Wednesday, January 25, 2006
# Study, called a 'realistic picture,' finds a mix of low-level pesticides like those found on farms may play a role in species' endangerment.
By Marla Cone, Times Staff Writer
Frogs exposed to a mix of pesticides at extremely low concentrations like those widely found around farms suffer deadly infections, suggesting that the chemicals could be a major culprit in the global disappearance of amphibians, UC Berkeley scientists reported Tuesday.
When tadpoles were exposed in laboratory experiments to each pesticide individually, 4% died before they turned into frogs. But when atrazine and eight other pesticides were mixed to replicate a Nebraska cornfield, 35% died.
The frogs developed an array of health problems, including meningitis, because the chemicals suppressed their immune systems. They also took longer to complete the transformation from tadpole to frog, which reduces their chances of survival.
At least one-third of amphibians worldwide, or 1,856 of the known species of frogs, toads, salamanders and caecilians, are in danger of extinction, according to an international group of conservation biologists.
A variety of factors are thought to be involved, including climate change, ultraviolet radiation, disease, parasites and habitat destruction.
"We demonstrated that a realistic pesticides mixture [based on a mixture applied to an actual field] at low, ecologically relevant concentrations can have dramatic effects on amphibian development and growth and ultimately, we predict, survivorship," Tyrone Hayes, a professor at the university's department of integrative biology, and his colleagues reported in the online version of the scientific journal Environmental Health Perspectives.
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