Coupling of phytoplankton uptake and air-water exchange of persistent organic pollutants

A dynamic model that couples air-water exchange and phytoplankton uptake of persistent organic pollutants has been developed and then applied to PCB d ata from a small experimental lake. A sensitivity analysis of the model, ta king into account the influence of physical environmental conditions such a s temperature, wind speed, and mixing depth as well as plankton-related par ameters such as biomass and growth rate was carried out for a number of PCB s with different physical-chemical properties. The results indicate that ai r-water exchange dynamics are influenced not only by physical parameters bu t also by phytoplankton biomass and growth rate. New phytoplankton producti on results in substantially longer times to reach equilibrium. Phytoplankto n uptake-induced depletion of the dissolved phase concentration maintains a ir and water phases out of equilibrium. Furthermore, PCBs in phytoplankton also take longer times to reach equilibrium with the dissolved water phase when the latter is supported by diffusive air-water exchange. However, both model analysis and model application to the Experimental Lakes Area of nor thwestern Ontario (Canada) suggest that the gas phase supports the concentr ations of persistent organic pollutants, such as PCBs, in atmospherically d riven aquatic environments.