First assessment of microplastic exposure from heated liquid herbal medicine: Packaging breakdown and ingestion risk

Microplastic (MP) contamination in beverages has emerged as a growing public health concern, yet limited attention has been paid to exposure from traditional herbal medicine (HM), particularly when packaged in flexible plastic pouches. This study assessed the release and estimated daily intake (EDI) of MPs from five types of liquid HM products subjected to three thermal preparation conditions: unheated (UH), microwave-heated (MW), and hot-water bath (HWB). Particle analysis using micro-Fourier transform infrared spectroscopy (µ-FTIR) revealed that heating significantly increased MP release. The average EDI from one-pack daily intake was 0.042 particles/kg bw/day under UH, increasing to 0.077 for MW and 0.148 for HWB. The HWB condition led to a 3.5-fold increase compared to UH and a 1.9-fold increase compared to MW. Estimated annual exposure under high-consumption scenarios reached over 11,000 particles per person. Across all samples, HWB consistently resulted in the highest MP abundance, with polyethylene, polypropylene, polystyrene, and polyethylene terephthalate identified as the dominant polymer types. The detected MPs ranged mainly from 20 to 500 µm, providing context for potential ingestion exposure. Scanning electron microscopy showed clear surface degradation of the sachets after heating, including microcracks and roughened textures. These findings demonstrate that thermal treatment is a critical factor influencing MP release and subsequent oral exposure. Given the widespread use of plastic-packaged HM and the frequency of heating before consumption, our results underscore improved packaging materials, such as heat-resistant or biodegradable polymers, and standardized monitoring protocols to better protect consumers from unintended plastic ingestion.