Two reason they’re so perennial – despite significant limits on their production and disposal in the last three decades – are because they don’t degrade spontaneously and they become more concentrated as they move up the food chain.***
Now, PCBs seem to be disrupting vitamin A pathways in harbor seals, according to a report in Aquatic Toxicology by Lizzy Mos and colleagues. Working in British Columbia and Washington, the team caught 24 wild baby harbor seals and took blood and blubber samples. Seals with high PCB levels had less vitamin A in their blood and less vitamin A stored in their blubber.
The vitamin is an essential nutrient involved in hormonal levels and the immune system. The authors note that vitamin A has a variety of hormonal and immune-system functions, and that other studies have implicated PCBs in both reproductive failures and disease outbreaks in marine populations.
But perhaps more worryingly, the scientists seem mainly interested in using vitamin A levels as a flag. In other words, PCBs may be damaging seals in more unobtrusive ways, and vitamin A is a useful way to keep an eye on them.
Adorable image by bibianadesign.com
***As you well-informed Scribble readers probably know, this is called bioaccumulation. At each step in the food chain, animals that eat PCB-laced food store the chemicals in their bodies. By the time you get up to the kinds of animals people tend to care about – ones that are delicious or cute – the rare chemicals are concentrated enough to be toxic. All in all, it’s a useful lesson about the staying power of decisions that sound good at the time.