The accumulation of tiny chemicals inside the bodies of killer whales is proving fatal for half of their populations around the world.

All the aquatic mammals who rely on the ocean and other marine systems for their survival are called Marine Mammals. Some common examples include whales, manatees, polar bear, seals, and sea otters. There is no systematic grouping in this category because they don’t share an immediate common ancestor but they are unified on the basis of a number of factors like their reliance on the marine environment for feeding. Marine mammals can be divided into sub-classes: fully aquatic and semiaquatic. The latter of the two spends most of their time in the water but performs some of the important activities, like breeding, on the land.

Different creatures have their own ways of dealing with the toxic materials in their environment. A lot of mammals rely on a gene called PON1 for destroying these poisonous components. However, a completely useless version of these chemical-busting proteins is present inside different marine mammals including dolphins and manatees. Consequently, these creatures become vulnerable to dangerous pesticides. These harmful chemicals are washed off by rainwater which ultimately reaches a sea after polluting the entire water channel. One of the common classes of pesticides that are generally sprayed on crops is called ‘Organophosphates’.

Just like the Organophosphates, Polychlorinated Biphenyls (PCBs) are also having an adverse impact on marine mammals, especially killer whales. These industrial chemicals can lead to a disruption in hormone signaling, weak immune responses, cancer, and infertility. For these reasons, a lot of countries including the United States banned these chemicals in 1979 but they can stay in the environment for extended periods of time as they don’t break down easily. As a result, the levels of PCBs in large mammals, like killer whales, can increase significantly over time. According to an estimate, some of the highest concentrations of PCBs ever measured in marine animals were found in killer whales.

An international team of researchers performed an in-depth analysis of the impact of these chemicals on these animals and found some extremely alarming results. Their research was published in the journal ‘Science’, which revealed that high concentrations of PCBs may lead to some devastating, long-term health complications to all the populations of killer whales around the globe. They arrived at this conclusion by observing that more than 50% of the world’s killer whales can get affected by PCBs. The researching team used the global data on PCBs concentrations to determine how these chemicals will affect the mortality and health of killer whales. Jean-Pierre Desforges, a Postdoctoral Researcher at the Aarhus University, talked about that and said,

“These results suggest that chronic exposure to persistent PCBs has the potential to affect long-term population viability in more than half of all studied killer whale populations.”

Having said that, the impact of PCBs will not be the same for all the populations. The degree of damage is heavily dependent on the location of the population as the ones closer to industrial areas will be affected the most. The study found that the results are pretty evident already and the researchers mentioned that in the following words:

“Killer whales once thrived in all oceans of the world, but only those in the less-contaminated waters of the Arctic and Antarctic today appear to be able to sustain growth.”

Although PCBs are the most massive threat to the existence of these large mammals, they have got some other issues as well. The limited supply of food is certainly one of them. The quantity of food needed by these large animals is surely not available following a wave of marine pollution. The disposal of industrial and domestic waste in seas is making it difficult for killer whales to survive as the number of smaller fish and other creatures are diminishing rapidly. Desforges referred to that by saying,

“Of course, that population is also struggling with limited food. But based on our simulations, the PCB effect alone should put them in the risky category. If you add additional stressors, you can only imagine what would happen.”

A lot of other experts like Dave Duffus, the Director of the Whale Research Lab at the University of Victoria, have acknowledged that the population of these large mammals is on a decline. Therefore, we need to react quick and fast before it becomes too late for these killer whales.