Metals and PAHs in surface sediment and biological effects on the amphipod Corophium orientale and on embryos of the oyster Crassostrea gigas

Surface sediments of the Venice lagoon were monitored in 2008 and 2011-2018 to evaluate sediment chemistry (with focus on metals and PAHs) and their toxicity on target organisms. The large dataset resulting from these investigations is evaluated in this study with respect to spatial distribution and background concentrations, chemical patterns and relationships of investigated chemicals with biological effects observed on the amphipod Corophium orientale (exposed to sediments), and on embryos of the oyster Crassostrea gigas (exposed to elutriates). The evaluation is performed considering mechanistic sediment quality guidelines and, for elutriate, toxicity data available in scientific literature (EC50, Effective Concentrations derived single substance laboratory test). Although exceedance of the background concentrations defined in previous studies were observed for Zn, Cu, Pb, Cd and Hg (but not for As, Cr and Ni), tested sediments generally do not display relevant toxicity to C. orientale, whilst elutriates prepared from surface sediments can determine toxic effects on C. gigas, most likely due to the high level of ammonia. The concentrations of metals in elutriates generally appear lower than the EC50 reported in literature but their influence on C. gigas toxicity cannot be totally excluded. PAHs, evaluated on the basis of the TU approach, are not a stressor of main concern in the surface sediments investigated in the surveys. The results can support further evaluations aimed at sediment management actions in the Venice lagoon, as well as sediment assessment in other areas characterized by similar conditions.