Study of trace elements in organs and tissues of striped dolphins (Stenella coeruleoalba) found dead along the Ligurian coasts (Italy)

Concentrations of copper, iron, manganese, zinc, selenium and mercury (total and organic) were measured in muscle tissue, brain, heart, lung, kidney, spleen, and liver of 18 dead striped dolphins (Stenella coeruleoalba) found stranded on the beaches of the Ligurian Sea. Distribution of the trace elements among the tissues and bioaccumulation are discussed. High levels of mercury were observed in all tissues analysed, with concentrations reaching 260 µg/g dry weight (dry wt.) in the muscle, 448 µg/g dry wt. in the lung, 1316 µg/g dry wt. in the spleen, and 2993 µg/g dry wt. in the liver. Mercury present in the organic form was, on average, approximately 30% of the total for all tissues with the exception of the heart, which showed higher values (mean 63%), and liver, where organic mercury was very low (mean 12%). In muscle tissue the organic mercury fraction decreased with increasing total mercury concentration. The liver accumulated trace elements to a greater extent than the other organs studied, with the exception of iron. Principal component analysis (PCA) revealed a grouping of the specimens on the basis of their estimated age. A strong positive correlation between the concentration of inorganic mercury and selenium was found for all the tissues analysed. In the liver the selenium to inorganic mercury molar ratio was very close to 1, confirming results of previous authors.