Marine top predators, including marine mammals, are known to bio-accumulate persistent pollutants such as polychlorinated biphenyls (PCBs), a serious conservation concern for these species. Although PCBs declined in European seas since the 1970s – 1980s ban, considerable levels still persist in European and Mediterranean waters.

This study evaluated PCB and other organochlorine contaminants in free-ranging common bottlenose dolphins (Tursiops truncatus) from the Gulf of Trieste (northern Adriatic Sea), one of the most human-impacted areas in the Mediterranean Sea. The authors tested for the effects of sex, parity and social group membership on contaminant concentrations.

The results show that 87,5% of dolphins had PCB concentrations above the toxicity threshold for physiological effects in experimental marine mammal studies, while 65,6% had concentrations above the highest threshold published for marine mammals based on reproductive impairment in ringed seals. It was also found that males had significantly higher organochlorine concentrations than females, suggesting offloading from reproducing females to their offspring via gestation and/or lactation.

It is highlighted that the potential population-level effects of such high contaminant levels are of concern particularly in combination with other known or suspected threats to this population.

Genov et al. (2019) Linking organochlorine contaminants with demographic parameters in free-ranging common bottlenose dolphins from the northern Adriatic Sea. Science of the Total Environment 657:200-212.