Scientists reveal nauseating composition of Sydney’s mysterious black beach blobs

"I always expected them to be like crude oil, and if you smell kerosene or ... even heavy oil, it doesn't smell that bad," said one researcher. "But this really smells disgusting. It smells much more like what you'd expect in a sewer. They really are gross."

Thousands of mysterious black balls recently washed up on Sydney beaches, including Bondi, Bronte, Tamarama, Maroubra, and Coogee Beach, prompting immediate closures and cleanup efforts. First spotted by lifeguards at Coogee Beach on October 15, the dark, sticky spheres raised concerns among authorities and the public. Initial fears suggested the black spheres could be toxic "tar balls," leading to health advisories and public warnings. However, subsequent analyses revealed that the spheres are not highly toxic to humans.

A multi-disciplinary team of scientists, including researchers from UNSW Science, the Mark Wainwright Analytical Centre, the Department of Climate Change, Energy, the Environment and Water (DCCEEW) Environmental Forensics, the Environmental Protection Agency (EPA), and Randwick Council, conducted a series of analytical tests to unravel the complex composition of the mysterious black blobs. Associate Professor Jon Beves, who led the investigation, stated, "At UNSW Science, we have been investigating the balls that appeared on Coogee Beach," and noted that the results from tests on samples revealed a more complicated and "much more disgusting" composition than expected.

"I always expected them to be like crude oil, and if you smell kerosene or ... even heavy oil, it doesn't smell that bad," said Beves. "But this really smells disgusting. It smells much more like what you'd expect in a sewer. They really are gross." The investigation utilized a combination of standard and advanced chemical analytical techniques to reveal the composition and potential sources of the material.

The first step was identifying the carbon composition of the balls, which would give the team an initial idea of the makeup of the debris. Radiocarbon dating of the samples indicated that the interior of the balls contained about 70% modern carbon and 30% fossil carbon, while the surface was made up of approximately 85% modern carbon and 15% fossil carbon. Modern carbon includes carbon derived from plants and animals. "This combination suggests a mix of substances derived from both fossil fuels and plant or animal sources," explained Associate Professor Beves. He added, "The higher concentration of modern carbon at the surface may result from the loss over time of components that evaporate more easily."

Analysis revealed that the black goop was mostly carbon, with significant levels of calcium and lower levels of other metals identified in the black balls. The dark, sticky material was composed of a complex mixture of fats, oils, calcium, and other metals, inconsistent with typical marine fuel or oil spills. Spectroscopic tests showed signatures in the black balls matching fats, oils, and greasy molecules often found in soap scum, cooking oil, and food sources.

About one-third to one-half of the mass of the black balls dissolved in organic solvents. Using mass spectrometry, the dissolved part revealed molecules found in vehicle-grade fuels, fatty acids, and glycerides. Solid-state nuclear magnetic resonance and Fourier transform infrared spectroscopy were used to analyze the part of the mass that couldn't be dissolved. The nuclear magnetic resonance data of the organic-soluble portion of the balls was consistent with fatty acids and olefins found in cooking oils and soap.

Industrial perfluoroalkyl substances (PFAS), steroidal compounds such as norgestrel, antihypertensive medications such as losartan, pesticides, and veterinary drugs were detected, consistent with contamination from sewage and industrial runoff. Markers of human faecal waste, such as epicoprostanol, were identified alongside residues of recreational drugs like THC (from marijuana) and methamphetamine, suggesting sewage or urban effluent as the likely origin. "The black balls found at Coogee Beach have high concentrations of fatty acids, glycerides, and calcium, similar to FOG deposits," said Associate Professor Beves.

FOG refers to fat, oil, and grease blobs commonly formed in sewage systems. Chemically, these blobs can form through supramolecular self-assembly, where fatty molecules cluster together through weak, non-covalent interactions. Calcium and other metal elements are known to enhance this blobbing process by binding to fatty acids and forming aggregates that don't dissolve in water, known as soap scum. These masses can become dense and stable, particularly when fats encounter cool water, leading to the creation of sticky blobs.

Professor William Alexander Donald, an analytical chemist involved in the research, said, "While we're not yet certain about the exact form of calcium in the samples, their presence suggests they might be combining organic components to form stable, water-insoluble, solid masses." He reflected on the investigative process, saying, "This was a significant analytical challenge, with highly complex mixtures containing hundreds to thousands of components. We had a lot of fun analyzing these mystery blobs, using deductive reasoning to trace the likely source to human waste."

Despite the extensive analysis, the exact origin of the washed-up balls remains uncertain. While the composition suggests they may be similar to fatbergs—a congealed mass of fats, oils, and greasy molecules that can accumulate in sewage—the exact origin cannot be definitively confirmed. Sydney Water has reported no known issues with their plants, leaving the origin of the balls unsolved. "Our analyses show that the material is not natural and cannot be attributed solely to an oil spill. It is most consistent with human-generated waste," stated Associate Professor Beves.

The black ball incident highlights the broader issue of pollution along Sydney's coastline. Recent reports indicate about 28% of monitored swimming sites in New South Wales are prone to pollution, with many receiving poor water quality ratings, especially after rain. Beaches such as Gymea Bay, Coogee Beach, Malabar Beach, and Frenchmans Bay have been identified as areas of concern, with advisories against swimming due to contamination from human faecal matter.

Analyzing and understanding urban waste pollution is a complex task that requires a multi-disciplinary approach. The team has been alerted to unconfirmed reports of smaller, similar balls washing up over the past two years. Further investigations could reveal whether these smaller balls have related compositions or not. The results emphasize the need for continued monitoring and vigilance to identify similar incidents, especially at smaller scales where they may go unnoticed.

"This uncertainty reflects the broader challenges faced by scientists and environmental agencies in tracking and addressing pollution in coastal areas," noted Associate Professor Beves. "By continuing to investigate the sources and composition of such pollutants, more can be learned about how urban waste management affects the health of coasts." The incident underscores the importance of thorough scientific analysis in understanding environmental issues.

Sources: Sydney Morning Herald, The Conversation, The Age, Phys.org

This article was written in collaboration with generative AI company Alchemiq