Atrazine in Drinking Water and Groundwater
Written by Mr. Brian Oram, PG
Residential Private Water Supply and Homeowner Drinking
Water Testing Evaluation Program
In Pa, Atrazine was primarily used as a herbicide to control selective
broadleaf weed for Corn.
What is atrazine?
Atrazine is a herbicide that selectively controls broadleaf (dicot) weeds, such as pigweed, cocklebur, velvetleaf and certain grass weeds in fields of corn and sorghum.
Selective control means that the target weeds are controlled, with little or no injury to the crop. Atrazine is well tolerated by actively growing corn and sorghum, which absorb and metabolize the herbicide and thereby detoxify it. In Pennsylvania, atrazine has been applied to over 90% of the corn crop.
Atrazine is still widely used today because it is economical and effectively reduces crop losses due to weed interference. Its use can also reduce or eliminate the need for inter-row cultivation in corn and sorghum fields. Atrazine is a frequently used herbicide used on corn, soybeans, sorghum, sugar cane, pineapple, pine trees, other crops and as a non-specific herbicide on industrial sites. It is of particular concern to water supplies due to its popularity, relatively long half life (60 to 100 days) and because it is not strongly absorbed by soil (Koc = ~100).
Toxicity is measured in different ways. Acute oral toxicity is a measure of how poisonous or toxic a substance is when swallowed as a single dose. The acute oral toxicity of atrazine in laboratory rats is 5100 mg/kg. If we assume the acute oral toxicity in humans is the same as that in laboratory rats, then a 150-pound person would have a 50 percent probability of dying from ingesting about 0.75 pound of atrazine in a single dose. By comparison, one-half pound of table salt or 2.5 ounces of aspirin would produce the same probability of death by acute poisoning.
The reason atrazine is effective for weed control, but relatively non-toxic to animals, is that it inhibits photosynthesis in susceptible plants. Photosynthesis is the process that occurs in green leaves and stems of plants, whereby light energy is converted to chemical energy (carbohydrates). This process is not present in animals.
Chronic toxicity is an estimate of how a substance would affect an organism over a long period of time -- a life span, for example -- at very low levels of exposure. In practice, measuring chronic effects on a population of laboratory animals is not feasible. Therefore, much higher concentrations of the substance are administered to laboratory animals for up to several generations, with the results extrapolated to trace level exposures to the human population. Whereas the methodology for determining acute toxicity is rather straightforward, the methodology to estimate chronic toxicity is much more subjective, and heavily influenced by public policy.
Long term -- chronic -- toxicology studies on animals are used to determine the "maximum tolerated level" and the "no observable effect level" for pesticides and other substances. Additional safety factors are applied to the "no observable effect" level in order to establish the EPA's drinking water limit, also called the "maximum contaminant level," or MCL. Normally a 100-fold safety factor is applied to the "no observable effect" level. For atrazine, however, a mammary tumor in a two-generation rat study triggered an additional safety factor. This resulted in an MCL for atrazine of 3 ppb, which has a 5000-fold safety factor. This is the concentration of atrazine that the EPA considers safe to consume in drinking water over an average 70-year human life span.
Acute Health Effects: EPA has found atrazine to potentially cause a variety of acute health effects from acute exposures at levels above the MCL. These effects include: congestion of heart, lungs and kidneys; hypotension; antidiuresis; muscle spasms; weight loss; adrenal degeneration.
Chronic Health Effects: Atrazine has the potential to cause weight loss, cardiovascular damage, retinal and some muscle degeneration, and mammary tumors from a lifetime exposure at levels above the MCL.
What about atrazine in private water supply wells?
Atrazine is sometimes detected in groundwater. In most instances, the source of atrazine in well water may be caused by leaching near the wellhead due to atrazine loading, cleanup activities or back siphoning accidents during sprayer loading . Atrazine is not recommended for use in areas where mixing of surface and groundwater could lead to atrazine contamination of shallow aquifers. This would include areas with shallow water tables and coarse-textured soils. The atrazine label also prohibits mixing, loading or application within 50 feet of a well.
For your information, EPA's Pesticides in Ground Water Database indicates numerous detections of atrazine at concentrations above the MCL in ground water in several States, including Delaware, Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska and New York. For Pennsylvania, atrazine has been detected in 22 % of the private water supplies tested in the corn producing regions of Pennsylvania.
1. Get your Water Tested and encourage your neighbors to do the same.
2. Compile information on the types and location of hazardous waste and industrial sites in your area- use an atrazine sceening kit.
3. Other water testing services- Water Check Testing Packages - multiple packages to fit your needs- Testing can include
20 herbicides, pesticides, and PCBs- Kit 9002.
4.Whole System treatment options for Organics (GAC Systems)
5. New Free Publication on Drinking Water Quality
Other trade names for Atrazine
Trade Names and Synonyms:
Water Quality Help Guides
Glossary of Water Terminology
Basics of Industrial Water Treatment