Health risk assessment of trihalomethanes mixtures from daily water-related activities via multi-pathway exposure based on PBPK model

Blood Trihalomethanes and Human Cancer: A Systematic Review and Meta-Analysis

The control of waterborne diseases through water disinfection is a significant advancement in public health. However, the disinfection process generates disinfection by-products (DBPs), including trihalomethanes (THMs), which are considered to influence the occurrence of cancer. This analysis aims to quantitatively evaluate the relationship between blood concentrations of THMs and cancer. Additionally, the relationship between blood chloroform concentration and cancer is analyzed separately. Following PRISMA guidelines, we conducted a thorough search in the PubMed, Web of Science, and CNKI databases. Statistical analysis was performed using Review Manager 5.4 software. After screening, seven studies meeting the evaluation criteria were included. A total of 1027 blood samples from patients with cancer and 7351 blood samples from the control group were collected. The average concentration of THMs in the blood of the experimental group was 46.71 pg/mL, while it was 36.406 pg/mL in the control group. The difference between the two groups was statistically significant (SMD = -0.36, 95% CI: -0.45 to -0.27, p < 0.00001). However, due to the limited research data on the relationship between blood THMs and cancer, the conclusions drawn exhibit high heterogeneity. Additionally, we discussed the carcinogenic mechanisms of THMs, which involve multiple biological pathways such as oxidative stress, DNA adduct formation, and endocrine disruption, with variations in accumulation and target sites potentially leading to different cancer types, for which evidence is currently lacking. In the future, further epidemiological and animal model studies on THMs should be conducted to obtain more accurate conclusions.

Advancing understanding of human variability through toxicokinetic modeling, in vitro-in vivo extrapolation, and new approach methodologies

The merging of physiology and toxicokinetics, or pharmacokinetics, with computational modeling to characterize dosimetry has led to major advances for both the chemical and pharmaceutical research arenas. Driven by the mutual need to estimate internal exposures where in vivo data generation was simply not possible, the application of toxicokinetic modeling has grown exponentially in the past 30 years. In toxicology the need has been the derivation of quantitative estimates of toxicokinetic and toxicodynamic variability to evaluate the suitability of the tenfold uncertainty factor employed in risk assessment decision-making. Consideration of a host of physiologic, ontogenetic, genetic, and exposure factors are all required for comprehensive characterization. Fortunately, the underlying framework of physiologically based toxicokinetic models can accommodate these inputs, in addition to being amenable to capturing time-varying dynamics. Meanwhile, international interest in advancing new approach methodologies has fueled the generation of in vitro toxicity and toxicokinetic data that can be applied in in vitro-in vivo extrapolation approaches to provide human-specific risk-based information for historically data-poor chemicals. This review will provide a brief introduction to the structure and evolution of toxicokinetic and physiologically based toxicokinetic models as they advanced to incorporate variability and a wide range of complex exposure scenarios. This will be followed by a state of the science update describing current and emerging experimental and modeling strategies for population and life-stage variability, including the increasing application of in vitro-in vivo extrapolation with physiologically based toxicokinetic models in pharmaceutical and chemical safety research. The review will conclude with case study examples demonstrating novel applications of physiologically based toxicokinetic modeling and an update on its applications for regulatory decision-making. Physiologically based toxicokinetic modeling provides a sound framework for variability evaluation in chemical risk assessment.

Ecological risk assessment methods for oxidative by-products in the oxidation degradation process of emerging pollutants: A review

The inherent toxicity and persistence of emerging contaminants such as antibiotics and endocrine disruptors pose substantial threats to the environment. Advanced oxidation processes (AOPs) employed for oxidative degradation could yield toxic oxidation by-products (OBPs), including organic acids and aromatic hydrocarbons. Despite their typically low concentrations, OBPs require scrutiny owing to their potential health risks. Although effective assessment methodologies are available, a comprehensive review focusing on the ecological and environmental effects of these pollutants is lacking. This study offers a succinct overview of existing ecotoxicological exposure assessments for emerging organic pollutants. Further, it encapsulates principal dose-response assessment techniques and provides a comparative analysis of several methods. The straightforward assessment factor method evaluates risk based on exposure and species sensitivity and is suitable for preliminary assessments of single pollutants; Species Sensitivity Distribution (SSD) compares species sensitivities to OBPs, emphasizing the importance of species-specific toxicological responses; microcosm and mesocosm methods simulate and predict the effects of OBPs on aquatic life by considering environmental diversity and biological community structures and are ideal for assessing the toxicity of multiple OBPs; the ecological risk analysis model employs mathematical and probabilistic approaches to comprehensively and accurately assess exposures and effects, accounting for the complexities and uncertainties inherent in ecotoxicological evaluations. Different risk characterization techniques are outlined in this study, including the risk quotient (RQ), which is ideal for quantifying and comparing risks; probabilistic ecological risk assessment (PERA), suitable for managing significant uncertainty; and the Environmental Pollution Index (EPI), the preferred method for quantitative assessment of OBP pollution levels. The merits and limitations of each of these quantitative assessment tools are evaluated, providing a comprehensive view of their applications in risk analysis. In addition, pressing contemporary challenges are identified and trajectories and pivotal issues suggested for future research.

Construction of a physiologically based pharmacokinetic model of paclobutrazol and exposure estimation in the human body

Paclobutrazol (PBZ) is a plant growth regulator that can delay plant growth and improve plant resistance and yield. Although it has been widely used in the growth of medicinal plants, human beings may take it by taking traditional Chinese medicine. There are no published studies on PBZ exposure in humans or standardized limits for PBZ in medicinal plants. We measured the solubility, oil-water partition coefficient (logP), and pharmacokinetics of PBZ in rats and established a physiologically based pharmacokinetic (PBPK) model of PBZ in rats. This was followed by extrapolation to healthy Chinese adult males as a theoretical foundation for future risk assessment of PBZ. The results showed that PBZ had low solubility and high fat solubility. Pharmacokinetic experiments showed that PBZ was absorbed rapidly but eliminated slowly in rats. On this basis, the rat PBPK model was successfully constructed and extrapolated to healthy Chinese adult males to predict the plasma concentration-time curve and exposure of PBZ in humans. The construction of the PBPK model of PBZ in this study facilitates the determination of the standard formulation limits and risk assessment of PBZ residues in medicinal plants.

Physiologically based toxicokinetic modelling of Tri(2-chloroethyl) phosphate (TCEP) in mice accounting for multiple exposure routes

Exposure routes are important for health risk assessment of chemical risks. The application of physiologically based toxicokinetic (PBTK) models to predict concentrations in vivo can determine the effects of harmful substances and tissue accumulation on the premise of saving experimental costs. In this study, Tri(2-chloroethyl) phosphate (TCEP), an organophosphate ester (OPE), was used as an example to study the PBTK model of mice exposed to different exposure doses by multiple routes. Different routes of exposure (gavage and intradermal injection) can cause differences in the concentration of chemicals in the organs. TCEP that enters the body through the mouth is mainly concentrated in the gastrointestinal tract and liver. However, the concentrations of chemicals that enter the skin into the mice are higher in skin, rest of body, and blood. In addition, TCEP was absorbed and accumulated very rapidly in mice, within half an hour after a single exposure. We have successfully established a mouse PBTK model of the TCEP accounting for multiple exposure Routes and obtained a series of kinetic parameters. The model includes blood, liver, kidney, stomach, intestine, skin, and rest of body compartments. Oral and dermal exposure route was considered for PBTK model. The PBTK model established in this study has a good predictive ability. More than 70% of the predicted values deviated from the measured values by less than 5-fold. In addition, we extrapolated the model to humans. A human PBTK model is built. We performed a health risk assessment for world populations based on human PBTK model. The risk of TCEP in dust is greater through mouth than through skin. The risk of TCEP in food of Chinese population is greater than dust.

Assessment of burden of disease induced by exposure to heavy metals through drinking water at national and subnational levels in Iran, 2019

The burden of disease attributable to exposure to heavy metals via drinking water in Iran (2019) was assessed at the national and regional levels. The non-carcinogenic risk, carcinogenic risk, and attributable burden of disease of heavy metals in drinking water were estimated in terms of hazard quotient (HQ), incremental lifetime cancer risk (ILCR), and disability-adjusted life year (DALY), respectively. The average drinking water concentrations of arsenic (As), cadmium (Cd), chromium (Cr), lead (Pb), mercury (Hg), and nickel (Ni) in Iran were determined to be 2.3, 0.4, 12.1, 2.5, 0.7, and 19.7 μg/L, respectively, which were much lower than the standard values. The total average HQs of heavy metals in drinking water in the entire country, rural, and urban communities were 0.48, 0.65 and 0.45, respectively. At the national level, the average ILCRs of heavy metal in the entire country were in the following order: 1.06 × 10^-4 for As, 5.89 × 10^-5 for Cd, 2.05 × 10^-5 for Cr, and 3.76 × 10^-7 for Pb. The cancer cases, deaths, death rate (per 100,000 people), DALYs, and DALY rate (per 100,000 people) attributed to exposure to heavy metals in drinking water at the national level were estimated to be 213 (95% uncertainty interval: 180 to 254), 87 (73-104), 0.11 (0.09-0.13), 4642 (3793-5489), and 5.81 (4.75-6.87), respectively. The contributions of exposure to As, Cd, Cr, and Pb in the attributable burden of disease were 14.7%, 65.7%, 19.3%, and 0.2%, respectively. The regional distribution of the total attributable DALY rate for all heavy metals was as follows: Region 5> Region 4> Region 1> Region 3> Region 2. The investigation and improvement of relatively high exceedance of As levels in drinking water from the standard value, especially in Regions 5 and 3 as well as biomonitoring of heavy metals throughout the country were recommended.

Bayesian toxicokinetic modeling of cadmium exposure in Chinese population

Cadmium (Cd) is a toxic heavy metal widely present in the environment. Estimating its internal levels for a given external exposure using toxicokinetic (TK) models is key to the human health risk assessment of Cd. In this study, existing Cd TK models were adapted to develop a one-compartment TK model and a multi-compartment physiologically based toxicokinetic (PBTK) model by estimating the characteristics of Cd kinetics based on Cd exposure data from 814 Chinese residents. Both models not only considered the effect of gender difference on Cd kinetics, but also described the model parameters in terms of distributions to reflect individual variability. For both models, the posterior distributions of sensitive parameters were estimated using the Markov chain-Monte Carlo method (MCMC) and the approximate Bayesian computation-MCMC algorithm (ABC-MCMC). Validation with the test dataset showed 1.4-22.5% improvement in the root mean square error (RMSE) over the original models. After a systematic literature search, the optimized models showed acceptable prediction on other Chinese datasets. The study provides a method for parameter optimization of TK models under different exposure environment, and the validated models can serve as new quantitative assessment tools for the risk assessment of Cd in the Chinese population.

Development of adaptive neuro-fuzzy inference system model for predict trihalomethane formation potential in distribution network simulation test

Trihalomethanes (THMs), which is one of the major classes of DBP known to be highly cytotoxic and genotoxic, were formed and modeled under controlled conditions by laboratory-scale distribution network simulation test. The formation potentials of THM depending on the parameters such as natural organic matter, bromide, chlorine, pH, and contact time were determined. Subsequently, the Adaptive Neuro-Fuzzy Inference System (ANFIS) model was developed using these parameters as inputs and THM formation potentials as output, and the correlation coefficient was 0.9817. In the range of the inputs, the ANFIS model representing the simulation test results were compared with THM formations of an actual distribution network system in dry and wet seasons. As a result, the predictions of the ANFIS model were little affected by the unidentified factors that were not used in model training but are known to affect THM formations in real waters and gave more consistent results than the EPA model.

Age-sex specific and cause-specific health risk and burden of disease induced by exposure to trihalomethanes (THMs) and haloacetic acids (HAAs) from drinking water: An assessment in four urban communities of Bushehr Province, Iran, 2017

Health risk and burden of disease induced by exposure to trihalomethanes (THMs, four compounds) and haloacetic acids (HAAs, 5 compounds) from drinking water through ingestion, dermal absorption, and inhalation routes were assessed based on one-year water quality monitoring in four urban communities (Bandar Deylam, Borazjan, Bushehr, and Choghadak) of Bushehr Province, Iran. The total average concentrations of THMs and HAAs at all the communities level were determined to be 92.9 ± 43.7 and 70.6 ± 26.5 μg/L, respectively. The dominant components of the THMs and HAAs were determined to be tribromomethane (TBM, 41.6%) and monobromoacetic acid (MBAA, 60.8%), respectively. The average contributions of ingestion, dermal absorption, and inhalation routes in exposure to the chlorination by-products (CBPs) were respectively 65.0, 15.4, and 19.6%. The total average non-carcinogenic risk as the hazard index (HI) and incremental lifetime cancer risk (ILCR) of the CBPs at all the communities level were found to be 4.03 × 10^-1 and 3.16 × 10^-4, respectively. The total attributable deaths, death rate (per 100,000 people), age-weighted disability-adjusted life years (DALYs), and age-weighted DALY rate for all ages both sexes combined at all the communities level were estimated to be 1.0 (uncertainty interval: UI 95% 0.3 to 2.8), 0.27 (0.08-0.75), 30.8 (11.3-100.1), and 8.1 (3.0-26.4), respectively. The average contribution of mortality (years of life lost due to premature mortality: YLLs) in the attributable burden of disease was 94.7% (94.4-95.6). Although in most of cases the average levels of the CBPs were in the permissible range of Iranian standards for drinking water quality, the average values of ILCRs as well as attributable burden of disease were not acceptable (the ILCRs were higher than the boundary limit of 10^-5); therefore, implementation of interventions for reducing exposure to CBPs through drinking water especially in Kowsar Dam Water Treatment Plant is strictly recommended.

Applicability of advanced oxidation processes in removing anthropogenically influenced chlorination disinfection byproduct precursors in a developing country

The studies on occurrence of contaminants of emerging concern in drinking water treatment plants or even wastewater treatment plants in developing country like India, are very limited. Trihalomethanes (THMs) is one such contaminant of concern in drinking water treatment sector. THMs are the major disinfection byproducts (DBPs) formed during the widely used chlorination process. Their identification and removal is of utmost importance in developed as well as developing nations. This study is first of its kind to assess the removal of mixture of urban run-off driven organic matter, agricultural run-off driven organic matter, untreated sewage effluent driven organic matter and little natural organic matter (NOM) (altogether NefOM) (major DBP precursors) using advanced oxidation processes (AOPs) in the Indian region. Since, NOM vary geographically, this study will add up to applicability of generally utilized AOPs for removal of site explicit (Indian) NefOM. Trihalomethanes at a conventional water treatment plant at Mathura and a moving bed biofilm based non-conventional water treatment plant at Agra were monitored over a year, demonstrating the inability of the water treatment plants to limit formation of DBPs from Yamuna inlet water at any time of the year. Various AOPs (UV-H₂O₂, O₃-H₂O₂, O₃) and UV (ultraviolet) photolysis were assessed for their ability to decrease the trihalomethane forming potential (THMFP) by degrading the contaminants in the waters of Yamuna. Kinetic studies were conducted to evaluate the selected AOPs based on their ability to mineralize dissolved organic carbon (DOC), and decrease UV₂₅₄ at various pH, UV intensities, and ozone and hydrogen peroxide concentrations. UV-L/H₂O₂ at an intensity of 47 mJ/cm²/min, pH = 7, and at hydrogen peroxide concentration of 0.5 mM provided an optimum reduction of DOC (64%) and UV₂₅₄ (87%). Fractionation studies indicated that treatment by UV-L/H₂O₂ leads to the most significant decrease in the hydrophobic fraction of the water, while further study indicated that UV-L/H₂O₂ also showed maximum attenuation of THMFP.

Data on THMs concentration and spatial trend in water distribution network (a preliminary study in center of Iran)

The Trihalomethanes (THMs) formed due to a reaction between water disinfection chlorine and some natural organic matters, as chlorinated by products. The aim of this study was determination of THMs values and spatial trend in Yazd city water distribution network, in center of Iran. Sampling of tap water was done in two autumn and winter seasons. The THMs value were measured by using a gas chromatograph-mass spectrometer (GC/MS), Agilent Company 6890 N. The spatial analysis of THMs values was carried out using ArcGIS 10.1 to show the spatial spreading. The Kriging method was used to draw distribution maps. Using the Kriging method to illustrate the difference or precision of forecasts is relatively easy compared to the other interpolation methods. Also, the acceptable level of % RMSE (Root mean square error) was calculated for Kriging method (% RMSE > 40). Thus, this protocol as integrated between data and geraphic could easily used for reporting of THMs level in studies of water distribution network.

Finally, the maximum THMs value were obtained lower than USEPA and WHO guidelines for drinking water (THMs < 40 ppb).