Mechanistic insights into the sediment accumulation and fractionation of PAHs: Role of sedimentary organic carbon and an assessment of environmental implications.

Increasing anthropogenic activities and carbon aging processes pose a significant global concern to understanding the accumulation mechanisms of polycyclic aromatic hydrocarbons (PAHs) in sediments, especially regarding the overlooked role of nonextractable residues (NERs). Herein, we investigated the accumulation patterns of three PAHs fractions (bioavailable-BPAHs, extractable -EPAHs, and NERs), hydrodynamic conditions, and organic matter sources of sediment across different types lakes. This study reveals a previously overlooked potential relationship among anthropogenic factors, hydrodynamic condition, sedimentary organic carbon (SOC) profiles, and PAH fractions based on the mantel's test and structural equation model (SEM). A significant feature influencing the occurrence of EPAHs and NERs was attributed to SOC fractions, especially for sedimentary labile (LOC) and recalcitrant organic carbon (ROC) pools. LOC mainly controlled the EPAH distributions, while ROC may further accelerate the sedimentary accumulation of NERs. The quantitative structure activity relationship (QSAR) modelling further suggested that a strong positive relationship between hydrophobic PAH and the proportion of EPAHs was attributed to molecular reactivity and mobility based on high Egap, increased entropy, and van der Waals interactions. However, the formation of NERs was primarily driven by molecular polarity (μ, α) and electrophilic potential (qC⁺). The inclusion of BPAHs into PAH-based risk calculations and subsequent sediment management strategies is recommended, improving our understanding of the environment significance of the three PAHs fractions. Overall, this study provided a mechanistic insight into the fate of PAHs in sediment by carbon cycling processes and molecular-scale interactions.