| Abstract |
Although the production and use of polychlorinated biphenyls were banned by the mid-1970s, these compounds continue to be present in the environment. In contrast, polybrominated diphenyl ethers are still applied as flame retardants and their concentrations in the environment have risen exponentially since 1980. PCBs and PBDEs are structurally similar and they generally have similar physicochemical properties. Consequently, PCBs and PBDEs behave analogously in the environment.
During the present study, the concentration of PCBs and PBDEs, was measured in the atmosphere of the marine background area of Finokalia (N.E. Crete). For both chemical groups, the concentrations were much lower than those measured in other sites around the world. The lack of temperature dependence for the atmospheric concentrations of PCBs and PBDEs and the results obtained from the Clausius-Clapeyron plots indicated that Finokalia is far away from significant sources of PCBs and PBDEs and that long-range transport will be the main factor influencing the atmospheric levels of these compounds in this area. In addition, by the investigation of air mass back-trajectories it was suggested that western Russia should be a large source of PCBs and PBDEs compared to western/northwestern Europe. It is possible that significant amounts of PCBs and PBDEs are emitted from that region and due to atmospheric long-range transport, influence the atmospheric levels of these compounds in the eastern Mediterranean.
The diurnal variation of PCBs and PBDEs in the atmosphere of Finokalia was in contrast to the findings of previous studies. The lower atmospheric concentrations observed for PCBs and PBDEs during daytime were attributed to the destruction of these compounds by hydroxyl radicals. The daytime depletion of PCBs and PBDEs was found to be higher for congeners possessing fewer chlorine and bromine substituents, respectively, and this trend was in accordance with the rate constants that have been previously measured from the reaction of individual PCB and PBDE congeners with hydroxyl radicals.
Previous studies have suggested that the reaction of PCBs with hydroxyl radicals in the gas phase of the atmosphere can lead to the formation of hydroxylated compounds (i.e. OH-PCBs). However, more recent laboratory experiments demonstrated that small amounts of OH-PCBs were produced, alongside larger amounts of chlorinated benzoic acids, on reaction of gaseous PCBs with hydroxyl radicals. In the present study we attempted to detect and identify OH-PCBs in the atmosphere of Finokalia using two different analytical methodologies. For all the samples analyzed, OH-PCB congeners were not detected. Additional studies, using different types of analytical techniques, would help in further understanding the gas-phase oxidation of PCBs and other persistent organic pollutants in the atmosphere.
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Μελέτη της ημερήσιας διακύμανσης των πολυχλωριωμένων διφαινυλίων και πολυβρωμιωμένων διφαινυλικών αιθέρων στην ατμόσφαιρα υπό συνθήκες έντονης φωτοχημείας
