顶空气相色谱法测定漓江底泥中的三氯乙烯和四氯乙烯

采用Na Cl溶液提取,顶空气相色谱法测定底泥中的三氯乙烯和四氯乙烯,方法在0.098 ng/L~1.03 ng/L范围内线性良好,三氯乙烯和四氯乙烯的方法检出限分别为0.013 ng/g和0.016 ng/g。对空白样品做3个质量比水平的加标回收试验,7次测定结果的RSD为2.0%~3.8%,平均加标回收率为94.0%~109%。将该方法用于桂林市漓江底泥样品的测定,结果三氯乙烯和四氯乙烯均为未检出,实际样品加标回收率为92.0%~107%。     

The ecological effects of trichloroacetic acid in the environment

Trichloroacetic acid (TCAA) is a member of the family of compounds known as chloroacetic acids, which includes mono-, di- and trichloroacetic acid. The significant property these compounds share is that they are all phytotoxic. TCAA once was widely used as a potent herbicide. However, long after TCAA's use as a herbicide was discontinued, its presence is still detected in the environment in various compartments. Methods for quantifying TCAA in aqueous and solid samples are summarized. Concentrations in various environmental compartments are presented, with a discussion of the possible formation of TCAA through natural processes. Concentrations of TCAA found to be toxic to aquatic and terrestrial organisms in laboratory and field studies were compiled and used to estimate risk quotients for soil and surface waters. TCAA levels in most water bodies not directly affected by point sources appear to be well below toxicity levels for the most sensitive aquatic organisms. Given the phytotoxicity of TCAA, aquatic plants and phytoplankton would be the aquatic species to monitor for potential effects. Given the concentrations of TCAA measured in various soils, there appears to be a risk to terrestrial organisms. Soil uptake of TCAA by plants has been shown to be rapid. Also, combined uptake of TCAA from soil and directly from the atmosphere has been shown. Therefore, risk quotients derived from soil exposure may underestimate the risk TCAA poses to plants. Moreover, TCE and TCA have been shown to be taken up by plants and converted to TCAA, thus leading to an additional exposure route. Mono- and di-chloroacetic acids can co-occur with TCAA in the atmosphere and soil and are more phytotoxic than TCAA. The cumulative effects of TCAA and compounds with similar toxic effects found in air and soil must be considered in subsequent terrestrial ecosystem risk assessments.     

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 delta2H of different TCEs ranged between +466.9 per thousand and +681.9 per thousand, for delta13C between -31.57 per thousand and -27.37 per thousand, and for delta37Cl between -3.19 per thousand and +3.90 per thousand. In the case of the TCAs, the isotope ratio for delta2H ranged between -23.1 per thousand and +15.1 per thousand, for delta13C between -27.39 per thousand and -25.84 per thousand, and for delta37Cl between -3.54 per thousand and +1.39 per thousand. 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 delta2H in manufactured TCEs (between +466.9 per thousand and +681.9 per thousand), the dechlorinated products had a very depleted delta2H (less than -300 per thousand). 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.     

Removal of trichloroethylene from soil using the hydration of calcium oxide

Quicklime addition to soil at a remediation site was observed to sufficiently reduce TCE levels, but the cause of the removal could not be confirmed with the field data collected. Potential mechanisms for CaO treatment of trichloroethylene (TCE) in soil include degradation and volatilization. Since earlier studies found TCE degradation to occur during the hydration of CaO under conditions where volatilization was limited, research was conducted on mechanisms of TCE removal from soil by CaO application under conditions where volatilization was allowed to occur. TCE volatilization in soil treated with 0%, 5%, 10%, and 20% CaO doses was measured in experiments where the degree of volatilization could be tracked. The total TCE removal from soil spiked with TCE at CaO doses from 5% to 20% ranged from 97% to 99% of the initial TCE mass. Volatilization accounted for 64.4-92.5% of the TCE removal, with unrecovered TCE and TCE degradation accounting for the remaining fraction. The greater heat encountered with higher CaO doses helped minimize obstacles to TCE volatilization, such as high soil organic and clay content. Treatment with a 20% CaO dose, however, led to the formation of byproducts such as dichloroacetylene. TCE degradation to dichloroacetylene at the 20% CaO dose ranged from 2.7% to 6.4% of the initial TCE. Volatilization was concluded to be the dominant process for TCE removal from soil during CaO treatment.     

三氯乙烯和四氯乙烯与羟基自由基加成反应的理论研究

用从头计算法在ＵＨＦ／６－３１Ｇ水平上研究了三氯乙烯和四氯乙烯与羟基自由基的加成反应，通过振动分析确认了过渡态，计算了内禀反应坐标（ＩＲＣ）。研究表明，该反应能生成较稳定的加成中间体，活化势垒分别为５０．８７ｋＪ·ｍｏｌ＾－１和６３．８３ｋＪ·ｍｏｌ＾－１，且二者反应在常温下均为熵减、放热、吉布斯自由能变化小于零，能自发进行的过程。     

生物降解三氯乙烯的研究及其进展

三氯乙烯（ＴＣＥ）的大规模使用，已使其成为地表水、地下水中分布最广泛的污染物之一。ＴＣＥ在环境中具有持久性，对生物的毒作用很强并具有致癌性，引起各国的普遍重视。该文综述了近年来生物降解转化ＴＣＥ的研究及其进展，由于ＴＣＥ生物降解过程中共代谢物的竞争性抑制和ＴＣＥ代谢毒性，使ＴＣＥ的降解受到很大限制，但通过创造和保持适当的环境条件，可ＴＣＥ降解取得很好的效果。     

Field study of TCE diffusion profiles below DNAPL to assess aquitard integrity

An area where a free-product accumulation of trichloroethylene (TCE) dense non-aqueous phase liquid (DNAPL) occurs at the bottom of a 10-m-thick surficial sand aquifer was studied to determine the integrity of the underlying, 20-m-thick, clayey silt aquitard formed of glaciolacustrine sediment. TCE concentration-versus-depth profiles determined from aquitard cores collected at five locations indicated penetration of detectable TCE 2.5 to 3.0 m into the aquitard. Two of the profiles show persistent DNAPL at the aquitard interface, while two others indicate that DNAPL, present initially, was completely dissolved away producing concentration declines at the aquitard interface. The fifth profile suggests shallow DNAPL penetration (<0.5 m) into the aquitard, however, this penetration, which was likely caused by cross-contamination during core collection or cone penetrometry (CPT) of the aquitard interface, did not increase the maximum depth of TCE penetration. Combining the field profiles with one-dimensional model simulations, downward migration of the aqueous TCE front, defined as the EPA MCL of 5 microg/l, which was below the analytical detection limit, was projected to a distance between 4 and 5 m below the top of the aquitard. Using a single set of estimated aquitard parameter values, simulations of aqueous TCE migration into the aquitard provided a good fit to four of the field profiles with a migration time of 35 to 45 years, consistent with the history of TCE use at the site. These simulations indicate aqueous TCE migration is diffusion-dominated with only small advective influence by the downward groundwater velocity of 2 to 3 cm/year or less in the aquitard due to pumping of the underlying aquifer to supply water to the facility in the past 50 years. The applicability of the parameter values was confirmed by in situ diffusion experiments of 1-year duration, in which stainless steel cylinders containing DNAPL were inserted into the aquitard. The diffusion-dominated nature of the profiles indicates that the aquitard provides long-term protection of the underlying aquifer from contamination from this DNAPL zone. Simulations of long-term migration of the TCE solute front indicate breakthrough to the lower aquifer at 1200 years for the no advection scenario and at 500 years if the strong downward hydraulic gradient persists. However, even after breakthrough, the mass flux through the aquitard to the underlying aquifer remains relatively low, and when considered in terms of potential impacts to pumping wells, concentrations are not expected to increase significantly above present-day MCLs. The use of contaminant profiles of different time and distance scales, in addition to hydraulic data, dramatically improves the ability to assess aquitard integrity, and provides improved transport parameter values for estimating contaminant arrival times and fluxes. The apparent lack of deep preferential pathways for TCE migration, such as open fractures, is probably due to the softness of the silty aquitard deposit and minimal physical or chemical weathering of the aquitard provides long-term protection of the underlying aquifer from contamination from this DNAPL zone. Simulations of long-term migration of the TCE solute front indicate breakthrough to the lower aquifer at 1200 years for the no advection scenario and at 500 years if the strong downward hydraulic gradient persists. However, even after the breakthrough, the mass flux through the aquitard to the underlying aquifer remains relatively low, and when considered in terms of potential impacts to pumping wells , concentrations are not expected to increase significantly above present-day MCLs. The use of contaminant profiles of different time and distance scales, in addition to hydraulic data, dramatically improves the ability to assess aquitard integrity, and provides improved transport parameter values for estimating contaminant arrival times and fluxes. The apparent lack of deep preferential pathways for TCE migration, such as open fractures, is probably due to the softness of the silty aquitard deposit and minimal physical or chemical weathering of the aquitard.     

Axi-symmetric simulation of soil vapor extraction influenced by soil fracturing

Fracturing, either pneumatic or hydraulic, is a method to improve the performance of soil vapor extraction (SVE) in relatively low permeability soils (< 10(-5) cm/s). A two-dimensional model is presented to simulate trichloroethylene (TCE) soil vapor extraction modified by fracturing. Flow and transport is modeled using mobile macropore and micropore networks, which also have been identified in the literature as dual porosity, dual permeability, or heterogeneous flow models. In this model, fluids can flow in both the macropore and micropore networks. This represents a more general model compared to immobile micropore, mobile macropore models presented thus far in the literature for vapor flow and transport in two dimensions. The model considers pressure- and concentration-driven exchange between the macropore and micropore networks, concentration-driven exchange between the gas and sorbed phases within each network, and equilibrium exchange between the gas and water and a sorbed phase within each network. The parameters employed in an example simulation are based on field measurements made at a fractured site. Considered in the simulations were the influence of the volume percentage of fractures, the length of fractures, the relative location of the water table, and the influence of pulsed pumping. For these simulations, internetwork concentration-driven exchange most significantly affected mass removal. The volume percentage of fractures more significantly influence flow and mass removal than the length of fractures. The depth of the water table below the contamination plume only significantly influenced flow and mass removal when the water table was within 60 cm of the bottom of the contaminated soil in the vadose zone for the parameters considered in this study. Pulsed pumping was not found to increase the amount of mass removed in this study.     

Restoring biochemical activity and bacterial diversity in a trichloroethylene-contaminated soil: the reclamation effect of vermicomposted olive wastes

Background, aim, and scope  In this work, the potential for using olive-mill solid waste as an organic amendment for biochemical and biological restoration of a trichloroethylene-contaminated soil, which has previously been stabilized through vermicomposting processes, has been explored. Materials and methods  Trichloroethylene-contaminated water was pumped into soil columns with a layer of vermicompost at 10-cm depth (biobarrier system). The impacts of the trichloroethylene on the microbial community were evaluated by determining: (1) the overall microbial activity (estimated as dehydrogenase activity) and enzyme activities related to the main nutrient cycles (β-glucosidase, o-diphenoloxidase, phosphatase, urease, and arylsulphatase activities). In addition, isoelectric focusing of the soil extracellular humic-β-glucosidase complexes was performed to study the enzymatically active humic matter related to the soil carbon cycle. (2) The soil bacterial diversity and the molecular mechanisms for the bacterial resistance to organic solvents were also determined. For this, polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) was used to detect changes in bacterial community structure and PCR-single-strand conformational polymorphism (SSCP) was developed and optimised for detection and discrimination of the resistance-nodulation-division (RND) genes amplified from the contaminated soils. Results  Vermicompost reduced, with respect to the unamended soil, about 30% of the trichloroethylene leaching during the first month of the experiment. Trichloroethylene had a marked negative effect on soil dehydrogenase, β-glucosidase, urease, phosphatase, and arylsulphatase activities. Nevertheless, the vermicompost tended to avoid this toxic effect. Vermicompost also displays stable humic-β-glucosidase complexes that increased the extracellular activity related to C-cycle in the contaminated soils. The isoelectric focusing technique showed a more biochemically active humic matter in the soil sampled under the vermicompost. The behaviour of the three main phyla of bacteria isolated from the DGGE bands was quite different. Bands corresponding to Actinobacteria disappeared, whereas those affiliated with Proteobacteria remained after the trichloroethylene contamination. The disappeared Actinobacteria became visible in the soil amended with the vermicompost. Bands corresponding to Bacteriodetes appeared only in columns of contaminated soils. In this study, six types of RND proteins were detected by PCR-SSCP in the natural soil, three in the trichloroethylene-contaminated soil and 7/5 in trichloroethylene-contaminated soil above/below the vermicompost in the biobarrier columns. Trichloroethylene tended to reduce or eliminate all the clones detected in the uncontaminated soil, whereas new efflux pumps appeared in the biobarrier columns. Discussion  Although enzymes incorporated into the humic substances of vermicomposted olive wastes are quite stable, trichloroethylene also inhibited the background levels of the soil extracellular β-glucosidase activity in the amended soils. The decrease was less severe in the biobarrier system, but in any case, no relation was found between the levels of trichloroethylene in soil and extracellular β-glucosidase activity, or between the latter and the quantity of humic carbon in soils. The isoelectric focusing technique was carried out in the humic fraction to determine whether the loss of activity occurred in overall extracellular β-glucosidase or in that linked to stable humic substances (humic–enzyme complexes). The contaminated soils showed the lower enzyme activities, whereas contaminated and amended soils presented greater quantity of focalised (and therefore stable) humic carbon and spectra heterogeneity: very different bands with higher enzyme activities. No clear relationship between trichloroethylene concentration in soil and diversity of the bacterial population was noted. Similar patterns could be found when the community structures of bacteria and microbial activity were considered. Since the use of the dehydrogenase assay has been recognised as a useful indicator of the overall measure of the intensity of microbial metabolism, these results could be attributed to PCR-DGGE methodology, since the method reveals the presence of dominant populations regardless of their metabolic state. Trichloroethylene maintained or even increased the number of clones with the DNA encoding for RND proteins, except for the contaminated soil located above the vermicompost. However, the main effect of trichloroethylene was to modify the structure of the community in contaminated soils, considering the type of efflux pumps encoded by the DNA extracted from soil bacteria. Conclusions  Trichloroethylene inhibited specific functions in soil and had a clear influence on the structure of the autochthonous bacterial community. The organic matter released by the vermicomposted olive waste tended to avoid the toxic effect of the contaminant. Trichloroethylene also inhibited the background levels of the soil extracellular β-glucosidase activity, even when vermicompost was present. In this case, the effect of the vermicompost was to provide and/or to stimulate the humic-β-glucosidase complexes located in the soil humic fraction >10⁴, increasing the resistance of the enzyme to the inhibition. The bacterial community from the soil presented significantly different mechanisms to resistance to solvents (RND proteins) under trichloroethylene conditions. The effect of the vermicompost was to induce these mechanisms in the autochthonous bacterial community and/or incorporated new bacterial species, able to grow in a trichloroethylene-contaminated ambient. Coupled biochemical and molecular methodologies are therefore helpful approaches in assessing the effect of an organic amendment on the biochemical and biological restoration of a trichloroethylene-contaminated soil. Recommendations and perspectives  Since the main biochemical and biological effects of the organic amendment on the contaminated soil seem to be the incorporation of biochemically active humic matter, as well as new bacterial species able to grow in a trichloroethylene-contaminated ambient, isoelectric focusing and PCR-SSCP methodologies should be considered as parts of an integrated approach to determine the success of a restoration scheme.     

Chronic inhalation effects of trichloroethylene on hepatic microsomal mixed function oxidase system in rats

Inhalation effects of trichloroethylene, at levels of 0, 200 and 600 ppm for a period of 4 and 12 weeks, on the contents of hepatic microsomal protein, cytochrome P₄₅₀, cytochrome b₅, and on the activities of NADPH cytochrome C reductase, aminopyrine N‐demethylase and aniline hydroxylase were investigated. Body weight remained unaltered at 200 ppm level, whereas at 600 ppm level a significant decrease in body weight was observed. Liver weight showed increases at an exposure level of 200 ppm by the end of 4 and 12 weeks. Relative liver weight (% body weight) showed an increase at 200 and 600 ppm level by the end of week 4, whereas, after 12 weeks increase was observed only in animals exposed to the 600 ppm level. Hepatic microsomal protein was decreased by the end of 4 weeks at both the exposure levels. Cytochrome P₄₅₀ and cytochrome b, contents were increased at the 200ppm level after 4 and 12 weeks. NADPH cytochrome C reductase activity showed a marked increase at both the 200 and 600 ppm levels after 4 and 12 weeks. Aminopyrine N‐demethylase activity was increased at the 200 ppm level and decreased at the 600 ppm level by the end of 4 weeks, whereas, at the end of 12 weeks the aminopyrine N‐demethylase activity was near control values. Aniline hydroxylase activity was increased at the 200 ppm level after 4 and 12 weeks. Similarly, at the 600 ppm level aniline hydroxylase activity was increased after 12 weeks.