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

Microplastics are pollutants formed from fragmented plastics and are also industrially manufactured for personal care and cosmetic products. They range from 1 µm to 5 mm and are ubiquitous in the environment due to their tiny size, lightweight, and wide applications. Ecotoxicological studies have shown that they can induce multiple harmful effects on exposed organisms and in humans. Wastewater treatment plants (WWTPs) have drawn the interest of researchers and regulatory bodies worldwide as a point source of microplastics discharge to the environment. 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 and patterns, analytical, size characterization, and quantification methods for microplastic in WWTPs. 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. Microplastics in WWTPs have 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. Microplastic size characterization has also been accomplished using two main methods: the sieve-based technique and the computing-based technique.