Heavy metals in dolphins from Northern Adriatic Sea and potential subtle toxic effects

Environmental pollution represents one of the main threats for marine ecosystems conservation. Top predators are particularly exposed to contaminants; due to their anatomical and physiological characteristics, cetaceans can reach very high pollutants tissue body burdens (i.e. organochlorine and heavy metals). These marine mammals are thus considered as good indicators of marine environmental pollutants and among them heavy metals are one of the major contaminants classes. Present research reports about the quantification of heavy metals in tissues of stranded bottlenose dolphins (Tursiops truncatus) from Northern Adriatic Sea and presents some speculation on possible subtle adverse effects exerted by these levels on the general health of the animals. Stranded dolphins were collected along Northern Adriatic Sea coasts during a 5 years period and underwent necropsy for the determination of the causes of death. During examination, organs were sampled and stored at -20°C until analysis, which was performed with an Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES) technique. Quantified metals were Cr, Ni, Cu, Zn, Hg, As, Se, Cd and Pb and data are reported as mg/kg (ppm) on a wet weight basis. When possible, gender and age of the animals were recorded. All metals were at detectable levels, presenting a huge variation among animals and tissues. Interestingly, some of the most common contaminants for marine environment were detected at low levels, often below limit of quantification, also in accumulation target organs like liver and kidney. Mean heavy metals detected were to be considered as low, but high enough to exert a potential immunotoxic effect on animals, as the levels detected are comparable to those which proved to be active in vitro on lymphocytic cytotoxicity, apoptosis, lymphocytic proliferation and phagocytic activity, as confirmed by some anatomo-pathological observations of lymph node swelling. Some speculation on potential reproductive effect of detected heavy metals levels are also proposed, even if no clear evidence of altered reproductive activity was observed. From obtained data there seems to be a reduced exposure to heavy metals, even thought a higher susceptibility to infectious diseases can be considered for studied animals.