Aerosol-water distribution of PCDD/Fs and PCBs in the Baltic Sea region

Atmospheric deposition is a major pathway of PCDD/Fs to the Baltic Sea. We studied the aerosol-water distribution for aerosols collected close to the Baltic Sea in order to investigate the availability of pollutants sorbed to aerosols deposited on water. Aerosols were analyzed for both total concentration (Soxhlet extraction) and the freely dissolved water concentration (extraction with 17-μm polyoxymethylene equilibrium passive samplers). Concentrations of PCDD/F and sum PCB-7 in aerosols were 65-1300 pg/g dw TEQ and 22-100 ng/g dw, respectively. Organic carbon (OC)-normalized aerosol-water distribution ratios (K(aer-water,OC)) were consistently lower (factor 2-60) than previously determined sediment organic carbon-water distribution ratios (K(sed,OC)). Hence PCDD/Fs and PCBs entering the Baltic Sea through aerosol deposition seem to be more available for desorption to the water phase than PCDD/Fs and PCBs sorbed to sediment. Further, we investigated whether aerosol-water distribution may be predicted from the air-aerosol partitioning constant multiplied by the Henry's Law constant. This proposed model for aerosol-water distribution underestimated measured values for PCBs by factors of 1-17 and for PCDD/Fs by more than a factor 10. These findings can be used to improve future fate modeling of PCBs and PCDD/Fs in marine environments and specifically the Baltic Sea.