WASHINGTON -- Male frogs exposed to even low doses of a common weed killer can develop multiple sex organs -- sometimes both male and female -- researchers in California have discovered.
"I was very much surprised," at the impact of atrazine on developing frogs, said Tyrone B. Hayes of the University of California at Berkeley.
Atrazine is the most commonly used weed killer in North America, he said, and can be found in rainwater, snow runoff and ground water.
"There is virtually no atrazine-free environment," Hayes said.
The Environmental Protection Agency permits up to 3 parts per billion of atrazine in drinking water.
But Hayes' team found it affected frogs at doses as small as 0.1 part per billion. As the amount of atrazine increased, as many as 20 percent of frogs exposed during their early development produced multiple sex organs or had both male and female organs.
Hayes' research team concluded that the effect on the frogs results from atrazine causing cells to produce the enzyme aromatase, which is present in vertebrates and converts the male hormone testosterone to the female hormone estrogen.
The effects on frogs in Hayes' study occurred at exposure levels more than 600 times lower than the dose that has been seen to induce aromatase production in human cells.
Asked if atrazine might also be a threat to people at low levels, Hayes said he did not know, adding that, unlike frogs, "we're not in the water all the time."
"I'm not saying it's safe for humans. I'm not saying it's unsafe for humans. All I'm saying is it that it makes hermaphrodites of frogs," he said.