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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION

MEMORANDUM

Date: March 23, 2011

SUBJECT: 2,4-D and Dicamba: Petition for the Establishment of Tolerances on Teff; 

Request for Registration of Latigo (EPA Reg No. 5905-564) on Teff.

PC Codes: 030001 and 029801 DP Barcode: D383628 and D381877

Decision No.: 440785 and 439344 Registration No.: 5905-564

Petition No.: 0F7796 and 0E7779 Regulatory Action: Section 3 Registration

Risk Assessment Type: Human Health Risk 

Assessment

Case No.: NA

TXR No.: NA CAS No.: 94-75-7 and 1918-00-9

MRID No.: NA 40 CFR: §180.142 and §180.227

FROM: Christine Olinger, Risk Assessor

Risk Assessment Branch VII

Health Effects Division (7509P)

THROUGH: Michael Metzger, Branch Chief

Risk Assessment Branch VII

Health Effects Division (7509P)

TO: Laura Nollen

RIMUERB, Registration Division (7505P)

This document provides the Health Effects Division (HED) human health assessment for the 

proposed establishment of tolerances and registration of new uses of the herbicides 2,4-D and 

dicamba on teff.

Introduction

The Interregional Research Project #4 (IR-4) has requested registration of Latigo (EPA Reg No. 

5905-564; Helena Chemical Company) for use on teff. Latigo is an emulsifiable concentrate 

formulation containing 24.62% 2,4-D acid and 18.28% dicamba acid. It is currently registered 

for control of a wide spectrum of annual, biennial, and perennial broadleaf weeds and brush in 
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pastures, rangeland, and grass (hay, silage), wheat, sugarcane, Conservation Reserve Program 

land, general farmstead areas, and other non-food agricultural sites. 

The petitioner, IR-4, on behalf of the states of Oregon, Oklahoma, Montana and Idaho, also

requests the establishment of tolerances for the combined residues of the herbicide dicamba (3,6-

dichloro-o-anisic acid) and its metabolite 3,6-dichloro-5-hydroxy-o-anisinic acid in or on the 

food commodities shown below. 

Commodity Proposed Tolerance (ppm)

Teff, forage 90.0 

Teff, grain 6.0

Teff, straw 30.0

Teff, hay 40.0

Addtionally, IR-4, requests the establishment of tolerances for the combined residues of the 

herbicide, plant regulator, and fungicide 2,4-D (2,4-dichlorophenoxyacetic acid), both free and 

conjugated, determined as the acid, in or on the food commodities as shown below. 

Commodity Proposed Tolerance (ppm)

Teff, bran 4.0

Teff, forage 25.0 

Teff, grain 2.0

Teff, straw 50.0

2,4-Dichlorophenoxyacetic acid (2,4-D) is an alkylchlorophenoxy herbicide used to control a 

variety of broadleaf weeds. It may also occasionally be used as a plant growth regulator or 

fungicide. Dicamba (3,6-dichloro-o-anisic acid) is a selective benzoic acid herbicide registered 

for the control of certain broadleaf weeds and woody plants before their emergence. It is an 

auxin agonist that is readily translocated symplastically and apoplastically with accumulation in 

meristemic regions of the plant. Sensitive plants exhibit rapid uncontrolled growth characterized 

by twisting and curling of stems and petioles, stem elongation and swelling and leaf cupping. 

Proposed Use

Latigo may be applied at 0.75-1.25 pints/A (0.22-0.37 lbs 2,4-D acid/A; 0.17-0.28 lbs. dicamba 

acid/A). Ground (10-20 gallons spray/A) and aerial (3-10 gallons of water/A) applications may 

be made. Applications may be made to teff grass seed crops, teff grown for hay and silage 

(pastures, rangeland and grass), and teff grown as a small grain to produce gluten-free flour for 

human consumption. The pre-harvest interval (PHI) is 14 days, although treated grasses being 

harvested for dry hay or silage should not be harvested within 37 days of treatment. There is no 

waiting period between treatment and grazing of forage for non-lactating animals, although meat 

animals being finished for slaughter should not graze fields within 30 days of slaughter. 

Lactating animals should not be grazed within 7 days of treatment. The Restricted Entry Interval 

(REI) is 48 hours. 
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Toxicity Data and Endpoint Selection

2,4-D

In the most recent comprehensive risk assessment for 2,4-D (HED’s Revised Human Health Risk 

Assessment for the Reregistration Eligibility Decision (RED) Revised to Reflect Public 

Comments, Timothy Dole, 5/12/05), the toxicity database was considered complete except for 

the submission of a developmental neurotoxicity study (DNT) and a repeat 2-generation 

reproduction study. Additionally, 40 CFR Part 158 was recently (12/2007) modified to include 

the requirement for a neurotoxocity screening battery and an immunotoxicity study. The toxicity 

database for 2,4-D includes acceptable acute and subchronic neurotoxicity studies; therefore, the 

requirements for the neurotoxicity screening battery have been met. To address the other

deficiencies, the registrant submitted an F1-extended one generation toxicity study in rats (Linda 

Taylor, Ph.D., 12/10/2010; MRID No. 47972101). This study has been reviewed and found 

acceptable, and fulfills the requirements for all three outstanding toxicity studies. The toxicity 

studies submitted since the last comprehensive risk assessment will not result in any changes in 

risk assessment points of departure. However, since the database is now complete, the need for 

the 10X FQPA database uncertainty factor must be reevaluated. Since aggregate risks to 2,4-D 

are acceptable even with the factor retained, 2,4-D endpoints will not be reevaluated as part of 

this action. 

Dicamba

In the most recent comprehensive risk assessment for dicamba (“Dicamba: Human-Health Risk 

Assessment for Proposed Section 3 New Uses on Sweet Corn”, Mary Clock-Rust, 3/6/08), the 

toxicity database was considered complete. However, 40 CFR Part 158 was recently (12/2007) 

modified to include the requirement for a neurotoxocity screening battery and an immunotoxicity 

study. The toxicity database for dicamba includes acceptable acute and subchronic neurotoxicity 

studies; therefore, the requirements for the neurotoxicity screening battery have been met. An 

immunotoxicity has recently been submitted and is in review (MRID No. 48081601; D378374). 

A screening level review of this study indicates that no effects, including immunotoxic effects, 

were observed at the highest dose tested of approximately 307 mg/kgbw/day. This value is 

higher than the doses currently used for risk assessment; therefore, risk assessment endpoints 

will not change. The toxicity database is now complete, and a 10X FQPA database uncertainty 

factor is not required. A complete review of this immunotoxicity study is pending.

Residue Data

No teff residue data were submitted with this petition. Rather, the petitioner proposes that 

residues in teff will be similar to those in wheat and other cereal grains. The uses described for 

wheat (grown for grain, or wheat and other small grains grown for hay and silage) on the 

currently registered Latigo label are the same as the proposed use directions for teff. Therefore, 

since cereal grains including teff are morphologically and taxonomically similar, HED concludes 

that residues in teff agricultural commodities (grain, forage, silage, hay) will be similar to those 

in wheat and other cereal grains.
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Aggregate and Occupational Risks

Teff is not included in the CSFII (Continuing Survey of Food Intakes by Individuals). However, 

because it is used to make flour in a manner similar to wheat and other cereal grains, it will likely 

substitute in the diet for cereal grain foods which will contain similar residues of 2,4-D and 

dicamba; therefore, significant increase in dietary exposure to residues of either compound from 

consumption of teff-containing foods, as a result of Latigo use on teff, will not occur. 

Furthermore, residues of 2,4-D and dicamba in teff livestock feeds will be similar to those in 

other forages, hays, and silages for which Latigo is currently registered. Therefore, there would 

be no increase in the livestock dietary burden should teff be substituted in the livestock diet for 

other hays and silages; residues in meat, milk, poultry and eggs will remain the same. 

Since the use rate for teff is consistent with that for wheat and lower than for some other crops, 

increased exposures to individuals through drinking water is not expected. 

No changes to residential exposures will occur as a result of the subject uses.

HED concludes that the aggregate exposures and risks will not increase for either 2,4-D or 

dicamba as a result of the proposed use; aggregate risks will be the same as those estimated in

previous HED risk assessments (For dicamba see “Dicamba: Human-Health Risk Assessment for 

Proposed Section 3 New Uses on Sweet Corn”, Mary Clock-Rust, 3/6/08; for 2,4-D see 2,4-D. 

“HED’s Revised Human Health Risk Assessment for the Reregistration Eligibility Decision 

(RED) Revised to Reflect Public Comments”, Timothy Dole, 5/12/05). 

Since the use pattern for Latigo on teff is identical to those for wheat and other cereal grains, 

occupational risks will be the same as those for cereal grains, and are not of concern 

Adequacy of the Proposed Tolerances

Proposed tolerances for residues of 2,4-D and dicamba on teff commodities are identical in most 

cases to the tolerances for these chemicals on wheat commodities (see Table below). Since the 

use patterns on wheat and teff are the same, and since cereal grains including teff are 

morphologically and taxonomically similar, HED agrees that these tolerance levels are 

appropriate. In one instance, dicamba on teff grain, the proposed tolerance is consistent with the 

barley grain tolerance rather than the wheat grain tolerance. Since residue data are being 

translated generally from other cereal grains to teff, HED agrees that use of the higher tolerance 

for barley is acceptable to assure that the tolerance level isn’t exceeded. 

Commodity 2,4-D Dicamba

Proposed Teff 

Tolerance (ppm)

Current Wheat 

Tolerance (ppm)

Proposed Teff 

Tolerance (ppm)

Current Wheat 

Tolerance (ppm)

Teff, bran 4.0 4.0 NA NA

Teff, forage 25.0 25 90.0 90.0

Teff, grain 2.0 2.0 6.0 6.0 (barley rather 

than wheat grain; 

wheat grain = 2.0 
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Commodity 2,4-D Dicamba

Proposed Teff 

Tolerance (ppm)

Current Wheat 

Tolerance (ppm)

Proposed Teff 

Tolerance (ppm)

Current Wheat 

Tolerance (ppm)

ppm)

Teff, straw 50.0 50 30.0 30.0

Teff, hay NA NA 40.0 40.0

Conclusions

The toxicity databases for 2,4-D and dicamba are considered complete. Adequate residue data 

are available to support the proposed use on teff, translated from other cereal grains (wheat and 

barley) which have identical use patterns. There will be no increase in aggregate exposure or 

risk from food, drinking water, or residential sources as a result of the proposed use; aggregate 

risks are acceptable for both 2,4-D and dicamba based on the most recent comprehensive risk 

assessments for each compound. Occupational exposures and risks are not of concern. 

Therefore, HED has no objections to granting the proposed registration of Latigo on Teff, or 

establishing tolerances as described below.

The Petitioner should revise the proposed tolerances expressions for 2,4-D and dicamba, 

respectively, as follows:

Tolerances are established for residues of the herbicide, plant regulator, and fungicide 

2,4-D, including its metabolites and degradates, in or on the commodities in the table 

below. Compliance with the tolerance levels is to be determined by measuring residues 

of 2,4-D (2,4-dichlorophenoxyacetic acid), both free and conjugated, determined as the 

acid. 

Commodity Proposed Tolerance (ppm)

Teff, bran 4.0

Teff, forage 25.0 

Teff, grain 2.0

Teff, straw 50.0

Tolerances are established for the residues of the herbicide dicamba (3,6-dichloro-oanisic acid), including its metabolites and degradates, in or on the commodities in the 

table below. Compliance with the tolerance levels is to be determined by measuring

residues of dicamba (3,6-dichloro-o-anisic acid) and its metabolite 3,6-dichloro-5-

hydroxy-o-anisinic acid in or on the food commodities shown.

Commodity Proposed Tolerance (ppm)

Teff, forage 90.0 

Teff, grain 6.0

Teff, straw 30.0

Teff, hay 40.0