(Beyond Pesticides, January 18, 2007) A new study conducted in Costa Ricaâ€™s mountain forests indicates that surprisingly high concentrations of pesticides are accumulating far above the low altitudes at which they are used. Previously thought to be safe from pesticides applied to distant agricultural areas, some remote mountain forests of Costa Rica were found to have pesticide levels almost ten times greater than those in low-lying areas closer to farms and plantations.
The study, led by University of Toronto, Scarborough professor Frank Wania, Ph.D., measured air and soil pesticide levels at 23 sites across Costa Rica in order to produce a model to predict potential accumulation of chemicals at high altitudes. The insecticide endosulfan and the fungicide chlorothalonil were found in the largest concentrations, with up to 1 part per billion (ppb) of chlorothalonil and 3 ppb endosulfan in soil.
The high concentrations can be explained by a process in which polluted air above the farms and plantations is pushed up into the mountains, where it then cools and becomes polluted rainwater or fog. The hydrophilic nature of modern pesticides makes the occurrence of this phenomenon much more likely; as Crispin Halsall, Ph.D., of Lancaster University (U.K.) explains, â€śMost 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 significance of high concentrations of pesticides at high altitudes is manifold. For one, the headwaters for water reservoirs often begin at high altitudes, meaning higher pesticide levels in the water supply. For another, there will be (and already are) negative affects on biodiversity. This study has helped to shed light on shrinking amphibian populations at high altitudes, which previously had been explained by a combination of climate change, parasitic chytrid infection, and chemical use. Scientists could not understand why areas with little human intervention would experience higher amphibian extinction rates. â€śThere 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,” Dr. Wania says.
These issues are by no means exclusive to Costa Rica. â€śThere is a whole series of mountain environments which are going to be susceptible to transport of pesticides,” Dr. Halsall adds, citing sensitive ecosystems in the Himalayas, Alps, and the Sierra Nevadas.
This research is consistent with a previous study of Californiaâ€™s Sierra Nevada Mountains by Southern Illinois Universityâ€™s Don Sparling. His research teamâ€™s 2001 paper in Environmental Toxicology and Chemistry reported on residues of endosulfan and organophosphates in amphibians and found increasing pesticide concentrations with higher altitudes.
The hope is that these studies will expand our general understanding of how localized pollution may have far-reaching effects. â€śWith 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 distant, sensitive locations, Dr. Halsall says. Dr. Wania agrees, â€śWe tend to think if we set land aside and leave it alone, that this protects it. But that may not be enough if we canâ€™t prevent contaminants from depositing or accumulating.”