Evaluating freshwater mussels (Unio elongatulus) as bioindicators and bioremediation agents for heavy metal pollution in Italian lake ecosystems

Freshwater mussels (FMs), specifically Unio elongatulus, have considerable potential as bioindicators and bioremediation tools due to their capacity to filter pollutants, particularly heavy metals, from aquatic environments. Within the framework of the Horizon SYMBIOREM Project (ID 101060361), our research focuses on developing integrated bioremediation systems capable of simultaneously mitigating multiple pollutants. This study takes advantage of a natural experimental setup involving the translocation of U. elongatulus from sites with low contamination (Lake Maggiore) to historically highly contaminated sites (Lake Orta) in Northern Italy. In parallel, we assessed populations of mussels that spontaneously recolonized Lake Orta approximately 25 years ago. Concentrations of key heavy metals (Hg, As, Pb, Cd, Cr, Ni, Cu, Zn, Co, Mn) were analyzed in mussel soft tissues, shells, and sediments, comparing these populations and correlating results with sediment contamination from corresponding sampling locations. Multivariate analyses (PCA and PLS-DA) performed on mussel soft tissues and shells revealed distinctions among sampling sites, especially between Lake Maggiore and Lake Orta. In soft tissues, discrimination among sites was mainly due to significant differences in the bioaccumulation of Cu, Pb, Cr, As, and Ni, whereas in shells, Ni, As, Se, Sb, Fe, Hg, and Cd emerged as the primary discriminants. Preliminary results clearly indicate significant variations in bioaccumulation patterns corresponding to environmental contamination gradients. Ongoing analyses, including characterization of the mussel microbiota and structural analyses of shells and tissues, will further elucidate these patterns, supporting the use of FMs as robust bioindicators and effective agents for the bioremediation of heavy metal pollution