Characterization and Performance of Granular Iron as Reactive Media for TCE degradation by Permeable Reactive Barriers

The application of Permeable Reactive Barriers (PRBs), an innovative clean-up technology for in-situ groundwater remediation, represents an effective alternative to traditional pump-and-treat systems and has raised strong interest during recent years. From recent statistics of the Italian Water Research Institute (IRSA), trichloroethylene (TCE) from industrial activities is the most widespread contaminant in groundwater. The goal of the research was to test the suitability and performance of a high purity granular iron reactive medium for TCE degradation by PRBs. The suitability was evaluated based on chemical and physical characteristics of the material and the performance of the granular iron, in terms of TCE removal efficiency, was evaluated by column tests.The experimental results showed that the characteristics of the granular iron are suitable for application as a reactive medium, since the hydraulic conductivity values were fully consistent with those reported in the literature, and the leaching tests indicated a reduced release of heavy metals. The overall removal efficiency of TCE was higher than 97% in all the tests performed at the flow rate of 0.25 cm³ min^-1 (corresponding to a groundwater flow velocity of 0.37 m d^-1) both for the 100% iron and the iron-sand columns. Moreover, TCE degradation around 60% was observed even in the first section of the columns fortypical groundwater flow velocity. The TCE reduction in the outlet stream was confirmed by the assessment of chlorine mass balance and by the absence of any reaction intermediate detected by GC-MS.Finally, the concentration profiles in the columns were not in agreement with those expected for a chemistry-controlled kinetic regime. This suggests that TCE degradation rate may have been limited by precipitation phenomena, hindering the contaminant transport to the iron surface.     

Hexahydro-1,3,5-Trinitro-1,3,5-Triazine (Rdx) Degradation in Biologically-Active Iron Columns

Flow-through columns were used to evaluate the efficacy of permeable reactive iron barriers to treat ground water contamination by RDX. Three columns were packed with iron filings (Fe⁰) between soil and sand layers, and were fed continuously with unlabeled plus ¹⁴C-labeled RDX to characterize its removal efficiency under different microbial conditions. One column was poison-sterilized to isolate chemical degradation processes, another was not poisoned to allow colonization of the Fe⁰ layer by indigenous microorganisms, and a third column was amended with anaerobic sludge to evaluate the benefits of enhancing biodegradation through bioaugmentation. Extensive RDX removal (>99%) occurred through the Fe⁰layer of all columns for more than one year, although ¹⁴C-label analysis indicated the presence of soluble byproducts such as methylenedinitramine. RDX byproducts accumulated to a lesser extent in biologically active columns, possibly due to enhanced mineralization by the cumulative action of microbial and chemical degradation processes. Denaturing gradient gel electrophoresis (DGGE) profiles and nucleotide sequencing revealed a predominance of Acetobacterium sp. in the iron layer of all columns after 95 days. Such homoacetogenic bacteria probably feed on hydrogen produced during Fe⁰ corrosion and participate on the RDX degradation process. This notion was supported by batch experiments with a mixed homoacetogenic culture isolated from the bioaugmented column, which degraded RDX and produced acetate when H₂ was present. Overall, this work suggests that Fe⁰barriers can effectively intercept RDX plumes, and that treatment efficiency can be enhanced by biogeochemical interactions though bioaugmentation.     

Alkalinity production in epilimnetic sediments: Acidic and non-acidic lakes

Interstitial water profiles in epilimnetic sediments of lakes with varying water column alkalinities were collected to assess the origin and importance of sedimentary alkalinity in freshwater lakes. Release of Ca²⁺ and NH₄ ⁺, and consumption of SO₄ ^? are the most important contributors to alkalinity production m sediments of non-acidic lakes. In acidic lakes, Fe²⁺ and Mn²⁺ replace Ca²⁺ as the dominant cation contributors to alkalinity production. The sedimentary alkalinity flux is an important component of the acid neutralizing capacity of freshwater lakes. However, the presence of large alkalinity gradients in sediment porewaters does not necessarily indicate a large source of alkalinity for the lake, as a significant portion of the alkalinity iu associated with the formation of Fe²⁺, Mn²⁺ and NH₄ ⁺ Oxidation of Fe²⁺ and Mn²⁺ at the anoxic-oxic interface and biological removal of NH₄ ⁺ in the overlying water column results in consumption of the co-diffusing alkalinity.     

Occurrence of acidic groundwater in precambrian crystalline bedrock aquifers,Southwestern Sweden

The pH and alkalinity of groundwater from 7651 wells drilled in the Precambrian crystalline bedrock of southwestern Sweden has been evaluated. The wells are generally less than 100 m deep. Analytical results were collected from different laboratories and authorities in the region. In areas with thin soil cover or coarse-grained deposits overlying the bedrock, alkalinity is normally less than 100 mg HCO₃ L^?1. Below the marine limit, where clayey sediments predominate, alkalinity sometimes even exceeds 200 mg HCO₃ L^?1. When comparing pH and alkalinity of groundwaters from Quaternary deposits with bedrock groundwaters, the latter always have higher pH and alkalinity values. The most acidic bedrock groundwaters are found in small areas close to the city of Göteborg due to additional factors of high acid loadings, high groundwater discharge and thin soil layers. A study of data from 1949 to 1985 in the province of Värmland suggests that no regional acidification of importance is in progress. However, results from public water supplies support the hypothesis that the groundwaters which are most sensitive to acidification are those where discharge from wells in small bedrock aquifers induces rapid groundwater recharge of acidic surficial water.     

Using Synchronous Fluorescence Technique as a Water Quality Monitoring Tool for an Urban River

This paper presents a study performed to evaluate the feasibility of implementing a series of heating rods within a zero-valent iron permeable reactive barrier (ZVI-PRB) to enhance the conventional design of PRBs, and thus to improve the barrier’s removal efficiency, and reduce construction and reactive material costs. A numerical modeling approach is undertaken where a hypothetical case is introduced and typical site values are assigned to it. The amount of electrical energy required to heat the barrier from an initial temperature, T ₁, to a final temperature, T ₂ is assessed. Through different simulation cases, the effect of (1) initial temperature of the groundwater entering the PRB, (2) different amounts of total heat injected, (3) distribution of the heating rods, and (4) different types of porous media, on the temperature increase within the PRB are evaluated. Results show that the amount of energy required to increase the temperature of our hypothetical case by 10°C is approximately 935 W, which could be provided by renewable energies such as solar. It is explained that there are multiple benefits for increasing the temperature within the PRB. Apart from boosting reaction rates, temperature increase can reduce water viscosity and increase flow within the barrier, which broadens a barrier’s catch area. It can enhance solubility of gases to reduce blockage caused by gas generation. An upward flow is formed inside the wall which can also help reduce gas blockage. By implementing heating rods, design widths are reduced, which could potentially reduce the materials (thus cost) used and/or justify the use of more expensive reactive material in PRBs. Heating the PRB was found to generate a heat plume of 20 m length downstream of the PRB after one year, which would increase biodegradation of the residual contaminants leaving the PRB within this zone. Overall, it is concluded that implementing the proposed technology within a ZVI-PRB can be justified, and is found to be beneficial in many aspects.     

Electron donor and pH relationships for biologically enhanced dissolution of chlorinated solvent DNAPL in groundwater

Biologically enhanced dissolution offers a method to speed removal of chlorinated solvent dense non-aqueous-phase liquid (DNAPL) sources such as tetrachloroethene (PCE) and trichoroethene (TCE) from aquifers. Bioremediation is accomplished by adding an electron donor to the source zone where fermentation to intermediates leading to acetic acid and hydrogen results. The hydrogen and possibly acetic acid are used by dehalogenating bacteria to convert PCE and TCE to ethene and hydrochloric acid. Reductive dehalogenation is thus an acid forming process, and sufficient alkalinity must be present to maintain a near neutral pH. The bicarbonate alkalinity required to maintain pH above 6.5 is a function of the electron donor: 800 mg/L of bicarbonate alkalinity is sufficient to achieve about 1.2 mM TCE dechlorination with glucose, 1.7 mM with lactate, and a much higher 3.3 mM with formate. Laboratory studies indicate that in mixed culture, formate can be used as an electron donor for complete conversion to ethene, contrary to pure cultures studies indicating it cannot. Various strategies can be used to add electron donor to an aquifer for DNAPL dehalogenation while minimizing pH problems and excessive electron donor usage, including use of injection-extraction wells, dual recirculation wells, and nested injection-extraction wells.     

Response of wheat genotypes to foliar spray of ZnO and Fe2O3 nanoparticles under salt stress

This study evaluated the effects of iron oxide (Fe₂O₃) and zinc oxide (ZnO) on two wheat genotypes (Kavir and Tajan) at three levels (0, 75, and 150 mM sodium chloride (NaCl)) of salinity. Spray treatments included two forms of normal and nanoparticles of Fe₂O₃ and ZnO, a mixture of nanoparticles of Fe₂O₃ and ZnO (2 g L^?1) and a non-spray treatment. The pot experiment was arranged as factorial in a randomized complete block design with four replications. Two forms of Fe₂O₃ and ZnO significantly accelerated plant height, leaf area, shoot dry weight, and the concentration of iron (Fe) and zinc (Zn) in comparison with non-spray treatment. The highest plant height and leaf Fe concentration belonged to Fe₂O₃ nanoparticles; however, it seems that the spray of nanoparticles may not be superior compared with normal forms in alleviation of salinity impacts.     

Electrokinetic-enhanced remediation of actual arsenic-contaminated soils with approaching cathode and Fe0 permeable reactive barrier

Purpose

The aim of this study was to investigate the remediation efficiency of actual arsenic-contaminated soils by electrokinetic (EK)-enhanced remediation with approaching cathode and Fe⁰ permeable reactive barrier (PRB).

Materials and methods

Experiments were conducted in a lab-made apparatus consisting of the anode reservoir, the soil specimen chamber, and the cathode reservoir.

Results and discussion

In this study, the enhanced combination methods (approaching cathode and Fe⁰-PRB) were assisted for EK remediation of actual arsenic-contaminated soils under a voltage gradient of 1 V/cm and a treatment period of 96 h. Experimental results showed that arsenic accumulated in the anode sections (I, II) of the soil by employing EK alone with an arsenic removal rate of less than 5%. In contrast, EK-enhanced remediation with either approaching cathode (EK/AC) or Fe⁰-PRB (EK/PRB) reduced the arsenic concentrations in both central and anode sections of the soil and afforded the removal rates of 20% in both cases. However, EK-enhanced remediation with the combination of approaching cathode and Fe⁰-PRB (EK/PRB/AC) reached the removal efficiency of 45% without arsenic accumulation in any soil sections. This phenomenon is mainly caused by the approaching cathode that creates an alkaline environment to promote the migration of arsenic, as well as PRB filled with Fe⁰ that achieves the adsorption and immobilization of arsenic.

Conclusions

The highest remediation efficiency was achieved in the EK/PRB/AC test, which was attributed to the fact that the combination of this two methods solved the problem of arsenic accumulation in treated soil and ensured a more thorough arsenic removal. Furthermore, enhanced remediation efficiency does not elevate the costs.

     

Evaluation of Natural Zeolite as a Material for Permeable Reactive Barrier for Remediation of Zinc-Contaminated Groundwater Based on Column Study

The permeable reactive barrier (PRB) filled with natural zeolite plays the role of a reactive treatment zone for remediation of contaminated groundwater. Based on column lab experiments, the volume of remediated solution, the distribution (K_d) and retardation (R_d) coefficients were evaluated, confirming successful removal and retention of zinc from contaminated groundwater. The effect of hydrodynamic dispersion on zinc capturing by zeolite in PRB was evaluated by the hydrodynamic dispersion coefficient (D_L) and retarded hydrodynamic dispersion coefficient (D_LR) using the Brigham method. For different assumed distances of the barrier, the simulation of one-dimensional zinc concentration profile from the point source through the barrier has been modeled by a simple analytical pulse model. The results show that the flow rate has the most significant effect on the concentration profile, peaks, and broadening of curves. The residence contact time (τ) corresponding to higher K_d and R_d as well as lower D_L and D_LR values outcomes the optimal range of 6.2–9.4 min. This interval corresponds to the experimental performance at the bed length of 8 and 12 cm and flow rate in the range of 6.38–9.57 PV/h. The calculated minimum thickness and longevity confirm the successful application of zeolite as a material in PRB for remediation of zinc contaminated groundwater.     

通过土壤泥浆中的过氧化氢处理三氯乙烯污染的土壤

Chlordecone, one of the most persistent organochlorine pesticides, was applied between 1972 and 1993 in banana fields in the French West Indies, which results in long-term pollution of soils and contamination of waters, aquatic biota, and crops. As human exposure to chlordecone is mainly due to food contamination, early research was focused on chlordecone transfer to crops. Field trials were conducted to investigate chlordecone contamination of yam, sweet potato, turnip, and radish grown on a ferralic Nitisol polluted by chlordecone. We also carried out trials on yam, courgette, and tomato under greenhouse conditions with homogenized Andosol and Nitisol, polluted by chlordecone to various extents. Our results indicated that i) all tubers were contaminated in accordance with the chlordecone content of the soils; ii) the contamination capacity of the Nitisol was greater than that of the Andosol; and iii) whatever the soil type, tuber contamination was related to the soil volumetric content of dissolved chlordecone. Nevertheless, no tubers showed sufficient chlordecone uptake for efficient soil decontamination by means of plant extraction. Soil contact accounted for most of the root crop contamination, which was inversely proportional to the tuber size. Internal transfer might also increase root crop contamination when the root central cylinder contained raw sap flow, as in the case of turnip or radish. Courgette fruits showed high contamination without soil contact. Thus, further research is needed to explore the pattern of both below- and aboveground plant chlordecone contamination and assess the hypothesis of its correlation with sap flow. Finally, we used our results to build a decision-making tool for farmers, relating soil pollution with the maximal contamination of the harvested organs to predict crop contamination and thus assisting farmers in making crop choices at planting in order to conform with the European Union’s regulations.     

Effect of reduced iron on the degradation of chlorinated hydrocarbons in contaminated soil and ground water: A review of publications

Chlorinated hydrocarbons are among the most hazardous organic pollutants. The traditional remediation technologies, i.e., pumping of contaminated soil- and groundwater and its purification appear to be costly and not very efficient as applied to these pollutants. In the last years, a cheaper method of destroying chlorine-replaced hydrocarbons has been used based on the construction of an artificial permeable barrier, where the process develops with the participation of in situ bacteria activated by zerovalent iron. The forced significant decrease in the redox potential (Eh) down to ?750 mV provides the concentration of electrons necessary for the reduction of chlorinated hydrocarbons. A rise in the pH drastically accelerates the dechlorination process. In addition to chlorine-organic compounds, ground water is often contaminated with heavy metals. The influence of the latter on the effect of zerovalent iron may be different: both accelerating its degradation (Cu) and inhibiting it (Cr). Most of the products of zerovalent iron corrosion, i.e., green rust, magnetite, ferrihydrite, hematite, and goethite, weaken the efficiency of the Fe⁰ barrier by mitigating the dechlorination and complicating the water filtration. However, pyrrhotite FeS, on the contrary, accelerates the dechlorination of chlorine hydrocarbons.     

Effect of bicarbonate on iron reduction by soybean roots 1

Release of reducing compounds by soybean (Glycine max (L.) Merr.] roots has been identified as an adaptive response mechanism to iron‐deficiency conditions which result in chlorosis. These compounds facilitate the conversion of Fe⁺³ to the metabolically active Fe⁺² form, allowing for increased uptake by roots in solution culture experiments. Degree of chlorosis is closely associated with HCO₃ concentration; however, the relationship between that ion and root reduction potential apparently has not been studied. We examined the effect of HCO₃‐ on root reduction potential of ten commercially‐grown soybean cultivars known to differ in chlorosis expression in the field. Root reduction potential was measured spectrophotometrically at 594 nm on samples of nutrient solution containing reduced Fe⁺² . Plants were grown with 5 mM NaHCO₃ or in HCO₃ ^‐‐free solutions. Averaged over cultivars, 0.205 umoles Fe⁺³ were reduced in the HCO₃ ^‐‐free solutions while only 0.009 umoles Fe⁺³ were reduced in the solutions containing HCO₃ ^‐. No significant differences were observed among cultivars for root reduction potential within either HCO₃ ^‐ treatment. Results from this study suggest that HCO₃ ^‐ may inhibit iron absorption by limiting the ability of roots to release reducing compounds which make available Fe⁺2 in the soil solution. This may partially explain the role of HCO₃ ^‐ in reducing chlorosis.     

Iron deficiency studies of sugar beet using an improved sodium bicarbonate‐buffered hydroponic growth system

A sodium bicarbonate (NaHCO₃)‐buffered hydroponic growth system was developed that simulates alkaline soil growth conditions necessary to screen sugar beet genotypes for iron (Fe) efficiency character. Three genotypes (NB1, NB4, and F, hybrid, NB 1xNB4) with differing capacities for Strategy I Fe responses were phenotyped successfully using this system. Genotypes NB1 and NB1xNB4 are Fe efficient, while NB4 is Fe inefficient. It was demonstrated that 5 mM NaHCO₃ provided buffering within an optimal range (pH 7.3 ‐ pH 6.3) for the duration of ‐Fe treatments, promoted enhanced H⁺ extrusion, and increased the in vivo capacity for Fe³⁺‐chelate reduction (Fe³⁺‐chelate reductase [FCR] activity), especially in the roots of the Fe efficient genotypes. The same concentrations of NaHCO₃ did not interfere with Fe supply to +Fe control plants of any genotype. The in vivo capacity for Fe³⁺‐chelate reduction increased over fivefold in both Fe efficient genotypes (NB1 and NB 1xNB4), but just under twofold in the Fe inefficient genotype (NB4). Localization and duration of enhanced Fe³⁺‐chelate reduction capacity were dependent upon the Fe efficiency character of each genotype.     

Influences of Humic Acid on Cr(VI) Removal by Zero-Valent Iron From Groundwater with Various Constituents: Implication for Long-Term PRB Performance

A 9-month-long continuous flow column study was carried out to investigate Cr(VI) removal by Fe⁰ with the presence of humic acid. The study focused on the influences of humic acid promoted dissolved iron release and humic acid aggregation in Fe⁰ columns receiving synthetic Cr(VI) contaminated groundwater containing various components such as bicarbonate and Ca. The effects of humic acid varied significantly depending on the presence of Ca. In Ca-free columns, the presence of humic acid promoted the release of dissolved iron in the forms of soluble Fe-humic acid complexes and stabilized fine Fe (hydr)oxide colloids. As a result, the precipitation of iron corrosion products was suppressed and the accumulation of secondary minerals on Fe⁰ surfaces was diminished, and a slight increase in Cr(VI) removal capacity by 18% was record compared with that of humic acid-free column. In contrast, in the presence of Ca, as evidenced by the SEM and FTIR results, humic acid greatly co-aggregated with Fe (hydr)oxides and deposited on Fe⁰ surfaces. This largely inhibited electron transfer from Fe⁰ surfaces to Cr(VI) and reduced the drainable porosity of the Fe⁰ matrix, resulting in a significant decrease in Cr(VI) removal capacity of Fe⁰. The Cr(VI) removal capacity was decreased by 24.4% and 42.7% in humic acid and Ca receiving columns, with and without bicarbonate respectively, compared with that of Ca and humic acid-free column. This study yields new considerations for the performance prediction and design of Fe⁰ PRBs in the environments rich in natural organic matter (NOM).     

GROWTH AND NUTRITION OF YOUNG BEAN PLANTS UNDER HIGH ALKALINITY AS AFFECTED BY MIXTURES OF AMMONIUM,POTASSIUM, AND SODIUM

High concentrations of bicarbonate (HCO^? ₃) cause alkalinity of irrigation water and are associated with suppression in plant growth and micronutrient deficiencies, such as iron (Fe) and zinc (Zn). Because reports indicate that the deleterious effects of alkalinity may be counteracted partially by supplementary potassium (K⁺) or ammonium (NH₄ ⁺) an experiment was designed to evaluate the response of bean plants (Phaseolus vulgaris L.) grown in high alkalinity conditions to varying proportions of NH₄ ⁺, K⁺, or sodium (Na⁺) (as a potential substitute for K⁺). Plants established in a growth chamber were grown in hydroponics for 21 days in solutions containing 5 mM HCO^? ₃ and a total of 5 mM of a mixture of NH₄ ⁺, K⁺, and Na⁺. The proportions of NH₄ ⁺, K⁺, and Na⁺ were designed according to mixture experiment methodology. Total N in all the mixture treatments was maintained at 10 mM by using nitrate (NO^? ₃)-N, thus the NH₄ ⁺:NO^? ₃ ratio varied according to the proportion of NH₄ ⁺ in the mixtures. Alkalinity caused suppression in plant growth and chlorophyll concentration in the younger leaves, whereas excessive NH₄ ⁺ was associated with leaf scorching and decreased leaf expansion. High proportions of K⁺ alleviated alkalinity symptoms and produced higher shoot and root dry mass provided that NH₄ ⁺ was included in the mixture. However, a proportion of NH₄ ⁺ higher than 0.333 in the mixture (>1.66 mM NH₄ ⁺) induced toxicity. The highest shoot dry mass occurred if the NH₄ ⁺:NO^? ₃ ratio was 0.19:0.81 and the NH₄ ⁺:K⁺:Na⁺ proportion was 0.38:0.38:0.24 (1.9 mM NH₄ ⁺ + 1.9 mM K⁺ + 1.2 mM Na⁺). Thus, an improvement in plant growth is achieved when NH₄ ⁺, K⁺, and Na⁺ are blended together, in spite of the high alkalinity treatment imposed. Optimum NH₄ ⁺ was associated with a decrease in solution pH and an increase in shoot Fe and Zn concentration.     

The Application of MnO2 in the Removal of Manganese from Acid Mine Water

The successive alkalinity-producing passive system (SAPPS) located in Gangneung, South Korea was designed to treat acid mine drainage. The performance of SAPPS has been monitored intensively for 3 years at the component level (influent, settling pond A, the successive alkalinity-producing system (SAPS), settling pond B, constructed wetland, and effluent). This study evaluated the ability of SAPPS to remove acidity and iron from influents at flow rates ranging from 17 to 160 m³/day. The concentration of soluble Fe_total was the highest, and the pH was the lowest at low flow rates (≤61 m³/day). When flow rates were over 80 m³/day, concentrations decreased and Fe_total was removed primarily at the SAPS stage. For flow rates of less than 61 m³/day, Fe_total was removed at the SAPS stage as well as in settling pond B and at the constructed wetland. Hydraulic retention times of 1 and 2 days were found to be appropriate and economical for use with the SAPS stage and for settling pond B and the constructed wetland, respectively The treatment of acid mine drainage by conventional SAPPSs is limited by the availability of alkaline materials. However, the new proposed system can address this weakness through the provisioning of a suitable alkalinity supply.     

Specific features of the chemical composition of groundwater in floodplain soils of the Selenga River delta (Lake Baikal region)

The chemical composition of groundwater has been studied at several test plots in the Selenga River delta. The fresh groundwater containing calcium bicarbonates favors the formation of nonsaline soils in the delta and, hence, contributes to preservation of fresh water in Lake Baikal. The role of groundwater as a source of dissolved organic matter, iron compounds, phosphorus, and other elements is discussed. It is shown that the depth and chemical composition of the groundwater in particular areas depend on the character of the mesotopography, the drainage of the area, and the soil properties. After the flood period, the concentrations of Ca²⁺, HCO ₃ ^? , Fe³⁺, and SO ₄ ^2? in the groundwater increase with the rise in the soil temperatures. In the dry periods, the concentrations of Na⁺ and Cl^? ions increase, whereas the concentration of C_total decreases.     

Effects of 5‐aminolevulinic acid on water uptake,ionic toxicity,and antioxidant capacity of Swiss chard (Beta vulgaris L.) under sodic‐alkaline conditions

Sodic‐alkalinity may be more deleterious to plant growth than salinity. The objectives of this study were to determine whether 5‐aminolevulinic acid (ALA: an essential precursor for chlorophyll biosynthesis) foliar application could improve the sodic‐alkaline resistance of Swiss chard (Beta vulgaris L. subsp. cicla ) by regulating water uptake, ionic homeostasis, photosynthetic capacity, and antioxidant metabolism. Eight‐week‐old uniform plants were grown in nutrient medium without and with a sodic‐alkaline regime generated by a mixture of NaHCO₃ and Na₂CO₃ (NaHCO₃ : Na₂CO₃ = 9:1 molar ratio) for 12 d, and leaves were sprayed daily with water or ALA. The Na⁺ and ALA concentrations were gradually increased to 60 mM and 120 μM, respectively. ALA foliar application alleviated the physiological damage from sodic‐alkalinity, as reflected by the increases in plant dry weight, relative growth rate, chlorophyll, Mg²⁺ concentration, and the decrease in Na⁺ concentration. However, ALA foliar application did not change the water uptake capacity or the concentration of K⁺, Fe³⁺, and endogenous ALA in leaf tissues under sodic‐alkaline conditions. ALA foliar application effectively mitigated damage from sodic‐alkalinity because of the increased activity of antioxidant enzymes (catalase and guaiacol peroxidase), particularly superoxide dismutase activity, which was maintained at the same level as for control plants. These results suggest that ALA foliar application alleviated sodic‐alkaline stress mainly owing to its antioxidant capacity, and superoxide dismutase has the main responsibility for reducing oxidative stress in Swiss chard.     

Mineral-catalyzed peroxidation of tetrachloroethylene

The treatment of perchloroethylene (PCE) was investigated by the promotion of Fenton-like reactions using the iron oxyhydroxide goethite (α-FeOOH) as the sole source of the iron catalyst. A silica sand-goethite matrix was contaminated with 5 mg L^?1 PCE and the oxidative treatments were conducted with 0.15 mM, 2 mM, 5mM, 10mM, 20mM, and 30mM H₂O₂. Perchloroethylene was effectively degraded within 96 hr and the most efficient treatment stoichiometry was observed using 0.15 mM H₂O₂ at pH 3. The degree of heterogeneous catalysis was evaluated by conducting oxidation reactions in parellel systems with an equivalent concentration of soluble iron. The results showed that, within the first 24 hr, up to 94% of the PCE degradation was attributed to heterogeneous catalysis. This modified Fenton's process, when used to treat 5 mg L^?1 PCE in natural subsurface materials with 2 mM H₂O₂ at pH 3, resulted in a residual of 0.20 mg L^?1 PCE after 96 hr.     

Seasonal Variations in Vertical Redox Stratification and Potential Influence on Trace Metal Speciation in Minerotrophic Peat Sediments

Seasonal variations in pore water and solid phase geochemistry were investigated in urbanized minerotrophic peat sediments located in southwestern Michigan, USA. Sediment pore waters were collected anaerobically, using pore water equilibrators with dialysis membranes (“peepers”) and analyzed for pH, alkalinity, dissolved ΣPO₄ ^?3, ΣNH₄ ⁺, ΣS^?2, SO₄ ^?2, Fe⁺³, Fe⁺², and Mn⁺² at 1-2 cm intervals to a depth of 50 cm. Cores collected adjacent to the peepers during all four seasons were analyzed for reactive solid phase Fe according to extraction methods proposed by Kostka and Luther (1994). The association of Fe and trace metals (Mn, Pb, Zn, Cu, Cr, Co, Cd, U) with operationally defined solid phase fractions (carbonates, iron and manganese oxides, sulfides/organics and residual) was assessed for cores extracted during winter and spring using extraction methods proposed by Tessier et al. (1979, 1982). Pore water Fe and S data demonstrate a clear seasonal variation in redox stratification of these sediments. The redox stratification becomes more compressed in spring and summer, with relatively more reducing conditions closer to the sediment water interface (SWI), and less reducing conditions near the SWI in fall and winter. In the upper 10–15 cm of sediment, the pool of ascorbate extractable Fe, thought to be indicative of reactive Fe(III) oxides, diminishes during spring and summer, in agreement with seasonal changes in redox stratification indicated by the pore water data. Tessier extractions indicate that the total extractable quantity of all metals analyzed in this study decrease with depth, and that the majority of the non-residual Fe, Pb, Zn, Cu, Cr, Co, Cd, and U is typically associated with the sulfide/organic fraction of the sediments at all depths. Non-residual Mn, in contrast, is significantly associated with carbonates in the upper 15–25 cm of the sediment, and predominantly associated with the sulfide/organic fraction only in deeper sediments.