An integrated approach to evaluate port sediment quality: From chemical characterization to multispecies bioassays

Management of dredged sediments results in an environmental and social cost. Based on their level of contamination, they can be intended for beach nourishment or for alternative uses. Sediment quality is established considering their specific chemical contamination level and setting up bioassays to evaluate their toxic effects on living organisms. The integration of these different Line of Evidence (LOE) generates toxicity indexes, the Hazard Chemical Quotient (HQc), and the Hazard Ecotoxicological Quotient (HQe), which are further elaborated using the SediQualSoft software, finally providing evidence on the levels of sediment contamination. In this study, four different dredged sediments were analysed. Except for one, which was sampled in a reference area, the others were assigned to the same class of toxicity, despite they presented different levels of chemical and ecotoxicological toxicity. As a novelty, this study introduces transcriptomics as a new LOE, to provide a new tool to better categorize sediment toxicity. C. gigas embryos were exposed to sediment elutriates, sampled at 5 and 18 h post-fertilization (hpf), and the expression of a set of genes involved in immune and stress response (hsp70, gpx, sod, dehf1, galectin, lysozyme, tg) was analysed by Real-time PCR. Molecular results suggested that the 18 hpf stage represents a sensitive window of exposure during development and can be suggested as a critical time point for ecotoxicity studies. Finally, by multivariate statistical analysis, integrating the well-established LOEs with molecular data, it was demonstrated that transcriptomics could be a useful and novel LOE with the ability to provide greater accuracy in the assessment of sediment toxicity.