Black ball-shaped debris washed ashore on Sydney beaches this week. Photo: Supplied / Randwick City Council Facebook
The black balls which shut down beaches in Sydney last month and stumped authorities are "disgusting" lumps of human faeces, drugs and PFAS chemicals, according to detailed analysis by researchers.
Initial reports suggested they were made of tar and could have come from an oil spill or waste from a ship, but a plethora of tests have revealed they are more similar to "fatbergs", commonly found in sewage systems.
University of NSW chemistry professor Jon Beves had the unfortunate job of analysing the smelly balls and said they also contained cooking oils, diesel or fuel and recreational drugs, including THC and methamphetamine.
"They're consistent with human-generated waste, the sort of thing that you would have in a sewer," he said.
"I don't know if it's come from our local sewer system, or if it's been discharged from a boat, or if it's been washed from the sewers into the stormwater, or some other origin that we really don't know.
"It's definitely not from an oil spill. It's human-generated waste or pollution that somehow made it into the water."
He said the balls were "extremely unpleasant" to work with and carted around the university to various departments for a range of different analyses.
"The balls have been sent all over the campus for people to do different sorts of analysis. And yeah, they do smell," he said.
Mystery of where they came from remains
On 16 October, lifeguards at Coogee Beach reported black balls on the sand, and there were soon more sightings at Bondi, Bronte, Tamarama and Maroubra beaches.
They were immediately closed while a clean-up effort took place and health authorities issues a public warning after initial testing by Randwick City Council concluded they may be tar balls, which are toxic.
Beves said the balls were "unusual to find at the beach" but are reasonably consistent in composition, suggesting they have all come from the one source.
"So it seems they haven't come from many different locations, they're consistent with all coming from one location at one time," he said.
The NSW Environment Protection Authority (EPA) said authorities had considered several possible causes including a shipping spill or wastewater outflow, but the "complex composition" of the balls meant they were unable to confirm their exact origin.
While the EPA has so far been unable to trace the source, final test results are due in the coming weeks.
After the balls were first discovered, Sydney Water stated there were no issues with their Bondi or Malabar water resource recovery facilities.
Transport for NSW Maritime also examined weather patterns in the days leading up to the event, but nothing conclusive could be determined.
- ABC News
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