Microplastics in urban freshwater streams in Adelaide, Australia: A source of plastic pollution in the Gulf St Vincent

The pollution of marine environments from plastic waste is anticipated to increase with current increases in plastic production. Reciprocally, escalating research efforts provide an improved understanding, monitoring, awareness, and mitigation of plastic contamination. Freshwater streams are recognised as one of the main contributors of microplastic pollution in marine environments. Presented here is the first investigation on the abundance of microplastic contamination (>20 μm and <5 mm) in freshwater streams in Adelaide, Australia. Composite samples were obtained from the sub-surface waters of eight freshwater streams (Magazine Wetland, Torrens River, Brownhill Creek, Sturt River, Field River, Christie Creek, Onkaparinga River and Pedler Creek), just before their connection to the Gulf St Vincent. Microplastics were found in all samples and microplastic abundance was 6.4 ± 5.5 particles.L ⁻¹ across all streams, with significant variations. Microplastic abundances found in the freshwater streams of Adelaide were comparatively higher than those found in areas of similar urbanisation, likely due to the varying methodologies used across studies. This work provides evidence, for the first time, of the prevalence of microplastic contamination in the sub-surface waters of eight freshwater streams in metropolitan Adelaide. These findings reinforce the need for long-term and on-going monitoring of freshwater streams for plastic contamination. Furthermore, spatial and temporal monitoring will allow for the identification in changes to the abundances of microplastics discharging from these sources into the Gulf St Vincent and observe if abundances increase or decrease with any future targeted waste management efforts.