Mass Transfer of TCDD/F from Suspended Sediment Particles

Experimentally determined mass transfer rates for the non-polar hydrophobic compounds known as tetra-chlorinated dibenzo-dioxin/furans (TCDD/F) were obtained by exposing contaminated sediment materials of two known size classes to a high grade distilled water in a completely mixed state for periods of up to 90 days. Water samples were removed at four time intervals, filtered through 1.2 µm and 0.7 µm glass fiber filters and subsequently analyzed for aqueous TCDD/F content using high resolution GC-MS methods. The results suggest that the mass transfer rates of highly hydrophobic compounds (log Kow>6) are affected primarily by the release of dissolved and colloidal size organic carbon materials and to a lesser degree by exposure time. The experimental data also suggest that the unquestioned use of equilibrium partitioning (EP) theory assumptions in water quality models may not be justified. An empirical model is presented that can predict water column TCDD/F concentrations due to chemical release from suspended solids.