• Pesticide;
  • Sierra Nevada Mountains;
  • Atmospheric transport;
  • Precipitation


Atmospheric inputs of pesticides transported from California's Central Valley to the Sierra Nevada mountains (California, USA) were investigated by collecting winter-spring precipitation (rain and snow) from Sequoia National Park and from the Lake Tahoe basin. Pesticides currently used in California's Central Valley were detected in snow and rain samples from two elevations in Sequoia National Park (SNP) in the southern Sierras. At the lower elevation site (533 m), chlorothalonil was present at the highest levels (<0.4–85 ng/L), followed by malathion (<0.046–24 ng/L), diazinon (<0.21–19 ng/L), and chlorpyrifos (1.3–4.4 ng/L). At 1,920 m elevation, chlorothalonil was also present at the highest levels (<0.57–13 ng/L) followed by diazinon (<0.057–14 ng/L), chlorpyrifos (1.1–13 ng/L), and malathion (<0.045–6 ng/L). Trifluralin, α- and γ-hexachlorocyclohexane (HCH), and α-and β-endosulfan were also detected at both locations and at lower concentrations, generally ranging from 0.5 to 2 ng/L. In the Lake Tahoe basin, elevation 2,200 m, malathion was also found in snow at concentrations ranging from <0.046 to 18 ng/L, as was diazinon (<0.057–7 ng/L), chlorpyrifos (0.30–3.4 ng/L), and chlorothalonil (0.66–1.7 ng/L). Chlorothalonil, chlorpryifos, α-and γ-HCH, and α-endosulfan were found in surface and deep water samples at two locations in Lake Tahoe and at concentrations similar to those found in snow within the lake basin. Lake Tahoe basin snow samples in general had lower concentrations than those from SNP. This difference in concentration levels reflects the closer proximity of downwind pesticide usage to SNP than the Lake Tahoe basin. An estimated annual loading of one chemical, chlorpyrifos, of 24 to 31 kg/year was made for the SNP land area. Comparisons of observed concentrations were made with reported aquatic toxicity and water criteria levels.