Chemical availability versus bioavailability of potentially toxic elements in mining and quarry soils

Abandoned mining and quarry areas are sources of potentially toxic elements (PTEs), through lixiviates or transfer processes of bioavailable fractions from mining wastes and tailings. In this study, earthworms (Eisenia fetida Savigny, 1826) were exposed for 28 days to two mining soils from a lead/zinc mine and two quarry soils from an old serpentine quarry. Despite their pseudo total metal contents, a previous characterization of these soils pointed out for a low chemical availability of PTEs. Therefore, a multibiomarker approach was used and the response of E. fetida to soils was assessed through the analysis of neurotoxic, oxidative stress, energy metabolism and DNA damage biomarkers (acetylcholinesterase, catalase, glutathione-s-transferase, lactate dehydrogenase, lipid peroxidation and DNA strand breaks). Metal bioaccumulation was also assessed to evaluate bioavailability and organism's exposure. Results showed that high contents of PTEs were recorded in the whole body of earthworms exposed to lead/zinc mine. However, the bioaccumulation factors for worms exposed to soils from both sampling sites were <1 due to the high PTEs contents in soils. Earthworms exposed to both types of soils displayed neurotoxic and energy metabolism effects. However, significant levels of oxidative stress and DNA damage were recorded only for earthworms exposed to lead/zinc mine soils. This study demonstrated that despite the low availability of PTEs showed by previous sequential chemical extractions, the results obtained from the direct toxicity assessment performed in this study, highlight the importance of a multibiomarker approach using soil organisms to provide a better evaluation of soils pollution.