PAHs, PCBs, PBDEs, and OCPs trapped and remobilized in the Lake of Cavazzo (NE Italy) sediments: Temporal trends, quality, and sources in an area prone to anthropogenic and natural stressors.

Under the present climatic emergency, the environmental quality of freshwater reservoirs is an increasingly urgent topic as its deterioration threatens humans and ecosystems. It is evident that pollution by natural and anthropogenic contaminants must be avoided or reduced. The Lake of Cavazzo (NE Italy) is a natural perialpine basin which, from the mid-20th century, has sustained several anthropogenic impacts that added to the effects of the intense regional seismicity. Starting from 2015, in response to concerns raised by local authorities, a multidisciplinary investigation of the lake floor and sub-floor was conducted, including a geophysical survey and the collection of sediment cores. Two of them were studied to detect contamination by Polycyclic Aromatic Hydrocarbons (PAHs) and specific Persistent Organic Pollutants (POPs; i.e. PolyChlorinated Biphenyls - PCBs, PolyBrominated Diphenyl Ethers - PBDEs, and OrganoChlorine Pesticides - OCPs), and to verify the link with known anthropogenic stressors. Results were interpreted in light of previous studies suggesting modified conditions after the '50s, and recognized the effects of the 1976-1977 MW 6.5 seismic sequence in resuspending sediments within the basin. Analyzed pollutants defined a potential critical situation only for few OCPs, above all 2,4'- and 4,4'-DDT isomers. In addition, PBDEs were found at concentrations exceeding those of other heavily polluted alpine lakes. Mass movements (either seismic or human induced) have likely resuspended and transferred pollutants from shallower locations to the lake depocenter, showing the potential of re-exposing contaminated layers to biomagnification processes along the lacustrine food chain. Local inputs of pollutants prevail over distributed sources, suggesting a link with local agricultural or industrial activities. Indeed, works connected to the construction of the hydroelectric power plant in the '50s might have reworked local sediments perturbing their natural accretion. Results of this work might inspire similar studies in other problematic lacustrine areas that sustain both natural and anthropogenic stressors.