Document ID: EPA-HQ-OPP-2022-0069-0014
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2023-08-15T04:00Z

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
                            WASHINGTON, D.C.  20460
                                                                               
                                                                               
                                                  OFFICE OF CHEMICAL SAFETY AND
                                                                                               POLLUTION PREVENTION 

MEMORANDUM

DATE: 	3/15/2023

SUBJECT: 	Trinexapac-ethyl. Human Health Risk Assessment for the New Use on Clover (Seed Crop).
 
PC Code: 112602  
DP Barcode:  464494
Decision No.: 579544 
Registration No.:  100-1677
Petition No.:  1E8966
Regulatory Action:  Section 3
Risk Assessment Type:  NA
Case No.:  7228
TXR No.:  NA
CAS No.:  95266-40-3
MRID No.:  NA
40 CFR:  §180.662

FROM:	Wade Britton, MPH, Environmental Health Scientist  
		Cynthia Browning, Ph.D., Toxicologist 
		Sheila Piper, Chemist  
		Risk Assessment Branch VI
		Health Effects Division (7509T)

THROUGH:	Peter Savoia, Branch Chief
		Risk Assessment Branch VI
		Health Effects Division (7509T)

TO:		Andrew Ertman, Chemical Reviewer
		Nancy Fitz, Team Leader, Minor Use Team
      And
      Mindy Ondish, Product Manager
		Lindsay Roe, Branch Chief 
		Herbicide Branch
      Registration Division (7505T)

                                       
                               Table of Contents
1.0	Executive Summary	4
2.0	HED Recommendations	7
2.1	Data Deficiencies	7
2.2	Tolerance Considerations	8
2.2.1	Enforcement Analytical Method	8
2.2.2	Recommended Tolerances	8
2.2.3	Revisions to Petitioned-For Tolerances	9
2.2.4	International Harmonization	9
2.3	Label Recommendations	10
3.0	Introduction	10
3.1	Chemical Identity	10
3.2	Pesticide Use Pattern	10
3.3	Anticipated Exposure Pathways	11
3.4	Consideration of Environmental Justice	11
4.0	Hazard Characterization and Dose-Response Assessment	11
4.1	Toxicology Studies Available for Analysis	11
4.2	Absorption, Distribution, Metabolism, & Elimination (ADME)	12
4.2.1	Dermal Absorption	13
4.3	Toxicological Effects	13
4.4	Safety Factor for Infants and Children (FQPA Safety Factor)	14
4.4.1	Completeness of the Toxicology Database	14
4.4.2	Evidence of Neurotoxicity	14
4.4.3	Evidence of Sensitivity/Susceptibility in the Developing or Young Animal	15
4.4.4	Residual Uncertainty in the Exposure Database	15
4.5	Toxicity Endpoint and Point of Departure Selections	16
4.5.1	Recommendation for Combining Routes of Exposures for Risk Assessment	18
4.5.2	Cancer Classification and Risk Assessment Recommendation	18
4.5.3	Summary of Points of Departure and Toxicity Endpoints Used in Human Risk Assessment	18
5.0	Dietary Exposure and Risk Assessment	21
5.1	Residues of Concern Summary and Rationale	21
5.2 	Food Residue Profile	21
5.3	Water Residue Profile	22
5.4	Dietary Risk Assessment	22
5.4.1	Description of Residue Data Used in Dietary Assessment	22
5.4.2	Percent Crop Treated Used in Dietary Assessment	23
5.4.3	Acute Dietary Risk Assessment	23
5.4.4	Chronic Dietary Risk Assessment	23
5.4.5	Cancer Dietary Risk Assessment	23
5.4.6	Dietary Summary Table	23
6.0	Residential (Non-Occupational) Exposure/Risk Characterization	24
7.0	Aggregate Exposure/Risk Characterization	25
7.1	Acute Aggregate Risk	25
7.2	Short -Term Aggregate Risk	25
7.3	Chronic Aggregate Risk	26
7.4	Cancer Aggregate Risk	26
8.0	Non-Occupational Spray Drift Exposure and Risk Estimates	26
10.0	Cumulative Exposure/Risk Characterization	28
11.0	Occupational Exposure/Risk Characterization	28
11.1	Short-/Intermediate -Term Handler Risk	28
11.2	Short-/Intermediate- Term Post-Application Risk	33
11.2.1	Dermal Post-application Risk	33
11.2.2	Inhalation Post-application Risk	34
12.0	References	35
Appendix A.  Toxicology Profile and Executive Summaries	36
A.1	Toxicology Data Requirements	36
A.2	Toxicity Profiles	37
Appendix B. Physical/Chemical Characteristics	43
Appendix C.  International Residue Limits	45

1.0	Executive Summary

HED has conducted a human health risk assessment for trinexapac-ethyl (ethyl 4-(cyclopropylhydroxymethylene)-3,5-dioxocyclohexanecarboxylate) to support a proposed new use on clover grown for seed in the Pacific Northwest.  The active ingredient, trinexapac-ethyl, is a plant growth regulator/herbicide that is registered for uses on cereal grains (wheat, barley, oats, triticale), sugarcane, and grasses grown for seeds.  It is formulated as an emulsifiable concentrate, wettable powder packed in water-soluble bags, and granule.  Trinexapac-ethyl is registered for use on turf in residential and commercial lawns, golf courses, parks, athletic fields, cemeteries, as well as grass grown for seed (non-food) and turf grown for sod. 

Proposed Use Profile

The proposed new use on clover is for a trinexapac-ethyl end use product, Palisade[(R)] LO (EPA Reg. No. 100-1677), which is formulated as an emulsifiable concentrate containing 11.3% ai (0.97 lb ai/gallon).  Applications are made by chemigation, aerial, and groundboom equipment at a single maximum application rate of 0.44 lb a.i./A (58 fl oz/A).  The use on clover (seed crop) is for a crop grown on less than 300,000 acres.  This use is for a regional registration in the Pacific Northwest. Mixers, loaders, applicators, and other handlers are required to wear baseline attire (i.e., long-sleeved shirt, long pants and shoes plus socks) when handling trinexapac-ethyl products.  The restricted entry interval (REI) is 12 hours as listed on the proposed label. 

Exposure Profile 

Humans may be exposed to trinexapac-ethyl in food and drinking water from the proposed uses since trinexapac-ethyl may be applied directly to growing crops and applications may result in trinexapac-ethyl reaching surface and ground water sources of drinking water.  The anticipated use pattern and current labeling indicate several occupational exposure scenarios based on the types of equipment and techniques that can potentially be used for trinexapac-ethyl applications.  The proposed uses are expected to result in short- and intermediate-term occupational exposure associated with handler (i.e., mixing, loading, and applying) and post-application activities (i.e., irrigation, scouting).  There are previously registered residential uses for trinexapac-ethyl.  There is the potential for non-occupational bystander exposure from spray drift following applications of trinexapac-ethyl.  

Hazard Characterization and Dose Response Assessment

The toxicology database for trinexapac-ethyl is complete and considered adequate for hazard characterization and endpoint selection for the anticipated routes (oral, dermal and inhalation) and durations of exposure (short- and intermediate-term) for the proposed use.  The Hazard and Science Policy Council (HASPOC) recommended that the subchronic inhalation study is not required at this time (A. Dunbar, 7/11/2013, TXR 0056699).  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%).  

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 following 90-day exposure to 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.  

There is 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).  Reproductive toxicity was not observed up to the limit dose.  To be protective of the in utero developmental effects seen in these studies and potential exposure to pregnant females, endpoints have been selected for acute dietary exposure (females 13-49 years of age), and oral, dermal, and inhalation exposures for adults and youths >= 11 years old (used in the occupational and residential risk assessments).  These lifestage groups encompass the female reproductive ages, as puberty starts around age 13.

Trinexapac-ethyl is classified as "Not likely to be Carcinogenic to Humans" based on no evidence of mutagenicity, no tumor formation seen in the mouse carcinogenicity study and no tumor type of human relevance seen in the combined chronic toxicity/carcinogenicity rat study. 

The acute toxicity of the technical material is low via the oral, dermal, or inhalation routes of exposure (Toxicity Categories III-IV), and it is not a sensitizer via any route. 

An acute reference dose (RfD) and population adjusted dose (PAD) for females 13-49 years of age was selected from the rabbit developmental study with a no-observed adverse effect level (NOAEL) of 60 mg/kg/day and a lowest-observed adverse effect level (LOAEL) of 360 mg/kg/day, based on a decrease in the mean number of fetuses/litter and an increase in post-implantation loss.  No acute dietary endpoint was appropriate for the general population. A chronic RfD/PAD for all populations was selected from the chronic dog oral toxicity study with a NOAEL of 31.6 mg/kg/day and a LOAEL of 357 mg/kg/day, based on elevated serum cholesterol values in females, mucoid feces in females, bloody feces in both sexes, and minimal focal vacuolation of the dorsal medial hippocampus and/or lateral midbrain in both sexes.  Point of departures (PODs) for short- and intermediate-term oral, dermal and inhalation exposure in adults and youths >= 11 years of age were selected from the rabbit developmental study with a NOAEL of 60 mg/kg/day and a LOAEL of 360 mg/kg/day, based on a decrease in the mean number of fetuses/litter and an increase in post-implantation loss.  These endpoints are most appropriate for pregnant females, however, they are protective of effects observed in males at higher doses.  No incidental oral, short- and intermediate-term dermal or inhalation endpoints were appropriate for youth < 11 years of age.  An uncertainty factor (UF) of 100X was applied to endpoints selected for all exposure routes (10X for interspecies extrapolation, 10X for intraspecies variation, and 1X for the Food Quality Protection Act Safety Factor (FQPA SF)). 

Residue Chemistry

The existing residue chemistry database for trinexapac-ethyl is adequate for risk assessment purposes.  The qualitative nature of the residue of trinexapac-ethyl in plants and animals is understood.  The residues of concern in plants and livestock for tolerance establishment and risk assessment purposes include free and conjugated residues of both parent and its acid metabolite, trinexapac.  There is the potential for secondary transfer of trinexapac-ethyl residues of concern in livestock tissues, milk, and egg with the existing uses on clover (forage and hay).  HED has previously concluded that there is no reasonable expectation of quantifiable residues of trinexapac-ethyl in poultry livestock commodities [40 CFR §180.6(a)(3)].  However, the new uses proposed herein will result in an increase in the dietary burden for livestock commodities; therefore, tolerances are required for all livestock commodities.  Although clover is not fed to hogs or poultry, the poultry/hog dietary burden and expected residues were revaluated using current practices and for purposes of harmonization.  Based on this analysis, HED is recommending the poultry/hog tolerances listed in Table 2.2.2.

An unrefined, acute and chronic dietary exposure assessment using tolerance-level residues, default DEEM processing factors, and assuming 100% crop treated (CT) for the proposed and registered commodities was conducted.  The estimated drinking water concentration (EDWC) of trinexapac-ethyl was previously provided by the Environmental Fate and Effects Division (EFED) and incorporated directly into the acute assessment.  The drinking water estimate was based on the use of trinexapac-ethyl on Tier I rice model in surface water.  There were no appropriate toxicological effects attributable to a single exposure (dose) for the general population or any other population subgroups except females 13-49 years old; therefore, these population subgroups were not included in this assessment.  For food and drinking water, the acute dietary risk estimate is below HED's level of concern (LOC) (<100% of the acute population adjusted dose (aPAD)) at the 95[th] percentile of exposure.  The acute dietary exposure estimates for females 13-49 years old is 2.5% of the aPAD.  Combined chronic dietary exposure estimates for food and drinking water are below HED's LOC.  The chronic risk estimates were 3% of the chronic population-adjusted dose (cPAD) for the general U.S. population and 7% of the cPAD for children 1-2 years old, the population with the highest estimated chronic dietary exposure for trinexapac-ethyl.  Trinexapac-ethyl is classified as "not likely to be carcinogenic to humans."  Therefore, a cancer dietary exposure analysis is not required.

Residential Exposure and Risk Assessment 

Since no new residential uses are being proposed at this time, an updated residential exposure assessment is not required.  There are registered residential uses for trinexapac-ethyl on turf that were assessed previously in 2013 (M. Hawkins, 9/18/2013, D413030).  The previously assessed residential handler margins of exposure (MOEs) range from 240 to 21,000,000 and are not of concern (i.e., the estimated MOEs are > the LOC of 100).  The residential post-application MOEs range from 450 to 61,000 and are also not of concern.  

Aggregate Risk Assessment

 The acute (females 13 -  49 years only) and chronic aggregate assessments are equivalent to the corresponding dietary (food plus water) risk estimates, which do not exceed HED's LOC.  The short/intermediate-term aggregate MOEs are 230 for adults 20 -  49 years old and 4,400 for youths (11 - 16 years old).  There are no oral, dermal or inhalation endpoints for young children (1 to <2 years old and 6 to < 11 years old) associated with trinexapac-ethyl; therefore, an aggregate risk assessment is not required for this population subgroup.

Occupational Exposure and Risk Assessment 

Occupational handlers are anticipated to be exposed to trinexapac-ethyl based on the currently proposed use on clover. Occupational handler combined (dermal and inhalation) MOEs range from 46 to 4,800 at baseline attire (i.e., single layer, no respirator). For all exposure scenarios, dermal exposure is the risk driver.  A single exposure scenario results in a combined risk of concern (mixer/loader, liquid, aerial, broadcast; MOE = 46); however, with the addition of chemical-resistant gloves, the combined MOE is no longer of concern (MOE = 270). 

Short- and intermediate-term occupational post-application dermal exposures are not of concern with MOEs ranging from 280 to 490 (LOC=100) on the day of product application (Day 0) using default dislodgeable foliar residue (DFR) data. 

2.0	HED Recommendations

There are no toxicological, residue chemistry, or occupational/residential exposure considerations that would preclude granting the requested new use on clover and establishing the tolerances recommended in Section 2.2.2. Tolerances on clover and updated tolerances on livestock are recommended. 

2.1	Data Deficiencies

None.

2.2	Tolerance Considerations

2.2.1	Enforcement Analytical Method

For plants and livestock, the LC/MS/MS method, Method GRM020.01A, is adequate for data collection and tolerance enforcement.  The method includes a strong acid hydrolysis/extraction procedure to release both free and conjugated residues of trinexapac-ethyl.  The reported limit of quantitation (LOQ) is 0.010 ppm for clover forage and 0.025 ppm for hay.  Validated analytical methods are available for both data collection and enforcement purposes.  

Also, trinexapac-ethyl was evaluated using the FDA multi-residue method Protocols C and D, and its acid metabolite, trinexapac, was evaluated using Protocol B.  These data indicate FDA multi-residue methods are not suitable for determining residues of trinexapac-ethyl and trinexapac in plant commodities.   

2.2.2	Recommended Tolerances

HED reviewed the available residue data and has determined the appropriate tolerance levels for the residues of trinexapac-ethyl. Table 2.2.2.1. below summarizes the clover (forage and hay) recommended tolerance levels which were derived using the Organization for Economic Cooperation and Development Maximum Residue Level (OECD MRL) calculation (plants) and the Langmuir Model (ver. 1.4; livestock). The current tolerance expression conforms to HED guidance.  

 Tolerances with regional registrations. Tolerances with regional registrations, as defined in §180.1, 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 only the free and conjugated forms of both trinexapac-ethyl, ethyl 4-(cyclopropylhydroxymethylene)-3,5-dioxocyclohexanecarboxylate and trinexapac, 4-(cyclopropylhydroxymethylene)-3,5-dioxocyclohexanecarboxylic acid, calculated as the stoichiometric equivalent of trinexapac-ethyl, in or on the commodity.

Table 2.2.2.1.  Recommended Tolerance Summary for Trinexapac-ethyl
                                   Commodity
                          Established Tolerance (ppm)
                                   Proposed
                                   Tolerance
                                     (ppm)
                                      HED
                          Recommended Tolerance (ppm)
                                   Comments
                         40 CFR §180.662 (a) General.
Cattle, fat
                                     0.02
                                     0.03
                                     0.03

Cattle, meat
                                     0.02
                                     0.03
                                     0.03

Cattle, meat byproducts
                                     0.04
                                      --
                                      0.1
To harmonize with Codex
Egg
                                      --
                                      --
                                     0.01

Goat, fat
                                     0.02
                                     0.03
                                     0.03

Goat, meat
                                     0.02
                                     0.03
                                     0.03

Goat, meat byproducts
                                     0.04
                                      --
                                      0.1
To harmonize with Codex
Hog, fat
                                     0.02
                                      --
                                     0.02

Hog, meat
                                     0.02
                                      --
                                     0.02

Hog, meat byproducts
                                     0.03
                                      --
                                      0.1
To harmonize with Codex
Milk
                                      --
                                      --
                                     0.01

Horse, meat
                                     0.02
                                      --
                                     0.03

Poultry, fat
                                      --
                                      --
                                     0.01

Poultry, meat
                                      --
                                      --
                                     0.01

Poultry, meat byproducts
                                      --
                                      --
                                      0.1

Sheep, fat
                                     0.02
                                     0.03
                                     0.03

Sheep, meat
                                     0.02
                                     0.03
                                     0.03

Sheep, meat byproducts
                                     0.04
                                      --
                                      0.1
To harmonize with Codex
         40 CFR §180.662 (c) Tolerances with regional registrations.
Clover, forage[1]
                                      --
                                       8
                                       8

Clover, hay[1]
                                      --
                                      15
                                      15

[1] Tolerance supports regional registration in the Pacific Northwest (ID, OR and WA only). 

2.2.3	Revisions to Petitioned-For Tolerances

A revised Section F was provided that reflects the recommended tolerances as shown in Table 2.2.2.1.  HED has recommended tolerances for ruminant meat byproduct at 0.1 ppm which will cover the individual tolerance for kidney and liver.  Also, a tolerance of 0.1 ppm for ruminant, meat byproduct will be harmonized with Codex.  There are established Codex MRLs for ruminant and fat at 0.01 ppm and HED recommends a tolerance at 0.03 ppm for ruminant meat and fat; therefore, HED will not be able to harmonize with Codex. Although clover is not feed to hogs or poultry, the poultry/hog dietary burden and expected residues were re-evaluated using current practices and for purposes of harmonization. HED recommends tolerances for milk and egg at 0.01 ppm which was previously omitted.  This proposed use on clover is for a regional registration in the Pacific Northwest. 

2.2.4	International Harmonization

Although there are no established tolerances on clover (forage and hay), there are established Codex, Canadian, and Mexican maximum residue limits (MRLs) for trinexapac-ethyl in or on livestock commodities.  The US is harmonized with Codex ruminant and hog meat, byproduct at 0.1 ppm; however, the ruminant and swine meat and fat will need to increase 0.03 ppm (0.01 ppm for Codex) based on the new uses for clover.  The International Residue Limit (IRL) Status Sheet is included in Appendix C.

2.3	Label Recommendations

None.

3.0	Introduction

3.1	Chemical Identity

Trinexapac-ethyl has a relatively low octanol/water partition coefficient.  At pH 5.3, the log KOW value is 2.44 (KOW = 275).  Trinexapac-ethyl has a low potential to leach into groundwater and is not expected to be volatile because of its low vapor pressure (2.16 x 10[-3] Pa at 25[o]C).  The nomenclature and physicochemical properties of trinexapac-ethyl are presented in the Appendix B.

3.2	Pesticide Use Pattern

The proposed new use on clover is for a trinexapac-ethyl end use product, Palisade[(R)] LO (EPA Reg. No. 100-1677), which is formulated as an emulsifiable concentrate containing 11.3% ai (0.97 lb ai/gallon).  Applications are made by chemigation, aerial, and groundboom equipment at a single maximum application rate of 0.44 lb a.i./A (58 fl oz/A).  The use on clover (seed crop) is for a crop grown on less than 300,000 acres.  This use is for a regional registration in the Pacific Northwest. Mixers, loaders, applicators, and other handlers are required to wear baseline attire (i.e., long-sleeve shirt, long pants and shoes plus socks) when handling trinexapac-ethyl products.  The REI is 12 hours as listed on the proposed label. 

Table 3.2.1.  Summary of Directions for Use of Trinexapac-ethyl
                               Type, and  Equip.
                                       
                                     Uses
                          Formulation [EPA Reg. No.]
                            Applic. Rate (lb ai/A)
                            No. Applic. per Season
                     Max. Seasonal Applic. Rate (lb ai/A)
                        Use Directions and Limitations
                                    Clover
                        Groundboom, Chemigation, Aerial
                              Single application
                               Palisade[(R)] LO, 
                           Emulsifiable concentrate
                            [EPA Reg. No. 100-1677]
                                  0.12-0.44 
                                       1
                                     0.44 
Do not apply to white clover.
Do not apply more than 58 fl oz (0.44 lb ai) per acre per year.
PHI: Clover grown for seed and forage  -  30 days; Clover grown for hay  -  52 days

                                       
                                       
                               Split application

                                  0.12-0.22 
                                   Minimum 2
                                     0.44 

 1 PHI = pre-harvest interval. 

3.3	Anticipated Exposure Pathways

Humans may be exposed to trinexapac-ethyl in food because trinexapac-ethyl may be applied directly to growing crops.  In addition, these applications can result in trinexapac-ethyl reaching surface and groundwater, both of which can serve as sources of drinking water.  Homeowners may be exposed to trinexapac-ethyl when applying to their lawns, and both adults and children may be exposed through contact with treated turf.  In an occupational setting, applicators may be exposed while handling the pesticide prior to application, as well as during application.  There is a potential for exposure for workers re-entering treated fields and by coming in contact with treated foliage.  This risk assessment considers all aforementioned exposure pathways based on the proposed new uses, but also considers the existing uses as well.  

3.4	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," (https://www.archives.gov/files/federal-register/executive-orders/pdf/12898.pdf).  As a part of every pesticide risk assessment, OPP considers a large variety of consumer subgroups according to well-established procedures.  In line with OPP policy, HED estimates risks to population subgroups from pesticide exposures that are based on patterns of that subgroup's food and water consumption, and activities in and around the home that involve pesticide use in a residential setting.  Extensive data on food consumption patterns are compiled by the U.S. Department of Agriculture's National Health and Nutrition Examination Survey, What We Eat in America, (NHANES/WWEIA) and are used in pesticide risk assessments for all registered food uses of a pesticide.  These data are analyzed and categorized by subgroups based on age and ethnic group.  Additionally, OPP is able to assess dietary exposure to smaller, specialized subgroups and exposure assessments are performed when conditions or circumstances warrant.  Whenever appropriate, non-dietary exposures based on home use of pesticide products and associated risks for adult applicators and for toddlers, youths, and adults entering or playing on treated areas post-application are evaluated.  Further considerations are also currently in development as OPP has committed resources and expertise to the development of specialized software and models that consider exposure to other types of possible bystander exposures and farm workers as well as lifestyle and traditional dietary patterns among specific subgroups.

4.0	Hazard Characterization and Dose-Response Assessment

4.1	Toxicology Studies Available for Analysis

The toxicology database for trinexapac-ethyl is considered complete and adequate for risk assessment purposes including FQPA evaluation, selection of PODs for the various routes of exposure, and for dose-response evaluation.  The Hazard and Science Policy Council (HASPOC) recommended that the subchronic inhalation study is not required at this time (A. Dunbar, 7/11/2013, TXR 0056699).  The toxicity profile is listed in the Appendix A. 

Trinexapac-ethyl's hazard database includes the following studies:

 Subchronic: 28-day dermal toxicity (rat); 90-day oral toxicity (rat, mouse, and dog) 
 Developmental toxicity: developmental toxicity (rat and rabbit)
 Reproduction: 2-generation reproduction (rat) 
 Chronic: chronic oral toxicity/carcinogenicity (rat); carcinogenicity (mouse); one-year oral toxicity (dog)
 Neurotoxicity: acute and subchronic neurotoxicity battery (rat)
 Immunotoxicity (mouse)
 Dermal penetration (rat)
 Other: mutagenicity battery; metabolism (rat)

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

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.  The data suggests that there was very little or no biliary absorption.  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 hr post-dosing) was less than 0.3% of administered dose for all dose groups indicating little potential for accumulation.  The major component in urine and fecal extracts was identified as 4-cyclopropyl-(hydroxy-methylene)-3,5-dioxo-cyclohexanecarboxylic 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 was rapid, with the majority of radioactivity being eliminated within 12 hr post-dosing via urine (greater than 85% of the administered dose at the low and high dose) and within 24 hr 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.  The data suggests minimal to no biliary excretion.  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. 

4.2.1	Dermal Absorption

A single dermal dose of 0.01, 0.1, or 1.0 mg/cm[2] [14]C-trinexapac-ethyl administered to male rats was rapidly absorbed, distributed and eliminated (MRID 42238105).  The amount absorbed increased with duration of exposure.  A dermal absorption factor of 77.5% was estimated based on the sum of 56.5% absorbed and excreted after 10 hours in the low dose group (0.01 mg/cm[2]), and 21% of applied dose that was associated with the application site after wash. 

4.3	Toxicological Effects

Examining 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 dogs decreased body weight gain and food consumption, diffuse thymic atrophy, and changes in the epithelial cells of the renal tubules were seen after 90-day oral exposure to 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.  

There is 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 data for each sex was analyzed separately.  Further evaluation of the individual litters 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.  

The immunotoxicity study in mice indicated that there is no evidence of immunotoxicity.  

The combined chronic toxicity/carcinogenicity study in the rat did not demonstrate an increase in any tumor type that would be relevant to humans.  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."    

Trinexapac-ethyl acute toxicity to mammals is low by all exposure routes (Toxicity Category III or IV), and it is not a dermal sensitizer.  It induces minimal eye irritation and slight dermal irritation, both of which clear within 72 hours and 7 days, respectively.

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

HED recommends that the 10X FQPA Safety Factor be reduced to 1X, as the toxicological database for trinexapac-ethyl is complete 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.  Although there is evidence of susceptibility in the rat and rabbit developmental studies and in the 2-generation rat reproduction study, the fetal/offspring effect only occurred at the highest dose tested, and there were clearly identified NOAELs.  Risk assessment points of departure were established which are protective for these effects.  

4.4.1	Completeness of the Toxicology Database

The toxicology database is complete.  Acceptable studies for developmental toxicity in rats and rabbits, immunotoxicity, 2-generation reproduction in rats, and acute and subchronic neurotoxicity are available.  The Hazard and Science Policy Council (HASPOC) recommended that the subchronic inhalation study is not required at this time (A. Dunbar, 7/11/2013, TXR 0056699).  The toxicity profile can be characterized for all effects, including potential developmental and reproductive toxicity, immunotoxicity, and neurotoxicity.  The toxicity profile can be characterized for all effects, including potential developmental and reproductive toxicity, immunotoxicity, and neurotoxicity.  

4.4.2	Evidence of Neurotoxicity 

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 (MRID 42779402/42779401) at the two highest doses tested (356 mg/kg/day: 3/8 dogs and 727 mg/kg/day: 8/8 dogs in the mid- and high dose groups, respectively).  The vacuolation was associated with the astrocytes and oligodendrocytes.  The lesions remained confined to the supporting cells in the central nervous system 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 within an intermediate-term (1-6 months) period of exposure.  

In an acute neurotoxicity study in the rat (MRID 48764506) the NOAEL for systemic toxicity was 1,000 mg/kg and the LOAEL for systemic toxicity was 2,000 mg/kg based on decreased body weight gain over the first day following treatment in both males and females, and decreased food consumption over the first day following treatment in the 2,000 mg/kg males.  The NOAEL for neurotoxicity was 2,000 mg/kg and the LOAEL for neurotoxicity was 2,000 mg/kg in male and female rats based on the absence of any treatment-related functional observational findings, locomotor activity changes, changes in brain weights or brain dimensions, and the absence of any neuropathological lesions. 

In a subchronic neurotoxicity study in the rat (MRID 48764507) the NOAEL for systemic toxicity was 948 mg/kg/day for males and 1,171 mg/kg/day for females, which was the highest dose tested.  The LOAEL was not identified for both systemic toxicity and neurotoxicity based on the absence of any treatment-related functional observational findings, locomotor activity changes, changes in brain weights or brain dimensions, and the absence of any neuropathological lesions. 

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 NOAELs were established in both the rat and rabbit developmental studies.  Reproductive toxicity was not observed in the rat reproduction study, but decreased pup survival and decreased pup body weight and body weight gain during lactation were observed above the limit dose with only reduced body weight and food consumption observed in the parental animals (>1,200 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 (360-1,200 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

Toxicity studies used to select PODs for each exposure scenario are presented in Appendix A.2.  The endpoints and PODs presented in Tables 4.5.3.1 and 4.5.3.2 were based on the previous risk assessment (V. Kurker, 07/13/2020, D454165).

Acute Dietary Endpoint - Females ages 13-49 years old: A prenatal developmental toxicity study in rabbits (MRID 41869524) was selected with a NOAEL of 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.  The aPAD of 0.6 mg/kg/day was derived from a NOAEL of 60 mg/kg/day and a 100-fold uncertainty factor (UF) that included a 10X UF for inter-species extrapolations, a 10X UF for intra-species variations, and 1X for FQPA SF. The aPAD is equivalent to the aRfD (0.6 mg/kg/day).  The route and duration of exposure are appropriate for selection of the acute dietary endpoint for females 13-49 years old.  This endpoint is protective of the developmental effects (increased incidence of asymmetrical sternebral) observed at higher dose levels (1,000 mg/kg/day) in the rat. 

Acute Dietary Endpoint for the General Population: No appropriate endpoint attributable to a single exposure (dose) was identified in the toxicology database that was applicable to general population.  An in utero effect from the developmental rabbit study provided an acute reference dose for females 13-49 years old but is not appropriate for the general population.

Chronic Dietary Endpoint for the General Population: For the chronic dietary endpoint, a chronic oral toxicity study in dogs (MRID 42779402/42779401) was selected with a NOAEL of 31.6 mg/kg/day and 39.5 mg/kg/day in males and females, respectively.  A LOAEL of 
365.7 mg/kg/day and 357.1 mg/kg/day in males and females, respectively, was established based on elevated serum cholesterol values in females, mucoid feces in females and bloody feces in both sexes, and minimal focal vacuolation of the dorsal medial hippocampus and/or lateral midbrain in both sexes.  The cPAD of 0.32 mg/kg/day was derived from a NOAEL of 31.6 mg/kg/day and a 100-fold UF that included a 10X UF for inter-species extrapolations, a 10X for intra-species variations and a 1X for FQPA SF.  The cPAD is equivalent to the cRfD (0.32 mg/kg/day).  The route and duration of exposure are appropriate for selection of the chronic dietary endpoint.  This endpoint is protective of chronic effects seen throughout the toxicology database since the dog is the most sensitive species.

Short- and Intermediate-Term Oral Endpoints (Adults and youth >= 11 years old): The short- and intermediate-term oral endpoints for adults and females >= 11 years old were based on the prenatal developmental toxicity study in rabbits (MRID 41869524) with a NOAEL of 60 mg/kg/day.  The developmental LOAEL is 360 mg/kg/day based on a decrease in the mean number of fetus/litter and an increase in post-implantation loss.  The LOC is 100 based upon a 10X UF for inter-species extrapolations, a 10X UF for intra-species variations, and 1X for FQPA SF.  The route and duration of exposure are appropriate for selection of the short- and intermediate-term endpoints.  This endpoint is only applicable to adults because it is based on in utero effects.  The occupational and residential assessments include a lifestage of kids 11 to <16. As puberty starts around age 13, this endpoint that is based on in utero effects is being applied to this lifestage.  While the Agency recognizes that this endpoint is most appropriate for pregnant females, it is protective of effects observed in males at higher doses.

Short-term Incidental Oral Endpoint (children): An endpoint for the incidental oral exposure scenario for children (<11 years old) 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, 1,000 mg/kg/day in the rat, and 1,212 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 mg/kg/day 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) (M. Hawkins, 11/23/2011, D392798). 

Short- (1-30 days) and Intermediate- (1-6 months) Term Dermal and Inhalation Endpoints (Adults and youth >= 11 years old): A prenatal developmental toxicity study (MRID 41869524) in rabbits was selected with a NOAEL of 60 mg/kg/day.  The developmental LOAEL is 360 mg/kg/day based on a decrease in the mean number of fetus/litter and an increase in post-implantation loss.  Although there is a 21-day dermal toxicity study in rabbits that did not identify adverse systemic effects at the limit dose of 1,000 mg/kg/day, the developmental rabbit toxicity study has been selected for the dermal endpoint because the dermal study did not evaluate the developmental effects on the fetus (decreased number of fetuses/litter and increased post-implantation loss).  The inhalation exposure endpoint is based on the NOAEL from an oral toxicity study for this exposure scenario since no route-specific study is available.  The HASPOC recommended that the subchronic inhalation study is not required at this time (A. Dunbar, 7/11/2013, TXR # 0056699).  In the absence of inhalation absorption data, toxicity by the inhalation route was considered equivalent to toxicity by the oral route of exposure.  The LOC for both the dermal and inhalation endpoints is 100 based upon a 10X UF for inter-species extrapolations, a 10X UF for intra-species variations, and 1X for FQPA SF. 

The short- and intermediate-term dermal and inhalation endpoints are only applicable to adults and youth >= 11 years old because the endpoint is based on in utero effects.  The ORE assessment includes a lifestage of kids 11 to <16.  As puberty starts around age 13, this endpoint that is based on in utero effects is being applied to this lifestage.  This endpoint is suitable for occupational exposure as it is protective of female workers that may become pregnant while exposed to trinexapac-ethyl.  While we recognize that this endpoint is most appropriate for pregnant females, it is protective of effects observed in males at higher doses. 

Based on use pattern, long-term dermal and inhalation exposures are not expected.

Short- (1-30 days) and Intermediate- (1-6 months) Term Dermal and Inhalation Endpoints (children < 11 years old): HED reviewed the full toxicological database for trinexapac-ethyl in an attempt to select endpoints for the dermal and inhalation exposures in children (<11 years old).  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,
 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 (effects only observed above the limit dose) in the 2-generation reproductive study in rats or in the chronic/carcinogenicity studies in rats and mice.

4.5.1	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 exposures can be combined for adults and youth >= 11 years old since the PODs are from the same study (rabbit developmental) and thus the effects are the same.

4.5.2	Cancer Classification and Risk Assessment Recommendation

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. 

4.5.3	Summary of Points of Departure and Toxicity Endpoints Used in Human Risk Assessment

Toxicological dose/endpoints selected for the trinexapac-ethyl risk assessment are provided in Tables 4.5.3.1 and 4.5.3.2.

Table 4.5.3.1 Summary of Toxicological Doses and Endpoints for Trinexapac-ethyl for use in Dietary and Non-Occupational Human Health Risk Assessments
                                       
                                   Exposure/
                                   Scenario
                                       
                              Point of Departure
                                      POD
                                       
                   Uncertainty Factors/ 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/day

UFA= 10X
UFH = 10X
FQPA SF= 1X

Acute RfD = 0.6 mg/kg/day

aPAD = 0.6 mg/kg/day
Developmental rabbit study
MRID 41869524

LOAEL = 360 mg/kg, based on a decrease in mean number of fetuses/litter and an increase in post-implantation loss
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
Oral 
(Short and Intermediate- Term) Adult and Youths (>=11 years old)
NOAEL = 60 mg/kg/day

UFA= 10X
UFH = 10X
FQPA SF= 1X

LOC for MOE = 100
Developmental rabbit study
MRID 41869524

LOAEL = 360 mg/kg, based on a decrease in mean number of fetuses/litter and an increase in post-implantation loss
Incidental Oral 
(Short and Intermediate- Term) (children) 
    No appropriate endpoint for the incidental oral scenario for children.
Dermal & Inhalation
Short- and Intermediate-term (adults and youths >=11 years old 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

LOC for MOE = 100

Developmental rabbit study
MRID 41869524

LOAEL = 360 mg/kg, based on a decrease in mean number of fetuses/litter and an increase in post-implantation loss
Dermal & Inhalation
Short- and Intermediate-term (children <11) 
 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.  

Table 4.5.3.2 Summary of Toxicological Doses and Endpoints for Trinexapac-ethyl for use in Occupational Human Health Risk Assessments
                                       
                                   Exposure/
                                   Scenario
                                       
                              Point of Departure
                                      POD
                                       
                   Uncertainty Factors/ FQPA Safety Factors
                RfD, PAD, Level of Concern for Risk Assessment
                                       
                        Study and Toxicological Effects
Dermal & Inhalation
Short- and Intermediate-term (adults and youths >=11 years old 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

LOC for MOE = 100
Developmental rabbit study
MRID 41869524

LOAEL = 360 mg/kg, based on a decrease in mean number of fetuses/litter and an increase in post-implantation loss
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 
S. Piper. Trinexapac-ethyl: Section 3 Registration for Clover (Seed Crop). Summary of Analytical Chemistry and Residue Data; D465447; 03/15/2023.

S. Piper. Trinexapac-ethyl: Acute and Chronic Aggregate Dietary (Food and Drinking Water) Exposure and Risk Assessments for a Section 3 Registration on Clover (Seed Crop); D465454; 03/15/2023.

5.1	Residues of Concern Summary and Rationale 

For plants (primary and rotational crops) and livestock commodities, the Residues of Concern Knowledgebase Subcommittee (ROCKS) recommends that parent trinexapac-ethyl and the free acid metabolite, trinexapac (CGA 179500) both free and conjugated forms, are the residues of concern for both the tolerance expression and the risk assessment.  For drinking water, the residues of concern are the parent ester including its free acid CGA-179500, CGA-313458, an open chain cyclohexane ring and an unidentified hydroproduct M3 (ROCKS memo, E. Holman, 07/05/2011, D390121).

Table 5.1.1. Summary of Metabolites and Degradates of Trinexapac-ethyl
Matrix
Residues included in Risk Assessment
Residues included in Tolerance Expression 
Plants
Primary Crop

Trinexapac-ethyl parent + Trinexapac acid (CGA 179500) free and conjugated

Trinexapac-ethyl parent + Trinexapac acid (CGA 179500) free and conjugated

Rotational Crop

Livestock
Ruminant

Poultry

Drinking Water
Total residues (parent + identified degradates)[1]
Not Applicable
[1] A total major residue approach is recommended, including parent and major environmental degradates trinexapac (CGA-179500), 2-(4-cyclopropyl-4-hydroxy-2-oxobutyl)succinic acid (CGA-313458), the open chain cyclohexane ring, and the unidentified hydroproduct M3.  

5.2 	Food Residue Profile

Available metabolism data shows that trinexapac-ethyl does translocate to the growing shoot when applied as a foliar application.  Trinexapac-ethyl is used at relatively low application rates, and the submitted field trial studies demonstrate that when applied at post-emergence, quantifiable residues are seen in sugarcane treated up to 7-45 days before harvest; cereal grains treated up to 52-100 days before harvest; and clover grown for seed treated up to 28-57 days. Also, quantifiable residues are seen in livestock at low levels in the animal feedstuff associated with this action.  

5.3	Water Residue Profile

EFED determined that no new drinking water estimates were needed since the IR-4-proposed Section 3 new use of trinexapac-ethyl on clover for seed (DP Barcodes 464371 & 464495), under the "New Use Policy" (NUP) titled "Streamlining Drinking Water and Ecological Risk Assessments", dated August 31, 2017.  The reason is that the proposed new use on clover is not likely to substantially increase exposure and/or exposure estimates beyond that of currently registered uses. Previously, Tier I rice model for drinking water assessment was conducted to support the human health risk assessment and the recommended EDWCs based on highest predicted values for surface water and ground water.  For surface water, application (1 application at 0.045 lb a.i./acre) to rice yielded the highest EDWCs.  The acute and chronic concentrations were estimated to be 31.68 ppb.  For ground water, based on the proposed highest annual use rate for turf (8 applications at 0.34 lb a.i./acre), the PRZM-GW (v.1.07) model estimated an acute concentration of 0.116 ppb and 30-year average (chronic) concentration of 0.054 ppb (C, Koper, D421848, 1-OCT-2014).

Water residues were incorporated in the DEEM-FCID into the food categories "water, direct, all sources" and "water, indirect, all sources."   Table 5.3.1 provides a summary of the Tier 1 modeled drinking water concentrations.  The model and its description are available at the EPA internet site: http://www.epa.gov/oppefed1/models/water/.  

Table 5.3.1.  Trinexapac-Ethyl Estimated Drinking Water Concentrations (EDWCs) for Surface Water and Ground Water 
                                       
                                    Proposed
                                   Label Use
                                       
                                        Model
                                       
                                   Method[1]
                             Maximum Application Rate
                                  1-in-10 year
                                      acute
                                    (ug/L)
                                  1-in-10 year
                                    chronic
                                    (ug/L)
                                30- year average
                                    (ug/L)
                                 Surface Water
                                     Rice
                               Tier 1 Rice Model
                                        NA
                            1 app @ 0.045 lb a.i./A
                                     31.68
                                     31.68
                                     31.68
                                 Ground Water
                                      Turf
                                    PRZM-GW
                                       G
                             8 app @ 0.34 lb a.i./A
                                     0.116
                                       NA
                                     0.054
1 G = foliar, ground application, NA = Not Applicable.
 
 
 

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 for trinexapac-ethyl were conducted using the Dietary Exposure Evaluation Model software with the Food Commodity Intake Database (DEEM-FCID) Version 4.02.  This software uses 2005-2010 food consumption data from the U.S. Department of Agriculture's (USDA's) National Health and Nutrition Examination Survey, What We Eat in America, (NHANES/WWEIA).  The unrefined acute and chronic dietary exposure assessments used tolerance-level residues, HED's default processing factors, and assumed 100% CT for the registered commodities.  EDWCs for trinexapac-ethyl were provided by EFED and incorporated directly into the assessment.  The assessments used surface water EDWCs of 0.032 ppm in the acute and chronic assessments. 
 
5.4.2	Percent Crop Treated Used in Dietary Assessment

The acute and chronic assessments were both based on the assumption that 100% of all commodities were treated with trinexapac-ethyl.

5.4.3	Acute Dietary Risk Assessment

There were no appropriate toxicological effects attributable to a single exposure (dose) for the general population or any other population subgroups except females 13-49 years old; therefore, these population subgroups were not included in this assessment.  For food and drinking water, the acute dietary risk estimate is below HED's LOC (<100% of the aPAD) at the 95[th] percentile of exposure. The acute dietary exposure estimates for females 13-49 years old is 2.5% of the aPAD.

5.4.4	Chronic Dietary Risk Assessment

Combined chronic dietary exposure estimates for food and drinking water are below HED's LOC.  The chronic risk estimates were 3% of the cPAD for the general U.S. population and 7% of the cPAD for children 1-2 years old, the population with highest estimated chronic dietary exposure for trinexapac-ethyl.

5.4.5	Cancer Dietary Risk Assessment

Trinexapac-ethyl is classified as "Not Likely to be Carcinogenic to Humans."  Therefore, a cancer dietary exposure assessment was not conducted.

5.4.6	Dietary Summary Table

 Table 5.4.6.1.  Summary of Dietary (Food and Drinking Water) Exposure and Risk Estimates for Trinexapac-ethyl[1]
                              Population Subgroup
                                 Acute Dietary
                              (95[th] Percentile)
                                Chronic Dietary
                                        
                                     Cancer
                                        
                                        
                          Dietary Exposure (mg/kg/day)
                                     % aPAD
                                Dietary Exposure
                                  (mg/kg/day)
                                       % 
                                      cPAD
                                Dietary Exposure
                                  (mg/kg/day)
                                      Risk
 General US population
                                      N/A
                                        
                                        
                                    0.008516
                                      2.7
                                      N/A
                                        
                                      N/A
                                        
 All Infants (<1 year old)
                                        
                                    0.009082
                                      2.8
                                        
                                        
 Children 1-2 years old
                                        
                                    0.021757
                                      6.8
                                        
                                        
 Children 3-5 years old
                                        
                                    0.020328
                                      6.4
                                        
                                        
 Children 6-12 years old
                                        
                                    0.014219
                                      4.4
                                        
                                        
 Youth 13-19 years old
                                        
                                    0.008451
                                      2.6
                                        
                                        
 Adults 20-49 years old
                                        
                                    0.007015
                                      2.2
                                        
                                        
 Adults 50-99 years old
                                        
                                    0.006044
                                      1.9
                                        
                                        
 Females 13-49 years old
                                    0.014829
                                      2.5
                                    0.006656
                                      2.1
                                       
                                       
  APAD=0.6 MG/KG/DAY FOR FEMALES 13-49 ONLY (NO APPROPRIATE ENDPOINT FOR GENERAL US POPULATION INCLUDING INFANTS AND CHILDREN) CPAD=0.32 MG/KG/DAY. NOT LIKELY TO BE CARCINOGENIC TO HUMANS.

 Residential (Non-Occupational) Exposure/Risk Characterization

There are no proposed residential uses at this time; however, there are existing residential uses that have been previously assessed using current data and assumptions.  The registered residential uses include residential lawns/turf and were most recently assessed in 2013 (M. Hawkins, 9/18/2013, D413030).  The combined dermal and inhalation MOEs for residential handlers ranged from 240 to 21,000,000.  The MOEs for all residential exposure scenarios assessed are not of concern (i.e., estimated MOEs are > the LOC of 100).  The residential recommendations for aggregate risk assessment remain unchanged for trinexapac-ethyl and are presented below.  There are no toxicological endpoints for short-term incidental oral or dermal exposures to young children (1 to <2 years old and 6 to < 11 years old); therefore, quantitative residential exposure assessments were not conducted for younger children.

 The recommended residential exposure estimate for use in the adult (females 13-49 years old) aggregate assessment is dermal and inhalation exposure from handler exposure to sprays that are applied on turf with backpack sprayers (edging/banding), which resulted in a MOE of 240.
 The recommended residential exposure estimate for use in the youth (11 to < 16 years old) aggregate assessment is dermal exposure from mowing turf that has been treated with a granular formulation, which resulted in a MOE of 13,000.
 There are no toxicological endpoints for short-term incidental oral or dermal exposures to young children (1 to <2 years old and 6 to < 11 years old); therefore, quantitative residential exposure assessments are not conducted for younger children.

The residential exposure/risk estimates and recommendations for the trinexapac-ethyl aggregate are provided below in Table 6.1.1.

Table 6.1.1.  Recommendations for the Residential Exposures for the Trinexapac-ethyl Aggregate Assessment[1]
                                   Lifestage
                    Residential Handler/Post- Application 

                              Dose (mg/kg/day)[2]
                                    MOE[3]

                                    Dermal
                                  Inhalation
                                     Total
                                    Dermal
                                  Inhalation
                                     Total
                                  Short-Term
Adult Handler 
Turf  application with backpack sprayer
                                    0.2482
                                    0.00034
                                     0.249
                                      240
                                    170,000
                                      240
Youth 11 to < 16 years old
Post-application
mowing activity 
following granular applications
                                    0.0050
                                      N/A
                                     0.005
                                    13,000
                                      N/A
                                    13,000
1	Bolded risk estimates should contribute to the residential exposure portion of the aggregate assessment. 
2	Residential Dose = the highest handler dose for each applicable lifestage of all scenarios assessed from the 2013 memo (M. Hawkins, 9/18/2013, D413030). Total = dermal + inhalation.
3	Residential MOE = the MOEs associated with the highest doses identified in the 2013 memo (M. Hawkins, 9/18/2013, D413030).  Total = 1 / (1/Dermal MOE) + (1/Inhalation MOE).

 Aggregate Exposure/Risk Characterization

In accordance with the FQPA, HED must consider and aggregate (add) pesticide exposures and risks from three major sources: food, drinking water, and residential exposures.  In an aggregate assessment, exposures from relevant sources are added together and compared to quantitative estimates of hazard (e.g., a NOAEL or PAD), or the risks themselves can be aggregated.  When aggregating exposures and risks from various sources, HED considers both the route and duration of exposure.

7.1	Acute Aggregate Risk

Acute aggregate risk results from exposure to residues in food and drinking water alone.  No appropriate endpoint for the general population, including infants (1 to < 2 years old) and children (6 to < 11 years old) was found; therefore, aggregate assessments are not required for these population subgroups.  The acute dietary exposure analysis for females 13-49 years included both food and drinking water.  Therefore, acute aggregate risk is equivalent to the acute dietary risk for this population subgroup, as discussed in Section 5.4.3, above.  All risk estimates are below HED's LOC.  

 Short -Term Aggregate Risk
 
 For residential exposure scenarios, only short-term exposures were assessed, and these scenarios are aggregated with average dietary exposure from food and water which are considered to be background exposure. 
 
 For the adult short-term aggregate risk assessment, chronic dietary exposure was added directly to the adult and youth (11< 16 years old) post-application exposure estimates.  The handler scenario was used in the aggregate because it resulted in higher exposure than the adult post-application scenario.  The chronic dietary exposure estimates for adults 20-49 years old and youth 13-19 years old were the recommended dietary population subgroups to combine to calculate the aggregate exposure and risk estimate.
 
 Short-term aggregate margins of exposure for adult and youth are not of concern (i.e., estimated MOEs are > the LOC of 100).  Short-term estimated exposure and risks are presented in Table 7.2.1.        

Table 7.2.1.  Short-Term Aggregate Risk Calculations
                                  Population
                                NOAEL mg/kg/day
                                    LOC[1]
                      Max Allowable Exposure mg/kg/day[2]
                 Average Food and Water Exposure mg/kg/day[3]
           Residential Post-application Dermal Exposure mg/kg/day[4]
                          Total Exposure mg/kg/day[5]
                Aggregate MOE (food, water, and residential)[6]
Youth (11-<16 years old)
                                      60
                                      100
                                     0.60
                                    0.00845
                                    0.0050
                                    0.0135
                                     4,400
Adults (20-49 years old)
                                       
                                       
                                       
                                    0.00702
                                     0.25
                                     0.26
                                      230
[1] An UF of 100x was applied to account for interspecies extrapolation (10x) and intraspecies variation (10x) and no additional uncertainty factors/safety factors are required.
[2] Maximum Allowable Exposure (mg/kg/day) = NOAEL/ (60 mg/kg/day)/LOC (100)
3 Average food and water exposure from chronic dietary exposure for youth 13-19 yrs old and adults 20-49 yrs old.  See Table 5.4.6.1. 
[4] Residential Exposure = See Table 6.1.1.
[5] Total Exposure = Avg Food & Water Exposure + Residential Exposure
[6] Aggregate MOE = NOAEL/Total Exposure

 Chronic Aggregate Risk

The chronic aggregate risk assessment combines exposures to trinexapac-ethyl in food and drinking water only.  The chronic (food and drinking water) exposure and risk estimates were <=6.8% of the cPAD for all population subgroups; therefore, there are no chronic aggregate risk estimates of concern (see Section 5.4.6.1). 

 Cancer Aggregate Risk

Consistent with previous assessments, trinexapac-ethyl is classified as "not likely to be carcinogenic to humans."  Therefore, aggregate cancer risk was not quantitatively assessed.

8.0	Non-Occupational Spray Drift Exposure and Risk Estimates

The approach to be used for quantitatively incorporating spray drift into risk assessment is based on a premise of compliant applications which, by definition, should not result in direct exposures to individuals because of existing label language and other regulatory requirements intended to prevent them.  Direct exposures would include inhalation of the spray plume or being sprayed directly.  Rather, the exposures addressed here are thought to occur indirectly through contact with impacted areas, such as residential lawns, when compliant applications are conducted.  Given this premise, exposures for children (1 to 2 years old) and adults who have contact with turf where residues are assumed to have deposited via spray drift thus resulting in an indirect exposure are the focus of this analysis analogous to how exposures to turf products are considered in risk assessment.  

Several trinexapac-ethyl products have existing labels for use on turf, thus it was considered whether the risk assessment for that use may be considered protective of any type of exposure that would be associated with spray drift.  It should be noted that the registered residential uses on turf result in exposure greater than potential exposure from spray drift; therefore, no new residential assessment needs to be completed.  If the maximum application rate on crops adjusted by the amount of drift expected is less than or equal to existing turf application rates, then the existing turf assessment is considered protective of spray drift exposure.  Note that this assumes similar formulations are being applied to the agricultural crops and the residential turf (i.e., if a granular product is registered for use on residential turf, the scenarios assessed for that use may not be protective of liquid applications made to agricultural crops).  The currently registered maximum single application rate of trinexapac-ethyl for grass is 0.5 lb ai/A.  The highest degree of spray drift noted for any application method immediately adjacent to a treated field (Tier 1 output from the aerial application using fine to medium spray quality) results in a deposition fraction of 0.26 of the application rate.  A quantitative spray drift assessment for trinexapac-ethyl is not required because the maximum application rate to a crop/target site multiplied by the adjustment factor for drift of 0.26 is less than the maximum direct spray residential turf application rate [(0.5 lb ai/A)] for any trinexapac-ethyl products.  The turf post-application MOEs have been previously assessed and are based on the revised SOPs for Residential Exposure Assessment (i.e., see above in Section 6.0).  

9.0       Non-Occupational Bystander Post-Application Inhalation Exposure and Risk Estimates

Volatilization of pesticides may be a source of post-application inhalation exposure to individuals nearby pesticide applications.  The Agency sought expert advice and input on issues related to volatilization of pesticides from FIFRA Scientific Advisory Panel (SAP) in December 2009, and received the SAP's final report on March 2, 2010.  The Agency has evaluated the SAP report and has developed a Volatilization Screening Tool and a subsequent Volatilization Screening Analysis (Human Health Bystander Screening Level Analysis: Volatilization of Conventional Pesticides). During Registration Review, the Agency will utilize this analysis to determine if data (i.e., flux studies, route-specific inhalation toxicological studies) or further analysis is required for trinexapac-ethyl.

      Cumulative Exposure/Risk Characterization

Unlike other pesticides for which EPA has followed a cumulative risk approach based on a common mechanism of toxicity, EPA has not made a common mechanism of toxicity finding as to trinexapac-ethyl and any other substances.  For the purposes of this action, therefore, EPA has not assumed that trinexapac-ethyl has a common mechanism of toxicity with other substances. 

In 2016, EPA's Office of Pesticide Programs released a guidance document entitled, Pesticide Cumulative Risk Assessment: Framework for Screening Analysis. This document provides guidance on how to screen groups of pesticides for cumulative evaluation using a two-step approach beginning with the evaluation of available toxicological information and if necessary, followed by a risk-based screening approach.  This framework supplements the existing guidance documents for establishing common mechanism groups (CMGs) and conducting cumulative risk assessments (CRA). 

Trinexapac-ethyl has not been classified in a group for screening.  At this time, EPA does not expect any exposures from other pesticides or substances that would warrant screening with the framework.  As a result, EPA concludes that trinexapac-ethyl does not have a common mechanism of toxicity with other substances that contribute to the risk assessment.  If other pesticides are registered that have the potential to be screened with trinexapac-ethyl, EPA will use the framework to examine the potential for a common mechanism of toxicity and the potential for cumulative risk as part of the ongoing registration review process.    

      Occupational Exposure/Risk Characterization
W. Britton. Trinexapac-ethyl.  Occupational and Residential Exposure Assessment for Establishing a New Use on Clover. 3/15/2023. D467243. 

11.1	Short-/Intermediate -Term Handler Risk

HED uses the term handlers to describe those individuals who are involved in the pesticide application process.  HED believes that there are distinct job functions or tasks related to applications and exposures can vary depending on the specifics of each task.  Job requirements (amount of chemical used in each application), the kinds of equipment used, the target being treated, and the level of protection used by a handler can cause exposure levels to differ in a manner specific to each application event.  

Based on the anticipated use patterns and current labeling, types of equipment and techniques that can potentially be used, occupational handler exposure is expected from the proposed use on clover.  The quantitative exposure/risk assessment developed for occupational handlers is based on the scenarios presented in Table 11.1.1. 

Occupational Handler Exposure Data and Assumptions

A series of assumptions and exposure factors served as the basis for completing the occupational handler risk assessments.  Each assumption and factor is detailed below on an individual basis.

Application Rate: 
The trinexapac-ethyl quantitative exposure/risk assessment developed for occupational handlers is based on the proposed application rates listed in Table 3.2.1.  

Unit Exposures:  
It is the policy of HED to use the best available data to assess handler exposure.  Sources of generic handler data, used as surrogate data in the absence of chemical-specific data, include PHED 1.1, the AHETF database, the Outdoor Residential Exposure Task Force (ORETF) database, or other registrant-submitted occupational exposure studies.  Some of these data are proprietary (e.g., AHETF data), and subject to the data protection provisions of FIFRA.  The standard values recommended for use in predicting handler exposure that are used in this assessment, known as "unit exposures", are outlined in the "Occupational Pesticide Handler Unit Exposure Surrogate Reference Table", which, along with additional information on HED policy on use of surrogate data, including descriptions of the various sources, can be found at the Agency website. 

Area Treated or Amount Handled:  
The inputs for area treated were based on information in ExpoSAC Policy 9.2.  

Exposure Duration: 
HED classifies exposures from 1 to 30 days as short-term and exposures 30 days to six months as intermediate-term.  Exposure duration is determined by many things, including the exposed population, the use site, the pest pressure triggering the use of the pesticide, and the cultural practices surrounding that use site.  For most agricultural uses, it is reasonable to believe that occupational handlers will not apply the same chemical every day for more than a one-month time frame; however, there may be a large agribusiness and/or commercial applicators who may apply a product over a period of weeks (e.g., completing multiple applications for multiple clients within a region).  

For trinexapac-ethyl, short and intermediate exposures are expected for handlers.  The short- and intermediate-term points of departure are the same for each exposure route, therefore only short-term handler exposures/risks were estimated, and are considered protective for intermediate-term exposure and risk.  Long-term exposures are not expected.

Personal Protective Equipment (PPE): 
Estimates of dermal and inhalation exposure were calculated considering the PPE listed on product labels, and any additional PPE necessary to identify risk estimates not of concern.  The attire and/or PPE that may be considered and assessed include: (1) baseline, defined as a single layer of clothing consisting of a long sleeved shirt, long pants, shoes plus socks, no protective gloves, and no respirator, (2) baseline with gloves and/or respirator, (3) double layer, defined as a coverall over a single layer of clothing, no protective gloves, and no respirator, (4) double layer with gloves and/or respirator, (5) single layer or double layer with a chemical resistant hat, and (5) engineering controls (such as closed systems, water soluble packets, etc).  The trinexapac-ethyl product labels direct mixers, loaders, applicators and other handlers to wear baseline attire.

Occupational Handler Non-Cancer Exposure and Risk Estimate Equations
The algorithms used to estimate non-cancer exposure and dose for occupational handlers can be found in Appendix A of the support occupational and residential exposure and risk assessment.  

Combining Exposures/Risk Estimates:
Dermal and inhalation risk estimates were combined in this assessment since the toxicological effects for these exposure routes were similar.  Dermal and inhalation risk estimates were combined using the following formula:

 Total MOE = Point of Departure (mg/kg/day) / Combined dermal + inhalation dose (mg/kg/day)

Summary of Occupational Handler Non-Cancer Exposure and Risk Estimates
Assuming baseline clothing (e.g., single layer of clothing, no gloves and no respirator) is worn, most of the occupational handler scenarios are not of concern (i.e., estimated MOEs are > the LOC of 100); MOEs range from 46 to 4,800.  However, one exposure scenario, mixer/loader for broadcast liquid aerial applications, requires additional PPE (i.e., gloves) to reach a combined MOE that is not of concern (MOE = 270).  

The Agency matches quantitative occupational exposure assessment with appropriate characterization of exposure potential.  While HED presents quantitative risk estimates for human flaggers where appropriate, agricultural aviation has changed dramatically over the past two decades.  According the 2012 National Agricultural Aviation Association (NAAA) survey of their membership, the use of GPS for swath guidance in agricultural aviation has grown steadily from the mid 1990's.  Over the same time period, the use of human flaggers for aerial pesticide applications has decreased steadily from ~15% in the late 1990's to only 1% in the most recent (2012) NAAA survey.  The Agency will continue to monitor all available information sources to best assess and characterize the exposure potential for human flaggers in agricultural aerial applications.

HED has no data to assess exposures to pilots using open cockpits.  The only data available is for exposure during aerial applications (covering both airplanes and helicopters) of liquid formulations to pilots in enclosed cockpits (data from AHETF) and of granule formulations in enclosed cockpits (data from PHED).  Therefore, risks to pilots are assessed using the engineering control (enclosed cockpits) and baseline attire (long-sleeve shirt, long pants, shoes, and socks); use of the data in this fashion is consistent with  the Agency's Worker Protection Standard (WPS) stipulations for engineering controls, which says label-required PPE for applicators can be reduced when using an enclosed cockpit (40 CFR 170.607(f)(3)) as well as a provision regarding use of gloves for aerial applications (40 CFR 170.607(f)(1)), which says pilots are not required to wear protective gloves for the duration of the application, unless gloves are required on the pesticide product labeling.  With this level of protection, there are no risk estimates of concern for applicators.

A 2019 study by the AHETF measured dermal and inhalation exposure for workers who loaded liquid pesticides using closed systems such as gravity feed, container breach, and suction/extraction systems.  After analyzing the exposure monitoring data, the AHETF observed that exposures were higher than expected and subsequently identified that, when using suction/extraction systems, removing and handling chemical extraction probes without rinsing them prior to removal from the pesticide container had the potential to result in high exposures via direct exposure to the liquid concentrate.  The AHETF therefore submitted to the Agency a dataset that excludes monitoring of those workers who handled unrinsed chemical extraction probes and recommended that the Agency take additional regulatory actions to ensure workers do not remove and handle chemical extraction probes still coated with the concentrated liquid formulation.
   
The Agency agreed with the AHETF proposal, recognizing that handling of unrinsed chemical extraction probes is inconsistent with the exposure reduction principles of closed systems.  Closed loading systems are an engineering control designed to prevent direct contact between users and the pesticide formulation, thereby reducing exposures.  According to EPA's Worker Protection Standard (WPS), a closed system must remove the pesticide from its original container and transfer the pesticide product through connecting hoses, pipes and couplings that are sufficiently tight to prevent exposure of handlers to the pesticide product, except for the negligible escape associated with normal operation of the system [40 CFR § 170.607(d)(2)(i)].  However, in addition to considerations regarding closed systems, given the high exposure potential from this activity, the Agency is requiring revisions to applicable product label instructions to restrict handling un-rinsed extraction probes and conducting stakeholder outreach and revising worker training modules to ensure that users of suction/extraction systems rinse the chemical extraction probes within the pesticide container prior to their removal so that they are not exposed to the concentrated liquid formulation.
Table 11.1.1.  Occupational Handler Non-Cancer Exposure and Risk Estimates for Trinexapac-ethyl
                               Exposure Scenario
                               Crop or Target[1]
                     Dermal Unit Exposure 
(μg/lb ai)[2]
                      Level of PPE or
Engineering control
                    Inhalation
Unit
Exposure
(μg/lb ai)[2]
                      Level of PPE or
Engineering control
                          Maximum
Application Rate[3]
                                 App Rate Unit
                    Area Treated or
Amount Handled Daily[4]
                       Area Treated/Amount
Handled Unit
                                    Dermal
                                  Inhalation
                                     Total

                              Dose (mg/kg/day)[5]
                                    MOE[6]
                                   (LOC=100)
                              Dose (mg/kg/day)[7]
                                    MOE[8]
                                   (LOC=100)
                                    MOE[9]
                                   (LOC=100)
                                 Mixer/Loader
                           Liquid, Aerial, Broadcast
                           Field crop, high-acreage
                                      220
                                    SL/No G
                                     0.219
                                     No-R
                                     0.44
                                  lb ai/acre
                                     1200
                                     acres
                                      1.3
                                      46
                                    0.00168
                                     36000
                                      46
                                       
                                       
                                     37.6
                                     SL/G
                                     0.219
                                     No-R
                                       
                                       
                                       
                                       
                                     0.224
                                      270
                                    0.00168
                                     36000
                                      270
                        Liquid, Chemigation, Broadcast
                           Field crop, high-acreage
                                      220
                                    SL/No G
                                     0.219
                                     No-R
                                     0.44
                                  lb ai/acre
                                      350
                                     acres
                                     0.381
                                      160
                                   0.000488
                                    120000
                                      160
                         Liquid, Groundboom, Broadcast
                           Field crop, high-acreage
                                      220
                                    SL/No G
                                     0.219
                                     No-R
                                     0.44
                                  lb ai/acre
                                      200
                                     acres
                                     0.218
                                      280
                                    0.00028
                                    210000
                                      280
                                  Applicator
             Spray
 (all starting formulations), Aerial, Broadcast
                           Field crop, high-acreage
                                     2.08
                                     EC/G
                                    0.0049
                                    EC/No-R
                                     0.44
                                  lb ai/acre
                                     1200
                                     acres
                                    0.0124
                                     4800
                                   0.0000375
                                    1600000
                                     4800
           Spray
 (all starting formulations), Groundboom, Broadcast
                           Field crop, high-acreage
                                     78.6
                                    SL/No G
                                     0.34
                                     No-R
                                     0.44
                                  lb ai/acre
                                      200
                                     acres
                                    0.0777
                                      770
                                   0.000433
                                    140000
                                      770
                                    Flagger
             Spray
 (all starting formulations), Aerial, Broadcast
                           Field crop, high-acreage
                                      11
                                    SL/No G
                                     0.202
                                     No-R
                                     0.44
                                  lb ai/acre
                                      350
                                     acres
                                     0.019
                                     3200
                                   0.000451
                                    130000
                                     3100
1 Crop/Target:  High acreage field crops include clover.  
2 Unit Exposures:  Based on the "Occupational Pesticide Handler Unit Exposure Surrogate Reference Table" (https://www.epa.gov/pesticide-science-and-assessing-pesticide-risks/occupational-pesticide-handler-exposure-data); Level of PPE: SL/No G = single layer, no gloves; SL/G = single layer, gloves; EC = engineering controls; No-R = no respirator.
3 Maximum Application Rate:  Based on the proposed label EPA Reg. No. 100-1677 (see Table 3.2.1).
4 Area Treated or Amount Handled:  Exposure Science Advisory Council Policy #9.2. 
5 Dermal Dose:  Dermal Dose = Dermal Unit Exposure (μg/lb ai) x Conversion Factor (0.001 mg/μg) x Application Rate (lb ai/acre) x Area Treated or Amount Handled Daily (A) x DAF (77.5 %) / BW (69 kg).
6 Dermal MOE:  Dermal MOE = Dermal POD (60 mg/kg/day) / Dermal Dose
 (mg/kg/day).  LOC = 100.
7 Inhalation Dose:  Inhalation Dose = Inhalation Unit Exposure (μg/lb ai) x Conversion Factor (0.001 mg/μg) x Application Rate (lb ai/acre) x Area Treated or Amount Handled Daily (A) / BW (69 kg).
8 Inhalation MOE:  Inhalation MOE = Inhalation POD (60 mg/kg/day) / Inhalation Dose (mg/kg/day).  LOC = 100.
9 Total MOE:  Total MOE = POD (60 mg/kg/day) / Dermal Dose + Inhalation Dose 

11.2	Short-/Intermediate- Term Post-Application Risk

11.2.1	Dermal Post-application Risk

Occupational Post-application Dermal Exposure Data and Assumptions

A series of assumptions and exposure factors served as the basis for completing the occupational post-application risk assessments.  Each assumption and factor is detailed below on an individual basis.

Exposure Duration:  
HED classifies exposures from 1 to 30 days as short-term and exposures 30 days to six months as intermediate-term.  For the proposed new use of trinexapac-ethyl on clover, short- and intermediate-term dermal exposure is expected. 

Transfer Coefficients: 
It is the policy of HED to use the best available data to assess post-application exposure.  Sources of generic post-application data, used as surrogate data in the absence of chemical-specific data, are derived from ARTF exposure monitoring studies, and, as proprietary data, are subject to the data protection provisions of FIFRA.  The standard values recommended for use in predicting post-application exposure that are used in this assessment, known as "transfer coefficients", are presented in the ExpoSAC Policy 3 which, along with additional information about the ARTF data, can be found at the Agency website.  

Table 11.2.1.1.  Anticipated Post-Application Activities and Dermal Transfer Coefficients
                                     Crops
                          Policy Crop Group Category
                                  Crop Height
                                Foliage Density
                       Transfer Coefficients (cm[2]/hr)
                                  Activities
                                 Forage Crop 
                                (i.e., Clover)
                          Field/row crop, low/medium
                                      Low
                                     Full
                                     1900
                             Irrigation (handset)
                                       
                                       
                                      Low
                                   Full/Min
                                     1100
                                   Scouting

Application Rate: 
The trinexapac-ethyl quantitative exposure/risk assessment developed for occupational post-application workers is based on the proposed application rates listed in Table 4.1.  

Exposure Time:  The average occupational workday is assumed to be 8 hours. 
Transferable Residues:  
Chemical-specific DFR data have not been submitted for trinexapac-ethyl.  Therefore, the assessment uses HED's default assumption that 25% of the application is available for transfer on day 0 following the application and the residues dissipate at a rate of 10% each following day.  A DFR study is not required for trinexapac-ethyl at this time since there are dermal MOEs are greater than 2 times the LOC based on default values for the fraction of application rate available for transfer after a foliar application.

Table 11.2.1.2.  Occupational Post-application Non-Cancer Exposure and Risk Estimates for Trinexapac-ethyl
                                   Crop/Site
                                  Activities
                        Transfer Coefficient (cm[2]/hr)
                          Application Rate (lb ai/A)
                                    DFR[1]
                                 Dermal Dose 
                                (mg/kg/day)[2]
                                      MOE
                                (LOC = 100)[3]
                                 Forage Crop 
                                 (i.e. Clover)
                             Irrigation (handset)
                                     1900
                                     0.44
                                     1.11
                                     0.211
                                      280
                                       
                                   Scouting
                                     1100
                                     0.44
                                       
                                     0.112
                                      490
1	DFR = Application Rate (lb ai/A) x F x (1-D)t x 4.54E8 ug/lb x 2.47E-8 acre/cm[2]; where F = 0.25 and D = 0.10 per day  
2	Daily Dermal Dose (mg/kg/day) = [DFR (ug/cm[2]) x Transfer Coefficient x 0.001 mg/ug x 8 hrs/day x dermal absorption (77.5 %)] ¸ BW (69 kg).
3	MOE = POD (60 mg/kg/day) / Daily Dermal Dose (mg/kg/day).  

Restricted Entry Interval
 Trinexapac-ethyl is classified as Toxicity Category III via the acute oral, acute dermal, and acute eye irritation and Toxicity Category IV for acute inhalation and acute dermal irritation.  It is not a skin sensitizer.  Short- and intermediate-term post-application risk estimates were not a concern on day 0 (12 hours following application) for all post-application activities.  Under 40 CFR 156.208 (c) (2), ai's classified as Acute III or IV for acute dermal, eye irritation and primary skin irritation are assigned a 12-hour REI.  Therefore, the [156 subpart K] Worker Protection Statement interim REI of 12 hours is adequate to protect agricultural workers from post-application exposures to trinexapac-ethyl.  HED would recommend the REI on the product labels be consistent with the WPS recommendations. This is the REI listed on the proposed label and is considered protective of post-application exposure.  

11.2.2	Inhalation Post-application Risk

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 FIFRA Scientific Advisory Panel (SAP) in December 2009, and received the SAP's final report on March 2, 2010.  The Agency has evaluated the SAP report and has developed a Volatilization Screening Tool and a subsequent Volatilization Screening Analysis (Human Health Bystander Screening Level Analysis: Volatilization of Conventional Pesticides).  During Registration Review, the Agency will utilize this analysis to determine if data (i.e., flux studies, route-specific inhalation toxicological studies) or further analysis is required for trinexapac-ethyl.

Although a quantitative occupational post-application inhalation exposure assessment was not performed, an inhalation exposure assessment was performed for occupational/commercial handlers.  Handler exposure resulting from application of pesticides outdoors is likely to result in higher exposure than post-application exposure, and all of the occupational handler scenarios resulted in inhalation risk estimates that were not of concern at baseline (i.e., all inhalation MOEs without a respirator >= the LOC).  Therefore, it is expected that these handler inhalation exposure estimates would be protective of most occupational post-application inhalation exposure scenarios.

  References

S. Piper. Trinexapac-ethyl: Section 3 Registration for Clover (Seed Crop). Summary of Analytical Chemistry and Residue Data; D465447; 03/15/2023

S. Piper. Trinexapac-ethyl: Acute and Chronic Aggregate Dietary (Food and Drinking Water) Exposure and Risk Assessments for a Section 3 Registration on Clover (Seed Crop); D465454; 03/15/2023

W. Britton. Trinexapac-ethyl.  Occupational and Residential Exposure Assessment for Establishing New Use on Clover. D467243. 3/15/2022.

A. Dunbar. Trinexapac-ethyl: Summary of Hazard and Science Policy Council (HASPOC) Meeting on June 20, 2013: Recommendations on the need for a subchronic inhalation study; TXR 0056699; 07/11/2013.

M. Hawkins. Trinexapac-ethyl: Occupational and Residential Exposure/Risk Assessment for Proposed Uses on grasses grown for seed, sugarcane, and cereals (wheat, barley and oats). D392798; 11/23/2011.

V. Kurker. Trinexapac-ethyl. Human Health Risk Assessment for the Petition to Amend the Pre-Harvest Intervals on Sugarcane. D454165. 07/13/2020.

M. Hawkins. Trinexapac-ethyl.   Preliminary Occupational and Residential Exposure/Risk Assessment for Registration Review. D413030. 9/18/2013.

A. Dunbar. Trinexapac-Ethyl:  Summary of Hazard and Science Policy Council (HASPOC) Meeting on June 20, 2013:  Recommendations on the need for a Subchronic Inhalation study.  TXR 0056699. 7/11/2013.

Appendix A.  Toxicology Profile and Executive Summaries

A.1	Toxicology Data Requirements
The requirements (40 CFR 158.500) for a food use for trinexapac-ethyl are in Table A.1 below. Use of the new guideline numbers does not imply that the new (1998) guideline protocols were used.  

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	Acute Eye Irritation	
870.2500	Acute Dermal Irritation	
870.2600	Skin 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	28-Day Dermal	
870.3250	90-Day Dermal	
870.3465	90-Day Inhalation	

yes
yes
yes
CR
CR

yes
yes
yes
no
waived[a]

870.3700a  Developmental Toxicity (rodent)	
870.3700b  Developmental Toxicity (nonrodent)	
870-3800    Reproduction	

yes
yes
yes

yes 
yes
yes 

870.4100a  Chronic Toxicity (rodent)	
870.4100b  Chronic Toxicity (nonrodent) ...........................
870.4200a  Carcinogenicity (rat)	
870.4200b  Carcinogenicity (mouse)	
870.4300    Combined Chronic Toxicity/Carcinogenicity ...........

yes
yes
yes
yes
yes

yes
yes
yes
yes
yes

870.5100	Mutagenicity -- Bacterial Reverse Mutation Test	
870.5300	Mutagenicity -- Mammalian Cell Gene Mutation Test 	
870.5375	Mutagenicity -- Structural Chromosomal Aberrations	
870.5395	Mutagenicity -- In Vivo Micronucleus	

yes
yes
yes
yes

yes
yes
yes
yes

870.6200a  Acute Neurotoxicity Screening Battery (rat)	
870.6200b  90 Day Neurotoxicity Screening Battery (rat)	
870.6300	Developmental Neurotoxicity	

yes
yes
 CR
yes
yes
no

870.7485	General Metabolism	
870.7600	Dermal Penetration	
870.7800    Immunotoxicity	

yes
CR
yes

yes
yes
yes
  CR = conditionally required
  [a]Data waiver granted by HASPOC, July 11, 2013 (A. Dunbar, 7/11/2013, TXR 0056699).  

A.2	Toxicity Profiles
      
Table A.2.1 Acute Toxicity Profile of Trinexapac-ethyl (97%)
                                   Guideline
                                      No.
                                  Study Type
                                    MRID(s)
                                    Results
                               Toxicity Category
                                   870.1100
Acute Oral (rat)
                                   41563908
LD50 = 4613 mg/kg (M)
LD50 = 4212 mg/kg (F)
LD50 = 4458 mg/kg (C)
                                      III
                                   870.1200
Acute Dermal (rat)
                                   41563910
LD50 > 4000 mg/kg (M & F)
                                      III
                                   870.1300
Acute Inhalation (rabbit) 
                                   41563912
LC50 > 5.3 mg/L (M & F)
                                      IV
                                   870.2400
Primary Eye Irritation (rabbit)
                                   41563914
Minimal irritant; cleared by 72 hours
                                      III
                                   870.2500
Primary Skin Irritation (rabbit)
                                   41563916
Slightly irritating; cleared by day 7
                                      IV
                                   870.2600
Dermal Sensitization (guinea pig)
                                   41869522
Not a dermal sensitizer (Maximization)
                                      N/A
M = male; F = female; C = Combined

Table A.2.2  Subchronic, Chronic and Other Toxicity Profile for Trinexapac-ethyl 
                                 Guideline No.
                                  Study Type
                    MRID No.  (year)/ Classification /Doses
                                    Results
870.3100

90-Day oral toxicity [rat]
MRID 41563921 (1989)

Acceptable/Guideline

0, 5, 50, 500, 5000, 20000 ppm
[M 0, 3, 34, 346, 1350 mg/kg/day] 
[F 0, 4, 38, 395, 1551 mg/kg/day]
NOAEL = 20000 ppm [males 1350/females 1551 mg/kg/day] HDT
870.3150

13-week oral toxicity in nonrodent [dog]

MRID 41563920 (1989)

Acceptable/Guideline

0, 50, 100, 15000, 30000 ppm
[M 0, 2.0, 34.9, 515.9, 927.1 mg/kg/day]
[F 0, 1.9, 38.8, 582.4, 890.8 mg/kg/day]
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

7-week pilot study
MRID 41869523

Acceptable/Guideline

0, 500, 5000, 15000-50000 ppm
[M 0, 22, 219, (686, 956, 734) * mg/kg/day]
[F 0, 23, 214, (680, 1373, 965) * mg/kg/day]
*15000 ppm (days 1-3); 30000 ppm (days 4-28); 50000 ppm (weeks 4-7)
Negative BWG in males HDT from week 5 on; HDT females from week 6 on; BW of HDT males 81% of control/females 74% control at week 7; severe decrease in food consumption HDT; tubular dilatation and degeneration/regeneration of epithelial cells of renal tubules at HDT; diffuse thymic atrophy at mid- and high-dose females and high-dose males
870.3200

21/28-Day dermal toxicity [rabbit]

MRID  41563922 (1989)
[46809310 (2006)]

Acceptable/Guideline

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

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)

Acceptable/Guideline; (does not fulfill 870.3700a because study pre-dates 1998 guideline)

0, 20, 200, 1000 mg/kg/day
gestation days 6-15
Maternal                                                             NOAEL = 1000 mg/kg/day (HDT)

Developmental                                                   NOAEL = 200 mg/kg/day                                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 [rabbit]
MRID 41869524 (1990)

Acceptable/Guideline; (does not fulfill 870.3700b because study pre-dates 1998 guideline)

0, 10, 60, or 360 mg/kg/day
gestation days 7-19
Maternal                                                           NOAEL = 360 mg/kg/day (HDT)

Developmental                                              NOAEL = 60 mg/kg/day                                   LOAEL = 360 mg/kg/day, based on a decrease in the mean number of 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)

Acceptable/Guideline; (does not fulfill 870.3800 because study pre-dates 1998 guideline)

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]

Parental                                                           NOAEL = 10000 ppm [males 593.5/females 751.1 mg/kg/day]
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 treatment-related effect on reproductive parameters up to and including 20000 ppm (HDT)
 
Offspring                                                            NOAEL = 10000 ppm [males 593.5/females 751.1 mg/kg/day]
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)

Acceptable/Guideline

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]
Systemic toxicity                                               NOAEL = 20000 ppm [males 806/females 1054 mg/kg/day] HDT
870.4100b

Chronic toxicity nonrodent [dogs]
MRID  42779402/42779401 (1991-92)

Acceptable/Guideline

0, 40, 1000, 10000, or 20000 ppm 
[M 0, 1.56, 31.62, 356.72, or 726.65 mg/kg/day]
[F 0, 1.37, 39.54, 357.13, 783.83 mg/kg/day]
Systemic toxicity                                               NOAEL = 1000 ppm [males 31.62/females 39.54 mg/kg/day]
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

Carcinogenicity [rat]

MRID 42238104 (1992)

Acceptable/Guideline

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]

See above under 870.4100a

There was a possible treatment-related increased incidence of squamous cell carcinoma of the forestomach in M at 20000 ppm (HDT); however, this is not considered toxicologically relevant to humans. 
No treatment-related difference detected in total number of animals with tumors or in the total number of benign or malignant tumors at 52 or 104 weeks. No 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)	 Acceptable/Guideline

Acceptable/Guideline

0, 7, 70, 1000, 3500, 7000 ppm
[M 0, 0.91, 9.01, 130.81, 450.72, 911.77 mg/kg/day]
[F 0, 1.08, 10.66, 154.08, 538.73, 1073.42 mg/kg/day]
Systemic toxicity 
NOAEL = 7000 ppm [males 911/females 1073 mg/kg/day] HDT

There was no treatment-related increase in tumors of any type in either sex at dose levels up to and including 7000 ppm (HDT)

Not Likely to be Carcinogenic to Humans
870.5100

Bacterial Reverse Gene Mutation Assay

46809308 (2001)

Acceptable/Guideline

Salmonella typhimurium
strains TA98, TA100, TA102, TA1535 and TA1537
Escherichia coli strain WP2uvrA
0, 312.5, 625, 1250, 2500, or 5000 ug/plate +- S9 metabolic activation
Negative 

870.5300

Mouse Lymphoma Cells/Mammalian Activation Gene Forward Mutation Assay at TK+/- locus
43128605 (1993)

Acceptable/Guideline

Mouse lymphoma
L5178Y cells (at the
thymidine kinase locus)
0, 7.54, 30.16, 120.62, or
1930 ug/mL for 4 hours
+- S9 metabolic activation
Negative 
870.5395

Structural chromosomal aberration test - micronucleus test [mouse]
41563926 (1989)
42081402 (1991)
41869527 (1991)
                        Acceptable/Guideline

M and F mouse bone marrow cells (erythrocytes)
0, 1000, 2000, or 4000 mg/kg bw (sacrifice at 16, 24, and 48 h)
Initial assay: 0 or 3000 mg/kg bw (sacrifice at 16, 24, and 48 h)
Confirmatory assay: 0, 750,
1500, or 3000 mg/kg bw
(sacrifice at 48 h)
Negative 
Significant increased frequency of micronucleated polychromatic erythrocytes in M and sexes combined at 48 h in the initial assay; however, values were within historical control range and not observed in the confirmatory assay at 3000 mg/kg bw at 48 h. In this study possible weak clastogen, however, weight of evidence suggests CGA-163935 not likely clastogenic.
870.5550

Other Genotoxicity 
In vitro UDS in primary rat hepatocytes
41604205 (1987) 41869528 (1991)

Acceptable/Guideline

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 

870.6200a

Acute neurotoxicity [rat]
MRID  48764506
                       Acceptable/Guideline

0, 500, 1000, or 2000 mg/kg

Systemic toxicity
NOAEL = 1000 mg/kg 
LOAEL = 2000 mg/kg based on decreased body weight gain over the first day following treatment in both males and females and decreased food consumption over the first day following treatment in the 2000 mg/kg males.

Neurotoxicity
NOAEL = >= 2000 mg/kg 
LOAEL = > 2000 mg/kg in male and female rats based on the absence of any treatment-related functional observational findings, locomotor activity changes, changes in brain weights or brain dimensions, and the absence of any neuropathological lesions.
870.6200b

Subchronic neurotoxicity [rat]

MRID  48764507

Acceptable/Guideline

0, 3750, 7500, or 15000 ppm 

[0, 233, 463, and 948 mg/kg bw/day for M] 

[0, 294, 588, and 1171 mg/kg/day for F]
Systemic toxicity
NOAEL = >= 15000 ppm (948 mg/kg/day for M and 1171 mg/kg/day for F, respectively) (HDT)
LOAEL = > 15000 ppm for both systemic toxicity and neurotoxicity based on the absence of any treatment related functional observational findings, locomotor activity changes, changes in brain weights or brain dimensions, and the absence of any neuropathological lesions.

870.7485

Metabolism and pharmacokinetics 
[rat]
MRID  41563927 (1990)

Acceptable/Guideline

i. v. 0.91 mg/kg [14C- CGA-163935]
oral 0.97 or 166 mg/kg [[14]C- CGA-163935]
oral 0.97 mg/kg/day [CGA-163935] for 14 days followed by 0.97 mg/kg [[14]C- CGA-163935]
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)	

Acceptable/Guideline

0, 0.01, 0.1, or 1.0 mg/cm[2] [[14]C- CGA-163935]
single dermal dose
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)	

Acceptable/Guideline

0, 500, 2000, and 5000 ppm
0, 160.2, 613.7, 1530.5 mg/kg/day
Systemic toxicity                                              NOAEL = 5000 ppm (1530.5 mg/kg/day) HDT                                         LOAEL was not established

Immunotoxicity                                                NOAEL for anti-SRBC AFC response and NK cell activity = 5000 ppm (1530.5 mg/kg/day)                                                     LOAEL was not established 

Appendix B. Physical/Chemical Characteristics

Table B.1.	Trinexapac-ethyl 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 (Palisade(TM) 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
CGA-313458
(Drinking water)

Open chain cyclohexane ring
(Drinking water)

Hydro-product M3
Unidentified

Table B.2.  Physicochemical Properties of Trinexapac-ethyl
Parameter
Value
Reference
Melting point/range
36.1-36.6°C
Provided in MRID 46809305
pH
3.3 

Density (20ºC)
1.215 g/cm[3]

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)
1.62 x 10[-5] mm Hg

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

Trinexapac-ethyl has a relatively low octanol/water partition coefficient.  At pH 5.3, the log KOW value is 2.44 (KOW = 275).  Trinexapac-ethyl has a low potential to leach into groundwater and is not expected to be volatile because of its low vapor pressure (2.16 x 10[-3] Pa at 25[o]C). 

              

Appendix C.  International Residue Limits 

Table C.1.  Summary of US and International Tolerances and MRLs 
Residue Definition
                                      US
                                     Codex
                                    Canada
                                    Mexico
40 CFR §180.662
Plants: Trinexapac-ethyl, ethyl 4-(cyclopropylhydroxymethylene)-3,5-dioxocyclohexanecarboxylate and trinexapac, 4-(cyclopropylhydroxymethylene)-3,5-dioxocyclohexanecarboxylic acid

Tolerance/MRL (ppm)
                                 Commodity[1]
                                      US
                                     Codex
                                    Canada
                                    Mexico
Cattle, fat
                                     0.03
                                     0.01
                                     0.01
                                     0.02
Cattle, meat
                                     0.03
                                     0.01
                                     0.01
                                     0.02
Cattle, meat byproducts
                                      0.1
                                      0.1
                                     0.02
                                     0.04
Clover, forage
                                       8
                                      --
                                      --
                                      --
Clover, hay
                                      15
                                      --
                                      --
                                      --
Egg
                                     0.01
                                      --
                                     0.01
                                      --
Goat, fat
                                     0.03
                                     0.01
                                     0.01
                                     0.02
Goat, meat
                                     0.03
                                     0.01
                                     0.01
                                     0.02
Goat, meat byproducts
                                      0.1
                                      0.1
                                     0.02
                                     0.04
Hog, fat
                                     0.02
                                     0.01
                                     0.01
                                     0.02
Hog, meat
                                     0.02
                                     0.01
                                     0.01
                                     0.02
Hog, meat byproducts
                                      0.1
                                      0.1
                                     0.02
                                     0.03
Milk
                                     0.01
                                      --
                                      --
                                      --
Horse, meat
                                     0.03
                                     0.01
                                     0.01
                                     0.02
Poultry, fat
                                     0.01
                                      --
                                      --
                                      --
Poultry, meat
                                     0.01
                                      --
                                       -
                                      --
Poultry, meat byproducts
                                      0.1
                                      --
                                      ---
                                      --
Sheep, fat
                                     0.03
                                     0.01
                                     0.01
                                     0.02
Sheep, meat
                                     0.03
                                     0.01
                                     0.01
                                     0.02
Sheep, meat byproducts
                                      0.1
                                      0.1
                                     0.02
                                     0.04
Completed by S. Piper using Global MRL; 05/10/2022
 Includes only commodities of interest for this action.
 Mexico adopts US tolerances for its export purposes.