In a previous study of 188 surface soil samples in the Tianjin
area, average PAH16 concentrations were 818 796 ng/g
(Zheng, 2002), which is much higher than the average PAHs
in this study. For soil PAHs, the accumulation and reduction
process may be influenced by plant uptake, photolysis, and
biotic and abiotic factors (Jones, 1991).