Submitted to: Environmental Toxicology and Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/20/2009
Publication Date: 2/1/2010
Publication URL: ddr.nal.usda.gov/dspace/handle/10113/42036
Citation: Bradford, D.F., Stanley, K., Mcconnell, L.L., Tallent-Halsell, N.G., Nash, M.S., Simonich, S.M., Sparling, D.W. 2010. Spatial patterns of atmospherically deposited organic contaminants at high elevation in the southern Sierra Nevada mountains, California, USA. Environmental Toxicology and Chemistry. 29:1056-1066. Interpretive Summary: The Sierra Nevada mountain range is an important ecosystem for many rare plants and animals and much of the area is protected as National Park lands. Scientists have observed severe declines in certain amphibian populations in remote areas of the Sierra Nevada Mountains. One potential contributor to these declines is atmospheric transport and deposition of airborne contaminants such as pesticides. The Central Valley of California is one of the most productive agricultural areas in the world, specializing in vegetable and fruit crops. Many of these crops require the use of pesticide products for weed and pest control. Earlier research has shown that pesticides can be transported in the atmosphere from the Central Valley to the Sierra Nevada Mountain region. This project was designed to determine if atmospheric sources of pollution from the Central Valley are important in high elevation watersheds of the Sierra Nevada Mountains. Fourteen areas in the Sequoia and Kings Canyon National Parks were sampled for air, sediment, and tadpoles during the summer of 2005. Contaminants were detected in all three types of samples; however, concentrations were very low and many samples were below detection limits. Results of statistical analysis did not reveal any clear patterns with respect to distance from the Central Valley; however, patterns of contamination within regions were similar. Therefore, sources of contaminants to the Sierra Nevada Mountains may be from multiple sources or may be too dispersed to observe patterns at the sampling resolution included in this study.
Technical Abstract: Airborne contaminants in the Sierra Nevada mountains of California have been implicated as a factor adversely affecting biological resources like 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 in Sequoia and Kings Canyon National Parks. Twenty-eight water bodies were represented in 14 dispersed areas (2785 – 3375 m elevation; 43 - 82 km from the Valley edge). We detected up to 15 chemicals frequently in sediment and tadpoles, including both current- and historic-use pesticides, polychlorinated biphenyls, and polycyclic aromatic hydrocarbons. Of the pesticides included as target analytes, only B-endosulfan was found frequently in air. Concentrations of all chemicals detected were low, averaging in the parts-per-billion range or less in sediment and tadpoles, and on the order of 10 pg/m3 for B-endosulfan in air. Principal components analysis indicated that chemical compositions were generally similar among sites, suggesting similar histories for chemical transport to the sites. Concentrations for some chemicals were significantly related to metrics for distance from the Valley, and in some analyses concentrations were higher for the watershed closest to the Valley than for the other two watersheds. Nevertheless, a general relationship for concentrations with distance across chemical, medium, and time was not apparent. The limited support for the distance-concentration hypothesis, coupled with the large variance in concentrations among nearby sites relative to variance among all sites, suggests on-site characteristics or processes dominate over chemical transport in explaining differences in chemical concentrations among high-elevation sites.