A QUT study of microplastics in the sediment of three Brisbane creeks has found that Kedron Brook had the highest load of plastic microparticles, followed by Bulimba and Enoggera creeks.
Bulimba, Enoggera, Kedron Brook creeks studied
Polyethylene, used to make just about everything, dominate microplastics in creek sediments
Seasons and gradient are key to variations in microplastic abundance
The study's first author PhD researcher Heshani Mudalige, from QUT's School of Chemistry and Physics, said analysis of the microplastic particles (MPs) found the dominant plastic types in all creeks were:
Polyethylene (PE), used to make packaging, bottles, toys, housewares, pipes and agricultural films
Polypropylene (PP) found in food containers, sportswear, car bumpers and medical equipment
PE, PP and Polymethyl methacrylate (PMMA) were the dominant plastic types in all creeks.
"We sampled six sites on each creek, from their upstream headwaters to estuarine level, four times over a year," Ms Mudalige said.
1."Kedron Brook had a median abundance of MPs with approximately 4400 items per kg of dry sediment and had the highest amount of PE of all three creeks with PP and PS also present.
"MP abundance peaked in March in Kedron Brook, due to high-flow periods from summer rains followed by deposition in the sediment.
"Kedron Brook's microplastic load is strongly influenced by its running through commercial and industrial areas, including the Brisbane Airport precinct, where ongoing construction, intensive disposal of single-use plastics, food packaging waste, and adjacent recreational areas all contribute to greater PE.
"Stormwater runoff, residential households, and recreational uses such as sports fields and parks also add to the creek's MP load.
"Kedron Brook has extensive flat areas surrounded by impervious surfaces which favour depositing of MPs through run-off and the retention of them."
2. Ms Mudalige said Bulimba Creek had the second-highest MP abundance at approximately 4100 items per kg with its MP load peaking in November.
"Bulimba Creek flows through predominantly residential and commercial areas, with ongoing construction/maintenance areas that showed high amounts of PE as well as PP and PMMA.
"This likely comes from food and consumer packaging, textiles and fibres, industrial raw materials, and household/appliance plastics that often blend PP and PMMA."
3. Enoggera Creek recorded the lowest MP load with approximately 2800 items per kg.
"The Enoggera Dam regulates the streamflow from upstream, impacting sediment movement while trapping a significant portion of the upstream MP load," Ms Mudalige said.
"The Creek's MP load peaked in March and declined towards November, in contrast to nearby Kedron Brook which had its lowest MP load in September."
Ms Mudalige said that the overall results indicate that seasonal variability exerted a dominant influence on microplastic abundance, while both creek-scale differences and site-specific conditions play important roles in controlling microplastic accumulation.
"This comparison shows that variations in MP load are associated with surrounding land-use and the intensity of human activity, while the creek's gradient also influenced deposition of MP load.
Associate Professor Prasanna Egodawatta, from QUT's School of Civil and Environmental Engineering, said highly urbanised creek catchments in Southeast Queensland were major contributors to microplastic pollution in Moreton Bay.
"This study is a first step towards quantifying land-based microplastic inputs to Moreton Bay via the stormwater pathway," Professor Egodawatta said
"The hydrologic and hydraulic characteristics of a creek, shaped by its morphology and longitudinal profile, dictate microplastic transport processes within the system."
The research team comprised PhD scholar Heshani Mudalige and team leader Professor Godwin Ayoko, from QUT's School of Chemistry and Physics; Associate Professor Prasanna Egodawatta, Professor Ashantha Goonetilleke, both from QUT's School of Civil and Environmental Engineering.
The study, Catchment characteristics and land-use influence on microplastics distribution in freshwater sediments, was published in the journal, Environmental Pollution.
(Image, from left Associate Professor Prasanna Egodawatta, Heshani Mudalige, Professor Godwin Ayoko)
