Plant-substrate biochar properties critical for mediating reductive debromination of 1,2-dibromoethane.

Dibromoethane is a widespread, persistent organic pollutant. Biochars are known mediators of reductive dehalogenation by layered FeII-FeIII hydroxides (green rust), which can reduce 1,2-dibromoethane to innocuous bromide and ethylene. However, the critical characteristics that determine mediator functionality are lesser known. Fifteen biochar substrates were pyrolyzed at 600 °C and 800 °C, characterized by elemental analysis, X-ray photo spectrometry C and N surface speciation, X-ray powder diffraction, specific surface area analysis, and tested for mediation of reductive debromination of 1,2-dibromoethane by a green rust reductant under anoxic conditions. A statistical analysis was performed to determine the biochar properties, critical for debromination kinetics and total debromination extent. It was shown that selected plant based biochars can mediate debromination of 1,2-dibromoethane, that the highest first order rate constant was 0.082/hr, and the highest debromination extent was 27% in reactivity experiments with 0.1 µmol (20 µmol/L) 1,2-dibromoethane, ≈ 22 mmol/L FeIIGR, and 0.12 g/L soybean meal biochar (7 days). Contents of Ni, Zn, N, and P, and the relative contribution of quinone surface functional groups were significantly (p < 0.05) positively correlated with 1,2-dibromoethane debromination, while adsorption, specific surface area, and the relative contribution of pyridinic N oxide surface groups were significantly negatively correlated with debromination.

Biochar catalyzed dechlorination - Which biochar properties matter?

Bone char catalyzed dechlorination of trichloroethylene (TCE) by green rust (iron(II)-iron(III) hydroxide, GR) has introduced a promising new reaction platform for degradation of chlorinated solvents. This study aimed to reveal whether a broader class of biochars are catalytically active for the dechlorination reaction and to identify which biochar properties are the most important for the catalytic activity. Biochars produced by pyrolysis of animal, plant, and sewage waste substrates at 950 °C were prepared for catalytic dechlorination of TCE by GR tested in batch experiments with 0.15 g L-1 biochar, 3.2 g L-1 GR, and ~ 20 µM TCE. The results showed that the biochar substrate significantly affects its catalytic activity, with the highest TCE reduction rate observed for bone and shrimp-based biochars (k ≥ 0.18 h-1), whereas no reactivity was seen for graphite and activated carbon references. Multivariate regression indicated that the biochar catalytic activity is controlled by multiple biochar properties - biochar surface area, TCE sorption, abundance of C-O groups, and pore size are the properties that impact the catalytic activity most. Derivation of biochar reactivity relationship for a broad spectrum of biochars provides a new approach for identifying proper biochar catalysts for pollutant degradation.

Single sheet iron oxide: An efficient heterogeneous electro-Fenton catalyst at neutral pH.

In order to overcome the inefficiency of heterogeneous electro-Fenton process for water treatment at neutral pH, single sheet iron oxide (SSI) derived from layered Fe(II)-Fe(III) double hydroxides (green rusts) was fabricated on an indium tin oxide electrode via layer by layer assembly and used in an undivided electrolysis cell. Use of radical scavengers demonstrated the formation of oxygen radicals by electrochemical reduction of oxygen at the SSI electrode, and the key role of hydroxyl radicals (OH) and superoxide anion (O2-) radicals in degradation of the azo dye orange II. Analysis of degradation products by UV-vis, LC-MS and GC-MS further demonstrated that direct reduction toke place in addition to indirect oxidation. The reactivity of SSI as a heterogeneous electro-Fenton catalyst is two order of magnitude higher than its homogenous counterparts. The SSI electrode was highly stable as the dye degradation did not decrease after use for 19 h with no Fe leaching. The high dye removal efficiency was maintained in a wide pH range from 7 to 10 and in different supporting electrolytes, demonstrating the application of this process under various conditions mimicking natural waters.

Copper-mediated reductive dechlorination by green rust intercalated with dodecanoate.

A layered FeII-FeIII hydroxide (green rust, GR) was intercalated with dodecanoate (known as GRC12) and then amended with CuII (GRC12(Cu)) before reaction with chloroform (CF), carbon tetrachloride (CT), trichloroethylene (TCE) or tetrachloroethylene (PCE). Reduction of CT by GRC12(Cu) was 37 times faster than with GRC12 alone before the active Cu species was consumed. The Cu mediated reaction followed the dichloroelimination pathway as observed for GRC12 alone, with carbon monoxide (82.5%) and formate (26.6%) as main degradation products. Also, CF was reduced by GRC12(Cu), which is not seen with GRC12. Neither GRC12(Cu) nor GRC12 reacted with PCE or TCE. The chlorinated solvents can partition into dodecanoate interlayer but only small CS molecules (CF, CT) can transport through the dodecanoate interlayer. Copper(II) added to GRC12 was reduced to CuI by FeII in GR, but CuI was not regenerated during the dechlorination. High resolution TEM showed that Cu was evenly distributed in the GR without formation of Cu nanoparticles on edges of GR. The active CuI sites are most likely located between the iron hydroxide layer and the hydrated negatively charged carboxylate groups in the interlayer of GR. This work shines new light on the Cu accelerated dechlorination by GR.

Screening of inorganic and organic contaminants in floodwater in paddy fields of Hue and Thanh Hoa in Vietnam.

In the rainy season, rice growing areas in Vietnam often become flooded by up to 1.5 m water. The floodwater brings contaminants from cultivated areas, farms and villages to the rice fields resulting in widespread contamination. In 2012 and 2013, the inorganic and organic contaminants in floodwater was investigated in Thanh Hoa and Hue. Water samples were taken at 16 locations in canals, paddy fields and rivers before and during the flood. In total, 940 organic micro-pollutants in the water samples were determined simultaneously by GC-MS method with automatic identification and quantification system (AIQS), while ICP-MS was used for determination of ten trace elements in the samples. The concentrations of 277 organic micro-pollutants and ten elements (As, Cu, Cd, Cr, Co, Pb, Zn, Fe, Mn, Al) ranged from 0.01 to 7.6 µg L-1 and 0.1 to 3170 µg L-1, respectively, in the floodwater. Contaminants originated from industrial sources (e.g. PAH) were detected at low concentrations, ranged from 0.01 to 0.18 µg L-1, while concentrations of pollutants originated from domestic sources (e.g. sterols, pharmaceuticals and personal care products and pesticides) were ranged from 0.01 to 2.12 µg L-1. Isoprocarb had the highest detection frequency of 90%, followed by isoprothiolane (88%) and fenobucarb (71%). The results indicated that contaminants in floodwater come from untreated wastewater from villages, and the agricultural activities are the major sources of increased pesticides resuspended in the floodwater in this study.

Glycine buffered synthesis of layered iron(II)-iron(III) hydroxides (green rusts).

Layered FeII-FeIII hydroxides (green rusts, GRs) are efficient reducing agents against oxidizing contaminants such as chromate, nitrate, selenite, and nitroaromatic compounds and chlorinated solvents. In this study, we adopted a buffered precipitation approach where glycine (GLY) was used in the synthesis of sulfate-interlayered GR (GRSO4) by aerial oxidation of FeII or co-precipitation by adding FeIII salt to an aqueous solution of FeII at constant pH. In both the oxidation and the co-precipitation methods pure crystalline GRSO4 was precipitated in the presence of 70mM GLY (pH 8.0), whereas in the absence of GLY, synthesis failed under similar conditions. Gycine functions as both a pH buffer and a ligand; FeII-GLY complexes serve as a source of base (FeII-GLY+H2O→FeII+H-GLY+OH-) during GR formation, supplying about 45% of the total base required for the synthesis. The GLY buffer decreases pH fluctuations during base addition and hence allows for fast GRSO4 precipitation, minimizing byproduct formation. The use of other pH buffers [4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid and 2-amino-2-(hydroxymethyl)-1,3-propanediol] was also tested but failed. Mössbauer spectroscopy, X-ray diffraction, Fourier transform infrared, transmission electron microscopy, and FeII measurements confirmed the purity, stoichiometry, and pyroaurite-type structure of the obtained GRSO4. The formula of GRSO4 was found to be FeII4.08FeIII1.98(OH)11.6(SO4)1.00, and the tabular GR crystals had a lateral size of 100-500nm and a thickness of about 40nm. Upscaling of the synthesis by either 25 times in volume or 20 times in FeII concentration resulted in pure GRSO4 products. Compared with the conventional unbuffered GRSO4 synthesis method, the present method can provide pure products with a controllable, fast, and low-cost process.

Graphene oxide-mediated rapid dechlorination of carbon tetrachloride by green rust.

Graphene-based nanomaterials can mediate environmentally relevant abiotic redox reactions of chlorinated aliphatic hydrocarbons. In this study as low amounts as ∼0.007 % of graphene oxide (GO) was found to catalyze the reduction of carbon tetrachloride by layered Fe(II)-Fe(III) hydroxide (Green Rust, GR) in aqueous solutions with chloroform being the reduction product. On the basis of sorption studies of carbon tetrachloride onto the GO surface it is suggested that it is the amphiphilicity of GO, which initiates the reaction by providing a suitable reaction platform for the reagents. This study indicates that traces of graphene oxide can affect reaction pathways as well as kinetics for dechlorination processes in anoxic sediments by facilitating a partial dechlorination.

Nitrogen regulation of the xyl genes of Pseudomonas putida mt-2 propagates into a significant effect of nitrate on m-xylene mineralization in soil.

The nitrogen species available in the growth medium are key factors determining expression of xyl genes for biodegradation of aromatic compounds by Pseudomonas putida. Nitrogen compounds are frequently amended to promote degradation at polluted sites, but it remains unknown how regulation observed in the test tube is propagated into actual catabolism of, e.g. m-xylene in soil, the natural habitat of this bacterium. To address this issue, we have developed a test-tube-to-soil model system that exposes the end-effects of remediation practices influencing gene expression of P. putida mt-2. We found that NO3- compared with NH4+ had a stimulating effect on xyl gene expression in pure culture as well as in soil, and that this stimulation was translated into increased m-xylene mineralization in soil. Furthermore, expression analysis of the nitrogen-regulated genes amtB and gdhA allowed us to monitor nitrogen sensing status in both experimental systems. Hence, for nitrogen sources, regulatory patterns that emerge in soil reflect those observed in liquid cultures. The current study shows how distinct regulatory traits can lead to discrete environmental consequences; and it underpins that attempts to improve bioremediation by nitrogen amendment should integrate knowledge on their effects on growth and on catabolic gene regulation under natural conditions.

Ptaquiloside in Irish Bracken Ferns and Receiving Waters, with Implications for Land Managers.

Ptaquiloside, along with other natural phytotoxins, is receiving increased attention from scientists and land use managers. There is an urgent need to increase empirical evidence to understand the scale of phytotoxin mobilisation and potential to enter into the environment. In this study the risk of ptaquiloside to drinking water was assessed by quantifying ptaquiloside in the receiving waters at three drinking water abstraction sites across Ireland and in bracken fronds surrounding the abstraction sites. We also investigated the impact of different management regimes (spraying, cutting and rolling) on ptaquiloside concentrations at plot-scale in six locations in Northern Ireland, UK. Ptaquiloside concentrations were determined using recent advances in the use of LC-MS for the detection and quantification of ptaquiloside. The results indicate that ptaquiloside is present in bracken stands surrounding drinking water abstractions in Ireland, and ptaquiloside concentrations were also observed in the receiving waters. Furthermore, spraying was found to be the most effective bracken management regime observed in terms of reducing ptaquiloside load. Increased awareness is vital on the implications of managing land with extensive bracken stands.

Electrochemical reduction of nitroaromatic compounds by single sheet iron oxide coated electrodes.

Nitroaromatic compounds are substantial hazard to the environment and to the supply of clean drinking water. We report here the successful reduction of nitroaromatic compounds by use of iron oxide coated electrodes, and demonstrate that single sheet iron oxides formed from layered iron(II)-iron(III) hydroxides have unusual electrocatalytic reactivity. Electrodes were produced by coating of single sheet iron oxides on indium tin oxide electrodes. A reduction current density of 10 to 30µAcm(-2) was observed in stirred aqueous solution at pH 7 with concentrations of 25 to 400µM of the nitroaromatic compound at a potential of -0.7V vs. SHE. Fast mass transfer favors the initial reduction of the nitroaromatic compound which is well explained by a diffusion layer model. Reduction was found to comprise two consecutive reactions: a fast four-electron first-order reduction of the nitro-group to the hydroxylamine-intermediate (rate constant=0.28h(-1)) followed by a slower two-electron zero-order reduction resulting in the final amino product (rate constant=6.9µM h(-1)). The zero-order of the latter reduction was attributed to saturation of the electrode surface with hydroxylamine-intermediates which have a more negative half-wave potential than the parent compound. For reduction of nitroaromatic compounds, the SSI electrode is found superior to metal electrodes due to low cost and high stability, and superior to carbon-based electrodes in terms of high coulombic efficiency and low over potential.

The naturally occurring carcinogen ptaquiloside is present in groundwater below bracken vegetation.

The present study demonstrates unequivocally the presence of the natural carcinogen ptaquiloside and its transformation product pterosin B in groundwater and surface water. Groundwater concentrations up to 0.23 nmol/L (92 ng/L) ptaquiloside and up to 2.2 nmol/L (0.47 µg/L) pterosin B were found. Of 21 groundwater samples, 5 contained ptaquiloside, exceeding the estimated threshold for drinking water (1.3-40 pmol/L). The results are critical for water abstraction in bracken-infested areas.

Efficient dechlorination of carbon tetrachloride by hydrophobic green rust intercalated with dodecanoate anions.

The reductive dechlorination of carbon tetrachloride (CT) by Fe(II)-Fe(III) hydroxide (green rust) intercalated with dodecanoate, Fe(II)(4)Fe(III)(2)(OH)(12)(C(12)H(23)O(2))(2) · yH(2)O (designated GR(C12)), at pH ~ 8 and at room temperature was investigated. CT at concentration levels similar to those found in heavily contaminated groundwater close to polluted industrial sites (14-988 µM) was reduced mainly to the fully dechlorinated products carbon monoxide (CO, yields >54%) and formic acid (HCOOH, yields >6%). Minor formation of chloroform (CF), the only chlorinated degradation product, was also detected (yields <6.3%). Reactions carried out with excess GR followed pseudo first-order kinetics with respect to CT with rate constants ranging from 6.5 × 10(-2) to 0.47 h(-1). These rate constants are comparable to those measured for CT dechlorinations mediated by zerovalent iron. Reduction of the highest concentration of CT (1.4 mM) proceeds until 56% of the Fe(II) sites of GR(C12) was consumed. This reaction ceased after 10 h due to surface passivation of GR(C12).

A liquid chromatography-electrospray ionization-mass spectrometry method for quantification of cyclotides in plants avoiding sorption during sample preparation.

Cyclotides are plant-produced, bioactive, cyclic mini-proteins with interesting pharmaceutical and agricultural applications. A reverse phase liquid chromatography electrospray ionization mass spectrometry (RP-LC-ESI-MS) method for analysis of cyclotides in plant materials with a minimum of sample pre-treatment is presented. Three exemplary cyclotides (kalata B1, kalata B2 and cycloviolacin O2) were used as reference substances for the method development. Linearity (r(2)>0.99) was achieved in the concentration range 0.05-10 mg/L and the limit of detection was 1.7-4.0 µg/L. The present study is the first to demonstrate that cyclotides dissolved in water sorb to glass vials, but the addition of 15% of acetonitrile or 40 mg/L of bovine serum albumin is sufficient to keep the cyclotides in solution. Cyclotides were extracted from candied violets, violet tea, and the plants Oldenlandia affinis and Viola odorata using 70% methanol containing 0.1% formic acid (v/v). The plant content was determined to be 23.5-14,200 µg/g (dry weight). The highest content of cyclotide was found in wild Danish V. odorata, and it is the highest content of cyclotide in a plant reported hitherto. Candied violets contained 0.00-8.66 µg/g (dry weight), while no cyclotides were detected in commercial violet tea.

Degradation of the potato glycoalkaloid alpha-solanine in three agricultural soils.

The toxic glycoalkaloids produced by the potato plant (Solanum tuberosum L.) have previously been found in upper soil from a potato field during several months. Further insight into the fate of the glycoalkaloids is needed, as only little information about their degradation in soil is available. Degradation of the glycoalkaloid, alpha-solanine, has been followed for 42d in three agricultural soils with common texture and carbon contents. A similar degradation pattern was found in all soils, and the kinetics was well described by a sum of two first-order equations. Overall, degradation rates for the initial first reaction were in the range 0.22-1.64d(-1). Estimated half-lives were in the range 1.8-4.1d for the three top soils at 15 degrees C; the fastest degradation was observed in the sandy soil. The major proportion of alpha-solanine in the sandy soil was degraded by the fast process, while the proportion was lower for the two other soils. Fast degradation appeared to be related to the presence of low amount of sorbents. Additionally, degradation was followed at 5 degrees C in A- and C-horizon soil from the sandy location, and for both horizons the half-lives were of similar length (4.7-8.7d). For the slow process, degradation rates were in the range 0.000-0.123d(-1), and residuals were still present in all soils and all temperatures at the end of the experiment (d 42). Overall, fast degradation was found in both top- and subsoil even at low temperatures, and the risk for alpha-solanine leaching to the groundwater appears to be low.

Degradation of the potato glycoalkaloids--alpha-solanine and alpha-chaconine in groundwater.

The potato glycoalkaloids alpha-chaconine and alpha-solanine are produced in high amounts in potato plants from where release to soil takes place. Degradation of the compounds in groundwater was investigated, as their fate in the terrestrial environment is unknown. Abiotic and microbial degradation were followed in groundwater sampled from below a potato field and spiked with the glycoalkaloids (115 nmol/l). Degradation was primarily microbial and the glycoalkaloids were degraded within 21-42 days. The metabolites beta(1)-solanine, gamma-solanine, and solanidine were formed from alpha-solanine, while beta-chaconine, gamma-chaconine and solanidine were detected from alpha-chaconine. Thus, indigenous groundwater microorganisms are capable of degrading the glycoalkaloids.

Fate of toxic potato glycoalkaloids in a potato field.

The toxic glycoalkaloids, alpha-solanine and alpha-chaconine, are present in all parts of the potato plant and are possibly transferred to the terrestrial environment. The amounts of glycoalkaloids in plant, soil, and groundwater were followed in a potato field to investigate their distribution and fate during the season. The amount of glycoalkaloids in the plants was up to 25 kg/ha during maturity and decreased to below 0.63 kg/ha during plant senescence. The glycoalkaloids were detected in the upper soil (up to 0.6 kg/ha); this amount accounted only for a minor fraction of the amount present in the plants. Maximum glycoalkaloid concentration of 2.8 mg/kg dry weight soil was detected in September. Dissipation during winter appeared to be slow because glycoalkaloids were still present in the soil in March. No traces of glycoalkaloids were detected in the groundwater (detection limit 0.2 microg/L). From these results, the leaching potential of the glycoalkaloids is evaluated to be small.

Quantification of ptaquiloside and pterosin B in soil and groundwater using liquid chromatography-tandem mass spectrometry (LC-MS/MS).

The carcinogenic compound ptaquiloside is produced by bracken fern (Pteridium aquilinum L.). Ptaquiloside can enter the soil matrix and potentially leach to the aquatic environment, and methods for characterizing ptaquiloside content and fate in soil and groundwater are needed. A sensitive detection method has been developed using liquid chromatography-tandem mass spectrometry (LC-MS/MS) for analyzing ptaquiloside and its transformation product pterosin B. Detection limits are 0.19 microg/L (ptaquiloside) and 0.15 microg/L (pterosin B), which are 300-650 times better than previously published LC-UV methods. Sequential soil extractions are made using 5 mM ammonium acetate for extraction of ptaquiloside, followed by 80% methanol extraction for pterosin B. Groundwater samples are cleaned-up and preconcentrated by a factor of 20 using solid-phase extraction. The LC-MS/MS method enables quantification of ptaquiloside and pterosin B in soil and groundwater samples at environmentally relevant concentrations and delivers a reliable identification because of the structure-specific detection method.

Potato glycoalkaloids in soil-optimising liquid chromatography-time-of-flight mass spectrometry for quantitative studies.

Potato glycoalkaloids are produced in high amounts in potato fields during the growth season and losses to soil potentially impact shallow groundwater and via tiles to fresh water ecosystems. A quantitative liquid chromatography-electrospray ionization time-of-flight mass spectrometry (LC-ESI-TOF-MS) method for determination and quantification of potato glycoalkaloids and their metabolites in aqueous soil extracts was developed. The LC-ESI-TOF-MS method had linearities up to 2000microg/L for alpha-solanine and alpha-chaconine and up to 760microg/L for solanidine. No matrix effect was observed, and the detection limits found were in the range 2.2-4.7microg/L. The method enabled quantification of the potato glycoalkaloids in environmental samples.

Microbial degradation pathways of the herbicide dichlobenil in soils with different history of dichlobenil-exposure.

This is the first detailed study of metabolite production during degradation of the herbicide 2,6-dichlorobenzonitrile (dichlobenil). Degradation of dichlobenil and three potential metabolites: 2,6-dichlorobenzamide (BAM), 2,6-dichlorobenzoic acid (2,6-DCBA) and ortho-chlorobenzamide (OBAM) was studied in soils either previously exposed or not exposed to dichlobenil using a newly developed HPLC method. Dichlobenil was degraded in all four soils; BAM and 2,6-DCBA were only degraded in soils previously exposed to dichlobenil (100% within 35-56 days and 85-100% in 56 days, respectively), and OBAM in all four soils (25-33% removal in 48 days). BAM produced from dichlobenil was either hydrolyzed to 2,6-DCBA or dechlorinated to OBAM, which was further hydrolyzed to ortho-chlorobenzoic acid. BAM was rapidly mineralized in previously exposed soils only. All potential metabolites and the finding that BAM was a dead-end metabolite of dichlobenil in soils not previously exposed to dichlobenil needs to be included in risk assessments of the use of dichlobenil.

Kinetics of ptaquiloside hydrolysis in aqueous solution.

Ptaquiloside (PTA) is a well-known toxin produced by the bracken fern (Pteridium aquilinum (L.) Kuhn). It is proposed that PTA from bracken stands can leach through soil and sediments into drinking-water reservoirs, thus representing a concern for human health. To predict the persistence of the toxin, a full understanding of the PTA degradation in aqueous environments is important. The kinetics of PTA hydrolysis was examined at 22 degrees C in aqueous buffered solutions (pH 2.88-8.93). The reaction was found to follow first-order kinetics with respect to PTA at all pH and temperature conditions. At pH lower than 4.43 (+/- 0.32), the reaction is acid-mediated, whereas the reaction is base-mediated at pH higher than 6.39 (+/- 0.28). The rate constants for the acid-catalyzed, base-catalyzed, and neutral hydrolysis are 25.70 (+/- 0.96), 4.83 (+/- 0.03) X 10(4), and 9.49 (+/- 6.02) x 10(-4) h(-1), respectively. The PTA hydrolysis at pH 4.46 is strongly dependent on temperature, with an activation energy of 74.4 (+/- 2.6) kJ mol(-1). Stoichiometric calculations, reaction kinetics, and ultraviolet-visible spectrophotometry strongly indicates the formation of an intermediary compound at pH 5.07 and 6.07 via a mechanism comprising two first-order consecutive reactions. Ptaquiloside has the lowest rate of hydrolysis at slightly acidic pH and low temperatures. Therefore, because PTA is not sorbed in soil, slightly acidic sandy soils in cold climates are most prone to PTA leaching to deeper soil layers and aquifers.