Microplastic release from fiber and coated commercial tea bags: a fluorescence microscopy screening of eight products

Consumers increasingly choose tea bags marketed as biodegradable or plastic-free, and polylactic acid (PLA) is common in these products. Whether the declared material predicts release during brewing remains unclear because the mesh, coating, and heat-seal can contain different polymers. Eight commercial tea-bag products were brewed in hot water (95 °C, 10 min; nine replicates each). Microplastics (MPs) retained on 0.7-µm-pore filters were screened by Nile Red fluorescence microscopy. Representative spectra from selected fluorescent features were compared with polymer references, bulk polymer composition was screened qualitatively by Py-GC/MS, and whole-bag counts and mass were estimated by Monte Carlo resampling. All products yielded retained Nile Red–positive features, with estimated releases of 1,200–13,700 features and model-based masses of 5.6–127 µg per bag, corresponding to 11.5- and 22.4-fold ranges. Spectra from seven products were consistent with polypropylene despite different declarations, whereas the highest-releasing product, a PLA-coated paper, yielded a PLA-consistent spectrum. For that product, one bag per day corresponded to a model-based intake of 2.1 µg kg⁻ 1 day⁻ 1 for a 60-kg adult. Declared material alone did not explain the product-level differences. The source components and human health risk were not determined.