Contribution of diet to heavy metals burden of bottlenose dolphins (Tursiop truncatus) from Northen Adriatic Sea

Being it a closed sea, with a reduced hydric exchange, Mediterranean is particularly exposed to risks derived from chemical pollution. Knowing pollution degree of this sea by estimating contaminants concentrations in marine species placed at the top of food chains, including marine mammals and cetacean, is thus mandatory. Despite the high number of studies focusing on heavy metals in tissues of different cetacean species, little information is available concerning contaminants transfer along their trophic chains, thus defining which could be main diet components contributing to toxicant body burden for each of the metal considered. Present work focuses on the evaluation of heavy metals (Pb, Cd, Cu, Zn) presence in some components of bottlenose dolphin diet from Northern Adriatic Sea, trying to define which could be the contribution that each of them give to the body burden of predators. A theoretical diet composition was created starting from the literature and heavy metals (Pb, Cd, Cu, Zn) content was analyzed from samples of each species included in the diet. Starting from analytical results, a maximum allowable concentration (MAC) and a risk quotient (RQ) were calculated, in order to evaluate if each metal considered represented a risk for bottlenose dolphins. Obtained data seems to be indicative of a reduced risk originating from fish species when As and Cd are considered (RQ always lower than 1, indicating no risk for the dolphins), while crustaceans and cephalopods present a RQ higher than 1. When Pb and Hg are considered, all species present a RQ higher than 1, so are to be considered a risk for dolphins. Starting from obtained data crustaceans and cephalopods are be considered as the most important risk factor in the diet of bottlenose dolphins, while fish species represent a risk only for some metals.