When hundreds of golf ball-sized black balls mysteriously washed onto the beaches of Sydney, it caused enough alarm for the areas to be closed off to the public.

But what scientists initially thought was a strange combination of fuel oil, fat and chemicals has now been revealed to be far more “disgusting” than first thought.

Researchers from the University of New South Wales discovered the balls were made of a combination of human faeces, cooking oil, chemicals and illicit drugs.

Following the discovery, made in October, local authorities closed a total of eight beaches for several days while a clean-up operation could be completed.