Docket Number: EPA-HQ-OPP-2010-0228 

www.regulations.gov

Linuron Final Work Plan 

Registration Review 

December 2010 

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LINURON FINAL WORK PLAN 

Introduction: 

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

registration review of linuron. This work plan includes the expected registration review 

timeline. The work plan also addresses public comments received concerning the 

Preliminary Work Plan in the Summary Document, which was posted in the linuron 

registration review docket (EPA-HQ-OPP-2010-0228), and any other comments 

concerning the initial docket postings. The Summary Document provided information 

on what EPA knows about the pesticide and what additional risk analyses and data or 

information the Agency believes are needed to make a registration review decision. 

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 will 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 at: http://www.epa.gov/oppsrrd1/registration_review/. 

Linuron is an herbicide that is registered for use on certain terrestrial food and 

feed crops, and non-food and feed crops to control germinating and newly emerging 

grasses and broad-leafed weeds. Linuron is registered for use on asparagus, carrots, 

celery, corn (field and sweet), cotton, kenaf, lentils, parsley, parsnips, potato, sorghum, 

soybeans, and wheat. There are also registered uses on non-cropland (roadsides, 

fencerows, etc.), hybrid poplar plantations (pulpwood source) and ornamental bulbs. 

There are no registered residential uses. Linuron was first registered for use in the United 

States (U.S.) in 1966. 

Comments Received on Preliminary Work Plan: 

Multiple comments were received during the 60-day public comment period on 

the Preliminary Work Plan. These comments are summarized in this document and 

changes to the work plan set out in the Preliminary Work Plan are explained. In the 

Preliminary Work Plan, EPA also solicited comments on three specific topics: 

environmental justice, water body impairment, and trade irritants. No comments or 

information were received during the comment period concerning environmental justice, 

trade irritants, or water body impairment. However, several comments were received that 

change the anticipated data requirements for linuron. For further discussion on these 

comments please see the Summary of Comments and Agency Responses section below. 

Anticipated Risk Assessment and Data Needs:
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The Agency anticipates requiring data needed to conduct comprehensive human 

health and ecological risk assessments, including an endangered species assessment, for 

the uses of linuron.

Ecological Risk: 

• A screening-level environmental fate and ecological risk assessment for linuron 

was conducted in support of the 1995 Linuron Reregistration Eligibility Decision 

(RED). 

• The Agency anticipates conducting an updated environmental fate and ecological 

risk assessment for linuron, including an endangered species assessment, during 

registration review. 

• The Agency has not conducted a risk assessment that supports a complete 

endangered species determination for linuron. The ecological risk assessment 

planned during registration review will allow the Agency to determine whether 

linuron’s uses have “no effect” or “may affect” federally listed threatened or 

endangered species (listed species) or their designated critical habitats. When an 

assessment concludes that a pesticide’s use “may affect” a listed species or its 

designated critical habitat, the Agency will consult with the U.S. Fish and 

Wildlife Service and/or National Marine Fisheries Service (the Services), as 

appropriate. 

• The Agency has conducted risk assessments for linuron that support endangered 

species determinations for the California red-legged frog (CRLF) in 2008 as well 

as for Pacific salmon and steelhead in 2004. In the 2008 CRLF endangered 

species assessment, the Agency made a “likely to adversely affect” determination 

for both direct and indirect effects of registered uses of linuron in California to the 

threatened red-legged frog. In the 2004 endangered species assessment for 

threatened Pacific salmon and steelhead, the Agency made a “may affect but are 

not likely to adversely affect” finding for seven listed Pacific salmon and 

steelhead Evolutionarily Significant Units (ESU) and a “no effect” finding on the 

remaining nineteen ESUs. The Agency concluded that the endangered species 

Level of Concern (LOC) for registered uses of linuron was exceeded for aquatic 

invertebrates for all use sites and for freshwater fish for wheat, asparagus, and 

rights of way (ROW) uses. 

• EPA anticipates requiring the following guideline studies in order to conduct the 

planned environmental fate and ecological risk assessments during the registration 

review of linuron: 

o 835.4100 Aerobic soil metabolism 

o 835.4200 Anaerobic soil metabolism 

o 835.4300 Aerobic aquatic metabolism 

o 850.1350 Aquatic invertebrate life cycle (estuarine/marine) 
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o 850.1500 Fish full life cycle (freshwater) 

o 850.1790 Whole sediment: chronic invertebrates freshwater and marine 

examining survival, growth, and reproduction (Hyaella azteca, 

Chironomus dilutus or C. tentans, and Leptocheirus plumulosus are the 

required species) 

o 850.2100 Avian oral toxicity (Passerine only) 

o 850.4100 Seedling emergence, Tier II 

o 850.4150 Vegetative vigor, Tier II 

• Please refer to Registration Review – Preliminary Problem Formulation for 

Ecological Risk, Environmental Fate, and Endangered Species Assessments for 

Linuron (PC Code 035506; DP Barcode D375455), dated April 2, 2010, located 

in docket EPA-HQ-OPP-2010-0228 on the internet at www.regulations.gov, for a 

detailed discussion of the anticipated ecological risk assessment and data needs. 

Human Health Risk:

• Human health risk assessments for linuron were conducted in support of the 1995 

Linuron RED and the 2002 Linuron TRED. 

• The most recent human health risk assessment for linuron was conducted in 2008 

to support a Section 18 Emergency Exemption for use on lentils in Washington 

and Idaho. 

• A drinking water exposure assessment was conducted in 2001 for linuron use on 

carrots in California. A drinking water exposure assessment for three linuron 

metabolites was conducted in 2002, also in support of linuron use on carrots in 

California. 

 

• U.S. tolerances for linuron, located in 40 CFR 180.184, are currently expressed in 

terms of “linuron and its metabolites convertible to 3,4-dichloroaniline, calculated 

as linuron.” During registration review, the Agency anticipates revising the 

residue definitions for plant commodities and for livestock commodities to 

include linuron and certain metabolites, in conjunction with the development of 

an improved enforcement method that is compound specific and more sensitive. 

• Additional residue data for sweet corn have been submitted to the Agency in 

response to the linuron TRED Data Call-In (DCI). The Agency anticipates 

reviewing these studies during registration review. 

• The Agency anticipates conducting new occupational handler and occupational 

postapplication exposure risk assessments, including the establishment of a 

revised Re-Entry Interval (REI) consistent with current policies, during 

registration review. 
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• The Agency also anticipates conducting new drinking water and dietary (food and 

water) exposure risk assessments during registration review to incorporate new 

field trial data. In conjunction with a pending review of proposed new uses, the 

Agency anticipates conducting a new aggregate exposure risk assessment for 

linuron. 

• The toxicity database is complete with the exception of the following guideline 

studies, which the Agency anticipates requiring in order to conduct the planned 

human health risk assessments during the registration review of linuron: 

○ 870.3200 21/28-Day Dermal Toxicity

○ 870.3465 90-Day Inhalation Toxicity (only 28 days required)

○ 870.6200 Neurotoxicity Battery, Acute and Subchronic Studies

○ 870.7800 Immunotoxicity

• Please refer to Linuron: Human Health Assessment Scoping Document in Support 

of Registration Review, dated April 1, 2010, and the Linuron: Addendum to the 

Human Health Assessment Scoping Document in Support of Registration Review,

dated May 28, 2010 located in docket EPA-HQ-OPP-2019-0228 on the internet at 

www.regulations.gov, for a detailed discussion of the anticipated human health 

risk assessment and data needs. 

Other Anticipated Data Needs: 

• Guideline # 830.7050 UV/Visible Light Absorption – this study is a new data 

requirement under 40 CFR part 158 (Product Chemistry Data Requirements) for 

registration of a pesticide (food and non-food uses). The Agency anticipates 

requiring this study to obtain basic information about the compound’s 

identity/composition and the wavelengths at which the compound may be 

susceptible to photochemical degradation. 

Endocrine Disruptor Screening Program: 

As required under FFDCA section 408(p), EPA has developed the Endocrine 

Disruptor Screening Program (EDSP) to determine whether certain substances (including 

pesticide active and other ingredients) may have an effect in humans or wildlife similar to 

an effect produced by a “naturally occurring estrogen, or other such endocrine effects as 

the Administrator may designate.” The EDSP employs a two-tiered approach to making 

the statutorily required determinations. Tier 1 consists of a battery of 11 screening assays 

to identify the potential of a chemical substance to interact with the estrogen, androgen, 

or thyroid (E, A, or T) hormonal systems. Chemicals that go through Tier 1 screening 

and are found to have the potential to interact with E, A, or T hormonal systems will 

proceed to the next stage of the EDSP where EPA will determine which, if any, of the 

Tier 2 tests are necessary based on the available data. Tier 2 testing is designed to 

identify any adverse endocrine related effects caused by the substance, and establish a 

quantitative relationship between the dose and the E, A, or T effect. 
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Between October 2009 and February 2010, EPA issued test orders/data call-ins 

for the first group of 67 chemicals, which contains 58 pesticide active ingredients and 9 

inert ingredients. This list of chemicals was selected based on the potential for human 

exposure through pathways such as food and water, residential activity, and certain postapplication agricultural scenarios. This list should not be construed as a list of known or 

likely endocrine disruptors. 

Linuron is among the group of 58 pesticide active ingredients on the initial list to 

be screened under the EDSP. For information on the status of the orders issued under the 

EDSP for each chemical, please visit our website at http://www.epa.gov/endo/ and click 

on the "Status of EDSP Orders/DCIs" in the Highlights Box. Additional information on 

the EDSP, including the policies and procedures, the list of 67 chemicals, the test 

guidelines and the Tier 1 screening battery, can also be found at the EDSP website. 

Timeline: 

The projected timeline for the completion of the linuron registration review is 

presented in Table 1. 

Table 1. Projected Linuron Registration Review Timeline 

Activity Estimated Date 

Opening the docket 

Open Registration Review Docket and 

Open Public Comment Period 

 2010 June 

Close Public Comment 2010 August 

Case Development 

Develop Final Work Plan (FWP) 2010 December 

Issue Data Call-In (DCI) 2011 July – September 

Data Submission 2013 July – September 

Complete Preliminary Risk Assessments and 

Open Public Comment Period 

 2015 January – March 

Close Public Comment Period 2015 April – June 

Registration Review Decision 

Develop Proposed Registration Review Decision and 

Open Public Comment Period 

 2015 July – September 

Close Public Comment Period 2015 October – 

December 

Complete Final Registration Review Decision and 

Begin Post-Decision Follow-up 

 2016 

Total (years) 6 

Summary of Comments and Agency Responses: 

The linuron registration review docket was open for a 60-day comment period 

beginning on June 23, 2010. During the comment period, multiple comments were 

received. Some of the comments received prompted changes in the linuron work plan. 
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Comments received regarding data requirements and comments received that necessitated 

changes to the work plan are summarized below. Please see Linuron. Response to 

Public Comments on Registration Review Preliminary Workplan, dated October 1, 2010, 

and Response to Comments on the Registration Review – Preliminary Problem 

Formulation for Ecological Risk, Environmental Fate, and Endangered Species 

Assessments for Linuron, dated November 23, 2010, located in docket EPA-HQ-OPP2010-0228 on the internet at www.regulations.gov, for EPA’s responses to other 

comments received. 

This document finalizes the work plan for the linuron registration review process. 

Comments by the Physicians Committee for Responsible Medicine (PCRM) [EPA-HQOPP-2010-0228-0008]

Comment 1: PCRM would like EPA to use Organisation for Economic Co-operation and 

Development (OECD) guideline for acute avian oral toxicity, which is on the verge of 

adoption by OECD. 

Response 1: The Agency requires a toxicity test be conducted to estimate the acute oral 

LD50 of linuron to passerine species. PCRM recommends that the new OECD test 

guideline be used for this test because it uses considerably fewer animals than the 

traditional LD50 test described by Test Guideline 850.2100. The new OECD test 

guideline for measuring avian acute oral toxicity with a sequential dosing procedure is 

Test Guideline (TG) 223. Current policy within the Office of Pesticide 

Programs/Environmental Fate and Effects Division (EFED) regarding the acceptance of 

avian acute effects studies conducted using the TG 223 protocol states the following: 

Until the OECD TG 223 validation process is completed and the guideline has 

been approved by OECD, studies that utilize this guideline should not be 

classified; pending results of the validation, they may then be classified as 

‘acceptable,’ assuming that they meet all other guideline requirements. 

To date the OECD has adopted the TG 223 guideline and has issued a validation report. 

At this time, EFED is actively evaluating the results of the OECD validation report to 

determine if the TG 223 effects endpoints and dose/response information adequately 

address the purposes of the avian acute oral data requirement as described in 40 CFR Part 

158. Until the Agency has completed its evaluation of that validation report, EFED will 

not classify avian toxicity studies performed using the OECD TG 223 protocol and the 

studies cannot be used to fulfill OPP data requirements. Therefore, we cannot say at this 

time whether or not avian toxicity studies completed following TG 223 will be acceptable 

to meet our data requirements. 

Validation work conducted on TG 223 to date has been limited to studies with the upland 

game birds (e.g., northern bobwhite). Because to date this TG 223 has not been validated 

for passerine species, it is doubtful that we would accept studies done under this 
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guideline for fulfilling requirements for passerine acute toxicity data until additional 

validation work with passerines is completed. 

Comment 2: PCRM recommends that the Agency resolve residual uncertainties 

regarding the 21/28-day Dermal Toxicity study (GLN 870.3200) by in vitro or in vivo 

percutaneous means. 

Response 2: The Agency appreciates the expressed concern and agrees with PCRM that 

unnecessary animal sacrifice should be minimized. However, in vivo studies provide 

results for assessing the systemic effects in a living animal. Therefore, in vivo testing 

remains the Agency’s current criteria for testing and affirming dermal toxicity. 

Comment 3: PCRM would like clarification on the data requirement for inhalation 

toxicity based on a discrepancy in the anticipated data needs section of the Summary 

Document. 

Response 3: The Agency would like to clarify that, based on exposure duration, the 28- 

day inhalation study is the only study required, not a 90-day inhalation study or both 

studies. 

 

Comments by the FIFRA Endangered Species Task Force (FESTF) [EPA-HQ-OPP2010-0228-0008]

Comment 1: The FIFRA Endangered Species Task Force (FESTF) submitted a comment 

that the Agency should ensure any company who is a technical registrant for linuron, but 

not a member of the FESTF (or a company having met its data compensation obligations) 

provide a formal offer-to-pay to FESTF in conjunction with their support of the active 

ingredient. 

Response 1: The Agency thanks FESTF for its comment and will consider this 

information as it completes the endangered species assessment and makes its registration 

review decisions. 

Comments by Tessenderlo Kerley, Inc. (TKI) [EPA-HQ-OPP-2010-0228-0009] 

Comment 1: TKI provided information on the use and usage of linuron. 

Response 1: The Agency will ensure that the assessments conducted for the registration 

review of linuron will incorporate only currently registered use sites and formulations. 

The Agency thanks TKI for its assistance in clarifying that information. 

Comment 2: TKI submitted comments on the linuron SLUA and stated that linuron is not 

registered for use on almonds, cabbage, onions, oranges, green peas, sweet corn, and 

tomatoes. TKI believes the treatment information for these crops is incorrect. 
10

Response 2: The Agency updated the SLUA with new data and these crops continue to 

show up in the updated version, possibly due to factor(s) including, but not limited to, 

usage from when the crop(s) did appear on labels, illegal usage, experimental usage, 

misreporting, etc. In the updated SLUA, the Agency has marked these “currently-notregistered” crops with plus signs to denote that these crops, which do not appear to have 

section 7, special local needs, or section 18 registrations according to our records. Please 

refer to the updated SLUA, dated September 13, 2010, in the linuron docket. 

Comment 3: TKI submitted two attachments summarizing current approved and typical 

use patterns for linuron. In addition, TKI stated that linuron is not registered for use on 

sweet corn (see comment 2 above). 

Response 3: The Agency concurs with TKI about sweet corn use not being listed on an 

active linuron registration. The most current linuron label (66330-218) in question, dated 

September 23, 1999, does not have sweet corn listed on the product label. The Agency 

did not find any Section 18 registrations in a database review. 

 

Comment 4: TKI submitted a comment stating that there are no Section 3 linuron 

products currently registered for use on lentils. 

Response 4: The Agency concurs with TKI’s statement. However, there are multiple 

active linuron lentil Section 18 registrations for control of dog fennel and prickly lettuce 

in Idaho and Washington state. 

Comment 5: TKI commented on the use of the daphnid acute toxicity studies and the 

acute-to-chronic ratio (ACR) determination. TKI requests the Agency reconsider the use 

of the chronic daphnid study in conducting its risk assessments. Specifically, TKI 

believes the Agency’s approach to determining the acute-to-chronic ratio is flawed and 

that the Agency should disregard the earlier acute daphnid toxicity study.

Response 5: The Agency notes the following: 

• MRID 43996501 is an acceptable acute daphnid toxicological study that fulfills 

the guideline requirement for an acute freshwater invertebrate study 

• MRID 42153401 is an acceptable chronic daphnid toxicological study that fulfills 

the guideline requirement for a freshwater invertebrate life cycle test 

Because the daphnid acute toxicity study (MRID 00142932) is the most sensitive and 

scientifically sound endpoint, the acute EC50 from this study will continue to be used in 

the risk assessment. The Agency encourages TKI to submit any additional information or 

evidence addressing the quality parameters and/or test substance that could inform the 

linuron hazard database. 

The Agency has determined that although the daphnid life cycle toxicity study is an 

acceptable guideline study, it will not serve as the sole basis for establishing a chronic 

invertebrate endpoint for use in risk assessment because the chronic value (derived from 
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MRID 42153401) is inconsistent with the acute toxicity value (derived from MRID 

00142932) for daphnia. A new freshwater invertebrate lifecycle study is not requested. 

Comment 6: 

TKI believes the Agency should use the sheepshead minnow data (MRID 43996502) for 

freshwater early lifestage instead of surrogate phenylurea herbicide data, and that there is 

no difference between fresh and saltwater species for risk assessment purposes. 

Response 6: 

The Agency believes the weight of evidence shows there may be differences between 

saltwater fish and freshwater fish species based on acute LC50 data from freshwater and 

saltwater fish. The Agency used surrogate phenylurea herbicide data for risk assessment 

purposes instead of sheepshead minnow data (MRID 43996502) because of the low 

number of replicates in the study. Other available data are insufficient for risk assessment 

purposes. If acceptable chronic aquatic toxicological data for linuron are submitted, the 

Agency may reconsider this approach. 

Comment 7: TKI submitted comments on the majority of the studies proposed to be 

required in the linuron registration review data call-in. 

Response 7: A summary of TKI’s comments and EPA’s responses is presented below in 

Table 3. 

Table 3. Summary of TKI Comments on Anticipated Linuron Data Requirements 

and EPA Response 

Guideline Number TKI Comment EPA Response 

830.7050 UV/Visible 

light absorption 

TKI states that DuPont previously 

submitted a study to satisfy this 

data requirement and requests that 

the Agency review this study prior 

to issuing a DCI for these data. 

The Agency thanks TKI for the 

comment and will review the submitted 

study to address the study acceptability 

in fulfilling the current data requirement 

prior to issuing the DCI. 

835.1230 Leaching and 

adsorption/desorption 

The Agency did not require the 

submission of these data in the 

Summary Document although it 

was identified as a data gap in the 

Problem Formulation. TKI 

provided additional information on 

previously submitted studies. TKI 

believes these studies should 

provide EPA with the transport 

data it had previously requested in 

the linuron RED and mentioned 

again in the Preliminary Problem 

Formulation document and no 

further data should be required. 

The Agency has removed this data 

requirement from the linuron work plan 

based on the information submitted by 

TKI. A new leaching and 

adsorption/desorption study is no longer 

required based on a review of 

information submitted by TKI. 

835.2410 

Photodegradation in soil 

TKI provided additional 

information and calculations on 

two soil photodegradation studies 

previously submitted by DuPont. 

TKI believes the second study 

(MRID 4171701) fulfills the data 

The Agency has removed this data 

requirement from the linuron work plan. 

Based on submitted calculations, MRID 

40171701 is upgraded to acceptable and 

a new soil photodegradation study is no 

longer required based on calculations 
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requirement, should be used for 

the environmental fate, ecological, 

and endangered species risk 

assessments, and no additional 

data should be required. 

submitted by TKI. 

835.4100 Aerobic soil 

metabolism 

TKI commits to conducting a new 

aerobic soil metabolism study as 

requested by the Agency. 

Acknowledged. 

835.4200 Anaerobic soil 

metabolism 

TKI commits to conducting a new 

anaerobic soil metabolism study as 

requested by the Agency. 

Acknowledged. 

835.4300 Aerobic aquatic 

metabolism 

TKI commits to conducting a new 

aerobic aquatic metabolism study 

as requested by the Agency. 

Acknowledged. 

835.4400 Anaerobic 

aquatic metabolism 

TKI provided additional 

information on a study (MRID 

40142501) previously submitted 

by DuPont and requested that the 

Agency reconsider its requirement 

for a new study. TKI believes the 

existing study provides sufficient 

information to conduct a risk 

assessment. 

The Agency has removed this data 

requirement from the linuron work plan. 

The Agency concurs with TKI that 

MRID 40142501 provides sufficient 

information to characterize the soil 

mobility of linuron degradates and that a 

new anaerobic aquatic metabolism study 

is no longer required. 

835.6100 Terrestrial field 

dissipation 

TKI has reserved comment on this 

data requirement until the Agency 

completes a science review and 

rebuttal to information TKI 

submitted to the Agency in 

response to the 2004 linuron 

TRED. 

Acknowledged. 

850.1035 Estuarine/ 

marine invertebrate acute 

toxicity using TEP 

(Mysid is the preferred 

species) 

850.1055 

Estuarine/marine 

invertebrate acute toxicity 

using TEP (Eastern 

Oyster is the preferred 

species) 

TKI states that linuron is not 

expected to enter into 

marine/estuarine environments 

because its rights-of-way uses are 

very limited and linuron is not 

widely used in these areas. As 

such, TKI does not believe that 

acute toxicity to saltwater 

invertebrates is warranted. TKI 

intends on submitting additional, 

more detailed, information to the 

Agency addressing these data 

requirements in the near future. 

The Agency has removed these data 

requirements from the linuron work 

plan. The Agency concurs with TKI and 

these estuarine/marine invertebrate acute 

toxicity studies are no longer required 

because the maximum EECs do not 

trigger the TEP data requirement. 

850.1350 Aquatic 

invertebrate life cycle 

(estuarine/marine) 

TKI states the existing data for 

linuron do not indicate a 

significant difference in marine to 

freshwater sensitivity. TKI does 

not believe a new marine 

invertebrate study is warranted 

based on the additional 

information submitted for the 

chronic daphnid study. 

An estuarine/marine invertebrate life 

cycle study is needed because chronic 

exposure is likely to occur based on 

linuron’s Rights-Of-Way uses and 

linuron’s persistence in the environment. 

850.1400 Fish early life 

stage (freshwater) 

TKI agreed to conduct a new 

freshwater fish early life stage 

study as originally requested by 

A fish early life stage study on 

freshwater fish is no longer required. 

The Agency has removed this data 
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the Agency. requirement from the linuron work plan. 

850.1500 Fish full life 

cycle (freshwater & 

estuarine/marine) 

TKI does not believe there is 

sufficient evidence that marine 

species are more sensitive to 

linuron than freshwater species. 

TKI requests that the Agency 

reserve these data requirements 

until after the data from the 

freshwater fish early life stage 

toxicity study is complete. TKI 

intends on submitting additional, 

more detailed, information to the 

Agency addressing this 

requirement in the near future. 

The fish full life cycle studies 

(freshwater/estuarine/marine) are 

required. The Agency notes the acute 

data demonstrates toxicity differences 

between saltwater and freshwater fish 

species. The Agency needs these data to 

complete the planned risk assessments 

for linuron based on an evaluation of 

linuron’s use pattern, mobility, potential 

reproductive effects in fish and birds, 

and the EEC. 

850.1790 Whole 

sediment: chronic 

invertebrates freshwater 

and marine examining 

survival, growth, and 

reproduction (Hyaella 

azteca, Chironomus 

dilutus or C. tentans and, 

Leptocheirus plumulosus) 

TKI states that they do not believe 

that rights-of-way uses are of 

consequence and new information 

would not provide new 

information for the risk 

assessment. 

Based on the criteria in 40 CFR 158, the 

parameters in the acute daphnid, aerobic 

soil and aquatic metabolism studies 

trigger the need for the whole sediment 

chronic toxicity data. 

The Agency acknowledges that TKI 

plans to submit additional information to 

the Agency to address these study 

requirements. However, these studies 

remain as data requirements. 

850.2100 Avian oral 

toxicity (Passerine only) 

TKI commits to conducting a new 

avian oral toxicity (passerine 

species) study as requested by the 

Agency. 

Acknowledged. 

850.4100 Seedling 

emergence, Tier II 

TKI commits to conducting a new 

seedling emergence study as 

requested by the Agency. 

Acknowledged. 

850.4150 Vegetative 

vigor, Tier II 

TKI commits to conducting a new 

vegetative vigor study as requested 

by the Agency. 

Acknowledged. 

870.3200 21/28-Day 

dermal toxicity 

TKI commits to conducting a new 

21/28-Day dermal toxicity study as 

requested by the Agency. 

Acknowledged. 

870.3465 90-Day 

inhalation toxicity (only 

28 days required) 

TKI indicates that a 2-week 

inhalation study was previously 

submitted to EPA by DuPont. TKI 

acknowledges that the 2-week 

study does not contain all the 

testing parameters in the current 

subchronic inhalation toxicity 

study protocol, but believes this 

study provides adequate scientific 

information to conduct a risk 

assessment. 

The Agency is in the process of 

reviewing the 2-week inhalation study to 

determine whether the parameters are 

sufficient for the needs of the human 

health risk assessment. Until the Agency 

makes this determination, the 28-day 

inhalation toxicity study remains to be a 

data requirement. 

870.6200 Neurotoxicity 

battery, acute and 

subchronic studies 

TKI commits to satisfying these 

data requirements. 

Acknowledged. 

870.7800 Immunotoxicity TKI commits to conducting a new 

immunotoxicity study as requested 

by the Agency. 

Acknowledged. 
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Comment 8: TKI submitted a number of comments regarding the details of the toxicity 

values and/or concentrations in various EFED studies including: the freshwater fish acute 

toxicity study, the freshwater fish early life stage study, the acute estuarine/marine 

invertebrate study, freshwater diatom study, and the acute and chronic data referenced in 

Appendix B of the EFED “Preliminary Problem Formulation for Ecological Risk, 

Environmental Fate, and Endangered Species Assessments for Linuron (PC Code 

035506; DP Barcode D375455).” 

Response 8: Specific responses to each comment toxicity value/concentration have been 

addressed in detail in Linuron. Response to Public Comments on Registration Review 

Preliminary Workplan, dated October 1, 2010, and Response to Comments on the 

Registration Review – Preliminary Problem Formulation for Ecological Risk, 

Environmental Fate, and Endangered Species Assessments for Linuron, dated November 

23, 2010, located in docket EPA-HQ-OPP-2010-0228 on the internet at 

www.regulations.gov. 

Next Steps: 

The Agency plans to issue a DCI for linuron in 2011 for the data gaps listed under 

the Risk Assessment and Data Needs section of this document. The information received 

in response to this DCI will be used to conduct the planned human health, ecological, and 

endangered species risk assessments for linuron.