United States
Environmental Protection
Agency
Prevention, Pesticides
And Toxic Substances
(7508C)
EPA-738-F-00-007
September, 2000
R.E.D. FACTS
Pesticide
Reregistration
Diclofop-Methyl
All pesticides sold or distributed in the United States must be registered by
EPA, 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 reregistration, 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 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 reregisters pesticides that meet the safety standard of
the FQPA and can be used without posing unreasonable risks to human health or
the environment.
When a pesticide is eligible for reregistration, EPA explains the basis for its
decision in a Reregistration Eligibility Decision (RED) document. This fact sheet
summarizes the information in the RED document for reregistration case 2160,
Diclofop-Methyl.
Use Profile Diclofop-methyl is a restricted use herbicide used on wheat, barley, and golf
courses (turf). Diclofop-methyl controls or suppresses various grass weed species.
The total annual domestic usage of diclofop-methyl is approximately 750,000
pounds of active ingredient (a.L).
Regulatory Diclofop-methyl was first registered in the United States in 1982 for the
History control or suppression of wild oats and annual grasses in wheat and barley. It is
currently also registered for goose grass control on established golf courses. The
use of diclofop-methyl on golf courses is authorized under Section 24(c) of FIFRA
in 11 states.
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Human Health
Assessment
Toxicity
Toxicity Categories, which range from 1 (most toxic) to 4 (least toxic),
placed diclofop-methyl in toxicity category n for the oral route of exposure, HI by
the dermal route, and IV via the inhalation route. In primary irritation studies,
diclofop-methyl produced moderate eye irritation (toxicity category HI) and slight
dermal irritation (toxicity category IV).
Diclofop-methyl is classified as a likely human carcinogen based on
laboratory studies in the rat and the mouse. The Agency used a linear low-dose
approach (Q*) to assess cancer risk to diclofop-methyl.
Dietary Exposure (food and water)
EPA's human health risk assessment for diclofop-methyl indicates few risk
concerns. Food risks, as measured by both an acute and chronic Population
Adjusted Doses (PAD), are well below the Agency's level of concern. When
considering the carcinogenic potential of diclofop-methyl, the dietary (food) risk
appears to be slightly above the level of concern
(1.2 x 10"6). Even though this cancer risk is slightly over the level of concern (10"6),
the Agency believes this overestimates the actual carcinogenic exposure to
diclofop-methyl in the food supply. Drinking water risk estimates are based on
surface and groundwater screening models. Limited monitoring data and a small
scale prospective ground water (PGW) study also support the conclusion that
diclofop-methyl is not likely to be found in drinking water. Drinking water risks are,
therefore, not of concern to the Agency.
Non-Occupational Risks (Golfers)
The only non-occupational source of exposure to diclofop-methyl is residues
on treated golf courses. Cancer risk for golfers is 2.2 x 10"6. The Agency believes
that the cancer risks associated with golfers on diclofop-methyl treated turf is an
upper-bound estimate since the post-application risk assessment is based on
protective assumptions related to golfer behavior and diclofop-methyl use practices.
The risk is overestimated because the Agency assumes the golfer is exposed
continuously during a round of golf (four hours, assuming the entire course is
treated), two days per year, for 50 years. But because diclofop-methyl is usually
applied as a spot treatment covering less than the entire course, the golfer would be
exposed for a much shorter duration. A more likely duration of exposure is
probably /^ hour rather than four hours. With /^ hour of exposure, the resulting
cancer risk would be 2.7xlO"7 and would not be of concern to the Agency. The
odds of a golfer encountering diclofop-methyl treatment twice a year for a lifetime is
also unlikely. The Agency is therefore not concerned with cancer risks to golfers
exposed to residues of diclofop-methyl on treated turf.
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Aggregate Risk
Under the Food Quality Protection Act, the Agency considers contributions
to risk from various exposure sources, specifically food, drinking water, and non-
occupational sources (e.g., golfers playing on treated courses). Four aggregate risk
assessments were calculated for diclofop-methyl.
The short-and intermediate term as well as the chronic (non-cancer)
aggregate are not of concern to the Agency. Although the cancer aggregate risk
appears to be of concern, the Agency does not believe that exposure to residues of
diclofop-methyl in food and drinking water contribute to an aggregate risk of
concern for the general population. The food cancer risk is based on a number of
protective exposure assumptions and the water cancer risk is based on screening
level modeling estimates.
Golfers who play on diclofop-methyl treated courses may be at a greater
aggregate cancer risk because the carcinogenic risk to golfers is
2.2 x 10"6. Any aggregation of carcinogenic exposure to golfers with carcinogenic
exposure from food and drinking water would ordinarily increase the risk further
above the level of concern. In this case, golfer exposure to diclofop-methyl is
probably much less than the assessment indicates. Because the cancer risk estimate
to golfers is based on high-end assumptions and may possibly overestimate risk,
aggregation with food and drinking water estimates does not result in a meaningful
estimate of aggregate carcinogenic risk. Overall, the Agency concludes that there is
neither an aggregate carcinogenic concern for the general population nor for golfers
who play on diclofop-methyl treated courses.
Tolerances
Tolerances (refer to 40#CFR §180.385) or maximum residue limits are
summarized below
• Revoke 2 tolerances for lentils and dry peas. The registrant no longer
supports these commodities.
• Establish 23 tolerances for the following: Barley hay, wheat forage, and
wheat hay. Tolerances will also be established for the following: cattle fat,
cattle meat, cattle meat byproducts (excluding kidney), cattle kidney, goat
fat, goat meat, goat meat byproducts (excluding kidney), goat kidney, hog
fat, hog meat byproducts (excluding kidney), hog kidney, horse fat, horse
meat, horse meat byproducts (excluding kidney), horse kidney, milk, sheep
fat, sheep meat, sheep meat byproducts (excluding kidney), and sheep
kidney.
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Occupational and Residential Exposure
The most significant human risk concern relates to handlers who mix, load,
and apply diclofop-methyl to agricultural sites. Non-cancer risks do not exceed the
Agency's level of concern. However, cancer risks associated with the use of
diclofop-methyl are of concern to the Agency. Cancer risk for handlers
incorporating both dermal and inhalation exposure range from 1.4xlO"2 to S.lxlO"6
without the use of personal protective equipment, 8.4xlO"5 to 6.0xlO"7 with PPE,
and 5.8xlO"5 to 1.4xlO"6 at the engineering controls level. The Agency's goal is to
reduce worker cancer risks to 10"6 or less, although risks somewhat higher than 10"
6 may be considered acceptable if measures to mitigate these risks are not available
and benefits of continuing use are demonstrated. Thus, for risks that are greater
than 10"6 and less than 10"4, the Agency carefully examines risks in this range
including the benefits of use, availability of alternatives, number of workers at risk,
and will seek ways to further mitigate these risks. Because all of the worker
scenarios described in Section in have cancer risk estimates in the range of 10"6 to
10"4, the Agency considered whether additional worker mitigation measures were
available.
FQPA Considerations
The FQPA Safety Factor is intended to provide up to an additional 10-fold
safety factor (10X), to protect for special sensitivity in infants and children to
specific pesticide residues in food or to compensate for an incomplete database.
The Agency reduced the FQPA Safety Factor to IX after evaluating the hazard
and exposure data for diclofop-methyl. The FQPA Safety Factor was reduced to
IX for the following reasons:
1. The toxicology database is complete for the assessment of the effects
following in utero and/or postnatal exposure to diclofop-methyl;
2. There is no indication of quantitative or qualitative increased susceptibility of
rats or rabbits to in utero and/or postnatal exposure to diclofop-methyl in the
available toxicity data;
3. The Agency determined that a developmental neurotoxicity study is not
required for diclofop-methyl; and
4. Adequate monitoring data, surrogate data, and/or modeling outputs are
available to satisfactorily assess dietary and non-occupational sources of
exposure and to provide a screening level drinking water exposure
assessment. The assumptions and models used in the assessments do not
underestimate the potential risk for infants and children.
Environmental Environmental Fate
Assessment Diclofop-methyl is not persistent in soil under aerobic conditions and has
very low persistence in anaerobic soil or water. The residues that do reach surface
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waters will likely be rapidly degraded by microbial metabolism. To better
understand the environmental fate and transport of diclofop-methyl and its free acid
metabolite in soil, soil water, and groundwater, a small scale prospective
groundwater (PGW) study was undertaken by the registrant. The results of the
PGW study indicated that neither diclofop-methyl or its acid degradate migrated to
the ground water during the two- plus- year study in a worst case scenario
application. When considering the existing environmental fate data, the Agency
concludes that diclofop-methyl is unlikely to reach surface and ground water.
Ecological Effects
The Agency has identified certain ecological risks of potential concern.
Although there are remaining uncertainties, diclofop-methyl poses a risk of
reproductive toxicity to mammals on an acute basis and may also pose a chronic
risk to mammals. Runoff and spray drift from diclofop-methyl pose a high risk to
nontarget grasses and sedges. Toxicity data are lacking for risks to aquatic plant
species and the Agency is requiring further studies to better characterize these risks.
Revised label language on reducing spray drift will help to reduce exposure to non-
target organisms.
Risk Mitigation
The Agency found that exposure to wheat and barley handlers could be
substantially reduced by employing appropriate engineering controls, such as closed
mixing/loading systems and enclosed application equipment. To minimize the
occupational cancer risk to such handlers, the registrant has agreed to implement
engineering controls to reduce exposure to all agricultural handlers.
Additional Data
Required
In addition to certain chemistry data requirements, EPA is requiring the
following additional generic studies for diclofop-melhyl to confirm its regulatory
assessments and conclusions:
Dermal Exposure (§ 875.2400)
• Foliar Dislodgeable Residue Dissipation (§ 875.2100)
• Bioaccumulation Study in Fish (§ 850.1730)
Aquatic Plant Toxicity (§ 850.4400 and 850.5400)
The Agency also is requiring product-specific data including product
chemistry and acute toxicity studies, revised Confidential Statements of Formula
(CSFs), and revised labeling for reregistation.
Product Labeling All diclofop-methyl end-use products must comply with EPA's current
Changes Rea uired pesticide product labeling requirements and with the specifications outlined in the
RED. For a comprehensive list of labeling requirements, please see Table 11 the
diclofop-methyl RED document.
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Regulatory
Conclusion
For More
Information
The Agency finds that the currently registered uses of diclofop-methyl are
eligible for reregistration, provided engineering controls for both aerial and
groundboom handlers are required for diclofop-methyl containing products and
reflected in product labeling,
The use of currently registered products containing diclofop-methyl in
accordance with approved labeling will not pose unreasonable risks or adverse
effects to humans or the environment. Therefore, all uses of these products are
eligible for reregistration.
Diclofop-methyl products will be reregistered once the required product-
specific data, revised Confidential Statements of Formula, and revised labeling are
received and accepted by EPA.
EPA is requesting public comments on the Reregistration Eligibility Decision
(RED) document for diclofop-methyl during a 60-day time period, as announced in
a Notice of Availability published in the Federal Register. To obtain a copy of the
RED document or to submit written comments, please contact the Pesticide
Docket, Public Information and Records Integrity Branch, Information Resources
and Services Division (7502C), Office of Pesticide Programs (OPP), US EPA,
Washington, DC 20460, telephone 703-305-5805.
Electronic copies of the RED and this fact sheet are available on the Internet.
See http://www.epa.gov/REDs.
Printed copies of the RED and fact sheet can be obtained from EPA's
National Service Center for Environmental Publications (EPA/NSCEP), PO Box
42419, Cincinnati, OH 45242-2419, telephone 1-800-490-9198; fax 513-489-
8695.
Following the comment period, the diclofop-methyl RED document also will
be available from the National Technical Information Service (NTIS), 5285 Port
Royal Road, Springfield, VA 22161, telephone 1-800-553-6847, or 703-605-
6000.
For more information about EPA's pesticide reregistration program, the
diclofop-methyl RED, or reregistration of individual products containing diclofop-
methyl, please contact the Special Review and Reregistration Division (7508C),
OPP, US EPA, Washington, DC 20460, telephone 703-308-8000.
For information about the health effects of pesticides, or for assistance in
recognizing and managing pesticide poisoning symptoms, please contact the
National Pesticide Telecommunications Network (NPTN). Call toll-free 1-800-
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. Their internet address is
ace.orst.edu/info/nptn.
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