Using bioindicators to assess the environmental risk of past mining activities in the Vosges Mountains (France)
Résumé
The environmental risk of trace metals (TMs) in a former lead (Pb)-silver (Ag) mining district in the Vosges Mountains (France) was assessed based on two biological indices: (i) the excess of transfer TM from the soil to biota (SET index) and (ii) the toxicological risk associated with these excess transfers (ERITME index). This study constitutes the first application of the SET and ERITME indices on a past contaminated site with the inclusion of Ag and of two exposure durations. Among the eight stations studied for TM transfers in a soil-plant-snail (Cantareus aspersus) system, an excess of transfer (Ag, arsenic (As) and Pb mainly) was highlighted in four of the stations. High concentrations of Pb, up to 2810 +/- 978, mu gg(-1), were measured in snails exposed to the contaminated environment with Pb soil concentrations up to 14,978 2270 mu gg(-1). An excess TM transfer has been evidenced in several stations, principally in two archaeological mining sites. Very high SET indices have been calculated for these two stations, and abnormal transfer was shown for a communal garden. The associated toxicological risk (ERITME index) is high and reflects the importance of investigating past contaminated sites, as is done for recent industrial sites. The use of these two indices highlights that the time elapsed since the deposition of TMs does not lead to TM immobilization, partly due to the acidic soil pH in all stations, which ranged from 3.7 to 5.7. The accumulation of TMs in snails was mainly modulated by the sources of exposure, i.e., soil, humus and vegetation, depending on the TM. The major influence of exposure sources on TM accumulation compared to the influence of soil characteristics may be due to the speciation of the TMs deposited several centuries ago and the importance of indirect transfers from vegetation and humus. Currently, signs of past mining activities in the valley have almost completely disappeared, but we show that their waste still presents a risk for environmental and human health.
