Plant selective uptake of halogenated flame retardants at an e-waste recycling site in southern China

Uptake, Subcellular Distribution, and Metabolism of Decabromodiphenyl Ethane in Vegetables under Different Exposure Scenarios

Decabromodiphenyl ethane (DBDPE), a key alternative to deca-BDE (BDE-209), has been ubiquitous in the receiving ecosystem. However, little is known about its uptake process and fate in plants. Here, the plant absorption, distribution, and metabolism of 14C-DBDPE under two distinct exposure pathways (i.e., soil-root and airborne dust-leaf) were investigated with three vegetables (cherry radish, water spinach, and eggplant). DBDPE was absorbed and primarily accumulated in directly exposed roots and leaves, with translocation factors to other tissues of 0.04-0.77 and 0.73-12.80 × 10-3, respectively. DBDPE in exposed leaves was more difficult to transport as most DBDPE did not enter the interior of the leaves but was stored in waxes (>90%). Furthermore, DBDPE within leaves was found to enter mostly through waxy layer penetration (>97%). The majority of 14C-DBDPE was localized in cell walls (52.6 and 75.6%, respectively) and organelles (22.7 and 45.5%, respectively) of exposed tissues, substantially restricting its in-plant translocation. Debrominated products were detected in exposed roots, but barely found in exposed leaves, as most DBDPE was blocked by the waxy layer. Moreover, DBDPE was stable in soils and dust without degradation. Our findings contribute to a deeper understanding of the environmental fate of DBDPE in soil-plant and airborne dust-plant systems.

Global occurrence and environmental behavior of novel brominated flame retardants in soils: Current knowledge and future perspectives

Since polybrominated diphenyl ethers (PBDEs) are on the list of regulated chemicals, novel brominated flame retardants (NBFRs) have been produced as alternatives and extensively used since the end of the 19th century. A comprehensive assessment of the environmental burden of NBFRs, which are emerging contaminants with bio-toxic and carcinogenic properties, is urgently needed. Given that soil is a major sink for organic pollutants, this study systematically reviewed global data on NBFRs in soil for the period of 1990-2024 via a bibliometric analysis of 70 publications from the Web of Science Core Collection, reaching the following achievements. (1) NBFRs in soils have been reported in 17 countries or regions worldwide, ranging from not detected to 8.46 × 104 ng/g dw, showing an increasing trend over time, with severe contamination in Asia and Australia. (2) NBFR concentrations varied significantly across land use types: manufacturing land > electronic waste disposal areas > urban soil > farmland > forest > remote areas. (3) NBFRs with log KOA > 10 tend to settle from the air into the soil, where they may be absorbed by plant roots and bioaccumulate in the food chain. (4) Organism dietary habits and metabolism, along with the hydrophobicity and molecular weight of NBFRs, contribute to bioaccumulation differences. (5) Successive reductive debromination is the primary degradation pathway for NBFRs, and microorganisms such as the white-rot fungus P. ostreatus show potential for remediating NBFR-contaminated soil. This review clarifies the pollution status of soil NBFRs and provides a solid reference to develop management policies. Future research should focus on studying the transport mechanisms of NBFRs between soil and other media, and assessing the cumulative effects of high trophic level organisms on NBFRs.

Effects of Decabromodiphenyl Ethane and Cadmium Coexposure on Their Bioaccumulation, Oxidative Stress, Root Metabolism, and Rhizosphere Soil Microorganisms in a Soil-Rice System

Decabromodiphenyl ethane (DBDPE) and cadmium (Cd) are typical pollutants in e-waste, seriously threatening crop growth. This study investigated the bioaccumulation and toxicity mechanisms of DBDPE and Cd in a soil-rice system. The results showed that 50 mg/kg DBDPE could reduce the level of accumulation of Cd in rice roots. DBDPE and Cd induced the antioxidant system (SOD, POD, and MDA) in rice seedlings. The combined exposure reduced the contents of carbohydrates, lipids, amino acids, and organic acids. Phenylalanine and phenylpropanoid metabolisms were identified as the key detoxification metabolic pathways under combined exposure. DBDPE and Cd disrupted the functional cycling of carbon and nitrogen in rhizosphere soil, while Gemmatimonadetes, Actinobacteria, and Bacteroidetes were the key bacterial groups responding to DBDPE and Cd stress. This work provides data for the toxicity risk evaluation of DBDPE and Cd combined exposure to food crops.

Uptake and translocation of brominated flame retardants in tomato plants (Solanum lycopersicum L.): Results from a standard soil-based biotest

The uptake and translocation of four polybrominated diphenyl ethers (PBDEs) and four novel brominated flame retardants (NBFRs) in tomato plants (Solanum lycopersicum L.) were investigated via the RHIZOtest, a standard soil-based biotest, optimized for organic compounds. Tomato plants were exposed to soil samples spiked with 0 (i.e. control), 5.00 or 50.00 ng g-1dw of each compound. Compared of those of the control, exposure to increasing spiking concentrations resulted in average reductions of 13% and 26% (w/w) in tomato plant biomass. Higher concentrations of NBFRs were analyzed both in roots, ranging from 0.23 to 8.01 ng g-1dw for PBDEs and from 1.25 to 18.51 ng g-1dw for NBFRs, and in shoots, ranging from 0.09 to 5.58 ng g-1dw and from 0.47 to 7.78 ng g-1dw for PBDEs and NBFRs, respectively. This corresponded to an average soil uptake of 5% for PBDEs and 9% for NBFRs at the lower soil-spiking level, and 3% for PBDEs and 6% for NBFRs at the higher soil spiking level. Consequently, among both initial spiking levels, the soil-root concentration factor (RCF) values were lower on average for PBDEs (0.13 ± 0.05 g dw soil g-1dw roots) than for NBFRs (0.33 ± 0.16 g dw soil g-1dw roots). Conversely, nondifferent values of the root-shoot transfer factor (TF) were calculated for both PBDEs (0.54 ± 0.13 g dw roots g-1dw shoots) and NBFRs (0.49 ± 0.24 g dw roots g-1dw shoots). The differences and similarities reported in the RCF and TF between and within the two groups of compounds can be explained by their properties. The calculated RCF and TF values of the PBDEs exhibited a decreasing trend as the number of bromine atoms increased. Additionally, a robust negative linear correlation was observed between RCF values and the respective logKow values for the PBDEs, at both soil-spiking levels. The root uptake of NBFRs exhibited a negative correlation with their hydrophobicity; however, this was not observed in the context of root-to-shoot transfer. The presence of a second aromatic ring appears to be the key factor influencing the observed variations in NBFRs, with biphenyl NBFRs (BTBPE and DBDPE) characterized by lower uptake and reduced translocation potential than monophenyl PBEB and HBB. Understanding the transfer of these compounds to crops, especially near plastic recycling waste sites, is crucial for understanding the risks of their potential inclusion in the human food chain.

Single injection by LC-ESI-MS/MS for simultaneous determination of organophosphate tri- and di-esters in plant tissue based on ultrasonic-assisted sequential extraction and single-step purification

A novel methodology based on ultrasonic-assisted sequential extraction, dispersive-SPE purification, and single-injection on liquid chromatography-tandem mass spectrometry (LC-MS/MS) is proposed, for the first time, to simultaneously measure 14 tri-OPEs and 9 di-OPEs in plant tissues. The samples were successively ultrasonicated with a mixture of hexane:dichloromethane (1:1, v/v) and 8% acetic acid in acetonitrile for extracting tri- and di-OPEs purified with graphitized carbon black and quantitated on LC-MS/MS at the same time. The recoveries of targeted tri- and di-OPEs in the matrix spike ranged from 66% to 120% and 71% to 110% respectively. The proposed method was validated by processing eight types of common vegetables including spinach (Spinacia oleracea L.), lettuce (Lactuca sativa), carrot (Daucus carota var. sativa Hoffm.), sweet potato (Solanum tuberosum L.), cucumber (Cucumis sativus L.), tomato (Solanum lycopersicum L.), green beans (Phaseolus vulgaris), and cowpeas (Vigna unguiculata), with the recoveries of surrogates ranging from 84% to 98%.

Polybrominated diphenyl ethers in dust, hair and urine: Exposure, excretion

Polybrominated diphenyl ethers (PBDEs) have been detected in various environmental media and human tissues. PBDEs concentrations in dust from college buildings and homes and in paired hair and urine samples from students were determined. This is of great significance to explore the accumulation and excretion patterns of PBDEs in the human body. The median PBDEs concentrations in the dust (College: 84.59 ng/g; Home: 170.32 ng/g) and hair (undergraduate: 6.16 ng/g; Home: 3.25 ng/g) samples were generally lower than were found in the majority of previous studies. The PBDEs concentrations in the hair and urine samples were subjected to principal component analysis, and the results combined with the PBDEs detection rates confirmed that hair is a useful non-invasive sampling medium for assessing PBDEs exposure and the risks posed. Body mass indices (BMIs) were used to divide students who had not been exposed to large amounts of PBDEs into groups. Body fat percentage is an important factor affecting the accumulation of PBDE in the human body. Environmental factors were found to affect the PBDEs concentrations in the hair and urine samples less for normal-weight students (BMI≤24) than overweight students (BMI>24). Short-term environmental changes to more readily affect the PBDEs concentrations in the tissues of the normal-weight than overweight students. PBDEs with seven or more bromine substituents were found not to be readily excreted in urine. Performing molecular docking simulations of the binding of isomers BDE-99 and BDE-100 to megalin. The binding energy was higher for BDE-100 and megalin than for BDE-99 and megalin, meaning BDE-99 would be more readily excreted than BDE-100.

Uptake, accumulation, and translocation of organophosphate esters and brominated flame retardants in water hyacinth (Eichhornia crassipes): A field study

Mechanisms underlying the plant uptake, accumulation, and translocation of organophosphate esters (OPEs) and brominated flame retardants (BFRs) in field environments remain ambiguous. To better understand these processes, we selected a typically polluted river with steady flow and rampant water hyacinth (Eichhornia crassipes) and investigated 25 OPEs and 23 BFRs in 24 sets of matched water-plant samples. Both OPEs and BFRs showed high or ultra-high levels in field water hyacinths, statistically positive water-plant/root concentration correlations, and dominant distributions in the roots. Passive root uptake was the dominant route for OPEs and BFRs to enter the water hyacinth. Both OPEs and BFRs in water hyacinth exhibited acropetal translocation from the root and possible basipetal translocation from the leaf. The accumulation and translocation of OPEs in water hyacinth were significantly affected by their substituents and structures, including the chlorination degree, alkyl chain length, side chain, and methylation degree of aryl-substituted OPEs. The translocation of BFRs in water hyacinth also showed close association with their bromination degree, but their accumulation in roots showed anomaly, indicating possible transformations. Overall, the enrichment and behavior of OPEs and BFRs in water hyacinth seemed to be mainly controlled by physicochemical parameters. OPE/BFR concentrations in total suspended particulate (TSP), TSP-associated organic carbon content, TSP concentration, and plant biomass all showed significant effects on their root accumulation and translocations in water hyacinth. This study provides rare field evidences and novel insights into the basipetal translocation of OPEs and BFRs in plants.

Composition profiles of halogenated flame-retardants in the surface soils and in-situ cypress leaves from two chemical industrial parks

There is limited information available regarding the investigation on typical organic pollutants between the soil and in-situ grown plant leaves. This study is to reveal whether the pollution characteristics of soil and leaves can reflect the long-term and short-term pollution situation, and to find the differences between halogenated flame-retardants in the surface soils and in-situ cypress leaves. Polybrominated diphenyl ethers (PBDEs), dechlorane plus (DP), and decabromodiphenyl ethane (DBDPE) in were investigated in two different industrial parks, which were located at the largest brominated flame-retardant-manufacturing center in Weifang, China. These chemicals were frequently detected with high median concentrations of PBDEs (1.22 × 10³ ng/g) and DBDPE (227 ng/g) in the soil samples, and DBDPE (881 ng/g) and PBDEs (461 ng/g) in the in-situ cypress leaves. The DP concentration was 1-4 orders of magnitude lower than the other two chemicals in both the matrices. Different composition profiles of the chemicals in soil and cypress leaves were observed. The PBDEs and DBDPE were found to be the predominant species in soils and cypress leaves, respectively. In comparison, the LG industrial parks had higher concentrations of PBDEs and DBDPE in both the soils and cypress leaves. No significant correlations were observed for these chemicals between the soil and leaf samples, although significant correlations (p < 0.05) were observed for several PBDE congeners among all samples from the industrial parks and a separate industrial park. The results indicated that the soil was not the important source of these chemicals in leaves. A large proportion of DBDPE was preferentially present in cypress leaves, which revealed the situation of recent pollution. The results deepen the understanding of chemical distribution characteristics among different environmental matrices in soils and leaves.

A Pilot Study on the Concentration, Distribution and Bioaccumulation of Polybrominated Diphenyl Ethers (PBDEs) in Tissues and Organs of Grassland Sheep

Polybrominated diphenyl ether (PBDE) concentrations in various tissues and organs of grassland sheep from Inner Mongolia, China, were determined. The abilities of PBDEs binding to ovine serum albumin (OSA) and Cytochrome P450 enzyme (CYP3A24) were assessed by fluorescence spectroscopy and molecular docking simulations. The PBDE concentrations in the sheep tissue and organ samples were 33.4-167 pg/g dw. The distribution of PBDEs in sheep organs and tissues is affected not only by the function of organs and tissues, but also by the characteristics of PBDEs. Adipose tissue tends to bioaccumulate more-brominated BDEs (BDE-154, -153, and -183), but muscle tissues and visceral organs mainly bioaccumulate less-brominated BDEs. The distribution of PBDEs in visceral organs is mainly affected by the transport of ovine serum albumin (OSA) and the metabolism of CYP3A24 enzyme. The distribution of PBDEs in adipose tissue and brain is mainly affected by their logKOW.

Thermal treatment of decabrominated diphenyl ether in its highly contaminated soil in Taiwan

Polybrominated diphenyl ethers (PBDEs) were commonly used flame retardants in the world, while some of PBDEs have been listed as persistent organic pollutants (POPs). Decabrominated diphenyl ether (BDE-209) was the most commercially used PBDEs. A farm near the factory located in Northern Taiwan was highly contaminated with BDE-209. Since PBDEs in the contaminated soils can be uptake by crops shown in our previous studies and could be potentially consumed by humans, it is very important to establish a feasible treatment method for PBDE remediation in this contaminated farm. Thermal treatment of PBDEs in soil was studied. The initial concentration of BDE-209 in contaminated soil was 1.472 mg/kg. A series of thermal experiments under different operating conditions including various temperature (105, 150, 200, 250, 300, 350, 400 and 450 °C), holding time (10, 20 and 30 min), heating rate (5, 10, 20 and 40 °C/min), and soil amount (10, 100, 1000 and 2000 g) were investigated. The optimal heating conditions for thermal treatment of contaminated soil were heating at 450 °C for 30 min with a heating rate of 10 °C/min. Under this condition, the removal of BDE-209 in the different weights of contaminated soil was tested. The soils in the contaminated farm were tested to further evaluate the feasibility of remediating the on-site PBDE contaminated soil through thermal treatment, suggesting that the holding time was extended to 2 h for the field-scale contaminated soil. The results showed that BDE-209 had been removed to below the detection limit in on-site soil. This investigation is the first study using thermal treatment to remediate soils really contaminated with PBDEs.

Plant accumulation and transformation of brominated and organophosphate flame retardants: A review

Plants can take up and transform brominated flame retardants (BFRs) and organophosphate flame retardants (OPFRs) from soil, water and the atmosphere, which is of considerable significance to the geochemical cycle of BFRs and OPFRs and their human exposure. However, the current understanding of the plant uptake, translocation, accumulation, and metabolism of BFRs and OPFRs in the environment remains very limited. In this review, recent studies on the accumulation and transformation of BFRs and OPFRs in plants are summarized, the main factors affecting plant accumulation from the aspects of root uptake, foliar uptake, and plant translocation are presented, and the metabolites and metabolic pathways of BFRs and OPFRs in plants are analyzed. It was found that BFRs and OPFRs can be taken up by plants through partitioning to root lipids, as well as through gaseous and particle-bound deposition to the leaves. Their microscopic distribution in roots and leaves is important for understanding their accumulation behaviors. BFRs and OPFRs can be translocated in the xylem and phloem, but the specific transport pathways and mechanisms need to be further studied. BFRs and OPFRs can undergo phase I and phase II metabolism in plants. The identification, quantification and environmental fate of their metabolites will affect the assessment of their ecological and human exposure risks. Based on the issues mentioned above, some key directions worth studying in the future are proposed.

Uptake and translocation of polybrominated diphenyl ethers in the rhizosphere soil-crop-atmosphere system in e-waste dismantling areas in Taizhou, China

Air, crop, and rhizosphere soil samples were collected from e-waste dismantling areas in Taizhou City (Zhejiang Province, China). The mean PBDEs (Polybrominated diphenyl ethers) concentrations in air in the Fengjiang and Binhai areas were 27.8 and 25.1 pg m^-3, respectively (no significant difference, P > 0.05). The mean PBDE concentrations in rhizosphere soil from Fengjiang and Binhai were 9.19 × 10⁴ and 1.34 × 10³ pg g^-1 dry weight, respectively (no significant difference, P > 0.05). The mean PBDE concentrations in the crop samples from Fengjiang and Binhai were 1.38 × 10³ and 6.64 × 10² pg g^-1 dry weight, respectively (no significant difference, P > 0.05). PBDEs with≥6 bromine atoms (BDEs-153, -154, -183, and -190) were not translocated from the crop roots to other tissues. PBDEs were taken up by crops selectively. The root epidermis effectively prevented PBDEs from entering edible crop parts and kept the PBDE concentrations in edible roots low. PBDEs with≤5 bromine atoms (BDEs-15, -28, -47, -66, -85, -99, and -100) were selectively enriched from the rhizosphere soil into crop roots, but PBDEs with more bromine substituents were not transferred from the rhizosphere soil to the crop roots. PBDEs with≥6 bromine atoms were selectively enriched from the atmosphere into crop leaves. Crop roots and leaves took up PBDEs with ortho bromine substituents more readily than PBDEs with meta bromine substituents because the octanol-water partition coefficients are lower for ortho-brominated than meta-brominated PBDEs.

Polybrominated Diphenyl Ethers and Heavy Metals in a Regulated E-Waste Recycling Site, Eastern China: Implications for Risk Management

Serious pollution of multiple chemicals in irregulated e-waste recycling sites (IR-sites) were extensively investigated. However, little is known about the pollution in regulated sites. This study investigated the occurrence of 21 polybrominated diphenyl ethers (PBDEs) and 10 metals in a regulated site, in Eastern China. The concentrations of PBDEs and Cd, Cu, Pb, Sb, and Zn in soils and sediments were 1-4 and 1-3 orders of magnitude lower than those reported in the IR-sites, respectively. However, these were generally comparable to those in the urban and industrial areas. In general, a moderate pollution of PBDEs and metals was present in the vegetables in this area. A health risk assessment model was used to calculate human exposure to metals in soils. The summed non-carcinogenic risks of metals and PBDEs in the investigated soils were 1.59-3.27 and 0.25-0.51 for children and adults, respectively. Arsenic contributed to 47% of the total risks and As risks in 71.4% of the total soil samples exceeded the acceptable level. These results suggested that the pollution from e-waste recycling could be substantially decreased by the regulated activities, relative to poorly controlled operations, but arsenic pollution from the regulated cycling should be further controlled.

Cost-benefit analysis of metal recovery from e-waste: Implications for international policy

The e-waste problem needs be tackled under a global framework, based upon the understanding that e-waste is a global issue and thus a shared responsibility. To illustrate this point, a cost-benefit analysis of metal recovery from e-waste was conducted with Europe, North America and China as representative regions of e-waste producers. The final profit associated with the entire e-waste recycling process was estimated by deducing the energy costs of metal recovery from the revenues of the manually dismantling stage and the metal recovery stage. Then, the potential job opportunities were estimated based on the final profit from the local e-waste recycling and average wage per year. Overall, profits of manually dismantling 1 ton of e-waste varied widely, but the final profits were positive. The potential job opportunities generated by local e-waste recycling ranged from 4.65 × 10⁵ person/year for North America to 2.03 × 10⁶ for China person/year. According to our study, the environmental load of 1 kg of e-waste would be 1-9 USD, indicating that this is the cost required to offset the environmental consequences of each kilogram of e-waste. By applying environmental load to per capita, the concept can act as a tool to encourage countries to fairly share the environmental responsibility of e-waste based on their e-waste generation. Based on this, we propose an e-waste emissions trading system that set a cap on the total amount of e-waste that could be generated globally and per country, to reduce e-waste and carbon emissions.

Field study on bioaccumulation and translocation of polybrominated diphenyl ethers in the sediment-plant system of a national nature reserve, North China

Polybrominated diphenyl ethers (PBDEs) are the ubiquitous contaminants in the coastal wetlands, with high persistence and toxicity. Environmental behaviors of PBDEs in sediment-plant system is a hot research area, where much uncertainties still occurred in field environment. In this study, the sediments and Suaeda heteroptera were synchronously collected to investigate the bioaccumulation and translocation of PBDEs in Liaohe coastal wetland. Mean concentrations of PBDEs in sediments, roots, stems and leaves were 8.37, 6.64, 2.42 and 1.40 ng/g d.w., respectively. Tissue-specific accumulation of PBDEs were detected in Suaeda heteroptera, with predominant accumulation in roots. Congener patterns of PBDEs were similar between sediments and roots, demonstrating root uptake as the key pathway of PBDE bioaccumulation. The proportions of lower brominated congeners increased from roots to leaves, implying the congener-specific translocation. Meanwhile, the lower brominated congeners exhibited higher sediment-tissue bioaccumulation (AFs) and translocation factors (TFs) compared to higher brominated congeners in Suaeda heteroptera, further verifying their preferential translocation. AFs and TFs of PBDEs were both not correlated with their log K_ow, which was inconsistent with those of laboratory studies, reflecting the complicated behaviors of PBDEs in field environment. This is the first comprehensive report on bioaccumulation and translocation of PBDEs within Suaeda heteroptera in Liaohe coastal wetland.

Effects of tourmaline catalyzed Fenton-like combined with bioremediation on the migration of PBDEs in soil-plant systems: Soil properties and physiological response of lettuce and selective uptake of PBDEs

A series of pollutants can be removed from soil using a Fenton-like oxidation and biological treatment. As a natural mineral, tourmaline has been used for as a material of Fenton-like reaction. In the present study, the risks of remediation technology tourmaline catalyzed Fenton-like reaction (TCFR) combined with Phanerochaete chrysosporium (TCFR + P) were assessed through measuring soil properties, physiological response of plant, and PBDEs migration from soil to plant. Batch pot experiments showed that the silicon contents, specific surface area and soil pore size of soil in TCFR and 5%TCFR + P groups increased obviously. TCFR and TCFR + P treatments promoted the lettuce growth compared to control. Moreover, chlorophyll content of lettuce in 2%TCFR + P and 5%TCFR + P group increased by 46.74% and 44.57% than that in the CK, respectively. The treatment of 2%TCFR decreased the total concentration of PBDEs in rhizosphere soil and non-rhizosphere soil by 52.0.2% and 64.17%, respectively, after 60 days compared to the soil of CK, and did not prompt the uptake of lower-brominated PBDEs by lettuce. TCFR and TCFR + P can alter the migration of BDE isomers from soil to plant, the ratio of BDE99/BDE100 in lettuce shoots decreased slightly. BDE-99/BDE-100 ratios in the shoots were lower than those in the roots, while BDE153/BDE154 ratios were higher than 1.0 and ratios in shoots were higher than those in roots. Therefore, our findings illustrated that the TCFR could be applied to remediate the agricultural soil, considering the appropriate doses of tourmaline.

Distribution and Chiral Signatures of Polychlorinated Biphenyls (PCBs) in Soils and Vegetables around an e-Waste Recycling Site

The distribution and composition of polychlorinated biphenyls (PCBs) within soil-plant systems around a notorious e-waste recycling site were investigated. The average total PCB concentrations in rhizospheric soils (RSs) and nonrhizospheric soils (NRSs) were 2160 and 1270 pg g^-1 dry weight (DW), respectively. PCBs were more enriched in RS than NRS for most vegetable species. PCB accumulation in plant tissues varied greatly among plant cultivars, ranging from 4020 to 14 500 pg g^-1 DW in shoots and from 471 to 24 400 pg g^-1 DW in roots. The compositions of PCBs in soil and plants showed that hexa- and hepta-chlorinated PCBs were preferentially accumulated in soils, while tri- and tetra-PCBs were abundant in plant tissues. These results indicated that low-chlorinated PCBs might be prone to accumulation and transfer within plants, which was confirmed by the relationship between the root concentration factor and octanol-water coefficient. The first eluting enantiomers of PCB 84 and PCB 95 were preferentially transferred between the soil and plants, while the stereoselectivity of PCB 136 varied among plant species. A significant difference in enantiomeric fractionation of PCB 84 between the soil and roots indicated that enantiomeric enhancement of PCB 84 occurred during its translocation from soil to root, whereas no such difference was observed in these chiral PCBs during their translocation from the root to the shoot.

Exposure pathways, levels and toxicity of polybrominated diphenyl ethers in humans: A review

Polybrominated diphenyl ethers (PBDEs) are extensively used as brominated flame retardants (BFRs) in different types of materials, which have been listed as Persistent Organic Pollutants (POPs) by the Stockholm Convention in 2009 and 2017. Due to their ubiquities in the environment and toxicities, PBDEs have posed great threat to both human health and ecosystems. The aim of this review is to offer a comprehensive understanding of the exposure pathways, levels and trends and associated health risks of PBDEs in human body in a global scale. We systematically reviewed and described the scientific data of PBDE researches worldwide from 2010 to March 2020, focusing on the following three areas: (1) sources and human external exposure pathways of PBDEs; (2) PBDE levels and trends in humans; (3) human data of PBDEs toxicity. Dietary intake and dust ingestion are dominant human exposure pathways. PBDEs were widely detected in human samples, especially in human serum and human milk. Data showed that PBDEs are generally declining in human samples worldwide as a result of their phasing out. Due to the common use of PBDEs, their levels in humans from the USA were generally higher than that in other countries. High concentrations of PBDEs have been detected in humans from PBDE production regions and e-waste recycling sites. BDE-47, -153 and -99 were proved to be the primary congeners in humans. Human toxicity data demonstrated that PBDEs have extensively endocrine disruption effects, developmental effects, and carcinogenic effects among different populations.

Polybrominated diphenyl ethers and alternative halogenated flame retardants in mangrove plants from Futian National Nature Reserve of Shenzhen City, South China

Halogenated flame retardants (HFRs) are ubiquitous in the environment, but little information is available about the bioaccumulation of HFRs in mangrove plants. In this study, three mangrove plant species were collected from Futian National Nature Reserve of Shenzhen City, South China to investigate the bioaccumulation of polybrominated diphenyl ethers (PBDEs) and several alternative halogenated flame retardants (AHFRs), including decabromodiphenyl ethane (DBDPE), 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), hexabromobenzene (HBB), pentabromotoluene (PBT), tetrabromop-xylene (pTBX), pentabromoethylbenzene (PBEB) and dechlorane plus (DP). The mean concentrations of PBDEs, DBDPE, BTBPE, pTBX, PBT, PBEB, HBB and DP in mangrove plant species were 2010, 1870, 36.2, 18.7, 40.1, 17.8, 9.68 and 120 pg g^-1 dry weight, respectively. PBDEs were the dominant HFRs in mangrove plant tissues, followed by DBDPE. The relative abundance of BDE 209 in three mangrove plant tissues were much lower than those in sediments. Significant negative relationships between log root bioaccumulation factors and log K_ow, and between log TF_r-s (from root to stem) and log K_ow were observed, indicating that HFRs with low hydrophobicity were easily absorbed by mangrove roots and stems. A positive correlation between log TF_s-l (from stem to leaf) and log K_ow were found, suggesting that air-leaf exchange may occur in mangrove plants. This study highlights the uptake of HFRs by mangrove plants, which can be used as remediation for HFRs contamination in the environment.

Concentrations and uptake pathways of polychlorinated biphenyls from soil to grass

Field coupled samples in soil and grass were collected to determine the concentrations and identify the uptake pathways of PCBs into the grass at a pasture from Scotland, UK. Concentrations of indicator PCBs (∑₇PCBs) in soils ranged from 0.20 to 0.88 ng g^-1 dw (dry weight), with a mean of 0.33 ng g^-1 dw, and in grass ranged from 0.20 to 2.14 ng g^-1 dw, with a mean of 0.48 ng g^-1 dw. The comprehensive factors of low concentrations and detection rate (PCB28: 18.8%; PCB52: 37.5%) of PCBs in soil, as well as continuously declined air concentrations of PCBs in the UK since the 1990s suggested that the secondary emission from the soil is becoming the supplied source of PCBs to air and grass. The significant correlations between bioconcentration factor (BCF) values and the log K_OW (R = -0.850, p < 0.05) and log K_OA (R = -0.860, p < 0.05) of indicator PCB congeners were found in the present study, indicating that these two parameters are likely to affect the bioaccumulation and uptake of grass. A generic one-compartment model was employed to identify uptake pathways of grass and evaluate the uptake amounts for PCBs. This suggested that the most important pathway for uptake of PCBs by grass was at the aerial part, and the difference of PCBs concentrations between leaves and roots was about four orders of magnitude. Removing and risk transfer of PCBs or other organic pollutants by grass need to be investigated and assessed further.

Concentration, uptake and human dietary intake of novel brominated flame retardants in greenhouse and conventional vegetables

The possible adverse effects of organic pollutants entering vegetables have attracted increasing attention in recent years. However, research on the behavior of novel brominated flame retardants (NBFRs) in soil-vegetable systems is still limited. This work was initiated to investigate the uptake of seven representative NBFRs by vegetables from bulk soil and suspended soil particles under greenhouse and conventional conditions. The mean concentrations of the sum of seven NBFRs (Σ₇ NBFRs) were 2.8 and 3.8 ng g^-1 dw in greenhouse tomatoes and cucumbers, respectively, and 1.1 and 1.7 ng g^-1 dw in conventional tomatoes and cucumbers, respectively. Greenhouse vegetables had higher concentrations of Σ₇ NBFRs than conventional vegetables. The root bioaccumulation factors (RBCFs) of tomatoes and cucumbers in response to NBFRs ranged from 0.6 to 6.3. The range of fruit bioaccumulation factors (FBCFs) was 0.3-7.0. The bioaccumulation factors (BCFs) in greenhouse vegetables were significantly higher than those in conventional vegetables, indicating that greenhouses increased the uptake of NBFRs by vegetables. To address human dietary exposure to NBFRs, the estimated dietary intake (EDI) and the amounts available for human absorption (EDI_ba) were calculated using vegetable consumption and gastrointestinal absorption, respectively. The mean EDI values of NBFRs from greenhouse and conventional tomato consumption were 344 ng d^-1 and 109 ng d^-1, respectively. The mean EDI values of NBFRs from greenhouse and conventional cucumber consumption were 445 ng d^-1 and 217 ng d^-1, respectively. The higher EDI values of NBFRs implied that consuming greenhouse vegetables was associated with higher health risks than consuming conventional vegetables. The mean EDI_ba values of the DBDPEs were 68 ng d^-1 and 46 ng d^-1 for tomatoes and cucumbers, respectively, and were significantly different from the EDI values due to lower bioaccessibility. Gastrointestinal absorption should not be neglected during risk assessments of human exposure to pollutants.

Dechlorane plus in greenhouse and conventional vegetables: Uptake, translocation, dissipation and human dietary exposure

In an attempt to evaluate the behavior of Dechlorane plus (DP) in soil-vegetable systems, this work investigated the uptake and translocation of DP by vegetables and the dissipation of DP in soil under greenhouse and conventional conditions. To address human dietary exposure to DP, estimated dietary intake via vegetable consumption was calculated. The uptake potential indexes of DP from soil into root for tomato and cucumber cultivated under different conditions ranged from 0.089 to 0.71. The ranges of uptake potential indexes of DP from resuspended soil particles into stem, leaf and fruit were 0.68-0.78, 0.27-0.42 and 0.39-0.75, respectively. The uptake potential indexes in greenhouse vegetables were generally higher than those in conventional vegetables when the vegetables had been planted in contaminated soil, indicating that greenhouse enhanced the uptake of DP with a high soil concentration by vegetables. The translocation factor (TF) values of DP in vegetables were in the range of 0.022-0.17, indicating that DP can be transported from root to fruit even though it has a high octanol water partition coefficient (K_OW). The half-lives of DP dissipation in soil ranged from 70 to 102 days. The dissipation of DP in greenhouse soil was slightly slower than that in conventional soil. Higher estimated dietary intake (EDI) values of DP via greenhouse vegetables were observed due to the higher concentration of DP in greenhouse vegetables than conventional vegetables. These results suggested that greenhouses should not be adopted for vegetable production in contaminated regions.

Translocation of polybrominated diphenyl ethers from field-contaminated soils to an edible plant

Polybrominated diphenyl ethers (PBDEs), recognised emerging contaminants, widely exist and persist in the environment. Samples were taken from a heavily contaminated farm in Taiwan located near a factory known to regularly use PBDEs. Sweet potato vines (Ipomoea batatas L., a commonly consumed vegetable in Asia) growing in the surrounding farmlands were found to contain a high concentration of PBDEs of 19.36 ng/g. The possibility of PBDEs translocation into sweet potato vines from soil samples was evaluated. To prevent the PBDEs from air through that factory, the pot experiments were performed in a greenhouse, which showed that the PBDEs concentration of 24 congeners (tri- through deca-BDE) in the sweet potato vine after 14-days cultivation was 29.90 ng/g, 40-times higher than that in the contaminated soil. After another 14-days, the PBDE concentration decreased to 12.30 ng/g as high-brominated PBDEs were transformed to medium- and/or low-brominated PBDEs in the sweet potato vine. The bioconcentration factor (BCF) values exceeded 20.0 for most of the deca-, nona-, and octa-BDEs but BCFs were below 18.9 for the rest of the medium- and low-brominated PBDEs. Our results demonstrate that high-brominated PBDEs can translocate into leafy vegetables from soils, and sweet potato vines tend to accumulate high-brominated PBDEs into their edible parts.

PBDE emission from E-wastes during the pyrolytic process: Emission factor, compositional profile, size distribution, and gas-particle partitioning

Polybrominated diphenyl ether (PBDE) pollution in E-waste recycling areas has garnered great concern by scientists, the government and the public. In the current study, two typical kinds of E-wastes (printed wiring boards and plastic casings of household or office appliances) were selected to investigate the emission behaviors of individual PBDEs during the pyrolysis process. Emission factors (EFs), compositional profile, particle size distribution and gas-particle partitioning of PBDEs were explored. The mean EF values of the total PBDEs were determined at 8.1 ± 4.6 μg/g and 10.4 ± 11.3 μg/g for printed wiring boards and plastic casings, respectively. Significantly positive correlations were observed between EFs and original addition contents of PBDEs. BDE209 was the most abundant in the E-waste materials, while lowly brominated and highly brominated components (excluding BDE209) were predominant in the exhaust fumes. The distribution of total PBDEs on different particle sizes was characterized by a concentration of finer particles with an aerodynamic diameter between 0.4 μm and 2.1 μm and followed by less than 0.4 μm. Similarly, the distribution of individual species was dominated by finer particles. Most of the freshly emitted PBDEs (via pyrolysis) were liable to exist in the particulate phase with respect to the gaseous phase, particularly for finer particles. In addition, a linear relationship between the partitioning coefficient (K_P) and the subcooled liquid vapor pressure (P_L⁰) of the different components indicated non-equilibrium gas-particle partitioning during the pyrolysis process and suggested that absorption by particulate organic carbon, rather than surface adsorption, governed gas-particle partitioning.

Characterisation and risk assessment of polycyclic aromatic hydrocarbons (PAHs) in soils and plants around e-waste dismantling sites in southern China

Environmental pollution due to primitive e-waste dismantling activities has been intensively investigated over the last decade in the south-eastern coastal region of China. In the present study, we investigated the distribution and composition of polycyclic aromatic hydrocarbons (PAHs) in soils and plants around e-waste recycling sites in Longtang, Guangdong province, South China. The results indicated that PAH concentrations in rhizosphere soil and non-rhizosphere soil were in the range of 133 to 626 ng/g and 60 to 816 ng/g, respectively, while PAH levels in plant tissue were 96 to 388 ng/g in shoots and 143 to 605 ng/g in roots. PAHs were enriched in rhizosphere soils in comparison with non-rhizosphere soils. The concentrations of PAHs in plant tissues varied greatly among plant cultivars, indicating that the uptake of PAHs by plants is species-dependent. Different profiles of PAHs in the soil and the corresponding plant tissue implied that PAH uptake and translocation by plants were selective.The total daily intakes of PAHs and carcinogenic PAHs through vegetables at the e-waste recycling site were estimated to be 99 and 22 ng/kg/day, respectively, suggesting that potential health risks associated with the consumption of contaminated vegetables should not be ignored.

Occurrence, distribution and bioaccumulation behaviour of hydrophobic organic contaminants in a large-scale constructed wetland in Singapore

This study involved a field-based investigation to assess the occurrence, distribution and bioaccumulation behaviour of hydrophobic organic contaminants in a large-scale constructed wetland. Samples of raw leachate, water and wetland plants, Typha angustifolia, were collected for chemical analysis. Target contaminants included polychlorinated biphenyls (PCBs), organochlorine pesticides (OCP), as well as several halogenated flame retardants (HFRs) and personal care products (triclosan and synthetic musks). In addition to PCBs and OCPs, synthetic musks, triclosan (TCS) and dechlorane plus stereoisomers (syn- and anti-DPs) were frequently detected. Root concentration factors (log RCF L/kg wet weight) of the various contaminants ranged between 3.0 and 7.9. Leaf concentration factors (log LCF L/kg wet weight) ranged between 2.4 and 8.2. syn- and anti-DPs exhibited the greatest RCF and LCF values. A strong linear relationship was observed between log RCF and octanol-water partition coefficient (log K_OW). Translocation factors (log TFs) were negatively correlated with log K_OW. The results demonstrate that more hydrophobic compounds exhibit higher degrees of partitioning into plant roots and are less effectively transported from roots to plant leaves. Methyl triclosan (MTCS) and 2,8-dichlorodibenzo-p-dioxin (DCDD), TCS degradation products, exhibited relatively high concentrations in roots and leaves., highlighting the importance of degradation/biotransformation. The results further suggest that Typha angustifolia in this constructed wetland can aid the removal of hydrophobic organic contaminants present in this landfill leachate. The findings will aid future investigations regarding the fate and bioaccumulation of hydrophobic organic contaminants in constructed wetlands.