A number of Sydney beaches have been closed after hundreds of tar balls washed ashore. But what are tar balls? Where have they come from? And are they dangerous?
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"It spreads out over the surface of the ocean, but over time, the oil bonds with other surface pollution, and also surface matter."
Scientia Professor Matthew England said tar balls slowly form when oil bonds with surface pollution and matter. (Supplied: Scientia Professor Matthew England)
Surface matter can include sand or small scale biota, according to Professor England.
"Those tar balls are spherical because of the action of wind, waves and weathering."
Steve Beaman, the executive director regulatory operations at the EPA, said the tar balls along Sydney's beaches had been found to be predominantly oil or hydrocarbon, an organic compound found in fossil fuels like petroleum and coal, based.
"At this stage, we know the material is predominantly hydrocarbon or oil based, and so we think the threat is low," he said.