Cysteine enhanced degradation of monochlorobenzene in groundwater by ferrous iron/persulfate process: Impacts of matrix species and toxicity evaluation in ISCO

Monochlorobenzene (MCB), a solvent and synthetic intermediate, has been widely detected in groundwater at industrial contaminated sites. Cysteine (Cys) enhanced Fe2+/persulfate (Fe2+/Cys/PS) process with high degradation efficiency of organic pollutants has the potential for in-situ chemical oxidation of MCB. In this study, we systematically explored the impacts of common anions (CO32-, HCO3-, SO42-, NO3-, NO2-, PO43-, HPO42-, H2PO4-, Cl-, Br-), cations (NH4+, Mg2+, Al3+, Mn2+, Cu2+) and natural organic matter (NOM) on the degradation kinetics of MCB by the novel Fe2+/Cys/PS process and evaluated the ecotoxicity. The results showed that the removal of MCB in absence of matrices was enhanced by Cys due to its reduction and complexation ability. All of the anions inhibited the MCB degradation through the scavenging of SO4•- and HO•, though the inhibition degree of SO42-and NO3- was slight. Cations such as NH4+, Mg2+ and Al3+ hardly interfered with the reaction. Low concentrations of Cu2+ and NOM promoted the MCB oxidation, but the promotion strength weakened and turned into inhibition with the increased concentration of Cu2+ and NOM. The toxicity assessment of the transformation products (TPs) in the presence of Cl- and Br- based on the quantitative structure-activity relationships model showed the potentially higher toxicity of some TPs than their parent MCB. These results indicate that groundwater matrices may interfere with the MCB oxidation process. To accurately evaluate the effects of groundwater matrices on Fe2+/Cys/PS process for MCB oxidation and its potential toxicity, the field tests should be carried out in the future.