A ‘cocktail of pollutants’ has been found in one of the last European populations of bottlenose dolphins
Photo courtesy of NOAA (Unslpash)
by Floriane Ramfos
A recent study published in the Journal of Scientific Reports found some of the highest recorded levels of toxic chemicals and mercury in the bodies of bottlenose dolphins, just off the French coast. Researchers took tissue samples from more than 80 dolphins living in waters off Normandy and Brittany, finding high concentrations of mercury in the animals’ skin and polychlorinated biphenyls (PCBs) in their blubber. They also found other industrial chemicals in blubber samples, such as dioxins and pesticides, altogether acting as a ‘cocktail of pollutants’, according to the research team.
Most of the pollutants that were found in the dolphins were banned in western Europe in the 1970s and 1980s, but the chemicals stay in the water, ‘including in the deepest ocean fauna’, the study reads. The chemicals then accumulate in the skin and blubber of dolphins over time. PCBs, for example, are used in plastics, paints and electrical equipment, were banned several decades ago, but still persist in the environment today.
Similarly, one killer whale found dead off the coast of Scotland in 2016 contained among the highest levels of polychlorinated biphenyls (PCBs) ever recorded. The animal, called Lulu, was found dead on the Isle of Tiree in Scotland after becoming entangled in fishing lines. Even back in 2016, the whale’s level of PCBs was deemed ‘shocking’ by Dr Andrew Brownlow, head of the Scottish Marine Animal Stranding Scheme and veterinary pathologist at Scotland's Rural College (SRUC).
The pollutants are passed by mother dolphins to their offspring during gestation and lactation, which means that it will be very difficult to get rid of the chemicals, as they are transmitted from generation to generation. ‘Female dolphins offload a significant portion of this cocktail to their offspring during gestation and lactation, placing foetuses and newborns at a higher risk’, the report notes. The team of researchers, led by Dr Krishna Das of the University of Liege in Belgium, stated that their results ‘indicated the important transfer of PCBs by females to their young, which may raise concern for the dolphin population’, given that the English Channel is home to one of the last remaining large European populations of bottlenose dolphins. Male dolphins are at risk too as they continue to bioaccumulate PCBs throughout life.
‘As apex predators, bottlenose dolphins are at higher risk of exposure to some of the chemicals mentioned in this study - and as many of the European coastal populations of bottlenose dolphins are relatively small in size, they may, therefore, be under greater conservation threat’, said Rob Deaville of the UK Cetacean Strandings Investigation Programme.
