Accumulation of mercury, cadmium, lead and arsenic in swordfish and bluefin tuna from the Mediterranean sea: a comparative study

In this paper, the presence and amount of mercury and polychlorobiphenyls (PCBs) were determined in more than 1000 food items collected monthly in the period 2001–2010 in commercial food shops in Siena (Tuscany, Italy), in order to assess risk to humans due to food consumption. The overall results clearly show a strong difference in concentration of the two contaminants between foods from the terrestrial trophic web and those from the marine trophic web. Particular attention was paid to study the Mediterranean swordfish (Xiphias gladius) and bluefin tuna (Thunnus thynnus) because anthropic impact on these species is great due to their topmost position in trophic webs; thus it is very important to know their health status and evaluate their toxicity for humans. Many samples of bluefin tuna and swordfish show mercury levels higher than 0.5 mg/kg f.w., which is the maximum level set by the European Commission (EC, Regulation n. 1881/2006) for most fish species. Taking into account the important nutritional contribution that fish makes to the diet, it is advisable that women of childbearing age, pregnant and breastfeeding women as well as young children select fish from a wide range of species, without giving undue preference to large predatory fish such as swordfish and tuna. In any case, it is interesting to note a significant decrease in levels of both mercury and PCBs in bluefin tuna and swordfish found in the Sienese market over the course of the past ten years.[...]