Iron and manganese transformation in louisiana salt and brackish marsh sediment

Abstract

The kinetics of the release of dissolved iron [Fe(II)], manganese [Mn(II)], and phosphate in salt and brackish marsh sediment and the exchange with the overlying water column were investigated. Sediment was incubated in laboratory microcosms and in sediment water columns in studying these exchanges. The rate constants of the dissolved Fe(II), Mn(II), and phosphate release in sediment suspensions were 2.02–2.28,0.08–0.117, and 4.18–5.38 μmol g^‐1 dry sediment d^‐1, respectively. In sediment‐water column studies, the rate constants (K) of dissolved Fe(II), Mn(II), and phosphate removal from the overlying water into the sediment were 0.755–0.989,0.0695–0.0949, and 0.315–0.448, day^‐1, respectively. The flux of dissolved Fe(II), Mn(II), and phosphates from the salt and brackish marsh sediment to the overlying water in the column studies were 2.56–4.93,1.05–1.689, and 208.6–428.9 mg m^‐2 d^‐1, respectively. The fluxes from salt marsh were slightly greater than those measured in brackish marsh, although these differences were not statistically significant.     

Influence of reducing conditions on the release of antimony and arsenic from a tailings sediment

Purpose

Burial treatment is a frequently used technology for contaminated solid materials, but little is known about the effect of redox changes on the mobility of metals and metalloids. Here, sediment contaminated by historical tailing slurry from an antimony (Sb) mine was incubated with sodium ascorbate solution (SAS), so as to gain insights into the remobilization of Sb and arsenic (As) under reducing conditions.

Materials and methods

Anaerobic incubation of a tailing sediment was incubated with SAS and high-purity water (HPW) as a comparison for 20 day. Metals and metalloids in various chemical fractions of the sediment were quantified by sequential extraction. Dissolved Sb and As species in the HPW and SAS over the incubation period were quantified by hydride generation atomic fluorescence spectrometry.

Results and discussion

In the tailing sediment, 30.8 % of iron (Fe) was found in Fe(III) oxyhydroxides, which hosted 26.7 % of Sb and 32.8 % of As. The water-soluble and exchangeable fractions of Sb (0.09 and 2.0 %) were approximately 10-fold that of As (0.01 and 0.2 %). When the sediment was incubated with the HPW, the behavior of manganese (Mn) was active and Sb was found to be concomitant with Mn. In the SAS, As was first released more weakly than Sb, but later released more strongly than Sb. The release of Sb before 72 h was approximately 2.6-fold that of As, and after 72 h the release of As was approximately 8.8-fold that of Sb. It was deduced that Sb and As were bound differently to Fe phases, with Sb mainly bound to the early dissolved Fe phases whereas As was mainly bound to the later-dissolved Fe phases.

Conclusions

This work indicated that both Mn and Fe phases played an important role on the behavior of Sb, and Fe phases played an important role on the behavior of As. Under reducing conditions, the reductive dissolution of Mn and Fe phases resulted in a strong release of Sb in the early stage and a strong release of As in the later stage, because Sb and As exhibited different chemical associations in the tailing sediment.

     

Enhanced Heavy Metal Phytoextraction from Marine Dredged Sediments Comparing Conventional Chelating Agents (Citric Acid and EDTA) with Humic Substances

Metal (Cu, Mn, Ni, Zn, Fe) concentrations in marine sediment and zooplankton were investigated in Izmir Bay of the Eastern Aegean Sea, Turkey. The study aimed to assess the levels of metal in different environmental compartments of the Izmir Bay. Metal concentrations in the sediment (dry weight) ranged between 4.26–70.8 μg g^?1 for Cu, 233–923 μg g^?1 for Mn, 14.9–127 μg g^?1 for Ni, 25.6–295 μg g^?1 for Zn, 12,404–76,899 μg g^?1 for Fe and 38,226–91,532 μg g^?1 for Al in the Izmir Bay. Maximum metal concentrations in zooplankton were observed during summer season in the inner bay. Significant relationships existed between the concentrations of certain metals (Al, Fe, Mn and Ni) in sediment, suggesting similar sources and/or similar geochemical processes controlling such metals. Higher concentrations of Cu, Zn and percent organic matter contents were found in the middle-inner bays sediments. Based on the correlation matrix obtained for metal data, organic matter was found to be the dominant factor controlling Cu and Zn distributions in the sediment. In general, mean Cu and Zn levels in the bay were above background concentrations in Mediterranean sediments. Zooplankton metal concentrations were similar to sediment distributions.     

Phosphorus Dynamics in a Small Eutrophic Italian Lake

Phosphorous dynamics within Lake Sirio (NW Italy) were investigated, considering both water and sediments. The total phosphorus (TP) concentration in the water is about 79 μg l^?1 after the winter mixing, that is in homogeneous conditions; then TP content increases up to an average of 360 μg l^?1 in late autumn in the deep hypolimnium (30–45 m). This deep lake portion accounts for only 1/12 of the water volume. Close to the water-sediment interface, TP concentrations up to 530 μg l^?1 are observed. Sediment sampled at depths of 20 and 33 m contains less than 2,000 mg kg^?1 of TP, whereas cores from the deepest sediments (46 m) display TP values of 2,000–4,000 mg kg^?1 at the water-sediment interface, increasing with depth to 16,000 mg kg^?1 at about 60–100 cm. In these deep sediments the main chemical form is the Al–Fe–Mn bound P (about 90% in the high TP cores) and Fe and Mn are also highly enriched (3 and 9 times more than in the shallow sediments respectively). The P–Fe association is confirmed by SEM-EDS and XRD analyses. The vertical distribution of the P content in the water column is consistent with its release from sediments, but in this hypothesis an unrealistic P release rate from 8.1 to 3.0 g m^?2y^?1 was estimated. A more complex model is therefore proposed, involving a process of P concentration in the sediments of the central (deepest) part of the lake, and a short term sediment-water exchange. The TP vertical variability and speciation in the cores suggests a change in the sediment retention capacity, connected to the lake shift to more eutrophic conditions.     

A Study on Al(III) and Fe(II) Ions Sorption by Cattle Manure Vermicompost

Cattle manure vermicompost has been used for the adsorption of Al(III) and Fe(II) from both synthetic solution and kaolin industry wastewater. The optimum conditions for Al(III) and Fe(II) adsorption at pH?2 (natural pH of the wastewater) were particle size of ≤250?µm, 1 g/10 mL adsorbent dose, contact time of 4 h, and temperature of 25°C. Langmuir and Freundlich adsorption isotherms fitted reasonably well in the experimental data, and their constants were evaluated, with R ² values from 0.90 to 0.98. In synthetic solution, the maximum adsorption capacity of the vermicompost for Al(III) was 8.35 mg g^?1 and for Fe(II) was 16.98 mg g^?1 at 25°C when the vermicompost dose was 1 g 10 mL^?1, and the initial adjusted pH was 2. The batch adsorption studies of Al(III) and Fe(II) on vermicompost using kaolin wastewater have shown that the maximum adsorption capacities were 1.10 and 4.30 mg g^?1, respectively, at pH?2. The thermodynamic parameter, the Gibbs free energy, was calculated for each system, and the negative values obtained confirm that the adsorption processes were spontaneous.     

Interaction of Oxidation Products from Caffeic Acid with Fe(III) and Fe(II)

Abstract

Phenolic substances in the soil–plant system can be oxidized by metal ions, inorganic components, molecular oxygen as well as by phenoloxidases, giving rise to the formation of products of low or high molecular weight. Interactions of these products with iron, in both reduced and oxidized form, can affect the iron mobility in soil and rhizosphere, and thus its availability to plants. Here we report the results of a study on the complexing and reducing activity of the oxidation products from caffeic acid (CAF), obtained via electrochemical means, towards Fe(III) and Fe(II) in aqueous solution in the 3.0–6.0 pH range. The HPLC analysis of the filtered solutions after the CAF oxidation showed the formation of two main groups of products: (i) CAF oligomers formed through radicalic reactions which do not involve the double bond of the CAF lateral chain and (ii) products where this bond is involved. These oxidation products (COP) were found to interact with both Fe(III) and Fe(II) with formation of soluble and insoluble Fe(III)‐, and Fe(II)‐COP complexes. The COP were found to be able to reduce Fe(III) to Fe(II) mainly at pH < 4.0. A low redox activity was observed at pH ≥ 4.5 due to Fe(III) hydrolysis reactions as well as to the decrease in the redox potential of the Fe(III)/Fe(II) couple. Formation of hydroxy Fe(III)‐COP polymers occurs at pH > 3.5.     

Sediment Retention by Alternative Filtration Media Configurations in Stormwater Treatment

Urban stormwater can be treated by infiltration at the source using systems like permeable paving. A critical component of such a system is the filtration media. Laboratory experiments were conducted using columns and boxes to evaluate the sediment retention efficiencies of different filtration media—crushed Greywacke, Greywacke mixed with 10% sand, and layered Greywacke and sand-Greywacke mix. Sediments of 0.001–6 mm were applied at concentrations of 460–4,200 mg/l along with water at flow rates of 100–900 ml/min. All columns showed between 96 and 91% sediment retention efficiency for single dry sediment applications, with lowered sediment retentions at higher flow rates. Decreasing the sediment loading, applying particles of <38 μm size, and suspending the particles in inflow as opposed to directly applying sediments to the column surface gave lower sediment retention efficiencies of 55 to 89%. Sediment retention primarily occurred in the top 20 mm of all columns and the 50th percentile value of retained sediments was 100–300 μm. The box tests showed little effect of flow and sediment loading on particle retention, with the tests showing an average retention of 93%. Similar to the column tests, the box tests showed lower sediment retention (84 to 88%) for <38 μm sediments and greater retention (approximately 95%) for larger sediments.     

Assessment of Bacterial and Fungal Aerosol in Different Residential Settings

The concentration and size distribution of bacterial and fungal aerosol was studied in 15 houses. The houses were categorized into three types, based on occupant density and number of rooms: single room in shared accommodation (type I), single bedroom flat in three storey buildings (type II) and two or three bedroomed houses (type III). Sampling was undertaken with an Anderson six-stage impactor during the summer of 2007 in the living rooms of all the residential settings. The maximum mean geometric concentration of bacterial (5,036 CFU/m³, ± 2.5, n?=?5) and fungal (2,124 CFU/m³, ± 1.38, n?=?5) aerosol were in housing type III. The minimum levels of indoor culturable bacteria (1,557 CFU/m³, ±1.5, n?=?5) and fungal (925 CFU/m³, ±2.9, n?=?5) spores were observed in housing type I. The differences in terms of total bacterial and fungal concentration were less obvious between housing types I and II as compared to type III. With reference to size distribution, the dominant stages for culturable bacteria in housing types I, II and III were stage 3 (3.3–4.7 μm), stage 1 (7 μm and above) and stage 5 (1.1–2.1 μm), respectively. Whereas the maximum numbers of culturable fungal spores were recovered from stage 2 (4.7–7 µm), in housing type I, and from stage 4 (2.1–3.3 μm) in both type II and III houses. The average geometric mean diameter of bacterial aerosol was largest in type I (4.7 μm), followed by type II (3.89 μm) and III (1.96 μm). Similarly, for fungal spores, type I houses had the highest average mean geometric diameter (4.5 μm), while in types II and III the mean geometric diameter was 3.57 and 3.92 μm, respectively. The results indicate a wide variation in total concentration and size of bioaerosols among different residential settings. The observed differences in the size distributions and concentrations reflect their variable airborne behaviour and, as a result, different risks of respiratory exposure of the occupants to bioaerosols in various residential settings.     

Accumulation of Metals in the Sediment and Reed Biomass of a Combined Constructed Wetland Treating Domestic Wastewater

This study assessed the accumulation of Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn in the sediment and biomass of P. australis (Cav.) Trin. ex Steud. in a combined constructed wetland (CW) designed for the treatment of domestic wastewater of 750 population equivalents. The CW consists of two vertical subsurface flow (VSSF) reed beds followed by two horizontal subsurface flow (HSSF) reed beds. The sediment in the VSSF reed bed was contaminated with Cu (201 ?±? 27 mg kg^?1 DM) and Zn (662 ?±? 94 mg kg^?1 DM) after 4 years of operation. Concentrations of Cd, Cu, Pb and Zn in the sediment generally decreased along the treatment path of the CW. On the contrary, higher Al, Cr, Fe, Mn and Ni concentrations were observed in the sediment of the inlet area of the HSSF reed bed. Redox conditions were presumably responsible for this observed trend. Metal concentrations in the reed biomass did not show excessive values. Accumulation in the aboveground reed biomass accounted for only 0.5 and 1.4% of, respectively, the Cu and Zn mass load in the influent. The sediment was the main pool for metal accumulation in the CW.     

Development of Analytical Procedure for the Determination of Exchangeable Cr(VI) in Soils by Anion-exchange Fast Protein Liquid Chromatography with Electrothermal Atomic Absorption Spectrometry Detection

Analytical procedure for the determination of exchangeable Cr(VI) was developed. In order to optimise the extraction procedure, the efficiency of extraction of exchangeable Cr(VI) in soil samples was investigated in KH₂PO₄–K₂HPO₄ buffer solutions (0.015 up to 0.2 mol l^?1), adjusted to the pH of the soil. Phosphate buffer was used to efficiently desorb Cr(VI) from soil particles. The extraction time (mechanical shaking) ranged from 1 up to 72 h. Cr(VI) in soil extracts was determined by anion-exchange fast protein liquid chromatography with electrothermal atomic absorption detection (FPLC-ETAAS). The study was performed on soil samples from the field treated with the tannery waste for seventeen years. Samples were analysed in the 16 year after the last waste application. It was experimentally proven that the optimal phosphate buffer concentration was 0.1 mol l^?1 and extraction time 16 h. An additional experiment was done to confirm that during the extraction, soluble Cr(III) was not oxidised to Cr(VI) by Mn(IV) oxides present in soil samples. For this purpose soil with the same characteristics, but not treated with tannery waste, was spiked with Cr(III) and the analytical procedure performed. No measurable Cr(VI) concentrations were detected. The repeatability of measurement was 2.5%, while the reproducibility of measurement was 6.9%. The accuracy of the analytical procedure was tested by spiking of soil samples with Cr(VI). The recoveries were better than 95%. The analytical procedure with limit of detection (LOD) 15 ng g^?1 of Cr(VI) was sensitive enough for the determination of exchangeable Cr(VI) in soils. In field soil samples analysed the concentrations of exchangeable Cr(VI) were found to be about 200 ng g^?1.     

Growth and Physiological Responses of Triticum aestivum and Deschampsia caespitosa Exposed to Petroleum Coke

Methylibium petroleiphilum PM1, which is capable of degrading of methyl tert-butyl ether (MTBE), was immobilized in calcium alginate gel beads. Various applications were explored to increase the mechanical strength of these gel beads. The introduction of 0.3 mol/L calcium chloride into the crosslinking solution, 0.002 mol/L calcium chloride into the growth medium, and 0.2% polyethyleneimine (PEI) as chemical crosslinking agent increased the stability of the Ca-alginate gel beads under the operation conditions of the bioreactor. The degradation rates of MTBE by the immobilized cells in the bioreactor system operated in batch and continuous mode , respectively, were compared. A MTBE biodegradation rate of 5.79 mg/L·h was reached for over 400 h (50 batches), and the immobilized cells in the bioreactor removed >96% MTBE during 50 days of operation. Molecular analysis of the PM1 cells revealed that microbial growth occurred predominantly as microcolonies in the outer area of the beads during the first 20 days of operation. The results of this study show that a continuous-mode, fixed-bed bioreactor reactor coupled with PM1-immobilized cells is a promising technology for remediating MTBE-contaminated groundwater.     

Determination of Elemental Sulfur in the Presence of Anaerobic Sediments by Extraction Procedure Using High-Performance Liquid Chromatography

Elemental sulfur is the most commonly found form of sulfur in anaerobic sediments. Accurate determination of elemental sulfur is the key step to know physical chemistry and biogeochemical processes in the sediments. A novel method was developed for the analysis of elemental sulfur using high-performance liquid chromatography (HPLC) with a C18 column. The procedure of determination of elemental sulfur concentrations from 0.1 to 100 mg/g (on a basis of the dry weight of sediment) is based on the direct injection of acetone extracts of sediments into a chromatographic column. The linearity range of 20–110 mg/L showed an excellent linearity of response (r = 0.999). The limit of detection and limit of quantitation for elemental sulfur were 9.41 and 4.18 μg/L, and converted sulfur mass per sediment mass was 1.88 × 10^?2 and 8.36 × 10^?3 μg/kg. Besides, a repetitive experiment (ten times) was carried out and the average chromatographic peak area was 141.47 mg L^?1. The sulfur concentration in the solution used for the determination of standard deviation and relative standard deviation was 1.02 and 0.727%, respectively. The average recovery ranges between 98 and 100%. The quantitation of elemental sulfur in sediment samples from anaerobic digestion reactor is obvious, and the average concentration of elemental sulfur on the basis of the dry weight of the sediment is 5.24 mg/g. The method was sensitive and exhibited good signal-to-noise ratio, as well as linear responses over a wide concentration range.     

Effect of Metal Ions on the Entomopathogenic Nematode Heterorhabditis Bacteriophora Poinar (Nematoda: Heterohabditidae) Under Laboratory Conditions

The effect of sixteen metal ions: Al, Cd, Co(II), Cr(III), Cr(VI), Cu(II), Fe(III), Li, Mg, Mn(II), Mo(VI), Ni(II), Pb(II), Se(IV), V(V), and Zn on the mortality and infectivity ofHeterorhabditis bacteriophora were observed over a 96 hr period. All ions except Pb(II) even at naturally unrealistic concentrations did not cause the mortality of the nematodes. A weak vitalizing effect could eventually be observed with Mn(II), Mg, Fe(III) and Ni(II) (Table 1). However, such treatment generally lowered infectivity of the nematodes with respect to wax moth caterpillars.Galleria mellonella. This effect was particularly significant with Ni(II) and Pb(II).     

Iron and arsenic speciation in marine sediments undergoing a resuspension event: the impact of biotic activity

Purpose

Changes in the chemical conditions of sediment following a resuspension event might lead to release of sequestered pollutants. In the present study, arsenic (As) and iron (Fe) speciation were investigated before and after such an event, in sediment from L'Estaque marina (France). This marina is located near an industrial plant which processed As-bearing ores for several decades.

Materials and methods

Cores (0–60 cm) and surface sediment (0–10 cm) were collected by a diver. Sediment properties along the length of the core were determined by coupling chemical extractions, and diffraction (i.e., X-ray diffraction) and spectroscopic techniques (i.e., micro-X-ray fluorescence, scanning electron microscopy coupled with energy dispersive spectroscopy, Raman spectroscopy, and X-ray absorption near-edge spectroscopy). Laboratory experiments mimicking resuspension and resettlement events were conducted over a period of 3 months in both biotic and abiotic (autoclaved) conditions. In both cases, oxidation proceeded by oxygen diffusion from the top to the bottom of the sediment.

Results and discussion

It was demonstrated that the unperturbed sediment was anoxic. Arsenic, almost fully under its trivalent As(III) form, had a concentration between 194 and 473 μg g^?1, and its main carrier phase was the Fe-monosulfide mackinawite; this mineral originated from in situ transformation of Fe oxides, partly emitted by the industrial plant. The observed progressive pyritisation of mackinawite was not accompanied by further reduction of As which means that As remained bound to mackinawite, as incorporation into the pyrite lattice would require that it reduced to its (?I) oxidation state. After oxidation during the resuspension event, and in abiotic conditions, As was fully pentavalent As(V) in the oxidized zone of the re-settled sediment. On the contrary, in the biotic experiment, the development of a bacterial mat, which consumed oxygen for respiration processes, preserved the sediment from total oxidation. Consequently, As was present under both As(III) and As(V) forms, the first one being minor (～20 % of total As) in the top of the sediment. The diversity of aioA genes was large, and was similar in the oxidized layer and the deeper black-colored sediment.

Conclusions

These results indicate that biological processes partly control the in situ geochemical system by inducing low redox areas in theoretically oxidized sediments.     

Integrated Flow-based System Displaying an In-line Mini Soil Column to Monitor Iron Species in Soils Leachates

ABSTRACT

Contamination of ground water as a consequence of soil leaching processes is an issue of major concern. In this context, a simulation of the soil leaching process was designed. A sequential injection (SI) method to monitor the soil leaching of iron complexes with in-line rain simulation for leachate production is described. The developed methodology comprises the SI determination of both iron(III) and 3-hydroxy-4-pyridinones iron(III) complexes, coupled to a mini soil column (mSC) for displaying in-line rain simulations. The described SI method enabled iron(III) determination within the range 2.0–35 µmol L^?1, with a detection limit of 0.42 µmol L^?1, and determination of iron(III) complexes in the range 1.0–45 µmol L^?1. It was successfully applied to leachates from laboratory scale soil columns (LSSC), with good precision for both iron(III) and iron complexes determinations: calculated relative standard deviation (RSD) of 5% and 6%, respectively. A step further in automation and miniaturization was attained with the incorporation of a mini soil column for the in-line leachate production. The system enabled the soil leachate production and assessment in less than 5 min, including determinations in triplicate.     

Magnesium-manganese interaction in soybean cultivars with different nutritional requirements

Manganese (Mn) deficiency in soybean has occurred mainly in soils with surface dolomite lime application, which increases pH and the magnesium (Mg) concentration in the surface layer. The objective of this study was to investigate the influence of Mg on the Mn uptake in four soybean cultivars with different nutritional requirements. The experiment was conducted under greenhouse conditions in a completely randomized design, in 4 × 2 × 4 factorial scheme [four soybean cultivars, two Mg rates (0.1 and 1.0 mmol L^?1) and four Mn rates (0.0, 1.0, 2.0, and 5.0 µmol L^?1)], with four replicates. The cultivars used in the experiment were: IAC 17 and FT Estrela (for soils fertility or high nutritional demand) and IAC 15–1 and DM Nobre (for soils partially corrected or medium nutritional demand). The root dry weight (RDW), shoot dry weight (SDW), SDW/RDW ratio, chlorophyll content, seed yield and foliar concentrations of nitrogen (N), phosphorus (P), potassium (K), Mg, calcium (Ca), iron (Fe), Mn, and zinc (Zn) were determined. The application of the highest Mg rate increased seed yield. This was also observed with a Mn rate up to 3.0 μmol L^?1. There was an interaction of Mg and Mn in the plant, and it was found that the IAC 17 cultivar was the most sensitive to Mn, while FT Estrela had the lowest performance. N, P, K, and Zn concentrations were significantly influenced by Mn rates. The Mg and Mn rates had a significant effect on Mg foliar concentrations. The rate of 1.0 mmol L^?1 of Mg provided the lowest levels of nutrients to the plant and increased SDW and seed yield, regardless of the nutritional requirement of each cultivar.     

Solid-Solution Metal Partitioning for the Upper Mero River Basin (NW Spain)

This study determines the seasonal variability of metal partition coefficients [aluminium (Al), iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn)] and analyses the importance of suspended sediments (SS), dissolved organic carbon (DOC) concentrations, pH, and discharge (Q) on the seasonal variability of metal partition coefficients (K_Ds) in the headwaters of the Mero River catchment, which drains an agroforestry area in northwestern Spain. Metal partition coefficients were used as an approach to relate dissolved and particulate fractions. Water samples were collected over 3 years (2005–2008) at the catchment outlet. The mean metal dissolved concentrations were: Fe (43.5 μg L^?1) > Al (23.3 μg L^?1) > Zn (1.8 μg L^?1) > Mn (1.2 μg L^?1) > Cu (0.3 μg L^?1). Partition coefficients followed the order Mn > Al > Fe > Zn > Cu, and their values exhibited low variability. Al, Cu, and Zn partition coefficients presented the greatest values in summer, except during 2007–2008, when the greatest K_Ds value was observed in autumn, whereas the K_Ds of Fe showed the greatest values in winter. The K_D of Mn has no seasonality. For Al, Cu, and Zn, the seasonal SS concentrations were closely related to Kd. For Fe, Kd was more closely related to DOC concentration than to SS concentration.     

Determination of the hydroperoxil group level in polyethylene glycols using a novel mimic enzyme Fe(III)-Mn(II)(HNAPTS)2

Two kinds of Schiff base metal complexes of 2-hydroxy-1-naphthaldehyde-2-amino-5-phenylthiazole (HANPTS), Mn(II)(HNAPTS)(2) and Fe(III)(HNAPTS)(2), were synthesized and used to mimic the active group of horseradish peroxidase (HRP). The catalytic characteristics of the mimic enzymes in the oxidation reaction of ascorbic acid (AsA) with the OOH group in polyethylene glycols (PEGs) have been studied by a spectrophotometric method. Fe(III) has remarkable coordinated catalysis to Mn(II)(HNAPTS)(2); as a result, the catalytic ability of Fe(III)-Mn(II)(HNAPTS)(2) is 75% of that of HRP. The possible mechanism of the reaction was discussed. The linear relationship between deltaA(265)(AsA) and OOH group concentrations was in the range of 1.5 x 10(-6) to 9.0 x 10(-4) mol/L. The proposed method was successfully applied to the determination of the OOH group level in different molecular weight PEGs.     

Diazinon Mitigation in Constructed Wetlands: Influence of Vegetation

In intensively cultivated areas, agriculture is a significant source of pesticides associated with storm runoff. When these pollutants enter aquatic receiving waters, they have potential to damage nearby aquatic ecosystems. Constructed wetlands are a best management practice (BMP) designed to help alleviate this potential problem. A constructed wetland system (180?×?30 m) comprised of a sediment retention basin and two treatment cells was used to determine fate and transport of a simulated storm runoff event containing the insecticide diazinon and suspended sediment. Wetland water, sediment, and plant samples were collected spatially and temporally over 55 d. Results indicated that 43% of the study’s measured diazinon mass was associated with plant material, while 23 and 34% were measured in sediment and water, respectively. Mean diazinon concentrations in water, sediment, and plants for the 55-d study were 18.1?±?4.5 μg/l, 26.0?±?8.0 μg/kg, and 97.8?±?10.7 μg/kg, respectively. Aqueous concentrations fluctuated in the wetlands between 51–86 μg/l for the first 4 h of the experiment; however, by 9 h, aqueous concentrations were approximately 16 μg/l. During the 55 d experiment, 0.3 m of rainfall contributed to fluctuations in diazinon concentrations. Results of this experiment can be used to model future design specifications for mitigation of diazinon and other pesticides.     

Extraction and speciation analysis of roxarsone and its metabolites from soils with different physicochemical properties

Purpose

The application of roxarsone (ROX), an arsenic-containing compound, as a feed additive in the animal production industry results in elevated soil levels of ROX and its metabolites, namely, monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), arsenate (As(V)), and arsenite (As(III)). This study was conducted to study the extraction and speciation analysis of ROX-related arsenicals in soils with different physicochemical properties and the possible effects of soil properties on the extraction of ROX and its metabolites.

Materials and methods

Analytical method based on high-performance liquid chromatography (HPLC)-inductively coupled plasma–mass spectrometry (ICP-MS) was employed to determine the concentrations of As(III), DMA, MMA, As(V), and ROX extracted by different extraction solvents from different soils spiked by arsenicals. Validity of the developed method was assessed by the recovery efficiencies of arsenic species in soil-dissolved matter solutions containing 20 μg As?·?L^?1 of each arsenic species. Effects of soil properties on the extraction of ROX and its metabolites were analyzed by Pearson’s correlation.

Results and discussion

Arsenic species were separated using gradient elution of water and 20 mmol?·?L^?1 (NH₄)₂HPO₄ + 20 mmol?·?L^?1 NH₄NO₃ + 5 % methanol (v/v) within 27 min. The linear ranges of all arsenicals were 0–200 μg As?·?L^?1 with R ²?>?0.9996. The developed method provided lower limits of detection for As(III), DMA, MMA, As(V), and ROX (0.80, 0.58, 0.35, 0.24, and 1.52 μg As?·?L^?1, respectively) and excellent recoveries (92.52–102.2 %) for all five species. Arsenic speciation was not altered by 0.1 mol?·?L^?1 NaH₂PO₄ + 0.1 mol?·?L^?1 H₃PO₄ (9:1, v/v), which offered better average extraction efficiencies for As(III), As(V), DMA, MMA, and ROX (32.49, 92.50, 78.24, 77.64, and 84.54 %, respectively). Extraction performance of arsenicals was influenced by soil properties, including pH, cation exchange capacity (CEC), total Fe, and amorphous Fe.

Conclusions

ROX and its metabolites from soils could be satisfactorily separated by the developed method for the studied arsenicals. To extract arsenic species from soils, 0.1 mol?·?L^?1 NaH₂PO₄ + 0.1 mol?·?L^?1 H₃PO₄ (9:1, v/v) was recommended. Extraction efficiencies of arsenicals were influenced more by solvent composition than soil physicochemical properties. The present study provides a valuable tool and useful information for determining the concentrations of ROX and its metabolites in contaminated soils.