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INTRODUCTION 

This is the Environmental Protection Agency’s (EPA or the Agency) Final Work Plan (FWP) for 

the registration review of clopyralid. This work plan addresses public comments received 

concerning the Preliminary Work Plan (PWP), which was posted in the clopyralid registration 

review docket (EPA-HQ-OPP-2014-0167). Clopyralid (3,6-dichloropyridine-2-carboxylic acid) 

is a pyridine herbicide. This case includes the clopyralid parent along with its potassium, 

triethylamine, and monoethanolamine salts. Pyridine herbicides are auxin growth regulators, 

which mimic naturally-occurring plant hormones, thereby disrupting growth processes and 

causing abnormal growth patterns in plants. Clopyralid is registered for use on a variety of 

agricultural crops, and non-crop use sites, including tree and sod farms, forests, pastures and 

rangelands, ornamental landscapes and nurseries, golf courses and recreational areas. Clopyralid 

may be applied as a broadcast foliar or soil-directed spray via aircraft, ground- and hand-held 

sprayers, granular spreader or via tree injection. 

The Agency is implementing the registration review program pursuant to Section 3(g) of the 

Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), and will review each registered 

pesticide every 15 years to determine whether it continues to meet the FIFRA standard for 

registration. Changes in science, public policy, and pesticide use practices occur over time. The 

registration review program is intended to make sure that, as the ability to assess risk evolves and 

as policies and practices change, all registered pesticides continue to meet the statutory standard. 

The public phase of registration review begins when the initial docket is opened for each case. 

Information on this program is provided on the Agency’s website.1

The FWP begins with any updates since the PWP was issued. Next is a summary of substantive 

comments received during the public comment period for the PWP concerning anticipated data 

needs, expected risk assessments, or the estimated timeline identified in the PWP, and a 

summary of the Agency’s responses to those comments. This section is followed by registration 

review planned data needs, risk assessments expected to be conducted, and the projected 

registration review timeline for clopyralid. Lastly, there is a discussion of next steps. 

UPDATES SINCE THE PWP WAS ISSUED 

On June 23, 2014, EPA, Health Canada’s Pest Management Regulatory Agency, and the 

California Department of Pesticide Regulation issued Guidance for Assessing Pesticide Risks to 

Bees. This guidance describes a tiered risk assessment process, and associated data 

requirements, for any pesticides with registered uses resulting in non-target exposure to bees. In 

accordance with this guidance, EPA has amended the ecological problem formulation for 

clopyralid to add the following three honey bee toxicity studies. For details, please see the 

September 8, 2014 memo, Addendum to the EFED Registration Review Problem Formulation 

for Clopyralid Regarding Tier I Honey Bee Toxicity Testing. 

 

- Pollinator Chronic Oral Toxicity – honeybee adult 

- Pollinator Acute Oral Toxicity – honeybee larvae 

- Pollinator Chronic Oral Toxicity – honeybee larvae 

 

1

 http://www.epa.gov/oppsrrd1/registration_review/ 
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Clopyralid uses include aerial applications to multiple agricultural crops, pastures, rangeland, 

agricultural fallow/idleland/conservation reserve, forest trees, and nonagricultural uncultivated 

areas/soils where spray drift may land on blooming non-target plants and could result in residues 

in pollen and nectar. The residues in pollen and nectar could then be transported to hives by adult 

forager bees and potentially affect larval honeybees. Given this potential exposure scenario and 

clopyralid’s highly persistent nature, as with other members of the picolinic acid family, the 

Agency plans to require the aforementioned studies for clopyralid. 

SUMMARY OF COMMENTS AND AGENCY RESPONSES 

During the 60-day public comment period on the Clopyralid Preliminary Work Plan, which 

opened on March 28, 2014 and closed on May 28, 2014, the Agency received 10 public 

comments. Comments were submitted by Dow AgroSciences, a technical registrant, and various 

stakeholders including: West Marin Compost Coalition, Florida Fruit & Vegetable Association, 

National Alfalfa & Forage Alliance, Chittenden Solid Waste District, Southern Minnesota Beet 

Sugar Cooperative, a certified crop advisor, FIFRA Endangered Species Task Force, and the 

Center for Biological Diversity. The comments do not address the timeline described in the 

PWP, but they do address the planned ecological and human health risk assessments and data 

needs. In the PWP, EPA also solicited comments on the specific topics of environmental justice, 

water quality concerns, and trade irritants, but no comments or information were received on 

those issues. 

This section does not capture every comment made about the PWP nor all of the Agency’s 

responses. Summarized below are public comments that resulted in changes to the anticipated 

registration review data needs, risk assessments, or timeline, or are of a broader regulatory 

nature. Public comments and EPA responses in their entirety are located in the docket, EPAHQ-OPP-2014-0167. 

Comments submitted by Dow AgroSciences’ (Dow) in EPA-HQ-OPP-2014-0167-0015. 

1. Comment: Dow provided use information on several clopyralid uses including key 

pests/uses. They also provided typical application rates for certain uses as well as 

information to better understand risk from residues in groundwater used as irrigation water. 

Dow also states that several use sites listed in supporting documents are not currently 

registered uses on clopyralid labels. These uses are as follows: alfalfa, almonds, beans, 

chestnuts, filberts, lentils, macadamia nuts, peas, pecans, pistachio nuts, potatoes, safflower, 

sorghum, soybeans, sunflowers, and walnuts. Dow also noted that no tolerances exist for the 

following crops: soybeans, tree nuts, lentils, alfalfa, beans, peas, potatoes, safflower, 

sorghum or sunflower. Additionally, Dow commented that it is initiating label amendments 

to better define non-specific use sites on labels.

Response: The Agency thanks Dow for the information provided, which will be used during 

the registration review of clopyralid. The Agency also concurs with Dow’s comment that the 

crops listed by Dow are not registered for clopyralid and that no tolerances exist for the crops 

noted above. In regard to non-specific use sites on labels, the EPA will work with Dow to 

amend labels to better define non-specific use sites prior to the preliminary risk assessment. 
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2. Comment: Dow states the CAS number is correct for clopyralid TEA (119308-91-7). 

However the definition of the form as clopyralid triethanolamine salt is incorrect and should 

read “triethylamine salt.”

Response: The Agency agrees that triethylamine salt is the correct nomenclature and will be 

used in future documents. 

3. Comment: Dow currently has only one registered end use product containing the clopyralid 

acid, Curtail M (62719-86). It is Dow’s opinion that a restricted entry interval (REI) based 

on the toxicity package for the integrated system (i.e., salt, not acid) is appropriate and 

protective of workers handling these formulations. If necessary, Dow is willing to add label 

language instructing workers to allow the spray to dry before reentry for liquid products 

containing the acid.

Response: The Agency concurs that the form, as applied, should be the form that dictates the 

REI. With regard to Dow’s opinion that an REI of 12 hours is adequate for the clopyralid 

product Curtail M (62719-86), further information is required to maintain the current REI of 

12 hours. 

4. Comment: Dow states that there are no residential use patterns or a use pattern that would 

allow professional application to residential turf or ornamentals. Therefore, home owners 

should not be exposed to clopyralid applications at their home.

Response: Unless a product is classified as a restricted-use pesticide, EPA assumes that the 

general public may apply the product. Under this assumption, the Agency conducts risk 

assessments as necessary based on the use patterns and hazard profile. 

5. Comment: Concerning the seedling emergence (GDLN 850.4100) and vegetative vigor 

(GDLN 850.4150) data requirements, Dow proposed to continue to rely on existing data 

from MRID 40081401 and supplement it with data for formulation EF-243. Where no typical 

end use products exist for the clopyralid salts, Dow does not propose to conduct these 

studies.

Response: The Agency has classified MRID 40081401 as supplemental due to a number of 

methodological limitations detailed in the data review (DP398834). This study does not 

fulfill the guideline requirement for tier 2 vegetative vigor and seedling emergence data for 

clopyralid. These studies are needed to assess risk to non-target terrestrial plants. EPA does 

agree that for the clopyralid triethylamine (TEA) salt (PC 117404) and the potassium salt (PC 

117423) there are currently no active registrations for single active ingredient products (i.e., 

not co-formulated); therefore these studies should be conducted with the technical active 

ingredient. The Agency welcomes any additional information that Dow believes will address 

this uncertainty. 
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Comments submitted by West Marin Compost Coalition (WMCC), Chittenden Solid 

Waste District (CSWD), in EPA-HQ-OPP-2014-0167-0013/0018. 

1. Comment: WMCC and CSWD expressed their opposition toward the continued registration 

of clopyralid, due to clopyralid’s persistence and presence in compost and the need for 

revised formulations that can reduce clopyralid’s presence in compost. WMCC also 

expressed an interest in EPA expanding a product stewardship program for the picolinic 

acids. Both stakeholders noted the economic cost of persistent herbicide contamination in 

compost. CSWD also pointed out that compost holding times would not be adequate 

mitigation due to the burden it puts on composters.

Response: The Agency thanks WMCC and CSWD for their comments regarding the 

picolinic acid herbicides and their persistence in compost. The agency is aware of these 

issues and will seek additional compost industry input during the registration review process. 

Comments submitted by Joe Hastings (a certified crop advisor), National Alfalfa & Forage 

Alliance (NAFA), Florida Fruit & Vegetable Association (FFVA), and Southern Minnesota 

Beet Sugar Cooperative (SMBSC) in EPA-HQ-OPP-2014-0167-0011/0012/0019/0020. 

1. Comment: Joe Hastings, NAFA, FFVA, and SMBSC expressed their support of the clopyralid 

registration noting its effectiveness as an herbicidal tool. FFVA also stressed the importance 

of maintaining the current post-harvest interval (PHI) of 1 day as strawberries are 

repeatedly harvested throughout the growing season. EPA’s Scoping Document currently 

states the need for an increase in PHI to 2 days for worker protection.

Response: EPA thanks Joe Hastings, NAFA, FFVA, and SMBSC for their comments, which 

will be considered during registration review. EPA is working with Dow and FFVA to 

resolve the PHI early in registration review. 

Comments submitted by Center for Biological Diversity (CBD), in EPA-HQ-OPP-2014-

0167-0017. 

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

consult with the U.S. Fish and Wildlife Service and the National Marine Fisheries Service 

(the Services) on the registration review of clopyralid in accordance with the Endangered 

Species Act (ESA). The CBD comments mention various aspects of the risk assessment 

process, including use of the best available data to develop endangered species risk 

assessments, and evaluation of effects on endangered and threatened species and their 

designated critical habitat. CBD also expresses concern regarding the rigor of the Agency’s 

preliminary determinations regarding the effects of clopyralid on endangered and threatened 

(listed) species and their designated critical habitat for the clopyralid registration review. 

Response: EPA has reviewed the comments from CBD on the registration review docket 

opening for clopyralid and plans to address many of the concerns raised by CBD as part of 

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

recommendations of the April 2013 National Academy of Sciences (NAS) report. EPA will 
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address concerns specific to clopyralid in connection with the development of its final 

registration review decision for this pesticide. 

In November 2013, the EPA, along with the Services and the USDA, released a summary of 

their joint Interim Approaches for assessing risks to endangered and threatened (listed) 

species from pesticides. The Interim Approaches were developed jointly by the agencies in 

response to the NAS recommendations and reflect a common approach to risk assessment 

shared by the agencies as a way of addressing scientific differences between the EPA and the 

Services. The NAS report outlines recommendations on specific scientific and technical 

issues related to the development of pesticide risk assessments that EPA and the Services 

must conduct in connection with their obligations under the ESA and FIFRA. 

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

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

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

Research and Evaluation Group (SFIREG) meetings. The agencies also held a stakeholder 

workshop in April 2014, allowing additional opportunities for stakeholders to comment on 

the Interim Approaches. Additional workshops are planned to enhance stakeholder 

involvement; the next workshop is scheduled for October 2014. As part of a phased, iterative 

process for developing the Interim Approaches, the agencies will also consider public 

comments on the Interim Approaches in connection with the development of upcoming 

registration review decisions. The details of the joint Interim Approaches are contained in 

the white paper, Interim Approaches for National-Level Pesticide Endangered Species Act 

Assessments Based on the Recommendations of the National Academy of Sciences April 2013 

Report, dated November 1, 2013. 

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

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

designated critical habitat, the ecological problem formulation supporting this Final Work 

Plan for clopyralid does not describe the specific ESA analysis, including effects 

determinations for specific listed species or designated critical habitat, to be conducted 

during registration review. In the ecological problem formulation document for clopyralid, 

EPA described the screening-level risk assessment to determine the potential effects of 

clopyralid on all taxa of non-target wildlife and plants, which will assume that listed species 

and their designated critical habitats may be present in the vicinity of the application of 

clopyralid. This screening-level assessment will allow EPA to focus its future evaluations 

on the types of species where the potential for effects exists once the scientific methods being 

developed by the agencies have been fully vetted. While the agencies continue to develop a 

common method for ESA analysis, the planned screening-level risk assessment for the 

registration review of clopyralid will describe the level of ESA analysis completed for this 

particular registration review case. Once the agencies have fully developed and implemented 

the scientific methods necessary to complete risk assessments for endangered and threatened 

(listed) species and their designated critical habitats, these methods will be applied to 

subsequent analyses for clopyralid as part of completing this registration review. 
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Comments submitted by FIFRA Endangered Species Task Force (FESTF), in EPA-HQOPP-2014-0167-0016. 

1. Comment: The technical registrants for clopyralid, as identified on the fact sheet included in 

the PWP, are Albaugh, Inc., and Dow AgroSciences LLC, which are FESTF members and 

are entitled to rely on FESTF data.

Response: EPA appreciates FESTF’s comments and will consider this information during 

registration review. EPA also notes that the fact sheet included in the PWP identified United 

Phosphorus Inc. as a technical registrant for clopyralid in addition to those mentioned in the 

comment. 
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PLANNED DATA NEEDS 

Table 1 below summarizes the data needs for clopyralid based on the EFED Registration Review 

Problem Formulation for Clopyralid, Addendum to the EFED Registration Review Problem 

Formulation for Clopyralid Regarding Tier I Honey Bee Toxicity Testing and Clopyralid. 

Human Health Assessment Scoping Document in Support of Registration Review. The table has 

been updated since the PWP to reflect updated guidance for assessing risk to bees, which 

resulted in the addition of three pollinator toxicity studies to the data needs. 

Table 1: Planned Data Needs for the Clopyralid Registration Review 

Guideline 

Number2 Study Title2 

Test Material 

Estimated 

Timeframe 

(Months from 

receipt of DCI) 

835.4100 Aerobic soil metabolism (3 additional soils) TGAI 24 

835.4300 Aerobic aquatic metabolism (2 sediments) TGAI 24 

850.1300 Chronic freshwater invertebrate TGAI 12 

850.1400 Freshwater fish early-life stage TGAI 12 

850.21003 Avian oral toxicity (passerine species) TGAI 12 

850.2300 Avian reproduction (upland game species) TGAI 24 

850.41004 Terrestrial plant toxicity, seedling emergence TEP 12 

850.41504 Terrestrial plant toxicity, vegetative vigor TEP 12 

850.4400 Aquatic vascular plant growth TEP 12 

850.4500 Aquatic non-vascular plant growth (2 additional 

species) TEP 12 

850.4550 Cyanobacteria Toxicity TEP 12 

850.6100 

Environmental chemistry methods and associated 

independent laboratory validations for soil, water, 

and compost 

Compost 

sourced from 

material treated 

with TEP 

12 

NonGuideline3 Dissipation Study in Compost

Compost 

sourced from 

material treated 

with TEP 

12 

 

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 On June 27, 2012, EPA announced certain revisions in harmonized guideline series 850 – Ecological Effects Tests 

– including renumbering and other designations or changes for some guideline studies. See “Final Test 

Guidelines; OCSPP 850 Series; Notice of Availability” 77 FR 38282, June 27, 2012. 

http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPPT-2009-0154-0028 3

 A protocol must be submitted to the Agency within 90 days of receipt of the DCI. 4

 Data are required for four typical end use products, one each containing clopyralid, clopyralid monoethanolamine 

salt, clopyralid triethylamine salt, and clopyralid potassium. Where no appropriate formulations exist for this 

purpose (i.e. for triethylamine salt, 117404 and potassium salt, 117423) studies should be conducted with the 

technical products. 
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Table 1: Planned Data Needs for the Clopyralid Registration Review 

Guideline 

Number2 Study Title2 

Test Material 

Estimated 

Timeframe 

(Months from 

receipt of DCI) 

NonGuideline3

Pollinator Chronic Oral Toxicity – honeybee 

adult TGAI 12 

NonGuideline3 Pollinator Acute Oral Toxicity – honeybee larvae TGAI 12 

NonGuideline3

Pollinator Chronic Oral Toxicity – honeybee 

larvae TGAI 12 

Anticipated Data Needs for Clopyralid End-Use Products Co-formulated with other Herbicides

850.41505 Terrestrial plant toxicity, vegetative vigor TEP 12 

TGAI = technical grade active ingredient; TEP = typical end-use product; 

RISK ASSESSMENTS FOR REGISTRATION REVIEW

During registration review, the Agency will conduct a comprehensive ecological risk assessment, 

including an endangered species assessment, for all uses of clopyralid. For human health, EPA 

will conduct revised dietary and aggregate risk assessments during registration review. If 

toxicological endpoints or points of departure are revised based on the data that are required for 

registration review, they will be considered in the new assessments, as well as any changes to the 

standard operating procedures or default exposure assumptions. 

Table 2 below summarizes the planned registration review risk assessments based on the EFED 

Problem Formulation, Addendum to the EFED Registration Review Problem Formulation for 

Clopyralid Regarding Tier I Honey Bee Toxicity Testing and HED Scoping Document. The 

planned assessments have been updated since the PWP to reflect updated Agency guidance, 

which resulted in the addition of a pollinator risk assessment. 

 

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 Data are required for representative TEPs co-formulated with other herbicides for the most sensitive crops from 

prior clopyralid studies (i.e., onion, snap bean, soybean, sunflower, tomato, and wheat). 
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Table 2: Planned Risk Assessments for the Clopyralid Registration Review 

Type of Risk Assessment Conduct? Notes 

Ecological and Environmental Fate 

Comprehensive ecological 

(species to be assessed 

include terrestrial and aquatic 

organisms), pollinator, 

including endangered species 

Y Given current clopyralid use patterns and anticipated 

pollinator exposure, a pollinator risk assessment will 

be conducted following recently completed guidance. 

Incidents Will check for 

updates 

For a discussion of reported ecological incidents for 

clopyralid, see page 15 of the Problem Formulation. 

Human Health 

Dietary 

Food Y The Agency plans to conduct an updated dietary 

assessment to incorporate new estimated drinking 

water concentrations. 

Drinking water Y 

Occupational 

Handlers (mixers, loaders, 

applicators) 

N The need for a spray drift and volatilization risk 

assessment for clopyralid will be examined during 

registration review. 

Post-application N 

Residential 

Handlers N The need for a spray drift and volatilization risk 

assessment for clopyralid will be examined during 

registration review. 

Post-application N 

Other 

Aggregate Y Evaluates the combined risk from dietary and 

residential/public recreational exposures. 

Cumulative N/A Clopyralid has not been identified as a member of a 

cumulative group that shares a common mechanism 

of toxicity. 

Tolerances Y The Agency anticipates working to harmonize 

tolerances/MRLs, where possible, during registration 

review. 
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Incidents Will check for 

updates 

For a discussion of reported human incidents for 

clopyralid, see page 10 of the Clopyralid. Human 

Health Assessment Scoping Document in Support of 

Registration Review. Due to the low frequency and 

generally low severity of incident cases reported for 

clopyralid there does not appear to be a concern at 

this time that would warrant further investigation. 

TIMELINE

EPA has created the following estimated timeline for the completion of the clopyralid 

registration review in Table 3 below. The projected timeline has not changed since the PWP. 

Table 3: Registration Review for Clopyralid – Projected Registration Review Timeline

Activities Estimated Date 

Opening the Docket 

Open Docket and 60-day Public Comment Period 2014 – March

Close Public Comment 2014 – May

Case Development 

Final Work Plan 2014 – September

Issue DCI 2014 Oct. – Dec.

Data Submission 2016 Oct. – Dec. 

60-day Public Comment Period for Draft Risk Assessments[1] 2018 April - June 

Registration Review Decision 

60-day Public Comment Period for Proposed Registration Review 

Decision 

2019 Jan. - March

Registration Review Decision and Begin Post-Decision Follow-up 2020 

Total (years) 6 

NEXT STEPS 

As noted previously, the Agency plans to require several environmental fate, ecological effects, 

and human health studies for clopyralid through a Data Call-In Notice, expected to be issued in 

2014. 

 

[1] The regulations governing Registration Review generally require the Agency to provide a public comment period 

of at least 30 calendar days for draft risk assessments; see 40 CFR Part 155.53(c). For conventional pesticides, the 

Agency plans to provide a 60 calendar day public comment period generally for draft risk assessments.