Temporospatial variation and health risk assessment of trihalomethanes (THMs) in drinking water (northwest Iran)

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.

Association of blood trihalomethane concentrations with hypertension in US adults: A nationwide cross-sectional study

Trihalomethanes (THMs), as the most common species of disinfection byproducts in chlorinated water, have been associated with hypertensive disorders in pregnancy. However, there is sparse epidemiological evidence regarding the possible link between THMs exposure and hypertension in general adults. In the present study, we aimed to characterize the associations between THMs exposure and hypertension in general adults. We performed cross-sectional analyses of 15,135 adults from the 1999-2018 National Health and Nutrition Examination Survey. In the general US adults, the median blood concentrations of the chloroform (TCM), bromodichloromethane (BDCM), dibromochloromethane (DBCM) and bromoform (TBM) were: 4.80 pg/mL, 0.71 pg/mL, 0.44 pg/mL and 0.71 pg/mL, respectively. And adults in the highest tertile of blood TBM and DBCM had odds ratios of 1.20 (95 % confidence intervals: 1.02, 1.42) and 1.15 (1.01, 1.30), respectively, for hypertension, compared with adults in the lowest tertile. Also, significant positive associations between blood brominated THM concentrations (sum of TBM, BDCM and DBCM) and prevalent hypertension were observed. In addition, significant interactions with BMI were demonstrated for Br-THMs (P for interaction = 0.017). Our study provides epidemiological evidence supporting a positive association between blood THMs and hypertension by using the nationally representative data, highlighting the need for further investigations to deepen our findings and elucidate the underlying mechanisms.

Trihalomethanes in developed and developing countries

The reactions between natural organic matter, anthropogenic contaminants, ions, and disinfectants lead to the formation of disinfection by-products (DBPs) such as trihalomethanes (THMs) in drinking water. The formation of THMs is strongly related to the chlorination of water. The study's central objective was to compare the concentration of THMs in twenty developed and developing countries and their disinfection techniques. The THM concentration in 11 developed and 9 developing countries ranged from 0.5 µg/L (Germany) to 215 µg/L (Russia) and 3 µg/L (China) to 439.2 µg/L (Bangladesh), respectively. The developed country has partially succeeded in reducing THM concentration in drinking water, whereas significant steps are needed in developing countries to reduce the existing high THM concentration. The concentration of THMs in water varies among these countries because of the different water sources, water quality, environmental conditions, and efficiency of water treatment technologies. A meaningful relationship has been observed between the properties of water and the THM formation. The use of chemical disinfectants will result in new forms of DBPs that are undesirable due to their carcinogenic and mutagenic effects on human health. The DBP guidelines by various national and international agencies have helped to control and manage the THM concentration in drinking water. However, these regulatory standards are not continuously monitored. Therefore, the formation of these compounds should be prevented either by removing THMs forming precursors or by using an integrated approach for controlling THM formation by implementing advanced water treatment technology. Extensive research is desirable in domains like THM minimization strategies which are easy to deploy, scalable, and cost-effective.

Bromoform exposure is associated with non-melanoma skin cancer: evidence from NHANES 2011-2020

Background

Non-melanoma skin cancer (NMSC) is a prevalent skin malignancy. It has been indicated in many studies that trihalomethanes (THMs) exposure has a strong association with tumors but has not been associated with NMSC. Our investigation aims to explore the association between THMs exposure and NMSC.

Methods

Cross-sectional data from the 2011 to 2020 National Health and Nutrition Examination Survey (NHANES) was collected. Poisson regression and subgroup analyses were performed to evaluate the association between individual THMs components and NMSC. Fitted smoothing curves and generalized additive models were also used.

Results

This study involved 5,715 individuals, 98 (1.7%) of whom self-reported NMSC. After adjusting for covariates, Poisson regression showed that higher blood TBM levels were associated with an increased likelihood of NMSC (OR = 1.03; 95% CI: 1.01-1.05, p = 0.002). However, the correlation between the blood levels of TCM, DBCM, and BDCM and the likelihood of NMSC was not statistically significant (all p > 0.05). Subgroup analysis and interaction tests showed no significant differences between blood TBM concentration and the likelihood of NMSC, indicating that age, gender, and race were significantly independent of this positive association (all p < 0.05).

Conclusions

Our results implied that among adults older than 65 years old in the U.S., elevated blood TBM concentrations were positively associated with NMSC. More prospective investigations are required to validate this relationship with the early prevention of NMSC.

Modeling the Operating Performance of a Drinking Water Biological Aerated Filter and the Formation of Organic Nitrogen

In this study, simultaneous storage and growth mechanism, as well as the formation processes of organic nitrogen (ON), were both introduced into activated sludge model 3 (ASM3), and ASM3-ON was formed to predict the operation of biofilm treatment processes and the formation of dissolved organic nitrogen (DON). ASM3-ON was applied to a lab-scale biological aerated filter (BAF) for water supply. During the simulation, the sensitivities of chemical oxygen demand (COD), ammonia nitrogen (NH₄⁺-N), nitrate nitrogen (NO_x^--N), and DON to the stoichiometric and kinetic coefficients in the model were analyzed first by the Sobol method. Then, the model prediction results were compared with experimental values to calibrate ASM3-ON. In the validation process, ASM3-ON was applied to predict the variations of COD, NH₄⁺-N, NO₂^--N, and NO₃^--N in BAF under different aeration ratios (0, 0.5:1, 2:1, and 10:1) and different filtration velocities (0.5, 2, and 4 m/h). The comparison with the experimental results showed that ASM3-ON could accurately predict the variation characteristics of COD, NH₄⁺-N, NO_x^--N, and DON in BAF. This study provided a practical model approach to optimize the operating performance of BAF and reduce the formation of ON through nonexperimental methods.

The occurrence, formation and transformation of disinfection byproducts in the water distribution system: A review

Disinfection is an effective process to inactivate pathogens in drinking water treatment. However, disinfection byproducts (DBPs) will inevitably form and may cause severe health concerns. Previous research has mainly focused on DBPs formation during the disinfection in water treatment plants. But few studies paid attention to the formation and transformation of DBPs in the water distribution system (WDS). The complex environment in WDS will affect the reaction between residual chlorine and organic matter to form new DBPs. This paper provides an overall review of DBPs formation and transformation in the WDS. Firstly, the occurrence of DBPs in the WDS around the world was cataloged. Secondly, the primary factors affecting the formation of DBPs in WDS have also been summarized, including secondary chlorination, pipe materials, biofilm, deposits and coexisting anions. Secondary chlorination and biofilm increased the concentration of regular DBPs (e.g., trihalomethanes (THMs) and haloacetic acids (HAAs)) in the WDS, while Br^- and I^- increased the formation of brominated DBPs (Br-DBPs) and iodinated DBPs (I-DBPs), respectively. The mechanism of DBPs formation and transformation in the WDS was systematically described. Aromatic DBPs could be directly or indirectly converted to aliphatic DBPs, including ring opening, side chain breaking, chlorination, etc. Finally, the toxicity of drinking water in the WDS caused by DBPs transformation was examined. This review is conducive to improving the knowledge gap about DBPs formation and transformation in WDS to better solve water supply security problems in the future.

Trihalomethane Cancer Risk Assessment for Private and Shared Residences: Addressing the Differences in Inhalation Exposure

The multi-pathway cancer risk (CR) assessment of trihalomethanes (THM) involves considering exposure via ingestion, dermal contact, and inhalation. Inhalation occurs during showering due to the volatilization of THMs from chlorinated water to the air. When assessing inhalation risks, exposure models commonly assume that the initial THM concentration in the shower room is zero. However, this assumption is only valid in private shower rooms where single or infrequent showering events take place. It fails to account for continuous or successive showering events in shared showering facilities. To address this issue, we incorporated the accumulation of THM in the shower room air. We studied a community (population ≈ 20,000) comprising two types of residences with the same water supply: population A with private shower rooms, and population B with communal shower stalls. The total THM concentration in the water was 30.22 ± 14.45 µg L^-1. For population A, the total CR was 58.5 × 10^-6, including an inhalation risk of 1.11 × 10^-6. However, for population B, the accumulation of THM in the shower stall air resulted in increased inhalation risk. By the tenth showering event, the inhalation risk was 2.2 × 10^-6, and the equivalent total CR was 59.64 × 10^-6. We found that the CR significantly increased with increasing shower duration. Nevertheless, introducing a ventilation rate of 5 L s^-1 in the shower stall reduced the inhalation CR from 1.2 × 10^-6 to 7.9 × 10^-7.

Probabilistic approach for health hazard assessment of trihalomethanes through successive showering events

Trihalomethanes (THMs) are common disinfection by-products in chlorinated tap waters. They can cause various cancers and non-cancer health hazards. Ingestion, dermal contact, and inhalation are the three exposure routes considered in the THM hazard or risk assessments. Among these, inhalation hazard is generally calculated by assuming the initial concentration as zero. This assumption fails to address the case of continuous or successive showers that can happen in shared showering facilities such as student hostels or gymnasiums. In the present study, the leftover THM concentration from the previous bath was considered to assess the chronic daily intakes (CDI) and hazard index (HI) for successive showers. For this, tap water of a university campus was analyzed to understand the extent of THM exposure at consumer points and the result obtained was used for the hazard assessment. Total THM concentrations varied from 0.51 to 68.9 µg L^-1. To address the variability of the model input parameters, 50,000 iterations of Monte Carlo simulation were carried out. Maximum HI values of 7.94E - 02 ± 3.63E - 02, and 6.69E - 02 ± 3.08E-02 were observed for the 1^st shower for females and males, respectively. This value increased exponentially up to the 5^th shower and thereafter, the value was constant. The methodology followed in the present study successfully determines the risk and hazard of THMs through successive showers.

Exposure and carcinogenic risk assessment of trihalomethanes (THMs) for water supply consumers in Addis Ababa, Ethiopia

Background

Trihalomethanes (THMs), a class of DBPs (disinfection byproducts) that includes chloroform, bromodichloromethane (BDCM), chlorodibromomethane (CDBM), and bromoform. To the best of authors' knowledge, no study has addressed the relationship between the concentration of THMs and lifetime cancer risks (LCR) in drinking water supply system in Addis Ababa, Ethiopia. Therefore, this study aimed to determine the lifetime cancer risks of exposure to THMs in Addis Ababa, Ethiopia.

Method

A total of 120 duplicate water samples were collected from 21 sampling points in Addis Ababa, Ethiopia. The THMs were separated by a DB-5 capillary column and detected by an electron capture detector (ECD). Cancer and non-cancer risk assessments were performed.

Results

The average total THMs (TTHMs)concentration in Addis Ababa, Ethiopia, was 76.3 μg/L. Chloroform was the most dominant THM species identified. The total cancer risk for males was higher than that for females. The average LCR for TTHMs via ingestion in drinking water in this study was unacceptably high risk 93.4 × 10 - 2 . An average LCR through dermal routes was also of unacceptably high risk 4.3 × 10 - 2 . The LCR by chloroform contributes the highest (72%) of the total risk, followed by BDCM (14%), DBCM (10%) and bromoform (4%).

Conclusions

The cancer risk of drinking water due to THMs in Addis Ababa was higher than the level recommended by the USEPA. The total LCR from the targeted THMs was higher via the three exposure routes. Males were at higher THM cancer risk than females. The hazard index (HI) indicated that the dermal route caused higher HI values than the ingestion route. It is essential to apply alternatives to chlorine, i.e., chlorine dioxide (ClO₂), ozone and ultraviolet radiation, in Addis Ababa, Ethiopia. The monitoring and regulation of the THMs is required on a regular basis to analyse the trends and guide the water treatment and distribution system.

Availability of data and materials

The datasets generated for this analysis are available from the corresponding author upon reasonable request.

Cumulative human health risk analysis of trihalomethanes exposure in drinking water systems

Chlorinated compounds on reaction with natural organic substances present in water leads to the formation of trihalomethanes (THMs), a major type of disinfection by-products (DBPs). Trihalomethanes (THMs) are the most widely investigated DBPs in drinking water systems because of their carcinogenic potential and subsequent adverse effects on human health. This study investigated the effect of gastro-intestinal absorption factor on human health risk assessment. Monitoring and analysis of water quality parameters and THMs levels in drinking water treatment plants revealed that the average values (306.5 μg/L) exceeded the recommended US EPA guidelines of 80 μg/L. Spearman rank (rho) correlation coefficient indicated that dissolved organic carbon is the major parameter influencing THMs formation. Monte Carlo simulations base risk assessment study was conducted for three different exposure pathways. The observed human health risk exposure effects due to THMs were below the recommended USEPA level (1.0 × 10^-6) for both the drinking water treatment plants. Seasonal disparity on risk estimation analysis revealed higher risk in summer season followed by autumn which is principally due to high concentration of THMs in summers.

Potential cancer risk estimates from trihalomethanes in peri-urban settings of Kawama East of Mufulira, Zambia

In this study, we report the formation and cancer risk estimation of trihalomethanes (THMs) emanating from 'ex-situ' chlorination of shallow hand-dug well water obtained from a peri-urban area of Mufulira District, Zambia. The aim of the study was to evaluate the potential cancer risks for people in this area where chlorine water disinfection at the household level is commonly practiced. Water samples from 13 randomly selected hand-dug wells (4-8 m deep) were collected and analyzed for pH, turbidity, and dissolved organic carbon before chlorination. Then another set of water samples from the same 13 wells was chlorinated using the methods commonly practiced in this area, consistent with WHO recommended doses. The chlorination degradation products, THMs, trichloromethane, bromodichloromethane (CHCl₂Br), dibromochloromethane (CHClBr₂), and tribromomethane, were determined at three different times of 60, 180, and 300 min after chlorination, while residual chlorine was determined immediately after chlorination and at 60 and 1,440 min after chlorination. THMs were determined using gas chromatography (GC), while residual chlorine was determined colorimetrically. Then cancer risk estimation from ingestion, inhalation, and dermal routes was carried out. All water samples from the 13 wells showed elevated amounts of THMs, which also increased with increasing contact time. For instance, the concentrations of THMs at 60 min after chlorination ranged from 24.3 ± 2.0 to 61.3 ± 1.0 μg/L, while at 180 and 300 min, ranged between 85.6 ± 4.3-146.9 ± 2.5 μg/L and 188.1 ± 7.1-250.1 ± 7.1 μg/L, respectively. It was observed that tribromomethane was not detected at all in all samples, while CHCl₂Br and CHClBr₂ were only detected at 180 and 300 min post chlorination. The lifetime cancer risk estimation results showed negligible risk at 60 min post chlorination. However, at 180 and 300 min post chlorination, the results were far above negligible, but within the regulatory US EPA limits. The overall risk, however, could not be ignored, given a multiplicity of exposure to various other contaminants, raising concerns over additivity and synergistic interactive effects, particularly for non-cancer hazard indices.