United States Prevention, Pesticides May 11, 2000

Environmental Protection And Toxic Substances

Agency (7506C)

 

 Questions & Answers

 Malathion Preliminary Risk Assessment 

 On May 11, 2000, EPA released the preliminary risk assessment for the

organophosphate pesticide malathion for public comment, in

accordance with the organophosphate pilot public participation

process. The following questions and answers provide summary

information about that risk assessment. 

What is malathion and how is it used?

Malathion is an organophosphate insecticide. The

main uses of malathion are:

• Cotton boll weevil and citrus medfly eradication

programs (59-61%)

• Other agricultural crops (16-20%)

• Public health mosquito control (8-15%)

• Home and garden uses (10%)

It is used on more than 100 food crops. Five crops

account for more than 50% of malathion’s

agricultural use in the U.S.: alfalfa, cotton, rice,

sorghum, and wheat. In addition, malathion uses

include treatment of stored commodities and

empty storage facilities, outdoor homeowner uses

(ornamental flowers, shrubs, and trees), golf

course uses (ornamental flowers, shrubs, and

trees), ornamental nursery stock, slash pine,

woody plants, Christmas tree plantations, garbage

dumps, outdoor dwellings, intermittently flooded

areas, irrigation systems, sewage systems,

pastures, and rangelands. 

What are the documents EPA is releasing?

This is a preliminary risk assessment. It

represents information available to EPA at the

time the assessment was prepared. Some of the

analyses could be further refined if EPA receives

new information that would make them more

comprehensive or realistic. EPA cautions against

premature conclusions based on these preliminary

assessments and against any use of information in

the preliminary risk assessments out of their full

context.

Is malathion a risk of concern in food or

drinking water?

No. Based on our preliminary findings, risks from

malathion residues in food and drinking water are

within acceptable limits for both short-term (acute)

and long-term (chronic) exposures to all groups,

including children.

Is malathion a carcinogen?

EPA evaluated malathion for chronic effects such

as cancer. The preliminary assessment has

determined that there is insufficient evidence to

assess the potential for causing cancer in humans,

and the suggestive evidence of carcinogenicity in

laboratory studies will be reviewed by our external

Scientific Advisory Panel. This classification

means that studies showed tumors in laboratory

animals only at very high dose levels 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. Also, the degradation product of

malathion, malaoxon, is not carcinogenic in rats. 

When malathion is used according to label

directions, our analyses show very low potential

for human exposure and therefore cancer risk

from malathion is not of concern. 

What about risks from malathion’s use to

control mosquitoes and eradicate boll

weevils?

EPA assessed risks to bystanders from use of

malathion in both aerial spraying and ground
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application. In all cases the risks to bystanders

from possible skin contact, inhalation, or incidental

ingestion (such as hand- or object-to-mouth

activities by children) were below EPA’s level of

concern. For more information see Malathion for

Mosquito Control, May 2000 (EPA 735-F-00-001

)*

Does malathion pose risks that are of

concern?

Risks from malathion are lower than for most

other organophosphate pesticides. However,

based on this preliminary assessment, there is

potential concern for exposures associated with

certain kinds of equipment and formulations used

by homeowners or others on lawns, ornamentals,

or small fruit and vegetable gardens. Also, skin

contact with residues in some commercial pickyour-own-produce operations results in risks that

are of potential concern to EPA.

In addition three of sixteen worker exposure

scenarios exceed EPA’s level of concern:

• Applying sprays with an airblast sprayer to

fruits and nuts

• Mixing/loading liquids for aerial application for

mosquito control

• Reentry of agricultural workers into treated

areas on the day of application

On what “effects” did EPA base its risk

assessment?

EPA bases its risk assessment on the harmful

effect that occurs at the lowest dose level in test

animals. In this preliminary risk assessment, EPA

is concerned about two potential effects: toxicity to

maternal animals (reduced weight gain) and

cholinesterase inhibition. Cholinesterase regulates

nerve signal transmission. Inhibition of

cholinesterase causes effects such as muscle

weakness and tremors. For more information on

EPA’s risk assessment process, see Assessing

Health Risks From Pesticides, January 1999 (EPA

735-F-99-002)*. 

Does malathion pose ecological risks?

Malathion degrades rapidly in the environment,

especially in moist soils. Malathion does not pose

risks to birds from short-term exposure in food. 

However, malathion is toxic to beneficial insects,

and there are risks of concern to aquatic animals.

When will EPA act to reduce risks that are

found to be above levels of concern?

EPA will accept public comment on this risk

assessment until July 10, 2000. At the end of the

comment period, EPA will see whether any new

information has been submitted that would result in

changes to the risk assessment. Once this review

and 

refinement process is complete, EPA will release

the revised risk assessment and open a public 

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 encourages the public to participate in this

review of the OP pesticides. Through a six-phase

pilot public participation process, developed in

consultation with the Tolerance Reassessment

Advisory Committee, the Agency is releasing for

review and comment its preliminary scientific risk

assessments for each OP. 

EPA is exchanging information with

stakeholders, including 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 when the necessary

methodology is available.

For more information on this process, see Public

Involvement Opportunities for the Organophosphate

Pesticides, April 1999 (EPA 735-F-99-012)*.
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participation period inviting risk management ideas

in Fall 2000. Risk management decisions would be

made following the close of the comment period. 

However, throughout this process, if unacceptable

risks are identified, EPA will act to reduce or

eliminate the risks.

For More Information

• The malathion risk assessment documents and

other background information about

organophosphate pesticides are available on the

Internet at www.epa.gov/pesticides/op/

• Fact sheets referenced in this document (marked

with an * following the EPA publication number)

can be found on EPA’s web site

(www.epa.gov/pesticides) or by calling the Office

of Pesticide Programs Communication Services

Branch at 703-305-5017.

• The National Pesticide Telecommunications

Network can answer questions about pesticide

toxicity. Contact NPTN at 800-858-7378 or on the

Internet at http://ace.orst.edu/info/nptn.