Occurrence and ecological risk of PAHs in urban road runoff in Beijing

The occurrence and ecological risks of 16 polycyclic aromatic hydrocarbons (PAHs) in different types of urban road runoff in Beijing during two typical rainfall events were studied. The average concentration of PAHs in road runoff particulate was in the order of Guanyuanqiao Road (ring road, 15,175 ng/L) > Huayuanqiao Road (primary road, 4,792 ng/L) > Dongcheng Alley (alley, 4,774 ng/L) > Nansihuan Viaduct (viaduct, 770 ng/L), much higher than dissolved PAHs. The total concentration of ∑16PAHs decreased with runoff scouring. Rainfall conditions and the accumulation of PAHs in the early rainfall period show a significant impact on PAHs pollution. The event mean concentration range of PAHs is 674-21,596 ng/L, following in the order of ring road > primary road > alley > viaduct. The proportion of four-ring PAHs was the highest. The first flush effect of PAHs is found in both rainfall events, and the effect of different ring PAHs is relatively similar. The content of PAHs is positively correlated with the amount of total organic carbon and suspended substance in runoff (r²> 0.72). The ecological risk assessment indicated that PAHs in road runoff except viaduct road corresponded to high risk.