United States
Environmental Protection
Agency
Prevention, Pesticides
And Toxic Substances
(7508C)
EPA-738-F-05-001
March 2005
R.E.D. FACTS
Pesticide
Reregistration
2,4-DB
All pesticides sold or distributed in the United States must be registered by
EPA (the Agency), based on scientific studies showing that they can be used without
posing unreasonable risks to people or the environment. Because of advances in
scientific knowledge, the law requires that pesticides, which were first registered
before November 1, 1984, be reregistered to ensure that they meet today's more
stringent standards.
In evaluating pesticides for reregi strati on, EPA obtains and reviews a
complete set of studies from pesticide producers, describing the human health and
environmental effects of each pesticide. To implement provisions of the Food
Quality Protection Act (FQPA) of 1996, EPA considers the special sensitivity of
infants and children to pesticides, as well as aggregate exposure of the public to
pesticide residues from all sources, and the cumulative effects of pesticides and other
compounds with common mechanisms of toxicity. The Agency develops any
mitigation measures or regulatory controls needed to effectively reduce each
pesticide's risks. EPA then registers pesticides that meet current health and safety
standards and can be used without posing unreasonable risks to human health or the
environment.
When a pesticide is eligible for reregi strati on, EPA explains the basis for its
decision with the Reregistration Eligibility Decision (RED) document. This fact
sheet summarizes the information in the RED document.
Use Profile
2,4-DB is manufactured as an acid (2,4-DB) and an amine salt (2,4-DB-
DMAS). 2,4-DB and 2,4-DB-DMAS are systemic herbicides used to control
broadleaf weeds in alfalfa, clover, peanuts, soybeans, peppermint, spearmint, and
birdsfoot trefoil. There are no registered residential uses. Approximately 375,000
pounds of 2,4-DB and 2,4-DB-DMAS are used annually. Applications are made
aerially or by ground equipment. There are six products containing 2,4-DB (four
technical products and two end-use-products) and 15 products containing 2,4-DB-
DMAS (one formulation intermediate and fourteen end-use-products). There is one
Section 24C Special Local Need registration for 2,4-DB-DMAS use on mint in Idaho.
All end-use product formulations are liquids.
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Regulatory
History
2,4-DB and 2,4-DB-DMAS have been registered for use on broadleaf weeds
since 1958.
EPA completed the tolerance reassessment for 2,4-DB and 2,4-DB-DMAS on
January 31, 2005. The Agency concluded that there is a reasonable certainly of no
harm to any population subgroup from aggregate exposure to 2,4-DB or 2,4-DB-
DMAS from dietary (food and water) exposure and all other non-occupational
sources for which there is reliable information.
Human Health
Assessment
Toxicity
Both 2,4-DB and 2,4-DB-DMAS are considered to have low acute toxicity,
with the exception of 2,4-DB-DMAS being a Toxicity Category I eye irritant
(Category I being the most severe). 2,4-DB is placed in the following acute Toxicity
Categories: oral III; dermal III; inhalation IV; eye irritation III; and, dermal irritation
IV. 2,4-DB-DMAS is placed in the following acute Toxicity Categories: oral III;
dermal III; inhalation IV; eye irritation I; and, dermal irritation IV. 2,4-DB and 2,4-
DB-DMAS are classified as "not likely to be a human carcinogen".
Dietary Risks
EPA determined that there is reasonable certainty that no harm to any
population subgroup will result from aggregate exposure to 2,4-DB or 2,4-DB-DMAS
when considering dietary (food and water) exposure. Both acute and chronic
exposures are below the Agency's level of concern. For acute dietary exposure, the
most sensitive group, females 13-49, was less than 1% of the acute Population
Adjusted Dose (aPAD). For chronic dietary exposure the general U.S. population
was less than 1% of the chronic Population Adjusted Dose (cPAD). Tolerance level
residues and 100% crop treated assumptions were used to determine the above acute
and chronic screening level risk estimates. 2,4-DB and 2,4-DB-DMAS are not
expected to accumulate in drinking water. Drinking water models showed that the
Estimated Drinking Water Concentrations (EDWCs) for ground water and surface
water are below the Agency's level of concern. Both the acute ground water EDWC
of 0.51 |ig/L and the acute surface water EDWC of 318.68 jig/L are less than the
acute drinking water level of concern (DWLOC) of 18,000 |ig/L for females 13-49.
In addition, both the chronic ground water EDWC of 209 |ig/L and the chronic
surface water EDWC of 72.40 |ig/L are below the chronic DWLOC of 290 |ig/L for
infants less than one year of age and 1,050 jig/L for the general population.
Therefore, exposure from drinking water is not of concern to the Agency.
Residential and Other Non-Occupational Risks
There are no registered residential uses for 2,4-DB and thus residential
exposure is not expected.
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FQPA Considerations
EPA has determined that there is a reasonable certainty that no harm to any
population subgroup will result from aggregate exposure to 2,4-DB and 2,4-DB-
DMAS when considering dietary (food and water) exposure and all other non-
occupational sources of pesticide exposure for which there is reliable information.
EPA did not perform a cumulative risk assessment as part of this reassessment
of 2,4-DB and 2,4-DB-DMAS because the Agency has not determined that there are
any other chemical substances that have a similar mechanism of toxicity.
Worker Risks
Occupational workers can be exposed to a pesticide through mixing, loading,
and/or applying a pesticide, or re-entering treated sites. Occupational handlers of 2,4-
DB and 2,4-DB-DMAS includes the following: individuals who mix, load, and/or
apply pesticides with aerial or ground equipment. Non-cancer risks for all of these
potentially exposed populations is measured by a Margin of Exposure (MOE) which
determines how close the occupational exposure comes to a No Observed Adverse
Effect Level (NOAEL) taken from an animal study. For 2,4-DB and 2,4-DB-DMAS,
MOEs greater than 100 do not exceed the Agency's level of concern. All short-term
and intermediate-term MOEs are not of concern to the Agency when applicators are
wearing baseline personal protective equipment (PPE) and mixers/loaders are
wearing baseline PPE and chemical resistant gloves. Post-application exposure to re-
entry workers is possible. Since 2,4-DB and 2,4-DB-DMAS are applied only once or
twice a season it is anticipated that exposure will be primarily short-term. No toxicity
endpoint for short-term dermal exposures was identified, therefore, short-term post-
application risks were not assessed. 2,4-DB-DMAS is a Toxicity Category I eye
irritant and protective eye-wear is required for early re-entry post-application
activities.
Environmental
Assessment
Ecological Fate
Available data indicates that 2,4-DB-DMAS rapidly dissociates in moist soils
and aquatic environments, therefore, ecological risks were only assessed for 2,4-DB.
In soil environments 2,4-DB dissipation is dependent on leaching and on oxidative
microbial-mediated degradation. 2,4-DB's metabolism half-life is 24.5 days in
mineral soils, and ranges from 6.3 - 17.2 days in aquatic environments. The primary
route of dissipation is transformation with the major transformation product being
2,4-D. 2,4-DB is not expected to bioaccumulate in the environment.
Ecological Risks
The ecological risk assessment shows that terrestrial plants are at the greatest
risk from 2,4-DB and 2,4-DB-DMAS applications. Potential effects to non-target
terrestrial plants are most likely to occur as a result of spray drift and runoff from
aerial and ground applications. All acute freshwater risk quotients (RQs) are not of
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concern to the Agency. The Agency is requiring additional studies to better
understand the potential risk to estuarine and marine invertebrates. The Agency is not
concerned with chronic risks to freshwater organisms. Both acute and chronic risks
to birds are not of concern to the Agency. Predicted residues from all uses of 2,4-DB
and 2,4-DB-DMAS are below the acute level of concern for mammals. No
mammalian chronic levels of concern were exceeded for scenarios when considering
one or two applications at average labeled rates and a default half-life of 35 days.
The risk assessment for threatened and endangered species indicates that 2,4-
DB and 2,4-DB-DMAS exceed the threatened and endangered species levels of
concern for the following use sites: freshwater fish (Texas alfalfa scenario); small
mammals feeding (soybean, alfalfa, and peanut scenarios); medium size mammals
(alfalfa); small and medium size birds (Texas alfalfa scenario); and, terrestrial plants
(at highest application rates). These findings are based solely on the Agency's
screening level assessment and do not constitute "may affect" findings under the
Endangered Species Act.
Risk Mitigation Dietary Risk
For all supported commodities, the acute and chronic dietary exposure
estimates (food and drinking water) are below the Agency's level of concern.
Therefore, no risk mitigation measures are required to address exposure to from food
and drinking water.
Occupational Risk
Currently, not all 2,4-DB and 2,4-DB-DMAS labels require mixers and
loaders wear chemical resistant gloves. Based on toxicity studies, the Agency is
requiring mixers and loaders to wear gloves made from chemically resistant material.
Because 2,4-DB-DMAS is a Toxicity Category I eye irritant, protective eyewear
should be worn by early re-entry workers and a re-entry interval of 48 hours will be
established for 2,4-DB-DMAS products.
Ecological Risk
The major contributing factor of risk associated with 2,4-DB and 2,4-DB-
DMAS is spray drift. To mitigate risk associated with spray drift, the registrant has
agreed to include droplet size restrictions on 2,4-DB and 2,4-DB-DMAS labels.
Labels must specify medium to coarse droplet size or a volume mean diameter of 300
microns or greater for spinning atomizer nozzles and prohibit fine sprays.
Additionally, for aerial applications, the boom length must not exceed 75% of the
wingspan or 90% of the rotor blade diameter to reduce spray drift. The Agency has
concluded that risks posed by 2,4-DB and 2,4-DB-DMAS to most mammalian, avian,
plant, and aquatic species will be substantially reduced by adhering to best
management practices for aerial applications.
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Additional Data
Required
Regulatory
Conclusion
The generic database supporting the reregi strati on of 2,4-DB and 2,4-DB-
DMAS has been reviewed and determined to be substantially complete. However,
the following additional data requirements have been identified by the Agency as
confirmatory and are listed below. Additionally, responses to outstanding data
requirements regarding spray drift and droplet size spectrum (OPPTS GLN 201-1) are
currently outstanding.
OPPTS GLN 850.4100/4500
OPPTS GLN 850.1075
OPPTS GLN 850.1025
Seedling Emergence and Vegetative
Vigor
Estuarine/Marine Fish Acute Toxicity
Estuarine/Marine Invertebrate Acute
Toxicity
The use of currently registered products containing 2,4-DB and 2,4-DB-
DMAS in accordance with approved labeling will not pose unreasonable risks or
adverse effects to humans or the environment if the risk mitigation measures and
label changes outlined in the RED are implemented. Therefore, all uses of these
products are eligible for reregi strati on. These products will be reregistered once the
required product specific data, confidential statements of formula (CSFs), and revised
labeling are received and accepted by EPA. Products which contain ingredients in
addition to 2,4-DB and 2,4-DB-DMAS will be reregistered when all of their other
active ingredients also are reregistered.
For More
Information
To obtain a copy of the 2,4-DB RED document, please contact the OPP Public
Docket (7502C), US EPA, Ariel Rios Building, 1200 Pennsylvania Avenue, NW,
Washington, DC 20460-0001, telephone: (703) 305-5805. Electronic copies of the
2,4-DB RED and all supporting documents are also available on the Agency's
electronic docket at http://www.epa.gov/edocket.
For more information about EPA's pesticide reregi strati on program or the 2,4-
DB RED, please contact the U.S. EPA, OPP, Special Review and Reregi strati on
Division (7508C), 1200 Pennsylvania Avenue, NW, Washington, DC 20460,
telephone (703) 308-8000.
For more information about the health effects of pesticides, or for assistance
in recognizing and managing pesticide poisoning symptoms, please contact the
National Pesticide Information Center (NPIC). Call toll-free (800) 858-7378, from
6:30 am to 4:30 pm Pacific Time, or 9:30 am to 7:30 pm Eastern Standard Time,
seven days a week. The NPIC internet address is http://www/npic.orst.edu.
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