New study shows that the current concentrations of PCBs in the oceans are threatening the world’s population of killer whales
12/07/2018 // Cassie B. // Views

Killer whales, or orcas, are one of the most widespread mammals on our planet, living in oceans from pole to pole. Part of the dolphin family, they are extremely social and smart creatures. Sadly, these enormous predators may one day be wiped off the face of the earth, however, thanks to pollution from polychlorinated biphenyls (PCBs).

According to a new study that was published in Science, half of the world’s killer whales could disappear within the next 30 to 50 years as a result the concentrations of PCBs seen in oceans. The international team of researchers say that 10 out of the 19 populations they studied showed a rapid decline in numbers, and they’ve warned that the species could disappear completely from some areas in the next few decades.

The problem is that the orcas tend to feed on large fish like sharks and tuna, as well as seals, that accumulate pollutants like PCBs from successive levels of the food chain. As the last link in a very long food chain, killer whales are the mammals that have the highest PCB levels in their tissues. In fact, researchers have found concentrations as high as 1300 mg per kilo within the blubber of killer whales. That is far greater than the 50 mg per kilo threshold at which infertility and serious immune system impacts can be seen.

There are some places, however, where they feed mostly on smaller fish like mackerel and herring, and their lower PCB content places the orcas in these areas at a lower risk of disappearing.

Why are PCBs so dangerous?

After being introduced in the 1930s, more than a million tons of PCBs were created for making goods like plastics and electrical components. They’ve been spreading in oceans across the planet ever since. Several countries banned them in the 1970s and ‘80s, and 2004 saw more than 90 countries agreeing to phase them out, but their very long half-life means they can stay in the environment for a long time. Making matters worse, the chemicals are passed from mothers to their offspring through milk.

The study looked at 350 individual killer whales, which is the biggest number ever studied. After using models to predict the effects PCBs would have on the whales, their immune systems and their offspring, they discovered that more than half of the world's populations are under threat.

Heavily contaminated areas have the greatest risk, including near the Strait of Gibraltar, around the U.K., Brazil and the Northeast Pacific. Populations in these areas have essentially reduced by half since PCBs were introduced, and fewer than 10 of these animals are left around the British Isles. The scientists also say that newborns are rarely seen in such areas.

In contrast, some unpolluted areas are actually seeing growing killer whale populations. These include Iceland, Alaska, the Antarctic, Norway and the Faroe Islands.

PCBs harm humans, too

The European Food Safety Authority recently lowered the tolerable intake level for PCBs after declaring they remain a health concern. The new tolerable weekly intake has been set at 2 picograms, or trillionths of a gram, per kilogram of body weight. That small amount should give you a good indication of just how harmful this group of chemicals is.

In humans, PCBs are considered a probable carcinogen. They’ve been linked to melanoma and cancers of the brain, breast, gastrointestinal tract, gall bladder and liver. Exposure has a negative impact on brain function, and they are also hormone disruptors. In addition, PCBs have been linked to developmental, immune system, and thyroid effects.

Stories like this show just how devastating the impact of chemicals in our environment can be. Sadly, companies like Monsanto that manufacture PCBs are more concerned about profits than safety. They continued to sell these chemicals for years after knowing about the health risks, and we are seeing the same thing happen now with glyphosate. How many animals and people will have to die before this behavior is stopped?

Read for more daily coverage of pollution issues affecting our world.

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