Toxicity of Ozonated Wastewater to HepG2 Cells: Taking Full Account of Nonvolatile, Volatile, and Inorganic Byproducts

Abstract

Wastewater ozonation forms various toxic byproducts, such as aldehydes, bromate, and organic bromine. However, there is currently no clear understanding of the overall toxicity changes in ozonated wastewater because pretreatment with solid phase extraction cannot retain inorganic bromate and volatile aldehydes, yet contributions of known ozonation byproducts to toxicity are unknown. Moreover, compared with bromate, organic bromine did not receive widespread attention. This study evaluated the toxicity of ozonated wastewater by taking aldehydes, bromate, and organic bromine into consideration. In the absence of bromide, formaldehyde contributed 96–97% cytotoxicity and 92–95% genotoxicity to HepG2 cells among the detected known byproducts, while acetaldehyde, propionaldehyde, and glyoxal had little toxicity. Both formaldehyde and dibromoacetonitrile drove toxicity among the known byproducts when bromide was present. Toxicity assays in HepG2 cells showed that when secondary effluents contained no bromide, the cytotoxicity of the nonvolatile organic fraction (NVOF) was reduced by 56–70%, and genotoxicity was completely removed after ozonation. However, the formed aldehydes (volatile organic fraction, VOF) led to increased overall toxicity. In the presence of bromide, compared with the secondary effluent, ozonation increased the cytotoxicity of the NVOFBr from 3.4–4.0 mg phenol/L to 10.3–13.9 mg phenol/L, possibly due to the formation of organic bromine. In addition, considering the toxicity of VOFBr (VOF in the presence of bromide, including aldehydes, tribromomethane, etc.), the overall cytotoxicity and genotoxicity became much higher than those of the secondary effluent. Although bromate had a limited impact on cytotoxicity and genotoxicity, it caused an increase in oxidative stress in HepG2 cells. Therefore, when taking full account of nonvolatile, volatile, and inorganic fractions, ozonation generally increases the toxicity of wastewater.

Essential role of sunlight irradiation in aqueous micropollutant transformations: influence of the water matrix and changes in toxicities

“…61,70,83,84 For these MPs, the increased nitrate concentrations (from 0 to 100 mg L −1 ) generally increased the photolysis rates, indicating that the radical species generated by nitrate play a dominant role in photodegradation rather than exhibit a light screening effect. 7,61,62,[85][86][87][88] Nitrate (<10 mg L −1 ) also shows a promotion effect on total organic halogen (TOX) photodegradation (an overall indicator referring to organic halogen generated during the disinfection process, which was confirmed to be an important toxic contributor [85][86][87] ) in wastewater and natural waters. 34 It could be explained by nitrate absorbing photons then forming reactive nitrogen species and ˙OH to induce accelerated TOX photodegradation.…”

Efficacious bioremediation of heavy metals and radionuclides from wastewater employing aquatic macro‐ and microphytes

“…As an example, during wastewater treatment through ozonation and UV radiation, workers can suffer with acute health damages like skin burns and acute radiation syndrome due to the exposure to UV radiation and the toxic ozone gas [13]. Also, different toxic by-products such as aldehydes, organic bromine and bromate and other micro pollutants and radioactive wastes are formed during ozonation and UV-based treatment, which calls for further downstream wastewater treatment [14]. Therefore, excess capital investment is required for the complete mineralization of these noxious contaminants from wastewater [15].…”

Micropollutant transformation and toxicity: Electrochemical ozonation versus biological metabolism

“…It is hypothesised that although CabECO (electrochemical oxidation) may have higher and broader removal efficiency than microbial degradation, the highly energized environment may generate free radicals and more toxic byproducts. 31 In contrast, microbial degradation may be more specific and targeted, but microbial evolution may potentially also select for metabolic processes generating less toxic by-products. [32][33][34][35] Similar studies often only evaluate removal efficiencies of micropollutant removal technologies, neglecting the toxicological effects of transformation products or metabolites after treatment.…”