TCE) And 1,1,1-trichloroethane Research Articles

Cyclodextrin-enhanced 1,4-dioxane treatment kinetics with TCE and 1,1,1-TCA using aqueous ozone

Enhanced reactivity of aqueous ozone (O3) with hydroxypropyl-β-cyclodextrin (HPβCD) and its impact on relative reactivity of O3 with contaminants were evaluated herein. Oxidation kinetics of 1,4-dioxane, trichloroethylene (TCE), and 1,1,1-trichloroethane (TCA) using O3 in single and multiple contaminant systems, with and without HPβCD, were quantified. 1,4-Dioxane decay rate constants for O3 in the presence of HPβCD increased compared to those without HPβCD. Density functional theory molecular modeling confirmed that formation of ternary complexes with HPβCD, O3, and contaminant increased reactivity by increasing reactant proximity and through additional reactivity within the HPβCD cavity. In the presence of chlorinated co-contaminants, the oxidation rate constant of 1,4-dioxane was enhanced. Use of HPβCD enabled O3 reactivity within the HPβCD cavity and enhanced 1,4-dioxane treatment rates without inhibition in the presence of TCE, TCA, and radical scavengers including NaCl and bicarbonate. Micro-environmental chemistry within HPβCD inclusion cavities mediated contaminant oxidation reactions with increased reaction specificity.

Effect of dose and exposure protocol on the toxicokinetics and first-pass elimination of trichloroethylene and 1,1,1-trichloroethane

Trichloroethylene (TCE) and 1,1,1-trichloroethane (TRI) are frequent contaminants of drinking water and of groundwater at hazardous waste sites. There is relatively little information on the target organ deposition of TRI, despite its ingestion and common occurrence in humans. An important aim of the study was to delineate and contrast the toxicokinetics (TK) and bioavailability (F) of TRI and its well metabolized congener, TCE. Blood profiles were obtained from male Sprague-Dawley rats given aqueous emulsions of 6 or 48 mg TRI/kg and 10 or 50 mg TCE/kg as an oral bolus (po) or by gastric infusion (gi) over 2 h. TCE exhibited nonlinear TK, with a disproportionate increase in AUC and decrease in clearance and F with increase in dose. TRI exhibited linear TK. F did not vary significantly with TRI dose or dosage regimen. F values were substantially higher for TRI than for the respective TCE groups. TRI was distributed widely to tissues of rats gavaged with 6 mg TRI/kg, with accumulation in fat. This experiment yielded tissue uptake and elimination profiles and in vivo tissue:blood partition coefficients (PCs). Finally, additional rats were given 10 mg/kg of TCE and TRI po, ia and iv, so that first-pass hepatic (FPh) and pulmonary (FPp) elimination could be measured directly. Total and FPh elimination of TCE exceeded that of TRI. TRI, with its higher air:blood PC, exhibited the higher FPp. TCE and TRI, despite several common physical and chemical properties resulting in similar absorption and systemic distribution, displayed dissimilar dosage and dose rate effects on their TK.

Thermally Activated Persulfate Oxidation of Trichloroethylene (TCE) and 1,1,1-Trichloroethane (TCA) in Aqueous Systems and Soil Slurries

Under thermally activated conditions (i.e., temperature of 40∼99°C), there is considerable evidence that the persulfate anion () can be converted to a powerful oxidant known as the sulfate free radical (), which could be used in situ to destroy groundwater contaminants. In this laboratory study only limited trichloroethylene (TCE) degradation and no 1,1,1-trichloroethane (TCA) degradation was observed at 20°C. However, TCE and TCA were readily oxidized at 40°, 50°, and 60°C as a result of thermally activated persulfate oxidation. Experiments revealed that the pseudo-first-order reaction rate constants describing contaminant degradation increased with temperature. In aqueous systems activation energies for the TCE and TCA oxidation at an oxidant/contaminant molar ratio of 10/1 were determined to be 97.74±3.04 KJ/mole and 163.86±1.38 KJ/mole at pH 6 and an ionic strength of 0.1, respectively. A significant degradation of TCE and TCA occurs at 40° and 50°C, respectively, within less than 6 h. Aqueous system experiments revealed that oxidation reactions proceed more rapidly at increased persulfate/contaminant molar ratios. Soil slurry tests were conducted using medium to fine sands containing a range of fraction of organic carbon (foc) levels. Soil slurries were prepared at a 1/5 soil/water (mass ratio). In soil slurries the foc exhibited significant competition for sulfate free radicals produced. Based on these results, it was anticipated that higher temperatures, longer treatment times, and higher dosages of persulfate are required for the effective treatment of target contaminants in soil systems vs. aqueous systems.

Stable hydrogen, carbon and chlorine isotope measurements of selected chlorinated organic solvents

Stable hydrogen isotopes of two chlorinated solvents, trichloroethylene (TCE) and 1,1,1-trichloroethane (TCA), provided by five different manufacturers, were determined and compared to their carbon and chlorine isotopic signatures. The isotope ratio for δ 2H of different TCEs ranged between +466.9‰ and +681.9‰, for δ 13C between −31.57‰ and −27.37‰, and for δ 37Cl between −3.19‰ and +3.90‰. In the case of the TCAs, the isotope ratio for δ 2H ranged between −23.1‰ and +15.1‰, for δ 13C between −27.39‰ and −25.84‰, and for δ 37Cl between −3.54‰ and +1.39‰. As well, a column experiment was carried out to dechlorinate tetrachloroethylene (PCE) to TCE using iron. The dechlorination products have completely different hydrogen isotope ratios than the manufactured TCEs. Compared to the positive values of δ 2H in manufactured TCEs (between +466.9‰ and +681.9‰), the dechlorinated products had a very depleted δ 2H (less than −300‰). This finding has strong implications for distinguishing dechlorination products (PCE to TCE) from manufactured TCE. In addition, the results of this study show the potential of combining 2H/ 1H analyses with 13C/ 12C and 37Cl/ 35Cl for isotopic fingerprinting applications in organic contaminant hydrogeology.

A History of the Production and Use of Carbon Tetrachloride, Tetrachloroethylene, Trichloroethylene and 1,1,1-Trichloroethane in the United States: Part 2—Trichloroethylene and 1,1,1-Trichloroethane

Carbon tetrachloride (CTC), tetrachloroethylene (PCE), trichloroethylene (TCE) and 1,1,1-trichloroethane (TCA) were four of the most widely used cleaning and degreasing solvents in the United States. Part 2 of this article describes the history of TCE and TCA. TCE production in the United States began in the early 1920s. TCE was used as a replacement for petroleum distillates in the dry-cleaning industry, and became the solvent of choice for vapor degreasing in the 1930s. TCE’s use as a degreaser decreased in the 1960s due to toxicity concerns and the increasing popularity of TCA. Significant TCA use began in the 1950s with the development of suitable stabilizer formulations. In the 1990s, TCA was phased out under the Montreal Protocol due to its role in stratospheric ozone depletion.

A History of the Production and Use of Carbon Tetrachloride, Tetrachloroethylene, Trichloroethylene and 1,1,1-Trichloroethane in the United States: Part 1—Historical Background; Carbon Tetrachloride and Tetrachloroethylene

Carbon tetrachloride (CTC), tetrachloroethylene (PCE), trichloroethylene (TCE) and 1,1,1-trichloroethane (TCA) were four of the most widely used cleaning and degreasing solvents in the United States. These compounds were also used in a wide variety of other applications. The history of the production and use of these four compounds is linked to the development and growth of the United States' synthetic organic chemical industry, and historical events that affected the development and use of chlorinated solvents in general. Part 1 of this article includes a discussion of the historical background common to each of the four solvents, followed by discussion on the history of CTC and PCE. In the early years of the 20th century, CTC became the first of the four solvents to come into widespread use. CTC was used as a replacement for petroleum distillates in the dry-cleaning industry, but was later replaced by PCE. In the 1990s, CTC was phased out under the Montreal Protocol due to its role in stratospheric ozone depletion.

Isotopic characterization of chlorinated solvents—laboratory and field results

Pure-phase chlorinated solvent δ 13C and δ 37Cl values of tetrachloroethylene (PCE), trichloroethylene (TCE), and 1,1,1-trichloroethane (TCA) from a new solvent batch from Dow and PPG were analyzed and compared to values obtained from a previous chlorinated solvent batch. These analyses were performed to determine if each chlorinated solvent had a distinct δ 13C and/or δ 37Cl value associated with each manufacturer. Results indicate that the δ 13C and the δ 37Cl values of TCA do not remain consistent from batch to batch. However, the δ 37Cl values for PCE and TCE did remain consistent from batch to batch. Furthermore, these tests show a consistent and significant δ 13C difference between PPG and DOW PCE that could allow the use of 13C/ 12C in conjunction with 37Cl/ 36Cl ratios for fingerprinting applications. Chlorinated solvent/water solutions having known δ 13C and δ 37Cl values were used to test a purge-and-trap unit to extract chlorinated solvents for isotope analyses. These results show that the purge-and-trap unit produces both accurate and reproducible results for dissolved chlorinated solvent δ 13C and δ 37Cl analyses. The δ 13C and δ 37Cl reproducibility of the purge-and-trap unit was better than 0.9‰ and 0.4‰, respectively. The purge-and-trap unit was tested at a field site that has a well-defined plume of dissolved PCE emanating from a dry cleaner located in Angus, Ontario. The δ 13C and δ 37Cl data suggest that the PCE forming the core of the groundwater plume is related to one manufacturer. The results of this study along with results from a chlorinated solvent contaminated site affected by biodegradation show the potential of 13C/ 12C and 37Cl/ 36Cl ratios for isotopic fingerprinting applications on the field of organic contaminant hydrogeology.

Molecular Structure-Based Prediction of the Toxicokinetics of Inhaled Vapors in Humans

The objectives of the present study were: (1) to evaluate the adequacy of setting hepatic extraction ratio (E) equal to 0 or 1 in physiologically based toxicokinetic (PBTK) models to generate the theoretically plausible envelope of venous blood concentration (Cv) profiles, and (2) to couple this approach with molecular structure-based estimation of blood:air and tissue: blood partition coefficients (PCs) to predictthe Cv profiles of volatile organic chemicals (VOCs) in humans. Setting E= 0 or 1 in PBTK models provided simulations of Cv envelopes that contained the Cv values determined in humans exposed to low concentrations of dichloromethane(DCM), ethylbenzene (EBZ), toluene (TOL), m-xylene(XYL), trichloroethy-lene (TCE), and 1,1,1-trichloroethane(TRI). Following the validation of using E= 0 or 1 in conventional PBTK models to predict the theoretically plausible envelope of Cv, a quantitative structure-toxicokinetic relationship (QSTkR) model was constructed. The QSTkR model used molecular structure information as the sole input to predict the PCs and considered E= 0 or 1 to generate simulations of the envelope of Cv. The experimental data on Cv were in most cases within the envelopes simulated using QSTkR models for DCM, EBZ, TOL, and XYL, but were outside the envelopes for TCE and TRI. The discrepancy observed between the Cv envelopes obtained using PBTK and QSTkR models can be explained by the fact that blood:air PCs of some VOCs were under-predicted while using molecular structure information. The modeling framework presented in this article represents the first animal-replacement tool that can provide a priori predictions of the toxicokinetic profiles of VOCs prior to laboratory experiments.

Attenuation of Methane and Nonmethane Organic Compounds in Landfill Gas Affected Soils

Landfill gas (LFG) contains high concentrations of methane, which contributes to the greenhouse effect. LFG also contains aromatic hydrocarbons and chlorinated aliphatics, which, by emission to ambient air, can be a local health threat. In addition, chlorinated aliphatics may also influence the earth’s ozone layer. The objectives of the study were to investigate the degradation of LFG constituents in LFG-affected soils, and to evaluate the importance of the degradation processes to the emission. High methane oxidation potentials were found in laboratory experiments at 25 °C. The degradation seemed to follow zero order reaction kinetics, and was 3-4 times slower at 10 °C than at 25 °C. High degradation rates for benzene and toluene were also observed. In soils sampled away from the landfill, where almost no LFG contamination had been observed, longer lag phases and lower degradation rates of the two aromatic hydrocarbons were observed. Slow cometabolic degradation of trichloroethylene (TCE) and 1,1,1-trichloroethane (TCA) was observed when methane was present in the batch experiments. The rates were much lower than the rates for the aromatic hydrocarbons. In the field at Skellingsted Landfill, Denmark, high methane emissions were observed in an area just outside the landfill area, probably as a result of the clay landfill covering, which has led to significant lateral migration of LFG. Indications of active methane oxidation in the field were observed by measuring soil gas profiles. By comparison of the results obtained in the laboratory with the field results, it is shown that degradation processes may have a significant effect on the emission of all the compounds studied. However, the subject needs much more attention.

Stable chlorine and carbon isotope measurements of selected chlorinated organic solvents

Stable Cl and C isotope ratio results for 3 selected chlorinated solvents, perchloroethylene (PCE), trichloroethylene (TCE) and 1,1,1-trichloroethane (TCA) provided by 4 different manufacturers are presented. The isotope ratio for all compounds range between −3.5 and +6.0‰ for δ 37Cl and from −37.2 to −23.3%. for δ 13C . The greatest 37Cl difference between manufacturers is observed in the TCE samples which show δ 37CI values of −2.5%o for PPG, +2.43‰ for ICI and +4.4‰ for DOW. TCAs show a smaller range (−2.4 to +2.0‰), while the TCEs have slightly different 37Cl contents. The 13C data show the most distinct δ 13C values for PCEs (−23.3 for DOW, −24.1 for Vulcan, −33.8 for PPG and −37.2‰ for ICI) while both TCEs and TCAs show a smaller δ 13C range, but still distinct differences. These preliminary data suggest that each manufacturer and solvent type may have distinctive δ 637Cl and δ 13C values. These results show that by using a combination of 37Cl and 13C, there is a potential to indicate a specific source of chlorinated solvents, as well as an ability to delineate contamination episodes caused by these compounds in groundwaters.