Up to 1.9 million pieces, many less than 1mm in size, were discovered in just one square metre off the west coast of Italy. The British team found the mass pollution at depths of up to 3,000ft, calling it “the highest level of microplastic ever recorded on the sea floor”. Most of the plastic was made up of fibres from textiles and clothing. Researchers warned it may be settling in areas rich in wildlife, where it can enter the food chain by being eaten by sealife feeding in the deep.
The international study by a team including experts from Manchester and Durham universities and the National Oceanography Centre found the plastic is washed into the seas by rivers.
It then gets carried down underwater canyons by avalanches of sediment before being deposited on the seabed by “bottom currents”.
The pieces of plastic then accumulate in large mounds of sediment. More than 10 million tons of the waste enter the oceans each year and the items seen floating on the sea’s surface represent just one per cent of the pollution.
Lead author Dr Ian Kane, of Manchester University, said: “Almost everybody has heard of the infamous ocean garbage patches of floating plastic, but we were shocked at the high concentrations of microplastics we found in the deep sea floor.
“We discovered that microplastics are not uniformly distributed across the study area.
“Instead they are distributed by powerful sea floor currents which concentrate them in certain areas.”
The findings were published in the journal Science.
It comes as a separate study revealed plastic waste is still continuing to reach the Antarctic.
British Antarctic Survey analysis of marine debris on Subantarctic islands washed up over 30 years showed an increase in rubbish.
The scientists said most of the debris found on Bird Island, off South Georgia and Signy Island in the South Orkneys, was plastic.
Lead author Dr Claire Waluda said: “While we found an increase in the quantity of beached plastic debris, recent surveys have shown increasing numbers of smaller pieces.
“This might be due to the breakdown of larger pieces of plastic which have been in the Southern Ocean for a long time.
“With the amount of plastic recovered on beaches peaking in the 1990s, our study suggests that the measures to restrict the amount of debris entering the Southern Ocean have been successful.”
The Antarctic study was published in Environment International.