Heavy metals in the tissues of common dolphins (Delphinus delphis) stranded on the Portuguese coast

The concentrations of Hg, Sn, Cr, Zn, Ni, Co, Cd, Mn, Fe and Cu were determined in the liver, kidney and muscle of 24 common dolphins stranded on the Portuguese coast between 1995 and 1998. Nitric acid was used to extract the metals from the tissues for analysis by inductively-coupled plasma/atomic emission spectroscopy (ICP/AES). Those metals with relatively higher concentrations included Fe, Zn and Hg, particularly in liver. Other metals including Cr, Ni and Cd tended to show much lower levels, or were even undetected (e.g. Co). Different metals seemed to show different temporal trends, although due to substantial variations of the mean concentrations for each year obtained, such temporal pattern has to be studied further. Total Hg concentration in the kidney, muscle and particularly liver, were higher in females than in males. Total Hg concentrations in all the organs increased with body length of dolphins, whilst those of Zn and Cu in muscle decreased with dolphin length. A strong correlation was found between essential metals Zn and Cu in muscle, possibly resulting from sequestration of these metals by metallothionein. In addition, significant co-associations existed between the same metal (e.g. Hg, Sn and Zn) in different organs.