Mercury concentrations in seabirds from colonies in the northeast Atlantic

Total mercury concentrations were determined in samples of body feathers from a range of common seabird species breeding at Låtrabjarg, northwest Iceland, St. Kilda, Foula and the Firth of Forth, Scotland and Bleiksøy, Syltefjord, and Hornøy, Norway. Seabirds from Låtrabjarg generally exhibited the highest mercury concentrations, with a trend of decreasing mercury concentrations in a southwest to northeast direction in seabirds at the other colonies; seabirds at Hornøy were generally found to have the lowest mercury concentrations. Some species at the Firth of Forth exhibited relatively elevated mercury concentrations compared to those at Foula and Norwegian sites. Inter-colony differences in diet were thought to be relatively small for most species and unlikely to account for the range of mercury concentrations measured in the seabirds (Låtrabjarg: lowest arithmetic mean mercury concentration in common guillemots Uria aalge, 1.6 micrograms/g, s.d. = 0.6, n = 45; highest arithmetic mean mercury concentration in kittiwakes Rissa tridactyla, 5.5 micrograms/g, s.d. = 1.7, n = 36). The oceanic transport of mercury, together with the effects of anthropogenic inputs of mercury to the northeast Atlantic, and the removal of mercury from the water column via biological activity are discussed as influential factors determining the observed patterns of mercury concentration in seabirds.