Reevaluation of air-water exchange fluxes of PCBs in Green Bay and southern Lake Michigan.

Air-water exchange of persistent organic pollutants (POPs) such as polychlorinated biphenyls (PCBs) is an import process for the delivery of contaminants to water bodies, as well as for their removal, and is thus a pivotal parameter in the construction of mass balances in aquatic systems. Simultaneous measurements of PCB concentrations in the gas and dissolved phases conducted in Green Bay in 1989 and in southern Lake Michigan in 1994-1995 were used to estimate air-water exchange fluxes. In this work, improved Henry's law constants for PCBs and new mass-transfer rates across the air-water interface were used to update the previous calculations. The new model calculations suggest that the net volatilization flux of PCBs out of Green Bay ranges from +170 to +5300 ng m(-2) day(-1), which is 2-20 times larger than previous estimates. The flux of PCBs in southern Lake Michigan exhibits net volatilization of +0.5 to +230 ng m(-2) day(-1) throughout the study period (May and July 1994, January 1995), whereas previous estimates reported that the net flux was seasonally absorptive. Thus, water-to-air fluxes are more important for the removal of PCBs from both Green Bay and Lake Michigan than previously recognized.