United States
Environmental Protection
Agency
Prevention, Pesticides
And Toxic Substances
(7508C)
EPA-738-F-05-002
September 2005
oEPA R.E.D FACTS
Pesticide
Reregistration
Dimethipin
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 (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 reregisters pesticides that meet current human health
and safety standards and can be used without posing unreasonable risks to human
health and 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 dimethipin (Chemical Code
Number: 118901).
DSC Profile Dimethipin is registered for use as a cotton growth regulator and desiccant. In
addition, it is an herbicide that is used post-emergence for selective control of weeds.
Dimethipin is registered for use on cotton and nonbearing apple nursery stock.
Annual domestic dimethipin usage is approximately 100,000 pounds. For
dimethipin, rates per application and rates per year are generally less than 0.31 Ibs
ai/A and 0.56 Ibs ai/A respectively. Dimethipin is used predominantly in Georgia,
Mississippi, and Alabama. Dimethipin is used alone and is also used as tank mix with
other plant growth regulating chemicals.
Regulatory Dimethipin has been registered in the United States since 1982. Several data
History call-ms (DCIs) have been issued for dimethipin. The Agency conducted a review of
the scientific data base underlying pesticide registrations and identified missing or
inadequate studies. Subsequent Data Call-Ins (DCIs) were issued in 1989, 1991, and
1995.
Human Health
Assessment
Toxicity
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In acute studies, dimethipin has moderate acute toxicity (Toxicity Category
II) via the oral and inhalation routes, and low (Toxicity Category HI) acute toxicity
via the dermal route of exposure. Dimethipin is not an eye or skin irritant, nor a
skin sensitizer.
In longer-term studies, dimethipin is toxic to the liver, kidneys, and lungs. In
rats, the lowest observed adverse effect levels (LOAELs) are based on decreased
body weight gains and body weight. The no observed adverse effect levels
(NOAELs) are based on cardiovascular toxicity in the gastrointestinal tract for
female rats and toxicity in the gastrointestinal tract for male rats.
Dimethipin has been classified as a Category C chemical, or possible human
carcinogen. However, a quantification of carcinogenic risk was not recommended,
based on the weight-of-evidence evaluation of available data.
There are no signs of neurotoxicity or developmental toxicity following
exposure to dimethipin.
Dietary Exposure and Risk
The dimethipin dietary risk assessment considered only chronic risks from
residues in food based on field trials because no acute endpoint was identified. The
chronic dietary (food) risk is estimated at less than 1% of the Chronic Population
Adjusted Dose (cPAD) for all population subgroups, and is not of concern.
The Agency estimates potential surface water and ground water pesticide
contamination using models and monitoring data. The maximum surface water
modeling concentration of 7.3 parts per billion (ppb), or micrograms per liter (ug/1),
was used to estimate the surface water EDWC. The ground water EDWC and
chronic drinking water exposure value is based on a ground water monitoring value of
99 ppb. Both the surface water and ground water EDWC values are below the
drinking water level of concern (DWLOCs) of 762 ppb for chronic exposure, and are
not of concern.
Aggregate Risk
An aggregate risk assessment looks at the combined risk from dietary
exposure (food and drinking water pathways), as well as exposures from non-
occupational sources (e.g., residential uses). Dimethipin has no residential uses, thus
the aggregate risk included food and water only. Additionally, there were no acute
endpoints identified therefore only chronic aggregate risk was calculated. The chronic
aggregate risk does not exceed the Agency's level of concern.
The DWLOC method was used to assess the aggregate risk of dimethipin. A
DWLOC is the portion of the chronic PAD (cPAD) remaining after estimated
dietary (food only) exposures have been subtracted and the remaining exposure has
been converted to a concentration (ug/liter or ppb). This concentration value
(DWLOC) represents the available or allowable exposure through drinking water.
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Chronic (non-cancer) aggregate risk. The chronic
DWLOCs range from 218 ppb to 762 ppb with the most sensitive population being
infants. The EDWCs, which range from 7.3 to 99 ppb, are less than the DWLOCs
which means that the risks are not of concern. In addition, the chronic aggregate
risks are not of concern because they are estimated at less than 1 percent of the
cPAD.
Occupational Exposure and Risk
Based on current use patterns, occupational handlers (mixers, loaders, and
applicators) may be exposed to dimethipin during normal use. The Agency identified
7 handler scenarios resulting from mixing/loading and applying dimethipin to crops.
For the occupational use of dimethipin, EPA is concerned with any MOE less than
100, which incorporates uncertainty factors of lOx for interspecies variation and lOx
for intraspecies variation.
The majority of short and intermediate term scenarios had inhalation MOEs
that exceeded the target of 100 with baseline PPE: no respirator, long sleeve shirt,
pants, shoes and socks. Aerial application requires a closed cockpit to achieve the
target MOE of 100. Long term worker exposure is not expected for dimethipin and
thus was not assessed. There are no post-application risks to workers because there
were no dermal endpoints identified.
FQPA Considerations
The Agency has concluded that the FQPA Safety Factor for dimethipin should
be reduced (equivalent to IX) based on a complete database for FQPA
consideration. The toxicity database for dimethipin includes acceptable
developmental and reproductive toxicity studies. Developmental toxicity studies were
conducted in rats and rabbits with no evidence of susceptibility. There is evidence of
decreased body weight and decreased body weight gains for females in the 2-
generation reproduction study in rats. There were no body weight changes for males.
After establishing developmental toxicity endpoints to be used in the risk
assessment with traditional uncertainty factors (lOx for interspecies variability and
lOx for intraspecies variability), the Agency has no residual concerns for the effects
seen in the developmental toxicity studies. Therefore, the 10X FQPA special safety
factor was reduced to IX.
Based on no evidence of developmental neurotoxicity, the Agency has
determined that a developmental neurotoxicity (DNT) study is not required for
dimethipin. The developmental and two generation reproduction studies were
complete. Therefore, the Agency determined that a database uncertainty factor
(UFDB) is not needed.
Tolerance Reassessment
The tolerances for dimethipin meet the FQPA safety standards for the U.S.
population and sensitive populations, including infants and children. There are
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seventeen tolerances that were reassessed in the dimethipin RED, and of these
seventeen 11 are proposed for revocation. The tolerances are for cotton seeds and
hulls, cattle, horse, goat, and sheep meat and byproducts, as well as the fat of horses,
goats, sheep, and cattle. EPA found that there is a reasonable certainty of no harm
to the general population and any subgroup from the use of dimethipin.
Environmental
Assessment
Environmental Fate
Dimethipin is persistent in most environmental conditions with biodegradation,
hydrolysis, and photolysis all occurring slowly. Half-lives for dimethipin range from a
few weeks to several months. Dimethipin is not expected to absorb in solids and
sediments, and thus has potential for leaching to groundwater or run-off to surface
water. Dimethipin does not bioaccumulate in aquatic organisms, and no major
degradates were identified in the environmental fate studies.
A complete database has been assembled for dimethipin. The dissipation of
dimethipin is dependent on the site-specific properties of the soil to which it is applied.
Data indicate that dimethipin is practically insoluble in water and stable to hydrolysis
and photolysis in soil. The aqueous photolysis half-lives are 60, 224, and 72 days at
pH levels of 5,7, and 9 respectively.
According to laboratory mobility studies, dimethipin is highly mobile in all soils.
Dimethipin has been detected in soil at depths of 90 cm below the soil surface.
Ecological Toxicity
Dimethipin is considered to be practically non-toxic to birds on an acute basis
with mortality as the endpoint. There is no chronic avian data thus chronic avian risk
cannot be precluded. Dimethipin is classified as moderately toxic to small mammals
on an acute oral basis with decreased body weight as the affected endpoint.
A honey bee acute toxicity study indicated that dimethipin is practically
non-toxic to the honey bee. There were no data available on terrestrial plants;
however, dimethipin is expected to be toxic to terrestrial plants as it is an herbicide.
Acute toxicity studies on dimethipin show that it is slightly toxic to aquatic
invertebrates, freshwater fish, and estuarine fish. In addition, dimethipin is acutely
toxic to freshwater plants.
Risks to Terrestrial and Aquatic Organisms
The Agency conducted a screening-level ecological risk assessment to
determine the potential impact of dimethipin use on non-target terrestrial and aquatic
organisms. The Agency used modeling to evaluate ecological risks for dimethipin.
The majority of ecological risk quotient (RQ) values do not exceed the
Agency's level of concern (LOG), with the following exceptions: for acute restricted
use, the RQ exceeds the LOG (0.2) for a 15g mammal feeding on short grass, and for
endangered species, the RQs for 15g mammals feeding on short grass, tall grass,
broadleaf plants, and small insects exceed the acute endangered risk LOG of 0.1.
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Risk
There was no mitigation needed for dimethipin as there are no human health
°f concern, and there were very few ecological risks of concern.
Additional Data EPA is requiring confirmatory data requirements for dimethipin. For a
complete listing of required studies with corresponding guideline number, see Section
V of the dimethipin RED document.
Ecological Data Requirements
EPA is requiring data on seedling germination and seedling emergence (Tier II) and a
vegetative vigor (Tier II) study. In addition, avian reproduction tests, early-life stage
freshwater fish, and fish life cycle studies must be submitted to fulfill guideline
requirements.
Toxicitv Data Requirements
The EPA is not requiring registrants to submit additional toxicity studies. However,
there is clarification needed on three existing toxicity studies: the test material
stability, homogeneity, and concentration in the dosing medium.
Chemistry Data Requirements
The Agency has identified several product and residue chemistry requirements. Crop
field trial data, confined accumulation in rotational crops, and storage stability data is
required.
ProdUCt LabGlJnQ ^ dimethipin products must comply with EPA's current pesticide product
ChanOPS RPtlLlirPd labeling requirements and with the labeling changes set forth in Section V of the
dimethipin RED document.
RGQlllatOry EPA has determined that all products containing dimethipin as the active
Conclusion ingredient are eligible for reregistration, provided changes specified in the dimethipin
RED are incorporated into the label and additional data identified in Section V of the
RED confirm this conclusion.
FOP MOFG
Information
Electronic copies of the RED and this fact sheet are available on the Internet.
http://www.epa.gov/pesticides/reregistration/status.htm or
http://www.epa.gov/edockets.
For more information about EPA's pesticide reregistration program, the
dimethipin RED, or reregistration of individual products containing dimethipin, 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 Information Center (NPIC). Call toll-free 1-800-858-7378, from 6:30 am to
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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://npic.orst.edu.
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