Jepson said great whites and tiger sharks are likely threatened the most from chemical contamination.
"Bull sharks also live near coasts and so might pick up PCBs from their proximity to land," he added. "These shark species are all feeding at a similar level in the food web to killer whales, so they may have similar exposures to PCBs. Unfortunately, very few studies have been done of PCBs and other POPs in marine apex predator sharks. We need to do more."
Based on studies involving marine mammals and other species, PCBs, DDT and other POPs suppress both immune system function and reproduction, according to the authors. The chemicals, which attach to small particles like sediment suspended in water, can also interfere with hormonal activity.
"In western and southern Europe, few remaining coastal or resident killer whale populations are very highly PCB-contaminated populations and have effectively stopped reproducing," Jepson said. "If you stop reproducing, you will eventually disappear."
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He said that the chemicals, which he calls "invisible killers," pose risks to human health as well. In countries like Finland, the dietary advice is to eat only one to two wild herring from the Baltic Sea per month because the fish contain so many of the pollutants.
"A large adult male killer whale off Norway or Iceland -- which mainly feed on herring -- may need to eat up to 100 kilograms (220.5) pounds of herring per day to survive, so you can see why we have the PCB problem we have in European killer whales and other dolphins," Jepson said.
Alex Aguilar, director of the Institute of Biodiversity Research at the University of Barcelona, told Discovery News that more research is needed on sharks to establish precisely how POPs affect them.
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Solving the problem requires a multi-pronged approach. Some countries still use POPs, such as DDT, so safer alternatives to the chemicals are needed. The authors also call for full compliance to the Stockholm Convention, which requires mitigating or destroying large stocks of PCBs or PCB-contaminated materials on land by 2028.
POPs, and especially PCBs, remain in industrial and electrical equipment, landfills, sediments in estuaries, joint sealants in high-rise buildings built from about the 1950s–1980s, and more.
As a result, the authors say that "there is an urgent need to review current methods of PCB mitigation in the marine environment -- both in Europe and elsewhere."