Suspended particulate oxides and organic matter interactions in trace metal sorption reactions in a small urban river

The relative scavenging abilities of suspended particulate oxides (SPOX), and organic matter (SPOM) for Cd, Zn and Cu were evaluated in a small, anthropogenically influenced river. In addition, the factor most important in influencing the sorption density (Ad: metal concentration associated with a given phase divided by the concentration of that geochemical phase in the suspended particulate pool) of each metal to SPOX and SPOM were identified through multiple linear regression analyses from the suite of: pH, temperature, dissolved metal concentration, and the concentration of the other particulate fraction. Results indicate that SPOX-SPOM interactions do occur in trace metal complexation reactions; and interactions are both phase and cation specific. Fe oxides are able to outcompete discrete organic binding sites for Cu and Zn as a relative decrease in the amount of these two cations sorbed to organic matter was observed with increasing particulate Fe oxides. SPOM concentration was identified as being most important in influencing Cu sorption densities associated with the SPOX fraction. Organic matter — oxide complexes are postulated to occur that enhance oxide sorption of Cu such that relatively more Cu is sorbed to particulate oxides with increasing particulate organic matter concentrations. Dissolved concentrations of Cd and Zn were found to be most important in influencing the sorption densities for these two metals associated with the oxides fraction. The sorption behaviour appears to follow Freundlich isotherm behaviour where the amount sorbed is a function of the dissolved concentration.