Questions & Answers:

EPA’s Preliminary

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 formulations with low malathion concentrations. For example,

the cooperative boll weevil eradication programs use

careful precision to apply malathion only to 

cotton fields. Because of application techniques and

the rural location of the 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 personal 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 involving hundreds of pesticides, including malathion, to

find if they meet the requirements of the Food Quality

Protection Act of 1996. As part of its review, EPA

released for public comment a preliminary risk

assessment on malathion. A revised assessment is

expected to be published in the winter of 2001.

EPA currently classifies malathion as having

“suggestive evidence of carcinogenicity, but the 

evidence is not sufficient to assess human carcinogenic potential.”

Q. So, does this mean malathion causes cancer?

A. According to the 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 that malathion

did not act as a mutagen to cause cancer.” EPA

states that “human exposures to malathion are generally quite low.” Because potential human exposure

is several orders of magnitude lower than dose levels

in animal studies and the studies show no firm evidence of cancer caused by malathion, EPA concluded

that when malathion is used according to label directions cancer risk is not a concern.

Q. What are the ecological effects of malathion?

A. EPA’s document acknowledges that malathion

degrades rapidly in the environment and does not

pose a risk to birds. However, EPA does note that

malathion is toxic to beneficial insects, and some

concerns exist about malathion’s effects on aquatic

animals.

Comprehensive risk assessments that evaluate

the way malathion is used in the U.S. Department of

Agriculture’s Animal and Plant Health Inspection

Services’ (APHIS) cooperative programs indicate little

to no effects on nontarget organisms. Years of environmental monitoring conducted in conjunction with

APHIS’ programs confirm that if ecological effects

occur, they are minimal, limited in duration, and confined to treatment areas.

Q. Does this assessment place new restrictions

on the use of malathion?

A. This preliminary analysis does not put new

restrictions on the agricultural uses of malathion.

However, this is a preliminary assessment that is

subject to review, comment, and revision.

Q. Does EPA’s preliminary risk assessment

change any of APHIS’ programs that are currently

underway?

A. APHIS has announced no changes to programs

that are currently underway.

EPA expressed concern about three workerexposure scenarios. APHIS determined that none of

these scenarios occur in current APHIS programs.

For several years, APHIS has been monitoring 

workers in its programs that use malathion, and there

has been no evidence of adverse effects.

Q. How does this affect APHIS programs in the

future?

A. To comply with existing laws, APHIS prepares

environmental documentation that analyzes the

potential impacts of its programs. The environmental

documentation considers alternative courses of

action and ensures that APHIS is using the most 

Factsheet

Plant Protection and Quarantine September 2001

APHIS
efficacious means to protect U.S. agriculture, while

remaining sensitive to human health and other 

ecological concerns.

APHIS is considering the implications of EPA’s

preliminary risk assessment. Upon publication of

EPA’s final risk assessment, APHIS will consider the

need to revise the environmental documentation for

programs that use malathion.

The U.S. Department of Agriculture (USDA) prohibits discrimination

in all its programs and activities on the basis of race, color, national

origin, sex, religion, age, disability, political beliefs, sexual orientation, or marital or family status. (Not all prohibited bases apply to

all programs.) Persons with disabilities who require alternative

means for communication of program information (Braille, large

print, audiotape, etc.) should contact USDA’s TARGET Center at

(202) 720–2600 (voice and TDD).

To file a complaint of discrimination, write USDA, Director, Office of

Civil Rights, Room 326–W, Whitten Building, 1400 Independence

Avenue, SW, Washington, DC 20250–9410 or call (202) 720–5964

(voice and TDD). USDA is an equal opportunity provider and

employer.

United States Department of Agriculture • Animal and Plant Health Inspection Service • Safeguarding American Agriculture