Removal of Polycyclic Aromatic Hydrocarbons from Precipitation in an Urban Forest of Guangzhou, South China

Polycyclic aromatic hydrocarbon (PAH) concentrations and fluxes were measured monthly in situ from rain events in an urban forest in the megapolitan city Guangzhou, China, to investigate impacts of forest canopy and soils on PAHs. Mean Σ9-PAH concentrations were 107.5, 101.6, 106.3, 107.1 and 42.4 ng L−1 in precipitation, throughfall, seepage water at the 30 and 60 cm soil depth, and runoff, respectively, indicating a great decrease in the form of runoff. Meanwhile, annual fluxes of total PAHs decreased from precipitation (205.9 µg m−2 year−1), to throughfall (156.3 µg m−2 year−1), and to seepage water (65.3 µg m−2 year−1 at 30-cm soil depth and 7.5 µg m−2 year−1 at 60-cm soil depth), but increased in runoff (34.1 µg m−2 year−1). When compared to precipitation, PAH fluxes decreased by 83.4 % in runoff, with 29 % contributed by forest canopy and 71 % by soils. Soil biodegradation explained 18.2 % of PAH reduction by the surface soil layer and 34.6 % by the middle soil layer.