Modelling the fate of mirex and lindane in Lake Ontario,off the Niagara river mouth

A seasonally averaged (June–November) fate model (toxfate) of organic contaminants was used to assess the relative importance of transport, degradation and volatization processes in the Niagara River and in Lake Ontario near the river mouth. The model predicts concentrations in several compartments, including suspended sediments, water, plankton, and fish. Two contaminants were modelled, Mirex and α-hexachlorocyclohexane (Lindane). Simulations show that the largest amount of contaminants is usually in the water fraction. About 70% of Mirex is in the water at the mouth of the Niagara River, compared with 99% for Lindane. For these two contaminants, the processes of degradation and volatilization are two to three orders of magnitude slower than the rate of transport through the river and the plume. In the water, the most important process is a change of phase, from the dissolved to the adsorbed state. This change of state is mostly relevant for strongly hydrophobic compounds like Mirex, and less so for Lindane. Simulations were performed for a 40-day period during which fish concentrations did not reach equilibrium with Mirex, but they did with Lindane. Spatial distributions of these contaminants were also predicted and compared with available data.