Screening Indian Mustard Genotypes for Phytoremediating Arsenic‐Contaminated Soils

Ten Indian mustard (Brassica juncea L.) genotypes were screened for their phytoremediation potential for arsenic (As) contaminated water under laboratory‐controlled conditions. The genotypes were grown in a hydroponic chamber for 20 days in 250‐mL beakers containing As‐contaminated water. During plant development, changes in plant growth, biomass, and total As were evaluated. Of the 10 genotypes (Pusa Agrani, BTO, Pusa Kranti, Pusa Bahar, Pusa Bold, Pusa Basant, Pusa Jai Kisan, Arka Vardhan, Varuna, and Vaibhav) Pusa Jai Kisan was the most effective in phytoremediating As‐contaminated water under hydroponic conditions. This will provide new information for Indian mustard genotypes for phytoremediating As‐contaminated soils.     

Investigation of Arsenotrophic Microbiome in Arsenic‐Affected Bangladesh Groundwater

Arsenotrophic bacteria contribute to the nutrient cycling in arsenic (As) affected groundwater. This study employed a culture‐independent and ‐dependent investigation of arsenotrophic microbiomes in As affected groundwater samples collected from Madhabpur, Sonatengra, and Union Porishod in Singair Upazila, Manikganj, Bangladesh. Total As contents, detected by Atomic Absorption Spectrophotometry (AAS) of the samples, were 47 µg/L (Madhabpur, SNGW‐1), 53 µg/L (Sonatengra, SNGW‐2), and 12 µg/L (Union porishod, SNGW‐3), whereas the control well (SNGW‐4; depths >150 m) showed As content of 6 µg/L. Denaturing Gradient Gel Electrophoresis (DGGE) analysis of the amplified 16S rRNA gene from As‐affected groundwater samples revealed the dominance of aerobic bacteria Pseudomonas within heterogeneous bacterial populations. DGGE of heterotrophic enrichments supplemented with arsenite [As (III)] for 4 weeks showed the dominance of Chryseobacterium, Flavobacterium, and Aquabacterium, whereas the dominant genera in that of autotrophic enrichments were Aeromonas, Acinetobacter, and Pseudomonas. Cultured bacteria retrieved from both autotrophic and heterotrophic enrichments were distinguished into nine genotypes belonging to Chryseobacterium, Acinetobacter, Escherichia, Pseudomonas, Stenotrophomonas, Janibacter, Staphylococcus, and Bacillus. They exhibited varying range of As(III) tolerance from 4 to 27 mM. As(III) transformation potential was confirmed within the isolates with oxidation rate as high as 0.143 mM/h for Pseudomonas sp. Sn 28. The arsenotrophic microbiome specifies their potential role in groundwater As‐cycling and their genetic information provide the scientific basis for As‐bioremediation.     

Antioxidant Enzymes Response in Vetiver Grass: A Greenhouse Study for Chelant‐Assisted Phytoremediation of Lead‐Contaminated Residential Soils

In a previous study we have demonstrated the suitability of using vetiver grass (Vetiveria zizanioides L.) for the phytostabilization of lead‐based paint contaminated residential soils. Vetiver did not show any growth retardation or toxicity symptoms despite high soil Pb levels. Antioxidant enzymes like superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) reportedly allow plants to combat metal stress. Thus, we hypothesized that in vetiver, these antioxidant enzymes can play an important role in combating Pb induced stress, and that chelant‐bound Pb is less toxic to vetiver compared to free Pb in soil. The response of antioxidant enzymes was studied in vetiver grass grown in Pb paint‐contaminated residential soils collected from San Antonio, Texas and Baltimore, Maryland. Chelating agents such as ethylenediaminetetraacetic acid (EDTA) and ethylenediaminedisuccinic acid (EDDS) were used to mobilize Pb from bound fractions to the labile pool, facilitating Pb uptake by vetiver. Although the Pb concentration in vetiver from these treatments was significantly higher than those grown in the absence of a chelant, the antioxidant enzymes activities were lower compared to the latter. Antioxidant enzymes activity of vetiver plants grown in the presence of chelants is lower compared to those in without chelant treatment, while they tended to increase with dose in treatments with varying chelant concentrations. Data obtained support the proposed hypothesis.     

Phytoremediation of Cadmium‐Contaminated Soil by Two Jerusalem Artichoke (Helianthus tuberosus L.) Genotypes

Jerusalem artichoke (Helianthus tuberosus L.) can be used not just for bioethanol production, bur potentially also for soil phytoremediation via removal of heavy metal pollutants. An experiment was carried out to characterize the phytoextraction efficiency of two Jerusalem artichoke genotype (NY2 and NY5) in cadmium (Cd) contaminated soil. After 90 days of growth, NY5 had greater plant biomass and greater Cd accumulation in tissues than NY2. The chlorophyll content and chlorophyll a fluorescence parameters were slightly higher when plants were grown in Cd‐contaminated versus control soil. It implies that this examined NY2 and NY5 can extract more Cd than some hyperaccumulators, indicating that NY2 and NY5 can be applied to clean up Cd‐contaminated soils. Compared with NY2, NY5 had higher phytoextraction potential due to more biomass and higher concentrations of Cd in tissues, and may therefore be the better candidates for phytoremediation in Cd‐contaminated soil.     

Bioremediation of Chlorinated Pesticides in Field‐Contaminated Soils and Suitability of Tenax Solid‐Phase Extraction as a Predictor of Its Effectiveness

Bioremediation is intensively studied today as a treatment method for soil contaminated with chlorinated pesticides, chemicals counted among persistent organic pollutants. In the presented work, results of desorption kinetics study using consecutive Tenax TA solid phase extraction (SPE) were tested as predictors of 3‐wk anaerobic soil bioremediation effectiveness for chlorinated pesticides γ‐HCH, DDT, and methoxychlor. Field‐contaminated samples were used in these experiments, and conditions of bioremediation tests were based on previous research. Amounts of pesticides removed during bioremediation (43–98% of initial concentrations) were in most cases much larger (average ratio 1.37) than rapidly desorbing fractions estimated in SPE using two‐compartment model of desorption kinetics. The scatter of results was also considerable (standard deviation 0.45). However, there was a statistically significant correlation between amounts removed and rapidly desorbing fractions (R² = 0.64), indicating a relationship between degradability and desorbability. Nonetheless, determination of rapidly desorbing fractions was considered rather a poor indicator of soil bioremediation efficiency for chlorinated pesticides. The total amounts of pesticides desorbed by Tenax in 72 h performed better in this respect (R² = 0.73, fraction removed/desorbed = 1.10 ± 0.20, average ± standard deviation). Disappearance of DDT during bioremediation was accompanied by DDD formation but this was considerably lower than results expected from stoichiometry.     

Further Study on the Kinetics of Bioremediation of Soils Contaminated with the Herbicide 2,4‐Dichlorophenoxy Acetic Acid

The bioremediation of soil contaminated with the herbicide 2,4‐dichlorophenoxy acetic acid has been studied applying the bacterium Ralstonia eutropha. The effects of temperature, pH, and moisture content of soils on the rate of degradation of this herbicide have been investigated. The Taguchi experimental design method was applied to determine the relative impacts of the pertinent system variables. According to this approach, four series of experiments were performed under various operating conditions. In all four series the herbicide was degraded efficiently, however, the highest rate was observed at a temperature of 35°C, pH 6, and at 80% moisture content of the soil. A kinetic model for the biodegradation of the herbicide was developed for this particular conditions based on the Monod type growth equation and autocatalytic behavior of the decomposition reaction. A close correlation has been observed between the experimental data and those predicted from the model. The degree of agreement was between 85–95%.     

Sorption of ortho‐Phenylphenol to Soils

Conflicting sorption coefficients for ortho‐phenylphenol (OPP) have been reported in the literatures, which resulted in the conflicting assessments on OPP mobility in soil. To ascertain the sorption coefficient of OPP, batch experiments were performed based on OECD guideline 106, using three types of soils. Headspace solid‐phase microextraction (HS‐SPME) and GC‐MS were applied to the determination of OPP concentration in the liquid phase. The sorption isotherms obtained for all three soils under equilibrium conditions were described well, assuming linear sorption. The organic carbon normalized distribution coefficients (K_oc) ranged from 894 to 1703 L kg^?1, which suggested that OPP is moderately mobile in soil. The results also showed that the K_oc value of OPP can be predicted precisely from K_ow, whereas it was underestimated by one order of magnitude when water solubility is used.     

Reinterpreting the Importance of Oxygen‐Based Biodegradation in Chloroethene‐Contaminated Groundwater

Chlororespiration is common in shallow aquifer systems under conditions nominally identified as anoxic. Consequently, chlororespiration is a key component of remediation at many chloroethene‐contaminated sites. In some instances, limited accumulation of reductive dechlorination daughter products is interpreted as evidence that natural attenuation is not adequate for site remediation. This conclusion is justified when evidence for parent compound (tetrachloroethene, PCE, or trichloroethene, TCE) degradation is lacking. For many chloroethene‐contaminated shallow aquifer systems, however, nonconservative losses of the parent compounds are clear but the mass balance between parent compound attenuation and accumulation of reductive dechlorination daughter products is incomplete. Incomplete mass balance indicates a failure to account for important contaminant attenuation mechanisms and is consistent with contaminant degradation to nondiagnostic mineralization products like CO₂. While anoxic mineralization of chloroethene compounds has been proposed previously, recent results suggest that oxygen‐based mineralization of chloroethenes also can be significant at dissolved oxygen concentrations below the currently accepted field standard for nominally anoxic conditions. Thus, reassessment of the role and potential importance of low concentrations of oxygen in chloroethene biodegradation are needed, because mischaracterization of operant biodegradation processes can lead to expensive and ineffective remedial actions. A modified interpretive framework is provided for assessing the potential for chloroethene biodegradation under different redox conditions and the probable role of oxygen in chloroethene biodegradation.     

Soil Gas Screening for Chlorinated Solvents at Three Contaminated Karst Sites in Tennessee

Soil gas was sampled using active sampling techniques and passive collectors at three sites in Tennessee to evaluate the effectiveness of these techniques for locating chlorinated solvent sources and flowpaths in karst aquifers. Actively collected soil gas samples were analyzed in the field with a portable gas chromatograph, and the passive soil gas collectors were analyzed in the lab with gas chromatography/mass spectrometry. Results of the sampling indicate that the effectiveness of both techniques is highly dependent on the distribution of the contaminants in the subsurface, the geomorphic and hydrogeologic characteristics of the site, and, in one case, on seasonal conditions. Both active and passive techniques identified areas of elevated subsurface chlorinated solvent concentrations at a landfill site where contamination remains concentrated in the regolith. Neither technique detected chlorinated solvents known to be moving in the bedrock at a manufacturing site characterized by thick regolith and an absence of surficial karst features. Passive soil gas sampling had varied success detecting flowpaths for chloroform in the bedrock at a train derailment site characterized by shallow regolith and abundant surficial karst features. At the train derailment site, delineation of the contaminant flowpath through passive soil gas sampling was stronger and more detailed under winter conditions than summer.     

Evaluation of Zerovalent Zinc for Treatment of 1,2,3‐Trichloropropane‐Contaminated Groundwater: Laboratory and Field Assessment

The efficacy and feasibility of using zerovalent zinc (ZVZ) to treat 1,2,3‐trichloropropane (TCP)‐contaminated groundwater was assessed in laboratory and field experiments. In the first portion of the study, the reactivity of commercially available granular ZVZ toward TCP was measured in bench‐scale batch‐reactor and column experiments. These results were used to design columns for on‐site pilot‐scale treatment of contaminated groundwater at a site in Southern California. Two of the ZVZ materials tested were found to produce relatively high rates of TCP degradation as well as predictable behavior when scaling from bench‐scale to field testing. In addition, there was little decrease in the rates of TCP degradation over the duration of field testing. Finally, no secondary impacts to water quality were identified. The results suggest that ZVZ may be an effective and feasible material for use in engineered treatment systems, perhaps including permeable reactive barriers.