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1.
13C CP-MAS NMR spectroscopy is a technique that has proved to be useful in studying soil organic matter (SOM). Nevertheless, NMR spectra exhibit a weak signal and have very low resolution due to: the low natural abundance of 13C (1.1 % of C) in SOM, the generally low SOM content of soils, and the presence of paramagnetic impurities. This paper studies the effects of soil chemical pre-treatments on 13CP-MAS NMR spectra quality and spectra representativity i.e. soil C mass balance. After chemical pre-treatment to increase total organic carbon (TOC) content and C/Fe ratio, eight soils characterized by different levels of organic carbon content and C/Fe ratios were studied using 13CP-MAS NMR. Moreover, where chemical treatments were not applicable due to high carbon losses, the number of 13CP-MAS NMR scans was increased in order to obtain satisfactory spectra. Results show that chemical pre-treatment of soils with C/Fe > 1 caused high C losses. Bulk soils were therefore studied by increasing the number of 13CP-MAS NMR scans. Acceptable spectra were obtained from 8K scans (1K = 1024 transient). On the other hand, even when a large number of scan (32K) are used, soil with C/Fe < 1 cannot be studied. As these soils are characterized by low C losses after HCl treatments (range of 2.9–25.4%), a pre-treatment of at least 1.39 mol l−1 HCl removes excess Fe and at the same time increases C/Fe ratio resulting in 32K scans providing good spectra. 相似文献
2.
The distribution coefficients ( Kd) and desorption rates of 137Cs and 241Am radionuclides in bottom sediments at different locations in the Black Sea were studied under laboratory conditions. The Kd values were found to be 500 for 137Cs and 3800 for 241Am at the steady state and described exponential curves. Rapid uptake of the radionuclides occurred during the initial period and little accumulation happened after four days. The desorption rates for 137Cs in different bottom sediments were best described by a three-component exponential model. The desorption half-times of 137Cs ranged from 26 to 50 d at the slow components. However, the desorption rate of 241Am described one component for all sediment samples and desorption half-time was found to be 75 d. In general, the results showed that the 241Am radionuclide is more effectively transferred to bottom sediment and has longer turnover time than 137Cs under Black Sea conditions. 相似文献
3.
The binding of three polychlorinated biphenyl (PCB) congeners to natural levels of dissolved organic carbon (DOC) was measured in 12 lakes and streams using Sep-Pak C 18 columns. The association coefficients calculated on the basis of DOC (i.e. K DOC mL/g C), varied by over an order of magnitude among the different freshwaters and ranged between 2.05 × 10 2 and 8.86 × 10 3 mL/g C for PCB 52 and 1.03 × 10 4 and 1.70 × 10 5 mL/g C for PCB 153. In general, there were no significant correlations (p > 0.05) between the K DOC values and various chemical parameters in the study lakes and streams. A relationship was derived between the fraction of bound PCB and the octanol-water partition coefficient. While this relationship explained almost 50% of the variation in the observed data, it is apparent that other factors influence KDOC values and that in natural freshwaters, only a small fraction of the DOC is involved in the binding of PCBs and other hydrophobic pollutants. 相似文献
4.
Technetium-99 was determined in samples from the 30-km zone around the Chernobyl reactor. Concentrations of 99Tc in soil samples taken from three forest sites ranged from 1.1 to 14.1 Bq kg −1 dry weight for the organic soil layers, and from 0.13 to 0.83 Bq kg −1 dry weight for the mineral soil layers. In particular, for the organic layers, the measured 99Tc concentrations were one or two orders of magnitude higher than those due to global fallout 99Tc. The 99Tc depositions (Bq m −2), based on the sum of the depositions measured in organic and mineral layers, ranged from 130 Bq m −2 within the 10-km zone to about 20 Bq m −2 close to the border of the 30-km zone. Taking the corresponding measured 137Cs depositions into account, it was found that the activity ratio of 99TW/ 137Cs ranged from 6 × 10 −5 to 1.2 × 10 −4. It was estimated that about 970 GBq of 99Tc had been released by the Chernobyl accident. This figure corresponded to 2%–3% of the total 99Tc inventory in the core. 相似文献
5.
For sulfonamides, the formation of non-extractable residues has been identified by laboratory testing as the most relevant concentration determining process in manured soil. Therefore, the present study has been focused on the chemical and biological characterization of non-extractable residues of 14C-labeled sulfadiazine or sulfamethoxazole. In laboratory batch experiments, the test substances were spiked via standard solution or test slurry to microbially active soil samples. After incubation periods of up to 102 d, a sequential extraction technique was applied. Despite the exhaustive extraction procedure, sulfadiazine residues mainly remained non-extractable, indicating the high affinity to the soil matrix. The remobilization of non-extractable 14C-sulfadiazine residues was monitored in the activated sludge test and the Brassica rapa test. Only small amounts (<3%) were transferred into the extractable fractions and 0.1% was taken up by the plants. In the Lumbricus terrestris test A, the release of non-extractable 14C-sulfamethoxazole residues by the burrowing activity of the earthworms was investigated. The residues mainly remained non-extractable (96%). The L. terrestris test B was designed to study the immobilization of 14C-sulfamethoxazole in soil directly after the test slurry application. The mean uptake by earthworms was 1%. Extractable and non-extractable residues amounted to 5% and 93%, respectively. Consequently, the results of all tests confirmed the high affinity of the non-extractable sulfonamide residues to the soil matrix. 相似文献
6.
The photocatalytic inactivation (PCI) of Escherichia coli (Gram-negative) and Bacillus subtilis (Gram-positive) was performed using polyoxometalate (POM) as a homogeneous photocatalyst and compared with that of heterogeneous TiO 2 photocatalyst. Aqueous suspensions of the microorganisms (10 7–10 8 cfu ml −1) and POM (or TiO 2) were irradiated with black light lamps. The POM-PCI was faster than (or comparable to) TiO 2-PCI under the experimental conditions employed in this study. The relative efficiency of POM-PCI was species-dependent. Among three POMs (H 3PW 12O 40, H 3PMo 12O 40, and H 4SiW 12O 40) tested in this study, the inactivation of E. coli was fastest with H 4SiW 12O 40 while that of B. subtilis was the most efficient with H 3PW 12O 40. Although the biocidal action of TiO 2 photocatalyst has been commonly ascribed to the role of photogenerated reactive oxygen species such as hydroxyl radicals and superoxides, the cell death mechanism with POM seems to be different from TiO 2-PCI. While TiO 2 caused the cell membrane disruption, POM did not induce the cell lysis. When methanol was added to the POM solution, not only the PCI of E. coli was enhanced (contrary to the case of TiO 2-PCI) but also the dark inactivation was observed. This was ascribed to the in situ production of formaldehyde from the oxidation of methanol. The interesting biocidal property of POM photocatalyst might be utilized as a potential disinfectant technology. 相似文献
7.
Potential of plants to remove radionuclides/toxic elements from soils and solutions can be successfully applied for removal of important radionuclides such as strontium-90 ( 90Sr) and cesium-137 ( 137Cs). When uptake of 137Cs and 90Sr by Calotropis gigantea plants incubated in distilled water spiked with the radionuclides either alone or in combination was studied, it was found to have a high efficiency for the removal of 90Sr, with 90% being removed from solutions (5 × 10 3 kBq l −1) within 24 h of incubation. However, in case of 137Cs, about 44% could be removed from solutions (5 × 10 3 kBq l −1) at the end of 168 h of incubation. Accumulation of 90Sr and 137Cs was higher in roots compared to shoots. The plants could remediate both 90Sr and 137Cs when they were added together to the solution. When two months old plants were incubated in low level nuclear waste, 99% of activity disappeared at the end of 15 days. The present study suggests that C. gigantea could be used as a potential candidate plant for phytoremediation of 90Sr and 137Cs. 相似文献
9.
The aerobic visible-light-photosensitised irradiation of methanolic solutions of either of the phenolic-type contaminants model compounds (ArOH) p-phenylphenol (PP), p-nitrophenol (NP) and phenol (Ph), and for two additional phenolic derivatives, namely p-chlorophenol (ClP) and p-methoxyphenol (MeOP), used in some experiments, was carried out. Employing the natural pigment riboflavin (Rf) as a sensitiser, the degradation of both the ArOH and the very sensitiser was observed. A complex mechanism, common for all the ArOH studied, operates. It involves superoxide radical anion (O 2√−) and singlet molecular oxygen (O 2( 1Δ g)) reactions. Maintaining Rf in sensitising concentrations levels (≈0.02 mM), the mechanism is highly dependent on the concentration of the ArOH. Kinetic experiments of oxygen and substrate consumption, static fluorescence, laser flash photolysis and time-resolved phosophorescence detection of O 2( 1Δ g) demonstrate that at ArOH concentrations in the order of 10 mM, no chemical transformation occurs due to the complete quenching of Rf singlet excited state. When ArOH is present in concentrations in the order of mM or lower, O 2√− is generated from the corresponding Rf radical anion, which is produced by electron transfer reaction from the ArOH to triplet excited Rf. The determined reaction rate constants for this step show a fairly good correlation with the electron-donor capabilities for Ph, PP, NP, ClP and MeOP. In this context, the main oxidative species is O 2√−, since O 2( 1Δ g) is quenched in an exclusive physical fashion by the ArOH. The production of O 2√− regenerates Rf impeding the total degradation of the sensitiser. This kinetic scheme could partially model the fate of ArOH in aquatic media containing natural photosensitisers, under environmental conditions. 相似文献
10.
An investigation involving the supplement of different concentrations of substrates and microorganisms was carried out under anaerobic condition to assess the feasibility of bioremediation of carbon tetrachloride (CCl 4) with the amendment of low concentrations of auxiliary substrate and microorganisms. The concentrations of substrate and microorganisms ranged from 10 to 100 mg/l and from 3.7 × 10 4 to 3.7 × 10 6 cell/ml, respectively. The biotransformation rate of CCl 4 increased progressively with the increase in the concentrations of the substrate and microorganisms. In the low biomass-amended system (3.7 × 10 4cells/ml), 28–71% and 57–96% of CCl 4 removals were exhibited when 10–100 mg/l of acetate or glucose was supplemented, respectively, whereas nearly complete degradation of CCl 4 was observed in the heavily inoculated systems (3.7 × 10 6 cells/ml). An addition of electron donor in the low microbial activity batches enhanced greater efficiency in dechlorination than in the high microbial activity batches. The second-order rate constants ranged from 0.0059 to 0.0092 l/mg/day in high biomass input system, while a two- to four-fold increase in rate constant was obtained in the low microbial activity system. This study indicates that biomass was the more important environmental parameter than substrate affecting the fate of CCl 4. The addition of auxiliary substrates was effective only in low biomass-amended batches (0.56 mg-VSS/l) and diminished inversely with the increase of microbial concentration. 相似文献
11.
Aerobic decomposition and stabilization of organic matter during the composting of waste materials is primarily due to the biochemical transformation of water-soluble compounds in the liquid phase by the microbial biomass. For this reason water-soluble organic matter represents the most active fraction of compost, both biologically and chemically, and thus should directly reflect the biochemical alteration of organic matter. This work aims to elucidate the microbial-mediated processes responsible for the distribution of soluble organic matter between stable and labile pools with composting time. Accordingly, chemical analysis as well as UV absorption, and 1H and 13C-NMR spectroscopy of samples collected during the industrial composting of urban waste revealed microbial induced transformation of water-extractable organic matter over time. The chemical composition changed from labile, hydrophilic, plant-derived organic compounds in the beginning to predominately stable, hydrophobic moieties comprising lignin-derived phenols and microbially-derived carbohydrates at later stages of composting. 相似文献
12.
A loamy clay soil containing unextractable 14C-ring labeled atrazine residues was incubated in microcosms under abiotic and biotic conditions. The mineralization activity of the soil microflora was evaluated by the release of total CO 2 and 14C0 2. After 63 days of sample incubation the total organic carbon mineralization was of 1.71%, that of 14C-residues was of 0.72% of the initial radioactivity. No direct relationship was established between the mineralization of atrazine residues and the global mineralization. The contribution of soil microorganisms in the release of 14C-residues was weak. The availability of non-extractable residues was mainly controlled by physico-chemical factors. The low value of the reextractability rate and the distribution of bound residues during the soil sample incubation shown the active role of organic matter in detoxification procedure. Ninety percent of the residues remained bound after 63 days of incubation and were thus, potentially available without biocide activity. The fractionation of soil organic matter allowed to specify the distribution of bound residues within the organic compartments. After a long-stay of pesticides in soils, approximately 65% of bound residues were associated with humin. 相似文献
13.
This study shows the important role of humic acids in the degradation of 14C and 13C labeled isomer of NP by Sphingomonas sp. strain TTNP3 and the detoxification of the resulting metabolites. Due to the association of NP with humic acids, its solubility in the medium was enhanced and the extent of mineralization of nonylphenol increased from 20% to above 35%. This was accompanied by the formation of significant amounts of NP residues bound to the humic acids, which also occurred via abiotic reactions of the major NP metabolite hydroquinone with the humic acids. Gel permeation chromatography showed a non-homogenous distribution of NP residues with humic acids molecules, with preference towards molecules with high-molecular-weight. Solid state 13C nuclear magnetic resonance spectroscopy indicated that the nonextractable residues resulted exclusively from the metabolites. The chemical shifts of the labeled carbon indicated the possible covalent binding of hydroquinone to the humic acids via ester and possibly ether bonds, and the incorporation of degradation products of hydroquinone into the humic acids. This study provided evidences for the mediatory role of humic acids in the fate of NP as a sink for bacterial degradation intermediates of this compound. 相似文献
14.
The Las Vegas Wash is an excavated waterway channel which drains all surface water and effluent discharge from sewage-treatment facilitates from the greater Las Vegas Metropolitan Area to Lake Mead. Fine and course sediment samples were collected at 100-m intervals and analyzed to determine the distribution of gamma-emitting radionuclides in the lower 5,500 m of the Las Vegas Wash. Results indicate depletion of long-lived fission products in upstream Wash sediments. However, trace levels of 137Cs measured in downstream sediments suggest the resuspension and transport of radioactive fallout within the Wash. Levels of 40K, 232Th, 235U, and 238U found in Wash sediments were consistent with levels typically found in southeast Nevada soils. 相似文献
15.
以2015年为基准年,基于拓展的STIRPAT模型预测2025年湖北省能源消费CO2和主要大气污染物排放量.通过设置基准(记为BAU)情景、低碳(记为LC)情景和强化低碳(记为ELC)情景3种控制情景,测算CO2和主要大气污染物的减排量,并运用污染物减排量交叉弹性法评价了CO2减排对主要大气污染物的协同效应.结果表明,... 相似文献
16.
Phenotypical dissection of helper (T4 +) and suppressor cytotoxic (T8 +) T lymphocytes using Leu 8 reagent reveal a significant increase of T8 + Leu 8 − subset in human after furan exposure. 相似文献
17.
Brominated dibenzo-p-dioxin and dibenzofuran (BDD/BDF) isomers, specifically having from one to three halogens located in the 2,3,7,8-substituent positions, that are [ 13C]-labeled for use as analytical internal standards in mass spectrometric methods are not yet commercially available. Based upon the current availability of [ 13C]-labeled dibenzo-p-dioxin and dibenzofuran (DD/DF) precursors, we have developed a simple and efficient synthetic procedure which produces brominated congeners that are predominantly substituted in the 2,3,7, and 8-positions. The gas/solid reaction of vaporized precursor and surface-supported iron (III) bromide occurs rapidly (seconds) at temperatures ≥ 240°C and can provide total product yields in the range of 30 to 50 mole % for initial precursor amounts between 1 μg and 10 mg. In this paper we shall describe the utility of this approach to produce 5 μg quantities of [ 13C 12]-2,7-dibromodibenzo-p-dioxin (27-DBDD) and [ 13C 12]-2,8-dibromodibenzo-p-dioxin (28-DBDD). 相似文献
18.
Radioisotopes carbon 14 and chlorine 36 were used to elucidate the environmental role of trichloroacetic acid (TCA) formerly taken to be a herbicide and a secondary air pollutant with phytotoxic effects. However, use of 14C-labeling posed again known analytical problems, especially in TCA extraction from the sample matrix. Therefore—after evaluation of available methods—a new procedure using decarboxylation of [1,2- 14C]TCA combined with extraction of the resultant 14C-chloroform with a non-polar solvent and its subsequent radiometric measurement was developed. The method solves previous difficulties and permits an easy determination of amounts between 0.4 and 20 kBq (10–500 ng g −1) of carrier-less [1,2- 14C]TCA in samples from environmental investigations. The procedure is, however, not suitable for direct [ 36Cl]TCA determination in chlorination studies with 36Cl. Because TCA might be microbially degraded in soil during extraction and sample storage and its extraction from soil or needles is never complete, the decarboxylation method—i.e. 2 h TCA decomposition to chloroform and CO 2 in aqueous solution or suspension in closed vial at 90 °C and pH 4.6 with subsequent CHCl 3 extraction—is recommended here, estimated V < 7%. Moreover, the influence of pH and temperature on the decarboxylation of TCA in aqueous solution was studied in a broad range and its environmental relevance is shown in the case of TCA decarboxylation in spruce needles which takes place also at ambient temperatures and might amount more than 10–20% after a growing season. A study of TCA distribution in spruce needles after below-ground uptake shows the highest uptake rate into current needles which have, however, a lower TCA content than older needle-year classes, TCA biodegradation in forest soil leads predominatingly to CO 2. 相似文献
19.
This study aimed to investigate the persistence of imidacloprid in soil after application to cotton seeds and to obtain a complete picture on the mass balance of this compound in soil and cotton plants. The study was carried out as a pot culture experiment under laboratory conditions using a Gaucho formulation containing 14C-labeled imidacloprid. Three treatments of cotton seeds were made in sandy loamy soil: live seeds grown in autoclaved soil, dead seeds put in live soil and live seeds grown in live soil. Results showed that total 14C recoveries decreased by time ranging 93.8–96.2, 77.1–88.4 and 53.5–62.4% of the applied radioactivity at 7, 14, and 21 d after application, respectively. The reduction in the extracted 14C from soil coincided with the increase of non-extracted ones. Levels of bound 14C was always less in autoclaved soil than in live ones. Results revealed also that only 1.8–6.8% of the applied 14C was taken up by the plants and fluctuated within the test period. 14C levels were higher in plants grown in autoclaved soil than those in live ones and the radioactivity tended to accumulate on the edges of cotton leaves. Most of the radioactivity in the soil extracts was identified as unchanged 14C-imidacloprid. 相似文献
20.
Roots of whole plants at four leaf stage grown in specialized soil treatment vessels were treated with 14C-atrazine. Plant tissues were exhaustively extracted with methanol and extracts were separated by preparative thin layer chromatography (TLC). The extracted material was separated in two TLC bands at Rf0.00 and Rf0.18 containing 33% and 67% of plant 14C-residues, respectively. Methanol extracts of these bands subjected to derivatization, hydrolysis and analysis by TLC, revealed the presence of a number of transformation products consisting of hydroxy analogues of atrazine and their dealkylated metabolites. The transformation products had variable distribution patterns amongst leaf, stalk and root tissues. Diaminohydroxyatrazine, hydroxyatrazine, and deethylhydroxyatrazine were the main 14C-residues. Stalk tissue contained more 14C-residues which were largely located at and just below the ligule. The significance of 14C-residue accumulation at the ligule and the transformation product compartmentalization are discussed. 相似文献
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