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United States Department of Agriculture

Agricultural Research Service

Title: Summertime Transport of Current Use Pesticides from California's Central Valley to the Sierra Nevada Mountain Range.

Authors
item Lenoir, James - DUPONT
item McConnell, Laura
item Fellers, Gary - USGS
item Cahill, Thomas - UNIV. NV RENO

Submitted to: Journal of Society of Environmental Toxicology and Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 30, 1999
Publication Date: N/A

Interpretive Summary: Agricultural activity in California's Central Valley may be an important source of pesticides to the Sierra Nevada Mountain range. Pesticides applied to this area of intensive crop production volatilize under high temperature, summer conditions and are transported through the atmosphere where residues may be deposited to the colder, high elevation regions of the Sierra Nevada Mountains. High voulume air, dry deposition, and surface water samples were collected in the Central Valley at different elevations in California's Sequoia National Park to determine the extent of summertime atmospheric transport of pesticides to this region. Results revealed the highest concentrations were for those compounds with heavy summertime agricultural use rates. A significant drop in pesticide concentrations in both air and water samples was observed within a few hundred meters elevation from the Valley; however, levels remained relatively constant between ~500-~2000-m. Water concentrations from two sites above 3000m contained levels 10 to 100 times lower than the other stations. The pesticides with the highest air concentrations within Sequoia National Park were detected at the 533m elevation site: chlorpyrifos (1.71 ng/m3), chlorpyrifos-oxon (2.86 ng/m3), a-endosulfan (1.07 ng/m3), and b-endosulfan (0.19 ng/m3). Highest concentrations of pesticides in Sierra Nevada mountain surface waters were chlorpyrifos (118 ng/L), and b-endosulfan(102 ng/L). Possible impact of these pesticide residues was determined using measured water concentrations to calculate total exposure of three aquatic species to organophosphate insecticides and their oxygen analogs. Results showed concentrations were well below 96-hour LC50 values for stonefly and rainbow trout but were at levels that might by harmful to amphipods.

Technical Abstract: Agricultural activity in California's Central Valley may be an important source of pesticides to the Sierra Nevada Mountain range. Pesticides applied to this area of intensive crop production volatilize under high temperature, summer conditions and are transported through the atmosphere where residues may be deposited to the colder, high elevation regions of the Sierra Nevada Mountains. High volume air, dry deposition, and surface water samples were collected in the Central Valley and at different elevations in California's Sequoia National Park to determine the extent of summertime atmospheric transport of pesticides to this region. Results revealed the highest concentrations were for those compounds with heavy summertime agricultural use rates. A significant drop in pesticide concentrations in both air and water samples was observed within a few hundred meters elevation from the Valley; however, levels remained relatively constant between ~500-~2000-m. Water concentrations from two sites above 3000m contained levels 10 to 100 times lower than the other stations. The pesticides with the highest air concentrations within Sequoia National Park were detected at the 533m elevation site. Results showed concentrations were well below 96-hour LC 50 values for stonefly and rainbow trout but were at levels that might be harmful to amphipods. While more work is required to determine actual annual flux values to the region, results from this project do indicate that pesticides volatilized from the Central Valley are a consistent source of these toxicants to the Sierra Nevada Mountains.

Last Modified: 8/21/2014
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