The World Health Organization's cancer research agency has classified atrazine the second most widely used herbicide in the United States " as "probably carcinogenic to humans," adding to growing concerns about toxic exposures in the nation's farm belt. The evaluation means the first and second most widely used herbicides in the U.S. " glyphosate and atrazine " are now both considered probable human carcinogens by the world's leading independent cancer-hazard authority. Atrazine is banned in the European Union and other countries due to health and environmental concerns, but remains widely used in the U.S., where it is a common contaminant in drinking water, according to the Environmental Protection Agency. Despite these concerns, U.S. regulators allow its continued use. The new assessment by the WHO's cancer agency comes 10 years after the agency's landmark finding that glyphosate, the world's most heavily used herbicide, is also "probably carcinogenic to humans." Both atrazine and glyphosate are also endocrine disruptors, meaning they can disrupt key hormone systems that regulate growth, development and metabolism. Both herbicides are also largely produced by companies outside the United States. Syngenta, owned by ChemChina, produces most of the atrazine used in the U.S., while Bayer, based in Germany, is the dominant producer of glyphosate. The cancer designation for atrazine comes amid reports of rising cancer rates across the U.S. Corn Belt.