Analytical tests show the latest debris to wash up on Sydney's beaches includes markers of human and animal waste.
Scientists from UNSW Sydney have conducted tests on the 'beach blobs' that recently washed up on the Northern Beaches and found that they are made up of a mixture of fatty acids and calcium, consistent with domestic soap scum.
Earlier this month, marble-sized balls washed up on Sydney's Northern Beaches, leading to the temporary closure of nine beaches along the famous coastline. This was after a similar episode last year, when hundreds of sticky blobs washed ashore along the eastern suburbs in October.
A team of chemists at UNSW, led by Professor Jon Beves, analysed the mysterious debris from Coogee beach back in October and found that its contents were largely consistent with human-generated waste.
This same team have now carried out a series of independent tests to analyse the beach blobs that were collected from the southern end of Dee Why beach.
These tests found that the recent set of balls are less complex than the spherical debris that they analysed a few months before.
"These balls are mostly saturated fatty acids and calcium salts," says Prof. Beves. "They have a composition similar to soap scum, or lime soap, that forms when fatty acids commonly found in soaps react with hard water to form insoluble salts."
Organic materials
With permission from the Northern Beaches Council, the UNSW scientists collected samples from Dee Why beach on 15 January, before the big storm hit Sydney.
"The balls are grey and much harder than the ones that washed up in Coogee, and much more homogenous," says Prof. Beves, who led the analysis. "The balls we analysed were all visually very similar, unlike the ones from Coogee where each one was clearly a different mixture of components. But they also smelled disgusting."
The team of chemists found the samples were mostly organic materials – over two-thirds of the untreated samples were carbon and hydrogen – and they melted at around 50 degrees, making the material consistent with low melting point organic compounds.
Calcium and soap scum
Initial analysis by the scientists using equipment in the Mark Wainwright Analytical Centre showed the balls were mostly saturated fatty acids and their calcium salts.
"Using a method known as X-ray fluorescence (XRF), we could find minimal traces of sodium or chloride – which is what you would expect to find from sea water – but instead we found a lot of calcium and some iron," says Prof. Beves. "These results suggest that we wouldn't have expected the material to form in salty water."
Fourier transform infrared (FTIR) spectroscopy also showed signals consistent with fatty acids. This chemical composition is similar to soap scum that you may find in your sink or shower. Soap scum is made when minerals in water bond with soap to create a substance that sticks to bath, kitchen, and laundry room surfaces.
"The calcium salts that form from fatty acids are extremely insoluble in water, which is why you end up with this scum stuck in your shower," says Professor William Alexander Donald, who was part of the team carrying out these latest tests.
"Calcium grease is hydrophobic and wants to minimise contact with water as much as possible."
With the debris that has been washing up on the Northern Beaches, the material was being bashed around in the water, bobbing on the surface of the ocean.
"This process could be responsible for them being rolled into shapes that minimise their surface area – spheres have the lowest surface area for their volume, which explains why they are so rounded," Prof. Donald says.
Further analysis
Using nuclear magnetic resonance (NMR), the researchers found that the soluble component of the beach balls was a saturated fatty acid with both proton and carbon signals consistent with palmitic acid.
Palmitic acid is a saturated fatty acid with 16 carbons commonly used in cosmetics, and is also found in a wide variety of biological sources, including in animals, plants and microorganisms.
"We also detected myristate, pentadecanoate and stearic anions, which are again consistent with materials from biological sources," says Prof. Beves.
Trace components: markers of humans and animals
More detailed screening to identify the precise composition of the debris found more than 25,000 different chemicals, including the herbivore faecal marker ethylcoprostanol. This differs from the contents of the beach balls found along the eastern beaches, which only contained the human faecal matter biomarker.
"We found lots of other interesting compounds like detergents, surfactants, emulsifiers, plasticisers, fatty acids and hydroxy fatty acids, along with fungicides, herbicides, and drugs used to treat infections caused by parasites in agriculture and aquaculture – called anthelmintics," says Prof. Beves.
"There were also a lot of plant-based metabolites, and organic chemicals, along with bile acids.
"While it may not be possible to pinpoint the exact origin of this debris, the chemical makeup derived from human sources is comparable to the balls found in Coogee, suggesting these beach blobs could come from similar domestic sources."
This analysis was a collaborative effort between Dr Matt Brett, Prof. Jonathon Beves, Dr Helen Wang, Dr Tasmia Zaman, Dr Jake Violi, Prof. William Alexander Donald, Prof. Tim Schmidt and Dr Sarah Hancock. We thank the Mark Wainwright Analytical Centre's X-ray & Elemental Facility, NMR Facility, and Bioanalytical Mass Spectrometry Facility for instrument access and data collection.
