London: Around four billion microscopic plastic fibres could be littering each square kilometre of deep sea sediment around the world, shows a study.
"It is alarming to find such high levels of contamination, especially when the full effect of these plastics on the delicate balance of deep sea ecosystems is unknown," said Lucy Woodall, zoologist at the Natural History Museum in Britain.
Marine plastic debris is a global problem, affecting wildlife, tourism and shipping.
The findings could explain why monitoring over the past decades has not seen increased concentration of plastic waste at the sea surface or along shorelines.
"The puzzle for marine scientists has been to establish where plastic debris is going. Part of the answer is that much of this waste is breaking down into fibres invisible to the naked eye and sinking to the sea floor," Woodall added.
The study focussed on deep-sea sediment and coral samples collected from 16 sites in the Mediterranean Sea, Atlantic and Indian Oceans.
Analysis of the non-natural particles confirmed microplastics were abundant in all the samples (ranging from 1.4-40 pieces per 50 ml of sediment).
Rayon - a manmade non-plastic polymer used in personal hygiene products and clothing - contributed to 56.9 percent of the total fibres seen, with polyester, polyamides, acetate and acrylic among the others recorded.
The study was published in the journal Royal Society Open Science.