Occurrence, behavior and fate of liquid crystal monomers in municipal wastewater

The role of pyroptosis in environmental pollutants-induced multisystem toxicities

The global ecosystem is adversely affected by environmental pollutants, which have numerous deleterious consequences on both the environment and human health. A multitude of human organs and systems, including the neurological, digestive, cardiovascular, reproductive, and respiratory systems, can be adversely affected by these pollutants. Pyroptosis is a form of programmed cell death, primarily involving the Caspase-1/Gasdermin D (GSDMD) classical inflammasome pathway, Caspase-4/5/11/GSDMD non-classical inflammasome pathway, Caspase-3/8 pathway, and other signaling pathways, which induce cell death and regulate the occurrence of inflammatory responses. Pyroptosis plays an important role in a range of diseases, including cancer, neurodegenerative diseases and cardiovascular disease. Evidence has emerged in recent years indicating that environmental pollutants exert various toxic effects by modulating pyroptosis. In this review, we examine hepatotoxicity, cardiovascular toxicity, nephrotoxicity, neurotoxicity, pulmonary toxicity, reproductive toxicity and the related mechanisms caused by environmental pollutants through the regulation of pyroptosis. We aim to provide theoretical references for future toxicity research on environmental pollutants.

CytoToxLCM: A Software to Predict Cytotoxicity of Emerging Contaminant Liquid Crystal Monomers

Liquid crystal monomers (LCMs) have emerged as a new class of contaminants, yet their health risks remain unclear due to limited toxicity data. This study assessed 46 structurally diverse LCMs using primary mouse hepatocytes, revealing significant cytotoxicity in 22 compounds, particularly 3OCB, tFMeO-3cHtFT, 2OdF3B, 2O2cHdFB, and 2CB. To predict cytotoxicity across thousands of reported LCMs, classification models and quantitative structure-activity relationship (QSAR) models were developed. For five optimal classification models, their sensitivity, specificity, and prediction accuracy for the respective training and validation sets were >0.900. In terms of quantitative prediction, we established a k-nearest neighbor-based QSAR model, and its coefficient of determination (R2), leave-one-out cross-validation Q2 (Q2LOO), externally explained variance (Q2EXT), and concordance correlation coefficient (CCC) were all greater than 0.850. These models were integrated into CytoToxLCM software, enabling the high-throughput screening of 1127 LCMs. The results of virtual screening showed that over 40% of the 1127 LCMs were predicted to be cytotoxic, with fluorinated LCMs ranking as the most toxic. The models established in this study are reliable for predicting the cytotoxicity of new or untested LCMs, aiding in better understanding their potential hepatotoxic effects and contributing to the design of safer industrial application alternatives.

Occurrence, Seasonal Variation, and Health Risks of PM2.5-bound Liquid Crystal Monomers (LCMs) in Beijing, China

Liquid crystal monomers (LCMs) are potentially persistent, bioaccumulative, and toxic emerging pollutants. However, their occurrence in outdoor PM2.5 and related human exposure risks remain unknown. In this study, 32 composite samples were analyzed, which were prepared from daily PM2.5 samples collected throughout the year 2021 -2022 in Beijing, China. In total, fifty-six of 78 LCMs were presented at a median concentration of 66.0 pg/m3 (range: 13.3-375.6 pg/m3), with fluorinated LCMs (FBAs) predominating and accounting for 90.7 % of the total LCMs. This concentration surpasses that of halogenated persistent organic pollutants (e.g., polychlorinated dibenzo-p-dioxins/furans) in ambient PM2.5. Higher concentrations of LCMs were found in spring and summer compared to autumn and winter, which could be explained by correlations of concentrations with temperature (p < 0.05). Trans,trans-3,4-Difluoro-4'-(4'-pentylbicyclohexyl-4-yl)biphenyl, trans,trans-3,4-Difluoro-4'-(4'-propylbicyclohexyl-4-yl)biphenyl, and trans,trans-3,4,5-Trifluoro-4'-(4'-propylbicyclohexyl-4-yl)biphenyl were identified for the first time as dominant compounds in ambient samples. Based on predicted biological toxicities, 48 LCMs were categorized as high priority due to their high potential for human absorption, including several compounds previously overlooked. The non-carcinogenic risks of LCMs through inhalation and dermal were negligible for children and adults. This study firstly established a priority list of LCMs in PM2.5, highlighting the need for heightened awareness of their health risks.

Integrative molecular and physiological insights into the phytotoxic impact of liquid crystal monomer exposure and the protective strategy in plants

Liquid crystal monomers (LCMs), the integral components in the manufacture of digital displays, have engendered environmental concerns due to extensive utilization and intensive emission. Despite their prevalence and ecotoxicity, the LCM impacts on plant growth and agricultural yield remain inadequately understood. In this study, we investigated the specific response mechanisms of tobacco, a pivotal agricultural crop and model plant, to four representative LCMs (2OdF3B, 5CB, 4PiMeOP, 2BzoCP) through integrative molecular and physiological approaches. The findings reveal specific impacts, with 4PiMeOP exerting the most pronounced effects, followed by 2BzoCP, 5CB, and 2OdF3B. LCM exposure disrupts the photosynthetic apparatus, exacerbating reactive oxygen species (ROS) levels in leaves, which in turn triggers the upregulation of antioxidative enzymes and the synthesis of antioxidant substances. Additionally, LCMs strongly stimulate the expression of genes involved in abscisic acid (ABA) biosynthesis and signalling pathways. The AI-assisted meta-analysis implicates ABA as a critical regulator in the tobacco response to LCMs. Notably, exogenous application of ABA alleviates LCM-induced toxicities, highlighting the pivotal role of ABA in stress amelioration. Our study provides novel insights into the toxicity and tolerance mechanisms of LCMs in plants, shedding light on both their harmful effects on the ecosystems and potential adaptation responses. This is crucial to develop sustainable agricultural systems by reducing the negative environmental impacts caused by emerging organic pollutants.

Hepatotoxicity of Three Common Liquid Crystal Monomers in Mus musculus: Differentiation of Actions Across Different Receptors and Pathways

Liquid crystal monomers (LCMs) of different chemical structures were widely detected in various environmental matrices. However, their health risk evaluation is lacking. Herein, three representative LCMs were selected from 74 LCM candidates upon literature review and acute cytotoxicity evaluation, then Mus musculus were exposed to the three LCMs for 42 days at doses of 0.5 and 50 μg/kg/d to investigate hepatotoxicity and mechanisms. Phenotypic and histopathological results showed that the three LCMs (DTMDPB, MeO3bcH, and 5OCB) induced hepatomegaly, and only 5OCB induced fatty liver. DTMDPB and MeO3bcH decreased the total cholesterol (TCHO) and triglyceride (TG) content, whereas 5OCB increased the TCHO, TG, and alanine aminotransferase levels. Transcriptome and molecular docking analysis revealed that DTMDPB induced hepatotoxicity by agonizing the farnesoid X receptor, resulting in the disruption of unsaturated fatty acid biosynthesis, ascorbic acid and antioxidant pathways, and circadian clock homeostasis. MeO3bcH promoted inflammation and altered unsaturated fatty acid, primary bile acid biosynthesis, and circadian rhythm by antagonizing the aryl hydrocarbon receptor. 5OCB antagonized peroxisome proliferator-activated receptors, leading to fatty liver caused by the disruption of steroid, cholesterol, and terpenoid backbone biosynthesis pathways. This study provides references for understanding the hepatotoxicity of LCMs with different structures and the selection of priority control LCMs.

Facile and rapid preparation of fluorinated imprinted adsorbent for magnetic solid phase extraction of liquid-crystal monomers

A new fluorinated imprinted adsorbent (MIA) for magnetic solid phase extraction (MSPE) of liquid crystal monomer (LCM) pollutants was one-pot prepared within 3.5 h using 4-[difluoro(3,4,5-trifluorophenoxy)methyl]-3,5-difluoro-4'-ethyl-biphenyl (DFBP) as template and 1H,1H,2H,2H-heptadecafluorodecyl acrylate/vinylanthracene as dual monomers. The structure, morphology, and magnetic properties of MIA fabricated were investigated by various characterization techniques. Under the optimal conditions the prepared MIA presented satisfactory specific recognition performance. The recognition factor and adsorption capacity towards DFBP were 2.7 and 15.9 mg/g, respectively. The specific recognition behaviors of MIA/MSPE towards DFBP were surveyed by means of adsorption kinetics and adsorption isotherms. Combining MSPE with HPLC coupled to a diode array detector (DAD), a sensitive, reliable and anti-interference method for the monitoring of LCMs residuals in various environmental water and soil samples was established. The achieved enrichment factors were 132-248 and 96-204 in water and soil samples, respectively. The corresponding limits of detection were 0.0017-0.0051 μg/L and 0.087-0.28 μg/kg, respectively. Moreover, confirmatory experiments were adopted to inspect the accuracy of the established MIA/MSPE-HPLC/DAD approach. To the best of our knowledge, this is the first time that an imprinted material has been used for specific isolation and capture of LCMs which have been classified as emerging organic pollutants.

Liquid crystal monomers in human, dog and cat feces from the United States

Little is known about exposure of humans and companion animals to liquid crystal monomers (LCMs), which are extensively used in digital displays. We determined the concentrations of 52 LCMs in feces of humans, pet dogs and cats from New York State, USA, using gas chromatography-high resolution mass spectrometry (GC-HRMS). Twenty-four, eight, and six LCMs, that were mainly fluorinated, were detected in human, dog, and cat feces, respectively. ∑LCMs concentrations in the feces of humans (mean: 8.01 ng/g dry weight [dw]) were significantly higher (p < 0.05) than those of dogs (mean: 1.82 ng/g dw) and cats (mean: 1.24 ng/g dw) and with concentrations measured as high as 39.8 ng/g dw. Rel-4'-((1r,1'r,4 R,4'R)-4'-ethyl-[1,1'-bi(cyclohexan)]-4-yl)-3,4-difluoro-1,1'-biphenyl (RELEEBCH or 2bcHdFB) was found at the highest detection frequency (DF) among LCMs analyzed in human (DF: 89 %), dog (DF: 28 %), and cat (DF: 50 %) feces, although this compound accounted only < 4 % of ∑LCM concentrations. The mean cumulative daily intakes of ∑LCMs, calculated through a reverse dosimetry approach, were 71.7, 87.5, and 10.7 ng/kg body weight (bw)/day for humans, dogs, and cats, respectively. This study provides evidence of exposure of both humans and pets to LCMs, highlighting the importance of assessing sources of exposure and associated health risks.

A review of liquid crystal monomers (LCMs) as emerging contaminants: Environmental occurrences, emissions, exposure routes and toxicity

The widespread occurrence of liquid crystal monomers (LCMs) in the environment has raised concerns about their persistence, bioaccumulation, and toxicity (PBT). Here we review the lifecycle of environmental LCMs, focusing on their occurrences, emission sources, human exposure routes, and toxicity. Industrial emissions from Liquid Crystal Display (LCD) manufacturing and e-waste recycling are the primary point sources of LCMs. In addition, emissions from LCD products, air conditioning units, wastewater treatment plants, and landfills contribute to environmental occurrence of LCMs as secondary sources. Dietary routes were identified as the primary exposure pathways to humans. E-waste dismantling workers and infants/children are vulnerable populations to LCMs exposure. Exposure to LCMs has been shown to potentially induce oxidative stress, metabolic disorders, and endocrine disruption. Accumulation of LCMs in the brain and liver tissues of exposed animals highlights the need for toxicokinetic studies.

First report on liquid crystal monomers in tree barks surrounding a display manufacturer: Insights for atmospheric transport and establishment of priority list

Tree bark has been proven as an effective passive air sampler, particularly where access to active sampling methods is limited. In this study, 60 target liquid crystal monomers (LCMs; comprising 10 cyanobiphenyl and analogs (CBAs), 13 biphenyl and analogs (BAs), and 37 fluorinated biphenyl and analogs (FBAs)) were analyzed in 34 tree barks collected from the vicinity of a liquid crystal display (LCD) manufacturer situated in the Pearl River Delta, South China. The concentrations of LCMs in tree barks ranged from 1400 to 16000 ng/g lipid weight, with an average of 5900 ng/g lipid weight. Generally, bark levels of BAs exponentially decreased within 5 km of the LCD manufacturer. The profiles of LCMs in tree barks are similar to previously reported patterns in gaseous phase, suggesting bark's efficacy as a sampler for gaseous LCMs. The inclusion of different congeners in existing studies on the environmental occurrence of LCMs has hindered the horizontal comparisons. Therefore, this study established a list of priority LCMs based on environmental monitoring data and the publicly accessible production data. This list comprised 146 LCMs, including 63 REACH registered LCMs that haven't been analyzed in any study and 56 belonging to 4 types of mainstream LCMs.

One-pot fabrication of task specific magnetic adsorbent for the efficient isolation and capture of liquid-crystal monomers pollutants in waters prior to chromatographic quantification

BACKGROUND

Liquid crystal monomers (LCMs) have been classified as emerging organic pollutants. Efficient isolation and extraction is a critical step in the determination, and then knowing the occurrence and distribution of LCMs in environmental waters. However, the reported sample preparation techniques still suffer some dilemmas such as using large amount of organic solvent, low extraction capacity, tedious operation procedure and employment of expensive extraction column. To circumvent the disadvantages, new extraction format and adsorbent with quickness, less consumption of organic solvent, superior extraction performance and low cost should be developed for the analysis of LCMs.

RESULTS

Using 1H,1H,2H,2H-heptadecafluorodecyl acrylate and 9-vinylanthracene as mixed functional monomers, a task specific magnetic adsorbent (TSMA) was prepared by one-pot hydrothermal technique for the highly efficient capture of LCMs under magnetic solid phase extraction (MSPE) format. Due to the abundant functional groups, the developed TSMA/MSPE presented satisfactory capture performance towards LCMs. Satisfactory enrichment factors (132-212) and high adsorption capacity (18 mg/g) were obtained. Additionally, the relevant adsorption mechanism was studied by the combination of density functional theory calculation and experiments about adsorption kinetics and adsorption isotherm. Under the beneficial conditions, a sensitive and reliable method for the monitoring of studied LCMs in environmental waters was established by the combination of TSMA/MSPE with HPLC equipped with diode array detector (DAD). The achieved limits of detection and spiked recoveries were 0.0025-0.0061 μg/L and 81.0-112 %, respectively. Finally, the developed method was employed to monitor LCMs levels in the North Creek watershed of Jiulong River.

SIGNIFICANCE AND NOVELTY

The current study provided a new adsorbent for quick and efficient capture of LCMs at trace levels. In addition, a sensitive, reliable and anti-intereference method for the monitoring of trace LCMs in actual waters was established. Moreover, for the first, the contents, occurrence and distribution of LCMs in North Creek watershed was investigated based on the developed method.

A new class of contaminants of concern? A comprehensive review of liquid crystal monomers

Liquid crystal monomers (LCMs) are a class of emerging contaminants of concern predicted to be persistent, bioaccumulative and toxic (PBT). Being one of the key components in liquid crystal displays (LCDs), the disposal of LCD containing devices is closely related to the emission of LCMs into the environment. LCMs have been detected in a wide range of environmental matrices including dust, sediment, soil, sewage leachate, and air, with concentration ranges between 17 and 2121 ng/g found in indoor residential dust. Furthermore, they have been detected on human skin at concentrations up to 2,071,000 ng/m2 and in the serum of e-waste dismantling workers, at concentrations ranging from 3.9 to 276 ng/mL. Despite the far-reaching contamination of these compounds, there is limited knowledge of their environmental behaviour, fate, and toxicity. Model predictions show that 297 of 330 LCMs are persistent and bioaccumulative compounds, with many more indicated as being toxic. However, current knowledge of their physicochemical and PBT properties is largely restricted to theoretical predictions and limited to a small number of experimental toxicity studies. As an emerging class of contaminants of concern, a lack of standardisation between studies was identified as a key challenge to advancing the state of knowledge of these compounds. Not only are harmonised analytical methods for their determination and quantification in environmental media yet to be established, but there is also a need for a universal abbreviation system. To further harmonise the reporting of data on LCMs we propose reporting the sum concentration of ten priority LCMs, selected on the basis detection frequency, toxicity and potential for human exposure. Of the ten priority LCMs five are fluorinated biphenyls and analogues, four are biphenyls/bicyclohexyls and analogues and one is a cyanobiphenyl.

Analysis of 78 trace liquid crystal monomers in air by gas chromatography coupled with triple quadrupole mass spectrometry

Liquid crystal monomers (LCMs) comprise a class of organic pollutants that have garnered considerable attention because of their dioxin-like toxicity (i.e., modulation of genes) and presence in various environments. However, limited information about the identities, occurrence, and distribution of LCMs has highlighted an urgent need for a high-throughput and sensitive analytical method. In this study, we developed and validated a rapid, simple, sensitive method that involves minimal solvent consumption. The method was applied for the simultaneous detection and identification of 78 LCMs in atmospheric total suspended particulate samples (dae < 100 μm) using gas chromatography coupled with triple quadrupole mass spectrometry. The results showed high degrees of linearity with correlation coefficients >0.995 in the concentration range of 5.0-500 ng/mL. The instrumental detection limits ranged from 0.7 to 5.3 pg, and the method detection limits ranged from 0.1 to 0.9 pg/m3. The accuracy of the method was between 70 % and 130 % for most analytes, and the relative standard deviations of six replicates were <15 % at three levels of spiking (10, 50, and 200 ng/mL). The developed analytical method was applied to analyze real air particulate samples from Beijing, China. Overall, 45 LCMs ranged from 65.5 to 145.7 pg/m3, with a mean concentration of 92.5 pg/m3. Among them, (trans,trans)-4-propyl-4'-ethenyl-1,1'-bicyclohexane (PVB) was the most abundant, with an average concentration of 33.6 pg/m3. The total estimated daily intakes of LCMs for adults and children were 15.6 and 46.6 pg/kg bw/day, respectively. Accordingly, the method described herein is suitable for quantifying LCMs in atmospheric particulate samples. This study will be valuable for investigating LCM environmental occurrence, behaviors, and risk assessments.

Comprehensive Characterization of Organic Light-Emitting Materials in Breast Milk by Target and Suspect Screening

Organic light-emitting materials (OLEMs) are emerging contaminants in the environment and have been detected in various environment samples. However, limited information is available regarding their contamination within the human body. Here, we developed a novel QuEChERS (quick, easy, cheap, effective, rugged, and safe) method coupled with triple quadrupole/high-resolution mass spectrometry to determine OLEMs in breast milk samples, employing both target and suspect screening strategies. Our analysis uncovered the presence of seven out of the 39 targeted OLEMs in breast milk samples, comprising five liquid crystal monomers and two OLEMs commonly used in organic light-emitting diode displays. The cumulative concentrations of the seven OLEMs in each breast milk sample ranged from ND to 1.67 × 103 ng/g lipid weight, with a mean and median concentration of 78.76 and 0.71 ng/g lipid weight, respectively, which were higher compared to that of typical organic pollutants such as polychlorinated biphenyls and polybrominated diphenyl ethers. We calculated the estimated daily intake (EDI) rates of OLEMs for infants aged 0-12 months, and the mean EDI rates during lactation were estimated to range from 30.37 to 54.89 ng/kg bw/day. Employing a suspect screening approach, we additionally identified 66 potential OLEMs, and two of them, cholesteryl hydrogen phthalate and cholesteryl benzoate, were further confirmed using pure reference standards. These two substances belong to cholesteric liquid crystal materials and raise concerns about potential endocrine-disrupting effects, as indicated by in silico predictive models. Overall, our present study established a robust method for the identification of OLEMs in breast milk samples, shedding light on their presence in the human body. These findings indicate human exposure to OLEMs that should be further investigated, including their health risks.

Particle size-dependent and route-specific exposure to liquid crystal monomers in indoor air: Implications for human health risk estimations

In indoor environments, liquid crystal monomers (LCMs) released from display devices is a significant concern, necessitating a comprehensive investigation into their distribution behaviors and potential health risks. Herein, we examined various LCMs in educational and workplace air and compared their associated health risks through inhalation and dermal absorption routes. 4-propyl-4'-vinylbicyclohexyl (3VbcH) and 4,4'-bis(4-propylcyclohexyl) biphenyl (b3CHB) with median concentrations of 101 and 1460 pg m-3, were the predominant LCMs in gaseous and particulate phases, respectively. Composition and concentration of LCMs differed substantially between sampling locations due to the discrepancy in the quantity, types, and brands of electronic devices in each location. Three models were further employed to estimate the gas-particle partitioning of LCMs and compared with the measured data. The results indicated that the HB model exhibited the best overall performance, while the LMY model provided a good fit for LCMs with higher log Koa (>12.48). Monte Carlo simulation was used to estimate and compared the probabilistic daily exposure dose and potential health risks. Inhalation exposure of LCMs was significantly greater than the dermal absorption by approximately 1-2 orders of magnitude, implying that it was the primary exposure route of human exposure to airborne LCMs. However, certain LCMs exhibited comparable or higher exposure levels via the dermal absorption route due to the significant overall permeability coefficient. Furthermore, the particle size was discovered to impact the daily exposure dose, contingent on the particle mass-transfer coefficients and accumulation of LCMs on diverse particle sizes. Although the probabilistic non-carcinogenic risks of LCMs were relatively low, their chronic effects on human beings merit further investigations. Overall, this study provides insights into the contamination and potential health risks of LCMs in indoor environments, underscoring the importance of considering particle sizes and all possible exposure pathways in estimating human health risks caused by airborne organic contaminants.