Binding of organic xenobiotics to dissolved organic macromolecules: comparison of analytical methods

Abstract

Partition coefficients ( K oc) between water and dissolved organic material (DOM) were measured for benzo(a)pyrene (BaP), 3,3′,4,4′-tetrachlorobiphenyl (TCBP) and 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD). DOM consisted of both natural humic substances from lake water and chlorolignin discharged from a bleached kraft pulp mill. The K oc values were determined by equilibrium dialysis and reverse-phase chromatography (SepPak). In addition, K oc values for BaP sorption to chlorolignin preparation were measured by thin layer chromatography (TLC), benzene extraction and fluorescence quenching methods. In all cases, equilibrium dialysis gave considerably higher K oc s compared to the reverse-phase measurement. In some samples, the difference was 10-fold for BaP and from threefold to fourfold for TCBP and TCDD. The K oc values for BaP binding to chlorolignin measured by benzene extraction, TLC and SepPak gave similar values while equilibrium dialysis and fluorescence quenching were similar. Thus, there are clear differnces between the methods which interfere with equilibrium between freely dissolved and bound xenobiotic fractions in the solution (extraction, TLC, SepPak) and those that do not (equilibrium dialysis and fluorescence quenching). K oc values were also used to predict the bioavailability (expressed as bioconcentration factors, BCF) of the xenobiotics to waterfleas ( Daphnia magna) in the presence of DOM. Predicted BCF values were then compared to the results obtained in bioaccumulation experiments with Daphnia. Equilibrium dialysis gave a better prediction of the xenobiotic bioavailability than the reverse-phase chromatography measurements.