Biomonitoring of trace metals (Cu, Cd, Cr, Hg, Pb, Zn) in Mali Ston Bay (eastern Adriatic) using the Mediterranean blue mussel (1998-2005)

Abstract

         In Mali Ston Bay, located on the eastern Adriatic coast, mussels and oysters have traditionally been cultivated. However, previous studies showed that water and sediments from Mali Ston Bay contain elevated levels of some trace metals, which was attributed to natural processes of sedimentation and drainage. In order to assess the bioavailability of trace metals in the bay, and to assess the health risk of consumption of shellfish species from Mali Ston Bay, a passive monitoring program was carried out in the period from December 1998 to August 2005. Samples of the whole soft tissue were collected seasonally at 4 shellfish breeding farms and analyzed for essential (Cu, Zn) and non-essential (Cd, Cr, THg, Pb) metals. Mean concentrations of analyzed metals in the edible tissue of mussels (Cd: 1.15 mg kg^-1 d.wt.; Cr: 1.65 mg kg^-1 d.wt.; Cu: 5.6 mg kg^-1 d.wt.; THg: 0.15 mg kg^-1 d.wt.; Pb: 1.09 mg kg^-1 d.wt.; Zn: 139 mg kg^-1 d.wt.) fell in the range of values usually found in low to moderately contaminated marine coastal areas. Examination of the spatial pattern of contaminants showed that there were no statistically significant differences among stations in Mali Ston Bay regarding trace metal content. Concentrations of Cd, Cu, Cr and THg were significantly higher during the autumn-winter period, while concentrations of Pb and Zn did not depend on the sampling season. Among six analyzed metals, only concentrations of Cd and THg were significantly negatively correlated with the condition index of the mussels. Analysis of temporal trends during the 7 years of monitoring showed that metal concentrations had not changed with time. According to EU and WHO legislation, consumption of the edible tissue of the mussels was not harmful for humans since all the values were well below the permissible limits for fresh seafood. In addition, results of the evaluation of the risks to human health associated with consumption of the mussels containing trace metals suggest that there is no health risk for moderate shellfish consumers.