Hydrodynamic perturbations on contaminant behavior in low-permeability sediments: porewater metal dynamics and risk assessment implications

Sediment quality assessments often rely on equilibrium partitioning theory to predict dissolved contaminant concentration in porewaters. Yet, the theory assumes static conditions and may overlook the influence of hydrodynamic forces on contaminant mobility, particularly in low-permeability sediments. In this study, hydrodynamic microcosms simulating shear stresses of 0.02–0.28 Pa were used to investigate porewater metal concentrations over 32 days. As shear stress increased, porewater concentrations of redox-sensitive Fe and Mn decreased, reflecting enhanced oxidation. In contrast, Ni, Cu, and Cd concentrations increased with rising shear stress but were ultimately constrained by solubility limits. Zn and Pb remained relatively stable, reflecting limited remobilization likely due to rapid scavenging. To account for the uncertainty induced by hydrodynamic variability, we developed a quantitative framework integrating site-specific shear stress into risk assessments. Monte Carlo simulations estimated the uncertainty ranges of metal concentrations, with interquartile ranges of 2.4- to 5.4-fold for Cu, 1.9- to 2.9-fold for Ni, and 1.1- to 2.3-fold for Cd, suggesting moderate hydrodynamic influence on Cu risk and relatively low impact on Cd, Ni, Zn, and Pb. These findings improve understanding of contaminant behavior in dynamic aquatic environments, providing practical insights for refining risk assessment frameworks and enhancing environmental management strategies.