Long-Term Sediment-Water Fluxes of Hydrophobic Organic Chemicals

Bottom sediments contaminated by hydrophobic organic chemicals (HOCs) are a major problem in rivers, lakes, and near-shore areas of the oceans. In order to determine the appropriate remedial action for these sediments, it is necessary to understand and quantify the flux of the HOCs between the bottom sediments and the overlying water not only for the near term, but also for the long term, as much as 20 to 50 years into the future. The emphasis here is on the quantitative prediction of the long-term fluxes of HOCs due to molecular diffusion and bioturbation as modified by time-dependent, non-equilibrium sorption. The effects of the partition coefficient on these fluxes are also illustrated. Numerical as well as approximate analytic solutions are presented and compared with each other and with experimental results. As a result of these calculations, it is demonstrated (a) that molecular diffusion is ubiquitous and more significant than ordinarily assumed and (b) effects of non-equilibrium sorption are significant and long-lasting.