The NSW Government will ask the manufacturers of facial scrubs and other toiletries to phase out the use of microplastics, after a study found widespread pollution from the particles in Sydney Harbour

Researchers recently tested 27 sites across the harbour and discovered up to 60 microplastics - fragments of plastic less than five millimetres long - per 100 milligrams of sediment.

State Environment Minister Robert Stokes said there was clear evidence that microplastics were "already having an impact on our marine environment".

The particles are commonly comprised of petrochemical plastics used inside cosmetics, toothpaste and shampoos.

"It's clear we need to address this looming environmental issue," he said.

Speaking to scientists at the launch of the Sydney Harbour Research Project, a review of research conducted in the harbour, Mr Stokes said the plastics were so small they were not caught by sewerage filters.

Instead, they flowed directly into the state's waterways, he said.

Mr Stokes said he would push for a voluntary phase-out of microplastics by industry and planned to hold a working party to discuss the matter with company representatives.

However, he stopped short of supporting an outright ban similar to that imposed in the US state of Illinois.

This map shows the number of microplastics per 100 millilitres of wet sediment found at 27 sites across Sydney Harbour. ( ABC News )

He said manufacturers such as Unilever, Johnson & Johnson and The Body Shop were working to find alternative materials to use in their products.

"There are a range of the big corporates who are moving in this direction," Mr Stokes said.

"But we need to obviously add a bit of pressure to that.

NSW Environment Minister Robert Stokes (left) talks to Professor Peter Steinberg from the Sydney Institute of Marine Science and Professor Emma Johnston from the University of NSW. ( ABC News: Nicole Chettle )

"Our preference is obviously to go down a voluntary path, but certainly everything remains on the table."

Asked if the Government would fund more testing across the Harbour, which could cost about $300,000, Mr Stokes said if more scientific knowledge was needed "then obviously we've got to commission that".

"But if there are alternatives to these microbead products, which there clearly are, then surely we should be doing everything we can in the meantime to encourage products that we know are going to be less harmful to the environment."

Sydney Institute of Marine Science chief executive Peter Steinberg welcomed the announcement.

"In some ways this is just the first step," he said.

Professor Steinberg said the microplastic pollution had "caught us quite by surprise as a new issue emerging on the marine environment".

Mr Stokes said he would talk to state and federal ministers about a proposal to phase out microplastics from cosmetics.