CONCENTRATIONS OF LEAD, MERCURY AND CADMIUM IN TWO SPECIES OF FRESHWATER FISH RAISED IN TEMPERATURE-CONTROLLED WATER TANKS: IMPLICATIONS FOR HUMAN DIET.

It is known that the bioaccumulation process in fish is influenced by temperature, water-hardness and diet. Particularly, the use of warm water such as that coming from a power station plant after cooling in vapour condensers, besides enhancing the growth of fish, could facilitate accumulation process of xenobiotics with increasing health hazard for human consumers. The concentrations of three heavy metals (Pb, Hg and Cd) were determined in two species of freshwater fishes, the sturgeon (Acipenser naccarii) and the carp (Cyprinus carpio) raised in thermal aquaculture using water from the river Po. One hundred fishes with an initial weight of about 80 g each fed on wet pellets (3% of live weight) and bred for two years at a temperature ranging form a minimum of 15 \ub0C in the winter and a max of 25 \ub0C in the summer. Every three months five fishes were sacrificed and the three elements were determined by AAS in muscle samples. After 24 months of breeding, the following mean levels (mg/kg dry weight) of heavy metals were detected in the muscles of the sturgeon and the carp, respectively: 1.89 +- 1.2 and 1.52 +- 0.6 of Pb; 0.73 +- 0.3 and 0.41 +- 0.2 Hg; 0.26 +- 0.1 and 0.10 +- 0.06 of Cd. Interestingly, the metal concentrations found in these fishes were about ten times lower than in wild ones living of the river Po, in spite of the same aquatic environment. Therefore, the results suggest that the use of the cooling water form thermoelectric plant for aquaculture is a highly efficient system. In fact, it allows considerable fish growth in short time but reducing the bioaccumulation of the heavy metals, so that the raised fish can be considered suitable for human consumption