Acid mine drainage and ecotoxicity in soils and sediments.

Measurements of acid volatile sulphide (AVS) and simultaneously extracted metals (SEM) in sediments are used to assess the toxicity of metals to native benthic organisms. The AVS is obtained from the sulphides contained in the sediments by addition of acid and the SEM are the metals extracted during the AVS treatment. The AVS/SEM method reflects a more precise estimation of sediment toxicity to benthic organisms than "total" metal values (cadmium, copper, lead, nickel and zinc) by measuring a "bioavailable" fraction of the metals present. Sediment toxicity is assessed by calculating the sum of the SEM (µmol/g dry weight) divided by the AVS concentration (in the same units): a ratio less than or equal to 1 indicates that the metals in the sediment are not bioavailable, while a ratio greater than 1 indicates that the metals are bioavailable.

In this case, they are applied to soils containing mining waste and marine sediments that were buried under these inputs in Portman Bay (SE Spain) and compared with the values obtained from the ecotoxicity tests used: microtox, ostracodes and gambarus for sediments and phytotoxicity tests for topsoil samples.

The results confirm the ecotoxic characteristics of some of the samples evaluated and also allow an approximation to be made of the impact that neighbouring materials may have if subjected to AMD, when there is intense precipitation and the waters of the wadis reach the bay with the runoff from the neighbouring mining areas.