Chronological variations in concentrations and isotopic compositions of anthropogenic atmospheric lead in sediments of a remote subalpine pond |
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| Authors: | H Shirahata RW Elias CC Patterson M Koide |
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| Institution: | Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, U.S.A.;Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92037, U.S.A. |
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| Abstract: | Lead concentrations decrease 4-fold in going from the surface of sediments in a mountain pond to relatively small values in layers 130 yr old. There is a corresponding change in the ratio in the sediments from industrial-like values of 1.18 near the surface to natural values of 1.24 at depth. Concentrations of Ca, Sr, and Ba remain relatively constant with depth. The excess Pb is shown to be of eolian anthropogenic origin, through isotopic, chemical, and mass balance relationships with metals in aerosols, dry deposition, and precipitation. This proves that inputs of contamination Pb were nearly absent centuries ago in a remote non-domesticated subalpine canyon, but are present today in that ecosystem in amounts more than 20 times the natural inputs and are irrefutably linked with industrial sources. As a consequence of these inputs, present Pb concentrations have been elevated 5-fold in plants and 50-fold in animals above natural levels. These Pb contamination effects are being caused by present-day atmospheric concentrations of ~10 ng Pb/m3. The ecosystem studied here characterizes the vast remote non-domesticated regions of North America, and these findings indicate that such regions are highly polluted by industrial Pb aerosols. |
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