Killer whales ( Orcinus orca ) is the last link in a long food chain and among the mammals that have the highest levels of PCBs (polykloredede biphenyls) in the tissue. Researchers have measured values of up to 1300 milligrams per kilo in frogs' fatty tissue (spikes). By comparison, a large number of studies show that animals with as low as 50 milligrams PCB per kilogram of adipose tissue can show signs of impaired or non-reproduction, as well as their immune system also affected.
Together with colleagues from a large number of foreign universities, researchers from the University of Aarhus have just documented that the number of kippers fell drastically in 10 out of the 19 investigated killer whales populations. The researchers have modeled the development over a 100 year period and see that PCBs in certain areas threaten to eradicate the species within a few decades, as the animals have already been affected by approx. 50 years.
The killer is particularly threatened in affected areas around Brazil, Gibraltar, England and along the east coast of Greenland. Around the British Isles, researchers estimate that now there are only less than 10 killer whales left.
PCB accumulates in the food chain
The killer is one of the most widely used mammals on earth and lives in all oceans from pole to pole. But today, only the populations living in the least polluted areas occur in a large number.
Overfishing and noise also respond to the welfare of the animals, but especially PCBs have a dramatic effect on the propagation capacity of the donkeys and their immune system.
PCBs accumulate through all stages of the food chain, and choppers living among other things marine mammals and large fish such as tuna and sharks, accumulate PCBs and other pollutants at a dangerous level. It is these populations of killer whales who have the highest PCB loads and where stocks are threatened to collapse. Cuttlefishers, who primarily eat less fish like herring and mackerel, have a significantly lower content of PCBs and are therefore not endangered.
PCB has been used around the world since the 1930s. More than one million tons were produced and used, among other things. in electrical components and plastic. Together with DDT and other organic pollutants - primarily spray poisons against weed plants and pests - PCBs spread across the globe through air and ocean currents.
Throughout the 1970s and 80's PCBs were banned in several countries and more than 90 countries have committed themselves to phasing out and destroying large amounts of PCB through the Stockholm Convention in 2004.
PCB only degrades slowly in the environment. Leprechaun mothers also pass large amounts of PCBs to their offspring through the fatty milk. The transport keeps the environmentally polluted substances in the body of the animals rather than getting them into the environment, after all, they can be deposited and degraded in the long run.
Gloves from all over the world investigated
"We know that PCBs, for example, deform genitals in, among other things, polar bears. Therefore, it was obvious to investigate the impact of PCB on the poor occurrence of killer whales around the world, "says Professor Rune Dietz of the Department of Bioscience and Arctic Research Center, Aarhus University, which is initiated by the killer whale investigations and co-author of the article.
The research group, which counts members from the United States, Canada, England, Greenland, Iceland and Denmark, reviewed the entire existing literature and compared all data with their own latest results. It provided information about PCB volumes in more than 350 killer whales around the world - the largest survey of killer whales ever.
Through models, researchers could then predict the effects of PCB on the amount of kids fed by the donor, as well as the immune system and mortality of the donor, over a period of 100 years.
More than 50% of the population threatened
"The results surprise us. We see that more than half of the hatcher populations we have studied are heavily influenced by PCB, "says Jean-Pierre Desforges, post-doc, from the University of Aarhus, who has been in charge of the investigations.
The effects result in fewer and fewer animals in these populations. Worst, it looks around Brazil, the Gibraltar tree, the northeastern Pacific and around England. Here the models show that stocks have been largely halved through the half-century where PCBs have been present
"In these areas, we rarely see newborn killer whales," says Ailsa Hall, who, together with Bernie McConnell, has developed the models used at the Sea Mammal Research Unit in Scotland.
"The animals have been under the influence of more than 50 years and it is scary to see that the models predict that the species is threatened to die in these areas within a 30-40 year period," says Jean-Pierre Desforges.
A killer whale gets up to 60-70 years old. And even though it was more than 40 years since the world took steps to phase out PCBs, the killer whales still have large amounts of PCBs in their bodies.
"This suggests that the efforts have not been effective enough to avoid accumulation of PCBs in species that live on as high trophic levels as long as the fox hunter. Therefore, there is a great need for further action than those decided under the Stockholm Convention, "concludes Paul D. Jepson, Institute of Zoology, the Zoological Society of London, England, who is expert in killer wholesalers and co-authors on the article.
Around, among other things, Faroe Islands, Iceland, Norway, Alaska and Antarctica look better. Here the populations are growing, and the models predict that populations will continue to grow through the next century.
This article has been republished from materials provided by Aarhus University. Note: material may have been edited for length and content. For further information, please contact the cited source.
Predicting global killer whale population collapse from PCB pollution. Jean-Pierre Desforges et al. Science 28 Sep 2018: Vol. 361, Issue 6409, pp. 1373-1376, DOI: 10.1126/science.aat1953.