AQUATIC POLLUTION AND BIOLOGICAL MONITORING OF THE MARINE ENVIRONMENT: TOXICOLOGY, HISTOPATHOLOGY AND ECOLOGICAL RISK OF SELECTED FISH SPECIES

The impact of multiple anthropogenic stressors on the marine environment has increased to large extents within the past few decades. Piscivorous fish can bioaccumulate pollutans to significantly higher concentrations than those found in the water or sediments, due to the lipid solubility and resistance of these compounds to numerous degenerative processes. The use of fish from different hydrological settings as bio-indicators represents a useful complementary choice to evaluate the levels and responses of marine organisms to pollutans, and to assess the global marine status. The purpose of this project is to evaluate the role of selected pelagic (Thunnus thynnus), and benthopelagic fish species (Dentex dentex and Pagellus bogaraveo) as biomonitors of Mediterranean sea pollution through the chemical identification and quantification of persistent organic and inorganic compounds in target tissues, the investigation of toxicopathic-related pathological changes, and the putative correlation between abnormal levels of pollutants and tissue lesions. Fish were selected based on length and weight. The mean concentration of metallic elements, polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCs) was calculated and compared to their acceptable levels when available. Blackspot seabreams had the highest PCB concentration, whereas OCs were highest in tunas. A different spread in distinct species was documented for the following elements: Al, K, Co, Mo, Ag, Cd, Sn, and Th. For the elements without maximum dietary limits, Fe was highest in tunas, while Th was significantly predominant in dentices. Several metals were found in quantities above the acceptable levels. Specifically, the median concentrations of Hg and Cd in the pooled species were significantly higher than their relative PTWI. Significant differences among species were reported for Se, inorganic As, Ni and Zn. Other elements (Al, Cr, Cu, Sn, Pb, and Mn) were found to be at or below the corresponding acceptable levels. Histopathology evidenced acute and chronic lesions in numerous organs, comprising muscular degeneration and necrosis, hepatic lipidosis, hepatocellular necrosis and dysplastic foci in all fish groups. Specifically, chronic lesions in liver, gills, immune and reproductive systems were common in all fish species encountered. Testicular atrophy, necrotizing branchitis, and proliferation of melanomacrophagic centers represented common findings. Although these findings revealed some differences in the patterns of histopathologic traits between pelagic and benthopelagic fishes, the overall level of histopathological injury was moderate and severe traits like neoplasms or pre-neoplastic foci were not observed. The concentrations of the other metallic elements did not influence the muscular H-indices in all species, with the exception of Na, where the interaction between concentration of Na and fish species was statistically significant. No significant differences were found between the H-indices of different species. Given the simultaneous presence of pollutans in dangerous concentrations and the putative relationship with subacute to chronic microscopic lesions, research on fish contamination and human exposure could not be framed in terms of a single contaminant. Our findings aim to encourage cross-disciplinary discussion and to establish research and monitoring priorities in order to protect the human health. Since the risks associated with high simultaneous levels of multiple compounds have not been quantified but represent a severe health hazard, monitoring data should be collected to characterize the spatial and vertical distribution of metals in seawaters across a range of marine ecosystems. Our work confirms that histopathological evaluation of target organs should be included as a tool to determine the potential consequences of chronic toxicant exposure in wild fish.