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Spatial Patterns of Atmospherically Deposited Organic Contaminants at High Elevation in the Southern Sierra Nevada Mountains, California
Citation:
BRADFORD, D. F., K. Stanley, L. L. McConnell, N. G. TALLENT-HALSELL, M. S. NASH, AND S. M. Simonich. Spatial Patterns of Atmospherically Deposited Organic Contaminants at High Elevation in the Southern Sierra Nevada Mountains, California. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY. Society of Environmental Toxicology and Chemistry, Pensacola, FL, 29(5):10-56-1066, (2010).
Impact/Purpose:
The Sierra Nevada mountain range lies adjacent to one of the highest pesticide-use areas in North America, the Central Valley of California [1]. The occurrence of pesticides and other airborne contaminants in the mountains has been well documented over several decades [e.g., 1, 2, 3-12], and evidence has been provided that the primary source of both current- and historic use pesticides in the Sierra is the adjacent valley [e.g., 5, 12]. Recently, airborne pesticides have been implicated as a causal factor in the dramatic population declines of several frog species in the Sierra Nevada region during the past several decades [6, 9, 13-16]. The strongest case has been made for frogs, Rana muscosa and R. sierrae, which formerly were nearly ubiquitous among high-elevation water bodies throughout the Sierra Nevada [9, 14]. Moreover, concentrations for dichlorodiphenyltrichloroethane (DDT)-related compounds and dieldrin in some fish collected recently at high elevation sites in Sequoia National Park exceeded human health thresholds for recreational fishing and/or wildlife health thresholds [11].
Description:
Atmospherically deposited contaminants in the Sierra Nevada mountains of California have been implicated as a factor adversely affecting biological resources such as amphibians and fish, yet the distributions of contaminants within the mountains are poorly known, particularly at high elevation. We evaluated contaminant distributions and tested the hypothesis that contaminant concentrations in a high-elevation portion of the Sierra Nevada decrease with distance from the adjacent San Joaquin Valley. We sampled air, sediment, and tadpoles twice at 28 water bodies in 14 dispersed areas in Sequoia and Kings Canyon National Parks (2785 to 3375 m elevation; 43 to 82 km from the Valley edge). We detected up to 15 chemicals frequently in sediment and tadpoles, including current- and historic-use pesticides, polychlorinated biphenyls, and polycyclic aromatic hydrocarbons. Of the target analytes for air, only β-endosulfan was found frequently. Concentrations of all chemicals detected were very low, averaging in the parts-per-billion range or less in sediment and tadpoles (dry-mass basis), and on the order of 10 pg/m3 for β-endosulfan in air. Principal components analysis indicated that chemical compositions were generally similar among sites, suggesting similar histories for chemical transport to the sites. A general relationship for concentrations as a function of distance from the valley was not evident across chemical, medium, and time. However, concentrations for some chemical/medium/time combinations showed significant negative relationships with metrics for distance from the Valley, and oncentrations for a few combinations were higher for the watershed closest to the Valley than for the other two watersheds. Nevertheless, the magnitude of distance effects observed among these high elevation sites was small relative to differences found in other studies between the valley edge and the nearest high-elevation sites.