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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 2,4-DP-p. This work plan addresses public comments received 

concerning the Preliminary Work Plan (PWP), which was posted in the 2,4-DP-p registration 

review docket (EPA-HQ-OPP-2013-0726). This case includes the following active ingredients: 

2,4-DP-p acid, 2,4-DP-p dimethylamine (DMAS), and 2,4-DP-p 2-ethylhexyl ester (EHE). The 

PC codes included in this case are: 031402, 031403, and 031465. These compounds are referred 

to collectively as 2,4-DP-p and individually as the acid, DMAS, and EHE. 2,4-DP-p is a nonsystemic herbicide in the phenoxy family of herbicides that is registered for non-agricultural use 

to control a variety of weeds on commercial and residential lawns; turfgrass; golf courses; sod 

farms; outdoor residential areas; and forest trees. It is registered for noxious weed and brush 

control use on uncultivated, non-agricultural areas such as rights-of-way, roadsides, and airports. 

There are no registered food or agricultural uses, and 2,4-DP-p products are used primarily in 

residential, commercial, institutional, and industrial areas. 

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 2,4-DP-p. Lastly, there is a discussion of next steps. 

UPDATES SINCE THE PWP WAS ISSUED 

The Registration Review: Preliminary Problem Formulation for Environmental Fate, Ecological 

Risk, Endangered Species, and Drinking Water Exposure Assessments for 2,4-Dp-p Containing 

R Isomer Compounds (2,4-DP-p acid, 2,4-DP-p Amine salt, and 2,4-DP-p 2-ethylhexyl ester), 

dated November 27, 2013, listed Guideline (GDLN) 835.6100, terrestrial field dissipation, as an 

anticipated data need. However, as indicated in the PWP, twelve studies were previously 

submitted by 2,4-DP-p registrants to EPA to fulfill GDLN 835.6100 and were in review at the 

time of the publication of the PWP. EPA’s review of this information indicated that eleven of 

the submitted studies were scientifically sound and classified as supplemental for risk assessment 

purposes. Additionally, this data also fulfills the anticipated data need for GDLN 850.6100 

environmental chemistry methods and associated independent laboratory validations (ECM/ILV) 

for soil. Therefore, EPA has determined that additional terrestrial field dissipation data and 

ECM/ILV for soil are no longer needed. Table 1 in the “Planned Data Needs” section of this 

 

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 http://www.epa.gov/oppsrrd1/registration_review/ 
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FWP has been updated to reflect this change. All other environmental fate and ecological effects 

data requirements remain as listed in the December 2013 PWP. 

SUMMARY OF COMMENTS AND AGENCY RESPONSES 

During the 60-day public comment period on the 2,4-DP-p Preliminary Work Plan, which 

opened on December 20, 2013 and closed on February 18, 2014, the Agency received five public 

comments. Comments were submitted by the California San Francisco Bay Regional Water 

Quality Control Board (San Francisco Bay Water Board), the California Central Valley Regional 

Water Quality Control Board (Central Valley Water Board), the Center for Biological Diversity, 

the FIFRA Endangered Species Task Force (FESTF), and the 2,4-DP-p Task Force. 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 requirements. In the PWP, EPA also 

solicited comments on the specific topics of environmental justice, water quality concerns, and 

trade irritants; comments pertaining to water quality concerns only were received. 

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 in their entirety are located in the docket, EPA-HQ-OPP-2013-0726. 

Summarized public comments that provide clarification and information that will be 

incorporated into the planned ecological risk assessment are in an addendum to Registration 

Review: Preliminary Problem Formulation for Environmental Fate, Ecological Risk, 

Endangered Species, and Drinking Water Exposure Assessments for 2,4-Dp-p Containing R 

Isomer Compounds (2,4-DP-p acid, 2,4-DP-p Amine salt, and 2,4-DP-p 2-ethylhexyl ester). No 

substantive comments were received on the planned human health risk assessment or data needs. 

Comments submitted by San Francisco Bay and Central Valley Water Boards in EPA-HQOPP-2013-0726-0013 and EPA-HQ-OPP-2013-0726-0014. 

1. Comment: The San Francisco Bay and Central Valley Water Boards’ comments center on 

considerations of the Clean Water Act and preventing water quality impairments of phenoxy 

family herbicides (2,4-D, 4-DB, and 2,4-DP-p). The Central Valley Water Board indicated that 

while 2,4-DP-p use in California is limited, 2,4-D is the most frequently detected herbicide in 

California urban waterways. The Board stated that for 2,4-DB and 2,4-DP-p registrations, 

additional fate and toxicity data should be required for 2,4-DCP, the common phenoxy 

herbicide degradate, in order to ensure conservative risk assessments are conducted and to 

prevent water quality impairments caused by 2,4-DB and 2,4-DP. 

Response: 2,4-DCP is a common degradate of 2,4-DB as well as 2,4-DP-p and 2,4-D. EPA’s 

review of the public literature database indicated that some data on the aquatic toxicity of 2,4-

DCP are available, and that 2,4-DCP may be more toxic than 2,4-DP-p to some aquatic species. 

If a further review of available data corroborates this initial determination, aquatic exposure 

estimates may be conducted for 2,4-DP-p and 2,4-DCP separately or based on a total 

equivalency factor (TEF) approach depending on the availability of additional 2,4-DCP data. 

Therefore, based on the availability of relevant public literature on 2,4-DCP, additional data are 

not required. However, the 2,4-DP-p Task Force also indicated in its public comments that it 

will submit relevant information on 2,4-DCP. The Agency welcomes this information and will 
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review relevant information regarding the toxicity of 2,4-DCP to confirm that the Agency’s 

assumptions regarding 2,4-DCP are appropriate. In the absence of data, values from ECOSAR, 

a toxicity endpoint modeling tool, may be used to predict the toxicity of 2,4-DCP. If a review 

of available data indicate that 2,4-DCP is not more toxic to aquatic species, toxicity of the 

degradate will be characterized using the total toxic residue approach, which would be expected 

to conservatively estimate the toxicity of 2, 4-DCP. 

2. Comment: The San Francisco Bay and Central Valley Water Boards also requested 

clarification on the approach that will be taken to consider cumulative risk of additive 

toxicities of phenoxy herbicides. 

Response: EPA agrees that exposure to mixtures of compounds may affect the overall toxicity 

of any chemical. However, a quantitative assessment of risks associated with mixtures requires 

extensive data. Currently EPA does not have adequate data and has not yet developed the 

methodology to quantitatively model and assess mixtures of chemicals in the environment. 

Therefore, a quantitative assessment of mixtures cannot be conducted at this time. EPA has a 

long-term goal to develop a quantitative approach including guidance on weight-of-evidence 

analysis for assessing risk of pesticide mixtures. In the interim, EPA intends to qualitatively 

discuss the potential for differential exposure and toxicity from mixtures of compounds. 

3. Comment: The San Francisco Water Board also commented that the Agency should consider 

the potential ecological risks of 2,4-DP-p in urban settings, including and in particular, the fate 

and aquatic toxicity impacts from the common degradate 2,4-DCP.

Response: The Agency is evaluating all registered uses of 2,4-DP-p during registration review. 

2,4-DP-p is primarily used on lawns, rights-of-ways, residential areas, and non-cultivated 

agricultural lands. The environmental fate properties and use patterns of 2,4-DP-p indicate that 

direct spray, spray drift, leaching through soil, and runoff represent potential transport 

mechanisms of 2,4-DP-p to non-target aquatic and terrestrial organisms and will be included as 

exposure pathways of concern for both urban and non-urban settings. However, for urban 

settings, the Agency has limited scenarios/tools to evaluate exposure for urban uses of 

pesticides. 

Comments submitted by the Center for Biological Diversity in EPA-HQ-OPP-2013-0726-

0011. 

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

independent duty under the Endangered Species Act (ESA) to consult with the U.S. Fish and 

Wildlife Service and the National Marine Fisheries Service (the Services) on the registration 

review of 2,4-DP-p. 

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

opening for 2,4-DP-p 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 

address concerns specific to 2,4-DP-p in connection with the development of its registration 

review decision for 2,4-DP-p. 
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At this time, EPA has not fully developed its risk assessment process for listed species. In 

November 2013, the EPA, along with the Services and the U.S. Department of Agriculture 

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

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

response to the National Academy of Sciences’ (NAS) recommendations and reflect a 

common approach to risk assessment shared by the Agencies as a way of addressing scientific 

differences between the EPA and the Services. The NAS report, available at 

http://www.nap.edu/catalog.php?record_id=18344, 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, allowing additional opportunities for 

stakeholders to comment on the Interim Approaches. As part of a phased, iterative process for 

developing the Interim Approaches, the Agencies will also consider public comments on the 

Interim Approaches in connection with the development of upcoming Registration Review 

decisions. The details of the joint Interim Approaches are contained in the 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, available at http://www.epa.gov/espp/2013/nas.html. 

Comments submitted by FESTF in EPA-HQ-OPP-2013-0726-0012. 

5. Comment: FESTF commented that the 2,4-DP-p technical registrants are current members 

of FESTF and, thus, entitled to rely on FESTF data on federally-listed threatened and 

endangered species. FESTF also indicated the data they have previously submitted to the 

Agency are the best available for the proximity analysis of 2,4-DP-p use and endangered 

species locations, and fulfill the requirements indicated in Pesticide Registration Notice 

2000-2. 

Response: EPA thanks FESTF for its comment and will consider all appropriate information 

as we conduct the registration review assessment and make our registration review decision. 

Comments submitted by 2,4-DP-p Task Force in EPA-HQ-OPP-2013-0726-0015. 

6. Comment: The 2,4-DP-p Task Force provided clarification on use sites and restrictions, 

including possible explanations for an apparent off-label use on pasture reported in the 

BEAD Chemical Profile for Registration Review. The Task Force believes that 2,4-D use is 

sometimes confused with 2,4-DP-p in grower surveys. Also, registered uses around pastures, 

such as fencerows, may be mistakenly reported as pasture use. Lastly, the Task Force stated 

that registered use on non-agricultural, uncultivated areas, including grasses grazed by 

nonfood/nonfeed animals such as horses, may be reported as pasture uses. The Task Force 

further indicated that USDA Census of Agriculture data on horse and pony populations 

coincide with EPA’s data on reported pasture use in Missouri and Tennessee. These states 

have the 5th and 4th largest horse and pony populations in the U.S. and are more likely to 

have cool season pasture and weed species that 2,4-DP-p is used on as compared to the 

states with the largest horse populations. 
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Response: EPA thanks the 2,4-DP-p Task Force for this information. The EPA concurs that 

use along fencerows and on non-agricultural, uncultivated lands may be reported as pasture 

use. However, EPA will continue to monitor usage data in registration review to determine if 

further information on reported 2,4-DP-p use on pastures is needed and if label clarifications 

and/or grower outreach may be warranted. 

7. Comment: The Task Force also provided information on the size of 2,4-DP-p spot treatment 

areas, the size of various granules in 2,4-DP-p end-use formulations, and a list of supported 

PC codes to differentiate between PC codes that were historically part of the 2,4-DP case 

and which PC codes are actively supported in registration review under the 2,4-DP-p case. 

The Task Force further indicated that it will continue to work with EPA to clarify label use 

directions and restrictions in registration review. 

Response: The EPA thanks the Task Force for this information and the clarification of 

supported PC codes. The Registration Review: Problem Formulation for Environmental 

Fate, Ecological Risk, Endangered Species, and Drinking Water Exposure Assessments for 

2,4-DP-p Containing R Isomer Compounds (2,4-DP-p acid, 2,4-DP-p Amine salt, and 2,4-

DP-p 2-ethylhexyl ester) has been amended to incorporate relevant granular and spot 

treatment information. 

PLANNED DATA NEEDS 

Table 1 on the following page summarizes the planned data needs for 2,4-DP-p based on the 

Registration Review: Preliminary Problem Formulation for Environmental Fate, Ecological 

Risk, Endangered Species, and Drinking Water Exposure Assessments for 2,4-DP-p Containing 

R Isomer Compounds (2,4-DP-p acid, 2,4-DP-p Amine salt, and 2,4-DP-p 2-ethylhexyl ester)

and the 2,4-DP-p (dichloroprop-p) Human Health Assessment Scoping Document in Support of 

Registration Review. The table has been updated since the PWP to reflect the completion of 

study reviews, which resulted in the removal of a terrestrial field dissipation study from the list 

of data needs. 

Table 1: Planned Data Needs for the 2,4-DP-p Registration Review 

Guideline 

Number2 Study Title1 

Test Material 

Estimated 

Timeframe 

(Months 

from receipt 

of DCI) 

835.41003 Aerobic soil metabolism TGAI 24 

835.4400 Anaerobic aquatic metabolism TGAI 24 

 

2

 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 single aerobic soil metabolism study has been submitted and classified acceptable. However, additional data for 

three soils are required under 40 CFR Part 158 for terrestrial outdoor uses and are anticipated data needs for this 

registration review. 
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Table 1: Planned Data Needs for the 2,4-DP-p Registration Review 

Guideline 

Number2 Study Title1 

Test Material 

Estimated 

Timeframe 

(Months 

from receipt 

of DCI) 

850.1010 Freshwater invertebrate acute toxicity TGAI 

(EHE) 12 

850.10254 Acute toxicity estuarine and marine 

organisms (oyster shell growth) 

TGAI (acid or 

DMAS5, and 

EHE) 

12 

850.10354 Acute toxicity estuarine and marine 

organisms (mysid) 

TGAI 

(acid or 

DMAS5

, and 

EHE) 

12 

850.1075 Acute toxicity estuarine and marine fish 

TGAI 

(acid or 

DMAS5

, and 

EHE) 

12 

850.1300 Aquatic invertebrate life cycle (freshwater) 

TGAI 

(acid or 

DMAS5) 

12 

850.1350 Aquatic invertebrates life cycle (saltwater) 

TGAI 

(acid or 

DMAS5) 

12 

850.14006 Fish early-life stage (freshwater and 

saltwater) 

TGAI 

(acid or 

DMAS5) 

12 

850.2100 Avian oral toxicity (passerine species) TGAI 12 

850.2300 Avian reproduction (upland game and 

waterfowl species) TGAI 24 

850.4100 Terrestrial plant toxicity, seedling emergence TEP 

(EHE)7 12 

850.4150 Terrestrial plant toxicity, vegetative vigor

TEP 

(DMAS and 

EHE8) 

12 

 

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 Data are required on one estuarine/marine mollusk and one estuarine/marine invertebrate. The DCI will provide 

that Guidelines 850.1045 and 850.1055 may be conducted in lieu of Guidelines 850.1025 and 850.1035. 

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 The DCI will provide that the test material be either 2,4-DP-p acid technical grade active ingredient (TGAI) or 2, 

4-DP-p DMAS TGAI. Data on the 2,4-DP-p EHE TGAI are also expected to be required. 

6

 Data are anticipated to be needed on both a freshwater and saltwater species. 7

 Data are required for 2,4-DP-p EHE for soybean. 

8

 Data are required for both 2,4-DP-p DMAS and EHE. For 2,4-DP-p EHE, data are required for soybean only. 
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Table 1: Planned Data Needs for the 2,4-DP-p Registration Review 

Guideline 

Number2 Study Title1 

Test Material 

Estimated 

Timeframe 

(Months 

from receipt 

of DCI) 

850.4500 Algal toxicity TGAI 

(EHE)9 12 

850.6100 

Environmental chemistry methods and 

associated independent laboratory validations 

for water 

TGAI 12 

870.3465

10 90-day inhalation toxicity TGAI 12 

NONGDLN11Pollinator acute oral toxicity (honeybee 

larvae) TGAI 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 2,4-DP-p. For human health, EPA 

will need to conduct revised dietary (drinking water only), residential, and occupational 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 and HED Scoping Document and the planned assessments have not 

changed from what was included in the PWP. 

 

9

 Data are required for 2,4-DP-p EHE for the freshwater diatom. 

10 For the inhalation toxicity study, an acceptable test of 28 days duration is expected to be sufficient to satisfy this 

data requirement. 

11 Refer to OECD 237 honey bee larval toxicity test for guidance. 
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Table 2: Planned Risk Assessments for the 2,4-DP-p Registration Review 

Type of Risk Assessment Conduct? Notes 

Ecological and Environmental Fate 

Comprehensive ecological 

(species to be assessed 

include terrestrial and aquatic 

organisms), including 

endangered species 

Y 

Incidents Will check for 

updates 

For a discussion of reported ecological incidents for 

2,4-DP-p, see page 13 of the Problem Formulation. 

Human Health 

Dietary 

Food N 2,4-DP-p is not currently registered for use on food or 

feed. 

Drinking water Y Updated dietary risk assessments may be needed 

during registration review to consider newly 

estimated drinking water concentrations and/or 

changes in the toxicological endpoints. 

Occupational 

Handlers (mixers, loaders, 

applicators) 

Y Updated occupational exposure assessment may be 

needed during registration review to consider new 

exposure estimates based on current science policies 

or if there are changes in the toxicological endpoints. 

Post-application N There is no evidence of systemic toxicity from dermal 

exposure. Appropriate re-entry intervals (REIs) are 

currently on product labels, thus significant dermal 

exposure from recently treated areas is not 

anticipated. 

Residential 

Handlers Y Updated residential exposure assessments may be 

needed during registration review to consider new 

exposure estimates based on current science policies 

or if there are changes in the toxicological endpoints. 

Post-application Y 

Other 

Aggregate Y Evaluates the combined risk from dietary (water) and 

residential exposures. 

Cumulative N 2,4-DP-p has not been identified as a member of a 

cumulative group that shares a common mechanism 

of toxicity. 

Tolerances N Tolerances are not established for 2,4-DP-p since it is 

not registered for use on food or feed at this time. 
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Table 2: Planned Risk Assessments for the 2,4-DP-p Registration Review

Human Health 

Other 

Incidents Will check for 

updates 

For a discussion of reported human incidents for 2,4-

DP-p, see page 10 of the Scoping Document and the 

Dichlorprop, 2,4-DP-p, 2,4-DP-p, amine salt, 

Dimethylamine-2-(2,4-dichlorophenoxy) propionate, 

Isooctyl 2-(2,4-dichlorphenoxy)propionate,Propionic 

acid, 2-(2,4 dichlorophenoxy)-, 2-ethylhexyl ester, and 

2,4-DP-p, 2-ethylhexyl ester: Tier I Review of Human 

Incidents.

TIMELINE

EPA has created the following estimated timeline for the completion of the 2,4-DP-p registration 

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

Table 3: Registration Review for 2,4-DP-p – Projected Registration Review Timeline

Activities Estimated Date

Opening the Docket

Open Docket and 60-day Public Comment Period Dec. 2013 – Completed

Close Public Comment Feb. 2014 – Completed

Case Development

Final Work Plan May 2014 – Completed

Issue DCI 2014: July – Sept. 

Data Submission 2016: July – Sept.

60-day Public Comment Period for Draft Risk 

Assessments[12]

2018: Jan. - March

Registration Review Decision

60-day Public Comment Period for Proposed Registration 

Review Decision

2018: Oct. – Dec. 

Registration Review Decision and Begin Post-Decision 

Follow-up

2019

Total (years) 6

NEXT STEPS 

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

and human health studies for 2,4-DP-p through a Data Call-In Notice, expected to be issued in 

August 2014. 

 

[12] 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.