GAS-EXCHANGE OF HEXACHLOROCYCLOHEXANE IN THE GREAT-LAKES

Concentrations of hexachlorocyclohexanes (HCHs) in air and water were measured in order to estimate the direction and magnitude of gas flux across the air-water interface in the four lower Great Lakes. Samples were collected in Green Bay, Lake Michigan during June, 1989, and in lakes Michigan, Huron, Erie, and Ontario during Aug 1990. Green Bay water was ''undersaturated'' with respect to the air due to low surface water temperatures (6-11-degrees-C) and a well-mixed water column, and the flux direction was from air to water for both alpha- and gamma-HCH. The magnitude of the flux was estimated at -70 and -45 ng m-2 day-1 for alpha- and gamma-HCH, respectively. Volatilization loss of HCHs was observed during August due to higher surface water temperatures (18-22-degrees-C) and stratified conditions (fluxes 23 and 1.7 ng M-2 day-1 for alpha- and gamma-HCH, combined mean from all four lakes). Volatilization is hypothesized to be a short-term situation occurring only during the warmest months of the year. Published data on HCH air concentrations, wind speed, surface water temperatures, and ice cover were used, assuming a constant water concentration, to produce a simple predictive model of monthly HCH gas fluxes for Lakes Michigan, Huron, Erie, and Ontario.