Evidence for particle-mediated transport of 2,3,7,8-tetrachlorodibenzofuran during gas sparging of natural water

Gas sparging was conducted in lake enclosures previously treated with [4,6-3H]-2,3,7,8-tetrachlorodibenzofuran (TCDF) to determine the fugacity or dissolved concentration of this hydrophobic contaminant under field conditions. Using a Henry's law constant for TCDF of 1.7 ± 0.8 Pa.m3/mol, measured experimentally by gas sparging, apparent dissolved TCDF concentrations of 7 to 22 pg/L were determined. These results were 100 times greater than concentrations of TCDF obtained by extraction of water samples from the same enclosures with dichloromethane. TCDF was found to be highly associated with naturally occurring particles in the water column, with 40% of sorbed TCDF associated with the 0.1- to 3-μm size fraction. The results are interpreted in light of previous reports that indicate that bubbles are effective scavengers of bacteria and particulates in natural waters, transporting these solids across the water/air interface as bubbles burst at the water surface. In the laboratory addition of a yeast suspension increased the amount of TCDF sparged from aqueous solutions, confirming that particle-mediated movement of highly sorbed contaminants can influence apparent water concentrations measured by gas sparging of natural waters.