Atrazine is one of the most widely used herbicides in the United States, and it shows up far beyond the farm fields where it’s applied. It contaminates surface water, groundwater, drinking water, rainfall, and soil across large portions of the country, particularly in agricultural regions of the Midwest and Southeast. Understanding where atrazine turns up helps explain why it remains one of the most closely monitored pesticides in the U.S.
Crops and Fields Where Atrazine Is Applied
Atrazine is sprayed primarily on corn, sorghum, and sugarcane to kill broadleaf weeds. Corn accounts for the vast majority of use. In several states, 80% to 90% of corn acreage is treated with atrazine every year. Louisiana, Oklahoma, and South Carolina lead the country, with roughly 90% of their corn crops receiving atrazine applications. States like Alabama, Arkansas, Delaware, Georgia, Kansas, Maryland, Missouri, North Carolina, and Virginia treat about 80% of their corn acreage. The EPA currently restricts annual application to 2 pounds of active ingredient per acre or less for corn and sorghum.
Outside of agriculture, atrazine is also applied to residential lawns and golf courses, especially in the southeastern United States. The EPA has moved to reduce allowable application rates on residential turf, cutting spray applications from 2.0 to 1.0 pounds of active ingredient per acre. So even if you don’t live near a farm, atrazine may be used in your neighborhood or at local recreational areas.
Surface Water and Streams
Surface water is where atrazine turns up most consistently. A U.S. Geological Survey study detected atrazine in 100% of surface water samples collected from eastern Iowa over a two-year period, with concentrations reaching as high as 100 parts per billion (ppb). Nationally, about 92% of surface water samples contain detectable levels of atrazine.
Concentrations fluctuate dramatically by season. Spring and summer, when farmers apply atrazine and rainfall washes it off fields, produce the highest levels. In Iowa’s public water systems that draw from surface water, seasonal peaks reached 11.2 ppb in spring and 25.5 ppb in summer. By fall, the maximum dropped to 1.9 ppb, and winter readings topped out at 3.6 ppb. For context, the EPA’s legal limit for atrazine in drinking water is 3 ppb, meaning seasonal spikes in untreated source water regularly exceed that threshold.
About 53% of public water system samples drawn from surface water sources contained detectable atrazine in one Iowa study. Only a small fraction exceeded the 3 ppb legal limit after treatment, but the raw water feeding those systems carried much higher concentrations, especially during peak application months.
Groundwater and Drinking Water
Atrazine reaches groundwater less frequently than surface water, but it still gets there. Roughly 13% of groundwater samples contain detectable levels, and about 1.7% of public water systems that rely on groundwater test positive for atrazine. How much atrazine leaches into groundwater depends on local soil type, depth to the water table, and how heavily the surrounding land is farmed.
The EPA sets the maximum contaminant level for atrazine in drinking water at 3 micrograms per liter (equivalent to 3 ppb). Water utilities in heavily agricultural areas must monitor for it and treat their water to stay below this limit. If your water comes from a private well in a farming region, it won’t be subject to the same monitoring requirements that public systems follow.
Rainfall and Air
Atrazine doesn’t stay on the ground. It evaporates from treated fields and travels through the atmosphere, returning to earth in rain. Researchers have measured atrazine in rainwater at concentrations up to 4 micrograms per liter during summer months. Even in national parks with no nearby agriculture, rainwater samples have contained up to 0.56 micrograms per liter of atrazine. This long-range atmospheric transport means atrazine reaches ecosystems that are nowhere near a treated field, depositing in forests, lakes, and protected areas far from its source.
Soil
After application, atrazine persists in topsoil for weeks to months. Its half-life in surface soils typically ranges from 14 to 109 days, with a median of about 39 days. That means half the applied atrazine breaks down within roughly five to six weeks under typical conditions, but in some soils it can linger for over three months.
Deeper in the soil or in waterlogged conditions where oxygen is scarce, atrazine breaks down much more slowly. Anaerobic degradation half-lives exceed 200 days. In lake and stream sediments, half-lives of over 200 days are common, and in some aquatic systems, researchers have observed essentially no degradation at all. This persistence is a key reason atrazine accumulates in waterways. It doesn’t break down fast enough to clear between growing seasons, so each year’s application adds to what’s already there.
Food
Despite heavy use on corn, atrazine residues in the edible parts of the crop are extremely low. Studies measuring residues at harvest consistently find levels below the limit of detection (0.01 milligrams per kilogram) in both fresh corn and dried corn kernels. Corn straw, the non-edible stalks and leaves, does carry measurable residues ranging up to 0.17 milligrams per kilogram. For consumers, drinking water in agricultural regions represents a far more significant exposure route than food.
Where Atrazine Is Banned
The European Union banned atrazine in October 2003, citing “ubiquitous and unpreventable water contamination.” That same month, the U.S. EPA approved its continued use. This split decision remains one of the most notable regulatory divergences between the EU and the U.S. on pesticides.
In the United States, atrazine is still registered and widely used, though the EPA continues to tighten restrictions. In December 2024, the agency proposed updated mitigation measures focused on reducing runoff into waterways. The proposal targets watersheds where monitoring and modeling show atrazine concentrations exceeding 9.7 micrograms per liter, a level the EPA considers harmful to aquatic plant communities. Farmers in those watersheds would need to adopt specific runoff-reduction practices, and new nationwide rules would prohibit application during rain or when soils are already saturated. Annual application rates would also be lowered across the board.
The regulatory picture continues to shift, but for now, atrazine remains embedded in American agriculture and, consequently, in water, soil, and rain across much of the country.