Eye-glass polishing wastewater as significant microplastic source: Microplastic identification and quantification

Microplastics (MPs) and nanoplastics (NPs) seriously contaminate environments by adsorbing environmentally hazardous chemicals. NPs (<1 µm) are not removed by conventional wastewater treatment processes, and have strong sorption capacity for the environmentally hazardous chemicals because of their high surface area. This study revealed that large amounts of MPs are generated in the eye-glass lens polishing process. Qualitative analyses of MPs were performed via Fourier-transform infrared (FTIR) and Raman spectroscopy. Particle size distribution was measured through particle size analysis based on light diffraction. MPs were quantified in the wastewater by measuring the mass balance using membrane filtration with polyaluminum chloride coagulation. One liter of wastewater contained 1380-62,539 mg MPs [corrected] and 0.0136-0.0324 mg NPs. Wastewater from 140,000 eye-glass shops in South Korea is discharged into wastewater plants, and about 57 g NPs per day pass through the wastewater treatment process. The amount of NPs that accumulate daily is likely to increase dramatically. Increased heavy metal concentrations after acid digestion confirmed that MPs in the wastewater adsorbed heavy metals. Detection of various types of volatile organic compounds in the wastewater indicated that workers in eye-glass shops are exposed to the significantly hazardous environments.