Differential Cytotoxicity of Haloaromatic Disinfection Byproducts and Lead Co-exposures against Human Intestinal and Neuronal Cells

Catalytic hydrodehalogenation activity and selectivity of polyiodinated phenolic disinfection byproducts at ambient conditions

Iodo-phenolic disinfection byproducts (DBPs) widely occur in disinfected water, posing potential risks to human health and the ecosystem as they possess higher toxicity than the bromo- and chloro-analogs. Herein, we elucidated the catalytic hydrodehalogenation (HDH) activity and selectivity of polyiodinated phenolic DBPs on supported noble metal catalysts at ambient conditions. Both 2,4,6-triiodophenol and 4-chloro-2,6-diiodophenol can be efficiently eliminated on Pd/TiO2 and Rh/TiO2 within 20 min, with Pd/TiO2 exhibiting higher turnover frequency. The HDH reactions proceeded in both stepwise and concerted pathways on Pd/TiO2, while they were dominantly stepwise on Rh/TiO2. Experimental results and theoretical calculations revealed that the HDH selectivity depends on the position and the bond energy of halo-substitutions. For the HDH of 2,4,6-triiodophenol, the para-substituted iodine was more favorable to be dehalogenated than the ortho-substituted ones due to the steric hindrance of the hydroxyl group. For the HDH of 4-chloro-2,6-diiodophenol, the ortho-substituted iodine was removed before the para-substituted chlorine as CI bond had higher reactivity than CCl bond. Significant catalyst deactivation was observed for the HDH of 4-chloro-2,6-diiodophenol on Pd/TiO2 due to iodine poisoning, resulting in 4-chlorophenol as the dominant product. In contrast, Rh/TiO2 can completely hydrodehalogenate 4-chloro-2,6-diiodophenol into cyclohexanone with little iodine poisoning. Our results suggest that HDH is an efficient process for abating iodo-phenolic DBPs. Rh/TiO2 is a more promising HDH catalyst for iodinated DBP removal than Pd/TiO2 with excellent resistance to iodine poisoning.

The influence of bromide and iodide ions on the sulfamethoxazole (SMX) halogenation during chlorination

Disinfection by-products (DBPs) were produced during the chlorination process, posing a threat to drinking water safety and human health. In the presence of bromide and iodide ions, brominated and iodinated DBPs will be generated, which might be more toxic than the parent compound. However, there are few studies on brominated and iodinated DBPs of antibiotics. Therefore, in this study, the fates of sulfamethoxazole (SMX) during chlorination in different systems (Blank; SMX + NaClO; SMX+ NaClO+ Br^-; SMX+ NaClO+I^-; SMX+ NaClO+ Br^- + I^-) were investigated. In different systems, all the reaction followed a pseudo-first-order kinetics, while the reaction rates of NaClO with SMX were different, the reaction rates were in order of SMX + NaClO + Br^- + I^- > SMX + NaClO + Br^- > SMX + NaClO + I^- > SMX + NaClO. When Br^- and I^- existed simultaneously, the reaction rate was the fastest. Iodide played an important role in oxidation and promoted the chlorination of SMX. SMX mainly underwent S-C cleavage, S-N hydrolysis, desulfonation, and substitution reactions. Nine disinfection by-products, including three reported for the first time, were identified using a non-targeted approach, and degradation pathways were proposed. Furthermore, EPI Suite software was applied to predict the environmental accumulation potential and environmental persistence of the degradation products. The results indicated that SMX and degradation products had little environmental accumulative potential and environmental persistence.

Occurrence of Iodophenols in Aquatic Environments and the Deiodination of Organic Iodine with Ferrate(VI)

Toxic and odorous iodophenols are commonly identified as disinfection by-products (DBPs) in drinking water. Herein, ng/L levels of iodophenols were identified in river water, wastewater treatment plant effluent, and medical wastewater, with the simultaneous identification of μg/L to mg/L levels of iodide (I^-) and total organic iodine (TOI). Oxidation experiment suggested that the I^-, TOI, and iodophenols could be oxidized by ferrate [Fe(VI)], and more than 97% of TOI had been transformed into stable and nontoxic IO₃^-. Fe(VI) initially cleaved the C-I bond of iodophenols and led to the deiodination of iodophenols. The resulted I^- was swiftly oxidized into HOI and IO₃^-, with the intermediate phenolic products be further oxidized into lower molecular weight products. The Gibbs free energy change (ΔG) of the overall reaction was negative, indicating that the deiodination of iodophenols by Fe(VI) was spontaneous. In the disinfection of iodine-containing river water, ng/L levels of iodophenols and chloro-iodophenols formed in the reaction with NaClO/NH₂Cl, while Fe(VI) preoxidation was effective for inhibiting the formation of iodinated DBPs. Fe(VI) exhibited multiple functions for oxidizing organic iodine, abating their acute toxicity/cytotoxicity and controlling the formation of iodinated DBPs for the treatment of iodide/organic iodine-containing waters.

Association between trichlorophenols and neurodegenerative diseases: A cross-sectional study from NHANES 2003-2010

PURPOSE OF THE RESEARCH

To evaluate the association of the exposure of trichlorophenols (TCPs) on the morbidity and mortality of patients with Parkinson's disease (PD) and Alzheimer's disease (AD) using the data from the National Health and Nutrition Examination Survey (NHANES) 2003-2010. Multivariable logistic regression models and COX regression were used to evaluate the association between TCP exposure and the AD and PD risk. Least Absolute Shrinkage and Selection Operator (LASSO) methods were used to screen latent covariates.

PRINCIPAL RESULTS

A total of 6333 participants over the age of 18 years were included in the analysis. After the adjustments for major confounders, participants with higher concentrations of urinary 2,4,6-TCP had higher risk of AD (odds ratios (ORs), 3.19; 95% CI: 1.07, 9.45) than the group below the limit of detection (LOD). Compared to group of below the LOD, higher urinary concentrations of 2,4,5-TCP was associated with higher risk of all-cause mortality in PD patients (log-rank P = 0.022) and all participants (log-rank P < 0.001) without adjustments for confounders. In addition, a higher risk of all-cause mortality in all participants with high urinary concentrations of 2,4,6-TCP (log-rank P = 0.001) was found without adjustments for confounders. With the adjustments for major confounders, participants with higher concentrations of urinary 2,4,5-TCP had a higher risk of death in patients with PD (hazard ratios (HRs), 53.19; 95% CI: 2.82, 1004.13) than in the group below the LOD.

MAJOR CONCLUSIONS

Exposure to high concentration of 2,4,6-TCP may increase the risk of AD, and the level of 2,4,5-TCP may be associated with the risk of death in patients with PD. Our findings reveal the potential toxicity of TCPs, highlight the potential impact of TCPs on neurodegenerative diseases, and express concerns regarding the use of organochlorine pesticides.

Synergistic cytotoxicity of bromoacetic acid and three emerging bromophenolic disinfection byproducts against human intestinal and neuronal cells

Halogenated disinfection byproducts (halo-DBPs) are drinking water contaminants of great public health concern. Nine haloaliphatic DBPs have been regulated by the U.S. Environmental Protection Agency and various halophenolic compounds have been identified as emerging DBPs. In this study, we evaluated the cytotoxic interactions of the regulated bromoacetic acid and three emerging bromophenolic DBPs, i.e., 2,4,6-tribromophenol, 3,5-dibromo-4-hydroxybenzoic acid, and 3,5-dibromo-4-hydroxybenzaldehyde. Cytotoxicity was measured for each DBP individually as well as each of their mixtures using in vitro human epithelial colorectal adenocarcinoma (Caco-2) and neuroblastoma (SH-SY5Y) cells. Concentration addition (CA) model and isobolographic analysis were employed to characterize the interactions among the DBPs. Our results show that the cytotoxicity of four bromo-DBPs against both cell-types followed the descending rank order of bromoacetic acid > 2,4,6-tribromophenol > 3,5-dibromo-4-hydroxybenzaldehyde > 3,5-dibromo-4-hydroxybenzoic acid. Compared with the toxicity data in literature, our finding that bromoacetic acid showed higher cytotoxicity than bromophenolic DBPs was consistent with the results from Chinese hamster ovary cells (a commonly used in vitro model of DBP toxicological studies); but different from the results obtained from in vivo biological models. Significantly, with CA model prediction, we found that mixtures of four bromo-DBPs exhibited synergistic cytotoxic effects on both human cell types. Isobolographic analysis of binary DBP mixtures revealed that, for Caco-2 cells, bromoacetic acid, 2,4,6-tribromophenol, and 3,5-dibromo-4-hydroxybenzoic acid induced synergism; for SH-SY5Y cells, bromoacetic acid induced synergism with all three bromophenolic DBPs. The production of reactive oxidative species (ROS) induced by DBP mixtures could be an important reason for the synergistic cytotoxicity.