ABSTRACT
Soils contain bio-organic materials that include dead and decaying plants and microbes, as well as live, actively-growing fungal, algal, and bacterial biofilms. These have a profound influence on physical-chemical properties of soils and the solubility of nutrients and trace elements. Nevertheless, modern soil chemistry still employs simplistic mineral solubility product and adsorption models in attempting to explain or predict toxic metal behavior in soils, despite accumulating evidence that complex biological processes can override physico-chemical equilibrium processes. Although semiempirical equations give crude estimates of toxic metal solubility based solely upon the soil physico-chemical properties pH and total metal concentration (McBride et al. 1997a; Sauve et al. 1997, 2000a; Gray et al. 1999), an important part of the spatial and temporal variability of metal solubility under environmentally realistic conditions remains unexplained.
