Theoretical investigation on the kinetics and mechanisms of hydroxyl radical-induced transformation of parabens and its consequences for toxicity: Influence of alkyl-chain length

Upcycling of waste disposable medical masks to high value-added gasoline fuel and surfactants products by sub/supercritical water degradation and partial oxidation

The amount of waste disposable medical masks (DMMs) and the potential environmental risk increased significantly due to the huge demand of disposable medical surgical masks. In this study, two effective and environmentally friendly processes, supercritical water degradation (SCWD) and subcritical water partial oxidation (SubCWPO), were proposed for the upcycling of DMMs. The optimal conditions for the SCWD process (conversion ratio>98 %) were 410 ℃, 15 min, and 1:5 g/mL. The oil products obtained from the SCWD process were mainly small molecule hydrocarbons (C7-C12) with a content of 86 % and could be recycled as fuel feedstock for gasoline. Alkyl radicals in the SCWD reaction formed double bonds and ring structures through hydrogen capture reactions, β-scission, and dehydrogenation reactions, and aromatic hydrocarbons were formed by olefin cyclization and cycloalkane dehydrogenation. The introduction of an oxidant (H2O2) to the reaction system could significantly reduce the reaction temperature and shorten the reaction time. At 350 ℃, 15 min, 1:20 g/mL, V(H2O2): V (H2O) of 1:1, the conversion ratio of the SubCWPO process was 88 %, which was higher than that of the SCWD process at 400 ℃ (71.49 %). Oil products produced from the SubCWPO process were rich in alcohols and esters, which could be used as raw materials for nonionic surfactant of polyol and fatty acid ester. The abundant hydroxyl radical in the SubCWPO system trapped hydrogen atoms on PP and reacted with the resulting alkyl radical to form alkanols, which was oxidized to form acids. The esterification of acids and alkanols formed high level of esters. The SCWD and SubCWPO processes proposed in this study are believed to be promising strategies for DMMs degradation and the recovery of high value-added hydrocarbons.

Accumulation of Parabens, Their Metabolites, and Halogenated Byproducts in Migratory Birds of Prey: A Comparative Study in Texas and North Carolina, USA

Parabens are alkyl esters of p-hydroxybenzoic acid that are commonly used as preservatives in personal care products such as cosmetics. Recent studies have revealed the presence of parabens in surface and tap water because of their use as disinfection products; however, little is known about their occurrence in biological samples and their bioaccumulation potential, particularly in raptor birds known as sentinels for pollutant detection. We examined the occurrence and tissue distribution of parabens, their metabolites, and halogenated byproducts in the liver, kidney, brain, and muscle of birds of prey from Texas and North Carolina (USA). Methylparaben (MeP), propylparaben (PrP), and butylparaben (BuP) were detected in more than 50% of all tissues examined, with the kidney exhibiting the highest concentration of MeP (0.65-6.84 ng/g wet wt). Para-hydroxybenzoic acid (PHBA), a primary metabolite, had the highest detection frequency (>50%) and a high accumulation range in the liver, of 4.64 to 12.55 ng/g. The chlorinated compounds chloromethylparaben and chloroethylparaben were found in over half of the tissues, of which dichloromethylparaben (2.20-3.99 ng/g) and dichloroethylparaben (1.01-5.95 ng/g) in the kidney exhibited the highest concentrations. The dibrominated derivatives dibromideethylparaben (Br2EtP) was detected in more than 50% of samples, particularly in muscle and brain. Concentrations in the range of 0.14 to 17.38 ng/g of Br2EtP were detected in the kidney. Dibromidepropylparaben (Br2PrP) was not frequently detected, but concentrations ranged from 0.09 to 21.70 ng/g in muscle. The accumulations of total amounts (sum) of parent parabens (∑P), metabolites (∑M), and halogenated byproducts (∑H) in different species were not significantly different, but their distribution in tissues differed among the species. Positive correlations were observed among MeP, PrP, BuP, and PHBA in the liver, suggesting similar origins and metabolic pathways. Environ Toxicol Chem 2024;00:1-12. © 2024 The Author(s). Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Reaction of methylene blue with OH radicals in the aqueous environment: mechanism, kinetics, products and risk assessment

Methylene Blue (MB) is an industrial chemical used in a broad range of applications, and hence its discharge is a concern. Yet, the environmental effects of its degradation by HO˙ radicals have not been fully studied yet. This study employs quantum chemical calculations to investigate the two-step degradation of MB by HO˙ radicals in aqueous environments. It was found that MB undergoes a rapid reaction with the HO˙ radical, with an overall rate constant of 5.51 × 109 to 2.38 × 1010 M-1 s-1 and has a rather broad lifetime range of 11.66 hours to 5.76 years in water at 273-383 K. The calculated rate constants are in good agreement with the experimental values (k calculation/k experimental = 2.62, pH > 2, 298 K) attesting to the accuracy of the calculation method. The HO˙ + MB reaction in water followed the formal hydrogen transfer and radical adduct formation mechanisms, yielding various intermediates and products. Based on standard tests these intermediates and some of the products can pose a threat to aquatic organisms, including fish, daphnia, and green algae, they have poor biodegradability and have the potential to induce developmental toxicity. Hence MB in the environment is of moderate concern depending on the ratio of safe to harmful breakdown products.

Ultrasonic treatment of endocrine disrupting compounds, pharmaceuticals, and personal care products in water: An updated review

Pharmaceuticals, personal care products (PPCPs), and endocrine-disrupting compounds (EDCs) have seen a recent sustained increase in usage, leading to increasing discharge and accumulation in wastewater. Conventional water treatment and disinfection processes are somewhat limited in effectively addressing this micropollutant issue. Ultrasonication (US), which serves as an advanced oxidation process, is based on the principle of ultrasound irradiation, exposing water to high-frequency waves, inducing thermal decomposition of H2O while using the produced radicals to oxidize and break down dissolved contaminants. This review evaluates research over the past five years on US-based technologies for the effective degradation of EDCs and PPCPs in water and assesses various factors that can influence the removal rate: solution pH, temperature of water, presence of background common ions, natural organic matter, species that serve as promoters and scavengers, and variations in US conditions (e.g., frequency, power density, and reaction type). This review also discusses various types of carbon/non-carbon catalysts, O3 and ultraviolet processes that can further enhance the degradation efficiency of EDCs and PPCPs in combination with US processes. Furthermore, numerous types of EDCs and PPCPs and recent research trends for these organic contaminants are considered.

Nonlinear responses of biofilm bacteria to alkyl-chain length of parabens by DFT calculation

Parabens can particularly raise significant concerns regarding the disruption of microbial ecology due to their antimicrobial properties. However, the responses of biofilm bacteria to diverse parabens with different alkyl-chain length remains unclear. Here, theoretical calculations and bioinformatic analysis were performed to decipher the influence of parabens varying alkyl-chain lengths on the biofilm bacteria. Our results showed that the disturbances in bacterial community did not linearly response to the alkyl-chain length of parabens, and propylparaben (PrP), with median chain length, had more severe impact on bacterial community. Despite the fact that paraben lethality linearly increased with chain length, the PrP had a higher chemical reactions potential than parabens with shorter or longer alkyl-chain. The chemical reactions potential was critical in the nonlinear responses of bacterial community to alkyl-chain length of parabens. PrP could impose selective pressure to disturb the bacterial community, because it had a more profound contribution to deterministic assembly process. Furthermore, N-acyl-homoserine lactones was also significantly promoted under PrP exposure, confirming that PrP could affect the bacterial community by influencing the quorum-sensing system. Overall, our study reveals the nonlinear responses of bacterial communities to the alkyl-chain lengths of parabens and provides insightful perspectives for the better regulation of parabens. ENVIRONMENTAL IMPLICATION: Parabens are recognized as emerging organic pollutants, which specially raise great concerns due to their antimicrobial properties disturbing microbial ecology. However, few study have addressed the relationship between bacterial community responses and the molecular structural features of parabens with different alkyl-chain length. This investigation revealed nonlinear responses of the bacterial community to the alkyl-chain length of parabens through DFT calculation and bioinformatic analysis and identified the critical roles of chemical reactions potential in nonlinear responses of bacterial community. Our results benefit the precise evaluation of ecological hazards posed by parabens and provide useful insights for better regulation of parabens.

In vitro exposure of porcine spermatozoa to methylparaben, and propylparaben, alone or in combination adversely affects sperm quality

Parabens (PBs) are widely used in the cosmetic, pharmaceutical, and food industries as preservatives of products. Because of its great use, humans and other organisms are highly exposed daily. However, little is known about the effect of PBs on male infertility. Therefore, the aim of the present study was to evaluate the effect of methylparaben (MePB) and propylparaben (PrPB), alone or in combination, on the physiological characteristics of pig in vitro exposed sperm to different concentrations (0, 200, 500, and 700 μM) for viability, motility, and acrosome integrity evaluation and (0, 200, 500, 700, 1000, and 2000 μM) for DNA fragmentation index evaluation, after 4 h of exposure. The results showed that sperm viability decreased after exposure to MePB from the concentration of 500 μM. In the PrPB and mixture groups, viability decreased at all concentrations except for the control. The decrease in viability of sperm exposed to PrPB was greater than that of the mixture and MePB groups. Sperm motility decreased in all the experimental groups exposed to PBs, at all concentrations, except for the control group. Acrosome integrity was not decreased in the MePB group; however, in the PrPB group, it decreased at a concentration of 200 μM and in the mixture at 500 μM. All groups exhibited DNA damage at different concentrations, except for the control group. Additionally, the effect of PBs on sperm quality was concentration-dependent. The results demonstrated that MePB and PrPB alone or in combination can have adverse effects on sperm quality parameters. MePB had lower toxicity than did both PrPB and the mixture. The mixture did not have an additive effect on any of the parameters evaluated. This could partially explain the link between PB exposure and infertility.

Butylparaben induced zebrafish (Danio rerio) kidney injury by down-regulating the PI3K-AKT pathway

Butylparaben, a common endocrine disruptor in the environment, is known to be toxic to the reproductive system, heart, and intestines, but its nephrotoxicity has rarely been reported. In order to study the nephrotoxicity and mechanism of butylparaben, we examined the acute and chronic effects on human embryonic kidney cells (HEK293T) and zebrafish. Additionally, we assessed the potential remedial effects of salidroside against butylparaben-induced nephrotoxicity. Our in vitro findings demonstrated oxidative stress and cytotoxicity to HEK293T cells caused by butylparaben. In the zebrafish model, the concentration of butylparaben exposure ranged from 0.5 to 15 μM. An assortment of experimental techniques was employed, including the assessment of kidney tissue morphology using Hematoxylin-Eosin staining, kidney function analysis via fluorescent dextran injection, and gene expression studies related to kidney injury, development, and function. Additionally, butylparaben caused lipid peroxidation in the kidney, thereby damaging glomeruli and renal tubules, which resulted from the downregulation of the PI3K-AKT signaling pathway. Furthermore, salidroside ameliorated butylparaben-induced nephrotoxicity through the PI3K-AKT signaling pathway. This study reveals the seldom-reported kidney toxicity of butylparaben and the protective effect of salidroside against toxicological reactions related to nephrotoxicity. It offers valuable insights into the risks to kidney health posed by environmental toxins.

Estrogenic disruption effects and formation mechanisms of transformation products during photolysis of preservative parabens

The ubiquitous presence of emerging contaminants (ECs) in the environment and their associated adverse effects has raised concerns about their potential risks. The increased toxicity observed during the environmental transformation of ECs is often linked to the formation of their transformation products (TPs). However, comprehension of their formation mechanisms and contribution to the increased toxicity remains an unresolved challenge. To address this gap, by combining quantum chemical and molecular simulations with photochemical experiments in water, this study investigated the formation of TPs and their molecular interactions related to estrogenic effect using the photochemical degradation of benzylparaben (BZP) preservative as a representative example. A non-targeted analysis was carried out and three previously unknown TPs were identified during the transformation of BZP. Noteworthy, two of these novel TPs, namely oligomers BZP-o-phenol and BZP-m-phenol, exhibited higher estrogenic activities compared to the parent BZP. Their IC50 values of 0.26 and 0.50 μM, respectively, were found to be lower than that of the parent BZP (6.42 μM). The binding free energies (ΔGbind) of BZP-o-phenol and BZP-m-phenol (-29.71 to -23.28 kcal·mol-1) were lower than that of the parent BZP (-20.86 kcal·mol-1), confirming their stronger binding affinities toward the estrogen receptor (ER) α-ligand binding domain. Subsequent analysis unveiled that these hydrophobic residues contributed most favorably to ER binding, with van der Waals interactions playing a significant role. In-depth examination of the formation mechanisms indicated that these toxic TPs primarily originated from the successive cleavage of ester bonds (OCH2C6H5 and COO group), followed by their combination with BZP*. This study provides valuable insight into the mechanisms underlying the formation of toxic TPs and their binding interactions causing the endocrine-disrupting effects. It offers a crucial framework for elucidating the toxicological patterns of ECs with similar structures.

Acesulfame degradation by thermally activated persulfate: Kinetics, transformation products and estimated toxicity

The existence of the artificial sweetener acesulfame (ACE) in quantities of significance can negatively impact water quality, and its consumption has been associated with deleterious health effects. The present investigation explores the efficacy of heat-activated sodium persulfate (SPS) for eliminating ACE. The complete degradation of 0.50 mg L-1 of ACE was achieved within 45 min under a reaction temperature of 50 °C and 100 mg L-1 of SPS. The impact of thermal decomposition on ACE at a temperature of 60 °C was negligible. This study considers several factors, such as the SPS and ACE loading, the reaction temperature, the initial pH, and the water matrix of the reactor. The results indicate that the method's efficiency is positively correlated with higher initial concentrations of SPS, whereas it is inversely associated with the initial concentration of ACE. Furthermore, higher reaction temperatures and acidic initial pH levels promote the degradation of acesulfame. At the same time, certain constituents of the water matrix, such as humic acid, chlorides, and bicarbonates, can hinder the degradation process. Additionally, the data from LC-QToF-MS analysis of the samples were used to investigate transformation through suspect and non-target screening approaches. Overall, ACE's eight transformation products (TPs) were detected, and a potential ACE decomposition pathway was proposed. The concentration of TPs followed a volcano curve, decreasing in long treatment times. The ecotoxicity of ACE and its identified TPs was predicted using the ECOSAR software. The majority of TPs exhibited not harmful values.

Effect of pH on UV/H2O2-mediated removal of single, mixed and halogenated parabens from water

Adjusting pH values in aqueous environments can significantly improve the efficiency by which parabens and halo-parabens are removed. In this study, 20 neutral and deprotonated species were selected as models to investigate their pH-dependent removal mechanisms and kinetics by a UV/H2O2 process using density functional theory (DFT). Compared to neutral species, deprotonated species exhibit higher reactivity to HO• due to their high electron cloud density. H atom abstraction (HAA) reactions on the substitution groups are the most favorable pathways for neutral species, while radical adduct formation (RAF) reactions are the most favorable for deprotonated species. Single electron transfer (SET) reactions can be neglected for neutral species, while these reactions become a viable route for deprotonated molecules. The total reaction rate constants range from 1.63 × 109 to 3.74 × 1010 M- 1 s- 1 at pH 7.0, confirming the experimental results. Neutral and weakly alkaline conditions are favorable for the degradation of MeP and halo-parabens in the UV/H2O2 process. The order of removal efficiency at optimum pH is dihalo-parabens > mono-halo-parabens ≈ F, F-MeP > MeP. Furthermore, the transformation products must undergo oxidative degradation due to their high toxicity. Our findings provide new insights into the removal of parabens and their halogenated derivatives from wastewater.

Degradation of Butylated Hydroxyanisole by the Combined Use of Peroxymonosulfate and Ferrate(VI): Reaction Kinetics, Mechanism and Toxicity Evaluation

Butylated hydroxyanisole (BHA), a synthetic phenolic antioxidant (SPA), is now widely present in natural waters. To improve the degradation efficiency of BHA and reduce product toxicity, a combination of peroxymonosulfate (PMS) and Ferrate(VI) (Fe(VI)) was used in this study. We systematically investigated the reaction kinetics, mechanism and product toxicity in the degradation of BHA through the combined use of PMS and Fe(VI). The results showed that PMS and Fe(VI) have synergistic effects on the degradation of BHA. The effects of operational factors, including PMS dosage, pH and coexisting ions (Cl-, SO42-, HCO3-, K+, NH4+ and Mg2+), and different water matrices were investigated through a series of kinetic experiments. When T = 25 °C, the initial pH was 8.0, the initial BHA concentration was 100 μM, the initial concentration ratio of [PMS]0:[Fe(VI)]0:[BHA]0 was 100:1:1 and the degradation rate could reach 92.4% within 30 min. Through liquid chromatography time-of-flight mass spectrometry (LC-TOF-MS) identification, it was determined that the oxidation pathway of BHA caused by PMS/Fe(VI) mainly includes hydroxylation, ring-opening and coupling reactions. Density functional theory (DFT) calculations indicated that •OH was most likely to attack BHA and generate hydroxylated products. The comprehensive comparison of product toxicity results showed that the PMS/Fe(VI) system can effectively reduce the environmental risk of a reaction. This study contributes to the development of PMS/Fe(VI) for water treatment applications.

Gross yield driving the mass fluxes of fishery drugs: Evidence of occurrence from full aquaculture cycle in lower Yangtze River Basin

Expanding aquaculture has generated pollutants like fishery drugs in wastewater, which affects the aquatic environments and hinders sustainable development of aquaculture. To evaluate the occurrence, mass fluxes and production factors of fishery drugs in aquaculture, full-aquaculture-cycle monitoring in finfish and crustacean wastewater was conducted in the lower Yangtze River Basin, and 28 pesticides and 15 antibiotics were detected. The results showed that individual fishery drugs varied from ppt to ppb levels. Among them, sulfonamides were dominant with a mean concentration of 105.95 ± 4.13 ng·L-1 in finfish aquacultural wastewater, and insecticides were prevailing in crustacean aquacultural wastewater with a content of 146.56 ± 0.66 ng·L-1. Since the susceptibility to finfish disease determined the aquaculture practice, there were significant differences between two types of aquacultural wastewater. Finfish aquacultural wastewater contained more drugs and reached peak earlier in rapid-growth period, yet crustacean aquacultural wastewater peaked at the harvest period, to prevent against disease. Meanwhile, higher ecological risk, especially for florfenicol, were found in finfish wastewater. With 6 production factors from Good Aquaculture Practice, the gross yield was the most influential factor of drug mass flux, explaining 98 % variance by stepwise regression. Apart from increasing concentrations of fishery drugs in wastewater, regional high-yield aquaculture also significantly impacted the corresponding mass flux. As estimated by linear regression, 1.63 tons of target drugs would be discharged by 1 Mt. aquatic products, and 7.77 tons were discharged from aquaculture in the lower Yangtze River Basin in 2021. This is the first report to quantify mass fluxes of fishery drugs and to highlight gross yield as the most influential factor, which provides guidance for the supervision and regulation of sustainable aquaculture.

Homogeneous and heterogeneous atmospheric ozonolysis of chlorobenzene:Mechanism, kinetics and ecotoxicity assessment

The reactions between chlorobenzene(CB) and ozone have been studied comprehensively in this paper. Chlorobenzene is a commonly found chlorinated aromatic volatile organic compound(VOC), and its emission into the atmosphere can cause harm to the ecosystem and human health. The frequent occurrence of mineral particles from sandstorms exerts a significant influence on the atmospheric chemistry of the troposphere. Mineral particles are abundant in SiO2 and Al2O3 content. Therefore, we investigated the homogeneous and heterogeneous reaction processes of CB and ozone in the atmosphere by using density functional theory (DFT) method at the M06-2X/6-311++g(3df,2p)//M06-2X/6-31+g(d,p) level. The atmospheric fate, reaction rate and toxicity evaluation of CB ozonation were studied in the gas-phase section. Toxicity evaluation results showed that ozonation of CB could effectively reduce its toxicity. For the heterogeneous process, we simulated three types of SiO2 clusters and nine types of (Al2O3)n clusters, and studied the configurations of CB adsorbed on the cluster surfaces. We found that adsorption of CB on the SiO2 clusters was achieved through hydrogen bonding, while adsorption of CB on the Al2O3 clusters was achieved through both hydrogen bonding and metal bonding. The energy for CB adsorption on the (Al2O3)n cluster surface was higher than that for the SixOy(OH)z cluster surface, and both types of clusters exhibited efficient adsorption of CB. As the SixOy(OH)z clusters grew larger, the rates for the reactions between O3 and CB increased. CB travelled long distances along the Al2O3 clusters, leading to an extended influence range.

Ethylparaben Toxicity on Cladocerans Daphnia Similis and Ceriodaphnia Silvestrii and Species Sensitivity Analysis

Parabens, a group of preservatives with a wide industrial range, threaten human and aquatic biota health due to their toxicity and endocrine disruption potential. As conventional wastewater treatment may not be enough to keep natural environments safe, toxicity studies are useful tools for supporting ecological risk assessments. Here, we focused on assessing ethylparaben's, one of the most common kinds of paraben, toxicity in the cladocerans Daphnia similis and Ceriodaphnia silvestrii. The EC50 sensitivity for D. similis and C. silvestrii was 24 (21-28) mg L- 1 and 25 (19-33) mg L- 1, respectively. Inhibition of reproduction and late development of females were observed in C. silvestrii exposed to 8 mg L- 1. Furthermore, species sensitivity distribution was used to assess ecological risk, and ethylparaben demonstrated low potential risk for aquatic biota.

Acid-induced tubular g-C3N4 for the selective generation of singlet oxygen by energy transfer: Implications for the photocatalytic degradation of parabens in real water environments

Parabens are widely present in aquatic environments and pose potential health risk. Although great progress has been made in the field of the photocatalytic degradation of parabens, the powerful Coulomb interactions between electrons and holes are the major limitations to photocatalytic performance. Hence, acid-induced tubular g-C3N4 (AcTCN) was prepared and applied for the removal of parabens from a real water environment. AcTCN not only increased the specific surface area and light absorption capacity, but also selectively generated 1O2 via an energy transfer-mediated oxygen activation pathway. The 1O2 yield of AcTCN was 11.8 times higher than that of g-C3N4. AcTCN exhibited remarkable removal efficiencies for parabens depending on the length of the alkyl group. Furthermore, the rate constants (k values) of parabens in ultrapure water were higher than those in tap and river water because of the presence of organic and inorganic species in real water environments. Two possible pathways for the photocatalytic degradation of parabens are proposed based on the identification of intermediates and theoretical calculations. In summary, this study offers theoretical support for the efficient enhancement of the photocatalytic performance of g-C3N4 for the removal of parabens in real water environments.

Key factors influencing pollution of heavy metals and phenolic compounds in mangrove sediments, South China

Concentrations of heavy metals (HMs) and phenolic compounds with factors which potentially affected their spatial distribution were investigated in mangrove sediments, South China. Compared to Qi'ao, Futian sediments exhibited higher levels of Pb and nonylphenol (NP), but lower levels of Co and Ni. Seasonal variation showed higher concentrations of Pb, Cr, Co, NP and bisphenol A (BPA), while lower concentration of methylparaben (MP) in wet than dry season. Contaminant levels in sediments collected at different tidal heights showed insignificant variations, except for Zn and NP. MP was found negatively correlated with nearly all HMs and BPA, whereas the latter exhibited positive correlations with each other. Sedimentary total carbon, total nitrogen, C/N and N/P ratios were screened as the most influential factors affecting the distribution of these contaminants. Additionally, both salinity and total phosphate exhibited positive, while both pH and sedimentary particle size registered negative correlation, with one or more contaminants.

Influences of Wastewater Treatment on the Occurrence of Parabens, p-Hydroxybenzoic Acid and Their Chlorinated and Hydroxylated Transformation Products in the Brazos River (Texas, USA)

Parabens are ubiquitous, being found in surface waters around the world. Although little is known about the release of paraben transformation products and fate of transformation products in surface water. This study evaluates both parabens and paraben transformation products in the Brazos River upstream and downstream of a wastewater facility located in Waco, Texas. Concentrations of thirteen compounds were reported in this study, five parent parabens and eight paraben disinfection by-products. Analyte concentrations were spatially evaluated to determine if release of wastewater effluent affects their concentrations in the river. Two Brazos River tributaries were also sampled to determine if they released parabens and related compounds to the Brazos. Sampling occurred weekly for one year with at least 40 samples collected at each site. Analyses were completed for both yearly and seasonal data. Sites downstream of wastewater treatment outfalls had lower concentrations of methyl paraben during the yearly analysis and across multiple seasons in the seasonal analysis with average yearly annual methyl paraben concentrations decreasing from 0.83 ng/L at site 3 to 0.09 ng/L at site 4. Para-hydroxybenzoic acid was the compound present in greatest concentration at most sites across most seasons, with the highest average annual concentration of 10.30 ng/L at site 2. Spatial changes in para-hydroxybenzoic acid varied by season, with seasonal trends only identifiable after normalization by flow. Dichlorinated paraben concentrations increased in the river at sites downstream of wastewater treatment with a yearly average dichlorinated methyl paraben concentration of 0.490 ng/L at site 3 to 1.53 at site 4, just downstream of the major wastewater treatment plant. Concentration increases indicate that wastewater effluent contains sufficiently high dichlorinated paraben concentrations to effect concentrations downstream of effluent discharges. Dichlorinated species also persisted in the environment, with no significant decreases at sites further downstream during any season with an annual average dichlorinated methyl paraben concentration of 1.23 ng/L at site 6. Methyl paraben concentrations decreased at the site furthest downstream to a concentration of 0.081 ng/L, while dichlorinated methyl paraben concentrations remained stable with a concentration of 1.10 ng/L at the site furthest downstream. Due to the dichlorinated species being released in higher concentrations in effluent than parents and being more resistant to degradation, the dichlorinated parabens are more likely to be environmentally relevant than are parent parabens.

Disparate toxicity mechanisms of parabens with different alkyl chain length in freshwater biofilms: Ecological hazards associated with antibiotic resistome

As emerging organic pollutants, parabens are of global concern because of their ubiquitous presence and adverse effects. However, few researchers have addressed the relationship between parabens' structural features and toxicity mechanisms. This study conducted theoretical calculations and laboratory exposure experiments to uncover the toxic effects and mechanisms of parabens with different alkyl chains in freshwater biofilms. The result demonstrated that parabens' hydrophobicity and lethality increased with their alkyl-chain length, whereas the possibility of chemical reactions and reactive sites were unchanged despite the alkyl-chain length alteration. Due to the hydrophobicity variation, parabens with different alkyl-chain presented different distribution patterns in cells of freshwater biofilms and consequently induced distinct toxic effects and led to diverse cell death modes. The butylparaben with longer alkyl-chain preferred to stay in the membrane and altered membrane permeability by non-covalent interaction with phospholipid, which caused cell necrosis. The methylparaben with shorter alkyl-chain preferred to enter into the cytoplasm and influence mazE gene expression by chemically reacting with biomacromolecules, thereby triggering apoptosis. The different cell death patterns induced by parabens contributed to different ecological hazards associated with antibiotic resistome. Compared with butylparaben, methylparaben was more likely to spread ARGs among microbial communities despite its lower lethality.

Evaluating seasonal differences in paraben transformation at two different wastewater treatment plants in Texas and comparing parent compound transformation to byproduct formation

Parabens are commonly used preservatives that are weakly estrogenic. Wastewater effluent is the greatest contributor to the spread of parabens into rivers and other surface water. While previous studies indicate parabens are well removed in wastewater treatment by way of transformation, not much is known about the paraben transformation products. This study evaluates paraben transformation and release at two different wastewater treatment plants in Texas. Paraben concentrations were quantified for influent and effluent by season and by year at both treatment plants. Both seasonal and annual transformation rates were compared between the two wastewater treatment plants. Compounds were compared to evaluate differences in transformation rates and to determine if decreases in parent product concentrations are correlated to changes in transformation product concentrations. The study took place over one year and evaluated each season. Spring had higher influent concentrations and transformation rates at treatment plant 1, while summer had higher influent concentrations and transformation rates at treatment plant 2. PHBA was present in greatest amounts in influent and effluent at both sites with average yearly influent concentrations at 223.9 pM at plant 1 and 211.4 pM at plant 2. Transformation rates of parent parabens were greater at plant 1 with concentration of all three shorter chained parabens decreasing by over 50% after treatment. Formation of dichlorinated transformation products were greater at plant 1 with concentrations of Cl₂MeP increasing by 1200% after treatment and Cl₂EtP increasing by 940%. While shorter chained parabens generally had a greater transformation rate, no correlations were found between decreases in methyl and ethyl parabens and the formation of their respective dichlorinated transformation products.

Efficiency of ozonation and O3/H2O2 as enhanced wastewater treatment processes for micropollutant abatement and disinfection with minimized byproduct formation

Ozonation, a viable option for improving wastewater effluent quality, requires process optimization to ensure the organic micropollutants (OMPs) elimination and disinfection under minimized byproduct formation. This study assessed and compared the efficiencies of ozonation (O₃) and ozone with hydrogen peroxide (O₃/H₂O₂) for 70 OMPs elimination, inactivation of three bacteria and three viruses, and formation of bromate and biodegradable organics during the bench-scale O₃ and O₃/H₂O₂ treatment of municipal wastewater effluent. 39 OMPs were fully eliminated, and 22 OMPs were considerably eliminated (54 ± 14%) at an ozone dosage of 0.5 gO₃/gDOC for their high reactivity to ozone or ^•OH. The chemical kinetics approach accurately predicted the OMP elimination levels based on the rate constants and exposures of ozone and ^•OH, where the quantum chemical calculation and group contribution method successfully predicted the ozone and ^•OH rate constants, respectively. Microbial inactivation levels increased with increasing ozone dosage up to ∼3.1 (bacteria) and ∼2.6 (virus) log₁₀ reductions at 0.7 gO₃/gDOC. O₃/H₂O₂ minimized bromate formation but significantly decreased bacteria/virus inactivation, whereas its impact on OMP elimination was insignificant. Ozonation produced biodegradable organics that were removed by a post-biodegradation treatment, achieving up to 24% DOM mineralization. These results can be useful for optimizing O₃ and O₃/H₂O₂ processes for enhanced wastewater treatment.

Theoretical study on the degradation mechanism, kinetics and toxicity for aqueous ozonation reaction of furan derivatives

The compounds including Furan-2,5-dicarboxylic acid (FDCA), 2-methyl-3-furoic acid (MFA), and 2-furoic acid (FA), containing Furan rings are considered to be possessing high ozone reactivity, although in depth studies of their ozonation processes have not been carried out yet. Hence, mechanism, kinetics and toxicity by quantum chemical, and their structure activity relationship are being investigated in this study. Studies of reaction mechanisms revealed that during the ozonolysis of three furan derivatives containing C=C double bond, furan ring opening occurs. At temperature (298 K) and pressure of 1 atm the degradations rates of 2.22 × 10³ M^-1 s^-1 (FDCA), 5.81 × 10⁶ M^-1 s^-1 (MFA) and 1.22 × 10⁵ M^-1 s^-1 (FA) suggested that the reactivity order is: MFA > FA > FDCA. In the presence of water, oxygen and ozone, the primary product of ozonation, the Criegee intermediates (CIs) would produce lower molecule weight of aldehydes and carboxylic acids by undergoing degradation pathways. The aquatic toxicity reveals that three furan derivatives play green chemicals roles. Significantly, most of degradation products are least harmful to organisms residing the hydrosphere. The mutagenicity and developmental toxicity of FDCA is minimum as compared to FA and MFA, which shows the applicability of FDCA in a wider and broader field. Results of this study revealed its importance in the industrial sector and degradation experiments.

Comparison of UV and UV-LED activated sodium percarbonate for the degradation of O-desmethylvenlafaxine

As an active metabolite of venlafaxine and emerging antidepressant, O-desmethylvenlafaxine (ODVEN) was widely detected in different water bodies, which caused potential harm to human health and environmental safety. In this study, the comparative work on the ODVEN degradation by UV (254 nm) and UV-LED (275 nm) activated sodium percarbonate (SPC) systems was systematically performed. The higher removal rate of ODVEN can be achieved under UV-LED direct photolysis (14.99%) than UV direct photolysis (4.57%) due to the higher values of photolysis coefficient at the wavelength 275 nm. Significant synergistic effects were observed in the UV/SPC (80.38%) and UV-LED/SPC (53.57%) systems and the former exhibited better performance for the elimination of ODVEN. The degradation of ODVEN all followed the pseudo-first-order kinetics well in these processes, and the pseudo-first-order rate constant (k_obs) increased with increasing SPC concentration. Radicals quenching experiments demonstrated that both ·OH and CO₃·^- were involved in the degradation of ODVEN and the second-order rate constant of ODVEN with CO₃·^- (1.58 × 10⁸ (mol/L)^-1 sec^-1) was reported for the first time based on competitive kinetic method. The introduction of HA, Cl^-, NO₃^- and HCO₃^- inhibited the ODVEN degradation to varying degrees in the both processes. According to quantum chemical calculation, radical addition at the ortho-position of the phenolic hydroxyl group was confirmed to be the main reaction pathways for the oxidation of ODVEN by ·OH. In addition, the oxidation of ODVEN may involve the demethylation, H-abstraction, OH-addition and C-N bond cleavage. Eventually, the UV-LED/SPC process was considered to be more cost-effective compared to the UV/SPC process, although the UV/SPC process possessed a higher removal rate of ODVEN.

New insight into molecular mechanism of P450-Catalyzed metabolism of emerging contaminants and its consequence for human health: A case study of preservative methylparaben

Hydroxylated metabolites in the living body are considered as a potential biomarker of exposure to emerging contaminations (ECs) and breast cancer, but their formation mechanism has not received enough attention. Besides, the adverse impacts of metabolites during the metabolic transformation of ECs largely remain unknown. In this study, we employed a density functional calculation combing with in-vitro incubation of human liver microsomes to explore the bio-transformation of preservative methylparaben (MPB) in human bodies. Our results showed that hydroxylated metabolites of MPB (OH-MPB) were observed experimentally, while a formation mechanism was revealed at the molecular level. That is, hydroxylated metabolite was exclusively formed via the hydrogen abstraction from the phenolic hydroxyl group of MPB followed by the OH-rebound pathway, rather than the direct hydroxylation on the benzene ring. The increasing of hydroxyl groups on ECs could improve the metabolisms. This was confirmed in the metabolism of ECs without hydroxyl group and with multiple-hydroxyl groups, respectively. Furthermore, toxicity assessments show that compared to parent MPB, the hydroxylated metabolites have increased negative impacts on the gastrointestinal system and liver. A semiquinone product exhibits potential damage in the cardiovascular system and epoxides are toxic to the blood and gastrointestinal system. The findings deepen our insight into the biotransformation of parabens in human health, especially by providing health warnings about the potential impacts caused by semiquinone and epoxides.

Estrogenic Effect Mechanism and Influencing Factors for Transformation Product Dimer Formed in Preservative Parabens Photolysis

The environmental transformation and health effects of endocrine disruptors (EDCs) need urgent attention, particularly the formation of transformation products with higher toxicity than parent EDCs. In this paper, an important transformation product dimer (short for ethyl 4-hydroxy-3-(2-((4-hydroxybenzoyl) oxy) ethyl) benzoate) with estrogenic activity was investigated and detected in the photolysis of preservative ethyl-paraben (EPB) dissolved in actual water. The environmental factors, such as the higher initial concentration of EPB, the stronger optical power and the lower pH could stimulate the formation of the dimer. Simultaneously, the interaction of multiple environmental factors was significant, especially the initial concentration and pH using the response surface methodology. Furthermore, the relationship between the environmental factors and the formation of the product dimer was further explained and the empirical model equation was built for predicting the amount of dimer in actual water. Quantum chemical and toxicological calculations showed the estrogenic effect mechanism of the product dimer and it was revealed further that the hydrogen bonds of the dimer and ERα proteins (ARG-394, Glu-353, His-524, GYY-521) were formed, with a lowest binding energy of -8.38 Kcal/mol during molecular docking. In addition, the health effect risk of the product dimer was higher than the parent compound in the blood, cardiovascular system, gastrointestinal system, kidney and liver. In short, the present study was of great significance for the transformation product in pollution control and health effects in the photolysis of EDCs.

Reactions of nicotine and the hydroxyl radical in the environment: Theoretical insights into the mechanism, kinetics and products

Nicotine (NCT) is a prevalent and highly poisonous tobacco alkaloid found in wastewater discharge. Advanced oxidative processes (AOP) are radical interactions between harmful pollutants and ambient free radicals that, theoretically, result in less toxic compounds. For a better understanding of the chemical transformations and long-term environmental effects of toxic discharges, the study of these processes is crucial. Here, quantum chemical calculations are used to investigate the AOP of the NCT in aqueous and lipidic environments. It was found that NCT interacted with HO^• in polar and nonpolar media, with an overall rate constant k_overall = 10⁶ - 10¹⁰ M^-1 s^-1. The computed kinetic data are reasonably accurate as seen by the comparison with the experimental rate constant in water (pH = 7.0), which results in a k_calculated/k_experimetal ratio of 1.4. The hydrogen transfer (C7, C9, C12)-single electron transfer pathways are the main mechanisms for the HO^• + NCT reaction in pentyl ethanoate solvent to form the cations as the primary products of the two-step reaction. However, in aqueous environments, the degradation of NCT by HO^• radicals increases with increasing pH levels. It is predicted that oxidation products are less toxic than nicotine itself, especially in an aqueous environment with a pH < 7.0.

Base-catalyzed hydrolysis of spectinomycin in aqueous solutions: Kinetics and mechanisms

Hydrolysis plays an imperative role in the abiotic transformation process of antibiotics in aqueous solutions. However, little information is available on the hydrolysis process of spectinomycin (an aminocyclitol antibiotic). This study systematically investigated the spectinomycin hydrolysis kinetics and mechanisms under different pH via experiments and density functional theory (DFT) computation. Hydrolysis was first conducted in a pure water system under pH of 4.0-9.0 and temperature of 25 °C, 50 °C and 70 °C, respectively. Results showed that hydrolysis was highly dependent on pH and temperature. When pH > 6.0, spectinomycin hydrolysis was accelerated by the catalysis of OH^-. Meanwhile, the hydrolysis rate increased with the elevation of temperature. Then, for the reference of the practical environment, the general base-catalyzed hydrolysis and mechanisms were studied under environmental pH 6.0-8.0 and 25 °C. DFT calculation demonstrated that base-catalyzed hydrolysis of spectinomycin could be more thermodynamically and kinetically favorable based on the lower Gibbs free energies of reaction and Gibbs free energies of activation. Further, instead of specific base catalysis (OH^-), the general base catalysis (e.g., phosphate buffer) was also found to promote hydrolysis efficiency. The antibacterial activity and ecotoxicities of the hydrolysis product were analyzed to be lower than the precursor, thereby decreasing the environmental impact of spectinomycin.

Toxic effects of waterborne benzylparaben on the growth, antioxidant capacity and lipid metabolism of Nile tilapia (Oreochromis niloticus)

Benzylparaben (BzP) is a potential endocrine disruptor; however, its antioxidant defense, lipotoxicity and underlying mechanism of BzP in aquatic organisms are unknown. This study investigated the impacts of waterborne low-, environmental-related and high-level benzylparaben on the growth, antioxidant capacity, lipid metabolism and lipidomic response of Nile tilapia (Oreochromis niloticus). Juvenile tilapia (0.60 ± 0.11 g) were exposed to 0, 5, 50, 500 and 5000 ng/L benzylparaben for 8 weeks in quadruplicate for each group. Benzylparaben increased the body crude fat content but decreased brain acetylcholinesterase activity in O. niloticus. Benzylparaben caused oxidative stress, leading to hepatic morphology damage and lipid metabolism disorders in fish. Lipidomic analysis identified 13 lipid classes in fish liver. Benzylparaben exposure induced metabolic disorders of glycerol phospholipids, glycerolipids and sphingomyelins in fish liver. These findings indicate that environmentally related benzylparaben levels (5 to 50 ng/L) could induce an antioxidant response, result in triglyceride accumulation, and increase adipocyte formation and fatty acid intake in tilapia. However, high benzylparaben concentrations inhibit lipid deposition, presumably due to the effects of the antioxidant system, and induce tissue inflammation. Therefore, this study provides new insights into the toxic effects and potential mechanism of benzylparaben in fish, especially from the aspect of lipid metabolism.

Atmospheric Autoxidation of Organophosphate Esters

Organophosphate esters (OPEs), widely used as flame retardants and plasticizers, have frequently been identified in the atmosphere. However, their atmospheric fate and toxicity associated with atmospheric transformations are unclear. Here, we performed quantum chemical calculations and computational toxicology to investigate the reaction mechanism of peroxy radicals of OPEs (OPEs-RO₂^•), key intermediates in determining the atmospheric chemistry of OPEs, and the toxicity of the reaction products. TMP-RO₂^• (R₁) and TCPP-RO₂^• (R₂) derived from trimethyl phosphate and tris(2-chloroisopropyl) phosphate, respectively, are selected as model systems. The results indicate that R₁ and R₂ can follow an H-shift-driven autoxidation mechanism under low NO concentration ([NO]) conditions, clarifying that RO₂^• from esters can follow an autoxidation mechanism. The unexpected autoxidation mechanism can be attributed to the distinct role of the ─(O)₃P(═O) phosphate-ester group in facilitating the H-shift of OPEs-RO₂^• from commonly encountered ─OC(═O)─ and ─ONO₂ ester groups in the atmosphere. Under high [NO] conditions, NO can mediate the autoxidation mechanism to form organonitrates and alkoxy radical-related products. The products from the autoxidation mechanism have low volatility and aquatic toxicity compared to their corresponding parent compounds. The proposed autoxidation mechanism advances our current understanding of the atmospheric RO₂^• chemistry and the environmental risk of OPEs.

Identifying potential paraben transformation products and evaluating changes in toxicity as a result of transformation

Parabens are a class of compounds often used as preservatives in personal care products, pharmaceuticals, and food. They have received attention recently due to findings that demonstrate estrogenic impacts and other adverse effects of parabens. Release into wastewater effluent is considered a major contributor to the spread of parabens into surface water. Current regulations in areas such as Japan, Europe, and Southeast Asia limit the concentrations of parabens that can be used in formulations but do not address concentrations discharged into waterbodies. Recent studies suggest that parent parabens are effectively eliminated by transformation during the wastewater treatment processes. Common tertiary treatments include ultrafiltration, chlorination, UV disinfection and ozonation. Ultrafiltration is used to remove solids before a disinfection step. Of the disinfection steps, ozonation is often the most effective at removing parabens. Not much is known about the toxicities of paraben transformation products. Of the transformation products, chlorinated parabens and PHBA are the most studied. Previous studies have shown that chlorinated parabens have greatly reduced estrogen agonistic activity when compared with the activity of parents. However, more recent studies have found that halogenated parabens actually have estrogen antagonistic activity. Further research involving chlorinated parabens could include other toxic endpoints. No known studies have evaluated adverse effects of oxygenated parabens. Parabens can interact with chlorine residues in the environment and form chlorinated products, this will occur at a faster rate during chlorination. Ozonation will oxidize parabens and UV disinfection can both oxidize and halogenate parabens. All studies determining potential transformation products have been done in laboratory settings or specific conditions. Further research is needed to determine if these transformations occur in situ. PRACTITIONER POINTS: Common chemical processes utilized by wastewater treatment facilities are effective at transforming parabens. Paraben transformation products are released in greater concentration in effluent than parent paraben compounds. Halogenated transformation products have been identified as estrogen receptor antagonists.

Remediation of preservative ethylparaben in water using natural sphalerite: Kinetics and mechanisms

As a typical class of emerging organic contaminants (EOCs), the environmental transformation and abatement of preservative parabens have raised certain environmental concerns. However, the remediation of parabens-contaminated water using natural matrixes (such as, naturally abundant minerals) is not reported extensively in literature. In this study, the transformation kinetics and the mechanism of ethylparaben using natural sphalerite (NS) were investigated. The results show that around 63% of ethylparaben could be absorbed onto NS within 38 hr, whereas the maximum adsorption capacity was 0.45 mg/g under room temperature. High temperature could improve the adsorption performance of ethylparaben using NS. In particular, for the temperature of 313 K, the adsorption turned spontaneous. The well-fitted adsorption kinetics indicated that both the surface adsorption and intra-particle diffusion contribute to the overall adsorption process. The monolayer adsorption on the surface of NS was primarily responsible for the elimination of ethylparaben. The adsorption mechanism showed that hydrophobic partitioning into organic matter could largely govern the adsorption process, rather than the ZnS that was the main component of NS. Furthermore, the ethylparaben adsorbed on the surface of NS was stable, as only less than 2% was desorbed and photochemically degraded under irradiation of simulated sunlight for 5 days. This study revealed that NS might serve as a potential natural remediation agent for some hydrophobic EOCs including parabens, and emphasized the significant role of naturally abundant minerals on the remediation of EOCs-contaminated water bodies.

A novel Fe-rectorite composite catalyst synergetic photoinduced peroxymonosulfate activation for efficient degradation of antibiotics

Developing a low-cost and efficient photocatalysts activated peroxymonosulfate (PMS) for organic pollutants degradation are recognized as an importance way for dealing with environmental pollution. In this work, Fe-rectorite catalyst was synthesized by a simple impregnation-calcine method to synergetic photo activate PMS for antibiotics degradation. As expected, the Fe-rectorite/PMS/Light system exhibits superior catalytic performance for tetracycline (TC) removal, which achieving 96.4% removal rate of TC (30 mg/L) under light within 60 min. Fe-retorite has better degradation performance for TC than rectorite under photo-mediation. The enhancement of the degradation performance of TC by Fe-retorite can be attributed to the improvement of the separation efficiency of photogenerated electrons and holes in the rectorite by the loading of Fe₂O₃, and the accelerated active Fe(Ⅱ)/Fe(Ⅲ) cycle on the surface under photo-mediation. The large specific surface area and abundant hydroxyl groups of rectorite can also provide active sites for PMS activation. The quenching experiment and electron paramagnetic resonance (EPR) test were indicated that the h⁺, SO₄•^-, •OH, and O₂^-• all contributed to TC degradation. And the possible degradation pathway was proposed by LC-MS. This work helps induced a novel direction that design green, efficient, and recyclable heterogeneous catalysts to synergetic photoinduced PMS activation for enhanced degradation of TC.

The transformation mechanism and eco-toxicity evaluation of butylated hydroxyanisole in environment

Butylated hydroxyanisole (BHA) is one of important phenolic antioxidants and its fate in the environment has attracted much attention in recent years. In this study, the initial reactions of BHA with OH radicals, including 8 abstraction reactions and 6 addition reactions, were calculated. The lowest energy barrier of 3.20 kcal mol^-1 was found from the abstraction reaction on phenolic hydroxyl group. The reaction barriers of addition paths are in the range of 5.48-9.28 kcal mol^-1, which are lower than those of the abstraction paths. The reaction rate constants were calculated by using transition state theory, and the rate constants are 8.12 × 10⁷ M^-1 s^-1and 4.76 × 10⁷ M^-1 s^-1 for the H-abstraction and OH-addition reactions, respectively. Through the calculation of the subsequent reactions of the abs-H₀-TS₁ and add-C₄-M₁ it was found that BHA would be further transformed into 2-tert-Butyl-1,4-benzoquinone (TBQ), tert-butylhydroquinone (TBHQ) etc. in the aqueous phase, and the eco-toxicities of these transformed products of BHA in the aqueous phase were significantly increased comparing with that of the BHA and they are toxic to aquatic organism.

A theoretical investigation on the degradation reactions of CH3CH2CH2NH and (CH3CH2CH2)2N radicals in the presence of NO, NO2 and O2

The degradation reactions of propylamino and dipropylamino radicals in the presence of NO, NO₂ and O₂ were investigated at the CCSD(T)/6-311++G (2d, 2p)//B3LYP/6-311++G (d,p) levels of theory. Result indicates that nitrosamines, nitramines, nitroso-oxy compounds and imines can be formed at atmosphere. Time dependent density functional theory (TDDFT) calculation shows that nitrosamines and nitroso-oxy compounds can photolyze under sunlight, while nitramines cannot undergo photolysis in the daytime. Moreover, the ecotoxicity assessment result implies that the degradation of propyl-substituted amines by OH radicals, NO and NO₂ will reduce their toxicity to fish, daphnia and green algae in the aquatic environment.

Theoretical insights into the gaseous and heterogeneous reactions of halogenated phenols with ˙OH radicals: mechanism, kinetics and role of (TiO2)n clusters in degradation processes

New insights into the mechanism of ˙OH-initiated degradation and the kinetics of halogenated phenols onto (TiO2)n clusters with controllable dimensions have been provided for the first time.

Enhanced solar light photocatalytic performance of Fe-ZnO in the presence of H2O2, S2O82-, and HSO5- for degradation of chlorpyrifos from agricultural wastes: Toxicities investigation

This study reported Fe doped zinc oxide (Fe-ZnO) synthesis to degrade chlorpyrifos (CPY), a highly toxic organophosphate pesticide and important sources of agricultural wastes. Fourier transform infrared, X-ray diffraction, scanning electron microscope, and energy-dispersive X-ray spectroscopic analyses showed successful formation of the Fe-ZnO with highly crystalline and amorphous nature. Water collected from agricultural wastes were treated with Fe-ZnO and the results showed 67% degradation of CPY by Fe-ZnO versus 39% by ZnO at 140 min treatment time. Detail mechanism involving reactive oxygen species production from solar light activated Fe-ZnO and their role in degradation of CPY was assessed. Use of H₂O₂, peroxydisulfate (S₂O₈^2-) and peroxymonosulfate (HSO₅^-) with Fe-ZnO under solar irradiation promoted removal of CPY. The peroxides yielded hydroxyl (OH) and sulfate radical () under solar irradiation mediated by Fe-ZnO. Effects of several parameters including concentration of pollutant and oxidants, pH, co-existing ions, and presence of natural organic matter on CPY degradation were studied. Among peroxides, HSO₅^- revealed to provide better performance. The prepared Fe-ZnO showed high reusability and greater mineralization of CPY. The GC-MS analysis showed degradation of CPY resulted into several transformation products (TPs). Toxicity analysis of CPY as well as its TPs was performed and the formation of non-toxic acetate imply greater capability of the treatment technology.

An in vitro assessment for human skin exposure to parabens using magnetic solid phase extraction coupled with HPLC

Skin contact was a significant source of human exposure to parabens during the use of personal care products. In this study, a novel and simple in vitro evaluation method for human skin exposure to parabens was established for the first time. Firstly, magnetic porous carbon (MPC) derived from discarded cigarette butts was prepared as an adsorbent of magnetic solid-phase extraction (MSPE), which provided a fast and efficient sample preparation method with satisfactory extraction performance for parabens in cosmetics and was easy to couple with high performance liquid chromatography. Secondly, the extraction conditions were optimized including the etching ratio of KOH, amount of MPC, extraction time, pH, salt concentration, desorption solvent volume and desorption time. Under the optimized conditions, the limits of detection were between 0.25 and 0.34 ng mL^-1 and the spiked recoveries were in the range of 85.8-112.6%. Thirdly, the developed method was successfully employed to determine five typical parabens in real unspiked cosmetic samples, and two parabens were detected at a relatively high level. Then, the developed method was applied to in vitro assays. The absorbable dose of parabens in cream was investigated and in vitro experiments were further designed with agarose-simulated skin to demonstrate the penetration ability of parabens. In conclusion, these results indicated that parabens did have the risk of entering the body through the skin and the exposure was preferably no more than 3 h with skin contact.

Experimental and theoretical studies into the hydroxyl radical mediated transformation of propylparaben to methylparaben in the presence of dissolved organic matter surrogate

Dissolved humic and biogenic substances might be present in the aphotic zone and contribute to the fate of parabens in natural aquatic ecosystem under the fluctuation of water multi-parameters. Through the combination of batch tests with quantum chemical calculation, hydroxyl radical (•OH) mediated degradation of propylparaben (PP) to methylparaben (MP) has been confirmed in the present study. The interaction of dissolved oxygen with environmental relevant concentration of humic acid (HA), algal and bacterial cell lysis leads to a slow production of •OH. Aqueous PP undergoes a mild removal process with the pseudo-first order rate constant (10^-7, s^-1) higher at 7.43 in HA than at 3.30-4.89 in biogenic cell lysis. PP removal is correlated with the aromaticity of DOM surrogate and the produced •OH concentration, which could be enhanced by the increase of light intensity and DO other than HA. The •OH mediated process on PP removal has been confirmed by the linearly inhibited effect of tert-butanol while totally inhibited effects of higher concentration of sodium azide and co-existent chemical (17β-estradiol). Based on the detection of byproduct MP, two possible reaction pathways, •OH attacking at β-carbon (path-β) and terminal γ-carbon (path-γ) of the propyl side chain of PP, are proposed. Through the analysis of thermal and kinetics parameters, the •OH initiated H-abstraction and the resulting C-C bond cleavage leading to the formation of MP and acetaldehyde in path-β is confirmed to be the dominant reaction mechanism. Considering the universal occurrence of parabens and these DOM surrogates, this mild removal process has special implications for the self-purification of organic pollutants in natural aquatic ecosystems, especially in DOM-rich matrices in the aphotic zone.

The reactivity of neurotransmitters and their metabolites towards various nitrogen-centered radicals: Experimental, theoretical, and biotoxicity evaluation

In the past few years, there has been a certain interest in nitrogen-centered radicals, biologically important radicals that play a vital role in various processes and constitute many important biological molecules. In this paper, there was an attempt to bridge a gap in the literature that concerns the antiradical potency of monoamine neurotransmitters (dopamine, epinephrine, and norepinephrine) and their metabolites towards these radicals. The most probable radical quenching mechanism was determined for each radical out of three common mechanisms, namely Hydrogen Atom Transfer (HAT), Single Electron Transfer followed by the Proton Transfer (SET-PT), and Sequential Proton Loss Electron Transfer (SPLET). Marcus' theory was then used to determine the reaction rates for the electron transfer process. SPLET was the most probable mechanism for both reactions with the aminyl and hydrazyl radicals, while HAT and SPLET were plausible mechanisms for reactions with the imidazolyl radical. Special emphasis was put on the investigation of the substituent effect on the preferred mechanism. The necessity of both thermodynamic and kinetic parameters for the comparison of the antiradical potency of compounds was discussed. The same methodology was applied for the theoretical investigation of the reactivity towards DPPH^⦁, a member of the hydrazyl radicals. An ecotoxicity analysis was performed to assess the impact the investigated radicals have on the ecosystem. Except for histidine, every other neutral form was either toxic or highly toxic to some of the analyzed marine organisms.

Anthropogenic disturbances on distribution and sources of pharmaceuticals and personal care products throughout the Jinsha River Basin, China

Pharmaceuticals and personal care products (PPCPs) are recognized as a group of emerging contaminants closely related to anthropogenic activities, which capture increasing attention worldwide. To evaluate the anthropogenic disturbances on PPCP distribution and sources, this study investigated the distribution and sources of 50 PPCPs along the 2300 km long Jinsha River and revealed different anthropogenic disturbances on PPCPs. Results showed that 40 out of the 50 PPCPs were ubiquitously detected among these river water samples, with the concentrations varied from less than 1 ng/L to more than 500 ng/L. Although most PPCPs concentrations were much lower in the Jinsha River than in highly developed rivers, the prevalence of PPCPs suggested the widespread use and improper disposal of PPCPs in the Jinsha River. The risk assessment also revealed that some PPCPs posed risks to aquatic organisms in the Jinsha River. Anthropogenic activities including human habitation and dam construction had different influence on PPCPs. PPCP distribution varied significantly across the "Hu Huanyong line", indicating human habitation significantly influenced PPCP distribution. Dam construction was insignificant in altering PPCP distribution throughout the Jinsha River. Moreover, the land use index indicated degradation level of multiple lands related to anthropogenic activities and represented the major sources of PPCPs in the Jinsha River. Most PPCPs were correlated with anthropogenic lands, for example, antibiotics, analgesics, and endocrine disrupting chemicals mainly originated from artificial surfaces, whereas other PPCPs mainly originated from cultivated lands. Together, this study indicates the disturbances of multiple anthropogenic activities on PPCP distribution and sources along the Jinsha River, which contributes to PPCP management in rural areas.

Atmospheric oxidation of fluoroalcohols initiated by ˙OH radicals in the presence of water and mineral dusts: mechanism, kinetics, and risk assessment

The transport and formation of fluorinated compounds are greatly significant due to their possible environmental risks. In this work, the ˙OH-mediated degradation of CF3CF2CF2CH2OH and CF3CHFCF2CH2OH in the presence of O2/NO/NO2 was studied by using density functional theory and the direct kinetic method. The formation mechanisms of perfluorocarboxylic/hydroperfluorocarboxylic acids (PFCAs/H-PFCAs), which were produced from the reactions of α-hydroxyperoxy radicals with NO/NO2 and the ensuing oxidation of α-hydroxyalkoxy radicals, were clarified and discussed. The roles of water and silica particles in the rate constants and ˙OH reaction mechanism with fluoroalcohols were investigated theoretically. The results showed that water and silica particles do not alter the reaction mechanism but obviously change the kinetic properties. Water could retard fluoroalcohol degradation by decreasing the rate constants by 3-5 orders of magnitude. However, the heterogeneous ˙OH-rate coefficients on the silica particle surfaces, including H4SiO4, H6Si2O7, and H12Si6O18, are larger than that of the naked reaction by 1.20-24.50 times. This finding suggested that these heterogeneous reactions may be responsible for the atmospheric loss of fluoroalcohols and the burden of PFCAs. In addition, fluoroalcohols could be exothermically trapped by H12Si6O18, H6Si2O7, and H4SiO4, in which the chemisorption on H12Si6O18 is stronger than that on H6Si2O7 or H4SiO4. The global warming potentials and radiative forcing of CF3CF2CF2CH2OH/CF3CHFCF2CH2OH were calculated to assess their contributions to the greenhouse effect. The toxicities of individual species were also estimated via the ECOSAR program and experimental measurements. This work enhances the understanding of the environmental formation of PFCAs and the transformation of fluoroalcohols.

Mechanistic insights into paracetamol transformation in UV/NH2Cl process: Experimental and theoretical study

The UV/monochloramine (NH₂Cl) process is an advanced oxidation process that can effectively remove emerging contaminants (ECs). However, the degradation mechanisms of reactive radicals with ECs are not clear. In this work, we combined theoretical calculations with experimental studies to investigate the kinetics and mechanism of radical-mediated degradation of paracetamol (AAP) in UV/NH₂Cl process. The degradation of AAP in UV/NH₂Cl process accords with the pseudo first-order kinetics. Impact factors including NH₂Cl dose, pH, natural organic matter, HCO₃^-, and NO₃^- were evaluated. The reaction mechanisms of AAP with hydroxyl radical (HO^·), reactive chlorine species (RCS), and reactive nitrogen species (RNS) were discussed in detail. Specifically, HO^· attacked AAP mainly through hydrogen atom transfer (HAT) and radical adduct formation (RAF), while Cl₂^·- play a certain role through single electron transfer (SET). ^·NH₂ and Cl^· destructed AAP mainly through HAT. Based on the mechanism analysis, the second-order rate constants of AAP reacts with HO^·, Cl^·, ^·NH₂, ClO^·, Cl₂^·- and ^·NO₂ were calculated through transition state theory as 2.66×10⁹ M^-1 s^-1, 2.61×10⁹ M^-1 s^-1, 1.02×10⁷ M^-1 s^-1, 7.74×10⁶ M^-1 s^-1, 1.32×10⁶ M^-1 s^-1, 1.48×10³ M^-1 s^-1 respectively. The second-order rate constants were then used to distinguish the contribution of radicals to the degradation of AAP. Thirteen transformation products were identified by high-resolution mass spectrometry. Combined active sites with potential energy surface, the detailed reaction pathways were proposed. Overall, this study provides deep insights into the mechanism of radical-mediated degradation of AAP.

Treating disinfection byproducts with UV or solar irradiation and in UV advanced oxidation processes: A review

This review focuses on the degradation kinetics and mechanisms of disinfection byproducts (DBPs) under UV and solar irradiation and in UV-based advanced oxidation processes (AOPs). A total of 59 such compounds are discussed. The processes evaluated are low pressure, medium pressure and vacuum UV irradiation, solar irradiation together with UV/hydrogen peroxide, UV/persulfate and UV/chlorine AOPs. Under UV and solar irradiation, the photodegradation rates of N-nitrosamines are much higher than those of halogenated DBPs. Among halogenated DBPs, those containing iodine are photodegraded more rapidly than those containing bromine or chlorine. This is due to differences in their bond energies (E_N-N < E_C-I < E_C-Br < E_C-Cl). Molar absorption coefficients at 254 nm and energy gaps can be used to predict the photodegradation rates of DBPs under low pressure UV irradiation. But many DBPs of interest cannot be degraded to half their original concentration with less than a 500 mJ cm^-2 dose of low pressure UV light. HO^• generally contributes to less than 30% of the degradation of DBPs except iodo-DBPs in UV/H₂O₂ AOPs. Reaction mechanisms under UV irradiation and in HO^•-mediated oxidation are also summarized. N-N bond cleavage initiates their direct UV photolysis of N-nitrosamines as C-X cleavage does among halogenated compounds. HO^• generally initiates degradation via single electron transfer, addition and hydrogen abstraction pathways. Information on the reaction rate constants of SO₄^•- and halogen radicals with DBPs is rather limited, and little information is available about their reaction pathways. Overall, this review provides improved understanding of UV, solar and AOPs.

Green toxicological investigation for biofuel candidates

To avoid potential risks of biofuels on the environment and human, ecotoxicity investigation should be integrated into the early design stage for promising biofuel candidates. In the present study, a green toxicology testing strategy combining experimental bioassays with in silico tools was established to investigate the potential ecotoxicity of biofuel candidates. Experimental results obtained from the acute immobilisation test, the fish embryo acute toxicity test and the in vitro micronucleus assay (Chinese hamster lung fibroblast cell line V79) were compared with model prediction results by ECOSAR and OECD QSAR Toolbox. Both our experimental and model prediction results showed that 1-Octanol (1-Oct) and Di-n-butyl ether (DNBE) were the most toxic to Daphnia magna and zebrafish among all the biofuel candidates we investigated, while Methyl ethyl ketone (MEK), Dimethoxymethane (DMM) and Diethoxymethane (DEM) were the least toxic. Moreover, both in vitro micronucleus assay and OECD QSAR Toolbox evaluation suggested that the metabolites present higher genotoxicity than biofuel candidates themselves. Overall, our results proved that this green toxicology testing strategy is a useful tool for assessing ecotoxicity of biofuel candidates.

Photochemical degradation of fragrance ingredient benzyl formate in water: Mechanism and toxicity assessment

Recently, fragrance ingredients have attracted increasing attention due to their imperceptible risks accompanying the comfortable feeling. To understand transformation mechanisms and toxicity evolution of benzyl formate (BF) in environment, its photochemical degradation in water was thoroughly studied herein. Results showed that 83.5% BF was degraded under ultraviolet (UV) irradiation for 30 min. Laser flash photolysis and quenching experiments demonstrated that triplet excited state (³BF*), O₂^•-, and ¹O₂ were three main reactive species found during BF photodegradation. Eight degradation intermediates, including benzaldehyde, benzyl alcohol, o-cresol, bibenzyl, benzyl ether, 1,2-diphenylethanol, benzoic acid, and benzylhemiformal, were mainly formed as identified by LC-Q-TOF/MS and GC-MS analyses. Furthermore, the degradation mechanism was explained as the bond cleavage of ³BF* and BF^•+, O₂^•-/¹O₂ oxidation, e_aq^- reduction, and ^•OH addition reactions. Aquatic assessment suggests that except benzyl alcohol, benzoic acid, and benzylhemiformal, all the products were persistent and could result in increased aquatic toxicity compared to original BF. Consequently, these degradation products may cause more toxicity to organisms if they remain accumulated in water environment for a long time.

Comparative studies on the separation of endocrine disrupting compounds from aquatic environment by emulsion liquid membrane and hollow fiber supported liquid membrane

Endocrine disrupting compounds have been found to limit the natural working of the endocrine system like synthesis, secretion, transference and binding. Endocrine disrupting compounds are released from humans, animals and from production industries to soil, surface water and sediments mostly through the sewage treatment system. Studies have revealed the impact of these compounds on the nervous system, lungs, liver, thyroid, prostate, metabolism, obesity and reproductive system. So removal of these compounds from sewage water/wastewater by appropriate processes is essential. Conventional techniques like coagulation, precipitation, flocculation, microfiltration and ultrafiltration are effective for the removal of these compounds but limitations like low molecular weight of these compounds and pore size of membrane restricts the complete removal. Liquid membrane is a promising technology which combines the steps like extraction and stripping in a single step thereby providing the instantaneous removal and recovery of solutes and also results in high selectivity and savings of chemicals. This paper mainly focuses on the use of liquid membrane techniques like emulsion liquid membrane and hollow fiber supported liquid membrane which are the promising techniques for the removal of endocrine disrupting compounds from aqueous streams. The working principle, mechanism and implementation of these two techniques in the removal of several endocrine disrupting compounds from aquatic streams are also discussed.

New insight into photodegradation mechanisms, kinetics and health effects of p-nitrophenol by ozonation in polluted water

P-nitrophenol (p-NP) is a recalcitrant organic compound attracted great environmental attention, but its degradation mechanism is indeterminacy, which challenges its treatment, migration, transformation and ecological impact in the environment. In the present study, the aqueous-phase decomposition process of p-NP initiated by O₃ has been investigated by a theoretical calculation method. The detailed possible reaction pathways for the oxidative degradation of p-NP by ozone have been proposed. The chemical reaction thermodynamics results show that the reaction barriers of all ozone-initiated pathways are below 15 kcal·mol^-1, indicating that ozone can completely initiate the oxidation of p-NP under natural conditions. However, the kinetic results show that the initiation reaction of p-NP by ozone alone is relatively slow compared to the reaction by OH. Interestingly, under ultraviolet (UV) radiation, the dissolved ozone interacts with water and produces two active radicals: OH and HO₂. The reaction rate of p-NP initiated with OH is much higher than that with ozone, implying that the OH produced in the photochemical process can improve the removal efficiency of p-NP. The intermediates generated in the ozone-initiated reaction have been found to decompose into small molecule organic acids, aldehydes and ketones. The potential carcinogenicities and teratogenicities of the transformation products have also been studied, and some of them still have carcinogenic activity, which deserve further attention. In addition, to our knowledge, this may be the first computational chemistry study on the degradation of p-NP initiated by HO₂. All the results provide a new fundamental understanding for the migration and transformation of p-NP in water environment, and indicate that further assessment is needed for the impact of p-NP and especially its transformation products on the ecological environment in a significant way.

Uptake and metabolism of nonylphenol in plants: Isomer selectivity involved with direct conjugation

Nonylphenol (NP), an environmental estrogen, is actually a complicated mixture of isomers, although it is commonly considered to be a single compound. There are many routes for crops to come into contact with NP; however, little is known about the plant uptake and metabolism of NP, especially at the isomer level. This study comparatively evaluated the uptake and in-planta metabolism of 4-n-NP and its 10 isomers using both carrot cells and intact plants. The rapid metabolism of 4-n-NP was observed in the callus tissues and intact plants with half-lives of 2 h and 4.72 d, respectively. Six conjugates of 4-n-NP were identified in the cell extracts using high resolution mass spectrometry. The primary transformation pathway was found to be the direct conjugation (Phase II metabolism) with the parent compound at the hydroxyl. Furthermore, 4-NP isomers with short side chains and/or bulky α-substituents were more resistant to plant metabolism and showed a greater tendency for accumulation. The influence of the side chains to the isomer selectivity was verified by the molecular docking between glycosyltransferase and 4-NP isomers. This study highlighted the necessity to consider isomer-specificity in the plant accumulation of NP and the environmental and human health implications of NP conjugates.