Historical Records of Metal Pollution in Sediments of Toronto and Hamilton Harbours

The sediments of Hamilton and Toronto Harbours contain some of the oldest records of metal pollution in the Great Lakes basin. The fluxes of Cd, Cr, Cu, Ni, Pb, Zn, Fe, and Mn into the two harbours have been estimated from the analyses of core samples dated by the Pb-210 technique. The contrasting metal levels in the two harbour sediments are viewed in relation to the differences in the disposal strategies of the dredged spoils and the sources of metal pollution in the harbours. The Zn and Fe concentrations of 5 to 8 mg g^?1 and 10 to 13 % dry wt. in Hamilton Harbour sediments, which are among the highest recorded in any harbour, can be related to effluent discharges from the large local iron and steel plants. An inventory of the sources and sinks of pollutant metals in Hamilton Bay shows a substantive export of the metals to Lake Ontario.