|Pollutants and seals - a review|
Holden, A.V. (1978). Pollutants and seals - a review. : 53-66
It is evident from the information so far available that high concentrations of several organochlorine compounds can be accumulated in the lipids of seals and other marine mammals in polluted areas. Yet there is still no conclusive evidence that even the highest concentrations are causing adverse effects on any species, although PCBs (rather than DDT) may be linked with the abnormally high abortion rate among Baltic Ringed seals. The PCB concentrations in the extractable fat of the seals affected averaged only 77 mg/kg, but several other populations have been found to contain higher concentrations. Only one of these populations, the California sealions, has also been found to suffer a high abortion rate. Some heavy metals are present at relatively high concentrations in several organs of seals, but with the possible exception of mercury there is no evidence that any of the concentrations are abnormal. Mercury has been shown to increase with age in liver (but probably not in the brain except in the early years), although the very high concentrations in old seals (over 700 mg/kg in a few specimens) do not necessarily reflect the influence of pollution. Perhaps surprisingly, the mercury is not methylated to any large extent, suggesting that seals can probably demethylate the mercury in fish. The linear relationship with selenium may also give a protective action against mercury toxication. Few other pollutants have been found in significant concentrations, and even oil, a common marine pollutant particularly in coastal waters, has rarely been associated with any measurable adverse effects. It would seem that a more detailed study of marine mammals might lead to a greater understanding of the mechanisms which appear to give the species some degree of protection from the unusually high concentrations of DDT, PCBs and mercury often found in their tissues. It is recognized, however, that experimental investigations on seals would present considerable practical difficulties.