New details emerge after mysterious tar balls washed up on Australia's most iconic beaches

Preliminary tests have revealed the make-up of 'tar balls' that have washed up on some of Sydney 's most famous beaches.

Scientists from the University of New South Wales believe weathered oil is the primary component of the balls which have been mysteriously washing onto beaches in Sydney's east since Tuesday.

Tests found the balls contain bituminous materials mixed with biological matter including fatty acids.

Beaches between Bondi and Botany Bay have been closed to the public intermittently throughout the week as the black tar balls continue to wash up .

The 'unusual' spheres were first discovered along Coogee Beach on Tuesday, prompting Randwick City Council to immediately shut the beach while testing was conducted.

Gordons Bay, Clovelly Beach and Maroubra Beach have also been closed to the public since then after the balls also washed up along their shoreline.

Bondi, Tamarama and Bronte beaches were also closed 'out of precaution ', Waverly Council said.

The beaches will be closed until further notice.

UNSW chemist Alex Donald said the findings confirmed the tar balls originated from weathered oil.

'It is still unclear whether they resulted from natural seepage or a crude oil spill,' he said.

'Further chemical analysis is needed to pinpoint the source.'

The researchers also studied the balls underneath UV radiation.

Specks of the balls are fluorescent, indicating organic compounds.

The tar balls 'likely originated from petroleum-based sources'.

'Whether caused by human activity or natural processes, solving the mystery of these sticky invaders requires ongoing scientific inquiry.'

'The source could be linked to oil spills, petrochemical processes, or environmental pollution involving hydrocarbons,' Professor Donald said.

The fluorescence points to marine algae becoming attached.

Similar balls show up on Californian coasts from oil seeping out of the seafloor. Golden Beach in Queensland and Ninety Mile Beach in Gippsland have seen similar blobs, after oil spills or shipping discharges.

Professor Donald said figuring out whether the tar balls came from a spill or naturally from the seafloor was important in shaping the correct environmental response.

An industrial spill could spark legal action, and requires an immediate cleanup.

'The toxic compounds in tar balls can leach into the water, posing long-term threats to marine biodiversity,' he said.

'The appearance of tar balls on beaches such as Coogee not only damages Australia's pristine coastal reputation but also threatens the health of ecosystems that support industries like fishing and tourism .'

The six UNSW scientists will continue to analyse the balls, being given samples by the Randwick City Council.

Clean-up efforts were launched on Wednesday to remove and safely dispose the debris from the popular beaches and are expected to continue.

Randwick Mayor Dylan Parker said the council would continue to remove the material across all beaches over the weekend.

'The safety of the community is our first priority. That's why Council has taken the precaution to close these beaches while we undertake the safe collection and disposal of this material,' he said.

'We don't yet know what has happened to produce the debris washing up on our beaches, but we will continue to work with relevant authorities to ensure the safety of the public and clean up our beaches.'