Atrazine, a widely used weedkiller, affects the sexual development of frogs, according to a team at the University of Ottawa who found that, at low levels comparable to those measured in the environment, fewer tadpoles reached the froglet stage. What’s more, the ratio of females to males went up. “Atrazine is one of the top-selling herbicides used worldwide and was designed to inhibit weed growth in cornfields,” the university said in a statement, Reuters reports. “It is so widely used that it can be detected in many rivers, streams and in some water supplies. This has raised the alarm on the possibility of other serious detrimental environmental effects.” But Syngenta AG, the Swiss manufacturer behind atrazine, has defended it, saying it’s one of the best-studied herbicides available. Some studies have tied it to low birth weight, birth defects and premature babies.