Microplastics in urban stormwater-developing a methodology for its monitoring

This study presents microplastics results for stormwater collected in retention ponds. A novel procedure was developed to collect microplastic (MP) particles by filtering stormwater using a purpose-built cascade filtration setup which included 4 steel filters of pore size, 48.5, 170, 2500 and 5000 μm. Based on the methodologies proposed in the literature, a novel procedure was developed incorporating a combination of optical and FTIR methods for quantification and identification of microplastics. The developed methodology was applied for determining and characterising MP from two retention ponds. Average concentrations of 2067 and 2133 MP/m³ were observed, respectively, for dry and wet periods at site 1. Similar concentrations were observed for site 2. The results showed a slight increase in the microplastics concentration for the wet period. Most MP particles existed in the size range 48.5-170 μm and 170-2500 μm. Among the type of MP particles, polyester was significantly more abundant than other types of plastics (78-94%). Comparing the data obtained in this study with those from the literature, it was apparent that the stormwater originated from two urban catchments has been subjected to considerable microplastic contamination. This can be attributed to anthropogenic activities in urban areas. Microplastic particles in the stormwater can have an adverse impact on aquatic life present in the receiving water bodies. Also, the presence of MP may suggest the existence of nanoplastics in urban stormwater. This finding can have broader implications for urban stormwater management.