Hazardous elements associated with UV-weathered polypropylene nanoplastics: Implications for elemental transport

Environmental nanoplastics can form through weathering-induced cracking and fragmentation, accompanied by surface oxidation and roughening that may alter their interactions with co-occurring contaminants. However, the operational association and redistribution of hazardous elements in the presence of UV-weathered polypropylene (PP) nanoplastics-and how this behavior differs from that of PP microplastics and mineral particles-remain poorly understood. Newly prepared and UV-weathered PP nanoplastics and microplastics, together with quartz sand, were exposed to a multielement standard solution containing hazardous elements (As, Be, Cd, Co, Cr, Ni, Pb, Se, and V) in a simplified, salt-free, pH-adjusted aqueous system (pH 8.1-8.3). Elemental masses in the floating, dissolved/filtrate, and settled fractions were quantified, and the Association and Transfer Index (ATI) was defined as the percentage of the total recovered elemental mass present in the operational floating fraction with plastics. The results showed that UV-weathered PP nanoplastics exhibited the highest mean ATI (86.8%), compared with newly prepared nanoplastics (36.1%), newly prepared microplastics (6.1%), and UV-weathered microplastics (3.5%). Under the applied experimental conditions, UV-weathered PP nanoplastics were associated with a pronounced redistribution of element-bearing phases toward the operational floating fraction. Meanwhile, TEM-EDS qualitatively demonstrated the co-occurrence of element-bearing phases with the analyzed UV-weathered PP nanoplastic material. The contrasting behavior among plastic sizes and weathering states suggests that these factors may influence the floating-versus-settled distribution of plastic-associated elements. Whether this redistribution translates into enhanced transport or prolonged retention in natural waters remains to be evaluated under environmentally relevant conditions.