Docket Number: EPA-HQ-OPP-2009-0846 www.regulations.gov



## Diquat Dibromide Final Work Plan Registration Review May 2010DIQUAT DIBROMIDE FINAL WORK PLAN

Introduction :

This is the Environmental Protection Agency’s (EPA’s) Final Work Plan for the registration review of diquat dibromide. 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 diquat dibromide registration revi ew docket (EPA-HQ-OPP-2009-0846), and any other comments concerning the in itial 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 registra tion review program and will review each registered pesticide every 15 years to determin e whether it continues to meet the Federal Insecticide, Fungicide, and R odenticide Act (FIFRA) standard for registration. Changes in science, public policy, and pesticide use practices will occur over time. The registration review program is intended to ma ke sure that, as the ability to assess risk evolves and as policies and pract ices change, all registered pe sticides continue to meet the statutory standard. The public phase of registration review begins when the initial docket is opened for each case. Inform ation on this program is provided at: http://www.epa.gov/oppsrr d1/registration_review/

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Diquat dibromide (Case 0288) is a non-selectiv e contact algicide, defoliant, desiccant and herbicide. As an herbicide/algicide it is regi stered for use to contro l broadleaf and grassy weeds in non-crop (including resi dential) and aquatic areas. As a desiccant/defoliant, it is registered for use on seed crops and potatoes.

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 c oncerning these issues.

Risk Assessment and Data Needs :

The Agency will conduct a comprehensive ec ological risk assessment, including an endangered species assessment, and intends to update the existing human health risk assessments for all uses of diquat dibromide. The Agency will require data in order to conduct the planned human health and ecologica l risk assessments. Below is a summary of the ecological and human hea lth issues relevant to the registration review of diquat

dibromide:

3Ecological Risk:

• The most recent ecological assessment for diquat dibromide was completed in 1995 in support of the Diquat Dibromid e Reregistration Eligibility Decision (RED).

• The Agency has not conducted a risk assessment that supports a complete endangered species determination. The eco logical risk assessment planned during registration review will allow the Agency to determine whether diquat dibromide’s use has “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 Services (the Services), as appropriate.

• The Agency will require the following data in order to conduct the planned ecological risk assessment, including an endangered species assessment, for all

uses:

o OCSPP Guideline 850.1450 - Fish Early-Life Stage Toxicity (estuarine/marine)

o OCSPP Guideline 850.1350 - Aquatic Inve rtebrate Life Cycle Toxicity (estuarine/marine)

o Special Study - Chronic Toxicity of Estuarine and Marine Sediment associated contaminants with the Amphipod Leptocheirus plumulosa

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o Special Study - Toxicity and Bio accumulation of Sediment-associated

contaminants with Freshwater Invertebrates.

o OCSPP Guideline 850.4150 - Vegetative Vigor Tier II

o OCSPP Guideline 835.6100 (7) - Envir onmental Chemistry Analytical

Methods - soil

o OCSPP Guideline 835.6200 (7) - Envir onmental Chemistry Analytical

Methods - water

• Please refer to Registration Review - Preliminary Problem Formulation for the Ecological Risk Assessment of Diquat Dibromide (Revised) , dated April 20, 2010, located in the docket, for a detailed di scussion of the planned risk assessment

needs.

Human Health Risk:

• The most recent diquat dibromide dietar y, residential, and aggregate human health

assessments were conducted in 2002 in s upport of the diquat dibromide Tolerance Reassessment Progress and Risk Manage ment Decision (TRED). The most recent comprehensive occupational asse ssment was conducted in support of the 1995 RED. A subsequent analysis of pos t-application risk from diquat dibromide

4use was conducted in February, 2002 in res ponse to a request from a registrant to reduce personal protective equipment (PPE) and restricted entry interval (REI) label requirements.

• The Agency will update the existing asse ssments to reflect current methodologies for assessing combined dietary and dr inking water exposures. Additionally, magnitude of the residue studies (Gui deline 830.1500) for sorghum and soybean aspirated grain fractions we re specified as confirmato ry data in the TRED and were required in a 2005 Data Call-In (D CI) for diquat dibromide. These data remain outstanding. However, in a le tter dated November 10, 2009, the technical registrant submitted a request to volunt arily terminate uses for sorghum and soybean. The Agency approved the request in a Cancellation Order published in the Federal Register (EPA-HQ-OPP- 2009-0979; FRL-8820-1) on April 7, 2010. The Agency is in discussion with diquat dibromide registrants whose products

have these uses listed. Provided the uses for sorghum and soybean are voluntarily removed from all diquat dibromide product labels, the magnitude of the residue studies for sorghum and soybean aspira ted grain fractions will no longer be required.

• The Agency will revise the diquat dibromide residential exposure assessment to incorporate updated standard prot ocols and exposure assumptions.

• As revisions to the dietary (food and drinking water) and residential assessments are expected, the Agency will revise the aggregate exposure (dietary and residential) risk assessment to support the registration review of diquat dibromide.

• The Agency will conduct a new occupationa l risk assessment to reflect changes in assessment standards and assumptions that the Agency has adopted since the last occupational risk assessment conducted in support of the 1995 RED. The new occupational exposure and risk assessment will include an assessment of diquat dibromide use in sewer systems.

• The toxicity database is complete with the exception of the following study, which the Agency will be requiring in or der to conduct a complete human health

assessment:

o OCSPP Guideline 870.7800 Immunotoxicity

After the Agency has reviewed the additional toxicity data, the points of departure and safety factors for diquat dibrobmide will be reexamined.

In the Preliminary Work Plan

, the Agency had indicated that a subchronic neurotoxicity study would be required. However, the Agency received a comment suggesting an appropriate st udy may have already been submitted. After review, the Agency found the exis ting subchronic neurot oxicity study for

5diquat dibromide acceptable, satisfying th e guideline requirement for this study. The Agency will not require an additional study.

• Product chemistry data are requi red for the Syngenta 41.1% and 37.3% formulation intermediates (EPA Re g. Nos. 100-1062 and 100-1063) including:

o OCSPP Guideline 830.1550 Product identity and composition

o OCSPP Guideline 830.1600 Description of materials used to produce the product

o OCSPP Guideline 830.1620 Descrip tion of production process

o OCSPP Guideline 830.1670 Discussion of formation of impurities

o OCSPP Guideline 830.1700 Preliminary analysis

o OCSPP Guideline 830.1750 Certified limits

o OCSPP Guideline 830.1800 Enforcement analytical method

o OCSPP Guideline 830.6302 Color

o OCSPP Guideline 830.6303 Physical state

o OCSPP Guideline 830.6304 Odor

o OCSPP Guideline 830.6313 Stability to nor mal and elevated temperatures, metals, and metal ions

o OCSPP Guideline 830.6314 Oxidation/reduction: chemical incompatibility

o OCSPP Guideline 830.6315 Flammibility

o OCSPP Guideline 830.6316 Explodability

o OCSPP Guideline 830.6317 Storage stability

o OCSPP Guideline 830.6319 Miscibility

o OCSPP Guideline 830.6320 Corrosion characteristics

o OCSPP Guideline 830.7000 pH

o OCSPP Guideline 830.UV/Visible abso rption (EPA Reg. No. 100-1063)

o OCSPP Guideline 830.7100 Viscosity

o OCSPP Guideline 830.7200 Melting point/melting point range

o OCSPP Guideline 830.7220 Boiling point/boiling point range

o OCSPP Guideline 830.7300 Density/rel ative density/bulk density

o OCSPP Guideline 830.7370 Dissociation constants in water

o OCSPP Guideline 830.7550/7560/7570 Pa rtition coefficient (noctanol/water)

o OCSPP Guideline 830.7840/7860 Water solubility

o OCSPP Guideline 830.7950 Vapor pressure

• The tolerance expression in 40 CFR § 180.226 will be reviewed during registration review to ensure that it appropriately covers the metabolites and degradates of diquat dibromide and that it specifies the residues to be measured for each commodity. Any proposed revisions would be to the chemical description rather than the individual tolerance levels.

6• Please refer to Diquat dibromide: Human Health Risk Scoping Document in Support of Registration Review located in the docket, for a detailed discussion of the planned risk assessment needs for human health.

Endocrine Disruptor Screening Program :

As required under FFDCA section 408(p), EP A has developed the Endocrine Disruptor Screening Program (EDSP) to determine whet her 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 em ploys a two-tiered approach to making the statutorily required determinations. Tier 1 cons ists of a battery of 11 screening assays to identify the potential of a chemical substan ce to interact with th e estrogen, androgen, or thyroid (E, A, or T) hormona l 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 th e substance, and esta blish a quantitative relationship between the dose a nd the E, A, or T effect.

Between October 2009 and February 2010, EPA a nd issuing test orde rs/data call-ins for the first group of 67 chemicals, which contains 58 pesticide active i ngredients and 9 inert ingredients. This list of chemicals was selected based on the potential for human exposure through pathways such as food and wa ter, residential activity, and certain postapplication agricultural s cenarios. This list should not be construed as a list of known or likely endocrine disruptors.

Diquat dibromide is not among the group of 58 pesticide active ingredients on the initial

list to be screened under the EDSP. Under FFDCA sec. 408(p) the Agency must screen all pesticide chemicals. Accordingly, EPA anticipates issuing future EDSP orders/data call-ins for all registration review cases, including those for which EPA has already opened a registration review docket fo r a pesticide active ingredient.

For further information on the status of the ED SP, the policies and procedures, the list of 67 chemicals, the test guidelines and the Tier 1 screening battery, please visit our

website: http://www.epa.gov/endo/

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7Timeline :

EPA has created the following estimated ti meline for completion of the registration review for diquat dibromide.

Registration Review for Diquat Dibromide – Projected Registrati on Review Timeline

Activities Estimated Date Opening the docket Open Docket and Public Comment Period Completed

– Dec. 16, 2009

Close Public Comment Completed

– Feb.16, 2010 Case Development

Final Work Plan Completed

– May 2010

Issue DCI 2011 – Jan. - Mar.

Data Submission 2013 – Jan. - Mar. Open Public Comment Period for Draft Risk Assessments 2014 – July - Sept.

Close Public Comment Period 2014 – Oct. - Dec. Registration Review Decision Open Public Comment Period for Proposed Registration Review

Decision 2015 – Jan. – Mar.

Close Public Comment Period 2015 – April - June Registration Review Decision and Begin Post-Decision Follow-up 2015 Total (years) 6

Summary of Comments Received During Comment Period :

The diquat dibromide registration review docket was open for a 60-day comment period beginning on December 16, 2009. During the co mment period, multiple comments were received, which are summarized below. Comm ents that prompted a change in the work plan, or are not addressed by other response documents included in the diquat dibromide docket, have responses included below. Wh ile some comments did facilitate minor changes to the work plan, they did no t affect the timeline set out in the Preliminary Work

Plan . Further, this document makes final the work plan for the diquat dibromide registration review process.

Comments from Syngenta Crop Protection Inc. :

Syngenta Crop Protection, Inc. (Syngent a) submitted comments on both the Registration Review – Preliminary Problem Formulation for the Ecological Risk Assessment of Diquat Dibromide (USEPA 2009b) and the Diquat Dibromide: Human Health Risk Scoping Document in Support of Registration Review (USEPA 2009c) documents. Concerning ecological risk, Syngenta’s comm ents dealt with ecological assessment endpoints and Agency anticipated data gaps. Concerning human health risk, Syngenta’s comments dealt with the Agency’s intention to update the human hea lth risk assessments and Agency anticipated data gaps.

8Response :

Ecological Risk:

The Agency has revised the Registration Review – Prelimin ary Problem Formulation for the Ecological Risk Assessment of Diquat Dibromide document, dated November 5, 2009, to correct two species names which S yngenta’s comments correctly noted were misspelled: Cyprinodon variegatus and Pse udokirchneriella subcapitata . Additionally, the MRID number for a hydrolysis half-life study referenced for diquat dibromide was incorrect and has been corrected, as well as the actual half-life value. The fish bioconcentration factor (BCF) of ≤ 2.5X for non-edible fish portion (viscera) and the wholefish BCF (1.03) are now correctly listed as well.

Human Health Risk:

In the Preliminary Work Plan

, the Agency had indicated that a subchronic neurotoxicity study would be required. However, the Agency received a comment suggesting an appropriate study may have already been s ubmitted. After review, the Agency found the existing subchronic neurotoxicity study for diquat dibromide acceptable, satisfying the guideline requirement for this study. The Agency will not require an additional study.

Comments from Dr. Richard Geller :

Dr. Richard Geller submitted a comment concer ning the Agency’s current findings on the acute oral, dermal, and inhalation toxicity characteristics of diquat dibromide.

Response :

The incident data Dr. Geller submitted to support his assertions on the toxicity characteristics of diquat dibromide have been added to the Agency’s Incident Database System (IDS)

. The Agency will consider informati on in the IDS during development of the registration review human health risk assessments for diquat dibromide. Please refer

to the document Diquat Dibromide: Response to Comments on the Human Health Risk Scoping Document in Support of Registration Review , dated April 15, 2010, for the Agency’s complete evaluation of Dr. Geller’s comments.

Comments from Douglas Products and Packaging :

Douglas Products suggests the Agency treat diquat dibromide similarly with regard to risk assessment assumptions and personal prot ective equipment requirements as another active ingredient with registrations for se wer root control use, metam sodium.

910 Response :

The Agency plans to conduct a new occupati onal risk assessment for diquat dibromide. Although not stated explicitly in the Preliminary Work Plan , the new occupational risk assessment will include an assessment of sewer applications. The workplan has been revised to provide additional clarity.

Comments from FIFRA Endangered Species Task Force (FESTF) :

FESTF stated that its data on endangered species proximity contained in the FESTF Information Management System and NatureServe data submissions to the Agency (MRIDs 46325901, 46486301, and 47260101) “...fulfill the data requirements spelled out in Pesticide Registration Notice 2000-2 and provide the best available data necessary for the proximity analysis of Diquat dibromid e use and listed species locations.” FESTF stated that Syngenta Crop Protection is a cu rrent member of FESTF, and as such, is entitled to the FESTF data on federally- listed threatened and endangered species.

Response :

The Agency thanks FESTF for their comments, and will consider this information as it conducts the registration review risk assessments for diquat dibromide.

Availability of Additional Agency Responses to Public Comments :

Comments relevant to human health have been addressed by the Health Effects Division’s document, Diquat Dibromide: Response to comments on the Human Health Risk Scoping Document in Support of Registration Review

, dated April 15, 2010. Comments regarding the ecological fate or effects of diquat dibromide have been addressed by the Environmental Fate and Effects Division’s document, EFED Response to Public Comments for Diquat Dibr omide PF: Docket ID# EPA-HQ-OPP-2009-0846

, dated April 20, 2010. These documents are available in the diquat dibromide docket (EPA-HQ-OPP-2009-0846).

Next Steps :

The Agency plans to develop a Data Call-In No tice for this pesticide and plans to issue it in early 2011. This new information will be used to conduct risk assessments for diquat

dibromide uses.