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Natural organic matter (NOM) can interact with engineered nanoparticles (NPs) in the environment and modify their behavior and toxicity to organisms. In the present study, the phytotoxicity of copper oxide (CuO) NPs to rice seedlings in the presence of humic acid as a model NOM was investigated. The results showed that CuO NPs induced the inhibition of root elongation, aberrations in root morphology and ultrastructure, and losses of cell viability and membrane integrity. The adverse effects partly resulted from the generation of reactive oxygen species caused by CuO NPs, which led to lipid peroxidation, mitochondrial dysfunction, and programmed cell death in rice seedlings. However, all the phytotoxicity was alleviated with the addition of humic acid because humic acid coatings on nanoparticle surfaces enhanced electrostatic and steric repulsion between the CuO NPs and the plant cell wall/membrane, reducing contact between NPs and plant and CuO NP-induced oxidative damage to plant cells. The present study's results shed light on the mechanism underlying NP phytotoxicity and highlight the influence of NOM on the bioavailability and toxicity of NPs. Environ Toxicol Chem 2015;34:1996-2003. © 2015 SETAC [ABSTRACT FROM AUTHOR]

Engineered nanoparticles (NPs) and natural organic matter (NOM) in the environment may interact with background contaminants such as heavy metals and modify their bioavailability and toxicity. In the present study, the combined influences of 2 common NPs (TiO2 and CeO2) and humic acid (HA; as a model NOM) on Cu(II) phytotoxicity to rice were investigated by a 3-d root elongation assay performed on filter paper media. The results showed that the adsorption coefficients of bare TiO2 and CeO2 NPs (100 mg/L) toward Cu2+ are 2.65 and 4.37, respectively, at an initial concentration of 10 mg/L, suggesting that Cu(II) could be strongly adsorbed by NPs, whereas HA-coated TiO2 and CeO2 NPs further enhanced the adsorption coefficients to 4.37 and 6.85, respectively. In addition, compared with Cu-alone treatment, the addition of bare TiO2 and CeO2 NPs (1000 mg/L) increased the length of rice root by 32.5% and 39.0%, respectively; however, the presence of HA-coated TiO2 and CeO2 NPs increased the root length by 90.2% and 100.1%, respectively, which indicated that the mitigation effect of HA-coated NPs on Cu(II) phytotoxicity was more visible than that of bare NPs. The results demonstrated that coexistence of NPs and HA significantly alleviated Cu(II) phytotoxicity as a result of a decrease in bioavailable soluble Cu(II) concentration, which contributes to an understanding of the potential behavior of NPs in the environment. Environ Toxicol Chem 2015;34:1588-1596. © 2015 SETAC [ABSTRACT FROM AUTHOR]

A hydroponics trial was employed to study the effects of Pseudomonas putida CZ1 (CZ1), a heavy-metal-resistant bacterial strain isolated from the rhizosphere of Elsholtzia splendens ( E. splendens), on the uptake and translocation of copper (Cu) in E. splendens. Significant promotion of plant growth coupled with the obvious plant-growth-promoting (PGP) characters of the bacteria suggested that CZ1 would be a plant-growth-promoting rhizobacterium (PGPR) to E. splendens under Cu stress condition. The results of inductively coupled plasma optical emission spectrometry (ICP-OES) showed that CZ1 increased the concentration of Cu in the shoots (up to 211.6 % compared to non-inoculation treatment) and translocation factor (TF) (from 0.56 to 1.83 %) of those exposed to Cu. The distribution of Cu in root cross section measured by synchrotron-based X-ray fluorescence microscopy (SRXRF) indicated that CZ1 promoted the transport of Cu from cortex to xylem in roots, which contributed to the accumulation of Cu in shoots. Furthermore, CZ1 improved the uptake of nutrient elements by plants to oppose to the toxicity of Cu. In summary, P. putida CZ1 acted as a PGPR in resistance to Cu and promoted the accumulation and translocation of Cu from root to shoot by element redistribution in plant root; hence, CZ1 is a promising assistance to phytoremediation. [ABSTRACT FROM AUTHOR]

The release of nanoparticles (NPs) to the environment poses an increasing potential threat to biological systems. This study investigated the phytotoxicity and accumulation of copper oxide (CuO) NPs to Elsholtzia splendens (a Cu-tolerant plant) under hydroponic conditions. The 50% effective concentration (EC50) of CuO NPs to E. splendens was about 480 mg/L, implying the tolerance of E. splendens to CuO NPs. The Cu content in the shoots treated with 1000 mg/L CuO NPs was much higher than those exposed to the comparable 0.5 mg/L soluble Cu and CuO bulk particles. CuO NPs-like deposits were found in the root cells and leaf cells. Cu K-edge X-ray absorption near-edge structure analysis further revealed that the accumulated Cu species existed predominantly as CuO NPs in the plant tissues. All these results suggested that CuO NPs can be absorbed by the roots and translocated to the shoots in E. splendens. [ABSTRACT FROM AUTHOR]

It has become apparent that the threat of an organic pollutant in soil is directly related to its bioavailable fraction and that the use of total contaminant concentrations as a measure of potential contaminant exposure to plants or soil organisms is inappropriate. In light of this, non-exhaustive extraction techniques are being investigated to assess their appropriateness in determining bioavailability. To find a suitable and rapid extraction method to predict phenanthrene bioavailability, multiple extraction techniques (i.e., mild hydroxypropyl- β-cyclodextrin (HPCD) and organic solvents extraction) were investigated in soil spiked to a range of phenanthrene levels (i.e., 1.12, 8.52, 73, 136, and 335 μg g dry soil). The bioaccumulation of phenanthrene in earthworm ( Eisenia fetida) was used as the reference system for bioavailability. Correlation results for phenanthrene suggested that mild HPCD extraction was a better method to predict bioavailability of phenanthrene in soil compared with organic solvents extraction. Aged (i.e., 150 days) and fresh (i.e., 0 day) soil samples were used to evaluate the extraction efficiency and the effect of soil contact time on the availability of phenanthrene. The percentage of phenanthrene accumulated by earthworms and percent recoveries by mild extractants changed significantly with aging time. Thus, aging significantly reduced the earthworm uptake and chemical extractability of phenanthrene. In general, among organic extractants, methanol showed recoveries comparable to those of mild HPCD for both aged and unaged soil matrices. Hence, this extractant can be suitable after HPCD to evaluate risk of contaminated soils. [ABSTRACT FROM AUTHOR]

We studied the effects of copper (Cu) phytoremediation on microbial community composition under laboratory conditions. A Cu accumulator, Commelina communis, was grown on a soil containing different gradients of Cu. Results showed that the biomass of C. communis grown with Cu differed from that of the control. Concentrations of Cu in the shoots of C. communis were 73.6, 160.9, and 319.1 mg kg-1 under 200, 500, and 1000 mg kg-1 Cu treatments, respectively. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) fingerprint analysis revealed that additions of Cu decreased the number of bands in the soil with C. communis or without plants. The principal component analysis explained 52.7% of the variance for the different rhizospheres of soil and Cu treatments in the soil samples. These results indicated significant effects on soil bacteria activity and community composition in the rhizosphere of C. communis and provided a basis for further studies of metal-accumulator plant effects on soil microorganisms. [ABSTRACT FROM AUTHOR]

Laser ablation coupled with inductively coupled plasma-mass spectrometry was used to find Cu and Zn concentration in surface tissue along a longitudinal developmental gradient with meristem, rapidly elongating tissue, and nongrowing tissue in a model system of seedling roots of Cucumis sativus L. (cucumber). Tissue metal accumulation was determined for roots of seedlings growing on cellulosic germination paper treated with nutrient solution (controls), and also treated with concentrations of Zn (40 ppm) and Cu (10 ppm) that reduced growth. Cu content of all roots is highest at the apex and falls sharply to lower values by 2 mm from the root tip. In contrast, at moderate Zn availability (0.07 ppm), Zn content rises from the apex to 2 mm then falls throughout the remainder of the growth zone. At high external Zn the spatial pattern resembles that of Cu. Cucumber root growth zones accumulate more of each metal with higher external availability. Metal deposition rates were calculated using a continuity equation with data on local metal content and growth velocity. Deposition rates of both metals are generally highest in the rapidly elongating region, 1.5–3.5 mm, even where metal concentration is decreasing with position and root age and even when the accumulation is inhibitory to growth. [ABSTRACT FROM AUTHOR]

A Cr(VI)-reducing bacteria ( Pseudochrobactrum saccharolyticum LY10) was selected to simulate the biofilm grown in unsaturated habitats containing Cr(VI) and the X-ray fluorescence and absorption methods were used to characterize the temporal and spatial distributions of metal elements in the unsaturated biofilms in the present study. The results indicated that Cr and other elements (Fe, Mn, Ca, K, and Zn) were selectively accumulated in the unsaturated biofilms. Synchrotron radiation micro X-ray fluorescence microscopy (SR-μXRF) analysis revealed that Cr mainly existed in the 10–45 μm layer near the bottom biofilm–membrane interface after 24 h of Cr exposure. The analysis of Cr speciation by X-ray absorption near-edge structure (XANES) spectroscopy analysis further confirmed the bioreduction of Cr(VI) to Cr(III), and the precipitate formed in the biofilms after reduction were most similar to CrPO 4 . This systematic understanding of the accumulation, distribution and reduction process of Cr in the unsaturated biofilms will elaborate to enhance the bioremediation efficiencies for Cr pollution in soil and other environment. [ABSTRACT FROM AUTHOR]

The toxic chemical element cadmium (Cd) in paddy fields triggered increasing problems of growth inhibition and food security in rice consistently. In this study, we found Metarhizium robertsii , which is widely used as a bioinsecticide and biofertilizer in agriculture and recently found to be resistant to Cd, developed intraradical and extraradical symbiotic hyphae in rice seedlings, and successfully colonized in the rice rhizosphere soil to more than 103 CFUs g−1 soil at harvesting. M. robertsii colonization significantly reduced Cd accumulations in both hydroponically cultured seedlings and the matured rice cultured in Cd contaminated potting soil (2 ppm). Notably, Cd accumulation reduction of the roots, stems, leaves, husks and grains of the matured rice induced by the fungus were 44.3%, 32.1%, 35.3%, 31.9% and 24.7%, respectively. It was caused by the M. robertsii -induced suppression of Cd intake transporter gene osNramp5 in the rice roots, and the chemical stabilizing of Cd to the residual fraction in the rhizosphere soil. In addition, the colonization of M. robertsii significantly promoted the growth characters and the photosynthesis of the rice plants. This is achieved by the increase of endogenous hormone levels of indole-3-acetic, gibberellin A 3 and brassinolide induced by M. robertsii. Furthermore, the fungus enhanced the antioxidative capacities via increasing enzyme activities of catalase, peroxidase and the production of glutathione, ascorbic acid, proline in the rice plants. Our work provides theoretical basis for expanding the use of M. robertsii as in situ Cd accumulation reduction and detoxification agents for rice in contaminated paddy fields. [Display omitted] • M. robertsii colonized well in the rice roots and the rhizosphere soil. • M. robertsii reduced Cd accumulation and promoted plant growth of rice. • Rice osNramp5 was suppressed and soil Cd ions were stabilized by the fungus. • Endogenous phytohormones IAA, GA 3 and BL were elevated by the fungus. • M. robertsii stimulated antioxidative capacities of rice. [ABSTRACT FROM AUTHOR]

Due to the high migration capacity in agricultural soil-crop systems, cadmium (Cd) is accumulated in various crops and severely inhibits plant growth. In this study, we showed that, under Cd stress, the plant-symbiotic fungus Metarhizium robertsii reduced Cd accumulation in Arabidopsis thaliana shoots and roots by 21.8 % and 23.8 %, respectively. This is achieved by M. robertsii colonization-induced elevation of Cd efflux capacity via upregulation of three PCR genes, which is confirmed by the fact that the extent to which M. robertsii reduced Cd accumulation in the WT plants was greater than the inactivating mutants of the PCR genes. M. robertsii also alleviated Cd-induced leaf etiolation in A. thaliana by increasing the chlorophyll amount and modified plant physiological status to increase Cd stress tolerance via increasing production of catalase, peroxidase and glutathione and upregulating multiple HIPP proteins involved in sequestration of Cd. Notably, consistent with that in A. thaliana , the colonization of M. robertsii also reduced the Cd accumulation in Oryza sativa seedlings by upregulating the PCR gene OsPCR1 , and increased chlorophyll amount and alleviated oxidative stress. Therefore, M. robertsii colonization reduced Cd accumulation in plants, and promoted plant growth and health by elevating Cd efflux capacity and modifying physiological status. [Display omitted] • M. robertsii reduces Cd content in A. thaliana and O. sativa by increasing the PCR genes to elevate the Cd efflux capacity. • Cd-induced leaf etiolation was alleviated and more chlorophyll was produced in plants colonized with M. robertsii. • M. robertsii decreased the oxidation level and increased the total antioxidant capacity in plants. [ABSTRACT FROM AUTHOR]

Impact of S fertilization on Cu mobility and transformation in contaminated paddy soils has been little reported. In this study, we investigated the dynamics and transformation of dissolved and colloidal Cu in the pore water of a contaminated paddy soil after applying ammonium sulphate (AS) and sulfur coated urea (SCU) with various flooding periods (1, 7 and 60 days). Compared to the control soil, the AS-treated soil released more colloidal and dissolved Cu over the entire flooding period, while the SCU-treated soil had lower colloidal Cu after 7-day flooding but higher colloidal and dissolved Cu after 60-day flooding. Microscopic X-ray fluorescence (μ-XRF) analysis found a close relationship between Fe and Cu distribution on soil colloids after 60-day flooding, implying the formation of colloidal Fe/Cu sulphide coprecipitates. Cu K-edge X-ray absorption near-edge structure (XANES) spectroscopy directly revealed the transformation of outer-sphere complexed Cu(II) species to Cu(II) sulphide and reduced Cu 2 O in the colloids of S-treated soils after 60-day flooding. These results demonstrated the great influence of S fertilization on pore-water Cu mobility by forming Cu sulphide under flooding conditions, which facilitated our understanding and control of Cu loss in contaminated paddy soils under S fertilization. [ABSTRACT FROM AUTHOR]

Background and aims: Metal species in rhizosphere soil profoundly influence their mobility and phytoavailability. Clarifying the speciation transformation of heavy metals helps understand their translocation and accumulation in plants. Methods: Single extraction, selective sequential extraction (SSE) and X-ray absorption near-edge structure (XANES) spectroscopy were employed to investigate the speciation transformation of lead (Pb) and its influence on metal accumulation in tea plants after the addition of tea polyphenols (TPs). Results: Pb content was decreased in young leaves and stems, whereas increased in roots, after TPs were amended to soil. Both SSE and XANES analysis suggested bioavailable Pb was transformed to organically bound Pb after the addition of TPs. The increased percentage of organically bound Pb might be fixed in the cell wall of plant root through a ternary complex formed between the Pb-organic matter complex and cell wall components. Therefore, Pb translocation from roots to young tissues was decreased. Conclusions: Pb phytoavailability change was driven by its speciation transformation after the addition of TPs. Combined SSE and XANES spectroscopy represent powerful tools to study metal speciation transformation in plant and soil systems. [ABSTRACT FROM AUTHOR]

The inhibitory effect of barley straw ( Hordeum vulgare) on cyanobacteria has been observed in many field and laboratory studies for over 30 years, although the compounds responsible for this anti-cyanobacterial effect have remained unknown. In this study, a pair of chiral flavonolignans were isolated from barley straw extract using a bioassay-guided isolation procedure against Microcystis sp. The structures of the allelopathic compounds were elucidated by NMR (nuclear magnetic resonance) and HPLC-MS (high performance liquid chromatography-mass spectrometry), and turned out to be salcolin A and B. The enantiomers differ in their anti-cyanobacterial abilities. Both enantiomers exhibited inhibitory effects on Microcystis sp., and the EC50 (concentration for 50% of maximal effect) of salcolin A and B were 6.02 × 10−5 and 9.60 × 10−5 mol l−1, respectively. Furthermore, the modes of actions of the enantiomers were investigated and compared at a single cell level by flow cytometry. Salcolin A was found to induce an increase on cyanobacterial intracellular ROS (reactive oxygen species) levels and to inhibit esterase activity, whereas salcolin B caused leakages of cyanobacterial cytoplasms. Thus, salcolin A was more 'algistatic', and salcolin B was more 'algicidal'. This study suggests that salcolin is the key allelochemical in barley straw's inhibitory effect on cyanobacteria and could be used as an agent in the future control of cyanobacterial harmful algae blooms. [ABSTRACT FROM AUTHOR]

Support vector machine (SVM) classification models were constructed using a radial basis functions (RBF). These models were used for classification according to dissolved oxygen, permanganate index, ammoniac nitrogen, total nitrogen, or total phosphorus. Cross-validation and grid-search were applied to find satisfactory parameters for RBF for the improved models. Then the improved models were used to assess water quality utilizing a real-world data set (surface water quality monitoring data). The data set was comprised of more than 2,000 water samples representing 172 different sites monitored for one hydrological year. The results showed that the method presented in this paper had excellent performance, and the SVM classification models performed relatively better than the Linear Discriminant Analysis and Quadratic Discriminant Analysis models for classification. [ABSTRACT FROM AUTHOR]

Abstract: Phytolacca americana L. (pokeweed) is a promising species for Cd phytoextraction with large biomass and fast growth rate. To further understand the mechanisms involved in Cd tolerance and detoxification, the present study investigated subcellular distribution and chemical forms of Cd in pokeweed. Subcellular fractionation of Cd-containing tissues indicated that both in root and leaves, the majority of the element was located in soluble fraction and cell walls. Meanwhile, Cd taken up by pokeweed existed in different chemical forms. Results showed that the greatest amount of Cd was found in the extraction of 80% ethanol in roots, followed by 1M NaCl, d-H2O and 2% HAc, while in leaves and stems, most of the Cd was extracted by 1M NaCl, and the subdominant amount of Cd was extracted by 80% ethanol. It could be suggested that Cd compartmentation with organo-ligands in vacuole or integrated with pectates and proteins in cell wall might be responsible for the adaptation of pokeweed to Cd stress. [Copyright &y& Elsevier]

Lead (Pb) and arsenic (As) exist in soil with different ionic forms, and it is difficult to immobilize simultaneously Pb and As in soil. The objective of this study is to determine the effects of water management including flooding (FL), alternate wetting and drying (AWD) and dry farming (DF) combined with addition of phosphate (P) on the accumulation of Pb and As in rice. Our results showed that Pb accumulated in root during vegetative stage, and most of As in root was transported to the above ground parts during the reproductive stage. Pb was evenly distributed in grains, and As was mostly accumulated in bran and aleurone layer. Water management had a reverse effect on the accumulation of Pb and As in rice. However, the effects of P on arid soil environment and Pb, As accumulation in rice were stronger than that in flooded soil. Application of P under AWD treatment could maintain a similar quantity of Fe plaque with flooding, decrease the availability of Pb in rhizosphere soil, reduce Pb and As accumulation in root, and result in the reduction of Pb and As accumulation in grains by 86% and 66% respectively. Besides, our study also found that flooding or AWD during vegetative stage facilitated the formation of iron plaque. In conclusion, AWD combined with P application could maintain a relatively lower concentrations of Pb and As in grains. [Display omitted] • Lead accumulated in root primarily during the vegetative stage. • Arsenic in root was transported to aboveground parts during the reproductive stage. • Flooding or AWD during the vegetative stage in soil would help to form iron plaque. • AWD combined with application of P could decrease simultaneously lead and arsenic in grains. • Lead was distributed evenly in grains, and arsenic was mostly accumulated in bran and aleurone layer. [ABSTRACT FROM AUTHOR]

The aggregation of nanoscale zero-valent iron (nZVI) particles and their limited transport ability in environmental media hinder their application in environmental remediation. In this study, the Cr(VI) removal efficiency, transport performance, and toxicity of nZVI and bentonite-modified nZVI (B-nZVI) were investigated. Compared with nZVI, B-nZVI improved the removal efficiency of Cr(VI) by 10%, and also significantly increased the transport in quartz sand and soil. Increasing the flow rate can enhance the transport of nZVI and B-nZVI in the quartz sand columns. The transport of the two materials in different soils was negatively correlated with the clay composition. Besides, modification of nZVI by bentonite could reduce toxicity to luminous bacteria (Photobacterium phosphereum T3) and ryegrass (Lolium perenne L.). Compared with Fe-EDTA, the transfer factors of nZVI and B-nZVI were 65.0% and 66.4% lower, respectively. This indicated that although iron nanoparticles accumulated in the roots of ryegrass, they were difficult to be transported to the shoots. The results of this study indicate that B-nZVI has a strong application potential in in situ environmental remediation. [ABSTRACT FROM AUTHOR]

• Cr(VI) reduction by P. oxalicum SL2 in medium was accelerated by Ca2+ and SO 4 2−. • High Ca2+ concentration resulted in the production of calcium oxalate crystals. • P. oxalicum SL2 could reduce the toxicity of Cr(VI) by synthesizing thiol compounds (Cys and GSH). Some ions in soils may affect the growth and metabolism of microorganisms and subsequently alter the remediation efficiency of Cr(VI). Here, the effects of different Ca2+ and SO 4 2− levels on the reduction of Cr(VI) by Penicillium oxalicum SL2 were investigated. The results showed that Cr(VI) reduction by P. oxalicum SL2 in potato dextrose liquid (PDL) medium was accelerated by the presence of exogenous Ca2+ and SO 4 2−. The Cr(VI) reduction rates were increased by 52.5% (200 mg L−1 Ca2+ treated) and 55.9% (2000 mg L−1 SO 4 2− treated), respectively. High concentration of Ca2+ in medium resulted in the production of calcium oxalate crystals, which was contributed to the adsorption of chromium. In addition, X-ray absorption near-edge spectroscopy (XANES) analysis showed that P. oxalicum SL2 could reduce the toxicity of Cr(VI) by synthesizing cysteine (Cys) and reduced glutathione (GSH). The decrease of thiol compounds (Cys and GSH) in P. oxalicum SL2 mycelia treated with SO 4 2− proved the alleviation of oxidative stress. In conclusion, exogenous Ca2+ could reduce the damage of Cr(VI) to P. oxalicum SL2 by maintaining the integrity of cell wall, and the addition of SO 4 2− alleviated the Cr(VI) toxicity to P. oxalicum SL2, thus accelerating the reduction of Cr(VI). [ABSTRACT FROM AUTHOR]