Scientists analysing the black debris that closed Sydney beaches this week believe the “tar balls” are likely from an oil spill but have not ruled out a link to a nearby sewage treatment plant.
Bondi, Bronte and Tamarama beaches reopened on Friday after they were closed along with several other eastern suburbs beaches when the mysterious dark spheres washed up on the sand. The balls were first spotted at Coogee beach on Tuesday afternoon.
Randwick council said on Wednesday evening that preliminary test results had identified the spheres as tar balls – which are formed when oil comes into contact with debris and water, usually as a result of oil spills or seepage.
Tests showed the debris was a hydrocarbon-based pollutant – the chief component of petroleum-based products.
Jon Beves, a chemistry expert from University of New South Wales who is part of a team of scientists analysing the debris, said the “most logical answer” was that the balls were formed from crude oil.
However, he said the balls also contained other greasy materials including fatty acids which meant they potentially had come from a sewage outflow instead of an oil spill or leak off the coast.
Beves said the dark spheres probably “mopped up” the fatty acids as they moved through the ocean. But his team was investigating whether the balls had come from a water treatment plant.
“I wouldn’t rule out it coming out from sewage treatment just yet,” he said.
Beves said locals had claimed they had also been collecting “a similar type of balls for a long time” and his team would try to obtain some to analyse them.
“We will see if these smaller grey balls are the same stuff or not.”
Sydney Water, which operates water treatment plants at Bondi and Malabar, has been contacted for comment.
Beves said further test results due next week should confirm if the balls had formed out of crude oil, but it was still possible authorities would never find out where they came from.
NSW Maritime’s executive director, Mark Hutchings, said later on Friday “we can now confirm the balls are made up of fatty acids, chemicals consistent with those found in cleaning and cosmetic products, mixed with some fuel oil”.
The New South Wales environment minister, Penny Sharpe, promised to “throw the book” at anyone found to be responsible.
Sharpe said government agencies were yet to determine the source of the tar balls but she suggested they had come from an offshore oil spill that wasn’t reported to authorities.
“I’m very worried about the fact that we’ve had our beautiful beaches polluted by something [and] we still don’t know where it’s come from,” the minister said.
Sharpe said investigators were trying to identify who was responsible. “I would hope that we can do that and I would also hope that, if we can, we will throw the book at those … involved,” she said.
Coogee, Clovelly, Gordons Bay and north Maroubra beaches remained closed on Friday.
Council employees on jetskis spotted a suspected oil slick out at sea on Wednesday morning, the Randwick council mayor, Dylan Parker, said at the time.
However, the Port Authority of NSW said no oil spills had been reported by vessels.
The EPA said balls had also been observed at Congwong, Frenchmans, Little Bay and Malabar beaches.
“At this stage, the origin and contents of the balls remains a mystery,” the watchdog said on Thursday.
“But the EPA is conducting extensive testing on a number of samples. While we understand initial Randwick city council testing suggests the presence of hydrocarbon, at this stage EPA tests cannot confirm the contents.”
CSIRO principal research scientist Dr Sharon Hook earlier this week suggested the tar balls could have been caused by a ship illegally emptying its bilge tank.
Hook said bilge tanks carried “weathered oil” that could form tar balls if released into the ocean.
At @UNSWScience we have been investigating the tar balls that washed up on Coogee and other Sydney beaches.
— Jon Beves (@JonBeves) October 18, 2024
What do we know (and not know!) so far?
Here comes our thread! pic.twitter.com/udBtkMDMsd
“I would hypothesise that it would have been pretty close [to shore] because everything has landed on a couple of beaches that are close together,” she told the ABC.
“Some oil will float and some oil will sink and especially the heavy stuff that forms tar balls is likely to sink, so it’s possible something happened and no one told the authorities.”
