UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

MEMORANDUM 

Date: 04-FEB-2016 

OFFICE OF 

CHEMICAL SAFETY AND 

POLLUTION PREVENTION 

SUBJECT: T riclopyr. Human Health Risk Assessment for Petition to Amend Tolerance 

Expressions to Include Triclopyr Choline Salt; and Petition to Remove Grazing 

Restrictions for Dairy Cattle. 

PC Codes: 1 16000, 11 600 I. 116002. 116004 

Decision Nos.: 491435. 4884 78 

OP Barcodes: 0420771. 0426071 

Registration Nos.: 62719-37, 627 19-53. 62719-87, 627 19-552, 62719-

637. 62719-AIT (687) 

Petition Nos.: 4F8249 and 4F8279 Regulatory Action: Section 3 

Risk Assessment Type: Single Chemical Aggregate 

TXRNo.: A 

Case No.: 2710 

CAS Nos.: 55335-06-3. 57213-69-1. 64700-56-7. 1048373-85-8 

MRID No.: A 40 CF'R: § 180.417 

FROM: Jennifer R. Tyler, Chemist rLata Venkateshwara, Environmental Scientist L """./-;&... V ......,..._ I. h...-'l..._ 

Monique M. Perron, Sc.D., Toxicologist f"&~ ~..__ 

Risk Assessment Branch 1 (RAB I )/Health Effects l)ivision (HED; 7509P) 

THROUGH: Charles W. Smith Ill, Branch Chief 

George F. Kramer, Ph.D., Senior Chemis~~~~~:;:::s_s~-::;:a--

RAB 1/HED (7509P) 

TO: Mindy Ondish, Risk Reviewer 

Reuben Baris, Product Manager 25 

Herbicide Branch (HB) 

Registration Division (RD, 7505P) 

The HED of the Office of Pesticide Programs (OPP) is charged with estimating the risk to human 

health from exposure to pesticides. The RD of OPP has requested that HED evaluate hazard and 

exposure data and conduct dietary, occupational, residential and aggregate exposure assessments, 

as needed, to estimate the risk to human health that will result from proposed and currently 

registered uses of the active ingredient (ai) triclopyr (2-[(3,5,6-trichloro-2-pyridinyl)oxy ]acetic 

acid). Dow AgroSciences has submitted 1) a petition to amend the tolerance expressions for 

triclopyr to include a new fonnulation, triclopyr choline salt (PP# 4F8279); and 2) a petition to 

remove the grazing restriction for lactating dairy cattle, and establish a tolerance for residues in 

milk, fat (0. 70 ppm) as well as increased tolerances for residues in milk (0.60 ppm), meat (0.08 

ppm), fat (0.09 ppm), and meat byproducts (0.70 ppm) (PP# 4F8249). The risk assessment, 

residue chemistry review and dietary exposure assessment were provided by Jennifer Tyler 

(RAB 1 ); the hazard characterization by Monique Perron (RAB l ); the occupational/residential 

exposure assessment by Lata Venkateshwara (RAB I); and the drinking water assessment by 

Larry Liu of the Environmental Fate and Effects Division (EFED). 

Page I of37 
Triclopyr Human Health Risk Assessment DP# D426071

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TABLE OF CONTENTS

1.0 Executive Summary............................................................................................................. 3

2.0 HED Recommendations....................................................................................................... 6

2.1 Data Deficiencies ............................................................................................................. 7

2.2 Tolerance Considerations................................................................................................. 7

2.3 Label Recommendations.................................................................................................. 8

3.0 Introduction.......................................................................................................................... 8

3.1 Chemical Identity ............................................................................................................. 9

3.2 Physical/Chemical Characteristics................................................................................. 10

3.3 Pesticide Use Pattern...................................................................................................... 10

3.4 Anticipated Exposure Pathways..................................................................................... 11

3.5 Consideration of Environmental Justice ........................................................................ 11

4.0 Hazard Characterization and Dose-Response Assessment................................................ 12

4.1 Toxicology Studies Available for Analysis ................................................................... 12

4.2 Absorption, Distribution, Metabolism, & Elimination (ADME)................................... 12

4.3 Toxicological Effects ..................................................................................................... 13

4.4 Safety Factor for Infants and Children (FQPA Safety Factor)....................................... 13

4.5 Toxicity Endpoint and Point of Departure Selections.................................................... 14

5.0 Dietary Exposure and Risk Assessment ............................................................................ 17

5.1 Residues of Concern Summary and Rationale............................................................... 18

5.2 Food Residue Profile...................................................................................................... 18

5.3 Water Residue Profile .................................................................................................... 19

5.4 Dietary Risk Assessment................................................................................................ 19

6.0 Residential (Non-Occupational) Exposure/Risk Characterization .................................... 21

6.1 Residential Handler Exposure........................................................................................ 21

6.2 Post-Application Exposure............................................................................................. 22

6.3 Residential Risk Estimates for Use in Aggregate Assessment ...................................... 23

6.4 Residential Bystander Post-application Inhalation Exposure ........................................ 25

6.5 Spray Drift...................................................................................................................... 25

7.0 Aggregate Exposure/Risk Characterization....................................................................... 25

7.1 Acute Aggregate Risk .................................................................................................... 26

7.2 Short- and Intermediate-Term Aggregate Risk.............................................................. 26

7.3 Chronic Aggregate Risk................................................................................................. 27

8.0 Cumulative Exposure/Risk Characterization..................................................................... 27

9.0 Occupational Exposure/Risk Characterization .................................................................. 28

Attachment 1. Toxicology Profile and Executive Summaries..................................................... 29

A.1 Toxicology Data Requirements...................................................................................... 29

A.2 Toxicity Profiles............................................................................................................. 30

Attachment 2. Summary of US and International Tolerances and Maximum Residue Limits. .. 34

Attachment 3. Summary of Updated Occupational Handler Inhalation Exposure and Risk 

Estimates for July 2014 HASPOC Meeting.................................................................................. 35
Triclopyr Human Health Risk Assessment DP# D426071

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1.0 Executive Summary

Dow AgroSciences has submitted 1) a petition to amend the tolerance expressions for triclopyr to 

include a new formulation, triclopyr choline salt (PP# 4F8279); and 2) a petition to remove the 

grazing restriction for lactating dairy cattle, and establish a tolerance for residues in milk, fat 

(0.70 ppm) as well as increased tolerances for residues in milk (0.60 ppm), meat (0.08 ppm), fat 

(0.09 ppm), and meat byproducts (0.70 ppm) (PP# 4F8249).

Triclopyr is a selective herbicide belonging to the pyridinoxy acid class of chemicals. It is 

currently registered in the U.S. for use on rice as well as several non-agricultural use sites 

including rights-of-way, pasture and rangelands, forests, and turf, including home lawns. It is 

also used to control aquatic weeds growing in lakes, ponds, reservoirs, and wetlands, and to 

control woody brush and herbaceous weeds in wetlands and on the banks and shores of aquatic 

sites. 

Currently, permanent tolerances are established for the combined residues of triclopyr per se, as 

a result of the application/use of butoxyethyl ester of triclopyr and triethylamine salt of triclopyr, 

in or on eggs; fish; grass forage and hay; milk; poultry fat, meat, and meat byproducts, except 

kidney; rice, grain and straw; and shellfish [40 CFR §180.417 (a)(1)]. In addition, permanent 

tolerances are established for residues of triclopyr acetic acid and its metabolite 3,5,6-trichloro-2-

pyridinol (TCP), as a result of the application/use of butoxyethyl ester of triclopyr and 

triethylamine salt of triclopyr, in or on the meat, fat, and meat byproducts of cattle, goats, hogs, 

horses, and sheep [40 CFR §180.417 (a)(2)].

A scoping document to support Registration Review of triclopyr, triethylamine salt (TEA); and 

triclopyr, butoxyethyl ester (BEE) was completed on 12-NOV-2014 (Memo, J. Tyler et al.; 

D417817). The most recent quantitative human health risk assessment was performed in 2002 in 

conjunction with the use of triclopyr on aquatic sites (Memo, W. Donovan et al., 24-JUL-2002; 

D263770). Risk assessment and characterization of the metabolite TCP derived from multiple 

chemicals have been assessed in a separate document (Memo, W. Donovan et al., 06-JUN-2002,

D283101). The conclusions of the 2002 TCP assessment that acute and chronic dietary 

aggregate exposure estimates are below HED’s level of concern) are still considered valid. 

Toxicity Profile: The toxicological database for triclopyr is adequate for hazard characterization, 

toxicity endpoint selection, and Food Quality Protection Act (FQPA) Safety Factor (SF) 

evaluation. Waivers have been submitted by the registrant for the acute neurotoxicity (ACN) 

and subchronic inhalation studies. The HED Hazard and Science Policy Council (HASPOC) 

discussed the need for these studies using a weight-of-evidence (WOE) approach (J. Leshin; 

TXR# 0057009). HASPOC concluded that the ACN is not required at this time. The subchronic 

inhalation study is required at this time and an additional 10X database uncertainty factor (UFDB)

will be applied for lack of the study when assessing inhalation exposure scenarios.

Overall, effects in the triclopyr database were indicative of kidney and liver toxicity in rats and 

dogs, respectively. The primary effect observed in rats was degeneration of the proximal tubule, 

which was seen at approximately the same dose (20-28 mg/kg/day) in the subchronic oral and 

two-generation reproduction toxicity studies. Body-weight decrements were also noted in rats in 

the subchronic neurotoxicity and immunotoxicity studies at much higher doses (200-250 

mg/kg/day). In dogs, liver toxicity was evidenced by increased liver enzymes, increase liver 

weights, and liver histopathology at a similar dose as rat effects (20 mg/kg/day). Changes in 
Triclopyr Human Health Risk Assessment DP# D426071

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hematological parameters (decreased packed cell volume, decreased hemoglobin, and decreased 

red blood cell count) were also observed in dogs at the same dose. 

 

There is evidence of increased qualitative susceptibility to offspring from triclopyr exposure in 

the rat two-generation reproduction study based on increased incidence of rare pup 

malformations observed in the presence of parental toxicity. There is also potential qualitative 

susceptibility in the rat developmental toxicity study; however, the evidence was not as 

conclusive as the reproduction toxicity study. Concern is low since effects are wellcharacterized with clearly established no-observed adverse-effect level/lowest-observed adverseeffect level (NOAEL/LOAEL) values, effects were seen in the presence of parental toxicity, and 

selected endpoints are protective of the observed effects.

Dose-response and FQPA Assessment: The triclopyr risk assessment team has evaluated the 

hazard and exposure data; and, based on these data, recommended that the FQPA SF be reduced 

to 1X for all exposure scenarios except inhalation based on the following considerations outlined 

in more detail in the sections below: (1) the toxicology database for triclopyr is adequate for 

FQPA SF consideration; (2) there is no evidence of neurotoxicity from triclopyr exposure; (3) 

selected endpoints are protective of any observed pre- or post-natal offspring susceptibility; and 

(4) the exposure databases are sufficient and unlikely to underestimate exposure

For inhalation exposures, the FQPA SF has been retained at 10X to incorporate the UFDB for 

lack of a subchronic inhalation study.

Residue Chemistry: The qualitative nature of the residue in rice, grass, fish, shellfish, and 

livestock is adequately understood based on the available metabolism studies. Adequate 

methods are available for tolerance enforcement and data collection. The available residue 

chemistry data support the request to 1) amend the tolerance expression for triclopyr to include a 

new formulation, triclopyr choline salt; and 2) the removal of the grazing restriction for lactating 

dairy cattle as well as establishment of the following permanent tolerances: milk at 0.60 ppm; 

meat of cattle, goats, horses, hogs, and sheep at 0.10 ppm; fat of cattle, goats, horses, hogs, and 

sheep at 0.10 ppm; and meat byproducts of cattle, goats, horses, hogs, and sheep at 0.50 ppm.

Drinking Water Exposure and Risk: A revised drinking water assessment was not required since 

the proposed uses will not have an effect on the concentration of triclopyr in drinking water. 

EFED provided estimated drinking water concentrations (EDWCs) for triclopyr based on the 

registered aquatic use (Memos, L. Liu, 04-JUN-2015, D419489; M. Mahoney, 17-JUN-2002, 

D283715). The EDWCs of triclopyr for surface water are estimated to be 1,049 parts per billion 

(ppb) for acute (peak) exposures and 390 ppb for chronic (annual average) exposures. EPA 

calculated and required setback distances from the application site to the functional potable water 

intake in order to maintain average drinking water concentration levels below 400 

ppb. Furthermore, since potable water intakes are required to be turned off until triclopyr 

concentration levels are below 400 ppb, EPA has determined that for acute and chronic dietary 

risk assessments, the water concentration value of 400 ppb is appropriate to use to assess the 

contribution to drinking water.

Dietary Exposure and Risk: Acute and chronic dietary exposure assessments were conducted 

using the using the Dietary Exposure Evaluation Model software with the Food Commodity 

Intake Database (DEEM-FCID) Version 3.16.
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The acute dietary analysis assumed default processing factors (as necessary), tolerance-level 

residues, 100% crop treated (CT) for all commodities and EDWCs (400 ppb) for direct and 

indirect water sources. For females 13-49 years old, the resulting acute (food and drinking 

water) risk estimate is not of concern to HED [<100% of the acute population-adjusted dose 

(aPAD)] at the 95th percentile of the exposure distribution (53% of the aPAD). For the general 

U.S. population and all other population subgroups, the resulting acute food and drinking water 

risk estimates are not of concern to HED (<100% aPAD) at the 95th percentile of the exposure 

distribution. The most highly exposed population subgroup, excluding females 13-49 years old,

is all infants (<1 year old) at 8% of the aPAD. It should be noted that females 13-49 years old 

have a lower aPAD (0.05 mg/kg/day) than the general U.S. population and all other population 

subgroups (1.0 mg/kg/day). As a result, even though the exposure estimate for females 13-49 

years old was lower than the estimate for the general U.S. population, females 13-49 years old 

have the highest risk estimate.

The chronic dietary analysis assumed default processing factors (as necessary), tolerance-level 

residues for all commodities except milk, 100% CT for all commodities and EDWCs (400 ppb) 

for direct and indirect water sources. An anticipated residue (AR) calculated from a recently 

submitted livestock feeding study was used for milk. The resulting chronic (food and drinking 

water) risk estimates are not of concern to HED [<100% of the chronic population-adjusted dose 

(cPAD)] for general U.S. population and all population subgroups. The most highly exposed 

population subgroup is all infants (<1 year old) at 46% of the cPAD.

Residential Exposure: The proposed uses do not involve applications by homeowners or 

commercial applicators in residential settings; therefore, no new residential exposures are

expected. However, there are existing residential uses that have been reassessed in this 

document to reflect updates to HED’s 2012 Residential standard operating procedures (SOPs)

along with policy changes for body-weight assumptions.

The results of the residential handler exposure and risk assessment indicate that short-term 

inhalation risks are not of concern [margins of exposure (MOEs) ≥ 1000] for all turf scenarios. 

Short-term incidental oral post-application risk estimates for all turf scenarios are not of concern 

to HED (i.e., MOEs ≥ 100). Short-term incidental oral post-application risk estimates are 

protective of intermediate-term because the point of departure (POD) and level of concern 

(LOC) are the same. 

Short-term inhalation post-application risk estimates for all swimmer scenarios are not of 

concern to HED (i.e., MOEs ≥ 1000). Furthermore, short-term inhalation post-application risk 

estimates are protective of intermediate-term because the POD is the same. The post-application 

ingestion risk estimates for swimmers are also not of concern to HED (i.e., MOEs ≥ 100).

Aggregate Risk: For the proposed uses, human health aggregate risk assessments have been 

conducted for the following exposure scenarios: acute aggregate exposure (food + drinking 

water), short-term aggregate exposure (food + drinking water + residential), and chronic 

aggregate exposure (food + drinking water). Although there are intermediate-term residential 

exposures, an intermediate-term aggregate was not quantitatively assessed since (1) the shortand intermediate-term PODs/LOCs are the same and (2) the short-term aggregate provides a 

worst-case estimate of residential exposure. For these reasons, the short-term aggregate is 

protective of the longer-term exposures. A cancer aggregate risk assessment was not performed 

because triclopyr is not carcinogenic. All potential exposure pathways were assessed in the 
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aggregate risk assessment as a conservative, health-protective measure. All aggregate risk 

estimates are not of concern to HED for the scenarios listed above. 

Occupational Exposure/Risk: The proposed action to remove a grazing restriction for dairy 

cattle is not expected to result in additional occupational exposures; and the proposed registration 

of the choline salt is covered by the previous actions. No new occupational assessments have 

been conducted. However, occupational handler inhalation exposure and risk estimates were 

updated to reflect all of the currently registered uses of triclopyr for the July 2014 HASPOC 

meeting in order to assess the inhalation waiver request submitted by the triclopyr registrants. A 

summary of the occupational handler inhalation risk estimates from these uses of triclopyr are 

presented in Attachment 3.

Environmental Justice Considerations: Potential areas of environmental justice concerns, to the 

extent possible, were considered in this human health risk assessment, in accordance with U.S. 

Executive Order 12898, "Federal Actions to Address Environmental Justice in Minority 

Populations and Low-Income Populations," http://www.archives.gov/federal-register/executiveorders/pdf/12898.pdf.

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. These 

data, which include studies from the Pesticide Handlers Exposure Database Version 1.1 (PHED 

1.1); the Outdoor Residential Exposure Task Force (ORETF) database; the Agricultural Re-entry 

Task Force (ARTF) database, are subject to ethics review pursuant to 40 CFR 26, have received 

that review, and are compliant with applicable ethics requirements. For certain studies, that 

review may have included review by the Human Studies Review Board. Descriptions of data 

sources as well as guidance on their use can be found at 

http://www2.epa.gov/pesticide-science-and-assessing-pesticide-risks/occupational-pesticidehandler-exposure-data and http://www2.epa.gov/pesticide-science-and-assessing-pesticiderisks/occupational-pesticide-post-application-exposure.

2.0 HED Recommendations

Provided a revised Section F is submitted, HED concludes that the toxicological, residue 

chemistry and occupational/residential databases support 1) the petition to amend the tolerance 

expressions for triclopyr to include a new formulation, triclopyr choline salt (PP# 4F8279); and 

2) the petition to remove the grazing restriction for lactating dairy cattle, and establish tolerances 

(PP# 4F8249) as listed in Section 2.2.2. HED is not recommending for any label modifications 

in conjunction with this petition.

The proposed action to remove a grazing restriction for dairy cattle is not expected to result in 

additional occupational exposures; and the proposed registration of the choline salt is covered by 

the previous actions. No new occupational assessments have been conducted. However, 

occupational handler inhalation exposure and risk estimates were updated to reflect all of the 

currently registered uses of triclopyr for the July 2014 HASPOC meeting in order to assess the 

inhalation waiver request submitted by the triclopyr registrants. Based on a WOE approach, the

HASPOC concluded that a subchronic inhalation study is required at this time and an additional 

10X database uncertainty factor will be applied for lack of the study when assessing inhalation 

exposure scenarios.
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2.1 Data Deficiencies

Toxicology

• 870.3465: Subchronic Inhalation Toxicity Study.

Residue Chemistry

• 860.1550: Revised Section F (see Section 2.2.2). 

2.2 Tolerance Considerations

2.2.1 Enforcement Analytical Method

Adequate methods are available for tolerance enforcement and data collection. Two gas 

chromatography methods (Methods I and II) with electron-capture detection (GC/ECD) are 

available for the determination of triclopyr residues of concern. Method I (Dow Chemical Co. 

Method ACR 77.4) separately determines residues of triclopyr, 3,5,6-trichloro-2-pyridinol, and 

2-methoxy-3,5,6-trichloropyridine and has successfully undergone an Agency method validation 

using grass commodities. Method II (Dow Chemical Co. Method ACR 77.2) determines 

residues of triclopyr per se in milk, cream, and tissues, and has detection limits of 0.05-0.1 ppm.

The Food and Drug Administration (FDA) PESTDATA database dated 1/94 (PAM Vol. I, 

Appendix I) indicates that triclopyr is completely recovered (>80%) using multiresidue method 

PAM Vol. I Section 402. Data pertaining to multiresidue methods testing of triclopyr and its 

metabolites through Protocols B, C, D, and E have been submitted and forwarded to FDA.

2.2.2 Recommended Tolerances

40 CFR §180.417(a) should be updated to state the following tolerance expression:

40 CFR 180.417(a)(1): “Tolerances are established for residues of the herbicide triclopyr, 

including its metabolites and degradates, in or on the commodities in the table below 

resulting from the application of the butoxyethyl ester of triclopyr, triethylamine salt of 

triclopyr, or choline salt of triclopyr. Compliance with the tolerance levels specified 

below is to be determined by measuring only triclopyr (2-[(3,5,6-trichloro-2-

pyridinyl)oxy]acetic acid).”

40 CFR 180.417(a)(2): Tolerances are established for residues of the herbicide triclopyr, 

including its metabolites and degradates, in or on the commodities in the table below 

resulting from the application of the butoxyethyl ester of triclopyr, triethylamine salt of 

triclopyr, or choline salt of triclopyr. Compliance with the tolerance levels specified 

below is to be determined by measuring the combined residues of triclopyr (2-[(3,5,6-

trichloro-2-pyridinyl)oxy]acetic acid) and its metabolite 3,5,6-trichloro-2-pyridinol 

(TCP), calculated as the stoichiometric equivalent of triclopyr.”
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Table 2.2.2. Tolerance Summary for Triclopyr.

Commodity

Established 

Tolerance 

(ppm)

Proposed 

Tolerance 

(ppm)

Recommended 

Tolerance (ppm)

Comments

Correct Commodity 

Definition

Milk1 0.01 0.60 0.60

Milk, fat1 - 0.70 -

Meat2,3 0.05 0.08 0.10

Fat2,3 0.05 0.09 0.10

Liver2,3 0.5 - NA

Kidney2,3 0.5 - NA

Meat byproducts, except kidney and liver2,3 0.05 - NA

Meat byproducts2,3 - 0.70 0.50

1. Triclopyr only.

2. Triclopyr and TCP.

3. Meat fat, liver, kidney, and meat byproducts of cattle, goats, horses, hogs, and sheep.

2.2.3 Revisions to Petitioned-For Tolerances

HED is recommending to increase the proposed tolerances for meat, fat, and meat byproducts of 

cattle, goats, horses, hogs, and sheep and lower the meat byproducts tolerance from what has 

been proposed in order to harmonize with established Canadian maximum residue limits 

(MRLs). Based on the available residue chemistry data, HED has determined that a tolerance for 

milk fat is not required. The current tolerances for liver (0.5 ppm), kidney (0.5 ppm), and meat 

byproducts, except liver and kidney (0.05 ppm) of cattle, goats, horses, hogs, and sheep should 

be deleted from 40 CFR §180.417(a)(2).

2.2.4 International Harmonization

The current U.S. tolerances and Canadian MRLs for milk are summarized in Attachment 2. The 

recommended U.S. tolerances are harmonized with Canadian MRLs for livestock meat, fat, and 

meat byproducts. During Registration Review, HED will consider the possibility of harmonizing 

with Canada for the commodities with differing tolerances.

2.3 Label Recommendations

HED is not recommending for any changes to the proposed label.

3.0 Introduction

Triclopyr products are used as selective herbicides to control broadleaf weeds and woody brush. 

Triclopyr products are registered for use on rice as well as a variety of non-agricultural sites 

including rights of way, pasture and rangelands, forests, rice, and turf (including home lawns), 

golf courses, cemeteries, parks, lakes, bayous, ponds, reservoirs, marshes, roadsides, fence rows, 

canals, ditch banks, athletic fields, storage yards, industrial sites, trails, patios, camp areas, 

homes and cabins (outdoor), and Christmas tree plantings.
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3.1 Chemical Identity

Table 3.1. Test Compound Nomenclature.

Compound

Common name Triclopyr

IUPAC name 3,5,6-trichloro-2-pyridyloxyacetic acid

CAS name 2-[(3,5,6-trichloro-2-pyridinyl)oxy]acetic acid

CAS registry number 55335-06-3

Compound

Common name Triclopyr TEA

Chemical name Triclopyr, triethylamine salt

CAS registry number 57213-69-1

Compound

Common name Triclopyr BEE

Chemical name Triclopyr, Butoxyethyl Ester

CAS registry number 64700-56-7

Compound

Common name Triclopyr choline salt

Chemical name Triclopyr choline salt

CAS registry number 1048373-85-8
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3.2 Physical/Chemical Characteristics

Table 3.2. Physicochemical Properties of the Technical Grade Test Compound Triclopyr.

Parameter Value Reference

Melting range 148-150°C

RD Memorandum, S. Mathur, 

10-OCT-2001; D276420

pH 3.03 ± 0.01 at 25 C

Density 0.308 g/mL at 20°C

Water solubility 0.408 g/L at 20°C

Solvent solubility 581 g/L in acetone

655 g/L in methanol

Vapor pressure 1.5 x 10-6 torr at 25°C

Dissociation constant, pKa Not available

Octanol/water partition coefficient log Kow = 0.42 (pH 5)

UV/visible absorption spectrum Not available

3.3 Pesticide Use Pattern

Proposed Use: Dow AgroSciences has submitted a petition to remove the grazing restriction for 

lactating dairy cattle on several registered labels for triclopyr (see Table 3.3.1). 

Table 3.3.1. Summary of Existing and Proposed Grazing Restrictions for Triclopyr.

Use Site Formulation

(EPA Reg. No.)

Existing Use 

Directions and 

Limitations

Proposed Use Directions and 

Limitations

Land Grazed by 

Lactating Dairy Animals 

(Rangelands, Pastures, 

CRP Acres, Non-Crop 

Areas, Forestry)

TEA MUP (EPA Reg. No. 62719-53)

BEE MUP (EPA Reg. No. 62719-87)

Garlon® 3A (EPA Reg. No. 62719-37)

Remedy® Ultra (EPA Reg. No. 62719-552)

PastureGard® HL (EPA Reg. No. 62719-637)

Do not allow lactating 

dairy animals to graze 

treated areas until the 

next growing season.

PHI (hay): 14 days.

Grazing or harvesting green forage: 

There are no grazing or haying 

restrictions for livestock including 

dairy animals on treated area.

Haying (harvesting of dried forage): 

Do not harvest within 14 days after 

application.

Registered Residential Uses: Triclopyr is registered for use on several terrestrial non-agricultural 

use sites including rights-of-way, pasture and rangelands, forests, and turf, including home lawns 

golf courses and athletic field. The residential lawn uses include spot and broadcast applications. 

It is also used in aquatic settings to control aquatic weeds growing in lakes, ponds, reservoirs, 

and wetlands, and to control woody brush and herbaceous weeds in wetlands and on the banks 

and shores of aquatic sites. 

According to the most recent scoping document, there are hundreds of products that contain 

triclopyr, triclopyr salts, and triclopyr esters. HED focused on a subset of these labels that 

covered a majority of the uses in order to identify relevant use sites and application rates for this 

reassessment. Table 3.3.2 summarizes the scenarios and rates assessed.
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Table 3.3.2. Summary of Relevant Residential Use Patterns for Reevaluation.

Chemical 

Name

Registration 

Number and 

Product Name

Use Site

Formulation 

and Percent 

Active 

Ingredient

Application 

method Maximum App Rate

Triclopyr 

triethylamine 

salt (116002) 

62719-226 Dow 

AgroSciences 

Brush & Weed 

Herbicide

For the control of 

woody plants, vines 

and broadleaf weeds 

around homes, cabins, 

fences, walkways and 

other non-crop areas. 

This product is for 

outdoor residential use 

only.

Soluble 

Liquid (SL) 

8.8%

Ground, hose-end 

sprayer, tank-type 

sprayer, backpack 

sprayer

9 lb ae/A

0.0375

lb ae/gal

0.0096 lb ae/ ft2

Triclopyr, 

butoxyethyl 

ester 

(116004)

62719-566 Turflon 

Ester Ultra

Golf course turf, 

ornamental lawn and 

turf 

EC 60.5% Ground (sprayer) 1.5 lb ae/A

Triclopyr 

triethylamine 

salt (116002)

62719-187 

Renovate* Aquatic areas/water SL 44.4 %

Spray boom, 

handgun, or other 

suitable 

equipment 

mounted on a 

boat or vehicle, 

helicopter.

6 lb ae/A

(equivalent to 0.552 

mg/L water 

concentration)

3.4 Anticipated Exposure Pathways

RD has requested an assessment of human health risk to support the 1) petition to amend the 

tolerance expressions for triclopyr to include a new formulation, triclopyr choline salt (PP# 

4F8279); and 2) petition to remove the grazing restriction for lactating dairy cattle, and establish 

a 0.70-ppm tolerance for residues in milk, fat and an increased tolerance of 0.03 ppm for residues 

in milk (PP# 4F8249). Humans may be exposed to triclopyr in food and drinking water, since 

triclopyr may be applied directly to growing crops and water, and application may result in 

triclopyr reaching surface and ground water sources of drinking water. There are currently

registered residential uses of triclopyr, so there is likely to be exposure in residential or nonoccupational settings. The proposed action to remove a grazing restriction for dairy cattle is not 

expected to result in additional occupational exposures; and the proposed registration of the 

choline salt is covered by the previous actions. No new occupational assessments have been 

conducted.

3.5 Consideration of Environmental Justice

Potential areas of environmental justice concerns, to the extent possible, were considered in this 

human health risk assessment, in accordance with U.S. Executive Order 12898, "Federal Actions 

to Address Environmental Justice in Minority Populations and Low-Income Populations," 

http://www.archives.gov/federal-register/executive-orders/pdf/12898.pdf. As a part of every 

pesticide risk assessment, OPP considers a large variety of consumer subgroups according to 

well-established procedures. In line with OPP policy, HED estimates risks to population 

subgroups from pesticide exposures that are based on patterns of that subgroup’s food and water 

consumption, and activities in and around the home that involve pesticide use in a residential 

setting. Extensive data on food consumption patterns are compiled by the U.S. Department of 

Agriculture (USDA) under the National Health and Nutrition Examination Survey, What We Eat 

in America, (NHANES/WWEIA) and are used in pesticide risk assessments for all registered 

food uses of a pesticide. These data are analyzed and categorized by subgroups based on age, 
Triclopyr Human Health Risk Assessment DP# D426071

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

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

when conditions or circumstances warrant. Whenever appropriate, non-dietary exposures based 

on home use of pesticide products and associated risks for adult applicators and for toddlers, 

youths, and adults entering or playing on treated areas post-application are evaluated. Further 

considerations are currently in development as OPP has committed resources and expertise to the 

development of specialized software and models that consider exposure to bystanders and farm 

workers as well as lifestyle and traditional dietary patterns among specific subgroups.

4.0 Hazard Characterization and Dose-Response Assessment

The bioequivalency of the three chemical forms of triclopyr (acid, triethylamine salt, and 

butoxyethyl ester) has been addressed through a variety of special studies with the salt and ester 

forms, including data on comparative disposition, plasma half-life, tissue distribution, and 

hydrolytic cleavage. These studies were found to adequately address the issue of 

bioequivalency. Therefore, studies conducted with any one form of triclopyr have been used to 

support the toxicology database as a whole. 

No new toxicity and/or metabolism data have been received since the last risk assessment. This 

assessment includes summaries of prior assessments.

4.1 Toxicology Studies Available for Analysis

The toxicological database for triclopyr is adequate for hazard characterization, toxicity endpoint 

selection, and FQPA SF evaluation. Since the most recent risk assessment for triclopyr, 

acceptable subchronic neurotoxicity (MRID 49306303) and immunotoxicity (MRID 49433001) 

studies have been submitted and show no evidence of neurotoxicity or immunotoxicity, 

respectively. Waivers have also been submitted by the registrant for the ACN and subchronic 

inhalation studies. The HED HASPOC discussed the need for these studies using a WOE

approach (J. Leshin; TXR# 0057009). HASPOC concluded that the ACN is not required at this 

time. The subchronic inhalation study is required at this time and an additional 10X UFDB will 

be applied for lack of the study when assessing inhalation exposure scenarios. 

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

In a rat metabolism study with 14C-triclopyr acid, absorption, distribution, metabolism, and 

excretion was assessed following single oral doses of 3 mg/kg or 60 mg/kg, repeated doses of 3 

mg/kg, and an intravenous dose at 3 mg/kg. Regardless of dose level or route of administration, 

triclopyr was well absorbed with peak plasma levels reached within 3-4 hours. Radioactivity in 

the tissues at 72 hours was minimal (<0.54%). At the low dose, >90% of the radioactivity was 

excreted within 24 hours primarily via the urine. The high dose yielded similar overall results 

except that urinary elimination was decreased between 0-12 hours due to saturation of renal 

excretion mechanisms. Un-metabolized parent represented >90% of the urinary radioactivity. 
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4.2.1 Dermal Absorption

Dermal absorption studies in rabbits and humans are available for triclopyr. In both studies, 

absorption was estimated at approximately 2%. There was no dermal hazard identified in the 

toxicological database for triclopyr. As a result, a dermal-absorption factor is not needed 

because a quantitative dermal assessment was not performed

4.3 Toxicological Effects

Overall, effects in the triclopyr database were indicative of kidney and liver toxicity in rats and 

dogs, respectively. The primary effect observed in rats was degeneration of the proximal tubule, 

which was seen at approximately the same dose (20-28 mg/kg/day) in the subchronic oral and 

two-generation reproduction toxicity studies. Body-weight decrements were also noted in rats in 

the subchronic neurotoxicity and immunotoxicity studies at much higher doses (200-250 

mg/kg/day). In dogs, liver toxicity was evidenced by increased liver enzymes, increase liver 

weights, and liver histopathology at a similar dose as rat effects (20 mg/kg/day). Changes in 

hematological parameters (decreased packed-cell volume, decreased hemoglobin, and decreased 

red blood cell count) were also observed in dogs at the same dose. 

Offspring and developmental effects occurred in the presence of maternal and parental toxicity. 

In the two-generation reproduction study with triclopyr acid, rare malformations, including 

exencephaly (brain protrudes outside of the skull) and ablepharia (absence of eyelids), were seen 

in rat pups at the mid- and high-doses (25 mg/kg/day and 250 mg/kg/day, respectively). These 

malformations were considered using a WOE approach to be evidence of qualitative increased 

susceptibility by the Hazard Identification Assessment Review Committee (HIARC) 

Developmental/Reproductive Toxicity Peer Review. A concern for qualitative susceptibility also 

exists in the rat developmental toxicity study with triclopyr acid although the evidence was not 

as conclusive as in the rat reproduction-toxicity study. Cleft palate, brachycephaly (flat head 

syndrome), and delayed ossification occurred at the highest dose tested (200 mg/kg/day) while 

the NOAEL for maternal toxicity was not established since clinical signs of severe toxicity due 

to the bolus administration of a low pH compound were seen at the lowest dose tested (50 

mg/kg/day). There were no other concerns for susceptibility identified in the other 

developmental studies where developmental and maternal effects were seen at 100 mg/kg/day 

and 300 mg/kg/day in the rabbit and rat, respectively.

Triclopyr has been classified has having low acute toxicity via the oral, dermal and inhalation 

routes (Toxicity Category III-IV). The salt form was found to be corrosive to the eye, while the 

ester form was only minimally irritating. Both the salt and ester forms of triclopyr were found to 

be dermal sensitizers, but not a dermal irritant. 

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

The RAB1 risk assessment team recommends that the FQPA SF be reduced to 1X for all 

exposure scenarios except inhalation based on the following considerations outlined in more 

detail in the sections below: (1) the toxicology database for triclopyr is adequate for FQPA SF 

consideration; (2) there is no evidence of neurotoxicity from triclopyr exposure; (3) selected 

endpoints are protective of any observed pre- or post-natal offspring susceptibility; and (4) the 

exposure databases are sufficient and unlikely to underestimate exposure.
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For inhalation exposures, the FQPA SF has been retained at 10X to incorporate the UFDB for 

lack of a subchronic inhalation study.

4.4.1 Completeness of the Toxicology Database

The existing toxicological database is adequate for characterizing triclopyr toxicity and 

quantification of hazard for dietary and occupational exposures. The developmental toxicity 

studies in rats and rabbits and two-generation reproduction toxicity studies in rats are available to 

assess potential fetal/offspring sensitivity. The 10X FQPA SF has been retained for inhalation 

exposures due to lack of a subchronic inhalation study. 

4.4.2 Evidence of Neurotoxicity

There is no evidence of neurotoxicity in the triclopyr toxicological database. 

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

There is evidence of increased qualitative susceptibility to offspring from triclopyr exposure in 

the two-generation reproduction toxicity study and potential qualitative susceptibility in the rat 

developmental toxicity study (see Section 4.3). Concern is low since effects are wellcharacterized with clearly established NOAEL/LOAEL values, effects were seen in the presence 

of parental toxicity, and selected endpoints are protective of the observed effects. 

4.4.4 Residual Uncertainty in the Exposure Database

There are no residual uncertainties with respect to exposure data. The dietary food exposure 

assessment utilizes tolerance-level residues (established or recommended) and 100% CT for all 

proposed/established commodities. By using these assumptions, the acute and chronic 

exposures/risks will not be underestimated. The dietary drinking water assessment utilizes water 

concentration values generated by models and associated modeling parameters that are designed 

to provide conservative, health-protective, high-end estimates of water concentrations that will 

not likely be exceeded. The residential handler and post-application exposure assessments are 

based upon the residential SOPs in conjunction with PHED unit exposures. The residential 

SOPs are based upon reasonable worst-case assumptions and are not expected to underestimate 

risk. These assessments of exposure are not likely to underestimate the resulting estimates of 

risk from exposure to triclopyr.

4.5 Toxicity Endpoint and Point of Departure Selections

Toxicity endpoints and PODs for triclopyr have not changed since the last risk assessment (W. 

Donovan; 24-JUL-2002; D263770), except one endpoint was selected to assess short- and 

intermediate-term durations for the dermal and inhalation exposure scenarios. Endpoints for 

long-term dermal and inhalation exposures are not needed because long-term exposures are not 

expected based on the use pattern for triclopyr. Additionally, no dermal hazard was identified; 

therefore, a dermal endpoint was not selected.
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4.5.1 Dose-Response Assessment

Acute Dietary Endpoint (general population including infants and children): The acute reference 

dose (aRfD) for the general population, including infants and children, was established using the 

NOAEL of 100 mg/kg/day from the developmental rat toxicity study (with the ester form). The 

LOAEL of 300 mg/kg/day is based on mortality in maternal animals observed earlier in the 

study; therefore, the deaths were considered attributable to a single dose. Other effects seen at 

this dose included clinical signs, necropsy findings, decreased food and water consumption, and 

increased kidney and liver weights. Deaths and abortions observed in the developmental rabbit 

studies were not considered to be attributable to a single dose because they occurred later in the 

studies after repeated dosing. The aPAD of 1.0 mg/kg/day is based on the NOAEL of 100 

mg/kg/day and a 100-fold uncertainty factor (10X for interspecies extrapolation, 10X for 

intraspecies extrapolation, and 1X for FQPA SF).

Acute Dietary Endpoint (females 13-49 years old): The aRfD for females 13-49 years old was 

established using the NOAEL of 5 mg/kg/day from the two-generation reproduction toxicity 

study in rats. The LOAEL of 25 mg/kg/day was based on an increased incidence of rare 

malformations (exencephaly and ablepharia), which are considered single dose effects. The 

aPAD of 0.05 mg/kg/day for females 13-49 years old is based on the NOAEL of 5 mg/kg/day 

and a 100-fold uncertainty factor (10X for interspecies extrapolation, 10X for intraspecies 

extrapolation, and 1X for FQPA SF).

Chronic Dietary Endpoint (all populations): Chronic dietary exposures were assessed using the 

two-generation reproduction toxicity study with a parental NOAEL of 5 mg/kg/day. The 

parental LOAEL of 25 mg/kg/day is based on degeneration of the proximal renal tubules. 

Offspring effects were seen at the same dose as parental toxicity. The study and endpoint are 

appropriate for the route and duration of exposure. It is protective of adverse effects seen in rats, 

mice, and dogs after chronic repeated exposures to triclopyr. The cPAD of 0.05 mg/kg/day is 

based on the NOAEL of 5 mg/kg/day and a 100-fold uncertainty factor (10X for interspecies 

extrapolation, 10X for intraspecies extrapolation, and 1X for FQPA SF).

Incidental Oral Exposure (short- and intermediate-term): The subchronic oral toxicity study in 

rats with the acid form was selected for evaluating incidental oral exposures with a NOAEL of 5 

mg/kg/day. The LOAEL of 20 mg/kg/day is based on degeneration of the proximal renal 

tubules. The two-generation reproduction study is supportive of this endpoint with similar 

NOAEL and LOAEL values of 5 and 25 mg/kg/day, respectively. This endpoint is protective of 

adverse effects seen in rats, mice, and dogs after subchronic repeated exposures to triclopyr. The 

LOC for incidental oral exposures is 100 (10X for interspecies extrapolation, 10X for 

intraspecies extrapolation, and 1X for FQPA SF).

Dermal Endpoints (all durations): A dermal endpoint was not selected. Since there is no 

concern for increased quantitative sensitivity/susceptibility to offspring from triclopyr exposure, 

the effects of concern in adults and offspring are adequately assessed in the dermal toxicity study 

where no adverse dermal or systemic effects were observed up to the limit dose (1000 

mg/kg/day).

Inhalation Endpoints (short- and intermediate-term): The subchronic oral toxicity study in rats 

with the acid form was selected for evaluating inhalation exposures with a NOAEL of 5 

mg/kg/day. The LOAEL of 20 mg/kg/day is based on degeneration of the proximal renal 
Triclopyr Human Health Risk Assessment DP# D426071

Page 16 of 37

tubules. The two-generation reproduction study is supportive of this endpoint with similar 

NOAEL and LOAEL values of 5 and 25 mg/kg/day, respectively. This endpoint is protective of 

adverse effects seen in rats, mice, and dogs after subchronic repeated exposures to triclopyr. 

Inhalation exposure is assumed to be equivalent to oral exposures. Due to lack of a subchronic 

inhalation study, the FQPA SF incorporates a UFDB of 10X. As a result, the LOC for inhalation 

exposures is 1000 (10X for interspecies extrapolation, 10X for intraspecies extrapolation, and 

10X for FQPA SF/UFDB).

4.5.2 Recommendation for Combining Routes of Exposures for Risk Assessment

When there are potential occupational and residential exposures to a pesticide, the risk 

assessment must address exposures from three major sources (oral, dermal, and inhalation) and 

determine whether the individual exposures can be combined if they have the same toxicological 

effects. For short- and intermediate-exposures, incidental oral and inhalation exposures can be 

combined for triclopyr since the same study and effects were chosen for both routes. No dermal 

endpoint was selected.

4.5.3 Cancer Classification and Risk Assessment Recommendation

A cancer risk assessment is not required. The Agency classified triclopyr as a “Group D 

Chemical – unable to be classified as to human carcinogenicity.” This is based on marginal 

evidence of mammary tumors in female rats and mice and benign adrenal pheochromocytomas 

in male rats. There was no evidence of mutagenicity in a full battery of studies for triclopyr.

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

Assessment

Table 4.5.4.1. Summary of Toxicological Doses and Endpoints for Triclopyr for Use in Dietary and NonOccupational Human Health Risk Assessments.

Exposure/Scenario POD Uncertainty/FQPA 

Safety Factors

RfD, PAD, LOC for 

Risk Assessment Study and Toxicological Effects

Acute Dietary

(General Population 

including infants and 

children)

NOAEL = 100 

mg/kg/day

UFA = 10X

UFH = 10X

FQPA = 1X

aRfD = 1.0 mg/kg/day

aPAD = 1.0 mg/kg/day

Developmental Rat Toxicity Study 

with ester form

Maternal LOAEL = 300 mg/kg/day 

based on mortality. Additional 

effects seen at this dose included 

clinical signs, necropsy findings, 

decreased food and water 

consumption, and increased kidney 

and liver weights.

Acute Dietary

(Females 13-49 

years old)

NOAEL = 5 

mg/kg/day

UFA = 10X

UFH = 10X

FQPA = 1X

aRfD = 0.05 mg/kg/day

aPAD = 0.05 mg/kg/day

Two-Generation Rat Reproduction 

Study with acid form

LOAEL = 25 mg/kg/day based on 

increased incidence of rare 

malformations (exencephaly and 

ablepharia).

Chronic Dietary

(All Populations)

NOAEL = 5 

mg/kg/day

UFA = 10X

UFH = 10X

FQPA = 1X

cRfD = 0.05 mg/kg/day

cPAD = 0.05 mg/kg/day

Two-Generation Rat Reproduction 

Study with acid form

LOAEL = 25 mg/kg/day based on 

degeneration of the proximal renal 

tubules.
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Table 4.5.4.1. Summary of Toxicological Doses and Endpoints for Triclopyr for Use in Dietary and NonOccupational Human Health Risk Assessments.

Exposure/Scenario POD Uncertainty/FQPA 

Safety Factors

RfD, PAD, LOC for 

Risk Assessment Study and Toxicological Effects

Incidental Oral 

Short-Term (1-30 

days) and 

Intermediate-Term 

(1-6 months) 

NOAEL = 5 

mg/kg/day

UFA = 10X

UFH = 10X

FQPA = 1X

Residential LOC for 

MOE = 100

Subchronic Oral Rat Toxicity Study 

with acid form

LOAEL = 20 mg/kg/day based on 

degeneration of the proximal renal 

tubules.

Dermal

Short-Term (all 

durations) 

No hazard was identified for dermal exposure; therefore a quantitative dermal assessment is not needed.

Inhalation

Short-Term (1-30 

days) and 

Intermediate-Term 

(1-6 months)

NOAEL = 5 

mg/kg/day

Inhalation assumed 

equivalent to oral

UFA = 10X

UFH = 10X

FQPA/UFDB = 10X

Residential LOC for 

MOE = 1000

Subchronic Oral Rat Toxicity Study 

with acid form

LOAEL = 20 mg/kg/day based on 

degeneration of the proximal renal 

tubules.

Cancer (oral, 

dermal, inhalation) Classified as a “Group D Chemical – unable to be classified as to human carcinogenicity.”

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). UFDB = database uncertainty factor. FQPA SF = FQPA 

Safety Factor. PAD = population-adjusted dose (a = acute, c = chronic). RfD = reference dose (a = acute, c = chronic). MOE = margin of 

exposure. LOC = level of concern. 

Table 4.5.4.2. Summary of Toxicological Doses and Endpoints for Triclopyr for Use in Occupational Human 

Health Risk Assessments.

Exposure/Scenario POD Uncertainty 

Factors

LOC for Risk 

Assessment Study and Toxicological Effects

Dermal

Short-Term (all 

durations) 

No hazard was identified for dermal exposure; therefore a quantitative dermal assessment is not needed.

Inhalation

Short-Term (1-30 

days) and 

Intermediate-Term 

(1-6 months)

NOAEL = 5 

mg/kg/day

Inhalation assumed 

equivalent to oral

UFA = 10X

UFH = 10X

UFDB = 10X

Occupational LOC for 

MOE = 1000

Subchronic Oral Rat Toxicity Study 

with acid form

LOAEL = 20 mg/kg/day based on 

degeneration of the proximal renal 

tubules.

Cancer (oral, 

dermal, inhalation) Classified as a “Group D Chemical – unable to be classified as to human carcinogenicity.”

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). UFL = use of a LOAEL to extrapolate a NOAEL. UFDB

= database uncertainty factor. MOE = margin of exposure. LOC = level of concern. 

5.0 Dietary Exposure and Risk Assessment 

The residue chemistry data submitted in support of proposed uses were evaluated by HED on 04-

FEB-2016 (Memo, J. Tyler; D419487). The drinking water assessment was completed by EFED 

on 17-JUN-2002 (Memo, M. Mahoney; D283715) and 04-JUN-2015 (Memo, L. Liu; D419489). 

The dietary exposure assessment was completed in a HED memorandum dated 04-FEB-2016 

(Memo, J. Tyler; D426072).
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5.1 Residues of Concern Summary and Rationale

The qualitative nature of the residue in rice, grass, fish, shellfish, and livestock is adequately 

understood based on the available metabolism studies. The residues of concern are as follows 

(Memos, W. Smith, 15-JUL-1996; W. Donovan, 27-APR-2001, D274243): triclopyr per se in 

grass, rice, milk, poultry, and eggs; triclopyr and TCP in meat, meat byproducts and drinking 

water; and triclopyr, TCP, and 2-methoxy-3,5,6-trichloropyridine (TMP) in fish and shellfish. It 

should be noted that §180.417(a)(1) lists the tolerance expression for fish and shellfish as 

triclopyr per se. 40 CFR §180.417 should be updated to include the recommended tolerance 

expression for fish and shellfish. TCP is part of the tolerance expression for triclopyr for meat 

and meat byproducts; therefore, it has been included in the dietary exposure assessment for this 

action. Risk assessment and characterization of TCP derived from multiple chemicals have been 

assessed in a separate document (Memo, W. Donovan et al., 06-JUN-2002, D283101). 

5.2 Food Residue Profile

PP# 4F8279: Dow AgroSciences has submitted a petition to amend tolerance expressions for 

triclopyr to include a new formulation, triclopyr choline salt. The company proposes that the 

tolerance expression in 40 CFR §180.417(a) be updated to state:

40 CFR 180.417(a)(1): “Tolerances are established for residues of the herbicide triclopyr 

(2-[(3,5,6-trichloro-2-pyridinyl)oxy]acetic acid), including its metabolites and degradates, 

in or on the commodities in the table below resulting from the application of the 

butoxyethyl ester of triclopyr, triethylamine salt of triclopyr, or triclopyr choline. 

Compliance with the tolerance levels specified below is to be determined by measuring 

only triclopyr.

and,

40 CFR 180.417(a)(2): Tolerances are established for residues of the herbicide triclopyr 

(2-[(3,5,6-trichloro-2-pyridinyl)oxy]acetic acid), including its metabolites and degradates, 

in or on the commodities in the table below resulting from the application of the 

butoxyethyl ester of triclopyr, triethylamine salt of triclopyr, or triclopyr choline. 

Compliance with the tolerance levels specified below is to be determined by measuring 

the combined residues of triclopyr and its metabolite 3,5,6-trichloro-2-pyridinol (TCP).”

In a memo dated 22-MAR-2012, HED reviewed a request to determine the bioequivalence 

between triclopyr and triclopyr choline salt, and agreed that bioequivalence was supported by the 

currently available information (Memo, G. Kramer, D399410). Therefore, HED recommends in 

favor of the request to amend the tolerance expressions for triclopyr to include triclopyr choline 

salt.

PP# 4F8249: Dow AgroSciences has submitted a petition to remove the grazing restriction for 

lactating dairy cattle on several registered labels for triclopyr. In addition, the company has also 

proposed the establishment of a tolerance for residues in milk, fat (0.70 ppm) as well as 

increased tolerances for residues in milk (0.60 ppm), meat (0.08 ppm), fat (0.09 ppm), and meat 

byproducts (0.70 ppm). The ruminant feed items associated with triclopyr are grass forage and 

hay, and rice grain. Using residues from previously submitted magnitude of the residue studies 

on grass and rice, and residues from the newly submitted dairy cattle feeding study (MRID# 
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497419001), HED recalculated the maximum reasonable dietary burden (MRDB) for dairy cattle 

to include these commodities, and determined that the following tolerances should be established 

for residues of triclopyr in/on milk and livestock commodities:

40 CFR §180.417 (a)(1)

Milk 0.60 ppm

40 CFR §180.417 (a)(2)

Meat* 0.10ppm

Fat* 0.10 ppm

Meat byproducts* 0.50 ppm

* of cattle, goat, hog, horse, and sheep.

A revised Section F should be submitted to include these tolerances.

5.3 Water Residue Profile

A revised drinking water assessment was not required since the proposed uses will not have an 

effect on the concentration of triclopyr in drinking water. Based on the greatest exposure 

scenario resulting from direct aquatic application of triclopyr to surface water, the EDWCs of 

triclopyr for surface water are estimated to be 1,049 ppb for acute (peak) exposures and 390 ppb 

for chronic (annual average) exposures. EPA calculated and required setback distances from the 

application site to the functional potable water intake in order to maintain average drinking water 

concentration levels below 400 ppb. Furthermore, since potable water intakes are required to be 

turned off until triclopyr concentration levels are below 400 ppb, EPA has determined that for 

acute and chronic dietary risk assessments, the water concentration value of 400 ppb is 

appropriate to use to assess the contribution to drinking water.

It should be noted that EDWCs were not incorporated directly in the 2002 dietary exposure 

assessment, but HED calculated drinking water levels of comparison (DWLOCs), which is a 

theoretical upper limit on a pesticide’s concentration in drinking water in light of total aggregate 

exposure to a pesticide in food, drinking water, and through residential uses. In this assessment, 

the EDWC of 400 ppb was incorporated directly in the acute and chronic dietary exposure 

assessments.

5.4 Dietary Risk Assessment

Unrefined acute and chronic aggregate dietary (food and drinking water) exposure and risk 

assessments were conducted using DEEM-FCID Version 3.16. This software uses 2003-2008 

food consumption data from USDA’s NHANES/WWEIA.

5.4.1 Description of Residue and Percent Crop Treated Data Used in Dietary Assessment

The acute dietary exposure assessment was unrefined, using tolerance-level residues and 

assuming 100% CT for all registered and proposed commodities. The chronic dietary exposure 

assessment was slightly refined, using tolerance-level residues for all commodities except milk 

and assuming 100% CT for all registered and proposed commodities. An AR calculated from a 

recently submitted livestock feeding study was used for milk. DEEM Version 7.81 default 

processing factors were used to estimate residues in processed commodities. Drinking water was 

incorporated directly into the dietary assessment.
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5.4.2 Acute Dietary Risk Assessment

For females 13-49 years old, the resulting acute (food and drinking water) risk estimate at the 

95th percentile of the exposure distribution is 53% of the aPAD. For the general U.S. population 

and all other population subgroups, the resulting acute food and drinking water risk estimates are 

not of concern to HED (<100% aPAD) at the 95th percentile of the exposure distribution. The 

most highly exposed population subgroup is all infants (<1 year old) at 8% of the aPAD.

It should be noted that females 13-49 years old have a lower aPAD (0.05 mg/kg/day) than the 

general U.S. population and all other population subgroups (1.0 mg/kg/day). As a result, even 

though the exposure estimate for females 13-49 years old was lower than the estimate for the 

general U.S. population, females 13-49 years old have the highest risk estimate.

5.4.3 Chronic Dietary Risk Assessment

The resulting chronic (food and drinking water) risk estimates are not of concern to HED 

(<100% cPAD) for general U.S. population and all population subgroups. The most highly 

exposed population subgroup is all infants (<1 year old) at 46% of the cPAD.

5.4.4 Cancer Dietary Risk Assessment

A cancer dietary assessment was not conducted because triclopyr is classified as a “Group D 

Chemical – unable to be classified as to human carcinogenicity.”

5.4.5 Summary Table

Table 5.4.5. Summary of Dietary Exposure and Risk for Triclopyr.*

Population Subgroup

Acute Dietary (Food and Drinking 

Water) (95th Percentile)

Chronic Dietary

(Food and Drinking Water)

Dietary Exposure 

(mg/kg/day) % aPAD Dietary Exposure(mg/kg/day) % aPAD

General U.S. Population 0.033198 3.3 0.010008 20

All Infants (<1 year old) 0.080077 8.0 0.023278 46

Children 1-2 years old 0.075543 7.6 0.017810 36

Children 3-5 years old 0.050707 5.1 0.013791 28

Children 6-12 years old 0.034563 3.5 0.009612 19

Youth 13-19 years old 0.025114 2.5 0.007325 15

Adults 20-49 years old 0.026457 2.6 0.009698 19

Adults 50-99 years old 0.024208 2.4 0.009580 19

Females 13-49 years old 0.026561 53 0.009493 19

*Population subgroup with the highest exposure and risk is in bold type. The aPAD for females 13-49 years of age is 0.05 mg/kg/day; aPAD for 

general U.S. population and all other population subgroups is 1.0 mg/kg/day. The cPAD for general U.S. population and all population 

subgroups is 0.05 mg/kg/day.

Risk assessment and characterization of TCP derived from multiple chemicals have been 

assessed in a separate document (Memo, W. Donovan et al., 06-JUN-2002, D283101). Since 

TCP is part of the tolerance expression for triclopyr for meat and meat byproducts, it has been 

included in the dietary exposure assessment for this action. The conclusions of the 2002 TCP 

assessment that acute and chronic dietary aggregate exposure estimates are below HED’s LOC

are still considered valid. 
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6.0 Residential (Non-Occupational) Exposure/Risk Characterization

The residential exposure assessment was completed in a HED memorandum dated 04-AUG2015 (Memo, L. Venkateshwara; D426070).

The proposed uses do not involve applications by homeowners or commercial applicators in 

residential settings. Therefore, no new residential exposure is expected. However, there are 

existing residential uses that have been reassessed in this document to reflect updates to HED’s 

2012 Residential SOPs (http://www2.epa.gov/pesticide-science-and-assessing-pesticiderisks/standard-operating-procedures-residential-pesticide) along with policy changes for bodyweight assumptions.

Based on the registered residential uses (turf and aquatic use; see Table 3.3.2), handler inhalation 

and post-application inhalation and ingestion exposures are expected for adults; post-application 

inhalation and ingestion exposure are expected for children (3 to <6 years old); and postapplication incidental oral exposures are expected for children (1 to <2 years old). The dermal 

route of exposure is not quantitatively assessed because there is no dermal hazard. Short-term 

exposures are anticipated for residential handlers, while short- and intermediate-term residential 

post-application exposures are expected. Short-term risk estimates are protective of 

intermediate-term because the POD is the same.

6.1 Residential Handler Exposure

Residential handler assessments were only conducted for the turf uses, and not the aquatic use 

sites because the aquatic sites are not residential in nature and homeowner applications are 

unlikely. It is noted that the aquatic label includes the following statements which imply 

commercial/professional applications: (1) state and/or local authorities are to be consulted prior 

to applying this product to public waters; and (2) state or local public agencies may require 

permits. The results of the residential handler exposure and risk assessment indicate that shortterm inhalation risks do not exceed HED’s LOC (i.e. an MOE <1000) for all turf scenarios.

Table 6.1. Residential Handler Exposure and Risk for Triclopyr, Triclopyr TEA, and Triclopyr BEE.

Exposure Scenario App. Rate1 Amount 

Handled2

Unit Exposure

(mg/lb ai)2

Dose 

(mg/kg/day)4

MOE5

(LOC = 1000)

Baseline 

Inhalation3

Baseline 

Inhalation

Baseline 

Inhalation

Mixing/Loading/Applicator – Turf

Mixing/Loading/Applying Liquids 

with Hose End Sprayer 9 lb ae/acre 0.5 acres 0.022 0.0012 4,000

Mixing/Loading/Applying Liquids 

with Manually Pressurized Handwand

0.0375

lb ae/gal 5 gallons 0.018 0.000042 120,000

Mixing/Loading/Applying Liquids 

with Sprinkler Can

0.0096 lb 

ae/ ft2

1000

ft2 0.022 0.0026 1,900

Mixing/Loading/Applying Liquids 

with Backpack

0.0375

lb ae/gal 5 gallons 0.14 0.00033 15,000

1. Application rate based on label Dow AgroSciences Brush &Weed Herbicide (Reg. No. 62719-226).

2. Unit exposure values and estimates for area treated or amount handled based on Exposure Science Advisory Council 2012 

Residential SOPs: http://www2.epa.gov/pesticide-science-and-assessing-pesticide-risks/standard-operating-proceduresresidential-pesticide.

3. Baseline Inhalation: no respirator.
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4. Inhalation Dose (mg/kg/day) = daily unit exposure (mg/lb ai) * application rate (lb ai/unit volume or area) * amount handled 

(unit volume or area) * inhalation absorption (100%) / body weight (80 kg).

5. MOE = NOAEL (short- term inhalation = 5 mg/kg/day) / daily dose (mg/kg/day). LOC = 1000.

6.2 Post-Application Exposure

Table 6.2.1 presents the post-application incidental oral MOE values calculated for the broadcast 

liquid application of triclopyr, triclopyr TEA, and triclopyr BEE to turf. The post-application 

MOEs for hand-to-mouth, object-to-mouth, and soil ingestion are not of concern to HED (MOEs 

range from 220 to 98,000). 

Table 6.2.1. Residential Post-application Non-cancer Exposure and Risk Estimates for Triclopyr, Triclopyr TEA, 

and Triclopyr BEE.

Lifestage Post-application Exposure Scenario Application 

Rate1

Dose 

(mg/kg/day)2

MOEs3

Use Site Route of Exposure (LOC = 100)

Child

(1 to <2 years old)

Liquid Application to 

Turf

ST Hand-to-Mouth

1.5 lb ae/A

0.0228 220

ST Object-to-mouth 0.00069 7,200

ST/IT Soil Ingestion 5.1E-04 98,000

1. Based on label Dow AgroSciences Turflon Amine (Reg. No. 62719-257). 

2. Dose (mg/kg/day) equations (see Appendix B)

3. MOE = NOAEL ÷ Daily Dose (mg/kg/day). ST/IT Incidental Oral and Inhalation NOAEL = 5 mg/kg/day. LOC = 100.

Tables 6.2.2 and 6.2.3 provide the post-application inhalation and ingestion risk estimates for 

exposure of swimmers to triclopyr. 

Table 6.2.2. Short-Term Post-application Exposure - Inhalation of Water by Swimmers.

Exposure Scenario Cw1 (mg/L) IR2 (L/hr) ET3 

(hr/day) BW4 (kg) Exposure5 Absorbed Dose6(mg/kg/day)

MOE7

(LOC = 

1000)

Swimmer; adult 0.552 0.64 0.025 80 9.1E-05 1.14E-06 4,400,000

Swimmer; child (3 to <6 years old) 0.42 0.076 19 1.8E-04 9.55E-06 520,000

1. Cw = concentration in water is based on the application rate provided on the product label. An assumption of 4 feet depth (and 

uniform distribution) was used to estimate the concentration in water. 

2. IR = inhalation of water; based on the Risk Assessment Guidance for Superfund (RAGS) Part A (http://www.epa.gov/risk/riskassessment-guidance-superfund-rags-part) which references a value from the Superfund Exposure Assessment Manual (USEPA, 

1988). The recommended point estimate for use in post-application incidental ingestion exposure assessments is 0.05 L/hr of 

swimming for adults and children 3 to <6 years old.

3. ET = exposure time; based on 2011 Exposure Factors Handbook (Table 16-20). 

4. BW = body weight; based on the Residential Pesticide Exposure Assessment SOP (February-2012). 

5. Exposure = (VVpp* IR * ET).

6. Absorbed Inhalation dose = (E x AF) ÷ BW.

7. MOE = NOAEL (5 mg/kg/day; adult and child) ÷ dose (mg/kg/day).

Table 6.2.3. Short-Term Post-application Exposure - Ingestion of Water by Swimmers.

Exposure Scenario Cw1 

(mg/L) IgR2 (L/hr) ET3 (hr/day) BW4 (kg) Oral Dose5 (mg/kg/day) MOE6(LOC = 100)

Swimmer; adult 0.552 0.05 0.025 80 0.000008625 580,000

Swimmer; child (3 to <6 years old) 0.05 0.076 19 0.0001104 45,000

1. Cw = concentration in water is based on the application rate provided on the product label. An assumption of 4 feet depth (and 

uniform distribution) was used to estimate the concentration in water. 

2. IgR = ingestion rate of water; based on the RAGS Part A (http://www.epa.gov/risk/risk-assessment-guidance-superfund-rags-part)

which references a value from the Superfund Exposure Assessment Manual (USEPA, 1988). The recommended point estimate for use

in post-application incidental ingestion exposure assessments is 0.05 L/hr of swimming for adults and children 3 to <6 years old.

3. ET = exposure time; based on 2011 Exposure Factors Handbook (Table 16-20). 

4. BW = body weight; based on the Residential Pesticide Exposure Assessment SOP (February-2012). 

5. Oral dose = (Cw x IgR x ET) ÷ BW.

6. MOE = NOAEL (5 mg/kg/day; adult and child) ÷ dose (mg/kg/day).
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6.3 Residential Risk Estimates for Use in Aggregate Assessment

Tables 6.3.1 and 6.3.2 reflects the residential risk estimates that are recommended for use in the 

aggregate assessment for triclopyr.

MOE Approach (Table 6.3.1)

• The recommended residential exposure for use in the short-term aggregate assessment for 

children 1 to <2 years old reflects hand-to-mouth incidental oral exposure due to 

applications to turf.

Aggregate Risk Index (ARI) Approach (Table 6.3.2)

• The recommended residential exposures for use in the short-term aggregate assessment 

for adults reflects handler inhalation exposures from spot applications to turf via sprinkler 

can.

• The recommended residential exposure for use in the short-term aggregate assessment for 

children 3 to <6 years old reflects combined inhalation and ingestion of water by 

swimmers.
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Table 6.3.1. Recommendations for the Residential Exposures for the Triclopyr Aggregate Assessment Using Total MOE Approach.

1

Lifestage

Residential Handler Residential Post-application

Dose (mg/kg/day)2 MOE3 Dose (mg/kg/day)4 MOE5

Dermal Inhalation Total Dermal Inhalation Total Dermal Inhalation Oral Total Dermal Inhalation Oral Total

Child (1 to <2 

years old) –

ST Hand-toMouth 

Exposure Due 

to Turf Use

N/A - - 0.0228 - - - 220 220

1. Bolded risk estimates should contribute to the residential exposure portion of the aggregate assessment. 

2. Residential Handler Dose = the highest handler doses for each applicable lifestage of all scenarios assessed. Not applicable.

3. Residential Handler MOE = the MOEs associated with the highest doses identified. Not applicable.

4. Residential Post-application Dose = the highest post-application dose for each applicable lifestage of all scenarios assessed (see Tables 6.2.1 through 6.2.3). Total = incidental oral.

5. Residential Post-application MOE = the MOEs associated with the highest doses identified (see Tables 6.2.1 through 6.2.3). Total MOE = 1/[(1/Inhalation MOE) + (1/Incidental oral MOE)], 

where applicable. 

Table 6.3.2. Recommendations for the Residential Exposures for the Triclopyr Aggregate Assessment Using ARI Approach.1

Lifestage

Residential Handler Residential Post-application

Dermal 

MOE

Dermal 

ARI

Inhalation 

MOE2

Inhalation 

ARI2

Dermal 

MOE

Dermal

ARI

Inhalation 

MOE2

Inhalation 

ARI2

Oral 

MOE3

Oral 

ARI3

Total 

ARI4

Adult – M/L/A Liquids to 

Turf with Sprinkler Can - - 1,900 1.9 N/A 1.9

Child (3 to <6 years old) –

Swimmer Exposure Due to 

Aquatic Use

N/A - - 520,000 520 45,000 450 240

1. Bolded risk estimates should contribute to the residential exposure portion of the aggregate assessment.

2. MOE inhalation residential exposure = [(short-term inhalation NOAEL)/(high-end inhalation residential exposure)]. ARI inhalation = [(MOE inhalation residential exposure)/(MOE target)]. 

Short-term inhalation NOAEL = 5 mg/kg/day; high-end inhalation residential handler exposure for adults = 0.0026 mg/kg/day; high-end inhalation residential post-application exposure for 

children 3 to <6 years old = 0.00000955 mg/kg/day (swimmer). MOE target = 1000.

3. MOE oral residential exposure = [(short-term oral NOAEL)/(high-end incidental oral residential exposure)]. ARI oral residential exposure = [(MOE oral residential exposure)/(MOE target)]. 

Short-term oral NOAEL = 5 mg/kg/day; high-end incidental oral residential exposure for children 3 to <6 years old (swimmer) = 0.00001104 mg/kg/day. MOE target = 100.

4. Total ARI = 1/[(1/ARI oral) + (1/ARI inhalation)].
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6.4 Residential Bystander Post-application Inhalation Exposure

Volatilization of pesticides may be a source of post-application inhalation exposure to 

individuals nearby pesticide applications. The agency sought expert advice and input on issues 

related to volatilization of pesticides from its Federal Insecticide, Fungicide, and Rodenticide Act 

(FIFRA) Scientific Advisory Panel (SAP) in December 2009, and received the SAP’s final report 

on March 2, 2010 

(http://archive.epa.gov/scipoly/sap/meetings/web/pdf/120309meetingminutes.pdf). The agency 

has evaluated the SAP report and has developed a Volatilization Screening Tool and a 

subsequent Volatilization Screening Analysis 

(http://www.regulations.gov/#!docketDetail;D=EPA-HQ-OPP-2014-0219). During Registration 

Review, the agency will utilize this analysis to determine if data (i.e., flux studies, route-specific 

inhalation toxicological studies) or further analysis is required for triclopyr.

6.5 Spray Drift

Spray drift is a potential source of exposure to those nearby pesticide applications. This is 

particularly the case with aerial application, but, to a lesser extent, spray drift can also be a 

potential source of exposure from the ground application methods (e.g., groundboom and 

airblast) employed for triclopyr. The agency has been working with the Spray Drift Task Force 

(a task force composed of various registrants which was developed as a result of a Data Call-In 

issued by EPA), 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).1 The Agency has also developed a policy on how to 

appropriately consider spray drift as a potential source of exposure in risk assessments for 

pesticides. The potential for spray drift will be quantitatively evaluated for each pesticide during 

the Registration Review process which ensures that all uses for that pesticide will be considered 

concurrently. The approach is outlined in the revised (2012) Standard Operating Procedures 

For Residential Risk Assessment (SOPs) - Residential Exposure Assessment Standard Operating 

Procedures Addenda 1: Consideration of Spray Drift. This document outlines the quantification 

of indirect non-occupational exposure to drift. 

7.0 Aggregate Exposure/Risk Characterization

In accordance with the FQPA, HED must consider and aggregate pesticide exposures and risks 

from three major sources: food, drinking water, and residential exposures. In an aggregate 

assessment, exposures from relevant sources are added together and compared to quantitative 

estimates of hazard (e.g., a NOAEL or PAD), or the risks themselves can be aggregated. When 

aggregating exposures and risks from various sources, HED considers both the route and 

duration of exposure. In the case of triclopyr, aggregate risk assessments were performed for 

acute aggregate exposure (food + drinking water), short-term aggregate exposure (food + 

drinking water + residential exposure), and chronic aggregate exposure (food + drinking water). 

A cancer aggregate risk assessment was not performed because triclopyr is not carcinogenic. All 

potential exposure pathways were assessed in the aggregate risk assessment. 

 1 Available: http://www2.epa.gov/reducing-pesticide-drift 
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7.1 Acute Aggregate Risk

No acute residential/recreational exposures are expected. In the case of triclopyr, the acute 

aggregate risk is composed of exposures to triclopyr residues in food and drinking water and is 

equivalent to the acute dietary risk discussed in Section 5.4.2. As shown in Table 5.4.5, for 

females 13-49 years old, the resulting acute dietary (food and drinking water) risk estimates are 

not of concern to HED (<100% aPAD) at the 95th percentile of the exposure distribution (53%). 

For the general U.S. population and all other population subgroups, the resulting acute food and 

drinking water risk estimates are not of concern to HED (>100% aPAD) at the 95th percentile of 

the exposure distribution. The most highly exposed population subgroup is all infants (<1 year 

old) at 8% of the aPAD.

7.2 Short- and Intermediate-Term Aggregate Risk

Short-term (1 to 30 day) and intermediate-term (1 to 6 months) aggregate risk assessments are 

necessary for both adults and children since there is potential for both handler exposure and postapplication exposure from the residential uses of triclopyr. Although there are intermediate-term 

residential exposures, an intermediate-term aggregate was not quantitatively assessed since (1) 

the short- and intermediate-term PODs are the same and (2) the short-term aggregate provides a 

worst-case estimate of residential exposure. For these reasons, the short-term aggregate is 

protective of the longer-term exposures.

For the short-term aggregate risk assessment, potential residential exposures were combined with 

food and drinking water exposures. Specifically, the short-term aggregate assessment for adults 

combines dietary (food + drinking water) exposures with handler inhalation exposures resulting 

from the registered turf use. For children 1 to <2 years old, the short-term aggregate assessment 

combines dietary (food + drinking water) exposure with potential post-application incidental oral 

exposure resulting from the registered turf use. For children 3 to <6 years old, the short-term 

aggregate assessment combines dietary (food + drinking water) exposure with potential postapplication inhalation and incidental oral swimmer exposure resulting from the registered aquatic 

use. See Section 6.3 for more information on the residential risk estimates that are recommended 

for use in the aggregate assessment for triclopyr.

For children 1 to <2 years old, the MOE approach was used to estimate short-term aggregate 

risk. HED’s LOC is for MOEs less than 100. As the short-term aggregate MOEs are greater 

than 100, risk estimates do not exceed HED’s LOC.

Table 7.2.1. Short- and Intermediate-Term Aggregate Risk Calculations Using MOE Approach.

Population

Short- or Intermediate-Term Scenario

NOAEL 

(mg/kg/day) LOC1

Max 

Allowable 

Exposure2

(mg/kg/day)

Average Food 

and Water 

Exposure 

(mg/kg/day)

Residential 

Exposure 

(mg/kg/day)

3

Total 

Exposure 

(mg/kg/day)

4

Aggregate 

MOE (food, 

water, and 

residential)5

Children 1 to <2 years 

old 5 100 0.05 0.017810 0.0228 0.040610 120

1. The level of concern (target MOE) includes 10X for interspecies extrapolation and 10X for intraspecies variation.

2. Maximum Exposure (mg/kg/day) = NOAEL/LOC.

3. Avg. Dietary Exposure. See Table 5.4.5.

4. Residential Exposure = Oral exposure for children (child 1 to <2 years old – hand-to-mouth exposure due to turf use). See Table 5.3.

5. Total exposure = Avg. Dietary Exposure + Residential Exposure.

6. Aggregate MOE = NOAEL ÷ Total Exposure.
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For adults and children 3 to <6 years old, a total ARI was used since the POD (5 mg/kg/day from 

the subchronic oral rat toxicity study with acid form) for the oral and inhalation exposure routes 

were the same, but the LOC values for oral exposure (100) and inhalation exposure (1000) are 

different. The target ARI is 1; therefore, ARIs of less than 1 are risk estimates of concern. For 

adults and children 3 to <6 years old, the short-term aggregate ARIs are greater than 1; therefore, 

risk estimates do not exceed HED’s LOC. 

Table 7.2.2. Short- and Intermediate-Term Aggregate Risk Calculations Using ARI Approach.1

Population

Short-Term Scenario

Dietary Exposure2 Oral Residential 

Exposure3

Dermal 

Residential 

Exposure

Inhalation 

Residential 

Exposure4

Aggregate 

ARI (food, 

water, and 

residential)5

MOE ARI MOE ARI MOE ARI MOE ARI

Adults 20 to 49 

years old 

(sprinkler can

applications)

500 5.0 NA NA NA NA 1,900 1.9 1.4

Children 3 to <6 

years old 364 3.6 45,000 450 NA NA 523,000 520 3.6

1. HED is concerned if the ARI is less than 1. ARI = Aggregate Risk Index.

2. MOE dietary = [(short-term oral NOAEL)/(chronic dietary exposure)]. ARI dietary = [(MOE dietary)/(MOE target)]. Short-term oral 

NOAEL = 5 mg/kg/day; chronic dietary exposure for adults 20 to 49 years old = 0.010008 mg/kg/day; chronic dietary exposure for 

children 3 to 5 years old = 0.0137791 mg/kg/day. MOE target = 100.

3. MOE oral residential exposure = [(short-term oral NOAEL)/(high-end incidental oral residential exposure)]. ARI oral residential 

exposure = [(MOE oral residential exposure)/(MOE target)]. Short-term oral NOAEL = 5 mg/kg/day; high-end incidental oral 

residential exposure for children 3 to <6 years old (swimmer) = 0.00001104 mg/kg/day. MOE target = 100.

4. MOE inhalation residential exposure = [(short-term inhalation NOAEL)/(high-end inhalation residential exposure)]. ARI inhalation = 

[(MOE inhalation residential exposure)/(MOE target)]. Short-term inhalation NOAEL = 5 mg/kg/day; high-end inhalation residential 

exposure for adults = 0.0026 mg/kg/day (M/L/A liquids to turf with sprinkler can); high-end inhalation residential exposure for 

children 3 to <6 years old = 0.00000955 mg/kg/day (swimmer). MOE target = 1000.

5. ARI Aggregate = 1/[(1/ARI dietary) + (1/ARI oral) + (1/ARI inhalation)].

7.3 Chronic Aggregate Risk

A long-term aggregate risk assessment was not performed, because long-term residential 

exposure to triclopyr (i.e., >6 months) is unlikely to occur based upon the use patterns. 

Specifically, in the case of triclopyr, the chronic aggregate risk is composed of exposures to 

triclopyr residues in food and drinking water and is equivalent to the chronic dietary risk 

discussed in Section 5.4.4. As shown in Table 5.4.5, the chronic risk estimates do not exceed the 

HED’s LOC for the general U.S. population and all population subgroups.

8.0 Cumulative Exposure/Risk Characterization

Unlike other pesticides for which EPA has followed a cumulative risk approach based on a 

common mechanism of toxicity, EPA has not made a common mechanism of toxicity finding as 

to triclopyr and any other substances. Risk assessment of TCP derived from multiple chemicals 

has been conducted in a separate document (Memo, W. Donovan et al., 06-JUN-2002, 

D283101). The conclusions of the 2002 TCP assessment that acute and chronic dietary 

aggregate exposure estimates are below HED’s level of concern are still considered valid. For 

the purposes of this tolerance action, therefore, EPA has not assumed that triclopyr has a 

common mechanism of toxicity with other substances. For information regarding EPA’s efforts 

to determine which chemicals have a common mechanism of toxicity and to evaluate the 

cumulative effects of such chemicals, see the policy statements released by EPA’s Office of 

Pesticide Programs concerning common mechanism determinations and procedures for 

cumulating effects from substances found to have a common mechanism on EPA’s website at 
Triclopyr Human Health Risk Assessment DP# D426071

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http://www.epa.gov/pesticide-science-and-assessing-pesticide-risks/cumulative-assessment-riskpesticides.

9.0 Occupational Exposure/Risk Characterization

The proposed action to remove a grazing restriction for dairy cattle is not expected to result in 

additional occupational exposures; and the proposed registration of the choline salt is covered by 

the previous actions. As a result, no new occupational assessments have been conducted for 

these actions. However, occupational handler inhalation exposure and risk estimates were 

updated to reflect all of the currently registered uses of triclopyr for the July 2014 HASPOC 

meeting in order to assess the inhalation waiver request submitted by the triclopyr registrants. 

The inhalation risk estimates for the registered forestry use triggered the requirement of a routespecific inhalation study (i.e., inhalation MOEs <1000); therefore, a 10X UFDB was applied to all 

inhalation exposure scenarios. However, as a part of this updated assessment, inhalation 

exposure and risks for the rangeland and pasture uses were updated and were not of concern 

(MOEs >1000). A summary of the occupational handler inhalation risk estimates are presented 

in Attachment 3.

Restricted Entry Interval: Triclopyr acid is classified as Toxicity Categories III and IV via the 

dermal route and Toxicity Category IV for skin irritation potential. It is not a skin 

sensitizer. Under 40 CFR 156.208 (c) (2), ai’s classified as Acute III or IV for acute dermal, eye 

irritation and primary skin irritation are assigned a 12-hour REI. Therefore, the [156 subpart K] 

Worker Protection Statement (WPS) interim REI of 12 hours is adequate to protect agricultural 

workers from post-application exposures to triclopyr choline salt. HED would recommend a REI 

of 12 hours. This is the REI listed on the proposed triclopyr choline salt labels, and is considered 

protective of post-application exposure.

RDI: RAB1 Branch (3/19/2015); G. Kramer (2/4/16); C. Smith (2/4/16)

J. Tyler:S10943:PY-S:(703)305-5564:7509P:RAB1
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Attachment 1. Toxicology Profile and Executive Summaries.

A.1 Toxicology Data Requirements

Study requirements (40 CFR 158.340) for use of triclopyr. Use of the new guideline numbers 

does not imply that the new (1998) guideline protocols were used.

Table A.1.1. Toxicology Data Requirements.

Study Technical

Required Satisfied

870.1100 Acute Oral Toxicity.......................................................

870.1200 Acute Dermal Toxicity..................................................

870.1300 Acute Inhalation Toxicity..............................................

870.2400 Acute Eye Irritation.......................................................

870.2500 Acute Dermal Irritation .................................................

870.2600 Skin Sensitization..........................................................

yes

yes

yes

yes

yes

yes

yes

yes

yes

yes

yes

yes

870.3100 90-Day Oral Toxicity in Rodents..................................

870.3150 90-Day Oral Toxicity in Nonrodents.............................

870.3200 21/28-Day Dermal Toxicity ..........................................

870.3250 90-Day Dermal Toxicity ...............................................

870.3465 90-Day Inhalation Toxicity ...........................................

yes

yes

yes

no

yes1

yes

yes

yes

--

no

870.3700a Prenatal Developmental Toxicity (rodent) ....................

870.3700b Prenatal Developmental Toxicity (nonrodent) ..............

870.3800 Reproduction and Fertility Effects ................................

yes

yes

yes

yes

yes

yes

870.4100a Chronic Toxicity (rodent)..............................................

870.4100b Chronic Toxicity (nonrodent)........................................

870.4200a Carcinogenicity (rat)......................................................

870.4200b Carcinogenicity (mouse) ...............................................

870.4300 Combined Chronic Toxicity/Carcinogenicity ...............

yes

yes

yes

yes

yes

yes2

yes

yes2

yes

yes

870.5100 Mutagenicity—Bacterial Reverse Mutation Test..........

870.5300 Mutagenicity—Mammalian Cell Gene Mutation Test...

870.5xxx Mutagenicity— Structural Chromosomal Aberrations...

870.5xxx Mutagenicity—Other Genotoxic Effects.......................

yes

yes

yes

yes

yes

yes

yes

yes

870.6200a Acute Neurotoxicity Screening Battery (rat).................

870.6200b Subchronic Neurotoxicity Screening Battery (rat)........

870.6300 Developmental Neurotoxicity .......................................

no3

yes

no

--

yes

--

870.7485 Metabolism and Pharmacokinetics................................

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

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

yes

yes

yes

Yes

yes

yes

1. HASPOC concluded that the subchronic inhalation study is required at this time (J. Leshin; TXR#0057009).

2. The combined chronic toxicity/carcinogenicity study satisfies the requirement of the study.

3. HASPOC concluded that the ACN is not required at this time (J. Leshin; TXR#0057009).
Triclopyr Human Health Risk Assessment DP# D426071

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A.2 Toxicity Profiles

Table A.2.1. Acute Toxicity Profile – Triclopyr Acid.

Guideline No. Study Type MRID Results Toxicity Category

870.1100 Acute oral 00031940 LD50 = 729 mg/kg (M)

LD50 = 630 mg/kg (F) III

870.1100 Acute oral 45451304 Combined LD50 = 1915 mg/kg III

870.1200 Acute dermal 00056009 LD50 >2000 mg/kg III

870.1200 Acute dermal 45451305 LD50 >5050 mg/kg IV

870.1300 Acute inhalation 45451306 LC50 >2.56 mg/L IV

870.2400 Primary eye irritation 45451307 moderate irritant III

870.2500 Primary skin irritation 45451308 mild irritant IV

870.2600 Dermal sensitization 45451309 not a sensitizer --

Table A.2.2. Acute Toxicity Profile – Triclopyr Triethylamine Salt.

Guideline No. Study Type MRID(s) Results Toxicity Category

870.1100 Acute oral 41443301 LD50 = 1847 mg/kg III

870.1200 Acute dermal 41443302 LD50 >2000 mg/kg III

870.1300 Acute inhalation 41443303 LC50 >2.6 mg/L III

870.2400 Primary eye irritation 41443304 corrosive I 

870.2500 Primary skin irritation 41443305 not irritating IV

870.2600 Dermal sensitization 41443306 sensitizer --

Table A.2.3. Acute Toxicity Profile – Triclopyr Butoxyethyl Ester.

Guideline No. Study Type MRID(s) Results Toxicity Category

870.1100 Acute oral 40557004 LD50 = 803 mg/kg III

870.1200 Acute dermal 40557005 LD50 >2000 mg/kg III

870.1300 Acute inhalation 40557006 LC50 > .8 mg/L III

870.2400 Primary eye irritation 40557007 minimally irritating III

870.2500 Primary skin irritation 40557008 not irritating IV

870.2600 Dermal sensitization 40557009 sensitizer --

Table A.2.4. Subchronic, Chronic, and Other Toxicity Profile – Triclopyr.

Guideline No. Study Type MRID No. (year)/ 

Classification /Doses Results

870.3100

90-Day Oral Toxicity 

in Rodents (rat)

Acid form

00150378 (1984)

Acceptable

0, 5, 20, 50, or 250 

mg/kg/day

NOAEL = 5 mg/kg/day.

LOAEL = 20 mg/kg/day based on degeneration of the 

proximal tubules of the kidneys.

870.3100

90-Day Oral Toxicity 

in Rodents (rat)

Ester form

42274901 (1992)

Supplementary

0, 7, 28, 70, or 350 

mg/kg/day

NOAEL = not established.

LOAEL = 7 mg/kg/day (F) based on decreased red blood 

cell content, hemoglobin content, and packed cell volume 

in females. Degeneration of the proximal tubules of the 

kidneys was seen in males at 70 and 350 mg/kg/day and 

females at 350 mg/kg/day (HDT).

870.3150

183-Day Oral 

Toxicity in NonRodent (dog)

00071794 (1976)

Acceptable

0, 0.1, 0.5, or 2.5 mg/kg/day

NOAEL = 2.5 mg/kg/day.

LOAEL = not established.

Non-significant decreased rate of phenolsulfothalein

(PSP) due to competition between triclopyr and PSP for 

renal excretion.
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Table A.2.4. Subchronic, Chronic, and Other Toxicity Profile – Triclopyr.

Guideline No. Study Type MRID No. (year)/ 

Classification /Doses Results

870.3200

21-Day Dermal 

Toxicity (rabbit)

Ester form

42212701 (1992)

Acceptable

0, 100, 500, or 1000 

mg/kg/day

NOAEL = 1000 mg/kg/day.

LOAEL = not established.

Decreased alkaline phosphatase in both sexes at 1000 

mg/kg/day and increased absolute and relative liver 

weights in males at 1000 mg/kg/day considered marginal 

and not biologically significant.

870.3700a

Prenatal 

Developmental in 

Rodent (rat)

Ester form

43675801, 45168801 (1994)

Acceptable/guideline

0, 5, 30, 100, or 300 

mg/kg/day

Maternal NOAEL = 100 mg/kg/day.

Maternal LOAEL = 300 mg/kg/day based on mortality, 

clinical signs, necropsy findings, decreased food 

consumption, increased water consumption, and increased 

relative kidney and liver weights.

Developmental NOAEL = 100 mg/kg/day.

Developmental LOAEL = 300 mg/kg/day based on 

incidence of hydrocephalus, cleft palate, 

microphthalmia/anophthalmia, retinal folds, thin 

diaphragm/protrusion of the liver, decrease fetal weight, 

and visceral and skeletal anomalies and variants.

870.3700a

Prenatal 

Developmental in 

Rodent (rat)

Salt form

43217602 (1994)

Acceptable/guideline

0, 30, 100, or 300 mg/kg/day

Maternal NOAEL = 100 mg/kg/day.

Maternal LOAEL = 300 mg/kg/day based on mortality.

Developmental NOAEL = 100 mg/kg/day.

Developmental LOAEL = 300 mg/kg/day based on 

decreased fetal weights, increased fetal and litter 

incidence of skeletal anomalies, and increased fetal 

incidence of unossified sternebrae.

870.3700a

Prenatal 

Developmental in 

Rodent (rat)

Acid form

00072441, 41688301, 

92189024 (1979)

Acceptable/guideline

0, 50, 100, or 200 mg/kg/day

Maternal NOAEL = not established.

Maternal LOAEL = 50 mg/kg/day based on increased 

clinical signs.

Developmental NOAEL = 100 mg/kg/day.

Developmental LOAEL = 200 mg/kg/day based on 

increased incidence of fetuses and litters with retarded 

ossification of skull bones and two litters (1 fetus per 

litter) with cleft palate and brachycephaly.

870.3700b

Prenatal 

Developmental in 

Non-Rodent (rabbit)

Ester form

43217601 (1994)

Core-minimum

0, 10, 30, or 100 mg/kg/day

Maternal NOAEL = 30 mg/kg/day.

Maternal LOAEL = 100 mg/kg/day based on mortality.

Developmental NOAEL = 30 mg/kg/day.

Developmental LOAEL = 100 mg/kg/day based on 

decreased total live fetuses and increased total fetal deaths 

and increased fetal and/or litter incidence of skeletal 

anomalies and variants.

870.3700b

Prenatal 

Developmental in 

Non-Rodent (rabbit)

Salt form

43217603 (1994)

Core-minimum

0, 10, 30, or 100 mg/kg/day

Maternal NOAEL = 30 mg/kg/day.

Maternal LOAEL = 100 mg/kg/day based on mortality, 

abortions, decreased food efficiency, increased liver and 

kidney weights.

Developmental NOAEL = 30 mg/kg/day.

Developmental LOAEL = 100 mg/kg/day based on 

decreased live fetuses and increased embryonic deaths 

due to abortions.

870.3800

Reproduction and 

Fertility Effects (rat)

Acid form

43545701

Acceptable/guideline

0, 5, 25, or 250 mg/kg/day

Parental NOAEL = 5 mg/kg/day.

Parental LOAEL = 25 mg/kg/day based on increased 

incidence of proximal tubular degeneration in both sexes.

Offspring NOAEL = 5 mg/kg/day.

Offspring LOAEL = 25 mg/kg/day based on increased 

incidences of F2 pups with exencephaly and ablepharia
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Table A.2.4. Subchronic, Chronic, and Other Toxicity Profile – Triclopyr.

Guideline No. Study Type MRID No. (year)/ 

Classification /Doses Results

870.4100b

228-Day Toxicity 

Study (dog)

Acid form

00071794(1976)

Core-minimum

0, 5, 10, or 20 mg/kg/day

NOAEL = 10 mg/kg/day.

LOAEL = 20 mg/kg/day based on decreased 

hematological parameters, changes in clinical chemistry 

and liver histopathology.

870.4100b

1-Year Chronic 

Toxicity

(dog)

41200301(1988)

Acceptable (with 228 day 

study)

0, 0.5, 2.5, or 5 mg/kg/day

NOAEL = 5 mg/kg/day.

LOAEL = not established.

Changes in clinical chemistry noted are due to a 

physiological response of the dog based on limited ability 

of the dog to excrete organic acids at higher plasma 

concentration.

870.4200a Carcinogenicity (rat) See 870.4300 See 870.4300

870.4200b Carcinogenicity 

(mouse)

40356601 (1987)

Core-minimum

0, 5.09/5.55, 26.5/28.6, or 

135/143 mg/kg/day (M/F)

NOAEL = 26.5/28.6 mg/kg/day (M/F).

LOAEL = 135/143 mg/kg/day (M/F)] based on decreased 

weight gains.

No evidence of carcinogenicity in males, but females had 

a significant trend (p<0.05) for mammary gland 

adenocarcinomas.

870.4300

Combined Chronic 

Toxicity/

Carcinogenicity (rat)

40107701 (1987)

Core-minimum

0, 3, 12, or 36 mg/kg/day

NOAEL = 36 mg/kg/day.

LOAEL = not established.

Marginal increase in proximal tubular degeneration 

observed at 6 months.

Increase in adrenal gland pheochromocytoma in males 

and significant trend (p<0.05) for mammary gland 

adenocarcinomas in females.

870.5265

Gene mutation

Ester form

41732202

Non-mutagenic up to 5,000 μg/plate or cytotoxic levels, 

in presence and absence of activation, in S. typhimurium

strains TA98, TA100, TA1535, and TA1537.

870.5265

Gene mutation

Acid form

00031939 (1975)

Supplementary

Non-mutagenic up to 10,000 μg/plate or cytotoxic levels, 

in presence and absence of activation, in S. typhimurium

strains TA98, TA100, TA1535, TA1537, and TA1538.

870.5300

Gene mutation

Acid form

00038408 (1980)

Acceptable

No evidence of growth inhibition for the repair competent 

(H17) or repair deficient (M45) B. subtilis baceterial 

strains when tested up to 2,000 μg/disk.

870.5300

Gene mutation

Acid form

00057085 (1973)

Acceptable

Negative for mutagenicity at doses up to 70 mg/kg in ICR 

random bred mice when tested against indicator 

organisms.

870.5395

In vivo Cytogenetic 

Assay (rat)

Acid form

00057086 (1973)

Acceptable

Negative for chromosomal aberrations in the cytogenetic 

assay when administered as a single dose or for 5 days up 

to 70 mg/kg/day.

870.5395

In vivo Mouse 

Micronucleus

Ester form

41747101 (1990)

Acceptable Not clastogenic up to 600 mg/kg (HDT).

870.5450

Dominant lethal assay 

(mouse)

Acid form

00028996 (1980)

Acceptable Negative at doses up to 70 mg/kg/day.

870.5450

Dominant lethal assay 

(rat)

Acid form

00057087 (1973)

Acceptable Negative at doses up to 70 mg/kg/day.

870.5550

Unscheduled DNA 

synthesis

Ester form

41747102 (1990)

Acceptable Did not cause DNA damage or inducible repair.
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Table A.2.4. Subchronic, Chronic, and Other Toxicity Profile – Triclopyr.

Guideline No. Study Type MRID No. (year)/ 

Classification /Doses Results

870.5550

Unscheduled DNA 

synthesis

Acid form

40057702 (1986)

Acceptable No evidence of unscheduled DNA synthesis.

870.6200

Subchronic 

Neurotoxicity 

Screening Battery 

(rat)

Acid form

49306303 (2012)

Acceptable/guideline

0, 5, 25, or 200 mg/kg/day

NOAEL = 25 mg/kg/day.

LOAEL = 200 mg/kg/day based on decreased body 

weights and food consumption in males.

870.7485 Metabolism and 

Pharmacokinetics

41353001 (1988)

Acceptable/guideline

3 or 60 mg/kg/day

Regardless of dose level or route of administration, 

triclopyr was well absorbed with peak plasma levels 

reached within 3-4 hours. Radioactivity in the tissues at 

72 hours was minimal (<0.54%). At the low dose, >90% 

of the radioactivity was excreted within 24 hours 

primarily via the urine. The high dose yielded similar 

overall results except that urinary elimination was 

decreased between 0-12 hours due to saturation of renal 

excretion mechanisms. Unmetabolized parent 

represented >90% of the urinary radioactivity. 

870.7600

Dermal Penetration 

Study (Human)

Ester form

45253601 (1989)

Supplementary

3.7 mg/kg; 8 hour exposure; 

observed up to 84 hours after 

dosing

In an oral and dermal pharmacokinetics study of triclopyr 

in human volunteers, triclopyr was administered orally 

and dermally to six human volunteers. More than 80% of 

the administered dose was found as unchanged triclopyr 

in the urine. An average of 1.65% of the dermally applied 

dose was recovered in the urine and represented dermal 

penetration of triclopyr.

870.7600

Dermal Penetration 

Study (rabbit)

Acid form

00153805 (1981)

Acceptable

2 g/kg

1.5% of an applied dose absorbed through the skin.

870.7800 Immunotoxicity

49433001 (2011)

Acceptable/guideline

0, 10, 50, or 250 mg/kg/day

Systemic NOAEL = 50 mg/kg/day.

Systemic LOAEL = 250 mg/kg/day based on decreased 

body weights and food consumption.

Immunotoxicity NOAEL = 250 mg/kg/day.

Immunotoxicity LOAEL = not established.
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Attachment 2. Summary of US and International Tolerances and Maximum Residue 

Limits.

Summary of US and International Tolerances and Maximum Residue Limits.

Residue Definition:

US Canada Mexico1 Codex

US [40 CFR §180.417 (1) Tolerances for residues of 

the herbicide triclopyr per se, as a result of the 

application/use of butoxyethyl ester of triclopyr and 

triethylamine salt of triclopyr

2-[(3,5,6-trichloro-2-pyridinyl)oxy]acetic acid None

Commodity Tolerance (ppm) /Maximum Residue Limit (mg/kg)

US Canada Mexico1 Codex

Milk 0.03 0.01

Milk, fat 0.07

Livestock:

US [40 CFR §180.417 (2) Tolerances for the 

combined residues of the herbicide triclopyr ((3,5,6-

trichloro-2-pyridinyl)oxy) acetic acid and its 

metabolite 3,5,6-trichloro-2-pyridinol (TCP), as a 

result of the application/use of butoxyethyl ester of 

triclopyr or the triethylamine salt of triclopyr

All commodities, except milk: 2-[(3,5,6-

trichloro-2-pyridinyl)oxy]acetic acid, 

including the metabolite 3,5,6-trichloro-2-

pyridinol

None

Commodity Tolerance (ppm) /Maximum Residue Limit (mg/kg)

US Canada Mexico1 Codex

Meat* 0.08 0.1

Fat* 0.08 0.1

Meat byproducts*

0.70

0.1 meat byproducts of 

cattle, goats, horses, 

hogs, and sheep (except 

kidney and liver)

0.5 kidney, liver (of 

cattle, goats, horses, 

hogs, and sheep)

* of cattle, goats, horses, hogs, and sheep

Completed: M. Negussie; 03/25/15
Triclopyr Human Health Risk Assessment DP# D426071

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Attachment 3. Summary of Updated Occupational Handler Inhalation Exposure and Risk 

Estimates for July 2014 HASPOC Meeting.

Occupational handler inhalation exposure and risk estimates were updated to reflect all of the

currently registered uses of triclopyr for the July 2014 HASPOC meeting in order to assess the 

inhalation waiver request submitted by the triclopyr registrants. Additionally, since the July 

2014 meeting, application rates for the aerial applications by helicopter have been changed to 

reflect a maximum labeled rate of 6 lb ae/A (rather than the 9 lb ae/A assumed for the July 2014 

meeting).

For mixers/loaders of the liquid formulation for aerial application by helicopter to forestry, the 

inhalation MOE is 41. The current label requires baseline PPE (single layer clothing with 

gloves). With the addition of a PF5 or PF10 respirator to the label, MOEs for this scenario 

would increase to 200 and 410, respectively. These estimates are considered conservative given 

aerial applications are only made by helicopter and the high acreage default of 7,500 acres would 

be an overestimate of the acreage that would be treated. Previously, data was obtained from the 

U.S. Army Corps of Engineers, University of South Florida, and the South Florida Water 

Management District that indicated typical acreage treated with triclopyr by helicopter was 100 

acres (J. Swackhammer; 22-JUL-2002; D269448). This estimate was not used for calculating 

MOEs for this evaluation because it is based on informal discussions from over a decade ago and 

commercial users were not included the estimate. More current, all-inclusive data regarding the 

typical acreage that is treated with triclopyr using aerial applications by helicopter would be 

needed to refine this exposure scenario.

Based on a weight of evidence approach and considering all of the available triclopyr hazard and 

exposure data, HASPOC concluded that a subchronic inhalation study is required at this time for 

triclopyr. As a result, a 10X database uncertainty factor was retained for assessing risk for

inhalation exposure scenarios.
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Table 9.1. Triclopyr: Summary of Occupational Handler Inhalation Risks for Currently Registered Uses.

Activity

Application Equipment Crop/Target

Inhalation 

Unit 

Exposure

(μg/lb ai)1 App Rate2 Acres3 Dose4

ST and IT 

Inhalation 

MOE 

(Baseline) Mitigation 5

Level

Mixer/Loader

Groundboom app. of 

liquid formulation

Range and pasture, forests and non-crop areas, including manufacturing and 

storage sites, rights-of-way such as electrical power lines, communication 

lines, pipelines, roadsides, railroads, fence rows, non-irrigation ditch banks, 

and around farm buildings; and applications to grazed areas, and 

establishment and maintenance of wildlife openings, and in Christmas tree 

plantations and aquatic sites.

0.219 

(baseline)

0.0438 (PF5)

9 lb ae/A 80 0.00198 2,500

Aerial/Helicopter app. of 

liquid formulation 6 lb ae/A 7,500

0.123 41

0.0246 200 (PF5)

0.00123 410 (PF10)

Groundboom app. of 

liquid formulation Rice 0.219

(baseline)

0.375 lb ae/A

0.373 lb ae/A

200 0.000205 24,000

Aerial app. of liquid 

formulation 1,200 0.00123 4,100

Applicator

Applicator, 

Aerial/Helicopter

Range and pasture, forests and non-crop areas, including manufacturing and 

storage sites, rights-of-way such as electrical power lines, communication 

lines, pipelines, roadsides, railroads, fence rows, non-irrigation ditch banks, 

and around farm buildings; and applications to grazed areas, and 

establishment and maintenance of wildlife openings, and in Christmas tree 

plantations and aquatic sites.

0.0049 (EC) 6 lb ae/A 7,500 0.00414 1,200 (EC)

Applicator, Open Cab 

Groundboom

0.34 

(baseline) 9 lb ae/A 200 0.00306 1,600

Applicator, Aerial

Rice 

0.0049 (EC)

0.375 lb ae/A

1,200 0.000027

6 180,000 (EC)

Applicator, Open Cab 

Groundboom

0.34 

(baseline) 200 0.0000404 16,000

Mixer/Loader/Applicator

M/L/A Backpack

Range and pastures and in non-crop areas including industrial manufacturing 

and storage sites, rights-of-way such as electrical power lines, 

communications lines, pipelines, roadsides, railroads, fence rows, nonirrigation ditch banks and around farm buildings. Use on these sites may 

include application to grazed areas, as well as establishment and maintenance 

of wildlife openings.

2.58 8 lb ae/A or 

0.75 lb ae/gal

40 

gallons 0.000968 5,200

M/L/A spray boom, 

handgun, or other suitable 

equipment mounted on a 

boat or vehicle, 

helicopter.

Aquatic Sites: For control of immersed, submersed and floating aquatic 

plants in aquatic sites such as ponds, lakes, reservoirs, non-irrigation canals 

and ditches which have little or no continuous outflow, marshes and 

wetlands, including broadleaf and woody vegetation on banks and shores 

within or adjacent to these and other aquatic sites.

3.9

6 lb ae/A or 

8.436 lb 

ae/A/100 gal 

or 0.08436 lb 

ae/gal

1,000 

gallons

0.00411 1,200
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Table 9.1. Triclopyr: Summary of Occupational Handler Inhalation Risks for Currently Registered Uses.

Activity

Application Equipment Crop/Target

Inhalation 

Unit 

Exposure

(μg/lb ai)1 App Rate2 Acres3 Dose4

ST and IT 

Inhalation 

MOE 

(Baseline) Mitigation 5

Level

M/L/A Handheld sprayer

Cool season turfgrass, and on non-crop areas including industrial sites, rightsof-way (such as roadsides, electric utility and communication transmission 

lines, pipelines and railroads), non-irrigation ditch banks, natural areas (such 

as wildlife management areas, wildlife openings, wildlife habitats, recreation 

areas, campgrounds, trailheads and trails) and grazed areas in and around 

these sites

30

2.0769 lb ae/A

2.9 fl oz/gal

0.23 lb ae/gal

40 

gallons

0.00345 1,400

Flagger

Aerial spray app.

Rice

0.35

(baseline)

0.375 lb ae/A

350

0.000574 8,700

Range and pasture, forests and non-crop areas, including manufacturing and 

storage sites, rights-of-way such as electrical power lines, communication 

lines, pipelines, roadsides, railroads, fence rows, non-irrigation ditch banks, 

and around farm buildings; and applications to grazed areas, and 

establishment and maintenance of wildlife openings, and in Christmas tree 

plantations and aquatic sites. 

9 lb ae/A 0.0138 360

1. Based on the “Occupational Pesticide Handler Unit Exposure Surrogate Reference Table”; Level of mitigation: Baseline, PPE (gloves), Eng. Controls.

2. Based on proposed labels.

3. Exposure Science Advisory Council Policy #9.1.

4. Inhalation Dose = Inhalation Unit Exposure (μg/lb ai) × Conversion Factor (0.001 mg/μg) × Application Rate (lb ai/acre) × Area Treated (A/day) x IAF (100 %) ÷ BW (80 kg).

5. Inhalation MOE = Inhalation NOAEL (5 mg/kg/day) ÷ Inhalation Dose (mg/kg/day).