Chlorpyrifos Facts
EPA 738-F-01-006
February 2002
EPA has assessed the risks of chlorpyrifos and reached an Interim Reregistration Eligibility Decision
(IRED) for this organophosphate (OP) pesticide. Provided that risk mitigation measures are adopted,
chlorpyrifos fits into its own "risk cup"— its individual, aggregate risks are within acceptable levels.
Chlorpyrifos also is eligible for reregistration, pending a full reassessment of the cumulative risk from
all OPs.
Used on a variety of food and feed crops, golf courses, as a non-structural wood treatment, and as an
adult mosquitocide, chlorpyrifos residues in food and drinking water do not pose risk concerns. With
mitigation eliminating virtually all homeowner uses, chlorpyrifos fits into its own "risk cup." With other
mitigation measures, chlorpyrifos worker and ecological risks also will be below levels of concern for
reregistration.
EPA's next step under the Food Quality Protection Act (FQPA) is to complete a cumulative risk
assessment and risk management decision encompassing all the OP pesticides, which share a common
mechanism of toxicity. The interim decision on chlorpyrifos cannot be considered final until this
cumulative assessment is complete. Further risk mitigation may be warranted at that time.
EPA is reviewing the OP pesticides to determine whether they meet current health and safety
standards. Older OPs need decisions about their eligibility for reregistration under FIFRA. OPs with
residues in food, drinking water, and other non-occupational exposures also must be reassessed to
make sure they meet the new FQPA safety standard.
The chlorpyrifos interim decision was made through the OP pilot public participation process, which
increases transparency and maximizes stakeholder involvement in EPA's development of risk
assessments and risk management decisions. EPA worked extensively with affected parties to reach
the decisions presented in this interim decision document, which concludes the OP pilot process for
chlorpyrifos.
Uses
Chlorpyrifos is an organophosphate insecticide, acaricide and miticide used to control foliage
and soil-borne insect pests on a variety of food and feed crops.
Approximately 10 million pounds are applied annually in agricultural settings. The largest
agricultural market for chlorpyrifos in terms of total pounds ai is corn (~5.5 million).
Health Effects
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Chlorpyrifos can cause cholinesterase inhibition in humans; that is, it can overstimulate the
nervous system causing nausea, dizziness, confusion, and at very high exposures (e.g.,
accidents or major spills), respiratory paralysis and death.
Risks
Dietary exposures from eating food crops treated with chlorpyrifos are below the level of
concern for the entire U.S. population, including infants and children. Drinking water risk
estimates based on screening models and monitoring data from both ground and surface
water for acute and chronic exposures are generally not of concern.
In June, 2000, the Agency entered into an agreement with the technical registrants to
eliminate virtually all homeowner uses, except ant and roach baits in child resistent
packaging.
Residential postapplication exposures may occur after termiticide use in residential structures.
To mitigate risks from this use, the technical registrants agreed in June 2000 to limit
termiticide treatments to 0.5% solution, and cancel all postconstruction uses. Pre-
construction use will remain until 2005, unless acceptable exposure data are submitted that
show that residential postapplication risks from this use are not a concern.
Occupational exposure to chlorpyrifos is of concern to the Agency. Exposures of concern
include mixing/loading liquids for aerial/chemigation and groundboom application, mixing
wettable powder for groundboom application, aerial application, and application by backpack
sprayer, high-pressure handwand, and hand-held sprayer or duster. Generally, these risks
can be mitigated by a combination of additional personal protective equipment and
engineering controls, and by reductions in application rates. Additionally, the Agricultural
Handler Task Force will be developing exposure data to better characterize the risk from
certain uses (e.g., applying granulars by air).
Risk quotients indicate that a single application of chlorpyrifos poses risks to small mammals,
birds, fish and aquatic invertebrate species for nearly all registered outdoor uses. Multiple
applications increase the risks to wildlife and prolong exposures to toxic concentrations. To
address these risks, a number of measures including reduced application rates, increased
retreatment intervals, reduced seasonal maximum amounts applied per acre, and no-spray
setback zones around water bodies will be needed.
Risk Mitigation
In order to support a reregistration eligibility decision for chlorpyrifos, the following risk mitigation
measures are necessary:
To mitigate risks to agricultural workers PPE consisting of double layers, chemical resistant
gloves, chemical resistant shoes plus socks, chemical resistant headgear for overhead
exposure, chemical resistant apron when cleaning and mixing or loading and a dust/mist
respirator are required for the following scenarios: mixing/loading liquids for groundboom
and airblast application, loading granulars for ground application, tractor drawn granular
spreader, and low pressure handwand.
engineering controls are required for the following scenarions: mixing wettable powder for
groundboom application (water soluble packaging), mixing wettable powder for airblast
application (water soluble packaging), and aerial application of sprays (enclosed cockpit).
There are still some occupational risk scenarios that are still below the target MOE of 100,
even with all feasible PPE or engineering controls. The risk assessments for these uses will
be refined with additional data.
To mitigate ecological risks the technical registrants have agreed to label amendments which
include the use of buffer zones to protect water quality, fish and wildlife, reductions in
application rates, number of applications per season, seasonal maximum amounts applied,
and increases in the minimum intervals for retreatment.
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The mitigation measures prescribed in the IRED along with mitigation that is already being
implemented as a result of the June, 2000, Memorandum of Agreement, will reduce risk to
both terrestrial and aquatic species. For example, many of the reported incidents of wildlife
mortality associated with chlorpyrifos use were related to residential lawn and termite uses
and use on golf courses. The residential uses have been eliminated, the termiticide use is
being phased out, and the application rate on golf courses has been reduced from 4 to 1
Ib/ai/A. Additionally, no-spray buffers around surface water bodies, as well as rate
reductions for agricultural uses will be implemented as a result of this IRED and will further
reduce the environmental burden of chlorpyrifos.
The OP Pilot Public Participation Process
The organophosphates are a group of related pesticides that affect the functioning of the nervous
system. They are among EPA's highest priority for review under the Food Quality Protection Act.
EPA is encouraging the public to participate in the review of the OP pesticides. Through a six-phased
pilot public participation process, the Agency is releasing for review and comment its preliminary and
revised scientific risk assessments for individual OPs. (Please contact the OP Docket, telephone 703-
305-5805, or see EPA's web site, Pesticide Reregistration Status.)
EPA is exchanging information with stakeholders and the public about the OPs, their uses, and risks
through Technical Briefings, stakeholder meetings, and other fora. USDA is coordinating input from
growers and other OP pesticide users.
Based on current information from interested stakeholders and the public, EPA is making interim risk
management decisions for individual OP pesticides, and will make final decisions through a cumulative
OP assessment.
Next Steps
Numerous opportunities for public comment were offered as this decision was being
developed. In addition, the chlorpyrifos IRED has been issued with a public comment period
(see Pesticide Reregistration Status).
When the cumulative risk assessment for all organophosphate pesticides is completed, EPA
will issue its final tolerance reassessment decision for chlorpyrifos and may request further
risk mitigation measures. The Agency will revoke the tomato tolerance and amend the grape
and apple tolerances for chlorpyrifos. For all OPs, raising and/or establishing tolerances will
be considered once a cumulative assessment is completed.
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