Concentrations of polychlorinated biphenyl (PCB) in the blubber of striped and bottlenose dolphins, and killer whales in European waters, are among the highest recorded globally for whales and dolphins, according to research published in Scientific Reports. The study suggests that these concentrations are likely to cause populations to decline and suppress their recovery.

PCB is a synthetic chemical compound that was used in electrical components until it was banned in 1979 in the USA and 1981 in the UK. However, their use was not phased out until 1987 in European countries that border the Mediterranean Sea. Blubber concentrations of PCB initially declined following a ban by the EU, but have since stabilised in UK harbour porpoises and striped dolphins in the western Mediterranean Sea.

Paul Jepson and colleagues performed a meta-analysis of blubber PCB concentrations in 1,081 stranded or biopsied European marine mammals from four species: harbour porpoise, striped dolphin, bottlenose dolphin and killer whale. The authors found that in bottlenose and striped dolphins, and killer whales, mean PCB levels exceeded toxicity thresholds for marine mammals. They also found that areas of the western and central Mediterranean Sea, SW Iberia, the Gulf of Cadiz and the Strait of Gibraltar were global PCB ‘hotspots’ for these mammals.

The authors argue that blubber PCB concentrations are still very high, despite a ban on their use and manufacture, because they may have reached a ‘steady state’ between environmental input and degradation. They suggest that the high levels of PCB in these species are likely to suppress reproduction and will continue to drive population declines.