Last year, a killer whale named Lulu, who was thought to have died after being entangled in fishing nets, washed ashore the Isle of Tiree in Scotland.

As mentioned by The Guardian, after a series of post-mortem examinations, results have revealed that Lulu's blubber contains shocking levels of a toxic chemical known as polychlorinated biphenyls (PCB) -- 950mg/kg, to be exact. In addition, it was found out that she never had a calf despite having lived for at least 20 years.

In 2016, a separate study found out that PCBs harm breeding success and immune systems of not just killer whales but many marine mammals, including dolphins. It also revealed that Europe's cetaceans have levels of PCBs that are among the highest found in the world.

PCB concentration of 9mg/kg is already considered damaging to marine mammals, meaning the PCBs found in Lulu's blubber extremely goes beyond the limit.

Dr. Andrew Brownlow, head of the Scottish Marine Animal Stranding Scheme and veterinary pathologist at Scotland's Rural College (SRUC), told BBC News, "The levels of PCB contamination in Lulu were incredibly high, surprisingly so. They were 20 times higher than the safe level that we would expect for cetaceans to be able to manage."

"That puts her as one of the most contaminated animals on the planet in terms of PCB burden, and does raise serious questions for the long-term survivability of this group (of UK killer whales)," Brownlow added.

Earth Touch News Network cited that PCB were most commonly used as insulating liquids in electronics. Due to their detrimental effects in the environment, these industrial organic chemicals were banned in the 1970s. However, it was already too late, as by that time, an estimated 1.5 billion pounds of PCBs had already leached into the land, rivers and the deepest parts of the ocean.

PCBs are dangerous as it they are not fat-soluble. It remains in the bodies of whales and is only excreted through breastfeeding.

Lulu was one of UK's last resident pod. It is feared that just like Lulu, all the other members of the pod are infertile, as well, since the coast has not seen a calf in 23 years.