Degradation of trichloroethylene by a growth-arrestedPseudomonas putida

A toluene-oxidizing strain ofPseudomonas mendocina KR1 containing toluene-4-mono-oxygenase (TMO) completely degrades TCE with the addition of toluene as a co-substrate in aerobic condition. In order to constructin situ bioremediation system for TCE degradation without any growth-stimulating nutrients or toxic inducers such as toluene, we used the carbon-starvation promoter ofPseudomonas putida MK1 (Kim, Y.et al., J. bacteriol., 1995). Upon entry into the stationary phase due to the deprivation of nutrients, this promoter is strongly induced without further cell growth. The TMO gene cluster (4.5 kb) was spliced downstream of the carbon starvation promoter ofPseudomona putida MK1, already cloned in pUC19. TMO under the carbon starvation promoter was not expressed inE. coli cells either in stationary phase or exponential phase. For TMO expression inPseudomonas strains,tmo and carbon starvation promoter region were recloned into a modified broad-host range vector pMMB67HES which was made from pMMB67HE (8.9 kb) by deletion oftac promoter andlacI ^q (about 1.5 kb). Indigo was produced by TMO under the carbon starvation promoter in aPseudomonas strain of post-exponential phase on M9 (0.2% glucose and 1mM indole) or LB. 18% of TCE was degraded in 14 hours after entering the stationary phase at the initial concentration of 6.6μ M in liquid phase.     

The effect of salinity on trichloroethylene co-metabolism by mixed cultures enriched on phenol

Summary This work examines the effects of salinity on the biodegradation of trichloroethylene (TCE) by four chemostat-cultivated cultures: LHPO-3, LHPO-6, HHPO-3 and HHPO-6, all of which had been enriched on phenol but grown under different conditions. Cultures LHPO-3 (with hydraulic retention time [HRT] of 3.1 days) and LHPO-6 (6.5-day HRT) were cultivated with fresh water, whereas cultures HHPO-3 (3.3-day HRT) and HHPO-6 (6.1-day HRT) were cultivated with seawater. Batch tests of TCE degradation by the four bacterial consortia in the absence of phenol were undertaken in solutions with salinities in the range 0–3.28% (w/v). Moreover, the effect of adding phenol on TCE degradation by LHPO-3 in 1.64% salinity solution was investigated. The results showed that the observed bacterial yields for the cultures LHPO-3, LHPO-6, HHPO-3 and HHPO-6 were 0.66, 0.47, 0.58 and 0.33 mg volatile suspended solids/mg phenol, respectively. In the absence of phenol, the extents of TCE degradation by cultures LHPO-3 and LHPO-6 increased with salinity stress, reaching 0.052 mg TCE/mg VSS for LHPO-3 and 0.033 mg TCE/mg VSS for LHPO-6, and then declined as salinity increased further. The tolerance of TCE degradation to salinity for culture LHPO-3 was around 3.28% and that for LHPO-6 was 1.64–2.33%. In the presence of phenol, the rate and extent of TCE degradation by LHPO-3 were enhanced when an optimal dosage of phenol of 10 mg phenol/mg TCE was applied. Degradation of TCE by cultures HHPO-3 and HHPO-6 was not observed.     

Fate and Transport of Trichloroethylene in a Chamber with Alfalfa Plants

Experiments in a laboratory chamber were used to investigate the influence of alfalfa plants on the fate and transport of trichloroethylene (TCE) fed at a concentration of 200 μl/L (~290 mg/L) in the entering groundwater. The dimensions of the chamber were 180 cm in axial length, 35 cm in depth and 10 cm in width. Concentrations of TCE were monitored in the aqueous and gas phases. Evapotranspirational fluxes of TCE from the soil to the headspace of the chamber were also measured. TCE concentration in the solid phase was measured as a function of depth. Mathematical modeling of the fate of TCE was developed assuming rate-independent physical equilibrium partitioning between solid, aqueous, and gas phases. The model included volatilization across a thin atmospheric boundary layer near soil surface. Numerical results were first validated with analytical results for simple cases and then compared with experimental data in the chamber. Results indicated that the water content and air content distributions significantly impact the transport and concentration of TCE in soils.     

A Study of Vadose Zone Transport Model VLEACH

Application of vadose zone transport models has been hampered by lack of model validation. Difficulties to validate vadose zone models using field data not only come from model assumptions that are uncertain to the subsurface transport processes but also from the uncertainties associated with soil contaminants’ release time and quantity, soil sampling, sample transport, and analytical procedures. This article first conducts a test of a popularly used vadose zone transport VLEACH by comparing model results with a set of laboratory soil column infiltration and volatilization study data. The comparison shows a close agreement between the VLEACH model results and the laboratory data. Second, the sorption coefficient K_d calculated in VLEACH is compared with field data. The comparison indicates that VLEACH may overestimate the mass leached from soil to groundwater. The article also discusses the selection of the model simulation timestep, the vertical dimension increment, the Courant criterion, and the lower boundary condition using the sensitivity analysis method based on a case study of soil remediation for trichloroethylene. The procedures presented in this paper are important to practical model application and modification. This level of work should be routinely conducted for any new or modified version of vadose zone models.     

Biotransformation of Trichloroethylene Using Butane-Oxidizing Bacteria

Mixed butane-utilizing cultures were obtained through sequential batch enrichment under 6% (vol/vol) butane in air using one sediment and four different soil samples with varying histories of contamination as inocula. Subsamples of each environmental sample were subjected to one of three pretreatments prior to inoculation: saturation with 30% ethanol, a 15-min exposure to 60°C, or no treatment. Thirteen of the 14 mixed cultures that were obtained appeared to cometabolize trichloroethylene (TCE) while growing at the expense of butane. All 13 caused a loss of at least one-third of TCE from initial aqueous levels between 4 and 25?µg/ml during 6 days of growth on butane provided at initial aqueous concentrations between 90 and 160?µg/ml. Two cultures cometabolized essentially all the available TCE during this test. One culture, which was obtained from an ethanol-pretreated inoculum, vigorously consumed butane while leaving TCE levels essentially unchanged. However, two other mixed cultures originally derived from the same environmental sample as the ineffective culture were moderately active in TCE cometabolism. Thus, TCE-cometabolizing butane oxidizers appeared to be present in all five of the environmental samples used in these studies.     

Trichloroethylene Carcinogenic Potency

Mention of tradename, specific equipment, or proprietary product does not constitute a guarantee or warranty by the State of California or imply approval to the exclusion of other products. The conclusions reached herein represent those of the author and do not necessarily represent those of the State of California. Current U.S. regulatory policy regarding the carcinogenic potential of trichloroethylene (TCE) in humans is conflicting. Weight-of-evidence considerations show either no or inconsistent associations between chronic TCE exposure and excess human cancer risk. Occupational exposure limits are so great (538,000 µg/m³) that daily absorbed doses are greater than the rodent no observed adverse effect level (NOAEL). Using the regulatory strength-of-evidence approach, recommended ambient air concentration limits (1.1 µg/m³) are derived using the default linearized multistage model. The latter assumes a radiomimetic mode of action, a highly questionable assumption in light of published TCE mechanism of action data. Given the current state of U.S. regulatory policy on this material, credible analyses of the data are needed from neutral nongovernmental organizations.     

USE OF NATIVE PLANTS FOR REMEDIATION OF TRICHLOROETHYLENE: I. DECIDUOUS TREES

Phytoremediation of trichloroethylene (TCE) can be accomplished using fast-growing, deep-rooting trees. The most commonly used tree for phytoremediation of TCE has been the hybrid poplar. This study looks at native southeastern trees of the United States as alternatives to the use of hybrid poplar. The use of native trees for phytoremediation allows for simultaneous restoration of contaminated sites. A 2-mo, greenhouse-based study was conducted to determine if sycamore (Plantanus L.), eastern cottonwood (Populus deltoides), sweetgum (Liquidambar styraciflua L.), and willow (Salix sachalinensis) trees possess the ability to degrade TCE by assessing TCE metabolite formation in the plant tissue. In addition to the metabolic capabilities of each tree species, growth parameters were measured including change in height, water usage, total fresh weight of each tissue type, and calculated total leaf surface area. Willow trees had the greatest increase in height among all trees tested; however, at higher concentrations TCE inhibits growth. Sycamore trees had the highest overall leaf surface area and total biomass, which correlated with sycamore trees also having the highest average water usage over the course of the experiment. Carbon tubes used to sample transpiration gases from sycamore, sweetgum, and cottonwood trees did not contain detectable levels of TCE. Tenex sample collection tubes used to sample willow trees during TCE exposure showed average TCE concentrations of up to 0.354 ng TCE cm^?2 leaf tissue. All exposed trees contained TCE in the root, stem, and leaf tissues. The concentration of TCE remaining in tissues at the conclusion of the experiment varied, with the highest levels found in the roots and the lowest levels found in the leaves. Metabolites were also observed in different tissue types of all trees tested. The highest concentrations of trichloroacetic acid were observed in the leaves of the sycamore trees and cottonwood trees. Based on the growth parameters tested and the ability to metabolize TCE, sycamore and native cottonwood species are the best candidates for phytoremediation from this study.