Neonicotinoid pesticides transport at the water-sediment interface: Integrating microcosm experiments and field-based fugacity modeling.

Neonicotinoid insecticides (NNIs) are widely detected in aquatic systems, yet the interfacial processes regulating their exchange between overlying water and sediments remain poorly quantified. This study integrated diffusive gradients in thin films (DGT)-based microcosm experiments, field monitoring, and fugacity modeling to determine the transport and fate of five NNIs at the water-sediment interface. Under microcosm conditions, NNIs rapidly transferred from overlying water to sediment and approached apparent interfacial equilibrium after 168 h. The experimentally derived effective interfacial diffusion coefficients (Deff) ranged from 0.88 to 3.19 × 10⁻⁵ m²/h. Incorporating these parameters into the fugacity model revealed that all five NNIs exhibited fugacity ratios exceeding 0.5, suggesting net diffusion from sediment to water and the potential role of sediments as secondary NNI sources under field conditions. Diffusion accounted for 93-99% of the sediment-to-water flux, whereas advection dominated system-scale removal. Model predictions reproduced the general concentration ranges observed in field measurements, with 100% of water phase and 81.8% of sediment comparisons falling within one order of magnitude. These findings demonstrate the dynamic role of sediments in NNI transport and provide experimentally constrained transport parameters for and an integrated framework for assessing pesticide fate at the water-sediment interface in riverine systems.