Origin, fate and ecotoxicity of manganese from legacy metallurgical wastes

Over the course of history, mining and metallurgical activities have influenced the socioeconomic development of human populations. However, these past and current activities can also lead to substantial environmental contamination by various metals. Here, we used an interdisciplinary approach (incorporating archaeology, mineralogy, environmental chemistry and ecotoxicology) to investigate the origin, fate and potential ecotoxicity of anomalous manganese (Mn) concentrations detected in the ancient mining district of Berthelange (medieval period, eastern France). Mineralogical investigations of slag samples showed that smelting temperature conditions in medieval bloomeries led to the production of slags mainly composed of Fe- and Mn-rich olivine, i.e., fayalites. Further mineralogical analyses of bulk soil and clay fractions allowed us to identify the presence of serpentine. This evidence of olivine weathering can account for the release of Mn from slags into the soil. In addition, chemical analyses of total and available (exchangeable and reducible) Mn concentrations in soil samples clearly showed the contribution of slags deposited 1000 years ago to soil contamination. A complementary ecotoxicity bioassay performed on soils from a slag heap using the land snail Cantareus aspersus confirmed that a significant fraction of the Mn detected in soils remains available for partitioning with the soil solution and transfer to soil organisms. Although no growth inhibition of snails was observed after 28 days of exposure, the animals accumulated quite elevated Mn concentrations in their tissues. Our study emphasizes the environmental availability and bioavailability of Mn from ancient metallurgical wastes to soil-dwelling invertebrates, i.e., snails, even one millennium after their deposition. Hence, as for more recent industrial sites, past mining ecosystems must be a cause of concern for the scientific community and public authorities.

Impact assessment of legacy wastes from ancient mining activities on current earthworm community

Mineral resource exploitation by human societies throughout history led to the deposit of mining and smelting wastes and the subsequent contamination of surrounding soils by trace metals. After several centuries, the impact of these legacy hazardous wastes may remain a cause of environmental concern, especially for indigenous soil invertebrate populations such as earthworms. Therefore, we conducted a passive biomonitoring campaign in a former metallurgical district (Vosges Mountains, eastern France). According to community descriptors, we evidenced a significant decrease of anecic and endogeic earthworm density in the former mining stations. To link these results to soil contamination and bioaccumulation levels in earthworm tissues, we propose an original modelling approach using nonlinear mixed-effects regression models. Beyond a dose-response relationship between metal internal concentrations and their levels in soils, we highlighted contrasted behaviors according to ecological groups (epianecics and endogeics most impacted). We interpreted these results in relation to some eco-physiological features without completely exclude the influence of textural characteristics of soil, especially for deep-burrowing species such as anecic strict. Nonetheless, the presence of earthworm populations currently living in highly contaminated sites and handling elevated internal concentrations raises the question of the acquisition of genetic adaptive traits and the trophic transfers of metals.

High-temporal resolution landscape changes related to anthropogenic activities over the past millennium in the Vosges Mountains (France)

Iron mining activities in the Bruche valley (Vosges Mountains, France) date historically from the Roman period to the mid-nineteenth century. The geochemical and palynological study of a core from the peat bog of Le Champ du Feu allows highlighting impacts of these activities over the past millennium. Trace metal contamination is recorded for lead (Pb), arsenic, zinc, and antimony during the Middle Ages, the sixteenth century, and from cal. AD 1750-1900, with several sources distinguished by Pb isotope analyses. Forest exploitation is attested by the palynological analysis of the core, with exploitation of Fagus for smelting processes and cutting of Abies for agro-pastoralism. This approach highlights several patterns of contamination, corresponding to the mixing sources and the contamination intensity, which can be linked to the pollen assemblage zones. Hence, anthropogenic activities such as mining and farming led to long-term modification of the landscape composition in this mountainous area.

Lead Highly Available in Soils Centuries after Metallurgical Activities

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.

Palaeo-pollution from mining activities in the Vosges Mountains: 1000 years and still bioavailable

Mining and smelting activities have contaminated the environment with trace metals (TMs) at a worldwide scale for at least two millennia. A combination of chemical approaches and active biomonitoring was performed to analyse the environmental availability and bioavailability of TM palaeo-pollution in a former PbAg mining district in the Vosges Mountains, France. Along a soil TM contamination gradient that covered eight stations, including two archaeological mining sites, the toxicokinetics of six TMs (Pb, Cd, As, Ag, Co, Sb) in the snail Cantareus aspersus revealed that palaeo-pollution from the studied sites remains bioavailable. This study provides the first data on the accumulation kinetics of Ag and Co for C. aspersus. The environmental availability of the TMs was estimated with three chemical extraction methods (aqua regia, EDTA 50 mM, CaCl2 10 mM). Univariate regression analyses showed that EDTA extraction is the best method for estimating the bioavailability of Pb, As, Ag, Co and Sb to snails. None of the three extractants was efficient for Cd. A multivariate analysis of bioaccumulation data revealed that TM bioavailability and transfer were modulated by exposure sources (soil, humus and vegetation) rather than by soil physico-chemical characteristics. Hence, although the deposition of mining wastes dates back several centuries, these wastes still represent a source of contamination that must be considered to develop relevant site management and environmental risk assessment.

Using seismic facies and pollen analyses to evaluate climatically driven change in a Scottish sea loch (fjord) over the last 20 ka

Loch Sunart is a glacially over-deepened sea loch (fjord) on the west coast of Scotland, UK. The loch is divided into three sub-basins, separated by relatively shallow and narrow sills. A programme of data collection including high-resolution bathymetric sonar and sub-bottom seismic surveys were conducted in the loch as part of an investigation into the sedimentological and climatic change signatures preserved in western sea lochs since the Last Glacial Maximum. Very-high-resolution sub-bottom profiles were obtained using the SEISTEC boomer system. The seismic profiles revealed an igneous and metamorphic basement covered by a 10–70 m thick sediment sequence. Five different acoustic facies were recognized and interpreted in terms of glacial activity, ice retreat and subsequent Holocene sedimentation. These facies have been correlated to sediments sampled in a radiocarbon-dated 12 m long giant piston core (MD04-2833) acquired from the main basin of Loch Sunart. Pollen analyses conducted along the length of the core, together with 14C dating, indicate a complex series of palaeoclimate changes in the loch. In particular, five distinct cooling events have been recognized c. 9.8, 8.2, 5.8, 1.2 cal ka BP and 771–1211 cal a BP (possibly the Little Ice Age), corresponding to phases of Holocene rapid climate change.