Identification of Environmental Liquid-Crystal Monomers: A Class of New Persistent Organic Pollutants-Fluorinated Biphenyls and Analogues-Emitted from E-Waste Dismantling

Fluorinated liquid-crystal monomers distribution in paired urine from mothers and infants

Fluorinated liquid-crystal monomers (FLCMs) are widespread environmental contaminants with potential endocrine-disrupting effects. Infants are particularly vulnerable, yet their exposure remains unclear. This study analyzed FLCMs in urine samples from 190 paired mothers and infants in Beijing, detecting 34 and 35 FLCMs, respectively. Median creatinine-corrected concentrations were 1.83 μg/g (unadjusted concentrations: 1.28 ng/mL) for mothers and 3.28 μg/g (0.60 ng/mL) for infants. 1-butoxy-2,3-difluoro-4-(trans-4-propylcyclohexyl) benzene (BDPrB) and 1-ethyl-4-[(4-fluorophenyl) ethynyl] benzene (EFPEB) were identified as the primary detected contaminants. A significant positive correlation in urine concentrations between mothers and infants was observed only for 2'-Fluoro-4″-propyl-[1,1':4',1″-terphenyl]-4-carbonitrile (FPTC) (rs = 0.23, p = 0.023). Certain FLCMs were associated with infant feeding patterns, maternal parity, and environmental exposure, including dust and cleaning frequency (p < 0.05). The results of the study showed that the median estimated daily intakes (EDIs) of ∑FLCMs for mothers and infants were 526 and 425 ng/kg bw/day, respectively, with no significant difference between them (p > 0.05). Further stratification of the data by sex revealed that for male infants, the EDI values for BDPrB and EFPEB were greater (p < 0.05). These findings emphasize the need for greater research on the health effects of FLCMs on infants, particularly considering gender differences.

Optimization, validation, and implementation of a new method for detecting liquid crystal monomers in dust using GC-MS/MS with atmospheric pressure chemical ionization

BACKGROUND

Liquid crystal monomers (LCMs) are a new class of emerging pollutants. To assess their occurrence, behaviour, and potential risks, a sensitive and selective analytical method is required for the determination of LCMs at trace levels in multiple environmental media. Toward this end, an improved GC-MS/MS method was developed and validated for the quantification of LCMs.

RESULTS

The method integrates atmospheric pressure chemical ionization (APCI) with GC-MS/MS. Under optimal instrumental conditions, the instrument quantification limits of LCMs reached as low as 0.02 pg·injection-1, which can be attributed to the generation of high-abundance molecular ions/quasi-molecular ions under APCI. Compared to previously published methods, the developed method in this study reduces the method detection limits of LCMs by approximately 1-38.7 times, enabling the analysis of LCMs at concentrations as low as 0.02 ng·g-1 in dust samples. This improved approach was applied to both indoor and outdoor dust samples. The concentrations of LCMs obtained in this study are consistent with those reported in previous research, demonstrating high detection frequencies of fluorinated LCMs and their predominance in dust.

SIGNIFICANCE

The developed method in this study is not only applicable to dust samples but also readily extends to other environmental matrices, thereby facilitating the investigation of the occurrence, origin, and migration of LCMs in various environments.

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.

Liquid crystal monomers in soil: Developing priority list based on the proposed soil health indicators

Liquid crystal monomers (LCMs) are emerging pollutants that have attracted attention recently due to their unique chemical properties and wide applications. However, in-depth research on LCMs' potential risks to soil health remains blank. Therefore, 107 LCMs and nine soil health characterization proteins/enzymes were selected as research objects in this study. A grading evaluation system for soil health toxicological effect indicators under LCMs exposure was constructed from five dimensions (i.e., soil animals, soil plants, soil microorganisms, soil carbon, nitrogen and phosphorus cycles, and human health) by molecular docking and molecular dynamics simulation methods. Priority control lists for soil health toxicological effects under LCMs exposure were developed based on the proposed evaluation system, with rationality verified through non-bonded interaction, 2D-QSAR and Meta-analysis. Results showed that 32, 56 and 19 LCMs presented unacceptable, potential, and acceptable soil health risks, respectively. The oxidative damage of LCMs to plant leaves, the toxicity to earthworm growth and development, and its effects on key enzymes of the soil nitrogen cycle were suggested to be the priority-attention indicators. This is the first study that provides theoretical support for revealing the toxicological effects of LCM exposure on soil health and relevant pollution control strategies.

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.

Liquid crystal monomers induce placental development and progesterone release dysregulation through transplacental transportation

Embryonic and fetal development can be affected during gestation by exposure to xenobiotics that cross the placenta. Liquid crystal monomers (LCMs) are emerging contaminants commonly found in indoor environments; however, whether they can cross the placenta and affect placental development remains unexplored. Here, we develop an evaluation system that integrates human biomonitoring, uterine perfusion in pregnant rats, and placental cells. We find fourteen out of the fifty-six LCMs that are detected in maternal and cord serum samples from ninety-three healthy pregnant women, at median levels of 13.9 and 18.1 ng/mL, respectively. Subsequent explorations of in utero exposure in rats indicate that aromatic amino acid transporter 1 (SLC16A10) mediates transplacental transportation of the LCMs. Placental cells exposed to LCMs exhibit delayed placental development and reduced progesterone release. These findings show that SLC16A10-mediated transplacental transportation of LCMs inhibits placental development and progesterone release, highlighting the importance of gestational exposure to emerging contaminants.

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.

Identifying the toxic mechanisms of emerging electronic contaminations liquid crystal monomers and the construction of a priority control list for graded control

Liquid crystal monomers (LCMs) are identified as emerging organic contaminations with largely unexplored health impacts. To elucidate their toxic mechanisms, support the establishment of environmental discharge and management standards, and promote effective LCMs control, this study constructs a database covering 20,545 potential targets of 1431 LCMs, highlighting 9 key toxic target proteins that disrupt the nervous system and metabolic functions. GO and KEGG pathway analysis suggests LCMs severely affect nervous system, linked to neurodegenerative diseases and mental health disorders, with toxicity variations driven by electronegativity and structural complexity of LCM terminal groups. To achieve tiered control of LCMs, construct toxicity risk control lists for 9 key toxic target proteins, suitable for the graded control of LCMs, management recommendations are provided based on toxicity levels. These lists were validated for reliability and offer reliable toxicity predictions for LCMs. SHAP analysis points to electronic properties, molecular shape, and structural characteristics of LCMs as primary health impact factors. As the first study integrating machine learning with computational toxicology to outline LCMs health impacts, it aims to enhance public understanding of LCM toxicity risks and support the development of environmental standards, effective management of LCM production and emissions, and reduction of public exposure risks.

Fluorinated liquid-crystal monomers in infant formulas and implication for health risk

Fluorinated liquid-crystal monomers (FLCMs), a new class of potential persistent, bioaccumulative and toxic (PBT) emerging pollutants, are extensively utilized in the display panel of various electronic devices. These compounds have been found in various environmental matrixes and dietary. Our previous studies have documented their ubiquitous occurrence in high fat foodstuffs. Infants, a vulnerable group, are more susceptible to the impacts of these pollutants compared to adults. Herein, we provided an assessment of the health risks posed by FLCMs to infants, focusing on their exposure through infant formula. The presence of FLCMs was detected in all infant formulas, with median concentration of 16.5 ng/g dry weight (dw) and the 95th percentile concentration of 65.7 ng/g dw. The most prevalent pollutant in these formulas was 2-fluoro-4-[4'-propyl-1,1'-bi(cyclohexyl)-4-yl] phenyl trifluoromethyl ether (FPrBP), with median and a 95th percentile concentration of 12.2 ng/g dw and 23.8 ng/g dw, accounting for 55.2% to the total FLCMs. Infants aged 0-6 months had the highest estimated daily intakes (EDIs) of FLCMs, with the EDImedian of 267 ng/kg bw/day. FPrBP and 4-[trans-4-(trans-4-Propylcyclohexyl) cyclohexyl]-1-trifluoromethoxybenzene (PCTB) together made up 83.3% of the total EDIs in median exposure scenario of 0-6 months infant. The highest EDI value was 1.30 × 103 ng/kg bw/day, 77.1% of which was attributed to a combination of FPrBP, 4″-ethyl-2'-fluoro-4-propyl-1,1':4',1″-terphenyl (EFPT), 2-[4'-[difluoro(3,4,5-trifluoro-2-methyl-phenoxy)methyl]-3',5'-difluoro-[1,1'-biphenyl]-4-yl]-5-ethyl-tetrahydro-pyran (DTMPMDP), 4-[Difluoro-(3,4,5-trifluoro-2-methyl-phenoxy)-methyl]-3,5-difluoro-4'-propyl-1,1-biphenyl (DTMPMDB), 2,3-difluoro-1-methyl-4-[(trans, trans)-4'-pentyl[1,1'-bicyclohexyl]-4-yl]benzene (DMPBB) and PCTB. It's worth noting that FLCMs have higher exposure risk. Based on the threshold of toxicological concern (TTC) method, the EDImedian of FPrBP (183 ng/kg bw/day) and FPCB (3.27 ng/kg bw/day) were beyond their TTC values (2.5 ng/kg bw/day) in 0-6 months infant, implying their prospective health risk.

A comparative study on contamination profiles of liquid crystal monomers (LCMs) between outdoor and indoor dusts, and the assessment of health risk of human exposure

Liquid crystal monomers (LCMs) are ubiquitous in various environmental samples, which has led to increasing concerns regarding their potential health risks to humans and wildlife. However, the comparison of the contamination patterns of LCMs between indoor and outdoor environments has rarely been studied. In this study, 35 LCMs were investigated in n = 55 dust samples collected from indoor (n = 20) and outdoor (n = 35) spaces in Yulin, Northwest China. The LCMs were widely detected in indoor and outdoor dusts; the total concentrations of LCMs ranged from 48.6 to 396 ng/g (median: 153 ng/g), and from not detectable to 388 ng/g (median: 56.4 ng/g) in indoor and outdoor dusts, respectively. The concentration levels of ΣLCMs in indoor dusts were significantly higher than those in outdoor dusts (p < 0.05). For each microenvironment, the ranking order of LCM concentrations was dormitory (mean: 202 ng/g) > teaching building (182 ng/g) > campus road (150 ng/g) > urban road (107 ng/g) > laboratory building (91.0 ng/g) > pedestrian street (20.1 ng/g). The mean estimated daily intake values of Σ35LCMs for adults were 2.48 × 10-2 and 1.37 × 10-3 ng/g BW/day in indoor and outdoor dusts, respectively. The hazard quotients of individual LCMs and hazard indices of all analytes were considerably less than one, indicating little health risk for humans via dust ingestion.

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.

First Report on the Trophic Transfer and Priority List of Liquid Crystal Monomers in the Pearl River Estuary

Liquid crystal monomers (LCMs) are emerging organic pollutants due to their potential persistence, toxicity, and bioaccumulation. This study first characterized the levels and compositions of 19 LCMs in organisms in the Pearl River Estuary (PRE), estimated their bioaccumulation and trophic transfer potential, and identified priority contaminants. LCMs were generally accumulated in organisms from sediment, and the LCM concentrations in all organisms ranged from 32.35 to 1367 ng/g lipid weight. The main LCMs in organisms were biphenyls and analogues (BAs) (76.6%), followed by cyanobiphenyls and analogues (CBAs) (15.1%), and the least were fluorinated biphenyls and analogues (FBAs) (11.2%). The most abundant LCM monomers of BAs, FBAs, and CBAs in LCMs in organisms were 1-(4-propylcyclohexyl)-4-vinylcyclohexane (15.1%), 1-ethoxy-2,3-difluoro-4-(4-(4-propylcyclohexyl) cyclohexyl) benzene (EDPBB, 10.1%), and 4'-propoxy-4-biphenylcarbonitrile (5.1%), respectively. The niche studies indicated that the PRE food web was composed of terrestrial-based diet and marine food chains. Most LCMs exhibited biodilution in the terrestrial-based diet and marine food chains, except for EDPBB and 4,4'-bis(4-propylcyclohexyl) biphenyl (BPCHB). The hydrophobicity, position of fluorine substitution of LCMs, and biological habits may be important factors affecting the bioaccumulation and trophic transfer of LCMs. BPCHB, 1-(prop-1-enyl)-4-(4-propylcyclohexyl) cyclohexane, and EDPBB were characterized as priority contaminants. This study first reports the trophic transfer processes and mechanisms of LCMs and the biomonitoring in PRE.

Fluorinated Liquid-Crystal Monomers in Serum from the General Population and Their Impact on Human Health

Fluorinated liquid-crystal monomers (FLCMs) are a potential emerging class of persistent, bioaccumulative, and toxic compounds. Humans inevitably ingest FLCMs via food and the environment. However, there are limited studies on internal exposure biomonitoring of FLCMs. Herein, we evaluated the estimated daily intakes (EDIs) of FLCMs in the general population based on serum residue levels. For the first time, 38 FLCMs were detected in 314 serum samples from the general population in Beijing, with a median value of 132.48 ng/g of lipid weight (lw). BDPrB is a predominant FLCM in serum. The median EDI of ∑38FLCMs in the general residents was 37.96 pg/kg bw/day. The residual levels of most FLCMs were higher in urban than in suburban areas (p < 0.05). The concentrations of EFPEB, EDPrB, EDFPBB, and PDTFMTFT in serum showed positive associations with blood glucose (GLU) (r = 0.126-0.275, p < 0.05). Logistic regression analysis showed that FLCMs were significantly positively correlated with dyslipidemia, with an odds ratio of 2.19; BDPrB was significantly positively correlated with hyperglycemia (OR: 2.48). Overall, the present study suggests the occurrence of FLCMs in the nonoccupational population, and the exposure of certain FLCMs may cause abnormal blood glucose and lipid levels.

Photochemical transformation of liquid crystal monomers in simulated environmental media: Kinetics, mechanism, toxicity variation and QSAR modeling

Liquid crystal monomers (LCMs) are a new class of emerging pollutants with high octanol-water partition coefficients; however, their transformation behavior and associated risk to environments with high organic matter content has rarely been reported. In this study, we investigated the photodegradation kinetics, mechanism, and toxicity variation of 23 LCMs on leaf wax models (e.g., organic solvents methanol and n-hexane). The order of the photolysis rates of these LCMs were biphenylethyne LCMs > phenylbenzoate LCMs > diphenyl/terphenyl LCMs under simulated sunlight, while the phenylcyclohexane LCMs were resistant to photodegradation. The phenylbenzoate and biphenylethyne LCMs mainly undergo direct photolysis, while the diphenyl/terphenyl LCMs mainly undergo self-sensitized photolysis. The main photolysis pathways are the cleavage of ester bonds for phenylbenzoate LCMs, the addition, oxidation and cleavage of alkynyl groups for biphenylethyne LCMs, and the cleavage/oxidation of chains attached to phenyls and the benzene ring opening for diphenyl/terphenyls LCMs. Most photolysis products remained toxic to aquatic organisms to some degree. Additionally, two quantitative structure-activity relationship models for predicting kobs of LCMs in methanol and n-hexane were developed, and employed to predict kobs of 93 LCMs to fill the kobs data gap in systems mimicking leaf surfaces. These results can be helpful for evaluating the fate and risk of LCMs in environments with high content of organic phase.

Concentrations, Profiles, and Potential Sources of Liquid Crystal Monomers in Residential Indoor Dust from the United States

Liquid crystal monomers (LCMs) are biphenyl- or cyclohexane-based organic chemicals used in electronic digital displays, and several of them possess bioaccumulative and toxic properties. Little is known about their occurrence in indoor dust from the United States. We analyzed 60 LCMs in 104 residential indoor dust samples collected from 16 states across the United States. Forty-seven of 60 LCMs were detected in dust samples at a median ∑LCM concentration of 402 ng/g (range: not detected to 4300 ng/g). Trans-4-propylcyclohexyl trans,trans-4'-propylbicyclohexyl-4-carboxylate (MPVBC) and (trans,trans)-4-fluorophenyl 4'-pentyl-[1,1'-bi(cyclohexane)]-4-carboxylate (FPeBC) were frequently detected in dust samples. We investigated potential sources of LCMs in dust by determining concentrations and profiles of these chemicals in smartphone screens, desktop and laptop computer monitors, and displays of other electronic devices and found that profiles in smartphones matched closely with those found in dust. The calculated median daily intake of ∑LCM through dust ingestion was 1.19 ng/kg bw/d for children, whereas that through dermal absorption was 0.18 ng/kg bw/d for adults in the United States.

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.

Informal E-waste dismantling activities accelerated the releasing of liquid crystal monomers (LCMs) in Pakistan: Occurrence, distribution, and exposure assessment

Liquid crystal monomers (LCMs) are emerging contaminants characterized by their persistence, bioaccumulation potential, and toxicity. They have been observed in several environmental matrices associated with electronic waste (e-waste) dismantling activities, particularly in China. However, there is currently no information on the pollution caused by LCMs in other developing countries, such as Pakistan. In this study, we collected soil samples (n = 59) from e-waste dismantling areas with different functions in Pakistan for quantification analysis of 52 target LCMs. Thirty out of 52 LCMs were detected in the soil samples, with the concentrations ranging from 2.14 to 191 ng/g (median: 16.3 ng/g), suggesting widespread contamination by these emerging contaminants. Fluorinated LCMs (median: 10.4 ng/g, range: 1.27-116 ng/g) were frequently detected and their levels were significantly (P < 0.05) higher than those of non-fluorinated LCMs (median: 6.11 ng/g, range: not detected (ND)-76.7 ng/g). The concentrations and profiles of the observed LCMs in the soil samples from the four functional areas varied. The informal dismantling of e-waste poses a potential exposure risk to adults and infants, with median estimated daily intake (EDI, ng/kg bw/day) values of 0.0420 and 0.1013, respectively. Calculation of the hazard quotient (HQ) suggested that some LCMs (e.g., ETFMBC (1.374) and EDFPB (1.257)) may pose potential health risks to occupational workers and their families. Considering the widespread contamination and risks associated with LCMs, we strongly recommend enhancing e-waste management and regulation in Pakistan.

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.

Photochemical behaviour and toxicity evolution of phenylbenzoate liquid crystal monomers in water

Liquid crystal monomers (LCMs) are a group of emerging pollutants that pose potential environmental risks because of their ubiquitous occurrence and toxicity. Understanding their environmental transformation is essential for assessing the ecological risk. In this study, we investigated the photochemical transformation kinetics, mechanism, and photo-induced toxicity of three phenylbenzoate LCMs in water. Their apparent photolytic rate constants were within (0.023 - 0.058) min-1, and the half-lives were < 30.0 min, showing lower persistence in water. Dissolved organic matter significantly inhibited their photolysis because of light-shielding effect and quenching of excited triplet states of LCMs. Their photolysis mainly occurred through excited triplet states, and the reactive oxygen species (i.e., ⋅OH, 1O2 and ⋅O2-) contributed to their degradation. The main photolysis pathways were ester bond cleavage, ⋅OH substitution/addition, and defluorination. Experiments and computational simulation revealed that some ·OH addition/substitution products have similar toxicity with LCMs. Additionally, the ∙OH reaction rate constants (kOH) of LCMs were determined to be > 1 × 109 M-1 s-1, evidence for their high reactivity toward ⋅OH. We have further developed reliable methods to estimate kOH of other phenylbenzoate-like LCMs with quantum chemical calculations. These results are useful for understanding the transformation and fate of LCMs in aquatic environments.

Investigation of the Role of Distances from Liquid Crystal Monomer (LCM) Factories on Distribution of LCMs in Surface Soil Samples

Liquid crystal monomers (LCMs), which are commonly used in electronic device screens, have attracted attention as a potential class of emerging organic pollutants with persistent, bioaccumulative, and toxic (PBT) properties. This study involved the collection of 54 surface soil samples around one LC industrial park at increasing spatial distances within 1 km, 1-3 km, and 3-5 km from the center of the LC industrial park. Our observations revealed the presence of LCMs in 46 of 54 surface soil samples examined. Of the 39 target LCMs, 36 were identified, comprising 14 non-fluorinated and 22 fluorinated LCMs. Nine LCMs were detected at frequencies exceeding 50%, with 3bcHdFB exhibiting the highest detection frequency of 59% in the soil samples. The total LCM concentrations across the 46 sampling locations varied from 0.0072 to 17.24 ng/g dw, with the highest total concentrations at sampling sites within 1 km of the liquid crystal plant, suggesting that manufacturing processes may be a potential source for LCM release into the environment. Differences were observed in the LCM contamination patterns among the three sampling areas. Additionally, we observed a decrease in the median LCM concentration with increasing distance from the center of the LC industrial park. However, no statistically significant differences (p > 0.05) in LCM concentrations were observed across the three distances assessed in this study. This may be owing to the limited variety of target compounds analyzed and the limited number of soil samples. Our results emphasize that further studies on the emissions and pollution characteristics of LCMs during production are warranted.

Aquatic photolysis of high-risk fluorinated liquid crystal monomers: Kinetics, toxicity evaluation, and mechanisms

Despite the frequent detection of fluorinated liquid-crystal monomers (FLCMs) in the environment, the level of understanding of their fate, toxicity, and transformation remains insufficient. Herein, we investigated the degradation kinetics and mechanism of an FLCM (4-cyano-3-fluorophenyl 4-ethylbenzoate, CEB-F) under ultraviolet (UV) photolysis in aquatic environment. Our findings demonstrated that the UV photolysis of CEB-F followed first-order kinetics. Photodegradation products were identified using liquid chromatography with mass spectrometry, and detailed reaction pathways were proposed. It is postulated that through the attack of reactive oxygen species, hydroxylation, and CO/C-F bond cleavage, CEB-F gradually degraded into small molecular compounds, releasing fluorine ions. Acute immobilization tests with Daphnia magna (D. magna) revealed significant acute toxicity of CEB-F, with LC50 values ranging from 1.023 to 0.0536 μM over 24 to 96 h, emphasizing the potential high risk of FLCMs in aquatic ecosystems if inadvertently discharged. Interestingly, we found that the toxicity of CEB-F photolysis reaction solutions was effectively reduced. Through catalase and acetylcholinesterase activities analysis along with molecular docking simulation, we proposed differences in the underlying toxicity mechanisms of CEB-F and its photolysis products to D. magna. These findings highlight the potential harmful effects of FLCMs on aquatic ecosystems and enrich our understanding of the photolysis behavior of FLCMs.

Identification of hazardous organic compounds in e-waste plastic using non-target and suspect screening approaches

End-of-life electric and electronic devices stand as one of the fastest growing wastes in the world and, therefore, a rapidly escalating global concern. A relevant fraction of these wastes corresponds to polymeric materials containing a plethora of chemical additives. Some of those additives fall within the category of hazardous organic compounds (HOCs). Despite the significant advances in the capabilities of analytical methods, the comprehensive characterization of WEEE plastic remains as a challenge. This research strives to identify the primary additives within WEEE polymers by implementing a non-target and suspect screening approach. Gas chromatography coupled to time-of-flight mass spectrometry (GC-QTOF-MS), using electron ionization (EI), was applied for the detection and identification of more than 300 substances in this matrix. A preliminary comparison was carried out with nominal resolution EI-MS spectra contained in the NIST17 library. BPA, flame retardants, UV-filters, PAHs, and preservatives were among the compounds detected. Fifty-one out of 300 compounds were confirmed by comparison with authentic standards. The study establishes a comprehensive database containing m/z ratios and accurate mass spectra of characteristic compounds, encompassing HOCs. Semi-quantification of the predominant additives was conducted across 48 WEEE samples collected from handling and dismantling facilities in Galicia. ABS plastic demonstrated the highest median concentrations, ranging from 0.154 to 4456 μg g-1, being brominated flame retardants and UV filters, the families presenting the highest concentrations. Internet router devices revealed the highest concentrations, containing a myriad of HOCs, such as tetrabromobisphenol A (TBBPA), tribromophenol (TBrP), triphenylphosphate (TPhP), tinuvin P and bisphenol A (BPA), most of which are restricted in Europe.

Accumulation characteristics of liquid crystal monomers in plants: A multidimensional analysis

Liquid crystal monomers (LCMs), identified as emerging contaminations, have been detected in soils and plants, but their accumulation characteristics in plants haven't been studied. Therefore, this study systematically investigated the accumulation characteristics of LCMs in plants from four dimensions (i.e., plant fruit species, soil types, plant growth stages, and LCMs categories) for the first time. The LCMs concentrations (9.96 × 10-4 to 114.608 ng/g) in 22 plant fruits were predicted by the partition-limited model. Grains with the highest lipid content showed the highest LCMs accumulation propensity. Plants grown in paddy soil showed a strong LCMs accumulation capacity. Results showed that the LCMs accumulation capacity in plants from soils decreased when the soil organic matter content increased. A preferential accumulation of LCMs in plant root systems during growth was found by the molecular dynamics simulations. Compared to polychlorinated biphenyls (as the reference contaminants of LCMs), LCMs exhibit higher accumulation in plant roots and lower translocation to shoots. For the fourth dimension, lipophilicity was found to be the main reason of LCMs accumulation by intergraded stepwise linear regression with sensitivity analysis. This is the inaugural research concentrating on LCMs accumulation in plants, providing insights and theoretical guidance for future LCMs management strategies multidimensionally.

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.

Heterogeneous Photodegradation Behavior of Liquid Crystal Monomers in Dust: Quantitative Structure-Activity Relationship and Product Identification

The heterogeneous photodegradation behavior of liquid crystal monomers (LCMs) in standard dust (standard reference material, SRM 2583) and environmental dust was investigated. The measured photodegradation ratios for 23 LCMs in SRM and environmental dust in 12 h were 11.1 ± 1.8 to 23.2 ± 1.1% and 8.7 ± 0.5 to 24.0 ± 2.8%, respectively. The degradation behavior of different LCM compounds varied depending on their structural properties. A quantitative structure-activity relationship model for predicting the degradation ratio of LCMs in SRM dust was established, which revealed that the molecular descriptors related to molecular polarizability, electronegativity, and molecular mass were closely associated with LCMs' photodegradation. The photodegradation products of the LCM compound 4'-propoxy-4-biphenylcarbonitrile (PBIPHCN) in dust, including •OH oxidation, C-O bond cleavage, and ring-opening products, were identified by nontarget analysis, and the corresponding degradation pathways were suggested. Some of the identified products, such as 4'-hydroxyethoxy-4-biphenylcarbonitrile, showed predicted toxicity (with an oral rat lethal dose of 50%) comparable to that of PBIPHCN. The half-lives of the studied LCMs in SRM dust were estimated at 32.2-82.5 h by fitting an exponential decay curve to the observed photodegradation data. The photodegradation mechanisms of LCMs in dust were revealed for the first time, enhancing the understanding of LCMs' environmental behavior and risks.

Toxicity Assessment of Environmental Liquid Crystal Monomers: A Bacteriological Investigation on Escherichia coli and Staphylococcus epidermidis

The widespread existence of liquid crystal monomers (LCMs) in various environmental matrices has been demonstrated, yet studies on the toxicological effects of LCMs are considerably scarce and are urgently needed to be conducted to assess the adverse impacts on ecology and human health. Here, we conducted a bacteriological study on two representative human commensal bacteria, Escherichia coli (E. coli) and Staphylococcus epidermidis (S. epidermidis), to investigate the effect of LCMs at human-relevant dosage and maximum environmental concentration on growth, metabolome, enzymatic activity, and mRNA expression. Microbial growth results exhibited that the highest inhibition ratio of LCMs on S. epidermidis reached 33.6% in our set concentration range, while the corresponding data on E. coli was only 14.3%. Additionally, LCMs showed more dose-dependent toxicity to S. epidermidis rather than E. coli. A novel in vivo solid-phase microextraction (SPME) fiber was applied to capture the in vivo metabolites of microorganisms. In vivo metabolomic analyses revealed that dysregulated fatty acid metabolism-related products of both bacteria accounted for >50% of the total number of differential substances, and the results also showed the species-specific and concentration-dependent metabolic dysregulation in LCM-exposed bacteria. The determination of enzymatic activity and mRNA relative expression levels related to oxidative stress confirmed our speculation that the adverse effects were related to the oxidative metabolism of fatty acids. This study complements the gaps in toxicity data for LCMs against bacteria and provides a new and important insight regarding metabolic dysregulation induced by environmental LCMs in human commensal bacteria.

Atmospheric fate of typical liquid crystal monomers in the tropospheric gas, liquid, and granular phases

Mineral aerosol particles significantly impact environmental risk prediction of liquid crystal monomers (LCMs). In this work, we investigated the reaction mechanisms and kinetics of three typical LCMs (4-cyano-3,5-difluorophenyl 4-ethylbenzoate (CEB-2F), 4-cyano-3-fluorophenyl 4-ethylbenzoate (CEB-F), and 4-cyanophenyl 4-ethylbenzoate (CEB)) with ozone (O3) in the atmospheric gas, liquid, and particle phases employing density functional theory (DFT). Here, O3 is prone to add to the benzene ring without F atom(s) in the selected LCMs. The ozonolysis products are aldehydes, carboxylic acids, epoxides, and unsaturated hydrocarbons containing aromatic rings. Those products undergo secondary ozonolysis to generate small molecular compounds such as glyoxal, which is beneficial for generating secondary organic aerosol (SOA). Titanium dioxide (TiO2), an essential component of mineral aerosol particles, has good adsorption properties for LCMs; however, it slightly reduces the reactivity with O3. At 298 K, the reaction rate constant of the selected LCMs reacting with O3 in the gas and atmospheric liquid phases is (2.74‒5.53) × 10-24 cm3/(mol·sec) and 5.58 × 10-3‒39.1 L/(mol·sec), while CEB-2F reacting with O3 on (TiO2)6 cluster is 1.84 × 10-24 cm3/(mol·sec). The existence of TiO2 clusters increases the persistence and long-distance transportability of LCMs, which enlarges the contaminated area of LCMs.

High-Resolution Mass Spectrometry Screening of Quaternary Ammonium Compounds (QACs) in Dust from Homes and Various Microenvironments in South China

Despite their ubiquitous use, information regarding the presence of quaternary ammonium compounds (QACs) in various microenvironments remains scarce and only a small subset of QACs has been monitored using targeted chemical analysis. In this study, a total of 111 dust samples were collected from homes and various public settings in South China during the COVID-19 pandemic and were analyzed for traditional and emerging QACs using high-resolution mass spectrometry. The total traditional QAC concentrations in residential dust (∑traditional QAC, sum of 18 traditional QACs) ranged from 13.8 to 150 μg/g with a median concentration of 42.2 μg/g. Twenty-eight emerging QACs were identified in these samples, and the composition of ∑emerging QAC (sum of emerging QACs) to ∑QAC (sum of traditional and emerging QACs) ranged from 19 to 42% across various microenvironments, indicating the widespread existence of emerging QACs in indoor environments. Additionally, dust samples from cinemas exhibited higher ∑QAC concentrations compared to homes (medians 65.9 μg/g vs 58.3 μg/g, respectively), indicating heavier emission sources of QACs in these places. Interestingly, significantly higher ∑QAC concentrations were observed in dust from the rooms with carpets than those without (medians 65.6 μg/g vs 32.6 μg/g, p < 0.05, respectively). Overall, this study sheds light on the ubiquitous occurrence of QACs in indoor environments in South China.

Liquid crystal monomers in soils near the e-waste recycling site and liquid crystal display manufacturer: Exponential decrease with distance

Liquid crystal monomers (LCMs) have been recognized as contaminants of emerging concerns. E-waste recycling sites and liquid crystal displays (LCDs) manufacturers are supposed to be critical sources. However, information regarding LCM contaminations in soils surrounding these sites are currently unavailable. In this study, soil samples were collected from two distinct areas in South China: e-waste recycling area (n = 36) and LCD manufacturer (n = 41), and 60 target LCMs (including 13 biphenyl and analogs (BAs), 10 cyanobiphenyl and analogs (CBAs), and 37 fluorinated biphenyl and analogs (FBAs)) were determined. The concentrations of LCMs in the soils from near the e-waste recycling area (0.32-18 ng/g, average: 4.2 ng/g) were higher than those surrounding the LCD manufacturer (ND - 7.2 ng/g, average: 1.5 ng/g). The compositional profiles of LCMs in soil samples from these two typical point sources were considerably different. The concentrations of FBAs exponentially decreased with distance from the e-waste recycling park, by >90 % within 2 km. The levels of BAs exhibited a similar exponential decrease with distance from the LCD manufacturer. The inventories of LCMs were estimated to be 21.0 kg in the e-waste recycling area and 10.8 kg in the LCD manufacturer area. Remarkably, the inventory of LCMs in soils from e-waste recycling area was one order of magnitude larger than that of hexabromocyclododecanes (HBCDs) in the same region, and 0.2 to 20 times the annual global emissions of LCMs from discarded LCD panels. More studies are required to elucidate the environmental occurrence, behavior, and fate of LCMs in multimedia environment surrounding typical point sources.

Aerobic Microbial Transformation of Fluorinated Liquid Crystal Monomer: New Pathways and Mechanism

Fluorinated liquid crystal monomers (FLCMs) have been suggested as emerging contaminants, raising global concern due to their frequent occurrence, potential toxic effects, and endurance capacity in the environment. However, the environmental fate of the FLCMs remains unknown. To fill this knowledge gap, we investigated the aerobic microbial transformation mechanisms of an important FLCM, 4-[difluoro(3,4,5-trifluorophenoxy)methyl]-3, 5-difluoro-4'-propylbiphenyl (DTMDPB), using an enrichment culture termed as BG1. Our findings revealed that 67.5 ± 2.1% of the initially added DTMDPB was transformed in 10 days under optimal conditions. A total of 14 microbial transformation products obtained due to a series of reactions (e.g., reductive defluorination, ether bond cleavage, demethylation, oxidative hydroxylation and aromatic ring opening, sulfonation, glucuronidation, O-methylation, and thiolation) were identified. Consortium BG1 harbored essential genes that could transform DTMDPB, such as dehalogenation-related genes [e.g., glutathione S-transferase gene (GST), 2-haloacid dehalogenase gene (2-HAD), nrdB, nuoC, and nuoD]; hydroxylating-related genes hcaC, ubiH, and COQ7; aromatic ring opening-related genes ligB and catE; and methyltransferase genes ubiE and ubiG. Two DTMDPB-degrading strains were isolated, which are affiliated with the genus Sphingopyxis and Agromyces. This study provides a novel insight into the microbial transformation of FLCMs. The findings of this study have important implications for the development of bioremediation strategies aimed at addressing sites contaminated with FLCMs.

Occurrence of liquid crystal monomers in indoor and outdoor air particle matters (PM10): Implications for human exposure indoors

Liquid crystal monomers (LCMs) are potentially persistent, bioaccumulating, and toxic substances. However, limited data are available on the occurrence of LCMs in indoor and outdoor air particle matter (PM10) in residential areas. Herein, residential areas near an e-waste dismantling center (Guiyu Town, Shantou City), as well as areas away from the e-waste site (Jiedong District, Jieyang City) were selected as the sampling areas. PM10 was collected from the indoor environments of Guiyu (IGY) and Jieyang (IJY), as well as those from the outdoor environments (OGY and OJY) using the high-volume air samplers (TH-10000C). The levels of 57 LCMs in PM10 were analyzed, and the highest concentrations of LCMs were found in IGY (0.970-1080 pg/m3), followed by IJY (2.853-455 pg/m3), OGY (0.544-116 pg/m3) and OJY (0.258-35.8 pg/m3). No significant difference was observed for LCM levels in indoor PM10 between the two areas (p > 0.05), which were significantly higher than those in outdoors (p < 0.05), indicating that the release of electronic products in general indoor environments is a source of LCMs that cannot be ignored. The compositions of LCMs in outdoors were not consistent with those of indoors. The correlation analysis of individual LCMs suggested potential different sources to the LCMs in indoor and outdoor environments. The median daily intake values of Σ46LCMs via inhalation were estimated as 0.440, 1.46 × 10-2, 0.170 and 1.19 × 10-2 ng/kg BW/day for adults, and as 2.27, 2.60 × 10-2, 0.880 and 2.10 × 10-2 ng/kg BW/day for toddlers, respectively, indicating much higher exposure doses of LCMs indoors compared with the outdoors, and much higher doses for toddlers compared with adults (p < 0.05). These results reveal the potentially adverse effects of LCMs on vulnerable populations, such as toddlers, in indoor environments.

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

Liquid crystal monomers (LCMs), the essential substances used in the display screen of electronic devices, have been proposed as a class of emerging chemicals of concern. Despite their detection in various environmental matrices, little is known about the presence of LCMs in municipal sewage systems. This study aimed to investigate the occurrence, distribution, and fate of 64 LCMs released into the aqueous environment from a municipal wastewater treatment plant (WWTP) in Hong Kong, China. In total 14 LCMs were detected in WWTP samples. Specifically, the Σ14LCMs concentrations in crude influent, final effluent, and final sludge were found to be 16.8 ± 0.3 ng/L, 2.71 ± 0.05 ng/L, and 19.2 ± 1.0 ng/g dry weight, respectively. Among them, 10 fluorinated LCMs (F-LCMs) were determined to be present at concentrations of 8.90 ± 0.10 ng/L, 1.69 ± 0.05 ng/L, and 9.94 ± 1.00 ng/g dry weight, respectively. The predominant non-fluorinated LCMs (NF-LCMs) detected in all samples were 3OCB and EPhEMOB, while 2OdF3B was the dominant F-LCM. The overall removal rate of total LCMs was 83.8 ± 0.3 %, with 25.4 ± 4.8 % being removed by biodegradation and UV treatment. Compared to NF-LCMs, F-LCMs were more resistant to biodegradation. Despite the significant removal of LCMs through WWTP, the remaining LCMs in final effluent could result in an annual emission of 3.04 kg of total LCMs from the population of Hong Kong. This study provides the first evidence of LCMs contamination in municipal wastewater, possibly arising from routine electronic devices usage. Further investigation is needed to elucidate the potential impact of LCMs emission via WWTP effluent on the aquatic receiving ecosystem.

A review of liquid crystal monomers: Environmental occurrence, degradation, toxicity, and human exposure of an emerging class of E-waste pollutants

Liquid crystal monomers (LCMs) are a class of organic compounds with diphenyl or dicyclohexane as the skeleton structure, which are widely used in the manufacturing of liquid crystal displays. They are recognized as novel organic compounds with persistence, bioaccumulation, toxicity, and potential for long-range transport. LCMs are inevitably released into the environment throughout the life cycle of electronic products, and their presence has been found in various abiotic matrixes (air, dust, sediment, leachate, soil) and biotic matrixes (aquatic organisms, human serum, and human skin wipe). Given that studies on LCMs are still in their infancy, this review comprehensively summarizes the extensive literature data on LCMs and identifies key knowledge gaps and future research needs. The physicochemical properties, production, and usage of LCMs are described. Their environmental distribution, degradation, toxicity, and human exposure are also discussed based on the available data and results. Existing data show that LCMs have large-scale environmental pollution and may pose potential ecological and health risks, but it is still insufficient to accurately assess their risks due to the lack of knowledge on LCMs in many areas, such as global contamination trend, environmental behavior, toxic effects, and human exposure assessment. We believe that future studies of LCMs need to investigate LCMs pollution on a large geographic scale, explore their sources, behavior, and fate in the environment, and assess their potential health hazards to organisms and humans.

Liquid crystal monomers in ventilation and air conditioning dust: Indoor characteristics, sources analysis and toxicity assessment

Indoor dust contaminated with liquid crystal monomers (LCMs) released from various commercial liquid crystal display (LCD) screens may pose environmental health risks to humans. This study aimed to investigate the occurrence of 64 LCMs in ventilation and air conditioning filters (VACF) dust, characterize their composition profiles, potential sources, and associations with indoor characteristics, and assess their in vitro toxicity using the human lung bronchial epithelial cells (BEAS-2B). A total of 31 LCMs with concentrations (ΣLCMs) ranging from 43.7 ng/g to 448 ng/g were detected in the collected VACF dust. Additional analysis revealed the potential interactions between indoor environmental conditions and human exposure risks associated with the detected LCMs in VACF dust. The service area and working time of the ventilation and air conditioning system, and the number of indoor LCD screens were positively correlated with the fluorinated ΣLCMs in VACF dust (r = 0.355 ∼ 0.511, p < 0.05), while the associations with the non-fluorinated ΣLCMs were not found (p > 0.05), suggesting different environmental behavior and fates of fluorinated and non-fluorinated LCMs in the indoor environment. Four main indoor sources of LCMs (i.e., computer (37.1%), television (28.3%), Brand A smartphone (21.2%) and Brand S smartphone (13.4%)) were identified by positive matrix factorization-multiple linear regression (PMF-MLR). Exposure to 14 relatively frequently detected LCMs, individually and in the mixture, induced significant oxidative stress in BEAS-2B cells. Among them, non-fluorinated LCMs, specifically 3cH2B and MeP3bcH, caused dominant decreased cell viability. This study provides new insights into the indoor LCMs pollution and the associated potential health risks due to the daily use of electronic devices.

Emerging organic contaminants of liquid crystal monomers: Environmental occurrence, recycling and removal technologies, toxicities and health risks

Liquid crystal monomers (LCMs) are a family of synthetic organic chemicals applied in the liquid crystal displays (LCDs) of various electric and electronic products (e-products). Due to their unique properties (i.e., persistence, bioaccumulative potential, and toxicity) and widespread environmental distributions, LCMs have attracted increasing attention across the world. Recent studies have focused on the source, distribution, fate, and toxicity of LCMs; however, a comprehensive review is scarce. Herein, we highlighted the persistence and bioaccumulation potential of LCMs by reviewing their physical-chemical properties. The naming rules were suggested to standardize the abbreviations regarding LCMs. The sources and occurrences of LCMs in different environmental compartments, including dust, sediment, soil, leachate, air and particulate, human serum, and biota samples, were reviewed. It is concluded that the LCMs in the environment mainly originate from the usage and disassembly of e-products with LCDs. Moreover, the review of the potential recycling and removal technologies regarding LCMs from waste LCD panels suggests that a combination of natural attenuation and physic-chemical remediation should be developed for LCMs remediations in the future. By reviewing the health risks and toxicity of LCMs, it is found that a large gap exists in their toxicity and risk to organisms. The fate and toxicity investigation of LCMs, and further investigations on the effects on the human exposure risks of LCMs to residents, especially to occupational workers, should be considered in the future.

Novel Fluorinated Biphenyl Compounds Synthesized via Pd(0)-Catalyzed Reactions: Experimental and Computational Studies

Five new difluorinated biphenyl compounds, 4'-(tert-butyl)-3,4-difluoro-1,1'-biphenyl (TBDFBP), 1-(3',4'-difluoro-[1,1'-biphenyl]-4-yl)ethanone (DFBPE), 3',4'-difluoro-2,5-dimethoxy-1,1'-biphenyl (DFDMBP), 3,4-difluoro-3'-nitro-1,1'-biphenyl (DFNBP), and (3',4'-difluoro-[1,1'-biphenyl]-3-yl)(methyl)sulfane (DFBPMS), have been successfully synthesized by the well-known Suzuki-Miyaura coupling with excellent yields averaging 78%. UV-visible, Fourier transform infrared ,and 13C NMR and 1H NMR spectroscopies along with single-crystal X-ray diffraction (SC-XRD) analysis (for TBDFBP and DFBPE) were used for the structure elucidation of the synthesized compounds. The SC-XRD results demonstrated the crystal systems of the studied compounds, TBDFBP and DFBPE, to be monoclinic, and their space groups were found to be P21/c. Also, a detailed density functional theory study was performed. The calculated structures for TBDFBP and DFBPE were found to agree quite well with the experimental results. The natural bonding orbital charge analysis suggested that molecules of these compounds should interact quite noticeably with each other in the solid phase and with polar solvent molecules. Molecular electrostatic potential analysis suggests that accumulation of positive and negative potential implies possibility of quite significant dipole-dipole intermolecular interactions in crystals of these compounds, as well as quite strong interactions with polar solvent molecules. The global reactivity parameters analysis suggests all compounds to be quite stable in redox reactions, with the compound DFNBP being relatively more reactive and the compounds TBDFBP and DFDMBP being relatively more stable.

Prioritization of risks posed by synthetic chemicals manufactured in China toward humans and the environment via persistence, bioaccumulation, mobility and toxicity properties

Over a third of the global chemical production and sales occurred in China, which make effective assessment and management for chemicals produced by China's chemical industry essential not just for China but for the world. Here, we systematical assessed the persistence (P), bioaccumulation (B), mobility (M) and toxicity (T) potency properties for the chemicals listed in Inventory of Existing Chemical Substances of China (IECSC) via experimental data retrieved from large scale databases and in silico data generated with well-established models. Potential PBT, PMT and PB&MT substances were identified. High risk potentials were highlighted for groups of synthetic intermediates, raw materials, as well as a series of biocides. The potential PBT and PMT synthetic intermediates and/or raw materials unique to the IECSC were dominated with organofluorines, for example, the intermediates used as electronic light-emitting materials. Meanwhile, the biocides unique to the IECSC were mainly organochlorines. Some conventional classes of insecticides, such as organochlorines and pyrethroids, were classified as being of high concern. We further identified a group of PB&MT substances that were considered to be both "bioaccumulative" and "mobile". Their properties and common substructures for several major clusters were characterized. The present results prioritized groups of substances with high potentials to cause adverse effects to the environment and humans, many of which have not yet been fully recognized.

Tunable Fluorine-Functionalized Scholl-Coupled Microporous Polymer for the Selective Adsorption and Ultrasensitive Analysis of Environmental Liquid-Crystal Monomers

Liquid-crystal monomers (LCMs), especially fluorinated biphenyls and analogues (FBAs), are identified to be an emerging generation of persistent organic pollutants. However, there is a dearth of information about their occurrence and distribution in environmental water and lacustrine soil samples. Herein, a series of fluorine-functionalized Scholl-coupled microporous polymers (FSMP-X, X = 1-3) were designed and synthesized for the highly efficient and selective enrichment of FABs. Their hydrophobicity, porosity, chemical stability, and adsorption performance (capacity, rate, and selectivity) were regulated preciously. The best-performing material (FSMP-2) was employed as the on-line fluorous solid-phase extraction (on-line FSPE) adsorbent owing to its high adsorption capacity (313.68 mg g^-1), fast adsorption rate (1.05 g h^-1), and specific selectivity for FBAs. Notably, an enrichment factor of up to 590.2 was obtained for FSMP-2, outperforming commercial C₁₈ (12.6-fold). Also, the underlying adsorption mechanism was uncovered by density functional theory calculations and experiments. Based on this, a novel and automated on-line FSPE-high-performance liquid chromatography method was developed for ultrasensitive (detection limits: 0.0004-0.0150 ng mL^-1) and low matrix effect (73.79-113.3%) determination of LCMs in lake water and lacustrine soils. This study offers new insight into the highly selective quantification of LCMs and the first evidence for their occurrence and distribution in these environmental samples.

Fluorinated liquid-crystal monomers in paired breast milk and indoor dust: A pilot prospective study

Fluorinated liquid-crystal monomers (FLCMs), one class of emerging persistent, bioaccumulative and toxic (PBT) compounds, are widely used in liquid-crystal displays (LCDs). As a result, they have been found in the environment and serum from occupational workers. However, little is known about their occurrence in non-occupational exposing populations. Herein, we provided an evaluation of the health risks of FLCMs for infants based on breastfeeding exposure and dust ingestion. The detection frequencies (DF) of FLCMs in indoor dust and breast milk was 100 %, with median concentrations of 12.00 ng/g dry weight (dw) and 133.40 ng/g lipid weight (lw), respectively. 1-butoxy-2,3-difluoro-4-(trans-4-propylcyclohexyl)benzene (BDPrB) was the predominant pollutant in indoor dust and human breast milk. Significant positive correlations were observed between the dust concentrations of seven FLCMs including BDPrB, and their breast milk concentrations (r = 0.275-0.660, P < 0.05). Further, associations were also found in some demographic and behavioral factors and concentrations of some FLCMs (P < 0.05). The highest EDI of ∑FLCMs was observed for infants who were < 1 month of age, with a median breast milk intake of 700.35 ng/kg bw/day, in which 1-ethoxy-2,3-difluoro-4-(trans-4-propylcyclohexyl)benzene (EDPrB), BDPrB, and 4'-[(trans, trans)-4'-butyl[1,1'-bicyclohexyl]-4-yl]-3,4-difluoro-1,1'-biphenyl (BBDB) collectively contributed 94.4 % of the total EDIs. Notably, the lactational intake of FLCMs was higher than that of some environmental pollutants (EPs). Overall, our results suggest higher exposure risks for infants and breastfeeding is the predominant exposure route for daily intake of FLCMs for infants.

Dietary Exposure and Health Risk of the Emerging Contaminant Fluorinated Liquid-Crystal Monomers

Fluorinated liquid-crystal monomers (FLCMs) widely used in liquid crystal displays are considered to be a new generation of persistent, bioaccumulative, and toxic contaminants. They have been widely detected in the environment. However, little is known about their occurrence in food and human dietary exposure until now. Herein, we provided an evaluation of dietary exposure and health risks of FLCMs in the Chinese adult population based on the fifth and sixth total diet studies (TDSs). The detection frequencies of FLCMs in the two surveys were 90.5 and 99.5%, with concentrations ranging from not detected ∼72.6 μg/kg wet weight (ww) and ND ∼74.7 μg/kg ww, respectively. All TDS samples contained the multiresidue of FLCMs. The mean estimated daily intakes (EDIs) of FLCMs were 172.86 and 163.10 ng/kg bw/day in the fifth and sixth TDS, respectively. Meats, vegetables, and cereals contributed the most to the EDI of FLCMs. According to the threshold of toxicological concern (TTC) method, the EDIs of 1-fluoro-4-[2-(4-propylphenyl)ethynyl]benzene (4.56 and 3.26 ng/kg bw/day) and 2-fluoro-4-[4'-propyl-1,1'-bi(cyclohexyl)-4-yl]phenyl trifluoromethyl ether (3.12 and 3.28 ng/kg bw/day) were above their TTC value (2.5 ng/kg bw/day), suggesting their potential health risk. This is the first comprehensive national dietary exposure assessment of FLCMs.

Occurrence, spatial distributions, and temporal trends of bisphenol analogues in an E-waste dismantling area: Implications for risk assessment

The environmental occurrences of bisphenol analogues (BPs) have been extensively reported, whereas their concentration profile, spatial distribution, and temporal trend in e-waste dismantling area are still poorly understood. Herein, typical BPs (BPA, BPS, TBBPA, TBBPA-DHEE, and TBBPA-MHEE) were investigated in water, soil, and biological samples from three representative regions (FJT, JJP, and RIB) in e-waste recycling area in Taizhou, Zhejiang Province. Overall, the detection frequency of BPs in all samples was 100 %, confirming widespread presence of BPs in e-waste recycling area. Wherein, BPA was the predominant BPs in water (33.3 %) and soil samples (34.9 %), but TBBPA accounted for the largest proportion (41.3 %) in biological samples. In addition, the concentration of BPs in FJT was lower than that in JJP and RIB owing to the renovations on FJT by the local government in recent years, whereas the higher BPs level in RIB implied that elevated BPs contents was related to massive e-waste dismantling activities. From 2017 to 2021, a decreased trend of BPs concentration was observed in FJT, but aggravation of BPs levels in RIB was caused by the ongoing e-waste dismantling. The risk assessment revealed that the BPs in e-waste recycling area posed a low ecological and human health risk. Our finding could provide a valuable reference for the development of strict legislation systems related to e-waste management in China.

Percutaneous Penetration of Liquid Crystal Monomers (LCMs) by In Vitro Three-Dimensional Human Skin Equivalents: Possible Mechanisms and Implications for Human Dermal Exposure Risks

Liquid crystal monomers (LCMs) are indispensable materials in liquid crystal displays, which have been recognized as emerging persistent, bioaccumulative, and toxic organic pollutants. Occupational and nonoccupational exposure risk assessment suggested that dermal exposure is the primary exposure route for LCMs. However, the bioavailability and possible mechanisms of dermal exposure to LCMs via skin absorption and penetration remain unclear. Herein, we used EpiKutis 3D-Human Skin Equivalents (3D-HSE) to quantitatively assess the percutaneous penetration of nine LCMs, which were detected in e-waste dismantling workers' hand wipes with high detection frequencies. LCMs with higher log K_ow and greater molecular weight (MW) were more difficult to penetrate through the skin. Molecular docking results showed that ABCG2 (an efflux transporter) may be responsible for percutaneous penetration of LCMs. These results suggest that passive diffusion and active efflux transport may be involved in the penetration of LCMs across the skin barrier. Furthermore, the occupational dermal exposure risks evaluated based on the dermal absorption factor suggested the underestimation of the continuous LCMs' health risks via dermal previously.

Predicted health and environmental hazards of liquid crystal materials via quantitative structure-property relationship modeling

Liquid crystal materials (LCMs) are considered as emerging contaminants with high persistent and bioaccumulative potentials, but their toxicological effects are not well understood. To address this issue, a list of 1431 LCMs commercially available in the market was established through literature reviews and surveys of LCM suppliers. Toxicological properties of 221 target LCMs were derived from the Classification and Labeling Inventory by the European Chemicals Agency. More than 80 % of target LCMs likely pose adverse effects on human health or aquatic ecosystems. Two quantitative structure-property relationship (QSPR) models developed from the toxicological properties of LCMs achieved approximately 90 % accuracy in external data sets. The probability-based approach was more efficient in defining the applicability domain for the QSPR models than a range- or distance-based approach. The highest accuracy was achieved for chemicals within the probability-based applicability domain. The QSPR models were applied to predict health and environmental hazards of 1210 LCMs that had not been notified to the Classification and Labeling Inventory, and 301 and 94 LCMs were recognized as posing potential hazards to human health and the environment, respectively. The present study highlights the potential detrimental effects of LCMs and offers a specific in silico technique for screening hazardous LCMs.

Liquid Crystal Monomer: A Potential PPARγ Antagonist

Liquid crystal monomers (LCMs) are a large family of artificial ingredients that have been widely used in global liquid crystal display (LCD) industries. As a major constituent in LCDs as well as the end products of e-waste dismantling, LCMs are of growing research interest with regard to their environmental occurrences and biochemical consequences. Many studies have analyzed LCMs in multiple environmental matrices, yet limited research has investigated the toxic effects upon exposure to them. In this study, we combined in silico simulation and in vitro assay validation along with omics integration analysis to achieve a comprehensive toxicity elucidation as well as a systematic mechanism interpretation of LCMs for the first time. Briefly, the high-throughput virtual screen and reporter gene assay revealed that peroxisome proliferator-activated receptor gamma (PPARγ) was significantly antagonized by certain LCMs. Besides, LCMs induced global metabolome and transcriptome dysregulation in HK2 cells. Notably, fatty acid β-oxidation was conspicuously dysregulated, which might be mediated through multiple pathways (IL-17, TNF, and NF-kB), whereas the activation of AMPK and ligand-dependent PPARγ antagonism may play particularly important parts. This study illustrated LCMs as a potential PPARγ antagonist and explored their toxicological mode of action on the trans-omics level, which provided an insightful overview in future chemical risk assessment.

Removing emerging e-waste pollutant DTFPB by synchronized oxidation-adsorption Fenton technology

Liquid crystal monomers (LCMs), an emerging group of organic pollutants related to electronic waste, have been frequently detected from various environmental matrices, including landfill leachate. The persistence of LCMs requires robust technology for remediation. The objectives of this study were to evaluate the feasibility, performance and mechanism of the remediation of a typical LCM 4-[difluoro(3,4,5-trifluorophenoxy)methyl]- 3,5-difluoro-4'-propylbiphenyl (DTFPB) via synchronized oxidation-adsorption (SOA) Fenton technology and verify its application in DTFPB-contaminated leachate. The SOA Fenton system could effectively degrade 93.5% of DTFPB and 5.6% of its total organic carbon (TOC_DTFPB) by hydroxyl radical oxidation (molar ratio of Fe²⁺ to H₂O₂ of 1/4 and pH 2.5-3.0) following a pseudo-first-order model under 0.378 h^-1. Additionally, synchronized adsorption of DTFPB and its degradation intermediates by in situ resultant ferric particles via hydrophobic interaction, complexation, and coprecipitation contributed to almost 100% of DTFPB and 33.4% of TOC_DTFPB removal. Three possible degradation pathways involving eight products were proposed, and hydrophobic interactions might drive the adsorption process. It was first confirmed that the SOA Fenton system exhibited good performance in eliminating DTFPB and byproducts from landfill leachate. This study provides new insights into the potential of the Fenton process for the treatment of emerging LCMs contamination in wastewater.

Metabolic profiling of the fluorinated liquid-crystal monomer 1-ethoxy-2,3-difluoro-4-(trans-4-propylcyclohexyl)benzene

1-Ethoxy-2,3-difluoro-4-(trans-4-propylcyclohexyl)benzene (EDPrB) is a typical fluorinated liquid-crystal monomer (LCM). LCMs contaminants are becoming increasingly concerning due to their potential persistence, bioaccumulation, toxicity, and broad prevalence in environmental and human samples. However, LCM metabolism is poorly understood. Herein, by introducing selected EDPrB into the appropriate liver microsomes in vitro, we examined the metabolic pathways of LCM in humans, rats, pigs, Cyprinus carpio, crucian carp, and Channa argus. A total of 20 species-dependent metabolites were identified and structurally elucidated by gas and liquid chromatography-high resolution mass spectrometry for the first time. Dealkylation, H-abstraction, and hydroxylation reactions are the primary metabolic pathways. Half of these in vitro metabolites were found in the urine, serum, and fecal samples of Sprague-Dawley rats exposed to EDPrB. Toxicity predictions indicate that 17 metabolites can be classified as toxic. According to the Ecological Structure Activity Relationships (ECOSAR), a number of metabolites exhibit equivalent or greater aquatic toxicity to that of EDPrB. Toxicity Estimation Software Tool (T.E.S.T.) predicts that some metabolites exhibit developmental toxicity and mutagenicity in rats. These findings suggest that biotransformation should be particularly emphasized, and more toxicological and monitoring studies should be performed to assess the ecological and human safety of LCMs.

Tissue-specific accumulation, bioaccumulation, and depuration of liquid crystal monomers (LCMs) in adult zebrafish (Danio rerio)

This study investigated the properties of bioaccumulation, tissue-specific accumulation, and depuration of liquid crystal monomers (LCMs) in adult zebrafish (Danio rerio) exposed to a mixture of 39 LCMs for 19 days followed by depuration for 12 days. Tissue-specific accumulation of LCMs was examined at the time point of day 19, and we observed that the distribution of LCMs varied among different tissues with the following order of Σ₃₉LCM concentrations, the intestine > brain > gill > liver > muscle. We also observed that the bioaccumulation potential of LCMs varied among LCM groups with different functional groups, and LCMs with the cyan group were prone to accumulate in zebrafish. Among the 39 target LCMs, nine exhibited bioconcentration factors (BCFs) >1000, indicating their great bioaccumulation potential in aquatic environments. The experimental BCFs of 22 LCMs in the present study were lower than the theoretical values predicted by the Estimation Programs Interface (EPI) Suite software developed by U.S. Environmental Protection Agency (USEPA), suggesting that their bioaccumulation potential might be overestimated by theoretical estimation techniques. Another interesting finding was the significant positive correlation relationship in both sexes of zebrafish (p < 0.01, r² = 0.66 for male; p < 0.01, r² = 0.41 for female) between logBCF_ww and logK_ow values of LCMs. Overall, this study provides fundamental information regarding the bioaccumulation potentials of LCMs, which could be helpful for further investigating the health risks of LCMs in aquatic environments.

Prediction of the Endocrine disruption profile of fluorinated biphenyls and analogues: An in silico study

Fluorinated biphenyls and their analogues (FBAs) are considered new persistent organic pollutants, but their endocrine-disrupting effects are still unknown. To fill this gap, the binding probability of 44 FBAs to different nuclear hormone receptors (NHRs) was predicted using Endocrine Disruptome. And molecular similarity and network toxicology analysis were used to strengthen the docking screening. The docking results showed that FBAs could have high binding potential for various NHRs, such as estrogen receptors β antagonism (ERβ an), liver X receptors α (LXRα), estrogen receptors α (ERα), and liver X receptors β (LXRβ). The similarity analysis found that the degree of overlap of the NHR repertoire was related to the Tanimoto coefficient of FBAs. Network toxicology verified a part of docking screening results and identified endocrine-disrupting pathways worthy of attention. This study found out potential endocrine-disrupting FBAs and their vulnerable, and developed a workflow that would leverage in silico approaches including molecular docking, similarity, and network toxicology for risk prioritization of potential endocrine-disrupting compounds.