PCB and heavy metals in beached sperm whales

Heavy Metals, Organochlorines and Polycyclic Aromatic Hydrocarbons in Sperm Whales Stranded in the Southern North Sea During the 1994/1995 Winter

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.

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 PAH's.

Main results of the study

High concentrations of cadmium (up to 300 µg/g dry weight in the kidney), total mercury (up to 130 µg/g dry weight in the liver) and PCB's (up to 5 µg/g in blubber) were retrieved in these sperm whales. Methylmercury averaged 4% of total mercury concentrations in the liver and 90% in the muscles. 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.

Stranded sperm whale © WHOI (Michael Moore)

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 PCB's or pesticides in the first decades of his live. Supposing he started accumulating organochlorines in the 1950's and 1960's, it becomes normal that his contamination levels are similar to the ones of the younger sperm whales, which were born in the 1960's.

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.

You can find more information of this study through this link