Quantificazione dei fenomeni di arricchimento degli elementi in traccia lungo la catena trofica come strumento per la valutazione della qualità degli ecosistemi marini e delle risorse demersali

Especially in the last centuries (Barbante et al., 2004), several anthropogenic activities have led to an increase of heavy metals global emissions (Gašpić et al., 2002; Fabris et al., 2006). Among trace elements released in environment, some are essential for organisms (Rainbow, 1988; Bustamante et al., 2000; Canli and Atli, 2003), due to their role in metabolic functioning (Barkay et al., 1992). Others play an important role in detoxification mechanisms, whereas those defined as not essential have no known role in biological system (Bustamante et al., 2000; Canli and Atli, 2003). Not essential metals are toxic even at low concentrations, thus representing a risk for human health (Barkay et al., 1992; Edwards et al., 2001). Heavy metals accumulation by marine organisms is a well known phenomenon (White and Rainbow, 1982; Bacci and Gaggi, 1998; Sandor et al., 2001; Canli and Atli, 2003; Mishra et al., 2007), especially in predator species at the top of the food chains (Storelli et al., 2001; Domi et al., 2005; Coelho et al., 2008; Suk et al., 2009). Predator species are often economically important and directly consumed by humans (Das et al., 2003; Debacker et al., 2001; Kai et al., 1978; Meaburn, 1978; Das et al., 2000; Storelli et al., 2001). This study’s aim was to provide data about cadmium, total mercury and lead concentrations in the muscle of Merluccius merluccius and Scyliorhinus canicula, that may be considered as good bioindicators of the extend of these elements contamination in the Sardinian waters. The behavior of elements was assessed in function of several parameters, with particular attention to the study of the bioaccumulation across trophic levels, estimated through stomach content analysis for both species (Schetagne et al., 2000; Storelli and Marcotrigiano, 2004; Kasper et al., 2009). Moreover, some hazard indices were calculated in order to measure potential risks for human race. Several factors seemed to interact with feeding dynamics of both species, among these, growing is probably the most influential. In addition, changes related to the reproductive process, like the decrease of feeding intensity in M. merluccius or the different bathymetric distribution of the two sexes in S. canicula, were known to be important as well. Finally, remarkable variations in the diet were related to the availability and abundance of preys, both in terms of geographic distributions and bathymetric distribution. Highest concentration of total mercury were found in the muscle of S. canicula, while lead was slightly more concentrated in M. merluccius. No differences for cadmium in both species were observed.Specie-specific differences were likely due to an higher intake rate or to a greater susceptibility to heavy metals contamination characteristics of the Chondrichthyes, as previously reported by Jeffree et al (2006) and Mathews et al. (2008). From a regulatory point of view regarding cadmium and lead, the intake of both species could be considered safe. On the contrary, health potential risks would arise from the intake of total and methylmercury. Consequently, despite the contribution of fish to diet is fundamental in maintaining a good state of health, regular consumption of both species, especially S. canicula, as the high levels of mercury should be discouraged. Moreover, it is necessary to note that intakes estimated in this work could be underestimated. They, in fact, do not take account for the intake from other food than fish, the variation in the consumption rate observed in different geographic areas, or the consumption of different tissues (liver, kidney, gonads), probably characterized by diverse concentrations of metals. In conclusion, the output of this work has to be considered as preliminary. More wide-ranging studies are necessary in order to better assess the environmental impact of heavy metals and the health risks related to the intake of fish from Sardinian waters.