The state of California has been working to list atrazine—the United States’ second most-widely used herbicide—as toxic to the reproductive system under the state’s Proposition 65, which requires public warnings to be posted when and where such chemicals are used. Now, a court decision coming as soon as January will determine how the state will move forward with the listing.

This is a big deal. And it comes at a time when several top herbicides are under fire. In March, the World Health Organization’s International Agency for Research on Cancer (IARC) classified glyphosate—the active ingredient in the pesticide Roundup—as a probable human carcinogen. In August, IARC declared that 2,4-D, is probably carcinogenic to humans. And earlier this month, the U.S. Environmental Protection Agency (EPA) withdrew its approval of a new herbicide called Enlist Duo, which combines glyphosate and 2,4-D.

These are the nation’s most used agricultural chemicals. If you buy conventional groceries, the odds are very good that you’ve eaten food from fields where they have been sprayed. Between them, glyphosate, atrazine, and 2,4-D are used on nearly all of the corn and soy grown in the U.S. as well as on many other crops, including fruit, vegetables, nuts, and wheat.

What sets atrazine apart is its environmental mobility and ability to contaminate water—it has been found in rainwater nearly 200 miles from where it has been sprayed. For these reasons it is no longer approved for use in the European Union. Nonetheless, about 70 million pounds of atrazine are used annually in the U.S. It is applied most intensively in the Midwest and is the herbicide the U.S. Geological Survey has found most frequently in surface water.

Atrazine as been used since the 1950s and was designed to kill weeds by inhibiting photosynthesis. Because atrazine is applied to crops used as livestock feed, its residues are found not only in crops, but also in milk and meat. While not considered acutely toxic to people, atrazine’s long term human health concerns include reproductive, developmental, and possible carcinogenic effects. Atrazine gained notoriety for its potential hormonal effects when, exposure was shown to feminize male frogs in laboratory studies conducted by University of California Berkeley biology professor Tyrone Hayes. These effects have also been shown in experiments with other animals.

New research continues to show adverse reproductive effects, says Hayes, whose atrazine research, has come under fire from Syngenta. And these effects “don’t stop at [a single] generation’s exposure,” Hayes told Civil Eats. There are “long term” and “multi-generational effects” resulting from atrazine’s “altering of modes of reproduction,” he explained.