Combined biological assays and X-ray spectroscopy techniques to assess the bioavailability of arsenic in two industrial contaminated soils

Arsenic (As) is a metalloid, naturally associated with gold, sulphur, iron and heavy metals and is often found in soils and wastes around former mines and industrial sites because of the processing of As-bare minerals. Assessment of the bioavailability of As in these soils is very important in order to protect human and ecosystems health. Earthworms are often used to assess the bioavailability of As in soils (Langdon et al., 2003). In this work, Eisenia andrei was exposed to As-polluted soils from Valle Anzasca and Scarlino (Italy) in order to evaluate the bioavailability of As. Different X-ray based techniques were used to evaluate the concentration and the distribution of As both in soils and earthworms. For this study, three soil samples per polluted site were collected, sieved (2 mm) and dried. The mineralogical characterization of the soils was carried out by X-ray powder diffraction (XRPD). The total As was estimated on site via portable X-ray fluorescence (XRF), while sequential extractions (Wenzel et al., 2001) coupled with total reflection XRF (TXRF) were used to study the mobility of As. Soil elemental maps were acquired using micro XRF (µXRF) in order to evaluate the As distribution and its correlation with other elements. All the above analyses were conducted also on two control soils. For the assessment of the bioavailability, ten sexually mature earthworms were exposed to each contaminated soil and controls. The mortality was assessed after 14 days of exposure (acute toxicity). Oxidative stress was estimated by mesauring H2O2, catalase, phenoloxidase, glutathione S-transferase and malondialdehyde. The effect of As on the reproduction (chronic toxicity), was assessed after 28 days of exposure. Earthworms were embedded in epoxidic resin and thin sections (100 μm thickness) were analyzed via μXRF in order to localize As accumulation. Since detoxification mechanisms seem to act mainly inside the coelom (e.g. for Cd, Panzarino et al., 2016), coelomic fluids (few µl) were electrically extruded from worms and analysed by TXRF in order to quantify the As concentration...