The team took soil and air samples at 23 sites across the country using a relatively new passive monitoring technique that relies on chemicals from the air diffusing into resin housed in a container little bigger than a soda can.
"We can put it wherever we want, in fact where nobody goes for a whole year," Wania said.
The system is very cheap, making it useful for sampling pesticides in locales where researchers don't know where to look for the highest chemical concentrations.
Based on this method, the Costa Rica samples revealed very little of the older, banned pesticides.
"The old stuff—these nasty pesticides, so to speak—were actually present in very low concentrations," Wania said.
But newer, legal chemicals showed up in surprisingly high levels in the team's samples, and in some higher areas pesticide levels were almost ten times higher than in lowland areas adjacent to farms.
The phenomenon is the result of small-scale climate variations, the researchers believe.
At the lower elevations where farms are cultivated, the temperatures are warmer on average. In these warmer climes many of today's pesticides stay in the gas phase, Wania explained. Even when it rains the chemicals stay in the air.
The pesticide-laden air above the farms is then carried up the sides of neighboring mountains.
The air is cooler at higher elevations. Cooler temperatures mean pesticides readily enter the liquid phase and can reach ground level and accumulate in rainwater and fog.
As a result of their work, the researchers are recommending that the Costa Rican government focuses on regulating the pesticides in current use rather than worrying about older, banned products.
Wania points out that his team's research doesn't directly prove a link between pesticides and rain forest extinctions. But, he says, the logical next step is to test for such a cause-and-effect relationship.
(Related photos: "Frog Survival Linked to Eco-Health" [July 10, 2006].)
"The two places where we had the highest concentrations are very remote and very wild," study co-author Castillo said.
"But a place could [still] look very wild, even if all the amphibians are dead. There could be impacts on the ecosystem that you wouldn't see if you walked through it."
Don Sparling, a zoologist at Southern Illinois University, has already taken steps to identify such a link in California.
There, he and colleagues have found modern agricultural pesticides in the bodies of tadpoles and frogs living far away in Yosemite and Sequoia National Parks.
In separate studies Sparling has revealed high death rates in frogs exposed to the chemicals, including up to 90 percent mortality for frogs exposed to low levels of the insecticide endosulfan.
Although no regulatory moves have been made as a result of the studies, Wania said that the Costa Rican Coffee Institute has taken an interest and plans to publicize the finds in an upcoming newsletter.
"That's actually just the sort of audience we want to reach," Wania said.
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