BBC – September 28, 2018
Scientists fear that the chemical PCB could cause orca populations to collapse entirely. Before they were banned decades ago, PCBs were prevalent in many every-day items such as electrical equipment, sealants and paints. But they persist in the environment for a long time, and researchers said blubber samples showed they were accumulating in the bodies of cetaceans, especially killer whales.
They affect fertility in whales and cause death through immunosuppression. The research is published today in the magazine Science. A new study suggested the long-term viability of more than half of the different orca groups around the globe was now in question. Some populations, such as those around the UK, the Strait of Gibraltar, off Brazil, Japan and California, are almost certainly doomed.
Keep in mind these were mathematical models that did not take many factors into account. They looked solely at PCB concentration.
Something I find VERY alarming in this study is the small sample sizes. The authors concluded that Hawaiian and Brazilian killer whale populations will collapse based on 1 sample from each group. Only 1! To conclude that whole populations will vanish based on the PCB concentrations in 1 whale from 1 age-sex class is not appropriate in my opinion. Other groups, like UK and Faroese whales, only had 2 samples. Again, that is really not enough to make meaningful conclusions.
PCBs are definitely harmful along with other persistent organic pollutants we see in killer whale populations. However, they are not automatic death sentences and it’s likely their impact on the health of the whale is dependent on other factors, like prey availability.
I think the media has overhyped this study and and didn’t think critically about its limitations before ringing alarm bells.