Occurrence of halogenated furanones in U.S. drinking waters

Recent progress in identification of water disinfection byproducts and opportunities for future research

Numerous disinfection by-products (DBPs) are formed from reactions between disinfectants and organic/inorganic matter during water disinfection. More than seven hundred DBPs that have been identified in disinfected water, only a fraction of which are regulated by drinking water guidelines, including trihalomethanes, haloacetic acids, bromate, and chlorite. Toxicity assessments have demonstrated that the identified DBPs cannot fully explain the overall toxicity of disinfected water; therefore, the identification of unknown DBPs is an important prerequisite to obtain insights for understanding the adverse effects of drinking water disinfection. Herein, we review the progress in identification of unknown DBPs in the recent five years with classifications of halogenated or nonhalogenated, aliphatic or aromatic, followed by specific halogen groups. The concentration and toxicity data of newly identified DBPs are also included. According to the current advances and existing shortcomings, we envisioned future perspectives in this field.

Effects of phosphate addition on the removal of disinfection by-product formation potentials by biological activated carbon filtration

In drinking water treatment plants (DWTPs), the widely used biological activated carbon filters (BACFs), as the last barrier before disinfection, can remove dissolved organic matter (DOM) known as precursors of disinfection by-products (DBPs). Whether phosphate addition can improve water purification and DBP control of BACFs is still controversial. This study investigated short-term and long-term effects of phosphate addition on controlling DBP formation potentials (FPs) by BACFs via column and batch experiments. The BAC columns presented good water purification performance: they removed around 50 % DOM, nearly all fulvic acid-likes and humic acid-likes as well as 5 %-70 % chlor(am)innated THM₄, HAA₉ and HAN₄ FPs (except chloraminated THM₄ FPs)， which was mainly contributed by aerobic bacteria not anoxic bacteria. Phosphate addition within 7-14 days further improved removals of DOM, aromatic organics, fluorescence fractions in DOM as well as HAA₉ and HAN₄ FPs (especially TCAA FP and TCAN FP) to different extent. However, this improvement did not last longer, and removals of DOM, aromatic organics, two fluorescence fractions (soluble microbial byproduct-likes and humic acid-likes) and DBP FPs decreased despite long-term phosphate addition. Oxic and anoxic batch experiments showed that the positive response of water purification to short-term phosphate addition was also mainly attributed to aerobic bacteria and not to anoxic bacteria. For example, the former decreased DOM and DBP FPs, while the latter increased protein- and tryptophan-like substances as well as chloraminated THM₄ FPs. Phosphate addition resulted in EPS increase in anoxic reactors and decrease in oxic reactors. These results indicated that a high dissolved oxygen in BACFs may be helpful for water purification and DBP control. Overall, short-term phosphate addition into phosphorus-limited water is beneficial for BACFs to control DBPs while long-term addition has no effect. Therefore, an intermittent phosphate addition into BACFs is suggested to control DBPs in DWTPs.

Reducing of specific carcinogenic disinfection by-products compounds from drinking water using chlorine dioxide as alternative for chlorine

Chlorination has significantly reducing the risk of pathogenic dirt but could pose a chemical hazard to human health due to formation of various disinfection by-products (DBPs). Chlorine dioxide is one of the most intriguing oxidants since it combines a high oxidation capacity with a minimal generation of harmful byproducts like chlorinated organics when used. As a result, it is widely utilized in the disinfection of drinking water and, more recently, in the disinfection of surfaces and structures. Trihalomethanes (THMs) that react with chlorine and organic materials are suspected carcinogens. THMs, haloacetic acids (HAAs), haloacetonitriles (HANs), and halogenated ketones are the most common disinfection by-products (DBPs). Cancer, abortion, poor birth weight, and congenital impairments are all increased by exposure to these by-products. This study aimed to highlight the ability to use chlorine dioxide as alternative for chlorine to reducing carcinogenic hazardous organic material formation. The study resulted that both the concentration of chlorine and chlorine dioxide is one of the major parameters in hazardous organic material formation.

Reactivity-directed analysis - a novel approach for the identification of toxic organic electrophiles in drinking water

Drinking water consumption results in exposure to complex mixtures of organic chemicals, including natural and anthropogenic chemicals and compounds formed during drinking water treatment such as disinfection by-products. The complexity of drinking water contaminant mixtures has hindered efforts to assess associated health impacts. Existing approaches focus primarily on individual chemicals and/or the evaluation of mixtures, without providing information about the chemicals causing the toxic effect. Thus, there is a need for the development of novel strategies to evaluate chemical mixtures and provide insights into the species responsible for the observed toxic effects. This critical review introduces the application of a novel approach called Reactivity-Directed Analysis (RDA) to assess and identify organic electrophiles, the largest group of known environmental toxicants. In contrast to existing in vivo and in vitro approaches, RDA utilizes in chemico methodologies that investigate the reaction of organic electrophiles with nucleophilic biomolecules, including proteins and DNA. This review summarizes the existing knowledge about the presence of electrophiles in drinking water, with a particular focus on their formation in oxidative treatment systems with ozone, advanced oxidation processes, and UV light, as well as disinfectants such as chlorine, chloramines and chlorine dioxide. This summary is followed by an overview of existing RDA approaches and their application for the assessment of aqueous environmental matrices, with an emphasis on drinking water. RDA can be applied beyond drinking water, however, to evaluate source waters and wastewater for human and environmental health risks. Finally, future research demands for the detection and identification of electrophiles in drinking water via RDA are outlined.

The occurrence, characteristics, transformation and control of aromatic disinfection by-products: A review

With the development of analytical technology, more emerging disinfection by-products (DBPs) have been identified and detected. Among them, aromatic DBPs, especially heterocyclic DBPs, possess relatively high toxicity compared with regulated DBPs, which has been proved by bioassays. Thus, the occurrence of aromatic DBPs is of great concern. This article provides a comprehensive review and summary of the characteristics, occurrence, transformation pathways and control of aromatic DBPs. Aromatic DBPs are frequently detected in drinking water, wastewater and swimming pool water, among which swimming pool water illustrates highest concentration. Considering the relatively high concentration and toxicity, halophenylacetonitriles (HPANs) and halonitrophenols (HNPs) are more likely to be toxicity driver among frequently detected phenyl DBPs. Aromatic DBPs can be viewed as important intermediate products of dissolved organic matter (DOM) during chlor(am)ination. High molecular weight DOM could convert to aromatic DBPs via direct or indirect pathways, and they can further decompose into regulated aliphatic DBPs such as trihalomethanes (THMs) and haloacetic acids (HAAs) by ring opening and side chain cleavage. Even though no single DBPs control strategy is efficient to all aromatic DBPs, the decrease of overall toxicity may be achieved by several methods including absorption, solar radiation and boiling. By systematically considering aromatic DBPs and aliphatic DBPs, a better trade-off can be made to reduce health risk induced by DBPs.

Integrated control of CX3R-type DBP formation by coupling thermally activated persulfate pre-oxidation and chloramination

The alternative disinfectant chloramine can lower the formation of carbonaceous DBPs (C-DBPs) but promote the formation of nitrogenous DBPs (N-DBPs), which are more cytotoxic and genotoxic. In this study, the combination of thermally activated persulfate pre-oxidation and post-chloramination (TA/PS-NH₂Cl) was proposed to control the formation and reduce the toxicity of both C-DBPs and N-DBPs. The formation, speciation and toxicity of trihalomethanes, haloacetic acids, haloaldehydes, haloacetonitriles, halonitromethanes and haloacetamides, collectively defined as CX₃R-type DBPs, under TA/PS-NH₂Cl process were compared with processes of chlorination alone (Cl₂), chloramination alone (NH₂Cl) and coupled thermally activated persulfate pre-oxidation with post-chlorination (TA/PS-Cl₂). Results showed that chloramination could reduce formation of C-DBPs and total organic halogen (TOX) while increase N-DBP formation, and the introduction of TA/PS pretreatment process slightly increased the formation of C-DBPs and TOX but sharply reduced the formation of N-DBPs with higher toxicity as well as brominated CX₃R-type DBPs that are more toxic than their chlorinated analogues. By comprehensive toxicity calculation, an outright decline of both cytotoxicity and genotoxicity risk of CX₃R-type DBPs was observed during TA/PS-NH₂Cl process compared with Cl₂, NH₂Cl, and TA/PS-Cl₂ processes. In summary, TA/PS-NH₂Cl process was a potential effective method for integrally controlling the formation of CX₃R-type DBPs and their toxicity and is suggested to be used to treat raw waters containing no bromide or low levels of bromide considering bromate caused by TA/PS pre-oxidation. The study may provide a feasible and economical method for DBP control on the background of global warming.

Application of ozonation for pharmaceuticals and personal care products removal from water

Due to the shortening on natural water resources, reclaimed wastewater will be an important water supply source. However, suitable technologies must be available to guaranty its proper detoxification with special concern for the emerging pharmaceutical and personal care products that are continuously reaching municipal wastewater treatment plants. While conventional biological systems are not suitable to remove these compounds, ozone, due to its interesting features involving molecular ozone oxidation and the possibility of generating unselective hydroxyl radicals, has a wider range of action on micropollutants removal and water disinfection. This paper aims to review the studies dealing with ozone based processes for water reuse by considering municipal wastewater reclamation as well as natural and drinking water treatment. A comparison with alternative technologies is given. The main drawback of ozonation is related with the low mineralization achieved that may lead to the production of reaction intermediates with toxic features. The use of hydrogen peroxide and light aided systems enhance ozone action over pollutants. Moreover, scientific community is focused on the development of solid catalysts able to improve the mineralization level achieved by ozone. Special interest is now being given to solar light catalytic ozonation systems with interesting results both for chemical and biological contaminants abatement. Nowadays the integration between ozonation and sand biofiltration seems to be the most interesting cost effective methodology for water treatment. However, further studies must be performed to optimize this system by understanding the biofiltration mechanisms.

Conventional drinking water treatment and direct biofiltration for the removal of pharmaceuticals and artificial sweeteners: A pilot-scale approach

The presence of endocrine disrupting compounds (EDCs), pharmaceutically active compounds (PhACs) and artificial sweeteners are of concern to water providers because they may be incompletely removed by wastewater treatment processes and they pose an unknown risk to consumers due to long-term consumption of low concentrations of these compounds. This study utilized pilot-scale conventional and biological drinking water treatment processes to assess the removal of nine PhACs and EDCs, and two artificial sweeteners. Conventional treatment (coagulation, flocculation, settling, non-biological dual-media filtration) was compared to biofilters with or without the addition of in-line coagulant (0.2-0.8 mg Al(3+)/L; alum or PACl). A combination of biofiltration, with or without in-line alum, and conventional filtration was able to reduce 7 of the 9 PhACs and EDCs by more than 50% from river water while artificial sweeteners were inconsistently removed by conventional treatment or biofiltration. Increasing doses of PACl from 0 to 0.8 mg/L resulted in average removals of PhACs, EDCs increasing from 39 to 70% and artificial sweeteners removal increasing from ~15% to ~35% in lake water. These results suggest that a combination of biological, chemical and physical treatment can be applied to effectively reduce the concentration of EDCs, PhACs, and artificial sweeteners.

Engineered biofiltration for the removal of disinfection by-product precursors and genotoxicity

Disinfection by-products (DBPs) are formed when naturally occurring organic matter reacts with chlorine used in drinking water treatment, and DBPs formed in chlorinated drinking water samples have been shown to cause a genotoxic response. The objective of the current study was to further understand the principles of biofiltration and the resulting impacts on the formation of DBPs and genotoxicity. Pilot-scale systems were utilized to assess the performance of engineered biofilters enhanced with hydrogen peroxide, in-line coagulants, and nutrients when compared to passively operated biofilters and conventional treatment (coagulation, flocculation, sedimentation, non-biological filtration). Organic fractionation was completed using liquid chromatography-organic carbon detection (LC-OCD). Water samples were chlorinated after collection and examined for the removal of trihalomethane (THM), haloacetic acid (HAA), and adsorbable organic halide (AOX) precursors. Additionally, the formation potential of two halogenated furanones, 3-chloro-4(dichloromethyl)-2(5H)-furanone (MX) and mucochloric acid (MCA), and genotoxicity was determined. Biofiltration was shown to preferentially remove more DBP precursors than dissolved organic carbon (DOC). Formation potential of the unregulated DBPs, including MX and MCA, and genotoxic response was shown to be correlated to THM formation. These results infer that monitoring for THMs and HAAs provide insight to the formation of more mutagenic DBPs such as halogenated furanones, and that biofiltration may preferentially remove precursors to DBPs at a rate exceeding the removal of DOC.

The Relationship between MX [3-Chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone], Routinely Monitored Trihalomethanes, and Other Characteristics in Drinking Water in a Long-Term Survey

MX (3-Chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone) is a drinking water disinfection byproduct (DBP). It is a potent mutagen and is of concern to public health. Data on MX levels in drinking water, especially in the UK, are limited. Our aim was to investigate factors associated with variability of MX concentrations at the tap, and to evaluate if routinely measured trihalomethanes (THMs) are an appropriate proxy measure for MX. We conducted quarterly water sampling at consumers' taps in eight water supply zones in and around Bradford, UK, between 2007 and 2010. We collected 79 samples which were analyzed for MX using GC-HRMS. Other parameters such as pH, temperature, UV-absorbance and free chlorine were measured concurrently, and total THMs were modeled from regulatory monitoring data. To our knowledge this is the longest MX measurement survey undertaken to date. Concentrations of MX varied between 8.9 and 45.5 ng/L with a median of 21.3 ng/L. MX demonstrated clear seasonality with concentrations peaking in late summer/early fall. Multivariate regression showed that MX levels were associated with total trihalomethanes, UV-absorbance and pH. However, the relationship between TTHM and MX may not be sufficiently consistent across time and location for TTHM to be used as a proxy measure for MX in exposure assessment.

Effects of coagulation on the removal of natural organic matter, genotoxicity, and precursors to halogenated furanones

Natural organic matter (NOM) in drinking water can react with disinfectants to form disinfection by-products (DBPs). Halogenated furanones are a group of emerging DBPs that can account for 20-60% of the total mutagenicity observed in drinking water. This study examined the impacts of bench-scale coagulation and subsequent chlorination on DBP formation as well as genotoxicity using three source waters located in Ontario, Canada. Two halogenated furanones 3-chloro-4-(dichloromethyl)-2(5H)-furanone (MX) and mucochloric acid (MCA) were analyzed; along with trihalomethanes (THMs), haloacetic acids (HAAs), and absorbable organic halides (AOX). NOM was quantified using liquid chromatography-organic carbon detection (LC-OCD). Measured MX and MCA formation was 6.9-15.3 ng/L and 43.2-315 ng/L following optimized coagulation and subsequent chlorination of the three waters tested. DBP formation and speciation were evaluated as a function of the specific NOM fractions present in the source waters. Humics, building blocks, and biopolymers were highly correlated with DBP formation. Correlations between DBPs were also investigated and a potential relationship between MCA and/or MX vs. HAAs was observed. MX was the only measured DBP that contributed to genotoxicity, representing less than 0.001% of AOX by mass but responsible for 40-67% of the genotoxic response in chlorinated Ottawa River water samples. Genotoxic potential decreased with alum dosages, signifying that coagulation was effective at removing genotoxic DBP precursors.

Four groups of new aromatic halogenated disinfection byproducts: effect of bromide concentration on their formation and speciation in chlorinated drinking water

Bromide is naturally present in source waters worldwide. Chlorination of drinking water can generate a variety of chlorinated and brominated disinfection byproducts (DBPs). Although substantial efforts have been made to examine the effect of bromide concentration on the formation and speciation of halogenated DBPs, almost all previous studies have focused on trihalomethanes and haloacetic acids. Given that about 50% of total organic halogen formed in chlorination remains unknown, it is still unclear how bromide concentration affects the formation and speciation of the new/unknown halogenated DBPs. In this study, chlorinated drinking water samples with different bromide concentrations were prepared, and a novel approach-precursor ion scan using ultra performance liquid chromatography/electrospray ionization-triple quadrupole mass spectrometry-was adopted for the detection and identification of polar halogenated DBPs in these water samples. With this approach, 11 new putative aromatic halogenated DBPs were identified, and they were classified into four groups: dihalo-4-hydroxybenzaldehydes, dihalo-4-hydroxybenzoic acids, dihalo-salicylic acids, and trihalo-phenols. A mechanism for the formation of the four groups of new aromatic halogenated DBPs was proposed. It was found that increasing the bromide concentration shifted the entire polar halogenated DBPs as well as the four groups of new DBPs from being less brominated to being more brominated; these new aromatic halogenated DBPs might be important intermediate DBPs formed in drinking water chlorination. Moreover, the speciation of the four groups of new DBPs was modeled: the speciation patterns of the four groups of new DBPs well matched those determined from the model equations, and the reactivity differences between HOBr and HOCl in reactions forming the four groups of new DBPs were larger than those in reactions forming trihalomethanes and haloacetic acids.

Predicting total organic halide formation from drinking water chlorination using quantitative structure-property relationships

Chlorinating water which contains dissolved organic matter (DOM) produces disinfection byproducts, the majority of unknown structure. Hence, the total organic halide (TOX) measurement is used as a surrogate for toxic disinfection byproducts. This work derives a robust quantitative structure-property relationship (QSPR) for predicting the TOX formation potential of model compounds. Literature data for 49 compounds were used to train the QSPR in moles of chlorine per mole of compound (Cp) (mol-Cl/mol-Cp). The resulting QSPR has four descriptors, calibration [Formula: see text] of 0.72 and standard deviation of estimation of 0.43 mol-Cl/mol-Cp. Internal and external validation indicate that the QSPR has good predictive power and low bias (‰<‰1%). Applying this QSPR to predict TOX formation by DOM surrogates - tannic acid, two model fulvic acids and two agent-based model assemblages - gave a predicted TOX range of 136-184 µg-Cl/mg-C, consistent with experimental data for DOM, which ranged from 78 to 192 µg-Cl/mg-C. However, the limited structural variation in the training data may limit QSPR applicability; studies of more sulfur-containing compounds, heterocyclic compounds and high molecular weight compounds could lead to a more widely applicable QSPR.

Change of genotoxicity for raw and finished water: role of purification processes

In China, the safety of drinking water becomes a significant issue due to serious aquatic environmental pollution. The genotoxic levels of raw and finished water from seven typical waterworks located in the five basins in China were then evaluated using umu test. Effect of conventional treatment processes (coagulation, filtration and disinfection) on the genotoxicity and the fate of dissolved organic matter (DOM) was discussed. The results showed that most of the selected finished water presented genotoxicity at or lower than 300 mL water sample exposure dose. The genotoxic effects of finished water were significantly higher than those of raw water. It also exhibited that there existed higher correlation between genotoxic effect and Br(-) than the other water quality parameters. The brominated trihalomethanes played a more important role in finished water genotoxicity than brominated haloacetic acids. The treatment processes could increase the genotoxic effects of finished water, especially for the chlorination treatment. The fluorescence spectra and high performance size-exclusion chromatogram analysis of DOM characters indicated that the proportion of low molecular weight acids, nitrogen containing aromatics, proteinaceous and microbially derived organic matters (200-300 Da) increased during purification processes, which indicated probably the release or formation of drinking water genotoxins.

Reactivity of mucohalic acids in water

One group of disinfection byproducts of increasing interest are the halogenated furanones, which are formed in the chlorination of drinking water. Among these halofuranones is mucochloric acid (MCA, 3,4-dichloro-5-hydroxyfuran-2(5H)-one), and mucobromic acid (MBA, 3,4-dibromo-5-hydroxyfuran-2(5H)-one). Both mucohalic acids (MXA) are direct genotoxins and potential carcinogens, with the capacity to alkylate the DNA bases guanosine, adenosine and cytosine, and they have been measured in concentrations ranging up to 700 ng/l in tap water. MCA and MBA react in basic aqueous medium to form mucoxyhalic acids (4-halo-3,5-hydroxyfuran-2(5H)-one). Since: i) this reaction may represent the first step in the abiotic decomposition of mucohalic acids, ii) mucoxyhalic acids have been proposed as possible intermediates in the reaction of MXA with DNA, a kinetic study of the reaction mechanism is of interest. Here, the following conclusions were drawn: a) At moderately basic pH, the reaction of mucohalic acids with OH(-) to form mucoxyhalic acids is kinetically significant. b) The nucleophilic attack of hydroxide ions on MXA occurs through a combination of two paths: one of them is first-order in hydroxide whereas the other is second-order and are proposed to occur through the deprotonation of the hydrate of MXA. c) The hydration constants of mucohalic acids -0.23 and 0.17 for MCA and MBA respectively - corresponds to the very significant hydrate concentrations. Since hydrates are not electrophilic, these values imply a decrease in the alkylating capacity of mucohalic acids.

Effect of reductive property of activated carbon on total organic halogen analysis

Total organic halogen (TOX) is a collective parameter and a toxicity indicator for all the halogenated organic disinfection byproducts (DBPs) in a water sample. TOX can be measured with the adsorption-pyrolysis method based on Standard Method 5320B. This method involves concentration of organic halogens from water by adsorption onto activated carbon (AC) and removal of inorganic halides present on the AC by competitive displacement by nitrate ions. Since AC can also act as a reductant, this work studied whether the reduction of chlorinated DBPs by AC occurs during the TOX measurement, to what extent the reduction affects the measurement of TOX, what type of chlorinated DBPs can be reduced by AC, and whether the method for the TOX measurement can be improved. Initially, chlorinated Suwannee River fulvic acid samples were prepared and pretreated with precipitation/dialysis/ultrafiltration to minimize the chloride levels in the samples. It was found that the fractions of TOX in the precipitated, dialyzed, and ultrafiltered samples that were reduced by AC in 5 min were around 13%, 20% and 24%, respectively. The formation of some N-chloroamino compounds and their reactivity with AC were examined. The results indicate that organic chloramines are one type of DBPs in TOX that could be reduced by AC. It was demonstrated that slight oxidation of AC with ozone basically inhibited its reduction for TOX and meanwhile maintained its adsorption capacity for TOX.

Modern approaches to the analysis of disinfection by-products in drinking water

The discovery and study of disinfection by-products (DBPs) of health and regulatory concern in drinking water have often been hampered by the lack of appropriate analytical methods, but, with the new tools and expertise now available to the drinking water industry, there is an opportunity to plug a major gap in our knowledge of the nature and identity of these chemicals. The challenge is that less than half of the halogenated by-products resulting from the chlorination of drinking water have been identified, and even less is known about those produced in waters treated with ozone, chloramines or chlorine dioxide. For the DBPs that have been identified, very little or no occurrence data exist for the unregulated chemicals to document how often a particular DBP is formed and in what quantity. The elucidation of the nature and identity of these by-products is hindered by two complicating factors. The first is the inherent aqueous solubility of many of these compounds, which renders their efficient extraction from water difficult to achieve. The second is the lack of established identity of specific potential by-products, which complicates targeted analytical approaches. This paper reviews existing and new methodologies that attempt to overcome some of these challenges.

The formation and control of emerging disinfection by-products of health concern

When drinking water treatment plants disinfect water, a wide range of disinfection by-products (DBPs) of health and regulatory concern are formed. Recent studies have identified emerging DBPs (e.g. iodinated trihalomethanes (THMs) and acids, haloacetonitriles, halonitromethanes (HNMs), haloacetaldehydes, nitrosamines) that may be more toxic than some of the regulated ones (e.g. chlorine- and bromine-containing THMs and haloacetic acids). Some of these emerging DBPs are associated with impaired drinking water supplies (e.g. impacted by treated wastewater, algae, iodide). In some cases, alternative primary or secondary disinfectants to chlorine (e.g. chloramines, chlorine dioxide, ozone, ultraviolet) that minimize the formation of some of the regulated DBPs may increase the formation of some of the emerging by-products. However, optimization of the various treatment processes and disinfection scenarios can allow plants to control to varying degrees the formation of regulated and emerging DBPs. For example, pre-disinfection with chlorine, chlorine dioxide or ozone can destroy precursors for N-nitrosodimethylamine, which is a chloramine by-product, whereas pre-oxidation with chlorine or ozone can oxidize iodide to iodate and minimize iodinated DBP formation during post-chloramination. Although pre-ozonation may increase the formation of trihaloacetaldehydes or selected HNMs during post-chlorination or chloramination, biofiltration may reduce the formation potential of these by-products.