Ontario Precipitation Chemistry and Heavy Metal Speciation

Abstract

<p>Gross Ontario rain and snow chemistry and heavy metal speciation was determined on samples collected from a precipitation sampling network established in Hamilton and Northern Ontario. Relative to surface waters, precipitation is normally a low conductivity (mean value = 34 μmho/ cm (25°)), low pH (4.3) system with elevated heavy metal (10 - 100 μg/l) and nutrient (50 - 100 μg/l P; 400 - 2000 μg/l N) concentrations. Anodic stripping voltammetry (ASV) was employed to determine "soluble" heavy metal speciation. ASV peak potential shifts and current measurements were used as criteria in making this determination. Unusual anodically shifted Cu peaks common to many precipitation samples suggested a Cu-colloid association. Duplication of polarographic behaviour observed for natural precipitation samples was obtained with synthetically prepared Fe-Mn colloids. In terms of "soluble" Cu speciation, Northern Ontario could be divided into two distinct regions; near Sudbury rain and snow contained aquo-Cu⁺⁺ ion at elevated concentrations, while in the remainder of the province, precipitation contained colloidally associated copper. Zn, Cd, and Pb were generally present as the aquo-species. Rain-out of colloidally associated copper into the higher ionic strength environment of lakes will probably result in metal desorption and colloid flocculation. Copper would then be available as a biologically toxic species.</p>