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Table of Contents

Contents

I. Introduction..............................................................................................................................3

II. Use and Usage..........................................................................................................................5

III. Scientific Assessments ............................................................................................................5

A. Human Health Assessment .....................................................................................................5

1. Hazard Characterization and Risk .................................................................................6

2. Risk Conclusions...........................................................................................................6

3. Tolerances......................................................................................................................7

4. Human Incidents............................................................................................................7

B. Environmental Assessment ....................................................................................................7

1. Public Comments...........................................................................................................7

2. Environmental Fate and Exposure.................................................................................8

3. Ecological Risk Assessment Uncertainties....................................................................9

4. Ecological Risk Characterization ..................................................................................9

5. Overview of Ecological Risk Conclusions....................................................................9

6. Effects on Terrestrial Organisms.................................................................................10

7. Effects on Aquatic Organisms.....................................................................................10

8. Ecological Incidents ....................................................................................................10

9. Ecological Risk Management Conclusions for Non-Listed Species...........................11

 C. Endangered Species Assessment..........................................................................................11

 D. Endocrine Disruptor Screening Program .............................................................................13

IV. Proposed Interim Registration Review Decision................................................................14

V. Next Steps and Timeline.....................................................................................................14

 A. Interim Registration Review Decision..................................................................................14

 B. Implementation of Mitigation Measures...............................................................................15

Appendix A: Summary of Actions Taken for Trinexapac-ethyl ..................................................16

Appendix B: Trinexapac-ethyl Label Table .................................................................................17
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I. Introduction

This document is the Environmental Protection Agency’s (EPA or the Agency) Proposed 

Interim Registration Review Decision for trinexapac-ethyl (PC Code 112602, Case 7228) and is 

being issued pursuant to 40 CFR sections 155.56 and 155.58. A registration review decision is 

the Agency's determination whether a pesticide meets, or does not meet, the standard for 

registration in the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA). The Agency 

may issue, when it determines it to be appropriate, a proposed interim registration review 

decision before completing a registration review. Among other things, the proposed interim 

registration review decision may require new risk mitigation measures, impose interim risk 

mitigation measures, identify data or information required to complete the review, and include 

schedules for submitting the required data, conducting the new risk assessment and completing 

the registration review. For further information on trinexapac-ethyl, additional documents can be 

found in EPA’s public docket (EPA-HQ-OPP-2008-0657) at www.regulations.gov.

FIFRA, as amended by the Food Quality Protection Act (FQPA) of 1996, mandated the 

continuous review of existing pesticides. All pesticides distributed or sold in the United States 

generally must be registered by the EPA based on scientific data showing that they will not cause 

unreasonable risks to human health or to the environment when used as directed on product 

labeling. The registration review program is intended to make sure that, as the ability to assess 

and reduce risk evolves and as policies and practices change, all registered pesticides continue to 

meet the statutory standard of no unreasonable adverse effects. Changes in science, public 

policy, and pesticide use practices will occur over time. Through the registration review 

program, the Agency periodically reevaluates pesticides to make sure that as these changes 

occur, products in the marketplace can continue to be used safely. Information on this program is 

provided as www.epa.gov/oppsrrd1/registration_review/.

In 2006, the Agency implemented the registration review program pursuant to FIFRA 

section 3(g) and will review each registered pesticide every 15 years to determine whether it 

continues to meet the FIFRA standard for registration.

Trinexapac-ethyl is a plant growth regulator registered for use on turf grass, several 

cereal grain crops, and sugarcane. On turf grass, trinexapac-ethyl reduces the frequency of 

mowing, and on crops it reduces the problem of lodging (stalk bending or breakage) before 

harvesting. On sugarcane, it maintains or increases the sugar content and induces internode 

shortening and harvest extension. It is formulated as an emulsifiable concentrate, granular, 

liquid, micro-encapsulated, and wettable powder and applied via chemigation and broadcast 

(aerial and ground) spray. It was first registered in 1993 for the management of warm and cool 

season turf grasses. Trinexapac-ethyl is registered for commercial and residential use. A 

Reregistration Eligibility Decision document (RED) for trinexapac-ethyl was not completed

because it was registered after 1984.

Pursuant to 40 CFR section 155.50, EPA formally initiated registration review for

trinexapac-ethyl (case 7228). The following highlights significant events that have occurred 

during the registration review of trinexapac-ethyl:
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 September 15, 2008 – Publication of trinexapac-ethyl Summary Document for a 60-day 

public comment period. The Summary Document included the Preliminary Work Plan

(PWP) and was accompanied by the scoping document and problem formulation.

 February 18, 2009 – Final Work Plan (FWP) for trinexapac-ethyl was issued. No public 

comments were received during the 60-day comment period for the Trinexapac-ethyl

PWP; thus, the FWP did not modify the PWP.

 March 11, 2010 – Generic Data Call-In (GDCI) for trinexapac-ethyl issued.

 September 27, 2013 – The Agency published the Registration Review - Ecological Risk 

Assessment and Effects Determination of Trinexapac-ethyl and the Trinexapac-ethyl:

Human Health Risk Assessment for Registration Review for a 60-day public comment 

period. Two sets of comments concerning the ecological risk assessment were received 

during the comment period; no comments were received about the human health risk 

assessment. 

 July 2014 – The Agency is now publishing the Response to Comments on the Preliminary 

Ecological Risk Assessment for the Registration Review of Trinexapac-ethyl and 

Use/Usage Refinement in Support of Registration Review of Trinexapac-ethyl.

 July 2014 – The Agency is now publishing the Trinexapac-ethyl Proposed Interim 

Registration Review Decision, dated June 2014 in docket number EPA-HQ-OPP-2008-

0657 for a 60-day public comment period.

Additional information on trinexapac-ethyl can be found in EPA’s public docket, EPA-HQOPP-2008-0657, accessed at www.regulations.gov.
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II. Use and Usage 

As described in the June 2014 Use/Usage Refinement in Support of Registration Review 

of Trinexapac-ethyl available in the trinexapac-ethyl docket, trinexapac-ethyl is a plant growth 

regulator (PGR) registered for use by homeowners and professional applicators to manage 

growth of turf grass, wheat, barley, oats, triticale, sugarcane, and grasses grown for seed. Turf

grass uses include golf courses, sod farms, commercial and residential lawns, athletic fields and 

parks. It is also registered for application around ornamental trees, shrubs, and flower beds. 

Trinexapac-ethyl inhibits the biosynthesis of the phytohormone gibberellin that promotes growth 

of turf grasses, reducing the frequency of mowing. Also, in turf grass, trinexapac suppresses 

seed head formation. In cereal grains, it reduces the length of internodes, which produces 

sturdier plants and reduces the problem of lodging before harvesting, minimizing yield loss. On 

sugarcane, it maintains or increases the sugar content for an extended harvest window and 

induces internode shortening to improve seed piece production.

Trinexapac-ethyl is reported to be widely used in professional turf and horticulture 

management, which includes golf courses, institutional turf facilities, turf farms, as well as 

professional lawn care and landscape management. In 2011, approximately 90,000 lbs of 

trinexapac-ethyl were applied, accounting for over 30% of total PGR usage in professional turf 

and horticulture management. Golf courses account for the majority of usage; it is reportedly the

second most commonly used PGR on golf courses, accounting for over 60,000 lbs active 

ingredient (a.i) annually. While fewer total pounds of trinexapac-ethyl are used on institutional 

turf facilities (approximately 8,000 lbs a.i.), this accounts for over 55% of total PGR use in these 

facilities. Similarly, while use of PGRs on turf farms is quite limited, nearly 100% of the usage 

is accounted for by trinexapac-ethyl (less than 7,000 lbs a.i.). Finally, low usage is reported 

among lawn care operators (less than 8,000 lbs a.i., less than 7% of total PGR use), and 

landscape contractors (less than 500 lbs a.i.).

Publicly available data on trinexapac-ethyl usage are limited. Data from the California 

Department of Pesticide Regulation (CDPR) indicate approximately 5,200 lbs a.i. are applied 

annually in California, nearly all of which are applied in landscape maintenance. Trinexapacethyl is also used in less than 1% of cut flower and bedding plant operations.

III. Scientific Assessments

A. Human Health Assessment

A summary of the Agency’s human health risk assessment is presented below. The 

Agency used the HED scoping document, its supporting documents, and the most updated 

Agency science policies and risk assessment methodologies to prepare a qualitative risk 

assessment in support of the registration review of trinexapac-ethyl. The most recent human 

health risk assessment was conducted on September 12, 2013. The human health risk assessment 

consisted of updated acute and chronic dietary (food and drinking water) exposure assessments, 

residential handler and post-application exposure assessments, an aggregate exposure 

assessment, and occupational handler and post-application exposure assessments. Risk estimates 

were below the Agency's level of concern for all human health scenarios assessed. For a detailed 
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discussion, see the Trinexapac-ethyl: Human Health Risk Assessment for Registration Review, 

published on September 27, 2013 in the public docket EPA-HQ-OPP-2008-0657, which can be 

accessed on http://www.regulations.gov/. 

1. Hazard Characterization and Risk

The acute toxicity for trinexapac-ethyl technical formulation is relatively low, and was 

classified as Toxicity Category II for acute oral, dermal, and eye irritation, and IV for acute 

inhalation and skin irritation. Trinexapac-ethyl is not a skin sensitizer. Trinexapac-ethyl is a low 

acute toxicity chemical with systemic effects occurring at or well above 300 mg/kg/day in 

subchronic and lifetime dosing studies. Evidence of increased qualitative and quantitative 

susceptibility to offspring exists at or above the limit dose (300 – 1,000 mg/kg/day) of the 

developmental and reproductive studies. 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.

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

increase in any tumor type that would be relevant to humans. 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.”

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. The 90-day 

subchronic dog study showed decreased body weight gain and food consumption, diffuse thymic 

atrophy, and changes in the epithelial cells of the renal tubules were seen in the 90-day dog study 

at 516/582 mg/kg/day (males/females). 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 was no evidence of neurotoxicity in the acute and chronic neurotoxicity studies in 

rat at the highest dose tested of 2000 mg/kg and 948/1171 mg/kg/day (male/female), 

respectively. The toxicity database for trinexapac-ethyl is complete under the revised 40 CFR 

Part 158 data requirements for conventional pesticides.

2. Risk Conclusions

The Agency conducted dietary, occupational, aggregate, and residential risk assessments 

to support the registration review of trinexapac-ethyl. No risk estimates exceeded the Agency’s 

level of concern (LOC) for existing uses of trinexapac-ethyl. It has not been determined that 

trinexapac-ethyl shares a common mechanism of toxicity with other chemicals; therefore a 

cumulative risk assessment was not required. 

In the most recent human health risk assessment, the Agency indicated that a 30-day 

plant-back restriction was needed on labels for cereal grains, as well as a prohibition of planting 

all other crops not listed on the label. However, comments received by Syngenta Crop 

Protection, LLC on the human health risk assessment referred to a previously submitted and 

reviewed rationale supporting a 0-day plant-back interval for crops currently on the label and a 
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30-day interval for all other crops. The rationale indicated that results of the confined 

accumulation in a rotational crop study (MRID 48043709) supported a 0-day plant-back interval 

for crops on the labels and a 30-day plant-back interval for all crops not on the label. The 

Agency accepted this rationale in a memorandum dated February 17, 2012, now available in the 

trinexapac-ethyl registration review docket (EPA-HQ-OPP-2008-0657). Therefore, a 0-day 

plant-back interval for crops currently on the label and a 30-day interval for all other crops is 

supported. Label changes to the plant-back interval are not required. 

3. Tolerances

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

metabolites and degradates, in or on plants and livestock in CFR 40 180.662. There are no 

established or proposed Codex, Canadian, or Mexican maximum residue limits (MRLs) for 

trinexapac-ethyl in or on any food or feed crops.

4. Human Incidents

A small number of minor human health incidents have been reported to the Agency 

involving trinexapac-ethyl. From January 1, 2009 to May 27, 2014, there were 3 incidents 

reported to the Office of Pesticide Program’s Main Incident Database System. These incidents 

were classified as moderate severity. A query of SENSOR-Pesticides 1998-2009 identifies a total 

of eight cases, stemming from eight events, involving trinexapac-ethyl. All cases were low in 

severity. Five cases involved multiple active ingredients and three involved a single active 

ingredient. These three cases were low in severity. The reported incidents do not suggest there 

is risk from the current uses of trinexapac-ethyl when used as directed by labels. The Agency has 

determined that the reported incidents are not of concern, but will continue to monitor the 

incident information and if a concern is triggered, additional analysis will be conducted.

B. Environmental Assessment

The risk assessment supporting this Proposed Interim Registration Review Decision 

evaluates risks to species that are not subject to the Endangered Species Act (ESA) and provides 

a screening level assessment for potential risks to listed species under ESA. A summary of the 

Agency’s environmental risk assessment for trinexapac-ethyl is presented below. For detailed 

discussions of all aspects of the environmental risk assessment, see the Registration Review -

Ecological Risk Assessment and Effects Determination of Trinexapac-ethyl, published on 

September 27, 2013 in the public docket EPA-HQ-OPP-2008-0657, which can be accessed on 

http://www.regulations.gov/. 

1. Public Comments

During the public comment period, the Agency received comments about the ecological 

risk assessment from Syngenta Crop Protection, LLC (Syngenta), and Crop Life America (CLA). 

Syngenta’s comments on the preliminary ecological risk assessment focused on conservative 

assumptions made in the review of submitted data and subsequent risk assessment. These 

comments are addressed in detail in the Response to Public Comment on the Trinexapac-ethyl 
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Registration Review Ecological Risk Assessment, dated June 3, 2014, available in the public 

docket EPA-HQ-OPP-2008-0657. 

One comment from Syngenta resulted in a change to the ecological risk assessment. 

Syngenta stated that the default half-life value of 35 days for turf uses was overly conservative 

and did not accurately represent the environmental fate of trinexapac-ethyl on turf. Syngenta 

noted that submitted studies (MRIDs 48043710, 48043711, 41869539, and 41869540) support a 

shorter half-life value of <1 day for trinexapac-ethyl turf scenarios. After review, the Agency 

agrees that the referenced studies do support a foliar dissipation half-life of 1.383 days, the 90th

percentile half-life estimate of the submitted studies, on turf scenarios excluding grasses grown 

for seed. The Agency’s findings after revising the terrestrial risk assessment are presented in the 

Response to Public Comments on the Trinexapac-ethyl Registration Review Ecological Risk 

Assessment.

CLA commented that the draft risk assessment for trinexapac-ethyl compared screening 

level estimates of exposure to the listed species level of concern. CLA further stated that 

screening tiers indicate whether a potential risk exists, but additional refinements to reduce 

uncertainties would indicate whether a risk of concern actually exists. CLA stated that risk 

mitigation decisions for listed species should not be considered until all data gathering and 

refinements have been completed to indicate what the risks actually are. 

EPA appreciates and acknowledges CLA’s comments about the preliminary ecological 

risk assessment for trinexapac-ethyl. EPA would like to reaffirm its interest in engaging in 

mitigation discussions with affected stakeholders as early as possible during registration review. 

EPA recognizes that in the case of listed species assessments, mitigation discussions may be 

most fruitful once the listed species assessment process has further matured. However, EPA 

believes that the Preliminary Risk Assessment (PRA) is an appropriate place in registration 

review to discuss potential risks of concern and risk mitigation as determined under FIFRA. 

Further, EPA notes that it is in the interests of stakeholders to engage at the earliest possible 

point in registration review to discuss risk mitigation, even prior to a potential listed species risk 

assessment. As per the Stakeholder Engagement Paper 

(www.epa.gov/pesticides/oppfead1/endanger/archive-2013.html), early engagement by 

stakeholders allows EPA to focus on potential risks of concern to listed and non-listed species 

identified either via litigation or risk assessments conducted to support prior regulatory

decisions. It may be possible to achieve “early risk reductions” as a result of alternative 

chemistries developed since the previous risk assessments were conducted, changes to labels that 

incorporate rate reductions, clarifications to use instructions, and/or existing conservation 

practices. Early risk reductions have the potential to narrow the scope of any necessary risk 

assessment for listed species, saving time and resources. For more information on the 

endangered species risk assessment process and screening level assessment specific to 

trinexapac-ethyl, please see the “Endangered Species Assessment” section of this document.

2. Environmental Fate and Exposure

Trinexapac-ethyl is considered to be moderately mobile to mobile in soil, while its major 

metabolite, trinexapac acid, is moderately mobile in soil. Trinexapac-ethyl is not expected to 
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accumulate in aquatic or terrestrial food chains. Trinexapac-ethyl is not volatile and, therefore, 

is not likely to be transported via atmospheric processes following application.

The primary route of degradation for trinexapac-ethyl is biodegradation in aerobic and 

anaerobic water bodies and aerobic terrestrial environments. Half-lives ranged between 2.8 

hours and 4.3 days, depending on the microbial environment of the application site. However, 

biodegradation was slower under anaerobic soil conditions. The estimated half-life is 25 days in 

a sandy loam soil. Trinexapac-ethyl is susceptible to hydrolysis under basic conditions. In

addition, photolysis does not appear to be a major degradation pathway in aqueous and soil 

environments.

3. Ecological Risk Assessment Uncertainties

While there are toxicity data gaps for some species, the database for trinexapac-ethyl is 

considered substantially complete and sufficient for risk assessment and regulatory decision 

making. Subsequent to the completion of the preliminary risk assessment, Syngenta submitted 

an acute honeybee oral toxicity study to address uncertainty identified in the EPA’s 2013 

ecological preliminary risk assessment for potential risk to non-target terrestrial invertebrates,

such as bees. While risks of concern were not identified for non-listed terrestrial invertebrates, 

this study will be reviewed prior to the completion of an endangered species risk assessment for 

trinexapac-ethyl.

4. Ecological Risk Characterization

To estimate potential ecological risk, EPA integrates the results of exposure and 

ecotoxicity studies using the risk quotient method. Risk quotients (RQs) are calculated by 

dividing acute and chronic estimated environmental concentrations (EECs) by ecotoxicity values 

for various wildlife and plant species. RQs are then compared to levels of concern (LOCs) and 

when the RQ exceeds the LOC for a particular category, the Agency evaluates the potential for a 

risk of concern to that category. Risk characterization provides further information about

potential adverse effects and the possible impact of those effects by considering the fate of the 

chemical and its degradates in the environment, organisms potentially at risk, and the nature of 

the effects observed. 

5. Overview of Ecological Risk Conclusions

Conservative assumptions were made in the conduct of the ecological risk assessment for 

trinexapac-ethyl to estimate the ecological risks (e.g. risk estimates are based on the maximum 

application rates and number of applications rather than typical rates and the most sensitive 

endpoints from toxicity studies applications). RQs were below the screening level LOCs for 

nearly all trinexapac-ethyl use scenarios, with only several turf and grasses grown for seed 

scenarios resulting in RQs slightly above the LOC. An acute RQ exceedance of 0.52 was 

identified for non-listed small (20 g) birds from granular turf use at the highest application rate, 

just above the LOC of 0.50. Similarly, RQ exceedances above the LOC of 1.0 ranged from 1.15-

1.70 for non-listed terrestrial plants from liquid turf and grasses grown for seed uses. There were 

no acute or chronic risks to non-listed terrestrial species identified as a result of the use of 

trinexapac-ethyl on cereal grains or sugarcane. 
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6. Effects on Terrestrial Organisms

The primary route of exposure for terrestrial organisms is the dietary route, from 

consumption of food items, such as plant leaves or insects that have trinexapac-ethyl residues as 

a result of spraying, or from the ingestion of trinexapac-ethyl granules. Direct contact and spray 

drift are the major routes of exposure assumed for terrestrial and riparian plants. 

 

Mammals

There were no acute or chronic risks of concern for non-listed mammals or terrestrial 

invertebrates from the registered uses of trinexapac-ethyl. 

Birds

Direct effects to non-listed terrestrial birds (surrogates for reptiles and amphibians) were 

identified for turf uses. One scenario exceeded the acute LOC and one scenario exceeded the 

chronic LOC; as explained below, both exceedances were minimal. For granular turf uses 

(assuming the highest registered use rate) the acute RQ for small (20g) birds was 0.52, an

exceedance of the LOC of 0.5. For the liquid turf uses, the chronic-dietary-based RQ for a bird 

eating a diet of short grass only was 1.2, which minimally exceeded the chronic dietary-based 

LOC of 1.0. However, RQs for liquid turf scenarios were recalculated after replacing the default 

foliar half-life value of 35 days with 1.383 days and presented in the Response to Comments on 

the Preliminary Ecological Risk Assessment for the Registration Review of Trinexapac-ethyl. As 

a result of this change, the chronic-dietary-based RQ for birds decreased from 1.2 to 0.83 and is

now below the LOC. 

Plants

For non-listed terrestrial and riparian plants, RQ exceedances ranged from 1.15-1.70 as a 

result of trinexapac-ethyl use on grasses grown for seed (dicot plants only) and turf use. No risks 

were identified as a result of trinexapac-ethyl cereal grain uses. 

7. Effects on Aquatic Organisms

The primary route of exposure to aquatic organisms is through direct contact with the 

water column, sediment, and pore water with residues from spray drift and/or runoff from areas 

treated with trinexapac-ethyl. Acute and chronic risk estimates were below the LOC for

freshwater and estuarine/marine fish (surrogates for aquatic-phase amphibians), freshwater and 

estuarine/marine invertebrates, and aquatic vascular and non-vascular plants for all uses of 

trinexapac-ethyl. Therefore, no risks of concern are anticipated for non-listed aquatic organisms 

based on the registered uses of trinexapac-ethyl. 

8. Ecological Incidents

A review of the Ecological Incident Information System (EIIS), the Aggregate Summary 

Module of the Office of Pesticide Program’s Incident Database, and the Avian Monitoring 

Information System (AIMS), which is maintained by the American Bird Conservancy, was 
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conducted on May 16, 2013 for trinexapac-ethyl. Neither the EIIS nor the AIMS database 

identified any adverse ecological incidents involving trinexapac-ethyl. Two aggregate incident 

summaries were documented in OPP’s Incident Database. One incident was reported as a minor 

fish and wildlife incident in 2000, the other was reported as a minor plant incident in late 2003 or 

2004. No other information was available. 

9. Ecological Risk Management Conclusions for Non-Listed Species

The preliminary risk assessment for trinexapac-ethyl identified an acute LOC 

exceedances for non-listed terrestrial birds at 0.62 and plants varying from 2.3-3.40 for the turf 

grass use; which was assessed at a single maximum application rate of 1.36 lb active ingredient/ 

Acre (a.i./A). However, the registered single maximum application rate for use on turf grass is 

intended to be 0.88 lb a.i./A for granular products, and 0.68 lb a.i./A for liquid products, but a 

statement on end-use liquid turf grass product labels also states that “for extended growth 

suppression up to 8 weeks, where temporary discoloration can be tolerated, a maximum of twice 

the recommended rate from the application rate table may be applied.” Therefore, risks were 

assessed at twice the intended single maximum application rate to account for this statement on 

end-use labels. EPA is working with the trinexapac-ethyl technical registrants to amend their 

labels to clarify that the single maximum application rate for liquid end-use products registered 

for use on turf grass is 0.68 lb ai/A, by requiring the following proposed label language: “ The 

single maximum application rate must not exceed 0.68 lb ai/A. DO NOT double the single 

maximum application rate for extended suppression”. Amended labels for technical and liquid 

end-use products registered on turf grass must be submitted to the Agency for approval within 60 

days of the publication of the final Interim Registration Review Decision for the registration 

review of trinexapac-ethyl. Therefore, once these changes to labels are made, risks identified as 

a result of the doubled single maximum application rate for liquid turf grass products would no 

longer be of concern.

Based on the low risk estimates, the anticipated clarification of the maximum single 

application rate for liquid turf uses, and the conservative nature of the risk assessment (e.g., risk 

estimates are based on maximum application and the most sensitive endpoints from toxicity 

studies), the Agency does not anticipate ecological risks of concern for assessed taxa from 

currently registered uses of trinexapac-ethyl. 

C. Endangered Species Assessment

Before completing this Registration Review, the Agency will conduct an ecological risk 

assessment to address the Agency’s obligations under both the Endangered Species Act (ESA) 

and FIFRA. While the risk assessment supporting this Proposed Interim Registration Review 

Decision evaluates risks to species that are not subject to the ESA, EPA is still in the process of 

conducting a risk assessment for endangered and threatened (listed) species and their designated 

critical habitats for trinexapac-ethyl. In this Proposed Interim Registration Review Decision, 

therefore, EPA has not completed effects determinations for listed species associated with the 

registered uses of trinexapac-ethyl. 

In November 2013, the EPA, along with the U.S. Fish & Wildlife Service (USFWS), the 

National Marine Fisheries Service (NMFS) (collectively, the Services), and the U.S. Department 
12

of Agriculture (USDA) released a summary of their joint Interim Approaches for assessing risks 

to listed species from pesticides. The “Interim Approaches for National-Level Pesticide 

Endangered Species Act Assessments Based on the Recommendations of the National Academy

of Sciences April 2013 Report” (Interim Approaches), dated November 1, 2013, were developed 

jointly by the agencies in response to the National Academy of Sciences’ (NAS)

recommendations and reflect a common approach to risk assessment shared by the agencies as a 

way of addressing scientific differences between the EPA and the Services. The NAS report

outlines recommendations on specific scientific and technical issues related to the development 

of pesticide risk assessments that EPA and the Services must conduct in connection with their 

obligations under the Endangered Species Act (ESA) and FIFRA. 

The joint Interim Approaches were released prior to a stakeholder workshop held on 

November 15, 2013. In addition, the EPA presented the joint Interim Approaches at the

December 2013 Pesticide Program Dialogue Committee (PPDC) and State-FIFRA Issues 

Research and Evaluation Group (SFIREG) meetings, and held a stakeholder workshop in April 

2014, allowing additional opportunities for stakeholders to comment on the Interim Approaches. 

As part of a phased, iterative process for developing the Interim Approaches, the agencies will 

also consider public comments on the Interim Approaches in connection with the development of 

upcoming Registration Review decisions. The details of the joint Interim Approaches are 

contained in the Interim Approaches white paper.

Given that the agencies are continuing to develop and work toward implementation of the 

Interim Approaches to assess the potential risks of pesticides to listed species and their 

designated critical habitat, the ecological risk assessment supporting this Proposed Interim 

Registration Review Decision for trinexapac-ethyl does not contain a complete ESA analysis that 

includes effects determinations for specific listed species or designated critical habitat. Although 

EPA has not yet completed effects determinations for specific species or habitats, for this 

preliminary assessment EPA conducted a screening-level assessment for all taxa of non-target 

wildlife and plants that assumes for the sake of the assessment that listed species and designated 

critical habitats may be present in the vicinity of the application of trinexapac-ethyl. This 

screening level assessment will allow EPA to focus its future evaluations on the types of species 

where the potential for effects exists once the scientific methods being developed by the agencies 

have been fully vetted. While the agencies continue to develop a common method for ESA 

analysis, the regulatory section of the Proposed Interim Registration Review Decision document 

will describe the level of ESA analysis completed for this particular registration review case. 

Once the agencies have fully developed and implemented the scientific methods necessary to 

complete risk assessments for endangered and threatened (listed) species and their designated 

critical habitats, these methods will be applied to subsequent analyses for trinexapac-ethyl as part 

of completing this registration review.

As part of the screening level assessment, the Agency has made several refinements to 

the list of endangered and threatened species that may be affected by trinexapac-ethyl sugarcane, 

and grasses grown for seed. The following refinement does not apply to turf grass uses. To date, 

there are 1421 listed species identified in the LOCATES database (v. 2.2.7, derived from 

USFWS and NMFS). For sugarcane and grasses grown for seed uses, a “no effect” 

determination for 342 of the species for direct and indirect effects can be made based on a lack of 

geographical overlap, based on a county level of resolution, between the species and trinexapac-
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ethyl uses. A further 46 species can be eliminated from consideration of direct effects based on 

species specific ecological and biological information from listed species trustee agencies. There 

are 794 species that will need to be considered in more depth before direct effects calls are made 

for the sugarcane and grasses grown for seed uses. Biological, geographical, and use pattern 

information will be necessary to further refine the assessment.

D. Endocrine Disruptor Screening Program

As required by FIFRA and FFDCA, EPA reviews numerous studies to assess potential 

adverse outcomes from exposure to chemicals. Collectively, these studies include acute, 

subchronic and chronic toxicity, including assessments of carcinogenicity, neurotoxicity, 

developmental, reproductive, and general or systemic toxicity. These studies include endpoints 

which may be susceptible to endocrine influence, including effects on endocrine target organ 

histopathology, organ weights, estrus cyclicity, sexual maturation, fertility, pregnancy rates, 

reproductive loss, and sex ratios in offspring. For ecological hazard assessments, EPA evaluates 

acute tests and chronic studies that assess growth, developmental and reproductive effects in 

different taxonomic groups. As part of its most recent registration decision for trinexapac-ethyl, 

EPA reviewed these data and selected the most sensitive endpoints for relevant risk assessment 

scenarios from the existing hazard database. However, as required by FFDCA section 408(p), 

trinexapac-ethyl is subject to the endocrine screening part of the Endocrine Disruptor Screening 

Program (EDSP). 

EPA has developed the EDSP to determine whether certain substances (including 

pesticide active and other ingredients) may have an effect in humans or wildlife similar to an 

effect produced by a “naturally occurring estrogen, or other such endocrine effects as the 

Administrator may designate.” The EDSP employs a two-tiered approach to making the 

statutorily required determinations. Tier 1 consists of a battery of 11 screening assays to identify 

the potential of a trinexapac-ethyl substance to interact with the estrogen, androgen, or thyroid 

(E, A, or T) hormonal systems. Chemicals that go through Tier 1 screening and are found to 

have the potential to interact with E, A, or T hormonal systems will proceed to the next stage of 

the EDSP where EPA will determine which, if any, of the Tier 2 tests are necessary based on the 

available data. Tier 2 testing is designed to identify any adverse endocrine-related effects caused 

by the substance, and establish a dose-response relationship between the dose and the E, A, or T 

effect. 

Under FFDCA section 408(p), the Agency must screen all pesticide chemicals. Between 

October 2009 and February 2010, EPA issued test orders/data call-ins for the first group of 67 

chemicals, which contains 58 pesticide active ingredients and 9 inert ingredients. A second list of 

chemicals identified for EDSP screening, which included trinexapac-ethyl, was published on 

June 14, 20131 and includes some pesticides scheduled for Registration Review and chemicals

found in water. For further information on the status of the EDSP, the policies and procedures, 

the lists of chemicals, future lists, the test guidelines and the Tier 1 screening battery, please visit 

our website.2 

 

1 See http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPPT-2009-0477-0074 for the final second list of 

chemicals.

2 http://www.epa.gov/endo/
14

In this Proposed Interim Registration Review Decision, EPA is making no human health 

or environmental safety findings associated with the EDSP screening of trinexapac-ethyl. Before 

completing this Registration Review, the Agency will make an EDSP FFDCA section 408(p) 

determination.

IV. Proposed Interim Registration Review Decision

In accordance with 40 CFR Sections 155.56 and 155.58, the Agency is issuing this 

Proposed Interim Registration Review Decision. EPA’s Proposed Registration Review Decision. 

Except for the EDSP and Endangered Species Act (ESA) components of the trinexapac-ethyl 

registration review case, the Agency has made the following interim decision: (1) no additional 

data are required at this time; and (2) changes are required to trinexapac-ethyl products registered 

for use on turf grass. The Agency has been working with the technical registrants for trinexapacethyl, and the registrants of all technical and end-use products registered for use on turf grass 

will submit revised labels to clarify the single maximum application rate for turf grass 

application.

In the interim, EPA is making no human health or environmental safety findings 

associated with the EDSP screening of trinexapac-ethyl. Before completing this Registration 

Review, the Agency will make an EDSP FFDCA section 408(p) determination. Likewise, before

completing this Registration Review, the Agency will conduct an ecological risk assessment to 

address the Agency’s obligations under both the Endangered Species Act (ESA) and FIFRA. 

While the risk assessment supporting this Proposed Interim Registration Review Decision 

evaluates risks to species that are not subject to the ESA, EPA is still in the process of 

conducting a risk assessment for endangered and threatened (listed) species and their designated 

critical habitats for trinexapac-ethyl. In this Proposed Interim Decision, therefore, EPA has not 

completed effects determinations for listed species associated with the registered uses of 

trinexapac-ethyl. The Agency is issuing a Proposed Interim Registration Review Decision

pending completion of the ESA and EDSP assessments.

V. Next Steps and Timeline

A. Interim Registration Review Decision

A Federal Register Notice will announce the availability of this Proposed Interim

Registration Review Decision for trinexapac-ethyl and allow a 60-day comment period. If there 

are no significant comments or additional information submitted to the docket during the 

comment period that leads the Agency to change its decision, EPA may issue an Interim

Registration Review Decision for trinexapac-ethyl (case 7228). However, a final decision for 

trinexapac-ethyl may be issued without issuing an interim decision. A final decision on the 

trinexapac-ethyl registration review case will occur after ESA and EDSP FFDCA section 408(p) 

determinations have been made. 
15

B. Implementation of Mitigation Measures

Within 60 days following issuance of the final Interim Registration Review Decision,

registrants are to submit to the Agency for review and approval proposed amended labels that 

include the risk mitigation to clarify single maximum application rates for end-use turf grass 

products. The mitigation measures and required label amendments are described in Appendices

A and B below.
Docket Number EPA-HQ-OPP-2008-0657

www.regulations.gov

16

Appendix A: Summary of Actions Taken for Trinexapac-ethyl

Registration Review Case#: 7228

PC Code:112602

Trinexapac-ethyl Type: Plant growth regulator

Trinexapac-ethyl Family: N/A

Mode of Action: Gibberellin inhibitor

Affected Population(s) Source of Exposure Route of Exposure Duration of 

Exposure

Risk of Concern Action(s) Taken Comment (use 

to briefly clarify 

or elaborate on 

risk or 

mitigation)

 Terrestrial Plants  Residues on 

site of 

treatment)

 Runoff

 Spray drift

 Acute

 Chronic

 Direct

 Indirect

 Clarify single 

maximum

application rate

for turf grass 

 Birds  Residues on 

site of 

treatment)

 Dietary

 Ingestion  Chronic  Direct  Clarify single 

maximum

application rate

for turf grass 
17

Appendix B: Trinexapac-ethyl Label Table

Summary of Labeling Changes for Trinexapac-ethyl Uses

Description Amended Labeling Language for Trinexapac-ethyl Use Products Placement on Label

Technical Products

Language to limit single 

maximum application 

rate for liquid turf grass 

products

“For liquid end-use turf products, the single maximum application rate must not exceed 0.68 lb ai/A. DO NOT 

double the single maximum application rate for extended suppression.”

Directions for Use

End Use Products

Language to limit single 

maximum application 

rate for liquid turf grass 

products

For liquid end-use turf products: “The single maximum application rate must not exceed 0.68 lb ai/A. DO NOT 

double the single maximum application rate for extended suppression.”

“Directions for Use” 

under “Application 

Information” and 

“Recommended 

Application Rate” table

Language to limit single 

maximum application 

rate for liquid turf grass 

products

Remove the statement: “For extended growth suppression up to 8 weeks, where temporary discoloration can be 

tolerates, a maximum of twice the recommended rate from the Application Rate Table may be applied.“

“Directions for Use” 

under “Application 

Information”