PCB and heavy metals in beached sperm whales

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Stranded sperm whale, 1994 © VLIZ (Debergh)

Context of the study

In the winter of 1994-1995, 21 sperm whales stranded along the North Sea shorelines. The reason for the mass stranding was that these sperm whales became trapped in the North sea. Because of the unfavorable conditions in the North Sea the animals starved and ultimately stranded. These animals can provide valuable information on the mechanics of stable pollutants and the overall health status of the sperm whale population. [1]

Content of the study

7 of the 21 sperm whales beached on Belgian and Dutch territory. One of them died at least a day before he stranded (possibly of old age, as he was estimated to be at least 60), the six others died shortly after stranding. The muscles, livers kidneys and fat of these 7 whales were examined for the presence of heavy metals, organochlorines and PAHs.

Main results of the study

High concentrations of cadmium (up to 300 µg/g dry weight in the kidney), mercury (up to 130 µg/g dry weight in the liver) and PCBs (up to 5 µg/g dry weight in blubber) were retrieved in these sperm whales. Methylmercury averaged 4% of total mercury concentrations in the liver and 90% in the muscles, showing that methylmercury is demethylated in the liver, or demethylated (somewhere) and then transported to the liver. Less than 66% of the cadmium found in the livers and kidney's was bound to metallothioneins; these are proteins which animals produce to counteract the harmful effects of metals. Therefore the remaining 33% might not have been detoxified.

Sperm whale © Kagari Aoki

Organochlorine concentrations in the blubber were low compared to other species. However, since similar levels have been shown to cause reproductive and immunodeficiency problems in other marine mammals, this doesn't necessary mean lack of effect.

Although stable pollutants (like PCB and mercury) are known to accumulate in marine mammals with increasing age, this study didn't find higher concentrations of any contaminant in the oldest animal (the one that died of old age before stranding). Since he was older than 60, he was born in the pre-organochlorine period and therefore didn't accumulate any PCBs or pesticides in the first decades of his live. Supposing he started accumulating organochlorines in the 1950s and 1960s, it becomes normal that his contamination levels are similar to the ones of the younger sperm whales, which were born in the 1960s.

The low PAH levels found were considered unlikely to affect marine mammals.

The study concluded that the pollutants present in the sperm whales didn't cause their death, but might have had an indirect influence on the health or behaviour of these animals.[1]


References

  1. 1,0 1,1 Holsbeek, L.; Joiris, C.R.; Debacker, V.; Ali, B.I.; Roose, P.; Nellissen, J.P.; Gobert, S.; Bouquegneau, J.-M.; Bossicart, M. (1999). Heavy metals, organochlorines and polycyclic aromatic hydrocarbons in sperm whales stranded in the southern North Sea during the 1994/1995 winter. Mar. Pollut. Bull. 38(4): 304-313


The main author of this article is Daphnis De Pooter
Please note that others may also have edited the contents of this article.