Extraction and analytical methods of microplastics in wastewater treatment plants: Isolation patterns, quantification, and size characterization techniques

Microplastics, due to their small size (1 mu m to 5 mm) and lightweight pose a continuous environmental threat owing to their widespread presence. This is buttressed by the induction of multiple harmful effects once exposed to organisms and humans as deduced from ecotoxicological studies. However, despite wastewater treatment plants (WWTPs) acting as point source of microplastics discharge to the environment, integration of microplastics removal and wastewater treatment is seldom explored. In the absence of a standardized methodology, microplastic monitoring in WWTPs has been marked by distinct variations in sample processing and analytical procedures which limit the comparison of results. This review provides a detailed analysis of the sample processing methods, patterns, analytical, size characterization, and quantification methods for microplastic in WWTPs. Microplastic size characterization has been accomplished using two main methods: the sieve-based technique and the computing-based technique. Microplastics in WWTPs have also been quantified using the gravimetry method, mass quantification method, and the sub-sample analysis method (based on extrapolation) with the latter being the most applied technique. According to the procedural steps for sample extraction reported in the reviewed studies, 12 sample processing patterns and three categories of analytical approaches (single, dual, and multiple) were identified.