Sightings of harbour porpoises in the English Channel and North Sea have fallen since the 1970s. Now evidence has come to light that exposure to polychlorinated biphenyls (PCBs) and mercury may have contributed to their decline.
Peter Bennett and Paul Jepson, of the Institute of Zoology in London, conducted post-mortem examinations on porpoises found dead around the coast since 1990. The average level of PCBs in 33 porpoises that had died from infectious disease was 31.1 milligrams per kilogram of blubber. This compared with 13.6 milligrams per kilogram in 34 animals that suffocated in fishing nets.
Mr Bennett said in New Scientist magazine: "We consider this association may be causal because PCBs have been shown to damage the immune systems of other mammals in the laboratory." The men have found similar links between fatal infections and mercury in the livers of harbour porpoises. They are investigating the possibility that mercury and PCBs act together to worsen the harm they cause.Reuse content