Weed Killers By The Glass
September 1, 1995

Weed Killers By The Glass: Introduction

The Safe Drinking Water Act amendments of 1986, which require the EPA to set drinking water standards for many pesticides, marked the beginning of the scientific community's focus on pesticides in drinking water as a threat to public health. Soon after these amendments went into effect, the first extensive national and regional studies of pesticides in ground and surface water began to define the scope of the problem.

By the early 1990s, numerous studies, primarily by scientists at the United States Geological Survey and in state environmental agencies, had found widespread evidence that commonly used corn and soybean herbicides were ubiquitous contaminants of water supplies. As early as September 1991, representatives of drinking water utilities requested that EPA place the herbicide atrazine into a special regulatory review, and impose mandatory use restrictions due to their concerns over the frequent appearance of atrazine in drinking water (Gloriod 1991).

In September 1994, the Environmental Working Group and Physicians for Social Responsibility released Tap Water Blues, the first-ever state-by-state, community-by-community analysis of the presence and adverse health impacts of pesticides in drinking water and source water for drinking water systems. The important findings of this study include:


1. Triazine herbicides such as atrazine, cyanazine, and simazine and acetanilide herbicides such as alachlor, metolachlor, and acetochlor contaminate virtually every surface-water-supplied, drinking water source in the Mississippi River basin.

EWG estimated that at least 11.7 million people in the Midwest and Louisiana drink water that is contaminated with a combination of these herbicides. This population includes hundreds of thousands of children who drink infant formula reconstituted with herbicide-contaminated water each day.


2. In late spring and early summer concen-trations of these herbicides in Mississippi River basin drinking water routinely exceed EPA's maximum contaminant levels (MCLs) and Lifetime Health Advisories (LHAs).

Results of finished tap water sampling in several states showed intermittent or sustained peak exposures well above federal health standards for atrazine and cyanazine.


3. Individuals are frequently exposed to multiple herbicides in a single glass of tap water.

Exposure to more than one pesticide is often the rule rather than the exception. Studies by the U.S. Geological Survey in the Mississippi River basin found two or more pesticides in 87 percent of all water samples, and four or more pesticides in 41 percent of all samples (Goolsby, et al. 1993). In Illinois, more than one in three samples of finished drinking water samples collected in 1993 and 1994 contained multiple pesticides (Illinois EPA 1994). A total of 67 different pesticides, including 25 probable or possible human carcinogens, have been found in drinking water sources in the Midwest. None of these pesticides are removed by conventional water treatment.


4. Pesticide application rate reductions will not solve the drinking water contamination problem.

In 1993 the Environmental Protection Agency required that growers reduce the amount of atrazine applied to corn and other crops. These use reductions have had virtually no effect on total chemical use, and have done little or nothing to reduce drinking water contamination.


5. Farmers have alternatives to current use of hazardous herbicides.

Currently, almost all herbicide applications in corn are prophylactic and made with no assessment of weed or weed seed populations. University studies have found that in an average year, farmers lose money on 30 to 50 percent of all herbicide applications in the Corn Belt. And newer, safer alternatives -- the sulfonylurea herbicides -- are readily available to replace the more hazardous triazine and acetanilide herbicides, but are not being used.

Although scientists and water utilities have known for years that weed killers contaminate drinking water supplies and treated tap water throughout the Midwest, better information on contamination of treated tap water will greatly improve the ability of regulators and public health officials to accurately describe the health risks associated with peak runoff periods in the spring and early summer.

At the time of the release of Tap Water Blues, the best data available were typified by data from the state of Illinois, which for one year had monitored treated drinking water for herbicides in 113 cities and towns that rely on surface water for drinking water. These data showed unequivocally that weed killers are present in tap water in major corn growing areas, often at levels exceeding federal health standards. This information, however, is only as good as the federal Safe Drinking Water Act requires, which means that only four quarterly samples were available for each town -- one sample during the peak contamination period.

The purpose of this study is to fill the gaps in knowledge so that regulators and the public may better understand the extent and nature of tap water contamination with atrazine and cyanazine, including the severity and duration of peak levels of exposure that routinely exceed federal health standards during the three- to four-month peak runoff period. Additional monthly analyses were performed to identify 11 other pesticides and pesticide by-products that contaminate tap water in the region.