Pesticides waft into pristine rainforests
New research shows that pesticides are transported to remote mountain areas in Costa Rica.
Throughout the tropics, chemical-intensive crops such as coffee and bananas grow in valleys and on hillsides near biologically diverse mountain forests, including rainforests that are home to disappearing frog species. New research published today on ES&T’s Research ASAP website (DOI: es0622709) reveals that surprisingly high levels of pesticides currently used in Costa Rica are being transported to high-altitude forests, some of which are in protected areas such as national parks and volcanoes.
The new data are the most complete for Costa Rica and the first to show that pesticides used in lowlands accumulate in tropical mountain forests miles away. Researchers say that a meteorological quirk created by mountain ranges carries the pesticides to destinations previously considered too far from agricultural areas to be of concern.
In a related paper also published today on ES&T’s Research ASAP website (es062349d), the same researchers survey older banned pesticides in Costa Rica and propose a simple method to detect and prioritize pesticides in the environment.
The team, led by Frank Wania of the University of Toronto, Scarborough (Canada), measured air and soil pesticide levels for both papers at 23 sites across Costa Rica and then modeled the potential accumulation of the chemicals at high altitudes.
Wania explains that air above farms is carried up the sides of mountains and then cools at higher altitudes. As the air cools, precipitation forms and carries the chemicals down in rainwater and fog.
The La Selva Biological Station was a typical sampling site. “La Selva looks like a picture-book jungle, as pristine as it gets, but agricultural activities are very close by. I drove through one banana plantation after another,” Wania says.
Pesticides are not only transported to mountain forests, the researchers say, but they also accumulate there. In some cases, the team found that levels were almost an order of magnitude greater on mountains than in low-lying areas closer to plantations.
Crispin Halsall of Lancaster University (U.K.) points out that high altitude environments are of special concern as headwaters for water catchments. “With currently used pesticides, most risk assessment is focused on the local environment and fails to take into account the subsequent evaporation or transport of the chemicals” to vulnerable locations, Halsall says.
“There is a whole series of mountain environments which are going to be susceptible to transport of pesticides,” Halsall adds, citing sensitive ecosystems in the Himalayas, Alps, and the Sierra Nevadas. Plus, he says, “Most currently used pesticides are quite soluble, unlike some of the older organochlorine pesticides. So they will dissolve into rain more readily than the hydrophobic pesticides of the past.”
The research in Costa Rica confirmed that the pesticides of greatest concern there are those in current use. The insecticide endosulfan and the fungicide chlorothalonil had the largest concentrations, with up to 1 ppb of chlorothalonil and 3 ppb endosulfan in soil. Pesticides banned by the Stockholm Convention on Persistent Organic Pollutants were found in much lower concentrations, likely because large-scale pesticide use was not common in Costa Rica before these products were prohibited, Wania says.
He adds that the team’s results might help explain recent puzzling declines in amphibian populations, for which climate change, parasitic chytrid infection, and chemical use have been blamed separately or in combination. “There tends to be a pattern of more extinction at high elevations, which is tricky to explain because most of the human activity is at low elevations. We might have an explanation, because pesticide concentrations are higher at high altitude,” Wania says.
The team’s models are consistent with research in California’s Sierra Nevada Mountains by Don Sparling of Southern Illinois University and colleagues. In a 2001 paper in Environmental Toxicology and Chemistry (DOI: 10.1897/1551-5028), that group reported on residues of endosulfan and organophosphates in amphibians and found increasing pesticide concentrations with higher altitudes.
When Sparling exposed frogs in the laboratory to 8 ppb endosulfan, they were partially paralyzed and would “swim in spirals... If fish came by, they would just gobble them up,” Sparling says. “At lower concentrations we see lethargy—the frogs just lay around until they die,” he says.
Sparling says the concentrations seen in Costa Rican soils would be of concern in water, but “direct comparisons of soil and water concentrations are difficult to make.” Wania says the team wants to return to Costa Rica to test water as well.
Wania hopes the team’s work will help inform management practices in the tropics. “We tend to think if we set land aside and leave it alone, that this protects it. But that may not be enough if we can’t prevent contaminants from depositing or accumulating,” he says.
