Atrazine a Challenge for Small Systems

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.