Europe’s orca whale is at a risk of extinction due to toxic chemicals harming marine mammals since a long time, warns a study published Thursday by journal Scientific Reports. Study researchers analyzed samples of 1,000 killer whales, porpoises and dolphins and found that polychlorinated biphenyl (PCB) threatens sea life.

PCB is a persistent chemical that is used in electrical equipment. Government had banned the chemical about 28 years ago when it was found harming the sea animal’s ability to reproduce. According to the new study, PCB has been found affecting immune systems of marine mammals. The researchers, after studying the samples of orcas and dolphins, found that the chemical use has driven killer whale population to extinction, despite the regulations reduced pollution by the contaminant.

The study also showed that the contaminant concentrations exceed when move up the food chain. It happens because PCB settles into the fatty tissue of large marine mammals, as per the study. “The levels are really high, probably the highest in the world right now. These are global PCB hotspots”, said Paul Jepson, lead author of the study and a researcher at the Zoological Society of London.

Jepson has been studying three dozen orcas off the coast of Portugal since a long time. According to the researchers, observations showed that the killer whale community has not produced any offspring since one decade. Jepson also said that due to the chemical use, orcas in Mediterranean and the North Sea have extinct, while a few remained in western European waters.

The study has linked the pollutant to declining population of the killer whales. The chemical has been transferring in the blubber of the orca off Europe, and in striped dolphins. When an orca gives birth, it transfers 90% of the PCBs accumulated to their calves.