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Temporal Patterns and Sources of Atmospherically Deposited Pesticides in Alpine Lakes of the Sierra Nevada, California , USA
Citation:
BRADFORD, D. F., E. M. HEITHMAR, N. G. TALLENT-HALSELL, G. MOMPLAISIR, C. G. ROSAL, K. E. VARNER, M. S. NASH, AND L. A. RIDDICK. Temporal Patterns and Sources of Atmospherically Deposited Pesticides in Alpine Lakes of the Sierra Nevada, California , USA. ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 44(10):4609-4614, (2010).
Impact/Purpose:
The Sierra Nevada mountains of California lie downwind from one of the most intensively cultivated areas in the United States, the Central Valley of California. Consequently, mountain ecosystems throughout the mountains, including those in national parks and wilderness areas, have been exposed to airborne pesticides and other pollutants (1). Pesticides from presumed regional sources have been documented in multiple physical and biotic media, including areas up to 3500 m elevation and many tens of kilometers from the nearest sources in the Central Valley (2-8). Although measured pesticide levels have generally been well below various acute toxicity levels, p,p’-DDE concentrations in fish in two alpine lakes in the southern Sierra recently exceeded a health threshold for kingfishers (7). There is also concern for ecological effects because most measurements have been made only once and thus do not capture temporal variation, an important consideration for a region where pesticides are applied year round and their use varies tremendously in time and space. Moreover, organisms in the Sierra are exposed to complex mixtures of pesticides, which may have greater effects than exposure to individual pesticides (3, 9), and some of these compounds may interact with other stressors such as disease (10).
Description:
Airborne agricultural pesticides are being transported large distances to remote mountain areas, and have been implicated as a cause or contributing factor for recent, dramatic population declines of several amphibian species in such locations. Largely unmeasured, however, are the magnitude and temporal variation of pesticide concentrations in these areas, and the relationship between pesticide application and pesticide appearance in the environment. We addressed these topics in the southern Sierra Nevada, California, by sampling water weekly or monthly from four alpine lakes (3042 - 3645 m elevation) from mid June to mid October 2003. The lakes are 46 - 83 km from the nearest pesticide sources in the intensively cultivated San Joaquin Valley, and 27 - 45 km apart from each other. Four of 40 target pesticide analytes were detected at frequencies that allowed evaluation of temporal patterns: endosulfan, propargite, dacthal, and simazine. Concentrations at all times were extremely low, generally less than 1 ng/L for the first three pesticides, and only slightly higher for simazine. The temporal patterns in concentrations differed among the four pesticides, whereas the temporal pattern for each pesticide was similar among the four lakes. For the two pesticides applied abundantly in the San Joaquin Valley during the sampling period, endosulfan and propargite, temporal variation in concentrations corresponded significantly with application rates in the Valley with a lag time of 1 and 2 weeks, respectively. A finer geographic-scale analysis suggests that a large fraction of these two pesticides reaching the lakes originated within nearby upwind areas within the San Joaquin Valley.