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Lead (Pb)-contaminated sites that resulted from past mining and smelting activities still pose toxicological and ecotoxicological issues worldwide. A large body of research has been dedicated to evaluating the contamination and proposing mitigation strategies for recently contaminated sites (from the 19th century until the present). The possible impact of older contaminations has been much less investigated. The present study focuses on soils affected by Pb-silver mining and smelting activities during the 15th to 18th centuries. A combination of sequential extractions and X-ray absorption spectroscopy was used to determine the Pb fractionation and speciation in these soils. Despite the long passage of time, Pb was still highly available (1 and 6% of Pb present in the exchangeable fraction and 46 to 71% in the reducible fraction) and mostly present as Pb sorbed on iron (oxyhydr)oxides. Galena (lead sulfide, PbS) was observed in a soil sample from a kitchen garden, suggesting the recent use of smelter slags as soil amendments. This study shows that Pb is still highly available on this site after almost five centuries, probably because of the acidic character of the soil and the soil composition. [ABSTRACT FROM AUTHOR]

Sedimentary geochemical proxies and carbon stable isotopes of subfossil chironomid head capsules (δ13C) were combined to reconstruct long-term changes in organic matter sources contributing to chironomid biomass in two soft-water lakes (Vosges Mountains, France). Here, we test how basal carbon sources fueling the benthic food web responded to two millennia of environmental changes., Sedimentary organic matter characteristics were strongly variable over time, and were mainly influenced by human activities within the watershed basin. During the pre-eutrophication phase, subfossil chironomid δ13C (δ13 CHC) values were lower than those of sedimentary organic matter. These results suggested that chironomid larvae preferentially fed on the autochthonous part of the total sedimentary organic matter., During the modern period, higher accumulation rates of organic matter and a decrease in C/N ratio suggested a steep rise in aquatic productivity for both lakes. As suggested by the synchronous increase in organic matter δ13C values, this higher productivity and the subsequent increase in dissolved CO2 uptake may have induced either a marked increase in atmospheric CO2 uptake by phytoplankton or a reduction in the phytoplankton trophic fractionation. These changes led to overlaps in terrestrial and aquatic carbon stable-isotopic baselines, hampering the reliable reconstruction of the chironomid palaeo-diet., These results seem to indicate the minor role of allochthony to sustain aquatic food webs of large and soft-water lakes, and underscore the necessity to apply an independent compound-specific stable-isotope analysis to better estimate the temporal changes in isotopic baseline and, thus, strengthen the reliability of the chironomid palaeo-diet reconstructions. [ABSTRACT FROM AUTHOR]