Natural and anthropogenic contributions to mercury in soils and stream sediments of the upper Thur river basin (Alsace, France)

Abstract
In an area where human activities (mainly chlorine and soda industry) have been releasing Hg in the environment, natural and anthropogenic contributions to mercury contents in soils and stream sediments could be assessed using mercury concentrations in the deepest soil horizons and in the stream bottom sediments located upstream from the industrial effluents. Hg concentrations have been measured by Cold Vapor Atomic Fluorescence Spectrometry. The regional natural background level could be estimated to  Fg.g- ^-1from, he Hg contents in the deepest soil horizons (Hg deriving ftom rock weathering) which appear to be proportional to the organic matter percentage. Hg concentrations in stream sediments vary between and  gg.g ^-1. The mercury enrichment factor (EF(Hg)) that could be calculated show that the anthropogenic contribution is not negligible, even in the upper part of the basin. The relationship between organic matter percentage and Hg content in the deepest soil horizons allows us to estimate by difference the anthropogenic contribution (18 to 86% of the total Hg content) in the upper stream sediments. This contribution could probably be attributed to regional atmospheric deposition of Hg.