Fate estimation of polycyclic aromatic hydrocarbons in soils in a rapid urbanization region, Shenzhen of China

Our previous study indicated that the current level of polycyclic aromatic hydrocarbons (PAHs) in Shenzhen soil is in the low-end of world soil PAH pollution. In this study, the fate of PAHs in the soil of Shenzhen was investigated. The mass inventories of Σ(27)PAHs and Σ(15)PAHs (defined as the sum of the 27 or 15 PAH compounds sought) in topsoil of Shenzhen were ～204 and ～152 metric tons, respectively. Fate estimation of Σ(15)PAHs shows that air-soil gaseous exchange is the primary environmental process with ～10,076 kg/year diffusing from soil to air. Rain washing (～1131 kg/year from air to soil) is the most important input pathway followed by wet (～17 kg/year) and dry deposition (～8 kg/year) to soils in Shenzhen. The transport of Σ(15)PAHs by soil erosion is a crucial loss process for soil PAHs in Shenzhen (1918 kg/year for water runoff and 657 kg/year for solid runoff from soil). Moreover, degradation is not ignorable at present (95 kg/year). Comparison of inventory and residue (defined as Σ(15)PAHs left in topsoils after all environmental loss processes) suggested that input and loss of high molecular weight PAHs for Shenzhen's soil reached apparent equilibrium. Soil PAH pollution in Shenzhen will stay in a quasi-steady state for a long period and the natural environmental processes can not significantly reduce the pollution.