Neurotoxicological evaluation of two disinfection by-products, bromodichloromethane and dibromoacetonitrile, in rats

In vitro bioassays for monitoring drinking water quality of tap water, domestic filtration and bottled water

BACKGROUND

Location-specific patterns of regulated and non-regulated disinfection byproducts (DBPs) were detected in tap water samples of the Barcelona Metropolitan Area. However, it remains unclear if the detected DBPs together with undetected DPBs and organic micropollutants can lead to mixture effects in drinking water.

OBJECTIVE

To evaluate the neurotoxicity, oxidative stress response and cytotoxicity of 42 tap water samples, 6 treated with activated carbon filters, 5 with reverse osmosis and 9 bottled waters. To compare the measured effects of the extracts with the mixture effects predicted from the detected concentrations and the relative effect potencies of the detected DBPs using the mixture model of concentration addition.

METHODS

Mixtures of organic chemicals in water samples were enriched by solid phase extraction and tested for cytotoxicity and neurite outgrowth inhibition in the neuronal cell line SH-SY5Y and for cytotoxicity and oxidative stress response in the AREc32 assay.

RESULTS

Unenriched water did not trigger neurotoxicity or cytotoxicity. After up to 500-fold enrichment, few extracts showed cytotoxicity. Disinfected water showed low neurotoxicity at 20- to 300-fold enrichment and oxidative stress response at 8- to 140-fold enrichment. Non-regulated non-volatile DBPs, particularly (brominated) haloacetonitriles dominated the predicted mixture effects of the detected chemicals and predicted effects agreed with the measured effects. By hierarchical clustering we identified strong geographical patterns in the types of DPBs and their association with effects. Activated carbon filters did not show a consistent reduction of effects but domestic reverse osmosis filters decreased the effect to that of bottled water.

IMPACT STATEMENT

Bioassays are an important complement to chemical analysis of disinfection by-products (DBPs) in drinking water. Comparison of the measured oxidative stress response and mixture effects predicted from the detected chemicals and their relative effect potencies allowed the identification of the forcing agents for the mixture effects, which differed by location but were mainly non-regulated DBPs. This study demonstrates the relevance of non-regulated DBPs from a toxicological perspective. In vitro bioassays, in particular reporter gene assays for oxidative stress response that integrate different reactive toxicity pathways including genotoxicity, may therefore serve as sum parameters for drinking water quality assessment.

Health risk assessment of heavy metals and disinfection by-products in drinking water in megacities in China: A study based on age groups and Monte Carlo simulations

Heavy metal(loid)s (HMs) and disinfection by-products (DBPs) in drinking water pose risks to human health and jeopardize drinking water. Water-related behaviors vary significantly among different age groups and regions. In this study, the carcinogenic and non-carcinogenic risks of HMs (As, Cd, Cr6+, Cu, Pb, and Zn) and DBPs (bromodichloromethane (BDCM), bromoform, chloroform, dibromochloromethane (DBCM), dichloroacetic acid (DCAA), and trichloroacetic acid (TCAA)) in drinking water in two Chinese megacities (Beijing in North China and Guangzhou in South China) via multiple exposure pathways were assessed. The results showed that children aged 9 months to 2 years had a total carcinogenic risk (TCR) and hazard index (HI) above acceptable levels, indicating that despite the drinking water quality in the selected megacities meeting the current Chinese national standards (GB 5749-2022), the health risks of exposure to HMs and DBPs in drinking water for local young children should not be neglected. Specifically, the carcinogenic risk (CR) of exposure to As in drinking water for children < 18-years-old, who were divided into different age groups, was 1.5-2.0- and 4.5-5.9-times higher than the TCR of exposure to DBPs in Beijing and Guangzhou, respectively. Regarding children aged 9 months to 2 years, the exposure to TCAA accounted for the largest proportion (35.6 %) of the TCR of exposure to DBPs in Beijing drinking water, 5.4-times higher than that in Guangzhou; whereas, the TCR of exposure to DBPs in Guangzhou drinking water was predominantly caused by exposure to chloroform, accounting for 40.6 % of the TCR and 1.5-times higher than that in Beijing. In addition, the CR of exposure to DCAA in drinking water in both megacities accounted for a large proportion of the TCR for children aged 9 months to 2 years. Monte Carlo simulations showed that 62.2 % and 42.6 % of the TCR of simultaneous exposure to As and DBPs in drinking water exceeded the acceptable level for sensitive populations, that is, children aged 1-2 years in Beijing (95th percentile = 4.2 × 10-4) and children aged 9-12 months in Guangzhou (95th percentile = 5.2 × 10-4), respectively. This elaborate health risk assessment sheds light on improving the water quality indices to guarantee drinking water safety in China.

Trimester-specific associations of maternal exposure to disinfection by-products, oxidative stress, and neonatal neurobehavioral development

BACKGROUND

Toxicological studies suggest that maternal exposure to disinfection by-products (DBPs) can impair fetal neurodevelopment. However, evidence from epidemiological studies is scarce and the underlying mechanisms remain unclear.

OBJECTIVE

To explore the trimester-specific associations between maternal blood trihalomethane (THM) and urinary haloacetic acid (HAA) concentrations and neonatal neurobehavioral development, and the potential mediating role of oxidative stress (OS).

METHODS

We included 438 pregnant Chinese women from the Xiaogan Disinfection By-Products (XGDBP) birth cohort. Biospecimens were repeatedly collected across trimesters and measured for blood THMs, urinary HAAs, and urinary OS biomarker concentrations. On the third day after birth, the Neonatal Behavioral Neurological Assessment (NBNA) test was administered to newborns. Associations of trimester-specific DBP measurements and OS biomarkers with neonatal NBNA scores were assessed using linear regression models with generalized estimating equations. The potential mediating role of maternal OS biomarkers was also investigated using mediation analyses.

RESULTS

After adjusting for potential confounders, blood bromodichloromethane (BDCM) concentrations in the first trimester were inversely associated with NBNA scores [percent change comparing the extreme BDCM tertiles = -28.1% (95% CI: -55.2%, -0.88%); p for trend = 0.043]. Besides, third-trimester urinary trichloroacetic acid (TCAA) concentrations were inversely associated with NBNA scores [percent change comparing the extreme TCAA tertiles = -32.9% (95% CI: -64.7%, -1.0%); p for trend = 0.046]. These inverse associations differed across pregnancy trimesters (Type 3p-value = 0.066 and 0.053, respectively) and were stronger in male infants and mothers aged ≥25 years. There was no evidence of mediating effect by 8-hydroxy-2-deoxyguanosine (8-OHdG), 4-hydroxy-2-nonenal-mercapturic acid (HNE-MA), or 8-iso-prostaglandin F_2α (8-isoPGF_2α).

CONCLUSIONS

Higher prenatal BDCM and TCAA concentrations during specific pregnancy trimesters were associated with lower NBNA scores. However, additional research is required to investigate underlying mechanisms.

Cumulative health risk assessment of disinfection by-products in drinking water by different disinfection methods in typical regions of China

Disinfection was essential to keep human healthy from microorganisms in drinking water. Meanwhile, disinfection by-products (DBPs) have been proved to be associated with some adverse health effects. The DBP levels were different in drinking water disinfected by different methods and may cause diverse health risks. However, studies in this field and systematic analysis about risk characteristics are limited. We estimated the health risks of DBPs exposure in drinking water through multi-pathways, and systematically analyzed the characteristics of different disinfection methods and influence factors of health risk of DBPs in China. Drinking water samples were collected and analyzed for DBPs from some representative water treatment plants in several typical regions in China. We adopted the additive method to estimate the health risks of DBPs exposure in drinking water through multi-pathways, and used descriptive and hierarchical analysis to understand their characteristics and influence factors. The concentrations of the six DBPs in drinking water ranged from 1.6 μg/L to 13.3 μg/L. The cumulative cancer risk of DBPs exposure through multi-pathways was 8.63 × 10^-5. The total HI of DBPs exposure was 1.70 × 10^-1. The health risks of DBPs in drinking water disinfected by chlorine dioxide and sodium hypochlorite were lower than by other disinfection methods. The health risk of DBPs in drinking water was dominated by risk through oral and inhalation route. The health risks in wet season were higher than that in dry season. There is no significant difference in health risk for males and females, but children experienced higher health risks than adults. Our study suggested the situation of that a large population experienced the high cancer risk of DBPs in drinking water in typical regions of China. It was suggested that potential higher risk should be concerned, and possible measures could be considered to decrease the health risks.

First-trimester blood concentrations of drinking water trihalomethanes and neonatal neurobehavioral development in a Chinese birth cohort

Toxicological evidence indicates that exposure to drinking water trihalomethanes (THMs) can impair neural development. However, no epidemiologic study to date has evaluated the relation of trihalomethanes exposure with neonatal neurobehavioral development. Here we aimed to evaluate if prenatal exposure to THMs during early pregnancy is associated with neonatal neurobehavioral development in 451 Chinese mother-child pairs. First trimester blood THMs [chloroform (TCM), bromodichloromethane (BDCM), dibromochloromethane (DBCM), and bromoform (TBM)] were determined by solid phase micro-extraction gas chramatography. Neonatal neurobehavioral development was assessed using neonatal behavioral neurological assessment (NBNA) on the third day after birth. Multivariable linear regression models and restricted cubic spline models were constructed to evaluate the associations between blood THMs and neonatal neurological development scores. Blood concentrations of BDCM, whether modeled as continuous or categorical variables, were inversely associated with total NBNA score of newborns based on the multivariable linear regression. The association was further confirmed in the cubic spline model, and a linear dose-response relationship was observed. Stratified analysis showed that the inverse association between blood BDCM and total NBNA score was more evident in male infants than females. Our findings suggest that exposure to THMs during early pregnancy may be associated with impaired neonatal neurobehavioral development.

Drinking water disinfection by-products during pregnancy and child neuropsychological development in the INMA Spanish cohort study

BACKGROUND

Disinfection by-products (DBPs) constitute a complex mixture of prevalent chemicals in drinking water and there is evidence of neurotoxicity for some of them.

OBJECTIVES

We evaluated the association between estimates of DBP exposure during pregnancy and child neuropsychological outcomes at 1 and 4-5years of age.

METHODS

We conducted a population-based mother-child cohort study in Spain with recruitment at first trimester of gestation (INMA Project, 2003-2008). Neuropsychological development was measured at 1year of age using the Bayley Scales of Infant Development and at 4-5years with the McCarthy Scales of Children's Abilities. Modeled tap water concentrations of trihalomethanes (THM) were combined with personal ingestion, showering and bathing habits to estimate exposure as ingestion uptake, all route (showering, bathing, ingestion) uptake (μg/day) and crude levels (μg/l) in the residence. Chloroform, brominated THMs (bromodichloromethane, dibromochloromethane, bromoform) and total THMs (chloroform and brominated THMs) were analysed separately. Nine haloacetic acids levels were available in one of the areas. Linear regression was used to estimate associations in 1855 subjects adjusting for covariables.

RESULTS

The median concentration of total THMs, chloroform, brominated THMs, total haloacetic acids, dichloroacetic acid, and trichloroacetic acid were, respectively 30.3μg/L, 9.4μg/L, 11.6μg/L, 10.5μg/L, 2.7μg/L, and 3.1μg/L. The associations between THM exposure and neuropsychological outcomes were null, except for total and brominated THM uptake though all routes and the general cognitive score at 4-5years, with a decrease in -0.54 points (95%CI -1.03, -0.05) and -0.64 (95%CI -1.16, -0.12), respectively, for doubling total and brominated THM uptake. A positive association found between dichloroacetic acid and the mental score at 1year did not persist at 4-5years.

CONCLUSIONS

Minor associations observed between DBP exposure during gestation and child neuropsychological development at 1year disappeared at 4-5years. Although a suggestive association is identified for exposure to brominated THMs and the cognitive score at 4-5years, chance cannot be ruled out.

Potential protective effect of taurine against dibromoacetonitrile-induced neurotoxicity in rats

Dibromoacetonitrile (DBAN) is a disinfection by-product of water chlorination. Epidemiological studies indicate that it might present a potential hazard to human health. The present study aimed to investigate the possible neurotoxicity of DBAN in rats and possible protection by taurine. Based on initial dose-response experiment, DBAN (60 mg/kg) was administrated orally for 7 days. DBAN administration significantly impaired behavior of rats. Further, DBAN produced significant decrease of monoamines, γ-aminobutyric acid (GABA), glutamate contents, acetylcholinestrase (AChE) and aspartate aminotransferase (AST) activities, in rat brain. On the other hand, a significant increase in malondialdehyde (MDA), nitric oxide (NO) contents and lactic dehydrogenase (LDH) activity was observed. Co-administration of taurine (200mg/kg, i.p.) with DBAN mitigated most tested parameters. In conclusion, the present study indicates that DBAN has the propensity to cause significant oxidative damage in rat brain. However, taurine has a promising role in attenuating the obtained hazardous effects of DBAN.