Formation Of Iodinated Disinfection Byproducts Research Articles

Impacts of hydraulic fracturing wastewater from oil and gas industries on drinking water: Quantification of 69 disinfection by-products and calculated toxicity

Oil and gas production generates large amounts of brine wastewater called “produced water” with various geogenic and synthetic contaminants. These brines are generally used in hydraulic fracturing operations to stimulate production. They are characterized by elevated halide levels, particularly geogenic bromide and iodide. Such salt concentrations in produced water may be as high as thousands of mg/L of bromide and tens of mg/L of iodide. Large volumes of produced water are stored, transported, reused in production operations, and ultimately disposed of by deep well injection into saline aquifers. Improper disposal may potentially contaminate shallow freshwater aquifers and impact drinking water sources. Because conventional produced water treatment typically does not remove halides, produced water contamination of groundwater aquifers may cause the formation of brominated and iodinated disinfection by-products (I-DBPs) at municipal water treatment plants. These compounds are of interest because of their higher toxicity relative to their chlorinated counterparts. This study reports a comprehensive analysis of 69 regulated and priority unregulated DBPs in simulated drinking waters fortified with 1 % (v/v) oil and gas wastewater. Impacted waters produced 1.3×–5× higher levels of total DBPs compared to river water after chlorination and chloramination. Individual DBP levels ranged from (<0.1–122 μg/L). Overall, chlorinated waters formed highest levels, including trihalomethanes that would exceed the U.S. EPA regulatory limit of 80 μg/L. Chloraminated waters had more I-DBP formation and highest levels of haloacetamides (23 μg/L) in impacted water. Calculated cytotoxicity and genotoxicity were higher for impacted waters treated with chlorine and chloramine than corresponding treated river waters. Chloraminated impacted waters had the highest calculated cytotoxicity, likely due to higher levels of more toxic I-DBPs and haloacetamides. These findings demonstrate that oil and gas wastewater if discharged to surface waters could adversely impact downstream drinking water supplies and potentially affect public health.

Overlooked Iodo-Disinfection Byproduct Formation When Cooking Pasta with Iodized Table Salt.

Iodized table salt provides iodide that is essential for health. However, during cooking, we found that chloramine residuals in tap water can react with iodide in table salt and organic matter in pasta to form iodinated disinfection byproducts (I-DBPs). While naturally occurring iodide in source waters is known to react with chloramine and dissolved organic carbon (e.g., humic acid) during the treatment of drinking water, this is the first study to investigate I-DBP formation from cooking real food with iodized table salt and chloraminated tap water. Matrix effects from the pasta posed an analytical challenge, necessitating the development of a new method for sensitive and reproducible measurements. The optimized method utilized sample cleanup with Captiva EMR-Lipid sorbent, extraction with ethyl acetate, standard addition calibration, and analysis using gas chromatography (GC)-mass spectrometry (MS)/MS. Using this method, seven I-DBPs, including six iodo-trihalomethanes (I-THMs) and iodoacetonitrile, were detected when iodized table salt was used to cook pasta, while no I-DBPs were formed with Kosher or Himalayan salts. Total I-THM levels of 11.1 ng/g in pasta combined with cooking water were measured, with triiodomethane and chlorodiiodomethane dominant, at 6.7 and 1.3 ng/g, respectively. Calculated cytotoxicity and genotoxicity of I-THMs for the pasta with cooking water were 126- and 18-fold, respectively, compared to the corresponding chloraminated tap water. However, when the cooked pasta was separated (strained) from the pasta water, chlorodiiodomethane was the dominant I-THM, and lower levels of total I-THMs (retaining 30% of the I-THMs) and calculated toxicity were observed. This study highlights an overlooked source of exposure to toxic I-DBPs. At the same time, the formation of I-DBPs can be avoided by boiling the pasta without a lid and adding iodized salt after cooking.

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.

Insights into the formation and mitigation of iodinated disinfection by-products during household cooking with Laminaria japonica (Haidai)

Iodinated disinfection by-products (I-DBPs) have attracted extensive interests because of their higher cytotoxicity and genotoxicity than their chlorinated and brominated analogues. Our recent studies have firstly demonstrated that cooking with seaweed salt could enhance the formation of I-DBPs with several tens of μg/L level. Here, I-DBP formation and mitigation from the reaction of disinfectant with Laminaria japonica (Haidai), an edible seaweed with highest iodine content, upon simulated household cooking process was systematically investigated. The total iodine content in Haidai ranged from 4.6 mg-I/g-Haidai to 10.0 mg-I/g-Haidai, and more than 90% of iodine is soluble iodide. During simulated cooking, the presence of disinfectant simultaneously decreased iodide by 15.0–32.8% to 2.7–5.8 mg/L and increased total organic iodine by 1.3–10.9 times to 0.5–1.8 mg/L in Haidai soup, proving I-DBP formation. The concentrations of iodinated trihalomethanes and haloacetic acids were at the levels of several hundreds of μg/L and several μg/L, respectively, which are 2–3 orders and 1–2 orders of magnitude more than those in drinking water. Effects of key factors including disinfectant specie, disinfectant dose, temperature and time on I-DBP formation were also ascertained, and temperature and disinfectant specie played a decisive role in the formation and speciation of I-DBPs. In order to avoid the potential health risk from the exposure of I-DBPs in Haidai soup, it is prerequisite to soak and wash dry Haidai sample over 30.0 min before cooking, which could effectively remove major soluble iodide. In general, this study provided the new insight into I-DBP formation from daily household cooking with Haidai and the corresponding enlightenment for inhabitants to eat Haidai in daily life.

Oxidation of iodide by PbO2, the major lead pipe corrosion product: Kinetics, mechanism and formation of toxic iodinated disinfection by-products

Lead oxide (PbO2) formed by the oxidation of lead pipes and lead-containing plumbing materials is an important corrosion product in some drinking water distribution systems. Under certain conditions it acts as an oxidant, and we report here the effects of pH on the oxidation of I¯ by PbO2, which leads to the formation of iodine (I2) and iodate (IO3¯) as well as dissolution of Pb2+. Oxidation of I¯ by PbO2 is a multi-step pH-dependent reaction, the rate of which can be expressed as: R = 6.92 × 109 × [SA]0.67 × [I¯]2.19 × [H+]0.59 (where SA is the PbO2 surface area). I2 was the major intermediate product formed along with some HOI, and was then further oxidized to IO3¯. Based on these results, a kinetic model was developed to simulate the evolution of I¯, I2 and IO3¯ in the PbO2/I¯ reaction system. In addition, the formation of iodinated disinfection by-products (I-DBPs) in the PbO2/I¯/NOM system was evaluated under different water quality conditions, and was found to be influenced by the form of the lead corrosion products in the order: Pb3O4 > PbO2 > Pb(CO3)2(OH)2 > PbCO3. Iodoform and monoiodoacetic acid were identified as the main I-DBPs, and their formation decreased with increasing pH. It is concluded that oxidation of I¯ by lead oxides in water distribution pipes probably contributes to the formation of I-DBPs as well as Pb2+ in tap water.

Fate and transformation of iodine species during Mn(VII)/sulfite treatment in iodide-containing water.

During oxidative treatment of iodide (I- )-containing waters, I- is easy to be oxidized into hypoiodous acid (HOI) by various oxidants and the further reaction of HOI with organic compounds can lead to the formation of iodinated disinfection by-products (I-DBPs). Oxidation of HOI to iodate (IO3 - ) or reduction of HOI to I- has been proposed to reduce the formation of I-DBPs. Because the reaction of HOI with sulfite proceeds rapidly, this study examined the fate of iodine and the formation of I-DBPs in Mn(VII)/sulfite process. Results showed that I- was oxidized to HOI but the further formation of IO3 - was suppressed due to the fast reduction of HOI to I- by sulfite. The reactions of HOI with SO3 2- and IO- with SO3 2- are the major pathways with species-specific second-order rate constants determined to be 1.12 × 105 M-1 s-1 and 9.43 × 107 M-1 s-1 , respectively. The rapid reaction of HOI with sulfite plays an essential role in minimizing the formation of iodinated products in HOI- and phenol-containing solutions. The toxic risk analysis showed that the toxicity of the generated DBPs from Mn(VII)/sulfite pre-oxidation followed by chlorination only changed slightly. PRACTITIONER POINTS: The decay of I- was negligible in Mn(VII)/sulfite process. The rapid reaction of HOI with SO3 2- resulted in the negligible generation of IO3 - . Mn(VII)/sulfite process exerted slight influence on the formation of I-DBPs. Mn(VII)/sulfite process is promising for the pretreatment of I- -containing water.

Activation of ferrate(VI) by sulfite for effectively degrading iodinated contrast media and synchronously controlling I-DBPs formation

Iodinated X-ray contrast media (ICM) are widely detected in the aqueous environment, which pose risks of iodinated disinfection by-products (I-DBPs) in the subsequent disinfection treatment. Herein, a novel advanced oxidation process of ferrate(VI) and sulfite (Fe(VI)/sulfite) was employed in removing ICM and controlling I-DBPs formation. The results showed that the Fe(VI)/sulfite process effectively degraded ICM and the removal efficiency of iopamidol (IPM) ranged from 55.4% to 87.7% at pH 6–10 within 120 s. Based on the results of quenching and probing experiments, SO4•- was identified as the predominant oxidant for IPM decomposition at pH 6–10. IPM transformation pathway mainly involved deiodination, hydrogen abstraction, hydroxyl addition, amide hydrolysis, and amino oxidation. The iodine on the benzene ring was released into the solution as I- and then I- was partly oxidized to IO3- during the oxidation of IPM, the concentration of I- and IO3- was 0.34 and 0.13 μM at pH 6, respectively. Then, the formation of I-DBPs in the subsequent disinfection was investigated. It was found that I-DBPs concentration increased with increasing pH and enlarging Fe(VI) dosage as well as slightly increased in the presence of humic acid. Additionally, when solutions were filtered at pH 6 after oxidation, the removal ratios of I- and IO3- were 41.2% and 53.8%, respectively. Because the generated I- and IO3- were adsorbed by in-situ formed ferric (oxyhydr)oxides from Fe(VI) reduction, the yield of I-DBPs was thereby reduced in the subsequent disinfection. Therefore, the Fe(VI)/sulfite process can effectively remove ICM and synchronously control I-DBPs formation in the subsequent disinfection.

Household cooking with seaweed salts and chloraminated tap water produce harmful iodinated disinfection by-products

• Dominate iodine species of seaweed salts are iodide and organic iodine rather than iodate. • Cooking with seaweed salt and chloraminated water produced I-DBPs with hundreds of μg/L level. • Effects of temperature, time, chloramine dose, and salt dose on I-DBP formation were examined. • Cooking with seaweed salts enhanced the toxicity of tap water by 4.6 ∼ 8.7 times on the basis of EC 50 . • The potential risks of I-DBPs generated from cooking with seaweed salts should be spotlighted. Among the harmful halogenated disinfection by-products (DBPs) produced from water disinfection, iodinated DBPs (I-DBPs) are of the highest toxicity. Here we reported for the first time that daily household cooking using seaweed salts and tap water with chloramine residual could produce high concentrations of I-DBPs. At a typical household cooking setting (1-hr heating at 80 °C), the reactions of chloramines (1.0 mg/L as Cl 2 ) with 10 g/L seaweed salt in ultrapure water generated 96.8 ± 3.2 μg/L of iodo-containing trihalomethanes (I-THMs) and 385.3 ± 10.9 μg/L of total organic iodine (TOI). The yields are 1 ∼ 3 orders of magnitude greater than their typical occurrence levels in drinking water. At the unintended scenario, chloramines reacted with iodine and trace dissolved organic matter, both of which derived from seaweed salts containing iodide and organic iodine species. When chloraminated tap water was used at the identical conditions, aliphatic I-DBPs (i.e. I-THMs and iodo-containing haloacetic acids) significantly increased up to 163.5 ± 3.9 μg/L as a result of more natural organic matter, which could serve as DBP precursors, present in the tap water. Speciation and concentrations of different I-DBPs generated relied heavily on temperature, heating duration, chloramine concentration, and salt dose. Following a simulated household cooking in the presence of seaweed salts, the toxicity of tap water to luminescent bacteria ( Vibrio qinghaiensis sp.-Q67) increased by 4.6 ∼ 8.7 times on the basis of EC 50 . These findings spotlight the potential risks of I-DBPs generated from daily household cooking with seaweed salts, because salt consumption contributes to more than half of daily iodine intake.

Iodinated disinfection byproduct formation in a MnO2/I−/EPS system

Manganese dioxide (MnO2) is a Mn deposit widely accumulated in the corrosion layer of pipelines, and iodide (I−) is a halogen ion frequently detected in waters. The biofilm dwelling on the corrosion scales often secretes extracellular polymeric substances (EPS) into drinking water. The paper aimed to study the I− oxidation by MnO2 and iodinated disinfection byproducts (I-DBPs) formation with biofilm EPS as a precursor. More than 93% of formed free iodine was finally converted into organic iodine in the MnO2/I−/EPS system. Compared with humic acid, EPS had a lower carbonaceous I-DBPs (C-IDBPs) formation while a higher nitrogenous I-DBPs (N-IDBPs) formation. The formation of iodomethanes (I-THMs), iodoacetonitriles (I-HANs) and iodoacetic acids (I-HAAs) decreased with the increase of pH due to the weakening of polarization effect and redox potential, while the iodoacetamides (I-HAcAms) formation achieved the maximum at pH 6.0 due to the difference between the hydrolysis rate of I-HANs and decomposition rate of I-HAcAms. The I-DBPs formation was positively correlated with I− concentration, while negatively correlated with MnO2 dose. Protein components displayed a higher formation of N-IDBPs and C-IDBPs than polysaccharide components due to higher nitrogen proportion and more iodination sites. Among 20 protein monomers, aspartic acid was considered as the most important precursor of the four investigated I-DBPs species. The paper is helpful to understand the I-DBPs formation when I− in the bulk water come into contact with Mn deposits attached by biofilm.

Formation of carbonaceous and nitrogenous iodinated disinfection byproducts from biofilm extracellular polymeric substances by the oxidation of iodide-containing waters with lead dioxide

Lead dioxide (PbO2) is an important form of lead mineral scales in drinking water pipes. Iodide (I−) widely presents in source waters and can be thermodynamically oxidized by PbO2 to the reactive iodine species (I2/HOI). Biofilm extracellular polymeric substances (EPS) are nonnegligible precursors of disinfection byproducts (DBPs). The aim was to study the oxidation of I− by PbO2 and formation of iodinated DBPs (I-DBPs) from EPS. At a high molar ratio of PbO2 to I− (> 100), the observed rate constants of I− oxidation decreased as pH increased from 6.0 to 9.0 with an H+ dependence of 0.79, and the rate constant (k) was 1.6 × 1011 M−2.79 s−1. Most of formed I2/HOI (> 92%) was transformed to organic iodine in the presence of EPS. EPS had a lower formation potential (FP) of carbonaceous I-DBPs (C-IDBPs), while a higher that of nitrogenous I-DBPs (N-IDBPs) than HA, resulting in a higher Chinese Hamster Ovary cell cytotoxicity. Generally, the formation of I-DBPs decreased with the increase of pH due to the reduction of surface positive charge and electrochemical driving force. PbO2 dose and I− concentration also had a significant effect on the I-DBPs formation. EPS proteins had a higher FP of both C- and N-IDBPs than polysaccharides on account of more electrophilic sites and higher nitrogen content. In proteins, aspartic acid was the main contributor to triiodomethane and iodoacetic acids formation, whereas aspartic acid, asparagine and tyrosine were the major precursors of diiodoacetonitrile and diiodoacetamide. The study helps to improve the control strategy of I-DBPs when biofilm outbreaks in lead-containing water pipes.

Kinetics of the reaction between hydrogen peroxide and aqueous iodine: Implications for technical and natural aquatic systems

Oxidative treatment of iodide-containing waters can lead to a formation of potentially toxic iodinated disinfection byproducts (I-DBPs). Iodide (I−) is easily oxidized to HOI by various oxidation processes and its reaction with dissolved organic matter (DOM) can produce I-DBPs. Hydrogen peroxide (H2O2) plays a key role in minimizing the formation of I-DBPs by reduction of HOI during H2O2-based advanced oxidation processes or water treatment based on peracetic acid or ferrate(VI). To assess the importance of these reactions, second order rate constants for the reaction of HOI with H2O2 were determined in the pH range of 4.0–12.0. H2O2 showed considerable reactivity with HOI near neutral pH (kapp = 9.8 × 103 and 6.3 × 104 M−1s−1 at pH 7.1 and 8.0, respectively). The species-specific second order rate constants for the reactions of H2O2 with HOI, HO2− with HOI, and HO2− with OI− were determined as kH2O2+HOI = 29 ± 5.2 M−1s−1, kHO2-+HOI = (3.1 ± 0.3) × 108 M−1s−1, and kHO2-+OI− = (6.4 ± 1.4) × 107 M−1s−1, respectively. The activation energy for the reaction between HOI and H2O2 was determined to be Ea = 34 kJ mol−1. The effect of buffer types (phosphate, acetate, and borate) and their concentrations was also investigated. Phosphate and acetate buffers significantly increased the rate of the H2O2–HOI reaction at pH 7.3 and 4.7, respectively, whereas the effect of borate was moderate. It could be demonstrated, that the formation of iodophenols from phenol as a model for I-DBPs formation was significantly reduced by the addition of H2O2 to HOI- and phenol-containing solutions. During water treatment with the O3/H2O2 process or peracetic acid in the presence of I−, O3 and peracetic acid will be consumed by a catalytic oxidation of I− due to the fast reduction of HOI by H2O2. The O3 deposition on the ocean surface may also be influenced by the presence of H2O2, which leads to a catalytic consumption of O3 by I−.

Coagulation of Iodide-Containing Resorcinol Solution or Natural Waters with Ferric Chloride Can Produce Iodinated Coagulation Byproducts.

Iodinated disinfection byproducts (I-DBPs) are of particular concern in drinking water due to the more cytotoxic and genotoxic properties than their chlorinated and brominated analogs. Formation of I-DBP primarily results from the oxidation of iodide-containing waters with various oxidants and the chlor(am)ination of iodinated organic compounds in drinking water. This study first reports that ferric chloride (FeCl3) can lead to the formation of iodinated coagulation byproducts (I-CBPs) from iodide-containing resorcinol solution or natural waters. The unwanted I-CBP formation involved the oxidation of iodide by ferric ions to generate various reactive iodine species, which further oxidize organic compounds. Although the oxidation rate of iodide by FeCl3 was several orders of magnitude slower than that by chlorine or chloramine, most of the converted iodide under the ferric/iodide system was transformed into iodine and iodinated organic compounds rather than iodate. Formation of four aliphatic I-CBPs was observed, and four aromatic I-CBPs were identified by gas chromatography mass-spectrometry and theoretical calculation. Coagulation of iodide-containing waters with FeCl3 also produced I-CBPs ranging from 12.5 ± 0.8 to 32.5 ± 0.2 μg/L as I. These findings call for careful consideration of the formation of I-CBPs from coagulation of iodide-containing waters with ferric salts.

Chloramination of iodide-containing waters: Formation of iodinated disinfection byproducts and toxicity correlation with total organic halides of treated waters

The formation of iodinated disinfection byproducts (I-DBPs) in drinking waters is of a concern due to their higher cyto- and genotoxicity than their chlorinated and brominated analogues. This study investigated the formation of I-DBPs under chloramination conditions using preformed chloramine and associated cyto- and geno-toxicities obtained with Chinese Hamster Ovary (CHO) cell assay. Cyto- and geno-toxicity of the samples were also calculated using DBP toxicity index values and correlated with total organic halide (TOX) formation. In low iodide (I-) (0.32 μM, 40 μg L−1) water, increasing dissolved organic carbon (DOC) concentration of selected waters from 0.1 to 0.25 mg L−1 increased the formation of iodinated trihalomethanes (I-THMs), while further increases from 0.25 to 4 mg L−1 produced an opposite trend. In high iodide water (3.2 μM, 400 μg L−1), increasing DOC from 0.5 to 4 mg L−1 gradually increased the I-THM formation, while a decrease was observed at 5.4 mg L−1 DOC. Iodoform was the most influenced species from the changes in DOC concentration. While increasing the initial iodide concentration from 0 to 5 μM increased the formation of iodoform, it did not make any considerable impact on the formation of other I-THMs. The measured cytotoxicity of samples was significantly correlated with increasing DOC concentration. Unknown TOCl and TOI showed a high correlation with measured cytotoxicity, while calculated total organic chlorine (TOCl) and total organic iodine (TOI) did not correlate. The comparison of measured and calculated cytotoxicity values showed that the calculated values do not always represent the overall cytotoxicity, since the formation of unknown DBPs are not taken into consideration during the toxicity calculations.

Comparison of diatrizoate degradation by UV/chlorine and UV/chloramine processes: Kinetic mechanisms and iodinated disinfection byproducts formation

This study compared the degradation efficiency of diatrizoate (DTA) by UV/chlorine and UV/chloramine processes. DTA could be effectively degraded by the UV/chlorine and UV/chloramine processes compared with chlorination and chloramination solely. Although the UV/chlorine process was more sensitive to the variations of oxidant dosages, solution pH, the concentration of bicarbonate and chloride, UV/chlorine degraded DTA more efficiently than UV/chloramine process. The reactive chlorine species (RCS) and hydroxyl radical (HO) are predominant contributors to DTA degradation in the UV/chlorine and UV/chloramine processes respectively, and the specific contribution of each reactive specie changed with solution pH. The performance of UV/chlorine and UV/chloramine processes on DTA degradation was obviously inhibited in natural waters (e.g., wastewater, rainwater, river water and tap water), however, degradation of DTA in the UV/chlorine are still satisfactory compared with UV/chloramine process. Formation of chloroform, dichloroacetonitrile, and iodoform (IF) from DTA was observed in both UV/chlorine and UV/chloramine processes. It is notable that formation potential of IF from DTA was significantly enhanced in UV/chloramine process, and thus the overall cytotoxicity of generated DBPs in UV/chloramine process is far greater than that in UV/chlorine process.

Degradation of iohexol by Co2+ activated peroxymonosulfate oxidation: Kinetics, reaction pathways, and formation of iodinated byproducts

Iodinated X-ray contrast media (ICM) are a group of tri-iodinated aromatic compounds used in medical imaging of soft tissues. They are regarded as emerging contaminants, and widely detected in the effluents of wastewater treatment plants, surface water, and groundwater. In the present study, degradation of iohexol, a typical ICM agent, was systematically investigated in a Co2+ activated peroxymonosulfate (Co2+/PMS) oxidation process at neutral conditions. Experimental data revealed that the apparent rate of iohexol degradation was first-order with respect to the concentrations of both Co2+ and PMS. SO4− was found to induce the oxidative degradation of iohexol primarily. Presence of humic acid (HA) significantly inhibited the iohexol degradation, while the influence of Cl− was negligible. A total of 11 intermediates were identified by HPLC-MS/MS and three transformation pathways, i.e., cleavage of side chain, H-abstraction from side chain, and oxidative deiodination, were proposed. The degradation started with the oxidation of the side chains in iohexol molecule and followed by deiodination on the aromatic ring. Following the degradation of iohexol, formation of free iodine and iodinated disinfection byproducts (I-DBPs) was found. When 50 µM was treated with 1 mM PMS and 1 µM Co2+, the yields of iodoform and triiodoacetic acid reached 38.12 and 577.99 µg/L, respectively, in 12 h. In addition, the formation of I-DBPs was prominently enhanced by the presence of HA. Because I-DBPs are highly toxic, this study suggests the potential risks when SO4− is applied to degrade ICM compounds.

Formation of Iodinated Disinfection Byproducts (I-DBPs) in Drinking Water: Emerging Concerns and Current Issues.

Formation of iodinated disinfection byproducts (I-DBPs) in drinking water has become an emerging concern. Compared to chlorine- and bromine-containing DBPs, I-DBPs are more toxic, have different precursors and formation mechanisms, and are unregulated. In this Account, we focus on recent research in the formation of known and unknown I-DBPs in drinking water. We present the state-of-the-art understanding of known I-DBPs for the six groups reported to date, including iodinated methanes, acids, acetamides, acetonitriles, acetaldehyde, and phenols. I-DBP concentrations in drinking water generally range from ng L-1 to low-μg L-1. The toxicological effects of I-DBPs are summarized and compared with those of chlorinated and brominated DBPs. I-DBPs are almost always more cytotoxic and genotoxic than their chlorinated and brominated analogues. Iodoacetic acid is the most genotoxic of all DBPs studied to date, and diiodoacetamide and iodoacetamide are the most cytotoxic. We discuss I-DBP formation mechanisms during oxidation, disinfection, and distribution of drinking water, focusing on inorganic and organic iodine sources, oxidation kinetics of iodide, and formation pathways. Naturally occurring iodide, iodate, and iodinated organic compounds are regarded as important sources of I-DBPs. The apparent second-order rate constant and half-lives for oxidation of iodide or hypoiodous acid by various oxidants are highly variable, which is a key factor governing the iodine fate during drinking water treatment. In distribution systems, residual iodide and disinfectants can participate in reactions involving heterogeneous chemical oxidation, reduction, adsorption, and catalysis, which may eventually affect I-DBP levels in finished drinking water. The identification of unknown I-DBPs and total organic iodine analysis is also summarized in this Account, which provides a more complete picture of I-DBP formation in drinking water. As organic DBP precursors are difficult to completely remove during the drinking water treatment process, the removal of iodide provides a cost-effective solution for the control of I-DBP formation. This Account not only serves as a reference for future epidemiological studies to better assess human health risks due to exposure to I-DBPs in drinking water but also helps drinking water utilities, researchers, regulators, and the general public understand the formed species, levels, and formation mechanisms of I-DBPs in drinking water.

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.

Formation and Occurrence of Iodinated Tyrosyl Dipeptides in Disinfected Drinking Water.

Iodinated disinfection byproducts (I-DBPs) are highly toxic, but few precursors of I-DBPs have been investigated. Tyrosine-containing biomolecules are ubiquitous in surface water. Here we investigated the formation of I-DBPs from the chloramination of seven tyrosyl dipeptides (tyrosylglycine, tyrosylalanine, tyrosylvaline, tyrosylhistidine, tyrosylglutamine, tyrosylglutamic acid, and tyrosylphenylalanine) in the presence of potassium iodide. High resolution mass spectrometry and tandem mass spectrometry (MS/MS) analyses of the benchtop reaction solutions found that all seven precursors formed both I- and Cl-substituted tyrosyl dipeptide products. Iodine substitutions occurred on the 3- and 3,5-positions of the tyrosyl-phenol ring while chlorine substituted on the free amino group. To reach the needed sensitivity to detect iodinated tyrosyl dipeptides in authentic waters, we developed a high performance liquid chromatography (HPLC)-MS/MS method with multiple reaction monitoring mode and solid phase extraction. HPLC-MS/MS analysis of tap and corresponding raw water samples, collected from three cities, identified four iodinated peptides, 3-I-/3,5-di-I-Tyr-Ala and 3-I-/3,5-di-I-Tyr-Gly, in the tap waters but not in the raw waters. The corresponding precursors, Tyr-Ala and Tyr-Gly, were also detected in the same tap and raw water samples. This study demonstrates that iodinated dipeptides exist as DBPs in drinking water.

Oxidation of iopamidol with ferrate (Fe(VI)): Kinetics and formation of toxic iodinated disinfection by-products

Presence of iodinated X-ray contrast media (ICMs) in source water is of high concern, because of their potential to form highly toxic iodinated disinfection by-products (I-DBPs). This study investigated kinetics, mechanisms and products for oxidation of one ICMs, iopamidol (IPM) by ferrate (Fe(VI)). The obtained apparent second-order rate constants for oxidation of IPM by Fe(VI) ranged from 0.7 M−1 s−1 to 74.6 M−1 s−1 at pH 6.0–10.0, which were highly dependent on pH. It was found that the oxidation of IPM by Fe(VI) led to the formation of highly toxic I-DBPs. Iodoform (IF), iodoacetic acid and triiodoacetic acid formations were observed during the oxidation and IF dominated the formed I-DBPs. The formation of I-DBPs was also governed by pH and the maximum formation of I-DBPs occurred at pH 9.0. Transformation pathways of IPM by Fe(VI) oxidation were speculated to proceed through deiodination, amide hydrolysis and oxidation of amine reactions. The deiodination reaction during the oxidation of IPM by Fe(VI) contributed to the formation of I-DBPs. The formation of I-DBPs during the oxidation of IPM by Fe(VI) was significantly higher than those of iohexol, diatrizoate and iopromide, which was consistent with the lowest molecular orbital energy gap of IPM. Although Fe(VI) is considered as a green oxidant, the formation of highly toxic I-DBPs during the oxidation of IPM should receive great attention.