Change in the water quality of industrial channels due to resuspension of sediments contaminated with heavy metals

Industrial channels were used extensively during the two previous centuries and have become heavily contaminated. This study investigates possible water quality changes in the Lachine Canal (Montreal) due to the release of heavy metals (Cd, Ni, Zn and Pb) into the water column during resuspension of anoxic sediments subjected to potential remediation. This release can be initiated by dredging activities for sediment removal. Equilibrium in the water from the Lachine Canal has been calculated using the program EQUILIB from the software FACT. The speciation of heavy metals in the water column was calculated with and without a solid phase before and after possible dredging. Speciation of heavy metals in pore water of anoxic sediments has been calculated, taking into account that corresponding sulfides are the solid phases controlling their solubility. The concentration of heavy metals under anoxic conditions considered could decrease by 8 orders of magnitude. The impact of various scenarios in the area of concern was reviewed from an ecotoxicological perspective. Dredging can possibly change the redox and acid–base conditions in the water column. The impact of dredging will be less if sediments contain calcium. Dredging can lead to an increase in the concentration of heavy metals in the water column and a change of metal speciation.