The uptake, translocation and biotransformation of organophosphate esters (OPEs) by wheat (Triticum aestivum L.) were investigated by a hydroponic experiment. The results demonstrated that OPEs with higher hydrophobicity were more easily taken up by roots, and OPEs with lower hydrophobicity were more liable to be translocated acropetally. A total of 43 metabolites including dealkylated, oxidatively dechlorinated, hydroxylated, methoxylated, and glutathione-, and glucuronide- conjugated products were detected derived from eight OPEs, with diesters formed by direct dealkylation from the parent triesters as the major products, followed with hydroxylated triesters. Molecular interactions of OPEs with plant biomacromolecules were further characterized by homology modeling combined with molecular docking. OPEs with higher hydrophobicity were more liable to bind with TaLTP1.1, the most important wheat nonspecific lipid transfer protein, consistent with the experimental observation that OPEs with higher hydrophobicity were more easily taken up by wheat roots. Characterization of molecular interactions between OPEs and wheat enzymes suggested that OPEs were selectively bound to TaGST4–4 and CYP71C6v1 with different binding affinities, which determined their abilities to be metabolized and form metabolite products in wheat. This study provides both experimental and theoretical evidence for the uptake, accumulation and biotransformation of OPEs in plants.

•Sludge-derived DOM containing more heteroatom S and N molecules than peat DOM.•Nano TiO2 reduce the molecular diversity of DOM under photo-irradiation.•High MW, high aromaticity, heteroatom S containing compounds are easily reduced.•The changes of average carbon oxidation state between DOMp and DOMs are opposite.Photochemical transformation of dissolved organic matter (DOM) plays a very important role in the cycling of organic carbon in aquatic systems. Increasing release of photoactive nanoparticles such as titanium dioxide nanoparticles (nano TiO2) into surface water may impact this process. The present study employed Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) to examine the molecular transformation of natural DOM (peat DOM, DOMp) and anthropogenic DOM (sludge-derived DOM, DOMs) under photo-irradiation as affected by nano TiO2. Differences in molecular components between DOMp and DOMs were observed. DOMs contained more heteroatom formulas (76%) with low aromaticity and low carbon oxidation state than did DOMp (22%). The presence of nano TiO2 resulted in significant decreases in both DOM content and molecular diversity under photo-irradiation. Consistent alterations were observed between DOMp and DOMs such that high molecular weight compounds, high aromaticity and/or heteroatom S-containing compounds were more easily photodegraded in the presence of nano TiO2; whereas the average carbon oxidation state decreased in DOMp but increased in DOMs, likely due to the significant differences in O abundance, especially in the contents of carboxyl moieties, between DOMp and DOMs. The findings of the present study suggest that the release of nano TiO2 into aquatic environment will accelerate the consumption of dissolved organic carbon and the attenuation of molecular diversity for both DOM in waters.Download high-res image (252KB)Download full-size image

•A novel solid-phase extraction isolation of dissolved organic matter is proposed.•Compounds are divided into three fractions prior to FT-ICR-MS analysis.•Molecules identified are 50% more than those obtained by conventional methods.Characterization of dissolved organic matter (DOM) at the molecular level will greatly improve our understanding of its bio-geochemical role in controlling the fate of contaminants in the environment, and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) is the most powerful analytical technique for this purpose. Before FT-ICR-MS analysis, isolation, desalination and concentration of DOM are necessary, and solid-phase extraction (SPE) is the most widely applied pretreatment procedure. However, some molecular information is lost using conventional SPE methods. Here, we propose a novel strategy of SPE enrichment using stepwise elution (SPE-SE). Compounds in DOM were divided into three fractions by this SPE-SE procedure according to their polarity and ionization efficiency. The diversity of DOM molecules identified by ESI-FT-ICR-MS using SPE-SE exceeded those using conventional SPE methods by more than 50%. This method is feasible and has the potential to be used as a pretreatment strategy for complex DOM matrixes prior to ESI-FT-ICR-MS analysis, especially for those rich in nitrogenous molecules, carbohydrates, lipids and/or aromatic compounds.

Diastereomer- and enantiomer-specific accumulation and biotransformation of hexabromocyclododecane (HBCD) in maize (Zea mays L.) were investigated. Molecular interactions of HBCD with plant enzymes were further characterized by homology modeling combined with molecular docking. The (−)α-, (−)β-, and (+)γ-HBCD enantiomers accumulated to levels in maize significantly higher than those of their corresponding enantiomers. Bioisomerization from (+)/(−)-β- and γ-HBCDs to (−)α-HBCD was frequently observed, and (−)γ-HBCD was most easily converted, with bioisomerization efficiency of 90.5 ± 8.2%. Mono- and dihydroxyl HBCDs, debrominated metabolites including pentabromocyclododecene (PBCDe) and tetrabromocyclododecene (TBCDe), and HBCD-GSH adducts were detected in maize roots. Patterns of hydroxylated and debrominated metabolites were significantly different among HBCD diastereomers and enantiomers. Three pairs of HBCD enantiomers were selectively bound into the active sites and interacted with specific residues of maize enzymes CYP71C3v2 and GST31. (+)α-, (−)β-, and (−)γ-HBCDs preferentially bound to CYP71C3v2, whereas (−)α-, (−)β-, and (+)γ-HBCDs had strong affinities to GST31, consistent with experimental observations that (+)α-, (−)β-, and (−)γ-HBCDs were more easily hydroxylated, and (−)α-, (−)β-, and (+)γ-HBCDs were more easily isomerized and debrominated in maize compared to their corresponding enantiomers. This study for the first time provided both experimental and theoretical evidence for stereospecific behaviors of HBCD in plants.

Adsorption by minerals is a common geochemical process of dissolved organic matter (DOM) which may induce fractionation of DOM at the mineral-water interface. Here, we examine the molecular fractionation of DOM induced by adsorption onto three common iron oxyhydroxides using electrospray ionization coupled with Fourier-transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR-MS). Ferrihydrite exhibited higher affinity to DOM and induced more pronounced molecular fractionation of DOM than did goethite or lepidocrocite. High molecular weight (>500 Da) compounds and compounds high in unsaturation or rich in oxygen including polycyclic aromatics, polyphenols and carboxylic compounds had higher affinity to iron oxyhydroxides and especially to ferrihydrite. Low molecular weight compounds and compounds low in unsaturation or containing few oxygenated groups (mainly alcohols and ethers) were preferentially maintained in solution. This study confirms that the double bond equivalence and the number of oxygen atoms are valuable parameters indicating the selective fractionation of DOM at mineral and water interfaces. The results of this study provide important information for further understanding the behavior of DOM in the natural environment.

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.

Engineered nanomaterials such as ZnO nanoparticles (NPs) will inevitably enter the environment because of the large quantities produced and their widespread application. Plants comprise a fundamental living component of terrestrial ecosystems; thus, understanding the interaction between ENMs and plants is important. In the present study we conducted an integrated study by employing a combination of microscopic and spectroscopic techniques to comparatively investigate the uptake of ZnO NPs and Zn2+ ions by maize in order to further elucidate plant uptake pathways of ZnO NPs. The results demonstrate that the majority of Zn taken up was derived from Zn2+ released from ZnO NPs, and Zn accumulated in the form of Zn phosphate. ZnO NPs were observed mainly in the epidermis, a small fraction of ZnO NPs were present in the cortex and root tip cells, and some further entered the vascular system through the sites of the primary root–lateral root junction. However, no ZnO nanoparticle was observed to translocate to shoots, possibly due to the dissolution and transformation of ZnO NPs inside the plants.

It is imperative to obtain information on the binding sites and distribution of organic contaminants in soils in order to understand their reactions and fates in soils. Here we propose a novel strategy that enables in situ observation at the micrometer scale of the spatial distribution of organobromine compounds and characterization of their associations with organic carbon (OC) forms (i.e., C-functional groups) in soils. According to the strategy, two complementary synchrotron radiation-based spectroscopic techniques (i.e., Fourier transform-infrared (FT-IR) and micro X-ray fluorescence (μ-XRF) spectromicroscopies) were applied to characterize the binding sites and distribution of Br (as a conservative tracer for organobromine compounds), OC forms, clay minerals, and other mineral elements within soil particles, respectively, at a 6–10 μm-scale spatial resolution. This study is the first in situ investigation on the microscale locations of organobromine compounds at environmental levels and their associations with OC forms and clay mineral/elements in natural soils. The strategy paves the way toward in situ characterization of the distribution, speciation, and binding sites of some organic contaminants, which is critical in understanding their associated environmental processes in soils.

•ZnO NPs undergo chemical transformation in the presence of insoluble phosphate.•HAP induced the transformation of ZnO NPs to scholzite under acid condition.•ZnO NPs transformed to amorphous phase under neutral and basic conditions.Recent studies have revealed that zinc phosphate is an important transformation product of zinc oxide nanoparticles (ZnO NPs) in the environment, and the role of soluble phosphate in the transformation of ZnO NPs to zinc phosphate has been confirmed. However, whether insoluble phosphate that exists widely in the environment can induce chemical transformation of ZnO NPs has not been addressed. Therefore, transformation of ZnO NPs in the presence of hydroxyapatite (HAP), selected as representative of insoluble phosphate, at different pH was investigated in the present study. Transformation products were identified by employing X-ray diffraction and synchrotron based X-ray absorption fine structure spectroscopy. The results indicate that under acidic condition (pH 5) phosphate ion (PO43−) and calcium anion (Ca2+) were released from HAP in aqueous solution, inducing a rapid transformation of about 80% ZnO NPs to scholzite within 4 h. Under neutral or basic conditions (pH 7 and 9) the adsorption of Zn2+ on HAP resulted in a slow transformation of about 60% ZnO NPs to amorphous inner-sphere Zn adsorption complexes within 30 days. This work suggests the important role of HAP in the transformation of ZnO NPs and may affect the behavior, fate and toxic effects of ZnO NPs in the environment.

•Hydrophobic and electrostatic interactions dominate TBBPA adsorption on soils.•Organic carbon and pH are the key factors determining TBBPA adsorption on soils.•Black carbon shows the highest adsorption capacity among all soil organic fractions.•Minerals exhibit the lowest adsorption capacity among all soil components.The adsorption of tetrabromobisphenol A (TBBPA) on several typical Chinese soils and soil mineral and organic components were comprehensively investigated in the present study. The adsorption isotherms were well described by the Freundlich equation and the corresponding adsorption capacity constant Kf ranged from 2.46 to 357.30 L/kg and 16.52 to 136,731.98 L/kg for the original soils and the soil components, respectively. Correlation analysis between the adsorption capacity and soil properties indicates that soil pH and soil organic carbon (SOC) content were the predominant factors determining TBBPA adsorption on the soils. At constant pH of 7.0, the soils with higher SOC content exhibited stronger adsorption affinity for TBBPA, suggesting the significant importance of SOC in the adsorption. The adsorption affinity of TBBPA became weaken for a given soil with increasing pH due to the enhanced electrostatic repulsion between the anionic TBBPA species and soil surface. Humins and black carbon of SOC played a predominant role in while soil minerals contributed slightly to the adsorption of TBBPA on the soils. The results of this study will provide a better understanding of the behaviors of TBBPA in soils.

The toxicity and fate of nanoparticles (NPs) have been reported to be highly dependent on the chemistry of the medium, and the effects of phosphate have tended to be ignored despite the wide existence of phosphate contamination in aqueous environments. In the present study the influence of phosphate on the dissolution and microstructural transformation of ZnO NPs was investigated. Phosphate at a low concentration rapidly and substantially reduced the release of Zn2+ into aqueous solution. Synchrotron X-ray absorption spectroscopy and X-ray diffraction analysis reveal that interaction between ZnO NPs and phosphate induced the transformation of ZnO into zinc phosphate. Transmission electronic microscopy observation shows that the morphology of the particles changed from structurally uniform nanosized spherical to anomalous and porous material containing mixed amorphous and crystalline phases of ZnO and zinc phosphate in the presence of phosphate. To our knowledge, this is the first study in which the detailed process of phosphate-induced speciation and microstructural transformation of ZnO NPs has been analyzed. In view of the wide existence of phosphate contamination in water and its strong metal-complexation capability, phosphate-induced transformations may play an important role in the behaviors, fate, and toxicity of many other metal-based nanomaterials in the environment.

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.

Adsorption behaviors of fulvic acid (FA) and humic acid (HA) on kaolinite, smectite and vermiculite were investigated. To explore the adsorption mechanism, characterization of both the adsorption FA/HA-clay complexes and suspensions was conducted by utilizing multiple analytical techniques including liquid-state 1H nuclear magnetic resonance spectroscopy, high performance size exclusion chromatography, UV–vis spectroscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Both FA and HA underwent fractionation during the adsorption due to different affinity for the functional moieties of FA/HA on the minerals. More HA was adsorbed than FA on kaolinite and smectite mainly via hydrophobic interaction. Electron transfer from aromatic units of FA to iron cation induced more FA than HA adsorbed onto vermiculite at higher FA/HA concentrations (>20 mg C/L). Specific surface area and pore volume analyses indicated HA with larger particle size was prone to accumulate on the external mineral surfaces, while FA was easier than HA to block pores of the minerals. The increased pH in clay suspensions after FA/HA adsorption suggested that ligand exchange occurred and FA/HA-clay complexes formed, particularly for the 2:1 type minerals of smectite and vermiculite with the increase of pH at 0.41 and 0.62 units, respectively. Furthermore, the increase of the equilibrium pH or the decrease of the ionic strength led to the reduction of FA/HA adsorption on all the three minerals. Due to rich in iron cation, more carboxyl and hydroxyl functional groups were facilitated for the ligand exchange and cation-bridging on vermiculite, and thus improved the adsorption capacity. The results of this study will improve our understanding of the roles of mineral interfacial properties, characteristics of FA and HA in the adsorption of FA/HA on clay minerals.Graphical abstractFA and HA have different adsorption behaviors on the clay minerals of kaolinite, smectite and vermiculite.Highlights► More HA is adsorbed on kaolinite and smectite than FA via hydrophobic interaction. ► More FA is adsorbed on vermiculite than HA due to an electron transfer mechanism. ► Ligand exchange is an important mechanism for FA and HA adsorption on clay minerals. ► Iron cation plays an important role in the adsorption of FA and HA on vermiculite.

Adsorption of bisphenol A on a lignin isolated from black liquor, a waste product of the paper industry, was investigated to assess the possibility of using the lignin to remove bisphenol A from waters. Effects of pH, ionic strength, heavy metals, and dissolved organic matter (DOM) on adsorption were examined. Adsorption equilibrium was approached within 5 h. The adsorption capacity of bisphenol A on lignin was as high as 237.07 mg/g. Ionic strength had no influence on the adsorption, while higher pH above 7.5 inhibited bisphenol A adsorption due to the repulsive electrostatic interaction between bisphenolate anion and the negatively charged lignin surface. The presence of heavy metals of copper and lead increased the adsorption by 11.90 and 26.80 %, respectively, possibly through modifying the physiochemical configuration characteristics of labile fraction of the lignin and reducing the polarity of it. No obvious impact of DOM on the adsorption was observed. The results of this study suggest that lignin is a promising adsorbent material to remove bisphenol A in wastewater containing complex components such as heavy metals and DOM, particularly at acid and neutral conditions.

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.

Humic substances such as fulvic acid (FA) and humic acid (HA) exist universally in the environment and play an important role in the interfacial reactions of contaminants. In this study, influences of surface-coated FA and HA on the adsorption of metal cations of Cu(II), Pb(II) and Zn(II) on SiO2 nanoparticles (nano-SiO2, 20 nm) were investigated. The results showed that nano-SiO2 had high adsorption capacities for the metal cations following the sequence of Pb(II) > Cu(II) > Zn(II), irrespective of coating with FA or HA. Nano-SiO2 had a strong affinity for FA and HA, and coating with FA and HA significantly enhanced the adsorption of the metal cations on nano-SiO2. Cation adsorption on the original and coated nano-SiO2 followed the same pronounced increasing trend with increasing pH. X-ray absorption spectroscopy (XAS) analysis by taking Cu(II) as an example revealed that Cu(II) was adsorbed on nano-SiO2 by forming inner-sphere complexes; whereas its adsorption on FA/HA coated nano-SiO2 was through complexing with the hydroxyl moieties and organic functional groups of FA/HA as bridges. This work demonstrates that FA and HA can significantly change the adsorption capacities and mechanisms for metal cations and thus likely influence their behaviors in the environment.Graphical abstractThe adsorption of metal cations on FA or HA coated SiO2 was significantly enhanced through complexing with the hydroxyl moieties and organic functional groups of FA and HA.Highlights► Coating with FA/HA obviously enhanced the adsorption of metal cations on nano-SiO2. ► Cation was adsorbed on nano-SiO2 by forming inner-sphere complexes. ► Cation was adsorbed on FA/HA coated SiO2 through complexing with functional moieties.

Information on the interaction of nanoparticles with natural organic matter (NOM) is essential for understanding their environmental impacts. In this study the adsorption and desorption of humic acids (HA) and fulvic acids (FA) on SiO2 particles in size of 20, 100 and 500 nm were investigated. The adsorption of HA and FA on 20 nm SiO2 was much stronger compared with their adsorption on 100 and 500 nm SiO2, probably due to the specific surface properties of the nanoparticles. The adsorption of HA and FA was pH-dependent, particularly for HA adsorption. The adsorption of HA showed apparent difference between the ionic strength of 0.01 and 0.1 mol/L NaNO3, but no obvious difference was observed for FA adsorption. Desorption results presented obviously hysteresis with more obvious for HA desorption. The results of this study demonstrated evidently that 20 nm SiO2 particles had much higher affinity to HA and FA than did 100 and 500 nm particles, which may have significant effects on their behaviors in the environment.Graphical abstractAdsorption isotherms of humic acids (HA) and fulvic acids (FA) on SiO2 particles at pH 4.0 and Langmuir model (real lines) and Freundlich model (dotted lines) fittings.Highlights► Adsorption of humic and fulvic acids on SiO2 heavily depends on particle sizes. ► Humic and fulvic acids interact differently with the nanoparticles. ► Cation bridge interaction contributes importantly to the humic substance adsorption.

Nonpolar nonionic compound (phenanthrene, PHE) and polar nonionic compound (1,3-dinitrobenzene, DNB) were used as probes to explore the dominant mechanism responsible for adsorption of nonionic organic compounds on different cation-modified clay minerals (i.e. smectite, kaolinite, and vermiculite). Batch experiments were conducted, and possible adsorption mechanisms were inferred from adsorption isotherms and characteristics of the modified clay minerals. The results demonstrate that cation-modified clay minerals can adsorb a larger amount of DNB than PHE. Smectite and vermiculite, 2:1 type layered silicate minerals, have a higher adsorption capacity for DNB than the 1:1 type layered kaolinite. K+-modified clay minerals have greater adsorption capacities for DNB than Na+- and Ca2+-modified clay minerals; while Ca2+-modified clay minerals with the exception of vermiculate have greater adsorption capacities of PHE than K+- and Na+-modified clay minerals. The results of this study suggest that hydrophobic interaction and inter-layer accommodation are likely to be the dominant mechanisms of PHE adsorption by clay minerals, whereas electrostatic interactions through hydrogen bond and formation of electron donor–acceptor complexes are responsible for DNB adsorption by clay minerals. This study will benefit understanding the adsorption mechanisms of nonionic organic compounds on minerals in the environments.Graphical abstractPhenanthrene and 1,3-dinitrobenzene exhibited contrasting adsorption behaviors on cation-modified kaolinite.Research highlights► Adsorption of PHE and DNB on minerals heavily depends on cation-modification. ► Hydrophobic interaction and inter-layer accommodation are dominant for PHN sorption. ► Electrostatic interactions are responsible for DNB adsorption on minerals.

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.

A new type of composite membrane is introduced to mimic plant uptake of hydrophobic organic contaminants (HOCs). Petroselinic acid (cis-6-octadecenoic acid), the major component of plant lipids, was embedded in the matrix of cellulose acetate polymer to form the petroselinic acid embedded cellulose acetate membrane (PECAM). Accumulation of the polycyclic aromatic hydrocarbons (PAHs) naphthalene (Nap), phenanthrene (Phe), pyrene (Pyr), and benz(a)pyrene (Bap) by PECAM was compared with their uptake by plants. The accumulation of Nap, Phe, Pyr, and Bap by PECAM reached equilibrium in 24, 48, 144, and 192 h, respectively. The petroselinic acid−water partition coefficients (log Kpw, 3.37, 4.90, 5.24, and 6.28 for Nap, Phe, Pyr, and Bap, respectively) were positively correlated with the hydrophobicity of the compounds (R2 = 0.995) and were almost the same as the lipid-normalized root partition coefficients (log Klip) for the corresponding compounds. Their relationship can be expressed as log Kpw = 0.98 log Klip. The normalized plant uptake coefficients (log Ku) obtained by in vivo experiments with a range of plant species (2.92, 4.43, 5.06, and 6.13 on average for Nap, Phe, Pyr, and Bap, respectively) were slightly lower than those of the log Kpw values for the corresponding compounds, presumably due to their acropetal translocation and biodegradation inside plants. This work suggests that PECAMs can well mimic plant partitioning and in vivo uptake of PAHs and may have good potential as a nonliving accumulator to mimic plant uptake of PAHs and perhaps other HOCs.

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, R2 = 0.81). The translocation factor (TF, Cshoot/Croot) 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, R2 = 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.

Soil contamination by combinations of heavy metals and organic contaminants has become an increasingly important environmental issue. Effects of heavy metal cations (Cu2+, Ni2+, and Pb2+) on phenanthrene sorption were systematically investigated using two soils with contrasting physicochemical properties. Spectral and microscopic analyses provide direct evidence for the modification of composition and conformation of dissolved organic carbon (DOC) and hydrophobicity of the interfaces in the presence of metal cations. Parts of rubbery organic carbon (including flexible DOC and humic acids) became condensed on solid surfaces in the presence of heavy metals as evidenced by an increase in the glass transition temperature of the soils. These modifications led to a significant increase in the capacity and nonlinearity of phenanthrene sorption in the soils. As the added metal cations aged for 70 days, the soil solution gradually recovered its original physicochemical properties, and the facilitating effects of the heavy metals on phenanthrene sorption were significantly attenuated. This work highlights the important implications of DOC properties and aging processes of metals in the sorption of hydrophobic organic compounds (HOCs) such as phenanthrene in soils and provides compelling evidence for the facilitating effects of heavy metals on HOC sorption in soils.

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.

Field experiments were carried out to investigate the dissipation of boscalid in strawberries and soils and its residual levels in strawberries at two different sites. Boscalid (50% water dispersible granule) was applied at two dosages (349.5 and 525.0 g a.i./ha). Soils and strawberry samples were collected at 0, 1, 2, 3, 5, 7, 14, 21 days after application of boscalid. The results showed that boscalid dissipation pattern followed the first order kinetics with the half-lives of 4.9 and 6.4 days in strawberries and 6.1 and 8.0 days in the soils of Jinan and Beijing trail sites, respectively. The boscalid residues in strawberries were below the EU maximum residue level (5 mg/kg) after three days of application. This study suggests that boscalid is acceptable to apply for strawberries under the recommended dosage.

Synchrotron-based X-ray techniques have been widely applied to the fields of environmental science due to their element-specific and nondestructive properties and unique spectral and spatial resolution advantages. The techniques are capable of in situ investigating chemical speciation, microstructure and mapping of elements in question at the molecular or nanometer scale, and thus provide direct evidence for reaction mechanisms for various environmental processes. In this contribution, the applications of three types of the techniques commonly used in the fields of environmental research are reviewed, namely X-ray absorption spectroscopy (XAS), X-ray fluorescence (XRF) spectroscopy and scanning transmission X-ray microscopy (STXM). In particular, the recent advances of the techniques in China are elaborated, and a selection of the applied examples are provided in the field of environmental science. Finally, the perspectives of synchrotron-based X-ray techniques are discussed. With their great progress and wide application, the techniques have revolutionized our understanding of significant geo- and bio-chemical processes. It is anticipatable that synchrotron-based X-ray techniques will continue to play a significant role in the fields and significant advances will be obtained in decades ahead.

Uptake and acropetal translocation of 14 priority polycyclic aromatic hydrocarbons (PAHs) by wheat (Triticum aestivum L.) grown in 15 field-contaminated soils were investigated in a growth chamber. PAH concentrations in roots correlated positively with the corresponding concentrations in soils and negatively with the contents of soil organic carbon (p < 0.01). No clear linear relationship was found between log RCF (root concentration factor, μg g−1root/μg g−1soil on dry weight basis) and log Kow of these PAHs. Four-ring PAHs had the highest tendency to be taken up by roots. PAH concentrations in shoots correlated well with their concentrations in soils and roots. Furthermore, distribution profiles of PAHs in shoots were fairly similar to those in soils. Acropetal translocation of 10 PAHs (with log Kow varying from 3.45 to 5.78) was also implicated by Rt (ratio of PAH from root-to-shoot translocation to the total accumulation in shoots) ranging from 53.6 to 72.6%. A negative linear relationship was found between log Rt and log Kow of these PAHs (p < 0.01), and acropetal translocation of PAHs depended on their chemical properties.

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 13C 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 KOC values and the aromatic carbon contents (r2 = 0.896, p < 0.01) and a negative correlation between the sorption affinity KOC values and polarity ((O + N)/C) of root cell fractions (r2 = 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.

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.

Effects of metal cations (Na+, Ca2+, and Al3+) on phenanthrene sorption were investigated using two soils with contrasting organic carbon (OC) contents. The presence of the polyvalent cations (i.e., Ca2+ or Al3+) at a concentration of 0.01 mol/L significantly increased the capacity and nonlinearity of phenanthrene sorption to soils compared with the monovalent Na+. The effects were governed by the content of soil OC. Rubbery OC (i.e., soft, amorphous OC including dissolved organic carbon (DOC)) tended to become condensed on soil surfaces as evidenced by a decrease in the signals of the 1H NMR spectra of DOC and an increase in the glass transition temperature (Tg) of the soils when the polyvalent cations were present. Increasing Ca2+ concentration led initially to an effect similar to that of the polyvalent cations in the low cation concentration range, and the effect was gradually attenuated as Ca2+ concentration further increased. These findings lead us to propose that the modifications in the physical configuration and chemical characteristics of OC resulting from the presence of metal cations account for the increase in the capacity and nonlinearity of phenanthrene sorption to the soils. This study points to an important role of metal cations in the sorption and fate of phenanthrene in the soil environment.

Triolein-embedded cellulose acetate membrane (TECAM) was buried in 15 field-contaminated soils in parallel with the cultivation of wheat to predict bioavailability of naphthalene, phenanthrene, pyrene, and benzo[a]pyrene to wheat roots, and the method was compared with chemical extraction methods. Although a good linear relationship was found between PAH concentrations in chemical extractants and wheat roots, the percentage of PAH in soil removed by chemical extraction was much higher than the corresponding percentage removed by wheat roots. In contrast to chemical extraction, a nearly 1:1 relationship was found between the amount of each PAH taken up by TECAMs and wheat roots (r2 = 0.798−0.925, P < 0.01). Furthermore, the uptake of PAHs by TECAMs and wheat roots had the same pathway of passive transport via the soil solution. Moreover, TECAM caused minimal disturbance to the soil and was easy to deploy. Therefore, TECAM is believed to be a useful tool to predict bioavailability of PAHs to wheat roots grown in contaminated soils.

To demonstrate the combined toxicity of cadmium (Cd) and arsenate (As) to early developmental stages of six wheat varieties, young seedlings were exposed to solutions containing both contaminants and seed germination frequency and seedling biomass, root length and shoot height, Cd and As uptake, amylase activity, superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), soluble protein and malondialdehyde (MDA) concentrations in the seedlings were investigated. Seed germination and seedling biomass and root and shoot elongation decreased significantly (P<0.01) with increasing concentrations of Cd and As and root length appeared to be the most sensitive parameter. Uptake of Cd and As by seedlings increased with increasing Cd and As concentrations in the test solutions and obeyed Michaelis–Menten kinetics. Average total amylolytic, α-amylase and β-amylase activities seemed to decrease with Cd concentrations >4 mg L−1 and As ⩾4 mg L−1. Seedling contents of soluble protein, MDA and POD increased and the activities of SOD and CAT decreased with increasing concentrations of Cd and As following an initial increase. The MDA content was linearly and positively correlated with seed germination frequency, biomass increment, root length and shoot height elongation (P<0.01), suggesting that MDA may be useful as a biological indicator of Cd and As toxicity in wheat. Combined exposure to Cd and As produced greater toxicity to wheat than single exposure to each metal separately, and Cd and As in combination had an additive effect on seed germination frequency and antagonistic effects on seedling biomass and shoot and root elongation.

To investigate the accumulation and phytotoxicity of technical hexabromocyclododecane (HBCD) in maize, young seedlings were exposed to solutions of technical HBCD at different concentrations. The uptake kinetics showed that the HBCD concentration reached an apparent equilibrium within 96 hr, and the accumulation was much higher in roots than in shoots. HBCD accumulation in maize had a positive linear correlation with the exposure concentration. The accumulation of different diastereoisomers followed the order γ-HBCD > β-HBCD > α-HBCD. Compared with their proportions in the technical HBCD exposure solution, the diastereoisomer contribution increased for β-HBCD and decreased for γ-HBCD in both maize roots and shoots with exposure time, whereas the contribution of α-HBCD increased in roots and decreased in shoots throughout the experimental period. These results suggest the diastereomer-specific accumulation and translocation of HBCD in maize. Inhibitory effects of HBCD on the early development of maize followed the order of germination rate > root biomass ≥ root elongation > shoot biomass ≥ shoot elongation. Hydroxyl radical (OH) and histone H2AX phosphorylation (γ-H2AX) were induced in maize by HBCD exposure, indicative of the generation of oxidative stress and DNA double-strand breaks in maize. An OH scavenger inhibited the expression of γ-H2AX foci in both maize roots and shoots, which suggests the involvement of OH generation in the HBCD-induced DNA damage. The results of this study will offer useful information for a more comprehensive assessment of the environmental behavior and toxicity of technical HBCD.The uptake and translocation of HBCD in maize are diastereomer-selective and HBCD accumulation results in the generation of oxidative stress and damage of DNA double-strand breaks in maize.Download high-res image (204KB)Download full-size image

The effects of an arbuscular mycorrhizal (AM) fungus (Glomus etunicatum) on atrazine dissipation, soil phosphatase and dehydrogenase activities and soil microbial community structure were investigated. A compartmented side-arm (‘cross-pot’) system was used for plant cultivation. Maize was cultivated in the main root compartment and atrazine-contaminated soil was added to the side-arms and between them 650 or 37 μm nylon mesh was inserted which allowed mycorrhizal roots or extraradical mycelium to access atrazine in soil in the side-arms. Mycorrhizal roots and extraradical mycelium increased the degradation of atrazine in soil and modified the soil enzyme activities and total soil phospholipid fatty acids (PLFAs). Atrazine declined more and there was greater stimulation of phosphatase and dehydrogenase activities and total PLFAs in soil in the extraradical mycelium compartment than in the mycorrhizal root compartment when the atrazine addition rate to soil was 5.0 mg kg−1. Mycelium had a more important influence than mycorrhizal roots on atrazine degradation. However, when the atrazine addition rate was 50.0 mg kg−1, atrazine declined more in the mycorrhizal root compartment than in the extraradical mycelium compartment, perhaps due to inhibition of bacterial activity and higher toxicity to AM mycelium by atrazine at higher concentration. Soil PLFA profiles indicated that the AM fungus exerted a pronounced effect on soil microbial community structure.

AbstractA hydroponic experiment was carried out to study intraspecific differences in the effects of different concentrations of cadmium (Cd) (0–10 mg/L) and arsenate (As(V)) (0–8 mg/L) on the growth parameters and accumulation of Cd and As in six wheat varieties Jing- 9428, Duokang-1, Jingdong-11, Jing-411, Jingdong-8 and Zhongmai-8. The endpoints of wheat seedlings, including seed germination, biomass, root length and shoot height, decreased with increasing the Cd and As concentrations. Significant differences in seed germination, biomass, root length, shoot height and the accumulation of Cd and As were observed between the treatments and among the varieties (p < 0.05). The lethal dosage 50% were about 20, 80, 60, 60, 80 and 20 mg As/L for Jing-9428, Duokang-1, Jingdong-11, Jing-411, Jingdong-8 and Zhongmai-8, respectively, and the corresponding values for Cd were about 30, 80, 20, 40, 60 and 10 mg Cd/L, respectively. Among the six varieties, Duokang-1 was found to be the most resistant to Cd and As toxicity, and Zhongmai-8 was the most sensitive to Cd and As co-contamination. The resistance of the six varieties was found dependant on the seedling uptake of Cd and As. Duokang-1 was the most suitable for cultivation in Cd and As co-contaminated soils.

Effects of inoculation with arbuscular mycorrhizal (AM) fungus Glomus mosseae on the accumulation and speciation of selenium (Se) in maize were systematically investigated using soil spiked with selenite (Se(IV)) and selenate (Se(VI)). Selenium speciation was analyzed by HPLC–ICP-MS. The results indicated that accumulation and speciation of Se in plants and the influence of mycorrhizal inoculation depend on the chemical form of Se that the soil was spiked with. There was no obvious influence of inoculation on Se species distribution, plant uptake and translocation for the experimental treatment that was supplied with Se(VI). When Se(IV) was supplied to the soil, mycorrhizal inoculation promoted oxidation of Se(IV) to Se(VI) in the soil, inhibited Se accumulation by maize, enhanced the accumulation of Se(VI) but reduced the accumulation of organic Se in maize. Microbeam X-ray fluorescence (μ-XRF) mapping confirmed that mycorrhizal inoculation inhibited the translocation of Se from the surface to the inner of roots when Se(IV) was added to soil. This study elucidates, for the first time, the speciation-dependent influence of mycorrhizal inoculation on the behavior of Se in the soil–plant system.