males and females at any dose level. No remarkable 

shifts in the pattern of habituation occurred in any of the test substance-treated groups when the 

animals were evaluated on study days 0, 7, and 14. No treatment related effects were apparent in 

brain weights or brain dimensions for the perfused animals and there were no treatment related 

neuropathological lesions.

Based on the data provided in this study, the NOAEL for Systemic Toxicity is 2000 mg/kg 

(limit dose) and the LOAEL was not established. 

Based on the data provided in this study, the NOAEL for Neurotoxicity is 2000 mg/kg 

(limit dose) and the LOAEL for Neurotoxicity was not established, based on the absence of 

any treatment-related functional observational findings, locomotor activity changes, 

changes in brain weights or brain dimensions, and the absence of any neuropathological 

lesions.

This study is classified as Acceptable-Guideline and as such satisfies the guideline 

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

Comment: This is an updated Executive Summary. The original Executive Summary was 

revised to change the NOAEL for systemic toxicity from 1000 mg/kg to 2000 mg/kg and the 

LOAEL from 2000 to not established because the only effect seen was decreased body weight 

gain in the absence of a corroborating effects on body weight; this is not sufficient to be 

considered evidence of an adverse toxic effect.

Subchronic Neurotoxicity Screening Battery

In a subchronic neurotoxicity study (MRID 48764507) Trinexapac-ethyl

(96.6%/95.8%,SM05D180/ SM08E551) was administered to 12 Crl:CD(SD) rats (Charles

River Laboratories, Inc., Raleigh, NC.)/sex/group at dose levels of 0, 3750, 7500, or 15000

ppm (equivalent to 0,233, 463, and 948 mg/kg bw/day for males and 0, 294, 588, and 1171

mg/kg/day for females, respectively) for 13 weeks. All animals were observed twice daily

for mortality and moribundity. Clinical observations, body weights, and food consumption 

were recorded weekly. The functional observational battery (FOB) and locomotor activity

parameters were recorded for all animals during pretest and then during study weeks 3, 7,

and 12. FOB parameters included home cage, handling, open field, sensory, neuromuscular,

and physiological parameters. Ophthalmic examinations were performed prior to the start of

test diet administration and during study week 11. At study week 13, 5 rats/sex/group were
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deeply anesthetized and were perfused in situ. Brain weights and brain dimensions (excluding

olfactory bulbs) were recorded. Neuropathological evaluation of selected tissues from the

central and peripheral nervous systems was performed on 5 animals/sex in the control and 

15,000 ppm groups.

All animals survived to study termination. There were no treatment-related effects on clinical 

findings. There were lower mean body weight gains with corresponding reduced mean food 

consumption for the 15,000 ppm females during study days 0-14. Following study day 14 the 

mean body weight gains and food consumption for the 15,000 ppm females were similar to 

control for the remainder of the study. These effects were not considered adverse since they 

were small and short lived. The mean body weights, body weight gains, and food consumption 

for the 3750 and 7500 ppm males and females and the 15,000 ppm males were unaffected by 

treatment. Also, there were no effects noted on FOB evaluations or for mean motor activity 

(ambulatory and total) counts at study weeks 1, 3, 7, and 12. There were no treatment-related 

changes in brain weight or brain measurements, or macroscopic or microscopic observations.

Based on the data provided in this study, the NOAEL for Systemic Toxicity is ≥ 15000 ppm 

(948 mg/kg/day for males and 1171 mg/kg/day for females, respectively) which is the 

highest dose tested. The LOAEL is > 15000 ppm for both systemic toxicity and 

neurotoxicity based on the absence of any treatment- related functional observational

findings, locomotor activity changes, changes in brain weights or brain dimensions, and the 

absence of any neuropathological lesions.

The study is classified as Acceptable-Guideline and as such satisfies the guideline

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

Metabolism and pharmacokinetics study (rat)

In a metabolism and pharmacokinetics study (MRID 41563927), the metabolism of [cyclohexyl14C] CGA-163935 was studied in male and female Crl: CD BR rats. The cyclohexyl-labeled 

compound was administered as a single intravenous (iv) dose of 0.91 mg/kg, as a single oral dose 

of 0.97 or 166 mg/kg or as a single oral dose of 0.97 mg/kg following a 14-day pretreatment with 

unlabeled CGA-169935 at 1 mg/kg/day. Recoveries of radioactivity in urine after oral dosing 

(94.5-97.3% of the dose) indicated extensive absorption of the compound from the GI tract. 

Total recovery of radioactivity 168 hours after treatment accounted for 97-99% of the dose in the 

orally doses animals, and up to 94.7-98.3% of the dose in the iv-treated rats. Among the orally 

dosed groups, approximately 94.5-97.3% of the dose was eliminated in urine and 1.0-2.4% of the 

dose was eliminated in feces. Most of the elimination occurred within the first 24 hours. No 

differences between the sexes or among dose groups were found. The low elimination of 

radioactivity in the feces by the iv-dosed group (1.1-1.6% of the dose) suggests that there is very 

little or no biliary excretion of the compound and/or its metabolites in rats. At sacrifice, total 

radioactive residues in the carcass was less than 0.28% of the dose in all groups. A preliminary 
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experiment indicated that by 72 hours after dosing, elimination of radioactivity in expired air 

amounted to less than 0.06% of the dose for the low-dose rats and less than 0.01% of the does for 

the high-dose rats.

Only one metabolite, CGA-179500, was found in the urine. Levels of CGA-179500 in urine 

accounted for 82.0-91.6% of the dose among the orally-dosed animals and for 74.1-75.3% of the 

dose among the iv-dosed animals. CGA-179500 is the carboxylic acid resulting from hydrolysis 

of the ester bond of parent CGA-163935.

The study is classified as Acceptable-Guideline and as such satisfies the guideline the 

guideline requirement for a metabolism and pharmacokinetic study [OPPTS 870.7485].

Dermal Absorption Study

A single dermal dose of 0.01, 0.1, and 1.0 mg/cm2 14C-CGA-163935 administered to male rats 

was rapidly absorbed, distributed and eliminated. The amount absorbed increased with duration 

of exposure. Using the direct procedure to calculate skin absorption, the average 14C-CGA163935 absorbed within 24 hours was 64.9, 63.86, and 30.85% of the applied dose for the low-, 

mid-, and high-dose groups, respectively. Using the indirect procedure to calculate skin 

absorption, the average 14C-CGA-163935 absorbed within 24 hours was 56.83, 66.74, and 

33.84% of the applied dose for the low-, mid-, and high- dose groups, respectively. The direct 

procedure is the more realistic procedure to use. A dermal absorption factor of 77.5% was 

estimated based on the sum of 56.5% absorbed after 10 hours in the low dose group (0.01 

mg/cm2), in addition to 21% of applied dose that was associated with the application site. 

Immunotoxicity study

In an immunotoxicity study (MRID 48444101), trinexapac- ethyl (96.6% a.i.; Lot no. 

SMO5D180) was administered to female B6C3F1 mice (10/dose) in the diet at dose levels of 0, 

500, 2000, or 5000 ppm (0, 160.2, 613.7, or 1530.5 mg/kg/day, respectively) for 28 days.

Animals were divided into two subsets, the splenic antibody-forming cell (AFC) group and the 

Natural Killer cell (NKC) group. In the AFC group, positive control mice were administered 

cyclophosphamide via intraperitoneal injection (50 mg/kg/day) once daily for 4 consecutive days 

(study days 24 through 27). On study day 24, all AFC group mice were immunized with 0.2 mL 

of sheep red blood cells (SRBC, 7.5x107/mL) via intravenous injections. In the NKC group, 

positive control mice were administered anti-asialo GM1 via a single intravenous injection (0.2 

mL/animal) on study day 27, approximately 24 hours prior to scheduled necropsy. On day 28, all 

animals were necropsied, gross pathology observations were performed and selected organs 

(spleen and thymus) weighted. The immunotoxicity assessment was evaluated with a splenic 

antibody-forming cell (AFC) assay and a Natural Killer cell (NKC) activity assay.

There were no treatment related effects on mortality, clinical observations, body weights, food 
Trinexapac-ethyl Human Health Risk Assessment DP No.419651

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consumption, thymus and spleen weights, or macroscopic findings in either the AFC or NKC 

groups of animals. 

The systemic toxicity NOAEL is 5000 ppm (1530.5 mg/kg/day, the highest dose tested), the 

LOAEL was not established.

In the AFC group, there were no effects attributed to trinexapac-ethyl on spleen cell numbers and 

anti-SRBC antibody-forming-cell (AFC) response in either specific activity (AFC/106cells) or 

total activity (AFC/spleen) to the T-cell-dependent antigen SRBC. The positive control 

(cyclophosamide) produced statistically significant decreases in specific activity (-100%) and 

total spleen activity (-100%) in the female B6C3F1 mice as expected, when compared to the 

vehicle control animals.

In the NKC group, there were no statistically significant effects attributed to trinexapac-ethyl at 

any E:T ratio as compared to the vehicle controls. The positive control (anti-asialo GM1) 

significantly decreased the functional response of the NK cells, reaching the level of statistical 

significance at the E:T ratios of 200:1 and 100:1, when compared to the vehicle control animals

The immunotoxicity NOAEL for anti-SRBC AFC response and NK cell activity is 5000 

ppm (1530.5 mg/kg/day), the LOAEL was not established.

This immunotoxicity study is classified Acceptable/guideline and satisfies the guideline 

requirement for an immunotoxicity study (OPPTS 870.7800).