Mercury and organochlorines in four sperm whales stranded on the Belgian coast, November 1994
1997
Joiris, C.R. | Holsbeek, L. | Bossicart, M. | Tapia, G. (Universite libre de Bruxelles (Belgium). Lab. for Ecotoxicology and Polar Ecology)
Four sperm whales (three subadult males stranded on the Belgian coast, a fourth older male found dead at sea) were analysed for total mercury, methylmercury and organochlorines. All four were part of a total of 24 sperm whales that stranded on the North Sea coasts over a period of six months, a highly unusual phenomenon. Total mercury levels ranged from 0.5 microg/g fw in kidney and 1 in muscle, up to 15 in liver. The finding of at least 90 per cent of the mercury in its inorganic form confirms the existence of detoxification mechanisms in the liver of cetaceans. PCB concentrations in muscle, liver, kidney and blubber ranged from 10 to 25 microg/g lipids. These results are in the same order of magnitude as literature data, which however does not imply that there is no impact on the populations. Social affiliation with a particular adult bull rather than a direct effect of pollutants may have been the primary cause of the stranding of the three younger animals: they apparently remained close to the older one (the leader?) dead at sea, and stranded in very shallow water. Indirect impact of anthropogenic pollutants influencing the behaviour and/or the health of a social cluster is one plausible hypothesis to explain why a large number of sperm whales got trapped in the North Sea, but limited data available on the large bull fail to support this.
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