Discovery of novel halogenated polycyclic aromatic hydrocarbons in urban particulate matters: occurrence, photostability, and AhR activity.

Halogenated aromatic compounds (HACs) in the environment have created great concern because of the associated adverse health implications. In this study we investigated the atmospheric behavior and exposure risk of brominated polycyclic aromatic hydrocarbons (BrPAHs) larger than three rings which were associated with particles in the urban air in Japan, and which were discovered as novel HACs in the air. Furthermore, the ambient levels of chlorinated polycyclic aromatic hydrocarbons (CIPAHs) and PAHs, in addition to BrPAHs, were also simultaneously investigated to emphasize the differences. Seven of 11 target BrPAHs were newly detected from the urban air samples in Japan between 2004 and 2005. Of the BrPAHs detected, 5,7-Br2BaA was most abundant (mean concentration, 8.7 pg m(-3)), followed by 7,12-Br2BaA (6.3 pg m(-3)) and 6-BrBaP (3.3 pg m(-3)). The mean concentrations of total BrPAHs, CIPAHs, and PAHs detected were 8.6 pg m(-3), 15.2 pg m(-3), and 1.2 ng m(-3), respectively, which showed that concentrations of such halogenated PAHs (Br-/Cl-PAHs) tended to be approximately 100-fold lower than PAHs. The BrPAHs had photolysis rates that were relatively faster than the corresponding CIPAHs. Comparing the ambient profiles among the PAH congeners suggested that ambient BrPAHs that came from the specific local emission sources differed from CIPAHs and PAHs, and/or could be driven by various seasonal factors, including photodecay processes. Most of the BrPAHs used showed inherent AhR-mediated activities. Toxic equivalents based on the relative potencies of each AhR activity and the ambient concentrations showed that either BrPAHs or CIPAHs accounted for a smaller proportion (approximately 1%) of the total.