Marine biologists are shocked at the high levels of microplastic pollution in the ocean sediments of Australia's south-east coast, with Bicheno in Tasmania being the worst.

Scientists from the Institute for Marine and Antarctic Studies at the University of Tasmania studied maritime sediments at 42 locations from Adelaide to Sydney.

The areas sampled included Sydney Harbour, Jervis Bay, Eden, Port Philip Bay, Port Adelaide and the coast south of Adelaide, as well as Hobart's Derwent Estuary and Tasmania's east coast.

Marine biologist Dr Scott Ling said the huge volume of plastics in the ocean and on beaches had received global attention but microplastics on the seafloor had been largely overlooked.

He said studies had estimated 70 per cent of marine litter would sink to the seafloor and enter marine sediments.

The new study was among the first in Australia to examine the sedimentary problem, taking samples to a depth of 10 centimetres.

Researchers had expected to find high levels of pollution close to major capitals but were surprised to find similar concentrations far from urban centres.

Microplastic sample found in Sydney Harbour. ( Supplied: Charlotte Levi )

"On average we found about 3.4 microplastics in every millilitre of sediment we sampled," Dr Ling said.

"To our surprise we found high levels of microplastics across the board."

He said microplastics were created by the fragmentation of larger pieces of plastic in the ocean and by being manufactured as micro beads for use in cosmetics, or micro fibres in clothing.

The filaments were often produced by household washing machines, and particles transported with litter and by industrial discharge.

Highest levels found at Bicheno

The waters off Bicheno are renowned the rich invertebrate and reef environment. ( Supplied )

The worst incidence of the pollution was off the east coast Tasmanian town of Bicheno — a concentration of 12 microplastics filaments per millilitre of sediment.

"What looked to be plastic rope particles, so in places where there was a lot of fishing activity and a lot of maritime activity, there is certainly potential for items that are used in those areas to end up on the seafloor," Dr Ling said.

Dr Ling said the next step was to investigate what impact the sea-floor microplastics had on sea life.

"In a lot of these places where there were higher plastic loads there were plenty of marine life, a diverse range of species that could potentially ingest or get entangled in these particles," he said.