Multiyear Temporal Changes in Chlorinated Solvent Concentrations at 23 Monitored Natural Attenuation Sites

Long-term (e.g., 5–15 years) groundwater concentration versus time records were compiled from 47 near-source zone monitoring wells at 23 chlorinated solvent sites (52 total records). Chlorinated volatile organic compound (CVOC) concentrations decreased significantly in most of the 52 temporal records, with a median reduction in concentration of 74%. A statistical method based on a Mann–Kendall analysis also showed that most sites had statistically significant decreasing concentration trends over time. Median point decay rate constants (kpoint) values were calculated for nine sites containing tetrachloroethene (PCE); 13 sites containing trichloroethene (TCE); two sites containing cis-1,2-dichloroethene (DCE); and six sites containing 1,1,1-trichloroethane (TCA). The TCA sites had the highest kpoint values (0.34/year) followed by PCE, DCE, and TCE (0.23/year, 0.16/year, and 0.11/year, respectively) (equal to decay half-lives of 2.0, 3.0, 4.3, and 6.1 years, respectively). If the median point decay rates from these sites are maintained over a 20 year period, the resulting reduction in concentration will be similar to the reported reduction in source zone concentrations achieved by active in situ source remediation technologies (typical project length: 1–2 years).     

Biodegradation of 1,4-Dioxane Using Trickling Filter

The ability of a laboratory-scale trickling filter to biodegrade cyclic ethers was investigated and a simple kinetic model was developed to predict ether biodegradation. The trickling filter received a feed solution designed to mimic ether concentrations typically encountered in contaminated groundwater. The reactor was operated for approximately 1 year and was capable of biodegrading 93–97% of 1,4-dioxane at various loading rates in the obligate presence of tetrahydrofuran (THF) as the growth substrate. A simple tanks-in-series hydraulic model combined with a kinetic model that incorporated cometabolism was utilized to simulate removal of THF and 1,4-dioxane. Model simulations of THF removal were satisfactory for all loading rates analyzed. However, the model somewhat over predicted 1,4-dioxane removal. This research demonstrates the ability to treat groundwater contaminated with low concentrations of ethers in attached growth reactors.     

2,4,6-Trinitrotoluene Transformation Using Spinacia Oleracea: Saturation Kinetics of the Nitrate Reductase Enzyme

A series of aqueous phase and soil-slurry phase microcosm studies were conducted on 2,4,6-trinitrotoluene (TNT) to obtain kinetic data for optimizing a treatment protocol using an enzyme extract from spinach (Spinacia oleracea). Crude extract was obtained by homogenization of fresh leaves with a buffered protease inhibitor, and employed as phytoremediation agent. Aqueous phase microcosms containing 20?mg/L TNT and soil–slurry microcosms containing 1 g of a characterized sandy loam soil contaminated with 2,500?mg/kg TNT and 1,000?mg/kg hexahydro-1,3,5-trinitro-1,3,5-triazine were dosed with fixed aliquots of extract and analyzed for TNT transformation over time. The TNT concentration was monitored using a colorimetric method for nitroaromatic compounds based on EPA Method 8515. Nitrate reductase activity of the applied crude extract was simultaneously quantified. The transformation of TNT was described by a pseudofirst-order reaction. Coupling kinetic rate information with enzyme activity allowed for estimation of a second-order rate constant with respect to activity. A rectangular hyperbola function normalized for enzyme activity described observed kinetic data based on enzyme saturation, similar to a Michaelis–Menten relationship. Pseudofirst-order rate constants for the aqueous phase and soil–slurry phase experiments were fit to this function. The maximum rate of reaction (kmax) for TNT transformation was 0.50 and 0.04?h?1 for aqueous phase and soil–slurry phase experiments, respectively, while respective half-saturation constants (Ksat*) were comparable in value at 0.63 and 0.28?U/μmol–NO2, respectively. A Hanes–Woolf plot of reaction velocity versus TNT concentration with and without soil suggests an uncompetitive inhibition mechanism may be affecting overall nitrate reductase efficacy. Temperature effects for both aqueous phase and soil–slurry phase microcosms followed the Arrhenius relationship with estimated activation energies of 54.7 and 26.1?kJ/mol, respectively.     

Microbial Reductive Dechlorination in Large-Scale Sandbox Model

Microbial reductive dechlorination is a naturally occurring transformation process tetrachloroethene (PCE) undergoes in aquifers. It contributes significantly to natural attenuation of chlorinated solvents. Stimulation of this process has been considered as a method of enhanced bioremediation. Experiments on the stimulation of reductive dechlorination were carried out in a large-scale quasi-2D sandbox model. The transformation of PCE to cis-1,2-dichloroethene (DCE) was attempted by inoculation with Dehalospirillum multivorans and that of DCE to ethene with a mixed culture. Ethanol used as the electron donor was introduced into the inlet of the domain, whereas water loaded with PCE was injected into a well. Limitations due to insufficient mixing could not be observed as high-permeability lenses enhanced the transverse exchange of the compounds. Both reductive dechlorination and competitive microbial reactions led to the acidification of the domain. The artificial aquifer was buffered by the concurrent injection of sodium sulfide with the electron donor. Under these conditions bioaugmentation of Dehalospirillum multivorans was successful, whereas stable dechlorination of DCE could not be achieved.     

Electrospray analysis of biological samples for trace amounts of trichloroacetic acid, dichloroacetic acid, and monochloroacetic acid

Trichloroethylene (TCE) has been identified as a widespread groundwater contaminant. Trichloroacetic acid (TCA) and dichloroacetic acid (DCA) are toxicologically relevant metabolites of TCE that produce tumors in B6C3F1 mice. A sensitive method for measuring these metabolites in plasma has been developed to obtain pharmacokinetic data from TCE exposure. This is particularly important because DCA is more potent at producing hepatoproliferative lesions than TCA. At present, it is unclear whether DCA is produced by humans. Existing gas chromatographic methods cannot detect DCA at low nanogram-per-milliliter levels. A Finnigan TSQ 700 mass spectrometer (MS) with electrospray ionization was used to measure TCA, DCA, and monochloroacetic acid (MCA) in plasma. The MS was operated in negative ion tandem MS mode. The limit of detection for TCA and DCA was 4 ng/ml, and the limit of detection for MCA was 25 ng/mL. Plasma samples from human subjects exposed to 100 ppm TCE for 4 h contained TCA at concentrations as high as 10 micrograms/mL. DCA concentrations were less than 5 ng/mL, and MCA was not detected (less than 25 ng/mL).     

Applying a One-Dimensional Mass Transport Model Using Groundwater Concentration Data

One-dimensional analytical mass transport models are familiar to environmental professionals because they are typically used as learning devices in undergraduate groundwater courses. The application of the models requires relatively certain knowledge of contaminant release to the saturated zone. However, release data are typically not reliably known at sites with uncontrolled contaminant releases. A mass balance approach has been developed to calculate contaminant release parameters based on site-specific groundwater concentration data. Standard numerical calibration and sensitivity analysis techniques were modified for use with the one-dimensional spreadsheet model. A groundwater concentration dataset from a Superfund site was used to evaluate three schemes for calculating the model initial concentration. The site application demonstrates how the spreadsheet model could be used for preliminary remediation system comparisons including restoration time estimating. The use of the spreadsheet model may reduce the effort associated with subsequent numerical modeling typically required for remedial design. The spreadsheet application highlights the importance of collecting physical data with groundwater concentration data.     

Use of Recombinant Bioluminescent Bacteria for On-Site Monitoring of Toluene Analogs at Petroleum Contaminated Sites

This paper describes the application of a genetically engineered microorganism, Pseudomonas putida mt-2 KG1206, to monitor toluene analogs in groundwater collected from petroleum hydrocarbon contaminated sites. KG1206 contains the intact TOL plasmid and a second plasmid with the Pm-lux gene allowing it to produce bioluminescence in the presence of toluene analogs and their derivatives such as toluene, xylenes, and m-toluate. The simple bioluminescence assay consisted of mixing one volume of groundwater sample with four volumes of broth culture followed by bioluminescence measurement after 30?min. The maximum bioluminescent response with pure chemicals followed the order: m-methyl benzyl alchohol>m-toluate>toluene>m-xylene>benzoate>p-xylene>o-xylene. The bioluminescence production was well correlated to the m-toluate concentrations (R2>0.97) in field samples, with concentrations predicted from the bioassay falling within 75–158% of true concentration. However, no strong correlation was observed between the bioluminescence intensity and the total inducer concentration in the groundwater. Results from this study demonstrate the potential of using recombinant bioluminescent bacteria as a rapid and simple tool for monitoring specific pollutants at contaminated sites.     

Bioremediation of Mixed Wastes (BTEX, TPH, TCE, and cis-DCE) Contaminated Water

Together with industrialization, more sites have become contaminated with mixed wastes of organics. Contamination of groundwater with benzene, toluene, ethylbenzene, and three isomers of xylene (BTEX) and chlorinated aliphatic hydrocarbons (CAHs) allows for the application of aerobic bioremediation to achieve mineralization of both types of compounds. In this study, the aerobic bioremoval of mixtures of these compounds [BTEX, BTEX/trichloroethylene (TCE), BTEX/cis-1,1-dichloroethylene (cis-DCE), BTEX/total petroleum hydrocarbons (TPH)/TCE, and toluene and ortho-xylene (ToX/TCE] was assessed under different environmental conditions (pH and temperature) by using indigenous microorganisms isolated from potentially contaminated regional sites. The highest TPH bioremoval efficiencies (<50%) occurred at 25°C and under neutral or alkaline conditions. TCE was cometabolized with toluene and o-xylene provided as growth substrates, and the highest bioremoval efficiency occurred at ToX/TCE, and pH and temperature impacted the mineralization of compounds. This study would help enhance the applicability of bioremediation technology to the mixed-wastes contaminated sites.     

Modeling Pd-Catalyzed Destruction of Chlorinated Ethenes in Groundwater

Groundwater contamination by chlorinated ethenes is a widespread environmental problem. Shortcomings in conventional remediation methods have motivated research into novel treatment technologies. A palladium/alumina catalyst in the presence of molecular hydrogen gas (referred to hereafter as the Pd/H2 system) has been demonstrated to destroy chlorinated ethenes in contaminated groundwater. This study presents a model for aqueous-phase destruction of chlorinated ethenes in contaminated groundwater using the Pd/H2 system that includes catalyst deactivation and regeneration. The model is validated using published data from laboratory column experiments from Stanford University. The model is then coupled with an analytical groundwater flow model to simulate application of in-well Pd/H2 reactors for in situ treatment of chlorinated ethene contaminated groundwater in a recirculating horizontal flow treatment Well (HFTW) system. Applying the model under realistic conditions results in approximately 130 days of HFTW system operation without significant catalyst deactivation. This suggests catalyst deactivation will not significantly affect system performance in a real remediation scenario. The model presented in this study, which simulates deactivation kinetics and regeneration of an in-well catalyst that is a component of a recirculating well system designed for in situ treatment of contaminated groundwater, represents an important step in transitioning the Pd/H2 technology to the field.     

Plasminogen activators: regulators of tumor cell adherence to sites of lower urinary tract surgical trauma

Tumor cell adherence (TCA) to sites of surgical injury is a requisite step in implantation-mediated tumor recurrence. This study examined the relationship between tumor-associated plasminogen activator (PA) and the ability of tumor cells to remain adherent to surgical injury sites. High (1E8) and low (3A9) PA producing clones from the murine transitional carcinoma cell line 4909 were selected using an in vitro 125I fibrinolysis assay. Net cellular PA activity of each clone was determined from cell lysates using a chromogenic substrate assay. In vitro TCA and fibrin substrate lysis as a function of time were simultaneously measured using a tetrazolium dye assay in combination with an 125I fibrinolysis assay. In vivo TCA to in situ cautery-injured rat bladders was measured 30 minutes (n = 12 animals/cell line) and 24 hours (n = 18 animals/cell line) following tumor exposure with a radiolabeled TCA assay. In vitro and in vivo competitive binding assays evaluated the relative adherence of mixtures of the 1E8 and 3A9 clones. Cellular PA activity was 0.022, 0.014 and 0.007 units per mg. protein for the 1E8, 4909 and 3A9 cell lines. In vitro TCA to fibrin in the presence of plasminogen was significantly different for each cell line and demonstrated an inverse relationship with both plasminogen-dependent fibrin lysis and cellular PA activity (p < 0.0001). The in vivo assay showed that the percentage of 1E8 cells remaining adherent 24 hours after tumor exposure was significantly less than that of the 3A9 cells (p = 0.01). Both in vitro and in vivo competitive binding assays demonstrated preferential adherence of the 3A9 cell line. Cellular PA production appears to be a tumor-intrinsic variable that modulates TCA to surgical injury sites.     

Analytical Model of Surge Flow in Nonprismatic Permeable Channels and Its Application in Arid Regions

A surge running down a dry wadi bed as a consequence of a controlled water release from a reservoir—e.g., for artificial groundwater recharge—represents a free boundary problem. After some time, when aiming for groundwater recharge, the infiltration equals inflow and thus forms a kind of “standing” wave. The numerical solution of such phenomena generally involves considerable problems. For avoiding the numerical inconvenience resulting from the complex interacting surface/subsurface flow, we present an analytical solution of the slightly modified zero-inertia (ZI) equations. The development introduces a momentum-representative cross section for portraying the transient development of momentum and refers to a channel with constant slope, irregular geometry, and a permeable channel bed with significant infiltration. Due to the structure of the solution, any arbitrary infiltration model can be used for quantifying the infiltration losses. For both synthetic prismatic and nonprismatic test channels, the robust and easy-to-use analytical ZI model shows an excellent match with the results of a comparative numerical simulation. Finally, the ZI model is employed for simulating a surge flow downstream of the Wadi Ahin groundwater recharge dam (Oman), in order to perform a scenario for artificial groundwater recharge in a natural wadi channel reach. This realistic application illustrates the potential of the new approach by even computing an almost standing wave and shows its applicability for an accurate and robust evaluation of release strategies.     

Modelling of 2,3,7,8-tetrachlorodibenzo-p-dioxin levels in a cohort of workers with exposure to phenoxy herbicides and chlorophenols

Several cohort studies of herbicide manufacturing workers have been conducted over the last years. Most of these studies used simple proxies of exposure in the analysis such as a crude grouping in exposure categories based on job titles, presence in certain production areas over a period of time or during an accident, and duration of exposure. Current serum 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) levels available for a subset of workers can be used to back-extrapolate TCDD levels at the end of exposure using first order kinetic models, and relate TCDD levels to job history using regression models. The regression model obtained can be used to estimate TCDD levels for all cohort members. In this paper, the effect of changes in model assumptions on estimated TCDD levels is explored. TCDD levels are back-extrapolated assuming different values for TCDD half-life. A range of regression models with different sets of exposure determinants is used to relate back-extrapolated TCDD levels to determinants of exposure. These models were used to predict TCDD levels in the epidemiological analysis of data from a Dutch cohort study. The results show that the predicted serum TCDD level is strongly dependent on the assumed half-life. However, the ranking of all individuals on the exposure axis (from low to high) is not affected by changes in the half-life. Predicted serum TCDD levels seem not sensitive to changes in assumption regarding TCDD half-life. Predicted TCDD levels were positively associated with increased (cause specific) mortality.     

Effect of chlorine-containing pesticides on the hemolytic stability and acetylcholinesterase activity of erythrocytes

The hemolytic action of the chlorine-containing pesticides, trichloroacetic acid (TCA), pentachlorophenolate (PCP), chlorophos and pentachloronitrobenzene (PCNB) on red cells was studied, as were their effects on acetylcholinesterase activity and resistance of red cells to mechanical hemolysis by ultrasound. The modifying action of pesticides on red cell membranes was shown to lead to their mechanical resistance. TCA, PCP and chlorophos were found to sensitize red cells whereas PCNB to make them resistant to the mechanical action of ultrasound. The kinetic characteristics of the structural functional disorders of red cells might be used as quantitative criteria of the efficacy of the action of pesticides on the cells.     

Failure of monochloroacetic acid and trichloroacetic acid administered in the drinking water to produce liver cancer in male F344/N rats

The chlorinated acetic acids monochloroacetic acid (MCA) and trichloroacetic acid (TCA) are found as chlorine disinfection by-products in finished drinking-water supplies. TCA has been demonstrated to be a mouse liver carcinogen. A chronic study in which male Fischer 344/N rats were exposed for 104 wk to TCA and MCA in the drinking water is described. Animals, 28 d old, were exposed to 0.05, 0.5, or 2 g/L MCA, or 0.05, 0.5, or 5 g/L TCA. The 2.0 g/L MCA was lowered in stages to 1 g/L when the animals began to exhibit signs of toxicity. A time-weighted mean daily MCA concentration (MDC) of 1.1 g/L was calculated over the 104-wk exposure period. Time-weighted mean daily doses (MDD) based upon measured water consumption were 3.5, 26.1, and 59.9 mg/kg/d for 0.05, 0.5, and 1.1 g/L MCA, respectively; TCA MDD were 3.6, 32.5, and 363.8 mg/kg/d. Nonneoplastic hepatic changes were for the most part spontaneous and age related. No evidence of hepatic neoplasia was found at any of the MCA or TCA doses. The incidence of neoplastic lesions at other sites was not enhanced over that in the control group. Drinking water concentrations of > or = 0.5 g/L MCA produced a moderate to severe toxicity as reflected by a depressed water consumption and growth rate. A no-observed-effects level (NOEL) for carcinogenicity of 0.5 g/L (26.1 mg/kg/d) MCA was calculated. TCA at drinking water levels as high as 5 g/L produced only minimal toxicity and growth inhibition and provided a NOEL of 364 mg/kg/d. Our results demonstrate that under the conditions of this bioassay, MCA and TCA were not tumorigenic in the male F344/N rat.     

Application of an Intraparticle Diffusion Model to Describe the Release of Polyaromatic Hydrocarbons from Field Soils

The fate and transport of chemicals of concern released from field soils must be known to protect human and ecological receptors. A mechanistic approach to modeling chemical release from soil is advantageous to implement effective remediation strategies at an impacted site. The focus of this research was to gain an understanding of the processes causing slow release of polyaromatic hydrocarbons (PAHs) from field soils collected at sites with historical releases. A mechanistically based intraparticle diffusion model was applied to experimentally measured hydrocarbon release data and particle size distributions obtained from three field soils. For these field soils, the intraparticle diffusion model was able to describe the measured chemical release data. Fitted effective diffusion coefficients (Deff) of the intraparticle diffusion model correlated to expected results. Trends were found to exist between the Deff and both the molecular weight (MW) and the octanol–water partition coefficient (Kow) of the PAH analyzed for the field soils with low organic carbon content. For these soils, the relationships suggest that intraparticle diffusion processes may be responsible for slow desorption and it may be possible to estimate Deff values for a soil or contaminated media with similar intraparticle properties using a readily measured chemical characteristic such as MW and Kow.     

Evaluation of Contaminant Resuspension Potential during Cap Placement at Two Dissimilar Sites

Capping is a common remediation technology for the containment/stabilization of contaminated sediments. During capping activities, clean material is commonly released from a barge at the water surface and falls through the water column to the sediment surface, providing an uncontaminated surface sediment layer. Little information exists on the potential release of in situ contaminated sediments during and after capping operations. This paper focuses on the measured release of contaminants during capping events at Boston Harbor, Mass. (confined aquatic disposal cells for contaminated sediment) and Eagle Harbor, Wash. (creosote-contaminated sediment from a wood treating facility). The water column was sampled during capping events to evaluate whether cap placement resulted in the release of polycyclic aromatic hydrocarbons (PAH)- or polychlorinated biphenyls (PCB)-contaminated sediments at Boston Harbor, or PAH-contaminated sediments at Eagle Harbor. Though results at both sites indicated some contaminant resuspension during capping operations, in general contaminant resuspension was relatively low for all capping events. PCB and PAH concentrations for most samples were in the low ng/L range. The most significant releases occurred when previously uncapped sediments were initially capped, and the magnitude of contaminant resuspension decreased with successive capping layers. These results may have important implications regarding sediment cap installation techniques and their potential impacts on water quality. Resuspension during capping may be minimized by placing cap material in lifts, where the first lift provides a uniform layer of clean material using techniques that minimize sediment disturbance and subsequent lifts are placed more aggressively once contaminated sediment is covered.     

Arsenic Removal by a Colloidal Iron Oxide Coated Sand

A novel treatment process for arsenic removal from contaminated groundwater has been developed for use as a reactive barrier or a small drinking water treatment unit. In this study, modified porous media was made by the deposition of colloidal iron oxide onto sand grains at intermediate pH and ionic strength. Kd values from column experiments were 0.016–0.37?L/kg for As(III) and 0.023–0.85?L/kg for As(V), being lower than those of batch experiments (0.50 and 1.30?L/kg for As(III) and As(V), respectively) due to lower availability of surface adsorption sites in the packed column. Media-independent Kd values reflect the enhancement of arsenic adsorption with an increase of colloidal iron oxide coated sand fraction, apparently due to adsorption equilibration during arsenic transport under the same flow column conditions. The heterogeneous composition of two groundwater samples also reduced arsenic adsorption. Therefore, arsenic elution near the initial breakthrough was regulated by available adsorption surface in a porous coated sand media as well as the effects of competing oxyanions. The exhaustion of adsorption capacity near the critical contamination level is sensitive to geochemical and remedial properties of the contaminants.     

Assessment of a radioactive waste disposal site at Enewetak Atoll

The 43 nuclear tests conducted at Enewetak Atoll by the United States between 1948 and 1958 produced close-in fallout that contaminated the islands and lagoon of the atoll with radioactive fission and activation products, and unfissioned nuclear fuel. In 1972, the U.S. government announced that it would conduct a cleanup and restoration operation to return the atoll to the Enewetak people. The radiological cleanup began in 1977 and lasted to 1980 and focused on reducing the concentration of the transuranium elements (238,239,240Pu and 241Am = TRU) in soils on some of the islands that might eventually be used for residence or for subsistence agricultural. The cleanup plan called for relocating soil and some other contaminated debris to Runit Island on the eastern perimeter of the Atoll. Some of the contaminated soil was mixed with cement and the mixture placed below the water level in the Cactus Crater that was formed by a nuclear explosion in 1958. The remainder of the contaminated material was mixed with concrete and placed above ground over the crater in the shape of a dome. A concrete cap was constructed over the dome of soil. Concern has been expressed by the people of Enewetak and by others over the possible aquatic impacts from the radionuclides entombed in the crater. A National Academy of Sciences committee examined the dome and concluded that the containment structure and its contents present no credible health hazard to the people of Enewetak, either now or in the future. The committee suggested that "at least part of the radioactivity contained in the structure is available for transport to the groundwater and subsequently to the lagoon and it is important to determine whether this pathway may be a significant one." Therefore, a surveillance program was started in 1980, in conjunction with other research efforts, to study the radionuclides in samples of fish, groundwater, and lagoon seawater. Our data and conclusions support the findings suggested by the National Academy committee over a decade ago in that any assumption of rapid remobilization of all or any of the dome's transuranics or other radionuclides is an extreme one. Any fear that this structure contains amounts of activity whose release would cause damage to the environment that will result in greater effect on human health is unfounded.