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Pesticides and amphibian population declines in California, USA

Authors

  • Donald W. Sparling,

    Corresponding author
    1. U.S. Geological Survey Patuxent Wildlife Research Center, 11510 American Holly Drive Laurel, Maryland 20708–4017, Beltsville, Maryland 20705
    • U.S. Geological Survey Patuxent Wildlife Research Center, 11510 American Holly Drive Laurel, Maryland 20708–4017, Beltsville, Maryland 20705
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  • Gary M. Fellers,

    1. U.S. Geological Survey Western Ecological Research Center, Point Reyes National Seashore, Point Reyes, California 94956, Beltsville, Maryland 20705
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  • Laura L. McConnell

    1. RU.S. Department of Agriculture-Agriculture Research Center, Environmental Chemistry Laboratory, Building 007, Room 225 BARC-W, Beltsville, Maryland 20705
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Abstract

Several species of anuran amphibians have undergone drastic population declines in the western United States over the last 10 to 15 years. In California, the most severe declines are in the Sierra Mountains east of the Central Valley and downwind of the intensely agricultural San Joaquin Valley. In contrast, coastal and more northern populations across from the less agrarian Sacramento Valley are stable or declining less precipitously. In this article, we provide evidence that pesticides are instrumental in declines of these species. Using Hyla regilla as a sentinel species, we found that cholinesterase (ChE) activity in tadpoles was depressed in mountainous areas east of the Central Valley compared with sites along the coast or north of the Valley. Cholinesterase was also lower in areas where ranid population status was poor or moderate compared with areas with good ranid status. Up to 50% of the sampled population in areas with reduced ChE had detectable organophosphorus residues, with concentrations as high as 190 ppb wet weight. In addition, up to 86% of some populations had measurable endosulfan concentrations and 40% had detectable 4,4′-dichlorodiphenyldichloroethylene, 4,4′-DDT, and 2,4′-DDT residues.

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