Occurrence, Composition, and Risk Assessment of Microplastics and Adsorbed Polycyclic Aromatic Hydrocarbons (PAHs) in Urban Drainage Sediments Along the Yangtze River, China

Microplastics (MPs) represent pervasive contaminants in aquatic ecosystems, acting as carriers for persistent organic pollutants like polycyclic aromatic hydrocarbons (PAHs). This study systematically investigated the occurrence, composition, and ecological risks of MPs and adsorbed polycyclic aromatic hydrocarbons in urban drainage sediments from three Yangtze River cities: Chongqing (Yongchuan), Changzhou (Jintan), and Shanghai (Tongji University campus). The key findings revealed MPs’ abundances ranging from 130 to 564 items/100 g (mean: 346 items/100 g), with peak concentrations in campus commercial areas (498.4 items/100 g) and academic zones (420 items/100 g). Predominant polymers included polypropylene (PP, 15.29%), polyethylene terephthalate (PET, 15.88%), and chlorinated polyethylene (CPE, 14.98%). Granular MPs (75–300 μm) dominated particle size (50.09%), while colored MPs (66.54%)—particularly red (32.84%) and black (27.92%)—were most prevalent. Polycyclic aromatic hydrocarbons adsorbed on MPs ranged from 0.88 to 120.59 ng/g (mean: 5.76–67.66 ng/g), dominated by four-ring compounds (44.59%). Sediment-associated polycyclic aromatic hydrocarbons ranged from 0.63 to 60.09 ng/g (mean: 2.12–36.96 ng/g), with 5–6-ring polycyclic aromatic hydrocarbons (42%) as primary constituents. Significant correlations emerged between four-ring polycyclic aromatic hydrocarbons and fibrous MPs ( r = 0.33, p = 0.021) and black MPs ( r = 0.23, p = 0.04). This study underscores urban drainage sediments as critical reservoirs and transport pathways for MPs and polycyclic aromatic hydrocarbons, which is crucial for sustainable management for urban drainage systems. We advocate for implementing targeted management strategies that prioritize three interconnected approaches: enhanced monitoring of high-risk zones (particularly commercial areas), focused control of small-sized MPs (<300 μm) due to their elevated ecological threats, and systematic mitigation of PAH-MP co-contamination in densely populated catchments to disrupt pollutant transmission pathways.