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Pesticides Float From Distant Farms to Protected Forests, Study Says

Anne Minard
for National Geographic News
March 2, 2007
 
High levels of pesticides are wafting into protected rain forests in
Costa Rica, even though the lowland farms being sprayed with the
chemicals are miles away, a recent study reports.

Modern pesticides dissolve more easily in water than older, longer-lasting ones, such as DDT. This means the chemicals break down faster in the environment and are less likely to travel long distances.

But because of a unique atmospheric system created by mountain ranges, large concentrations of pesticides are able to drift with the wind and fall with the rain into sensitive habitats previously thought to be unreachable.

"These chemicals have shown they can make it from the places where they are used to the places that are protected," said study leader Frank Wania of the University of Toronto in Canada.

Wania and colleagues reported their findings in two related papers published in the January 10 issue of the journal Environmental Science & Technology.

Wania said the discovery could explain why amphibian extinctions in Costa Rica's protected forests are more common at higher altitudes.

The findings could also mean that mountain habitats within a dozen or so miles (about 20 kilometers) of agricultural fields anywhere in the world could be at risk of pesticide contamination.

Regional Climate Shifts

Costa Rica's most famous crops have long been bananas and coffee. Luisa Castillo, a study co-author and professor at Costa Rica's National University Pesticide Program, said chemical-intensive production of pineapples is also on the rise.

The small country, which contains about as much land as West Virginia, imports an estimated 9,900 tons (9,000 metric tons) of pesticides a year.

Wania and his team originally went to Costa Rica looking for evidence of older, infamous pesticides such as DDT, many of which were banned by the 2001 Stockholm Convention on Persistent Organic Pollutants.

"Our colleagues in Costa Rica were also worried about what people are using right now," Wania said.

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.

Next Steps

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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