August 13th, 2009 · No Comments

From Green Right Now Reports

Birds, bees and frogs. We’ve known for a long time that they’re affected by pesticides and chemical pollution.

In the last few years, many scientists have come to see frogs, whose populations are in steep decline, as one of the most vulnerable; humankind’s canary in the coal mine.

Now researchers at Southern Illinois University in Carbondale are illuminating why frogs are in such deep trouble. They’ve found that just a few grains of a pesticide ingredient commonly used in California agriculture can make mountain streams lethal to frogs.

Don Sparling, a professor of zoology at SIU, recently discovered that the neurotoxin pesticides used on crops (peaches, grapes, nuts, tomatoes) in California’s Central Valley are making their way into the snow and streams of the nearby Sierra Mountains, contaminating the environment for the native frogs that breed there.

Sparling’s study, being published this month, found that Pacific tree frogs and foothill yellow-legged frogs are declining in population because natural waterways are polluted with of endosulfan — the active ingredient in many pesticides used in the area.

Sparling and his team found that .3 parts per billion of endosulfan in water was enough to kill half of the frogs exposed. At higher concentrations, the waters were lethal.

“At 0.8 parts per billion, we lose all of them,” Sparling said in a news announcement.  “We always thought there was an association between pesticides and declining amphibian populations, and we’re building up a body of evidence to show this is the case.”

Sparling and his team discovered that the most likely way the chemicals used in the agriculture-intense Central Valley found their way into the Sierras was by wind.

“These pesticides are applied by airplanes and we found that the wind would blow some of it up into the mountains, for instance,” Sparling said. “In other cases, these chemicals would volatize after being applied, turning into a gaseous state, which could also be picked up and spread into the mountains by wind.”

With only a tiny amount needed to alter the water — literally only a few grains were enough to infect 500 gallons of water — the pesticides appeared to be playing a big role in the frogs’ decline, he explained. The agricultural calendar which calls for pesticide applications in late winter and early spring, also contributes to the problem because this is when the frogs’ larvae are most vulnerable.

Even “sub-lethal” concentrations of the pesticide result in fatal outcomes for the frogs, with tadpoles growing off-center tails that render them incapable of swimming away from predators or paralyzing muscles, creating frogs with impaired mobility.

Sparling said he believes pesticides are needed in growing crops – not everyone agrees – but that the levels and types of chemicals being used should be examined.

Losing frogs creates a weak-link in the ecosystem that can devastate the ecology of the area, and also serves as a warning to humans of the potential damage from chemically grown or treated foods.

The study is being published in the August edition of Environmental Toxicology and Chemistry.

(Photo credit: Don Sparling and graduate student David Dimitrie show tadpole research tanks, SIU.)