Long-term aging-driven evolution of microplastic ecological risks: New insights from rooftop-deposited microplastics on urban buildings of varying ages

Airborne microplastics (AMPs) can accumulate various toxic chemicals during aging. However, the temporal variations of AMPs' ecological risks remain poorly characterized, particularly over decadal timescales. Studying AMPs deposited on roofs of buildings of varying ages provides key insights into their long-term ecological risks. This study investigated AMPs on rooftops of buildings of different ages in Chengdu and Nanchong, China. Sample analysis revealed that AMPs particle size and abundance varied significantly with building age. AMPs abundance peaked in 5-8-year-old buildings, while the proportion of small-sized AMPs increased with building age. Using Multi-Characteristic Potential Ecological Risk Index, we assessed the long-term aging risk of AMPs in buildings of different ages. Differential dynamics models were established for simulating the evolution of AMPs' long-term aging risk. It indicated a nonlinear increase in AMPs ecological risk with building age, exhibiting a "fast-then-slow" growth pattern. Sensitivity analysis of model parameters showed that urban human activities emissions and long-term aging fragmentation of AMPs are key drivers of AMPs' long-term risks in the short and long term, respectively. The city‑scale spatial distribution patterns of AMPs ecological risks are revealed by web crawling techniques. AMPs in urban cores were found to have higher ecological risks than those in peripheral zones, aligning with the urban spatial expansion hypothesis. With the popularity of green roofs that can enhance the connectivity of urban ecological networks, this work gives new insight into the ecological risk of AMPs to the roof microecosystem.