Dual-method analysis of microplastics in lake and wastewater treatment effluents: comparison of micro-FTIR and differential scanning calorimetry technique

• FTIR and DSC show similar MPs pollution trends, but their specific results differ. • Total MPs concentrations ranges 0.38 - 4.0 no./L (μFTIR) and 0.38 - 5.34 μg/L (DSC). • μFTIR detect various polymer types and size, but mass estimation lead overestimation. • DSC offers superior quantification of MPs mass with treated large volume (500–1000 L). • Dual analysis enabled balanced representation of MPs pollution in water environment. Microplastics (MPs) pollution presents a significant analytical challenge in aquatic environments. This study compares two analytical techniques for MPs detection, spectroscopic analysis using micro-Fourier transform infrared (μFTIR) spectroscopy and thermal analysis using differential scanning calorimetry (DSC), to comprehensively assess MPs. Samples were collected in March and October 2024 from Uiam Lake and effluents discharged by two wastewater treatment plants (WWTPs) in Chuncheon, South Korea. In both sampling periods, MPs concentrations ranged from 0.38 to 4.0 no./L (μFTIR) and 0.38 to 5.34 μg/L (DSC). The detected MPs varied in size (17–5000 μm), color, and were mostly fragmented. The highest concentration and largest MPs were observed at the most downstream site of Uiam Lake, indicating MPs accumulation primarily through nonpoint sources and significant influence from anthropogenic contamination. Using both μFTIR and DSC analyses, PMMA, PET, and PS MPs were commonly detected in Uiam Lake and effluents from both WWTPs consistently contained PMMA, PET, PS, and PE MPs. However, certain polymers were detected by only one of the methods. This discrepancy caused by differences in sample volumes, 500–1000 L for DSC and 5–10 L for μFTIR analysis, as well as the limited range of polymers that can be analyzed by DSC. Therefore, while μFTIR is more effective for identifying a broad range of polymer types, DSC offers superior quantification of MPs mass. A dual analytical strategy thus provides a balanced representation of both particle- and mass-based data, which is essential for accurate environmental assessment and source attribution of MPs pollution.