NEWCASTLE (REUTERS) - Man-made pollutants have been found in the deepest parts of the Pacific Ocean.

A study of the Mariana and Kermadec trenches on the seafloor showed high levels of industrial chemicals, including PCBs - banned since the 1970s.

"They don't exist in nature, which makes them an ideal tracer to look for in more and more more environments because if you're looking for a kind of legacy story or a footprint of human activity things like PCBs are an ideal thing to look for because they have to have come from industrial activity," said Dr Alan Jamieson, Senior Lecturer in Marine Ecology at Newcastle University.

Pollutants were probably transported by industrial accidents, discharges, and landfill leakages.

Non-degradable, they're consumed by amphipods like these, which are voracious eaters that populate the seafloor. The crustaceans are ideal for such research.

Eaten by larger fauna, the polluted contents of their stomachs make their way up the food chain.

"The biggest surprise was that the Mariana trench samples were so high. They were huge, they were just unbelievable...the levels were, at face value, 50 times higher than what's considered to be one of the most polluted rivers in China," said Dr Jamieson.

This self-made deep sea lander was used to plumb the trenches' depths and bring amphipods to the surface.

"On the vehicle itself there are cameras and things like pressure sensors and temperature sensors and water samplers and traps, in this case. And it freefalls - it just falls straight down to the sea floor, so at a full ocean depth of 11 kilometres, it would take about four hours in freefall to reach the bottom and it crash lands, and we bait it with fish we find in that area," said Dr Jamieson.

Contaminants were found inside the stomachs of every amphipod tested.

Researchers plan further studies to find how such pollution affects the wider ecosystem.