Specific Disinfection By-products Research Articles

Recognizing high-priority disinfection byproducts based on experimental and predicted endocrine disrupting data: Virtual screening and in vitro study

So far, about 130 disinfection by-products (DBPs) and several DBPs-groups have had their potential endocrine-disrupting effects tested on some endocrine endpoints. However, it is still not clear which specific DBPs, DBPs-groups/subgroups may be the most toxic substances or groups/subgroups for any given endocrine endpoint. In this study, we attempt to address this issue. First, a list of relevant DBPs was updated, and 1187 DBPs belonging to 4 main-groups (aliphatic, aromatic, alicyclic, heterocyclic) and 84 subgroups were described. Then, the high-priority endocrine endpoints, DBPs-groups/subgroups, and specific DBPs were determined from 18 endpoints, 4 main-groups, 84 subgroups, and 1187 specific DBPs by a virtual-screening method. The results demonstrate that most of DBPs could not disturb the endocrine endpoints in question because the proportion of active compounds associated with the endocrine endpoints ranged from 0 (human thyroid receptor beta) to 32% (human transthyretin (hTTR)). All the endpoints with a proportion of active compounds greater than 10% belonged to the thyroid system, highlighting that the potential disrupting effects of DBPs on the thyroid system should be given more attention. The aromatic and alicyclic DBPs may have higher priority than that of aliphatic and heterocyclic DBPs by considering the activity rate and potential for disrupting effects. There were 2 (halophenols and estrogen DBPs), 12, and 24 subgroups that belonged to high, moderate, and low priority classes, respectively. For individual DBPs, there were 23 (2%), 193 (16%), and 971 (82%) DBPs belonging to the high, moderate, and low priority groups, respectively. Lastly, the hTTR binding affinity of 4 DBPs was determined by an in vitro assay and all the tested DBPs exhibited dose-dependent binding potency with hTTR, which was consistent with the predicted result. Thus, more efforts should be performed to reveal the potential endocrine disruption of those high research-priority main-groups, subgroups, and individual DBPs.

Fluorescent Dissolved Organic Matter Components as Surrogates for Disinfection Byproduct Formation in Drinking Water: A Critical Review.

Disinfection byproduct (DBP) formation, prediction, and minimization are critical challenges facing the drinking water treatment industry worldwide where chemical disinfection is required to inactivate pathogenic microorganisms. Fluorescence excitation-emission matrices-parallel factor analysis (EEM-PARAFAC) is used to characterize and quantify fluorescent dissolved organic matter (FDOM) components in aquatic systems and may offer considerable promise as a low-cost optical surrogate for DBP formation in treated drinking waters. However, the global utility of this approach for quantification and prediction of specific DBP classes or species has not been widely explored to date. Hence, this critical review aims to elucidate recurring empirical relationships between common environmental fluorophores (identified by PARAFAC) and DBP concentrations produced during water disinfection. From 45 selected peer-reviewed articles, 218 statistically significant linear relationships (R2 ≥ 0.5) with one or more DBP classes or species were established. Trihalomethanes (THMs) and haloacetic acids (HAAs), as key regulated classes, were extensively investigated and exhibited strong, recurrent relationships with ubiquitous humic/fulvic-like FDOM components, highlighting their potential as surrogates for carbonaceous DBP formation. Conversely, observed relationships between nitrogenous DBP classes, such as haloacetonitriles (HANs), halonitromethanes (HNMs), and N-nitrosamines (NAs), and PARAFAC fluorophores were more ambiguous, but preferential relationships with protein-like components in the case of algal/microbial FDOM sources were noted. This review highlights the challenges of transposing site-specific or FDOM source-specific empirical relationships between PARAFAC component and DBP formation potential to a global model.

Fertilization regime shifts the molecular diversity and chlorine reactivity of soil dissolved organic matter from tropical croplands

Soil-derived dissolved organic matter (SDOM) is an important site-specific disinfection byproduct (DBP) precursor in watersheds. However, it remains unclear how fertilization regime shifts the molecular diversity and chlorine reactivity of SDOM in cropland-impacted watersheds. Here, we analyzed the spectroscopic and molecular-level characteristics of the SDOM from croplands that had different fertilization regimes (i.e., non-fertilization, chemical fertilization, straw return, and chemical fertilization plus straw return) for 5 years and evaluated the chlorine reactivity of the SDOM by determining the 24-h chlorine consumption and specific DBP formation potential (SDBP-FP). The SDOM level decreased by chemical fertilization and was not significantly altered by straw return alone or combined with chemical fertilizer. However, all fertilization regimes elevated the molecular diversity of SDOM by increasing the abundance of protein-, lignin-, and tannin-like compounds. The chlorine reactivity of SDOM was reduced by chemical fertilization, but was significantly increased by straw return. Typically, straw return increased the formation potential of specific trihalomethane and chloral hydrate by 339% and 56% via increasing the aromatics in SDOM, whereas chemical fertilization could effectively decrease about 231% of the increased specific trihalomethane formation potential caused by straw return. This study highlights that fertilization regime can significantly shape the molecular diversity and chlorine reactivity of the SDOM in croplands and that partially replacing chemical fertilizer with crop straw is an advantageous practice for reducing DBP risks in drinking water in cropland-impacted watersheds.

Research Progress of the Endocrine-Disrupting Effects of Disinfection Byproducts.

Since 1974, more than 800 disinfection byproducts (DBPs) have been identified from disinfected drinking water, swimming pool water, wastewaters, etc. Some DBPs are recognized as contaminants of high environmental concern because they may induce many detrimental health (e.g., cancer, cytotoxicity, and genotoxicity) and/or ecological (e.g., acute toxicity and development toxicity on alga, crustacean, and fish) effects. However, the information on whether DBPs may elicit potential endocrine-disrupting effects in human and wildlife is scarce. It is the major objective of this paper to summarize the reported potential endocrine-disrupting effects of the identified DBPs in the view of adverse outcome pathways (AOPs). In this regard, we introduce the potential molecular initiating events (MIEs), key events (KEs), and adverse outcomes (AOs) associated with exposure to specific DBPs. The present evidence indicates that the endocrine system of organism can be perturbed by certain DBPs through some MIEs, including hormone receptor-mediated mechanisms and non-receptor-mediated mechanisms (e.g., hormone transport protein). Lastly, the gaps in our knowledge of the endocrine-disrupting effects of DBPs are highlighted, and critical directions for future studies are proposed.

Tracking spatio-temporal dynamics of fluorescence characteristics of Huangpu River, China by parallel factor analysis: Correlation with disinfection by-product precursor and pesticide level variations

The components and characteristics of dissolved organic matter (DOM), the main precursor of toxic disinfection by-products (DBPs), have attracted increasing attention in water sources. In this study, fluorescence excitation-emission matrix (EEM) coupled with parallel factor (PARAFAC) analysis was used to investigate the DOM fluorescence characteristics of river water along the Huangpu River, China. Four fluorescence components were identified, including two protein-like components (C1 and C2) and two humic-like components (C3 and C4). The fluorescence characteristics showed spatial and temporal variations with the highest total fluorescence intensities observed in autumn, and the increased relative abundance of humic-like substance in the metropolitan area of Shanghai. Fluorescence index and biological index indicated that the DOM of Huangpu River water had both terrestrial and microbial origins and mainly autochthonous characteristic. Moreover, the formation potentials (FPs) of DBP for Huangpu River water were determined, and trihalomethanes were the predominant species formed in all samples. The correlation analysis further showed that PARAFAC C4 (microbial humic-like fluorescence) significantly correlated with the FP of N-DBPs, providing an insight for drinking water treatment to control specific DBPs precursor. In addition, the humic-like components also correlated with the concentrations of triazole and organophosphate pesticides detected in the Huangpu River. These results indicated that fluorescence-PARAFAC analysis is a promising tool to assess the DBPFPs and pesticide occurrence in surface waters.

Analytical discovery of water disinfection byproducts of toxicological relevance: highlighting halobenzoquinones

Analytical advancement enables discoveries in water research, and challenges in the identification and determination of a wide range of trace level toxic compounds in water drives the development of new analytical platforms and tools. The identification of toxic disinfection byproducts (DBPs) in disinfected drinking water is an excellent example. Water disinfection is necessary to protect the public from waterborne disease. However, an unintentional consequence is the formation of DBPs resulting from reactions of disinfectants with natural organic matter in source water. To date, regulated DBPs do not account for the increased bladder cancer risk estimated in epidemiological studies. The majority of halogenated DBPs remain unidentified and the discovery of unknown DBPs of toxicological relevance continues to be a major focus of current water research. This review will highlight halobenzoquinones as a class of DBPs that serves as an example of analytical development and toxicological studies. We will feature recent trends and gaps in analytical technologies for identification of unknown DBPs and bioassays for evaluation of the toxicological effects of specific DBPs and their mixtures.

DNA pyrimidine bases in water: Insights into relative reactivity, byproducts formation and combined toxicity during chlorination

Soluble microbial products (SMPs), as precursors of disinfection byproducts (DBPs) in water treatment, are composed of polysaccharides, humic acid, proteins and DNA, and have caused widespread concerned. Pyrimidine bases (cytosine and thymine) are significant nitrogenous constituents of DNA, which could pose an adverse impact on water quality during chlorination. This study focused on the correlation between relative reactivity, formation of DBPs and combined toxicity in the chlorination of a binary pyrimidine base mixture. The relative reactivities of cytosine and thymine were quite different at a low disinfectant concentration; cytosine reacted more actively with chlorine than thymine did, at the chlorine/total pyrimidine bases molar ratio = 10. The chlorination of binary pyrimidine bases can produce both carbonous DBPs (C-DBPs) and nitrogenous DBPs (N-DBPs). In particular, the total yields of trichloromethane (TCM) and trichloronitromethane (TCNM) were lower than the additive yields of monadic cytosine and monadic thymine (“monadic” refers to “separate”), whereas the total yields of haloacetic acids (HAAs) and haloacetonitriles (HANs) were promoted evidently. High reactivity of cytosine with chlorine, greater potential of cytosine to produce specific DBPs and the alkylation of transformation products of thymine may synthetically account for the diversity in total DBPs yields, especially the increased formation of HAAs and HANs. In our toxicity trial, even though the antagonistic effect predominated at fa > 0.4 (fa refers to the affected fraction), the synergism at low concentration levels could enhance the combined toxicity by promoting the yields of N-DBPs.

The combined influence of hydrophobicity, charge and molecular weight on natural organic matter removal by ion exchange and coagulation

Three different source waters were investigated using virgin and pre-used anion exchange resins, coagulation, and ion exchange combined with coagulation (IEX&Coagulation). The hydrophobicity, size distribution and charge of natural organic matter (NOM) were used to evaluate its removal. Dissolved organic carbon (DOC) removal by pre-used IEX resin was 67–79%. A consistent ratio of different hydrophobicity fractions was found in the removed DOC, while the proportion and quantity of the molecular weight fraction around 1 kDa was important in understanding the treatability of water. For pre-used resin, organic compounds were hypothesised to be restricted to easily accessible exchange sites. Comparatively, virgin resin achieved higher DOC removals (86–89%) as resin fouling was absent. Charge density and the proportion of the hydrophobic fraction were found to be important indicators for the specific disinfection byproduct formation potential (DBP-FP). Treatment of raw water with pre-used resin decreased the specific DBP-FP by between 2 and 43%, while the use of virgin resin resulted in a reduction of between 31 and 63%. The highest water quality was achieved when the combination of IEX and coagulation was used, reducing DOC and the specific DBP-FP well below that seen for either process alone.

The combined toxicity of UV/chlorinated products from binary ibuprofen (IBP) and tyrosine (Tyr) on Escherichia coli: Emphasis on their occurrence and underlying mechanism

In this study, the combined toxicity of UV/chlorinated products on Escherichia coli (E. coli) was investigated when ibuprofen (IBP) and tyrosine (Tyr) were used as two precursors. The median-effect equation and combined index (CI)-isobologram equation were used to evaluate the combined toxicity of UV/chlorinated products. Results revealed that the UV/chlorinated products originated from binary Tyr and IBP showed a synergism in toxicity on Escherichia coli at low concentration level while it turned into a clear antagonism effect above a fa value of 0.2 in the toxicity trial. The combined toxic effects on E. coli were determined by both the potential toxicity mode of specific disinfection byproducts (DBPs) and the complicated interaction caused by Tyr and IBP. The addition of IBP decreased the yield of N-DBPs generated from Tyr, which dominated the effect of combined toxicity. Even though the antagonism predominated in toxicity effect on E. coli, the synergistic toxicity at low dose levels should be getting attention, which was more close to the natural concentration of N-DBPs in waters.

Associations Between Craniofacial Birth Defects and Disinfection By-Product Exposures in Massachusetts, USA

Epidemiological studies suggest that women exposed to disinfection by-products (DBPs) in treated water have an increased risk of delivering babies with some birth defect types, though evidence for craniofacial defects (CFDs) and specific DBPs is limited. We used a case-control design of birth defects in Massachusetts from 2000-2004 with complete trihalomethane (THM) and haloacetic acid (HAA) data. We randomly matched each case (n=371) to 10 controls based on week of conception. We used first trimester DBP exposures weight-averaged across quarterly water sampling locations linked to individuals based on residence at birth. Adjusted odds ratios (aORs) were calculated for four CFDs in relation to 13 DBP exposures categorized based on available data distributions, including chloroform (TCM), bromodichloromethane (BDCM), dibromochloromethane (DBCM), dichloroacetic acid (DCA), trichloroacetic acid (TCA), THM4 (sum of bromoform, TCM, BDCM, DBCM), HAA5 (sum of DCA, TCA, monochloroacetic, monobromoacetic, and dibromoacetic acids) and DBP9 (sum of THM4 and HAA5). Comparing highest to lowest exposure groups, we detected elevated aORs for cleft palate (n=131) for quintiles of DBP9 (aOR=6.36; 95%CI: 1.55-26.10) and THM4 (aOR=2.54; 95%CI: 0.60-10.74), quartiles of DCA (aOR=2.25; 95%CI: 0.68-7.42) and TCA (aOR=2.10; 95%CI: 0.64-6.89), BDCM tertiles (aOR=1.32; 95%CI: 0.65-2.71), the upper DBCM decile (aOR=1.30; 95% CI: 0.57-2.99), and a positive exposure-response relationship for HAA5 quintiles (aOR range: 1.53-3.30). We detected elevated aORs for eye defects (n=67) with THM4 tertiles (aOR=3.81; 95%CI: 0.74-19.52), TCA quartiles (aOR=4.05; 95%CI: 0.52-31.59), and the upper BDCM decile (aOR=2.64; 95%CI: 0.66-10.58). No elevated aORs were detected for cleft lip or ear defects. Though our analyses were limited by small case numbers, this is the first study to examine HAAs with CFDs, and the third to examine brominated DBPs, thus adding specificity to previous research.

Performance of novel media in stratified filters to remove organic carbon from lake water

Disinfection by-products (DBPs) are an ever-increasing occurrence in water networks, particularly those which abstract water from peatland areas. Although much research has been carried out to discover novel methods to remove specific DBPs, the removal of natural organic matter (NOM) from source water may provide a more sustainable solution in many areas. This study focuses on the removal of NOM by novel filters, which could be retrospectively fitted to any conventional water treatment facility. The filters comprised stratified layers of a variety of media, including sand, Bayer residue, granular activated carbon (GAC), and pyritic fill. The filters were operated under two loading regimes, continuous and intermittent, at loading rates similar to recognised design standards. The most successful filter design comprised stratified layers of sand, GAC, and pyritic fill. Over the duration of a 240 day study, these filters obtained average dissolved organic carbon removal rates of 40%, and achieved average specific ultra-violet absorbance reductions from 2.9 to 2.4 L mg−1 m−1. The study demonstrates that these novel filters may be used to reduce NOM levels, thus reducing the potential for DBP formation. Such designs can incorporate the use of waste media, making the overall design more sustainable and robust.

Growing Algae Alter Spectroscopic Characteristics and Chlorine Reactivity of Dissolved Organic Matter from Thermally-Altered Forest Litters.

Previous studies demonstrated that wildfires alter spectroscopic characteristics of terrestrial dissolved organic matter (DOM) and increase specific disinfection byproduct formation potential (SDBP-FP). However, it is unclear whether characteristics of thermally altered DOM (TA-DOM) are altered by biogeochemical processes (e.g., transformed by growing algae) before entering water treatment facilities. The freshwater green algae Pseudokirchneriella subcapitata and blue-green algae Microcystis aeruginosa were separately incubated in the mixture of cultural medium and pine (Pinus palustris) litter-derived TA-DOMs (50 °C, 250 °C, and 400 °C) over 7 days to demonstrate the effects of algal growth on alterations in SDBP-FP. TA-DOM optical characteristics and SDBP-FP were quantified by absorption and fluorescence spectroscopy and chlorination-based DBP-FP experiments. After the inoculation with P. subcapitata, TA-DOM aromaticity (indicated by SUVA254) increased from 1.19 to 1.90 L/mg/m for 50 °C-extract but decreased from 4.95 to 3.75 L/mg/m for 400 °C-extract. The fraction of tyrosine-like components decreased from 25.9 to 9.3% for 50 °C-extract but increased from 0.9 to 1.3% for 400 °C-extract. Same patterns were also observed for M. aeruginosa. Growing algae generally increased chlorine reactivities and formations of trihalomethanes, haloacetonitriles, chloral hydrate, and haloketones. Our data suggest that the biodegradable dissolved organic carbon in TA-DOM decreases as fire intensity (i.e., temperature) increases. Postfire algal blooms can increase chlorine reactivity of fire-affected terrestrial DOM for DBP formation.

A non-target approach to identify disinfection byproducts of structurally similar sulfonamide antibiotics

There is growing concern over the formation of new types of disinfection byproducts (DBPs) from pharmaceuticals and other emerging contaminants during drinking water production. Free chlorine is a widely used disinfectant that reacts non-selectively with organic molecules to form a variety of byproducts. In this research, we aimed to investigate the DBPs formed from three structurally similar sulfonamide antibiotics (sulfamethoxazole, sulfathiazole, and sulfadimethoxine) to determine how chemical structure influences the types of chlorination reactions observed. We conducted free chlorination experiments and developed a non-target approach to extract masses from the experimental dataset that represent the masses of candidate DBPs. Structures were assigned to the candidate DBPs based on analytical data and knowledge of chlorine chemistry. Confidence levels were assigned to each proposed structure according to conventions in the field. In total, 11, 12, and 15 DBP structures were proposed for sulfamethoxazole, sulfathiazole, and sulfadimethoxine, respectively. The structures of the products suggest a variety of reaction types including chlorine substitution, SC cleavage, SN hydrolysis, desulfonation, oxidation/hydroxylation, and conjugation reactions. Some reaction types were common to all of the sulfonamide antibiotics, but unique reaction types were also observed for each sulfonamide antibiotic suggesting that selective prediction of DBP structures of other sulfonamide antibiotics based on chemical structure is unlikely to be possible based on these data alone. This research offers an approach to comprehensively identify DBPs of organic molecules and fills in much needed data on the formation of specific DBPs from three environmentally relevant sulfonamide antibiotics.

Characterization of the precursors of trihalomethanes and haloacetic acids in the Yuqiao Reservoir in China.

To identify the primary precursors of trihalomethanes and haloacetic acids in the Yuqiao Reservoir in China, dissolved organic matters in the source water were isolated and fractionated into five different fractions (with XAD resin), and both trihalomethane and haloacetic acid formation potentials in each fraction were analysed by liquid-liquid extraction and GC-ECD. The primary precursors of trihalomethanes and haloacetic acids were identified using the index of disinfection by-product formation potential and specific disinfection by-product formation potential. In addition, the relationship between the specific ultraviolet absorbance and the specific disinfection by-product formation potential was studied using correlation analysis. The results indicated that during the sampling period, the hydrophobic acids and hydrophilic matter are the primary organic fractions in the Yuqiao Reservoir, accounting for 27.6-40.9% and 21.2-32.5%, respectively. Among the five fractions, the hydrophobic acids had the highest disinfection by-product formation potential and specific disinfection by-product formation potential, indicating that the hydrophobic acids were the primary precursors of the disinfection by-products in the Yuqiao Reservoir. A correlation analysis indicates that the specific ultraviolet absorbance had a moderately positive correlation with the specific disinfection by-product formation potential; therefore, the specific ultraviolet absorbance can be a reference index to analyse the ability of organic matter to generate disinfection by-products.

Disinfection by-products formation and precursors transformation during chlorination and chloramination of highly-polluted source water: Significance of ammonia

Many studies have demonstrated the different trends of disinfection by-products (DBPs) formation between chlorination and chloramination. However, the reactions between precursors and disinfectants are widely assumed to be “black box” and the reasons for abovementioned difference are not well illustrated. This study focused on source water with high levels of natural organic matter (NOM) and bromide, and compared the transformation of NOM specific characteristics and the ratios of specific DBPs as an equivalent of chlorine to total organic halogen (TOX) among three disinfection scenarios of chlorination, chloramination and chlorine–chloramine sequential treatment (Cl2–NH2Cl process). A three-reaction-phrases model was proposed thereafter to illustrate the major reactions involved in, i.e., stage-I: rapid consumption of fast reactive sites (DOC1), which transformed to slow reactive sites (DOC2) and measured DBPs, i.e., trihalomethanes, haloacetic acids, etc; stage-II: oxidation and/or halogenation of DOC2 into unknown TOX (UTOX) intermediates; stage-III: oxidation of UTOX intermediates into measured DBPs. The effect of ammonia was also quantified. Ammonia is observed to inhibit the formation of measured DBPs by 68–92%, 94–99%, and 92–95% of that in chlorination in Stage-I, II, and III, respectively, and the formation of UTOX is reduced by 2–80%, 60–94%, and 82–93% accordingly. These effects lead to the steady accumulation of DBPs intermediates such as UTOX, and to the elevated UTOX/TOX during chloramination and Cl2–NH2Cl process thereafter. The results illustrate the mechanism of ammonia participating in DBPs formation, and are valuable to fill in the gap between the transformation of precursors and the formation of different DBPs.

Removal of Specific DBP by GAC in Galatsi (Athens) WTP

The objective of this pilot-study is to evaluate the Granular Activated Carbon (GAC)
 performance for the removal of specific disinfection by-products (DBPs), trihalomethanes
 (THMs) and haloacetic acids (HAAs), from Athens drinking water. For this purpose, a GAC
 pilot filter-adsorber was operated in Galatsi WTP, Athens, for 235 days, until the GAC
 removal efficiency for individual THMs, HAAs and DOC was almost eliminated
 (breakthrough). From the experimental results, GAC bed life, GAC loading, carbon usage
 rate, and operation time to breakthrough for most THMs and HAAs were calculated.
 The average influent concentrations of the more chlorinated THMs and HAAs were higher
 than those of less chlorinated and more brominated species and their mass adsorbed on the
 GAC column was also higher, as expected according to Freundlich isotherm. TCA, TCM and
 DCA had the highest influent concentrations and they seemed to be better adsorbed than the
 rest. TBM, TBA and DBCA were almost not detected in feed water.
 Comparison of the GAC loading at breakthough for pairs of compounds with similar average
 influent concentration showed that TCA is better adsorbed than TCM and that BDCA is better
 adsorbed than MCA, BDCM and DBCM.
 Desorption phenomena of some THMs and HAAs, probably caused by a sudden drop in
 influent concentration, were also noticed.
 The above findings represent real operation conditions for Athens drinking water.
 Further research is recommended on methods to reduce desorption from carbon beds.

Adverse reproductive health effects of exposure to chlorination disinfection by-products

Chlorination disinfection by-products (DBPs) are formed when water is chlorinated and the
 organic matter in the water reacts with chlorine to form these by-products. There have
 been concerns about the potential health effects of these by-products, including cancer and
 reproductive effects. Here we have reviewed the literature on reproductive health effects.
 Epidemiological studies on neural tube defects, urinary tract defects and small for gestation
 age/intra growth retardation have shown the most consistent statistically significant
 associations with an index of DBPs, but generally the risk estimates are small. The
 interpretation of the studies is not straight forward because they may not be directly
 comparable because of differences in DBP mixtures, exposure categories and actually
 uptake of DBPs due to differences in e.g. ingestion rates, showering, bathing, and
 swimming. Only few specific DBPs have been studied and THMs have often been used as
 a marker for other DBPs, since they are often routinely available. Sample sizes, and
 therefore power, have at times been low, particularly when the population was split into
 exposure categories. Although most studies considered some confounders, (residual)
 confounding by other water contaminants or other factors related to water intake, cannot
 always be excluded. Case ascertainment, for outcomes such as spontaneous abortion and
 certain congenital anomalies is far from straight forward, and for the latter at times
 anomalies are lumped together with different aetiology, which may be inappropriate.
 Furthermore, as with many reproductive epidemiological, if the putative agent affects both
 early pregnancy loss and later birth outcomes such as congenital anomalies, interpretation
 of later birth outcomes may be more difficult.

Health impact of disinfection by-products in swimming pools

This article is focused on the epidemiological evidence on the health impacts related to disinfection by-products (DBPs) in swimming pools, which is a chemical hazard generated as an undesired consequence to reduce the microbial pathogens. Specific DBPs are carcinogenic, fetotoxic and/or irritant to the airways according to experimental studies. Epidemiological evidence shows that swimming in pools during pregnancy is not associated with an increased risk of reproductive outcomes. An epidemiological study suggested an increased risk of bladder cancer with swimming pool attendance, although evidence is inconclusive. A higher prevalence of respiratory symptoms including asthma is found among swimming pool workers and elite swimmers, although the causality of this association is unclear. The body of evidence in children indicates that asthma is not increased by swimming pool attendance. Overall, the available knowledge suggests that the health benefits of swimming outweigh the potential health risks of chemical contamination. However, the positive effects of swimming should be enhanced by minimising potential risks.

Effects of UV irradiation and UV/chlorine co-exposure on natural organic matter in water

The effects of co-exposure to ultraviolet (UV) irradiation (with either low- or medium-pressure UV lamps) and free chlorine (chloramine) at practical relevant conditions on changes in natural organic matter (NOM) properties were investigated using four waters. The changes were characterized using the specific disinfection by-product formation potential (SDBPFP), specific total organic halogen formation potential (STOXFP), differential UV absorbance (∆UVA), and size-exclusion chromatography (SEC). The results for exposure to UV irradiation alone and for samples with no exposure were also obtained. The SDBPFPs in all UV-irradiated NOM waters observed were higher than those of non-irradiated samples. UV irradiation led to increases in STOXFPs as a result of chlorination, but no changes, or only small decreases, from chloramination. UV irradiation alone led to positive ∆UVA spectra of the four NOM waters; co-exposure to UV and chlorine gave larger negative ∆UVA spectra than those obtained by chlorine exposure alone. No obvious changes in SEC results were observed for samples only irradiated with UV light; co-exposure gave no detectable changes in the abundances of small fractions for exposure to chlorine only. Both UV photooxidation and photocatalytic oxidation appear to affect the reactivity of the NOM toward subsequent chlorination, and the magnitude of the changes is generally greater for medium-pressure lamps than for low-pressure lamps. These results suggest that applying UV disinfection technology to a particular source may not always be disinfection by-product-problem-free, and the interactions between UV light, chlorine, and NOM may need to be considered.

Reactivity of Litter Leachates from California Oak Woodlands in the Formation of Disinfection By‐Products

Litter materials from forested watersheds can be a significant source of dissolved organic matter (DOM) to surface waters that can contribute to the formation of carcinogenic disinfection by-products (DBPs) during drinking-water chlorination. This study characterized the reactivity of DOM from litter leachates of representative vegetation in oak woodlands, a major plant community in the Foothill Region of California. Leachates from fresh and decomposed litter (duff) from two oak species, pine, and annual grasses were collected for an entire rainy season to evaluate their reactivity to form DBPs on chlorination. Relationships among specific ultraviolet absorbance (SΔUVA), fluorescence index (FI), specific differential ultraviolet absorbance (SΔUVA), specific chlorine demand (SCD), and the dissolved organic carbon:dissolved organic nitrogen (DOC:DON) ratio to the specific DBP formation potential (SDBP-FP) were examined. The DOM derived from litter materials had considerable reactivity in forming trihalomethanes (THMs) (1.80-3.49 mmol mol), haloacetic acid (HAAs) (1.62-2.76 mmol mol(-1)), haloacetonitriles (HANs) (0.12-0.37 mmol mol(-1)), and chloral hydrate (CHD) (0.16-0.28 mmol mol). These values are comparable to other identified watershed sources of DBP precursors reported for the California Delta, such as wetlands and organic soils. Vegetation type and litter decomposition stage (fresh litter versus 1-5 yr-old duff) were key factors that determined characteristics of DOM and their reactivity to form DBPs. Pine litter had significantly lower specific THM formation potential compared with oak and grass, and decomposed duff had a greater DON content, which is a precursor of HANs and other nitrogenous DBPs. The SΔUVA and SDBP-FP were temporally variable and dependent on vegetation type, degree of decomposition, and environmental conditions. Among the optical properties of DOM, SΔUVA was the only parameter that was consistently correlated with SDBP-FP.