Overlooked Cytotoxicity and Genotoxicity to Mammalian Cells Caused by the Oxidant Peroxymonosulfate during Wastewater Treatment Compared with the Sulfate Radical-Based Ultraviolet/Peroxymonosulfate Process

Abstract

Byproduct formation (chlorate, bromate, organic halogen, etc.) during sulfate radical (SO4 •–)-based processes like ultraviolet/peroxymonosulfate (UV/PMS) has aroused widespread concern. However, hypohalous acid (HOCl and HOBr) can form via two-electron transfer directly from PMS, thus leading to the formation of organic halogenated byproducts as well. This study found both PMS alone and UV/PMS can increase the toxicity to mammalian cells of wastewater, while the UV/H2O2 decreased the toxicity. Cytotoxicity of two wastewater samples increased from 5.6–8.3 to 15.7–29.9 mg-phenol/L, and genotoxicity increased from 2.8–3.1 to 5.8–12.8 μg 4-NQO/L after PMS treatment because of organic halogen formation. Organic halogen formation from bromide rather than chloride was found to dominate the toxicity increase. The SO4 •–-based process UV/PMS led to the formation of both organic halogen and inorganic bromate and chlorate. However, because of the very low concentration (<20 μg/L) and relatively low toxicity of bromate and chlorate, contributions of inorganic byproducts to toxicity increase were negligible. PMS would not form chlorate and bromate, but it generated a higher concentration of total organic halogen, thus leading to a more toxic treated wastewater than UV/PMS. UV/PMS formed less organic halogen and toxicity because of the destruction of byproducts by UV irradiation and the removal of byproduct precursors. Currently, many studies focused on the byproducts bromate and chlorate during SO4 •–-based oxidation processes. This work revealed that the oxidant PMS even needs more attention because it caused higher toxicity due to more organic halogen formation.

Degradation of Butylated Hydroxyanisole by the Combined Use of Peroxymonosulfate and Ferrate(VI): Reaction Kinetics, Mechanism and Toxicity Evaluation

“…However, SO 4 •− is also susceptible to the influence of aqueous components (e.g., halides and natural organic matter), leading to the generation of some potentially toxic byproducts and unwanted oxidant consumption [ 22 , 23 ]. PMS-based advanced oxidation processes have been reported to produce more organochlorine acids, thereby increasing the toxicity of wastewater to mammalian cells [ 24 ].…”

Suppressing Organic Bromine but Promoting Bromate: Is the Ultraviolet/Ozone Process a Double-Edged Sword for the Toxicity of Wastewater to Mammalian Cells?

“…Br − concentrations higher than 1 mg/L were detected in 3 WWTPs in southern Scandinavia, 8 and around 2.0 mg/L Br − was detected in the SE from WWTPs in Shenzhen, China. 9 During the ozonation process, Br − can be oxidized by O 3 to form the reactive bromine species hypobromous acid (HOBr), which can further generate bromate and organic bromine, resulting in elevated toxicity. 3,10 Much of the current research on the risk of ozonation in wastewater has focused on bromate control, but organic bromine also deserves attention.…”

“…In coastal areas, higher Br – concentrations occur more frequently due to the influence of seawater. Br – concentrations higher than 1 mg/L were detected in 3 WWTPs in southern Scandinavia, and around 2.0 mg/L Br – was detected in the SE from WWTPs in Shenzhen, China . During the ozonation process, Br – can be oxidized by O 3 to form the reactive bromine species hypobromous acid (HOBr), which can further generate bromate and organic bromine, resulting in elevated toxicity. , …”