Export of mirex from Lake Ontario to the St. Lawrence Estuary

The relative importance of migrating eels and suspended particulate material (biotic and abiotic) as transporters of mirex from Lake Ontario to the St. Lawrence River Estuary is evaluated in the context of a possible adverse impact on the St. Lawrence beluga population. Our estimates suggest that transport of mirex out of Lake Ontario by eels (2270 g annually) is almost twice that due to suspended particulate flux (1370 g annually). Mass balance calculations for mirex in Lake Ontario indicate that transport by migrating eels and particulate matter, combined with coverage of surficial sediments by continuing deposition of new material, could effectively "cleanse" Lake Ontario of mirex inputs in 100 years or less. Using mirex as a prototype to simulate the fate of hydrophobic organic chemicals in Lake Ontario led to a revised sediment budget for this final lake in the Great Lakes-St. Lawrence system. According to this budget, 94% of the suspended particulate material entering Lake Ontario is retained in the depositional basins and, by inference, most hydrophobic organic contaminants and metal forms having a dominant association with the particulate phase, would be expected to behave in a similar fashion.