Speciation of some metals in river surface water, rain and snow, and the interactions of these metals with selected soil matrices

Abstract

Some metal species in river surface water, rain and snow were characterized by size and molecular weight, using filtration and ultrafiltration, and by their chemical reactivity on Chelex cation-exchange resin using both column and batch techniques. Trace metal species were determined in samples of atmospheric precipitation, and wet-deposition of trace metal species through runoff into the Rideau river (Ottawa, Ontario, Canada) was estimated by determining the concentrations of metal species in the rain water before and after contact with selected soils in the laboratory. Two types of soils, Plainfield Sandy soil and Green Belt soil (Ottawa, Ontario, Canada), were used as models for studying the transformation of metal species from rain water to soil. Aluminium, Cd, Cu, Ni, Pb and Zn complexes in the samples of rain and snow were found to have relatively low molecular weight (< 1000). A significant fraction of the metal species in the sample of Rideau river surface water were found to have a relatively high molecular weight (>3000). Kinetic studies of the metal speciation revealed that the metal species in the sample of snow were similar to those in the model solutions studied earlier by the present authors, and were probably complexes of inorganic ligands or small organic ligands, and that the metal species in the Rideau river surface water had low dissociation rates and were probably metals bound to strong binding sites of humic compounds and/or bound to or trapped in colloidal materials. Most metal species in the sample of rain water were transformed from simple, small and labile species originally present in the rain water to larger, non-labile species (the metals were probably bound to humic compounds, and/or colloidal materials) after the rain water was equilibrated with the soils investigated.