Atrazine, a widely used agricultural weedkiller that disrupts hormones, contaminates tap water supplies for about 7.6 million Americans at potentially harmful levels. But the federal government is doing little to counter the threat.

EWG’s Tap Water Database, based on water tests by public water systems nationwide, shows that in 2015 atrazine was detected in more than 800 systems in 19 states at levels exceeding a health-protective guideline. The annual average atrazine level did not exceed the legal limit set by the federal Safe Drinking Water Act in these systems, but that level is 20 times a non-enforceable public health goal determined by California state scientists.

High levels of atrazine were found in 237 water systems serving more than 3 million people in Texas, and in 192 systems serving more than a million people in Kansas. Other states struggling with widespread atrazine contamination of drinking water are Kentucky, Missouri and Ohio. To see if atrazine contaminates your tap water supply, search for your local water utility in EWG’s database.

Atrazine, manufactured by the agro-chemical giant Syngenta, is one of the most heavily sprayed pesticides in American agriculture. EWG's analysis of data from the U.S. Geological Survey and the EPA for 2014, the most recent year available, found that most of the 70 million to 80 million pounds of atrazine used each year are sprayed on corn during the spring. The highest levels of atrazine in tap water are detected in May and June.

In 2012 Syngenta settled a class action lawsuit brought by water utilities with atrazine contamination for $105 million. The settlement money was distributed to communities with the most contamination, but for many systems even this was too little money to cover costs of long-term water treatment.

Atrazine has been banned in Europe since the 1980s under laws that prohibit the use of any pesticide that contaminates drinking water. But in U.S., the federal government places few restrictions on its use.

Atrazine harms hormones in people and wildlife

Tyrone Hayes, a biologist at the University of California, Berkeley, has found that atrazine can cause male frogs to become “functionally female,” or hermaphroditic. In humans, atrazine disrupts the male and female hormone systems.

Recent studies of American communities with atrazine-contaminated water associate exposure with increased cancer risk, shorter pregnancy and altered menstrual cycles. These studies examine people drinking water with atrazine concentrations well below the federal legal limit of 3 parts per billion, or ppb. A part per billion is about one drop of water in an Olympic-size swimming pool. In contrast, scientists at the California Office of Environmental Health Hazard Assessment determined in 1999 that atrazine contamination of tap water above 0.15 ppb increases the lifetime risk of developing cancer.

Federal atrazine rules fail to protect young children and the developing fetus

The EPA's monitoring data for 2014 show that some Midwestern communities experience atrazine spikes in the spring and summer at levels well above the legal limit. In 2014, atrazine concentrations in 18 communities exceeded the legal limit of 3 ppb, sometimes for weeks. For example, atrazine contamination peaked at 32 ppb in Blanchester, Ohio, from May 5 to June 9, and at 21 ppb in Beloit, Kan., from June 9 to July 7.

The EPA monitoring program targets water systems most vulnerable to atrazine contamination. The systems monitored change from year to year, which can make comparison between years and analysis of trends difficult. The EPA has not yet released data for 2015 or 2016 – information should be immediately released to let families, utilities and regulators know if their communities are at risk of exposure to unsafe levels of the pesticide.

Atrazine poses the biggest health risks during pregnancy and infancy. Because of their small size and limited diets, bottle-fed babies consume five to six times higher doses of water pollutants than adults in the same household. Scientists don't how long children must be exposed before suffering harm – but when it comes to children’s health, why take a risk?

EWG and our supporters have demanded that the EPA ban this water-contaminating pesticide. Until this happens, EWG recommends filtering your tap water. Check out EWG’s Water Filter Buying Guide to find the right home water filter for your budget and living circumstances.

Read more about atrazine here.