key: cord-0993569-w1ws67q7
authors: Liu, Xiaoyu; Hong, Yuntao; Ding, Shunke; Jin, Wei; Dong, Shengkun; Xiao, Rong; Chu, Wenhai
title: Transformation of antiviral ribavirin during ozone/PMS intensified disinfection amid COVID-19 pandemic
date: 2021-05-27
journal: Sci Total Environ
DOI: 10.1016/j.scitotenv.2021.148030
sha: 89fdd8b94fb81216488097a1459676587a549086
doc_id: 993569
cord_uid: w1ws67q7

Due to the spread of coronavirus disease 2019 (COVID-19), large amounts of antivirals were consumed and released into wastewater, posing risks to the ecosystem and human health. Ozonation is commonly utilized as pre-oxidation process to enhance the disinfection of hospital wastewater during COVID-19 spread. In this study, the transformation of ribavirin, antiviral for COVID-19, during ozone/PMS-chlorine intensified disinfection process was investigated. •OH followed by O3 accounted for the dominant ribavirin degradation in most conditions due to higher reaction rate constant between ribavirin and •OH vs. SO4•− (1.9 × 109 vs. 7.9 × 107 M−1 s−1, respectively). During the O3/PMS process, ribavirin was dehydrogenated at the hydroxyl groups first, then lost the amide or the methanol group. Chloride at low concentrations (e.g., 0.5~2 mg/L) slightly accelerated ribavirin degradation, while bromide, iodide, bicarbonate, and dissolved organic matter all reduced the degradation efficiency. In the presence of bromide, O3/PMS process resulted in the formation of organic brominated oxidation by-products (OBPs), the concentration of which increased with increasing bromide dosage. However, the formation of halogenated OBPs was negligible when chloride or iodide existed. Compared to the O3/H2O2 process, the concentration of brominated OBPs was significantly higher after ozonation or the O3/PMS process. This study suggests that the potential risks of the organic brominated OBPs should be taken into consideration when ozonation and ozone-based processes are used to enhance disinfection in the presence of bromide amid COVID-19 pandemic.

Since the first report of patients with coronavirus disease 2019 in December 2019, COVID-19 has raised international concern due to its rapid spread, and the pandemic is difficult to control in many countries and regions (Lu et al., 2020a) . In order to control the spread of COVID-19, large amount of antivirals such as ribavirin, chloroquine phosphate, alpha interferon, lopinavir and ritonavir have been consumed (Hung et al., 2020; Wong et al., 2021) . Ribavirin can be effective against both RNA and DNA viruses, and owing to its broad-spectrum action, it was extensively used to treat viral diseases such as herpes, hepatitis C, and Lassa fever (Ye et al., 2020) .

As wastewater treatment processes were not designed for micropollutant removal, up to 20 ng/L of ribavirin was detected in the influent and effluent of wastewater treatment plant previously (Gani et al., 2020; . Despite being low in concentration, potential risks of these antiviral drugs to both human and ecological health are still a concern due to chronic exposure (Nannou et al., 2020 ). An in vitro bioassay employing human-induced pluripotent stem cells showed that ribavirin could cause DNA damage and the accumulation of reactive oxygen species (Ye et al., 2020) . Besides, antiviral resistance may be developed after chronic exposure to antiviral drugs (Nannou et al., 2019) . The expanded use of ribavirin during the COVID-19 pandemic probably resulted in the substantial increase of ribavirin in wastewater effluent, especially in hospital wastewater. Therefore, the potentially increased release and transmission of ribavirin from wastewater during COVID-19 pandemic demands attention.

To prevent the transmission of the COVID-19, intensified disinfection has been implemented in hospital wastewater amid COVID-19 pandemic . Chlorine and chlorine-based disinfectants are commonly-used for disinfection. However, increased chlorine consumption would significantly promote disinfection by-product (DBP) formation, and both residual chlorine 2 Materials and methods

Ribavirin, PMS, sodium persulfate (PS), tert-butyl alcohol (TBA), methanol (MeOH), sodium bromide, sodium chloride, potassium iodide, humic acid and sodium hypochlorite were purchased from Aladdin Industrial Inc. (Shanghai, China) . All other chemical reagents were of at least analytical grade and obtained from Sinopharm Chemical Reagent Co., Ltd (Shanghai, China) unless otherwise specified. O 3 stock solution (20-30 mg/L) was prepared by sparging O 3 /O 2 gas through 4 °C ultrapure water and the concentration of dissolved O 3 was determined by measuring absorbance at 260 nm (ε = 3200 M −1 cm −1 ) (Mao et al., 2020; Yang et al., 2015) . All solutions were prepared using ultrapure water produced from the Milli-Q water purification system (Millipore, USA).

Batch experiments were carried out in 250 mL conical flask containing 10 μM ribavirin solution under ambient temperature (25 ℃), and the pH of solution was buffered with 5 mM phosphate.

Reaction initiated once certain volumes of O 3 and PMS stock solution were added. At predetermined time intervals, solution was withdrawn and quenched with excess sodium hyposulfite for further analysis.

To determine the contribution of •OH, SO 4 • − and O 3 to the degradation of ribavirin, second-order rate constants of ribavirin with •OH (k •OH/RBV ), SO 4 • − (kso 4-·/RBV ) and O 3 (K O3·/RBV ) were determined in UV/H 2 O 2 , UV/PS and ozone system, respectively, by competitive dynamics reaction. Benzoic acid (BA) and atrazine (ATZ) with known reaction rate constant with •OH,

The steady-state concentration of •OH and SO 4 • − in the process was evaluated by monitoring the degradation of probe compounds (BA and nitrobenzene (NB)) with known reaction constants.

Due to different reaction kinetics between probe compounds and oxidants (k •OH/NB = 5.90 × 10 9 M −1 S −1 , and k •OH/NB < 10 6 M −1 S −1 ), steady-state concentration and contribution of •OH and SO 4 • − may be determined by experiment process and kinetic calculation provided in Text S1.

[ Figure 1 ]

The formation of halogenated OBPs during O 3 /PMS, O 3 /H 2 O 2 and O 3 process in the presence of halide was also investigated, and the experimental procedure was showed in Fig. 1 . After 30 min pre-oxidation, 10 mL sample was withdrawn to determine the formation of halogenated OBPs.

Besides, another 40 mL sample was put into 40.0 mL brown glass bottles and added appropriate amount of chlorine (4 mg/L or 8 mg/L). After 24 h chlorination at room temperature in the dark, the sample was quenched for further DBP analysis. The ascorbic acid which hardly resulted in DBP hydrolysis and affected DBP detection was chosen as quenching agent. The oxidants were nearly complete consumed after 30 min reaction, which showed limited effect on subsequent chlorination experiments (Table S1 ).

Ribavirin, NB, BA and ATZ were determined by high performance liquid chromatography (HPLC-2010, SHIMAZU, Kyoto, Japan) with a UV detector and an Agilent Shim-pack C18 column (250 mm × 4.6 mm, 5 μm). The detailed parameters of HPLC-UV have been listed in Table   S2 . OBPs and DBPs including trihalomethanes (THMs), haloacetonitriles (HANs), halonitromethane (HNMs) and haloacetaldehyde (HALs) were quantified by gas chromatography J o u r n a l P r e -p r o o f Journal Pre-proof with an electron capture detector (GC-ECD, Shimadzu QP2010plus, Kyoto, Japan) and a RTX-5 column (30 m, 0.25 mm ID, 0.25 μm film thickness, Restek Corporation, Bellefonte, USA). HAAs were derivatised to their corresponding esters using 10% sulfuric acid in methanol (v/v), and then measured with a gas chromatography/mass spectrometer (GC-MS-QP2020, Shimadzu

Corporation, Japan). The detailed step of OBPs/DBPs analysis was available in previous researches (Fang et al., 2019; Hou et al., 2018) and the limits of detection and quantitation for

OBPs/DBPs were available in Table S3 . Chlorine concentrations were measured using a portable colorimeter (HACH Pocket Colorimeter TMII, Loveland, CO, USA) and a DPD free chlorine reagent (HACH, Loveland, CO, USA). Dissolved ozonation were determined by indigo regent (HACH, Loveland, CO, USA) and spectrophotometer (HACH DR6000, Loveland, CO, USA).

PMS and H 2 O 2 concentrations were measured using the ABTS method and potassium titanium (IV) oxalate method (Sellers, 1980; Yang et al., 2015) . Dissolved organic carbon (DOC) was measured with a total organic carbon analyser (Shimadzu TOC-VCPH, Kyoto, Japan). The proposed degradation pathways were proposed using TSQ Quantum quadrupole mass spectrometer (ESI-tqMS, Thermo Scientific MAX) with an electrospray ionization (ESI) source, and the detailed experiment steps and parameters were available in Text S2.

The quantum chemical calculation of ribavirin was carried out by Gaussian 09 (Revision C.01) with the input structures created by GaussView 5.0 based on density functional theory (DFT/B3LYP/6-31G (d, p)) (M. J. Frisch, 2016) .

The degradation of ribavirin by PMS alone, O 3 alone, O 3 /PMS and O 3 /H 2 O 2 process was compared in Fig. 2 . Less than 5% ribavirin was degraded by PMS alone, which indicated poor oxidation of ribavirin by PMS. The pseudo-first-order rate constants of ribavirin degradation by O 3 and O 3 /PMS process were 3.84 × 10 -2 and 4.32 × 10 -1 s -1 , respectively, indicating that PMS could significantly promote the degradation efficiency of ribavirin during ozonation. Similar results were reported in previous research (Cong et al., 2015; Mao et al., 2020) . The higher J o u r n a l P r e -p r o o f Journal Pre-proof removal efficiencies of the O 3 /PMS process were attributed to the increased formation of free radicals (e.g., •OH and SO 4 • − ) from reactions between O 3 and PMS (Eqs. 3-6), and accelerated ozone consumption (Fig. S1 ) (Yang et al., 2015) .

As shown in Fig. S2 , although ribavirin was effectively eliminated by O 3 and the O 3 /PMS process, the decrease of DOC value was negligible, indicating that limited mineralization happened and some intermediates have been produced.

[ Figure 2 ] the pseudo first-order rate constant of ribavirin with specific oxidants, and k represents the apparent second-order rate constants of the reaction between ribavirin and corresponding oxidants. Due to negligible degradation of ribavirin by PMS alone (Fig. 3) , the contribution of PMS was not considered. According to the result of competitive kinetics experiments (Fig. S2 ), the second-order rate constants of ribavirin with •OH, SO 4 • − and ozone were determined to be 1.9 × 10 9 , 7.9 × 10 7 M −1 s −1 and 9.8 M −1 s −1 , respectively. Therefore, the contribution of different species in the O 3 /PMS process could be calculated by the model in Text S1. The result was illustrated in conditions, since k obs remarkably decreased when TBA was added. The removal efficiency was largely dependent on pH. With the increase of pH, the k obs increased from 8.1 × 10 -2 s -1 to 6.7 × 10 -1 s -1 . Ribavirin degradation driven by •OH increased significantly from 3.2 × 10 -2 s -1 to 3.6 × 10 -1 s -1 when pH increased from 6 to 7, then further increased to 5.4 × 10 -1 s -1 when pH reached 8.

The ribavirin degraded by SO 4 • − also steadily increased with pH, while the contribution of O 3 decreased. These results could be attributed to the follow reasons: 1) the alkaline environment could accelerate the decomposition of O 3 and formation of the reactive •OH (von Gunten, 2003a).

Besides, the increased formation of •OH would enhance the formation of SO 4 • − through Eq. 5 and Eq. 10 (Mao et al., 2020) ; 2) pH would affect the speciation of PMS, and the deprotonated PMS J o u r n a l P r e -p r o o f Journal Pre-proof (i.e., SO 5 2− ) was reported to be the main species that reacted with O 3 (Yang et al., 2015) . Thus, an alkaline environment, in which PMS generally exists in the deprotonated form, would accelerate the reaction between PMS and O 3 and produce more radicals; 3) at higher pH, SO 4 • − would be transformed into •OH (Eq. 9), and the latter is less selective and reacts rapidly with ribavirin.

•-+ OH -→ •OH + SO 4 2-k= 7.3 × 10 7 M -1 s -1 (9)

•OH + SO 5 -→ OH -+ SO 5 •-(10)

As the PMS dosage increased from 0.125 mM to 0.5 mM, the k obs increased from 9.1 × 10 -2 s -1 to 8.2 × 10 -1 s -1 . Besides, the contribution of •OH and SO 4 • − both increased with the PMS dosage. When the PMS dosage increased form 0.125 mM to 0.5 mM, the contribution of •OH and SO 4 • − increased from 3.0 × 10 -2 s -1 and 4.6 × 10 -3 s -1 to 7.4 × 10 -1 s -1 and 5.0 × 10 -2 s -1 . However, the contribution of O 3 decreased from 5.6 × 10 -2 s -1 to 2.9 × 10 -2 s -1 , then slightly increased to 3.1 × 10 -2 s -1 . On one hand, increased PMS dosage accelerated O 3 degradation. Previous research showed that the k obs of O 3 consumption increased significantly with PMS when the PMS/ozone ratio was lower than 1:1 (Yang et al., 2015) . Therefore, less O 3 was left to react with ribavirin. On the other hand, PMS would compete with ribavirin for O 3 and produce more SO 4 • − and •OH, which led to the increased contribution of •OH and SO 4 • − .

[ Figure 5 ]

Inorganics including halide ion and bicarbonate are ubiquitous in water, and could significantly affect the degradation efficiency of AOPs. Therefore, the effect of chloride, bromide, iodide and bicarbonate on the removal of ribavirin by the O 3 /PMS process was studied and the results were illustrated in Fig. 5 . The existence of low-concentration chloride slightly increase the removal efficiency of the O 3 /PMS process. Upon addition of 2 mg/L chloride, the k obs of ribavirin degradation increased from 4.32 × 10 -1 s -1 to 5.05 × 10 -1 s -1 , and the k obs steadily increased with chloride concentration when the chloride dosage was below 2 mg/L, which was consistent with J o u r n a l P r e -p r o o f Journal Pre-proof previous research . Yang et al. (2014) also observed that the presence of low-level chloride hardly affected the formation of •OH in AOPs. On one hand, the reaction between chloride and •OH is reversible (Eq 11), which resulted in limited scavenging effect of chloride on •OH (von Gunten, 2003b) . On the other hand, the Cl• formed from the reaction shown in Eq. 13 could be further transformed into •OH via the reverse reactions in Eqs. 11 and 12, and Cl• could rapidly react with ribavirin (Yang et al., 2014) . Besides, the Cl• formed from the reaction described in Eq. 12 could also contribute to the degradation of ribavirin .

When the chloride concentration further increased to 10 mg/L, the degradation efficiency of ribavirin decreased to 48%, which can be explained by the consumed Cl• and the formation of less reactive Cl 2 • -(Eq. 13) (Fang et al., 2014; Yang et al., 2014) .

Unlike chloride, bromide and iodide would result in lower removal efficiency of ribavirin. As bromide and iodide concentration increased from 0 to 2 mg/L, the k obs of ribavirin degradation decreased from 4.32 × 10 -1 s -1 to 8.9 × 10 -2 s -1 and 7.15 × 10 -2 s -1 , respectively ( Fig. 5B and Fig.   5C ). Previous research showed that iodide was quickly oxidized to iodate by ozone and PMS, and the half-time HOI/OI − was extremely short (< 2.0 min and 20 s at pH 7.0 and 8.0, respectively), which could hardly react with DOM during ozonation (Allard et al., 2013; Li et al., 2020) . Both of the competition between iodide and ribavirin for oxidation as well as the negligible reactions between the reactive iodine species (RISs) and ribavirin may result in lower removal efficiency. Lu et al. (2020b) found that bromide could enhance the degradation efficiency of ciprofloxacin by O 3 due to the formation of reactive bromine species (RBSs). However, in most cases, bromide would lower the removal efficiency of AOPs (e.g. UV/PS) due to the formation of selective RBSs (Eq. 15) as a result of the rapid and irreversible reactions between bromide and free radicals (e.g.,

•OH and SO 4 •−) Yang et al., 2014) . Radicals rather than O 3 played important roles in the elimination of ribavirin during the O 3 /PMS process. Thus, similar to iodide, bromide resulted in decreased removal efficiency, and the higher inhibition effect of iodide may be because of the higher reaction rate between iodide and oxidants than bromide, as even PMS alone could rapidly oxidize iodide to iodate .

As Fig. 5D showed, the degradation of ribavirin was hardly affected when the bicarbonate concentration was below 10 mg/L, and the degradation efficiency only slightly decreased when Humic acid was applied to investigate the effect of DOM on O 3 /PMS process, which was illustrated in Fig. 6 . As the concentration of humic acid increased to 0.5 mg/L, the k obs of ribavirin degradation slightly decreased from 4.32 × 10 -1 s -1 to 3.93 × 10 -1 s -1 and the degradation efficiency further decreased with the humic acid dosage increased. Similar results were also found in the degradation of iopamidol during the O 3 /PMS process, which was mainly attributed to the scavenging effect of humic acid (Wu et al., 2019a; Yang et al., 2015) . Besides, the fast degradation stage was obviously shortened, which may be related to accelerated O 3 and PMS consumption. S5 . The m/z of TP-1 (m/z=241) was slightly lower than that of ribavirin (m/z=245), which suggested the increase of unsaturation degree. The multiple losses of 28 (CO) in TP-1 product ion scan spectra revealed that TP-1 may contain at least two carbonyl groups. Besides, the losses of 41 also indicated that the alcoholic group remained intact in TP-1. Therefore, TP-1 may be the product of dehydrogenation on the hydroxyl groups. As for TP-2, the losses of 16 (NH 2 ) and 28

(CO) suggested that TP-2 may possess amine and carbonyl groups. Considering the m/z of TP-2 (m/z=211) and TP-1 (m/z=241), the TP-2 may have originated from TP-1 through loss of alcoholic group. According to the nitrogen rule, there were odd number of nitrogen atoms in TP-3.

Besides, the loss of 17 implied that TP-3 may contain hydroxyl group. Thus, TP-3 may be derived from TP-1 via loss of the amide group, and the result of quantum chemical calculation also showed that the amide group may be easily attacked (Table S3 ). Similar to TP-1, the product ion •OH, which readily occured oxidation reaction, rather than electrophilic substitution. Therefore, limited chlorinated OBPs were produced. However, the reaction between bromide and oxidants could produce RBSs including HOBr/BrOand Br•. Even though the selectivity of RBSs resulted in lower removal efficiency, RBSs readily underwent electrophilic substitution, which resulted in the formation of brominated OBPs.

As shown in Fig. 8 (Wen et al., 2018) . Thus, the concentration of HOBr/OBrwas decreased, which may reduce the formation of brominated OBPs (Wen et al., 2018; Wu et al., 2020) . However, PMS could significantly increase the degradation of ribavirin during ozonation, thus more organic intermediates with lower MW may be produced, which may result in increased brominated OBP formation at high bromide concentration. Besides, at higher bromide concentration, the ozone may outperform O 3 /PMS process on ribavirin oxidation, since bromide facilitates ozonation while deteriorates oxidation during O 3 /PMS process. Thus, more

TPs were available and more OBPs were produced during ozonation than O 3 /PMS process at higher bromide..

The formation of brominated OBPs during O 3 /H 2 O 2 process remained negligible at 2 mg/L bromide. Decreased formation of total organic bromine (TOBr) and brominated OBPs during O 3 /H 2 O 2 process was also observed in the research by Wu et al. (2020) . Previous research showed that adding H 2 O 2 could inhibit bromate formation during ozonation because H 2 O 2 could readily reduce HOBr/Brto bromide, which is crucial to the formation of bromate (Yang et al., 2019) . This can also be used to explain the decreased brominated OBP formation when H 2 O 2 was added.

Bromate is a commonly recognized DBP of ozonation and ozonation-based processes, and is a potentially carcinogenic compound that has attracted much attention (von Gunten, 2003b; Yang et al., 2019) . However, according to Wagner and Plewa (2017) , the LC 50 (the dose of chemical that J o u r n a l P r e -p r o o f Journal Pre-proof could show effect in 50% of the population studied) of some brominated OBPs including dibromoacetaldehyde and tribromoacetaldehyde (4.7 × 10 −6 M and 3.6 × 10 −6 M respectively)

were several magnitude lower than that of bromate (9.6 × 10 −4 M), which means that the brominated OBPs may possess much higher cytotoxicity than bromate. Wu et al. (2019b) also observed that both the brominated organic matter and bromate contributed to the toxicity of ozonized wastewater. Thus, more attention should be paid to organic OBPs after ozonation and ozone-based processes.

[ Figure 9 ]

Ozonation and ozone-based AOP could significantly alter the characteristic of DOM, and further affect the formation of DBPs during subsequent chlorination. Thus, formation of DBPs including THMs, HALs, HANs and HNMs during subsequent chlorination was evaluated and illustrated in Fig. 9 . The formation of specific DBPs was available in Fig. S7 and Fig. S8 . The effect of various ozone-based pre-oxidation processes, bromide and chlorine dosages were also investigated. Vera et al., 2015; Mao et al., 2018; Yang et al., 2012) . Due to negligible decrease in DOC, the slight decrease in THM formation may be attributed to the oxidation of the electronic-rich triazole structure, which led to fewer available halogenation sites for THM formation. As aldehyde and ketone were common oxidation products of ozonation, the increased HALs was reasonable. Considering the relatively lower DBP formation after the O 3 /PMS process, PMS may be more suitable than H 2 O 2 to enhance the efficiency of ozonation.

Despite being at lower concentration, nitrogenous DBPs have attracted much attention due to their higher cytotoxicity and genotoxicity (Wagner and Plewa, 2017) . After ozonation or O 3 /PMS process, the formation of HANs was slightly decreased, while the O 3 /H 2 O 2 process hardly affected the formation of HANs. However, ozonation or ozone-based pre-oxidation resulted in increased formation of HNMs. Those were mainly attribute to oxidation of nitrogenous functional groups including amide and triazole.

The disinfection condition including chlorine dosage could significantly affect the formation and speciation of DBPs. Generally, higher chlorine dosage could result in increased DBP formation, since higher chlorine dosage facilitated chlorination of ribavirin and its TPs. However, the formation of THMs, HANs and HALs was decreased at higher chlorine dosage in some experimental groups. The decreased HALs and HANs may be explained by accelerated hydrolysis induced by excess chlorine.

Bromine is more reactive to DOM than Cl 2 and is prone to forming DBPs than chlorine. Thus, the formation of DBPs in the presence of bromide was much higher than that without bromide (Zhu and Zhang, 2016) . With bromide, formation of brominated DBPs was much higher after ozonation and ozone-based processes, and the promotion effect of O 3 /H 2 O 2 was the most obvious.

To better evaluate the effect of ozone and ozone-based processes on DBP speciation, the bromine As illustrated in Figure S9 , ozonation and ozone-based process could increase the BSF of THMs by 12%-157%, and the BSF of trihaloacetonitriles was only slightly increased after pre-oxidation. However, the variation of BSF for HALs was not obvious. Similar phenomenon was also observed in previous research where pre-ozonation were applied to natural DOM Hua and Reckhow, 2013) . Since the concentrations of OBPs formed during pre-oxidation were relatively low, RBSs formed during pre-oxidation may not be the main contributor to the increased brominated DBP formation. Thus, it is more likely that some oxidation products that were more reactive to bromine than chlorine were produced during ozonation and ozone-based processes. However, whether the above phenomenon was similar to that in the presence of DOM needs further investigation.

Due to the spread of COVID-19, large amount of antivirals were consumed and released into the environment. This study showed that compared to ozonation, the O 3 /PMS process effectively degraded ribavirin via simultaneous •OH and SO 4 • − production. As ozonation is commonly used to intensify disinfection during COVID-19, PMS-enhanced ozonation seems to be a convenient and efficiency way to remove antivirals for COVID-19 such as ribavirin from hospital wastewater, part of which may eventually cycle back to source waters. However, brominated OBPs with high toxicity may be produced during ozonation and the O 3 /PMS process in the presence of bromide.

Therefore, H 2 O 2 rather than PMS is recommended to be used to enhance the ozonation of bromide-containing water. When ozonation is applied as a pre-oxidant with subsequent chlorination, PMS may be more suitable than H 2 O 2 to enhance ozonation due to significantly less DBP formation. Further investigations are needed to evaluate the effect of the O 3 /PMS process on DBP formation from wastewaters to evaluate the feasibility of its practical application in wastewater treatment, especially for hospital wastewater. 

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