The biography of microplastics (MPs): occurrences, sources, weathering/degradation, characterization, ecological/human risks, removal methods, policy development, and current trends and future perspectives

Abstract

The environment provides endless assistance for the wellbeing of all living organisms. However, the environment can be stressed due to anthropogenic and non-anthropogenic pollutants. Plastics have been identified as a persistent pollutant that has been stressing the environment for over a few decades. Among these hazardous plastics, the accumulation of microplastics (MPs) has been identified as a growing global issue. MPs are generally defined as small pieces of plastic less than 5 mm in diameter. Considering the source, two categories are identified, primary and secondary MPs, and it has been recognized that MPs are released into the environment during plastic production, transportation, product usage, and product maintenance. Different processes including physical, chemical, photodegradation, and biological degradations tend to break plastics into MP fragments, which include MPs as well as nanoplastics. Among these degradation processes, physical degradation is prominent in the coastal regions, and chemical degradation can occur due to corrosive chemicals, acids, gases, and atmospheric pollutants, which was the case during the recent MV X-Press Pearl disaster in the Indian Ocean. Different methodologies can be applied for the pretreatment, separation, detection, identification, and quantification of MPs. Digestion of complex substances and ultracentrifugation or ultrafiltration are utilized as pretreatment methods, whereas density, magnetic and electrostatic separations, filtration, and size-exclusion chromatography are practiced as separation methods for MPs. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, atomic force microscopy (AFM), and mass spectrometry can be identified as the main analytical methods for MP detection. The ecological risk of MPs affects the marine environment, freshwater environment, and soil environment, ultimately influencing human health. To remediate the issue, removal methods for MPs are being developed, with currently progressing methods being physical sorption and filtration, biological removal and ingestion, chemical treatments, membrane processes, and magnetic separation. Considering the prospects, the need to conduct meta-analyses, and compare data from different studies done in various geographic regions is important, which, among other related topics such as policy development, are discussed thoroughly through this review article.