Modeling the transport and fate of hydrophobic organic chemicals in a fluvial system during resuspension events.

摘要

Contaminated sediment resuspension in fluvial systems and subsequent release of hydrophobic organic compounds (HOCs) from resuspended sediments poses an exposure risk to rivers and to the lake or reservoir to which they are tributary. The accuracy and reliability of transport and fate models for predicting the impact of this phenomenon are greatly affected by the formulation of two critical mechanisms: sediment resuspension and phase partitioning. This dissertation will examine the assumption in most models that phase artitioning is defined by a local equilibrium relationship. It does so by incorporating a non-equilibrium sorption sub-model into a whole system fate and transport modeling framework.; In this study, non-equilibrium phase partitioning was described using a two-compartment sorption kinetic model. This kinetic sorption model assumed that sorbed PCBs can be found in one of two independent compartments: one undergoes faster adsorption or desorption and is conceptually related to the outer surface of particles, while the other undergoes slower adsorption or desorption and is related to the inner porous structure of particles. The interaction between the dissolved phase and each sorbed phase is conceptualized as a reversible first-order reaction.; This sub-model for sorption kinetics was then incorporated into a full sediment and PCB transport model. The model was first used to evaluate the transport of PCBs in a hypothetical river and then applied to a typical Great Lakes tributary system—the Buffalo River of western New York State. The application demonstrated that, for a typical flow-induced resuspension event, resuspended sediments either redeposited or were exported from the river long before their sorbed PCBs reached phase equilibrium in the surrounding water column. Using a local equilibrium partitioning assumption in place of sorption kinetics submodel computed higher water column dissolved phase PCB exposure and export from a river. Sorption kinetics, spatially-variable sediment resuspension, and resuspended sediment deposition rates all combine with the physical and hydraulic characteristics of the fluvial system under investigation in determining the phase partitioning and export of PCBs from that system during a sediment resuspension event. The analysis of several events with different flow conditions and for PCB congeners with different partitioning properties demonstrated these relationships.