Current trends and analytical methods for evaluation of microplastics in stormwater

Stormwater runoff is an important source of microplastics (plastic particles <5 mm) into the aquatic environment and studies documenting the microplastics abundance and their characteristics are constantly expanding. The lack of standardized methods as well as the development of many analytical techniques to evaluate microplastics greatly influence reported results and calls for a better understanding of approaches adopted by microplastic studies in stormwater. Hence, this paper aims to systematically review currently employed methods for sampling, isolating and identifying microplastics and to summarize the data on the abundance of microplastics in the samples of water, sediment and biota collected from stormwater, stormwater catchment areas and stormwater discharging sites. There were significant methodological variations between the studies throughout the experimental procedures and different techniques including, sieving, digestion (chemical and enzyme), density separation and filtration were reported for microplastics extraction from sample matrix. A combination of visual sorting and spectroscopic approaches such as infrared and Raman was adopted to identify and study microplastic characteristics such as shape, size, color and polymer. The microplastic abundance in each sample matrix was different with relatively high concentrations of smaller size particles (10−500 μm), majorly fibrous shaped (51 %) and polymers of polypropylene (27 %) and polyethylene (26 %). Finally, we conclude by identifying analytical challenges and suggesting appropriate methods that can be implemented to enable effective monitoring and comparison of microplastic contamination in stormwater.