MERCURY LEVELS AND ITS CHEMICAL FORM IN TISSUES AND ORGANS OF SEABIRDS

Liver, muscle, kidney, and feather samples from nine species of seabir ds were analyzed for total and organic (methyl) mercury (MM). Total me rcury (TM) levels in liver showed great intra- and inter-species varia tions, with the concentrations varied from 306 mu g/g (dry weight) in black-footed albatross (Diomedea nigripes) to 4.9 mu g/g in arctic ter n (Sterna paradisaea), while MM levels were less relatively variable. The order of MM concentrations in tissues of all the seabirds except o ldsquaw (Clangula hyemalis) was as follows: liver > kidney > muscle. T he mean percentage of MM in total was 35%, 36%, and 66% in liver, kidn ey, and muscle, respectively, for all the species. Statistically signi ficant negative correlations were found between the proportion of MM t o TM and concentrations of TM in the liver and muscle of black-footed albatross and in the liver of laysan albatross. Furthermore, the perce ntage of MM decreased with an increase in TM concentrations in the liv er, muscle, and kidney of all the species. Black-footed albatross had the highest concentration and burden of mercury in the liver, wherein more than 70% of the TM occurred as inorganic mercury. On the other ha nd, the mercury burdens in feathers were less than 10% of the body bur dens, indicating that excretion of mercury by moulting is negligible. The results suggest that some seabirds are capable of demethylating MM in the tissues (mainly in liver), and store mercury as an immobilizab le inorganic form in the liver. It is noteworthy that the species with a high degree of demethylation capacity and slow moulting pattern sho wed low mercury burdens in feathers.