Removal of Iodine-Containing X-ray Contrast Media from Environment: The Challenge of a Total Mineralization.

Iodinated X-ray contrast media (ICM) as emerging micropollutants have attracted considerable attention in recent years due to their high detected concentration in water systems. It results in environmental issues partly due to the formation of toxic by-products during the disinfection process in water treatment. Consequently, various approaches have been investigated by researchers in order to achieve ICM total mineralization. This review discusses the different methods that have been used to degrade them, with special attention to the mineralization yield and to the nature of formed by-products. The problem of pollution by ICM is discussed in the first part dedicated to the presence of ICM in the environment and its consequences. In the second part, the processes for ICM treatment including biological treatment, advanced oxidation/reductive processes, and coupled processes are reviewed in detail. The main results and mechanisms involved in each approach are described, and by-products identified during the different treatments are listed. Moreover, based on their efficiency and their cost-effectiveness, the prospects and process developments of ICM treatment are discussed.

The interaction between iodinated X-ray contrast agents and macrocyclic GBCAs provides a signal enhancement in T1 -weighted MR images: Insights into the renal excretion pathways of Gd-HPDO3A and iodixanol in healthy mice.

PURPOSE: This work aims to investigate the supramolecular binding interactions that occur between iodinated X-ray contrast agents (CAs) and macrocyclic gadolinium (Gd)-based MRI contrast agents (GBCAs). This study provides some new insights in the renal excretion pathways of the two types of imaging probes. METHODS: The water-proton relaxivities (r1 ) of clinically approved macrocyclic and linear GBCAs have been measured in the presence of different iodinated X-ray contrast agents at different magnetic field strengths in buffer and in serum. The in vivo MRI and X-ray CT of mice injected with either Gd-HPDO3A or a Gd-HPDO3A + iodixanol mixture were then acquired to assess the biodistribution of the two probes. RESULTS: A significant increase in r1 (up to approximately 200%) was observed for macrocyclic GBCAs when measured in the presence of an excess of iodinated X-ray CAs (1:100 mol:mol) in serum. The co-administration of Gd-HPDO3A and iodixanol in vivo resulted in a marked increase in the signal intensity of the kidney regions in T1 -weighted MR images. Moreover, the co-presence of the two agents resulted in the extended persistence of the MRI signal enhancement, suggesting that the Gd-HPDO3A/iodixanol adduct was eliminated more slowly than the typical washing out of Gd-HPDO3A. CONCLUSIONS: The reported results show that it is possible to detect the co-presence of iodinated agents and macrocyclic GBCAs in contrast-enhanced MR images. The new information may be useful in the design of novel experiments toward improved diagnostic outcomes.

Efficient Degradation of Iopromide by Using Sulfite Activated with Mackinawite.

Iopromide (IOP), an iodinated X-ray contrast medium (ICM), is identified as a precursor to iodide disinfection byproducts that have high genotoxicity and cytotoxicity to mammals. ICM remains persistent through typical wastewater treatment processes and even through some hydroxyl radical-based advanced oxidation processes. The development of new technologies to remove ICMs is needed. In this work, mackinawite (FeS)-activated sulfite autoxidation was employed for the degradation of IOP-containing water. The experiment was performed in a 500 mL self-made temperature-controlled reactor with online monitoring pH and dissolved oxygen in the laboratory. The effects of various parameters, such as initial pH values, sulfite dosages, FeS dosages, dissolved oxygen, and inorganic anions on the performance of the treatment process have been investigated. Eighty percent of IOP could be degraded in 15 min with 1 g L-1 FeS, 400 µmol L-1 sulfite at pH 8, and high efficiency on the removal of total organic carbon (TOC) was achieved, which is 71.8% via a reaction for 1 h. The generated hydroxyl and oxysulfur radicals, which contributed to the oxidation process, were identified through radical quenching experiments. The dissolved oxygen was essential for the degradation of IOP. The presence of Cl- could facilitate IOP degradation, while NO3- and CO32- could inhibit the degradation process. The reaction pathway involving H-abstraction and oxidative decarboxylation was proposed, based on product identification. The current system shows good applicability for the degradation of IOP and may help in developing a new approach for the treatment of ICM-containing water.

The impact of iodinated X-ray contrast agents on formation and toxicity of disinfection by-products in drinking water.

The presence of iodinated X-ray contrast media (ICM) in source waters is of high concern to public health because of their potential to generate highly toxic disinfection by-products (DBPs). The objective of this study was to determine the impact of ICM in source waters and the type of disinfectant on the overall toxicity of DBP mixtures and to determine which ICM and reaction conditions give rise to toxic by-products. Source waters collected from Akron, OH were treated with five different ICMs, including iopamidol, iopromide, iohexol, diatrizoate and iomeprol, with or without chlorine or chloramine disinfection. The reaction product mixtures were concentrated with XAD resins and the mammalian cell cytotoxicity and genotoxicity of the reaction mixture concentrates was measured. Water containing iopamidol generated an enhanced level of mammalian cell cytotoxicity and genotoxicity after disinfection. While chlorine disinfection with iopamidol resulted in the highest cytotoxicity overall, the relative iopamidol-mediated increase in toxicity was greater when chloramine was used as the disinfectant compared with chlorine. Four other ICMs (iopromide, iohexol, diatrizoate, and iomeprol) expressed some cytotoxicity over the control without any disinfection, and induced higher cytotoxicity when chlorinated. Only iohexol enhanced genotoxicity compared to the chlorinated source water.

A sensitive multi-residue method for the determination of 35 micropollutants including pharmaceuticals, iodinated contrast media and pesticides in water.

A sensitive, multi-residue method using solid-phase extraction followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed to determine a representative group of 35 analytes, including corrosion inhibitors, pesticides and pharmaceuticals such as analgesic and anti-inflammatory drugs, five iodinated contrast media, ß-blockers and some of their metabolites and transformation products in water samples. Few other methods are capable of determining such a broad range of contrast media together with other analytes. We studied the parameters affecting the extraction of the target analytes, including sorbent selection and extraction conditions, their chromatographic separation (mobile phase composition and column) and detection conditions using two ionisation sources: electrospray ionisation (ESI) and atmospheric pressure chemical ionisation (APCI). In order to correct matrix effects, a total of 20 surrogate/internal standards were used. ESI was found to have better sensitivity than APCI. Recoveries ranging from 79 to 134 % for tap water and 66 to 144 % for surface water were obtained. Intra-day precision, calculated as relative standard deviation, was below 34 % for tap water and below 21 % for surface water, groundwater and effluent wastewater. Method quantification limits (MQL) were in the low ng L(-1) range, except for the contrast agents iomeprol, amidotrizoic acid and iohexol (22, 25.5 and 17.9 ng L(-1), respectively). Finally, the method was applied to the analysis of 56 real water samples as part of the validation procedure. All of the compounds were detected in at least some of the water samples analysed. Graphical Abstract Multi-residue method for the determination of micropollutants including pharmaceuticals, iodinated contrast media and pesticides in waters by LC-MS/MS.

Study of the retention behavior of iodinated X-ray contrast agents in hydrophilic interaction liquid chromatography, comparing bare silica and zwitterionic stationary phases.

Iodinated X-ray contrast media are the most widely used pharmaceuticals for intravascular administration in X-ray diagnostic procedures. The increasing concern of the fate of these compounds into the environment has led to the development of analytical methods to determine them. However, these methods present problems due to the polar character of these analytes. In this paper, hydrophilic interaction LC is presented as an alternative technique. The retention of iodinated X-ray contrast media was studied in two bare silica phases with different particle designs (i.e. porous and Fused Core™) and a zwitterionic sulfoalkylbetaine phase. The effect of the most important parameters of the mobile phase was studied for each stationary phase. It was observed that optimal mobile phase conditions included buffers with a high buffering capacity. Additionally, the retention mechanisms involved were studied in order to provide some insight into the possible occurring interactions. The contributions of partition and adsorption and the effect of the temperature on the retention of analytes were evaluated on all of the stationary phases.

Graphene-based nanomaterials for adsorption of iodinated X-ray contrast media from contaminated water: A comparative study.

Iodinated X-ray contrast media (ICM) was frequently detected in the aqueous environment. In this work, the applicability of three graphene-based nanomaterials (graphene nanosheets (GNS), graphene oxide (GO), and reduced graphene oxide (rGO)) for the adsorptive removal of the six ICMs including iohexol, iopamidol, iomeprol, iopromide, iodixanol and ioversol from aqueous solution was firstly evaluated by batch adsorption method. Among the three graphene-based nanomaterials, the GNS displayed the best adsorption performances for the adsorption of the six ICMs. The maximum uptakes of the six ICMs by the GNS (161.5 mg g-1 for iohexol, 267.2 mg g-1 for iodixanol, 197.7 mg g-1 for iopromide, 197.0 mg g-1 for iopamidol, 109.6 mg g-1 for iomeprol, and 168.2 mg g-1 for ioversol) can rapidly achieved within 10 min and indicate no dependence on pH in the range of 4-9. The results obtained from the calculations of isotherms, kinetics and thermodynamic supported the occurrence of a chemisorption of the GNS for the six ICMs. The π-π interactions between benzene ring of the ICMs and the sp2-hybridized two-dimensional sheet of GNS were deemed the predominant adsorption mechanism.

Performance of zwitterionic hydrophilic interaction LC for the determination of iodinated X-ray contrast agents.

This study compares the separation performance of a group of iodinated X-ray contrast media on four different columns. The first three were two stationary phases (SPs) modified with C18 and a polar-embedded SP (polar amide group bonded to an alkyl chain), all of which worked under RP-LC mode. The fourth was a zwitterionic sulphoalkylbetaine SP, working under the hydrophilic interaction LC (HILIC) mode. After the optimisation of the different parameters, the zwitterionic column displayed the best separation, which also overcomes the problems encountered when these analytes were separated under RP-LC. Moreover, when HILIC is coupled to MS/MS, sensitivity is enhanced. However, when sewage samples were analysed by SPE followed by the optimal HILIC-MS/MS, the sensitivity of the method was affected due to the high matrix effect, which had to be solved by dilution of the extract. Finally, the method was preliminarily validated with sewage and the figures of merit were comparable to those of the SPE-RP-LC-MS/MS.

Occurrence and risk of iodinated X-ray contrast media in source and tap water from Jiangsu province, China.

Microcontaminants in the water environment have received increasing attention due to their adverse effects on human health and wildlife. However, iodinated X-ray contrast media (ICM), a type of microcontaminants, have not yet been systematically documented in source and tap water. This study investigated ICM in water samples via a sampling activity from 25 drinking water sources and their corresponding 30 household taps in south-central Jiangsu Province, China. The total concentrations of ICM ranged from 14.2 to 138.5 ng/L in source water and 3.7 to 101.3 ng/L in tap water, respectively. The calculated average water treatment efficiency to remove ICM is 38.3% with large variation under different processes (ranging from 7.3% to 75.7%), which implied that ICM could not be effectively removed using current treatment technologies. By integrating other ICM into the predominant compound iohexol with relative potency factors, the health risks of total ICM through water consumption were assessed using the Monte Carlo simulation. The results concluded that the risk of ingesting ICM through tap water was not a major health concern for adults, teens, or children in the study area. Nevertheless, due to the lack of long-term toxicity data relevant for humans for ICM, this risk may be underestimated, which requires further research.

Fate and removal of iodinated X-ray contrast media in membrane bioreactor: Microbial dynamics and effects of different operational parameters.

Iodinated X-ray contrast media (ICM) are mainly used in medical sector, and their presence in environmental waters is a cause of concern as they are capable of forming highly toxic iodinated disinfection byproducts. In the present study, the removal mechanisms of the three ICM- iohexol, iopromide, and iopamidol were elucidated in a lab-scale aerobic membrane bioreactor (MBR). At steady-state operation (solids retention time (SRT)- 70 days, organic loading rate (OLR)- 0.80 KgCOD/m3-day, nitrogen loading rate (NLR)- 0.08 KgNH4-N/m3-day, hydraulic retention time (HRT)- 12 h), the average removal of iohexol and iopromide was found to be 34.9 and 45.2 %, respectively, whereas iopamidol proved to be highly recalcitrant in aerobic conditions of the MBR (removal <10 % in all phases of the MBR operation). Further, through batch kinetic studies and mass balance analysis, it was observed that ICM were primarily biotransformed in the MBR system and biosorption (Kd < 10 L/Kg) was negligible. The biodegradation rate coefficient values (Kbiol) of the ICM were found to be <0.65 L/g-d which indicate that biotransformation rate of ICM was slow. Increased OLR (1.60 KgCOD/m3-day) and reduced SRT (20 days) were found to negatively affect the removal of the ICM. Further, the removal of ICM was found to depend on its initial concentration, and the increment in the ammonium loading (0.16 KgNH4-N/m3-day) did not favor its removal. The dosing of ICM altered the microbial dynamics of the mixed liquor and reduced the microbial diversity and richness. Bdellovibrio, Zoogloea, and bacteria belonging to TM7-3 class, Cryomorphaceae and Hyphomonadaceae families may contribute in ICM biotransformation.

Investigating the biodegradability of iodinated X-ray contrast media in simultaneous nitrification and denitrification system.

The present study investigated the biodegradation of three iodinated X-ray contrast media (ICM), namely, iopamidol, iohexol, and iopromide, in simultaneous nitrification-denitrification (SND) system maintained in a sequencing batch reactor (SBR). The results showed that variable aeration patterns (anoxic-aerobic-anoxic) and micro-aerobic condition were most effective in the biotransformation of ICM while achieving organic carbon and nitrogen removal. The highest removal efficiencies of iopamidol, iohexol, and iopromide were 48.24%, 47.75%, and 57.46%, respectively, in micro-aerobic condition. Iopamidol was highly resistant to biodegradation and possessed the lowest Kbio value, followed by iohexol and iopromide, regardless of operating conditions. The removal of iopamidol and iopromide was affected by the inhibition of nitrifiers. The transformation products after hydroxylation, dehydrogenation, and deiodination of ICM were detected in the treated effluent. Due to the addition of ICM, the abundance of denitrifier genera Rhodobacter and Unclassified Comamonadaceae increased, and the abundance of class TM7-3 decreased. The presence of ICM affected the microbial dynamics, and the diversity of microbes in SND resulted in improving the biodegradability of the compounds.

Transformation mechanisms of iopamidol by iron/sulfite systems: Involvement of multiple reactive species and efficiency in real water.

Although the ability of iron/sulfite system for decontamination purposes has been investigated, the complex reactive species generated and the underlying transformation mechanisms remain elusive. Here, we have comprehensively examined the transformation of iopamidol (IPM), a representative of iodinated X-ray contrast media, by iron catalyzed sulfite oxidation process under different water chemistry conditions. Multiple reactive intermediates including Fe(IV), SO4•-, and SO5•- were identified by conducting a series of experiments. Eight transformation products were detected by mass spectrometry analysis, and correlation with the nature of involved reactive species has been made. Further, the transformation pathways including amide hydrolysis, deiodination, amino and hydroxyl groups oxidation were proposed. Interestingly, these transformation products could be removed through adsorption to iron precipitates formed via pH adjustment. Combining Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, we revealed an effective way to reduce the amount of transformation products in the treated solutions. Since the iron/sulfite process appears to be less sensitive to natural organic matter, it exhibited very good efficiency for IPM removal in real water samples, even with a high organic carbon loading. These findings may have strong implications in the development of novel oxidation process based on the sulfite/iron systems for wastewater treatment.

Assessing the skin irritation and sensitizing potential of concentrates of water chlorinated in the presence of iodinated X-ray contrast media.

Chemical disinfection of water provides significant public health benefits. However, disinfectants like chlorine can react with naturally occurring materials in the water to form disinfection byproducts (DBPs). Natural levels of iodine have been reported to be too low in some source waters to account for the levels of iodinated DBPs detected. Iodinated X-ray contrast media (ICM) have been identified as a potential source of iodine. The toxicological impact of ICM present in source water at the time of disinfection has not been fully investigated. Iopamidol, iohexol, iopromide, and diatrizoate are among the ICM most frequently detected in water. In this study, source water containing one of these four ICM was chlorinated; non-chlorinated ICM-containing water samples served as controls. Reactions were conducted at an ICM concentration of 5 µM and a chlorine dose of 100 µM over 72 hr. Water concentrates (20,000-fold) were prepared by XAD-resin/ethyl acetate extraction and DMSO solvent exchange. We used the MatTek® reconstituted human epithelial skin irritation model to evaluate the water concentrates and also assessed the dermal irritation and sensitization potential of these concentrates using the LLNA:BrdU ELISA in BALB/c mice. None of the water concentrates tested (2500X) resulted in a skin irritant response in the MatTek® skin irritation model. Likewise, none of the concentrates (2500X, 1250X, 625X, 312.5X, 156.25X) produced a skin irritation response in mice: erythema was minimal; the maximum increase in ear thickness was less than 25%. Importantly, none of the concentrates produced a positive threshold response for allergic skin sensitization at any concentration tested in the LLNA:BrdU ELISA. We conclude that concentrates of water disinfected in the presence of four different ICM did not cause significant skin irritation or effects consistent with skin sensitization at the concentrations tested.

The application of UV-C laser in persulfate activation for micropollutant removal: Case study with iodinated X-ray contrast medias.

A novel light source UV-C laser was applied in persulfate (PS) activation to effectively remove iodinated X-ray contrast medias (ICMs) including iohexol (IOX), iopamidol (IPM) and diatrizoate (DTZ) in this study. Significant ICMs degradation was observed in UV-C laser/PS systems with pseudo first-order rate constants of 0.022-0.067 s-1. Sulfate radicals (SO4•-) were the main active species in the three ICMs degradation, and the steady-state concentrations ([SO4•-]ss) were 3.629 × 10-11 M (IOX), 1.702 × 10-11 M (IPM) and 1.148 × 10-11 M (DTZ), respectively. Under the high intensity of UV-C laser, the optimal reaction efficiency was achieved at pH = 7.0 with PS concentration of 1.0 mM, and the degradation efficiency for IOX reached 93.8% within only 40 s. Both bicarbonate and chloride ions could inhibit the three ICMs degradation and the inhibition rate increased with the increase of ions concentration. The kinetic models were established and the steady-state concentrations of radicals were calculated. Density functional theory (DFT) calculations combined with experiments were used to derive the reaction pathways for three ICMs. Cyclic voltammetry measurements detected a lower redox potential peak in IOX degradation, revealing the existence of electron shuttles under the UV-C laser irradiation to promote the redox reaction. This study is the first report of UV-C laser activation of persulfate. It is a new advanced oxidation process mediated by very effective photolysis and active species formation.

The fate and transformation of iodine species in UV irradiation and UV-based advanced oxidation processes.

Iodinated disinfection byproducts (I-DBPs) formed in water treatment are of emerging concern due to their high toxicity and the tase-and-odor problems associated with iodinated trihalomethanes (I-THMs). Iodoacetic acid and dichloroiodomethane are currently regulated in Shenzhen, China and the Ministry of Health of the People's Republic of China has also been considering regulating I-DBPs. Iodide (I-), organoiodine compounds (e.g., iodinated X-ray contrast media [ICM]), and iodate (IO3-) are the three common iodine sources in aquatic environment that lead to I-DBP formation. While UV irradiation effectively inactivate a wide range of microorganisms in water, it induces the transformation of these iodine sources, enabling the formation of I-DBPs. This review focuses on the fate and transformation of these iodine sources in UV-based water treatment (i.e., UV irradiation and UV-based advanced oxidation processes [UV-AOPs]) and the formation of I-DBPs in post-disinfection. I- released in UV-based treatments of ICM and can be oxidized in subsequent disinfection to hypoiodous acid (HOI), which reacts with natural organic matter (NOM) to produce I-DBPs. Both UV and UV-AOPs are not able to fully mineralize ICM and completely oxidize the released I- to (except UV/O3). Results reveal that UV and UV-AOPs are adequate for I-DBP degradation but require high UV doses. While the ideal I-DBP mitigation strategy awaits to be developed, understanding their sources and formation pathways aids in informed selections of water treatment processes, empowers water suppliers to meet drinking water standards, and minimizes consumers' exposure to I-DBPs.

Kinetics and model development of iohexol degradation during UV/H2O2 and UV/S2O82- oxidation.

The degradation rates and kinetics of one commonly used iodinated contrast medium, iohexol, were investigated and compared during ultraviolet (UV) photolysis, UV/H2O2 and UV/S2O82- advanced oxidation processes (AOPs). Results indicate that the iohexol degradation rate increased in the order of UV/H2O2 < UV irradiation < UV/S2O82- and followed pseudo-first-order kinetics. Increasing persulfate concentration significantly increased iohexol degradation rate, whereas increasing H2O2 concentration caused reverse effect. Radical scavenging test results show that UV photolysis, OH and radicals all contributed to iohexol degradation during UV/S2O82-, but OH was the main contributor during UV/H2O2 and was consumed by excess H2O2. The kinetic models of iohexol degradation by both AOPs were developed, and the reaction rate constants with OH and were calculated as 5.73 (±0.02) × 108 and 3.91 (±0.01) × 1010 M-1 s-1, respectively. Iohexol degradation rate remained stable at pH 5-9 during UV irradiation and UV/H2O2, but gradually decreased at pH 5-7 and remained stable at pH 7-9 during UV/S2O82-. The presence of anions displayed inhibitory effects on iohexol degradation during UV/S2O82- in the order of Cl- >HCO3- ≫ SO42-. UV/S2O82- AOP exhibited high degradation efficiency and stability on the basis of UV irradiation, which can be applied as a promising degradation method for iohexol. UV/S2O82- AOP can effectively mineralize iohexol to CO2 but promoted the generation of toxic iodoform (CHI3), and the subsequent chlorination had the potential to reduce the content of disinfection by-products; therefore, further evaluation of possible environmental hazards is warranted.

Distribution and relevance of iodinated X-ray contrast media and iodinated trihalomethanes in an aquatic environment.

Distribution and relevance of iodinated X-ray contrast media (ICM) and iodinated disinfection byproducts (I-DBPs) in a real aquatic environment have been rarely documented. In this paper, some ICM were proven to be strongly correlated with I-DBPs through investigation of five ICM and five iodinated trihalomethanes (I-THMs) in surface water and two drinking water treatment plants (DWTPs) of the Yangtze River Delta, China. The total ICM concentrations in Taihu Lake and the Huangpu River ranged from 88.7 to 131 ng L-1 and 102-252 ng L-1, respectively. While the total I-THM concentrations ranged from 128 to 967 ng L-1 in Taihu Lake and 267-680 ng L-1 in the Huangpu River. Iohexol, the dominant ICM, showed significant positive correlation (p < 0.01) with CHClI2 in Taihu Lake. Iopamidol and iomeprol correlated positively (p < 0.01) with some I-THMs in the Huangpu River. The observed pronounced correlations between ICM and I-THMs indicated that ICM play an important role in the formation of I-THMs in a real aquatic environment. Characteristics of the I-THM species distributions indicated that I-THMs may be transformed by natural conditions. Both DWTPs showed negligible removal efficiencies for total ICM (<20%). Strikingly high concentrations of total I-THMs were observed in the finished water (2848 ng L-1 in conventional DWTP and 356 ng L-1 in advanced DWTP). Obvious transformation of ICM to I-THMs was observed during the chlorination and ozonization processes in DWTPs. We suggest that ICM is an important source for I-DBP formation in the real aquatic environment.

Different sample treatments for the determination of ICM-XR in fish samples followed by LC-HRMS.

Iodinated X-ray contrast media (ICM-XR) are a group of pharmaceuticals widely used in medicine. Due to their low biodegradation rate, which makes their removal at wastewater treatment plants difficult, and the high doses at which they are administered, they have been detected in aquatic environments. In the present paper, a method for the quantitative determination of a group of ICM-XR in different fish species was developed and validated for the first time. Two extraction techniques were compared: pressurised liquid extraction (PLE) and QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe), with PLE being selected, followed by liquid chromatography-high resolution mass spectrometry. In addition, several clean-up strategies were evaluated. The optimised method provided PLE recoveries ranging from 60% to 88% and limits of detection ranging from 5ng/g to 25ng/g (dry weight). The method was applied in order to evaluate the presence of the selected ICM-XR in different fish species.

Photodecomposition of iodinated contrast media and subsequent formation of toxic iodinated moieties during final disinfection with chlorinated oxidants.

Large amount of iodinated contrast media (ICM) are found in natural waters (up to µg.L(-)(1) levels) due to their worldwide use in medical imaging and their poor removal by conventional wastewater treatment. Synthetic water samples containing different ICM and natural organic matter (NOM) extracts were subjected to UV254 irradiation followed by the addition of chlorine (HOCl) or chloramine (NH2Cl) to simulate final disinfection. In this study, two new quantum yields were determined for diatrizoic acid (0.071 mol.Einstein(-1)) and iotalamic acid (0.038 mol.Einstein(-1)) while values for iopromide (IOP) (0.039 mol.Einstein(-1)), iopamidol (0.034 mol.Einstein(-1)) and iohexol (0.041 mol.Einstein(-1)) were consistent with published data. The photodegradation of IOP led to an increasing release of iodide with increasing UV doses. Iodide is oxidized to hypoiodous acid (HOI) either by HOCl or NH2Cl. In presence of NOM, the addition of oxidant increased the formation of iodinated disinfection by-products (I-DBPs). On one hand, when the concentration of HOCl was increased, the formation of I-DBPs decreased since HOI was converted to iodate. On the other hand, when NH2Cl was used the formation of I-DBPs was constant for all concentration since HOI reacted only with NOM to form I-DBPs. Increasing the NOM concentration has two effects, it decreased the photodegradation of IOP by screening effect but it increased the number of reactive sites available for reaction with HOI. For experiments carried out with HOCl, increasing the NOM concentration led to a lower formation of I-DBPs since less IOP are photodegraded and iodate are formed. For NH2Cl the lower photodegradation of IOP is compensated by the higher amount of NOM reactive sites, therefore, I-DBPs concentrations were constant for all NOM concentrations. 7 different NOM extracts were tested and almost no differences in IOP degradation and I-DBPs formation was observed. Similar behaviour was observed for the 5 ICM tested. Both oxidant poorly degraded the ICM and a higher formation of I-DBPs was observed for the chloramination experiments compared to the chlorination experiment. Results from toxicity testing showed that the photodegradation products of IOP are toxic and confirmed that the formation of I-DBPs leads to higher toxicity. Therefore, for the experiment with HOCl where iodate are formed the toxicity was lower than for the experiments with NH2Cl where a high formation of I-DBPs was observed.

Comparison of iodinated trihalomethanes formation during aqueous chlor(am)ination of different iodinated X-ray contrast media compounds in the presence of natural organic matter.

Iodinated trihalomethanes (I-THMs) formation during chlorination and chloramination of five iodinated X-ray contrast media (ICM) compounds (iopamidol, iopromide, iodixanol, histodenz, and diatrizoate) in the presence of natural organic matter (NOM) was evaluated and compared. Chlorination and chloramination of ICM in the absence of NOM yielded only a trace amount of I-THMs, while levels of I-THMs were enhanced substantially in raw water samples. With the presence of NOM, the order with respect to the maximum yield of I-THMs observed during chlorination was iopamidol >> histodenz > iodixanol > diatrizoate > iopromide. During chloramination, I-THM formation was enhanced for hisodenz, iodixanol, diatrizoate, and iopromide. The order with respect to the maximum yield of I-THMs observed during chloramination was iopamidol > diatrizoate > iodixanol > histodenz > iopromide. With the exception of iopamidol, I-THM formation was favored at relatively low chlorine doses (≤100 µM) during ICM chlorination, and significant suppression was observed with high chlorine doses applied (＞100 µM). However, during chloramination, increasing monochloramine dose monotonously increased the yield of I-THMs for the five ICM. During chlorination of iodixanol, histodenz, and diatrizoate, the yields of I-THMs exhibited three distinct trends as the pH increased from 5 to 9, while peak I-THM formation was found at circumneutral pH for chloramination. Increasing bromide concentration not only considerably enhanced the yield of I-THMs but also shifted the I-THMs towards bromine-containing ones and increased the formation of higher bromine-incorporated species (e.g., CHBrClI and CHBr2I), especially in chloramination. These results are of particular interest to understand I-THM formation mechanisms during chlorination and chloramination of waters containing ICM.