[Show abstract][Hide abstract] ABSTRACT: Polybrominated diphenyl ethers (PBDEs), methoxylated PBDEs (MeO-PBDEs), and hydroxylated PBDEs (OH-PBDEs) are widely found in various environmental media, which is of concern given their biological toxicity. In this study, the phytotoxicities of BDE-47, 6-MeO-BDE-47, and 6-OH-BDE-47 to maize (Zea mays L.) were investigated by an in vivo exposure experiment. Results showed that BDE-47, 6-MeO-BDE-47, and 6-OH-BDE-47 inhibited seed germination and seedling development, and elevated malondialdehyde (MDA), carbonyl groups, and phosphorylated histone H2AX levels in maize roots, suggesting the inducement of lipid peroxidation, protein carbonylation, and DNA damage to maize. Exposure to BDE-47, 6-MeO-BDE-47, and 6-OH-BDE-47 caused the overproduction of H2O2, O2(•-), and •OH, and elevated the activities of antioxidant enzymes in the roots. In addition, 6-OH-BDE-47 caused more severe damage and reactive oxygen species (ROS) generation in maize than did BDE-47 and 6-MeO-BDE-47. These results demonstrated the phytotoxicities of BDE-47, 6-OH-BDE-47, and 6-MeO-BDE-47 to maize, and clarified that overproduction of ROS was the key mechanism leading to toxicity. This study offers useful information for a more comprehensive understanding of the environmental behaviors and toxicities of PBDEs, MeO-PBDEs, and OH-PBDEs.
Chemical Research in Toxicology 02/2015; 28(3). DOI:10.1021/tx500484m · 4.19 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Brominated phenols (BPs), a widely used group of emerging flame retardants, are important environmental contaminants and exhibit endocrine disrupting potential. Method for simultaneous determination of tetrabromobisphenol A (TBBPA), tribromophenol (TBP), dibromophenols (DBPs) and monobromophenols (MBPs) in soils using gas chromatography-mass spectrometry analysis (GC/MS) was successfully developed. Cleanup methods for soil extracts including several solid-phase extraction cartridges and different elution solvents were compared and optimized. Florisil cartridge with dichloromethane as the elution reagent was selected for sample cleanup owing to its high and reproducible recoveries of the target analytes in soils. Derivatization conditions were tested and the optimal conditions were obtained with 20 μL silylation reagent at room temperature. The chromatographic separation was optimized with different columns and DB-XLB column was selected for its excellent separation of the analytes. The limits of detection for the target compounds were from 0.04 to 0.19 ng/g. Mean recoveries of the compounds from spiked soils exceeded 84% with a good reproducibility, excepting that the recovery of 2-bromophenol was relatively poor (lower than 55%) due to its instability. The developed method was applied to the determination of the BPs in the soils collected from e-waste sites. The contents of BPs in the soils were at ng/g levels with TBBPA and TBP the most frequently detected. To our knowledge, this is the first report for the simultaneous determination of TBBPA, TBP, DBPs and MBPs in soils.
[Show abstract][Hide abstract] ABSTRACT: In order to characterize polybrominated diphenyl ethers (PBDEs), and hydroxylated and methoxylated PBDEs (OH-PBDEs and MeO-PBDEs) in the soil-plant system, soil and plant samples were collected from an e-waste recycling area in China. Forty one PBDEs, twelve OH-PBDEs and MeO-PBDEs were detected in the soil and plant samples. Concentrations of PBDEs in roots were significantly correlated to their concentrations in the soils, but the percentages of lower brominated congeners in the plants were higher than those in the soils. Significant positive linear relationships exist between concentrations of ∑OH-PBDEs and ∑MeO-PBDEs with higher levels of ∑MeO-PBDEs than those of ∑OH-PBDEs in the soils, plant roots and leaves. A majority of the OH-/MeO-PBDEs had the hydroxyl or methoxy group at the ortho-positions to the biphenyl bond for most of the plant species. However the occurrence of meta- and para- substituted OH-/MeO-PBDEs in soils and plants were also confirmed.
[Show abstract][Hide abstract] ABSTRACT: In order to investigate the enzyme transformation of PBDEs and to track the key enzymes involved in PBDE degradation in plants, in vivo exposure of plants of ryegrass, pumpkin and maize and in vitro exposure of their root crude enzyme extracts to PBDEs were conducted. Degradation of PBDEs in the root crude enzyme solutions fit well with the first order kinetics (R(2)=0.52-0.97, P<0.05), and higher PBDEs degraded faster than the lower ones. PBDEs could be transformed to lower brominated PBDEs and hydroxylated-PBDEs by the root crude enzyme extracts with debromination as the main pathway which contributed over 90% of PBDE depletion. In vitro and in vivo exposure to PBDEs produced similar responses in root enzyme activities of which the nitroreductase (NaR) and glutathione-transferase (GST) activities decreased significantly, while the peroxidase, catalase and cytochrome P-450 activities had no significant changes. Furthermore, higher enzyme concentrations of NaR and GST led to higher PBDE debromination rates, and the time-dependent activities of NaR and GST in the root crude enzyme extracts were similar to the trends of PBDE depletion. All these results suggest that NaR and GST were the key enzymes responsible for PBDE degradation. This conclusion was further confirmed by the in vitro debromination of PBDEs with the commercial pure NaR and GST.
[Show abstract][Hide abstract] ABSTRACT: Hexabromocyclododecane (HBCD), a brominated flame retardant, has become a ubiquitous contaminant due to its wide application, persistence, and toxicity. HBCD diastereoisomers have different physical and chemical properties and may differ in their bioaccumulation and toxicity in plants. Accumulation and toxicity of α-, β-, and γ-HBCDs in maize were investigated in the present study. The accumulation was in the order β-HBCD > α-HBCD > γ-HBCD in roots and β-HBCD > γ-HBCD > α-HBCD in shoots. Both the inhibitory effect of the diastereoisomers on the early development of maize and the intensities of hydroxyl radical and histone H2AX phosphorylation in maize exposed to 2 μg L(-1) HBCD followed the order α-HBCD > β-HBCD > γ-HBCD, indicating the diastereomer-specific oxidative stress and DNA damage in maize. It was further confirmed that the generation of reactive oxygen species was one, but not the only, mechanism for DNA damage in maize exposed to HBCDs.
Journal of Agricultural and Food Chemistry 08/2012; 60(34). DOI:10.1021/jf302682p · 3.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Sequestration and diffusion of three polycyclic aromatic hydrocarbons (PAHs) in seven Chinese soils were investigated for up to 200 days in sterile soil microcosms as functions of soil property and aging time. The aging of the PAHs, assessed using a mild extractant that removes primarily the labile fraction, showed a biphasic behavior. The rapid diffusion from labile to nonlabile domains was mainly dependent upon the distribution of meso- and micropore fraction and total organic carbon content. Meanwhile, the slow diffusion was found to decrease with the increase of the content of soil organic carbon, particularly of hard organic carbon (p < 0.01) and the meso- and micropore fraction, as well as with the increasing molecular size of PAHs. This work offers evidence that analyses of organic carbon fractionation and porosity are important to adequately assess the mechanistic basis of sequestration and diffusion of organic contaminants in soils.
[Show abstract][Hide abstract] ABSTRACT: A hydroponic experiment was conducted to investigate the debrominated, hydroxylated and methoxylated metabolism of polybrominated diphenyl ethers (PBDEs, BDE-15, -28 and -47) in maize. A total of six debrominated metabolites (de-PBDEs), seven hydroxylated PBDEs (OH-PBDEs, including two unidentified OH-di-PBDEs and one unidentified OH-tri-PBDE) and four methoxylated PBDEs (MeO-PBDEs) were determined in the exposed plants. The metabolic products were detected in maize only after 12h of exposure to the PBDEs. However, the concentration of each type of the metabolites (de-PBDEs, OH-PBDEs or MeO-PBDEs) decreased at the later exposure time, possibly due to further metabolism. The removal of a bromine atom or the introduction of a hydroxyl/methoxy group was easier at the ortho-positions on the biphenyl structure than at the para-positions. Concentration ratios of the total debrominated, hydroxylated or methoxylated metabolites to the parent congener (BDE-28 or -47) generally followed the order of leaves>stems≫roots, and MeO-PBDEs>de-PBDEs≫OH-PBDEs. These results suggest that metabolism occurred preferentially in leaves and stems than in roots. Less transformation and shorter elimination half-life of OH-PBDEs would contribute to the lower concentrations of OH-PBDEs than of de-PBDEs or MeO-PBDEs in maize.
[Show abstract][Hide abstract] ABSTRACT: Uptake, translocation and debromination of three polybrominated diphenyl ethers (PBDEs), BDE-28, -47 and -99, in maize were studied in a hydroponic experiment. Roots took up most of the PBDEs in the culture solutions and more highly brominated PBDEs had a stronger uptake capability. PBDEs were detected in the stems and leaves of maize after exposure but rarely detected in the blank control plants. Furthermore, PBDE concentrations decreased from roots to stems and then to leaves, and a very clear decreasing gradient was found in segments upwards along the stem. These altogether provide substantiating evidence for the acropetal translocation of PBDEs in maize. More highly brominated PBDEs were translocated with more difficulty. Radial translocation of PBDEs from nodes to sheath inside maize was also observed. Both acropetal and radial translocations were enhanced at higher transpiration rates, suggesting that PBDE transport was probably driven by the transpiration stream. Debromination of PBDEs occurred in all parts of the maize, and debromination patterns of different parent PBDEs and in different parts of a plant were similar but with some differences. This study for the first time provides direct evidence for the acropetal translocation of PBDEs within plants, elucidates the process of PBDE transport and clarifies the debromination products of PBDEs in maize.
[Show abstract][Hide abstract] ABSTRACT: Atrazine accumulation, oxidative stress, and defense response in maize seedlings exposed to extraneous atrazine were studied. Accumulation of atrazine in maize increased with increasing exposure concentration. The abscisic acid (ABA) content was positively correlated with the atrazine concentrations in maize roots and shoots (p < 0.05). Hydroxyl radical (*OH) in maize was determined in vivo with electron paramagnetic resonance spectroscopy. Its intensity was positively correlated with atrazine concentration in roots and shoots (p < 0.05), and higher level of *OH generated in roots than in shoots corresponded to the major accumulation of atrazine in roots. Superoxide dismutase, peroxidase and catalase in roots were up-regulated by atrazine exposure at 1 mg/L compared to the control and malondialdehyde content in roots was enhanced when atrazine exposure concentration reached 10 mg/L. These results suggested the exposure and accumulation of atrazine caused oxidative toxicity and antioxidant response in maize.
[Show abstract][Hide abstract] ABSTRACT: Effects of arbuscular mycorrhizal fungus (Glomus mosseae) on the accumulation and speciation of selenium (Se) in alfalfa, maize, and soybean were investigated by using Se(IV)-spiked soil. Mycorrhizal inoculation decreased Se accumulation in roots and shoots of all the plants at Se spiked level of 0 or 2 mg kg(-1), while an increased Se accumulation was observed in alfalfa shoots and maize roots and shoots at the spiked level of 20 mg kg(-1). Concentration of inorganic Se (especially Se(VI)) in roots and shoots of the three plants was much higher in mycorrhizal than non-mycorrhizal treatment. Mycorrhizal inoculation decreased the portion of total organic Se in plant tissues with the exception of alfalfa and maize shoots at Se spiked level of 20 mg kg(-1), in which organic Se portion did not reduced greatly (<5%) for mycorrhizal treatment. Mycorrhizal effects on alfalfa and maize were more obvious than on soybean in terms of root colonization rate, biomass, and Se accumulation.
Biological trace element research 12/2011; 143(3):1789-98. DOI:10.1007/s12011-011-8973-5 · 1.61 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A method was developed for the analysis of hydroxylated brominated diphenyl ethers (OH-PBDEs) in plant samples using an ultra performance liquid chromatography-triple quadrupole mass spectrometer (UPLC-ESI-MS/MS) in negative mode. Plant samples were extracted and cleaned up through florisil column, resolved on a 100 mm C18 column with linear gradient elution and detected by mass spectrometry in multiple reaction monitoring (MRM) mode. The method provided good recoveries ranging from 68.2% to 94.6%, relative standard deviation (RSD) in the range of 3.2%–9.1%, and limits of quantification (LOQ) defined as the signal-to-noise ratio of 10 of 0.3–2.1 ng/g. It allowed a fast separation and sensitive quantification of the isomers and homologues of seven OH-PBDE congeners 2′-OH-BDE-3, 3′-OH-BDE-7, 4′-OH-BDE-17, 3′-OH-BDE-28, 3-OH-BDE-47, 5-OH-BDE-47 and 6-OH-BDE-47. The method was successfully applied to identify and quantify the formation of hydroxylated metabolites in alfalfa exposed to BDE-209. Five OH-PBDEs were detected in plant tissues, and more congeners were found in roots than in shoots. To our knowledge, this work represents the first attempt to validate UPLC-MS/MS method to quantify OH-PBDEs in plant samples without derivatization.
[Show abstract][Hide abstract] ABSTRACT: A hydroponic experiment was conducted in the present study to investigate and compare plant uptake, translocation and metabolism of polybrominated diphenyl ethers (PBDEs) of BDE-15, BDE-28 and BDE-47 and polychlorinated biphenyls (PCBs) of PCB-15, PCB-28 and PCB-47 in maize. Root concentrations of BDE-15, BDE-28 and BDE-47 were consistently higher than PCB-15, PCB-28 and PCB-47, respectively. A significantly positive correlation was found between logRCF (root concentration factor) and logKow of these PBDEs and PCBs, suggesting a control role of their partitioning in plant uptake. The translocation factors (TFs, Cstem/Croot) of PBDEs were generally lower than those of PCBs of the same halogen-substitutions, demonstrating easier transport of PCBs than PBDEs. Metabolites mono-, di- and tri-BDEs and PCBs were detected, suggesting the existence of in vivo metabolism of PBDEs and PCBs in maize. Dehalogenation and rearrangement of halogen atoms were identified, and some similarities but also significant differences existed between the PBDEs and PCBs. PBDEs in maize were, in general, more susceptible to metabolism compared with PCBs of the same halogen-substitutions. This is the first comparative report on the uptake, translocation and metabolism of PBDEs and PCBs in plants.
[Show abstract][Hide abstract] ABSTRACT: A rhizobox experiment was conducted to investigate degradation of decabromodiphenyl ether (BDE-209) in the rhizosphere of ryegrass and the influence of root colonization with an arbuscular mycorrhizal (AM) fungus. BDE-209 dissipation in soil varied with its proximity to the roots and was enhanced by AM inoculation. A negative correlation (P < 0.001, R(2) = 0.66) was found between the residual BDE-209 concentration in soil and soil microbial biomass estimated as the total phospholipid fatty acids, suggesting a contribution of microbial degradation to BDE-209 dissipation. Twelve and twenty-four lower brominated PBDEs were detected in soil and plant samples, respectively, with a higher proportion of di- through hepta-BDE congeners in the plant tissues than in the soils, indicating the occurrence of BDE-209 debromination in the soil-plant system. AM inoculation increased the levels of lower brominated PBDEs in ryegrass. These results provide important information about the behavior of BDE-209 in the soil-plant system.
[Show abstract][Hide abstract] ABSTRACT: To investigate the enantioselective oxidative damage of the pesticide dichlorprop (DCPP) to maize, young seedlings were exposed to solutions of DCPP enantiomers and racemate at different concentrations. Early root development was more influenced by (R)-DCPP than racemic (rac)- and (S)-DCPP. Inhibition rates of seed germination, seedling biomass, and root and shoot elongation were all in the order of (R)-DCPP > (rac)-DCPP > (S)-DCPP treatments. The antioxidant enzyme activities of superoxide dismutase (SOD) and peroxidase (POD) were significantly upregulated by exposure to lower concentrations of (R)-DCPP than (rac)- and (S)-DCPP. Direct determination of the formation of hydroxyl radical (•OH) with electron paramagnetic resonance (EPR) spectroscopy indicated that the •OH level in maize roots followed the order of (R)-DCPP > (rac)-DCPP > (S)-DCPP treatments. All of these results provide solicited evidence of the significant enantioselective phytotoxicity of DCPP to maize with a higher toxicity of (R)-DCPP than (S)- and (rac)-DCPP.
Journal of Agricultural and Food Chemistry 03/2011; 59(8):4315-20. DOI:10.1021/jf200213z · 3.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Plant uptake and dissipation of weathered PBDEs in the soils of e-waste recycling sites were investigated in a greenhouse study. Eighteen PBDE congeners (tri- through deca-) were detected in the plant tissues. The proportion of lower brominated PBDEs (mono- through hexa-) in plant roots was higher than that in the soils. A concentration gradient was observed of PBDEs in plants with the highest concentrations in the roots followed by the stems and lowest in the leaves. Reduction rates of the total PBDEs in the soils ranged from 13.3 to 21.7% after plant harvest and lower brominated PBDEs were associated with a higher tendency to dissipate than the higher brominated PBDEs. This study provides the first evidence for plant uptake of weathered PBDEs in the soils of e-waste recycling sites and planting contributes to the removal of PBDEs in e-waste contaminated soils.
[Show abstract][Hide abstract] ABSTRACT: Effects of inoculation with the arbuscular mycorrhizal (AM) fungus Glomus mosseae on the behavior of Hg in soil-plant system were investigated using an artificially contaminated soil at the concentrations of 0, 1.0, 2.0, and 4.0 mg Hg kg(-1). Mercury accumulation was lower in mycorrhizal roots than in nonmycorrhizal roots when Hg was added at the rates of 2.0 and 4.0 mg kg(-1), while no obvious difference in shoot Hg concentration was found between mycorrhizal and nonmycorrhizal treatments. Mycorrhizal inoculation significantly decreased the total and extractable Hg concentrations in soil as well as the ratio of extractable to total Hg in soil. Equilibration sorption of Hg by soil was investigated, and the results indicated that mycorrhizal treatment enhanced Hg sorption on soil. The uptake of Hg was lower by mycorrhizal roots than by nonmycorrhizal roots. These experiments provide further evidence for the role of mycorrhizal inoculation in increasing immobilization of Hg in soil and reducing the uptake of Hg by roots. Calculation on mass balance of Hg in soil suggests the presence of Hg loss from soil presumably through evaporation, and AM inoculation enhanced Hg evaporation. This was evidenced by a chamber study to detect the Hg evaporated from soil.
[Show abstract][Hide abstract] ABSTRACT: Effects of inoculation with three different arbuscular mycorrhizal (AM) fungi (Glomus etunicatum, Glomus constrictum, and Glomus mosseae) on arsenic (As) accumulation by maize were investigated by using soil spiked with As at rates of 0, 25, 50, and 100 mg kg−1. The root colonization rates by the three fungi were significantly different (G. mosseae > G. etunicatum > G. constrictum) and decreased markedly with increasing As concentration in the soil. Inoculation with G. etunicatum or G. mosseae increased maize biomass and phosphorus (P) accumulation (G. mosseae > G. etunicatum) and reduced As accumulation in shoots (G. mosseae ≈ G. etunicatum), whereas inoculation with G. constrictum had little effect on these parameters. Inoculation with G. mosseae produced greater biomass and P uptake and less shoot As accumulation, and therefore it may be a promising approach to reduce As translocation from contaminated soils to plants.
Communications in Soil Science and Plant Analysis 03/2010; 41(6-6):735-743. DOI:10.1080/00103620903563964 · 0.42 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Deca-bromodiphenyl ether (BDE-209) is the major component of the commercial deca-BDE flame retardant. There is increasing concern over BDE-209 due to its increasing occurrence in the environment and in humans. In this study the behavior of BDE-209 in the soil-plant system was investigated. Accumulation of BDE-209 was observed in the roots and shoots of all the six plant species examined, namely ryegrass, alfalfa, pumpkin, summer squash, maize, and radish. Root uptake of BDE-209 was positively correlated with root lipid content (P < 0.001, R(2) = 0.81). The translocation factor (TF, C(shoot)/C(root)) of BDE-209 was inversely related to its concentration in roots. Nineteen lower brominated (di- to nona-) PBDEs were detected in the soil and plant samples and five hydroxylated congeners were detected in the plant samples, indicating debromination and hydroxylation of BDE-209 in the soil-plant system. Evidence of a relatively higher proportion of penta- through di-BDE congeners in plant tissues than in the soil indicates that there is further debromination of PBDEs within plants or low brominated PBDEs are more readily taken up by plants. A significant negative correlation between the residual BDE-209 concentration in soil and the soil microbial biomass measured as the total phospholipid fatty acids (PLFAs) (P < 0.05, R(2) = 0.74) suggests that microbial metabolism and degradation contribute to BDE-209 dissipation in soil. These results provide important information about the behavior of BDE-209 in the soil-plant system.
[Show abstract][Hide abstract] ABSTRACT: Plant cells have been reported to play an important role in the uptake of organic contaminants. This study was undertaken to provide an insight into the role of the root cell walls and their subfractions on sorption of phenanthrene to roots of wheat (Triticum aestivum L.). Root cell walls were isolated and further sequentially fractioned by removing pectin, hemicellulose one, and hemicellulose two. They were characterized by elemental analysis, Fourier transform infrared spectroscopy, and solid-state (13)C NMR. Root cell walls had a greater proportion of aromatic carbon and exhibited a lower polarity than the bulk roots. There was a stepwise increase in aromatic carbon content and a decrease in polarity following the sequential fractionation. The sorption affinity of phenanthrene increased gradually following the sequential extraction of root cells. A significant positive correlation between the sorption affinity K(OC) values and the aromatic carbon contents (r(2) = 0.896, p < 0.01) and a negative correlation between the sorption affinity K(OC) values and polarity ((O + N)/C) of root cell fractions (r(2) = 0.920, p < 0.01) were obtained. Improved modeling was achieved for phenanthrene sorption by involving the contribution of root cell walls as a source of root carbohydrates instead of using root lipids alone, which further confirms the significant contribution of root cell walls to phenanthrene sorption on wheat roots. The results provide evidence for the importance of the root cell walls in the partitioning of phenanthrene by plant roots.
[Show abstract][Hide abstract] ABSTRACT: Effects of inoculation with arbuscular mycorrhizal (AM) fungus (Glomus mosseae) on arsenic (As) accumulation and speciation in maize were investigated by using As spiked soil at the application levels of 0, 25, 50, and 100 mg kg(-1). Inorganic As was the major species in plants, and mycorrhizal inoculation generally decreased concentrations of arsenite [As(III)] in maize roots and concentrations of As(III) and arsenate [As(V)] in the shoots. Dimethylarsenic acid (DMA) concentrations (detected in every plant sample) were higher in maize shoots for mycorrhizal than for nonmycorrhizal treatment, but no significant differences were observed for roots. Monomethylarsenic acid (MMA) was only detected in roots with mycorrhizal colonization. The uptake of As(V) was much lower by excised mycorrhizal than nonmycorrhizal roots, and the differences for the uptake of As(III) were negligible. Arsenate reductase (AR) activity was detected in maize roots, and it was reduced with mycorrhizal inoculation. Activities of peroxidase (POD) and superoxide dismutase (SOD) were detected in both maize shoots and roots, and they were suppressed by mycorrhizal inoculation. AM inoculation inhibited the uptake of As(V) and its reduction to As(III), reducing oxidation stress and thereby alleviating As toxicity to the host plant.
Journal of Agricultural and Food Chemistry 04/2009; 57(9):3695-701. DOI:10.1021/jf900107y · 3.11 Impact Factor