A multibiomarker approach in clams (Ruditapes philippinarum) for a toxicological evaluation of dredged sediments

The Lagoon of Venice is often dredged for channel maintenance. To avoid harmful consequences to the ecosystem, a proper disposal of bottom sediments requires a preliminary evaluation of its potential toxicity before excavation. Here we evaluated the effects of polluted sediments on clams (Ruditapes philippinarum) using a multibiomarker approach. Bivalves were exposed for 3 and 14 days to five sediment samples collected along a navigation canal between Venice historical centre and the industrial area of Porto Marghera. Immunological, antioxidant, detoxification, and neurotoxicity biomarkers were analysed in haemolymph, gill, and digestive gland. As a control, sediment collected far from pollution sources was used. Two experiments were performed to assess potential seasonal/gametogenic influence in clam sensitivity. A different response of clam biomarkers was observed during the two experiments and among sampling sites. Clams' digestive gland resulted to be the most sensitive tissue analysed showing significant differences among sites in all biomarkers analysed. Greater differences were present due to seasonality rather than exposure. The concentrations of metals and organic pollutants increased from the city centre to the industrial area, highlighting the influence that industrial activities had on the lagoon ecosystem. However, bioaccumulation in clams did not follow the same clear pattern, suggesting low bioavailability of compounds due to relatively high organic matter content. Biomarkers modulation was mainly driven by metals, both present in sediments and bioaccumulated. In comparison, effects of organic pollutants on the biomarkers tested were negligible. Other sources of contamination not investigated (e.g. pesticides) were suggested by neurotoxicity biomarkers alteration.