Occurrence and fate of polycyclic aromatic hydrocarbons from electronic waste dismantling activities: A critical review from environmental pollution to human health

Mechanism of cytochrome P450s mediated interference with glutathione and amino acid metabolisms from halogenated PAHs exposure

Epidemiological evidence indicates that exposure to halogenated polycyclic aromatic hydrocarbons (HPAHs) is associated with many adverse effects. However, the mechanisms of metabolic disorder of HPAHs remains limited. Herein, effects of pyrene (Pyr), and its halogenated derivatives (1-chloropyrene (1-Cl-Pyr), 1-bromopyrene (1-Br-Pyr)) on endogenous metabolic pathways were investigated, in human hepatoma (HepG2) and HepG2-derived cell lines expressing various human cytochrome P450s (CYPs). Non-targeted metabolomics results suggested that 1-Br-Pyr and Pyr exposure (625 nM) induced disruption in glutathione and riboflavin metabolism which associated with redox imbalance, through abnormal accumulation of oxidized glutathione, mediated by bioactivation of CYP2E1. Conversely, CYP2C9-mediated 1-Cl-Pyr significantly interfered with glutathione metabolism intermediates, including glycine, L-glutamic acid and pyroglutamic acid. Notably, CYP1A1-mediated Pyr-induced perturbation of amino acid metabolism which associated with nutrition and glycolipid metabolism, resulting in significant upregulation of most amino acids, whereas halogenated derivatives mediated by CYP1A2 substantially downregulated amino acids. In conclusion, this study suggested that Pyr and its halogenated derivatives exert potent effects on endogenous metabolism disruption under the action of various exogenous metabolic enzymes (CYPs). Thus, new evidence was provided to toxicological mechanisms of HPAHs, and reveals potential health risks of HPAHs in inducing diseases caused by redox and amino acid imbalances.

Lagging pollution of polycyclic aromatic hydrocarbons in the rebuilt e-waste site: From the perspective of characteristics, sources, and risk assessment

Little information is known regarding how the lagged pollution of polycyclic aromatic hydrocarbon (PAH) influenced the environment and human health after an e-waste dismantling site was rebuilt. This study investigated the characteristics, sources, and risk assessment of PAHs in a rebuilt e-waste site and its surrounding farmland by analyzing the samples of soil, dust, water, and vegetable. Concentrations of PAHs in soil, vegetable and water in the rebuilt site were relatively higher than in its surrounding farmland. The concentrations in surface soils, soil columns, dust, vegetables, and water varied from 55.4 to 3990 ng g-1, 1.65 to 5060 ng g-1, 2190 to 2420 ng g-1, 2670 to 10,300 ng g-1, and 46.8 to 110 μg L-1 in the e-waste site, respectively. On the farmland, PAH concentrations in surface soils, vegetables, and water ranged from 41.5 to 2760 ng g-1, 506 to 7640 ng g-1, and 56.6 to 89.2 μg L-1, respectively. A higher proportion of high-molecular-weight PAHs (HMW-PAHs) appeared in all multimedia compared with low-molecular-weight PAHs (LMW-PAHs). Diagnostic ratio together with positive matrix factorization (PMF) revealed that vehicle emission was the primary source in this area, and the activity of e-waste disposal was another important source in the rebuilt e-waste site. Based on the deterministic health risks, people working in the reconstructed e-waste site were exposed to low risks, whereas the residents living near the surrounding farmland were exposed to low risk. Sensitivity analyses indicated that exposure frequency and PAH concentrations were the main factors that influenced exposure risk. This study provides valuable insight into the comprehension of the lagging pollution effects of PAH on the environment and human health after the e-waste site was rebuilt.

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

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

Emission characteristics of (halogenated) polycyclic aromatic hydrocarbons during printed circuit board combustion and estimated emission intensity of a typical e-waste dismantling site in South China

The pollution of polycyclic aromatic hydrocarbons (PAHs) and halogenated PAHs (Cl/Br-PAHs) caused by electronic waste dismantling activities have attracted considerable attention. The present study investigated the emissions and formation of PAHs and Cl/Br-PAHs based on the combustion of printed circuit boards simulating electronic waste dismantling process. The emission factor of ΣPAHs was 648 ± 56 ng/g, which was much lower than that of ΣCl/Br-PAHs (8.80 × 104 ± 9.14 × 103 ng/g). From 25 to 600 °C, the emission rate of ΣPAHs reached a sub-peak of 7.39 ± 1.85 ng/(g•min) at 350 °C, then increased gradually with the fastest rate of 19.9 ± 21.8 ng/(g•min) at 600 °C, whereas that of ΣCl/Br-PAHs was the fastest at 350 °C with a rate of 597 ± 106 ng/(g•min), then decreased gradually. The present study suggested that the formation pathways of PAHs and Cl/Br-PAHs are by de novo synthesis. Low molecular weight PAHs were readily partitioned into gas and particle phases, whereas high molecular weight fused PAHs were only detected in oil phase. However, the proportion of Cl/Br-PAHs in particle and oil phases were different from that of gas phase, whereas similar to that of the total emission. In addition, PAH and Cl/Br-PAH emission factors were used to estimate the emission intensity of pyrometallurgy project in Guiyu Circular Economy Industrial Park, and it was shown that approximately 1.30 kg PAHs and 176 kg Cl/Br-PAHs would be emitted annually. This study revealed that Cl/Br-PAHs would be formed by de novo synthesis, and for the first time provided the emission factors of Cl/Br-PAHs during the heat treatment process of printed circuit board, as well as estimated the contribution of pyrometallurgy, a new electronic waste recovery technology, to environmental Cl/Br-PAH pollution, which provides potential scientific information for governmental decision-making on the control of Cl/Br-PAHs.

A sustainable management of polycyclic aromatic hydrocarbons to synthesize microporous organic polymers for adsorptive desulphurization of fuels

A sustainable management of carcinogenic polycyclic aromatic hydrocarbons (PAHs) to synthesize a series of high surface area (SABET of 563-1553 m2 g-1) microporous polymeric adsorbents is reported. The products with high yield (>90%) were obtained within only 30 min at a low temperature of 50 °C using a microwave-assisted approach with 400 W microwave power followed by 30 min of ageing by raising the temperature to 80 °C. The synthesized adsorbents are used for removing another category of carcinogenic pollutants i.e., polycyclic aromatic sulphur heterocycles (PASHs) from model and real fuels. Adsorptive desulphurization experiment in batch mode could reduce the sulphur from high concentrated model (100 ppm) and real (102 ppm) fuels to 8 ppm and 45 ppm respectively. Similarly, desulphurization of model and real fuels with ultralow sulphur concentrations of 10 and 9 ppm, respectively, reduced the final concentration of sulphur to 0.2 and 3 ppm, respectively. Adsorption isotherms, kinetics, and thermodynamic studies have been conducted using batch mode experiments. Adsorptive desulphurization using fixed bed column studies show the breakthrough capacities of 18.6 and 8.2 mgS g-1, for the same high concentrated model and real fuels, respectively. The breakthrough capacities of 1.1 and 0.6 mgS g-1 are estimated for the ultralow sulphur model and real fuels, respectively. The adsorption mechanism, based on the spectroscopic analysis (FTIR and XPS) demonstrates the role of π-π interactions between the adsorbate and adsorbent. The adsorptive desulphurization studies of model and real fuels from batch to fixed bed column mode would offer an in-depth understanding to demonstrate the lab-scale findings for industrial applications. Thus, the present sustainable strategy could manage two classes of carcinogenic petrochemical pollutants, PAHs and PASHs, simultaneously.

Different effects of continuous and pulsed Benzo[a]pyrene exposure on metabolism and antioxidant defense of large yellow croaker: Depend on exposure duration

This study aims to compare differential effects of continuous and pulsed BaP exposures on metabolism and antioxidant defense in the liver of large yellow croaker. Fish were subjected to BaP for 4 days and 36 days in three exposure regimes with the same time-averaged concentration of BaP: 4 μg/L BaP continuously, 8 μg/L BaP for 24 h every other day or 16 μg/L BaP for 24 h every 4 days. Our results showed that compared to pulsed BaP exposures, continuous BaP exposure reduced BaP metabolism (CYP1A, CYP3A and AHR transcriptional expressions, GSH content, GSH/GSSG ratio, EROD and GST activities) and antioxidant defense (T-SOD activity) on day 4, resulting to the increases in MDA and PC contents, indicating that continuous BaP exposure induced more severe oxidative damage during the early stage of exposure. But continuous BaP exposure reduced MDA and PC contents by improving BaP metabolism and antioxidant defense during the late stage of exposure. CYP1B transcriptional expression and CAT activity were unsuitable biomarkers of both continuous and pulsed BaP exposures. In conclusion, our results demonstrated differential effects of continuous and pulsed exposures on BaP metabolism and antioxidant responses, which were depend on exposure duration.

Preferential association of polycyclic aromatic hydrocarbons (PAHs) with soil colloids at an e-waste recycling site: Implications for risk of PAH migration to subsurface environment

Polycyclic aromatic hydrocarbon (PAH) contamination at e-waste recycling sites poses high ecological and human-health risks. Of note, PAHs in surface soils can be mobilized through colloid-facilitated transport, and may migrate into the subsurface and pollute groundwater. Here, we show that the colloids released from the soil samples at an e-waste recycling site in Tianjin, China contain high concentrations of PAHs, with total concentrations of 16 PAHs as high as 1520 ng/g dw. Preferential association of the PAHs with the colloids is observed, with the distribution coefficients of PAHs between colloids and bulk soil often above 10. Source diagnostic ratios show that soot-like particles are the main source of PAHs at the site, due to the incomplete combustion of fossil fuels, biomass, and electronic wastes during the e-waste dismantling practices. Due to their small sizes, a large fraction of these soot-like particles can be remobilized as colloids, and this explains the preferential association of PAHs with colloids. Moreover, the colloids-soil distribution coefficients are higher for the low-molecular-weight PAHs than for the high-molecular-weight ones, possibly attributable to the different binding routes/modes of these two groups of PAHs to the particles during combustion. Notably, the preferential association of PAHs with colloids is even more pronounced for the subsurface soils, corroborating that the presence of PAHs in the deeper soils is primarily the results of downward migration of PAH-bearing colloids. The findings highlight the important role of colloids as a vector for the subsurface transport of PAHs at e-waste recycling sites, and call for further understanding of colloid-facilitated transport of PAHs at e-waste recycling sites.

Construction of Models To Predict the Effectiveness of E-Waste Control through Capture of Volatile Organic Compounds and Metals/Metalloids Exposure Fingerprints: A Six-Year Longitudinal Study

The significant health implications of e-waste toxicants have triggered the global tightening of regulation on informal e-waste recycling sites (ER) but with disparate governance that requires effective monitoring. Taking advantage of the opportunity to implement e-waste control in the Guiyu ER since 2015, we investigated the temporal variations in levels of oxidative DNA damage, 25 volatile organic compound metabolites (VOCs), and 16 metals/metalloids (MeTs) in urine in 918 children between 2016 and 2021 to demonstrate the effectiveness of e-waste control in reducing population exposure risks. The hazard quotients of most MeTs and levels of 8-hydroxy-2'-deoxyguanosine in children decreased significantly during this time, indicating that e-waste control effectively reduces the noncarcinogenic risks of MeT exposure and levels of oxidative DNA damage. Using mVOC-derived indexes as a feature, a bagging-support vector machine algorithm-based machine learning model was constructed to predict the extent of e-waste pollution (EWP). The model exhibited excellent performance with accuracies >97.0% in differentiating between slight and severe EWP. Five simple functions established using mVOC-derived indexes also had high accuracy in predicting the presence of EWP. These models and functions provide a novel human exposure monitoring-based approach for assessing e-waste governance or the presence of EWP in other ERs.

Polycyclic Aromatic Hydrocarbons in Air and Dust Samples from Vietnamese End-of-life Vehicle Processing Workshops: Contamination Status, Sources, and Exposure Risks

Concentrations of 18 unsubstituted polycyclic aromatic hydrocarbons (PAHs) and 11 methylated derivatives (Me-PAHs) were measured in polyurethane foam-based passive air (PUF-PAS) and settled dust samples collected from end-of-life vehicle (ELV) processing workshops in northern Vietnam. Concentrations of total 29 PAHs ranged from 42 to 95 (median 57) ng/m³ and from 860 to 18,000 (median 5700) ng/g in air and dust samples, respectively. PAH levels in ELV air and dust samples were 1.5 ± 0.4 and 9.4 ± 7.9 times higher than levels found in a control house, suggesting ELV processing as potential PAH emission sources. Concentrations and proportions of Me-PAHs in total PAHs of the ELV air (26% ± 7%) and dust (41% ± 14%) were higher than those found in control house (18% in both air and dust). The occurrence of PAHs and Me-PAHs in the ELV workshops are attributed to not only pyrogenic but also petrogenic sources (i.e., improper treatment and management of fuels, lubricants, and vehicle oils).

PM-bound polycyclic aromatic compounds (PACs) in two large-scale petrochemical bases in South China: Spatial variations, sources, and risk assessment

Polycyclic aromatic compounds (PACs) are potential pollutants emitted from the petrochemical industry, whereas their occurrence and sources in petrochemical regions are still poorly known. The present study revealed the spatial variations, compositional profiles, sources and contributions, and health risks of PM-bound PACs in two large-scale petrochemical bases (GDPB and HNPB) in South China. The concentrations of parent polycyclic aromatic hydrocarbons (PAHs) were 7.14 ± 3.16 ng/m³ for ∑₁₈PAHs and 0.608 ± 0.294 ng/m³ for the PAHs with molecular weight of 302 amu (MW302 PAHs) in the GDPB base and 2.55 ± 1.26 ng/m³ and 0.189 ± 0.088 ng/m³ in the HNPB base. Oxygenated PAHs (OPAHs) showed comparable concentrations to the parent PAHs in both the bases and nitrated PAHs (NPAHs) had the lowest mean levels (260 pg/m³ and 59.4 pg/m³ in the two regions). Coronene, 2,8-dinitrodibenzothiophene, and dibenzo[a,e]fluoranthene showed remarkably higher contributions to the PAC and can be PAC markers of the petrochemical industry source. Five sources of PACs were identified respectively in both petrochemical bases by the positive matrix factorization (PMF) model. The vehicle (and ship) traffic exhaust was the primary source of PACs (contributed 33% to the ∑PACs), and the sources related to the coking of coal and heavy petroleum and refinery exhaust were identified in both bases, with contributions of 10-20%. PACs in GDPB also contributed from secondary atmospheric reactions (17.3%) and the usage of sulfur-containing fuels (20.9%), while the aromatics industry made a significant contribution (20.1%) to the PACs in the HNPB region. The cumulative incremental lifetime cancer risks (ILCRs) induced by inhalation of PM-bound PACs in both petrochemical bases were low (10^-8-10^-6). For the sources related to the petrochemical industry, coking activities and the aromatic industry were the significant contributors to the ∑ILCRs in GDPB and HNPB, respectively. This research has implications for further source-targeted control and health risk reduction of PACs in petrochemical regions.

Recent Developments in the Design and Fabrication of Electrochemical Biosensors Using Functional Materials and Molecules

Electrochemical biosensors are superior technologies that are used to detect or sense biologically and environmentally significant analytes in a laboratory environment, or even in the form of portable handheld or wearable electronics. Recently, imprinted and implantable biosensors are emerging as point-of-care devices, which monitor the target analytes in a continuous environment and alert the intended users to anomalies. The stability and performance of the developed biosensor depend on the nature and properties of the electrode material or the platform on which the biosensor is constructed. Therefore, the biosensor platform plays an integral role in the effectiveness of the developed biosensor. Enormous effort has been dedicated to the rational design of the electrode material and to fabrication strategies for improving the performance of developed biosensors. Every year, in the search for multifarious electrode materials, thousands of new biosensor platforms are reported. Moreover, in order to construct an effectual biosensor, the researcher should familiarize themself with the sensible strategies behind electrode fabrication. Thus, we intend to shed light on various strategies and methodologies utilized in the design and fabrication of electrochemical biosensors that facilitate sensitive and selective detection of significant analytes. Furthermore, this review highlights the advantages of various electrode materials and the correlation between immobilized biomolecules and modified surfaces.

Effect-directed analysis for revealing aryl hydrocarbon receptor agonists in sediment samples from an electronic waste recycling town in China

Exposure to electronic and electrical waste (e-waste) has been related to a few adverse health effects. In this study, sediment samples from an e-waste recycling town in China were collected, and aryl hydrocarbon receptor (AhR) agonists in the samples were identified using an effect-directed analysis (EDA) strategy. The CBG2.8D cell line reporter gene bioassay was used as a toxicity test, while suspect screening against chemical databases was performed for potential AhR agonist identification where both gas chromatography- and liquid chromatography-high resolution mass spectrometry analyses were run. When the original sample extract showed high AhR-mediated activity, sample fractionation was performed, and fractions exhibiting high bioactivity were chemically analyzed again to reveal the corresponding AhR agonists. In total, 23 AhR agonists were identified, including 14 commonly known ones and 9 new ones. Benzo [k]fluoranthene and 6-nitrochrysene were the dominant AhR agonists, covering 16-71% and 2.7-12%, respectively, of the AhR activation effects measured in the parent extracts. The newly identified AhR-active chemicals combined explained 0.13-0.20% of the parent extracts' effects, with 7,12-dimethylbenz [a]anthracene and 8,9,11-trimethylbenz [a]anthracene being the major contributors. A diagnostic isomer ratio analysis of polycyclic aromatic hydrocarbons suggested that the major source of AhR agonists identified in these e-waste related sediment samples were probably petroleum product combustion and biomass combustion. In the future, for a more comprehensive AhR agonist investigation, in-house chemical synthesis and purification, and, when necessary, a secondary sample fractionation, would be beneficial.

Origin of metabolites diversity and selectivity of P450 catalyzed benzo[a]pyrene metabolic activation

Polycyclic Aromatic Hydrocarbon (PAHs) presents one of the most abundant class of environmental pollutants. Recent study shows a lab-synthesized PAHs derivative, helicenium, can selectively kill cancer cells rather than normal cells, calling for the in-depth understanding of the metabolic process. However, the origin of metabolites diversity and selectivity of P450 catalyzed PAHs metabolic activation is still unclear to a great extent. Here we systematically investigated P450 enzymes catalyzed activation mechanism of a representative PAHs, benzo[a]pyrene (BaP), and found the corresponding activation process mainly involves two elementary steps: electrophilic addition and epoxidation. Electrophilic addition step is evidenced to be rate determining step. Two representative binding modes of BaP with P450 were found, which enables the electrophilic addition of Heme (FeO) to almost all the carbons of BaP. This electrophilic addition was proposed to be accelerated by the P450 enzyme environment when compared with the gas phase and water solvent. To dig deeper on the origin of metabolites diversity, we built several linear regression models to explore the structural-energy relationships. The selectivity was eventually attributed to the integrated effects of structural (e.g. O-C distance and O-C-Fe angle) and electrostatic parameters (e.g. charge of C and O) from both BaP and P450.

Source Apportionment and Toxic Potency of PM2.5-Bound Polycyclic Aromatic Hydrocarbons (PAHs) at an Island in the Middle of Bohai Sea, China

Polycyclic aromatic hydrocarbons (PAHs) have attracted more attention because of their high atmospheric concentration and toxicity in recent decades. In this study, a total of 60 PM2.5 samples were collected from Beihuangcheng Island in Bohai Sea, China, from August 2017 to March 2018 for analyzing 16 congeners of PAHs (Σ16PAHs). Sources of PAHs were apportioned by a positive matrix factorization (PMF) model and the carcinogenic risk due to exposure to the PAHs was estimated by the toxicity equivalent of BaP (BaPeq). The results showed that the average concentration of Σ16PAHs was 35.3 ± 41.8 ng/m3. The maximum concentration of Σ16PAHs occurred in winter, followed by spring and autumn, and summer. The PMF modeling apportioned the PAHs into four sources, coal combustion, biomass burning, vehicle exhaust, and petroleum release, contributing 43.1%, 25.8%, 24.7%, and 6.39%, respectively. The average ΣBaPeq concentration was 2.32 ± 4.95 ng/m3 during the sampling period, and vehicle exhaust was the largest contributor. The finding indicates that more attention should be paid to reduce the emissions from coal combustion and vehicle exhaust because they were the largest contributors to the PAH concentration in PM2.5 and ΣBaPeq concentration, respectively.