Pesticides pose a health threat not only because of their

toxicity, but also because of their widespread use in the U.S.

There are now about 21,000 registered pesticide products,

with almost 900 active ingredients. In a typical year, about

1.2 billion pounds of conventional pesticides and other

chemicals are used in the U.S. for pest control in agriculture,

of their extensive use over the last half-century, pesticides

are ubiquitous in our environment, and human exposure is

virtually inevitable. National population-based surveys of

pesticide urinary metabolites in adults indicate widespread

Drinking water can be a significant source of chronic

pesticide exposure, especially in agricultural regions where

U.S. Geological Survey (USGS) found pesticides in more

than 95% of stream samples and almost 50% of ground water

contamination is critically important because 38% of the

water used for public water supplies is obtained from ground

seasonal surface water concentrations of pesticides frequently

exceeded federal drinking water standards in agricultural

and ground water vary considerably with the seasons and

local geology, with highest concentrations often occurring

For many pesticides, our understanding of human health

effects is based largely on occupational or accidental

exposures, or laboratory animal studies, in which doses can

be relatively high. Effects such as weight loss, organ damage,

muscle degeneration, neurological damage, and cancer have

been documented based on such studies. In fact, more than

160 pesticide active ingredients have been classified as known

However, environmental exposures to pesticides, such as

through drinking water, usually involve relatively low

concentrations that may occur over long periods of time.

While the human health effects associated with chronic, lowlevel

pesticide exposures are not yet well understood, a

growing body of scientific evidence suggests that

environmental pesticide exposures are associated with

neurological and reproductive damage, effects on growth

and development, birth defects, endocrine disruption, cancer,

and other adverse effects.

Given the ubiquitous nature of pesticides in our

environment, this emerging evidence raises serious public

health concerns. Every effort must be made to use

precautionary strategies to minimize or prevent pesticide

exposures while further evidence is collected through

research. This fact sheet summarizes health effects

information for many of the most commonly found pesticides

in public drinking water supplies, and offers suggestions on

ways that health professionals can help to reduce this public

health threat.

The triazine class of pesticides includes some of the most

widely used agricultural herbicides, including atrazine and

simazine. Atrazine has been found in up to 97% of surface

(Table 1). A study by the Environmental Working Group

estimated that atrazine contaminates tap water delivered to

The triazine pesticides simazine, cyanazine, and propazine

are classified as “possible human carcinogens” by the EPA.

Atrazine was also in the same category until it was recently

downgraded by the EPA to “not likely to be a human

Cancer (IARC) has stated that atrazine “is not classifiable as

to its carcinogenicity in humans,” but that there is “sufficient

evidence in experimental animals for carcinogenicity of

association between exposure to triazine herbicides in

evidence of associations between triazine pesticide exposure

According to EPA, lifetime exposure to atrazine at levels

above the drinking water standard has the potential to cause

weight loss; cardiovascular damage; retinal and some muscle

shown to cause chromosomal damage at low concentrations

(comparable to the EPA drinking water standard) in animal

evidence that atrazine and other triazine herbicides are

simazine can cause tremors; damage to testes, kidneys, liver,

epidemiological study in Iowa found an association between

maternal exposure to triazine herbicides in drinking water

(See PSR’s drinking water fact sheet on atrazine for further

information about this particular pesticide).

Chlorophenoxy herbicides are widely used for control of

broadleaf weeds in agriculture; control of vegetation along

roadsides, railways, and utility rights-of-way; and

maintenance of parks, golf courses, and home lawns and

gardens. The chlorophenoxy herbicides 2,4-D and dicamba

are among the most commonly occurring pesticides found

According to EPA, chronic exposure to 2,4-D above the

federal drinking water standard has the potential to cause

Agricultural use of 2,4-D has also been linked to mortality

2,4-D as having “inadequate evidence for carcinogenicity

in humans.” Epidemiological studies have also reported

an association between exposure to 2,4-D and non-

The organochlorine insecticides aldrin and dieldrin were

widely used in the U.S. from the 1950s to the early 1970s.

Most uses for aldrin and dieldrin were banned in 1975, based

on potential for carcinogenicity in humans, and they are no

longer produced in the U.S. Lindane has not been produced

in the U.S. since 1977, but is still imported for restricted

uses. Despite these restrictions, organochlorine insecticides

are still found in drinking water supplies (Table 1) because

they are highly resistant to degradation in the environment.

These insecticides have been associated with lymphoma,

leukemia, soft tissue sarcoma, neuroblastoma, and cancers

health effects have been associated with chronic exposure

to organochlorine insecticides. Animal studies suggest that

these compounds may cause birth defects and may decrease

In addition to the pesticides described above, a wide variety

of other pesticides commonly contaminate treated drinking

water and water sources. The herbicides alachlor and

metolachlor have been frequently detected in public drinking

certain organophosphate insecticides, including chlorpyrifos,

diazinon, and malathion, are commonly found in streams

Despite their frequent occurrence as surface water

contaminants, EPA has not established drinking water

maximum contaminant levels (MCLs) for these insecticides

and does not require that they be monitored in public water

supplies. Many of the long-term health effects of low-dose

exposure to these chemicals are not yet known. However,

the failure to monitor and regulate these chemicals

in drinking water raises serious public health concerns, given

the potential for these chemicals to cause effects such as

cancer, birth defects, behavioral effects, and neurological

damage.

Studies have shown that resident farm families, farm workers,

and their children are among those most highly exposed to

infants, and children may be more susceptible to the adverse

effects of pesticides than the general population. Infants that

are fed formula reconstituted with contaminated tap water may

be at significant health risk, particularly in areas of the Midwestern

U.S. where tap water contamination with herbicides is

Children are disproportionately exposed to pesticides

because they eat and drink more than adults in relation to

mouth contact by toddlers and young children can also

increase exposure to pesticides in the home. In a

comprehensive evaluation of childhood pesticide exposure,

a committee of the National Academy of Sciences (NAS)

concluded in 1993 that there are significant differences in

the toxicity of pesticides between children and adults.

Children have immature metabolic systems and are generally

less able than adults to detoxify pesticides. The NAS

committee also determined that, on occasion, childhood

exposures to pesticides through food and diet can exceed

safe levels.

EPA does not regulate levels of many pesticides that

commonly occur in drinking water or source water. The EPA

has developed MCLs for fewer than 25 registered pesticides.

In addition, MCLs are based on single chemical exposures

and may not adequately protect against adverse health effects

from exposure to mixtures of pesticides or pesticide

breakdown products. It is also important to recognize that

EPA does not regulate the quality of drinking water from

domestic wells. It is the responsibility of the homeowner to

have their water tested to ensure it is safe to drink.

The 1993 NAS review of children’s exposure to pesticides

resulted in the recommendation that EPA change its

decision-making process for establishment of acceptable

levels of pesticides in food, known as tolerances. Rather than

focusing on economics and agricultural practices, decisions

should be driven by health considerations. This

recommendation led to the enactment of the Food Quality

Protection Act (FQPA) in 1996. The FQPA requires that

food tolerances for pesticides take into account all exposures

to pesticides, including exposure via drinking water. Under

this law, aggregate exposure must be safe for infants and

children, and pesticide use on food crops is prohibited if the

risk from pesticides in drinking water exceeds the safety

standards set in the law. This law has particular significance

for areas of the Midwest where there is widespread

contamination of drinking water supplies by herbicides used

of the FQPA, recent congressional sessions have seen

increasing support for industry-led attempts to dismantle

this important legislation.

live in areas where water contamination is known or

suspected to use ready-to-feed infant formula instead of

formula reconstituted with tap water.

tested for pesticide contamination. Local health

departments or EPA’s Safe Drinking Water Hotline can

direct well owners to certified laboratories that can perform

such tests. If contamination is found, home water filtration/

treatment units can be effective at removing pesticides and

other contaminants. Contact NSF International (listed

below) for information on certified products.

the Consumer Confidence Report from their water utility.

effects of pesticides to prepare yourself for questions from

patients.

ground water. Urge your patients and your community

to use pesticides as a last defense against pests. Nonchemical

control methods and other sustainable

alternatives are available to meet many different needs. If

they do use pesticides in or around the house, urge them

to use caution and to carefully read product safety labels.

protections. Press EPA and Congress to implement

health-protective standards for the many pesticides that

threaten our drinking water supplies. Advocate for

enactment of stronger drinking water “right-to-know”

provisions that will inform all consumers—in a timely

manner—about pesticide contamination in their drinking

water. Become involved in efforts to preserve the vital

health protections provided by the FQPA. For assistance