It is looking more and more likely that orcas swimming in European waters will soon be a thing of the past. An extensive study investigatingfour species of whales and dolphins living off the coast of Europe has found that the levels of a harmful chemical, polychlorinated biphenyl, inthe marine mammals’ fat are the highest recorded anywhere in the world. They have also concludedthat the highconcentrations of this chemical in the animalsis likelythe cause of supressed reproduction rates seen among the orca and other species around Europe since the 1960s.
Before they were banned, polychlorinated biphenyl compounds or PCBs were commonly used in electronics, paints, and as fire retardants, until it was discovered that they were highly toxic, and subsequently banned. PCBs are known to bioaccumulate, meaning that they build up in the food chain,often becoming concentrated in the animals that take the top spots, such as whales and dolphins. As with many harmful chemicals, they have managed to persist in the environment, and are still having a major impact on these marine mammals found in the north eastern Atlantic and Mediterranean.
Orca are espcially vulnerable to PCBs as they are at the top of the food chain. This is one of the last eight surviving orca living off the north West coast of the U.K.Kerry Froud_Hebridean Whale and Dolphin Trust
In the striped dolphins, bottle nosed dolphins, and killer whales, we have mean PCB levels that are excessive, explained Dr. Paul Jepson, lead author of the study published in Scientific Reports. They are probably the highest in the world right now, by some way. Europe is a big hotspot for PCBs, in particular the western Mediterranean Sea and around the Iberian Peninsula.
After their use was banned in the 1980s, the levels of PCBs found in whale blubberdid drop until around 2000, when the concentrations found in the marine mammals plateaued. So its quite likely now that were in a steady state condition where whatever PCB is metabolised or excreted is topped up by new inputs, says Dr. Jepson.
The study also looked at striped dolphins (pictured), bottle nosed dolphins, and harbor porpoises. Andrea Izzotti/Shutterstock
And these inputs are expansive. After the chemical was banned in the 1980s, only around 10 percent of it was destroyed. Due to its high resistance to heat, one of the exact reasons it was so popular in manufacturing, its incredibly difficult to get rid of. This meant that the vast majority of the PCB produced was simply buried in landfill. It is from these sources thatthe chemical is slowly seepinginto the oceans, as well as the dredging of sedimentsstirring up the PCB from the sea floor, topping up the concentration of the PCBin the food chain, and eventually reaching whales and dolphins.
This has resulted in the decline in populations, particularly of bottle nosed dolphins and orca, as the chemicals impact the mammals’ ability to reproduce, while also supressing their immune system. In fact, there are now no pods of orca that live year round in the North Sea, and only eight individuals living off the north west coast of the U.K. Despite having been studied for a long time, this last remaining population of orca has never bred, and is unlikely to in the future.
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