Questions & Answers: EPA's Preliminary Risk Assessment on Malathion

Plant Protection & Quarantine

September 2001

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 worker-exposure 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 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, gender, 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 and Independence Avenue, SW, Washington, DC 20250-9410 or call (202) 720-5964 (voice and TDD). USDA is an equal opportunity provider and employer.

The US Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, gender, 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, 14th and Independence Avenue, SW, Washington, DC 20250-9410 or call (202)720-5964 (voice and TDD). USDA is an equal opportunity provider and employer.

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