Detection and characterization of micro- and nano-plastics in wastewater: Current status of preparatory & analytical techniques

Micro- and nano-plastics (MNPs) are ubiquitous emerging pollutants that have gained global traction due to their persistent nature and potential risks to the environment and human health. The physico-chemical properties of MNPs such as size, shape, density, surface charge and hydrophobicity are quite different from macro-plastics, which render them unique behavior exemplified by high rate of diffusion, high mobility, easy uptake by organisms, high toxicity, and potential of bioaccumulation. Human exposure to MNPs causes serious health impacts including apoptosis, necrosis, inflammation, oxidative stress, metabolic disorders, and hampered immune responses. The hazardous nature and high persistence of MNPs in the environment necessitates accelerated studies focused upon their detection, quantification, impact analysis, and risk assessment. All kinds of wastewaters whether municipal, agricultural, or industrial, consist of significant loads of MNPs and act as secondary source of MNP pollution in groundwater and soil. Wastewater is highly complex in composition and there are several impediments in the accurate detection and identification of MNPs in this matrix owing to the in-efficient sampling methods, lack of standardized methodologies, and non-reproducibility of data. This review provides an overview of currently available techniques for sampling, detection, identification, and characterization of MNPs in wastewater. A critical commentary on the challenges and limitations of these techniques has been given and strategic combinatorial methods have been suggested for efficient and reliable MNP analysis in wastewater samples. The article also highlights novel sensor-based methods enabling rapid and accurate detection of MNPs in wastewater.