Different senescent HDPE pipe-risk: brief field investigation from source water to tap water in China (Changsha City)

Long-term exposure to 2,4-di-tert-butylphenol impairs zebrafish fecundity and affects offspring development

As a widely used antioxidant, 2,4-di-tert-butylphenol (2,4-DTBP) has been frequently detected in the environment and biota. Although a few studies reported its hormone-like activity in vitro, the endocrine disrupting potential of 2,4-DTBP and its effect on reproduction are not yet elucidated. In this study, adult zebrafish were exposed to 5 and 50 nM 2,4-DTBP for 60 days. Reduction in cumulative egg production was observed after 45 days of exposure. Gonadal maturation was also delayed in both female and male zebrafish following 2,4-DTBP exposure. The impaired fecundity was attributed to an imbalance of 17β-estradiol/testosterone ratio (E2/T) and altered transcripts involved in the hypothalamic-pituitary-gonadal (HPG) axis. Upon exposure, aromatase (CYP19) and E2 levels were significantly decreased in females, but were increased in males. Additionally, molecular docking revealed potential binding of 2,4-DTBP to estrogen receptors and CYP19, highlighting molecular initiating events that may interfere with steroid hormone synthesis. We also showed that 2,4-DTBP can be transferred to offspring, affecting their development and compromising immunity. The expression of triiodothyronine (T3) and hatching-related genes (esr2α, esr2β, and zhe2) were altered, suggesting that parental exposure to 2,4-DTBP resulted in intergenerational toxicity in F1 larvae. Taken together, these findings provide novel insight into the reproductive toxicity of 2,4-DTBP, contributing to its ecological risk assessment.

Occurrence, sources, and human exposure assessment of amine-based rubber additives in dust from various micro-environments in South China

Despite the ubiquitous use and potential health effects of amine-based rubber additives, information regarding their occurrences in indoor environments remains scarce and is basically investigated in traffic-related environments. In this study, a total of 140 dust samples collected from eight indoor micro-environments were analyzed for twelve amine-based rubber additives. Overall, 1,3-diphenylguanidine (DPG), dicyclohexylamine (DCHA), N-(1,3-dimethylbutyl)-N'-phenyl-p-penylenediamine (6PPD), 6PPD-quinone (6PPDQ), and hexa(methoxymethyl)melamine (HMMM) were frequently detected across all micro-environments with detection frequencies of 97 %, 51 %, 71 %, 99 %, and 77 %, respectively. The highest total concentration of amine-based rubber additives was found in parking lots (median 10,300 ng/g), indicating heavier emission sources of these compounds in vehicle-related indoor environments. Despite this, amine-based rubber additives were also frequently detected in various non-vehicle-related environments, such as markets, cinemas, and hotels, probably due to the widespread use of consumer products and more frequent air exchanges with outdoor environments. Further tracking of tire rubber products and paint particles from flooring materials in parking lots revealed that paint particles might be an overlooked contributor to amine-based rubber additives in indoor environments. Finally, the highest estimated daily intakes (EDIs) of all amine-based rubber additives via dust ingestion at home were observed for toddlers (3.48 ng/kg bw/d). This research provides a comprehensive overview of human exposure to a variety of amine-based rubber additives in various indoor environments. ENVIRONMENTAL IMPLICATION: This study highlights the presence of high concentrations of amine-based additives in indoor dust from both traffic-related and non-traffic-related indoor environments. Additional efforts are needed to identify potential sources of amine-based rubber additives indoors, beyond just tire rubber. This is critical because the widespread presence of rubber products in indoor settings could pose a risk to human health.

Trans-Placental Transfer Mechanisms of Aromatic Amine Antioxidants (AAs) and p-Phenylenediamine Quinones (PPD-Qs): Evidence from Human Gestation Exposure and the Rat Uterine Perfusion Model

Aromatic amine antioxidants (AAs), as rubber additives, and their ozone photochemical oxidation products of p-phenylenediamine quinone (PPD-Qs) have attracted great attention recently due to their wide environmental occurrences and toxicity. However, there is currently no research on the exposure risks during pregnancy and their trans-placental transfer mechanisms. Herein, 20 AAs and six PPD-Qs were analyzed in 60 maternal urine and fifty-six amniotic fluid samples (n = 53 pairs). ΣAAs (median: 8.57 and 15.4 ng/mL) and ΣPPD-Qs (0.236 and 2.29 ng/mL) were both observed, where the median concentration of PPD-Qs was significantly (p < 0.05) higher than that of the parent PPDs (0.130 and 0.092 ng/mL) in the maternal urine and amniotic fluid samples, respectively. The result of the self-established rat uterine perfusion model and molecular docking analysis suggested that passive diffusion and active transport patterns were involved in the trans-placental transfer. This study will raise concerns regarding intrauterine exposure and the trans-placental transfer mechanisms to AAs/PPD-Qs during pregnancy.

Comprehensive analysis of water and sediment from holy water body 'Pokhri' reveals presence of biomolecules that may educe skin, gastroenterological and neurological dysfunction

'Pokhri mai' refers to the natural pond amidst the hilly forest slopes of the Buxa tiger reserve (BTR) nearby Jayanti considered to be sacred by the local ethnic groups serving as the prime source of water for wild animals and occasionally by neighbouring inhabitants. However, the water body is designated to be noxious by a group of native people with no scientific validation. This paper focuses to explore its toxicity status and allied environmental concerns through Pokhri water and sediment sample analysis through physicochemical assessment, in vitro antioxidant assay, microbiological investigation followed by AAS, GC-MS and in silico study. pH of soil and water samples were found to be quite high (>6.8) with organic matter, carbon and available nitrogen content being 1.5308 ± 0.28 %, 0.89 ± 0.17 % and 0.072 ± 0.34 % respectively. Profuse microbial growths were observed in both sediment and water samples with consortia obtained exhibiting tolerance against a range of antifungals and antibiotics. Inhibition zone was absent for sediment consortium whereas consortium of water samples portrayed susceptibility against various heavy metals viz. Cu2+, Pb2+, Zn2+, Fe3+ and Al3+ salts with corresponding AAS quantified values of sediment samples being 133, 223.3, 86.8, 1449 and 481.5 ppm. A summative of 18 metabolites were identified by GC-MS in Pokhri lake sediment among which 13 (occupying 96.35 % peak area) were investigated to be potentially toxic with 2,4-Di-tert-butylphenol (53.38 %) as the major compound. Biomolecular characterization, ADMET test and molecular docking study with dermal, gastrointestinal and neural peptides exhibiting high binding affinity scores (ranging between -2.6 to -8.3 kcal/mol) further affirmed the toxicity attributes of the GC-MS deciphered molecules. The findings clearly justifies the local 'myth' of Pokhri water to be deleterious with prospective dermatotoxic, neurotoxic and being evident of gastrointestinal toxicity emphasizing ecological risk to the environment, wildlife and microflora of the adjoining forests.

Autophagy and PPARs/NF-κB-associated inflammation are involved in hepatotoxicity induced by the synthetic phenolic antioxidant 2,4-di-tert-butylphenol in common carp (Cyprinus carpio)

The synthetic phenolic antioxidant 2,4-di-tert-butylphenol (2,4-DTBP) is an emergent contaminant and can disrupt the delicate balance of aquatic ecosystems. This study aimed to investigate 2,4-DTBP-induced hepatotoxicity in common carp and the underlying mechanisms involved. Sixty common carp were divided into four groups and exposed to 0 mg/L, 0.01 mg/L, 0.1 mg/L or 1 mg/L 2,4-DTBP for 30 days. Here, we first demonstrated that 2,4-DTBP exposure caused liver damage, manifested as hepatocyte nuclear pyknosis, inflammatory cell infiltration and apoptosis. Moreover, 2,4-DTBP exposure induced hepatic reactive oxygen species (ROS) overload and disrupted antioxidant capacity, as indicated by the reduced activity of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px). In addition, transmission electron microscopy revealed that 2,4-DTBP exposure induced autophagosome accumulation in the liver of common carp. Western blot analysis further revealed that 2,4-DTBP exposure significantly decreased the protein levels of mTOR and increased the LC3II/LC3I ratio. Furthermore, 2,4-DTBP exposure inhibited lysozyme (LZM) and alkaline phosphatase (AKP) activity; decreased immunoglobulin M (IgM), complement 3 (C3), and complement 4 (C4) levels in the serum; increased the mRNA levels of proinflammatory cytokines (NF-κB, TNF-α, IL-1β and IL-6); and increased the mRNA levels of three types of proliferator-activated receptors (PPARs) (α, β/δ and γ). Molecular docking revealed that 2,4-DTBP directly binds to the internal active pocket of PPARs. Overall, we concluded that 2,4-DTBP exposure in aquatic systems could induce hepatotoxicity in common carp by regulating autophagy and controlling inflammatory responses. The present study provides new insights into the hepatotoxicity mechanism induced by 2,4-DTBP in aquatic organisms and furthers our understanding of the effects of 2,4-DTBP on public health and ecotoxicology.

Widespread Antioxidants during Storm Events Could Serve as Precursors of Regulated, Priority, and New Disinfection Byproducts

Widely used antioxidants can enter the environment via urban stormwater systems and form disinfection byproducts (DBPs) during chlorination in downstream drinking water processes. Herein, we comprehensively investigated the occurrence of 39 antioxidants from stormwater runoff to surface water. After a storm event, the concentrations of the antioxidants in surface water increased by 1.4-fold from 102-110 ng/L to 128-139 ng/L. Widespread antioxidants during the stormwater event could transform into toxic DBPs during disinfection. Moreover, the yields of trihalomethanes, haloacetaldehydes, haloacetonitriles (HANs), and halonitromethanes during the chlorination of widely used antioxidants considerably increased with an increasing chlorine dose and contact time. Specifically, the yields of dichloroacetonitrile during the chlorination of diphenylamine (DPA) and N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) were higher than those of most reported amino acid precursors, indicating that DPA and 6PPD might be important precursors of HANs. Exploring the intermediates using GC × GC-time-of-flight high-resolution mass spectrometry helped reveal potential pathways from DPA to HANs, whose formation could be attributed to the intermediate carbazole and indole moieties detected in this study. This study provides insights into the transport and transformation of commonly used antioxidants in a water environment and during water treatment processes, highlighting the potential risks of anthropogenic pollutants from a DBP perspective.

Effects of the plastic additive 2,4-di-tert-butylphenol on intestinal microbiota of zebrafish

Plastic additives such as the antioxidant 2,4-di-tert-butylphenol (2,4-DTBP) have been widely detected in aquatic environments, over a wide range of concentrations reaching 300 μg/L in surface water, potentially threatening the health of aquatic organisms and ecosystems. However, knowledge of the specific effects of 2,4-DTBP on aquatic vertebrates is still limited. In this study, adult zebrafish were exposed to different concentrations of 2,4-DTBP (0, 0.01, 0.1 and 1.0 mg/L) for 21 days in the laboratory. The amplicon sequencing results indicated that the diversity and composition of the zebrafish gut microbiota were significantly changed by 2,4-DTBP, with a shift in the dominant flora to more pathogenic genera. Exposure to 2,4-DTBP at 0.1 and 1.0 mg/L significantly increased the body weight and length of zebrafish, suggesting a biological stress response. Structural assembly defects were also observed in the intestinal tissues of zebrafish exposed to 2,4-DTBP, including autolysis of intestinal villi, adhesions and epithelial detachment of intestinal villi, as well as inflammation. The transcriptional expression of some genes showed that 2,4-DTBP adversely affected protein digestion and absorption, glucose metabolism and lipid metabolism. These results are consistent with the PICRUSt2 functional prediction analysis of intestinal microbiota of zebrafish exposed to 2,4-DTBP. This study improves our understanding of the effects of 2,4-DTBP on the health of aquatic vertebrates and ecosystems.

Innovative non-targeted screening approach using High-resolution mass spectrometry for the screening of organic chemicals and identification of specific tracers of soil and dust exposure in children

Environmental contamination through direct contact, ingestion and inhalation are common routes of children's exposure to chemicals, in which through indoor and outdoor activities associated with common hand-to-mouth, touching objects, and behavioral tendencies, children can be susceptible and vulnerable to organic contaminants in the environment. The objectives of this study were the screening and identification of a wide range of organic contaminants in indoor dust, soil, food, drinking water, and urine matrices (N = 439), prioritizing chemicals to assess children's environmental exposure, and selection of unique tracers of soil and dust ingestion in young children by non-targeted analysis (NTA) using Q-Exactive Orbitrap followed data processing by the Compound Discoverer (v3.3, SP2). Chemical features were first prioritized based on their predominant abundance (peak area>500,000), detection frequency (in >50% of the samples), available information on their uses and potential toxicological effects. Specific tracers of soil and dust exposure in children were selected in this study including Tripropyl citrate and 4-Dodecylbenzenesulfonic acid. The criteria for selection of the tracers were based on their higher abundance, detection frequency, unique functional uses, measurable amounts in urine (suitable biomarker), and with information on gastrointestinal absorption, metabolism, and excretion, and were further confirmed by authentic standards. We are proposing for the first time suitable unique tracers for dust ingestion by children.

Exposure to environmental levels of 2,4-di-tert-butylphenol affects digestive glands and induces inflammation in Asian Clam (Corbicula fluminea)

2,4-Di-tert-butylphenol (2,4-DTBP) is used as an antioxidant added to plastics. Due to its potential toxicity and relatively high concentrations in environments and presence in human tissue, concern has been raised for 2,4-DTBP as a contaminant associated with adverse health outcomes. However, studies on the toxicity of 2,4-DTBP are relatively limited, especially for benthic aquatic organisms. In this study, Asian clams (Corbicula fluminea) were exposed to environmentally relevant concentrations of 2,4-DTBP (0.01-1 μM, corresponding to 2.06-206.32 μg/L) for 21 days. Accumulation of 2,4-DTBP was noted in both gills and digestive glands, with the latter presenting as the primary target tissue. Increased damage rate of digestive tube and cellular DNA damage were observed in the digestive glands of 2,4-DTBP exposed clams. The injury was attributed to the imbalance of the antioxidant system, characterized by elevated oxidative stress and inflammation (upregulation of ROS, MDA, NO, and pro-inflammatory factors). In contrast, upon 2,4-DTBP exposure, antioxidant system in gills was activated, while ROS and NO were not promoted. Moreover, NF-κB and IL-1 were significantly decreased. These results suggested that biochemical mechanisms were activated in gills to maintain homeostasis. Internal exposure in the digestive gland was significantly correlated with the biochemical biomarkers tested, underscoring the potential risk associated with the bioaccumulation of 2,4-DTBP from contaminated environments. These findings provide novel insights into toxicity of 2,4-DTBP in bivalves, contributing valuable knowledge to risk assessment and chemical management.

Adverse effects of plastic leachate and its component 2,4-DTBP on the early development of zebrafish embryos

Plastic waste has become a global environmental problem threatening the health of aquatic organisms especially via leachate. In this study, the test of zebrafish embryo showed adverse effects of leachate from some agricultural mulching films after UV light aging for 60 h. A typical phenolic antioxidant 2,4-di-tert-butylphenol (2,4-DTBP) was detected in the leachate and tested further for the zebrafish embryo biotoxicity. The microplastic leachate (6, 8 g/L, mass concentration measured by weight of plastic) increased the death and malformation rates, and reduced the hatching rate, heart rate, and body length of zebrafish larvae in the 96-hour early development period. Similar adverse effects were also caused by the 2,4-DTBP (0.01, 0.1, 1.0 mg/L, corresponding to 0.049, 0.49, and 4.85 μM) to some degree but could not completely explain the significant influences caused by the plastic leachate. Transcriptome analysis of zebrafish embryos exposed to the 2,4-DTBP for 96 h showed that the protein, fat, and carbohydrate digestion and absorption pathways, pancreatic secretion, PPAR signaling pathway, tryptophan metabolism, and adipocytokine signaling pathway were considerably down-regulated, but the cholesterol metabolism pathway was up-regulated in larval zebrafish. The altered transcriptional expression of mRNA at early development stage (96 h post fertilization) of zebrafish suggested that the 2,4-DTBP caused reduction of digestive capacity and pancreatic secretory function, and adversely affected processes associated with energy metabolism and glycolipid metabolism of larval zebrafish. This study helps us further understanding the effects of plastic leachate on the early development of fishes.

1,3-Diphenylguanidine, benzothiazole, benzotriazole, and their derivatives in soils collected from northeastern United States

1,3-Diphenylguanidine (DPG), benzothiazole (BTH), benzotriazole (BTR), and their derivatives are high-production-volume chemicals widely used in tires, corrosion inhibitors and plastic products. Vehicular traffic is an important source of these chemicals in the environment. Despite this, little is known about the occurrence of these chemicals in roadside soils. In this study, we determined the concentrations, profiles, and distribution patterns of 3 DPGs, 5 BTHs, and 7 BTRs in 110 soil samples collected from northeastern United States. We found widespread occurrence of 12 out of the 15 analytes measured in roadside soils, at detection frequencies ≥71 % and median concentrations in the range of 0.38-380 ng/g (dry weight). DPGs were the predominant chemicals accounting for 63 % of the sum concentrations of three chemical classes determined, followed by BTHs (28 %) and BTRs (9 %). The concentrations of all analytes (except for 1-, 4-, and 5-OH-BTRs) exhibited significant positive correlations (r: 0.1-0.9, p < 0.01), suggestive of their common sources and/or similar environmental fates. Higher concentrations of DPGs, BTHs and BTRs were found in soils from highways, rubberized playgrounds, and indoor parking lots than those from gardens, parks, and residential areas. Our findings suggest the release of DPGs, BTHs and BTRs from rubber products, especially automobile tires. Further studies are needed to investigate the environmental fate and toxicities of these chemicals to humans and wildlife.

Occurrence of 1,3-Diphenylguanidine, 1,3-Di-o-tolylguanidine, and 1,2,3-Triphenylguanidine in Indoor Dust from 11 Countries: Implications for Human Exposure

1,3-Diphenylguanidine (DPG), 1,3-di-o-tolylguanidine (DTG), and 1,2,3-triphenylguanidine (TPG) are synthetic chemicals widely used in rubber and other polymers. Nevertheless, limited information is available on their occurrence in indoor dust. We measured these chemicals in 332 dust samples collected from 11 countries. DPG, DTG, and TPG were found in 100%, 62%, and 76% of the house dust samples, at median concentrations of 140, 2.3, and 0.9 ng/g, respectively. The sum concentrations of DPG and its analogues varied among the countries in the following decreasing order: Japan (median: 1300 ng/g) > Greece (940) > South Korea (560) > Saudi Arabia (440) > the United States (250) > Kuwait (160) > Romania (140) > Vietnam (120) > Colombia (100) > Pakistan (33) > India (26). DPG accounted for ≥87% of the sum concentrations of the three compounds in all countries. DPG, DTG, and TPG exhibited significant correlations (r: 0.35-0.73; p < 0.001). Elevated concentrations of DPG were found in dust from certain microenvironments (e.g., offices and cars). Human exposure to DPG through dust ingestion were in the ranges 0.07-4.40, 0.09-5.20, 0.03-1.70, 0.02-1.04, and 0.01-0.87 ng/kg body weight (BW)/day for infants, toddlers, children, teenagers, and adults, respectively.

Insights into the efficient ozonation process focusing on 2,4-di-tert-butylphenol - A notable micropollutant of typical bamboo papermaking wastewater: Performance and mechanism

The present study applied the ozonation process to degrade 2,4-di-tert-butylphenol (2,4-DTBP), an emerging micropollutant detected in typical bamboo pulp and papermaking wastewater (BPPW). The effects of various influencing factors on the degradation performance and corresponding degradation mechanism were investigated. The results showed that ozone could degrade 2,4-DTBP rapidly with a reaction rate constant of (1.80 ± 0.05) × 10⁵ M^-1·s^-1. The removal efficiency of 2,4-DTBP (5 mg/L) could reach 100% when the ozone dosage exceed 6 mg/L in a neutral medium. The presence of coexisting chemicals in BPPW such as Cl^- and HCO₃^- promoted the removal performance of 2,4-DTBP. In contrast, NH₄⁺ and humic acid presented inhibition on 2,4-DTBP removal. The ozonation of 2,4-DTBP was dominated by the ozone molecule, and this was primarily attributed to electrophilic substitution and 1,3-dipolar cycloaddition reactions. Twenty-seven kinds of intermediate products were identified by UPLC-Q-TOF/MS. The variations in their productions were based on the changes in ozone dosage. The degradation pathways were proposed. The toxicity of 2,4-DTBP was weakened after ozonation. As for the ozonation of actual biochemical effluent of BPPW, the desirable treatment performance was obtained. This study proved the feasibility of ozonation and provided data basis for subsequent pilot study.

Occurrence and risks of 23 tire additives and their transformation products in an urban water system

Tire wear particles (TWPs) enter road surface with the friction between tires and road surfaces. Under the volatilization, leaching, and transformation action on TWPs by sunlight and rain, tire additives are released into urban water systems, such as surface rainfall runoff, wastewater treatment plants (WWTPs), receiving surface waters, and drinking water treatment plant (DWTP). In this study, we investigated the occurrence of 23 tire additives and their transformation products in the urban water system of the Pearl River Delta region, South China. Nineteen target compounds were detected in the surface runoff, with 1,3-Diphenylguanidine (DPG) showing highest maximum concentration of 58780 ng/L. Benzothiazole and its transformation products are detected at the frequency of 100 % with the total concentrations of 480-42160 ng/L. The antioxidant derivative N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone (6PPD-Q) was also detected up to 1562 ng/L, which was considerably higher than that of the parent compound 6PPD (the maximum concentration of 7.52 ng/L). Eleven and 8 compounds were detected in WWTPs influents and effluents, respectively, with removal rates of - 62-100 %. Seventeen compounds were detected in the receiving Zhujiang and Dongjiang rivers, while 9 compounds were detected in drinking water sources and DWTP samples. Road runoff, with total concentrations of target compounds up to 79200 ng/L, is suggested as the main non-point source for receiving rivers, while WWTPs effluents are the point sources due to incomplete removal of target compounds after accepting the initial runoff. 6PPD-Q and other 10 compounds displayed median to high ecological risks in surface waters, and the human daily intake of tire additives was estimated to be 2.63 × 10^-8-3.16 × 10^-5 mg/(kg d) via drinking water. This is the first report of the 6PPD-Q and 1,3-Diphenylurea levels in surface waters in China.

Environmental concentrations of 2, 4-DTBP cause immunotoxicity in zebrafish (Danio rerio) and may elicit ecological risk to wildlife

Synthetic phenolic antioxidant 2,4-di-tert-butylphenol (2,4-DTBP) has gained growing concerns due to relatively high concentrations in aquatic ecosystems. There are, however, significant knowledge gaps regarding its potential toxicity to aquatic organisms. In this study, zebrafish (Danio rerio) larvae were exposed to 0.01, 0.1, or 1 μM 2,4-DTBP for 6 d. Transcriptomic analysis of larvae revealed that biological processes related to anti-inflammatory function of macrophage M2 lineage were inhibited by 0.01 μM 2,4-DTBP. Decreases of transcripts related to the IL1B-MYD88-NF-κB pathway (i.e., il1b, il1rl1, myd88, irak4, irak1, traf6, ikbkg, nfkbia, nfkb) and protein levels of NF-κB in larvae intestine confirmed anti-inflammatory effects of 2,4-DTBP. Subsequently, larvae exposed to 2,4-DTBP were challenged with E. coli and showed higher survival rate, suggesting sustained activation of inflammation via LPS can be attenuated by 2,4-DTBP. Moreover, histological examination revealed that intestine barrier was compromised and there was an imbalance of intestine macrophage homeostasis. Food intake was also reduced following exposure to 0.1 and 1 μM 2,4-DTBP. In addition, a risk assessment revealed that 2,4-DTBP in surface water pose low to high ecological risks to aquatic organisms. Taken together, exposure to environmentally relevant concentrations of 2,4-DTBP could negatively affect immune response in zebrafish and may elicit ecological risk in fish population.

Genotoxic effects of chlorinated disinfection by-products of 1,3-diphenylguanidine (DPG): Cell-based in-vitro testing and formation potential during water disinfection

1,3-diphenylguanidine (DPG) is a commonly used rubber and polymer additive, that has been found to be one of the main leachate products of tire wear particles and from HDPE pipes. Its introduction to aquatic environments and potentially water supplies lead to further questions regarding the effects of disinfection by-products potentially formed. Using different bioassay approaches and NGS RNA-sequencing, we show that some of the chlorinated by-products of DPG exert significant toxicity. DPG and its chlorinated by-products also can alter cell bioenergetic processes, affecting cellular basal respiration rates and ATP production, moreover, DPG and its two chlorination products, 1,3-bis-(4-chlorophenyl)guanidine (CC04) and 1-(4-chlorophenyl)-3-(2,4-dichlorophenyl)guanidine (CC11), have an impact on mitochondrial proton leak, which is an indicator of mitochondria damage. Evidence of genotoxic effects in the form of DNA double strand breaks (DSBs) was suggested by RNA-sequencing results and further validated by an increased expression of genes associated with DNA damage response (DDR), specifically the canonical non-homologous end joining (c-NHEJ) pathway, as determined by qPCR analysis of different pathway specific genes (XRCC6, PRKDC, LIG4 and XRCC4). Immunofluorescence analysis of phosphorylated histone H2AX, another DSB biomarker, also confirmed the potential genotoxic effects observed for the chlorinated products. In addition, chlorination of DPG leads to the formation of different chlorinated products (CC04, CC05 and CC15), with analysed compounds representing up to 42% of formed products, monochloramine is not able to effectively react with DPG. These findings indicate that DPG reaction with free chlorine doses commonly applied during drinking water treatment or in water distribution networks (0.2-0.5 mg/L) can lead to the formation of toxic and genotoxic chlorinated products.

Occurrence, Distribution, and Environmental Behavior of Persistent, Mobile, and Toxic (PMT) and Very Persistent and Very Mobile (vPvM) Substances in the Sources of German Drinking Water

Persistent, mobile, and toxic (PMT) and very persistent and very mobile (vPvM) substances have been recognized as a threat to both the aquatic environment and to drinking water resources. These substances are currently prioritized for regulatory action by the European Commission, whereby a proposal for the inclusion of hazard classes for PMT and vPvM substances has been put forward. Comprehensive monitoring data for many PMT/vPvM substances in drinking water sources are scarce. Herein, we analyze 34 PMT/vPvM substances in 46 surface water, groundwater, bank filtrate, and raw water samples taken throughout Germany. Results of the sampling campaign demonstrated that known PMT/vPvM substances such as 1H-benzotriazole, melamine, cyanuric acid, and 1,4-dioxane are responsible for substantial contamination in the sources of German drinking water. In addition, the results revealed the widespread presence of the emerging substances 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and diphenylguanidine (DPG). A correlation analysis showed a pronounced co-occurrence of PMT/vPvM substances associated predominantly with consumer or professional uses and also demonstrated an inhomogeneous co-occurrence for substances associated mainly with industrial use. These data were used to test the hypothesis that most PMT/vPvM substances pass bank filtration without significant concentration reduction, which is one of the main reasons for introducing PMT/vPvM as a hazard class within Europe.

Neurotoxic effects of synthetic phenolic antioxidants on dopaminergic, serotoninergic, and GABAergic signaling in larval zebrafish (Danio rerio)

Synthetic phenolic antioxidants (SPAs) are an environmental concern because they are widely detected in aquatic ecosystems and can pose potential threats to organisms. Studies have reported developmental deficits and behavioral changes in response to SPAs, indicating possible neurotoxic effects. However, their neuroactive potency as well as their mode of action (MoA) remain unclear. As such, this study evaluated the potential neurotoxicity of three SPAs [butylated hydroxytoluene (BHT), 2,4-di-tert-butylphenol (2,4-DTBP), and 4-tert-octylphenol (4-t-OP)] at three concentrations (0.01, 0.1 and 1 μM) to zebrafish larvae. Both 2,4-DTBP and BHT decreased spontaneous tail coiling (STC) at 28 hpf (hours post fertilization) whereas 4-t-OP increased STC. Locomotor activity, based on the velocity and distance of larvae (144 hpf) travelled, was promoted by 2,4-DTBP while it decreased in larvae with exposure to 4-t-OP and BHT. In the light-dark preference assay, exposure to either 2,4-DTBP or BHT resulted in variability in the visiting frequency to the dark zone, and larvae (144 hpf) spent less time in the dark, suggesting anxiety-like behavior. Conversely, zebrafish exposed to 4-t-OP, especially at 1 μM concentration, were hypoactive and spent more time in dark, suggestive of anxiolytic-like responses. RNA-seq was conducted to discern mechanisms underlying behavioral responses. Transcriptomic analysis revealed that gene networks related to neuroactive ligand-receptor interaction as well as neurotransmitter-related pathways were altered by all three SPAs based on gene set and subnetwork enrichment analysis. Modulation of dopaminergic, serotoninergic, and/or GABAergic signaling at the transcript level was noted for each of the three SPAs, but different expression patterns were observed, indicating SPA- and dose-specific responses of the transcriptome. The present study provides novel insight into potential mechanisms associated with neurotoxicity of SPAs congeners.

Carcinogenic Risk of 2,6-Di-tert-Butylphenol and Its Quinone Metabolite 2,6-DTBQ Through Their Interruption of RARβ: In Vivo, In Vitro, and In Silico Investigations

Thousands of contaminants are used worldwide and eventually released into the environment, presenting a challenge of health risk assessment. The identification of key toxic pathways and characterization of interactions with target biomacromolecules are essential for health risk assessments. The adverse outcome pathway (AOP) incorporates toxic mechanisms into health risk assessment by emphasizing the relationship among molecular initiating events (MIEs), key events (KEs), and adverse outcome (AO). Herein, we attempted the use of AOP to decipher the toxic effects of 2,6-di-tert-butylphenol (2,6-DTBP) and its para-quinone metabolite 2,6-di-tert-butyl-1,4-benzoquinone (2,6-DTBQ) based on integrated transcriptomics, molecular modeling, and cell-based assays. Through transcriptomics and quantitative real-time PCR validation, we identified retinoic acid receptor β (RARβ) as the key target biomacromolecule. The epigenetic analysis and molecular modeling revealed RARβ interference as one MIE, including DNA methylation and conformational changes. In vitro assays extended subsequent KEs, including altered protein expression of p-Erk1/2 and COX-2, and promoted cancer cell H4IIE proliferation and metastasis. These toxic effects altogether led to carcinogenic risk as the AO of 2,6-DTBP and 2,6-DTBQ, in line with chemical carcinogenesis identified from transcriptome profiling. Overall, our simplified AOP network of 2,6-DTBP and 2,6-DTBQ facilitates relevant health risk assessment.

A quest to identify suitable organic tracers for estimating children's dust ingestion rates

Chemical exposure via dust ingestion is of great interest to researchers and regulators because children are exposed to dust through their daily activities, and as a result, to the many chemicals contained within dust. Our goal was to develop a workflow to identify and rank organic chemicals that could be used as tracers to calculate children's dust ingestion rates. We proposed a set of criteria for a chemical to be considered a promising tracer. The best tracers must be (1) ubiquitous in dust, (2) unique to dust, (3) detectable as biomarkers in accessible biological samples, and (4) have available or obtainable ADME information for biomarker-based exposure reconstruction. To identify compounds meeting these four criteria, we developed a workflow that encompasses non-targeted analysis approaches, literature and database searching, and multimedia modeling. We then implemented an ad hoc grading system and ranked candidate chemicals based on fulfillment of our criteria (using one small, publicly available dataset to show proof of concept). Initially, five chemicals (1,3-diphenylguanidine, leucine, piperine, 6:2/8:2 fluorotelomer phosphate diester, 6:2 fluorotelomer phosphate diester) appeared to satisfy many of our criteria. However, a rigorous manual investigation raised many questions about the applicability of these chemicals as tracers. Based on the results of this initial pilot study, no individual compounds can be unequivocally considered suitable tracers for calculating dust ingestion rates. Future work must therefore consider larger datasets, generated from broader measurement studies and literature searches, as well as refinements to selection criteria, to identify robust and defensible tracer compounds.

A rapid method for quantification of persistent and mobile organic substances in water using supercritical fluid chromatography coupled to high-resolution mass spectrometry

Persistent and mobile organic substances (PM substances) are a threat to the quality of our water resources. While screening studies revealed widespread occurrence of many PM substances, rapid trace analytical methods for their quantification in large sample sets are missing. We developed a quick and generic analytical method for highly mobile analytes in surface water, groundwater, and drinking water samples based on enrichment through azeotrope evaporation (4 mL water and 21 mL acetonitrile), supercritical fluid chromatography (SFC) coupled to high-resolution mass spectrometry (HRMS), and quantification using a compound-specific correction factor for apparent recovery. The method was validated using 17 PM substances. Sample preparation recoveries were between 60 and 110% for the vast majority of PM substances. Strong matrix effects (most commonly suppressive) were observed, necessitating a correction for apparent recoveries in quantification. Apparent recoveries were neither concentration dependent nor dependent on the water matrix (surface or drinking water). Method detection and quantification limits were in the single- to double-digit ng L⁻¹ ranges, precision expressed as relative standard deviation of quadruplicate quantifications was on average < 10%, and trueness experiments showed quantitative results within ± 30% of the theoretical value in 77% of quantifications. Application of the method to surface water, groundwater, raw water, and finished drinking water revealed the presence of acesulfame and trifluoromethanesulfonic acid up to 70 and 19 μg L⁻¹, respectively. Melamine, diphenylguanidine, p-dimethylbenzenesulfonic acid, and 4-hydroxy-1-(2-hydroxyethyl)-2,2,6,6-tetramethylpiperidine were found in high ng L⁻¹ concentrations.

Chlorination and bromination of 1,3-diphenylguanidine and 1,3-di-o-tolylguanidine: Kinetics, transformation products and toxicity assessment

This works investigates the chlorination and bromination of two rubber and polymer related chemicals, which have emerged as relevant water contaminants, i.e. 1,3-di-o-tolylguanidine (DTG) and 1,3-diphenylguanidine (DPG). Kinetic constants at different pH values were obtained and modelled, taking into account the pK_a values of DTG/DPG and HClO, showing that the maximum reaction rate (k_app > 10⁴ M^-1 s^-1) is obtained at pH values 8.8 for DPG and 9.1 for DTG. Bromination is also very fast, although unlike chlorination, deviation from the model was observed at neutral pH, which was attributed to formation of metastable transformation product (TP). A total of 35 TPs, corresponding to halogenation, hydroxylation, formation of monophenylguanidine derivatives and cyclization reactions, were tentatively identified. Furthermore it was found that chloroform can be formed up to a 25% molar yield, while dichloroacetonitrile was formed into less than a 3% yield. Several ecotoxicological endpoints were predicted by quantitative structure-activity relationship models (QSAR) for the TPs, some of which were predicted to be more toxic than DPG/DTG. Also a chlorinated solution investigated by a Vibrio Fisheri acute toxicity test, confirmed that toxicity increases with chlorination.

Occurrence of emerging persistent and mobile organic contaminants in European water samples

The release of persistent and mobile organic chemicals (PMOCs) into the aquatic environment puts the quality of water resources at risk. PMOCs are challenging to analyze in water samples, due to their high polarity. The aim of this study was to develop novel analytical methods for PMOCs and to investigate their occurrence in surface and groundwater samples. The target compounds were culled from a prioritized list of industrial chemicals that were modeled to be persistent, mobile, and emitted into the environment. Analytical screening methods based on mixed-mode liquid chromatography (LC), hydrophilic interaction LC, reversed phase LC, or supercritical fluid chromatography in combination with mass spectrometric detection were successfully developed for 57 target PMOCs and applied to 14 water samples from three European countries. A total of 43 PMOCs were detected in at least one sample, among them 23 PMOCs that have not been reported before to occur in environmental waters. The most prevalent of these novel PMOCs were methyl sulfate, 2-acrylamino-2-methylpropane sulfonate, benzyltrimethylammonium, benzyldimethylamine, trifluoromethanesulfonic acid, 6-methyl-1,3,5-triazine-diamine, and 1,3-di-o-tolylguanidine occurring in ≥50% of the samples at estimated concentrations in the low ng L^-1 up to μg L^-1 range. The approach of focused prioritization combined with sensitive target chemical analysis proved to be highly efficient in revealing a large suite of novel as well as scarcely investigated PMOCs in surface and groundwater.

Identification of potentially mobile and persistent transformation products of REACH-registered chemicals and their occurrence in surface waters

Transformation of industrial chemicals might be a significant source of hitherto unknown persistent and mobile organic contaminants (PMOC, PM chemicals) present in the aquatic environment. Herein we depicted a three-step strategy consisting of (I) the prioritization of potential PMOC precursors among REACH-registered chemicals, (II) their lab scale transformation through hydrolysis, photolysis, MnO₂ oxidation, and biotransformation and subsequent structural elucidation of derived transformation products, and finally (III) the assessment of their environmental relevance. The proposed procedure was utilized to investigate eleven chemicals, for nine of which a concentration reduction was observed. For six of these chemicals transformation products were at least tentatively identified and partially confirmed with a commercially available reference standard. Retrospective assessment of high-performance liquid chromatography - high-resolution mass spectrometry data as well as a target screening method for the identified TPs and some of the prioritized REACH chemicals revealed the widespread presence of the following chemicals in the environment: 2-pyrrolidone (hydrolysis product of vinylpyrrolidone), TP 216 (4-hydroxy-2,2,6,6-tetramethylpiperidine-1-acetic acid, biotransformation product of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-ethanol), and 1,3-diphenylguanidine (prioritized chemical with experimental evidence of environmental stability). 2-Pyrrolidone was detected in 23/25 investigated surface water samples and present in concentrations of up to 400 ng/L. TP 216 was detected in 20/25 surface water samples and an additional sampling of a waste water treatment plant and the receiving surface water confirmed that TP 216 is formed in waste water treatment plants. The vulcanisation agent 1,3-diphenylguanidine was present in all investigated samples. A leaching experiment with a tire suggested that tires and thus tire wear particles are a potential source of 1,3-diphenylguanidine. With these data the depicted approach was proven successful and suitable for true unknowns like TP 216, and thus an alternative to non-target screenings or suspect-screenings with predicted TPs to identify environmentally relevant transformation products.