Accusations are flying over the latest University of California, Berkeley study on the effects of a widely-used weed killer on amphibian sexuality.

The study was conducted by Tyrone Hayes, a professor of Integrative Biology, and found that feeding atrazine to tadpoles reshaped their sexuality as they grew to adults. Ten percent of the 80 males he tested for the study had become anatomically female and capable of mating with other males, while three-fourths of the remainder were sterile, The San Francisco Chronicle reported last week.

The study opens a new chapter in the controversy over the safety of the herbicide, which is being reviewed by the federal Environmental Protection Agency.

Farmers spray atrazine on half of all corn grown in America, according to Syngenta, the major manufacturer of the herbicide.

Other studies, like one discussed in 2008 by David Skelly, an ecology professor at Yale University, have produced cross-cutting results about amphibians with scrambled sexes. Dr. Skelly also found hermaphrodite frogs in Connecticut ponds, but found more in suburban areas than rural ones, even though atrazine is more prevalent near rural, agricultural areas.

In a recent article in The Connecticut Post, Dr. Skelly said a likely cause is the presence of estrogen, the female hormone used in birth-control drugs, and related compounds that are infiltrating the groundwater.

In August, a New York Times investigation found that, in recent years, there have been unusual spikes in the atrazine content of drinking water and reported that 43 water systems in six states – Illinois, Indiana, Iowa, Kansas, Mississippi and Ohio – have sued atrazine’s manufacturers to force them to pay for removing the chemical from drinking water.

Earlier this month, The Huffington Post reported that 16 midwestern cities near agricultural fields have already banded together to file a new federal lawsuit against Syngenta for failing to alert them of atrazine’s presence in their drinking water at unsafe levels.

Sygenta has aggressively sought to discredit Mr. Hayes’ findings. The company cites almost 6,000 scientific reviews that, it said, show that atrazine has no impact on the safety of drinking water or amphibian development.