The chemical form of mercury stored in South Atlantic seabirds

Concentrations of total mercury and organic (methyl) mercury were measured in the liver tissue of adults of 12 seabird species collected at colonies on Gough Island, South Atlantic Ocean. Total mercury levels showed both great intra- and interspecies variation, ranging from a mean of 1343.0 microg g(-1) dry weight in wandering albatrosses to a mean of 0.8 microg g(-1) dry weight in broad-billed prions. Organic mercury levels were less variable both between, but especially within, species. Organic mercury levels, expressed as a percentage of total mercury levels, ranged from a mean of 2.6% in wandering albatrosses up to a mean of 92.6% in littee shearwaters. Within each species, individuals with the highest total mercury levels tended to have the lowest percentage organic mercury, this trend being statistically significant in several species. Two species exhibited a significant positive correlation between organic mercury levels, in absolute terms, and total mercury levels. When all 12 species were considered, a highly significant negative correlation between mean percentage organic mercury and mean total mercury was found (rs = -0.888, P < 0.001). These results provide evidence to suggest that some seabirds may be capable of demethylating organic mercury in a species-dependent and that eliminatory pathways for the excretion of dietary mercury may influence the mode of response of a particular species.