Particle release from disposable coffee cups in context: hazard screening with liner-derived polyethylene micro- and nanoplastics

Disposable coffee cups, with over 50 billion consumed annually in the United States and hundreds of billions used globally each year, represent a substantial yet underrecognized source of consumer exposure to micro- and nanoscale particles (MNPs). Here we quantify MNP release from commercial coffee cups under consumer-relevant conditions and evaluate the cytotoxicity of particles derived from cup materials. MNP release was strongly influenced by temperature, exposure time, and agitation. Under extreme conditions (85 °C and vigorous agitation), nanoparticle concentration reached 6.7 ± 1.7 × 108 particles mL-1 (n = 3, p < 0.01), exceeding microscale particle concentrations by approximately 2–3 orders of magnitude. Pre-use rinsing reduced particle release by 75 ± 10% (range: 65–85%, n = 3, p < 0.001), consistent with removal of loosely adhered residues. Raman spectroscopy identified predominantly polyethylene (PE) and polypropylene (PP) within microscale particles, while AFM-IR analyses revealed heterogeneous chemical signatures at nanoscale indicating contributions from both the PE liner and the cellulosic substrate. Scanning electron microscopy showed irregular, fractured morphologies indicative of thermal and mechanical degradation. Cup liner-derived PE fragments induced dose- and time-dependent cytotoxicity in human kidney proximal tubule epithelial (HK-2) cells, with a 72 h IC50 of 271.6 µg mL-1 (95% CI: 129.00–850.70 µg mL-1, R2=0.88) and caused time-dependent hemolysis in red blood cells (17% after 4 h at 1000 µg mL-1). Together, these findings identify disposable coffee cups as a source of micro- and nanoscale particle exposure and highlight practical mitigation and materials-design considerations.