Questions and Answers:
EPA’s Risk Assessment on
Malathion
Q. What is malathion and how is it used?
A. Malathion is a commonly used organophosphate
insecticide. In an agricultural setting, malathion is
used to eliminate pests, such as boll weevils and fruit
flies, that threaten the productivity of important crops
like cotton and citrus. Human exposure is minimized
in agricultural programs by targeting host crops or
plants, and, in some programs, by using bait formula-
tions with low malathion concentrations. For exam-
ple, the cooperative boll weevil eradication program
uses careful precision to apply malathion only to
infested cotton fields. Because of application tech-
niques and the rural location of most cotton fields,
the risk of human exposure is low.
In an urban setting, malathion is used to control
mosquitoes that can carry West Nile virus and other
diseases of public health importance. It is also used
as an insecticide to control pests in homes and per-
sonal gardens. Malathion is approved by the U.S.
Food and Drug Administration as a prescription drug
for the treatment of head lice on humans.
Q. What document is the Environmental
Protection Agency releasing?
A. The Environmental Protection Agency (EPA) is
undertaking an extensive reregistration effort involv-
ing hundreds of pesticides, including malathion, to
ensure that they meet the requirements of the Food
Quality Protection Act of 1996. As part of its review,
in September 2005, EPA released a revised risk
assessment on malathion for public comment.
EPA currently classifies malathion as having
“suggestive evidence of carcinogenicity, but the evi-
dence is not sufficient to assess human carcinogenic
potential.”
Q. So, does this mean malathion causes cancer?
A. According to EPA’s document, studies conducted
on rats and mice “showed tumors only at very high
dose levels [of malathion] or that the number of
tumors was so low that they could have occurred by
chance rather than as a result of exposure to
malathion. In addition, studies showed