Binding of endocrine disrupters and herbicide metabolites to soil humic substances

Abstract

The interactions of the two phenolic endocrine disrupters nonylphenol and bisphenol A and of two herbicide metabolites (hydroxydesethyl terbuthylazine and desethyl terbuthylazine) with dissolved humic and fulvic acids were investigated by means of dialysis, using 14C-labeled compounds. Experiments were carried out at different pH values. The strength of xenobiotic-organic matter interactions was quantified by calculating organic carbon-normalised distribution coefficients KDOC. The results show that pH changes in the range of 3 to 10 had little or no impact on the association of both phenols and desethyl terbuthylazine to humic acids. In contrast, the KDOC values for hydroxy-desethyl terbuthylazine association to humic acids at pH 3 and 4.5 were nearly one order of magnitude higher than those at neutral and basic pH. Association of the xenobiotics to fulvic acids was only observed at low pH and about one order of magnitude weaker than to humic acids under identical conditions. We conclude that the binding of the investigated xenobiotics occurs mainly via hydrophobic interactions. Results from additional soil sorption experiments indicated similar binding mechanisms to soil organic matter and dissolved humic acids for nonylphenol and bisphenol A. Due to strong interactions between dissolved humic acids and soil, the xenobioticorganic matter interactions did not affect the sorption of the investigated compounds to soil. © 2005 Springer-Verlag Berlin Heidelberg.