Degradation Of Iopamidol Research Articles

The solar/chlorine system degradation of iopamidol: Roles of reactive species, degradation pathway, and toxicity

The study systematically examined the changing trends of the percentage contributions of reactive species to the degradation of Iopamidol (IPM) under various conditions in the solar/chlorine system. Results showed that compared with chlorine alone and solar radiation system, the solar/chlorine system had an obvious effect on the degradation of IPM under control experiment conditions. HO• and reactive chlorine species played major roles in the apparent pseudo-first-order rate constants of IPM degradation (kobs). The increase of oxidant dosage significantly promoted the steady-state concentration of RCS and the contributions of those to kobs. The concentrations of various radicals at pH 9 were lower than those of at pH 5, while only the percentage contribution of ClO• on kobs was increased. The presence of Cl- could increase the steady-state concentration of Cl•, which further promoted the kobs. NOM would significantly reduce the steady-state concentration of ClO• and Cl•, which leads to a significant increase in the percentage contribution of Cl2−• to kobs, indicating the important role of Cl2−• on organic removal in real water. HCO3-/CO32- had almost no effect on kobs. The degradation products of IPM were identified through HPLC-MS, and the Fukui function was employed to ascertain the sites of degradation, which were formulated by deiodination reactions and the production of organic radicals. According to structure Activity Relationships Program v.2.2 and acute toxicological tests, byproducts did not exhibit significant toxicity. The findings illustrate that the solar/chlorine system is effective in decomposing IPM into non-toxic and non-hazardous small molecules, with potential applications.

Degradation of iopamidol in the permanganate/sulfite process: Evolution of iodine species and effect on the subsequent formation of disinfection by-products

Permanganate/sulfite (Mn(VII)/S(IV)) process is a promising pre-oxidation technology for sequestering the emerging organic contaminants in drinking water treatment plant. Iopamidol (IPM), a representative of iodinated X-ray contrast media, has been widely detected in water sources and has the risk of forming iodinated disinfection byproducts (I-DBPs) in water treatment system. In this study, we investigated the evolution of iodine species during the IPM degradation by the Mn(VII)/S(IV) process and its effect on the subsequent formation of I-DBPs during chlorination at pH 7.0 and 8.0. IPM could be effectively degraded in the Mn(VII)/S(IV) process at environmentally relevant pH (pH 7.0 and 8.0). The results of quenching and competitive oxidation kinetic experiments revealed that SO4·– was the major reactive oxidizing species contributing to the degradation of IPM whereas the contributions of HO· and reactive manganese species were negligible in the Mn(VII)/S(IV) process. I– and IO3– were generated while no HOI was detected during the degradation of IPM in the Mn(VII)/S(IV) process. The effects of IPM oxidation by Mn(VII)/S(IV) on the subsequent formation of chlorinated disinfection by-products (Cl-DBPs) during chlorination were related to the category of Cl-DBPs. The pre-oxidation of IPM by Mn(VII)/S(IV) resulted in the generation of I-DBPs during the disinfection process although no I-DBPs were detected if no pre-oxidation was applied. The finding of this study suggested that attention should be paid to the toxicity of DBPs when water containing iodinated organic contaminants is treated by Mn(VII)/S(IV) process or other pre-oxidation technologies.

Fe3+-enhanced zero valent iron/peroxymonosulfate (ZVI/PMS) process for the transformation of iopamidol during coagulation and reduction of iodinated disinfection by-products

The traditional coagulation process in drinking water treatment cannot effectively remove the organic precursors of highly toxic iodinated disinfection by-products (I-DBPs). This study proposes a combination of zero-valent iron (ZVI) and peroxymonosulfate (PMS) to remove the organic precursor of I-DBPs during the coagulation stage. This study investigated the degradation of iopamidol (IPM), a typical organic precursor of I-DBPs, by the combination of ZVI/peroxymonosulfate (PMS) and the influence on the generation of I-DBPs during disinfection. IPM was effectively decomposed by ZVI/PMS, because of the formation of hydroxyl (HO•) and sulfate (SO4•−) radicals. SO4•− was a major contributor (>64.7 %) to the degradation. The anions (Cl− and SO42−) in the conventional coagulants have a weak effect on the removal of IPM by the ZVI/PMS process, while the common cations (Fe3+) further enhance the removal of IPM by the ZVI/PMS process. The formation of I-THMs was obviously decreased during the chlorination of IPM in the presence of the ZVI/PMS process (14.4 μg/L) compared to that in the presence of the ZVI process (258.1 μg/L) and the chlorination alone process (29.7 μg/L). The formation of I-THMs was increased by more than 1.7-fold in the presence of natural organic matter (NOM). The presence of Fe3+ further reduced the formation of I-DBPs to below the limit of quantitation (LOQ). Therefore, it is feasible to use the ZVI/PMS process to degrade IPM in the coagulation stage of drinking water treatment, and it can also reduce the I-DBPs formed by subsequent disinfection.

Efficient degradation and deiodination of iopamidol by UV/sulfite process: Assessment of typical process parameters and transformation paths.

Iopamidol (IPM) is widely used in medical clinical examination and treatment and has immeasurable harm to the ecological environment. The combination of UV and sulfite (UV/sulfite) process was developed to degrade IPM in this study. In contrast to that almost no removal of IPM was observed under sulfite reduction alone, the UV/sulfite process could efficiently reductively degrade IPM with the observed rate constant (kobs) of 2.08 min-1, which was nearly 4 times that of UV irradiation alone. The major active species in the UV/sulfite process were identified as hydrated electrons (eaq-) by employing active species scavengers. The influence of the initial pH, sulfite dosage, IPM concentration, UV intensity and common water matrix were evaluated. The degradation of IPM reached nearly 100% within only 2.5 min at pH 9, and kobs increased at higher initial sulfite dosages and greater UV intensities. HCO3- had a limited effect on the degradation of IPM, while humic acid (HA) was found to be a strong inhibitor in the UV/sulfite process. With the synergistic action of UV/sulfite, most of the iodine in IPM was found to release in the form of iodide ions (up to approximately 98%), and a few formed iodide-containing organic compounds, reducing significantly the toxicity of degradation products. Under direct UV irradiation and free radical reduction (mainly eaq-), 15 transformation intermediates of IPM were produced by amide hydrolysis, deiodination, hydroxyl radical addition and hydrogen abstraction reactions, in which free radical attack accounted for the main part. Consequently, the UV/sulfite process has a strong potential for IPM degradation in aquatic environments.

Degradation of iopamidol by UV365/NaClO: Roles of reactive species, degradation mechanism, and toxicology

The degradation of iopamidol (IPM) was investigated using a UV365/NaClO system. The reactive species (HO·, ClO·, ozone, Cl·, and Cl2−·) in the system were identified, and the changing trends of the percentage contributions of these reactive species to IPM removal under various conditions were systematically evaluated. The results showed that ClO· and HO· played the most significant roles in the apparent pseudo-first-order rate constants of IPM degradation (kobs, min−1) in the control experiment, and their percentage contributions to kobs were 41.31% and 34.45%, respectively. In addition, Cl· and Cl2−· together contributed 22% to the kobs. Furthermore, the contribution of ozone to the IPM removal could be neglected. The concentrations of these species increased significantly when the concentration of NaClO was increased from 50 µM to 200 µM, while the percentage contribution of ClO· to kobs was greatly increased. The concentrations and percentage contributions of HO· and ClO· decreased significantly as the solution pH increased from 5 to 9, with Cl2−· playing a greater role in the degradation of IPM under alkaline conditions. While Cl− or HCO3−/CO32− significantly promoted the generation of Cl2−· or CO3−·, neither had an obvious effect on kobs, suggesting that Cl2−· and CO3−· should have a certain reactivity with IPM. Compared with that of Cl2−·, the percentage contribution of ClO· and Cl· to kobs was more likely to be inhibited by NOM. In addition, the organic and inorganic oxidation products of IPM were detected. The oxidation mechanisms of IPM degradation in the UV365/NaClO system, such as the H-extraction reaction, deiodination, substitution reaction, amide hydrolysis, and amine oxidation, were proposed according to the obtained 15 organic products. No effect on acute toxicity towards Vibrio fischeri and Photobacterium phosphoreum was detected during the oxidation of IPM by the UV365/NaClO system. Furthermore, the engineering feasibility of the oxidation system was demonstrated, by the effective degradation of IPM in actual water. However, HOI rapidly accumulated during the removal of IPM in the UV365/NaClO system, which poses certain environmental risks and will needs to be investigated.

A comparative study of free chlorine and peroxymonosulfate activated by Fe(II) in the degradation of iopamidol: Mechanisms, density functional theory (DFT) calculatitons and formation of iodinated disinfection by-products

Both Fe(II)/free chlorine (Fe(II)/FC) and Fe(II)/peroxymonosulfate (Fe(II)/PMS) have a faster reactive species formation rate than the classic Fenton process, so their efficiencies of removing pollutants are better than that of the Fenton process. In this study, we compared the differences in the mechanisms and kinetics of iopamidol (IPM) degradation by Fe(II)/FC and Fe(II)/PMS. Although the production rate of reactive species of the two processes is at the same level (104 M−1 s−1), the Fe(II)/PMS process performed better regarding IPM removal. Reactive chlorine species (RCS) were the major contributor to the degradation of IPM (73.8%) by Fe(II)/FC, and hydroxyl radicals (HO•) and sulfate radicals (SO4•–) contributed 50.7% and 49.3% to the degradation of IPM by Fe(II)/PMS, respectively. Fe(IV) showed low contributions (<0.1%) to the degradation of IPM during the Fe(II)/FC and Fe(II)/PMS processes because of the low values of kFe(IV), IPM ((25 ± 5) M−1 s−1) and the low steady-state concentration of Fe(IV) in the Fe(II)/FC ((5.1 ± 0.7) × 10−8 M) and Fe(II)/PMS processes ((2.2 ± 0.09) × 10−8 M) at pH 3. Based on density functional theory (DFT) calculations and the MS results, the transformation pathway of IPM has been confirmed to mainly occur on chains B and B’ and the iodine group in between. The formation of disinfection by-products (DBPs) indicates that the Fe(II)/PMS process has lower environmental hazards. In general, we should pay more attention to the type of active species to evaluate the Fenton-like process. This study provides a basis for choosing a suitable alternative to the Fenton process and understanding the process in the Fenton-like procedure.

Degradation of iopamidol by silicate-based microfiltration membrane activated peroxymonosulfate in aqueous solution: Efficiency, mechanism and degradation pathway

Iopamidol (IPM) was frequently detected in drinking water and effluents from wastewater treatment plants (WWTPs). A silicate-based microfiltration membrane (SFM) was successfully synthesized using silicate cement as raw material and pore-forming agent. In this study, peroxymonosulfate (PMS) was activated by SFM for the first time to effectively degrade and mineralize IPM. The removal efficiency and mineralization rate of IPM were 99.7% and 49.5% respectively within 30 min in the SFM/PMS process, which were higher than those obtained by PMS oxidation only (12.8% and 1.26%) and SFM adsorption (negligible). The effects of solution pH, PMS dosage, reaction temperature, natural organic matter (NOM), chloride ion (Cl−), bicarbonate (HCO− 3), and water matrixes on the degradation of IPM were systematically evaluated. Based on radical inhibition examinations and X-ray photoelectron spectroscopy (XPS) analysis, the potential activation mechanism was elucidated. It was found that the Fe(II) and alkaline hydration products on the surface of SFM could promote the activation of PMS. Radical scavenging tests and electron spin resonance (ESR) experiments suggested that hydroxyl radicals (•OH), sulfate radicals (SO4·−), singlet oxygen (1O2) and superoxide radicals (O2·−) generated in SFM/PMS system played a critical role for IPM degradation. Finally, eleven intermediates in the degradation process of IPM were identified and five degradation pathways were proposed, mainly including hydroxyl oxidation, amide hydrolysis, amino oxidation, hydroxyl substitution and dehydroxylation. The results show that the SFM/PMS process with its excellent catalytic activity is a promising strategy for effectively removing and mineralizing organic contaminants.

Formation and control of disinfection by-products from iodinated contrast media attenuation through sequential treatment processes of ozone-low pressure ultraviolet light followed by chlorination

Different groups of disinfection by-products (DBPs) were studied through the degradation of iopamidol by the sequential oxidation process of ozone-low pressure ultraviolet light (O3-LPUV) followed by chlorination. This paper investigates the attenuation of iopamidol under this sequential treatment and the effect of chlorine contact time (30 min versus 3 days) to control the formation potential of DBPs: trihalomethanes (THMs), haloacetonitriles (HANs) and haloacetamides (HAMs). Thirty target DBPs among the 9 iodinated-DBPs (I-DBPs), were monitored throughout the sequential treatment. Results showed that O3-LPUV removed up to 99% of iopamidol, while ozone and LPUV alone removed only 90% and 76% respectively. After chlorine addition, O3-LPUV yielded 56% lower I-DBPs than LPUV. Increasing chlorine contact time resulted in higher concentrations of all DBP groups (THMs, HANs, and HAMs), with the exception of I-DBPs. One new iodinated-haloacetamide, namely chloroiodoacetamide (CIACM) and one iodoacetonitrile (IACN) were detected. These results suggest the iodine incorporated in iopamidol may be a precursor for iodinated-nitrogenous-DBPs, which are currently not well studied.

Iodinated trihalomethanes formation in iopamidol-contained water during ferrate/chlor(am)ination treatment

Iopamidol is a commonly used iodinated X-ray contrast media in medical field, and its residue in water can react with disinfectants to form highly toxic iodinated disinfection by-products (I-DBPs). This study investigated the degradation of iopamidol and formation of DBPs, especially iodinated trihalomethanes (I-THMs), during ferrate (Fe(VI)) pre-oxidation and subsequent chlor(am)ination under raw water background. It was found that iopamidol degradation efficiency in raw water by Fe(VI) at pH 9 could reach about 80%, which was much higher than that at pH 5 and pH 7 (both about 25%). With Fe(VI) dose increasing, iopamidol removal efficiency increased obviously. During the iopamidol degradation by Fe(VI), IO3− was the dominant product among all the iodine species. After pre-treated by Fe(VI), yields of THM4 and I-THMs can be reduced in subsequent chlor(am)ination. Besides, pH was a crucial factor for Fe(VI) pre-oxidition controlling DBPs. With the pH increasing from 5 to 9, the yield of THM4 kept increasing in subsequent chlorination but showed the highest amount at pH 6 in subsequent chloramination. The yield of I-THMs increased first and then decreased with the increase of pH in both subsequent chlorination and chloramination. I-THM concentrations in chlorinated samples were lower than chloraminated ones under acidic conditions but became higher under neutral and alkaline conditions. The total CTI of THMs during Fe(VI)-chloramination was higher than that during Fe(VI)-chlorination under neutral condition, but sharply decreased under alkaline conditions. In summary, Fe(VI)-chloramination subsequent treatment under alkaline conditions should be an effective method for iopamidol removal and DBP control.

Sulfite enhanced transformation of iopamidol by UV photolysis in the presence of oxygen: Role of oxysulfur radicals

UV/sulfite process in the absence of oxygen was previously applied as an advanced reduction process for the removal of many halogenated organics and inorganics in water and wastewater. Here, it was found that UV/sulfite process in the presence of oxygen could act as an advanced oxidation process. Specifically, the oxysulfur radicals (including sulfate radical (SO4·−) and sulfite/peroxomonosulfate radicals (SO3·−/SO5·−)) played important roles on the degradation of iopamidol (IPM) as a typical iodinated contrast media (ICM). Furthermore, the contribution of SO4·− on IPM removal gradually increased as pH increased from 5 to 7 and that of SO3·−/SO5·− decreased. Besides, all water quality parameters (i.e., chloride (Cl−), iodide (I−) and natural organic matter (NOM)) investigated here exhibited inhibitory effect on IPM removal. Three inorganic iodine species (i.e., I−, reactive iodine species and iodate (IO3−)) were detected in UV/sulfite process in the presence of oxygen, while only I− was detected in that without oxygen. During UV/sulfite/ethanol, UV photolysis and UV/peroxydisulfate (PDS)/tert-butyl alcohol (TBA) processes, thirteen transformation products including eleven deiodinated products of IPM were identified by ultra HPLC quadrupole time of flight-mass spectrometry (UPLC-Q-TOF-MS). Besides, these products generated by direct UV photolysis, SO4·− and SO3·−/SO5·− were further distinguished. The acute toxicity assay of Vibrio fischeri indicated that transformation products by UV/sulfite under aerobic conditions were less toxic than that by direct UV photolysis.

Transformation of iopamidol and atrazine by peroxymonosulfate under catalysis of a composite iron corrosion product (Fe/Fe3O4): Electron transfer, active species and reaction pathways

Cast iron pipes are commonly applied in drinking water distribution systems (DWDSs); peroxymonosulfate (PMS) is a promising alternative for drinking water disinfection; organic micropollutants is still present in drinking water after waterworks' treatment. However, iron corrosion products may affect the reactions between a disinfectant and organic micropollutants. The study investigated the transformation of iopamidol (IPM) and atrazine (ATZ) by PMS under the catalysis of a composite iron corrosion product (Fe/Fe3O4). The pseudo-first-order rate constants (k) for the degradation of IPM and ATZ were 1.47 and 1.03 min-1, respectively. Electron paramagnetic resonance (EPR) experiments indicated that PMS was effectively activated to yield sulfate radical (SO4•-) and hydroxyl radical (HO•), mainly via the reduction by Fe component, dissolved Fe2+ and generated Feocta2+. SO4•- contributed more than HO• to the degradation of IPM and ATZ, and the radical yield achieved 0.97 mol/mol. The k values reached maximum with Fe/Fe3O4 and PMS doses of 2.5 g L-1 and 25 mg L-1, respectively. The optimum mass fraction of Fe3O4 in Fe/Fe3O4 (MFmag) and pH were 10% and 7.0, respectively. The k values increased with increasing temperature, while decreased in the presence of water matrix. Most of the iodine released from IPM was oxidized to IO3-, and NH4+ was the dominant species of nitrogen released from ATZ. The identification of transformation intermediates showed that the radical chain reactions of IPM was mainly initiated from single electron transfer and radical adduct formation, while those of ATZ was primarily initiated from hydrogen atom abstraction and radical adduct formation.

Comparison of UV-induced AOPs (UV/Cl2, UV/NH2Cl, UV/ClO2 and UV/H2O2) in the degradation of iopamidol: Kinetics, energy requirements and DBPs-related toxicity in sequential disinfection processes

The UV-induced advanced oxidation processes (AOPs, including UV/Cl2, UV/NH2Cl, UV/ClO2 and UV/H2O2) degradation kinetics and energy requirements of iopamidol as well as DBPs-related toxicity in sequential disinfection were compared in this study. The photodegradation of iopamidol in these processes can be well described by pseudo-first-order model and the removal efficiency ranked in descending order of UV/Cl2 > UV/H2O2 > UV/NH2Cl > UV/ClO2 > UV. The synergistic effects could be attributed to diverse radical species generated in each system. Influencing factors of oxidant dosage, UV intensity, solution pH and water matrixes (Cl−, NH4+ and nature organic matter) were evaluated in detail. Higher oxidant dosages and greater UV intensities led to bigger pseudo-first-order rate constants (Kobs) in these processes, but the pH behaviors exhibited quite differently. The presence of Cl−, NH4+ and nature organic matter posed different effects on the degradation rate. The parameter of electrical energy per order (EE/O) was adopted to evaluate the energy requirements of the tested systems and it followed the trend of UV/ClO2 > UV > UV/NH2Cl > UV/H2O2 > UV/Cl2. Pretreatment of iopamidol by UV/Cl2 and UV/NH2Cl clearly enhanced the production of classical disinfection by-products (DBPs) and iodo-trihalomethanes (I-THMs) during subsequent oxidation while UV/ClO2 and UV/H2O2 exhibited almost elimination effect. From the perspective of weighted water toxicity, the risk ranking was UV/NH2Cl > UV/Cl2 > UV > UV/H2O2 > UV/ClO2. Among the discussed UV-driven AOPs, UV/Cl2 was proved to be the most cost-effective one for iopamidol removal while UV/ClO2 displayed overwhelming advantages in regulating the water toxicity associated with DBPs, especially I-THMs. The present results could provide some insights into the application of UV-activated AOPs technologies in tradeoffs between cost-effectiveness assessment and DBPs-related toxicity control of the disinfected waters containing iopamidol.

Accelerated oxidation of iopamidol by ozone/peroxymonosulfate (O3/PMS) process: Kinetics, mechanism, and simultaneous reduction of iodinated disinfection by-product formation potential

Iopamidol (IPM) is a potential source of toxic iodinated byproducts (I-DBPs) during water disinfection. In this work, we determined the kinetics and mechanism of degradation of IPM by a combination of ozone (O3) and peroxymonosulfate (PMS, HSO5−), and assessed its effect on the formation of iodinated trihalomethanes (I-THMs) during chlorination treatment. The degradation of IPM was accelerated by the O3/PMS process, and the hydroxyl (HO•) and sulfate (SO4•−) radicals were major contributors to the degradation. Using identification of the second order reaction rate between SO4•− and IPM (kSO4•−, IPM = 1.6 × 109 M−1 s−1), the contribution of HO• to the degradation was determined to be 78.3%. The degradation of IPM was facilitated by pH > 7, and natural organic matter (NOM) and alkalinity had limited effects on the degradation of IPM in the O3/PMS process. The transformation products of IPM were determined and inferred by QTOF-MS/MS, and the degradation pathways were elucidated. These include amide hydrolysis, amino oxidation, hydrogen abstraction, deiodination, and hydroxyl radical addition. Interestingly, oxidation of IPM by O3/PMS also decreased its potential for formation of I-THMs. After oxidation of IPM, the I-THMs formed from 5-μΜ IPM decreased from 14.7 μg L−1 to 3.3 μg L−1 during chlorination. Although the presence of NOM provided the precursor of I-THMs during chlorination of IPM, the O3/PMS process decreased I-THMs formation by 71%, because oxidation of released iodide into iodate effectively inhibited I-THMs formation. This study provides a new approach for the accelerated degradation of IPM and control of the formation of I-DBPs.

Degradation of iopamidol by three UV-based oxidation processes: Kinetics, pathways, and formation of iodinated disinfection byproducts

In this study, the degradation kinetics of iopamidol (IPM) by three different UV-based oxidation processes including UV/hydrogen peroxide (H2O2), UV/persulfate (PDS) and UV/chlorine (NaClO) were examined and the potential formation of iodinated disinfection byproducts (I-DBPs) in these processes followed by sequential chlorination was comparatively investigated. Increasing pH led to the decrease of IPM degradation rate in UV/NaClO, while it showed negligible impact in UV/PDS and UV/H2O2. Common background constituents such as chloride ions (Cl−), carbonate (HCO3−) and natural organic matter (NOM) inhibited IPM degradation in UV/H2O2 and UV/PDS, while IPM degradation in UV/NaClO was only suppressed by NOM but not Cl− and HCO3−. The differences in transformation products of IPM treated by hydroxyl radical (HO*), sulfate radical (SO4*-), as well as Cl2*- and ClO* generated in these processes, respectively, were also analyzed. The results suggested that hydroxyl radical (HO*) preferred to form hydroxylated derivatives. Sulfate radical (SO4*-) preferred to oxidize amino group of IPM to nitro group, while Cl2*- and ClO* favored the generation of chlorine-containing products. Moreover, specific I-DBPs (i.e., iodoform (IF) and monoiodacetic acid (MIAA)) were detected in the three processes followed by chlorination. The addition of NOM had little effect on IF formation of three processes, while MIAA formation decreased in all processes except UV/H2O2. Given that the formation of I-DBPs in UV/NaClO was less than those formed in the other two processes, UV/NaClO seems to be a more promising strategy for effectively removing IPM with alleviation of I-DBPs in treated water effluents.

Comparative investigation of X-ray contrast medium degradation by UV/chlorine and UV/H2O2

The degradation of iopamidol and diatrizoate sodium (DTZ) by UV/chlorine was carried out according to efficiency, mechanism, and oxidation products, and compared to that by UV/H2O2. The pseudo-first order rate (k′) of iopamidol and DTZ was accelerated by UV/chlorine compared to that by UV and chlorine alone. k′ of iopamidol and DTZ by UV/chlorine increased with increasing chlorine dosage. Both of iopamidol and DTZ could not be effectively removed by UV/H2O2 compared to that by UV/chlorine. Secondary radicals (Cl2− and ClO) rather than primary radicals (HO and Cl) were demonstrated to be mainly responsible for the enhanced removal of iopamidol and DTZ by UV/chlorine. The oxidation products of iopamidol and DTZ resulting from UV/chlorine and UV/H2O2 process were identified, and differences existed in the two systems. IO3− (the desired sink of I−) was the major inorganic product in the UV/chlorine process whereas I− was the predominant inorganic product in the UV/H2O2 process. The formation of chlorine-containing products during the degradation of iopamidol and DTZ by UV/chlorine was also observed. H-abstraction, additions, de-iodination were shared during the degradation of iopamidol by UV/chlorine and UV/H2O2. Neutral pH condition was preferred for the removal of iopamidol and DTZ by UV/chlorine. UV/chlorine could also be applied in real waters for the removal of iopamidol and DTZ.

Accelerated degradation of iopamidol in iron activated persulfate systems: Roles of complexing agents

As an environment-friendly activator, iron ions (Fe(II) and Fe(III)) have been extensively studied in homogeneous activation of persulfate (PS) to remove organic pollutants from water. However, the slow reduction of Fe(III) to Fe(II) and the subsequent low activation efficiency limit the wide applications of PS/Fe(II) or PS/Fe(III). In this study, the roles of four complexing agents, including gallic acid (GA), ethylene diamine tetraacetic acid, (S,S)-ethylenediamine-N,N′-disuccinic acid trisodium salt and citric acid in the activation of PS/Fe(III) were comparatively investigated with iopamidol (IPM) used as a model organic pollutant. Results indicate that GA was the most effective with an increase in the observed pseudo-first-order rate constant (kobs) by 9.2 folds for IPM degradation by PS/Fe(III). Through radical scavenger (ethanol and tert-butanol) tests and electron paramagnetic resonance analysis, HO and SO4− were identified to be responsible for the accelerated degradation of IPM, and HO played a more important role. Intrinsically, the promoted Fe(III) reduction and PS decomposition accelerated the degradation of IPM. The transformation by-products of IPM in the PS/Fe(III)/GA system were identified and potential degradation pathways were proposed. Besides, the accelerated degradation of other three organic pollutants (methyl orange, congo red, and diclofenac) further demonstrated the applicability of the PS/Fe(III)/GA system to water treatment.

Enhanced degradation of iopamidol by peroxymonosulfate catalyzed by two pipe corrosion products (CuO and δ-MnO2)

Peroxymonosulfate (PMS) is a promising alternative for drinking water disinfection; also many organic micropollutants may be present in drinking water sources nowadays. However, pipe corrosion products (PCPs) may impact the reactions between a disinfectant and organic micropollutants in water distribution systems. This study investigated iopamidol (IPM) degradation by PMS under catalysis of two PCPs (i.e., CuO and δ-MnO2). The pseudo-first-order rate constant of IPM degradation in the CuO/PMS system (CuPS) was 3.7 times of that in the δ-MnO2/PMS system (MnPS), with values of 0.218 and 0.059 min−1, respectively. Sulfate radical (SO4−) was the major contributor to IPM degradation in the CuPS, while hydroxyl radical (HO) also played an important role in the MnPS. The radical yield ratio was 0.89 and 0.69 mol/mol in the CuPS and MnPS, respectively. The IPM degradation rate increased with increasing PMS dose, and reached a maximum with a PCP dose of 1.0 and 1.5 g L−1 in the CuPS and MnPS, respectively. The highest degradation efficiency was achieved at pH 7.0 in the two systems. The water matrix (i.e., natural organic matter, alkalinity and chloride) had detrimental effects on IPM degradation to different degrees. The majority of the iodine released from IPM was oxidized to iodate (IO3−) and a small fraction of the initial total organic iodine was transformed to iodoform (CHI3). The IPM degradation by PMS mainly proceeded through two pathways: (1) amide hydrolysis of side chain A, amino oxidation, and amide hydrolysis of side chains B and B′ in sequence; and (2) deiodination reactions.

Transformation of iopamidol during chlorination.

The transformation of the iodinated X-ray contrast media (ICM) iopamidol, iopromide, iohexol, iomeprol, and diatrizoate was examined in purified water over the pH range from 6.5 to 8.5 in the presence of sodium hypochlorite, monochloramine, and chlorine dioxide. In the presence of aqueous chlorine, only iopamidol was transformed. All other ICM did not show significant reactivity, regardless of the oxidant used. Chlorination of iopamidol followed a second order reaction, with an observed rate constant of up to 0.87 M(-1) s(-1) (±0.021 M(-1) s(-1)) at pH 8.5. The hypochlorite anion was identified to be the reactive chlorine species. Iodine was released during the transformation of iopamidol, and was mainly oxidized to iodate. Only a small percentage (less than 2% after 24 h) was transformed to known organic iodinated disinfection byproducts (DBPs) of low molecular weight. Some of the iodine was still present in high-molecular weight DBPs. The chemical structures of these DBPs were elucidated via MSn fragmentation and NMR. Side chain cleavage was observed as well as the exchange of iodine by chlorine. An overall transformation pathway was proposed for the degradation of iopamidol. CHO cell chronic cytotoxicity tests indicate that chlorination of iopamidol generates a toxic mixture of high molecular weight DBPs (LC50 332 ng/μL).

Reductive and oxidative degradation of iopamidol, iodinated X-ray contrast media, by Fe(III)-oxalate under UV and visible light treatment

Iopamidol, widely employed as iodinated X-ray contrast media (ICM), is readily degraded in a Fe(III)-oxalate photochemical system under UV (350 nm) and visible light (450 nm) irradiation. The degradation is nicely modeled by pseudo first order kinetics. The rates of hydroxyl radical (OH) production for Fe(III)-oxalate/H2O2/UV (350 nm) and Fe(III)-oxalate/H2O2/visible (450 nm) systems were 1.19 ± 0.12 and 0.30 ± 0.01 μM/min, respectively. The steady-state concentration of hydroxyl radical (OH) for the Fe(III)-oxalate/H2O2/UV (350 nm) conditions was 10.88 ± 1.13 × 10−14 M and 2.7 ± 0.1 × 10−14 M for the Fe(III)-oxalate/H2O2/visible (450 nm). The rate of superoxide anion radical (O2−) production under Fe(III)-oxalate/H2O2/UV (350 nm) was 0.19 ± 0.02 μM/min with a steady-state concentration of 5.43 ± 0.473 × 10−10 M. Detailed product studies using liquid chromatography coupled to Q-TOF/MS demonstrate both reduction (multiple dehalogenations) and oxidation (aromatic ring and side chains) contribute to the degradation pathways. The reduction processes appear to be initiated by the carbon dioxide anion radical (CO2−) while oxidation processes are consistent with OH initiated reaction pathways. Unlike most advanced oxidation processes the Fe(III)-oxalate/H2O2/photochemical system can initiate to both reductive and oxidative degradation processes. The observed reductive dehalogenation is an attractive remediation strategy for halogenated organic compounds as the process can dramatically reduce the formation of the problematic disinfection by-products often associated with oxidative treatment processes.

UV and solar-based photocatalytic degradation of organic pollutants by nano-sized TiO2 grown on carbon nanotubes

A new photocatalyst based on nano-sized TiO2 supported on single wall carbon nanotubes (SWCNTs) with tailored photocatalytic properties upon irradiation by both UV and solar simulated light was successfully employed for the degradation of a mixture of 22 organic pollutants in both ultrapure water and real secondary wastewater effluent. First-order degradation rates showed that under UV irradiation nano-sized TiO2 supported on SWCNTs is much more effective than conventional Degussa P25 for degradation of iopamidol, iopromide, diatrizoic acid, diclofenac, triclosan and sulfamethoxazole in ultrapure water. For the remaining organics the degradation rates were comparable being in most of the cases Degussa P25 slightly more effective than nano-sized TiO2 supported on SWCNTs. Reactions performed in real secondary wastewater effluent showed a general reduction of degradation rates. Specifically, such a reduction was in the range 9–87% and 9–96% for the Degussa P25 and the nano-sized TiO2 supported on SWCNTs, respectively. Overall, the nano-sized TiO2 supported on SWCNTs under UV irradiation displayed comparable degradation rates with respect to convention Degussa P25. Under simulated solar irradiation the new prepared photocatalyst showed lower efficiency than Degussa P25 in ultrapure water. Such a gap was greatly reduced when the reactions were carried out in real secondary wastewater effluent. The nano-sized TiO2 supported on SWCNTs demonstrated to have the addition benefit to be easily removed from the aqueous solution by a mild centrifugation or a filtration step and, consequently, can be reused for a further photocatalytic treatment batch. Therefore, the obtained results showed that new photocatalyst based on nano-sized TiO2 supported on SWCNTs has proved to be a promising candidate to be used in a photocatalytic based-AOP and to be integrated with a biological step for the effective removal of emerging organic pollutants.