Trace metals and metallothionein in tissues of Caretta caretta from Mediterranean Sea

Biomonitoring of heavy metals in wild marine fauna is an important task due to the toxic effects of these pollutants on organisms at the top of the food chain. Metal homeostasis and bioaccumulation is strictly related to the induction of metallothionein (MT). Our research was advised to investigate the relathionship between trace metal concentration in tissues and their chelation by MT. Cd, Zn, and Cu concentrations were determined by AAS in liver, kidney, muscle, heart, lung and gonads of loggerhead turtle (Caretta caretta) which is the most common turtle in the Mediterranean Sea. Kidney displayed the highest Cd concentration, reaching a maximum of 2.4 µg/g wet weight (w.w.), while the lowest metal level was present in the muscle. The highest Cu concentrations were found in the liver (4.98±0.58 µg/g w.w.); finally highest Zn levels were present in the heart (46.6±5.2 µg/g w.w.). MT was isolated and quantified in the liver and kidney; in the liver MT bound mainly Cu, due to the high metal concentration in the organ, whereas in the kidney Cd co-eluted with MT peak and only a minor percentage of Cu was bound to the protein. Metal levels determined in this research are similar to those reported by other authors for the same species from Mediterranean Sea; in contrast Cd concentrations in loggerhead turtle from other locations were considerably higher than those reported here. Differences in heavy metals concentrations may be explained by differences in the diet and age. The low MT expression in liver and kidney is consistent with a low exposure to the investigated metals.