Airborne microplastics as concentrators of anthropogenic heavy metals: Differentiation of intrinsic additive-derived metals and post-emission enrichment.

Microplastics (MPs) can act as both carriers of intrinsic additive metals and scavengers of ambient contaminants, yet information regarding metal-associated atmospheric MPs remains limited. This study investigated the spatial and seasonal characteristics of suspended MPs and associated metals in science park, urban, and rural regions of Hsinchu, Taiwan. Total suspended particulate samples were collected, and MPs were characterized using fluorescence microscopy and μFTIR. Additive and adsorbed metals associated with MPs were operationally separated through density fractionation and acid digestion and quantified using ICP-MS. Science park areas exhibited the highest MP concentrations, particularly during the cold season. Polyethylene (PE), polystyrene (PS), polypropylene (PP), and rayon were the dominant polymers across sites, but their relative distributions varied spatially. Suspended MPs contained approximately 3-50% of the corresponding metal concentrations measured in TSP, with elevated enrichment factors observed for anthropogenic metals including Cr, Cu, Zn, As, Cd, Sb, and Pb. Seasonal differences were evident, as adsorbed metals dominated during the cold season whereas additive-derived metals contributed more prominently during the warm season. Multivariate analyses identified resuspended dust as a common source connecting the MPs and their metals. Comparisons with locally collected plastic products suggested that packaging materials and consumer plastics contributed substantially to intrinsic metal signatures in suspended MPs. These findings demonstrate that atmospheric MPs function as sources and sinks of hazardous metals and highlight the importance of considering both additive and adsorption processes when evaluating the environmental and health risks of airborne MPs.