Ferrate(VI) assists in reducing cytotoxicity and genotoxicity to mammalian cells and organic bromine formation in ozonated wastewater.

Ozonation of wastewater containing bromide (Br-) forms highly toxic organic bromine. The effectiveness of ozonation in mitigating wastewater toxicity is minimal. Simultaneous application of ozone (O3) (5 mg/L) and ferrate(VI) (Fe(VI)) (10 mg-Fe/L) reduced cytotoxicity and genotoxicity towards mammalian cells by 39.8% and 71.1% (pH 7.0), respectively, when the wastewater has low levels of Br-. This enhanced reduction in toxicity can be attributed to increased production of reactive iron species Fe(IV)/Fe(V) and reactive oxygen species (•OH) that possess higher oxidizing ability. When wastewater contains 2 mg/L Br-, ozonation increased cytotoxicity and genotoxicity by 168%-180% and 150%-155%, respectively, primarily due to the formation of organic bromine. However, O3/Fe(VI) significantly (p < 0.05) suppressed both total organic bromine (TOBr), BrO3-, as well as their associated toxicity. Electron donating capacity (EDC) measurement and precursor inference using Orbitrap ultra-high resolution mass spectrometry found that Fe(IV)/Fe(V) and •OH enhanced EDC removal from precursors present in wastewater, inhibiting electrophilic substitution and electrophilic addition reactions that lead to organic bromine formation. Additionally, HOBr quenched by self-decomposition-produced H2O2 from Fe(VI) also inhibits TOBr formation along with its associated toxicity. The adsorption of Fe(III) flocs resulting from Fe(VI) decomposition contributes only minimally to reducing toxicity. Compared to ozonation alone, integration of Fe(VI) with O3 offers improved safety for treating wastewater with varying concentrations of Br-.

Reduction of cytotoxicity and DNA double-strand break effects of wastewater by ferrate(VI): Roles of oxidation and coagulation.

Ferrate(VI) (Fe(VI)) can oxidize individual pollutants, but the pollutant oxidation does not necessarily result in toxicity reduction. Besides, Fe(VI) resultant Fe(III) particles has previously been used to remove heavy metals, but its influence on organic matter and toxicity of wastewater is unknown. This study investigated influence of Fe(VI) on the cytotoxicity and DNA double-strand break (DSB) effects of secondary effluents from wastewater treatment plants to Chinese hamster ovary cells. Adding 5.0 mg/L Fe(VI) as Fe reduced the cytotoxicity and genotoxicity of secondary effluents by 44%-71% and 40%-59%, respectively. The toxicity reduction could be explained by the alleviation of oxidative stress in cells when they were exposed to the Fe(VI)-treated organic matter. Oxidation and coagulation accounted for 60 and 40% of the reductions in cytotoxicity and genotoxicity, demonstrating that both oxidation and coagulation processes can play important roles in reducing toxicity. Molecular weight (MW)-distribution analysis showed that the oxidation process was favored for removing ultraviolet absorbance and fluorescence intensity of organic matter, while the coagulation process removed more dissolved organic carbon (DOC), especially the DOC of fractions with MW < 500 Da. Compared with ferric chloride, the Fe(VI) resultant Fe(III) showed better coagulation performance on organic matter, cytotoxicity and genotoxicity removal, because of the different particle sizes and crystalline structures. This study highlights the benefit of using Fe(VI) in advanced treatment as Fe(VI) reduced the overall toxicity of secondary effluents.

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

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.

Comprehensive GC×GC-qMS with a mass-to-charge ratio difference extraction method to identify new brominated byproducts during ozonation and their toxicity assessment.

Ozonation might increase the risk of wastewater due to byproduct formation, especially in the presence of bromide. In this study, a new analytical method was developed to identify new brominated disinfection byproducts (Br-DBPs) during ozonation, using comprehensive two-dimensional gas chromatography-single quadrupole mass spectrometry (GC×GC-qMS) connected with an electron capture detector in parallel. The obtained data were analyzed using a mass-to-charge ratio (m/z) difference extraction method. Over 1304 DBPs were detected in an ozonated phenylalanine solution. Further screening of 635 DBPs was conducted using the m/z difference extraction method. Finally, the structures for 12 Br-DBPs were confirmed and for 4 Br-DBPs were tentatively proposed by comparison with the NIST library and standard compounds. Eight of the confirmed Br-DBPs are first reported and identified: 2-bromostyrene, 1-bromo-1-phenylethylene, 2-bromobenzaldehyde, 3-bromobenzaldehyde, 4-bromobenzaldehyde, 2-bromophenylacetonitrile, 3-bromophenylacetonitrile and 4-bromophenylacetonitrile. These DBPs and 2,4,6-tribromophenol were detected at nanogram- to microgram-per-liter concentrations during ozonation of authentic water samples like algal bloom waters, wastewater treatment plant effluents, and surface water. The toxicities of these compounds were generally higher than that of bromate. The developed analytical method is a powerful technique for analyzing complex compounds and provides a novel way of identifying byproducts in future studies.

Non-volatile disinfection byproducts are far more toxic to mammalian cells than volatile byproducts.

Water is often chlorinated to protect public health, but chlorination causes harmful disinfection byproducts to form. Currently available in vitro assays generally determine non-volatile disinfection byproduct (NVDBP) toxicities because of the limitation of pretreatments used, but chemical analyses and regulations are focused on volatile disinfection byproducts (VDBPs) such as trihalomethanes. The gap of VDBP toxicities have been of concern for some time. In this study, we extracted VDBPs from two chlorinated effluent organic matters and one chlorinated natural organic matter, using a helium aeration-liquid nitrogen condensation system, and systematically assessed the VDBP and NVDBP toxicities to mammalian cells. VDBPs accounted for 10%-20% of the total organic halogen concentrations in three chlorinated water samples. VDBPs were much less cytotoxic, caused fewer DNA double-strand breaks, induced less reactive oxygen species and DNA/RNA oxidative damage marker of 8-hydroxyl(deoxy)guanosine in cells than did NVDBPs. Moreover, by collecting the VDBPs, toxicity measurement of the full range of DBPs was achieved. Cytotoxicity, reactive oxygen species and 8-hydroxyl(deoxy)guanosine levels were significantly higher for cells exposed to the mixture of VDBPs and NVDBPs than only NVDBPs, but not by large percentages (20%-30% for cytotoxicity), suggesting NVDBPs mainly contributed to the toxicity of chlorinated water. Our study suggested that future research should focus more on NVDBP toxicity and identifying toxicity drivers from NVDBPs.

Ammonia-Mediated Bromate Inhibition during Ozonation Promotes the Toxicity Due to Organic Byproduct Transformation.

Ammonia (NH4+) and hydrogen peroxide (H2O2) have been widely used to inhibit bromate formation during ozonation. However, organic byproducts can also pose a risk under these conditions. During bromate inhibition, the influence of NH4+ and H2O2 on organic byproducts and their toxicity should be elucidated. Our study found that NH4+ suppressed organic bromine, but might result in increased toxicity. Adding 0.5 mg/L of NH4+-N substantially increased both the formation of cytotoxicity and genotoxicity (DNA double-strand breaks) of organic byproducts from 0.6 to 1.6 mg-phenol/L, and from 0.3 to 0.8 µg-4-NQO/L (0.5 mg/L Br-, 5 mg/L O3). NH4+ decreased bromate, but increased the overall toxicity of the integrated byproducts (organic byproducts and bromate). Organic nitrogen measurements and 15N isotope analysis showed enhanced incorporation of nitrogen into organic matter when NH4+ and Br- coexisted during ozonation. NH4+ decreased the formation of brominated acetonitriles, but enhanced the formation of brominated nitromethanes and brominated acetamides. These brominated nitrogenous byproducts were partially responsible for this increase in toxicity. Different from ammonia, H2O2 could reduce both bromate and the toxicity of organic byproducts. In the presence of 0.5 mg/L Br- and 10 mg/L O3, adding H2O2 (0.5 mM) substantially suppressed bromate, cytotoxicity formation and genotoxicity formation by 88%, 63% and 67%. This study highlights that focusing on bromate control with NH4+ addition might result in higher toxicity. Efforts are needed to effectively control the toxicities of bromate and organic byproducts simultaneously.