Efficiency of ozonation and sulfate radical - AOP for removal of pharmaceuticals, corrosion inhibitors, x-ray contrast media and perfluorinated compounds from reverse osmosis concentrates.

This study investigated the elimination of pharmaceuticals, corrosion inhibitors, x-ray contrast media and perfluorinated compounds from reverse osmosis concentrates during ozonation and UV/persulfate processes. Second-order rate constants for the reactions of candesartan, irbesartan, methyl-benzotriazole, and chloro­benzotriazole with sulfate radical (SO4·-) were determined for the first time. Experiments were conducted in buffered pure water, in buffered water added with the matrix substituents chloride, carbonate, NOM, and reverse osmosis concentrate with spiked micropollutants (MP). UV/persulfate eliminated all MP to a higher extent than ozonation in RO concentrates due to the higher yield of oxidative species and photolytic degradation. Compounds with electron-rich moieties such as carbamazepine, diclofenac, metoprolol, and sulfamethoxazole were completely eliminated with small ozone doses (< 0.5 mg O3 / mg DOC) and with a small fluence (< 5000 J m-2) in UV/persulfate processes. Photosensitive compounds with high reactivity towards hydroxyl radicals (·OH) and SO4·- like the x-ray contrast media Iopamidol, Iohexol, and Amidotrizoic acid were successfully eliminated with a reasonable fluence in UV/persulfate, whereas these compounds persist in ozonation at common ozone dosages. However, much higher fluences and ozone dosages were required for the least reactive compounds like the class of benzotriazoles. Comparing the application of both oxidative processes to the RO concentrate, ozonation has the disadvantage of forming bromate. The energy input of both processes strongly depends on the target compounds to be eliminated. For the elimination of compounds such as sulfamethoxazole, ozonation is a feasible technique, whereas UV/persulfate is better suited for the elimination of recalcitrant compounds such as x-ray contrast media. In general, oxidative process treatment of RO concentrate could be applied to partly abate micropollutants before discharge.

Oxidation of the N-containing phosphonate antiscalants NTMP and DTPMP in reverse osmosis concentrates: Reaction kinetics and degradation rate.

N-containing organophosphonate antiscalants such as Aminotris (methylene phosphonic acid) (NTMP/ATMP) and Diethylenetriamine penta(methylene phosphonic acid) (DTPMP) are commonly used in reverse osmosis (RO) to prevent scaling, as well as to increase permeate yields. However, the concentrate in RO still contains antiscalants which can cause adverse effects in the environment such as mobilization of heavy metals. The abatement of antiscalants from RO concentrate can promote the precipitation of oversaturated scale-forming substances and reduce the risk of adverse environmental effects. In the present study, the degradation of NTMP and DTPMP as representatives for N-containing organophosphonate by ozone, hydroxyl radicals (•OH), and sulfate radicals (SO4•-) are studied regarding reaction kinetics and degradation in different matrices. The results show that NTMP and DTPMP react fast with ozone and sulfate radicals (formed in UV/persulfate). Reaction rate constants of ozone showed a strong pH dependency due to the dissociation of the amine. The apparent reaction rates for pH 7 have been determined to be kapp(NTMP + ozone) = 1.44 × 105 M-1 s-1 and kapp(DTPMP + ozone) = 1.16 × 106 M-1 s-1. Reaction kinetics of •OH and SO4•- did not play a distinctive pH dependency (k(•OH) = 109-1010 M-1 s-1 and k(SO4•-) = 107-108 M-1 s-1). Furthermore, real water experiments have shown that ozonation and UV/persulfate are effective tools to abate organophosphonates in RO concentrates. The formation of carcinogenic bromate in ozonation is minimized by the presence of N-containing organophosphonates presumably due to enhanced ozone consumption and scavenging of free bromine.

Effects of organic matter and alkalinity on the ozonation of antiviral purine derivatives as exemplary micropollutant motif.

Ozonation of micropollutants strongly depends on the water matrix. Natural organic matter is known to highly affect the hydroxyl radical exposure due to radical promoting and inhibiting effects. Other important matrix components in ozonation are carbonate species which scavenge hydroxyl radicals. However, additional factors such as the formation of other radicals might also play a role but are generally not covered in research or considered in modelling of micropollutant degradation. Hence, the ozonation of purine derivatives, the basic structure of various antiviral micropollutants, in different artificial water matrices is investigated in this study with focus on the impact of natural organic matter and increasing alkalinity on the degradation and product formation. The degradation of purine and adenine is inhibited by bicarbonate in the water matrix due to the anion's scavenging of hydroxyl radicals. This effect is already observed for low bicarbonate concentrations of 0.3 mM. However, formed carbonate radicals contribute to the compounds' degradation and also affect the stability of transformation products. This effect gains in relevance with increasing alkalinity and needs consideration in evaluating ozonation of very hard waters. Three ozonation products are evaluated in detail, which are affected by the matrix due to impacts on ozone stability, hydroxyl radical yield and carbonate radical formation. One product of adenine with the mass 147 was reported for the first time and only occurs in presence of matrix components. Under typical water treatment conditions rough predictions of pollutants' degradation are possible by the Rct concept using ozone and hydroxyl radical exposures. However, other reactive species such as carbonate radicals are not considered leading to deviations between modelled and experimental data at extreme conditions such as industrial wastewater. A general correlation between the Rct and the fraction f of hydroxyl radicals scavenged by bicarbonate (ln(Rct) = - 5.9  ×  f - 16.3) calculated from the concentration of organic matter and alkalinity was observed for various water samples allowing the estimation of micropollutant degradation during ozone treatment at moderate conditions by simple organic and inorganic carbon measurements.

Reaction Mechanisms of Chlorine Dioxide with Phenolic Compounds─Influence of Different Substituents on Stoichiometric Ratios and Intrinsic Formation of Free Available Chlorine.

Chlorine dioxide (ClO2) is an oxidant applied in water treatment processes that is very effective for disinfection and abatement of inorganic and organic pollutants. Thereby phenol is the most important reaction partner of ClO2 in reactions of natural organic matter (NOM) and in pollutant degradation. It was previously reported that with specific reaction partners (e.g., phenol), free available chlorine (FAC) could form as another byproduct next to chlorite (ClO2-). This study investigates the impact of different functional groups attached to the aromatic ring of phenol on the formation of inorganic byproducts (i.e., FAC, ClO2-, chloride, and chlorate) and the overall reaction mechanism. The majority of the investigated compounds reacted with a 2:1 stoichiometry and formed 50% ClO2- and 50% FAC, regardless of the position and kind of the groups attached to the aromatic ring. The only functional groups strongly influencing the FAC formation in the ClO2 reaction with phenols were hydroxyl- and amino-substituents in ortho- and para-positions, causing 100% ClO2- and 0% FAC formation. Additionally, this class of compounds showed a pH-dependent stoichiometric ratio due to pH-dependent autoxidation. Overall, FAC is an important secondary oxidant in ClO2 based treatment processes. Synergetic effects in pollutant control and disinfection might be observable; however, the formation of halogenated byproducts needs to be considered as well.

Oxidation of the nitrogen-free phosphonate antiscalants HEDP and PBTC in reverse osmosis concentrates: Reaction kinetics and degradation rate.

Reverse osmosis (RO) is an advanced technology used to produce potable water from a variety of water sources, including surface water, seawater and wastewater. The yield of the product water from the RO systems is increased by the addition of antiscalants which prevent scaling from calcium and other ions. Removal of antiscalants from RO concentrate can induce the precipitation of oversaturated scale-forming substances, enable additional water recovery from RO concentrates, and reduce the risk of eutrophication after concentrate disposal into the receiving water (e.g., river water). This study aims to provide a better insight into oxidation reactions of the N-free phosphonate antiscalants 1-hydroxyethane-1,1-diphosphonic acid (HEDP) and 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC) with ozone, hydroxyl radical (•OH) and sulfate radicals (SO4•-). Ozone barely reacts with HEDP and PBTC at pH 7 (k < 10 M-1s - 1), while second order reaction rates of SO4•- and •OH were determined to be in the range 107-108M - 1s - 1. Sulfate, silicate and chloride matrices increased HEDP ozone degradation rate possibly due to metal complexation effect. Whereas carbonate and chloride hindered PBTC ozone degradation, and natural organic matter (NOM) inhibited both HEDP and PBTC degradation through scavenging of •OH. The SO4•-- radical based oxidation process of HEDP and PBTC is mainly inhibited by carbonate and NOM, interestingly only HEDP degradation is inhibited by chloride whereby the PBTC could not be fully degraded (degradation < 60%). The oxidation of PBTC is in real RO concentrates in both processes limited to 10% degradation, whereas HEDP could be degraded up to 60% with ozone and UV/persulfate application.

Reaction of Chlorine Dioxide with Saturated Nitrogen-Containing Heterocycles and Comparison with the Micropollutant Behavior in a Real Water Matrix.

Chlorine dioxide (ClO2) is a very selective oxidant that reacts with electron-rich moieties such as activated amines and thus can degrade specific N-containing micropollutants. N-containing heterocycles (NCHs) are among the most frequent moieties of pharmaceuticals. In this study, the reactions of ClO2 with ritalinic acid and cetirizine, two abundant micropollutants, and model compounds representing their NCH moiety were investigated. The pH-dependent apparent reaction rates of all NCHs with ClO2 were measured and modeled. This model showed that neutral amines are the most important species having reaction rates between 800 and 3200 M-1 s-1, while cationic amines are not reactive. Ritalinic acid, cetirizine, and their representative model compounds showed a high stoichiometric ratio of ≈5 moles ClO2 consumption per degraded ritalinic acid and ≈4 moles ClO2 consumption per degraded cetirizine, respectively. Investigation of chlorine-containing byproducts of ClO2 showed that all investigated NCHs mostly react by electron transfer and form above 80% chlorite. The reactions of the model compounds were well comparable with cetirizine and ritalinic acid, indicating that the model compounds indeed represented the reaction centers of cetirizine and ritalinic acid. Using the calculated apparent reaction rate constants, micropollutant degradation during ClO2 treatment of surface water was predicted for ritalinic acid and cetirizine with -8 to -15% and 13 to -22% error, respectively. The results indicate that in ClO2-based treatment, piperidine-containing micropollutants such as ritalinic acid can be considered not degradable, while piperazine-containing compounds such as cetirizine can be moderately degraded. This shows that NCH model compounds could be used to predict micropollutant degradation.

Linking reaction rate constants and isotope fractionation of ozonation reactions using phenols as probes.

Ozonation is nowadays a widely used method in drinking water treatment for disinfection and pollutant control. However, transformation products of ozonation can be more toxic than their parent compounds. Therefore, the knowledge of the reaction mechanisms and product formation is essential for a safe application. Different analytical methods such as high-resolution mass spectrometry (HRMS) and compound-specific isotope analysis (CSIA) can be applied to elucidate products and primary attack positions of oxidation agents such as ozone. During the investigation of the ozonation of phenolic compounds in water by CSIA, a reaction rate depending carbon isotope fractionation was observed. The fractionation strongly depends on the phenol speciation. With decreasing pH values and reaction rates <105 M-1 s-1, the isotope enrichment factor ε increases (ε is between -5.2 and -1.0‰). For faster reactions (>105 M-1 s-1), the carbon isotope enrichment was not significant anymore (ε is between -1.0 and 0‰). Based on these data a concept to correlate isotope enrichment factors with kinetic data for aromatic compounds is proposed. The additional investigation of aliphatic double and triple bonds did not fit this correlation suggesting different rate-limiting steps. However, double and triple bond showed a similar enrichment factor, which implies the same rate-limiting step in the reaction with ozone, the monodentate addition of ozone.

Influence of water matrix on the degradation of organic micropollutants by ozone based processes: A review on oxidant scavenging mechanism.

The prevalence of organic micropollutants (OMPs) in aquatic environment has expedited scientific and regulatory efforts to retrofit existing wastewater treatment plants (WWTPs). The current strategy involves WWTPs upgrading with post-ozonation i.e., ozone (O3) and/or peroxone process (O3 +H2O2). Still, ozone-based degradation of OMPs faces several challenges. For example, the degradation mechanism and kinetics of OMPs could largely be affected by water matrix compounds which include inorganic ions and natural organic matter (NOM). pH also plays a decisive role in determining the reactivity of the oxidants (O3, H2O2, andHO•), stability and speciation of matrix constituents and OMPs and thus susceptibility of OMPs to the reactions with oxidants. There have been reviews discussing the impact of matrix components on the degradation of OMPs by advanced oxidation processes (AOPs). Nevertheless, a review focusing on scavenging mechanisms, formation of secondary oxidants and their scavenging effects with a particular focus on ozonation and peroxone process is lacking. Therefore, in order to broaden the knowledge on this subject, the database 'Web of Science' was searched for the studies related to the 'matrix effect on the degradation of organic micropollutants by ozone based processes' over the time period of 2004-2021. The relevant literature was thoroughly reviewed and following conclusions were made: i) chloride has inhibitory effects if it exits at higher concentrations or as free chlorine i.e. HOCl/ClO-. ii) The inhibitory effects of chloride, bromide, HOBr/OBr- and HOCl/ClO- are dominant in neutral and alkaline conditions and may result in the formation of secondary oxidants (e.g., chlorine atoms or free bromine), which in turn contribute to pollutant degradation or form undesired oxidation by-products such as BrO3-, ClO3- and halogenated organic products. ii) NOM may induce inhibitory or synergetic effects depending on the type, chemical properties and concentration of NOM. Therefore, more efforts are required to understand the importance of pH variation as well as the effects of water matrix on the reactivity of oxidants and subsequent degradation of OMPs.

Bromide strongly influences the formation of reaction products during the ozonation of diclofenac, metoprolol and isoproturon.

Bromide as an omnipresent matrix component in wastewater can react with ozone to form hypobromous acid (HOBr). This secondary oxidant can subsequently react with micropollutants but also with formed intermediates. Therefore, bromide and especially HOBr can highly influence the formation of transformation products (TPs). This has already been reported for the ozonation of N,N-dimethylsulfamide leading to the formation of the cancerogenic N-nitrosodimethylamine only in bromide containing waters. In this study, the influence of different bromide and ozone concentrations on the formation of TPs during the ozonation of isoproturon (ISO), metoprolol (METO) and diclofenac (DCF) were investigated. Additionally, TPs were identified, which are formed in the direct reaction of the micropollutants with HOBr with and without subsequent ozonation. The results showed that even if the reactions of ozone with the substances should be favored bromide can highly influence the formation of TPs already at low concentrations. In summary, new TPs after the reaction with HOBr (and subsequent ozonation) could be postulated for ISO, METO and DCF. This underlines that the present water matrix can have a high influence on the formation of TPs and that these mechanisms need to be investigated further.

Matrix composition during ozonation of N-containing substances may influence the acute toxicity towards Daphnia magna.

Micropollutants reach the aquatic environment through wastewater treatment plant effluents. Ozonation, applied in wastewater treatment for micropollutants abatement, can yield transformation products (TP), which might be of ecotoxicological concern. Previous studies on TP formation were mostly performed in ultrapure water. However, the water matrix can have a substantial influence and lead to unpredictable yields of TPs with toxicological potential. In this study the acute toxicity (immobilization) of the parent substances (isoproturon and metoprolol) and also of available TPs of isoproturon, metoprolol and diclofenac towards Daphnia magna (D. magna) were investigated. Further, the acute toxicity of TP mixtures, formed during ozonation of isoproturon, metoprolol and diclofenac was evaluated in the following systems: in the presence of radical scavengers (tert-butanol and dimethyl sulfoxide) and in the presence of hypobromous acid (HOBr), a secondary oxidant in ozonation. For all tested substances and TP standards, except 2,6-dichloroaniline (EC50 1.02 mg/L (48 h)), no immobilization of D. magna was detected. Ozonated pure water and wastewater did not show an immobilization effect either. After ozonation of diclofenac in the presence of dimethyl sulfoxide 95% (48 h) of the daphnids were immobile. Ozonation of parent substances, after the reaction with HOBr, showed no effect for isoproturon but a high effect on D. magna for diclofenac (95% immobilization (48 h)) and an even higher effect for metoprolol (100% immobilization (48 h)). These results emphasize that complex water matrices can influence the toxicity of TPs as shown in this study for D. magna.

Determination of free chlorine based on ion chromatography-application of glycine as a selective scavenger.

Free available chlorine (FAC) is the most widely used chemical for disinfection and in secondary disinfection; a minimum chlorine residual must be present in the distribution system. FAC can also be formed as an impurity in ClO2 production as well as a secondary oxidant in the ClO2 application, which has to be monitored. In this study, a new method is developed based on the reaction of FAC with glycine in which the amine group selectively scavenges FAC and the N-chloroglycine formed can be measured by ion chromatography with conductivity detector (IC-CD). Utilizing IC for N-chloroglycine measurement allows this method to be incorporated into routine monitoring of drinking water anions. For improving the sensitivity, IC was coupled with post-column reaction and UV detection (IC-PCR-UV), which was based on iodide oxidation by N-chloroglycine resulting in triiodide. The method performance was quantified by comparison of the results with the N,N-diethyl-p-phenylenediamine (DPD) method due to the unavailability of an N-chloroglycine standard. The N-chloroglycine method showed limits of quantification (LOQ) of 24 µg L-1 Cl2 and 13 µg L-1 Cl2 for IC-CD and IC-PCR-UV, respectively. These values were lower than those of DPD achieved in this research and in ultrapure water. Measurement of FAC in the drinking water matrix showed comparable robustness and sensitivity with statistically equivalent concentration that translated to recoveries of 102% for IC-CD and 105% for IC-PCR-UV. Repeatability and reproducibility performance were enhanced in the order of DPD, IC-CD, and IC-PCR-UV. Measurement of intrinsic FAC in the ClO2 application revealed that the N-chloroglycine method performed considerably better in such a system where different oxidant species (ClO2, FAC, chlorite, etc.) were present.

Ozonation of Sitagliptin: Removal Kinetics and Elucidation of Oxidative Transformation Products.

Due to the increasing use and high excretion rates, high quantities of the antidiabetic drug sitagliptin (STG) enter wastewater treatment plants (WWTPs). In conventional biological treatment, only a moderate removal was achieved, and thus, STG can be detected in WWTP effluents with concentrations in the higher ng/L range. Ozonation is a widely discussed technique for advanced wastewater treatment. In lab-scale experiments, STG showed pH-dependent removal kinetics with a maximum apparent rate constant of k ∼1 × 104 M-1 s-1 at pH ≥ 9. With an apparent rate constant of kO3 = (1.8 ± 0.7) × 103 M-1 s-1 at pH 8, STG can be considered to be readily degraded by ozonation of WWTP effluents. Ozone attacks the primary amine moiety of STG, leading to nitro-STG (TP 437) (the primary amine moiety is transformed into a nitro group). Furthermore, a diketone (TP 406) was formed, which can be further degraded by ozone. Lab-scale and pilot-scale experiments on ozonation of WWTP effluents confirmed that the ozone attack of STG was incomplete even at high ozone doses of 1.7 and 0.9 mg O3/mg DOC, respectively. These experiments confirmed that nitro-STG was formed as the main TP in the wastewater matrix. Two other TPs, TP 421c and TP 206b, were also detected, albeit with low intensities.

Effect of ozone stress on the intracellular metabolites from Cobetia marina.

A GCxGC-MS system was employed with a non-polar × mid-polar column set for the metabolic non-target analysis of Cobetia marina, the model bacteria for marine biofouling. C. marina was treated with ozone to investigate the intracellular metabolic state change under oxidative stress. A minimal inhibitory concentration test was involved to guarantee that the applied ozone dosages were not lethal for the cells. In this study, non-target analyses were performed to identify the metabolites according to the NIST database. As a result, over 170 signals were detected under normal living conditions including 35 potential metabolites. By the comparison of ozone-treated and non-treated samples, five compounds were selected to describe observed trends of signals in the contour plots. Oleic acid exhibited a slight growth by increasing ozone dosage. In contrast, other metabolites such as the amino acid L-proline showed less abundance after ozone treatment, which was more evident once ozone dosage was raised. Thus, this work could provide a hint for searching for up/downregulating factors in such environmental stress conditions for C. marina. Graphical abstract.

Carbon Isotope Fractionation of Substituted Benzene Analogs during Oxidation with Ozone and Hydroxyl Radicals: How Should Experimental Data Be Interpreted?

Oxidative processes frequently contribute to organic pollutant degradation in natural and engineered systems, such as during the remediation of contaminated sites and in water treatment processes. Because a systematic characterization of abiotic reactions of organic pollutants with oxidants such as ozone or hydroxyl radicals by compound-specific stable isotope analysis (CSIA) is lacking, stable isotope-based approaches have rarely been applied for the elucidation of mechanisms of such transformations. Here, we investigated the carbon isotope fractionation associated with the oxidation of benzene and several methylated and methoxylated analogs, namely, toluene, three xylene isomers, mesitylene, and anisole, and determined their carbon isotope enrichments factors (εC) for reactions with ozone (εC = -3.6 to -4.6 ‰) and hydroxyl radicals (εC = 0.0 to -1.2‰). The differences in isotope fractionation can be used to elucidate the contribution of the reactions with ozone or hydroxyl radicals to overall transformation. Derivation of apparent kinetic isotope effects (AKIEs) for the reaction with ozone, however, was nontrivial due to challenges in assigning reactive positions in the probe compounds for the monodentate attack leading to an ozone adduct. We present several options for this step and compare the outcome to quantum chemical characterizations of ozone adducts. Our data show that a general assignment of reactive positions for reactions of ozone with aromatic carbons in ortho-, meta-, or para-positions is not feasible and that AKIEs of this reaction should be derived on a compound-by-compound basis.

Development of an LC-MS method for determination of nitrogen-containing heterocycles using mixed-mode liquid chromatography.

N-containing heterocycles (NCHs) are largely used as precursors for pharmaceuticals and can enter the environment. Some NCHs have been shown to be toxic, persistent, and very mobile in the environment. Thus, they have received increasing attention in the past years. However, the analysis of these polar compounds in environmental samples is still a challenge for liquid chromatography. This paper investigates the use of mixed-mode liquid chromatography (MMLC), which has reversed-phase and ion exchange characteristics for measurements of NCHs in water. NCHs with low pKa (i.e., < 2.5) display mainly reversed-phase interactions (neutral species) with the stationary phase and those with higher pKa (i.e., > 5) interact by a mixture of reversed-phase/ion exchange/HILIC mechanism. It was also shown that the presented method performs well in the quantification of the majority of the selected NCHs in surface water with MDLs between 3 and 6 µg/L, a low matrix effect and recoveries in the range of 77-96% except for pyridazine exhibiting 32% were achieved. The method was successfully employed to follow the degradation of NCHs in ozonation.

Polycyclic aromatic hydrocarbons (PAHs) leachates from cigarette butts into water.

Cigarette butts (CBs) are the most common littered items in the environment and may contain high amounts of polycyclic aromatic hydrocarbons (PAHs) from incomplete tobacco leave burning. The potential relevance of PAHs stemming from CBs for aquatic systems remain unclear since to date there is no systematic study on PAHs leaching from CBs. Therefore, in this study the leaching concentrations of 16 EPA-PAHs (except benzo(ghi)perylene) in 3 different types of water were measured. The concentrations of ΣPAHs leachates from 4 h to 21 days ranged from 3.9 to 5.7, 3.3-5.5, and 3.0-5.0 µg L-1 for deionized, tap, and river waters, respectively. For all contact times, there were no substantial differences of the leachate concentrations of PAHs among different water types. Lighter PAHs had the highest concentrations among the detected PAHs and they were detected in the leachates already after 4 h. Concentrations of indeno(1,2,3-cd)pyrene, and dibenz(a,h)anthracene were below the limit of detection in all water samples at different contact times. At all contact times naphthalene and fluorene had the highest concentrations among the studied PAHs. Tap and river water samples with addition of sodium azide as chemical preservative contained significantly higher concentration of ΣPAHs. Our leaching data showed that leached concentrations of PAHs exceeded the Water Framework Directive (WFD) standards and considering the number of CBs annually littered this may pose a risk to aquatic organisms and potentially also humans.

Ozonation of Tamoxifen and Toremifene: Reaction Kinetics and Transformation Products.

The oxidation of the two antiestrogenic pharmaceuticals tamoxifen and toremifene with ozone in water was investigated concerning kinetics, reaction pathway, and transformation product formation. For both compounds a high dependency of second order rate constants and products on pH was determined. In case of full protonation of the amine (cation) ozone attacks with a second order rate constant of 1.57 × 104 M-1 s-1 for tamoxifen and 4.37 × 103 M-1 s-1 for toremifene. The neutral tertiary amine has an unexpected high second order rate constant of 3.17 × 108 M-1 s-1 for tamoxifen and 1.46 × 108 M-1 s-1 for toremifene. For the reaction of ozone and the tertiary amine only N-oxide formation was observed. p Ka values for tamoxifen (9.49 ± 0.22) and toremifene (9.57 ± 0.22) can be reported based on experimental data. Eight transformation products (TPs) were observed and identified based on MS/MS spectra or a reference standard. Products observed derived from Criegee reaction and hydroxylation as well as N-oxide formation. Further TPs from reactions with TAM products were combinations of N-oxides, Criegee products and hydroxylation products. Thus, reaction pathways can be derived and primary and secondary TPs distinguished for the first time.

Ecotoxicological effects prior to and after the ozonation of tamoxifen.

The endocrine disrupting micropollutant tamoxifen can induce several effects on aquatic organisms. It is introduced into the environment mainly by wastewater treatment plant effluents. To reduce the discharge of micropollutants into surface waters, ozonation can be used as additional wastewater treatment option. For only few transformation products (TPs) formed by ozonation ecotoxicological data are available. To enable an initial estimation of ecotoxicological potentials of the TPs formed after the ozonation of tamoxifen, acute toxicity (immobilization) to Daphnia magna and green algae growth inhibition using Desmodesmus subspicatus were determined for several ozone doses spiked at pH 3 and pH 7. The initial immobilization of D. magna by tamoxifen was not further observed after ozonation. In contrast, the green algae growth inhibition increased due to ozonation of tamoxifen. Overall, five transformation products were observed. For three TPs, positive correlations of green algae growth inhibition and peak area were determined, whereas two TPs do not induce the residual effects. Based on our observations, TP 270 can be assumed as most potent of the formed TPs concerning green algae growth inhibition. Since the effect is not induced by formed N-oxides, green algae growth inhibition could be reduced by sufficient ozone exposure during wastewater treatment.

Chlorine Dioxide-Pollutant Transformation and Formation of Hypochlorous Acid as a Secondary Oxidant.

Chlorine dioxide (ClO2) has been used as a disinfectant in water treatment for a long time, and its use for micropollutant abatement in wastewater has recently been suggested. Surprisingly, a mechanistic understanding of ClO2 reactions in (waste)water matrices is largely lacking. The present study contributes to this mechanistic understanding by performing a detailed investigation of ClO2 reactions with organic matter using phenol as a surrogate for reactive phenolic moieties. A concept for indirectly determining HOCl using 2- and 4-bromophenol was developed. The reaction of phenol with ClO2 formed chlorite (62 ± 4% per ClO2 consumed) and hypochlorous acid (HOCl) (42 ± 3% per ClO2 consumed). The addition of ClO2 to wastewater (5 × 10-5 M ClO2) resulted in 40% atenolol and 47% metoprolol transformation. The presence of the selective HOCl scavenger glycine largely diminished their transformation, indicating that atenolol and metoprolol were transformed by a fast reaction with HOCl (e.g., k (atenolol + HOCl) = 3.5 × 104 M-1 s-1) that formed in ClO2 reactions with the wastewater matrix. The formation of HOCl may thus increase the number of transformable micropollutants in ClO2 applications. However, chlorine related byproducts may also be formed.