Revealed: the complex composition of Sydney's beach blobs

A multidisciplinary team of scientists has made significant progress in understanding the composition of the mysterious black balls that recently washed onto Sydney beaches — and it’s even more disgusting than first thought.

A few weeks ago, thousands of sticky, round blobs washed up on Sydney’s beaches, leaving scientists with a series of questions about the origin and formation of the debris. UNSW Science — partnering with UNSW’s Mark Wainwright Analytical Centre, the NSW Department of Climate Change, Energy, the Environment and Water, the NSW Environment Protection Authority and Randwick City Council — has now run a series of analytical tests to try and unravel this unusual marine mystery.

Preliminary analysis suggested the debris was consistent with the makeup of tar balls — dark, spherical, sticky blobs formed from weathered oil which have been appearing on coastlines around the word for decades. But according to UNSW Associate Professor Jon Beves, who led the investigation, “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.”

The investigation used a combination of standard and advanced chemical analytical techniques to reveal the composition and potential sources of the material. As stated by Beves, “We found the sticky spheres contained hundreds of different components, including molecules that derive from cooking oil and soap scum, PFAS chemicals, steroidal compounds, antihypertensive medications, pesticides and veterinary drugs.”

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, as opposed to fossil fuels.

“This combination suggests a mix of substances derived from both fossil fuels and plant or animal sources,” Beves said. “The higher concentration of modern carbon at the surface may result from the loss over time of components that evaporate more easily.”

The joint efforts of the research teams revealed that 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. The team also used advanced analytical techniques to characterise the material.

Elemental analysis, X-ray fluorescence (XRF) and energy-dispersive X-ray spectroscopy (EDS) revealed significant levels of calcium and lower levels of other metals. Professor William Alexander Donald, an analytical chemist involved in the research, noted, “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.”

Spectroscopy tests evaluated the absorption and emission of light to reveal atoms and molecules in a sample. Fourier-transform infrared spectroscopy matched the functional groups in the black balls to those found in soap scum and cooking oil, reinforcing the presence of domestic waste materials. This also matched the nuclear magnetic resonance (NMR) data of the organic-soluble portion of the balls, which was consistent with fatty acids and olefins found in cooking oils and soap.

The team also used a range of mass spectrometry techniques to identify a wide range of chemical components. The analyses revealed the presence of alkanes typical of diesel fuel, fatty acids and other compounds commonly found in used cooking oils and soap. Additionally, perfluoroalkyl substances (the forever chemicals known as PFAS), steroidal compounds, antihypertensive medications, pesticides and veterinary drugs were detected, consistent with contamination from sewage and industrial runoff.

Markers of human faecal waste such as epicoprostanol, and recreational drug residues like THC (from marijuana) and methamphetamine, were also identified — consistent with contributions from domestic sources.

The presence of fats, oils, and high calcium levels in the black balls suggests they could potentially be related to fat, oil, and grease (FOG) blobs commonly formed in sewage systems. Chemically, FOG 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 (soap scum). These masses can become dense and stable, particularly when fats encounter cool water, leading to the creation of sticky blobs.

The exact origin of the washed-up balls remains uncertain — with Sydney Water reporting that there are no known issues with its plants — so the results emphasise the need for continued monitoring and vigilance to identify similar incidents, especially at smaller scales where they may go unnoticed.

“Carbon-14 dating suggested they weren’t purely from an oil spill, as the material was mostly modern carbon, loaded with fats, oils and greasy molecules,” Donald said. “Detecting markers of human faecal waste like coprostanol, alongside recreational drugs like THC and industrial PFAS ‘forever chemicals’, pointed us to sewage and other sources of urban effluent as the most consistent origins.”

The team has also been alerted to unconfirmed reports of smaller, similar balls washing up over the past two years, and further investigations could reveal whether these have related compositions or not.

Image credit: UNSW Chemistry.