New study reveals scale of microplastic pollution along ocean floor

Microplastics are defined as pieces of plastic that have been worn down into tiny fragments, smaller than 5 millimetres.

In a bid to determine how much of this material is sitting on the ocean floor, researchers used a robotic submarine to collect samples of deep-sea sediments up to 3,000 metres deep from six sites in the Great Australian Bight, up to 380 km (236 miles) off the coast of South Australia.

Analysis of the 51 samples taken in March and April 2017 revealed there was an average of 1.26 microplastic pieces per gram of sediment. The team said that represented up to 25 times more microplastics than previous deep-sea studies had found.

The researchers then scaled up their data to determine a global estimate on the weight of microplastics in deep-sea sediment and reached an estimate of 14.4 million metric tons - a figure they said is conservative because of the remote nature of the location from which the samples were taken.

Dr Denise Hardesty, Principal Research Scientist and co-author of the study, said they were "surprised to observe high microplastic loads in such a setting, far away from urban population centres.

"Our research found that the deep ocean is a sink for microplastics," she said. "By identifying where and how much microplastic there is, we get a better picture of the extent of the problem."

Some 150 million metric tons of plastic are already present in the world's oceans, with a further eight million metric tons being added every year, according to the Ocean Conservancy, a US-based environmental advocacy group.

While much of the material makes its way down to the ocean floor or floats on the surface of the planet's marine environments, the majority of this plastic ends up on coastlines, the CSIRO researchers said.

And given the rising severity of the crisis, Dr Hardesty said it is more urgent than ever to find effective solutions to stop plastic pollution before it reaches the oceans as well as to cut plastic use in general.

"This will help to inform waste management strategies and create behavioural change and opportunities to stop plastic and other rubbish entering our environment," she said.

"Government, industry and the community need to work together to significantly reduce the amount of litter we see along our beaches and in our oceans."