The effect of dissolved organic matter on the bioavailability of polychlorinated dibenzo- p-dioxins

The extent to which dissolved organic matter (DOM) influences the bioavailability of polychlorinated dioxins (PCDDs) was determined using Aldrich humic acid or filtered natural lake water as sources of DOM. The bioconcentration factors (BCFs) for rainbow trout ( Salmo gairdneri) of four PCDD congeners were determined using both centrifuged and reverse-phase cartridge extractable water concentrations. Aldrich humic acid (DOM) reduced the apparent uptake rate constants of PCDDs by reducing the free water concentrations available to the fish. However, DOM from natural lake water had little effect on the apparent uptake rate constants relative to Aldrich humic acid. Although Aldrich humic acid overestimated the influence of DOM on BCFs relative to natural lake waters it did provide a useful tool to examine these interactions. Measured apparent BCFs of PCDDs were below those predicted by their octanol to water partition coefficients ( K ow) alone but only part of this reduction was explained by calculating the true BCFs using the estimated free water concentrations. Although this may be due to experimental errors leading to an overestimation of the free water concentrations, steric hindrances, solubility factors, or metabolic transformation may also be important factors controlling the BCFs of PCDDs.