United States Prevention, Pesticides April 25, 2002

Environmental Protection and Toxic Substances

 Agency (7508C)

Report of the Food

Quality Protection Act

(FQPA) Tolerance

Reassessment Progress

and Risk Management

Decision (TRED)

Diquat Dibromide 
2

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

OFFICE OF 

PREVENTION, PESTICIDES

AND TOXIC SUBSTANCES

April 25, 2002

CERTIFIED MAIL

Mr. Jerry Wells

Syngenta Crop Protection, Inc.

P.O. Box 18300

Greensboro, NC 27419-8300

Dear Mr. Wells:

This is the Environmental Protection Agency’s (hereafter referred to as EPA or the Agency)

“Report of FQPA Tolerance Reassessment Eligibility Decision (TRED) for diquat dibromide. A

Notice of Availability, soliciting public comment for a thirty day period will be published in the Federal

Register (FR) shortly. 

The Federal Food, Drug and Cosmetic Act (FFDCA), as amended, requires EPA to reassess

all the tolerances for registered chemicals in effect on or before the date of the enactment of the Food

Quality Protection Act (FQPA) in August of 1996 against the new safety standard adopted in the

FQPA. In reassessing these tolerances, the Agency must consider, among other things, aggregate risks

from non-occupational sources of pesticide exposure, whether there is increased susceptibility to infants

and children, and the cumulative effects of pesticides with a common mechanism of toxicity. The

tolerances are considered reassessed once the safety finding has been made. A reregistration eligibility

decision (RED) for diquat dibromide was completed in July 1995, prior to FQPA enactment. 

Therefore, it needed to be updated to reassess the tolerances under the FQPA standard.

The Agency has evaluated the dietary risk associated with diquat dibromide and has

determined that there is a reasonable certainty that no harm to any population subgroup will result from

aggregate exposure to diquat dibromide when considering dietary exposure and all other nonoccupational sources of pesticide exposure for which there is reliable information. Therefore, no

mitigation measures are needed, and the forty-four tolerances established for residues of diquat

dibromide in/on raw agricultural commodities are now considered reassessed as safe under section

408(q) of the FFDCA.
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FQPA requires that EPA consider “available information” concerning the cumulative effects of

a particular pesticide’s residues and “other substances that have a common mechanism of toxicity.” 

The reason for consideration of other substances is due to the possibility that low-level exposures to

multiple chemical substances that cause a common toxic effect by a common mechanism could lead to

the same adverse health effect, as would a higher level of exposure to any of the other substances

individually. EPA did not perform a cumulative risk assessment as part of this reregistration review of

diquat dibromide, because the Agency has not determined that there are any other chemical substances

that have a mechanism of toxicity common with that of diquat dibromide. If EPA identifies other

substances that share a common mechanism of toxicity with diquat dibromide, then a cumulative risk

assessment will be conducted that includes diquat dibromide once the final framework EPA will use for

conducting cumulative risk assessments is available. Further, EPA is in the process of developing

criteria for characterizing and testing endocrine disrupting chemicals and plans to implement an

Endocrine Disruptor Screening Program. Diquat dibromide will be reevaluated at that time and

additional studies may be required. 

The Agency’s human health findings for the pesticide diquat dibromide were discussed in a

closure conference call and are summarized in the enclosed chemical overview of the risk assessments. 

The risk assessments and other documents pertaining to the diquat dibromide tolerance reassessment

decision are listed at the end of this document and are available on the Internet at

http://www.epa.gov/pesticides/reregistration/diquat_dibromide.htm and the public docket for viewing.

The Codex Commission has established several maximum residue limits (MRLs) for residues of

diquat dibromide in/on various raw agricultural and processed commodities. The Codex MRLs are

expressed in terms of diquat dibromide per se. The Codex MRLs and the U.S. tolerances will be

incompatible when the U.S. tolerance expression for plant commodities is revised to include both

residues of diquat dibromide.

Tolerances are established for residues of diquat dibromide in/on raw agricultural commodities

as defined in 40 CFR 180.226. The tolerance reassessment for diquat dibromide recommends raising

tolerances for fat, meat byproducts, and meat for the following: cattle, goats, hogs, horses, poultry, and

sheep. The tolerance reassessment also recommends raising tolerances for avocados, cottonseed,

eggs, citrus fruits, small fruits, hops, fruiting vegetables, leafy vegetables, seed/pod vegetables, fish,

forage grasses, forage legumes and shellfish. 

New tolerance recommendations have been established for alfalfa seed, clover seed, sorghum

grain, soybean hulls and soybean seed. Table I summarizes EPA’s tolerance reassessment decision.
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Table I: Diquat Dibromide Tolerance Reassessment Summary.

Commodity Current Tolerance

(ppm)

Tolerance

Reassessment (ppm)

Comment/[Correct

Commodity Definition]

Tolerances Listed Under 40 CFR §180.226(a)

Cattle, fat 0.02 0.05 The established tolerance for

ruminant, swine and egg

commodities may be raised to

achieve compatibility with the

Codex MRL.

[Cattle, meat byproducts]

[Goat, meat byproducts]

[Hog, meat byproducts]

[Horse, meat byproducts]

Cattle, mbyp 0.02 0.05

Cattle, meat 0.02 0.05

Eggs 0.02 0.05

Goats, fat 0.02 0.05

Goats, mbyp 0.02 0.05

Goats, meat 0.02 0.05

Hogs, fat 0.02 0.05

Hogs, mbyp 0.02 0.05

Hogs, meat 0.02 0.05

Horses, fat 0.02 0.05

Horses, mbyp 0.02 0.05

Horses, meat 0.02 0.05

Milk 0.02 0.02

Potatoes 0.1 0.1 [Potato]

Poultry, fat 0.02 0.05 The established tolerance for

poultry fat, meat and meat

byproducts may be raised to

achieve compatibility with

Codex.

[Poultry, meat byproducts]

Poultry, mbyp 0.02 0.05

Poultry, meat 0.02 0.05

Sheep, fat 0.02 0.05 The established tolerance for

ruminant commodities may be

raised to achieve compatibility

with Codex.

[Sheep, meat byproducts]

Sheep, mbyp 0.02 0.05

Sheep, meat 0.02 0.05

Additional Tolerances That Need To Be Proposed Under 40 CFR §180.226(a)

Alfalfa seed None 3.0 [Alfalfa, seed]

Clover seed None 2.0 [Clover, seed]

Sorghum, grain None 2.0 [Sorghum, grain, grain]

Sorghum, grain, aspirated grain

fractions

None TBD [Aspirated grain fractions]

Soybean, seed None 0.2 [Soybean, seed]

Soybean, aspirated grain fractions None TBD [Aspirated grain fractions]
Commodity Current Tolerance

(ppm)

Tolerance

Reassessment (ppm)

Comment/[Correct

Commodity Definition]

5

Tolerances Listed Under 40 CFR §180.226(a)(2)(I) (Irrigation Uses)

Avocados 0.02 0.2 Higher tolerances are needed

based on available data.

[Avocado]

[Cotton, undelinted seed]

Cottonseed 0.02 0.2

Cucurbits 0.02 0.02 [Vegetable, cucurbit, group]

Fish 0.1 2.0 Higher tolerances are needed

based on available data.

Fruits, citrus 0.02 0.05 [Fruit, citrus, group]

Fruits, pome 0.02 0.02 [Fruit, pome, group]

Fruits, small 0.02 0.05 [Fruit, small and berry group]

Fruits, stone 0.02 0.02 [Fruit, stone, group]

Grain, crops 0.02 0.02 [Grain, cereal, group] and

[Grain, cereal, forage, fodder,

and straw, group]

Grasses, forage 0.1 0.2 [Grass, forage, fodder and

hay, group]

Hops 0.02 0.2 Higher tolerances are needed

based on available data.

[Hop, dried cones]

Legumes, forage 0.1 0.2 [Vegetable, foliage of legume,

group]

Nuts 0.02 0.02 [Nut, tree, group]

Shellfish 0.1 20 Higher tolerances are required

based on available data.

Sugarcane 0.02 0.2 Higher tolerances are required

based on available data.

Vegetables, fruiting 0.02 0.05 Higher tolerances are required

based on available data.

[Vegetable, fruiting, group]

Vegetables, leafy 0.02 0.05 Higher tolerances are required

based on available data.

[Vegetable, leafy, except

Brassica, group] and

[Vegetable, brassica, leafy,

group]

Vegetables, root crop 0.02 0.02 [Vegetable, root and tuber,

group]
Commodity Current Tolerance

(ppm)

Tolerance

Reassessment (ppm)

Comment/[Correct

Commodity Definition]

6

Vegetables, seed and pod 0.02 0.05 [Vegetable, seed and pod,

group]

Processed potatoes (including

potato chips)

0.5 0.5 Based on the 5.3x

concentration factor observed

in dried potato.[Expressed in

terms of potatoes,

granules/flakes at 0.50 ppm and

potato chips at 0.50 ppm.]

[Potato, chips]

[Potato, granules/flakes]

Processed potato waste 1.0 1.0 [Potato, processed potato

waste]

Tolerances Listed Under 40 CFR §180.226(a)(3)

Banana 0.05 0.05 Tolerance with no US

Registration / Banana

Coffee 0.05 0.05 Tolerance with no US

Registration / Coffee

Additional Tolerances That Need To Be Proposed

Soybean, hulls None 0.6 A tolerance is needed based

on a concentration factor of

-3x in soybean hulls.

[Soybean, hulls]
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Table II lists generic and/or product specific data requirements for this chemical. Note that you

will be sent a Federal Insecticide, Fungicide and Rodenticide Act (FIFRA) section 3(c)(2)(B) data callin (DCI) letter in a separate mailing.

Table II: Data Requirements.

Guideline

Number

Guideline Name Products

Required 

Comment

860.1200 Directions for Use All

860.1500 Magnitude of residue in plant

studies for sorghum and soybean

aspirated grain fractions.

The soybean processing data indicate that

residues of diquat dibromide concentrated

2.6x in soybean hulls processed from soybean

bearing detectable residues. No

concentration was observed in other soybean

processed fractions.

The sorghum processing data indicate that

residues of diquat dibromide concentrated 4x

in sorghum dry milling bran fraction

processed from sorghum bearing detectable

residues. Residue data are not needed for

flour at this time, since sorghum flour is used

exclusively in the U.S. as a component for

drywall, and not as either a human or animal

feed item. The Agency reserves the right to

require data if needed at a later date.

830.1700 Batch Analysis 100-1062 Due to presence of ethylene dibromide (EDB).

830.7050 UV/Visible Absorption 100-1062 Data will be used to satisfy requirement for

100-1062 and 100-1063.

If you have questions on this document, please contact the Chemical Review Manager, Tyler

Lane, at (703) 305-2737.

Sincerely,

/SIGNED 4-25-02/

Lois A. Rossi, Director

Special Review and 

 Reregistration Division

2 Enclosures:

Diquat Dibromide Overview (4/2/02).

Diquat Dibromide Summary (4/2/02).
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Relevant Documents:

1) Use Closure Memo. Tyler Lane (10/31/01).

2) HED Risk Assessment for Tolerance Reassessment Eligibility Document (TRED). 

B. Daiss (4/25/02, D281890).

3) Tier I Drinking Water and Aquatic Ecological Exposure Assessments for Diquat Dibromide. J

Breithaupt (3/5/02, D281199).