TRACE-METAL COMPOSITION AND SPECIATION IN STREET SEDIMENT - SAULT-STE-MARIE, CANADA

Street sediment collected in Sault Ste. Marie, Ontario was examined fo r trace element composition (As, Cd, Cr, Cu, Fe, Pb, Hg, Ni and Zn) an d the metal partitioning to various sediment properties was determined by sequential extraction. Total Ni, Cu, Zn and Pb concentrations exce eded the lowest effect levels specified in the Ontario Provincial Sedi ment Quality Guidelines for Metals (Environment Ontario, 1992) and der ived from bioassay studies. According to these Guidelines, the disposa l of such sediment has to be guided by environmental considerations. A significant fraction of these metals was extractable in 0.5 N HCl ove r a 12-hour period and considered as potentially bioavailable. The maj or accumulative phases of toxic metals in this sediment are exchangeab le, carbonate, Fe/Mn oxides and organic matter but the relative import ance of each phase varied for individual metals. Approximately 20% of the total extractable Cd is found in each of these four fractions. Pb, Zn and Mn are predominantly bound to carbonates, Fe/Mn oxides and org anic matter. Cu shows a high affinity for organic matter and to a less er extent for carbonates. Elevated levels of Cd, Pb, Cu, Zn, Mn and Cr in the exchangeable and/or soluble phase suggest that sediment associ ated metals, mobilised from streets in Sault Ste. Marie during runoff and snowmelt, would adversely impact water quality in the receiving wa ters. However, large fractions of the total metal load are associated with coarser particles which are unlikely to be transported through th e drainage system into receiving waters.