More than 40 years after the first initiatives were taken to ban the use of PCB (Polychlorinated biphenyl), the toxic chemical pollutant remains a deadly threat to the animals at the top of the food chain. A new study shows that the current concentrations of PCBs could lead to the disappearance of half of the populations of killer whales from the most polluted areas within a period of 30-50 years.
More than 40 years after the first initiatives were taken to use PCBs, the toxic chemical pollutant remains a deadly threat to the animals at the top of the food chain. A new study recently published in the journal Science shows that the current concentrations of PCBs could lead to the disappearance of half of the populations of killer whales from the most polluted areas within a period of 30-50 years.
Researchers from Aarhus University together with colleagues from a wide range of universities and international research institutes have found that the number of killer whales is declining rapidly in 10 of the 19 populations studied, and that the species may disappear completely from several areas within a few decades.
The killer whales (Orcinus orca or Killer Whales) are the top link in a long food chain and are among the mammals with the highest concentration of PCBs in their tissues. The researchers measured values of up to 1300 milligrams per kilogram of body weight in the fat tissue of killer whales. For comparison, a large number of studies show that animals with low levels of PCB (less than 50 milligrams per kilogram of body weight), suffer from fertility problems and their immune system is also damaged.
Various types of PCB compounds were once widely used, especially as insulating material in transformers, capacitors and cooling fluids, and in the United States also for insulating and cooling chokes for operating fluorescent lamps. Due to the toxicity of the PCB and its classification as a persistent organic pollutant, PCB production was banned by the United States Congress in 1979, and by the Stockholm Convention for the Prevention of Organic Pollution in 2001. Concerns about the toxicity of PCB materials are largely based on the similarity of the chemical structure of these compounds. to the chemical structure of the toxic substance dioxin. PCB compounds have been shown to have toxic effects, including disruption of the nervous system and the hormonal system.
The killer whales are especially threatened in areas where pollution is high such as the coasts of Brazil, the Straits of Gibraltar and around Great Britain. The researchers estimate that the population around the British Isles numbers less than ten killer whales. Also along the east coast of Greenland, the killer whales suffer because they live there by hunting large marine mammals.
The killer whale is one of the most common marine mammals on Earth and is found in all oceans of the world from pole to pole. But today, only the populations living in the less polluted areas count a large number of individuals. Overfishing and man-made noise may also affect the animals' health, but PCBs have a dramatic effect on the killer whales' reproductive and immune systems.
Killer whales that feed, among other things, on large marine mammals, and large fish such as tuna and sharks may also absorb with the food high concentrations of substances that have accumulated along the food chain. These populations of killer whales have a high concentration of PCBs and are at high risk of extinction. In areas where killer whales eat mainly small fish such as matias and mackerel, there is less danger and low concentrations of PCBs were also measured. PCBs have been used worldwide since the 20s. During the period, more than a million tons of PCBs were produced, which were used, among other things, in electrical and plastic components. Along with DDT and other organic pesticides, PCBs spread throughout the oceans.
PCBs break down slowly in the environment. Also, PCBs are transferred from the mother of the killer whale to her offspring through her rich breast milk. This means that the dangerous substances remain in the animals' bodies, instead of being released into the environment where they eventually break down.
Global research on killers
"We know that PCBs distort the reproductive organs of animals such as polar bears. It was only natural to examine the effect of PCBs on rare populations of killer whales around the world," says Prof. Ron Dietz from the Department of Environmental Sciences and the Arctic Research Center at Aarhaus University, who initiated the research and is the main author of the article.
The research group, which includes participants from the United States, Canada, England, Greenland, Iceland and Denmark, reviewed all existing literature and compared all data with the results of field tests. The study provided information on PCB levels in more than 350 killer whales worldwide – the largest number of killer whales ever studied.
The researchers examined the effects of PCBs on the number of offspring as well as the immune system and mortality rates of killer whales over a period of one hundred years.
More than 50% of the population is at risk
"The findings are surprising, we see that more than half of the whale populations that have died worldwide are severely affected by PCBs," says Jean-Pierre Desforges, a postdoctoral researcher at Aarhus University, who led the study.
"In the polluted areas we rarely see young killer whales," says Alyssa Hall, who along with Bernie McConnell developed the models used by the Marine Research Unit in Scotland.
"It is frightening to see that the models predict a high risk of population collapse in these areas within a period of 30-40 years," says Desforges.
A female killer whale can live 60-70 years. For 40 years they accumulated PCBs and still have high levels of the toxic substance in their bodies.
"This means that the efforts to prevent the spread of PCBs were not enough, at least as far as the predators at the top of the food chain are concerned. Therefore, there is an urgent need for additional initiatives to those formulated in the Stockholm Convention", concludes Paul Dipson, Institute of Zoology, Zoological Society of London, England, expert on killer whales and co-author of the article.
In the oceans around the Faroe Islands, Iceland, Norway, Alaska and Antarctica, the future is not so bleak for the killer whales. Here, killer whale populations are growing and the forecast is that they will continue to grow over the next century.
to the notice of the researchers
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