Critical Limits for Hg(II) in soils, derived from chronic toxicity data |
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Authors: | E Tipping S Lofts B Frey C Svendsen |
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Institution: | a Centre for Ecology and Hydrology, Lancaster Environment Centre, Library Avenue, Bailrigg, Lancaster LA1 4AP, United Kingdom b Centre for Ecology and Hydrology, Wallingford, OX10 8BB, United Kingdom c Swiss Federal Research Institute WSL, 8903 Birmensdorf, Switzerland |
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Abstract: | Published chronic toxicity data for Hg(II) added to soils were assembled and evaluated to produce a data set comprising 52 chronic end-points, five each for plants and invertebrates and 42 for microbes. With end-points expressed in terms of added soil Hg(II) contents, Critical Limits were derived from the 5th percentiles of species sensitivity distributions, values of 0.13 μg (g soil)−1 and 3.3 μg (g soil organic matter)−1 being obtained. The latter value exceeds the currently recommended Critical Limit, used to determine Hg(II) Critical Loads in Europe, of 0.5 μg (g soil organic matter)−1. We also applied the WHAM/Model VI chemical speciation model to estimate concentrations of Hg2+ in soil solution, and derived an approximate Critical Limit Function (CLF) that includes pH; log Hg2+]crit = −2.15 pH −17.10. Because they take soil properties into account, the soil organic matter-based limit and the CLF provide the best assessment of toxic threat for different soils. For differing representative soils, each predicts a range of up to 100-fold in the dry weight-based content of mercury that corresponds to the Critical Limit. |
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Keywords: | Chemical speciation Critical Limit Free ion concentration Mercury (II) Organic matter Soil |
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