Spatial–temporal variations, possible sources and soil–air exchange of polychlorinated biphenyls in urban environments in China

Abstract

Herein, we analyzed and explored the spatial–temporal variations, possible sources, and evaluated soil–air exchange of polychlorinated biphenyls (PCBs) in urban environments in China. For the 11 Chinese cities that were considered in the study, the Spearman correlations of −0.418 (p = 0.201) for autumn (2004) and −0.797 (p = 0.003) for spring (2008) between the atmospheric concentrations of PCBs and average temperature were obtained during the sampling period, suggesting that temperature can affect the atmospheric concentrations of PCBs in spring, but not in autumn, which may be driven by comprehensive factors. The Pearson correlation coefficients for the relationship between the concentrations of different PCB homologues among these cities indicate that in 2004 and 2008, the sources of PCBs in the urban atmosphere were different. In 2008, PentaCB to HeptaCB in the atmosphere possibly originated from intentionally produced PCBs (IP-PCBs), whereas DiCB to TetraCB might have been derived from the unintentionally produced PCBs (UP-PCBs) and e-waste (EW-PCBs). These results indicate a shift in the emission sources of PCBs in urban atmosphere from IP-PCBs to a combination of IP-PCBs, UP-PCBs, and EW-PCBs. Moreover, UP-PCBs and EW-PCBs are considered supplementary or major emission sources in the current environment, and thus the reduction and control of UP-PCBs and EW-PCBs should be paid more attention. The results of the study on soil–air exchange of PCBs showed that in 2008, the soil still acted as a sink and the net flux was from air to soil for all the PCB congeners, whereas in 2013–2014, the direction of the net flux was reversed, from soil to air for PCB28 and PCB52, indicating that in 2013–2014, secondary emissions could be an important source of these two PCB congeners.