APHIS Factsheet

Plant Protection and Quarantine May 2007

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 formulations with low 

malathion concentrations. For example, the cooperative 

Boll Weevil Eradication Program uses careful precision 

to apply malathion only to infested cotton fields. Because 

of application techniques 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 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. Why did the Environmental Protection Agency 

(EPA) release a reregistration document for 

malathion in 2006?

A. In 2006, EPA completed an extensive reregistration effort involving 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, on November 30, 2006, EPA released for public 

comment a malathion reregistration eligibility decision 

and revised the human health risk assessment on 

malathion.

 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 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.

 In addition, malathion, if left on hard, dry surfaces 

(e.g., swingsets, backyard toys, and decks) or in chlorinated water, can result in an increase in malaoxon 

levels. Malaoxon is a degradation product of malathion under certain conditions. Studies are being done 

to determine the environmental impact of malaoxon 

under such conditions. The EPA has recently suggested that malaoxon, previously viewed as a lowlevel contaminant of malathion, may be up to 22 times 

as toxic as malathion. However, the high purity of the 

malathion used in boll weevil eradication (typically 

97- to 99-percent pure malathion) means that the 

amount of malaoxon, and any human health risk 

associated with such treatments, is negligible. 

 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. All APHIS 

programs have adequate measures in place to protect 

endangered species. 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. No. Thus far, the reregistration eligibility decision 

and the revised human health risk assessment have 

not resulted in new restrictions on the agricultural uses 

of malathion. However, the documents contain new 

risk mitigation measures that may be necessary. For 

example, additional worker protection measures have 

been proposed. 

 The reregistration eligibility decision and the 

revised human health risk assessment are both subject to review, comment, and further revision. However, because the Boll Weevil Eradication Program’s 
protective measures have proven effective, APHIS 

anticipates no changes concerning how malathion is 

used within the program. 

Q. Does EPA’s revised malathion 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 the potential risk 

from malaoxon to toddlers near cotton fields, and 

in chlorinated drinking water near citrus-production 

areas. However, the high purity of malathion used 

in boll weevil eradication (typically 97- to 99-percent 

pure malathion) means that the amount of malaoxon, 

and any human health risk associated with such 

treatment is negligible. Nevertheless, as an additional precaution, parents may want to keep toddlers 

from playing on grass adjacent to treated cotton fields 

for 2 hours after a malathion application.

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. In preparing the 

environmental documentation, APHIS officials consider alternative courses of action and ensure that 

the agency 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 

reregistration eligibility decision. APHIS is working 

closely with EPA to further refine both the reregistration eligibility decision and the revised human health 

risk assessment.

 Upon publication of EPA’s final document, 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, age, disability, and where applicable, sex, marital 

status, familial status, parental status, religion, sexual orientation, 

genetic information, political beliefs, reprisal, or because all or part 

of an individual’s income is derived from any public assistance 

program. (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 to USDA, 

Director, Office of Civil Rights, 1400 Independence Avenue, S.W. , 

Washington , D.C. 20250–9410 , or call (800) 795–3272 (voice) or 

(202) 720–6382 (TDD). USDA is an equal opportunity provider and 

employer. 

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

Q. Who can I contact for more information?

A. For additional information regarding malathion 

and the Boll Weevil Eradication Program, please call 

APHIS’ Environmental Compliance staff in Riverdale, 

MD, at (301) 734–8247.