United States
Environmental Protection
Agency
Prevention, Pesticides
And Toxic Substances
(7508C)
EPA-738-F-03-005
May, 2003
&EPA I.R.E.D. FACTS
Pesticide
Reregistration
Use Profile
Methyl Parathion
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 interim RED (IRED) document for reregistration
case 0153, Methyl Parathion.
Methyl parathion is used to control many types of pests, including mites,
thrips, weevils, aphids, and leafhoppers. Methyl parathion is used on row crops
such as alfalfa, almonds, barley, dried beans, cabbage, corn, cotton, grass forage/
fodder/hay hops, lentils, oats, onion, pastures, dried peas, pecans, rangeland, rape
seed (canola), rice, rye, soybeans, sugar beets, sunflower, sweet potatoes, walnuts,
wheat, white potatoes, and yams.
Methyl parathion is formulated as a microencapsulate (ME) (20.9% a.i.) and
as an emulsifiable concentrate (EC) (ranges from 27.59 to 52.7% a.i.). The EC
products contain a stenching agent to deter indoor misuse. Methyl parathion is
formulated with other active ingredients.
Methyl parathion can be applied by aerial, ground and airblast equipment or
through irrigation equipment.
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Regulatory Methyl parathion was first registered in 1954 for use as an
History insecticide/acaricide. In December 1986, the Agency published Guidance for the
Reregistration of Pesticide Products Containing Methyl Parathion. Some label
changes to enhance worker safety were imposed by this document and several
Data Call Ins were issued to support continued registration. In 1996, agreement
was reached with the registrants producing the EC formulation to make various
changes designed to end illegal home use of methyl parathion. These changes
included tracking of all containers and reuseable/returnable closed containers for all
EC products. On August 2, 1999, a Memorandum of Agreement was signed by
methyl parathion registrants and EPA to voluntarily cancel a number of crop uses to
address dietary concerns and to commit to conducting studies to refine potential
occupational risk concerns.
Currently, twelve methyl parathion products are registered along with 13
Special Local Needs Labels.
Human Health
Assessment
Toxicity
Methyl parathion is an organophosphorous (OP) pesticide. The OPs as a
class are characterized by the effect of acetyl-cholinesterase inhibition. Methyl
parathion is very toxic by oral, dermal, and inhalation routes (Toxicity Category 1),
but is not a strong eye or dermal irritant and is not a skin sensitizer (Toxicity
Categories 3 and 4).
The toxicity endpoints selected for the human health risk assessment are
based primarily on neurotoxic effects, including neuropathology and acetyl
cholinesterase (ChE) inhibition. Additional effects of chronic exposure include
retinal degeneration and sciatic nerve degeneration. No evidence of carcinogenicity
was seen in any study
Dietary Exposure
People may be exposed to residues of methyl parathion through the diet.
Tolerances or maximum residue limits have been established for several
commodities (please see 40 CFR 180.122). EPA is not proposing to alter
tolerance levels at this time. A complete tolerance reassessment will be completed
when the organophosphate cumulative assessment has been finalized.
Based on current labels, at the 99.9th percentile, the dietary risk, food only, is
below levels of concern for all population subgroups, including the most exposed
population subgroup, children age 6-12, at 77% of the aPAD.
The chronic dietary risk estimate is below the Agency's level of concern and
is estimated to be less than 8% of the cPAD for all population subgroups.
These fractions of the allowable PAD are considered to be an acceptable
dietary exposure risk.
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Environmental
Assessment
Occupational and Residential Exposure
Based on current use patterns, handlers (mixers, loaders, and applicators)
may be exposed to methyl parathion during and after applications in agricultural
settings. Biomonitoring data for mixers and loaders showed that closed mixing and
loading systems provided adequate protection from exposure to methyl parathion
for large applications of the ME formulation and all applications of the EC
formulation.
There is some concern for workers entering fields after applications.
FQPA Considerations
Methyl parathion can be used on food/feed crops and therefore a dietary
(food plus water) assessment was conducted for the FQPA analysis. There are no
residential uses; therefore the aggregate assessment consists of exposures from the
diet. The (food alone) dietary assessment is highly refined, using all available
monitoring, processing and cooking factors. Dietary exposures from methyl
parathion in food alone are considered to be within the risk cup.
Estimates of exposure from residues in drinking water are based on
monitoring data from a cotton growing region and are slightly above the aPAD for
some populations. These monitoring data are thought to be from use of methyl
parathion on cotton. Maximum rates have been reduced for many crops; in
particular, the maximum allowable seasonal rate for applications to cotton has been
reduced from 30 Ibs ai/A to 4 Ibs ai/A; single maximum application rates have been
reduced from 3 Ibs ai/A to 1 Ib ai/A. These reductions are expected to result in
lowered concentrations of residues in water and no further mitigation is required at
this time.
The FQPA 10X database safety factor was retained for methyl parathion
based on lack of a developmental neurotoxicity study (DNT) and suggestions of
fetal and neonate susceptibility in registrant submitted studies and in open literature
citations. The DNT has been submitted to the Agency and is under review.
Pending results of that review, the Agency may reduce or eliminate this safety factor
for the FQPA assessment if the study warrants this change.
Environmental Fate
The major routes of dissipation for methyl parathion are microbial
degradation, aqueous photolysis, hydrolysis, and incorporation into soil organic
matter. Methyl parathion degrades rapidly with a half-life of less than 5 days in soil
and water.
Methyl parathion is mobile to relatively mobile in soil; thus, runoff and
leaching could be potential routes of dissipation. However, the low persistence of
methyl parathion is expected to limit the extent of off-site movement, \blatilization
is another route of dissipation, and while laboratory studies with methyl parathion
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indicate low volatility, methyl parathion has been detected in air and rain samples
across the United States.
Ecological Effects
Methyl parathion is highly toxic to very highly toxic to all non target terrestrial
species on a acute basis from single oral doses, dermal exposures and from short
term dietary exposure. Methyl parathion is moderately to highly toxic to fish and
very highly toxic to aquatic invertebrates.
Environmental Risk Characterization
In general, ecological risk assessment indicates that methyl parathion may
pose risks to birds, mammals, non-target insects, fish and aquatic invertebrates.
Methyl parathion use may result in acute and chronic risk of adverse effects to
birds. These effects include direct mortality, as well as sub-lethal effects such as
reproduction effects, changes in maternal care and viability of young birds, anorexia,
increased susceptibility to predation, and greater sensitivity to environmental stress.
Estimated environmental concentrations suggest that levels of concern for acute risk
to freshwater fish are exceeded only at the highest use rate, although there is high
uncertainty in this analysis.
Extensive field incident data indicate that methyl parathion poses risks to
honey bees.
Benefit
Assessments
Benefit assessments were conducted for methyl parathion use on: field and
sweet corn, walnuts, cotton, soybeans, sweet potatoes, sunflowers, and rice. High
benefits were shown for soybeans, sweet potatoes and rice; and moderate benefits
were shown for sunflowers. For sweet corn, high benefits were shown in control
of silk fly, and therefore, use is retained for this pest only. For field corn, walnuts,
and cotton, benefits are considered to be low, but the alternatives also have serious
ecological risks, and little risk reduction would be attained by promoting a shift to
these alternative pesticides.
Formal benefit assessments were not conducted for methyl parathion use on
crops where reported usage was low. Consultations with USDA indicated benefits
for use on alfalfa, barley, grass, oats, onions, rape seed, rye, and potatoes. These
crops have low use, primarily focused on certain pests in isolated areas of the
country. These uses could be considered to be of high benefit for those areas, and
therefore use is retained.
Benefit assessments are available on the EPA website and in the docket for
methyl parathion.
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Risk Mitigation Several mitigation measures are being required to reduce risks of methyl parathion to
workers and non-target organisms.
1. Deletion of use on cabbage, dried beans, dried peas, hops, lentils, pecans,
and sugar beets.
2. Use on sweet corn is limited to control of silk fly. References to all other
pests will be deleted from the sweet corn instructions on the labels.
3. Methyl parathion may not be mixed/loaded or otherwise handled in areas
prone to runoff or movement into aquatic environments or wetlands, except
for aquatic applications such as applications to rice.
4. Closed delivery (mixing/loading and transfer) systems are required for aerial
applications of the ME formulation. These systems are currently employed
for all applications of the EC formulation.
5. Engineering controls such as a closed cab are required for all applications.
6. Use of human flaggers is prohibited.
7. Applicator biomonitoring studies must be submitted to confirm that the closed
systems are adequately protective for applicators.
8. Maximum Single and Maximum Seasonal Rates are reduced for many of the
uses.
9. Re-entry intervals for postapplication workers range from 3-6 days for EC
applications and 9-31 days for the ME Formulation.
Additional Data EPA is requiring the following additional generic studies for methyl parathion
Required to confirm its regulatory assessments and conclusions:
Applicator Biomonitoring Studies for EC and Microencapsulated Formulation for each
Application Method. (Guideline OPPTS 875.1500)
Residue Analytical Method (Guideline OPPTS 860.1340)
• Magnitude of Residues Crop Field Trial Data for the EC Formulation — wheat forage,
wheat hay (Guideline OPPTS 860.1500)
Magnitude of Residues Crop Field Trial Data for the Microencapsulated Formulation -
rice straw (Guideline OPPTS 860.1500)
Magnitude of Residues, meat/milk/poultry/eggs (Guideline OPPTS 860.1480)
Anaerobic Aquatic Metabolism. (Guideline OPPTS 835.4400)
Field Volatility (Guideline OPPTS 835.8100)
Terrestrial Field Dissipation for the ME Formulation (Guideline OPPTS 835.6100)
Estuarine and Marine Fish Early Life Stage Test (Guideline OPPTS 850.1400)
Vegetative Vigor (Guideline OPPTS 850.4150)
Seedling Emergence (Guideline OPPTS 850.4100)
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 reregistration.
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Product Labeling All methyl parathion end-use products must comply with EPA's current
Changes Required pesticide product labeling requirements. For a comprehensive list of labeling
requirements, please see the methyl parathion IRED document.
Regulatory EPA has determined that products containing methyl parathion are eligible for
Conclusionreregistration except for use on the following crops: cabbage, dried beans, dried peas,
hops, lentils, pecans, and sugar beets. The use of eligible methyl parathion products in
accordance with labeling specified in this RED will not pose unreasonable adverse
effects to humans or the environment. These products will be reregistered once the
required confirmatory generic data, product specific data, CSFs, and revised labeling
are received and accepted by EPA. Products which contain active ingredients in
addition to methyl parathion will be reregistered when all of their other active
ingredients also are eligible for reregistration.
For More EPA is requesting public comments on the interim Reregistration Eligibility Decision
lnforination(IKED) document for methyl parathion 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 IRED and this fact sheet are available on the Internet. See
http://www.epa.gov/pesticides/reregistration/status.htm.
Printed copies of the IRED 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 methyl parathion IRED 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 methyl
parathion IRED, or reregistration of individual products containing methyl parathion,
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 Information Center (NPIC). 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 http://npic.orst.edu.
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