Sediment Contamination in the St. Lawrence River Along the Cornwall, Ontario Waterfront

Abstract

Studies from 1970 to 1997 repeatedly showed that sediment was contaminated with mercury and zinc and, to a lesser extent, lead and copper in the north channel of the St. Lawrence River along the Cornwall, Ontario waterfront. Mercury contamination was greatest at two depositional zones: downstream of the Cornwall canal discharge near Lamoureux Park boat launch (maximum 18.0 μg/g, 1975) and downstream of Windmill Point (maximum 44.0 μg/g, 1975). Contaminant concentrations decreased with increasing distance from local point sources. The latter depositional zone extended approximately 2 km downstream and had the highest concentrations of mercury as well as high zinc, copper, and lead concentrations. Concentrations of As, Fe, Mn, Cd, Ni, Cr, TP, TKN, and TOC showed no significant local enrichment. Patterns of sediment contamination suggest local sources of PAHs; however, concentrations were not high enough to be of concern. The studies indicated that mercury and zinc were primarily from local industrial sources, a conclusion supported by patterns of contamination in the north versus south channels and downstream into Lake St. Francis. Although mercury concentrations in surface sediment appear to be decreasing over time, contaminants remain at high concentrations in Cornwall waterfront sediment. The two major local point sources of mercury closed their Cornwall industrial operations in the 1990s, but contaminated sediment can act as an important long-term source of mercury to the aquatic food chain. Conclusions drawn from this review will be used in the development of a strategy for managing contaminated sediment in Cornwall and may be applicable to other areas of contaminated sediment for which similar assessments are required.