Sorption behavior of trichloroethylene in arsenic contaminated soil: Batch experiment and mechanism insight

Co-contamination of chlorinated hydrocarbons and arsenic is frequently observed in the chemically contaminated sites and their surroundings in China. However, the interaction between these complex contaminants in soil remains is unclear. This study collected ten background soils with varying properties from various regions throughout China, and investigated the sorption and desorption process of trichloroethylene (TCE) in the exogenous arsenate (As(V)) contaminated soils. The results of the batch experiments demonstrated that TCE was rapidly adsorbed by soil organic matter (SOM). Both SOM and minerals contributed to the slow sorption equilibrium process. The sorption isotherms were linear, while the desorption isotherms were non-linear. In Heilongjiang (HLJ) soil, As(V) contamination increased the TCE sorption contribution of black carbon and decreased the contribution of minerals. During the aging process of As(V) in soils, SOM was replaced by AsO₄^3-, which formed complexes with soil Fe/Al oxides, resulting in a significant increase in hydroxyl groups and hydrophilicity of the soil surface. This hindered the hydrophobic sorption of TCE. Additionally, As(V) contamination affected soil geotechnical properties, and the As-cations precipitation could block the sorption micropores. The collective results of these processes caused a reduction in the sorption of TCE on the majority of As(V)-contaminated soils (702-5854 mg/kg) in comparison to background soils (1194-6374 mg/kg). The systematic investigation of sorption-desorption behaviors of TCE in As(V)-contaminated soils will provide a scientific basis for the calculation of soil environmental capacity of heavy metal- organic combined contamination in the future.