Pesticide Drift from Fields Impact Amphibian Populations

(Beyond Pesticides, July 23, 2009)

A new study published in the August 2009 issue of Environmental Toxicology and Chemistry found that insecticides used in highly populated agricultural areas of California’s Central Valley affect amphibians that breed in the Sierra Nevada Mountains to the east. This study adds to the increasing evidence that pesticides impact areas and wildlife species that are miles from sources of pesticide application.

Researchers from the Cooperative Wildlife Research Laboratory, Southern Illinois University and U.S. Geological Survey (USGS) examined the chronic toxicity of two of the insecticides most commonly used in the Central Valley- chlorpyrifos and endosulfan, to larval Pacific treefrogs (Pseudacris regilla) and foothill yellow-legged frogs (Rana boylii), the amphibians with declining populations that live and breed in meadows surrounding the Sierra Nevada. The results are discussed in “Toxicity of Two Insecticides to California, USA, Anurans and Its Relevance to Declining Amphibian Populations.” The study used laboratory testing to examine how the insecticides affected the two frogs at environmentally realistic concentrations. During testing, tadpoles were observed at various stages of development to see how the insecticides affected their growth and health.

The researchers found that endosulfan was more toxic than chlorpyrifos to both species, and tadpoles of both species developed abnormalities when exposed to high endosulfan concentrations. Endosulfan also affected the growth and development rates in both species. The researchers say this affects the amphibians’ behavior and increases their vulnerability to predators and hydrological events such as floods and droughts. The yellow-legged frogs, which rely more on standing water during reproduction and have seen higher population declines compared with other species like the tree frog, was the more sensitive of the two.

Winds blow insecticide residues into the mountains, and they fall as rain or snow, say the researchers, Donald Sparling, PhD, of Southern Illinois University, and Garry Fellers, PhD, of the USGS’ Western Ecology Research Center in Point Reyes. Here, the chemicals breakdown more slowly due to cooler temperatures. “Concentrations of insecticides in the Sierra Nevada Mountains of California may have the ability to inflict serious damage on native amphibians,” Dr. Sparling and Dr. Fellers write. “The present study adds to the increasing evidence that pesticides are very harmful to amphibians living in areas that are miles from sources of pesticide application.”

A previous study reported that endosulfan was 1,000-times more lethal to amphibians than other pesticides examined in the study. Declining amphibian populations have been recorded in pristine areas far downwind from areas of active pesticide use. Another USGS study found that the breakdown products of chlorpyrifos, and other pesticides are ten to 100 times more toxic to amphibians than their parent compounds, which are already highly toxic to amphibians. Endosulfan is banned in Europe and many other countries around the world due to the serious toxic effects attributed to its use. It is an organochlorine pesticide, in the same family as DDT and lindane, and like DDT and lindane, it bioaccumulates and has been found in places as far from point of use as the arctic. It is also a suspected endocrine disruptor, affecting hormones and reproduction in aquatic and terrestrial organisms.