Tracing and Quantifying Anthropogenic Mercury Sources in Soils of Northern France Using Isotopic Signatures

The mercury (Hg) isotopic composition was investigated in topsoils from two case studies in north of France. The Hg isotope composition was first determined in agricultural topsoils contaminated by a close by Pb−Zn smelter. The Hg isotopic composition was also measured in topsoils from an urban area in northeastern France (Metz). In both cases, no significant mass independent isotope fractionation could be found in the soils. However, the soil isotopic composition (δ²⁰²Hg) was enriched in the heavier isotopes as the Hg concentration increased in the soils. A linear relationship between the δ²⁰²Hg in soils and 1/[Hg] indicated a mixing between a contamination source and the Hg derived from the geogenic background soils. Such findings demonstrate that the contamination signature was preserved in the soils and that the deposition of anthropogenic Hg was predominant compared to reactions leading to isotope fractionation such as biotic and abiotic reduction of Hg(II) and resulting in Hg mobility or evasion from the soils. It was therefore possible, for the first time in the case of Hg, to evaluate the contribution of the contamination source relative to the background Hg source in urban topsoils using relative isotope abundances.