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

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.

Chronic exposure to liquid crystal monomer EBCN at environmentally relevant concentrations induces testicular dysfunction via the gut-testis axis

4-Cyano-4'-ethoxybiphenyl (EBCN) is a representative cyano liquid crystal monomer (LCM). While prior studies have documented the widespread occurrence of LCMs in diverse environmental and biological samples, research on their reproductive effects in vivo remains limited. This study employed 35-day and 70-day exposure models in mice to assess the short-term and long-term effects of environmentally relevant concentrations of EBCN on testicular health. Our findings indicate that EBCN exposure, irrespective of duration, had minimal impact on body weight, testis weight, and testicular organ coefficient. However, it induced dose-dependent reductions in seminiferous tubule area, sperm count, accompanied by decreases in Leydig cells and spermatogenic cells, along with disruptions in sex hormone levels. Moreover, EBCN exposure led to the upregulation of inflammatory factors in serum, partially attributable to the activation of necroptosis-related pathways. Additionally, 16S rRNA sequencing and metabolomic analysis revealed a decline in gut microbiome diversity and a decrease in anti-inflammatory metabolites, specifically L-carnosine, in the intestine, potentially contributing to the observed testicular toxicity. Supplementation with exogenous L-carnosine mitigated EBCN-induced testicular dysfunction by inhibiting the expression of necroptosis-related genes. In conclusion, our study suggests that prolonged EBCN exposure at environmentally relevant concentrations adversely impacts testicular function via the gut-testis axis.

Insights into hepatotoxicity of fluorinated liquid crystal monomer 1-ethoxy-2,3-difluoro-4-(trans-4-propylcyclohexyl) benzene (EDPrB) in adult zebrafish at environmentally relevant concentrations: Metabolic disorder and stress response

Fluorinated liquid crystal monomers (FLCMs) are widely employed in liquid crystal display (LCD) panels. As emerging environmental contaminants with persistent, bioaccumulative, and toxic properties, FLCMs were proven to accumulate in liver, raising great concern regarding potential hepatotoxicity. 1-Ethoxy-2,3-difluoro-4-(trans-4-propylcyclohexyl) benzene (EDPrB), as one representative FLCM, was chosen to investigate the hepatotoxicity in adult zebrafish (Danio rerio) at environmentally relevant concentrations (1, 10, and 100 μg/L) with long-term exposure (21 days). EDPrB caused morphological abnormalities, elevated transaminase activities, and inhibited antioxidant levels in zebrafish liver. The contents of total cholesterol and triglyceride were reduced by 2.3- and 1.82-fold, respectively, at 100 μg/L of EDPrB. Transcriptomic analysis revealed that EDPrB disrupted the lipid and glucose metabolisms, protein processing in endoplasmic reticulum (ER), and P53 signal pathway by dysregulating genes, such as fasn, acaca, acsl1b, hkdc1, xbp1, and ero1lb. EDPrB induced ER stress by activating PERK-eIF2α pathway, leading to hepatic metabolic dysfunction. PERK-eIF2α and P53-Bax/Bcl2 pathways were involved in EDPrB-induced apoptosis. Additionally, molecular simulation confirmed that EDPrB had a strong binding affinity to some lipid metabolism proteins (-8.9∼-6.7 kcal/mol) and stress proteins (-9.3∼-5.8 kcal/mol). The findings elucidate EDPrB-induced hepatotoxicity and underlying mechanisms, which contribute to assessing the ecological risk and pollution control of FLCMs.

Hepatotoxicity, developmental toxicity, and neurotoxicity risks associated with co-exposure of zebrafish to fluoroquinolone antibiotics and tire microplastics: An in silico study

This study aimed to investigate the differences in the mechanisms of microscopic hepatotoxicity, developmental toxicity, and neurotoxicity in aquatic organisms co-exposed to styrene-butadiene rubber tire microplastics (SBR TMPs) and fluoroquinolone antibiotics (FQs). We found that hepatotoxicity in zebrafish induced by SBR TMPs and FQs was significantly higher than developmental toxicity and neurotoxicity. Furthermore, the main effects of the FQs primarily manifested as synergistic toxicity, whereas the low- and high-order interactions of the FQs mainly exhibited synergistic and antagonistic effects, respectively. Factorial analysis and the mixture toxicity index revealed that the synergistic effects of lomefloxacin × moxifloxacin and ciprofloxacin × lomefloxacin × enrofloxacin interactions significantly contributed to hepatotoxicity in zebrafish exposed to SBR TMP. SBR TMPs and antibiotics primarily induced hepatotoxicity, developmental toxicity, and neurotoxicity in zebrafish by affecting the activities of Cyp1a, Acox1, TRα, and mAChR. The observed toxicities were closely linked to the hydrophilic/hydrophobic groups, electronegativity, group mass, and structural complexity of the FQ molecules. This study provides new insights regarding the toxicological risks to aquatic organisms from co-exposure to SBR TMPs and FQs from a microscopic perspective. Future studies should include a broader range of antibiotics and tire microplastics and consider their long-term adverse effects on aquatic life.

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 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.

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.

Determination of Bisphenol Compounds and the Bioaccumulation after Co-Exposure with Polyethylene Microplastics in Zebrafish

Knowledge regarding the combined toxicity mechanism of bisphenol compounds and microplastics (MPs) on organisms remains limited. In this study, we first developed an accurate and sensitive method to simultaneously quantify two bisphenol compounds and evaluate their accumulation and tissue distribution after co-exposure with MPs in zebrafish. Then, we determined the bioaccumulation potential of bisphenol A (BPA) and bisphenol S (BPS) in adult zebrafish in the absence and presence of MPs. Bisphenol compounds were found to accumulate in different tissues of zebrafish, with BPS showing lower accumulation levels compared to BPA. Importantly, we discovered that the presence of MPs could exacerbate the accumulation of bisphenol compounds in biological tissues. These findings highlight the enhanced bioavailability and risk posed by the co-exposure of bisphenol compounds and MPs, underscoring the need for further investigation into their combined environmental and biological health impacts.

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.

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.

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.

Liquid crystal monomers (LCMs) in indoor residential dust from Beijing, China: occurrence and human exposure

Liquid crystal monomers (LCMs) are widely used in electronic devices and emerging as an environmental pollutant, while their occurrence in indoor environments is still less studied. In this study, 32 out of 37 target LCMs were detected in indoor residential dust samples (n = 112) from Beijing, China. Concentrations of Σ32LCMs ranged from 17.8 to 197 ng/g, with a median value of 54.7 ng/g. Fluorinated biphenyls and analogs (FBAs) and cyanobiphenyls and analogs (CBAs), with median concentrations of 22.8 and 15.9 ng/g, respectively, were the main kinds of LCMs. Although 32 LCMs can be detected, four monomers with the highest contamination levels contributed to almost 70% of the total LCMs. Spearman correlation analysis found significant correlations among some monomers, which indicated that they might share similar sources in the residential environment. Estimated daily intakes (EDIs) of LCMs via indoor dust for Beijing residents were calculated, and the results showed that dust ingestion and dermal contact were both main intake pathways to LCMs, and younger people may face higher exposure to LCMs. A comparison to the results of China's total diet study showed that EDIs of LCMs via food consumption might be higher than that via dust intake, while health risks caused by exposure of LCMs for the general population, both through food and dust, were insignificant at present.

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.

Predicting environmental risks of pharmaceutical residues by wastewater surveillance: An analysis based on pharmaceutical sales and their excretion data

Pharmaceutical residues are increasingly becoming a significant source of environmental water pollution and ecological risk. This study, leveraging official national pharmaceutical sales statistics, predicts the environmental concentrations of 33 typical pharmaceuticals in the Tianjin area. The results show that 52 % of the drugs have a PEC/MEC (Predicted Environmental Concentration/Measured Environmental Concentration) ratio within the acceptable range of 0.5-2, including atenolol (1.21), carbamazepine (1.22), and sulfamethoxazole (0.91). Among the selected drugs, tetracycline, ciprofloxacin, and acetaminophen had the highest predicted concentrations. The EPI (Estimation Programs Interface) biodegradation model, a tool from the US Environmental Protection Agency, is used to predict the removal efficiency of compounds in wastewater treatment plants. The results indicate that the EPI predictions are acceptable for macrolide antibiotics and β-blockers, with removal rates of roxithromycin, spiramycin, acetaminophen, and carbamazepine being 14.1 %, 61.2 %, 75.1 %, and 44.5 %, respectively. However, the model proved to be less effective for fluoroquinolone antibiotics. The ECOSAR (Ecological Structure-Activity Relationships) model was used to supplement the assessment of the potential impacts of drugs on aquatic ecosystems, further refining the analysis of pharmaceutical environmental risks. By combining the concentration and detection frequency of pharmaceutical wastewater, this study identified 9 drugs with significant toxicological risks and marked another 24 drugs as substances of potential concern. Additionally, this study provides data support for addressing pharmaceutical residues of priority concern in subsequent research.

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.

Tissue-specific accumulation, depuration and histopathological effects of 3,6-dichlorocarbazole and 2,7-dibromocarbazole in adult zebrafish (Danio rerio)

Although polyhalogenated carbazoles have been detected with increasing frequency in aquatic ecosystems, their bioaccumulation in fish and corresponding pathological effects related to bioaccumulation are still unclear. Here, we investigated the tissue-specific accumulation, depuration, and histopathological effects of two typical PHCZs, 3,6-dichlorocarbazole (36-CCZ) and 2,7-dibromocarbazole (27-BCZ), in adult zebrafish at three levels (0, 0.15 μg/L (5 × environmentally relevant level), and 50 μg/L (1/10 LC50). The lowest concentrations of 36-CCZ (1.2 μg/g ww) and 27-BCZ (1.4 μg/g ww) were observed in muscle, and the greatest concentrations of 36-CCZ (3.6 μg/g ww) and 27-BCZ (4 μg/g ww) were detected in intestine among the tested tissues. BCFww of 36-CCZ and 27-BCZ in zebrafish ranged from 172.9 (muscle) to 606.6 (intestine) and 285.2 (muscle) to 987.5 (intestine), respectively, indicating that both 36-CCZ and 27-BCZ have high potential of bioaccumulation in aquatic system. The 0.15 μg/L level of 36-CCZ or 27-BCZ caused lipid accumulation in liver, while 50 μg/L of 36-CCZ or 27-BCZ induced liver lesions such as fibrous septa, cytolysis, and nuclear dissolution. Brain damage such as multinucleated cells and nuclear solidification were only observed at 50 μg/L of 27-BCZ. This study provided valuable information in assessing the health and ecological risks of 36-CCZ and 27-BCZ.

Probing the bioconcentration and metabolism disruption of bisphenol A and its analogues in adult female zebrafish from integrated AutoQSAR and metabolomics studies

Plenty of emerging bisphenol A (BPA) substitutes rise to wait for assessment of bioconcentration and metabolism disruption. Computational methods are useful to fill the data gap in chemical risk assessment, such as automated quantitative structure-activity relationship (AutoQSAR). It is not clear how AutoQSAR performs in predicting the bioconcentration factor (BCF) in adult zebrafish. Herein, AutoQSAR was used to predict the logBCFs of BPA, bisphenol AF (BPAF), bisphenol B, bisphenol F and bisphenol S (BPS). For the test set, a linear relationship was shown between the observed and predicted logBCFs with a slope of 0.97. The predicted logBCFs of these five bisphenols were quite close to their experimental data with a slope of 0.94, suggesting better performance than directed message passing neural networks and EPI Suite with a slope of 0.69 and 0.61, respectively. Thus, AutoQSAR is powerful in modeling logBCFs in fish with minimal time and expertise. To link bioconcentration with metabolic effects, female zebrafish were exposed to BPA, BPAF and BPS for metabolomics analysis. BPA caused a significant disturbance in amino acid metabolism, while BPAF and BPS significantly altered another three metabolic pathways, showing chemical-specific responses. BPAF with the highest logBCF elicited the strongest metabolomic responses reflected by the metabolic effect level index, followed by BPA and BPS. Thus, BPAF and BPS elicited higher or similar metabolism disruption compared with BPA in female zebrafish, respectively, reflecting consequences of bioconcentration.

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 simulation study of the decomposition, biotoxicity, and transfer of LCMs in LCD panels after being in contact with sulfuric acid and extraction/stripping agents

For indium recycling from LCD panels, the decomposition of 9 commonly used liquid crystal monomers (LCMs) that were in contact with sulfuric acid (i.e., leaching agent) and extraction/stripping agents, has been investigated in the present study. Also their biological toxicity changes and transfer have been studied. The results showed that 7 of the 9 LCMs were decomposed in the sulfuric acid agent, while the reaction time and temperature had no effect on the types of the decomposition products. The maximum decomposition rate was 96% when the concentration of the sulfuric acid was increased to 12 M. The time required for a 100% decomposition of the various LCMs in a 5 M sulfuric acid ranged from 41 h to 150 h. Also, Estimation Programs Interface (EPI) and ECOSAR calculations were used to compare the biotoxicity of the LCMs and the decomposition products. The results from the EPI calculations showed that the biological half-lives of the decomposition products were significantly reduced as compared with the LCMs, from the original highest value of 329.2 days-92.71 days. Furthermore, the ECOSAR calculations showed that the biological toxicity of the decomposition products for aquatic organisms was lower than for the LCMs, but they were still toxic and harmful substances. In addition, the transfer rates of the undecomposed LCMs and decomposition products in different extractants remained above 90%, and reached 100% at most. After stripping with hydrochloric acid, more than 70% of the undecomposed LCMs became enriched in the aqueous solution, while the products were enriched in the extractant.

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.

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.

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.