The environmental toxin methylmercury (MeHg) is spreading in marine ecosystems and threatening health and existence of living organisms. A recently published study demonstrates how geographical tracking combined with analyses of blood and feathers from little auks, the smallest of our alcids, can help unravel the sources of methylmercury and how exposure to this pollutant varies in time and space.

Accumulation in the food chain

Methylmercury is a naturally-occurring organic form of mercury (Hg) but is also released into the ecosystem through emissions from various industrial processes. This neurotoxin is assimilated via food by marine organisms in particular, and accumulates in increasing concentrations along the food chain. Even though anthropogenic sources of methylmercury in the Arctic are few, very high concentrations of the substance are measured in this region, and several studies suggest that methylmercury is formed in oxygen-rich waters and transported to the Arctic from other regions. Seabirds migrating between breeding grounds and wintering areas and thus feeding in different regions throughout the year are thus excellent bioindicators of mercury exposure. To improve our understanding of the sources and pathways of methylmercury, researchers have analysed blood and feather samples from little auks in several colonies in the Arctic. Equipped with geolocators from the SEATRACK project, the birds provided valuable data on timing and geographical variation in exposure to the environmental toxin.

The little auk – the smallest of the alcids – feeds its chick with small copepods which it carries from the ocean in a pouch on the throat.
Photo: Emma A. Sørensen, SEAPOP

Exposure is highest in the west and outside the breeding season

Consistent longitudinal patterns both in summer and winter reflected a higher accumulation of methylmercury in little auks from western regions, such as Northwest Greenland, whereas birds breeding in northern Arctic regions seemed to be exposed to lower concentrations. The results also suggested that methylmercury is formed and accumulates in living organisms in shallow, high-Arctic waters. Moreover, the exposure to methylmercury appeared to be highest outside the breeding season. This might be explained by the little auks’ diet shift from mainly copepods in the summer to krill, fish larvae and other prey items higher up in the food chain in the winter. The study is a good example of how the pathways of methylmercury can be traced in time and space by combining tissue sampling and tracking technology.

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Contact person: Hallvard Strøm, Norwegian Polar Institute