Page 1 of 28

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

OFFICE OF CHEMICAL SAFETY

AND POLLUTION PREVENTION

MEMORANDUM

DATE: October 12, 2011

SUBJECT: Trinexapac-Ethyl: Occupational and Residential Exposure/Risk Assessment for 

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

and oats).

PC Code: 112602 DP Barcode: D392798

Decision No.: Registration No.: 

Petition No.: NA Regulatory Action: Section 3 New Use

Risk Assessment Type: NA Case No.: 

TXR No.: NA CAS No.:

MRID No.: NA 40 CFR:

FROM: Monica Hawkins, Ph.D., M.P.H., Environmental Health Scientist

Risk Assessment Branch 6

Health Effects Division (7509P)

THROUGH: Charles Smith, Senior Environmental Scientist

Risk Assessment Branch 6

Health Effects Division (7509P)

TO: Sheila Piper, Senior Chemist/Risk Assessor

Bethany Benbow, Biologist

Herbicide Branch

Registration Division (7505P)
Page 2 of 28

INTRODUCTION

The registrant, Syngenta Crop Protection Incorporated has submitted a Section 3 registration 

application for proposed new uses of the active ingredient (ai) trinexapac-ethyl on cereals, 

sugarcane, and grasses grown for seed production. This memorandum contains an occupational 

and residential exposure and risk assessment for the requested use. An analysis of the 

occupational and residential exposures and risks from all currently registered uses of trinexapacethyl is also included since significant changes were made to the trinexapac-ethyl hazard 

assessment since the last trinexapac-ethyl assessment was completed by the Health Effects 

Division (HED) (Kelly Schumacher, DP 356118, 9/5/08). 

HED has examined the occupational and residential exposure (ORE) databases for trinexapacethyl. Based on the attached ORE assessment, HED has determined that there no risks that 

exceed HED’s level of concern (MOEs ≥ 100). Prior to the Registration Division (RD)

granting the requested uses, HED recommends that:

1) The proper REIs are put in place on the labels to reflect the acute toxicity of 

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

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

Per the Worker Protection Standard (WPS), a 12-hr restricted entry interval 

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

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

the labels to reflect these requirements.

Note: This memorandum was reviewed by the Exposure Science Advisory Council (ExpoSAC) 

on 08/4/2011.
Page 3 of 28

Table of Contents

1.0 EXECUTIVE SUMMARY ......................................................................................................4

2.0 HAZARD PROFILE.................................................................................................................6

3.0 USE PROFILE ..........................................................................................................................8

4.0 OCCUPATIONAL EXPOSURE ...........................................................................................10

4.1 Occupational Handler Exposure and Risk .........................................................................10

4.2 Occupational Post-application Exposure and Risk ...........................................................19

5.0 RESIDENTIAL (NON-OCCUPATIONAL) EXPOSURE .......................................................22

5.1 Residential (Non-Occupational) Handler Exposure and Risk................................................23

5.2 Residential Post-Application Exposure and Risk ..................................................................24

5.3 Spray Drift................................................................................................................................27
Page 4 of 28

1.0 EXECUTIVE SUMMARY 

Use Profile

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

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

used for formulation only. A Section 3 registration is being requested by Syngenta Crop 

Protection, Incorporated, for trinexapac-ethyl for use on wheat, barley, oats, and sugar cane and 

to amend the use on grass grown for seed production at a rate of 0.5 lb ai/A. The maximum 

single application rate proposed for wheat, barley, and oats is 0.11 lb ai/A and for sugarcane is 

0.31 lb ai/A. The end-use products are Palisade EC (EPA Reg. No. 100-949, emulsifiable 

concentrate and Palisade 2EC (EPA Reg. No. 100-1241, emulsifiable concentrate). Trinexapacethyl is also registered for use on turf areas such as sod farms, golf courses, sports fields, and 

cemeteries and similar areas. The label-required personal protective equipment (PPE) for 

occupational applicators is a long-sleeved shirt, long pants, shoes, and socks.

Hazard Profile

The Trinexapac-ethyl risk assessment team evaluated the toxicology database and toxicity 

endpoint and point of departure selections for risk assessment. Quantification of dermal and 

inhalation risks were performed using a developmental toxicity rabbit study. The LOAEL 

(Lowest Observed Adverse Effect Level) from this study was 360 mg/kg/day based on a 

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

NOAEL (No Observed Adverse Effect Level) from this study was 60 mg/kg/day. A target MOE 

of 100 is considered adequate for adults and children (10X for interspecies extrapolation, 10X 

for intraspecies variability, and a 1X for LOAEL to NOAEL extrapolation). Based on a dermal 

absorption study in male rats, absorption of Trinexapac-ethyl was determined to be 77.5% at 10 

hours. The female body weight of 60 kilograms (kg) was used in the short-term dermal and 

inhalation assessment because the dose and endpoint were selected from a developmental study 

in which fetal effects were observed (a decrease in the mean number of fetuses/litter and an 

increase in post-implantation loss). The use of the 60 kg body weight is protective of all 

workers, including males and females.

 

An endpoint of concern for the incidental oral scenario (hand to mouth behavior in children 1-6 

years) is not available from the trinexapac-ethyl toxicity studies.

Since the effects seen in the developmental rabbit study (selected for the short-term/intermediateterm assessment) and the chronic oral dog toxicity study (selected for the shortterm/intermediate-term assessment) are the same, these routes of exposure should be combined.

Trinexapac-ethyl is classified as “Not likely to be carcinogenic to humans.” This is based on the 

lack of carcinogenic potential noted in the available studies. There is no concern for 

mutagenicity and clastogenicity.

Occupational Exposure/Risk
Page 5 of 28

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

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

Occupational Handler

No chemical specific data were available to assess potential exposure to pesticide handlers. The 

estimates of exposure to pesticide handlers are based upon surrogate study data available in the 

Pesticide Handlers Exposure Database (PHED) Version 1.1 and the Agricultural Handler 

Exposure Task Force (AHETF). The occupational handler assessment was completed assuming 

the maximum label application rate for each crop. Based on the activity use pattern, the duration 

of exposure is expected to be short-term (1 to 30 days) and intermediate-term (1 to 6 months). 

Long-term exposures (greater than 6 months) are not anticipated based on the proposed use 

pattern. Dermal and inhalation risks for short- and intermediate-term exposures were combined 

in this assessment, since the toxicological effects for the dermal and inhalations routes were the 

same. A Margin of Exposure (MOE) greater than or equal to 100 for dermal and inhalation 

routes is deemed adequate to protect occupational trinexapac-ethyl handlers. All handler 

scenarios resulted in MOEs greater than the level of concern LOC (i.e., MOEs ≥ 100) when 

wearing labeled personal protective equipment (PPE) (e.g., long-sleeve shirt, long pants, shoes, 

socks, chemical-resistant gloves, and protective eyewear) and, therefore are not of concern. 

Occupational Post-application

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

activities. Chemical-specific data relevant to post-application exposure (i.e., dislodgeable foliar 

residue [DFR] data) were not submitted; therefore, post-application exposure estimates were 

calculated using standard HED Exposure SAC assumptions (body weight and exposure duration) 

and transfer coefficients (SOP # 3.2). Using default DFR values, risks are not a concern for any 

post-application occupational scenario on day 0, except for hand-harvesting sugarcane where 

risks are of concern until 8 days after application (short-term and intermediate-term postapplication).

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

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

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

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

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

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

reflect these requirements.

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

sugarcane were estimated to be 8 days for short-term and intermediate-term exposure. However, 

HED does not recommend that sugarcane REI’s be changed on the trinexapac-ethyl labels at this 

time based on two main issues. One, almost all sugarcane harvesting in the United States is done 

mechanically. Two, the proposed trinexapac-ethyl labels have a 28-day pre-harvest interval 

(PHI) for sugarcane so hand harvesting should not occur until after 28 days which is protective 
Page 6 of 28

of the estimated REIs.

Residential Exposure/Risk

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

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

residential risk assessments. Intermediate-term and chronic exposures were not assessed for 

residential handler and post-application risk assessments. 

Residential Handler

No chemical-specific handler exposure data were submitted in support of this registration. It is 

the policy of the HED to use data from the PHED Version 1.1. In addition, data from the 

Outdoor Residential Exposure Task Force (ORETF) is used, as appropriate. The combined 

dermal plus inhalation risks to residential handlers do not exceed HED’s level of concern for all 

scenarios (i.e., MOEs ≥ 100). 

Residential Post-application

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

residential areas, such as lawns, sports fields, and golf courses that could lead to postapplication exposures to adults and children. 

Short-term dermal risks were assessed for adults and children (3 to < 6 year olds). The 

residential post-application MOEs ranged from 450 to 24,000 and therefore do not exceed 

HED’s level of concern (MOE ≥ 100). 

Review of Human Research

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

were intentionally exposed to a pesticide or other chemical. Many such studies, involving 

exposure to many different pesticides, comprise generic pesticide exposure databases such as the 

PHED, the AHETF, and the Agricultural Reentry Task Force (ARTF) Database. EPA has 

reviewed all the studies in these multi-pesticide generic exposure databases, and on the basis of 

available evidence has found them to have been neither fundamentally unethical nor significantly 

deficient relative to standards of ethical research conduct prevailing when they were conducted. 

There is no regulatory barrier to continued reliance on these studies, and all applicable 

requirements of EPA’s Rule for the Protection of Human Subjects of Research (40 CFR Part 26) 

have been satisfied.

2.0 HAZARD PROFILE 

The acute toxicity for trinexapac-ethyl technical formulation was classified as Toxicity Category

III for acute oral, dermal, and eye irritation, and IV for acute inhalation and skin irritation (Table 

1).

Table 1. Acute Toxicity Profile - Trinexapac-ethyl (97%)
Page 7 of 28

Guideline 

No. Study Type MRID Results

Toxicity 

Category

870.1100 Acute oral [rat]

41563901

♂ LD50 = 4613 mg/kg

♀ LD50 = 4212 mg/kg

Combined LD50 = 4458 mg/kg

III

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

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

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

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

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

Short-term and inhalation risks are based on systemic effects (decrease in the mean number of 

fetus/litter and an increase in post-implantation loss) observed at the LOAEL of 360 mg/kg/day 

in the developmental toxicity rabbit study. The NOAEL from this study was 60 mg/kg/day. A 

target MOE of 100 is considered adequate for adults and children (10X for interspecies 

extrapolation, 10X for intraspecies variability, and a 1X for LOAEL to NOAEL extrapolation). 

Based on a dermal absorption study in male rats, absorption of Trinexapac-ethyl was 77.5% at 10 

hours. The female body weight of 60 kg was used in the short-term dermal and inhalation 

assessment because the dose and endpoint were selected from a developmental study in which 

fetal effects were observed (a decrease in the mean number of fetuses/litter and an increase in 

post-implantation loss). The use of the 60 kg body weight is protective of all workers, including 

males and females. 

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

trinexapac-ethyl toxicity studies. The rationale for this conclusion is based on the following 

weight of evidence considerations: 1) the toxicity observed during the appropriate duration of 

concern (short/intermediate term) were observed only at high doses [LOAEL = 900 mg/kg/day in 

the dog, 1000 mg/kg/day in the rat, and 1212 mg/kg/day in the reproduction study]; 2) the brain 

lesions observed in the chronic dog study are not appropriate for this scenario since the brain

lesions were seen only at termination (i.e. after exposure to 1-year) and toxicity observed after 

chronic exposure is not appropriate for application to the short/intermediate term scenarios; 3) 

the brain lesion observed in the chronic study are not expected to occur after short term 

exposure due to the lack of similar lesions or associated toxicity (i.e., clinical neurologic signs) 

in the 90-day studies in rats or dogs; 4) the cause for concern for the brain lesions is low because 

of the minimal lesion severity, lack of associated changes (i.e., gliosis, myelin loss astrocyte 

hypertrophy, neuronal necrosis etc), and the non-specific nature of the lesions (i.e., focal 

vacuoles); 5) the overall toxicity profile of this chemical clearly shows that toxicity is observed 

only at high doses (lowest LOAEL = 360 m/k/d in the chronic dog study); and 6) the in utero

endpoint identified in the rabbit study is not appropriate for this population of concern (children).

Since the effects seen in the developmental rabbit study (selected for the short-term/intermediateterm assessment) and the chronic `oral dog toxicity study (selected for the shortterm/intermediate-term assessment) are the same, these routes of exposure should be combined. 

Trinexapac-ethyl is classified as “Not likely to be carcinogenic to humans.” This is based on the 

lack of carcinogenic potential noted in the available studies. There is no concern for 

mutagenicity and clastogenicity. 
Page 8 of 28

Table 2 presents the selected points of departure for Trinexapac-ethyl.

Table 2. Summary of Toxicological Doses and Endpoints for Trinexapac-ethyl for use in Occupational 

Human Health Risk Assessments.

Exposure/

Scenario

Point of 

Departure

Uncertainty/ 

FQPA Safety 

Factors

RfD, PAD, 

Level of 

Concern for 

Risk 

Assessment

Study and Toxicological Effects

Acute Dietary

(General 

Population, 

including 

Infants and 

Children)

No appropriate endpoint for the general population including infants and children

Acute Dietary

(Females 13-

49 years of 

age)

NOAEL = 60 

mg/kg

UFA= 10x

UFH = 10x

FQPA SF= 1x

Acute RfD = 0.6 

mg/kg

aPAD = 0.6 

mg/kg

Developmental rabbit study

MRID 41869524

LOAEL = 360 mg/kg, based on a 

decrease in mean number of 

fetuses/litter and an increase in postimplantation loss

Chronic 

Dietary (All 

Populations)

NOAEL= 31.6 

mg/kg/day

UFA= 10x

UFH = 10x

FQPA SF= 1x

Chronic RfD = 

0.32

mg/kg/day

cPAD = 0.32 

mg/kg/day

Chronic oral toxicity study – dog

MRID 42779402/ 42779401

LOAEL = 357 mg/kg/day, based on 

elevated serum cholesterol values in 

females, mucoid feces in females and 

bloody feces in both sexes, and 

minimal, focal vacuolation of the 

dorsal medial hippocampus and/or 

lateral midbrain in both sexes

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. 
Page 9 of 28

Table 2. Summary of Toxicological Doses and Endpoints for Trinexapac-ethyl for use in Occupational 

Human Health Risk Assessments.

Exposure/

Scenario

Point of 

Departure

Uncertainty/ 

FQPA Safety 

Factors

RfD, PAD, 

Level of 

Concern for 

Risk 

Assessment

Study and Toxicological Effects

Incidental 

Oral 

(Short and 

IntermediateTerm )

No appropriate endpoint was available for the incidental oral scenario.

Dermal & 

Inhalation

Short and

IntermediateTerm (all 

populations)

(1-6 months)

NOAEL= 60 

mg/kg/day

Dermal 

absorption rate 

= 77.5% of oral 

absorption

Inhalation 

absorption rate 

= 100% of oral 

absorption

UFA= 10x

UFH = 10x

FQPA SF= 1x

Residential LOC 

for MOE = 100

Occupational 

LOC for MOE = 

100

Developmental rabbit study

MRID 41869524

LOAEL = 360 mg/kg, based on a 

decrease in mean number of 

fetuses/litter and an increase in postimplantation loss

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. 

3.0 USE PROFILE 

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

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

used for formulation only. A Section 3 registration is being requested by Syngenta Crop 

Protection, Incorporated for Trinexapac-ethyl for use on wheat, barley, oats, and sugar cane and 

to amend the use on grasses grown for seed production at a rate of 0.5 lb ai/A. The maximum 

application rate proposed for wheat, barley, and oats is 0.11 /b ai/A and sugarcane is 0.31 lb ai/A. 

The use pattern for the proposed new uses of Palisade 2EC (trinexapac-ethyl 25.5%, emulsifiable 

concentrate) and Palisade EC (trinexapac-ethyl 12%, emulsifiable concentrate), is summarized in 

Table 3. Trinexapac-ethyl is also registered for use on turf areas such as sod farms, golf courses, 

sports fields, and cemeteries and similar areas. 

 

The personal protective equipment (PPE) requirements proposed on the Palisade 2EC

and Palisade EC labels, that is consistent with current registrations, are:
Page 10 of 28

o Applicators and other handlers must wear: long-sleeved shirt and long pants, chemicalresistant gloves, shoes plus socks, and protective eyewear.

Table 3. Proposed Use Patterns and Formulations

Product Formulation Use Sites Application 

Rates

Application 

Equipment

Max App 

Rate per 

crop season

REI

Palisade 

2EC

(EPA Reg. 

No. 100-

1241)

Emulsifiable 

Concentrate

Grasses 

grown for 

seed

 0.04 – 0.5 

lb ai/A Aerial, ground, 

handheld, and 

chemigation

0.5 lb ai/A

4 hours Cereals 0.04 – 0.11 

lb ai/A 0.11 lb ai/A

Sugarcane 0.07 – 0.31 

lb ai/A 0.31 lb ai/A

Palisade EC 

(EPA Reg. 

No. 100-

949)

Emulsifiable 

Concentrate

Grasses 

grown for 

seed

0.05 – 0.5 lb 

ai/A Aerial, ground, 

and 

chemigation

0.5 lb ai/A

0 days

Cereals 0.05 – 0.11 

lb ai/A 0.11 lb ai/A

Sugarcane 0.06 – 0.31 0.31 lb ai/A

4.0 OCCUPATIONAL EXPOSURE 

4.1 Occupational Handler Exposure and 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 that exposures can vary depending on the specifics of each task. Job 

requirements (e.g., amount of chemical to be used in an 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. The first step in the handler risk 

assessment process is to identify the kinds of individuals that are likely to be exposed to 

Trinexapac-ethyl during the application process. In order to do this in a consistent manner, HED 

has developed a series of general descriptions for tasks that are associated with pesticide 

applications. 

Exposure Scenarios

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

pesticide handlers in the following scenarios:

Mixing/loading liquids for aerial applications

Mixing/loading liquids for groundboom applications

Mixing/loading liquids for chemigation
Page 11 of 28

Mixing/loading liquids for LCO handgun applications

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

Mixing/loading wettable powders in water soluble bags for chemigation

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

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

Mixing/loading granules for aerial applications

Mixing/loading granules for tractor drawn spreader applications

Applying sprays for aerial applications

Applying sprays for groundboom equipment

Applying granules for tractor drawn spreader applications

Flagging (liquids) during aerial applications

Flagging (granules) during aerial applications

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

Mixing/loading/applying liquids for backpack sprayer applications

Mixing/loading/applying liquids for handgun sprayer applications

Mixing/loading/applying liquids for low pressure handwand applications

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

applications

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

Mixing/loading/applying granules for belly grinder applications

Mixing/loading/applying granules for push type spreader applications

Area or the Amount Treated

The daily areas treated were defined for each handler scenario (in appropriate units) by 

determining the amount that can be reasonably treated in a single day. When possible, the 

assumptions for daily areas treated are taken from HED ExpoSAC Policy #9: “Standard Values 

for Daily Acres Treated in Agriculture”, which was revised on July 5, 2000. Values used for 

area treated in each scenario include: 350 acres for application with fixed-wing aircraft, flagging, 

and chemigation; 80 acres for groundboom application (40 acres for groundboom application for 

golf courses), 100 acres for mixing/loading for multiple LCO handgun applications, 80 acres for 

tractor drawn spreader application (40 acres for golf courses), 0.023 (1,000 ft2) acres for low 

pressure handwand application, backpack sprayer application, and belly grinder application; and 

5 acres for handgun sprayer application.

Personal Protective Equipment

Occupational handler exposure assessments are completed by HED using different levels of 

personal protection. HED typically evaluates all exposures with a tiered approach. The lowest 

tier is represented by the baseline exposure scenario (i.e., long-sleeved shirt, long pants, shoes, 

and socks) followed by increasing the levels of personal protective equipment or PPE (e.g., 

gloves, double-layer body protection, and respirators) and engineering controls (e.g., enclosed 

cabs and closed mixing/loading systems). This approach is always used by HED in order to be 

able to define label language using a risk-based approach. In addition, the minimal level of 

adequate protection for a chemical is generally considered by HED to be the most practical 
Page 12 of 28

option for risk reduction (i.e., over-burdensome risk mitigation measures are not considered a 

practical alternative).

Unit Exposures

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

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

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

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

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

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

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

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

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

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

“Occupational Pesticide Handler Unit Exposure Surrogate Reference Table” 

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

There are three basic risk mitigation approaches considered appropriate for controlling 

occupational exposures. These include administrative controls, the use of personal protective 

equipment or PPE, and the use of engineering controls. Occupational handler exposure 

assessments are often completed by HED using baseline, PPE, and engineering controls. [Note: 

Administrative controls available generally involve altering application rates for handler 

exposure scenarios. These are typically not utilized for completing handler exposure 

assessments.] The baseline clothing level scenario for occupational exposure scenarios is 

generally an individual wearing long pants, a long-sleeved shirt, no chemical resistant gloves, 

and no respirator. The first level of mitigation generally applied is PPE. PPE may involve the 

use of an additional layer of clothing, chemical-resistant gloves, and a respirator. The next level 

of mitigation considered in the risk assessment process is the use of appropriate engineering 

controls which, by design, attempt to eliminate the possibility of human exposure. Examples of 

commonly used engineering controls include enclosed tractor cabs and cockpits, closed 

mixing/loading/transfer systems, and water-soluble packets.

Typically, HED completes short- and intermediate-term assessments for occupational scenarios 

in all cases because both durations are likely and acceptable use/usage data are not available to 

justify deleting intermediate-term scenarios. Based on use data and label instructions, HED 

believes that occupational exposures for trinexapac-ethyl may occur over a single day or up to 

weeks at a time for many use-patterns and that intermittent exposure over several weeks may 

also occur. Some applicators may apply these products over a period of weeks, because they are 

commercial applicators who are completing multiple applications for multiple clients. Longterm exposures are not expected; therefore, a long-term assessment was not conducted.

Equations and Calculations:

Daily Exposure: Daily dermal and inhalation handler exposures are estimated for each 

applicable handler task with the application rate, the area treated or amount handled in a day, and 
Page 13 of 28

the applicable unit exposure using the following formula:

Daily Exposure (mg ai/day) = Unit Exposure (mg ai/lb ai handled) x Application Rate (lbs ai/area) x Daily Area 

Treated (area/day)

Where: 

Daily Exposure = Amount (mg ai/day) inhaled that is available for inhalation absorption;

Unit Exposure = Unit exposure value (mg ai/lb ai) derived from August 1998 PHED 

data;

Application Rate = Normalized application rate based on a logical unit treatment, such as 

acres; and

Daily Area Treated = Normalized application area based on a logical unit treatment such as 

acres (A/day). 

Daily Dose: Daily dermal and inhalation dose is calculated by normalizing the daily exposure 

by body weight and adjusting, if necessary, with an appropriate dermal or inhalation absorption 

factor using the following formula:

Average Daily Dose (mg/kg/day) = Daily Exposure (mg ai/day) x (Absorption Factor (%/100)) / Body Weight (kg)

Where:

Average Daily Dose = Absorbed dose received from exposure to a pesticide in a given 

scenario (mg ai/kg body weight/day);

Daily Exposure = Amount (mg ai/day) inhaled that is available for inhalation absorption;

Absorption Factor = A measure of the amount of chemical that crosses a biological 

boundary such as the skin or lungs (% of the total available absorbed); 

and

Body Weight = Body weight determined to represent the population of interest in a risk 

assessment (kg).

Margin of Exposure (MOE): The daily dermal dose and daily inhalation dose received by 

occupational handlers are compared to the appropriate point of departure (i.e., NOAEL) to assess 

the risk to occupational handlers for each exposure route. All MOE values are calculated 

separately for dermal and inhalation exposure levels using the following equation:

MOE = NOAEL (mg/kg/day) / Average Daily Dose (mg/kg/day)

Where:

MOE = Margin of exposure value used by HED to represent risk or how close a 

chemical exposure is to being a concern (unitless),

ADD = Average daily dose is the absorbed dose received from exposure to pesticide (mg/kg/day)

NOAEL = No Observable Adverse Effect Level (mg/kg/day)

Combined Risks: Dermal and inhalation risks for short- and intermediate-term exposures were 

combined in this assessment, since the toxicological effects for the dermal and inhalations routes 

were the same. Dermal and inhalation risks were combined using the following equation:

Total MOE = 1/ ((1/ Dermal MOE) + (1/Inhalation MOE))
Page 14 of 28

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

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

inhalation, and combined dermal and inhalation exposures when wearing labeled PPE (longsleeve shirt, long pants, shoes, socks, chemical-resistant gloves, and protective eyewear) and, 

therefore are not of concern.

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

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

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

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

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

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

professional judgement.
Page 15 of 28

Table 4. Short-Term and Intermediate-Term Occupational Handler Dermal and Inhalation Exposures 

Crop Grouping Target MOE

Dermal Unit 

Exposure 

(mg/lb ai)

Inhalation Unit 

Exposure

(mg/lb ai)

Application 

Ratea

Area Treated 

Dailyb PPE-G Baseline Inhalation Total

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

(mg/kg/day)

Dermal 

MOEd Dosee MOEf MOEg

Mixer/Loader (Liquids) - Aerial Application

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

Sod 100 0.0376 0.000219 0.34 350 0.058 1000 0.00043 140000 1000

Sugarcane 100 0.0376 0.000219 0.31 350 0.053 1100 0.0004 150000 1100

Cereals 100 0.0376 0.000219 0.11 350 0.019 3200 0.00014 430000 3200

Mixer/Loader (Liquids)- Groundboom Application

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

Sod 100 0.0376 0.000219 0.34 80 0.013 4500 0.000099 600000 4500

Sugarcane 100 0.0376 0.000219 0.31 80 0.012 5000 0.000091 660000 4900

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

Cereals 100 0.0376 0.000219 0.11 80 0.0043 14000 0.000032 1900000 14000

Mixer/Loader (Liquids)- Chemigation

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

Sod 100 0.0376 0.000219 0.34 350 0.058 1000 0.00043 140000 1000

Sugarcane 100 0.0376 0.000219 0.31 350 0.053 1100 0.0004 150000 1100

Cereals 100 0.0376 0.000219 0.11 350 0.019 3200 0.00014 430000 3200

Mixer/Loader (Liquids)- LCO Handgun Application

Turf 100 0.0376 0.000219 0.34 100 0.017 3600 0.00012 480000 3600

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

Sod 100 0.0098 0.00024 0.34 350 0.015 4000 0.00048 130000 600

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

Sod 100 0.0098 0.00024 0.34 350 0.015 4000 0.00048 130000 600

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

Sod 100 0.0098 0.00024 0.34 80 0.0034 17000 0.00011 550000 2600

Golf Course 100 0.0098 0.00024 0.17 40 0.00086 70000 0.000027 2200000 10000
Page 16 of 28

Table 4. Short-Term and Intermediate-Term Occupational Handler Dermal and Inhalation Exposures 

Crop Grouping Target MOE

Dermal Unit 

Exposure 

(mg/lb ai)

Inhalation Unit 

Exposure

(mg/lb ai)

Application 

Ratea

Area Treated 

Dailyb PPE-G Baseline Inhalation Total

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

(mg/kg/day)

Dermal 

MOEd Dosee MOEf MOEg

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

Turf 100 0.0098 0.00024 0.34 100 0.0043 14000 0.00014 440000 2100

Mixer/Loader (Granules) - Aerial Application

Sod 100 0.0069 0.0017 0.44 350 0.014 4400 0.0044 14000 3300

Mixer/Loader (Granules ) - Tractor Drawn Spreader Applications

Sod 100 0.0069 0.0017 0.44 80 0.0031 19000 0.001 60000 15000

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

Applicator (Sprays)- Aerial

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

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

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

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

Applicator (Sprays)- Groundboom Equipment

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

Sod 100 0.0161 0.00034 0.34 80 0.0057 11000 0.00015 390000 10000

Sugarcane 100 0.0161 0.00034 0.31 80 0.0052 12000 0.00014 430000 11000

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

Cereals 100 0.0161 0.00034 0.11 80 0.0018 33000 0.00005 1200000 32000

Applicator (Granules) - Tractor Drawn Spreader Applications

Sod 100 0.0072 0.0012 0.44 80 0.0033 18000 0.0007 85000 15000

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

Flagger (Liquids)- Aerial Spray Application

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

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

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

Cereals 100 -- 0.00035 0.11 350 -- -- 0.00022 270000 --
Page 17 of 28

Table 4. Short-Term and Intermediate-Term Occupational Handler Dermal and Inhalation Exposures 

Crop Grouping Target MOE

Dermal Unit 

Exposure 

(mg/lb ai)

Inhalation Unit 

Exposure

(mg/lb ai)

Application 

Ratea

Area Treated 

Dailyb PPE-G Baseline Inhalation Total

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

(mg/kg/day)

Dermal 

MOEd Dosee MOEf MOEg

Flagger (Granules) - Aerial Application

Sod 100

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

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

Edging/Banding 100

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

Turf 100

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

Golf Course 100

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

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

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

Turf 100 2.5 0.03 0.34 0.023 0.00025 240000 0.0000039 15000000 230000

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

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

Turf 100 0.45 0.0015 0.34 5 0.0099 6100 0.000043 1400000 6000

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

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

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

Turf 100 0.33 0.0027 0.34 0.023 0.000033 1800000 0.00000035 170000000 1800000

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

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

Edging/Banding 100

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

Turf 100

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

Golf Course 100

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

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

Turf 100

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

Golf Course 100

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

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

Edging/Banding 100 9.3 0.062 0.88 0.023 0.0024 25000 0.000021 2900000 24000
Page 18 of 28

Table 4. Short-Term and Intermediate-Term Occupational Handler Dermal and Inhalation Exposures 

Crop Grouping Target MOE

Dermal Unit 

Exposure 

(mg/lb ai)

Inhalation Unit 

Exposure

(mg/lb ai)

Application 

Ratea

Area Treated 

Dailyb PPE-G Baseline Inhalation Total

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

(mg/kg/day)

Dermal 

MOEd Dosee MOEf MOEg

Turf 100 9.3 0.062 0.44 0.023 0.0012 49000 0.00001 5700000 49000

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

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

Turf 100 0.22 0.0073 0.44 0.5 0.0063 9600 0.00027 220000 9200

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

a. Application Rates based on proposed labels.

b. Science Advisory Council Policy No. 9.1

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

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

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

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

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

-- = Data Not Available or Liquids Exposure Scenario is considered protective of this scenario
Page 19 of 28

4.2 Occupational Post-application Exposure and Risk

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

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

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

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

exposures during postapplication activities were estimated using dermal transfer coefficients 

from the Science Advisory Council for Exposure Policy Number 3 

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

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

requires compensation to the ARTF under FIFRA. 

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

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

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

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

application using the following equations:

Equations/Calculations:

Daily Dermal Exposure: Daily dermal exposures were calculated on each post-application day 

after application using the following equation (see equation D2-20 from Series 875-

Occupational and Residential Test Guidelines: Group B-Post-application Exposure Monitoring 

Test Guidelines and Residential SOP 3.2: Post-application Dermal Potential Doses from 

Pesticide Residues on Gardens):

DE(t) (mg/day) = (DFR(t) (μg/cm2) x TC (cm2/hr) x DA x Hr/Day)/1000 (μg/mg)

Where:

DE(t) = Daily exposure or amount deposited on the surface of the skin at time (t) attributable

attributable for activity in a previously treated area, also referred to as potential dose

(mg ai/day);

DFR(t) = Transferable residues that can either be dislodgeable foliar or turf transferable 

residue at time “t” (μg/cm2);

TC = Transfer Coefficient (cm2/hour); 

DA = Dermal Absorption (%); and

Hr/day = Exposure duration meant to represent a typical workday (8 hours).

Default DFR (μg/cm2) = AR (lb ai/A) x F x (1- D)t x CF1 x CF2

Where:

AR = Maximum application rate

F = Fraction of ai retained on the foliage (unitless)

D = Fraction of residue that dissipates daily (unitless)

t = Post-application day

CF1 = 4.54E+8 μg/lb

CF2 = 2.47E-8 A/cm2

Daily Dermal Dose: Daily dermal dose is calculated by normalizing the daily exposure by body 

weight and adjusting, if necessary, with an appropriate dermal absorption factor using the 
Page 20 of 28

following formula:

Daily Dermal Dose (mg/kg/day) = Daily Exposure (mg ai/day) x (Absorption Factor (%/100)) / Body Weight (kg)

Where:

Daily Dermal Dose = Absorbed dose received from exposure to a pesticide in a given 

scenario (mg ai/kg body weight/day);

Daily Exposure = Amount (mg ai/day) inhaled that is available for inhalation absorption;

Absorption Factor = A measure of the amount of chemical that crosses a biological 

boundary such as the skin or lungs (% of the total available absorbed); 

and

Body Weight = Body weight determined to represent the population of interest in a risk 

assessment (kg).

Margin of Exposure (MOE): The daily dermal dose received by occupational postapplication 

workers are compared to the appropriate point of departure (i.e., NOAEL) to assess 

postapplication risks. All MOE values are calculated for dermal exposure levels using the 

following equation:

MOE = NOAEL (mg/kg/day) / Daily Dermal Dose (mg/kg/day)

Where:

MOE = Margin of exposure value used by HED to represent risk or how close a 

chemical exposure is to being a concern (unitless),

DDD = Daily dermal dose is the absorbed dose received from exposure to pesticide (mg/kg/day)

NOAEL = No Observable Adverse Effect Level (mg/kg/day)

A summary of the estimated occupational post-application risks as calculated per default DFR 

data are provided in Table 5. The post-application MOEs at day 0 range from 47 to 12,000. The 

results indicate that occupational post-application risks, as calculated per HED default values, do 

not exceed HED’s level of concern (an MOE ≥100) on day zero after application for all postapplication tasks that were assessed except for hand-harvesting sugarcane where the MOE 

increases to 110 within 8 days of application (short-term and intermediate-term post-application).
Page 21 of 28

Table 5. Summary of Trinexapac-ethyl Occupational Short-Term and Intermediate-Term Postapplication Risks Using Default Data

Crop Grouping Crop

Exposure 

Potential

Max 

Foliar 

Rate 

(lb ai/ 

acre)

Transfer 

Coefficient 

(cm2/hr)

Activities

MOE 

at 

Day 

Zero

Day 

Acceptable 

MOE

Field/Row Crop 

(Low)

Turf/Sod

(Golf 

Course)

Low 0.17 3700 Maintenance 410 --

Field Row

Crop (Low)

Turf/Sod

(Sod) Low 0.34

0

Roll 

Harvesting -- --

6700

Maintenance, 

Slab 

Harvesting, 

Transplanting

/

Planting

110 --

Field/Row Crop 

(Low/Medium) Sugarcane

Low

0.31

0 Transplanting -- --

70 Hand 

Weeding 12000 --

High

0

Mechanical 

Harvesting, 

Mechanical 

Weeding

-- --

1100 Scouting 760

17600 Hand 

Harvesting 47 8

Field/Row Crop 

(Low/Medium)

Grasses 

grown for 

seed

Low 0.5

0

Mechanical 

Harvesting, 

Fertilizing, 

Irrigation 

(non-hand 

set)

-- --

1100 Scouting 470 --

1900 Irrigation 

(hand set) 270 --

Field/Row Crop 

(Low/Medium) Cereals Low 0.11

0

Irrigation 

(non-hand 

set), 

Mechanical 

Harvesting

-- --

1100 Scouting 2100 --

Occupational Post-application Inhalation

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

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

acute inhalation toxicity (Toxicity Category IV). However, there are multiple potential sources 
Page 22 of 28

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

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

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

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

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

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

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

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

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

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

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

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

post-application inhalation exposure assessment for trinexapac-ethyl.

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

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

assessment resulted in risks that did not exceed HED’s level of concern at baseline inhalation 

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

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

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

inhalation exposure scenarios.

Restricted Entry Interval: Current trinexapac-ethyl labels have either no REI or a 4 hour REI. 

The trinexapac-ethyl technical material has been classified in Toxicity Category III for acute 

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

irritation. Per the Worker Protection Standard (WPS), a 12-hr restricted entry interval (REI) is 

required for chemicals classified under Toxicity Category III/IV. The Registration Division 

(RD) should ensure the proper REIs are put in place on the labels to reflect these requirements.

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

sugarcane were estimated to be 8 days for short-term and intermediate-term exposure. However, 

HED does not recommend that REI’s be changed on the trinexapac-ethyl labels at this time 

based on two main issues. One, almost all sugarcane harvesting in the United States is done 

mechanically. Two, the proposed trinexapac-ethyl labels have a 28-day pre-harvest interval 

(PHI) for sugarcane so hand harvesting should not occur until after 28 days which is protective 

of the estimated REIs.

5.0 RESIDENTIAL (NON-OCCUPATIONAL) EXPOSURE

Trinexapac-ethyl is currently registered for use on residential lawns, athletic fields, parks, and 

golf courses by residential consumers as well as applied by PCOs and commercial applicators; 

therefore, a residential handler assessment has been completed. The combined dermal plus 

inhalation risks to residential handlers did not exceed HED’s (LOC) for all scenarios. Short-term 

dermal postapplication risks were assessed for adults, youths, and toddlers and did not exceed 

HED’s LOC for all residential post-application scenarios. 
Page 23 of 28

5.1 Residential (Non-Occupational) Handler Exposure and Risk

Assessing exposures and risks resulting from residential uses is very similar to assessing 

occupational exposures and risks, except that residential handler exposure scenarios do not use a 

tiered approach for personal protection using increasing levels of PPE in residential handler risk 

assessments. Homeowner handler assessments are based on the assumption that individuals are 

wearing shorts, short-sleeved shirts, socks, and shoes, and homeowner handlers are expected to 

complete all tasks associated with the use of a pesticide product including mixing/loading if 

needed as well as the application. Residential handler exposure scenarios are considered to be 

short-term only, due to the infrequent use patterns associated with homeowner products.

It has been determined that exposure to pesticide handlers is likely during the residential use of 

trinexapac-ethyl on lawns. The quantitative exposure/risk assessment developed for residential 

handlers is based on the following scenarios:

Mixer/Loader/Applicators

Liquid: Low Pressure Handwand;

Wettable Powders: Low Pressure Handwand;

Liquid: Hose End Sprayer;

Liquid: Backpack Sprayer;

Granules: Push Type Spreader; and 

Granules: Belly Grinder

The methods for assessing exposures for residential handlers were based primarily on EPA’s 

Draft Standard Operating Procedures (SOPs) for Residential Exposure Assessments (December 

1997), and updates contained in HED’s Science Advisory Council Policy 12 (February 2001). 

According to Table A-1 of the SOPs, the method used for estimating residential applicator 

exposure is believed to produce a central tendency to high-end estimate of exposure.

Non-occupational handler’s exposure and risk estimates are summarized in Table 6. The 

combined dermal plus inhalation risks to residential handlers do not exceed HED’s level of 

concern for all scenarios (i.e., MOEs ≥ 100). 

Table 6. Short-Term Residential Handler Baseline Dermal and Inhalation Exposures 

Crop 

Grouping

Target 

MOE

Dermal 

Unit 

Exposure 

(mg/lb ai)

Inhalation 

Unit 

Exposure 

(mg/lb ai) Application 

Ratea

(lb ai/A)

Area 

Treated 

Dailyb

(acres/day)

Baseline Baseline Inhalation Total

Baseline Baseline

Dermal 

Dosec

(mg/kg/day)

Dermal 

MOEd Dosee MOEf

Baseline 

Dermal + 

Baseline 

Inhalation 

MOEg

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

Turf 100 100 0.03 0.34 0.023 0.01 5800 0.0000039 15000000 5800

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

Turf 100 250 1.063 0.34 0.023 0.026 2300 0.00014 430000 2300

Mixer/Loader/Applicator (Liquids) - Hose End Sprayer Application
Page 24 of 28

Turf 100 11 0.017 0.34 0.5 0.025 2400 0.000048 1200000 2400

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

Turf 100 5.1 0.03 0.34 0.023 0.00053 110000 0.0000039 15000000 110000

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

Turf 100 0.67 0.00088 0.44 0.5 0.002 31000 0.0000032 19000000 30000

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

Turf 100 110 0.062 0.44 0.023 0.015 4000 0.00001 5700000 4000

a. Application rates based on proposed labels. 

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

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

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

absorption / body weight (60 kg).

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

inhalation absorption / body weight (60 kg). 

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

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

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

5.2 Residential Post-Application Exposure and Risk

HED uses the term “post-application” to describe exposure to individuals that occur as a result of 

being in an environment that has been previously treated with a pesticide. Trinexapac-ethyl can 

be used in many areas that can be frequented by the general population including residential areas 

(e.g., home lawns, recreational turf). As a result, individuals can be exposed by entering these 

areas if they have been previously treated. HED refers to these exposures as “residential” in

nature.

Short-term dermal post-application exposures and risks have been assessed for trinexapac-ethyl. 

There is the potential for incidental oral exposure, however, since there is no point of departure 

for that route, a quantitative assessment was not conducted. The populations that were considered 

in the assessment include:

Residential Adults: these individuals are members of the general population that are exposed to 

chemicals by engaging in activities at their residences (e.g., in their lawns) and also in areas not 

limited to their residence (e.g., golf courses or parks) previously treated with a pesticide. These 

kinds of exposures are attributable to a variety of activities and are usually addressed by HED in 

risk assessments by considering a representative activity as the basis for the exposure calculation.

Residential Children: children are members of the general population that can also be exposed in 

their residences (e.g., on lawns and other residential turfgrass areas). These kinds of exposures are 

attributable to a variety of activities such as playing outside. Children (ages 3-6) have been 

selected as the representative population for lawn turf assessments. Youth (ages 10-12) have been 

selected as the representative population for golf course turf.

There are several post-application scenarios associated with the use of trinexapac-ethyl on 

recreational turf: adults golfing, high contact lawn activities, and mowing and children high 

contact lawn activities. Duration of such recreational exposure is anticipated to be short-term 

(<30 days). A short-term post-application dermal exposure/risk estimate for golfing, high contact 

lawn activities, and mowing was produced based on following assumptions and calculations:
Page 25 of 28

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

labels, the following residential post-application exposure scenarios are evaluated:

● Dermal Dose from pesticide residues on treated turf: Post-application exposure calculations 

for homeowners (adults and children) from skin contact with pesticide residues on treated turf;

The assumptions and factors used in this residential post-application assessment include:

● HED combines risks resulting from exposures to individual when it is likely they can occur 

simultaneously based on the use pattern and the behavior associated with the exposed population. 

For this assessment, HED combined risks (i.e., MOEs) for different kinds of exposures within 

the turf (dermal) exposure scenario. These represent the standard set of exposures that are 

typically added together when chemicals are used on turf, because it is logical they can co-occur.

● Exposures to adults and children on treated turf were addressed using the latest HED standard 

operating procedures for this scenario including:

o 5 percent of the application rate has been used to calculate the day-zero TTR 

residue levels used for assessing risks from dermal and hand-to-mouth exposures, 

since trinexapac-ethyl specific turf transferable residue study data are not 

available; 

o 20 percent of the application rate has been used to calculate the day-zero residue 

levels used for assessing risks from object-to-mouth behaviors (a higher percent 

transfer has been used for object-to-mouth behaviors, because it involves a 

teething action believed to be more analogous to DFR/leaf wash sample collection 

where 20 percent is also used);

o 3 to < 6 year old children are expected to weigh 15 kilograms (representing an 

average weight from years one to six);dermal exposures for playing on treated turf 

are based on a transfer coefficient of 14,500 cm2/hr for adults or 5,200 cm2/hr for 

children;

o dermal exposures for golfing are based on a transfer coefficient of 500 cm2/hr for 

adults;

o exposure duration for the turf grass scenario is estimated to be 2 hours based on 

information in HED’s Exposure Factors Handbook;

o exposure duration for golfing is estimated to be 4 hours (assuming chemical is 

used on all parts of a course [greens, tees and fairways] and an adult plays 18 

holes of golf).

Post-application exposures/risks from treated turf were calculated using the following equations:

Dermal Exposure to Pesticide Residues on Treated Turf

The approach used to calculate the dermal exposures that are attributable to the contact of 

pesticide residues on treated turf is:

ADD = (TTR0 * CF1* Tc * ET) * DA / BW
Page 26 of 28

where:

ADD = average daily dose (mg/kg/day);

TTR0 = turf transferable residue on day "0" (μg/cm2);

CF1 = weight unit conversion factor to convert the μg of residues on the grass to 

mg (0.001 mg/μg);

Tc = transfer coefficient (14,500 cm2/hr for adults, 5,200 cm2/hr for children);

ET = exposure time (2 hr/day);

DA = dermal absorption factor (100% or 8%); and

BW = body weight (adult = 60 kg, children =15 kg).

and

TTR0 = AR * F * (1-D) 0*CF2 * CF3 

where:

AR = application rate (lb ai/A)

F = fraction of ai retained on turf (5%); 

CF2 = conversion rate from pounds active ingredient to micrograms of active 

ingredient (4.54E+08 μg/lb); and

CF3 = conversion rate from acres to cm2(2.47E-08 A/cm2).

Dermal MOE = NOAEL (60 mg/kg/day) 

 ADD (mg/kg/day) 

The dermal MOEs calculated for adults golfing, mowing and high contact lawn activities are all 

greater than 100 and therefore, the risk does not exceed HED’s level of concern. The dermal 

MOEs calculated for children high contact lawn activities is greater than 100 and therefore, the 

risks do not exceed HED’s level of concern.

Although exposure to children golfing could be almost twice that of the adult golfer because of 

increased surface area/body weight (SA/BW) ratios, younger golfers are not expected to use the 

golf course for the same length of time as adolescents and adults. The shorter duration on the 

golf course for younger golfers offsets the higher SA/BW; therefore, risks from short-term postapplication exposures to young golfers are likely to be similar to risks for adult golfers.

The residential post-application MOEs ranged from 450 to 24,000 and therefore do not exceed 

HED’s level of concern (MOE ≥ 100). A summary of the residential post-application 

exposures/risks is presented in Table 7 and 8.

Table 7. Short- and Intermediate-Term Residential Postapplication Exposure and 

Risk Estimates for Trinexapac-ethyl (Liquids)

Lifestage Postapplication Exposure Scenario Application Rate Dose MOEs

Adult Turf - sprays

High Contact Lawn 

Activities (Dermal) 0.34 0.071 840
Page 27 of 28

Table 7. Short- and Intermediate-Term Residential Postapplication Exposure and 

Risk Estimates for Trinexapac-ethyl (Liquids)

Lifestage Postapplication Exposure Scenario Application Rate Dose MOEs

Golfing (Dermal) 0.17 0.0025 24000

Mowing (Dermal) 0.34 0.0025 24000

Child High Contact Lawn 

Activities (Dermal) 0.34 0.1 590

Table 8. Short- and Intermediate-Term Residential Postapplication Exposure and 

Risk Estimates for Trinexapac-ethyl (Granular Formulations)

Lifestage Postapplication Exposure Scenario Application Rate Dose MOEs

Adult

Turf - granules

High Contact Lawn 

Activities (Dermal) 0.44 0.092 650

Golfing (Dermal) 0.17 0.0025 24000

Mowing (Dermal) 0.44 0.0032 19000

Child High Contact Lawn 

Activities (Dermal) 0.44 0.13 450

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

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

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

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

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

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

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

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

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

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

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

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

for trinexapac-ethyl.

5.3 Spray Drift

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

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

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

The Agency has been working with the Spray Drift Task Force, EPA Regional Offices and State 

Lead Agencies for pesticide regulation and other parties to develop the best spray drift 

management practices (see the Agency’s Spray Drift website for more information at 

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

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

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

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

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

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

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

management practices to reduce off-target drift and risks associated with aerial as well as other 
Page 28 of 28

application types where appropriate. 

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

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

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

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

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

References

Author Barcode Date Title

Kelly Schumacher D356118 9/5/2008 Trinexapac-ethyl: Revised Human Health 

Assessment Scoping Document in Support 

of Registration Review