Steady-state and unsteady-state mass balance models based on the QWASI fugacity/aquivalence model (Mackay 1991; Mackay and Diamond 1989) are used to describe the fate of lead, zinc, copper, cadmium, chromium, arsenic and nickel in Hamilton Harbour. To examine the effect of sediment “hot spots” on chemical dynamics in the harbour, a steady-state model with two sediment segments was developed. Model results indicate that the major contamination sources are land-based; sediments are of secondary importance as a source, and Lake Ontario can play a relatively important role as a diluent in some cases. The correspondence between measured and observed water and sediment concentrations obtained with the steady-state model suggests that average sediment concentrations are supported by present inputs rather than historical loadings. We suggest that a 20% annual loading reduction can decrease the average sediment concentrations of Zn, Cr and Cu to below the “severe effect level” of the provincial sediment quality guidelines in 2 to 6 years. The “lowest effect level” can be achieved within 10 years for As and Ni, and more than 20 years for the remaining chemicals at this loading rate. The results of the two-sediment model are illustrative since input values are uncertain, but are consistent with our understanding of harbour dynamics: the central zone accumulates more chemical and is slower to loose chemical, whereas chemical is lost from the nearshore sediment more rapidly.

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