Bioretention systems (BRSs) have been increasingly used as a water-sensitive urban design element for stormwater runoff management in urban environments. This technology has been known for its effectiveness in flood prevention and pollutant removal and is implemented on a large scale in South East Queensland in Australia. However, much of the research on the pollutant removal effectiveness of these systems has focused on common urban stormwater pollutants such as sediments, nutrients, pathogens, and heavy metals with little to no consideration of the fate of emerging pollutants.

Urban areas are characterized by various emerging contaminants, one of them being plastics. Plastics under environmental influences, such as sunlight and oxygen, degrade to form minute plastic particles known as microplastics (i.e., plastic particles ≤ 5 mm). Contamination of the urban environment with microplastics is being recognized as a significant issue, with its prevalence considered an environmental hazard in aquatic environments including both freshwater and marine environments. Recently, microplastic contamination has received global concerns due to its persistent, toxic, and bio accumulative nature, and various terrestrial sources and pathways have been identified as contributors to marine microplastic contamination. While microplastics have been identified in stormwater runoff, little is known about their presence in green stormwater infrastructures. More importantly, the lack of efficient methods to extract and identify microplastics in soil media has led to misestimations of microplastic abundance.

In this thesis, the presence of microplastics in BRSs were studied to provide an initial understanding of the characteristics and dynamics of microplastics in green urban stormwater infrastructure. To achieve this, a novel enzymatic purification protocol was developed and validated for microplastics in soil media with large quantities of biogenic materials. This was followed by plastic particle recovery in soil media collected from functioning BRSs using the developed method, evaluating the effect of enzymatic purification on polymer integrity. Finally, mesocosm scale experiments were conducted to understand the fate of microplastics in bioretention soil media. [...]