Mercury levels and its chemical form in tissues and organs of seabirds

Abstract

Liver, muscle, kidney, and feather samples from nine species of seabirds were analyzed for total and organic (methyl) mercury (MM). Total mercury (TM) levels in liver showed great intra- and inter-species variations, with the concentrations varied from 306 μg/g (dry weight) in black-footed albatross (Diomedea nigripes) to 4.9 μg/g in arctic tern (Sterna paradisaea), while MM levels were less relatively variable. The order of MM concentrations in tissues of all the seabirds except oldsquaw (Clangula hyemalis) was as follows: liver > kidney > muscle. The mean percentage of MM in total was 35%, 36%, and 66% in liver, kidney, and muscle, respectively, for all the species. Statistically significant negative correlations were found between the proportion of MM to TM and concentrations of TM in the liver and muscle of black-footed albatross and in the liver of laysan albatross. Furthermore, the percentage of MM decreased with an increase in TM concentrations in the liver, 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 hand, the mercury burdens in feathers were less than 10% of the body burdens, 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 immobilizable inorganic form in the liver. It is noteworthy that the species with a high degree of demethylation capacity and slow moulting pattern showed low mercury burdens in feathers.