Page 1 of 5 UNITED STA

TES ENVIRONMENTA L PROTECTION AGENCY WASHINGTON, D.C. 20460 OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION MEMORANDUM May 12 , 2010 SUBJECT: Diquat Dibromide: Human Health Risk Assessment for Section 3 Use on Canola PC Code: 032201 DP Barcode: 372014 Decision No .: 423144 Registration No. : 100
- 1061, 100
- 1062 Petition No.: 9F7639 Regulatory Action: Section 3 Registration Risk Assessment Type: Single Chemical Aggregate Case No.: 0288 T XR No.: NA CAS No.: 85
- 00
- 7 MRID No.: NA 40 CFR: 180. 226 FROM: Becky

Daiss , Biologist Risk Assessment Branch 4 , HED (7509 P ) THROUGH: Susan V. Hummel , Branch Senior Scientist

Risk Assessment Branch 4 , HED (7509 P ) TO: Bethany

Benbow , Risk Manager Reviewer Herbicide Branch Registration Division (750 5 P) This document provides Health Effects Division’s (HED’s) assessment of a Section 3 request for use of diquat dibromide on c anola
. HED recently completed a risk assessment f or a Section 18 Emergency Exemption for use of diquat dibromide on c anola grown in Oklahoma and Kentucky ( 1 2/09)
. The use requested for this Section 3 registration is essentially identical to that assessed for the Section 18 request. Since there is no change in anticipated residues and no changes in use patterns , no new risk assessment is needed. The Section 18 assessment concluded that available data were insufficient to support a permanent tolerance for canola. However , additional data have been submitted with this petition . The additional data supp ort a tolerance and conditional registration for use of diquat dibromide on c anola
. This assessment summarizes the new residue chemistry data submitted with this petition and provides HED’s determination that the submitted data support a tolerance and con ditional registration for use of diquat dibromide on c anola
. R isk assessments conducted for the Section 18 and for the Tolerance Reassessment Eligibility

Decision (TRED) issued in April 2002 provide supporting information for this assessment
. Supportin g Documents Risk Assessment for Section 18

– M. Doherty , D355407, 12/3/09 Risk Assessment for TRED

– B. Daiss, D 281366, 3/6/02 Residue Chemistry

Assessment

– B. Daiss, 372014, 5/12 /10Page 2 of 5

Background This assessment provides information to support an amend ed Section 3 registration for the use of diquat dibromide on canola . The risk assessment recently conducted for a Section 18 Emergency Exemption for use of diquat dibromide on c anola adequately addresses the dietary and occupational exposure and risk associ ated with the use requested for this Section 3 registration. Since there is no change in anticipated residues and no changes in use patterns , no new risk assessment is needed. The TRED conducted in April 2002 provides supporting information
. Use Profil e Diquat dibromide is a non
- selective contact herbicide, algicide, dessicant, and defoliant. As a herbicide/algicide, it is used to control aquatic and terrestrial weeds. It is used as a preharvest dessicant/defoliant to facilitate the harvest of potat oes and various crops grown for seed. Its largest use is as a dessicant on potatoes. Other minor food use applications include use as a dessicant on crops grown for seed that is used for feed, i.e., alfalfa, sorghum, soy bean, and clover. Additionally , u se of irrigation water containing residues of diquat may result in diquat residues in plants and livestock. Tolerances are established for residues of diquat dibromide in/on raw agricultural commodities as defined in 40 CFR §180.226. Non
- food use applications include use as a preharvest dessicant on carrot, radish and turnip grown for seed; as a post
harvest dessicant on cantaloupe, cucumber, pepper, squash, tomato, and watermelon; as a dessicant/defoliant for commercial greenhouses and nurseries, ornamental seed crops, and commercial and residential landscaping; and as an herbicide to control tree root intrusions in drainage sy stems. Diquat dibromide works as a dessicant by reacting with molecular oxygen to produce a superoxide anion in treated plants. The oxidative activity , which occurs subsequent to formation of the oxygen radicals, rapidly destroy s plant cell membranes. Diquat dibromide is formulated as a soluble concentrate and ready
- to - use liquid. As an herbicide/algicide used to control algae an d aquatic weeds, it is applied by direct pouring, hand
- held or mechanical sprayer, and injection below the water surface. As a terrestrial herbicide and crop dessicant/defoliant, it is applied by

hand
- held sprayer, aircraft, or ground equipment. Propo sed New Use Under PP#9 F7639 , Sy

ngenta Crop Protection Inc is supporting the use of diquat dibromide as a harvest aid / dessicant on canola
. Sy

ngenta has submitted the label Reglone Desiccant (EPA Reg. No. 100
- 1061 ) . Reglone Dessicant is a soluble concentrate containing 3.73 lbs diquat dibromide salt per gallon equivalent to 2 lb s diquat cation per gallon. An application rate of 0. 5 lb ai/A is proposed with a limit of one application per season. A 7 day pre harvest interval (PHI ) is required with harv est no later than 10 day s after application
. Ground or aerial application equipment is permitted.Page 3 of 5

Tolerance Recommendation There are no residue chemistry issues that would preclude establishing a tolerance and granting a conditional registration for the requested use of diquat dibromide or establishment of the following tolerances for residues of the diquat cation dibromide : Canola, seed
................................ ................................ ..................... 2.0 ppm Canola, meal
................................ ................................ .................... 6 .0 ppm The recommended tolerance on canola seed has been increased from the proposed 1 ppm tolerance to harmonize with Codex. The registration should be conditional based on the submission of the US field trial data being prepared by I R4 on preharvest dessicant use of diquat dibromide on canola. The current tolerance expression is adequate. Hazard Characterization The toxicity

data base is adequate to support the Section 3 request for a new use of diquat dibromide on canola . There are no residual uncertainties for pre
- and/or post natal toxicity
. There are no indicati ons in the available studies that organs associated with immune function, such as the thy

mus and spleen, are affected by diquat dibromide. Therefore, the default FQPA Safety Factor may

be removed. However, an immunotoxicity study ( 870.7800) is required. This is a new data requirement under 40 CFR Part 158 for registration of a pesticide (food and non
food uses). Residue Chemistry Residues in Crops Sy ngenta Crop Protection, Inc. has submitted field trial data for use of diquat dibromide as a preharve st dessicant on canola. In eight trials conducted in West Germany and six conducted in the United Kingdom, a 20% ai liquid formulation (Reglone 40) was applied to canola as a single 0.6 kg ai/ha (0.54 lb ai/A) application using various ty pes of spray

equi pment. Applications were made in spray volumes of 400
- 500 L/ha in the UK and 600 L/ha in West Germany , corresponding to an application concentration of 1
- 1.2 g ai/L. Applications did not include the use of an adjuvant. Treated samples of canola were har vested at 5
- 8 day s after treatment (DAT) from each West German site and at 7, 10
- 13, and 20 DAT from each UK site. The HED ChemSAC determined that the EU data would support the establishment of a tolerance of 1 ppm on canola seed and the conditional r egistration of diquat dibromide on canola as a harvest aid/desiccant. The tolerance on canola seed has been increased from 1 ppm to 2 ppm to harmonize with the Codex MRL , and a tolerance of 6 ppm is recommended for canola meal, based on a maximum theoreti cal concentration factor of 3X. HED is aware that IR
- 4 is currently conducting studies in the U.S. to support the preharvest desiccant use of diquat dibromide onPage 4 of 5

canola. Residues of diquat dibromide on canola grown in the U.S. are not expected to differ significantly

from residues reported in the EU studies, since harvest aid/desiccant applications are made late in the growing season with little time between application and harvest. I n addition, since the recommended tolerances for canola seed and meal h ave been increased by a factor of 2X to harmonize with Codex, there is little chance residues in the U.S. trials will exceed these tolerances. Nevertheless, since the IR
- 4 field work has already been completed and the study reports will be available in Ju ly , 2011, HED recommends that these studies be required as a condition of registration to confirm the recommended tolerance levels. Residues in Processed Foods A maximum theoretical concentration factor of 3X has been applied for the processed fraction canola meal. Residue data from field trials conducted in Germany demonstrated that diquat residues were not found in any of the oil samples. Therefo re no tolerance is needed for diquat residues on canola oil
. Analy tical Method Sy ngenta has proposed a n ew enforcement method for the determination of residues of diquat in crops, including oil seed crops , Analy tical Method Number RAM 272/02 “The Determination of Residues of Paraquat and Diquat in crops and Soil

– A High Performance Li quid Chromatographic Me thod.” Based on HED’s analy sis, the proposed analy tical method is classified as scientifically acceptable
. Dietary Assessment HED is recommending tolerance s of 2 ppm for canola seed and 6 ppm for canola meal in order to harmonize with the C odex m axi mum r esidue l imit (MRL )
. The dietary analy sis for the Section 18 Emergency

Exemption assessment assumed a canola seed tolerance of 1 ppm and a livestock dietary

burden calculated assuming diquat residues of 3 ppm on canola meal. HED recalculated the diet ary

burden for livestock commodities using 6 ppm on canola meal. Based on that analy sis, the current tolerances on livestock commodities are adequate and anticipated residues will not exceed those used in the dietary exposure assessment conducted for the Section 18. HED reassessed dietary exposure using a 2 ppm tolerance for canola seed. The increased tolerance did not change the results of the dietary assessment conducted for the Section 18
. Therefore a separate dietary exposure assessment is not requi red for th e Section 3 proposed new use analy sis. Data Requirements

- Submission of US field trial data being prepared by I R4 on preharvest dessicant use of diquat dibromide on canola is required.Page 5 of 5

- Data on length of storage of canola samples prior to analy sis from the W. German and UK trials should be submitted
. Although the length of storage prior to analy sis is unknown, based on the structure of diquat, residues in frozen storage are expected to be stable much longer than the 6 to 8 months for which storage stability data are available. Therefore, lack of data on length of storage is not expected to impact the risk assessment.

- An immunotoxicity ( 870.7800 ) study is required under the revised 40 CFR Part 158 Toxicology

Data Requirements.