Formation potential of disinfection byproducts during chlorination of petroleum hydrocarbon-contaminated drinking water.

Recent leaks of underground fuel storage tanks in the Pearl Harbor region have led to direct release of un-weathered petroleum hydrocarbons (PHCs) into drinking water sources, which then directly underwent chlorination disinfection treatment. Since the control of disinfection byproducts (DBPs) traditionally focuses natural organic matters (NOM) from source water and little is known about the interactions between free chlorine and un-weathered PHCs, laboratory chlorination experiments in batch reactors were conducted to determine the formation potential of DBPs during chlorination of PHC-contaminated drinking water. Quantitative analysis of regulated DBPs showed that significant quantities of THM4 (average 3,498 µg/L) and HAA5 (average 355.4 µg/L) compounds were formed as the result of chlorination of un-weathered PHCs. Amongst the regulated DBPs, THM4, which were comprised primarily of chloroform and bromodichloromethane, were more abundant than HAA5. Numerous unregulated DBPs and a large diversity of unidentified potentially halogenated organic compounds were also produced, with the most abundant being 1,1-dichloroacetone, 1,2-dibromo-3-chloropropane, chloropicrin, dichloroacetonitrile, and trichloracetonitrile. Together, the results demonstrated the DBP formation potential when PHC-contaminated water undergoes chlorination treatment. Further studies are needed to confirm the regulated DBP production and health risks under field relevant conditions.

Pharmacokinetics of bromoform in dairy heifers.

AIMS: To determine the pharmacokinetics in dairy heifers after oral and IV administration of bromoform, a potential antimethanogenic agent found in red seaweed, Asparagopsis spp. METHODS: Twenty-four dairy heifers with a mean weight of 319 (SD 36.9) kg were used. The study was conducted in two phases, and each cohort of 12 heifers received an escalating dose of bromoform. In the first phase, 12 heifers successively received doses of 200, 400, 800, and 1600 mg of bromoform orally, separated by a 72-hour washout period. In the second phase, a different cohort of 12 dairy heifers was used. Each heifer received a total of four doses of bromoform separated by a wash-out period of 72 hours. Sequentially the treatments were (for each of the 12 heifers) an oral dose of 50 mg, followed by an IV dose of 50 mg, followed by an oral dose of 100 mg and finally an IV dose of 100 mg.Blood samples were assayed by gas chromatography-mass spectrophotometry for bromoform and dibromomethane to estimate the pharmacokinetic parameters using a non-compartmental analysis. RESULTS: Bromoform was rapidly absorbed as indicated by a short time to the maximum observed concentration of 15 minutes. For the routes of administration and dose ranges investigated, the mean terminal half-life ranged from 0.32 (SE 0.03) hours to 5.73 (SE 1.64) hours when administered orally or IV. With values for the mean area under the curve (AUC) to dose ratio ranging from 0.25 (SE 0.04) to 0.82 (SE 0.19) for oral and 1.39 (SE 0.39) to 4.02 (SE 0.37) for IV administration, bromoform appeared to exhibit non-proportional pharmacokinetic behaviour. The mean absolute bioavailability was 39.13 (SE 10.4)% and 3.36 (SE 0.83)% for 50-mg and 100-mg doses, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Bromoform is rapidly absorbed and exhibits dose dependent elimination kinetics.

Non-target screening and prioritization of organic contaminants in seawater desalination and their ecological risk assessment.

The impact of desalination brine on the marine environment is a global concern. Regarding this, salinity is generally accepted as the major environmental factor in desalination concentrate. However, recent studies have shown that the influence of organic contaminants in brine cannot be ignored. Therefore, a non-targeted screening method based on comprehensive two-dimensional gas chromatography-quadrupole mass spectrometry (GC × GC-qMS) was developed for identifying organic contaminants in the desalination brine. A total of 404 compounds were tentatively identified from four seawater desalination plants (three reverse osmosis plants and one multiple effect distillation plant) in China. The identified compounds were prioritized based on their persistence, bioaccumulation, ecotoxicity, usage, and detection frequency. Twenty-one (21) compounds (seven phthalates, ten pesticides, four trihalomethanes) were then selected for further quantitative analysis and ecological risk assessment, including compounds from the priority list along with substances from the same chemical classes. Ecologically risky substances in brine include diisobutylphthalate and bis(2-Ethylhexyl) phthalate, atrazine and acetochlor, and bromoform. Most of the contaminants come from raw seawater, and no high risk contaminants introduced by the desalination process have been found except for disinfection by-products. In brine discharge management, people believed that all pollution in raw seawater was concentrated by desalination process. This study shows that not all pollutants are concentrated during the desalination process. In this study, the total concentration of pesticide in the brine increased by 58.42%. The concentration of ∑PAEs decreased by 13.65% in reverse osmosis desalination plants and increased by 10.96% in the multi-effect distillation plant. The concentration of trihalomethane increased significantly in the desalination concentrate. The change in the concentration of pollutants in the desalination concentrate was related to the pretreatment method and the chemical characteristics of the contaminants. The method and results given in this study hinted a new idea to identify and control the environmental impact factors of brine.

Control of chlorination disinfection by-products in drinking water by combined nanofiltration process: A case study with trihalomethanes and haloacetic acids.

Disinfection by-products (DBPs) are prevalent contaminants in drinking water and are primarily linked to issues regarding water quality. These contaminants have been associated with various adverse health effects. Among different treatment processes, nanofiltration (NF) has demonstrated superior performance in effectively reducing the levels of DBPs compared to conventional processes and ozone-biological activated carbon (O3-BAC) processes. In this experiment, we systematically investigated the performance of three advanced membrane filtration treatment schemes, namely "sand filter + nanofiltration" (SF + NF), "sand filter + ozone-biological activated carbon + nanofiltration" (SF + O3-BAC + NF), and "ultrafiltration + nanofiltration" (UF + NF), in terms of their ability to control disinfection by-product (DBP) formation in treated water, analyzed the source and fate of DBP precursors during chlorination, and elucidated the role of precursor molecular weight distribution during membrane filtration in relation to DBP formation potential (DBPFP). The results indicated that each treatment process reduced DBPFP, as measured by trihalomethane formation potential (THMFP) and haloacetic acid formation potential (HAAFP), with the SF + O3-BAC + NF process being the most effective (14.27 µg/L and 14.88 µg/L), followed by the SF + NF process (21.04 µg/L and 16.29 µg/L) and the UF + NF process (26.26 µg/L and 21.75 µg/L). Tyrosine, tryptophan, and soluble microbial products were identified as the major DBP precursors during chlorination, with their fluorescence intensity decreasing gradually as water treatment progressed. Additionally, while large molecular weight organics (60-100,000 KDa) played a minor role in DBPFP, small molecular weight organics (0.2-5 KDa) were highlighted as key contributors to DBPFP, and medium molecular weight organics (5-60 KDa) could adhere to the membrane surface and reduce DBPFP. Based on these findings, the combined NF process can be reasonably selected for controlling DBP formation, with potential long-term benefits for human health.

Sunlight enhanced the formation of tribromomethane from benzotriazole degradation during the sunlight/free chlorine treatment in the presence of bromide.

The coexistence of free chlorine and bromide under sunlight irradiation (sunlight/FC with Br-) is unavoidable in outdoor seawater swimming pools, and the formation of brominated disinfection byproducts could act more harmful than chlorinated disinfection byproducts. In this study, benzotriazole was selected as a model compound to investigate the degradation rate and the subsequent formation of disinfection byproducts via sunlight/FC with Br- process. The rate constants for the degradation of benzotriazole under pseudo first order conditions in sunlight/FC with Br- and sunlight/FC are 2.3 ± 0.07 × 10-1 min-1 and 6.0 ± 0.7 × 10-2 min-1, respectively. The enhanced degradation of benzotriazole can be ascribed to the generation of HO•, bromine species, and reactive halogen species (RHS) during sunlight/FC with Br-. Despite the fact that sunlight/FC with Br- process enhanced benzotriazole degradation, the reaction results in increasing tribromomethane (TBM) formation. A high concentration (37.8 µg/L) of TBM was detected in the sunlight/FC with Br-, which was due to the reaction of RHS. The degradation of benzotriazole was notably influenced by the pH value (pH 4 - 11), the concentration of bromide (0 - 2 mM), and free chlorine (1 - 6 mg/L). Furthermore, the concentration of TBM increased when the free chlorine concentrations increased, implying the formation potential of harmful TBM in chlorinated seawater swimming pools.

[Determination of six halogenated solvent residues in olive oil by headspace gas chromatography].

The residual amount of halogenated solvents in olive oil is an important indicator of its quality. The National Olive Oil Quality Standard GB/T 23347-2021 states that the residual amount of individual halogenated solvents in olive oil should be ≤0.1 mg/kg and that the total residual amount of halogenated solvents should be ≤0.2 mg/kg. COI/T.20/Doc. No. 8-1990, which was published by the International Olive Council, describes the standard method used for the determination of halogenated solvents in olive oil. Unfortunately, this method is cumbersome, has poor repeatability and low automation, and is unsuitable for the detection and analysis of residual halogenated solvents in large quantities of olive oil. At present, no national standard method for determining residual halogenated solvents in olive oil is available in China. Thus, developing simple, efficient, accurate, and stable methods for the determination of residual halogenated solvents in olive oil is imperative. In this paper, a method based on automatic headspace gas chromatography was established for the determination of residual halogenated solvents, namely, chloroform, carbon tetrachloride, 1,1,1-trichloroethane, dibromochloromethane, tetrachloroethylene, and bromoform, in olive oil. The samples were processed as follows. After mixing, 2.00 g (accurate to 0.01 g) of the olive oil sample was added into a 20 mL headspace injection bottle and immediately sealed for headspace gas chromatography analysis. Blank virgin olive oil was used to prepare a standard working solution and the external standard method for quantification. The solvents used in the preparation of halogenated solvent standard intermediates were investigated and methanol was selected as a replacement for N,N-dimethylacetamide to prepare a halogenated solvent standard intermediate owing to its safety. The effects of different injection times (1, 2, 3, 4, 5, 6 s), equilibration temperatures (60, 70, 80, 90, 100, 110, 120 ℃), and equilibration times (4, 5, 8, 10, 20, 30, 40 min) of the headspace sampler on the detection of the residual amounts of the six halogenated solvents were investigated. The optimal injection time and equilibration temperature were 3 s and 90 ℃, respectively. The method demonstrated good analytical performance for the six halogenated solvents when the equilibration time was 30 min. A methodological study was conducted on the optimized method, and the results showed that the six halogenated solvents exhibited good linear relationships in the range of 0.002-0.200 mg/kg, with correlation coefficients of ≥0.9991. The limits of detection (LODs) and quantification (LOQs) of 1,1,1-trichloroethane and bromoform were 0.0006 and 0.002 mg/kg, respectively. The LODs and LOQs of chloroform, carbon tetrachloride, dibromochloromethane, and tetrachloroethylene were 0.0003 and 0.001 mg/kg, respectively. The average recoveries under different spiked levels were 85.53%-115.93%, and the relative standard deviations (n=6) were 1.11%-8.48%. The established method was used to analyze 13 olive oil samples available in the market. Although no halogenated solvents were detected in these samples, a limited number of samples does not represent all olive oils. Hence, monitoring residual halogenated solvents in olive oil remains necessary for its safe consumption. The LOQs of the method for the six halogenated solvents were significantly lower than that of the COI/T.20/Doc. No. 8-1990 standard method (0.02 mg/kg). In addition, the developed method can be conducted under short operation times with high precision and degree of automation as well as good accuracy. Thus, the proposed method is suitable for the determination and analysis of the residues of the six halogenated solvents in large batches of olive oil samples.

Trihalomethanes in global drinking water: Distributions, risk assessments, and attributable disease burden of bladder cancer.

This study aimed to assess the global spatiotemporal variations of trihalomethanes (THMs) in drinking water, evaluate their cancer and non-cancer risks, and THM-attributable bladder cancer burden. THM concentrations in drinking water around fifty years on a global scale were integrated. Health risks were assessed using Monte Carlo simulations and attributable bladder cancer burden was estimated by comparative risk assessment methodology. The results showed that global mean THM concentrations in drinking water significantly decreased from 78.37 µg/L (1973-1983) to 51.99 µg/L (1984-2004) and to 21.90 µg/L (after 2004). The lifestage-integrative cancer risk and hazard index of THMs through all exposure pathways were acceptable with the average level of 6.45 × 10-5 and 7.63 × 10-2, respectively. The global attributable disability adjusted of life years (DALYs) and the age-standardized DALYs rate (ASDR) dropped by 16% and 56% from 1990-1994 to 2015-2019, respectively. A big decline in the attributable ASDR was observed in the United Kingdom (62%) and the United States (27%), while China experienced a nearly 3-fold increase due to the expanded water supply coverage and increased life expectancy. However, China also benefited from the spread of chlorination, which helped reduce nearly 90% of unsafe-water-caused mortality from 1998 to 2018.

The insightful water quality analysis and predictive model establishment via machine learning in dual-source drinking water distribution system.

Dual-source drinking water distribution systems (DWDS) over single-source water supply systems are becoming more practical in providing water for megacities. However, the more complex water supply problems are also generated, especially at the hydraulic junction. Herein, we have sampled for a one-year and analyzed the water quality at the hydraulic junction of a dual-source DWDS. The results show that visible changes in drinking water quality, including turbidity, pH, UV254, DOC, residual chlorine, and trihalomethanes (TMHs), are observed at the sample point between 10 and 12 km to one drinking water plant. The average concentration of residual chlorine decreases from 0.74 ± 0.05 mg/L to 0.31 ± 0.11 mg/L during the water supplied from 0 to 10 km and then increases to 0.75 ± 0.05 mg/L at the end of 22 km. Whereas the THMs shows an opposite trend, the concentration reaches to a peak level at hydraulic junction area (10-12 km). According to parallel factor (PARAFAC) and high-performance size-exclusion chromatography (HPSEC) analysis, organic matters vary significantly during water distribution, and tryptophan-like substances and amino acids are closely related to the level of THMs. The hydraulic junction area is confirmed to be located at 10-12 km based on the water quality variation. Furthermore, data-driven models are established by machine learning (ML) with test R2 higher than 0.8 for THMs prediction. And the SHAP analysis explains the model results and identifies the positive (water temperature and water supply distance) and negative (residual chlorine and pH) key factors influencing the THMs formation. This study conducts a deep understanding of water quality at the hydraulic junction areas and establishes predictive models for THMs formation in dual-sources DWDS.

Formation and control of disinfection by-products during the trichloroisocyanuric acid disinfection in swimming pool water.

The increasing demand for trichloroisocyanuric acid (TCCA) in swimming pool disinfection highlights the need to evaluate its applicability in terms of disinfection by-product (DBP) formation. Nevertheless, there is limited understanding of DBP formation and control during TCCA disinfection, particularly concerning the effects of various management parameters. This study aimed to fill this knowledge gap by comprehensively investigating DBP formation during TCCA chlorination, with a particular focus on assessing the contribution and interaction of influencing factors using Box-Behnken Design and response surface methodology. Results indicated that the concentrations of trichloroacetaldehyde, chloroform, dichloroacetic acid, trichloroacetic acid, and dichloroacetonitrile produced by TCCA disinfectant were 42.5%, 74.0%, 48.1%, 94.7% and 42.6% of those by the conventional sodium hypochlorite disinfectant, respectively. Temperature exhibited the most significant impact on chloroform formation (49%), while pH played a major role in trichloroacetaldehyde formation (44%). pH2 emerged as the primary contributor to dichloroacetic acid (90%) and trichloroacetic acid (93%) formation. The optimum water quality conditions were determined based on the minimum total DBPs (pH = 7.32, Temperature = 23.7 °C, [Cl-] = 437 mg/L). Chlorine dosage and contact time exhibited greater influence than precursor concentration on chloroform, dichloroacetonitrile, trichloroacetaldehyde, trichloroacetic acid, and total DBPs. Although the interaction between water quality parameters was weak, the interaction between disinfection operating parameters demonstrated substantial effects on DBP formation (8.56-19.06%). Furthermore, the DBP predictive models during TCCA disinfection were provided for the first time, which provides valuable insights for DBP control and early warning programs.

Rapid degradation of brominated haloacetaldehydes at elevated temperature: Kinetics and newly discovered mechanisms.

As an important class of disinfection byproducts (DBPs) of emerging concern, haloacetaldehydes (HALs) undergo degradation and transformation under environmentally relevant conditions. In this study, the stability of chlorinated and brominated HALs was investigated at different pHs and water temperatures. Results indicated that the degradation of HALs followed second-order kinetics. Surprisingly, rapid degradation of Br-HALs at elevated temperature was newly discovered in this study. At 50 °C and pH 7.5, over 90 % of TBAL degraded in 8 min, while the degradation of TCAL was ∼1 %. Moreover, increasing pH also facilitated the degradation of HALs and the alkaline degradation rate constants ( [Formula: see text] ) were found to be 7-9 orders of magnitude higher than their neutral degradation rate constants ( [Formula: see text] ). Under conditions relevant to environment and DBP measurement, HALs mainly degraded to form corresponding trihalomethanes and formate via decarburization pathway, which accounted for 70-93 % of HALs loss. The remaining 7-30 % of HAL loss was attributed to the dehalogenation pathway newly proposed in this study, successfully closing halogen balance during HAL degradation. In addition, a quantitative structure-activity relationship (QSAR) model was established for HAL degradation and the degradation rate constants for three mono-HALs were predicted at different temperature. The kinetic models and reaction rate constants obtained in this study can be used for quantitative predictions of HAL concentrations in drinking water, which is beneficial for monitoring and control of these emerging DBPs. Furthermore, considering the rapid degradation of Br-HALs into corresponding products, the temperature during sample pre-treatment can have a significant impact on DBP analysis.

Performance of public drinking water purifiers in control of trihalomethanes, antibiotics and antibiotic resistance genes.

Point-of-use water purifiers are widely applied as a terminal treatment device to produce drinking water with high quality. However, concerns are raised regarding low efficiency in eliminating emerging organic pollutants. To enhance our understanding of the reliability and potential risks of water purifiers, the removal of trihalomethanes, antibiotics, and antibiotic resistance genes (ARGs) in four public water purifiers was investigated. In the four public water purifiers in October and November, the removal efficiencies of trichloromethane (TCM) and bromodichloromethane (BDCM) were 15%-69% (averagely 37%) and 6%-44% (averagely 23%). The levels of TCM and BDCM were lowered by all water purifiers in October and November, but accelerated in effluent compared to the influent in one public water purifier in December. The removal efficiencies of twelve antibiotics greatly varied with species and time. Out of twelve sampling cases, the removal efficiencies of total antibiotics were 25%-75% in ten cases. In the other two cases, very low removal efficiency (6%) or higher levels of antibiotics present in effluent compared to the influent were observed. Two public water purifiers effectively remove ARGs from water, with log removal rates of 0.45 log-3.89 log. However, in the other two public water purifiers, the ARG abundance accidently increased in the effluents. Overall, public water purifiers were more effective in removing antibiotics and ARGs compared to household water purifiers, but less or equally effective in removing trihalomethanes. Both public and household water purifiers could be contaminated and release the accumulated micro-pollutants or biofilm-related pollutants into effluent. The production frequency and standing time of water within water purifiers can impact the internal contamination and purification efficacy.

Climate change and future water demand: Implications for chlorine and trihalomethanes management in water distribution systems.

The global change in surface water quality calls for increased preparedness of drinking water utilities. The increasing frequency of extreme climatic events combined with global warming can impact source and treated water characteristics such as temperature and natural organic matter. On the other hand, water saving policies in response to water and energy crisis in some countries can aggravate the situation by increasing the water residence time in the drinking water distribution system (DWDS). This study investigates the individual and combined effect of increased dissolved organic carbon (DOC), increased temperature, and reduced water demand on fate and transport of chlorine and trihalomethanes (THMs) within a full-scale DWDS in Canada. Chlorine and THM prediction models were calibrated with laboratory experiments and implemented in EPANET-MATLAB toolkit for prediction in the DWDS under different combinations of DOC, temperature, and demand. The duration of low chlorine residuals (<0.2 mg/L) and high THM (>80 µg/L) periods within a day in each scenario was reported using a reliability index. Low-reliability zones prone to microbial regrowth or high THM exposure were then delineated geographically on the city DWDS. Results revealed that water demand reduction primarily affects chlorine availability, with less concern for THM formation. The reduction in nodal chlorine reliability was gradual with rising temperature and DOC of the treated water and reducing water demand. Nodal THM reliability remained unchanged until certain thresholds were reached, i.e., temperature >25 °C for waters with DOC <1.52 mg/L, and DOC >2.2 mg/L for waters with temperature = 17 °C. At these critical thresholds, an abrupt network-wide THM exceedance of 80 µg/L occurred. Under higher DOC and temperature levels in future, employing the proposed approach revealed that increasing the applied chlorine dosage (which is a conventional method used to ensure sufficient chlorine coverage) results in elevated exposure toTHMs and is not recommended. This approach aids water utilities in assessing the effectiveness of different intervention measures to solve water quality problems, identify site-specific thresholds leading to major decreases in system reliability, and integrate climate adaptation into water safety management.

Impact of source water quality on total organic carbon and trihalomethane removal efficiency in a water treatment plant: A case study of Upper Awash, Ethiopia.

This study addresses the limited understanding of factors affecting the efficiency of water treatment plants in reducing trihalomethane (THM) formation through total organic carbon (TOC) removal, highlighting significant challenges in improving treatment effectiveness. The aim of this study was to examine the influence of water quality on the efficiency of water treatment plants to remove TOC and reduce THM formation. Linear regression and correlation analyses were conducted to examine the relationship between water quality parameters and THM concentrations. The results showed that there was a negative relationship between turbidity, metals, and TOC concentration with TOC removal efficiency. Positive correlations were found between parameters and the formation of THMs in water. Of these parameters, water temperature was observed to have relatively less influence on THM formation. It was observed that seasonal variations in water quality affect the efficiency of TOC removal and THM content in treated water. THM levels in chlorinated water were found to be within the permissible range of the World Health Organization's drinking water quality guidelines. However, it is still important to maintain continuous monitoring and take measures to reduce THMs. The model demonstrated a strong correlation (R2 = 0.906) between predicted and measured THM values.

Copper ion affects oxidant decay and combined aspartic acid transformation during chlorination in water pipes: Differentiated action on the yield of trihalomethanes and haloacetonitriles.

The chlorination of extracellular polymeric substances (EPS) secreted by biofilm often induces the formation of high-toxic disinfection byproducts (DBPs) in drinking water distribution systems. The protein components in EPS are the main precursors of DBPs, which mostly exist in the form of combined amino acids. The paper aimed to study the action of a pipe corrosion product (Cu2+) on the formation of DBPs (trihalomethanes, THMs; haloacetonitriles, HANs) with aspartic acid tetrapeptide (TAsp) as a precursor. Cu2+ mainly promoted the reaction of oxidants with TAsp (i.e., TAsp-induced decay) to produce DBPs, rather than self-decay of oxidants to generate BrO3‒ and ClO3‒. Cu2+ increased THMs yield, but decreased HANs yield due to the catalytic hydrolysis. Cu2+ was more prone to promote the reaction of TAsp with HOCl than with HOBr, leading to a DBPs shift from brominated to chlorinated species. The chemical characterizations of Cu2+-TAsp complexations demonstrate that Cu2+ combined with TAsp at the N and O sites in both amine and amide groups, and the intermediate identification suggests that Cu2+ enhanced the stepwise chlorination process by promoting the substitution of chlorine and the breakage of CC bonds. The effect of Cu2+ on THMs yield changed from promoting to inhibiting with the increase of pH, while that on HANs yield was inhibiting regardless of pH variation. Additionally, the impact of Cu2+ on the formation of DBPs was also affected by Cu2+ dose, Cl2/C ratio and Br- concentration. This study helps to understand the formation of EPS-derived DBPs in water pipes, and provides reference for formulating control strategies during biofilm outbreaks.

Exposure to disinfection by-products and risk of cancer: A systematic review and dose-response meta-analysis.

Disinfection by-products (DBPs), including trihalomethanes (THMs) and haloacetic acids (HAAs), have attracted attention due to their carcinogenic properties, leading to varying conclusions. This meta-analysis aimed to evaluate the dose-response relationship and the dose-dependent effect of DBPs on cancer risk. We performed a selective search in PubMed, Web of Science, and Embase databases for articles published up to September 15th, 2023. Our meta-analysis eventually included 25 articles, encompassing 8 cohort studies with 6038,525 participants and 10,668 cases, and 17 case-control studies with 10,847 cases and 20,702 controls. We observed a positive correlation between increased cancer risk and higher concentrations of total trihalomethanes (TTHM) in water, longer exposure durations, and higher cumulative TTHM intake. These associations showed a linear trend, with relative risks (RRs) and 95 % confidence intervals (CIs) being 1.02 (1.01-1.03), 1.04 (1.02-1.06), and 1.02 (1.00-1.03), respectively. Gender-specific analyses revealed slightly U-shaped relationships in both males and females, with males exhibiting higher risks. The threshold dose for TTHM in relation to cancer risk was determined to be 55 µg/L for females and 40 µg/L for males. A linear association was also identified between bladder cancer risk and TTHM exposure, with an RR and 95 % CI of 1.08 (1.05-1.11). Positive linear associations were observed between cancer risk and exposure to chloroform, bromodichloromethane (BDCM), and HAA5, with RRs and 95 % CIs of 1.02 (1.01-1.03), 1.33 (1.18-1.50), and 1.07 (1.03-1.12), respectively. Positive dose-dependent effects were noted for brominated THMs above 35 µg/L and chloroform above 75 µg/L. While heterogeneity was observed in the studies for quantitative synthesis, no publication bias was detected. Exposure to TTHM, chloroform, BDCM, or HAA5 may contribute to carcinogenesis, and the risk of cancer appears to be dose-dependent on DBP exposure levels. A cumulative effect is suggested by the positive correlation between TTHM exposure and cancer risk. Bladder cancer and endocrine-related cancers show dose-dependent and positive associations with TTHM exposure. Males may be more susceptible to TTHM compared to females.

Bromoform Toxicity to Marine Microalgae: Studies using the Diatom Chaetoceros lorenzianus as a Model Organism.

Bromoform is the most prominent, relatively long-lived chlorination by-product in condenser effluents from seawater-based power plant cooling systems. There are few reports on the potential toxicity of this trihalomethane to marine phytoplankton. We investigated this using a marine diatom, Chaetoceros lorenzianus as the model organism. The study was conducted by exposing the diatom to bromoform concentrations 0, 50, 100, 150, 250, 500 and 1000 µg/L for exposure time of 3 and 24 h. The mode of action of bromoform was examined using endpoints which include chlorophyll a fluorescence, cell viability by SYTOX® green stain and genotoxicity by comet assay. The relative fluorescence unit and percent viability changed significantly at all concentrations in duration of study. The 24-h IC50 for viability and chlorophyll was estimated to be 255.6 µg/L and 343.5 µg/L, respectively. The tail DNA of 5-20% observed by comet assay indicated low-level DNA damage. Bromoform manages to target cell membrane and internal machinery, DNA and chlorophyll molecule of cell, leading to cause damage at multiple physiological levels. Based on the present data, the current discharge levels of bromoform 50-250 µg/L cause significant impact on the phytoplankton under investigation. However, the impact can be limited under actual field conditions wherein mixing of cooling water with natural water bodies is considered. Nevertheless, more studies are required to understand the toxicological response of organisms to bromoform, so that discharge levels can be continued to be kept within safe levels.

Trihalomethane prediction model for water supply system based on machine learning and Log-linear regression.

Laboratory determination of trihalomethanes (THMs) is a very time-consuming task. Therefore, establishing a THMs model using easily obtainable water quality parameters would be very helpful. This study explored the modeling methods of the random forest regression (RFR) model, support vector regression (SVR) model, and Log-linear regression model to predict the concentration of total-trihalomethanes (T-THMs), bromodichloromethane (BDCM), and dibromochloromethane (DBCM), using nine water quality parameters as input variables. The models were developed and tested using a dataset of 175 samples collected from a water treatment plant. The results showed that the RFR model, with the optimal parameter combination, outperformed the Log-linear regression model in predicting the concentration of T-THMs (N25 = 82-88%, rp = 0.70-0.80), while the SVR model performed slightly better than the RFR model in predicting the concentration of BDCM (N25 = 85-98%, rp = 0.70-0.97). The RFR model exhibited superior performance compared to the other two models in predicting the concentration of T-THMs and DBCM. The study concludes that the RFR model is superior overall to the SVR model and Log-linear regression models and could be used to monitor THMs concentration in water supply systems.

Lifetime exposure to brominated trihalomethanes in drinking water and swimming pool attendance are associated with chronic lymphocytic leukemia: a Multicase-Control Study in Spain (MCC-Spain).

BACKGROUND: Chronic lymphocytic leukemia (CLL) etiology is poorly understood, and carcinogenic chemicals in drinking and recreational water are candidates. OBJECTIVE: To evaluate the association between drinking-water exposure to trihalomethanes (THMs) and nitrate as well as lifetime swimming pool attendance and CLL. METHODS: During 2010-2013, hospital-based CLL cases and population-based controls were recruited in Spain, providing information on residential histories, type of water consumed and swimming pool attendance. Average THMs and nitrate levels in drinking water were linked to lifetime water consumption. Odds ratios (OR) and 95% confidence intervals (CI) were estimated using mixed models. RESULTS: Final samples for residential tap water analyses and swimming pool attendance analyses were 144 cases/1230 controls and 157 cases/1240 controls, respectively. Mean (SD) values for average lifetime residential brominated THMs and chloroform in tap water (µg/L), and ingested nitrate (mg/day) were 48.1 (35.6), 18.5 (6.7) and 13.7 (9.6) respectively in controls; and 72.9 (40.7), 17.9 (5.4), and 14.1 (8.8) in CLL cases. For each 10 µg/L increase of brominated THMs and chloroform lifetime-average levels, the ORs (95% CI) were 1.22 (1.14, 1.31) and 0.54 (0.34, 0.87), respectively. For each 5 mg/day increase of ingested nitrate, the OR of CLL was 0.91 (0.80, 1.04). The OR of lifetime pool users (vs. non-users) was 2.38 (1.61, 3.52). Upon performing annual frequency of attending pools analysis through categorization, the second and third categories showed an ORs of 2.36 (1.49, 3.72) and 2.40 (1.51, 3.83), respectively, and P-trend of 0.001. IMPACT STATEMENT: This study identifies an association of long-term exposure to THMs in drinking water, at concentrations below the regulatory thresholds and WHO guidelines, and swimming pool attendance, with chronic lymphocytic leukemia (CLL). These unprecedented findings are highly relevant since CLL is an incurable cancer with still unknown etiology and because the widespread exposure to chlorination by-products that remain in drinking and recreational water worldwide. Despite the demonstrated carcinogenicity in animals of several chlorination by-products, little is known about their potential risks on human health. This study makes a significant contribution to the search for environmental factors involved in the etiology of CLL and to the evidence of the health impact of these high prevalent water contaminants.

Risks of obstructive genitourinary birth defects in relation to trihalomethane and haloacetic acid exposures: expanding disinfection byproduct mixtures analyses using relative potency factors.

BACKGROUND: Some disinfection byproducts (DBPs) are teratogens based on toxicological evidence. Conventional use of predominant DBPs as proxies for complex mixtures may result in decreased ability to detect associations in epidemiological studies. OBJECTIVE: We assessed risks of obstructive genitourinary birth defects (OGDs) in relation to 12 DBP mixtures and 13 individual component DBPs. METHODS: We designed a nested registry-based case-control study (210 OGD cases; 2100 controls) in Massachusetts towns with complete quarterly 1999-2004 data on four trihalomethanes (THMs) and five haloacetic acids (HAAs). We estimated temporally-weighted average DBP exposures for the first trimester of pregnancy. We estimated adjusted odds ratios (aORs) and 95% confidence intervals (CIs) for OGD in relation to individual DBPs, unweighted mixtures, and weighted mixtures based on THM/HAA relative potency factors (RPF) from animal toxicology data for full-litter resorption, eye defects, and neural tube defects. RESULTS: We detected elevated aORs for OGDs for the highest of bromodichloromethane (aOR = 1.75; 95% CI: 1.15-2.65), dibromochloromethane (aOR = 1.71; 95% CI: 1.15-2.54), bromodichloroacetic acid (aOR = 1.56; 95%CI: 0.97-2.51), chlorodibromoacetic acid (aOR = 1.97, 95% CI: 1.23-3.15), and tribromoacetic acid (aOR = 1.90; 95%CI: 1.20-3.03). Across unweighted mixture sums, the highest aORs were for the sum of three brominated THMs (aOR = 1.74; 95% CI: 1.15-2.64), the sum of six brominated HAAs (aOR = 1.43; 95% CI: 0.89-2.31), and the sum of nine brominated DBPs (aOR = 1.80; 95% CI: 1.05-3.10). Comparing eight RPF-weighted to unweighted mixtures, the largest aOR differences were for two HAA metrics, which both were higher with RPF weighting; other metrics had reduced or minimally changed ORs in RPF-weighted models.

Identification of reproductive sex-biased gene expression in Asparagopsis taxiformis (lineage 6) gametophytes.

The sub-tropical red seaweed Asparagopsis taxiformis is of significant interest due to its ability to store halogenated compounds, including bromoform, which can mitigate methane production in ruminants. Significant scale-up of aquaculture production of this seaweed is required; however, relatively little is known about the molecular mechanisms that control fundamental physiological processes, including the regulatory factors that determine sexual dimorphism in gametophytes. In this study, we used comparative RNA-sequencing analysis between different morphological parts of mature male and female A. taxiformis (lineage 6) gametophytes that resulted in greater number of sex-biased gene expression in tips (containing the reproductive structures for both sexes), compared with the somatic main axis and rhizomes. Further comparative RNA-seq against immature tips was used to identify 62 reproductive sex-biased genes (59 male-biased, 3 female-biased). Of the reproductive male-biased genes, 46% had an unknown function, while others were predicted to be regulatory factors and enzymes involved in signaling. We found that bromoform content obtained from female samples (8.5 ± 1.0 mg·g-1 dry weight) was ~10% higher on average than that of male samples (6.5 ± 1.0 mg·g-1 dry weight), although no significant difference was observed (p > 0.05). There was also no significant difference in the marine bromoform biosynthesis locus gene expression. In summary, our comparative RNA-sequencing analysis provides a first insight into the potential molecular factors relevant to gametogenesis and sexual differentiation in A. taxiformis, with potential benefits for identification of sex-specific markers.