Atrazine has been a major agricultural herbicide for more than 40 years and
may be found in some public or private drinking water supplies. It may cause
health problems if found in amounts greater than the health standard
established by the US Environmental Protection Agency (EPA), which is 3 parts
per billion (ppb).
The EPA established the maximum contaminant level (MCL) for
atrazine in 1994. This is an enforceable level for public drinking water
systems and, according to the EPA, is a concentration that is safe to drink
over a 70-year lifetime with no adverse effects.
Recent findings indicate that elevated amounts of atrazine
are running off fields and entering surface water resources. It may also be
released to the environment in wastewater from manufacturing facilities.
Installing advanced treatment systems for removing atrazine
could result in substantial costs to small water systems and their consumers.
Alternative strategies focus on controlling atrazine at its
source and preventing or limiting its discharge into surface water. Atrazine
runoff is lessened when: atrazine is applied to a dry soil surface; there is at
least seven days between herbicide application and the first rainstorm-caused
runoff; and the first rain after application is of low intensity.
Checking water sources
Public water supplies that use ground/surface water sources
must follow this schedule for water sampling and monitoring:
- Initial frequency. Four quarterly samples must be
taken every three years.
- Repeat frequency. If atrazine is not detected
during the initial round, sampling can be reduced to two quarterly samples each
year if serving more than 3,300 people - one sample every three years for
smaller systems.
- Triggers. Systems must return to initial testing
frequency if atrazine is detected at more than 0.001 milligrams per liter.
The EPA has recently decided that atrazine is a greater
public health threat than previously supposed, especially for children.
The agency upgraded its assessment of atrazine from a
"possible" to a "likely" carcinogen. EPA officials also
determined that as little as a single day of exposure may cause serious
developmental and reproductive disabilities in fetuses, children and young
males.
Health effects of atrazine include the following:
- Short-term. The EPA has found atrazine to
potentially cause congestion of heart, lungs and kidneys, low blood pressure,
muscle spasms and weight loss and damage to adrenal glands when people are
exposed to levels above the MCL for relatively short periods of time.
- Long-term. Atrazine has the potential to cause the
following effects from a lifetime exposure at levels above the MCL: weight
loss, cardiovascular damage, retinal and some muscle degeneration, cancer.
Detection is frequent
The combination of widespread use and relative persistence
in the environment help account for its frequent detection in surface and
groundwaters. Microbial activity and other chemicals may break down atrazine in
soil and water, particularly in alkaline conditions.
Photodegradation and volatilization do not reduce its
presence. It may bind to some soils, but generally tends to leach to
groundwater. Atrazine is not likely to be taken up in the tissues of plants or
animals.
If the contaminant levels are above the MCL, water suppliers
must take steps to reduce the amount of atrazine so that it is consistently
below that level. If a utility detects atrazine in the water source, then it
has to implement nonpoint source controls in the watershed or treat the raw
water.
Granular activated carbon (GAC) has been approved by the EPA
as the best available technology (BAT) for the control of herbicides, including
atrazine. GAC has been shown to reduce atrazine levels to below analytical
detection limits. GAC has an advantage in that it addresses other treatment
requirements, such as taste and odor, and provides continuous control.
Most small systems do not have a granular activated charcoal
system in place, and adding it would increase their operating costs. Activated
charcoal filters are available for household treatment of drinking water at the
point of use.
There are other alternatives: Powdered activated carbon
(PAC) treatment has been considered appropriate for full-scale treatment. PAC
is cheaper - it doesn't require the capital equipment of GAC - and can be added
easily to the water during treatment. This makes PAC an attractive alternative
for water suppliers experiencing seasonal herbicide occurrences.
Some other techniques that show promise, but require further
study include ozone, advanced oxidation, reverse osmosis, photocatalytic
reactions and synthetic resins.
If the levels of atrazine exceed the MCL, systems must
notify the public via newspapers, radio, television and other means. Additional
actions, such as providing alternative drinking water supplies, may be required
to prevent serious risks to public health.
The 1996 amendments to the Safe Drinking Water Act required
the EPA to re-evaluate its limit for atrazine in drinking water, and the
revised standard was due in August 1999. However, that deadline has not been
met.
The EPA now says it may alter the 3-ppb standard, based on
annual average levels, to protect vulnerable populations from seasonal peaks.
Utilities could be required to test for the chemical daily during peak
contamination periods.
Banning atrazine would reduce water contamination, but could
also increase other health and environmental risks. Adoption of best management
practices for atrazine on an individual field is the preferred method for
reducing risks while retaining benefits. The environmental risk of atrazine can
be managed by altering the application rates, timing and placement of the
herbicide.
Zacharia M. Lahlou, Ph.D., is the technical assistance
coordinator for the National Drinking Water Clearinghouse, Morgantown, WV. He
can be reached by e-mail at mlahlou2@wvu.edu.
