Widespread occurrence of emerging E-waste contaminants - Liquid crystal monomers in sediments of the Pearl River Estuary, China

The role of pyroptosis in environmental pollutants-induced multisystem toxicities

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

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.

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.

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.

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.

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

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

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.

Assessment of heavy metal contamination in the surface sediments, seawater and organisms of the Pearl River Estuary, South China Sea

Coastal heavy-metal contamination poses significant risks to marine ecosystems and human health, necessitating comprehensive research for effective mitigation strategies. This study assessed heavy-metal pollution in sediments, seawater, and organisms in the Pearl River Estuary (PRE), with a focus on Cd, Cu, Pb, Zn, As, Hg, and Cr. A notable reduction in heavy metal concentrations in surface sediments was observed in 2020 compared to 2017 and 2018, likely due to improved pollution management and COVID-19 pandemic restrictions. Spatial analysis revealed a positive correlation between elevated heavy-metal concentrations (Cu, Pb, Zn, Cd, and As) and areas with significant human activity. Source analysis indicated that anthropogenic activities accounted for 63 % of the heavy metals in sediments, originating from industrial effluents, metal processing, vehicular activities, and fossil fuel combustion. Cd presented a high ecological risk due to its significant enrichment in surface sediments. Organisms in the PRE were found to be relatively enriched with Hg and Cu, with average As concentrations slightly exceeding the Chinese food-health criterion. This study identified high-risk ecological zones and highlighted Cd as the primary pollutant in the PRE. The findings demonstrate the effectiveness of recent pollution control measures and emphasize the need for ongoing monitoring and mitigation to safeguard marine ecosystems and human health.

Space-use strategy drives fine-scale spatial variation of chlorinated paraffins in indo-pacific humpback dolphins

Contaminant accumulation in organisms can be influenced by both biological traits and environmental conditions. However, delineating the main factors affecting contaminant burdens in organisms remains challenging. Here, we conducted an initial investigation into the impact of diet and habitat on the accumulation of short- (SCCPs) and medium-chain chlorinated paraffins (MCCPs) in Indo-Pacific humpback dolphins (2003-2020, n = 128) from the Pearl River Estuary (PRE), a highly polluted estuary in China. The detected levels of SCCPs (5897 ± 3480 ng g-1 lw) and MCCPs (13,960 ± 8285 ng g-1 lw) in blubber samples of humpback dolphin are the highest among recorded values marine mammals. Both SCCPs and MCCPs exhibited biomagnification factor values exceeding 1, suggesting their biomagnification potential within the dolphins and their diet. Quantitative diet analysis using the dolphin fatty acid signatures revealed that humpback dolphins inhabiting the western PRE consumed a larger proportion of carnivorous fish than those from the eastern PRE. However, spatial analysis showed that humpback dolphins in the western PRE contained lower SCCP/MCCP concentrations than those from the eastern PRE. Based on these findings we suggest that, compared to diet differences, spatial variations of SCCPs/MCCPs in humpback dolphins may be predominantly influenced by their space-use strategies, as the eastern PRE is closer to the pollutant discharge source and transfer routes.

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.

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

BACKGROUND

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

RESULTS

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

SIGNIFICANCE AND NOVELTY

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

Risk assessment of e-waste - Liquid Crystal Monomers re-suspension caused by coastal dredging operations

The Pearl River Estuary (PRE), one of the primary e-waste recycling centers in the world, has been suffering from the pollution of Liquid Crystal Monomers (LCMs), critical materials with persistent, bio-accumulative, and toxic substances used in electronic devices. It has been detected in seabed sediment with both high frequency and concentration near PRE - Hong Kong (HK) waters. In the same area, dredging operations with in-situ sediment have been frequently used in the last decades for coastal land reclamation projects. Dredging is known to cause a huge amount of sediment re-suspension into water columns, with potential damage to marine ecosystems and biodiversity. In this study, we proposed a new risk assessment strategy to estimate the secondary pollution due to the re-suspension sediment highly contaminated by LCMs. We formulate a robust and reliable probabilistic approach based on unsupervised machine learning and hydrodynamic and sediment transport numerical simulation. New risk indexes were also proposed to better quantify the impact of contaminated sediments. We applied the methodology to assess the potential impact of dredging operations in the PRE and Hong Kong waters on the local marine ecosystem. The results of the analysis showed how the potentially contaminated areas depended on the dredging locations.

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.

Characteristic structures of liquid crystal monomers in EI-MS analysis and the potential application in suspect screening

Liquid crystal monomers (LCMs) are of emerging concern due to their ubiquitous presence in indoor and outdoor environments and their potential negative impacts on human health and ecosystems. Suspect screening approaches have been developed to monitor thousands of LCMs that could enter the environment, but an updated suspect list of LCMs is difficult to maintain given the rapid development of material innovations. To facilitate suspect screening for LCMs, in-silico mass fragmentation model and quantitative structure-activity relationship (QSPR) models were applied to predict electron ionization (EI) mass spectra of LCMs. The in-silico model showed limited predictive power for EI mass spectra, while the QSPR models trained with 437 published mass spectra of LCMs achieved an acceptable absolute error of 12 percentage points in predicting the relative intensity of the molecular ion, but failed to predict the mass-to-charge ratio of the base peak. A total of 41 characteristic structures were identified from an updated suspect list of 1606 LCMs. Multi-phenyl groups form the rigid cores of 85% of LCMs and produce 154 characteristic peaks in EI mass spectra. Monitoring the characteristic structures and fragments of LCMs may help identify new LCMs with the same rigid cores as those in the suspect list.

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.

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.

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.

In vivo and in silico toxicity assessment of four common liquid crystal monomers to Daphnia magna: Novel endocrine disrupting chemicals in crustaceans?

Liquid crystal monomers (LCMs) are widely used in liquid crystal displays (LCDs) and are proposed to be a new generation of environmentally persistent, bioaccumulative and toxic (PBT) substances that are increasingly detected in rivers and seas. However, there is a lack of in vivo data that characterize adverse responses and toxic mechanisms of LCMs on aquatic organisms. The aim of this study was to comprehensively investigate the effect of four typical LCMs on the lethality, growth, molting, and reproductive capacity of Daphnia magna (D. magna), a highly studied aquatic species in environmental toxicology. Whole body and enzymatic biomarkers (i.e., body length, chitobiase, acetylcholinesterase, antioxidant defense) were measured to assess the toxicity of LCMs. The 48 h mortality rate and observations of disrupted thorax development and inhibition of ecdysis indicate that D. magna are sensitive to LCMs exposure. Oxidative stress, impaired neurotransmission, and disruptions in molting were observed in short-term biomarker tests using LCMs. A 21 day exposure of D. magna to LCMs resulted in reduced growth, reproduction, and population intrinsic growth rate. In addition, chitobiase and 20-hydroxyecdysone, enzymes important for the molting process, were altered at 7, 14 and 21 d. This is hypothesized to be related to endocrine imbalance resulting from LCM exposure. Based on molecular docking simulations, there is evidence that LCMs bind directly to ecdysteroid receptors; this may explain the observed endocrine disrupting effects of LCMs. These data support the hypothesis that LCMs are endocrine disrupting chemicals in aquatic species, impacting the process of molting. This may subsequently lead to lower reproduction and unbalanced population dynamics.

Environmental DNA metabarcoding reveals the effect of environmental selection on phytoplankton community structure along a subtropical river

The Dongjiang River, a major tributary of the Pearl River system that supplies water to more than 40 million people in Guangdong Province and neighboring regions of China, harbors rich biodiversity, including many endemic and endangered species. However, human activities such as urbanization, agriculture, and industrialization have posed serious threats to its water quality and biodiversity. To assess the status and drivers of phytoplankton diversity, which is a key indicator of aquatic ecosystem health, this study used Environmental DNA (eDNA) metabarcoding combined with machine learning methods to explore spatial variations in the composition and structure of phytoplankton communities along the Dongjiang River, including its estuary. The results showed that phytoplankton diversity exhibited spatial distribution patterns, with higher community structure similarity and lower network complexity in the upstream than in the downstream regions. Environmental selection was the main mechanism shaping phytoplankton community composition, with natural factors driving the dominance of Pyrrophyta, Ochrophyta, and Cryptophyta in the upstream regions and estuaries. In contrast, the downstream regions was influenced by high concentrations of pollutants, resulting in increased abundance of Cryptophyta. The random forest model identified temperature, dissolved oxygen, chlorophyll a, NO2-, and NH4+ as the main factors influencing the primary phytoplankton communities and could be used to predict changes during wet periods. This study provides valuable insights into the factors influencing phytoplankton diversity and community composition in the Dongjiang River, and demonstrates the application value of eDNA metabarcoding technique in large-scale, long-distance river biodiversity monitoring.

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.

Degradation of organic UV filters in the water environment: A concise review on the mechanism, toxicity, and technologies

Organic ultraviolet filters (OUVFs) have been used globally for the past 20 years. Given that OUVFs can be quickly released from sunscreens applied on human skins, they have been frequently detected in aquatic environments and organisms. Some byproducts of OUVFs might be more recalcitrant and toxic than their parent compounds. To further assess the toxicity and potential risk of OUVFs' byproducts, it is necessary to determine the fate of OUVFs and identify their transformation products. This review summarizes and analyzes pertinent literature and reports in the field of OUVFs research. These published research works majorly focus on the degradation mechanisms of OUVFs in aquatic environments, their intermediates/byproducts, and chlorination reaction. Photodegradation (direct photolysis, self-sensitive photolysis and indirect photolysis) and biodegradation are the main transformation pathways of OUVFs through natural degradation. To remove residual OUVFs' pollutants from aqueous environments, novel physicochemical and biological approaches have been developed in recent years. Advanced oxidation, ultrasound, and bio-based technologies have been proven to eliminate OUVFs from wastewaters. In addition, the disinfection mechanism and the byproducts (DBPs) of various OUVFs in swimming pools are discussed in this review. Besides, knowledge gaps and future research directions in this field of study are also mentioned.

Emerging contaminants and their potential impacts on estuarine ecosystems: Are we aware of it?

Emerging contaminants (ECs) are becoming more prevalent in estuaries and constitute a danger to both human health and ecosystems. These pollutants can infiltrate the ecosystem and spread throughout the food chain. Because of the diversified sources and extensive human activities, estuaries are particularly susceptible to increased pollution levels. A thorough review on recent ECs (platinum group elements, pharmaceuticals and personal care products, pesticides, siloxanes, liquid crystal monomers, cationic surfactant, antibiotic resistance genes, and microplastics) in estuaries, including their incidence, detection levels, and toxic effects, was performed. The inclusion of studies from different regions highlights the global nature of this issue, with each location having its unique set of contaminants. The diverse range of contaminants detected in estuary samples worldwide underscores the intricacy of ECs. A significant drawback is the scarcity of research on the toxic mechanisms of ECs on estuarine organisms, the prospect of unidentified ECs, warrant research scopes.

Driving sustainable circular economy in electronics: A comprehensive review on environmental life cycle assessment of e-waste recycling

E-waste, encompassing discarded materials from outdated electronic equipment, often ends up intermixed with municipal solid waste, leading to improper disposal through burial and incineration. This improper handling releases hazardous substances into water, soil, and air, posing significant risks to ecosystems and human health, ultimately entering the food chain and water supply. Formal e-waste recycling, guided by circular economy models and zero-discharge principles, offers potential solutions to this critical challenge. However, implementing a circular economy for e-waste management due to chemical and energy consumption may cause environmental impacts. Consequently, advanced sustainability assessment tools, such as Life Cycle Assessment (LCA), have been applied to investigate e-waste management strategies. While LCA is a standardized methodology, researchers have employed various routes for environmental assessment of different e-waste management methods. However, to the authors' knowledge, there lacks a comprehensive study focusing on LCA studies to discern the opportunities and limitations of this method in formal e-waste management strategies. Hence, this review aims to survey the existing literature on the LCA of e-waste management under a circular economy, shedding light on the current state of research, identifying research gaps, and proposing future research directions. It first explains various methods of managing e-waste in the circular economy. This review then evaluates and scrutinizes the LCA approach in implementing the circular bioeconomy for e-waste management. Finally, it proposes frameworks and procedures to enhance the applicability of the LCA method to future e-waste management research. The literature on the LCA of e-waste management reveals a wide variation in implementing LCA in formal e-waste management, resulting in diverse results and findings in this field. This paper underscores that LCA can pinpoint the environmental hotspots for various pathways of formal e-waste recycling, particularly focusing on metals. It can help address these concerns and achieve greater sustainability in e-waste recycling, especially in pyrometallurgical and hydrometallurgical pathways. The recovery of high-value metals is more environmentally justified compared to other metals. However, biometallurgical pathways remain limited in terms of environmental studies. Despite the potential for recycling e-waste into plastic or glass, there is a dearth of robust background in LCA studies within this sector. This review concludes that LCA can offer valuable insights for decision-making and policy processes on e-waste management, promoting environmentally sound e-waste recycling practices. However, the accuracy of LCA results in e-waste recycling, owing to data requirements, subjectivity, impact category weighting, and other factors, remains debatable, emphasizing the need for more uncertainty analysis in this field.

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

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

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.

Aquatic toxicity, ecological effects, human exposure pathways and health risk assessment of liquid crystal monomers

Liquid crystal monomers (LCMs), one of the key materials for liquid crystal displays, have been considered as emerging pollutants in recent years. However, the environmental behaviors of LCMs have not yet been well investigated. The toxicity data of 1173 LCMs were calculated by integrated computational simulation methods in this study. It showed that 64.6% LCMs exhibited PBT (persistent, bioaccumulative, and toxic) properties. Based on the results, 1173 LCMs were identified as molecules possessing the highest level of acute toxicity to aquatic organisms. Among which, and a human health risk priority control list about LCMs was generated in this study, among which 435 were classified as requiring priority control LCMs. It was confirmed that LCMs could eventually accumulate in the human body along the aquatic food chain or penetrate the bloodstream through the dermis, thereby causing harm to health by identifying the exposure pathways of LCMs in humans. Additionally, the electronegativity of the side chain group of LCMs is the main factor causing toxicity differences; therefore, the LCMs containing halogens presented significant acute and chronic toxic effects. This study provided a more comprehensive understanding of LCMs for the public and scientific strategies for controlling LCMs.

A state-of-art-review on emerging contaminants: Environmental chemistry, health effect, and modern treatment methods

Pollution problems are increasingly becoming e a priority issue from both scientific and technological points of view. The dispersion and frequency of pollutants in the environment are on the rise, leading to the emergence have been increasing, including of a new class of contaminants that not only impact the environment but also pose risks to people's health. Therefore, developing new methods for identifying and quantifying these pollutants classified as emerging contaminants is imperative. These methods enable regulatory actions that effectively minimize their adverse effects to take steps to regulate and reduce their impact. On the other hand, these new contaminants represent a challenge for current technologies to be adapted to control and remove emerging contaminants and involve innovative, eco-friendly, and sustainable remediation technologies. There is a vast amount of information collected in this review on emerging pollutants, comparing the identification and quantification methods, the technologies applied for their control and remediation, and the policies and regulations necessary for their operation and application. In addition, This review will deal with different aspects of emerging contaminants, their origin, nature, detection, and treatment concerning water and wastewater.

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.

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.

Release Behavior of Liquid Crystal Monomers from Waste Smartphone Screens: Occurrence, Distribution, and Mechanistic Modeling

Liquid crystal display (LCD) screens can release many organic pollutants into the indoor environment, including liquid crystal monomers (LCMs), which have been proposed as a novel class of emerging pollutants. Knowing the release pathways and mechanisms of LCMs from various components of LCD screens is important to accurately assess the LCM release and reveal their environmental transport behavior and fate in the ambient environment. A total of 47, 43, and 33 out of 64 target LCMs were detected in three disassembled parts of waste smartphone screens, including the LCM layer (LL), light guide plate (LGP), and screen protector (SP), respectively. Correlation analysis confirmed LL was the source of LCMs detected in LGP and SP. The emission factors of LCMs from waste screen, SP, and LGP parts were estimated as 2.38 × 10^-3, 1.36 × 10^-3, and 1.02 × 10^-3, respectively. A mechanism model was developed to describe the release behaviors of LCMs from waste screens, where three characteristics parameters of released LCMs, including average mass proportion (AP), predicted subcooled vapor pressures (P_L), and octanol-air partitioning coefficients (K_oa), involving coexistence of absorption and adsorption mechanisms, could control the diffusion-partitioning. The released LCMs in LGP could reach diffusion-partition equilibrium more quickly than those in SP, indicating that LCM release could be mainly governed through SP diffusions.

Evaluating the spatial and temporal distribution of emerging contaminants in the Pearl River Basin for regulating purposes

Little information is available on how the types, concentrations, and distribution of chemicals have evolved over the years. The objective of the present study is therefore to review the spatial and temporal distribution profile of emerging contaminants with limited toxicology data in the pearl river basin over the years to build up the emerging contaminants database in this region for risk assessment and regulatory purposes. The result revealed that seven groups of emerging contaminants were abundant in this region, and many emerging contaminants had been detected at much higher concentrations before 2011. Specifically, antibiotics, phenolic compounds, and acidic pharmaceuticals were the most abundant emerging contaminants detected in the aquatic compartment, while phenolic compounds were of the most profound concern in soil. Flame retardants and plastics were the most frequently studied chemicals in organisms. The abundance of the field concentrations and frequencies varied considerably over the years, and currently available data can hardly be used for regulation purposes. It is suggested that watershed management should establish a regular monitoring scheme and comprehensive database to monitor the distribution of emerging contaminants considering the highly condensed population in this region. The priority monitoring list should be formed in consideration of historical abundance, potential toxic effects of emerging contaminants as well as the distribution of heavily polluting industries in the region.

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.

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.

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.

Direct evidence on occurrence of emerging liquid crystal monomers in human serum from E-waste dismantling workers: Implication for intake assessment

Liquid crystal monomers (LCMs) are widely used chemicals and ubiquitous emerging organic pollutants in the environment, some of which have persistent, bio-accumulative, and toxic potentials. Elevated levels of LCMs have been found in the e-waste dismantling associated areas. However, information on their internal exposure bio-monitoring is scarce. For the first time, occurrences of LCMs were observed in the serum samples of occupational workers (n = 85) from an e-waste dismantling area in South China. Twenty-nine LCMs were detected in serum samples of the workers, with a median value of 35.2 ng/mL (range: 7.78-276 ng/mL). Eight noticed LCMs were found to have relatively high detection frequencies ranging from 52.9% to 96.5%. The correlation analysis of individual LCMs indicated potential common applications and similar sources to the LCMs in occupational workers. Fluorinated LCMs were identified as the predominant monomers in the workers. Additionally, the estimated daily intake of the LCMs in the occupational workers was significantly higher than those in residents from the reference areas (p < 0.05, Mann-Whitney U Test, median values: 1.46 ng/kg bw/day versus 0.40 ng/kg bw/day), indicating a substantially higher exposure level to e-waste dismantling workers.