A new perspective on volatile halogenated hydrocarbons in Chinese agricultural soils

Soil contamination by volatile organic compounds has been greatly studied. However, there is still limited information regarding the occurrence, distribution and health effects of typical volatile halogenated hydrocarbons (VHCs) in soils on a national scale. In this study, headspace-based extraction with gas chromatography/mass spectrometry (HS-GC/MS) detection was optimized for the simultaneous analysis of 18 VHCs (haloalkanes, haloalkenes and halogenated aromatics) in 112 surface agricultural soil samples across China in 2016. The results show that 100% of the soil samples were contaminated by VHCs, and 13 of the 18 VHCs investigated were detected. The haloalkanes were the dominant group. Five VHC components had detection rates greater than 35%, including dichloromethane (DCM), chloroform (CF), 1,2-dichloroethane (1,2-DCA), chlorobenzene (CB) and 1,4-dichlorobenzene (1,4-DCB). For total VHCs, North and Southwest China were the hotspots for contamination. The highest concentrations were found in Shanxi Province and Chongqing municipality, which could be the result of long-term aerial deposition and wet deposition from various accidental industrial leakages or natural sources. In addition, the applications of sewage sludge and pesticides in agricultural activities may also contribute to soil VHC pollution. By using the health risk-assessing models recommended by the U.S. Environment Protection Agency (U.S. EPA), the estimated hazard indices (HIs) of all VHCs were below 1, and the carcinogenic risk (CR) values were all at acceptable levels (<1 × 10^-6). These findings indicated that the agricultural soils may not trigger serious long-term health impacts on public health nationwide. The results from this study can initially grasp the agricultural soil VHC pollution level and provide an understanding to avoid potential ecological and human health risks.