Public Health Statement for Methyl Parathion
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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 ToxFAQs™, 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 1-800-232-4636.
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.
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 What recommendations has the federal government made to protect human health?). In these ways, exposure to methyl parathion can
be controlled and accidental exposures can be prevented.
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.
For more information, see Chapters 4, 5, and 6 of the toxicological profile.
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.
For more information, see Chapter 6 of the toxicological profile.
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 to 1 ppm. The FDA has monitored
the food supply for 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
For more information, see How can families reduce the risk of exposure to methyl parathion? and Chapter 6 of the toxicological profile.
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.
For more information, see Chapter 3 of the toxicological profile.
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 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, short-term
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.
You can find more information on the
health effects associated with exposure to methyl parathion
in Chapters 2 and 3 of the toxicological profile.
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 How can methyl parathion affect my health? 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.
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, 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
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.
For more information, see Chapters 3 and 7 of the toxicological profile.
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
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
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 0.11
ppm of methyl parathion is allowed in or on the other crops
(fruits, vegetables, nuts, and grains) that may be eaten by
For more information, see Chapter 8 of the toxicological profile.
Agency for Toxic Substances and Disease Registry (ATSDR). 2001. Toxicological profile for Methyl Parathion. Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service.
Where can I get more information?
If you have questions or concerns, please contact your community or state health or environmental quality department or:
For more information, contact:
Agency for Toxic Substances and Disease Registry
Division of Toxicology and Human Health Sciences
4770 Buford Highway
Chamblee, GA 30341-3717
Phone: 1-800-CDC-INFO 888-232-6348 (TTY)
Email: Contact CDC-INFO
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.