United States
Environmental Protection
Agency
Prevention, Pesticides
and Toxic Substances
(7508C)
EPAF-00-020
October 2000
&EPA Tribufos Facts
EPA has assessed the risks of tribufos and reached an Interim Reregistration Eligibility Decision
(IRED) for this organophosphate (OP) pesticide. Tribufos is eligible for reregistration, pending a full
reassessment of the cumulative risk from all OPs.
Used only on cotton crops, tribufos
residues in food and drinking water do not pose
risk concerns. Tribufos has no residential uses.
With the implementation of certain risk
mitigation measures, worker and ecological
risks from tribufos use are believed to be
significantly reduced. Additional data are also
to be submitted to the Agency to confirm this
conclusion.
EPA is reviewing the OP pesticides to
determine whether they meet current health and
safety standards. OPs need decisions about
their eligibility for reregistration under FIFRA.
Additional OPs with residues in food, drinking
water, and other non-occupational exposures
also must be reassessed to make sure they meet
the new Food Quality Protection Act (FQPA)
safety standard.
EPA's next step under the 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 tribufos cannot be
considered final until this cumulative assessment is complete. Further risk mitigation may be necessary
at that time.
The tribufos IRED 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 tribufos.
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.
-------
Uses
Tribufos is an organophosphate defoliant used for cotton crops. It is specifically used to
defoliate cotton in preparation for machine harvesting.
There are about 4,500,000 pounds of active ingredient (ai) applied annually to between 4 and 5
million acres (A) or about 35% of planted cotton acreage in the United States. The typical rate
of application varies from 0.50 Ib ai/A tol.875 Ib ai/A. Tribufos is most often applied in a
tank-mix. When it is tank-mixed, the application rate is typically significantly lower than the
maximum label rate.
• There are no residential uses of tribufos.
Health Effects
Tribufos 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 risks from food and drinking water are not of concern to the Agency for all segments of
the population, including children.
• The current occupational risk assessment indicates risk concerns for aerial mixers/loaders and
aerial applicators (with closed mixing/loading systems and enclosed cockpits). However, the
Agency believes actual exposures are lower. Risks to workers who mix, load, and apply
tribufos via groundboom are not of concern to the Agency but risks to workers who enter fields
shortly after treatment are of concern.
• Ecological risks include acute and chronic concerns for both birds and mammals. The Agency
is also concerned with acute risks to marine fish. Several studies conducted in a variety of
climates where tribufos is used resulted in risks of concern to freshwater and marine
invertebrates.
Risk Mitigation
To mitigate risks to workers, the following measures are necessary:
1) The maximum application rate is to be reduced to 1.5 pints/A (1.125 Ibs ai/A) in all states,
except California and Arizona, which would remain at the higher rate of 2.5 pints/A (1.875 Ib
ai/A). California and Arizona grow hardier varieties of cotton, which require more defoliant
-------
2) The restricted entry interval (REI) is to be increased from 24 hours to 7 days;
3) Tribufos products are to be distributed in closed systems starting with the 2002 season.
4) Aerial applicators are to be in enclosed cockpits.
5) A biomonitoring study is to be conducted to confirm the Agency's risk management
decision that occupational risks associated with the use of tributes are not of concern. The
biomonitoring study will be submitted to the Agency by September 2003.
The Agency also examines the benefits associated the use of a chemical when worker and
ecological risks are of concern to the Agency. For tributes, the Agency has received and
reviewed benefits analyses from several stakeholders that ascertain the benefits from the use of
tribufos are numerous, including its efficacy at lower temperatures. The Agency has considered
these submissions and concurs that the benefits from tribufos are numerous and its loss to the
cotton industry would be substantial.
Although the Agency's analyses indicate concern for several ecological species, the Agency is
confident that the above mitigation measures that will be implemented to address human health
risks will also reduce ecological risks. For instance, it is expected that a reduction in the
application rate, largely through tank-mixing, will result in less pesticide availability in the
ecosystem.
Next Steps
Numerous opportunities for public comment were offered as this decision was being
developed. The tribufos IKED, 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.
To implement risk mitigation as quickly as possible, time frames for making the changes
required by the Tribufos IKED are shorter than those in a usual RED. Tribufos labels must be
amended to include the above mitigation and submitted to the Agency within 90 days after
issuance of this IKED.
When the cumulative risk assessment for all organophosphate pesticides is completed, EPA will
issue its final tolerance reassessment decision for tribufos and may result in further risk
mitigation measures. Similarly, the Agency may reconsider any part of this interim decision
based on new information which may come to the Agency's attentioa The Agency will revoke
one tolerance because there are no registered uses and amend one tolerance. For all OPs,
raising and/or establishing tolerances will be considered once a cumulative assessment is
completed.
-------
------- |