United States
Environmental Protection
Agency
Prevention, Pesticides
and Toxic Substances
(7508C)
EPA738-F-00-011
January 2001
Fenthion Facts
EPA has assessed the risks of fenthion and reached an Interim Reregistration Eligibility Decision
(IRED) for this organophosphate (OP) pesticide. Provided that risk mitigation measures are adopted,
fenthion fits into its own "risk cup"-- its individual, aggregate risks are within acceptable levels.
Fenthion is not eligible for reregistration at this time but may be pending a decision by the Agency on
appropriate mitigation after consultation with stakeholders.
Used as an adult mosquiticide in Florida only,
fenthion residues in food and drinking water do not
pose risk concerns. With mitigation limiting
homeowners' and children's exposure via home
lawns and other turf, fenthion fits into its own "risk
cup." With other mitigation measures, fenthion's
worker and ecological risks also would be below
levels of concern for reregistration. The Agency is
seeking input from stakeholders at a January 17,
2001, meeting on what mitigation measures to
impose. EPA will then announce a final determination
on the risk mitigation it believes must be adopted in
order for products containing fenthion to remain
eligible for reregistration.
After this individual decision on fenthion,
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 fenthion 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 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, www.epa.gov/pesticides/op .)
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.
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The fenthion interim decision is being 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 continues to work extensively with affected parties
to address the risks discussed in this interim decision document, which concludes the OP pilot process
for fenthion.
Uses
An insecticide, fenthion is used to control adult mosquitos in Florida only and dragonfly larvae
in contained ornamental fish production ponds in Arkansas, Florida, and Missouri only.
Annual domestic use is low— use data from 1990 to 1998 indicate an average of about
246,100 a.i. was used domestically per year (up to 343,100 Ibs a.i./year maximum). The
average amount used for mosquito control was about 96,500 Ibs a.i./year (up to 118.600 Ibs
a.i./year maximum).
Health Effects
Fenthion 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.
Ecological Effects
Risks
Fenthion is very highly toxic to birds and highly toxic to estuarine/marine invertebrates and non-
target organisms. The mosquito adulticide use of fenthion has been implicated in several bird
kill incidents, including recent bird kills on Marco Island, Florida. These kills on Macro Island
are currently under investigation by the US Fish and Wildlife Service.
Dietary exposures from eating food crops exposed to fenthion are above the level of concern
for the entire U.S. population, including infants and children. However, these uses are being
voluntarily cancelled by the registrant, and the Agency will not refine the fenthion dietary
exposure analyses. Drinking water is not a significant source of exposure.
Although there are no homeowner uses for fenthion, residential exposure to adults and children
can occur because fenthion is used in mosquito control operations that involve wide area
adulticide applications to residential areas in Florida. There are no risks of concern for
homeowners performing yard work or performing other recreational activities on the treated
areas. There are no risks of concern for children engaging in activities after typical applications.
However there is a concern for children if they are exposed to repeated levels at the maximum
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allowed rate. The inputs and approaches used to calculate the exposures result in conservative
estimates.
• EPA also has risk concerns for workers who mix, load, and/or apply fenthion for both aerial
and ground mosquito adulticide applications.
• There are potential risk concerns for acute dietary risks to birds, freshwater invertebrates and
estuarine/marine invertebrates at maximum aerial and/or ground applications.
Risk Mitigation
In order to support a reregistration eligibility decision for fenthion, the following risk mitigation
measures are being considered and will be discussed at the upcoming stakeholder meeting:
• To mitigate risks to workers who mix, load and apply fenthion for ground and aerial
applications:
require generic mixer/loader/applicator exposure data for all mosquito pesticide
applications;
• handlers must use closed systems only. The current labels give protective clothing
statements for both closed system and non-closed systems. The Agency believes that
requiring closed systems for all types of mosquito control applications will result in less
exposure to workers;
• add a prohibition of human Saggers to the label;
• change the use rate on the label to allow the highest rate only for public health use (i.e.,
with confirmation of mosquito-vectored diseases).
• To mitigate risks from aquaculture use:
• eliminate the backpack sprayer method of application;
require a handwand sprayer.
• To mitigate risks to residential bystanders:
• require chemical-specific deposition and turf transferable residue studies to refine the
risk assessment;
require a developmental neurotoxicity study;
• change the use rate on the label to allow the highest rate only for public health use (i.e.,
with confirmation of mosquito-vectored diseases).
To mitigate ecological risks:
• require avian reproduction studies for the northern bobwhite and the mallard to refine
the risk assessment;
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require three acute toxicity studies for the mysid shrimp: one using a formulation, one
using the sulfoxide degradate, and one using the suflone degradate.
restrict the use of fenthion to mosquito control districts in Florida that have developed a
plan to identify critical/sensitive bird habitats and endangered species in their counties
and have addressed ways to avoid exposure to those areas;
change the use rate on the label to allow the highest rate only for public health use (i.e.,
with confirmation of mosquito-vectored diseases);
require buffer zones to protect aquatic organisms, especially invertebrates;
require certain label changes to improve applications and lessen risk to non-target
organisms.
Next Steps
Numerous opportunities for public comment were offered as this decision was being
developed. The fenthion IRED therefore is issued in final (see www.epa.gov/REDs/ or
www.epa.gov/pesticides/op ) without a formal public comment period. The docket remains
open, however, and any comments submitted in the future will be placed in this public docket.
The Agency is sponsoring a public stakeholder meeting to gather information and hear concerns
and comments about risks and possible risk mitigation for fenthion. This meeting will be held on
January 17, 2001, from 9:00 am to 5:00 pm at the Embassy Suites, 8978 International Drive,
Orlando, Florida 32819.
The Agency will revoke all fenthion tolerances because the registrant has agreed to cancel all
food uses. When the cumulative risk assessment for all organophosphate pesticides is
completed, EPA may need to pursue further risk management for fenthion.
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