As was reported by the magazine Science, many populations of orcas may disappear entirely during the next 100 years, due to polychlorinated biphenyls, or PCBs, building up in their tissue. That contamination may cause multiple killer whale populations to crash in the coming decades, which would have a ripple effect throughout the food chain.
Until they were recognized as highly toxic and carcinogenic, polychlorinated biphenyls (PCBs) were once used widely. Their production was banned in the United States in 1978, though they are still produced globally and persist in the environment. Persistent organic compounds, like PCBs, magnify across trophic levels, and thus apex predators are particularly susceptible to their ill effects. Desforges et al. looked at the continuing impact of PCBs on one of the largest marine predators, the killer whale. Using globally available data, the authors found high concentrations of PCBs within killer whale tissues. These are likely to precipitate declines across killer whale populations, particularly those that feed at high trophic levels and are the closest to industrialized areas.
Killer whales (Orcinus orca) are among the most highly polychlorinated biphenyl (PCB)–contaminated mammals in the world, raising concern about the health consequences of current PCB exposures. Using an individual-based model framework and globally available data on PCB concentrations in killer whale tissues, we show that PCB-mediated effects on reproduction and immune function threaten the long-term viability of >50% of the world’s killer whale populations. PCB-mediated effects over the coming 100 years predicted that killer whale populations near industrialized regions, and those feeding at high trophic levels regardless of location, are at high risk of population collapse. Despite a near-global ban of PCBs more than 30 years ago, the world’s killer whales illustrate the troubling persistence of this chemical class.
- The international team of researchers examined available data on PCB concentrations in about 350 killer whales worldwide and compared them to levels known to affect reproduction and immune system functionality.
- They incorporated this information into a population model to forecast the predicted effects of PCBs on population growth for the next century.
Per the study published Thursday in Science:
- More than half of the 19 studied populations of killer whales have “achievable growth rates” that are low enough to cause them to decline, potentially inexorably.
- Brazilian, Northeast Pacific Bigg’s, Canary Islands, Greenlandic, Hawaiian, Japanese, Strait of Gibraltar and U.K. orca populations are all “at high risk of collapse over the next 100 years,” the study states.
- Orcas farther away from industrialized countries tend to be better off, such as those in the Arctic and Antarctic.
Study co-author Paul Jepson, a specialist in wildlife population health at the Zoological Society of London, told Axios:
“I would agree with their findings that these high-risk populations very likely are going through a decline associated with elevated PCBs,” said Brendan Hickie, a senior lecturer at Trent University’s School of the Environment who was not involved in the study.
This study has implications for conservation efforts, as few populations of killer whales have legal protections, and these are not specific to PCBs.
“I think very few countries globally are doing very much at all to mitigate the risk of PCBs to killer whales,” Jepson said.