While the exact origins of the waste remain uncertain, their composition is more disgusting than first thought.
A multi-disciplinary team of scientists have made significant progress in understanding the origins of the mysterious black balls washing ashore on Sydney beaches.
A few weeks ago, thousands of sticky, round blobs washed up on shore after lifeguards first spotted them at Coogee beach, which left scientists with a series of questions about the origin and formation of the debris.
UNSW Science - partnering with UNSW's Mark Wainwright Analytical Centre (MWAC), DCCEEW Environmental Forensics, the NSW Environment Protection Authority (EPA), and Randwick Council - have run a series of analytical tests, to try and unravel this unusual marine mystery.
"At UNSW Science, we have been investigating the balls that appeared on Coogee Beach," said Associate Professor Jon Beves, from the School of Chemistry, 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.
"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," says Prof. Beves.
A combination of carbon
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," says Beves. "The higher concentration of modern carbon at the surface may result from the loss over time of components that evaporate more easily."
Comprehensive chemical analysis
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. "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," says Professor William Alexander Donald, an analytical chemist involved in the research.
Spectroscopy tests evaluated the absorption and emission of light to reveal atoms and molecules in a sample. A type of spectroscopy, known as Fourier Transform Infrared (FTIR) 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.
