Washington, Sep 28 (IANS): Chemical pollutants banned more than 40 years ago are still having a devastating effect on marine life and could lead to the disappearance of half of the world's killer whale populations before the end of the century, a new study revealed.

The study, published in the journal Science, found that killer whales, or orcas, were most at risk from polychlorinated biphenyls (PCBs), which were once widely used as coolants and in the production of carbonless copy paper before they were found to be highly toxic and carcinogenic, CNN reported on Friday.

Production of PCBs were banned in the US in 1979 and under an international treaty in 2001, but they are still in use in many parts of the world and not due to be completely phased out until 2025.

This has led to PCBs seeping into the oceans, where they present a particular risk to marine mammals at the top of the food chain like orcas. Because the chemicals do not readily break down, the concentration of them builds up in the bodies of predators as they eat more and more fish contaminated with PCBs.

For mammals, PCB contamination is inter-generational, with mothers passing the chemicals to their offspring through milk.

Orcas are the last link in a long food chain and are therefore among the most affected by this problem over the course of their 50 to 80 year lifespan.

Researchers found levels of PCB as high as 1,300 milligrams per kilo in the blubber of some orca, studies show that just 50 milligrams per kilo can cause infertility and immune system problems.

"The findings are surprising. We see that over half of the studied killer whales populations around the globe are severely affected by PCBs" Jean-Pierre Desforges of Aarhus University in Denmark said in a statement.

The situation is worst in Brazil, the Strait of Gibraltar, the northeast Pacific and around the British Isles.

ORCA, a UK-based charity which studies and protects whales and other marine mammals in Europe, described the findings as an "absolutely tragic state of affairs and one that needs immediate action".