SYDNEY, Nov. 7 (Xinhua) -- Mysterious black balls that washed ashore and forced the closure of several Sydney beaches in October have been identified as a complex mix of fats, drugs and human waste.

Seven beaches in eastern Sydney, including the iconic Bondi, were closed for several days in mid-October after thousands of the black ball-shaped debris washed ashore, prompting a major clean-up operation and investigation into their origin.

Following a series of analytical tests, a team led by scientists from the University of New South Wales (UNSW) said on Wednesday night that the balls consisted of hundreds of different components, including molecules from cooking oils, soap scum, medications, recreational drugs, pesticides and PFAS chemicals.

Initial testing conducted by a local council in October identified the debris as tar balls, which form when oil comes into contact with debris and water, usually as the result of an oil spill or seepage at sea.

However, the more comprehensive analysis by the UNSW, the Environmental Protection Authority (EPA), environmental forensics authorities, and the council found that the balls were composed of a majority of modern carbon derived from plants and animals rather than fossil carbon from fossil fuels.

"Our analyses show that the material is unnatural and cannot be attributed solely to an oil spill. It is most consistent with human-generated waste," Jon Beves, leader of the investigation from the UNSW School of Chemistry, said.

The modern carbon included chemical markers of human feces, blood pressure medications, veterinary drugs, PFAS forever chemicals, as well as illicit substances methamphetamine and THC, the active ingredient in cannabis.

The team said the findings were consistent with contamination from sewage and industrial runoff.

The EPA in the state of New South Wales (NSW) said in a statement that the findings indicated the balls likely originated from a source that releases mixed waste.

"Due to the complex composition of the balls and the time they have spent in the water, testing has not been able to confirm their exact origin. As a result, authorities have so far been unable to trace the source, but final results are due in the coming weeks," it said.

NSW's environment minister, Penny Sharpe, said in October that the state government would harshly punish those responsible for the pollution.