Foliar retention of atmospheric microplastics: Influence of leaf surface properties and rainfall intensity

Plant leaves are considered as temporary sinks for atmospheric microplastics (MPs), but factors influencing MPs retention on leaves remain poorly understood. This study examines leaf surface properties and rainfall on the foliar MPs retention. We collected field samples, conducted indoor MPs deposition experiments and rainfall simulation experiments using five common urban tree species. Our results show that leaf samples from a nearby landfill retained more MPs (0.09-0.80 items/cm²) than those from a university campus (0.03-0.55 items/cm²), with seasonal accumulation following the trend: autumn > summer > spring. MPs deposition experiments with polyethylene terephthalate (PET) particles revealed a positive correlation between MPs retention and leaf surface area, and a negative correlation with water contact angle, emphasizing the role of intrinsic leaf properties. Rainfall simulations indicated that higher rainfall intensity and duration significantly reduced MPs retention. These findings suggest that tree species with larger surfaces, smaller water contact angles, and greater hydrophilicity exhibit higher MPs retention and more stable wash-off rates during rainfall, making them potential biomonitors of atmospheric MPs pollution.