| Semi-volatile organic compounds, such as the polybrominated diphenyl ethers (PBDEs) have the potential to undergo long-range atmospheric transport (LRAT) to remote locations, which can increase the exposure of sensitive ecosystems to potentially harmful substances. Regulatory instruments, such as the Stockholm Convention on persistent organic pollutants (POPs), have been implemented to limit and/or prevent this exposure. Through the acquisition of scientific data, knowledge can be gained about the environmental fate and human exposure of chemical substances, and the risks associated with using those substances assessed. PBDEs are a class of flame retardants that are used in a wide range of commercial products. In response to growing concern over the detection of PBDEs in remote regions, a number of regulatory bodies have implemented measures to restrict the use of PBDEs. Using a suite of environmental fate models it is shown that PBDEs will most likely partition to organic carbon in soil and sediment, and that their persistence in the environment will be strongly influenced by their reactivity in those compartments. The transport potential of the PBDEs is investigated using the transport and persistence level III model TaPL3, using model environments with and without vegetation. It is suggested that the LRAT potential of the PBDEs is likely to be greater for the more volatile lower brominated congeners than for the higher brominated congeners, and that the LRAT may be sensitive to seasonal changes in the environment, such as temperature, vegetation and changes in precipitation. Furthermore, model results suggest that the PBDEs may be subject to a "spring pulse" effect, whereby concentrations are elevated in air during the early spring. Field studies support the theory of a "spring pulse" effect, where concentrations were observed to be five times greater during the period between snowmelt and bud burst than the average concentration before and after, but conclude that this phenomenon is likely to be important only during the period of a few days. Passive air samplers (PAS) deployed on a seasonal basis suggest that the "spring pulse" effect is not likely to dominate the seasonal trend, but do indicate that areas with high population densities, such as large urban areas, are likely sources of PBDEs to the atmosphere. PAS are thus useful in qualitatively identifying spatial and temporal trends of PBDEs, investigating source-receptor relationships, and may help to assess the effectiveness of regulatory restrictions in the future by monitoring the temporal trend of PBDEs in air. The PBDE congener profile in air is shown to be dominated by decaBDE, which is currently exempt from regulatory restrictions. The presence of decaBDE in air is shown to be almost entirely associated with particles. It is concluded that improving our understanding of particle-bound transport is necessary to better assess the environmental fate of decaBDE. |
