Transport of organic pollutants and their atmospheric fates

Suspended sediment samples from ∼30 locations along the Mississippi River and six of its major tributaries collected between 2002 and 2003 were found to contain high levels of persistent organic pollutants (POPs) such as toxaphene and polybrominated diphenyl ether (PBDE) flame retardants. We found that the loss of these pollutants from terrestrial source areas via rivers is insignificant compared to loss via volatilization into the atmosphere. Analysis of pollutants in a sediment core from Siskiwit lake on Isle Royale, a remote island in Lake Superior support the theory that PBDEs undergo long-range atmospheric transport from source areas to regions where they were never used. The congener pattern of PBDEs in the lake sediment suggests that multiple processes act to remove PBDEs from the atmosphere after they are volatilized. Atmospheric removal of PBDEs due to processes such as reactions with OH radical and photolysis were studied using a heated small-volume reaction chamber with online detection of reactants and products by mass spectrometry. Relative rate constants for the reaction of OH with 7 diphenyl ethers having 0 to 2 bromine substituents were determined. Photolysis decays measured for selected PBDE congeners in the gas-phase were substantial, indicating that their photolysis quantum yields are significant. Dibenzofuran production was observed when PBDE congeners containing ortho-bromines were photolyzed in helium. From estimates of removal rates of PBDEs from the lower troposphere, we find that wet and dry deposition account for greater than 95% of the removal of BDE-209, while photolysis accounts for about 90% of the removal of gas-phase congeners such as BDE-47. These results help explain the deposition patterns of PBDEs found in lake and river sediments and have important implications concerning the inclusion of photolysis as a fate process in multi-media models. Relative rate constants were also determined for the reaction of OH with acetone and 3-buten-2-ol. Product studies were carried out for the reaction of OH with acetone and alpha-pinene and show that secondary and heterogeneous reactions may impact product yields measured in laboratory systems.