Docket Number EP A-HQ-OPP-2008-0657 

www.regulations.gov 

Trinexapac-ethyl 

Interim Registration Review Decision 

Case Number 7228 

December 2014 

Approved by: ~~p ~~,:J:> 

Richard P. Keigwin, Jr. 

Director 

Pesticide Re-evaluation Division 

Date: /.;J. - !) -/ '-/ 
Table of Contents 

Contents 

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

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

III. Scientific Assessments ......................................................................................................... 6 

A. Human Health Assessment .................................................................................................... 6 

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

2. Risk Conclusions .......................................................................................................... 7 

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

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

B. Environmental Assessment .................................................................................................... 8 

1. Envirorunental Fate and Exposure ................................................................................ 8 

2. Ecological Risk Assessment Uncertainties ................................................................... 8 

3. Ecological Risk Characterization ................................................................................. 8 

4. Overview of Ecological Risk Conclusions ................................................................... 9 

5. Effects on Terrestrial Organisms .................................................................................. 9 

6. Effects on Aquatic Organisms .................................................................................... 10 

7. Ecological Incidents ................................................................................................... 1 0 

8. Ecological Risk Management Conclusions for Non-Listed Species .......................... 10 

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

D. Endocrine Disrupter Screening Program ......................................................................... 12 

IV. Interim Registration Review Decision ............................................................................... 13 

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

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

B. Implementation of Mitigation Measures ......... ...................................................................... 14 

Appendix A: Summary of Action~ Taken for Trinexapac-ethyl .................................................. 15 

Appendix B: Trinexapac-ethyl Label Table ................................................................................. 16 

2 
I. Introduction 

This document is the Environmental Protection Agency's (EPA or the Agency) 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, an interim registration .review decision before completing 

a registration review. Among other things, the 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/oppsrrd 1/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 ofwarm 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: 

3 
• 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 t~e 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 ofTrinexapac-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 published the Trinexapac-ethyl Proposed Interim Registration 

Review Decision for a 60-day public comment period and the Response to Comments on 

the Preliminary Ecological Risk Assessment for the Registration Review ofTrinexapacethyl and Use/Usage Refinement in Support of Registration Review ofTrinexapac-ethyl. 

Several comments were received during the comment period. Two comments were 

received from Syngenta Crop Protection, LLC concerning the ecological risk assessment. 

One comment was received from the Center for Biological Diversity regarding the 

Agency's obligations under the Endangered Species Act. 

• December 2014 - The Agency is now publishing the Trinexapac-ethyl Interim 

Registration Review Decision and the Response to Comments on the Proposed Interim 

Decision for the Registration Review ofTrinexapac-ethyl. 

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

Public Comments 

During the public comment period for the proposed interim decision, the Agency 

received comments from Syngenta Crop Protection, LLC and the Center for Biological 

Diversity. Syngenta's comments on the proposed interim decision focused on conservative 

assumptions made in the ecological risk assessment. These comments are addressed in detail in 

the Response to Public Comment on the Trinexapac-ethyl Registration Review Proposed Interim 

Decision, dated November 18,2014, available in the public docket EPA-HQ-OPP-2008-0657. 

Comment Received from the Center for Biological Diversitv 

Comment: The Center for Biological Diversity 's (CBD) comments focus on the EPA 's duty to 

consult with the US. Fish and Wildlife Service and the National Marine Fisheries Service (the 

Services) on the registration review of trinexapac-ethyl in accordance with the ESA. The CBD 

4 
comments mention various aspects of the risk assessment process, including use of the best 

available data to develop endangered species risk assessments, and evaluation of effects on 

endangered and threatened species and their designated critical habitat. CBD also expresses 

concern regarding the rigor of the Agency's preliminary determinations regarding the effects of 

trinexapac-ethyl on endangered and threatened (listed) species and their designated critical 

habitat for the trinexapac-ethyl registration review. 

Response: EPA has reviewed the comments from CBD on the Trinexapac-ethyl Proposed 

Interim Registration Review Decision and plans to address many of the concerns raised by CBD 

as part of the implementation plan for assessing the risks of pesticides to listed species based on 

the recommendations ofthe April2013 National Academy of Sciences (NAS) report. EPA will 

address concerns specific to trinexapac-ethyl in connection wi~h the development of its final 

registration review decision for this pesticide. See Endangered Species Assessment on page 9 of 

this document for more information. 

II. Use and Usage 

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

ofTrinexapac-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 ofturf 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 orn~ental 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 more than 60,000 lbs active 

ingredient (a.i) annually. While fewer total pounds oftrinexapac-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 PGR 

use is trinexapac-ethyl (less than 7,000 lbs a.i.). Final)y, 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. 

5 
III. Scientific Assessments 

A. Human Health Assessment 

A swnmary of the Agen y~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 

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 mglkg/day in 

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

susceptibility to offspring exists at or abov~ 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 mglkg/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 mglkg/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 mglkg/day (male/female), 

6 
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 oftrinexapac-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 

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 oftrinexapac-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 oftrinexapac-ethyl when used as directed by labels. The Agency has 

determined that the reported incidents are not of c<,:mcern, but will continue to monitor the 

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

7 
B. Environmental Assessment 

The risk assessment supporting this 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 ofTrinexapac-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. Environmental Fate and Exposure 

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

metabolite, trinexapac acid, is mo~erately mobile in soil. Trinexapac-ethyl is not expected to 

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. 

2. 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 trinexapacethyl. 

3. Ecological Risk Characterization 

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

ecotoxicity stu~ies 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 

8 
chemical and its degradates in the environment, organisms potentially at risk, and the nature of 

the effects observed. 

4. 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 of0.50. Similarly, RQ exceedances above the LOC of 1.0 ranged from 1.1 5-

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. 

5. 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 aJ?d 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 of0.5. 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 ofTrinexapac-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. 

9 
Plants 

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

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

were identified as a result oftrinexapac-ethyl cereal grain uses. 

6. 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 oftrinexapac-ethyl. 

7. Ecological Incidents 

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

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

Information System (AIMS), which is maintained by the American Bird Conservancy, was 

conducted on May 16, 2013 for trinexapac-ethyl. Neither the EllS 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. 

8. 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 and end-use 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 Interim Registration Review Decision for the 

registration review oftrinexapac-ethyl. Therefore, once these changes to labels are made, risks 

10 
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 label 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 

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 

of Agriculture (USDA) released a summary of the joint Interim Approaches in the white paper 

"Interim Approaches for National-Level Pesticide Endangered. Species Act Assessments Based 

on the Recommendations of the National Academy of Sciences April2013 Report," dated 

November 1, 2013. 

The Interim Approaches 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 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 stakeholder workshops in April 

and October 2014, allowing additional opportunities for stakeholders to comment on the Interim 

Approaches. Additional workshops are planned to enhance stakeholder involvement. 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. 

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 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 oftrinexapac-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, 

11 
the regulatory section of the 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 refmements 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 1421listed 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-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 FFDCA1 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 

12 
by the substance, and establish a dose-response relationship between the dose and theE, 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 

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

environmental safety fmdings 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. Interim Registration Review Decision 

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

Interim Registration Review Decision for trinexapac-~thyl. 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. As the Agency 

works toward implementing its Guidance for Assessing Pesticide Risks to Bees3, additional data 

may be required for trinexapac-ethyl to assess non-target exposure to bees. 

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

associated with the EDSP screening oftrinexapac-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 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 Interim Decision, therefore, EPA has not completed effects 

determinations for listed species associated with the registered uses of trinexapac-ethyl. The 

Agency is issuing an Interim Registration Review Decision pending completion of the ESA and 

EDSP assessments. 

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

chemicals. 

2 http://www.epa.gov/endo/ 3 http://www2.epa. gov/sites/production/files/20 14-

06/documents/pollinator risk assessment guidance 06 19 14.pdf. 

13 
V. Next Steps and Timeline 

A. Interim Registration Review 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. 

B. Implementation of Mitigation Measures 

Registrants must submit amended labels that include the risk mitigation to clarify single 

maximum application rates for end-use turf grass products to the Agency for approval within 60 

days of publication ofthis Interim Decision. The mitigation measures and required label 

amendments are described in Appendices A and B below. 

14 
~ppendix 

A: Summary of Actions Taken for Trinexapac-ethyl 

Registration Review Case#: 7228 

PC Code:112602: 

rrrinexapac-ethyl Type: Plant growth regulator 

rrrinexapac-ethyl Family: N/A 

Mode of Action: Gibberellin inhibitor 

Affected Population(s) Source of Exposure Route of Exposure Duration of Risk of Concern Action(s) T

Exposure 

./ Terrestrial Plants ./ Residues on ./ Runoff ./ Acute ./ Direct ./ Clarify sin

site of ./ Spray drift ./ Chronic ./ Indirect maximum 

treatment) applicatio

for turf g

./ Birds ./ Residues on ./ Ingestion ./ Chronic ./ Direct ./ Clarify sin

site of maximum 

treatment) applicatio

./ Dietary for turf g
apac-ethyl Label Table 

Summary of Labeling Changes for Trinexapac-ethyl Uses 

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

Technical Products 

Directions for Use 

r liquid end-use turf products, the single maximum application rate must not exceed 0.68 lb ail A. DO NOT 

ble the single maximum application rate for extended suppression." 

End Use Products 

 liquid end-use turf products: ''The single maximum application rate must not exceed 0.68 lb ai/A. DO NOT "Directions for Use" 

ble the single maximum application rate for extended suppression." under "Application 

Information" and 

"Recommended 

Application Rate" table 

"Directions for Use" 

move the statement: "For extended growth suppression up to 8 weeks, where temporary discoloration can be under "Application 

rates, a maximum of twice the recommended rate from the Application Rate Table may be applied." Information" 

17