The Complexation of Metal Ions by Humic Substances in Natural Waters

Abstract

Metal ions interact in various ways with inorganic and organic dissolved components and particles in natural waters. The relative importance of each of these interactions will change from one sample and locality to another. Many books and review articles have delt with different aspects of these reactions (Aiken et al.,1985; Buffle,1988; Christman and Gjessing, 1983; Kramer and Duinker,1984; Leppard,1983). Special attention has been focussed on dissolved organic compounds, in particular those termed humic substances, because of their potential effect on the bioavailability of toxic metals. It is generally assumed that free metal ions are more toxic to aquatic biota than metal ions bound to large organic molecules like the humic substances. However, the organic matter responsible for an eventual decreased toxicity is seldom well characterized, partly because of the difficulties of such a characterization. Attention has been focussed mostly on the interaction of copper with humic substances, but other trace metals like cadmium and lead have also been studied to some extent. Recently, the complexation of aluminum by humic substances has attracted much attention, because of the possible effects of aluminum on fish mortality, as a result of increased mobilization of this metal due to acid rain.