Health risk assessment of haloacetonitriles in drinking water based on internal dose

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.

Haloacetonitriles adsorption using a low-cost adsorbent derived from canvas fabric

The characteristics of canvas fabric-derived adsorbents and their removal efficiency on five haloacetronitriles (HANs) were investigated. In addition, the effect of chemical activation with ferric chloride (FeCl3) and ferric nitrate (Fe(NO3)3) solutions on HANs removal efficiency was determined. The results indicated that the surface area increased from 262.51 m2/g to 577.25 and 370.83 m2/g, respectively, after being activated with FeCl3 and Fe(NO3)3 solutions. Increases in surface area and pore volume had a direct impact on the effectiveness of HANs removal. As compared to the non-activated adsorbent, the activated adsorbent effectively removed five species of HANs. TCAN was highly removed by the Fe(NO3)3-activated adsorbent (94%) due to the presence of mesoporous pore volume after activation with Fe(NO3)3. On the other hand, MBAN had the lowest removal efficiency of all adsorbents in this study. The activation with FeCl3 and Fe(NO3)3 showed equal removal efficiency for DCAN, BCAN, and DBAN, with percent removal higher than 50%. The hydrophilicity of HANs species affected the removal efficiency. The hydrophilicity order of five HANs species was MBAN, DCAN, BCAN, DBAN, and TCAN, respectively, which well corresponded to the obtained removal efficiency. The canvas fabric-derived adsorbents synthesized in this study were proven to be utilized as low-cost adsorbents to efficiently remove HANs from the environment. Future research will focus on the adsorption mechanism and recycling method to realize the potential for large-scale utilization.

NRF2-ARE signaling is responsive to haloacetonitrile-induced oxidative stress in human keratinocytes

Humans are exposed to disinfection by-products through oral, inhalation, and dermal routes, during bathing and swimming, potentially causing skin lesions, asthma, and bladder cancer. Nuclear factor E2-related factor 2 (NRF2) is a master regulator of the adaptive antioxidant response via the antioxidant reaction elements (ARE) orchestrating the transcription of a large group of antioxidant and detoxification genes. Here we used an immortalized human keratinocyte model HaCaT cells to investigate NRF2-ARE as a responder and protector in the acute cytotoxicity of seven haloacetonitriles (HANs), including chloroacetonitrile (CAN), bromoacetonitrile (BAN), iodoacetonitrile (IAN), bromochloroacetonitrile (BCAN), dichloroacetonitrile (DCAN), dibromoacetonitrile (DBAN), and trichloroacetonitrile (TCAN) found in drinking water and swimming pools. The rank order of cytotoxicity among the HANs tested was IAN ≈ BAN ˃ DBAN ˃ BCAN ˃ CAN ˃ TCAN ˃ DCAN based on their LC₅₀. The HANs induced intracellular reactive oxygen species accumulation and activated cellular antioxidant responses in concentration- and time-dependent fashions, showing elevated NRF2 protein levels and ARE activity, induction of antioxidant genes, and increased glutathione levels. Additionally, knockdown of NRF2 by lentiviral shRNAs sensitized the HaCaT cells to HANs-induced cytotoxicity, emphasizing a protective role of NRF2 against the cytotoxicity of HANs. These results indicate that HANs cause oxidative stress and activate NRF2-ARE-mediated antioxidant response, which in turn protects the cells from HANs-induced cytotoxicity, highlighting that NRF2-ARE activity could be a sensitive indicator to identify and characterize the oxidative stress induced by HANs and other environmental pollutants.

A pipeline to evaluate the discrepant interactions between typical nitrogenous disinfection byproduct haloacetonitriles and human hemoglobin

To evaluate the interaction between haloacetonitriles (HANs) and human hemoglobin (Hb), a pipeline was established based on fluorescence spectra, mass spectra and molecular docking. Fluorescence spectra analysis showed the fluorescence of Hb was statically quenched by HANs in the sequence of TCAN > DBAN > DCAN > IAN > BAN > CAN. HANs could combine to multiple surface sites of Hb accounting for "hydrogen bonds" and "van der Waals forces". The high-resolution mass spectra analysis for Hb with and without HANs further confirmed the formation of multiple HAN-Hb complexes with different conversion rates. With the assistance of MOE molecule docking, the potential combination sites and related interactions parameters between HANs and Hb were filtrated. By analyzing the correlations between the candidate interactions parameters and fluorescence quenching constants/MS conversion rates, the combination sites of HANs were fixed at Asp₁₂₆ (α₁/α₂), Lys₁₂₇ (α₁/α₂) in the form of "hydrogen bonds" X → Asp₁₂₆ (α₁/α₂), N → Lys₁₂₇ (α₁/α₂). In this way, the potential interactions between HANs and Hb were effectively evaluated.

Health risks and predictive modeling of disinfection byproducts in swimming pools

Disinfection is an indispensable water treatment process used to inactivate pathogens and prevent outbreaks of infectious diseases in swimming pools. However, toxic disinfection byproducts (DBPs) are inevitably formed during the process. To improve the supervision and regulation of DBPs in swimming pools, the reliability of using trihalomethanes (THMs) as the sole indicator of organic DBPs and the possibility of using easily detectable water quality parameters as predictors of DBPs were discussed based on the occurrence of 29 typical DBPs in swimming pools. Among the target DBP categories, THMs and haloacetic acids (HAAs) were the prominent species, and the concentrations of HAAs were the highest. The risk assessment results indicated that the total risk values in most pools were higher than the acceptable value (10^-6). Compared with nitrosamines and THMs, HAAs were the main contributors to the cancer risks posed by dermal absorption and ingestion. THMs (r = 0.619; p < 0.01) and HAAs (r = 0.989; p < 0.01) were both significantly correlated with total DBPs (the sum of 29 DBPs). A stepwise multivariate regression model was developed by analyzing the correlations between total DBPs and water quality parameters, and the relationship coefficient R² was 0.756. This study provides important information and perspectives for the improvement and implementation of standards for swimming pool water.

Incorporating Exogenous and Endogenous Exposures into Dietary Risk Assessment of Nitrates and Nitrites in Vegetables: A Probabilistic Integrated Toxicokinetic Modeling Approach

This study aimed to estimate the dietary risk of nitrates and nitrites in vegetables based on internal dose in a probabilistic manner by integrating exogenous exposure based on measured concentrations in vegetables with endogenous exposure using a toxicokinetic (TK) model. We optimized and validated a previous TK model and incorporated Monte Carlo simulations to account for variability across different age populations for predicting internal dose. High levels of nitrates were detected in leafy vegetables (from 545 ± 274 to 1641 ± 873 mg/kg). Nitrite contents of vegetables were generally low (from 1.26 ± 1.40 to 8.20 ± 14.1 mg/kg). The dietary risk was found to be different based on internal versus external dose, suggesting that it is critical to include endogenous nitrite formation into risk assessment. Nitrate and nitrite exposure from vegetables is unlikely to result in appreciable risks for most populations but may be a potential risk for preschoolers.