Pb dispersion pathways in mountain soils contaminated by ancient mining and smelting activities

Over the last millennia, mining and smelting activities have produced large amounts of mine and metallurgical wastes that remain enriched in potentially toxic trace elements (PTE). A spatial distribution of Pb content was coupled to mineralogical observations and single extraction tests to characterise the Pb contamination legacy and Pb dispersion trajectories in an ancient mining and smelting site that has been abandoned for approximatively 200 years. In the Peisey-Nancroix Pb-Ag mine (Savoy, France), extreme anthropogenic Pb contamination is located close to the slag heaps and along ore and slag transport paths. The contamination gradient is restricted to a few hundred metres downhill, down to background Pb values. The Pb-bearing phases change along the contamination gradient. The most contaminated soils contain significant amounts of galena and slags that are more or less weathered into pyromorphite and cerussite. Pb-bearing Mn (hydr-)oxides are the most stable and ubiquitous forms of Pb, which proportions increase downgradient. Despite the presence of some stable Pbbearing phases (pyromorphite, Pb-bearing Mn (hydr-)oxides), extraction tests indicate that a small proportion of Pb may still be mobile over time.

Automated summary

Mining and smelting activities have generated significant amounts of potentially toxic trace elements in mine and metallurgical wastes. A study was conducted on an abandoned mining and smelting site in France to characterize the legacy and dispersion of lead (Pb) contamination. The most severe Pb contamination was found near the slag heaps and along transportation paths, with a limited contamination gradient downhill. The presence of different Pb-bearing phases was observed, with the most stable and widespread forms being Pb-bearing Mn (hydr-)oxides.