https://orcid.org/0009-0008-8385-500X
ABSTRACT
Disinfection is essential for protecting human health from microorganisms in drinking water. In addition to killing microorganisms, disinfection can introduce disinfection byproducts (DBPs), which impose detrimental effects on human health. In this study, a total of 15,280 water samples were monitored in 120 counties of Hunan Province, Central China, in periods ranging from 1 July 2023 to 31 December 2024. We evaluated the health risks of DBPs in drinking water through various exposure routes and conducted a comprehensive analysis of different factors that impact the health risks associated with these DBPs. The overall carcinogenic and noncarcinogenic risks resulting from exposure to DBPs through multiple pathways were 1.15 × 10−5 and 2.59 × 10−2, respectively. For different exposure routes, oral exposure to DBPs contributed the most to carcinogenic risk (1.13 × 10−5) and noncarcinogenic risk (2.52 × 10−2). The subgroup analysis revealed that the younger the child, the greater health risk they faced. The carcinogenic and noncarcinogenic risks for children aged 1–2 years were 2.56 × 10−5 and 5.75 × 10−2, respectively. Our study indicated that the potential carcinogenic risk of DBPs should be considered, and possible actions should be implemented to mitigate these health risks.
HIGHLIGHTS
Disinfection byproducts in drinking water have carcinogenic risks.
Risk of different exposure routes: oral route > dermal route > inhalation route.
The younger the child, the greater health risk they faced.
INTRODUCTION
Drinking water safety is a basic guarantee for human health. The disinfection of drinking water is one of the most significant achievements in the field of global public health, as it can ensure the safety of drinking water efficiently. The World Health Organization (WHO) has set a goal to achieve equal access to safe drinking water for all individuals by 2030 (WHO 2022a). Microbial contamination is the greatest threat to drinking water safety, with contaminated drinking water estimated to result in approximately 505,000 diarrheal deaths each year (WHO 2023). In China, diarrheal diseases rank as the second most prevalent notifiable infectious disease based on incidence rates (Shuaibing et al. 2019; Lan et al. 2022). To prevent illnesses caused by bacteria, viruses, protozoa and other pathogenic microorganisms in drinking water, the sanitary standards for drinking water require that drinking water should be disinfected (Ministry of Health of the People's Republic of China 2022).
Disinfection of drinking water is a double-edged sword. On the one hand, disinfection can effectively kill bacteria, viruses, protozoa and other microorganisms that are harmful to humans. On the other hand, the chlorination of drinking water facilitates the chemical interaction between chlorine disinfectant and dissolved organic compounds, resulting in the generation of DBPs. Previous studies reported that DBPs have adverse effects on human health (Lee et al. 2004; Liu et al. 2020; Koley et al. 2024; Zheng et al. 2024). Chlorination- and chlorine dioxide-based disinfection methods are the two most common drinking water disinfection methods. Different disinfection methods can produce different types of DBPs due to different treatment processes, concentration and type of natural organic matter in water and water quality. Since the detection of trihalomethanes (THMs) in drinking water in 1974 (Bellar et al. 1974), more than 800 DBPs have been detected in drinking water. Currently, THMs and haloacetic acids (HAAs) are the top two categories of DBPs in drinking water (Čulin & Mustać 2015).
Several epidemiological studies have shown that DBPs are linked to bladder and colorectal cancers (Rahman et al. 2010; Costet et al. 2011). A previous study estimated the burden of THMs on bladder cancer in 28 European countries and reported that 4.9% of bladder cancer cases could be attributed to THMs exposure in drinking water (Evlampidou et al. 2020). One study estimated that out of the 79,000 annual cases of bladder cancer in the United States, approximately 8,000 cases could be attributable to DBPs in drinking water systems (Weisman et al. 2022). Furthermore, some studies have demonstrated that exposure to DBPs is associated with noncarcinogenic effects, such as neurotoxicological effects, nonalcoholic fatty liver disease, spontaneous abortion, fetal growth restriction and prematurity (Waller et al. 1998; Save-Soderbergh et al. 2020; Jiang et al. 2024). Toxicological studies have revealed that some of the identified DBPs exhibit cytotoxic, neurotoxic and genotoxic properties as well as carcinogenic, teratogenic and mutagenic properties (DeAngelo et al. 1991; DeMarini et al. 1995; Tang et al. 2024).
The WHO Guidelines for Drinking-water Quality provide comprehensive standards and recommendations, which include specific provisions for 15 DBPs (WHO 2022b). Similarly, the USEPA has established stringent regulatory standards for two major groups of disinfection byproducts: total THMs and HAAs, reflecting their significance in water safety management (USEPA 2021). The Chinese national standards for drinking water quality (GB 5749-2022) were revised in 2022, accounting for the potential negative health effects of exposure to DBPs and the increased demand for safe drinking water. The updated standards included adjustments in the regulation of four types of THMs, including chloroform (TCM), dibromochloromethane (DBCM), bromodichloromethane (BDCM) and bromoform (TBM), and two types of HAAs, namely dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA). Among the six indicators mentioned above, except for TCM, all of them shifted from expanded indices to regular indices. Regular indices reflect the basic status of drinking water quality indicators and expanded indices reflect the regional drinking water quality characteristics and water quality status in a certain period of time or under special circumstances. This change indicates that drinking water safety supervision in China has moved from the initial stage of ensuring biosafety to the stage of controlling biological risks and chemical risks. Evaluating the health risks associated with concurrent exposure to these six DBPs in drinking water is crucial. Previous studies have reported that the carcinogenic risk of DBPs exceeds the permissible threshold (Mishra et al. 2014). However, the health risks associated with different subgroups, such as disinfecting approaches, seasons, water sources, genders and age groups, have been ignored (Du et al. 2021; Zhao et al. 2023). Additionally, no study has focused on the contamination status of DBPs in drinking water in Hunan Province, Central China. Therefore, it is essential to evaluate the health risks of DBPs in drinking water across various demographic groups to identify the most vulnerable populations.
The aim of this research was to assess the potential carcinogenic and noncarcinogenic risks of exposure to DBPs resulting from different disinfection methods in drinking water in Hunan Province, Central China, from 1 July 2023 to 31 December 2024. Additionally, we analyzed the health risk of DBPs in different subgroups, such as year, season, water source, sex and age. This study could provide public health strategies for formulating drinking water safety policies and ensuring human safety.
METHODS AND MATERIALS
Study location and sample collection
Geographical distribution and number of drinking water samples.
Quality control
We focused on the newly included regular indices of DBPs involved in GB 5749-2022, including TCM, DBCM, BDCM, TBM, DCAA and TCAA. According to the Chinese drinking water examination methods (GB/T 5750-2023), the limits of detection (LOD) of TCM, DBCM, BDCM, TBM, DCAA and TCAA are 0.032, 0.016, 0.015, 6.0, 0.041 and 1.0 μg/L, respectively. If the concentrations of DBPs were below the LOD, half of the LOD value was considered instead. The qualification rates for TCM, DBCM, BDCM, TBM, DCAA and TCAA were 99.96, 100.00, 100.00, 100.00, 99.86 and 99.98%, respectively. To ensure the accuracy of the testing results, we conducted professional training on sample collection, sample testing and data submission. The water sample was collected according to GB 5749-2022, and the water sample was tested according to GB/T 5750-2023.
Health risk assessment
According to the International Agency for Research on Cancer, TCM, BDCM, DCAA and TCAA are classified as group 2B (possibly carcinogenic to humans). In addition, DBCM and TBM, which are classified as group 3, demonstrate analogous exposure characteristics in terms of population distribution and exposure routes. Their metabolic transformation, mediated by the hepatic cytochrome P450 system, potentially leads to hepatotoxicity and nephrotoxicity at elevated exposure levels (WHO 2025). Health risk assessment was performed following the guidelines of USEPA. Our assessment focused on the carcinogenic and noncarcinogenic risks associated with DBP exposure in drinking water. Three exposure routes, namely oral, dermal and inhalation absorption, were considered in this study. The population exposure parameter values were obtained from the Exposure Factors Handbook of the Chinese Population (China 2013, 2016a, b). The chemical parameters for calculating the health risk of DBPs were obtained from the Integrated Risk Information System and Risk Assessment Information System.
Chronic daily intake
Carcinogenic risk
Noncarcinogenic risk
Analysis of the characteristics of health risks
In this study, hierarchical analysis methods were employed to analyze the health risk of different subgroups. We calculated the health risk stratified by year (2023 and 2024), season (wet and dry seasons), area (urban and rural areas), water source (surface water and groundwater), water sample category (finished water, secondary water supply and tap water), disinfection method (calcium hypochlorite, chlorine dioxide, liquid chlorine and sodium hypochlorite), sex (female and male) and age (1–2, 2–3, 3–4, 4–5, 5–6, 6–9, 9–12, 12–15, 15–18 and >18 years).
Sensitivity analysis
Sensitivity analysis was performed to check the robustness of the study results. We modified the concentrations of DBPs below the LODs using values of zero, LODs or half of the LODs.
The R software (version 4.3.3) was used to analyze the data to ensure the traceability of all results. The data were organized using ‘tidyverse’, and the graphs were plotted using ‘ggplot2’.
RESULTS
Descriptive statistics
Table 1 lists the characteristics of the DBPs in drinking water. The 95th percentile concentrations of the six DBPs varied from 1.00 to 34.21 μg/L. Urban drinking water presented higher concentrations of DBPs than rural drinking water. The secondary water supply samples presented higher concentrations of DBPs than the other two types of samples. The 95th percentile concentrations of the six DBPs followed the order of TCM > TCAA > DCAA > BDCM > DBCM > TBM. The 95th percentile concentrations of DBPs in drinking water treated with liquid chlorine and sodium hypochlorite were generally greater than those in drinking water treated with calcium hypochlorite and chlorine dioxide.
Characteristics of DBPs in drinking water (50th–95th percentiles, μg/L)
| Characteristics | TCM | DBCM | BDCM | TBM | DCAA | TCAA |
|---|---|---|---|---|---|---|
| Year | ||||||
| 2023 | 0.05–35.00 | 0.01–4.00 | 0.01–9.70 | 0.02–1.00 | 1.00–18.00 | 0.50–26.00 |
| 2024 | 0.10–33.00 | 0.01–3.60 | 0.01–8.00 | 0.02–1.00 | 1.00–24.80 | 0.50–23.00 |
| Season | ||||||
| Wet season | 0.02–34.30 | 0.01–3.60 | 0.01–8.16 | 0.02–1.00 | 1.00–22.10 | 0.50–24.00 |
| Dry season | 1.70–34.00 | 0.01–4.60 | 0.21–10.51 | 0.02–1.33 | 1.00–20.00 | 0.50–30.00 |
| Area | ||||||
| Urban | 11.02–39.00 | 0.01–5.30 | 2.70–11.00 | 0.02–1.00 | 1.00–18.00 | 0.50–30.00 |
| Rural | 0.02–29.00 | 0.01–2.40 | 0.01–6.52 | 0.02–1.00 | 1.00–24.90 | 0.50–22.00 |
| Water source | ||||||
| Surface water | 1.40–36.00 | 0.01–4.10 | 0.01–9.40 | 0.02–1.00 | 1.00–23.99 | 0.50–28.00 |
| Groundwater | 0.02–16.68 | 0.01–1.90 | 0.01–5.60 | 0.02–2.00 | 1.00–16.04 | 0.50–12.20 |
| Samples | ||||||
| Finished water | 0.02–29.00 | 0.01–2.16 | 0.01–6.50 | 0.02–1.00 | 1.00–23.00 | 0.50–26.00 |
| Secondary water supply | 14.00–40.23 | 0.41–4.82 | 4.00–10.00 | 0.02–1.00 | 1.00–13.80 | 0.50–30.00 |
| Tap water | 0.50–35.50 | 0.01–4.20 | 0.01–9.30 | 0.02–1.00 | 1.00–22.30 | 0.50–23.00 |
| Disinfection method | ||||||
| Calcium hypochlorite | 0.02–21.00 | 0.01–1.80 | 0.01–5.70 | 0.02–2.30 | 1.00–9.11 | 0.50–13.11 |
| Chlorine dioxide | 0.02–18.31 | 0.01–1.63 | 0.01–4.00 | 0.02–1.00 | 1.00–18.96 | 0.50–20.00 |
| Liquid chlorine | 12.00–37.00 | 0.01–5.99 | 2.50–10.39 | 0.02–1.00 | 1.00–18.12 | 0.50–25.00 |
| Sodium hypochlorite | 14.00–40.23 | 0.41–4.82 | 4.00–10.00 | 0.02–1.00 | 1.00–13.80 | 0.50–30.00 |
| Total | 0.07–34.21 | 0.01–4.00 | 0.01–8.80 | 0.02–1.00 | 1.00–22.00 | 0.50–24.00 |
| Characteristics | TCM | DBCM | BDCM | TBM | DCAA | TCAA |
|---|---|---|---|---|---|---|
| Year | ||||||
| 2023 | 0.05–35.00 | 0.01–4.00 | 0.01–9.70 | 0.02–1.00 | 1.00–18.00 | 0.50–26.00 |
| 2024 | 0.10–33.00 | 0.01–3.60 | 0.01–8.00 | 0.02–1.00 | 1.00–24.80 | 0.50–23.00 |
| Season | ||||||
| Wet season | 0.02–34.30 | 0.01–3.60 | 0.01–8.16 | 0.02–1.00 | 1.00–22.10 | 0.50–24.00 |
| Dry season | 1.70–34.00 | 0.01–4.60 | 0.21–10.51 | 0.02–1.33 | 1.00–20.00 | 0.50–30.00 |
| Area | ||||||
| Urban | 11.02–39.00 | 0.01–5.30 | 2.70–11.00 | 0.02–1.00 | 1.00–18.00 | 0.50–30.00 |
| Rural | 0.02–29.00 | 0.01–2.40 | 0.01–6.52 | 0.02–1.00 | 1.00–24.90 | 0.50–22.00 |
| Water source | ||||||
| Surface water | 1.40–36.00 | 0.01–4.10 | 0.01–9.40 | 0.02–1.00 | 1.00–23.99 | 0.50–28.00 |
| Groundwater | 0.02–16.68 | 0.01–1.90 | 0.01–5.60 | 0.02–2.00 | 1.00–16.04 | 0.50–12.20 |
| Samples | ||||||
| Finished water | 0.02–29.00 | 0.01–2.16 | 0.01–6.50 | 0.02–1.00 | 1.00–23.00 | 0.50–26.00 |
| Secondary water supply | 14.00–40.23 | 0.41–4.82 | 4.00–10.00 | 0.02–1.00 | 1.00–13.80 | 0.50–30.00 |
| Tap water | 0.50–35.50 | 0.01–4.20 | 0.01–9.30 | 0.02–1.00 | 1.00–22.30 | 0.50–23.00 |
| Disinfection method | ||||||
| Calcium hypochlorite | 0.02–21.00 | 0.01–1.80 | 0.01–5.70 | 0.02–2.30 | 1.00–9.11 | 0.50–13.11 |
| Chlorine dioxide | 0.02–18.31 | 0.01–1.63 | 0.01–4.00 | 0.02–1.00 | 1.00–18.96 | 0.50–20.00 |
| Liquid chlorine | 12.00–37.00 | 0.01–5.99 | 2.50–10.39 | 0.02–1.00 | 1.00–18.12 | 0.50–25.00 |
| Sodium hypochlorite | 14.00–40.23 | 0.41–4.82 | 4.00–10.00 | 0.02–1.00 | 1.00–13.80 | 0.50–30.00 |
| Total | 0.07–34.21 | 0.01–4.00 | 0.01–8.80 | 0.02–1.00 | 1.00–22.00 | 0.50–24.00 |
Health risk assessment
Table 2 lists the cumulative carcinogenic and noncarcinogenic risks of the six types of DBPs and the four types of disinfection methods through the three exposure routes. The overall carcinogenic risk of DBPs through multiple pathways was 1.15 × 10−5. The order of the contributions to the carcinogenic and noncarcinogenic risks remained the same for the different exposure routes, with the oral route contributing more than the dermal route and the dermal route contributing more than the inhalation route. The risk through the oral route was approximately 50 times greater than that through the dermal route. For the six DBPs, the total cancer risk ranged from 5.16 × 10−9 to 1.52 × 10−6. The total cancer risk of the DCAA and TCAA exceeded the minimum risk level set by the USEPA. When the different disinfection methods were compared, the overall carcinogenic risk of DBPs associated with each of the four methods ranged from 2.90 × 10−6 to 3.38 × 10−5. The cancer risk associated with the four types of disinfection methods can be ranked as follows: liquid chlorine has the highest risk, followed by sodium hypochlorite, calcium hypochlorite and chlorine dioxide.
Health risks of the different DBPs and disinfection methods through the different exposure routes
| Characteristics | Risk | HI | ||||||
|---|---|---|---|---|---|---|---|---|
| Oral | Dermal | Inhalation | Total | Oral | Dermal | Inhalation | Total | |
| DBPs | ||||||||
| TCM | 6.76 × 10−8 | 3.11 × 10−9 | 5.02 × 10−13 | 7.07 × 10−8 | 2.18 × 10−4 | 1.00 × 10-5 | 6.23 × 10−7 | 2.29 × 10−4 |
| DBCM | 1.56 × 10−8 | 3.03 × 10−10 | 6.81 × 10−11 | 1.59 × 10−8 | 2.51 × 10−5 | 4.88 × 10−7 | 5.24 × 10−8 | 2.56 × 10−5 |
| BDCM | 1.98 × 10−8 | 5.35 × 10−10 | 5.90 × 10−11 | 2.03 × 10−8 | 1.18 × 10−5 | 3.18 × 10−7 | 3.10 × 10−8 | 1.21 × 10−5 |
| TBM | 5.08 × 10−9 | 8.04 × 10−11 | 3.49 × 10−12 | 5.16 × 10−9 | 3.21 × 10−5 | 5.09 × 10−7 | 4.54 × 10−8 | 3.27 × 10−5 |
| DCAA@ | 1.50 × 10−6 | 1.27 × 10−8 | – | 1.52 × 10−6 | 7.84 × 10−3 | 6.39 × 10−5 | – | 7.90 × 10−3 |
| TCAA@ | 1.32 × 10−6 | 1.29 × 10−8 | – | 1.33 × 10−6 | 7.84 × 10−4 | 7.66 × 10−6 | – | 7.91 × 10−4 |
| Disinfection method | ||||||||
| Calcium hypochlorite | 3.86 × 10−6 | 5.40 × 10−8 | 1.31 × 10−10 | 3.92 × 10−6 | 1.03 × 10−2 | 1.02 × 10−4 | 2.72 × 10−7 | 1.04 × 10−2 |
| Chlorine dioxide | 2.88 × 10−6 | 2.81 × 10−8 | 1.31 × 10−10 | 2.90 × 10−6 | 8.74 × 10−3 | 7.57 × 10−5 | 2.72 × 10−7 | 8.82 × 10−3 |
| Liquid chlorine | 3.29 × 10−5 | 9.37 × 10−7 | 2.58 × 10−8 | 3.38 × 10−5 | 3.29 × 10−5 | 9.37 × 10−7 | 2.58 × 10−8 | 3.38 × 10−5 |
| Sodium hypochlorite | 1.22 × 10−5 | 2.43 × 10−7 | 1.77 × 10−10 | 1.25 × 10−5 | 2.75 × 10−2 | 5.86 × 10−4 | 9.68 × 10−6 | 2.84 × 10−2 |
| Total | 1.13 × 10−5 | 2.11 × 10−7 | 1.89 × 10−10 | 1.15 × 10−5 | 2.52 × 10−2 | 4.34 × 10−4 | 7.95 × 10−6 | 2.59 × 10−2 |
| Characteristics | Risk | HI | ||||||
|---|---|---|---|---|---|---|---|---|
| Oral | Dermal | Inhalation | Total | Oral | Dermal | Inhalation | Total | |
| DBPs | ||||||||
| TCM | 6.76 × 10−8 | 3.11 × 10−9 | 5.02 × 10−13 | 7.07 × 10−8 | 2.18 × 10−4 | 1.00 × 10-5 | 6.23 × 10−7 | 2.29 × 10−4 |
| DBCM | 1.56 × 10−8 | 3.03 × 10−10 | 6.81 × 10−11 | 1.59 × 10−8 | 2.51 × 10−5 | 4.88 × 10−7 | 5.24 × 10−8 | 2.56 × 10−5 |
| BDCM | 1.98 × 10−8 | 5.35 × 10−10 | 5.90 × 10−11 | 2.03 × 10−8 | 1.18 × 10−5 | 3.18 × 10−7 | 3.10 × 10−8 | 1.21 × 10−5 |
| TBM | 5.08 × 10−9 | 8.04 × 10−11 | 3.49 × 10−12 | 5.16 × 10−9 | 3.21 × 10−5 | 5.09 × 10−7 | 4.54 × 10−8 | 3.27 × 10−5 |
| DCAA@ | 1.50 × 10−6 | 1.27 × 10−8 | – | 1.52 × 10−6 | 7.84 × 10−3 | 6.39 × 10−5 | – | 7.90 × 10−3 |
| TCAA@ | 1.32 × 10−6 | 1.29 × 10−8 | – | 1.33 × 10−6 | 7.84 × 10−4 | 7.66 × 10−6 | – | 7.91 × 10−4 |
| Disinfection method | ||||||||
| Calcium hypochlorite | 3.86 × 10−6 | 5.40 × 10−8 | 1.31 × 10−10 | 3.92 × 10−6 | 1.03 × 10−2 | 1.02 × 10−4 | 2.72 × 10−7 | 1.04 × 10−2 |
| Chlorine dioxide | 2.88 × 10−6 | 2.81 × 10−8 | 1.31 × 10−10 | 2.90 × 10−6 | 8.74 × 10−3 | 7.57 × 10−5 | 2.72 × 10−7 | 8.82 × 10−3 |
| Liquid chlorine | 3.29 × 10−5 | 9.37 × 10−7 | 2.58 × 10−8 | 3.38 × 10−5 | 3.29 × 10−5 | 9.37 × 10−7 | 2.58 × 10−8 | 3.38 × 10−5 |
| Sodium hypochlorite | 1.22 × 10−5 | 2.43 × 10−7 | 1.77 × 10−10 | 1.25 × 10−5 | 2.75 × 10−2 | 5.86 × 10−4 | 9.68 × 10−6 | 2.84 × 10−2 |
| Total | 1.13 × 10−5 | 2.11 × 10−7 | 1.89 × 10−10 | 1.15 × 10−5 | 2.52 × 10−2 | 4.34 × 10−4 | 7.95 × 10−6 | 2.59 × 10−2 |
Regarding the noncarcinogenic risk, the cumulative HI value of DBP exposure was 2.59 × 10−2. All of the noncarcinogenic risks associated with DBPs in drinking water were lower than 1. Among the different exposure routes, the primary source of health risk related to DBPs in drinking water is oral absorption. The HI values of exposure to DBPs through the oral, dermal and inhalation routes were 2.52 × 10−2, 4.34 × 10−4 and 7.95 × 10−6, respectively. The overall noncarcinogenic risk of DBPs varied across the different disinfection methods, ranging from 3.38 × 10−5 to 2.84 × 10−2. With respect to the noncarcinogenic risk caused by the different disinfection approaches, the pattern was similar to that of the carcinogenic risk.
Characteristics of the health risk
Health risks of DBPs in different times and water sources.
Health risks of DBPs in different sex and age.
Sensitivity analysis
Table 3 provides the sensitivity analysis results. To account for data below the LODs, we replaced those values with values of zero, half of the LODs or LODs and then evaluated the associated health risks. The findings indicated that there were no significant differences in health risks between different substitution values.
Sensitivity analysis for replacing the data below the LODs with different values
| Variables | Risk | HI | ||||||
|---|---|---|---|---|---|---|---|---|
| Oral | Dermal | Inhalation | Total | Oral | Dermal | Inhalation | Total | |
| Zero | 9.11 × 10−6 | 1.92 × 10−7 | 5.89 × 10−11 | 9.41 × 10−6 | 1.70 × 10−2 | 3.86 × 10−4 | 7.86 × 10−6 | 1.77 × 10−2 |
| 1/2 of LOD | 1.13 × 10−5 | 2.11 × 10−7 | 1.89 × 10−10 | 1.15 × 10−5 | 2.52 × 10−2 | 4.34 × 10−4 | 7.95 × 10−6 | 2.59 × 10−2 |
| LOD | 1.34 × 10−5 | 2.32 × 10−7 | 3.20 × 10−10 | 1.37 × 10−5 | 3.31 × 10−2 | 5.01 × 10−4 | 8.15 × 10−6 | 3.34 × 10−2 |
| Variables | Risk | HI | ||||||
|---|---|---|---|---|---|---|---|---|
| Oral | Dermal | Inhalation | Total | Oral | Dermal | Inhalation | Total | |
| Zero | 9.11 × 10−6 | 1.92 × 10−7 | 5.89 × 10−11 | 9.41 × 10−6 | 1.70 × 10−2 | 3.86 × 10−4 | 7.86 × 10−6 | 1.77 × 10−2 |
| 1/2 of LOD | 1.13 × 10−5 | 2.11 × 10−7 | 1.89 × 10−10 | 1.15 × 10−5 | 2.52 × 10−2 | 4.34 × 10−4 | 7.95 × 10−6 | 2.59 × 10−2 |
| LOD | 1.34 × 10−5 | 2.32 × 10−7 | 3.20 × 10−10 | 1.37 × 10−5 | 3.31 × 10−2 | 5.01 × 10−4 | 8.15 × 10−6 | 3.34 × 10−2 |
DISCUSSION
This study focused on evaluating the potential carcinogenic and noncarcinogenic risks caused by DBPs in drinking water through the oral, dermal and inhalation routes in Hunan Province, Central China. Among the various exposure routes, oral ingestion posed the greatest health risks related to DBPs in drinking water. DBPs pose a total cumulative cancer risk of 1.15 × 10−5 across all disinfection methods, indicating a moderate level comparable to that reported in previous studies (Hamidin et al. 2008; Mosaferi et al. 2021; Mishaqa et al. 2022). However, the cancer risk exceeded the minimum or negligible risk level set by the USEPA, at 1.00 × 10−6. Pollution control for DBPs in drinking water should be strengthened to ensure the safety of drinking water. The overall noncarcinogenic risk through the multiple pathways was 2.59 × 10−2, which is within the acceptable to low range reported in most studies (Alidadi et al. 2019; Tafesse et al. 2023).
The different disinfection methods and DBPs pose different health risks. The carcinogenic risk of drinking water disinfected with chlorine dioxide was the lowest, and that of drinking water disinfected with liquid chlorine was the highest. Previous studies (Kali et al. 2021; Dong et al. 2023) have reported that the concentrations of THMs and HAAs in water samples from pipe networks using chlorine as a disinfectant are much greater than those in water samples from other pipe networks and that the generation of THMs as DBPs can be reduced by using chlorine dioxide as a disinfectant. In this study, we found that drinking water disinfected with chlorine dioxide posed lower health risks resulting from the six DBPs investigated than those of drinking water disinfected with the other methods. When considering the health risks caused by different DBPs, the carcinogenic risk posed by DCAA and TCAA in drinking water exceeded the USEPA minimum or negligible risk level, which indicated that more attention should be given to the health hazards linked to DCAA and TCAA.
The subgroup analyses revealed different features of health risk. The cancer risk was 1.67 times greater during the dry season than during the wet season, which could potentially be explained by river connectivity. Previous studies reported that river connectivity is significantly reduced when rainfall and runoff are lower, resulting in an increase in solute concentrations (Zhang et al. 2024). Therefore, the higher the concentration of DBPs, the greater the health risk. The concentrations of DBPs in the secondary water supply and tap water samples exceeded those in the finished water samples, indicating that interactions can occur as free residual chlorine or bromine reacts with natural organic matter in water distribution systems. Furthermore, the concentration of DBPs during the dry season was comparable to that during the wet season, which differs from previous research findings (Pang et al. 2022). This result could be attributed to lower water flow and higher turbidity, which provide more organic precursors for the generation of byproducts resulting from chlorination disinfection. There were no notable differences in health risks between males and females, which agrees with previous studies reporting no notable differences in the health risks associated with exposure to DBPs in drinking water on the basis of sex (Du et al. 2021; Zhu et al. 2023). To date, few comprehensive studies have evaluated the health impacts of DBPs on different population groups. Based on this study, we observed that children faced greater health risks resulting from DBPs in drinking water than adults. The health risks of DBP exposure decreased with age, with younger children experiencing greater risks. The younger the individual is, the greater the sensitivity to DBPs. This can also be attributed to the rate of water intake per body weight rather than the rate of water intake (Zhao et al. 2023). Therefore, it is crucial to prioritize the health risks related to exposure to DBPs in drinking water, particularly for vulnerable children.
There are several limitations in this study. First, to assess the health risk of DBPs, we substituted any values below the LOD with half of the LOD value. This method could introduce uncertainty regarding the calculated health risks. Therefore, we performed a sensitivity analysis where we substituted the DBP concentrations below the LODs with values of zero, LODs and half of the LODs. Second, the absence of individual-level exposure data, individual water consumption patterns and personalized exposure parameters introduces uncertainties in the present risk assessment outcomes, highlighting the need for more accurate risk characterization in subsequent research. Thirdly, the data analyzed pertained only to Hunan Province, Central China, and did not include other regions. As a result, the findings may not be applicable to other areas. However, we followed the health risk assessment guidelines provided by the USEPA, allowing for the comparison of DBP health risks across different regions.
CONCLUSIONS
In this study, we evaluated the health risks associated with DBPs in Hunan Province, Central China. The overall carcinogenic risk of DBP exposure through multiple routes was moderate, whereas the noncarcinogenic risk was within the acceptable to low range. These results indicate that some people in the area face considerable carcinogenic risk resulting from DBP exposure in drinking water. Moreover, different disinfection methods used for treating drinking water pose different health risks. Therefore, the development of safe drinking water disinfection methods is necessary to minimize the health risks associated with DBPs. Additionally, we found that children experienced greater health risks than adults. Hence, proper actions should be implemented to reduce the health risks of DBPs in drinking water, especially for children. In the future, we will conduct more in-depth research on people's health and environmental monitoring.
FUNDING
This work was supported by the Health Research Project of Hunan Provincial Health Commission (W20243212) and the ‘Qinghe’ Youth Cultivation Fund Project of Hunan Provincial Center for Disease Control and Prevention (QHJJ2023007).
DATA AVAILABILITY STATEMENT
Data cannot be made publicly available; readers should contact the corresponding author for details.
CONFLICT OF INTEREST
The authors declare there is no conflict.
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