A facile approach to microplastic identification and quantification using differential scanning calorimetry

The ubiquity of microplastics (MP) in aquatic environments has been raising concerns. Although the μ-Fourier transform infrared spectroscopy (μ-FTIR) technique is commonly used to detect MPs, it is an expensive and time-consuming process that requires expert operation. Moreover, the mass concentration of MPs cannot be determined, thereby necessitating the development of an inexpensive and simple analytical technique for identifying and quantifying MPs in aquatic environments using thermal-based technologies. This study aimed to develop a method for identifying and quantifying MPs using differential scanning calorimetry (DSC), with six types of semi-crystalline polymers (polypropylene, low-density polyethylene, high-density polyethylene, polyamide, polyethylene terephthalate, and polytetrafluoroethylene) and four amorphous polymers (polyvinyl chloride, polystyrene, polycarbonate, and polymethyl methacrylate) as representative polymers. The melting point and glass transition temperature of each polymer were determined using the heating-cooling-heating method (20 °C/min), and Gaussian and asymmetry double sigmoidal models were chosen for peak deconvolution. As a case study, the effluent of a wastewater treatment plant in Chuncheon, South Korea, was analyzed using the established analysis protocol, and the results were compared with those from μ-FTIR analysis. The MP concentration was measured to be 0.70-0.79 μg/L using DSC, meaning that 105-117.75 g/d of MPs were discharged to Uiam Lake. This value differs from the 0.54-2.03 μg/L obtained by μ-FTIR analysis, which might be due to bias from the conversion method. This study demonstrates the feasibility of using DSC analysis as an economical and simple method for identifying and quantifying MPs in aquatic environments.