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PUBLIC HEALTH STATEMENT 

METHYL PARATHION 

CAS#: 298-00-0 

Division of Toxicology September 2001 

This Public Health Statement is the summary 

chapter from the Toxicological Profile for Methyl 

Parathion. It is one in a series of Public Health 

Statements about hazardous substances and their 

health effects. A shorter version, the ToxFAQsTM, is 

also available. This information is important 

because this substance may harm you. The effects 

of exposure to any hazardous substance depend on 

the dose, the duration, how you are exposed, 

personal traits and habits, and whether other 

chemicals are present. For more information, call 

the ATSDR Information Center at 1-888-422-8737. 

This public health statement tells you about methyl 

parathion and the effects of exposure. The 

Environmental Protection Agency (EPA) identifies 

the most serious hazardous waste sites in the nation. 

These sites make up the National Priorities List 

(NPL) and are the sites targeted for long-term 

federal cleanup activities. Methyl parathion has 

been found in at least 16 of the 1,585 current or 

former NPL sites. However, the total number of 

NPL sites evaluated for this substance is not known. 

As more sites are evaluated, the sites at which 

methyl parathion is found may increase. This 

information is important because exposure to this 

substance may harm you and because these sites 

may be sources of exposure. 

When a substance is released from a large area, 

such as an industrial plant, or from a container, such 

as a drum or bottle, it enters the environment. This 

release does not always lead to exposure. You are 

exposed to a substance only when you come in 

contact with it. You may be exposed by breathing, 

eating, or drinking the substance, or by skin contact. 

If you are exposed to methyl parathion, many 

factors determine whether you’ll be harmed. These 

factors include the dose (how much), the duration 

(how long), and how you come in contact with it. 

You must also consider the other chemicals you’re 

exposed to and your age, sex, diet, family traits, 

lifestyle, and state of health. 

1.1 WHAT IS METHYL PARATHION? 

Methyl parathion is a pesticide that is used to kill 

insects on crops. Usually, it is sprayed on the crops. 

Methyl parathion comes in two forms: a pure form 

of white crystals and a technical-grade solution 

(brownish liquid), which contains methyl parathion 

(80%) and inactive ingredients in a solvent. The 

technical-grade methyl parathion smells like rotten 

eggs or garlic. Methyl parathion is a manufactured 

chemical, so it is found in the environment only as a 

result of its manufacture or use. Methyl parathion 

has been manufactured in the United States since 

1952 and has been used to kill insects on many 

types of crops since this time. Because methyl 

parathion can be dangerous to humans, the EPA has 

restricted how it can be used and applied. Methyl 

parathion must be sprayed on crops from the air or 

from the ground in certain ways to minimize the 

danger of being exposed, and only trained people 

are allowed to spray methyl parathion. Methyl 

parathion is no longer used on food crops 

commonly consumed by children, and the 

maximum amount of methyl parathion that can be 

present as a residue on specific crops is regulated 

(see Section 1.9). In these ways, exposure to methyl 

parathion can be controlled and accidental 

exposures can be prevented. 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 
 

 

 

 

 

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PUBLIC HEALTH STATEMENT 

METHYL PARATHION 

CAS#: 298-00-0 

Division of Toxicology September 2001 

1.2 WHAT HAPPENS TO METHYL 

PARATHION WHEN IT ENTERS THE 

ENVIRONMENT? 

Once methyl parathion is introduced into the 

environment from spraying on crops, droplets of 

methyl parathion in the air fall on soil, plants, or 

water. While most of the methyl parathion will stay 

in the areas where it is applied, some can move to 

areas away from where it was applied by rain, fog, 

and wind. Methyl parathion stays in the 

environment from a few days to several months. It 

is degraded to other chemical compounds by water, 

sunlight, and bacteria found in soil and water. On 

soil, methyl parathion sticks to the soil, and then is 

rapidly degraded by bacteria. It generally does not 

leach through the ground and end up in the 

groundwater. In water, methyl parathion breaks 

down quickly by the action of the water, bacteria in 

the water, and sunlight. In water and air, methyl 

parathion is broken down by sunlight to form a 

more toxic product called methyl paraoxon. If 

concentrated amounts of methyl parathion are 

present in soil, such as at landfills and hazardous 

waste sites, methyl parathion does not degrade as 

fast. 

1.3 HOW MIGHT I BE EXPOSED TO 

METHYL PARATHION? 

Most people are not exposed to methyl parathion in 

the air they breathe or on things they touch, unless 

they live next to areas being sprayed. The people 

who are at the greatest risk of being exposed to 

methyl parathion are those who work with this 

chemical. These include farm workers, chemical 

sprayers, and people who work in factories that 

make methyl parathion. They are exposed to methyl 

parathion on things they touch where it can pass 

through their skin, or by breathing it after it has 

been sprayed. Overexposure to methyl parathion 

may cause severe poisoning or death. Persons may 

be exposed to dangerous amounts if they go into 

fields too soon after spraying. The people most 

likely to be exposed to methyl parathion can be 

protected by wearing special clothing and breathing 

equipment and by staying out of sprayed fields for 

at least 2 days. 

Individuals can also be exposed if they live near 

landfills where methyl parathion has been dumped 

or near water containing methyl parathion that 

washes off nearby land or that is accidentally 

spilled. The greatest amounts of methyl parathion 

are expected to be present near or on the farms 

where methyl parathion is used. After spraying, 

some methyl parathion can be transported by the 

wind or fog to areas away from where it is used, but 

the amounts present at these locations are not 

expected to be at dangerous levels. In 1988, one 

location in Mississippi had groundwater that 

contained 88 parts of methyl parathion per billion 

parts of water (ppb). More recent studies of water 

samples taken near where methyl parathion was 

sprayed indicate methyl parathion is not found in 

the groundwater. The risk of exposure to methyl 

parathion from drinking groundwater appears to be 

low, but the EPA is currently examining this issue. 

Methyl parathion is approved only for use on crops. 

The maximum amount of methyl parathion residue 

allowed by the Food and Drug Administration 

(FDA) and EPA on crops used as food is 0.1–1 

ppm. The FDA has monitored the food supply for 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 
 

 

 

 

 

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PUBLIC HEALTH STATEMENT 

METHYL PARATHION 

CAS#: 298-00-0 

Division of Toxicology September 2001 

pesticides for a number of years. FDA purchases 

many kinds of foods through Market Basket 

Surveys and analyzes them for residue levels of 

pesticides. These FDA studies allow scientists to 

estimate the daily intake of pesticides. Generally, 

the FDA monitoring studies conclude that the U.S. 

food supply contains only very small amounts of 

pesticides that are not a concern. However, there 

have been some reports of the illegal use of methyl 

parathion inside homes. 

1.4 HOW CAN METHYL PARATHION 

ENTER AND LEAVE MY BODY? 

Methyl parathion can enter your body if you eat 

food or drink water containing it; if you swim, 

bathe, or shower in contaminated water; if you 

touch recently sprayed plants or soil; if you touch 

contaminated soil near hazardous waste sites; or if 

you breathe air that contains methyl parathion, such 

as near factories or recently sprayed farm fields (or 

in recent accounts of the illegal use of methyl 

parathion, if you breathe air or touch contaminated 

surfaces inside homes where methyl parathion has 

been used to kill insects). By any means of 

exposure, methyl parathion goes into your body 

quickly and gets into your blood. From your 

bloodstream, methyl parathion goes to your liver, 

brain, and other organs. Your liver changes some of 

methyl parathion to a more harmful chemical called 

methyl paraoxon. Both methyl parathion and methyl 

paraoxon can bind to enzymes of your nerves within 

minutes or hours. Your liver breaks down methyl 

parathion and methyl paraoxon into less harmful 

substances. These less harmful substances leave 

your body in urine within hours or days. 

1.5 HOW CAN METHYL PARATHION 

AFFECT MY HEALTH? 

Methyl parathion interferes with the normal way 

that the nerves and brain function. Exposure to very 

high levels of methyl parathion for a short period in 

air or water may cause death, loss of consciousness, 

dizziness, confusion, headaches, difficult breathing, 

chest tightness, wheezing, vomiting, diarrhea, 

cramps, tremors, blurred vision, and sweating. 

Some people who have been exposed to substances 

similar to methyl parathion have experienced 

changes in mental state that lasted several months 

after exposure to high levels of these substances 

ended. If people are exposed to levels of methyl 

parathion below those that affect nerve function, 

few or no health problems seem to occur. There is 

no evidence that methyl parathion causes birth 

defects in humans or affects the ability of humans to 

produce children. There is also no proof that methyl 

parathion causes cancer in people who are regularly 

exposed, such as farmers and pesticide applicators. 

To protect the public from the harmful effects of 

toxic chemicals and to find ways to treat people 

who have been harmed, scientists use many tests. 

One way to see if a chemical will hurt people is to 

learn how the chemical is absorbed, used, and 

released by the body; for some chemicals, animal 

testing may be necessary. Animal testing may also 

be used to identify health effects such as cancer or 

birth defects. Without laboratory animals, scientists 

would lose a basic method to get information 

needed to make wise decisions to protect public 

health. Scientists have the responsibility to treat 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 
 

 

 

 

 

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PUBLIC HEALTH STATEMENT 

METHYL PARATHION 

CAS#: 298-00-0 

Division of Toxicology September 2001 

research animals with care and compassion. Laws 

today protect the welfare of research animals, and 

scientists must comply with strict animal care 

guidelines. 

Animal studies show effects of methyl parathion 

similar to those seen in people. In addition, shortterm high exposure of animals to methyl parathion 

caused decreased heart rate. This may be the result 

of methyl parathion's effects on the nerves that 

control the heart. Methyl parathion decreased the 

ability of animals to fight infections in some 

studies, but not in others. It is not known whether 

any of these effects occur in people. It is not known 

whether methyl parathion affects the ability of 

animals to reproduce. Studies in animals have not 

shown that methyl parathion causes cancer. 

1.6 HOW CAN METHYL PARATHION 

AFFECT CHILDREN? 

This section discusses potential health effects from 

exposures during the period from conception to 

maturity at 18 years of age in humans. Children are 

likely to be exposed to methyl parathion in the same 

ways as adults, mainly by eating foods or drinking 

milk or water that contain residues of this chemical. 

Because of their smaller weight, children’s intake of 

methyl parathion per kilogram of body weight may 

be greater than that of adults. The FDA and EPA 

permit residues of pesticides to be present in crops 

used as food, and these amounts are considered to 

be safe. The EPA, however, has recently used 

stricter regulations and has canceled the use of 

methyl parathion on food crops commonly eaten by 

children. As a result, the exposure of children to 

methyl parathion from foods will be very small. 

Children are affected by methyl parathion in the 

same manner as adults. Exposure to high levels of 

methyl parathion, even for short periods, may result 

in changes in the nervous system, leading to 

headaches, dizziness, confusion, blurred vision, 

difficulty breathing, vomiting, diarrhea, loss of 

consciousness, and death (see also Section 1.5 for a 

more complete description of how methyl parathion 

affects human health). It is not known whether 

children are more sensitive to the effects of methyl 

parathion than adults. There is some indication that 

young rats may be more sensitive than adults to 

nervous system effects. 

There is no evidence in humans that methyl 

parathion causes birth defects. Birth defects have 

not been seen when methyl parathion was given to 

animals by mouth, but minor birth defects did occur 

in one study in which high doses were injected into 

pregnant animals. It is not known whether these 

effects occur in people. It is unlikely that people 

would be exposed by breathing, touching, or eating 

as much methyl parathion as was injected in the 

animal studies. Animal studies have also shown that 

methyl parathion can be transferred from a pregnant 

mother to the developing fetus. Methyl parathion 

caused changes in the behavior of young animals 

whose mothers were given methyl parathion during 

pregnancy, and this effect needs to be studied more. 

Methyl parathion has been detected in small 

amounts in breast milk, but only in a few localities 

in central Asia. Studies of mother animals fed 

methyl parathion show that methyl parathion can be 

transferred into their milk and their nursing 

newborn babies. 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 
 

 

 

 

 

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PUBLIC HEALTH STATEMENT 

METHYL PARATHION 

CAS#: 298-00-0 

Division of Toxicology September 2001 

1.7 HOW CAN FAMILIES REDUCE THE 

RISK OF EXPOSURE TO METHYL 

PARATHION? 

If your doctor finds that you have been exposed to 

significant amounts of methyl parathion, ask 

whether your children might also be exposed. Your 

doctor might need to ask your state health 

department to investigate. 

The only approved use of methyl parathion is on 

crops, including crops used as foods. Effective 

December 31, 1999, the EPA cancelled the use of 

methyl parathion on many kinds of crops used as 

foods because of a concern for exposure risks to 

children and to workers. This action will reduce the 

risks to families of methyl parathion exposure from 

food. The general population is not likely to be 

exposed to large amounts of methyl parathion. The 

populations living in the areas where methyl 

parathion is used on crops, however, may be 

exposed to greater amounts of methyl parathion. 

Methyl parathion is often detected in foods and air 

samples collected where methyl parathion is used. 

People who live close to areas of methyl parathion 

use also may be exposed to larger amounts of 

methyl parathion, because small amounts of the 

pesticide will move from the place where it is used 

to nearby areas. These exposures may include such 

things as touching contaminated plants, breathing 

the mist formed from the sprayed chemical, 

drinking contaminated water, or eating recently 

sprayed fruits and vegetables. People who are most 

likely to receive the highest exposures are those 

who work in the factories that make methyl 

parathion, workers who spray it on crops, and 

farmers. Entry of methyl parathion into the body 

after contact with the skin is expected to be the 

major exposure pathway for those working in these 

operations. Breathing the mist containing methyl 

parathion may also occur. 

Families can reduce the risk of exposure to methyl 

parathion in the soil, on plants, or in the air by 

staying away from fields that have been recently 

sprayed. If families wait at least 4–5 days before 

entering sprayed fields, then the amount of methyl 

parathion present in the air or on plants is expected 

to be small. Families should also be aware that 

sometimes methyl parathion has been illegally 

sprayed inside the home to kill insects. Your 

children may be exposed to methyl parathion if an 

unqualified person applies pesticides containing it 

around your home. In some cases, the improper use 

of pesticides banned for use in homes has turned 

homes into hazardous waste sites. Make sure that 

any person you hire is licensed and, if appropriate, 

certified to apply pesticides. Your state licenses 

each person who is qualified to apply pesticides 

according to EPA standards and further certifies 

each person who is qualified to apply “restricted 

use” pesticides. Ask to see the license and 

certification. Also ask for the brand name of the 

pesticide, a Material Safety Data Sheet (MSDS), the 

name of the product’s active ingredient, and the 

EPA registration number. Ask whether EPA has 

designated the pesticide “for restricted use” and 

what the approved uses are. This information is 

important if you or your family react to the product. 

If you buy over-the-counter pesticide products to 

apply yourself, be sure the products are in unopened 

pesticide containers that are labeled and contain an 

EPA registration number. Carefully follow the 

instructions on the label. If you plan to spray inside, 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 
 

 

 

 

 

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PUBLIC HEALTH STATEMENT 

METHYL PARATHION 

CAS#: 298-00-0 

Division of Toxicology September 2001 

make sure the pesticide in intended for indoor use. 

If you feel sick after a pesticide has been used in 

your home, consult your doctor or local poison 

control center. 

1.8 IS THERE A MEDICAL TEST TO 

DETERMINE WHETHER I HAVE BEEN 

EXPOSED TO METHYL PARATHION? 

Several medical tests can determine whether you 

have been exposed to methyl parathion. The first 

medical test measures methyl parathion in your 

blood or measures 4-nitrophenol, which is a 

breakdown product of methyl parathion, in your 

urine. These tests are only reliable for about 24 

hours after you are exposed because methyl 

parathion breaks down quickly and leaves your 

body. These tests cannot tell whether you will have 

harmful health effects or what those effects may be. 

The next medical test measures the levels of a 

substance called cholinesterase in your blood. If 

cholinesterase levels are less than half of what they 

should be and you have been exposed to methyl 

parathion, then you may get symptoms of 

poisoning. However, lower cholinesterase levels 

may also only indicate exposure and not necessarily 

harmful effects. The action of methyl parathion may 

cause lower cholinesterase levels in your red blood 

cells or your blood plasma. Such lowering, 

however, can also be caused by factors other than 

methyl parathion. For example, cholinesterase 

values may already be low in some people, because 

of heredity or disease. However, a lowering of 

cholinesterase levels can often show whether 

methyl parathion or similar compounds have acted 

on your nerves. Cholinesterase levels in red blood 

cells can stay low for more than a month after you 

have been exposed to methyl parathion or similar 

chemicals. 

1.9 WHAT RECOMMENDATIONS HAS THE 

FEDERAL GOVERNMENT MADE TO 

PROTECT HUMAN HEALTH? 

The federal government develops regulations and 

recommendations to protect public health. 

Regulations can be enforced by law. Federal 

agencies that develop regulations for toxic 

substances include the Environmental Protection 

Agency (EPA), the Occupational Safety and Health 

Administration (OSHA), and the Food and Drug 

Administration (FDA). Recommendations provide 

valuable guidelines to protect public health but 

cannot be enforced by law. Federal organizations 

that develop recommendations for toxic substances 

include the Agency for Toxic Substances and 

Disease Registry (ATSDR) and the National 

Institute for Occupational Safety and Health 

(NIOSH). Regulations and recommendations can be 

expressed in not-to-exceed levels in air, water, soil, 

or food that are usually based on levels that affect 

animals; then they are adjusted to help protect 

people. Sometimes these not-to-exceed levels differ 

among federal organizations because of different 

exposure times (an 8-hour workday or a 24-hour 

day), the use of different animal studies, or other 

factors. Recommendations and regulations are also 

periodically updated as more information becomes 

available. For the most current information, check 

with the federal agency or organization that 

provides it. Some regulations and recommendations 

for methyl parathion include the following: 

NIOSH recommends that a person not be exposed 

in the workplace to more than 0.2 mg/m3 of methyl 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 
 

 

 

 

 

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PUBLIC HEALTH STATEMENT 

METHYL PARATHION 

CAS#: 298-00-0 

Division of Toxicology September 2001 

parathion for a 10-hour workday, 40-hour 

workweek. 

According to EPA, the following levels of methyl 

parathion in drinking water are not expected to 

cause effects that are harmful to health: 0.3 mg/L 

for 1 or 10 days of exposure for children, 0.03 mg/L 

for longer term exposure for children, and 0.002 

mg/L for lifetime exposure of adults. 

It is illegal to use methyl parathion indoors. Methyl 

parathion is approved only for use on agricultural 

crops. In 1999, EPA canceled the use of methyl 

parathion on many food crops, particularly those 

consumed by children, such as apples, peaches, 

pears, carrots, and peas, and also canceled nonfood 

uses such as ornamental plants and nursery stock 

uses. Methyl parathion use is still allowed on other 

crops eaten by people or by farm animals. A 

maximum of 0.1–1 ppm of methyl parathion is 

allowed in or on the other crops (fruits, vegetables, 

nuts, and grains) that may be eaten by people. 

1.10 WHERE CAN I GET MORE 

INFORMATION? 

If you have any more questions or concerns, please 

contact your community or state health or 

environmental quality department or: 

Agency for Toxic Substances and Disease Registry 

Division of Toxicology 

1600 Clifton Road NE, Mailstop F-32 

Atlanta, GA 30333 

Information line and technical assistance: 

Phone: 888-422-8737 

FAX: (770)-488-4178 

ATSDR can also tell you the location of 

occupational and environmental health clinics. 

These clinics specialize in recognizing, evaluating, 

and treating illnesses resulting from exposure to 

hazardous substances. 

To order toxicological profiles, contact: 

National Technical Information Service 

5285 Port Royal Road 

Springfield, VA 22161 

Phone: 800-553-6847 or 703-605-6000 

Reference 

Agency for Toxic Substances and Disease Registry 

(ATSDR). 2001. Toxicological profile for methyl 

parathion. Update. Atlanta, GA: U.S. Department of 

Health and Human Services, Public Health Service. 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov