Two common water pollutants can function in shellfish as the female sex hormone estrogen does. However, new studies show different behavioral effects of those contaminants on two species.

Elliptio complanata is a freshwater mussel whose populations are seriously declining in the United States. Katherine Flynn of Adelphi University in Garden City, N.Y., and her colleagues exposed lab-kept mussels to the weed killer atrazine or to estrogen for a week. Atrazine has exhibited estrogenic effects in other species (SN: 11/2/02, p. 275: http://www.sciencenews.org/articles/20021102/fob1.asp).

At an atrazine concentration of 15 parts per billion (ppb), a value permitted in U.S. waters by the Environmental Protection Agency, the mussels were 30 percent less likely to burrow than were mussels kept in clean water. Atrazine doses far higher and lower didn't impair this defensive behavior, the researchers reported in Montreal at the Society of Environmental Toxicology and Chemistry meeting in November. The animals had the same response when the exposed to low concentrations of true estrogen.

Flynn's coworker, Josephine A. Bonventre of Rutgers University in Piscataway, N.J., observed radically different responses of the clam Corbicula fluminea to estrogen and another estrogenlike pollutant.

She exposed this invasive species for 1 day to between 0.1 and 15 ppb of bifenthrin, an insecticide (SN: 2/4/06, p. 74: http://www.sciencenews.org/articles/20060204/bob9.asp). Clams receiving the highest bifenthrin dose produced 46 percent more of the protein vitellogenin than did clams in water without insecticides. Animals normally produce vitellogenin only in response to estrogen. However, no dose of bifenthrin or exposure to true estrogen deterred this species from burrowing.

"Maybe that contributes to its success as an invasive species," Flynn says. If these clams are immune to bifenthrin's behavior—disrupting effects, more of the clams can burrow and avoid predators, she notes.

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