Frogs with multiple sex organs

WASHINGTON (AP) -- Male frogs exposed to even very 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. Many had small, feminized larynxes.

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.

Their research is reported in Tuesday's issue of Proceedings of the National Academy of Science. 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."

Water fleas also affected "I'm not saying it's safe for humans. I'm not saying its unsafe for humans. All I'm saying is it that it makes hermaphrodites of frogs," he said.

Stanley I. Dodson of the University of Wisconsin at Madison called the work "the most important paper in environmental toxicology in decades. "It shows the effect of the most commonly used herbicide on amphibians in environmentally relevant concentrations," he said.

Asked if people should be worried, he also said: "We don't know." "It's like a canary in the mine shaft sort of thing," Dodson said, referring to the former practice of miners of bringing canaries with them as warnings of dangerous gases. The birds are very sensitive to gases and would die before the concentration of the gas was enough to harm the miners.

Dodson said that in his research he had found that low exposures of atrazine changes the ratio of males to females among water fleas.

In addition to its effects on developing frogs, the Berkeley researchers found that male frogs exposed to atrazine after reaching maturity had a decrease in testosterone to levels equivalent to that found in females.

Effects of atrazine on embryos, larvae, and adults of anuran amphibians.

AUTHOR: Allran J.W. & Karasov W.H.

SOURCE: Environ. Toxicol. Chem. 20(4): 769-775.

PUBL. YEAR: 2001

ABSTRACT: We examined the effects of atrazine (0-20 mg/L) on embryos, larvae, and adult anuran amphibian species in the laboratory.   Atrazine treatments did not affect hatchability of embryos or 96-h posthatch mortality of larvae of Rana pipiens, Rana sylvatica, or Bufo americanus. Furthermore, atrazine had no effect on swimming speed (measured for R. pipiens only).   However, there was a dose-dependent increase in deformed larvae of all three species with increasing atrazine concentration.

In adult R. pipiens, atrazine increased buccal and thoracic ventilation, indicating respiratory distress. However, because atrazine had no affect on hemoglobin, this respiratory distress was probably not indicative of reduced oxygen-carrying capacity of the blood. Frogs exposed to the highest atrazine concentration stopped eating immediately after treatment began and did not eat during the 14-d experiment. However, no decreases in mass were measured even for frogs that were not eating, probably because of compensatory fluid gain from edema.

Atrazine concentrations found to be deleterious to amphibian embryos and adults are considerably higher than concentrations currently found in surface waters in North America. Therefore,  direct toxicity of atrazine is probably not a significant factor in recent amphibian declines.

Developmental analysis of limb deformities in amphibians.


AUTHOR: Hecker L. & Sessions S.K.

SOURCE: Bios 72(1): 9-13.

PUBL. YEAR: 2001

ABSTRACT: Biologist believe that amphibians, which have thin skin and live in aquatic environments, are particularly sensitive to environmental toxins and changes in the environment. Since natural populations of amphibians in North America have high incidence of limb abnormalities.

Comparison of nitrate tolerance between different populations of the common frog, Rana temporaria.

AUTHOR: Johansson M., Rasanen K. & Merila J. [Räsänen K., Merilä J.]

SOURCE: Aquat. Toxicol. 54: 1-14. PUBL. YEAR: 2001

ABSTRACT: Numerous reports of malformed amphibians from across North America have prompted investigations into the cause(s) of the abnormalities and their implications for affected populations.  While many agents may be responsible for the national phenomenon, reports of amphibian limb  dalformations in the western U.S. correlate strongly to infection by a parasitic trematode (Ribeiroia ondatrae). The info is there, you just have to bother to read it.  Here is another one, server was busy so I couldn't get into it.