Washable Face Masks: An Emerging Source of Metal and Nanoparticle Contamination in Aquatic Environments

Metal nanoparticle (MNP)-added face masks are increasingly marketed as washable antimicrobial products, yet their potential to release metals and MNPs during use and disposal remains poorly understood. In this study, three types of commercially available masks incorporating MNPs (Ag-, Cu-, and Pt-masks) were obtained to characterize their metal composition and to evaluate the release of metals and MNPs under simulated leaching conditions using ultrapure water and a simulated detergent solution. Apart from Pt, As, and Cd, all masks contained measurable Ag, Cu, Cr, Ni, Pb, and Sb, indicating the widespread incorporation of multiple metals during fabrication. These metals and their corresponding MNPs were subsequently detected in the leachates. Although higher metal contents in the masks often resulted in greater leachate concentrations, the proportion of released metals did not consistently correspond to their initial in-mask abundance. The significant correlation observed between Cu NPs and Pb NPs in Cu-mask leachates suggests shared release pathways or coupled mobilization processes. Prolonged immersion further contributed to increased particle size and broader size distribution of Ag NPs and Cu NPs. Single-particle analysis showed that, compared with ultrapure water, the detergent promoted a more pronounced release of most metals and facilitated the initial desorption of relatively larger nanoparticles. These findings demonstrate that improperly discarded masks can serve as a non-negligible source of metal and MNP contamination, underscoring the need for strengthened environmental risk assessment and supporting the development of improved regulatory oversight and end-of-life management strategies.