Page 2 of 68

Table of Contents

1.0 Executive Summary.................................................................................................................. 4

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

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

2.2 Tolerance Considerations.......................................................................................................... 8

2.2.1 Enforcement Analytical Method................................................................................................8

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

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

2.2.4 Revisions to Petitioned-For Tolerances...................................................................................10

2.3 Label Recommendations......................................................................................................... 10

2.3.1 Recommendations from Residue Reviews ..............................................................................10

2.3.2 Recommendations from Occupational Assessment.................................................................10

2.3.3 Recommendations from Residential Assessment ....................................................................10

3.0 Ingredient Profile .................................................................................................................... 11

3.1 Chemical Identity.................................................................................................................... 11

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

3.3 Summary of Existing/Proposed Uses...................................................................................... 12

3.4 Anticipated Exposure Pathways ............................................................................................. 14

3.5 Consideration of Environmental Justice ................................................................................. 14

4.0 Hazard Characterization and Dose-Response Assessment..................................................... 15

4.1 Hazard and Dose-Response Characterization......................................................................... 15

4.1.1 Database Summary ..................................................................................................................15

4.2 Absorption, Distribution, Metabolism, & Elimination (ADME)............................................ 15

4.2.1 Dermal Absorption...................................................................................................................16

4.3 Toxicological Effects.............................................................................................................. 16

4.4 Safety factor for Infants and Children (FQPA Safety Factor)................................................ 18

4.4.1 Completeness of the Toxicology Database..............................................................................18

4.4.2 Evidence of Neurotoxicity and Immunotoxicity......................................................................19

4.4.3 Evidence of Sensitivity/Susceptibility in the Developing or Young Animal ..........................20

4.4.4 Residual Uncertainty in the Exposure Database......................................................................20

4.5 Toxicity Endpoint and Point of Departure Selections ............................................................ 20

4.5.1 Dose-Response Assessment.................................................................................................... 20

4.5.2 Recommendation for Combining Routes of Exposures for Risk Assessment........................ 22

4.5.3 Classification of Carcinogenic Potential................................................................................. 22

4.5.4 Summary of Points of Departure and Toxicity Endpoints Used in Human Risk 

Assessment.............................................................................................................................. 23

5.0 Dietary Exposure and Risk Assessment ................................................................................. 24

5.1 Metabolite/Degradate Residue Profile.................................................................................... 24

5.1.1 Summary of Plant and Animal Metabolism Studies................................................................24

5.1.2 Summary of Environmental Degradation ................................................................................25

5.1.3 Comparison of Metabolic Pathways........................................................................................26

5.1.4 Residues of Concern Summary and Rationale.........................................................................27

5.2 Food Residue Profile............................................................................................................... 27
Page 3 of 68

5.3 Water Residue Profile ............................................................................................................. 29

5.4 Dietary Risk Assessment ........................................................................................................ 30

5.4.1 Description of Residue Data Used in Dietary Assessment......................................................30

5.4.2 Percent Crop Treated Used in Dietary Assessment .................................................................30

5.4.3 Acute Dietary Risk Assessment...............................................................................................30

5.4.4 Chronic Dietary Risk Assessment ...........................................................................................30

5.4.5 Cancer Dietary Risk Assessment.............................................................................................31

5.4.6 Dietary Summary Table...........................................................................................................31

6.0 Residential (Non-Occupational) Exposure/Risk Characterization ......................................... 31

6.1 Handlers.................................................................................................................................. 32

6.2 Post-application Exposure ...................................................................................................... 32

6.2.2 Inhalation Post-application Exposure ......................................................................................33

6.2.3 Spray Drift ...............................................................................................................................34

7.0 Aggregate Exposure/Risk Characterization............................................................................ 34

7.1 Acute Aggregate Risk ............................................................................................................. 35

7.2 Short- and Intermediate-Term Aggregate Risk....................................................................... 35

7.3 Cancer Aggregate Risk ........................................................................................................... 36

7.4 Cancer Aggregate Risk ........................................................................................................... 36

8.0 Cumulative Exposure/Risk Characterization.......................................................................... 36

9.0 Occupational Exposure/Risk Pathway.................................................................................... 36

9.1 Handlers.................................................................................................................................. 36

9.2 Occupational Post-application ................................................................................................ 43

9.2.1 Occupational Post-application Dermal ....................................................................................43

9.2.1 Occupational Post-application Inhalation ................................................................................45

10.0 References............................................................................................................................... 45

Appendix A: Toxicology Profile and Executive Summaries.......................................................... 47

A.1 Toxicology Data Requirements .............................................................................................. 47

Table A.2.3 Acute Toxicity Profile – PrimoTM Formulation (12% Trinexapac-ethyl )................ 48

A.3 Hazard Identification and Endpoint Selection ............................................................................. 54
Page 4 of 68

1.0 Executive Summary

Trinexapac-ethyl is a plant growth regulator used on perennial grass grown for seed. It is 

proposed for its first food uses on sugarcane and cereal grains (barley, oats, triticale, and wheat). 

Previously, Syngenta proposed registration of the 1 lb/gal EC product on grasses to include 

grasses grown for seed throughout the U.S. However, a number of deficiencies were noted in the 

petition that precluded establishing permanent tolerances for trinexapac-ethyl in grass and 

livestock commodities and resulted in a regionally restricted registration on ryegrass.

Syngenta has re-proposed use of trinexapac-ethyl in/on grasses grown for seed throughout the 

U.S. and proposes registration and tolerances of the 1 and 2 lb/gal EC products for this use

(PP#0F7719). The proposed use directions would allow for a single or split application of 

trinexapac-ethyl to grasses grown for seed during stem elongation and floral development, at a 

maximum application rate of 0.5 lb ai/A. The registrant has proposed a maximum seasonal rate 

of 0.5 lb ai/A, a 35-day preharvest interval (PHI) for mature grass, and a 49-day pre-grazing 

interval (PGI) for regrowth of forage and hay following harvest. In addition, the registrant is 

proposing new uses and tolerances to support the use of the 1 and 2 lb/gal EC products on cereal 

grains (barley, oats, triticale, and wheat) and sugarcane (PP#0F7720). The registrant proposes to 

allow a maximum seasonal rate of 0.11 lb ai/A and a 45-day PHI for cereal grains and a 

maximum seasonal rate of 0.31 lb ai/A and a 28-day PHI for sugarcane.

Hazard Characterization

The toxicity database for trinexapac-ethyl is incomplete under the new 40 CFR Part 158 data 

requirements for conventional pesticides, which requires certain generic testing, including acute

(in review) and subchronic neurotoxicity studies. However, the Agency believes that the current 

toxicity database is adequate to evaluate the hazards associated with these new uses. 

Trinexapac-ethyl is a cyclohexadione plant growth regulator that inhibits the biosynthesis of 

gibberellin (GA1), which is a phytohormone that promotes growth of various plant organs. In 

mammals, the compound is rapidly and extensively absorbed (> 95% of the administered dose) 

and rapidly eliminated (> 85% of the administered dose eliminated within 12 h), with no 

significant bioaccumulation. Significant residues identified in the rat metabolism study were the 

acid metabolite of trinexapac-ethyl (approximately 80 – 90% of radioactivity) and the parent 

compound (<1%). The acute toxicity is low via the oral, dermal, or inhalation routes of exposure 

(Categories III-IV), and it is not a dermal sensitizer. The toxicity profile of trinexapac-ethyl is 

attached (Appendix A; Table A2). 

Trinexapac-ethyl is a low toxicity chemical with a high acute oral LD50 (oral LD50 = 5,000 

mg/kg) and systemic effects occurring at or well above 300 mg/kg/day in subchronic and lifetime 

dosing studies. At higher doses, however, there is evidence of increased qualitative and 

quantitative susceptibility in the developmental and reproduction studies. Developmental 

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

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

loss) at the highest dose tested, with no evidence of maternal toxicity observed at the highest 
Page 5 of 68

dose tested in either species. Clear no-adverse-effect-levels (NOAELs) were established in these 

developmental studies. In the multi-generation rat reproduction study, parental and offspring 

toxicity occurred at the limit dose; however, the type of effect in the offspring was more severe 

(decreased pup survival). No reproductive toxicity was observed up to the limit dose.

An in utero effect from the developmental rabbit study provided an acute reference dose for 

females 13-49 yrs old but is not appropriate for the general population. An acute dietary endpoint 

was not identified for the general population. The chronic reference dose (cRfD) was based on 

the chronic dog toxicity study which is considered conservative since the NOAEL is more than 

10-fold lower (i.e., more protective) than the dose LOAEL at which neurotoxicity was observed

in the same dog study. Since the point of departure for the chronic assessment is also 

approximately 10-fold lower than the dose levels where developmental toxicity was seen in the 

developmental rabbit study, it is also protective of any developmental or offspring toxicity. 

Endpoints of concern for the incidental oral, dermal and inhalation scenarios for children are not 

available from the trinexapac-ethyl toxicity studies. The short- and intermediate-term dermal and 

inhalation adult scenarios were based on the developmental rabbit study. Since the dermal and 

inhalation scenarios are based on the same study, they can be combined when assessing 

occupational exposure.

HED recommends that the 10x FQPA Safety Factor be reduced to 1x, as the toxicological 

database for trinexapac-ethyl is adequate. The toxicological database for trinexapac-ethyl is 

complete with regard to pre-and postnatal toxicity, acute neurotoxicity (in review),

immunotoxicity, and there are no residual uncertainties. In addition, the exposure databases are 

of high quality such that dietary and residential exposures will not be underestimated. 

Trinexapac-ethyl has been classified as ―not likely to be carcinogenic to humans,‖ and therefore, 

does not require quantification of cancer risk. 

Metabolism/Metabolites and Degradates of Concern

The metabolism of trinexapac-ethyl in plants and animals has been adequately delineated. The 

primary degradation pathway in both livestock and plants involves trinexapac-ethyl rapidly 

undergoing hydrolysis of the ethyl ester to form trinexapac.

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 trinexpacethyl and its acid metabolite, trinexapac. In drinking water, 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. 

Food Residue Profile

The residue profile for the proposed commodities is adequate. For all commodities, the 

registrants submitted adequate field trial data for parent trinexapac-ethyl as trinexapac. The 

recommended tolerances range from 0.4 ppm in barley straw to 40.0 ppm in grass seeds. For all 
Page 6 of 68

field grown crops, adequate numbers of trials were performed in the recommended NAFTA 

growing zones. Concentration was observed in some processed commodities such that separate 

tolerances are needed on, wheat middling only. Based on cattle and hen feeding studies 

tolerances are needed for the meat, fat, and meat byproducts of cattle, goats, horses, sheep and 

hog. The recommended tolerances for all commodities are listed in Table 2.2.3. 

Dietary Exposure and Risk

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

conducted. These unrefined assessments are based on tolerance-level residues, 100% crop 

treated assumptions for all commodities, and default processing factors. The acute and chronic 

dietary risk estimates are below HED’s level of concern for all population subgroups, including 

those comprised of infants and children. Because such conservative assumptions were made in 

the assessments, HED is confident that the acute and chronic dietary exposure assessments do 

not underestimate risk to the general U.S. population or any population subgroup. 

Residential Exposure and Risk

HED determined that there is a potential for residential exposure to trinexapac-ethyl from the 

currently registered turf uses. HED assumes that only short-term exposures are applicable to 

residential handler risk assessments, and are considered to be protective of intermediate-term 

exposure and risk. The combined dermal plus inhalation risk estimates to residential handlers 

do not exceed HED’s level of concern for all scenarios (i.e., MOEs ≥ 100). 

HED determined that there is a potential for exposure from entering trinexapac-ethyl-treated 

residential areas, such as lawns, sports fields, and golf courses that could lead to postapplication exposures to adults. Short-term dermal risk estimates were estimated for adults 

only. The residential post-application margin of exposure (MOEs) ranged from 650 to 24,000

and therefore, do not exceed HED’s level of concern (MOE ≥ 100). 

Aggregate Exposure and Risk

The acute (females only) and chronic aggregate risks are equivalent to the corresponding dietary 

(food plus water) risks, which are not of concern. The short- and intermediate-term dermal and 

inhalation toxicological endpoints for trinexapac-ethyl are the same. The resulting aggregate 

short- and intermediate-term risk estimates (MOE ≥ 100); therefore, the short- and intermediateterm aggregate risks of exposure to trinexapac-ethyl are not of concern.

Occupational Exposure and Risk

It is anticipated that there will be occupational handler and post-application exposure from the 

proposed agricultural uses as well as all of the currently registered uses of trinexapac-ethyl.

Dermal and inhalation risks for short- and intermediate-term exposures were combined in this 

assessment, since the toxicological effects for the dermal and inhalations routes were the same. 

MOEs greater than or equal to 100 for dermal and inhalation routes is deemed adequate to 

protect occupational trinexapac-ethyl handlers. All handler scenarios resulted in MOEs greater 
Page 7 of 68

than the level of concern (i.e., MOEs ≥ 100) when wearing labeled personal protective 

equipment (PPE) (e.g., long-sleeve shirt, long pants, shoes, socks, chemical-resistant gloves, and 

protective eyewear) and, therefore are not of concern. The label restricted entry interval (REI) of 

12-hour is appropriate and in compliance of the Worker Protection Standard requirements. 

Occupational short- and intermediate-term dermal exposures are expected from post-application 

activities. Chemical-specific data relevant to post-application were not submitted; therefore, 

post-application exposure estimates were calculated using standard HED default assumptions. 

Using default dislodgeable foliar residue values, risk estimates are not a concern for any postapplication occupational scenario on day 0, except for hand-harvesting sugarcane where the 

MOE increases to 110 within 8 days of application (short- and intermediate-term postapplication). However, HED does not recommend that sugarcane REI’s be changed on the 

trinexapac-ethyl labels at this time based on two main issues. First, almost all sugarcane 

harvesting in the United States is done mechanically. Secondly, 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.

Human Studies

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

intentionally exposed to a pesticide or other chemical. These studies, which comprise the 

Pesticide Handlers Unit Exposure Reference Table (OPHED), the Agricultural Reentry Task 

Force (ARTF), and the Outdoor Residential Exposure Task Force (ORETF) databases, have been 

determined to require a review of their ethical conduct, have received that review, and have been 

determined to be ethical.

2.0 HED Recommendations

Provided the registrant submits a revised Section F, there are no human health risk estimates of 

concern that would preclude the establishment of tolerances for the residues of trinexapac-ethyl.

A new entry should be made in the 40 CFR for the active ingredient trinexapac-ethyl to support 

the new uses. 

2.1 Data Deficiencies/Conditions of Registration

The registrant is required to submit a revised Section F in which the recommended tolerances 

listed in Table 2.2.3. are proposed.

The following data should be submitted:

TOXICOLOGY

870.6200 Neurotoxicity
Page 8 of 68

The acute (in review) and subchronic neurotoxicity studies are required under 40 CFR 

Part 158 for registration of a pesticide (food and non-food uses).

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). The new method includes a strong acid hydrolysis/extraction 

procedure to release both ―free‖ and ―conjugated‖ residues of CGA179500 from field grown 

grass commodities. The reported limit of quantitation (LOQ) is 0.010 ppm. The method has 

been adequately validated. Also, trinexapac-ethyl was evaluated using the FDA multiresidue 

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. 

2.2.2 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).

2.2.3 Recommended Tolerances

Tolerances should be established for residues of the plant growth regulator trinexpac-ethyl,

including its metabolite and degradate, in or on the commodities listed below. For plant and 

livestock commodities, the tolerances should be established as follows: 

Tolerances are established for residues of trinexapac-ethyl, including its metabolites and 

degradates, in or on the commodities in the table below. Compliance with the tolerance 

levels specified below is to be determined by measuring both trinexapac-ethyl, ethyl 4-

(cyclopropylhydroxymethylene)-3,5-dioxocyclohexanecarboxylate and the associated 

metabolite trinexpac, 4-(cyclopropylhydroxymethylene)-3,5-dioxocyclohexanecarboxylic 

acid, calculated as the stoichiometric equivalent of trinexapac-ethyl. 
Page 9 of 68

Table 2.2.3 Tolerance Summary for Trinexapac-ethyl.

Commodity Proposed Tolerance

(ppm)

Recommended Tolerance

(ppm)

Comment

(correct commodity definitions)

PP# 0F7719

Grass, forage 1.6 1.5

Grass, hay 3.5 4.0

Grass, seed screenings 45.0 40.0

Grass, straw 12.0 10.0

Cattle, fat 0.05 0.02

Cattle, meat 0.05 0.02

Cattle, meat byproducts 0.05 0.04 Based on highest residue in 

cattle kidney

Goat, fat 0.05 0.02

Goat, meat 0.05 0.02

Goat, meat byproducts 0.05 0.04 Based on highest residue in 

cattle kidney

Horse, fat 0.05 0.02

Horse, meat 0.05 0.02

Horse, meat byproducts 0.05 0.04 Based on highest residue in 

cattle kidney

Sheep, fat 0.05 0.02

Sheep, meat 0.05 0.02

Sheep, meat byproducts 0.05 0.04 Based on highest residue in 

cattle kidney

PP# 0F7720

Barley, grain 1.60 2.0

Barley, hay 0.70 0.8

Barley, straw 0.35 0.4

Cattle, kidney 0.05 Not needed Based on the recommended 

tolerance for ―cattle, meat 

byproducts‖ an individual 

tolerance for kidney is not 

needed.

Sugarcane, cane 0.80 0.8

Hog, fat None 0.02

Hog, meat None 0.02

Hog, kidney 0.05 0.03 Hog, meat byproducts

Based on highest residue in 

cattle kidney

Oat, forage 1.00 1.0 Data translated from wheat 

forage

Oat, grain 4.10 4.0 Data translated from wheat 

grain

Oat, hay 1.30 1.5 Data translated from wheat hay

Oat, straw 0.70 0.9 Data translated from wheat 

straw
Page 10 of 68

Table 2.2.3 Tolerance Summary for Trinexapac-ethyl.

Commodity Proposed Tolerance

(ppm)

Recommended Tolerance

(ppm)

Comment

(correct commodity definitions)

Wheat, forage 1.00 1.5

Wheat, grain 4.10 4.0

Wheat, hay 1.30 1.5

Wheat, straw 0.70 0.9

Tolerances that need to be proposed

Wheat middling None 6.5

2.2.4 Revisions to Petitioned-For Tolerances

As noted in Table 2.2.3 many of the proposed tolerances are different from the tolerances being 

recommended by HED. The reason for the differences may be that the Agency imputing the 

mean residue values from each trial site instead of the individual residue values into the OECD 

MRL calculator. Also, HED dietary burden was calculated differently (using the highest residue 

instead of tolerance level residues). The registrant should submit a revised Section F in which 

the proposed tolerances are the same as those recommended by HED.

2.3 Label Recommendations

2.3.1 Recommendations from Residue Reviews

The label must be modified to specify a 30-day plantback restriction for cereal grains and leafy 

vegetables, and prohibit the planting of all other crops not listed on the label.

 

2.3.2 Recommendations from Occupational Assessment

Not all of the current trinexapac-ethyl labels have the proper REIs in place to reflect the acute 

toxicity of trinexapac-ethyl (Toxicity Category III for acute dermal, oral, and primary eye 

irritation, and Category IV for acute inhalation and primary skin irritation). Per the Worker 

Protection Standard (WPS), a 12-hr restricted entry interval (REI) is required for chemicals 

classified under Toxicity Category III/IV. The Registration Division (RD) should ensure the 

proper REIs are put in place on the labels to reflect these requirements.

2.3.3 Recommendations from Residential Assessment

No label revisions are needed for residential purposes and no recommendations are being made 

by HED.
Page 11 of 68

3.0 Ingredient Profile

Trinexapac-ethyl is a new plant growth regulator being proposed by Syngenta Crop Protection 

for use on grasses grown for seed, sugarcane and cereal grains throughout the U.S. Trinexapacethyl inhibits internodal elongation and growth in cereal grains, grasses and several 

dicotyledonous species. 

3.1 Chemical Identity

Table 3.1. Test 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

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). It has a low vapor pressure (2.16 x 10-3PA at 25oC), which decreases 

its potential for inhalation exposure. Trinexapac-ethyl has a low potential to leach into 

OH

O

O

O

O

H3C

O

O

O

HO OH
Page 12 of 68

groundwater and is not expected to be volatile, because of the low vapor pressure (2.16 x 10-3Pa 

at 25oC). See Table 3.2 for a listing of trinexapac-ethyl physical and chemical properties. 

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 10-3Pa

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 Summary of Existing/Proposed Uses

Trinexapac-ethyl is a cyclohexadione plant growth regulator that is marketed as an emulsifiable 

concentrate, wettable powder packed in water-soluble bags, granule, and as a technical chemical 

used for formulation only. The formulations being proposed by Syngenta for use on cereal 

grains (barley, oats, triticale, and wheat), sugarcane, and grasses grown for seed are the 1 lb/gal 

EC (12% ai, PalisadeTM EC; EPA Reg. No. 100-949) and the 2 lb/gal EC (25.5%, Palisade®

2EC; EPA Reg. No. 100-1241). An analysis of the exposures and risk estimates resulting from 

the currently registered uses of trinexapac-ethyl has also been included because significant 

changes have been made to the trinexapac-ethyl hazard assessment. Both EC formulations are 

currently registered for use on perennial ryegrass in the Pacific Northwest. Trinexapac-ethyl also 

has multiple products (e.g., liquids, granules, and wettable powders packed in water soluble 

bags) that are registered for use on turf areas such as sod farms, golf courses, sport fields, and 

cemeteries. The proposed new uses are summarized in Table 3.3.
Page 13 of 68

Table 3.3 Summary of Directions for the Proposed Uses of Trinexapac-Ethyl.

Applic. Timing, 

Type, and Equip.

Form.

[EPA Reg. 

No.]

Applic. 

Rate 

(lb ai/A)

Max. No. 

Applic. 

per 

Season

Max. 

Seasonal 

Applic. Rate

(lb ai/A)

RTI 

(days)

PHI 

(days) Use Directions and Limitations

Grasses grown for seed1

Broadcast foliar 

application

1.0 lb/gal 

EC

[100-949]

2.0 lb/gal 

EC

[100-1241]

0.09-

0.50 1

0.5 7-10 235

For single application, apply 

before or during stem 

elongation stage of 

development (Zadoks 30-37 

or Feekes 5-8). For split 

application, apply the first 

application before or during 

stem elongation stage of 

development (Zadok 30-37 

or Feekes 5-8) followed by a 

second application 7-10 days 

later. Do not allow livestock 

to graze or cut for feed 

within 49 days of the last 

application. Other crops 

may be planted 30 days after 

the last application. Apply 

in a minimum of 5 and 10 

gal/A using aerial and 

ground equipment, 

respectively. 

0.05-

0.25 2

Cereal Grains including Wheat (Winter, Spring, and Durum), Barley (Winter and Spring), Oats, and 

Triticale

Broadcast foliar 

application 

1.0 lb/gal 

EC

[100-949]

2.0 lb/gal 

EC

[100-1241]

0.09-

0.11 1

0.11

NA3

45

Apply at Feekes 5 (leaf 

sheath strongly erect) to 

Feekes growth stage 8 

(ligule of flag leaf visible). 

Apply before the flag leaf 

sheath extends. For barley, 

it is recommended to apply 

before the third node. For 

improved root development, 

apply at Feekes 3-5 (tillers 

formed to leaf sheath 

strongly erect). Apply in a 

minimum of 20 gal/A.

Broadcast foliar 

application 0.05 2 NS3

For split applications, apply 

at Feekes 4-5 (leaf sheaths 

lengthening to leaf sheath 

strongly erect) and then 

again at Feekes 7 (second 

node visible). For barley, 

apply at Feekes 6-7 (1st to 

2

nd nodes visible) and then 

again at 8 (flag leaf just 

visible). Apply in a 

minimum of 20 gal/A.
Page 14 of 68

Table 3.3 Summary of Directions for the Proposed Uses of Trinexapac-Ethyl.

Applic. Timing, 

Type, and Equip.

Form.

[EPA Reg. 

No.]

Applic. 

Rate 

(lb ai/A)

Max. No. 

Applic. 

per 

Season

Max. 

Seasonal 

Applic. Rate

(lb ai/A)

RTI 

(days)

PHI 

(days) Use Directions and Limitations

Sugarcane

Broadcast foliar 

application for 

ripening

1.0 lb/gal 

EC

[100-949]

2.0 lb/gal 

EC

[100-1241]

0.18-

0.31 1

0.31

NA328

Application may be made 

28-60 days prior to harvest 

to increase sugar content 

and/or extend harvest 

window.

Broadcast foliar 

application for 

internode 

shortening for 

seed piece 

production

0.06-0.2 2 NS 3 NS

For split applications, make 

first application when 6 fully 

developed full size leaves 

have appeared. Note the 

bottom leaf should be 

feeding internodes above the 

soil surface. Make a second 

application when 6 

additional fully developed 

full size leaves have 

appeared. 

1 PP#0F7719, Section B for grasses grown for seed specifies that other crops may be planted 30 days after the last 

application. 

2

For split applications, the second application should be made 7-10 days following the first application.

3 NA = Not Applicable; NS = Not Specified

3.4 Anticipated Exposure Pathways

The Registration Division requested that HED perform an assessment of human health risk to 

support the proposed new use of trinexapac-ethyl on cereal grains, sugarcane, turf grass, sod 

farms, golf courses, and residential lawns. Humans might be exposed to trinexapac-ethyl in food 

and drinking water 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. The uses on turf grass result in the potential for 

both residential and occupational exposures. In addition, because of the agricultural uses,

applicators might be exposed while handling the pesticide prior to application, mixing/loading 

the pesticide, and during application. There is a potential for post-application exposure for 

workers re-entering treated fields. 

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 
Page 15 of 68

pesticide exposures that are based on patterns of that subgroup’s food and water consumption, 

and activities in and around the home that involve pesticide use in a residential setting. 

Extensive data on food consumption patterns are compiled by the USDA under the Continuing 

Survey of Food Intake by Individuals (CSFII) and are used in pesticide risk assessments for all 

registered food uses of a pesticide. These data are analyzed and categorized by subgroups based 

on age, season of the year, ethnic group, and region of the country. Additionally, OPP is able to 

assess dietary exposure to smaller, specialized subgroups and exposure assessments are 

performed when conditions or circumstances warrant. Whenever appropriate, 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 Hazard and Dose-Response Characterization

Table A.2.1 (see Appendix A) summarizes the acute toxicity of the technical grade of trinexapacethyl. As demonstrated, technical trinexapac-ethyl is relatively non-toxic when administered 

acutely to laboratory animals. Table A.2.4 (see Appendix A) summarizes the subchronic, 

chronic and other toxicity studies of the technical grade of trinexapac-ethyl.

4.1.1 Database Summary

The toxicology database for trinexapac-ethyl is considered adequate for risk assessment in 

support of the current registration action under FIFRA Section 3 for food use with the exception 

of an acute (in review) and subchronic neurotoxicity studies that are required as part of EPA 

guideline requirements (40 CFR §158). Toxicity studies submitted in support of registration are 

detailed in the following section and a brief summary of the findings is discussed in section 4.3, 

Toxicological Effects.

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

Absorption: Trinexapac-ethyl was rapidly and extensively absorbed in both sexes of rat 

following single or repeat low-dose (0.97 mg/kg bw) administration and single high-dose (166 

mg/kg bw) administration. Greater than 95% of the administered dose was absorbed following 

single or repeat low-dose administration and single high-dose administration. Data suggests that 

there was very little or no biliary absorption. Distribution: The highest residue levels were 

observed in the fat, lungs, kidneys and liver; however, mean recovery of radioactivity in 

tissues/carcass at sacrifice (at 168 h post-dosing) was less than 0.3% of administered dose for all 

dose groups indicating little potential for accumulation. Metabolism: The major component in 
Page 16 of 68

urine and fecal extracts was identified as 4-cyclopropyl- hydroxy-methylene)-3,5-dioxocyclohexanecarboxylic acid, the free acid derivative of trinexapac-ethyl resulting from 

hydrolysis of the ester bond of the parent compound accounting for approximately 82–91.6% of 

the administered dose. The only other residue found (found in fecal extract only) was identified 

as the parent compound, accounting for less than 0.1% of the administered dose. Excretion: 

Excretion was rapid, with the majority of radioactivity being eliminated within 12 h post-dosing 

via urine (greater than 85% of the administered dose at the low and high dose) and within 24 h 

post-dosing via feces (0.56–1.43 and 0.80–2.01% at the low and high dose, respectively). The 

major route of excretion was via urine, accounting for approximately 95% of administered dose 

at both dose levels. Fecal excretion accounted for approximately 1.0–2.4% of administered dose 

at both dose levels. By 72 hr less than 0.01% of the administered dose was recovered in expired 

air. Data suggest that there was very little or no biliary excretion. Significant qualitative 

differences were not found in absorption, distribution, metabolism or excretion of trinexapacethyl between the sexes, between single and repeat low-dose administration, or between single 

low-dose and high-dose administration. These results indicate that toxicity of both the parent 

and acid metabolite has been accounted for in the submitted toxicity studies. 

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. 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 after wash. 

4.3 Toxicological Effects

The acute toxicity of the technical material is low via the oral, dermal, or inhalation routes of 

exposure (Categories III-IV), and it is not a dermal sensitizer. The toxicity profile of trinexapacethyl is attached in Appendix A. With the exception of an acute neurotoxicity (ACN-has been 

submitted) and subchronic neurotoxicity (SCN) required by the new Part 158 guidelines, the 

toxicology database is complete and adequate to support non-food and food uses.

Trinexapac-ethyl is a low acute toxicity chemical with a high acute oral LD50 (oral LD50 = 5,000 

mg/kg) and systemic effects occurring at or well above 300 mg/kg/day in subchronic and lifetime 

dosing studies. There is, however, evidence of increased qualitative and quantitative 

susceptibility in the rat (increased incidence of asymmetrical sternebrae) and rabbit (decreased 

number of live fetuses/litter and increased post-implantation loss) developmental studies, but 

only at relatively high doses (300 – 1,000 mg/kg/day). Qualitative sensitivity was observed in 

the 2-generation reproduction study but only above the limit dose (1,000 mg/kg/day). Decreased 

pup survival when analyzed with sexes combined resulted in statistical significance (5-7%), but 

was not significant when analyzed separately. Further evaluation of the individual litters 
Page 17 of 68

suggested that one or two litters were not the cause of the reduced pup survival at the highest 

dose tested. Reproductive toxicity was not observed up to the limit dose. Refer to Table 4.3.1 

for a comparison of the effects across toxicity studies.

Looking across the available toxicity studies, the dog appears to be the most sensitive species. In 

adult animals, no systemic adverse effects were seen in rats, rabbits, or mice below 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, dose-related neuropathology of the brain 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. They 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. 

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 because trinexapac-ethyl would not be in contact 

with the human tissues for a significant period of time compared to the length of time with which 

it would have been in contact with the rat stomach. Follicular adenocarcinoma of the thyroid 

was significantly increased in males (5%) at 806 mg/kg/day, but 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.‖

Study summaries of the toxicology studies for trinexapac-ethyl are provided in Appendix A.

Table 4.3.1 Comparison of NOAELs/LOAELs for consideration in risk assessment for trinexapacethyl

Study NOAEL 

mg/kg/day

LOAEL

mg/kg/day Endpoint

Rat Developmental

Maternal 1000 >1000 none

Developmental 200 1000

Based on increased incidence of 

asymmetrically-shaped sternebrae 

Rabbit Developmental

Maternal 360 (HDT) >360 none
Page 18 of 68

Developmental 60 360 (HDT)

Based on a decrease in the mean number 

of fetuses/litter and an increase in postimplantation loss

2-Generation Reproduction- Rat

Parental 594 1212

Based on reduced premating and gestation 

body weight/body-weight gain and food 

consumption

Offspring 594 1212

Based on decreased F1 postnatal survival 

and reduced pup body weights in both 

generations [both sexes].

Chronic Dog

Adult males and 

females 31.6 357

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. 

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

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

and residential (turf) exposure to infants and children; however,was not assessed due to lack of 

an appropriate endpoint). 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 toxicological database for 

trinexapac-ethyl is complete with regard to pre-and postnatal toxicity, immunotoxicity and 

neurotoxicity (SCN is required), and there are no residual uncertainties. Additionally, the dietary 

exposure assessment is based on conservative, health-protective 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 is complete with the exception of acute (in review) and subchronic 

neurotoxicity studies (OPPTS 870.6200a and b) which are new data requirements under 40 CFR 

Part 158 for registration of a pesticide (food and non-food uses).

There are no residual uncertainties in the toxicological database and EPA has determined that an 

additional database uncertainty factor for lack of all guideline studies is not needed at this time. 
Page 19 of 68

The rationale is based on the following: 1) although there is evidence of brain neurotoxicity in 

the chronic dog study, there are clear NOAELs/LOAELs for this effect; 2) there is a large dose 

spread in the chronic dog study such that the PoD or NOAEL from the chronic dog study is 10-

fold lower than the dose at which neuropathology is observed and therefore sufficiently 

protective; 3) there are no concerns for children via incidental oral ingestion exposures since no 

endpoint of concern (i.e. non in-utero) was identified in the available studies; and 4) the 

registrant has submitted the acute neurotoxicity study (in review) and is currently conducting the 

subchronic neurotoxicity study. Preliminary review of the ACN showed no signs of 

neurotoxicity at the highest dose tested (NOAEL=2000 mg/kg). 

Currently, an oral toxicity study is being used to assess inhalational exposure. However, with the

oral NOAEL currently used for inhalation risk assessment, all of the occupational and residential 

inhalation MOEs are well above the LOC and the conventional 100X safety factor has been 

applied to inhalation risk assessments. Therefore, even if an inhalation study were to provide a 

lower point of departure than the oral study, it's not expected to have a significant impact on 

aggregate risk.

4.4.2 Evidence of Neurotoxicity and Immunotoxicity

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 

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 reported in the 90-day dog study, although, there was an inconsistency in the 

level of screening of the brain in the 90- day study. It is highly unlikely, however, that lesions 

would develop within a short-term (1-30 days) period of exposure. 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. 

The registrant has submitted the acute neurotoxicity study (in review) and is currently 

conducting the subchronic neurotoxicity study. Preliminary review of the ACN showed no signs 

of neurotoxicity at the highest dose tested (NOAEL=2000 mg/kg). 

An immunotoxicity study (MRID 48444101) in mice was submitted for trinexapac-ethyl. This 

study satisfies the guideline requirement for an immunotoxicity study (OPPTS 870.7800). There 

were no treatment related effects on mortality, clinical observations, body weights, food 

consumption, thymus and spleen weights, or macroscopic findings in the splenic antibodyforming cell (AFC) and the Natural Killer cell (NKC) groups. 
Page 20 of 68

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

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

high doses in the developmental rat and rabbit studies, and 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 at this dose level. 

However, clearly identified no effect levels 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 with only reduced body weight and food consumption observed in 

the parental animals (>1200 mg/kg/day). 

Although, there is evidence of susceptibility in the rat and rabbit developmental studies and 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 (60-593 

mg/kg/day) for each fetal/offspring effect. 

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 that 

the exposure estimates are underestimated. The dietary exposure assessment is based on 

conservative, health-protective 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. 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 database is adequate to characterize any potential for prenatal or postnatal risk for infants 

and children. The details for selecting toxicity endpoints and points of departure are presented in 

Appendix A2. 

4.5.1 Dose-Response Assessment

The acute reference dose (aRfD) is based on the most sensitive acute endpoint observed in the 

database, which are fetal effects observed in the rabbit developmental study. It is, therefore, 

considered protective of all of the developmental effects observed in the rat or rabbit. 
Page 21 of 68

The chronic reference dose (cRfD) is also based on the neuropathy from the chronic dog toxicity 

study. The NOAEL (31.6 mg/kg/day) from this study is more than 10-fold lower than the 

LOAEL (357 mg/kg/day) at which brain vacuolization is observed. Since the point of departure 

for the chronic assessment (31.6 mg/kg/day) is approximately 10-fold lower than the dose levels 

where developmental toxicity was observed in the developmental rabbit study (360 mg/kg/day), 

it is also considered protective for any developmental toxicity. 

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

trinexapac-ethyl toxicity studies. The rationale for 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).

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. 

The short- and intermediate-term dermal and inhalation endpoints selected for adults 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 for 

these scenarios based on the following reasons:

dermal irritation effects are mild after 21/28 days of exposure in the rabbit study,
Page 22 of 68

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, and

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,.

The Toxicological Doses and Endpoints for trinexapac-ethyl are shown on Tables 4.5.4.1 and 

4.5.4.2. The trinexapac-ethyl risk assessment team has recommended that that the FQPA safety 

factor be reduced to 1X (Section 4.4).

4.5.2 Recommendation for Combining Routes of Exposures 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 aggregates 

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

similar durations and routes of exposure. In the case of trinexapac-ethyl, short- and 

intermediate-term dermal and inhalation can be combined since the PoDs are from the same 

study (rabbit developmental) and thus the effects are the same.

4.5.3 Classification of Carcinogenic Potential

Trinexapac-ethyl is classified as ―Not likely to be carcinogenic to humans‖, and therefore, 

quantification of cancer risk is not necessary. The mutagenicity database is considered complete, 

and there was no evidence of mutagenicity. 
Page 23 of 68

4.5.4 Summary of Points of Departure and Toxicity Endpoints Used in Human Risk 

Assessment

Table 4.5.4. 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

Acute 

Dietary

(Females 13-

49 years of 

age)

NOAEL = 60 

mg/kg

UFA= 10x

UFH = 10x

FQPA SF= 

1x

Acute RfD = 

0.6 mg/kg

aPAD = 0.6 

mg/kg

Developmental rabbit study

MRID 41869524

LOAEL = 360 mg/kg, based on a 

decrease in mean number of 

fetuses/litter and an increase in postimplantation loss

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 and 

IntermediateTerm )

No appropriate endpoint for the incidental oral scenario for children
Page 24 of 68

Table 4.5.4. 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 

Intermediateterm (adults 

only)

NOAEL= 60 

mg/kg/day

Dermal 

absorption 

rate = 77.5% 

of oral 

absorption

Inhalation 

absorption 

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 postimplantation loss

Dermal & 

Inhalation

Short- and 

Intermediateterm 

No appropriate endpoint for the dermal and inhalation 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. 

5.0 Dietary Exposure and Risk Assessment 

5.1 Metabolite/Degradate Residue Profile

5.1.1 Summary of Plant and Animal Metabolism Studies
Page 25 of 68

Primary Crops

The nature of the residue in plants (primary and rotational crops) and livestock commodities are 

adequate. The registrant submitted rice, grass and wheat metabolism studies on [1,2,6-

14Ccyclohexyl]trinexapac-ethyl. The major metabolite in rice and grass is metabolite trinexapac, 

CGA 179500. The parent was detected at 2% of the total radioactive residue (TTR). In rice and 

grass, the metabolism of 14C-trinexapac-ethyl rapidly undergoes hydrolysis of the ethyl ester to 

form trinexapac. Also, the tricarboxylic acid metabolite, CGA 275537 was identified at the 4x 

rate in rice (3-17%TRR) at 60 DAT and in grass (9-15% TRR). CGA 275537 has the potential 

for inhibiting the citric acid cycle. 

Rotational Crops 

In field rotation crop studies on lettuce, radish and wheat, the TRR values in all raw agricultural 

commodities (RACs) were low; only 30-day plant-back interval (PBI) lettuce, wheat forage and 

hay samples had TRR >0.01 ppm. No parent trinexapac-ethyl was found as a radiolabeled 

residue in any extracted RAC at any PBI. Trinexapac was found in 30-day PBI wheat forage 

(20%TRR) and wheat hay (9% TRR). The aconitic acid metabolite (CGA 312753) was found 

only in wheat hay at 30-day PBI (18% TRR) and 120-day PBI (11% TRR). The formation of 

aconitic acid, which is an intermediate in the citric acid cycle, results in the incorporation of the 

molecule into natural plant components. 

Livestock

The metabolism of trinexapac-ethyl was investigated in both laying hens and lactating goats. For 

poultry, the major residues were identified as the parent compound trinexapac-ethyl (31% TRR) 

and its metabolite CGA 179500 (20% TRR). In a ruminant metabolism study, trinexapac-ethyl 

was not detected in any goat matrices analyzed. The major 14C-residue in milk and all tissues 

was the acid metabolite, CGA 179500, accounting for 66% of the TRR in liver and 84-97% of 

the TRR in milk and the remaining tissues. The metabolite CGA 113745 was also identified in 

the liver (16% TRR), kidney (6% TRR) and fat (11%), but was not detected in muscle or milk. 

5.1.2 Summary of Environmental Degradation

The major environmental degradates of trinexapac-ethyl include its free acid CGA-179500, 

CGA-313458, an open chain cyclohexane ring, CO2 and an unidentified hydroproduct M3. 

Environmental transport of trinexapac-ethyl can occur through surface water runoff after rain 

events, soil and possible wind erosion and spray drift. Leaching into groundwater is not 

expected to be a major dissipation pathway based on submitted terrestrial field dissipation 

studies which showed that trinexapac-ethyl has a low potential to leach. Surface water runoff 

from the areas of application is assumed to follow topography. Spray drift will follow the wind 

directions. Potential emission of volatile compounds is not considered as a viable release 

mechanism for trinexapac-ethyl, since volatilization is not expected to be a significant route of 

dissipation. 

Considering abiotic degradation, trinexapac-ethyl is stable to hydrolysis in acidic and neutral 

conditions and appears to hydrolyze under basic conditions (t1⁄2 = 8.1 days). Photodegradation 

does not appear to be a major degradation pathway in aqueous and soil environments. The 
Page 26 of 68

aqueous photolysis study shows an environmental phototransformation half-life of about 18 

days. The compound was considered stable in the soil photolysis study since the extrapolated 

half-life was well beyond the duration of the study. 

Biodegradation appears to be the major dissipation pathway for trinexapac-ethyl, specifically 

aerobic biotransformation in terrestrial environments and aerobic and anaerobic 

biotransformation in aquatic environments. Half-lives ranged from 2.8 hours in a loam soil to 

4.3 days in a loamy sand soil in an aerobic soil metabolism study. Half-lives ranged from 2.8 

days in a river water-sand sediment system to 4.0 days in a pond water-sandy clay loam sediment 

system in an aerobic aquatic metabolism study. Half-lives averaged 3.5 days in pond water and 

lake water-sediment systems in an anaerobic aquatic metabolism study. Biodegradation was 

slower under anaerobic soil conditions. The estimated half-life is about 25 days in a sandy loam 

soil.

5.1.3 Comparison of Metabolic Pathways

The metabolism of trinexapac-ethyl in crops, livestock, and rats has been well characterized. 

Major residues identified in plant metabolism and crop field trials include parent trinexapac-ethyl 

and metabolites trinexapac (CGA 179500), aconitic acid metabolite CGA 312753, and 

tricarboxylic acid metabolite CGA 275537. Exposure to trinexapac-ethyl results primarily in 

systemic toxicity in multiple species including rat, rabbit, and dog, as well as thyroid effects in 

dogs. Based on rat metabolism studies, trinexapac-ethyl is rapidly and extensively absorbed 

(>95% of administered doses absorbed), and with little potential for accumulation (>85% 

eliminated w/in 12 hours via urine; 2% via feces w/in 24 hours). The major component in urine 

and fecal extracts was trinexapac, the free acid derivative of trinexapac-ethyl resulting from 

hydrolysis of the ester bond of the parent compound accounting for approximately 82.0–91.6% 

of the administered dose. The only other residue found (found in fecal extract only) was 

identified as the parent compound, accounting for less than 0.1% of the administered dose. 

Significant qualitative differences were not found in absorption, distribution, metabolism or 

excretion of trinexapac-ethyl between the sexes, between single and repeat low-dose 

administration, or between single low-dose and high-dose administration. These results indicate 

that toxicity of both the parent and acid metabolite has been accounted for in the submitted 

toxicity studies.

The proposed metabolic pathways in rats, livestock and plants are common. Trinexpac-ethyl 

involves hydrolysis of the ethyl ester to yield trinexapac (CGA 179500). Trinexapac undergoes 

cleavage of the hexane ring to yield the succinic acid metabolite, CGA 313458, which then 

undergoes stepwise oxidation/ decarboxylation to yield saturated and unsaturated tricarboxylic 

acids, such as CGA 275537 (tricarboxylic acid) and CGA 312753 (aconitic acid). 

For drinking water, a total residue approach was used for the risk assessment. The primary 

degradates that EFED identified were parent, trinexapac (CGA 179500), CGA 313458, the open 

chain cyclohexane ring, and the unidentified hydroproduct M3. See appendix table A.2.5 for the 

structures of these metabolites and degradates.
Page 27 of 68

5.1.4 Residues of Concern Summary and Rationale

For plants (primary and rotational crops) and livestock commodities, the HED recommends that 

parent trinexapac-ethyl and the metabolite trinexapac (CGA 179500) be the residues of concern 

for both the tolerance expression and the risk assessment. For drinking water, a total residue 

approach should be used for the risk assessment. See Table 5.1.4 for the summary of metabolites 

and degradates to be included in the risk assessment.

Table 5.1.4. Summary of Metabolites and Degradates to be included in the Risk Assessment 

and Tolerance Expression.

Matrix Residues included in Risk Assessment Residues included in Tolerance 

Expression 

Plants Primary Crop Trinexapac-ethyl parent + Trinexapac 

metabolite (CGA 179500)

Trinexapac-ethyl parent + Trinexapac 

metabolite (CGA 179500)

Rotational Crop Trinexapac-ethyl parent + Trinexapac 

metabolite (CGA 179500)

Trinexapac-ethyl parent + Trinexapac 

metabolite (CGA 179500)

Livestock Ruminant Trinexapac-ethyl parent + Trinexapac 

metabolite (CGA 179500)

Trinexapac-ethyl parent + Trinexapac 

metabolite (CGA 179500)

Poultry Trinexapac-ethyl parent + Trinexapac 

metabolite (CGA 179500)

Trinexapac-ethyl parent + Trinexapac 

metabolite (CGA 179500)

Drinking Water Total residues (parent + identified 

degradates)1

Not Applicable

1 A total major residue approach is recommended, including parent and major environmental degradates CGA179500, CGA-313458, the open chain cyclohexane ring, and the unidentified hydroproduct M3. 

5.2 Food Residue Profile

The registrant submitted adequate field trial data from trials comparing trinexapac-ethyl as 

trinexapac (CGA179500) residues in/on barley, wheat, sugarcane and grass grown for seed 

following application of an EC formulation containing 2.1 lb ai/gal. Each field trial included 

one treated plot in which trinexapac-ethyl was applied to barley, wheat and sugarcane as a foliar 

spray application at a target rate of 0.115 lb ai/A and grass grown for seed at 0.5 lb ai/A (~1x the 

proposed maximum seasonal rate). The recommended MRLs ranged from 0.4 ppm in barley 

straw to 40.0 ppm in grass seeds. In the residue decline studies, residues declined from the initial 

to the final sampling. For all field grown crops, adequate numbers of trials were performed in 

the recommended NAFTA growing zones. Table 5.2 provides a summary of the crop field trials 

that were performed for trinexapac-ethyl.

The submitted confined rotational crop study is adequate to satisfy data requirements. TRR 

values in all RACs were low; only 30-day PBI lettuce, wheat forage and wheat hay samples had 

TRR >0.01 ppm. The maximum TRR was 0.017 ppm (30-day PBI mature lettuce). No parent 

trinexapac-ethyl was found as a radiolabeled residue in any extracted RAC at any PBI. The 

submitted confined rotational crop study is adequate to satisfy data requirements. TRR values in 

all RACs were low; only 30-day PBI lettuce, wheat forage and wheat hay samples had TRR 

>0.01 ppm. The maximum TRR was 0.017 ppm (30-day PBI mature lettuce). The data from the 
Page 28 of 68

confined rotational crop study indicate that trinexapac residues were greater than 0.01 ppm and 

were detected at the 30-day PBI. Therefore, the label must be modified to specify a 30-day 

plantback restriction for cereal grains and leafy vegetables, and prohibit the planting of all other 

crops not listed on the label.

In the processing studies that were performed, residues concentrated in some commodities but 

not in others. These data suggest that a tolerance is needed for wheat middling at 6.5 ppm. 

Freezer storage stability data are available which demonstrate that residues of trinexapac are 

stable under frozen storage conditions for up to 24 months for wheat grain, 12 months for wheat 

straw, and up to 9 months in grass. To support the sample storage durations in the dairy cattle 

feeding study, samples were stored frozen (≤ -18oC) for up to 121 days and then analyzed with 

freshly fortified samples. To support the sample storage durations in the poultry feeding study, 

samples were stored frozen (-20°C) and then analyzed at 0 and 31-82 days with freshly fortified 

samples.

The residue data from the cattle feeding study are adequate to satisfy data requirements. HED 

concludes that the following tolerances are appropriate for the free and conjugated residues of 

both parent and its acid metabolite, trinexapac in livestock commodities: 0.02 ppm for the fat 

and meat of cattle, goat, horse, and sheep; 0.04 ppm for the meat byproduct of cattle, goat, horse, 

and sheep; and 0.02 ppm for the fat and meat of hog; 0.03 ppm for the meat byproduct of hog.

The trinexapac residue data from the poultry feeding study is adequate to satisfy data 

requirements. Based on the transfer coefficients for hen tissues and the relatively low dietary 

burden for poultry of 3.00 ppm for trinexapac, no tolerances are needed for poultry. Although 

secondary residues occur in poultry kidney, no tolerance is required since poultry kidney is not 

considered a commodity used as human food [OPPTS 860.1480(d)(4)(iv)]. 

Table 5.2. Summary of Residue Data from Crop Field Trials with Trinexapac-ethyl

Commodity Analyte

Total Applic. 

Rate

(lb ai/A)

PHI 

(days)

Residue Levels (ppm) 1

n Min. Max. HAFT Mean Std.

Dev.

Barley (proposed use = 0.11 lb ai/A total application rate, 45-day PHI)

Barley, hay CGA179500 0.113-0.119 30 24 <0.01 0.54 0.48 0.19 0.1

Barley, straw CGA179500 0.114-0.120 45 24 <0.01 0.29 0.24 0.11 0.1

Barley, grain CGA179500 0.114-0.120 45 24 <0.01 1.3 1.2 0.59 0.3

Wheat (proposed use = 0.11 lb ai/A total application rate, 45-day PHI)

Wheat, forage CGA179500 0.114-0.120 30 40 <0.01 0.98 0.94 0.16 0.2

Wheat, hay CGA179500 0.114-0.120 30 39 <0.01 1.3 1.2 0.27 0.3

Wheat, straw CGA179500 0.113-0.120 45 40 <0.01 0.64 0.60 0.19 0.2

Wheat, grain CGA179500 0.113-0.120 45 3930.07 4.0 3.3 0.73 0.7

Sugarcane (proposed use = 0.31 lb ai/A total application rate, 28-day PHI)

Sugarcane CGA179500 0.313-0.341 28 16 <0.01 0.43 0.41 0.16 0.1

Grass grown for seed (proposed use = 0.5 lb ai/A total application rate, 35-day PHI for mature grass and 49-day PHI for 

regrowth of forage and hay following harvest)

Grass, forage CGA179500 0.505-0.537 49 24 0.031 1.2 0.88 0.24 0.3

Grass, hay CGA179500 0.505-0.537 49 22 0.10 3.4 2.6 0.65 0.8

Grass, straw CGA179500 0.505-0.537 35 24 0.19 5.7 5.4 2.0 2

Grass, seed 

screenings CGA179500 0.505-0.537 35 22 0.32 20.0 18.3 6.5 7
Page 29 of 68

1 The LOQ is 0.010 ppm.

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: ―Tier II 

Drinking Water Assessment for Trinexapac-Ethyl use on Turf‖ (C. Koper, D395601, 10/28/11) 

and incorporated directly into the dietary assessment. 

Based on the ROCKS memorandum (D390121, 7/12/11), the parent ester including its free 

acid CGA-179500, CGA-313458, an open chain cyclohexane ring and an unidentified 

hydroproduct M3 should be included in a TTR approach for the drinking water assessment. 

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

all sources‖ and ―water, indirect, all sources.‖ A Tier II screening-level drinking water 

assessment was conducted to support the human health risk assessment for the proposed first 

food use registration for trinexapac-ethyl. The recommended estimated drinking water 

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

value for surface water and groundwater (see Table 5.3). The recommended EDWCs in 

surface water and ground water are based on 8 applications of 0.34 lbs. a.i./acre/year on 

Pennsylvania turf. For surface water, a foliar ground application to Pennsylvania turf yielded 

the highest EDWCs. The 1-in-10 yr annual peak (acute) concentration was 12.61 μg/L, the 1-

in-10 yr annual mean (chronic) concentration was 1.56 μg/L and the 30-year annual mean 

(cancer chronic) concentration was 1.04 μg/L. For groundwater, based on the proposed highest 

annual use rate for turf, the SCI-GROW model estimated the trinexapac ethyl concentration at 

0.009 μg/L. 

 

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. Trinexapac-Ethyl Estimated Drinking Water Concentrations (EDWCs)1for 

Surface Water and Ground Water based on selected Crop Scenarios

Proposed

Label Use

PRZM/EXAMS

Scenario1

(first app date)

Method2

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)

Primo® WSB

Surface Water

Turf 

FL Turf

(Feb 15 – foliar) G 8 app @ 0.34 lb a.i./acre 10.16 1.22 0.84

PA Turf

(April 15 – foliar) G 8 app @ 0.34 lb a.i./acre 12.61 1.56 1.04

Ground Water

SCIGROW Turf -- 8 app @ 0.34 lb a.i./acre 0.009 0.009 0.009
Page 30 of 68

Table 5.3. Trinexapac-Ethyl Estimated Drinking Water Concentrations (EDWCs)1for 

Surface Water and Ground Water based on selected Crop Scenarios

Proposed

Label Use

PRZM/EXAMS

Scenario1

(first app date)

Method2

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)

1 For surface water (PRZM/EXAMS), EDWC values adjusted with a Percent Cropped Area (PCA) factor of 1.0. For 

ground water (SCI-GROW), no PCA adjustment was utilized. 

2 G = ground application.

Bold numbers denote maximum EDWC values. 

5.4 Dietary Risk Assessment

5.4.1 Description of Residue Data Used in Dietary Assessment

Acute and chronic aggregate dietary (food and drinking water) exposure and risk assessments 

were conducted using the Dietary Exposure Evaluation Model DEEM-FCIDTM, Version 2.03 

which uses food consumption data from the U.S. Department of Agriculture’s (USDA’s) 

Continuing Surveys of Food Intakes by Individuals (CSFII) from 1994-1996 and 1998.

The acute and chronic analyses are based on tolerance-level residues, 100% crop treated 

assumptions for all commodities and default processing factors. The drinking water estimates 

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

model available for the proposed crops. HED is confident that the acute and chronic dietary 

exposure assessments significantly overestimate risk to the general U.S. population and various

population subgroups.

5.4.2 Percent Crop Treated Used in Dietary Assessment

As stated above, the acute and chronic assessments were both based on the assumption that 

100% of all commodities with trinexapac-ethyl recommended tolerances will be treated.

5.4.3 Acute Dietary Risk Assessment

The acute dietary exposure was estimated for females 13-49 years old only, since an acute 

endpoint of concern was not identified for the general U.S. population. The acute dietary 

exposure estimate for females 13-49 years old is 0.014348 mg/kg/day (2% of the acute 

population adjusted dose (aPAD)).

5.4.4 Chronic Dietary Risk Assessment

The chronic dietary exposure and risk estimates are conservative since they assume that 100% of 

crops are treated and that the residues are present at the recommended tolerance levels. 

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 0.007884 

mg/kg/day for the general U.S. population, which is equivalent to 2.5% of the chronic population 

adjusted dose (cPAD), and 0.019496 mg/kg/day, equivalent to 6% of the cPAD for children 1-2 
Page 31 of 68

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

trinexapac-ethyl. Results for all population subgroup are summarized in Table 5.4.6, below.

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

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

Trinexapac-ethyl.

Population Subgroup

Acute Dietary1

(95th% Percentile) Chronic Dietary

Dietary 

Exposure 

(mg/kg/day)

% aPAD

Dietary 

Exposure

(mg/kg/day)

% cPAD

General U.S. Population 0.007884 2.5

All Infants (< 1 year old) 0.005505 2

Children 1-2 years old 0.019496 6

Children 3-5 years old 0.019289 6

Children 6-12 years old 0.013202 4

Youth 13-19 years old 0.007655 2

Adults 20-49 years old 0.006283 2

Adults 50+ years old 0.005236 2

Females 13-49 years old1

0.014348 2 0.005895 2

1

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

including infants and children) and cPAD=0.32 mg/kg/day.

Not likely to be Carcinogenic to Humans 

6.0 Residential (Non-Occupational) Exposure/Risk Characterization

Trinexapac-ethyl is currently registered (e.g., liquids, granules, and wettable powders packed in 

water soluble bags) for use on residential lawns, athletic fields, parks, and golf courses by 

residential consumers as well as applied by pest control operators (PCOs) and commercial 

applicators. Based on these uses, residential handler and residential post-application exposure is 
Page 32 of 68

expected. HED assumes that only short-term exposures are applicable to residential handler risk 

assessments, and are considered to be protective of intermediate-term exposure and risk. The 

details regarding the assumptions and calculations used to evaluate residential exposure and risk 

are described in a separate memo (M. Hawkins, DP392798, 8/31/11). 

6.1 Handlers

All handler scenarios resulted in MOEs that do not exceed HED’s level of concern (i.e., MOEs ≥ 

100). 

Table 6.1.a. Short-Term Residential Handler Baseline Dermal and Inhalation Exposures 

Crop 

Grouping

Target 

MOE

Dermal 

Unit 

Exposure 

(mg/lb ai)

Inhalation 

Unit 

Exposure 

(mg/lb ai) Application 

Ratea

(lb ai/A)

Area 

Treated 

Dailyb

(acres/day)

Baseline Baseline Inhalation Total

Baseline Baseline

Dermal 

Dosec

(mg/kg/day)

Dermal 

MOEd Dosee MOEf

Baseline 

Dermal + 

Baseline 

Inhalation 

MOEg

Mixer/Loader/Applicator (Liquids) - Low Pressure Handwand Application

Turf 100 100 0.03 0.34 0.023 0.01 5800 0.0000039 15000000 5800

Mixer/Loader/Applicator (Wettable Powders) - Low Pressure Handwand Application

Turf 100 250 1.063 0.34 0.023 0.026 2300 0.00014 430000 2300

Mixer/Loader/Applicator (Liquids) - Hose End Sprayer Application

Turf 100 11 0.017 0.34 0.5 0.025 2400 0.000048 1200000 2400

Mixer/Loader/Applicator (Liquids) - Backpack Sprayer Application

Turf 100 5.1 0.03 0.34 0.023 0.00053 110000 0.0000039 15000000 110000

Mixer/Loader/Applicator (Granules) - Push Type Spreader Application

Turf 100 0.67 0.00088 0.44 0.5 0.002 31000 0.0000032 19000000 30000

Mixer/Loader/Applicator (Granules) - Belly Grinder Application

Turf 100 110 0.062 0.44 0.023 0.015 4000 0.00001 5700000 4000

a. Application rates based on proposed labels. 

b. Based on HED Science Advisory Committee Policy 12: Recommended Revisions to the Standard Operating Procedures for Residential

Exposure Assessment (February 22, 2001), and on professional judgment.

c. Dermal Dose (mg/kg/day) = daily unit exposure (mg/lb ai) x application rate (lb ai/acre or lb ai/gal) x acres or gal treated x 75.5% dermal 

absorption / body weight (60 kg).

d. Inhalation Dose (mg/kg/day) daily unit exposure (μg/lb ai) x application rate (lb ai/acre or lb ai/gal) x acres or gal treated x 100% 

inhalation absorption / body weight (60 kg). 

e. Dermal MOE = NOAEL (60 mg/kg/day) / dermal daily dose (mg/kg/day). Level of concern = 100.

f. Inhalation MOE = NOAEL (60 mg/kg/day) / inhalation daily dose (mg/kg/day). Level of concern = 100.

g. Combined Dermal + Inhalation MOE = NOAEL (60 mg/kg/day) / Combined dermal + inhalation dose (mg/kg/day).

6.2 Post-application Exposure

Based on the SOPs for Residential Exposure Assessment and the uses specified in the proposed 

labels, the following residential post-application exposure scenarios are evaluated:
Page 33 of 68

Dermal dose from pesticide residues on treated turf: Post-application exposure 

calculations for homeowners (adults only) from skin contact with pesticide residues on 

treated turf. 

Short-term dermal risk estimates were assessed for adults. The residential post-application 

MOEs ranged from 650 to 24,000 and therefore do not exceed HED’s level of concern (MOE ≥ 

100). 

Table 6.1.a. Short- Term Residential Postapplication Exposure and Risk Estimates for 

Trinexapac-ethyl (Liquids)

Lifestage Postapplication Exposure Scenario Application 

Rate Dosea MOEsb

Adult Turf - sprays

High Contact 

Lawn Activities 

(Dermal)

0.34 0.071 840

Golfing 

(Dermal) 0.17 0.0025 24,000

Mowing 

(Dermal) 0.34 0.0025 24,000

a=Turf Transferable Residue x Weight Unit Conversion Factor x Transfer Coefficient x Exposure 

Time x 0.775/60 (kg)

b=NOAEL (60 mg/kg/day)/Average Daily Dose (mg/kg/day)

Table 6.1.b. Short-Term Residential Postapplication Exposure and Risk Estimates for 

Trinexapac-ethyl (Granular Formulations)

Lifestage Postapplication Exposure Scenario Application 

Rate Dosea MOEsb

Adult Turf - granules

High Contact Lawn 

Activities (Dermal) 0.44 0.092 650

Golfing (Dermal) 0.17 0.0025 24,000

Mowing (Dermal) 0.44 0.0032 19,000

a=Turf Transferable Residue x 6

Weight Unit Conversion Factor x Transfer Coefficient x Exposure Time x 0.775/60 (kg)

b=NOAEL (60 mg/kg/day)/Average Daily Dose (mg/kg/day)

6.2.2 Inhalation Post-application Exposure

Based on the Agency's current practices, a quantitative post-application inhalation exposure 

assessment was not performed for trinexapac-ethyl at this time primarily because of the low 

acute inhalation toxicity (Toxicity Category IV). However, volatilization of pesticides may be a 
Page 34 of 68

potential source of post-application inhalation exposure to individuals nearby to pesticide 

applications. The Agency sought expert advice and input on issues related to volatilization of 

pesticides from its Federal Insecticide, Fungicide, and Rodenticide Act Scientific Advisory Panel 

(SAP) in December 2009. The Agency received the SAP’s final report on March 2, 2010 

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

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

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

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

Agency may revisit the need for a quantitative post-application inhalation exposure assessment 

for trinexapac-ethyl.

6.2.3 Spray Drift

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

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

potential source of exposure from the ground application method employed for trinexapac-ethyl. 

The Agency has been working with the Spray Drift Task Force, 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 at 

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

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

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

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

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

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

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

management practices to reduce off-target drift and risks associated with aerial as well as other 

application types where appropriate. 

Although a quantitative residential post-application inhalation exposure assessment was not 

performed as a result of pesticide drift from neighboring treated agricultural fields, an inhalation 

exposure assessment was performed for occupational flaggers. This exposure scenario is 

representative of a worse case inhalation (drift) exposure and may be considered protective of 

most outdoor agricultural and commercial post-application inhalation exposure scenarios. 

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.
Page 35 of 68

7.1 Acute Aggregate Risk

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

acute dietary exposure analysis 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. 

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 chronic dietary exposure from food and 

water which is considered to be background exposure. The levels of concern 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 postapplication exposure estimate. To be health protective, the 

postapplication scenario was used in the aggregate because it resulted in higher exposure than the 

handler scenario. The chronic dietary exposure estimate for the general U.S. population was 

used to determine the aggregate risk estimate.

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

is added directly to the adult postapplication dermal exposure estimates. The results of the 

adult’s aggregate risk determinations are given in Table 7.2.a. 

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

Population

Short- or Intermediate-Term Scenario

NOAEL 

mg/kg/day LOC1

Average 

Food and 

Water 

Exposure 

mg/kg/day

Residential

Postapplication 

Dermal Exposure 

mg/kg/day3

Total 

Exposure 

mg/kg/day4

Aggregate 

MOE (food, 

water, and 

residential)5

U.S. Pop 60 100 0.007884 Liquid 

Products6 0.071 0.078884 761

U.S. Pop 60 100 0.007884 Granular 

Products7 0.092 0.099884 601

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/LOC

3 Residential Exposure = Dermal exposure from treated turf (see table 6.1.a). 

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

5 Residential Exposure)]
Page 36 of 68

6

See Table 6.1.a

7

See Table 6.1.b

7.3 Cancer Aggregate Risk

The chronic aggregate risk assessment results from long-term exposure to residues in food and 

drinking water, as there are no residential scenarios that result in long-term exposure. The 

chronic dietary exposure analysis included both food and drinking water and, therefore, the 

chronic aggregate risk assessment is equivalent to the chronic dietary risk assessment discussed 

in Section 5.4.4 above. All risk estimates are below HED’s level of concern.

7.4 Cancer Aggregate Risk

The CARC classified trinexapac-ethyl as ―not likely to be carcinogenic to humans.‖ The chronic 

dietary risk assessment is protective of cancer effects and, therefore, cancer risk resulting from 

exposure to trinexapac-ethyl is not of concern.

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 Handlers

An analysis of the exposures and risk estimates resulting from the currently registered uses of 

trinexapac-ethyl has also been included because significant changes have been made to the 

trinexapac-ethyl hazard assessment since the last trinexapac-ethyl assessment was completed by 

the HED. Based upon the proposed trinexapac-ethyl use patterns, HED assessed risks to 

occupational pesticide handlers in the following scenarios:
Page 37 of 68

Mixing/loading liquids for aerial applications

Mixing/loading liquids for groundboom applications

Mixing/loading liquids for chemigation

Mixing/loading liquids for LCO handgun applications

Mixing/loading wettable powders in water soluble bags for aerial applications

Mixing/loading wettable powders in water soluble bags for chemigation

Mixing/loading wettable powders in water soluble bags for groundboom applications

Mixing/loading wettable powders in water soluble bags for LCO handgun applications

Mixing/loading granules for aerial applications

Mixing/loading granules for tractor drawn spreader applications

Applying sprays for aerial applications

Applying sprays for groundboom equipment

Applying granules for tractor drawn spreader applications

Flagging (liquids) during aerial applications

Flagging (granules) during aerial applications

Mixing/loading/applying wettable powders for low pressure handwand applications

Mixing/loading/applying liquids for backpack sprayer applications

Mixing/loading/applying liquids for handgun sprayer applications

Mixing/loading/applying liquids for low pressure handwand applications

Mixing/loading/applying wettable powders in water soluble bags for backpack sprayer 

applications

Mixing/loading/applying water soluble bags for handgun sprayer applications

Mixing/loading/applying granules for belly grinder applications

Mixing/loading/applying granules for push type spreader applications

No chemical-specific handler exposure data were submitted in support of the Section 3 

registration. To assess handler exposures for regulatory actions when chemical-specific 

monitoring data are not available, HED relies on the most scientifically-reliable surrogate data 

currently available from various sources such as the Pesticide Handler Exposure Database 

(PHED), the Agricultural Handler Exposure Task Force (AHETF), and the Outdoor Residential 

Exposure Task Force (ORETF). Some of this data, such as the industry task force data, is 

compensatory, subject to the data protection provisions of the Federal Insecticide, Fungicide, and 

Rodenticide Act (FIFRA). HED policy on use of surrogate data is described in more detail on 

the Agency's website (http://www.epa.gov/pesticides/science/handler-exposure-data.html). 

Scenario-specific surrogate exposure data, including their sources, are presented in the 

―Occupational Pesticide Handler Unit Exposure Surrogate Reference Table‖ 

(http://www.epa.gov/pesticides/science/handler-exposure-table.pdf). 

Handlers’ Exposure and Risk

Short-term and intermediate-term risk estimates for occupational handlers are included in Table 

9.1.a. All handler scenarios resulted in MOEs greater than the LOC (MOEs ≥ 100) for dermal, 

inhalation, and combined dermal and inhalation exposures when wearing labeled PPE (long-
Page 38 of 68

sleeve shirt, long pants, shoes, socks, chemical-resistant gloves, and protective eyewear) and, 

therefore are not of concern.

The handler exposure estimates in this assessment are based on a central tendency estimate of 

unit exposure and an upper-percentile assumption for the application rate, and are assumed to be 

representative of high-end exposures. The uncertainties associated with this assessment stem 

from the use of surrogate exposure data (e.g., differences in use scenario and data confidence), 

and assumptions regarding the amount of chemical handled. The estimated exposures are 

believed to reasonable high-end estimates based on observations from field studies and 

professional judgment.
Page 39 of 68

Table 9.1.a. Short-Term and Intermediate-Term Occupational Handler Dermal and Inhalation Exposures 

Crop Grouping Target MOE

Dermal Unit 

Exposure 

(mg/lb ai)

Inhalation Unit 

Exposure

(mg/lb ai)

Application 

Ratea

Area Treated 

Dailyb PPE-G Baseline Inhalation Total

PPE-G Baseline (lb ai/A) (acres/day) Dermal Dosec

(mg/kg/day)

Dermal 

MOEd Dosee MOEf MOEg

Mixer/Loader (Liquids) - Aerial Application

Grasses Grown for Seed 100 0.0376 0.000219 0.5 350 0.085 710 0.00064 94000 700

Sod 100 0.0376 0.000219 0.34 350 0.058 1000 0.00043 140000 1000

Sugarcane 100 0.0376 0.000219 0.31 350 0.053 1100 0.0004 150000 1100

Cereals 100 0.0376 0.000219 0.11 350 0.019 3200 0.00014 430000 3200

Mixer/Loader (Liquids)- Groundboom Application

Grasses Grown for Seed 100 0.0376 0.000219 0.5 80 0.019 3100 0.00015 410000 3100

Sod 100 0.0376 0.000219 0.34 80 0.013 4500 0.000099 600000 4500

Sugarcane 100 0.0376 0.000219 0.31 80 0.012 5000 0.000091 660000 4900

Golf Course 100 0.0376 0.000219 0.17 40 0.0033 18000 0.000025 2400000 18000

Cereals 100 0.0376 0.000219 0.11 80 0.0043 14000 0.000032 1900000 14000

Mixer/Loader (Liquids)- Chemigation

Grasses Grown for Seed 100 0.0376 0.000219 0.5 350 0.085 710 0.00064 94000 700

Sod 100 0.0376 0.000219 0.34 350 0.058 1000 0.00043 140000 1000

Sugarcane 100 0.0376 0.000219 0.31 350 0.053 1100 0.0004 150000 1100

Cereals 100 0.0376 0.000219 0.11 350 0.019 3200 0.00014 430000 3200

Mixer/Loader (Liquids)- LCO Handgun Application

Turf 100 0.0376 0.000219 0.34 100 0.017 3600 0.00012 480000 3600

Mixer/Loader(Wettable Powders in Water Soluble Bags) (Engineering Controls) - Aerial Application

Sod 100 0.0098 0.00024 0.34 350 0.015 4000 0.00048 130000 600

Mixer/Loader (Wettable Powders in Water Soluble Bags) (Engineering Controls)- Chemigation

Sod 100 0.0098 0.00024 0.34 350 0.015 4000 0.00048 130000 600

Mixer/Loader (Wettable Powders in Water Soluble Bags) (Engineering Controls) - Groundboom Application

Sod 100 0.0098 0.00024 0.34 80 0.0034 17000 0.00011 550000 2600

Golf Course 100 0.0098 0.00024 0.17 40 0.00086 70000 0.000027 2200000 10000
Page 40 of 68

Table 9.1.a. Short-Term and Intermediate-Term Occupational Handler Dermal and Inhalation Exposures 

Crop Grouping Target MOE

Dermal Unit 

Exposure 

(mg/lb ai)

Inhalation Unit 

Exposure

(mg/lb ai)

Application 

Ratea

Area Treated 

Dailyb PPE-G Baseline Inhalation Total

PPE-G Baseline (lb ai/A) (acres/day) Dermal Dosec

(mg/kg/day)

Dermal 

MOEd Dosee MOEf MOEg

Mixer/Loader (Wettable Powders in Water Soluble Bags) (Engineering Controls) - LCO Handgun Application

Turf 100 0.0098 0.00024 0.34 100 0.0043 14000 0.00014 440000 2100

Mixer/Loader (Granules) - Aerial Application

Sod 100 0.0069 0.0017 0.44 350 0.014 4400 0.0044 14000 3300

Mixer/Loader (Granules ) - Tractor Drawn Spreader Applications

Sod 100 0.0069 0.0017 0.44 80 0.0031 19000 0.001 60000 15000

Golf Course 100 0.0069 0.0017 0.17 40 0.00061 99000 0.00019 310000 75000

Applicator (Sprays)- Aerial

Grasses Grown for Seed 100 -- -- 0.5 350 -- -- -- ----

Sod 100 -- -- 0.34 350 -- -- -- -- --

Sugarcane 100 -- -- 0.31 350 -- -- -- ----

Cereals 100 -- -- 0.11 350 -- -- -- ----

Applicator (Sprays)- Groundboom Equipment

Grasses Grown for Seed 100 0.0161 0.00034 0.5 80 0.0083 7200 0.00023 260000 7000

Sod 100 0.0161 0.00034 0.34 80 0.0057 11000 0.00015 390000 10000

Sugarcane 100 0.0161 0.00034 0.31 80 0.0052 12000 0.00014 430000 11000

Golf Course 100 0.0161 0.00034 0.17 40 0.0014 42000 0.000039 1600000 41000

Cereals 100 0.0161 0.00034 0.11 80 0.0018 33000 0.00005 1200000 32000

Applicator (Granules) - Tractor Drawn Spreader Applications

Sod 100 0.0072 0.0012 0.44 80 0.0033 18000 0.0007 85000 15000

Golf Course 100 0.0072 0.0012 0.17 40 0.00063 95000 0.00014 440000 78000

Flagger (Liquids)- Aerial Spray Application

Grasses Grown for Seed 100 -- 0.00035 0.5 350 -- -- 0.001 59000 --

Sod 100 --0.00035 0.34 350 -- -- 0.00069 86000 --

Sugarcane 100 -- 0.00035 0.31 350 -- -- 0.00063 95000 --

Cereals 100 -- 0.00035 0.11 350 -- -- 0.00022 270000 --
Page 41 of 68

Table 9.1.a. Short-Term and Intermediate-Term Occupational Handler Dermal and Inhalation Exposures 

Crop Grouping Target MOE

Dermal Unit 

Exposure 

(mg/lb ai)

Inhalation Unit 

Exposure

(mg/lb ai)

Application 

Ratea

Area Treated 

Dailyb PPE-G Baseline Inhalation Total

PPE-G Baseline (lb ai/A) (acres/day) Dermal Dosec

(mg/kg/day)

Dermal 

MOEd Dosee MOEf MOEg

Flagger (Granules) - Aerial Application

Sod 100

-- 0.00015 0.44 350 -- -- 0.00039 160000 --

Mixer/Loader/Applicator (Wettable Powders in Water Soluble Bags) (Engineering Controls) - Low Pressure Handwand Application

Edging/Banding 100

-- -- 0.68 0.023 -- -- -- -- --

Turf 100

-- -- 0.34 0.023 -- -- -- -- --

Golf Course 100

-- -- 0.17 0.023 -- -- -- -- --

Mixer/Loader/Applicator (Liquids) - Backpack Sprayer Application

Edging/Banding 100 2.5 0.03 0.68 0.023 0.00051 120000 0.0000078 7700000 120000

Turf 100 2.5 0.03 0.34 0.023 0.00025 240000 0.0000039 15000000 230000

Golf Course 100 2.5 0.03 0.17 0.023 0.00013 480000 0.000002 31000000 470000

Mixer/Loader/Applicator (Liquids) - Handgun Sprayer Application

Turf 100 0.45 0.0015 0.34 5 0.0099 6100 0.000043 1400000 6000

Golf Course 100 0.45 0.0015 0.17 5 0.0049 12000 0.000021 2800000 12000

Mixer/Loader/Applicator (Liquids) - Low Pressure Handwand Applications

Edging/Banding 100 0.33 0.0027 0.68 0.023 0.000067 900000 0.0000007 85000000 890000

Turf 100 0.33 0.0027 0.34 0.023 0.000033 1800000 0.00000035 170000000 1800000

Golf Course 100 0.33 0.0027 0.17 0.023 0.000017 3600000 0.00000018 340000000 3600000

Mixer/Loader/Applicator (Wettable Powders in Water Soluble Bags) (Engineering Controls) - Backpack Sprayer Application

Edging/Banding 100

-- -- 0.68 0.023 -- -- -- -- --

Turf 100

-- -- 0.34 0.023 -- -- -- -- --

Golf Course 100

-- -- 0.17 0.023 -- -- -- -- --

Mixer/Loader/Applicator (Wettable Powders in Water Soluble Bags) (Engineering Controls) - Handgun Sprayer Application

Turf 100

-- -- 0.34 5 -- -- -- -- --

Golf Course 100

-- -- 0.17 5 -- -- -- -- --

Mixer/Loader/Applicator (Granules) - Belly Grinder Application

Edging/Banding 100 9.3 0.062 0.88 0.023 0.0024 25000 0.000021 2900000 24000
Page 42 of 68

Table 9.1.a. Short-Term and Intermediate-Term Occupational Handler Dermal and Inhalation Exposures 

Crop Grouping Target MOE

Dermal Unit 

Exposure 

(mg/lb ai)

Inhalation Unit 

Exposure

(mg/lb ai)

Application 

Ratea

Area Treated 

Dailyb PPE-G Baseline Inhalation Total

PPE-G Baseline (lb ai/A) (acres/day) Dermal Dosec

(mg/kg/day)

Dermal 

MOEd Dosee MOEf MOEg

Turf 100 9.3 0.062 0.44 0.023 0.0012 49000 0.00001 5700000 49000

Golf Course 100 9.3 0.062 0.17 0.023 0.00047 130000 0.000004 15000000 130000

Mixer/Loader/Applicator (Granules) - Push Type Spreader Application

Turf 100 0.22 0.0073 0.44 0.5 0.0063 9600 0.00027 220000 9200

Golf Course 100 0.22 0.0073 0.17 0.5 0.0024 25000 0.0001 580000 24000

a. Application Rates based on proposed labels.

b. Science Advisory Council Policy No. 9.1

c. Dermal Dose (mg/kg/day) = daily unit exposure (mg/lb ai) x dermal absorption (75.5%) application rate (lb ai/acre or lb ai/gal) x acres or gallons treated / body weight (60 kg).

d. Dermal MOE = NOAEL (60 mg/kg/day) / dermal daily dose (mg/kg/day). Level of concern = 100.

e. Inhalation Dose (mg/kg/day) daily unit exposure (μg/lb ai) x application rate (lb ai/acre or lb ai/gal) x acres treated or gallons treated / body weight (60 kg). 

f. Inhalation MOE = NOAEL (60 mg/kg/day) / inhalation daily dose (mg/kg/day). Level of concern = 100.

g. Combined Dermal + Inhalation MOE = NOAEL (60 mg/kg/day) / Combined dermal + inhalation dose (mg/kg/day) 

-- = Data Not Available or Liquids Exposure Scenario is considered protective of this scenario
Page 43 of 68

9.2 Occupational Post-application 

9.2.1 Occupational Post-application Dermal

In the case of trinexpac-ethyl, there is a potential for postapplication dermal exposure to field 

workers following foliar applications of trinexpac-ethyl to agricultural crops. Chemical and 

crop-specific data relevant to post-application exposure (i.e., dislodgeable foliar residue (DFR) 

data) for the new trinexpac-ethyl proposed uses were not submitted. Therefore, dermal 

exposures during postapplication activities were estimated using dermal transfer coefficients 

from the Science Advisory Council for Exposure Policy Number 3 

(http://www.epa.gov/pesticides/science/exposac_policy3.pdf). This policy reflects adoption of 

all Agricultural Reentry Exposure Task Force (ARTF) data. Use of the data in this policy 

requires compensation to the ARTF under FIFRA. 

In the absence of chemical-specific DFR data, HED assumes that 20% of the initial application is 

available for transfer on day 0 (i.e., 12 hours after application) and that the residue dissipates at a 

rate of 10% per day. Furthermore, HED also assumes an 8 hour workday for post-application 

workers. Average daily doses (ADD) were calculated on each post-application day after 

application.

Equations/Calculations: The assumptions, equations, and calculations used to determine 

occupational post-application exposure and risk estimates are given in the ORE memo prepared 

in support of this registration action (Monica Hawkins, D392798, 8/31/11).

The post-application MOEs at day 0 range from 47 to 12,000. The results indicate that 

occupational post-application risk estimates, as calculated per HED default values, do not exceed 

HED’s level of concern (an MOE ≥100) on day zero after application for all post-application 

tasks that were assessed except for hand-harvesting sugarcane where the MOE increases to 110 

within 8 days of application (short-and intermediate-term post-application).

Table 9.2.a. Summary of Trinexapac-ethyl Occupational Short-Term and IntermediateTerm Post-application Risk Estimates Using Default Data

Crop Grouping Crop

Exposure 

Potential

Max 

Foliar 

Rate 

(lb ai/ 

acre)

Transfer 

Coefficient 

(cm2/hr)

Activities

MOE 

at 

Day 

Zero

Day 

Acceptable 

MOE

Field/Row Crop 

(Low)

Turf/Sod

(Golf 

Course)

Low 0.17 3700 Maintenance 410 --

Field Row

Crop (Low)

Turf/Sod

(Sod) Low 0.34

0

Roll 

Harvesting -- --

6700

Maintenance, 

Slab 

Harvesting, 

Transplanting

110 --
Page 44 of 68

Table 9.2.a. Summary of Trinexapac-ethyl Occupational Short-Term and IntermediateTerm Post-application Risk Estimates Using Default Data

Crop Grouping Crop

Exposure 

Potential

Max 

Foliar 

Rate 

(lb ai/ 

acre)

Transfer 

Coefficient 

(cm2/hr)

Activities

MOE 

at 

Day 

Zero

Day 

Acceptable 

MOE

/

Planting

Field/Row Crop 

(Low/Medium) Sugarcane

Low

0.31

0 Transplanting -- --

70 Hand 

Weeding 12000 --

High

0

Mechanical 

Harvesting, 

Mechanical 

Weeding

-- --

1100 Scouting 760

17600 Hand 

Harvesting 47 8

Field/Row Crop 

(Low/Medium)

Grasses 

grown for 

seed

Low 0.5

0

Mechanical 

Harvesting, 

Fertilizing, 

Irrigation 

(non-hand 

set)

-- --

1100 Scouting 470 --

1900 Irrigation 

(hand set) 270 --

Field/Row Crop 

(Low/Medium) Cereals Low 0.11

0

Irrigation 

(non-hand 

set), 

Mechanical 

Harvesting

-- --

1100 Scouting 2100 --

Restricted Entry Interval: Current trinexapac-ethyl labels have either no REI, 0 days, or a 4 

hour REI. The trinexapac-ethyl technical material has been classified in Toxicity Category III 

for acute dermal, oral, and primary eye irritation and Category IV for acute inhalation and 

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

interval (REI) is required for chemicals classified under Toxicity Category III/IV. The 

Registration Division (RD) should ensure the proper REIs are put in place on the labels to 

reflect these requirements.

Based on HED’s occupational postapplication exposure assessment, REIs for hand-harvesting 

sugarcane were estimated to be 8 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. First, almost all sugarcane harvesting in the United States is 
Page 45 of 68

done mechanically. Secondly, 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.

9.2.1 Occupational Post-application Inhalation

Based on the Agency's current practices, a quantitative post-application inhalation exposure 

assessment was not performed for trinexapac-ethyl at this time primarily because of the low 

acute inhalation toxicity (Toxicity Category IV). However, there are multiple potential sources 

of post-application inhalation exposure to individuals performing post-application activities in 

previously treated fields. These potential sources include volatilization of pesticides and 

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

advice and input on issues related to volatilization of pesticides from its Federal Insecticide, 

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

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

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

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

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

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

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

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

post-application inhalation exposure assessment for trinexapac-ethyl.

Although a quantitative occupational post-application inhalation exposure assessment was not 

performed, an inhalation exposure assessment was performed for occupational handlers. 

Handler exposure resulting from application of pesticides outdoors is likely to result in higher 

exposure than post-application exposure. Therefore, it is expected that these handler inhalation 

exposure estimates would be protective of most occupational post-application inhalation 

exposure scenarios.

10.0 References

DP#: 378491, 328850, 328853, 328898

Subject: Trinexapac-ethyl: Application for Section 3 Registration for Use on Cereal Grains 

and Sugarcane (PP#0F7720) and Grasses Grown for Seed (PP#0F7719). 

Summary of Analytical Chemistry and Residue Data.

From: S. Piper

To: B. Benbow and K. Montague

Date: 11/23/11

MRIDs: 48043701-09, 47101606, 47101603, 48043601-04, 45898901-09, 46809305-06
Page 46 of 68

DP#: 394830

Subject: Trinexapac-ethyl: Acute and Chronic Dietary Exposure and Risk Assessment for 

Proposed Uses on Cereal Grains, Sugarcane and Grasses Grown for Seed. 

From: S.Piper

To: B. Benbow and K. Montague

Date: 10/28/11

MRIDs: NA

DP#: 390121

Subject: Trinexapac-ethyl: Report of the Residues of Concern Knowledgebase 

Subcommittee (ROCKS). 

From: E. Holman

To: Trinexapac-Ethyl Risk Assessment Team

Date: 07/05/11

MRIDs: NA

DP#: 392798

Subject: Trinexapac-ethyl: Occupational and Residential Exposure/Risk Assessment for 

Proposed Uses on grasses grown for seed, sugarcane, and cereals (wheat, barley, 

and oats).

From: M. Hawkins

To: M. Waller/T. Stowe

Date: 08/31/11

MRIDs: NA

DP#: 395601

Subject: Tier II Drinking Water Assessment for Trinexapac-Ethyl use on Turf

From: C. M. Koper

To: B. Benbow and S.Piper

Date: 10/28/11

MRIDs: NA
Page 47 of 68

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 1 below.

Use of the new guideline numbers does not imply that the new (1998) guideline protocols were 

used. A description of the outstanding study is in Table A.2.1.

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

no

yes

yes

yes

---

---

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

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

---

---

no

no

no

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

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

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

yes

no

yes

yes

yes

no

Non guideline Thyroid MOA Investigation Study No ---

CR=pending results of acute and subchronic neurotoxicity studies.
Page 48 of 68

A.2.1 Toxicity Profiles

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

Guideline 

No. Study Type MRID Results

Toxicity 

Category

870.1100 Acute oral [rat] 4156390

1

♂ LD50 = 4613 mg/kg

♀ LD50 = 4212 mg/kg

Combined LD50 = 4458 mg/kg

III

870.1200 Acute dermal [rabbit] 4156391

0

LD50 > 4000 mg/kg III

870.1300 Acute inhalation [rat] 4156391

2

LC50 ≥ 5.3 mg/L IV

870.2400 Acute eye irritation 

[rabbit]

4156391

4

Minimal irritant; cleared by 72 

hours

III

870.2500 Acute dermal irritation 

[rabbit]

4156391

6

Slightly irritating; cleared by 

day 7

IV

870.2600 Skin sensitization [guinea 

pig]

4186952

2

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

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
Page 49 of 68

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, 20000 ppm

[males 0, 3, 34, 346, 1350 

mg/kg/day] 

[females 0, 4, 38, 395, 1551 

mg/kg/day]

acceptable/guideline

NOAEL = 20000 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, 15000, 30000 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, 15000-50000 ppm

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

mg/kg/day]

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

965)* mg/kg/day]

*15000 ppm (days 1-3); 30000 

ppm (days 4-28); 50000 ppm 

(weeks 4-7)

NOAEL = 15000 ppm [males 515.9/females 582.4 

mg/kg/day

LOAEL = 30000 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 midand 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,

acceptable/guideline

Systemic toxicity

NOAEL: 1000 mg/kg/day

LOAEL: Not determined

Local dermal irritation

NOAEL: 10 mg/kg/d

LOAEL: 100 mg/kg/d

based on hyperkeratosis and subacute lymphocytic 

infiltrates in the skin

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 

Note: Performed under the old protocol guideline 83-

3a. 

83-3b

Prenatal 

developmental in 

nonrodent 

MRID 41869524 (1990)

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

gestation days 7-19

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

dose tested

Developmental toxicity NOAEL = 60 mg/kg/day

Developmental toxicity LOAEL

based on a decrease in the mean number of 
Page 50 of 68

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

Guideline No./ 

Study Type

MRID No. (year)

Classification /Doses

Results

(rabbit)

Acceptable/guideline; (does not 

fulfill 870.3700b because study 

pre-dates this 1998 guideline)

fetuses/litter and an increase in post-implantation loss

Note: Performed under the old protocol guideline 83-

3b. 

83-4

Reproduction 

and fertility 

effects (rats)

MRID 43128604 (1991)

0, 10, 1000, 10000, 20000 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; (does not 

fulfill 870.3800 because study 

pre-dates this 1998 guideline)

Parental toxicity NOAEL = 10000 ppm [males 

593.5/females 751.1 mg/kg/day]

Parental toxicity LOAEL 20000 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 = 20000 ppm [males 

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

including 20000 ppm (HDT)

Offspring NOAEL = 10000 ppm [males 

593.5/females 751.1 mg/kg/day]

Offspring LOAEL = 20000 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].

Note: Performed under the old protocol guideline 83-

4. 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.

870.4100a

Chronic toxicity 

rodents (rat)

MRID 42238104 (1992)

0, 10, 100, 3000, 10000, 20000 

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 = 20000 ppm [males 

806/females 1054 mg/kg/day, highest dose tested.

870.4100b

Chronic toxicity 

nonrodent (dogs)

MRID 42779402/42779401 

(1991-92)

0, 40, 1000, 10000, or 20000 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 = 10000 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 MRID 42238104 (1992) see above under 870.4100a
Page 51 of 68

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

Guideline No./ 

Study Type

MRID No. (year)

Classification /Doses

Results

Carcinogenicity 

(rat)

Sprague-Dawley

0, 10, 100, 3000, 10000, 20000 

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

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 

treatment-related 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

Not Likely to be Carcinogenic to Humans

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 acceptable/guideline

870.5300

Mouse 

Lymphoma 

Cells/Mammalia

n Activation 

Gene Forward 

Mutation Assay 

at TK+/-locus

43128605 (1993

Mouse lymphoma

L5178Y cells (at the

thymidine kinase locus)

0, 7.54, 30.16, 120.62, or

1930 μg/mL for 4 hours

± S9 metabolic activation

Negative acceptable/guideline

870.5395

Structural 

chromosomal 

aberration test - 

Micronucleus 

41563926 (1989)

42081402 (1991)

41869527 (1991)

M and F mouse bone marrow cells 

(erythrocytes)

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

Negative acceptable/guideline

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 
Page 52 of 68

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

Guideline No./ 

Study Type

MRID No. (year)

Classification /Doses

Results

Test Mouse (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)

confirmatory assay

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

clastogen, however, weight of evidence suggests

CGA-163935 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

Negative acceptable/guideline

870.7485

Metabolism and 

pharmacokinetic

s 

(rat)

MRID 41563927 (1990)

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

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

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

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

acceptable/guideline

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 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

(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. 
Page 53 of 68

Table A.2.5. Structures of Trinexapac-ethyl Major Metabolites and Degradates

Code Name Chemical Abstracts Name

(IUPAC Name) Structure

Trinexapacethyl ethyl 4 

(cyclopropylhydroxymethylene)-

3,5-dioxocyclohexanecarboxylate

Trinexapac

(CGA179500)

4-(cyclopropylhydroxymethylene)-3,5-

dioxocyclohexanecarboxylic acid

CGA 113745 3,5-dioxo-cyclohexanecaroxylic acid

Aconitic acid

CGA 312753

(1E)-prop-1-ene-1,2,3-tricarboxylic 

acid 

Tricarboxylic 

acid

CGA-275537

propane-1,2,3-tricarboxylic acid

CGA-313458 2-(4-Cyclopropyl-2,4-dioxo-butyl)-

succinic acid

O

O

OH

O

O

H C3

*

*

*

O

O

O

HO OH

HO

HO

O

O

OH

O

HO OH

O O

O OH

OH

O O O

O OH
Page 54 of 68

Table A.2.5. Structures of Trinexapac-ethyl Major Metabolites and Degradates

Code Name Chemical Abstracts Name

(IUPAC Name) Structure

Open chain 

cyclohexane 

degradate

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 83-3

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 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 be protective of the fetal effects [increased incidence of asymmetrical sternebrae] 

observed at higher dose levels [1000 mg/kg/day] in the rat. 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 

in the toxicology database. An in utero effect from the developmental rabbit study provided an 

acute reference dose for females 13-49 yrs 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
Page 55 of 68

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 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 level of 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)

Study Selected: –No appropriate endpoint was available for the incidental oral exposure

A.3.5 Dermal and Inhalation Exposure (Short and IntermediateTerm- Adults only

Study Selected: Prenatal Developmental Toxicity Study– rabbit

MRID No.: 41869524

Summary: See Appendix A, Guideline 83-3

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 at the developmental 

toxicity LOAEL of 360 mg/kg/day.

Uncertainty Factor(s): LOC for MOE =100. 100X [10 interspecies; 10X intraspecies] FQPA 

SF = 1X, UFDB = 1X.

Comments about Study/Endpoint/Uncertainty Factor: The developmental toxicity study in 

rabbits (an oral study) is selected for the short and intermediate -term dermal and inhalation 

exposure scenarios for adults only. This endpoint is protective of female workers that may 

become pregnant while exposed to trinexacpac-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, is 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 
Page 56 of 68

NOAEL pf 31.6 mg/kg/day. While we recognize that this endpoint is most appropriate for 

pregnant adults and not applicable to children and men, it is, nonetheless, protective of these two 

populations which have effects at higher doses. Although there is a 21-day dermal toxicity study 

in rabbits that did not identify adverse systemic effects at the limit dose of 1000 mg/kg/day, it did 

not evaluate the developmental effects on the fetus (decreased number of fetuses/litter and 

increased post-implantation loss). 

Dermal irritation was observed in the dermal toxicity study at 100 mg/kg/day (NOAEL = 10 

mg/kg/day), however, this was not relied upon for use in risk assessment because of the transient 

nature of irritation. The Agency prefers to preclude irritation through product labeling and the 

use of gloves and/or other clothing to minimize dermal contact. The proposed endpoint, 

however, will protect for irritation for children playing on the lawn. If a dermal absorption factor 

of 77.5% is applied to the developmental NOAEL of 60 mg/kg/day, the derived dermal 

equivalent dose (DED) would be 77.4 mg/kg/day. This endpoint will also be protective of the 

fetal effects (increased incidence of asymmetrical sternebrae) observed at higher oral dose levels 

(1000 mg/kg/day) in the rat. Note: While the idea of separate endpoints for pregnant women and 

children were discussed, it was decided that this was not necessary. The point of departure based 

on the developmental rabbit study would be protective of the potential impact of children’s 

dermal exposure to trinexapac-ethyl since the dermal NOAEL for children would be higher than 

for pregnant women (594 mg/kg/day vs. 60 mg/kg/day, respectively).

The inhalation exposure limit is based on the NOAEL from an oral toxicity study for this 

exposure scenario, since no route-specific study is available. In the absence of inhalation 

absorption data, toxicity by the inhalation route was considered to be equivalent to toxicity by 

the oral route of exposure.

Based on use pattern, long term exposures are not expected.

A.4 Executive Summaries

Subchronic Rat

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 20000 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 20000 ppm, both sexes displayed slight decreases in body weight throughout 

most of the study [93%-94% of control at study termination], and overall body-weight 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. 
Page 57 of 68

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 20000 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 20000 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 20000 ppm for 

104 weeks indicates that these findings should not be considered adverse.

The systemic toxicity NOAEL is 20000 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

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, 

15000 ppm, or 30000 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, 15000, or 30000 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 

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 30000 ppm dose level 

are considered to be changes that would be expected due to decreased body weight/body-weight 

gain. Both sexes at the 30000 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 30000 ppm. No other treatment-related organ-weight effects were reported in either sex. 
Page 58 of 68

Diffuse thymic atrophy was observed in all dogs [both sexes] at the 30000 ppm dose level 

compared with none of the controls [either sex]. Focal thymic atrophy was not observed at the 

30000 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 30000 ppm most likely occurred secondary to the nutritional 

imbalances related to reduced food consumption and body-weight loss. 

The systemic toxicity NOAEL is 15000 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 30000 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, 5000, 15000, or 15000-50000 ppm. At 

the highest dietary level, dogs were fed 15000 ppm for 3 days, 30000 ppm from day 4 to 28, and 

50000 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 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, 15000 ppm, 30000 ppm, and 50000 ppm dose levels, respectively. 
Page 59 of 68

The dose levels used in the subchronic study are considered adequate [30000 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 20000 ppm and in one male and two female 

dogs at 10000 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 

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.
Page 60 of 68

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

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 

body-weight 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 

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 sternabrae at the LOAEL of 1000 mg/kg/day (limit dose). 
Page 61 of 68

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 

treatment-related 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 and mean numbers of resorptions were comparable among the groups, and 

there were no dead fetuses. Pre- [24.3%] and post- [24.8%] implantation losses were 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 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

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, 10000, or 20000 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 20000 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 
Page 62 of 68

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 10000 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 20000 ppm, although the deficit 

diminished with time. The overall body-weight gain (days 0-21) at 20000 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 [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 20000 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. 
Page 63 of 68

The NOAEL for reproductive toxicity is 20000 ppm [males 1212 mg/kg/day; females 1485 

mg/kg/day (highest dose tested; HDT)].

The NOAEL for parental systemic toxicity is 10000 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 20000 (males1212 

mg/kg/day; females 1485 mg/kg/day).

The offspring systemic toxicity NOAEL is 10000 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 20000 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, 10000, or 20000 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 10000 ppm and/or 20000 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 10000 ppm [89% of control] and 20000 ppm [90% of control] and in 

females at 20000 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 20000 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 10000 ppm [66% of control] and 20000 ppm [76% of control] displayed the 

lowest body-weight gain, although there was no dose-response. Females at 20000 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 

20000 ppm. Testes (absolute*, relative-to-body/brain) and uterus weights (absolute*, relative-tobody*/brain) were significantly decreased at the three highest dose levels, but there was no doseresponse 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 20000 ppm and in one male and two female dogs at 10000 ppm. Dose levels up to 20000 ppm 

were well tolerated by both sexes and are considered adequate. The LOAEL is 10000 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 
Page 64 of 68

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, 10000 ppm, or 20000 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, 10000, or 20000 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 20000 ppm dose level throughout the study beginning at day 7. At 13 weeks, 

both sexes at 20000 ppm displayed an 8% decrease in body weight. At study termination, males 

at 20000 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 20000 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 20000 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 10000 ppm and 20000 ppm dose levels 

throughout the study, although no histopathological correlations accompanied these findings. 

In males, decreased absolute and relative-to-brain heart weights were observed at 20000 ppm at 

52 weeks. There was a slight but significant increase in relative liver and lung weights in females 

at the 20000 ppm dose level at 52 weeks. At termination [104 weeks], the increased relative 

organ weights were considered due to decreased body weight at 20000 ppm. No treatmentrelated organ-weight effects were reported in either sex at 10000 ppm. 
Page 65 of 68

In the liver, there was a statistically-significant increase in bile duct hyperplasia in males at 

20000 ppm at study termination [16, 11, 13, 13, 18, 35** with increasing dose]. Females at 

20000 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 

20000 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 20000 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 

20000 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 20000 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 20000 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 [20000 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

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, 
Page 66 of 68

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. No LOAEL was 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.

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, 
Page 67 of 68

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 

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).

COMPLIANCE: Signed and dated Data Confidentiality, GLP Compliance, Flagging, and 

Quality Assurance statements were provided.

References

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.
Page 68 of 68

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. 

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

Dogs.

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