Harbor porpoises and protected dolphins have difficulty breeding because of banned chemical pollutants that are present in European waters.

A study led by researchers from the Zoological Society of London (ZSL), which was published the journal PLOS ONE on July 22 revealed that polychlorinated biphenyls (PCBs), chemicals that were once used in certain paints and electrical components, accumulated in the fat tissue of cetaceans such as dolphins, whales and porpoises and these can remain there for the entire lifetime of the animal.

Exposure to this chemical can weaken the immune systems of cetaceans and reduce their breeding success.

The researchers of the study examined the concentration of PCB in 329 harbor porpoises that were stranded on beaches in the UK and found that the marine animals have high concentration of the chemical in their body fat.

The researchers also reported that about 200 bottle-nosed dolphins found in the Moray Firth were found to have higher levels of the banned chemical compared with the harbor porpoises.

The scientists believe that PCB, which was banned in the UK over three decades ago, is responsible for the widespread evidence of miscarriages, stillbirths and spontaneous abortions among the female cetaceans that were examined.

Experts said that nearly a fifth of the sexually mature female porpoises showed signs of reproductive failure and 16.5 percent were found to have infections or tumors in their reproductive organs that could be attributed to their inability to breed.

Study researcher Sinead Murphy, from the Zoological Society of London, said that a low pregnancy rate of 50 percent was also estimated for females that were considered healthy adding that reproductive failure may have occurred in a large percentage of the females that were examined in the study.

"A lower pregnancy rate of 50% was estimated for "healthy" females that died of traumatic causes of death, compared to other populations," Murphy and colleagues wrote in their study. "Whether or not PCBs are part of an underlying mechanism, we used individual PCB burdens to show further evidence of reproductive failure in the North-east Atlantic harbor porpoise population, results that should inform conservation management."

Murphy said that PCBs may have reduced the survival odds of fetuses and newborns and this has been observed not just in cetaceans but in other mammals as well. PCBS were banned in the UK in 1981 but the levels of the chemical are still high in many UK porpoises, which could have negative implications on the animals' health and breeding.

Photo: Alessandro Caproni | Flickr

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