Multi-biomarker approach to investigate the state of contamination of the R. Lambro/R. Po confluence (Italy) by zebra mussel (Dreissena polymorpha)

This study assesses the response of the zebra mussel (Dreissena polymorpha) to chemical pollution derived from the R. Lambro/R. Po confluence, which is one of the most polluted aquatic environments in Europe. The mussels were tested under laboratory conditions to water sampled in the spring and fall at three sites located upstream or downstream of the confluence or directly in R. Lambro alone. We performed on mussel specimens a biomarker battery composed by eight different assays: single cell gel electrophoresis, apoptosis determination, the micronucleus test and Neutral Red retention, as well as catalase, superoxide dismutase, glutathione peroxidase and glutathione transferase activities. We also evaluated the bioaccumulation of several organic pollutants (PAHs, PCBs, DDTs, HCHs and HCB) to characterize the sampling sites. Significant increases in DNA strand breaks, apoptosis and micronuclei were observed, with no significant seasonal differences. We observed a clear induction of the enzyme activities measured in the spring, but the enzymatic activity trend in the fall was very complex, with several enzymes returning to baseline levels of activity, suggesting a possible seasonal change in chemical mixture characteristics.