Scientists may have found another smoking gun in one of the
great international intrigues of modern biology.
In the case of the worldwide disappearance of frogs and other
amphibians, the new prime suspect is pesticides, researchers
reported here Saturday.
For the first time, scientists have shown how a pesticide can
disrupt reproduction in frogs.
"It looks like pesticides are one more nail in the coffin for
amphibians," said Brent Palmer, a reproductive biologist with Ohio
University, in Athens.
The finding is part of a growing body of evidence that
extremely small amounts of pesticides can trigger major health
problems in animals, including humans.
The finding was one of many prepared for presentation at the
American Society of Zoology meeting, which began Wednesday at the
Adam's Mark Hotel downtown. About 800 scientists are attending the
meeting, which ends Sunday.
In lab experiments, tiny amounts of the pesticide DDT injected
into frogs and turtles disrupted the animals' hormone systems, said
Palmer and Kyle Selcer, a reproductive endocrinologist with
Duquesne University, in Pittsburgh.
That disruption can make either the animal or its offspring
infertile, they said.
"We're talking about populations that are `the living extinct,'
" Palmer said. "If they can't reproduce, they will go extinct."
Palmer, Selcer and other scientists from North America and
Europe focused on new evidence that pesticides disrupt the
endocrine system, which regulates a wide array of hormones in
humans and other animals.
Their research centers on chemicals called "environmental
endocrine disrupters." These include widely used chemicals:
pesticides, herbicides and such byproducts of manufacturing as
These chemicals can have enormous impact on animals and humans
even in concentrations less than those that can cause cancer, many
Tiny concentrations of endocrine disrupters can seriously
impair an organism's nervous and immune systems and its
reproductive organs, research shows.
Much of the concern has focused on how chemicals affect
embryos. That early stage of life is a critical time. That's when a
small clump of identical cells begins to organize into a complex
animal with intricately balanced systems.
At the meeting, scientists reported that the chemicals
influence sex determination in developing alligators. They may have
been the reason a beluga whale from the St. Lawrence River
developed both male and female sex organs.
And studies showed that a single, tiny dose of dioxin to a
mother rat lowers the sperm count of her male offspring.
Biologists already have shown that endocrine disrupters harm
birds, reptiles and fish. …