Virus removal during simulated soil-aquifer treatment

Removals of indigenous coliphage and seeded poliovirus type 1 during simulated soil-aquifer treatment were evaluated during transport of secondary effluent under unsaturated flow conditions in 1-m soil columns. Independent variables included soil type (river sand or sandy loam) and infiltration rate. Removal of coliphage was in all cases less than removal of poliovirus type 1 (strain LSc-2ab), supporting contentions that indigenous coliphage can act as a conservative indicator of groundwater contamination by viral pathogens of human origin. Coliphage retention was significantly more efficient (p<0.001) in the finer-grained sandy loam (93%) than in sand (76%). Increasing reactor detention time from 5 to 20 h increased coliphage attenuation from 70% to 99% in a 1-m sand column. There was a significant linear correlation (p=0.012) between log-transformed (fractional) coliphage concentration [log(C/C(0))] and reactor detention time. Re-mobilization of attached coliphage occurred during simulated rainfall using low-ionic-strength water. Inhibition of aerobic respiration resulted in significantly less efficient coliphage attenuation (p=0.033), suggesting the involvement of aerobic microorganisms in the survival/retention of this virus.     

Atrazine mineralization potential in two wetlands

The fate of atrazine in agricultural soils has been studied extensively but attenuation in wetland systems has received relatively little attention. The purpose of this study was to evaluate the mineralization of atrazine in two wetlands in central Ohio. One was a constructed wetland, which is fed by Olentangy River water from an agricultural catchment area. The other was a natural fen (Cedar Bog) in proximity to atrazine-treated cornfields. Atrazine mineralization potential was measured by 14CO2 evolution from [U-ring-14C]-atrazine in biometers. The constructed wetland showed 70-80% mineralization of atrazine within 1 month. Samples of wetland water that were pre-concentrated 200-fold by centrifugation also mineralized 60-80% of the added atrazine. A high extent of atrazine mineralization (75-81% mineralized) was also associated with concentrated water samples from the Olentangy River that were collected upstream and downstream of the wetland. The highest levels of mineralization were localized to the top 5 cm zone of the wetland sediment, and the activity close to the outflow at the Olentangy wetland was approximately equal to that near the inflow. PCR amplification of DNA extracted from the wetland sediment samples showed no positive signals for the atzA gene (atrazine chlorohydrolase), while Southern blots of the amplified DNA showed positive bands in five of the six Olentangy wetland sediment samples. Amplification with the trzD (cyanuric acid amidohydrolase) primers showed a positive PCR signal for all Olentangy wetland sediment samples. There was little mineralization of atrazine in any of the Cedar Bog samples. DNA extracted from Cedar Bog samples did not yield PCR products, and the corresponding Southern hybridization signals were absent. The data show that sediment microbial communities in the Olentangy wetland mineralize atrazine. The level of activity may be related to the seasonality of atrazine runoff entering the wetland. Comparable activity was not observed in the Cedar Bog, perhaps because it does not directly receive agricultural runoff. Qualitatively, the detection of the genes was associated with measurable mineralization activity which was consistent with the differences between the two study sites.     

The fate of heavy oil wastes in soil microcosms. I: A performance assessment of biotransformation indices

A controlled soil microcosm study was used to evaluate the performance of selected oil biotransformation indices using samples of Nigerian crude, a blended ballast oil and No. 6 fuel oil. Biotic losses were demonstrated through loss of solvent extractable matter (SEM) and changes in class fraction distribution in weathered soil extracts relative to sterilised controls. GC-EI MS peak identification and quantification was achieved for selected (sigma) n-alkanes, the isoprenoid alkanes norpristane (iC18), pristane (iC19) and phytane (iC20), combined mono-substituted (1-, 2-, 3- and 9-) methylphenanthrenes (sigma methylphenanthrenes), combined dimethylphenanthrenes (sigma dimethylphenanthrenes) and the hopane isomers 17 alpha(H)21 beta(H)-hopane and 17 alpha(H)21 beta(H)-30-norhopane. The [sigma n-alkanes:17 alpha(H)21 beta(H)-hopane] index was most sensitive to oil biotransformation and most accurately reflected depletion of oil from contaminated soils in this study. This index was found to be the most reliable for the No. 6 fuel oil saturates, dropping from 81.9 to 18.1 over the course of the 256-day microcosm study. In terms of sensitivity, and taking into account the results of an ANOVA analysis, the biotransformation indices most sensitive to oil biotransformation were (in order of decreasing sensitivity): [sigma C14-28:17 alpha(H)21 beta(H)-hopane] > [sigma C14-28:sigma dimethylphenanthrenes] > [C18:phytane].     

Assessing the transfer of pentachlorophenol through soil columns using 13[C]isotope

The transfer of organic pollutants was studied through soil columns using 13[C]-labelled pentachlorophenol (PCP) as a model compound. The organic carbon content and the 13[C]/12[C] ratio were measured in two soil sections, 0-3 cm and 3-6 cm, and in percolated water using an Elemental Analyser coupled with a Magnetic Mass Sector. The mass balance of carbon was evaluated and the amount of PCP was calculated in each compartment of the soil-water systems. The results show that more than 80% of the PCP-derived 13[C] remained in the upper layer of the soil column. Approximately 20% was transferred to the lower soil layer, and less than 1% was found in the water leachates. The 13[C]-labelled tracers may thus be used as an alternative to radioactive compounds to follow the fate of organic pollutants in soil and water under field conditions.     

Degradation of soil-sorbed trichloroethylene by stabilized zero valent iron nanoparticles: effects of sorption, surfactants, and natural organic matter

Zero valent iron (ZVI) nanoparticles have been studied extensively for degradation of chlorinated solvents in the aqueous phase, and have been tested for in-situ remediation of contaminated soil and groundwater. However, little is known about its effectiveness for degrading soil-sorbed contaminants. This work studied reductive dechlorination of trichloroethylene (TCE) sorbed in two model soils (a potting soil and Smith Farm soil) using carboxymethyl cellulose (CMC) stabilized Fe-Pd bimetallic nanoparticles. Effects of sorption, surfactants and dissolved organic matter (DOC) were determined through batch kinetic experiments. While the nanoparticles can effectively degrade soil-sorbed TCE, the TCE degradation rate was strongly limited by desorption kinetics, especially for the potting soil which has a higher organic matter content of 8.2%. Under otherwise identical conditions, ∼44% of TCE sorbed in the potting soil was degraded in 30 h, compared to ∼82% for Smith Farm soil (organic matter content = 0.7%). DOC from the potting soil was found to inhibit TCE degradation. The presence of the extracted SOM at 40 ppm and 350 ppm as TOC reduced the degradation rate by 34% and 67%, respectively. Four prototype surfactants were tested for their effects on TCE desorption and degradation rates, including two anionic surfactants known as SDS (sodium dodecyl sulfate) and SDBS (sodium dodecyl benzene sulfonate), a cationic surfactant hexadecyltrimethylammonium (HDTMA) bromide, and a non-ionic surfactant Tween 80. All four surfactants were observed to enhance TCE desorption at concentrations below or above the critical micelle concentration (cmc), with the anionic surfactant SDS being most effective. Based on the pseudo-first-order reaction rate law, the presence of 1×cmc SDS increased the reaction rate by a factor of 2.5 when the nanoparticles were used for degrading TCE in a water solution. SDS was effective for enhancing degradation of TCE sorbed in Smith Farm soil, the presence of SDS at sub-cmc increased TCE degraded by ∼10%. However, effect of SDS on degradation of TCE in the potting soil was more complex. The presence of SDS at sub-cmc decreased TCE degradation by 5%, but increased degradation by 5% when SDS dosage was raised to 5×cmc. The opposing effects were attributed to combined effects of SDS on TCE desorption and degradation, release of soil organic matter and nanoparticle aggregation. The findings strongly suggest that effect of soil sorption on the effectiveness of Fe-Pd nanoparticles must be taken into account in process design, and soil organic content plays an important role in the overall degradation rate and in the effectiveness of surfactant uses.     

Effects of molecular weight of natural organic matter on cadmium mobility in soil environments and its carbon isotope characteristics

We investigated the role of natural organic matter in cadmium mobility in soil environments. We collected the dissolved organic matter from two different types of natural waters: pond surface water, which is oxic, and deep anoxic groundwater. The collected organic matter was fractionated into four groups with molecular weights (unit: Da (Daltons)) of <1 x 10(3), 1-10 x 10(3), 10-100 x 10(3), and >100 x 10(3). The organic matter source was land plants, based on the carbon isotope ratios (delta(13)C/(12)C). The organic matter in surface water originated from presently growing land plants, based on (14)C dating, but the organic matter in deep groundwater originated from land plants that grew approximately 4000 years ago. However, some carbon was supplied by the high-molecular-weight fraction of humic substances in soil or sediments. Cadmium interacted in a system of siliceous sand, fractionated organic matter, and water. The lowest molecular weight fraction of organic matter (<1 x 10(3)) bound more cadmium than did the higher molecular weight fractions. Organic matter in deep groundwater was more strongly bound to cadmium than was organic matter in surface water. The binding behaviours of organic matter with cadmium depended on concentration, age, molecular weight, and degradation conditions of the organic matter in natural waters. Consequently, the dissolved, low-molecular-weight fraction in organic matter strongly influences cadmium migration and mobility in the environment.     

Natural Attenuation-Untersuchungen an einem mit LCKW kontaminierten Altdeponiestandort

The Natural Attenuation of chlorinated hydrocarbons leaking from an abandoned landfill was the focus of an investigation conducted within the framework of the Bavarian joint research project “Nachhaltige Altlastenbewältigung unter Einbeziehung des natürlichen Reinigungsvermögens”. The research focused on two contaminant plumes, one having a diffuse TCE/PCE source and the other a cis- DCE source. The TCE/PCE plume had a maximum concentration of 52 μg/l total chlorinated hydrocarbons near the source area. Cis-DCE concentrations near the source of the second plume were up to 7,000 μg/l. In addition, degradation products (VC and Ethylene) were detected in this region, which indicate reductive dechlorination of the cis-DCE, TCE or PCE pollutants. However, other investigations indicate that the natural attenuation potential of the site is low and that the reduction in concentration is dependant more on dilution and other unknown processes. Stemming from this research, a new approach was developed using Solid Phase Micro Extraction (SPME) and GC/FID analytical techniques for microcosm testing. Furthermore, an airtight column was developed that allows the detection of sorption of highly volatile substances in low concentrations within an aquifer material.     

Quantification of copper doses to settlement plates in the field using diffusive gradients in thin films

A study of carbon (C) storage in the 0-0.75-m profile of soils subtending various types of grasslands on the Qinghai-Tibetan Plateau showed that the organic carbon content of the 1,627,000 km2 of such lands in the region reaches 33.52 Pg of C. Organic carbon is mainly stored in the meadow and steppe soils of the Plateau, which combined, represents 23.2 Pg of C stored in organic form. This represents 23.44% of China's total organic soil-stored carbon and 2.5% of the global pool of soil carbon as of 1996. Carbon emissions from the grassland soils were estimated based on the two major modes of emission: (i) natural soil respiration and (ii) shifts in net C flux to/from soil due to land-use changes and their potential influence on organic matter decomposition. Annual soil respiration-driven CO2 emissions from the grassland soils of the plateau reached 1.17 Pg C year(-1), accounting for 26.4% of China's total soil respiration and 1.73% of global soil respiration. Because the grassland area accounts for 1.02% of the global terrestrial land and 16.9% of China's total terrestrial land, this CO2 emission rate is significantly higher than the country's mean annual rate (approx. 4.2 Pg C year(-1)) and even higher than the global mean rate (approx. 68 Pg C year(-1)). In the last 30 years, approximately 3.02 Pg C have been emitted from the grassland soils of the plateau due to land-use changes and grassland degradation. The total CO2 emissions rate from the grassland soils of the plateau reached 1.27 Pg C year(-1). Protecting grasslands on the Qinghai-Tibetan Plateau is of great importance in limiting global climate change.     

Treatment of atrazine in nursery irrigation runoff by a constructed wetland

To investigate the treatment capability of a surface flow wetland at a container nursery near Portland, Oregon, atrazine was introduced during simulated runoff events. Treatment efficiency was evaluated as the percent atrazine recovered (as percent of applied) in the water column at the wetland's outlet. Atrazine treatment efficiency at the outlet of the constructed wetland during a 7-d period ranged from 18-24% in 1998 (experiments 1-3) and 16-17% in 1999 (experiments 4 and 5). Changes in total flow, or frequency and intensity of runoff events did not affect treatment. For experiment 6 in 1999, where the amount, frequency, and duration of runoff events exceeded all other experiments, treatment was compromised. For all experiments, deethylatrazine (DEA) and deisopropylatrazine (DIA) accounted for 13-21% of the initial application. Hydroxyatrazine (HA) was rarely detected in the water. Organic carbon adsorption coefficients (Koc) were determined from batch equilibrium sorption isotherms with wetland sediment, and they decreased in the order of HA > DIA > atrazine > DEA. Static water-sediment column experiments indicated that sorption is an important mechanism for atrazine loss from water passing through the constructed wetland. The results of the MPN assay indicated the existence in the wetland of a low-density population of microorganisms with the potential to mineralize atrazine's ethyl side chain.     

Binding and mobility of mercury in soils contaminated by emissions from chlor-alkali plants

Chlor-alkali plants are known to be an important source of Hg emissions to the atmosphere and related contamination of soils in their vicinity. In the present study, the results of Hg speciation and mobility of Hg in soils affected by Hg emissions from three chlor-alkali plants are compared. Solid phase mercury speciation analyses was carried out using a mercury-thermo-desorption technique with the aim of distinguishing elemental Hg [Hg(0)] from Hg(II)-binding forms. Mercury species in soil leachates were distinguished using an operationally defined method, which is based on the reactivity of soluble Hg compounds. Results show that the Hg(0) emitted from the plants could not be detected in any of the investigated soils. This indicates quantitative re-emission or oxidation of this Hg species in the atmosphere or soils. In most soils Hg was predominately bound to organic matter. Only in sandy soils deficient in organic matter was Hg, to a larger extent, sorbed onto mineral soil components. Leachable Hg in most soils occurred as non-reactive, soluble organic Hg complexes such as fulvic acid-bound Hg, and reach their highest values (90 microg kg(-1)) in soils rich in organic matter. Concentrations of reactive, soluble Hg compounds were highest in sandy soils where the content of organic matter was low. Leachability of Hg was found to be inhibited in soils with a high content of clayey soil components. The distribution of Hg in soil profiles suggests that migration of Hg to deeper soil layers (approx. 20 cm) is most effective if Hg is bound to soluble organic complexes, whereas reactive Hg or weak Hg complexes are effectively retained in the uppermost soil layer (5 cm) through sorption on mineral surfaces.     

Retention and release of Zn and Cd in spodic horizons as determined by pH(stat) analysis and single extractions

In the northern Campine in Belgium, large areas are contaminated by heavy metals such as Zn and Cd due to the (former) non-ferro metal industry. In the sandy soils, the heavy metal adsorption/attenuation in the spodic horizon represents the main retention mechanism of leached pollutants from the contaminated topsoils. In this study, the pH-dependent behaviour of the elements in these spodic horizons was tested by pH(stat) experiments and compared to sandy loam soils. Extractions with CaCl(2) 0.01 M and EDTA 0.05 M provided a further insight into the binding mechanisms. The results indicate that organic matter is the main factor responsible for the mobility of Cd, Zn and Ca in the spodic horizons. The binding of elements is not very strong, however, and highly dependent on pH. A slight decrease in pH can cause a significant release of metals from the spodic horizons, with up to 60% of Cd and 90% of Zn being released within a 1.5 unit change in pH (starting from the naturally occurring pH). This pH change can happen rapidly in these soils, due to the low buffering capacity, and is realistic given the acidification in Flanders. For the sandy loam soils, a pH decrease of 3 units is needed to release 40% of Cd and 20% of Zn, and the acid neutralization capacity is exhausted more gradually, suggesting that slower buffering mechanisms take place. For the sandy loam soils, Cd retention is mainly governed by organic matter, while for Zn other factors such as the clay minerals also play an important role. Despite the high potential mobility and pH dependence of the heavy metal retention in the spodic horizons, the actual risk for groundwater pollution is limited. For the diffusely contaminated areas, where traditional remediation is not an option, spodic horizons may therefore contribute to a natural attenuation of the soil contamination.     

Studies of hexavalent chromium attenuation in redox variable soils obtained from a sandy to sub-wetland groundwater environment

Laboratory experiments were conducted to characterize and quantify the capacity and kinetics of the combined effects of natural attenuation processes, such as adsorption, reduction, and precipitation, for hexavalent chromium [Cr(VI)] in a variable geochemical (i.e. fraction of organic carbon [foc], redox) environment of glaciated soils. Equilibrium attenuation terms: linear sorption (K(d)), estimated capacity, and non-linear Langmuir (K(L), Q) sorption parameters; varied over several orders of magnitude. The pseudo-first-order rate of disappearance of Cr(VI) from aqueous:soil slurries ranged from approximately 10(-5) to approximately 10(-1)/min. An operationally defined kinetic attenuation term, attenuation capacity (AC), describing the quantity of Cr(VI) disappearing from the slurries, ranged from 1.1 to approximately 12 microg Cr(VI)/g soil/7 days. The linear K(d)'s and estimated attenuation capacities were indirectly and directly related to increasing soil pH and foc, respectively. The AC values decreased and increased as a function of increasing soil pH and foc, respectively. The parameters determined in this work were used to evaluate the kinetics, capacity, and stability of chromium attenuation in the sub-wetland saturated soils in Hellerich (2004. A field, laboratory, and modeling study of natural attenuation processes affecting the fate and transport of hexavalent chromium in a redox variable groundwater environment. Ph.D. Dissertation, Department of Civil and Environmental Engineering, University of Connecticut-Storrs) using a statistical simulation framework.     

North American prairie wetlands are important non-forested land-based carbon storage sites

We evaluated the potential of prairie wetlands in North America as carbon sinks. Agricultural conversion has resulted in the average loss of 10.1 Mg ha(-1) of soil organic carbon on over 16 million ha of wetlands in this region. Wetland restoration has potential to sequester 378 Tg of organic carbon over a 10-year period. Wetlands can sequester over twice the organic carbon as no-till cropland on only about 17% of the total land area in the region. We estimate that wetland restoration has potential to offset 2.4% of the annual fossil CO(2) emission reported for North America in 1990.     

Evaluation of strategies for anaerobic bioremediation of high concentrations of halomethanes

Bioremediation is being considered for groundwater at an industrial site contaminated with carbon tetrachloride (CT), trichlorofluoromethane (CFC-11), and chloroform (CF), at concentrations typically considered too high for biological treatment. 1,1-Dichloroethene is also present. The objective of this study was to evaluate in situ anaerobic remediation by biostimulation alone (lactate, emulsified vegetable oil, and corn syrup), biostimulation (corn syrup) supplemented with vitamin B₁₂ (cyanocobalamin), and bioaugmentation in combination with catalytic levels of B₁₂. Three cultures were evaluated for enhancing biotransformation of CT, CFC-11 and CF: two were sulfate reducing enrichments (grown on lactate and ethanol, respectively), based on a high concentration of sulfate in the groundwater; the other was a fermentative enrichment grown on corn syrup. A microcosm study with soil and groundwater (neutralized to pH 7) from the site revealed that bioaugmentation is a potentially feasible treatment approach, with complete biotransformation of 8.8 mg/L CT, 26 mg/L CFC-11, and 500 mg/L of CF in approximately 500 days. The lactate-grown sulfate reducing culture and the corn syrup-grown fermentative culture were the most effective. Subsequent bioaugmentation with a chloroethene-respiring culture yielded rapid reduction of 1,1-dichloroethene (9.1 mg/L) to ethene. Complete transformation of CT, CFC-11 and CF was also observed with corn syrup + B₁₂, although the time required was twice as long compared to bioaugmentation. In the presence of B₁₂, biotransformation of [¹⁴C]CT and [¹⁴C]CF yielded mainly CO, CO₂, and organic acids. CT was consistently transformed first, followed by CFC-11 and then CF. Corn syrup was only partially effective for halomethane removal without B₁₂, but was more effective than emulsified vegetable oil or lactate.     

Effect of superabsorbent polymer on soil and plants on steep surfaces

In this study, a superabsorbent polymer (SAP; Super‐AB‐A‐200) was used for the amendment of the water‐holding capacity of soil on a steep surface. Three concentrations of SAP [0.20, 0.40 and 0.60% (w w^?1)] and a control (0%) were blended with sandy soil. This study aimed to evaluate the evaporation rate, water retention capacity and saturated water content of polymer‐treated soils for determining plant survival and seed germination rate through cylinder and steep surface experiments. The results demonstrated that sandy soil treated with SAP showed significantly enhanced soil water holding compared with the controls. Furthermore, the seed germination rate was significantly higher in polymer‐treated soils than in the controls. The survival times of grass and ligneous plants were lengthened under water stress conditions. Finally, treatment with 0.40% SAP was the optimum selection for sandy soil amendment on steep surfaces.     

Pesticides in fluvial wetlands catchments under intensive agricultural activities

A survey on pesticides (73 compounds) in the Bay St. Fran?ois wetland and its catchment (part of the wetlands of Lake St. Pierre area [St. Lawrence River, Québec]) was achieved in 2006. The metabolites as well as the active ingredients of pesticides (11 compounds) were detected in the wetland and its catchment. This wetland ecosystem was active in the degradation of agricultural pesticides (e.g., atrazine). The measured pesticides were individually below the criteria for aquatic species in natural water, except chlorpyrifos. Overall, the pesticides lost from agricultural field towards the streams were <1% of the quantity applied. The environmental fates of the pesticides were found to vary according to the size of the watershed. Over large catchments, half-life times were important in terms of global loss from the agricultural lands to wetlands whereas over small catchments, soil organic carbon/water distribution coefficient (Koc) was an important term for pesticides losses to water system since half-life times were not limiting factors.     

Fate of the antiretroviral drug tenofovir in agricultural soil

Tenofovir (9-(R)-(2-phosphonylmethoxypropyl)-adenine) is an antiretroviral drug widely used for the treatment of human immunodeficiency virus (HIV-1) and Hepatitis B virus (HBV) infections. Tenofovir is extensively and rapidly excreted unchanged in the urine. In the expectation that tenofovir could potentially reach agricultural lands through the application of municipal biosolids or wastewater, and in the absence of any environmental fate data, we evaluated its persistence in selected agricultural soils. Less than 10% of [adenine-8-¹⁴C]-tenofovir added to soils varying widely in texture (sand, loam, clay loam) was mineralized in a 2-month incubation under laboratory conditions. Tenofovir was less readily extractable from clay soils than from a loam or a sandy loam soil. Radioactive residues of tenofovir were removed from the soil extractable fraction with DT₅₀s ranging from 24 ± 2 to 67 + 22 days (first order kinetic model) or 44 + 9 to 127 + 55 days (zero order model). No extractable transformation products were detectable by HPLC. Tenofovir mineralization in the loam soil increased with temperature (range 4 °C to 30 °C), and did not occur in autoclaved soil, suggesting a microbial basis. Mineralization rates increased with soil moisture content, ranging from air-dried to saturated. In summary, tenofovir was relatively persistent in soils, there were no extractable transformation products detected, and the response of [adenine-8-¹⁴C]-tenofovir mineralization to soil temperature and heat sterilization indicated that the molecule was biodegraded by aerobic microorganisms. Sorption isotherms with dewatered biosolids suggested that tenofovir residues could potentially partition into the particulate fraction during sewage treatment.     

Comparison of pulsed and continuous addition of H2 gas via membranes for stimulating PCE biodegradation in soil columns

Column experiments were performed to investigate a technology for remediating aquifers contaminated with chlorinated solvents. The technology involves installation of hollow-fiber membranes in the subsurface to supply hydrogen gas (H2) to groundwater to support biological reductive dechlorination in situ. Three laboratory-scale columns [control (N2 only), continuous H2, and pulsed H2] were packed with aquifer material from a trichloroethene (TCE)-contaminated wetland in Minnesota and supplied with perchloroethene (PCE)-contaminated synthetic groundwater. The main goals of the research were: (1) evaluate the long-term performance of the H2 supply system and (2) compare the effects of pulsed (4 h on, 20 h off) versus continuous H2 supply (lumen partial pressure approximately 1.2 atm) on PCE dechlorination and production of by-products (i.e. methane and acetate). The silicone-coated fiberglass membranes employed in these experiments were robust, delivering H2 steadily over the entire 349-day experiment. Methane production decreased when H2 was added in a pulsed manner. Nevertheless, the percentage of added H2 used to support methanogenesis was similar in both H2-fed columns (92-93%). For much of the experiment, PCE dechlorination (observed end product = dichloroethene) in the continuous and pulsed H2 columns was comparable, and enhanced in comparison to the natural attenuation observed in the control column. Dechlorination began to decline in the pulsed H2 column after 210 days, however, while dechlorination in the continuous H2 column was sustained. Acetate was detected only in the continuous H2 column, at concentrations of up to 36 microM. The results of this research suggest that in situ stimulation of PCE dechlorination by direct H2 addition requires the continuous application of H2 at high partial pressures, favoring the production of bioavailable organic matter such as acetate to provide a carbon source, electron donor, or both for dechlorinators. Unfortunately, this strategy has proven to be inefficient, with the bulk of the added H2 used to support methanogenesis.     

Bench-scale and field-scale evaluation of catechol 2,3-dioxygenase specific primers for monitoring BTX bioremediation

The objective of this work was to test a molecular genetic method for in situ monitoring of aerobic benzene, toluene, and xylene (BTX) biodegrading microorganisms. Catechol 2,3-dioxygenase (C23DO) genes occur in bacteria that biodegrade benzene, toluene, xylenes, phenol, biphenyl, and naphthalene. A competitive quantitative polymerase chain reaction (QC-PCR) technique using a single set of primers specific for an entire subfamily of C23DO genes was recently developed. To determine whether bacteria containing these C23DO genes actually exist in environments contaminated by BTX, aerobic microcosms containing previously uncontaminated soil were amended with different aromatic hydrocarbons and DNA extracts were analyzed by QC-PCR for C23DO genes. Anaerobic microcosms were established to confirm that oxygen was also necessary for the enrichment of C23DO genes. Field testing was done at two sites undergoing monitored natural attenuation. In microcosm experiments naphthalene, m-xylene, and p-xylene strongly enriched for C23DO genes while benzene, toluene, and o-xylene produced only transient, weakly detectable genes. In the field study, C23DO genes were detected in groundwater samples contaminated with either xylenes or naphthalene. The results of this study demonstrated that molecular genetic techniques can provide an accurate and rapid method to detect microorganisms capable of aromatic hydrocarbon biodegradation. Such a technique would be useful for monitoring the effectiveness of aeration technologies and for documenting microbial processes for monitored natural attenuation.     

Identifizierung und Quantifizierung natürlicher Abbauprozesse in einem mit Chlorethenen kontaminierten Grundwasserleiter

This article discusses the results of an investigation into natural attenuation processes at a former landfill which is leaching aliphatic hydrocarbons and chlorinated ethenes. The high degree of metabolisation of the chlorinated ethenes downstream of the landfill indicates the occurrence of reductive dechlorination, which was quantified by geochemical investigations and reactive transport modelling. In the vicinity of the deposit, the contaminated Buntsandsteinaquifer is divided into at least two subaquifers, the upper one of which is the most highly contaminated. Directly downstream of the landfill, the redox-environment is highly reduced, allowing reductive degradation processes to continue. The high transformation rates in this area lead to a conversion of more than 90% of the Perchloroethene (PCE) and Trichloroethene (TCE) leached from the landfill and leaves Cis-Dichloroethene (Cis-DCE) as the main contaminant found in the subsurface. Further downstream, the redox-environment becomes increasingly oxidised where (cometabolic) aerobic degradation processes will probably dominate, which will especially degrade the less chlorinated ethenes. Over the short term, however, the continuous delivery of PCE and TCE from the landfill will prevent the retreat of the contamination in the subsurface by natural attenuation alone. Nevertheless, in combination with source control measures, natural attenuation could be an alternative strategy for plume management.