Chlorobenzenes In Soil Research Articles

Insight into the degradation mechanism of peroxyacetic acid for pentachlorophenol by thermal activation in soil system

In this study, inorganic and organic radicals generated from a thermally activated peroxyacetic acid (PAA) system were used to degrade pentachlorophenol (PCP) in contaminated soils. In addition, the effects of various operating parameters on PCP removal were fully considered, including reaction temperature, PAA dosage, initial pH and natural organic matter (NOM). The experimental results showed that PCP was more easily degraded under the conditions that temperature was higher than 40 °C and near neutral pH, and PAA dosage was more than 750 mM/kg. In contrast, humic acid (HA) exhibited a significant inhibitory impact on PCP degradation. The results from the chemical quenching and electron para-magnetic resonance (EPR) experiments further indicated that in the PAA system, HO• has much better degradation ability for PCP than 1 O 2 . Moreover, the degradation of PCP was dominated by R-O• radicals, including CH 3 C(O)O• and CH 3 C(O)OO•. Besides, the potential degradation pathways of PCP by PAA system were investigated, based on the degradation intermediates and the density functional theory (DFT) calculation. The present study results indicated that the combined process of PAA and heat treatment has a significantly high efficiency in the degradation of chlorobenzenes in soils. This study is the first to use thermally activated PAA for soil remediation without the use of other chemicals as activators, and provides a novel, efficient and economical technique for the remediation of actual chlorinated hydrocarbon contaminated sites. • PCP can be efficiently degraded through thermal activation PAA in soil systems. • Higher temperature, near neutral pH, and higher PAA dose were more beneficial for degrading PCP. • HA shows an inhibitive effect on PCP decomposition. • R-O• dominated PCP degradation.

Fate Processes of Chlorobenzenes in Soil and Potential Remediation Strategies: A Review

Chlorobenzenes (CBs) are a group of organic pollutants that pose a high environmental risk due to their toxicity, persistence and possible transfer in the food chain. Available data in literature show that CBs are detected in different environmental compartments such as soil, water, air and sediment. The widespread presence of CBs in the environment is related to their former extensive use in agriculture and industry. Some CBs are ranked in the list of priority pollutants by the Stockholm Convention, and their reduction or elimination from the environment is therefore of high importance. Environmental risk assessment of CBs requires knowledge on the role and importance of the main environmental fate processes, especially in soil. Furthermore, development of remediation strategies for reduction or elimination of CBs from the environment is related to the enhancement of fate processes that increase their dissipation in various environmental compartments. The main objectives of the current review were to present up-to-date data on fate processes of CBs in the soil environment and to explore possible remediation strategies for soils contaminated with CBs. Dechlorination of highly-chlorinated benzenes is the main degradation pathway under anaerobic conditions, leading to the formation of lower-chlorinated benzenes. Biodegradation of lower-chlorinated benzenes is well documented, especially by strains of adapted or specialized microorganisms. Development of techniques that combine dechlorination of highly-chlorinated benzenes with biodegradation or biomineralization of lower-chlorinated benzenes can result in useful tools for remediation of soils contaminated with CBs. In addition, immobilization of CBs in soil by use of different amendments is a useful method for reducing the environmental risk of CBs.

Does powder and granular activated carbon perform equally in immobilizing chlorobenzenes in soil?

The objective of this study is to compare the efficacies of powder activated carbon (PAC) and granular activated carbon (GAC) as amendments for the immobilization of volatile compounds in soil. Soil artificially-spiked with chlorobenzenes (CBs) was amended with either PAC or GAC to obtain an application rate of 1%. The results showed that the dissipation and volatilization of CBs from the amended soil significantly decreased compared to the unamended soil. The bioavailabilities of CBs, which is expressed as butanol extraction and earthworm accumulation, were significantly reduced in PAC and GAC amended soils. The lower chlorinated and hence more volatile CBs experienced higher reductions in both dissipation and bioavailability in the amended soils. The GAC and PAC equally immobilized more volatile CBs in soil. Therefore, it could be concluded that along with environmental implication, applying GAC was the more promising approach for the effective immobilization of volatile compounds in soil.

Impact of soil depth on the dissipation of chlorobenzenes

The fate processes of volatilization and biodegradation were quantified in an aerobic batch experiment for the chlorobenzenes (CBs): 1,2-dichlorobenzene (DCB), 1,2,3-trichlorobenzene (TCB) and hexachlorobenzene (HCB) in soil sampled from different depths: topsoil (0-5 cm) and subsoil (80-100 cm) of a soil profile. Sterilized and unsterilized soils with soil organic carbon content of 0.41% for the subsoil and 1.58% for the topsoil were incubated in a microcosm chamber with the spiked chlorobenzenes for 120 days. The data regarding the depletion of the chlorobenzenes suggest that the lower chlorinated benzenes (DCB and TCB) were depleted relatively quickly compared to the higher chlorinated HCB, with DCB being the first to be reduced to undetectable level in the unsterilized soil. In addition volatilization was the main mechanism for the loss of the chlorobenzenes in soil, with more volatilization losses on the subsoil relative to the topsoil for 1,2-DCB and 1,2,3-TCB, which may be explained by the higher organic carbon on the topsoil than on the subsoil. HCB volatilization losses however did not vary with soil depth and lasted till the end of the incubation period. It is likely that the strong binding to soil of the more hydrophobic HCB was responsible for its stronger retention across depths. This therefore indicates higher risk of persistence of HCB in the soil. Keywords: chlorobenzenes, volatilization, biodegradation, topsoil, subsoil Nigerian Journal of Technological Research

Immobilization of Chlorobenzenes in Soil Using Wheat Straw Biochar

Biochar has shown great potential for immobilizing organic contaminants in soil. In this study, pentachlorobenzene (PeCB), 1,2,4,5-tetrachlorobenzene (1,2,4,5-TeCB), and 1,2,4-trichlorobenzene (1,2,4-TCB) artificially spiked soil was amended with wheat straw biochar at 0.1%, 0.5%, 1%, and 2% application rates, respectively. The sorption, dissipation, and bioavailability of chlorobenzenes (CBs) in soil were investigated. The sorption of PeCB by biochar was significantly higher than that of its sorption by both biochar-amended and unamended soil (p < 0.05). The dissipation and volatilization of CBs from biochar-amended soil significantly decreased relative to unamended soil (p < 0.05). Bioavailability of CBs, expressed as butanol extraction efficiency and earthworm (Eisenia fetida) bioaccumulation factor, significantly decreased with increasing aging time and biochar application rate. The effect of biochar content in soil on the bioavailability of CBs was more pronounced for 1,2,4-TCB relative to other CBs. This study suggested that wheat straw biochar, even at low application rates, could effectively immobilize the semivolatile CBs in soil and thus reduce their volatilization and bioavailability.

Chemical extraction to assess the bioavailability of chlorobenzenes in soil with different aging periods

Bioavailability is mainly influenced by aging and desorption of contaminants in soil. The purpose of this study was to investigate the desorption kinetics of chlorobenzenes (CBs) in soil and to investigate whether chemical extractions are suitable for the bioavailability assessment of CBs in soil. A soil spiked with CBs and aged for different periods was extracted with Tenax, hydroxypropyl-β-cyclodextrin (HPCD), and butanol to assess the bioavailability of CBs in soil, respectively. Earthworm (Eisenia foetida) accumulation was used as bioassay in parallel experiments to evaluate the chemical extractions. The results showed that desorption of CBs from soil with consecutive Tenax extraction fitted into triphasic kinetics model. Different chemical methods extracted different amounts of CBs over different aging periods. For hexachlorobenzene (HCB), the extraction efficiency was in the order of butanol > Tenax-6h > HPCD extraction, while the order of butanol > HPCD > Tenax-6h extraction for pentachlorobenzene (PeCB). The bioaccumulation by earthworm decreased with increasing aging period and was significantly higher for HCB than for PeCB (p < 0.05). Earthworm accumulated CBs correlated well with all the three chemical extracted CBs. However, HPCD extraction showed the converse extraction tendency with earthworm uptake of CBs. Chemical extraction could be used to assess the bioavailability of contaminants in soil; however, they were method and compound specific. Tenax and butanol extractions were more reliable than HPCD extraction for bioavailability assessment of the tested CBs and the soil used since they showed the consistent extraction tendency with earthworm uptake of CBs.

Development of pressurized subcritical water extraction combined with stir bar sorptive extraction for the analysis of organochlorine pesticides and chlorobenzenes in soils

An analytical method for the determination of several organochlorine pesticides (OCPs) like hexachlorocyclohexanes (HCHs), cyclodiene derivates (dieldrin, aldrin, endrin, heptachlor, heptachlor epoxide, endrin aldehyde, endosulfan and ensodulfan sulphate) and DDX compounds ( p, p′-DDE, p, p′-DDD and p, p′-DDT) as well as chlorobenzenes in soils has been developed. The procedure is based on pressurized subcritical water extraction (PSWE) followed by stir bar sorptive extraction (SBSE) and subsequent thermodesorption–gas chromatography/mass spectrometry analysis. Significant PSWE and SBSE parameters were optimized using spiked soil and water samples. For the PSWE of the organochlorine compounds, water modified with acetonitrile as the extraction solvent, at an extraction temperature of 120 °C, and three cycles of 10 min extraction proved to be optimal. Under optimized conditions, the figures of merit, such as precision, accuracy and detection limits were evaluated. The detection limits obtained for soil samples were in the range 0.002–4.7 ng/g. Recoveries between 4.1 and 85.2% were achieved from samples spiked at a concentration level of 25–155 ng/g. The main advantages of this method are the avoidance of clean-up and concentration procedures as well as the significant reduction of the required volume of organic solvents. The described method was applied to the determination of the pollutants in soil samples collected from a polluted area, the Bitterfeld region (Germany). The results obtained by PSWE–SBSE were in a good agreement with those obtained by a reference method, a conventional pressurized liquid extraction (PLE).

A solid-phase microextraction fiber coated with diglycidyloxycalix[4]arene yields very high extraction selectivity and sensitivity during the analysis of chlorobenzenes in soil

A novel fiber coated with novel sol-gel (5,11,17,23-tetra-tert-butyl-25,27-dihydroxy-26,28-diglycidyloxycalix[4]arene/hydroxy-terminated silicone oil; diglycidyloxy-C[4]/OH-TSO) was prepared for use with headspace solid-phase microextraction (HS-SPME) combined with gas chromatography (GC) and electron capture detection (ECD), which was applied in order to determine nine chlorobenzenes in soil matrices. Due to the improved fiber preparation, which increases the percentage of calixarene in the coating, the new calixarene fiber exhibits very high extraction selectivity and sensitivity to chlorine-substituted compounds. Various parameters affecting the extraction efficiency were optimized in order to maximize the sensitivity during the chlorobenzene analysis. Interferences from different soil matrices with different characteristics were investigated, and the amount extracted was strongly influenced by the matrix. Therefore, a standard addition protocol was performed on the real soil samples. The linear ranges of detection for the chlorobenzenes tested covered three orders of magnitude, and correlation coefficients >0.9976 and relative standard deviations (RSD) <8% were observed. The detection limits were found at sub-ng/g of soil levels, which were about an order of magnitude lower than those given by the commercial poly(dimethylsiloxane) (PDMS) coating for most of the compounds. The recoveries ranged from 64 to 109.6% for each analyte in the real kaleyard soil matrix when different concentration levels were determined over the linear range, which confirmed the reliability and feasibility of the HS-SPME/GC-ECD approach using the fiber coated with diglycidyloxy-C[4]/OH-TSO for the ultratrace analysis of chlorobenzenes in complex matrices.

Solid phase microextraction as a tool to predict internal concentrations of soil contaminants in terrestrial organisms after exposure to a laboratory standard soil

Uptake and accumulation of three chlorobenzenes was studied in both biota ( Enchytraeus crypticus) and 30 μm polydimethylsiloxane (PDMS) solid phase microextraction (SPME) fibers after exposure to spiked OECD soil. The OECD soil was spiked with three different concentrations of all contaminants. Uptake of all three chlorobenzenes in E. crypticus was fast and steady state levels were reached within 2–4 days. Also in the PDMS-SPME fibers uptake was very fast for all three compounds, with steady state levels reached after 1 day. Comparison of steady state levels in biota and in the PDMS-SPME fibers showed a relationship which was consistent over the range of concentrations of chlorobenzenes in soil and the difference in log K ow. This shows that measuring the concentrations of hydrophobic chemicals in a hydrophobic phase such as PDMS can be used as a simple tool to estimate internal concentrations of these chemicals in biota exposed to complex matrices such as soil.

Strategies for the analysis of chlorobenzenes in soils using solid-phase microextraction coupled with gas chromatography–ion trap mass spectrometry.

Solid-phase microextraction (SPME) was examined as a possible alternative to Soxhlet extraction in the analysis of chlorobenzenes at high concentrations (up to 65 μg g −1) in soils. Gas chromatography–ion trap mass spectrometry (GC–IT-MS) was used and different strategies were tested in order to obtain suitable responses for chlorobenzenes. Two headspace SPME methods, using fibres coated with polydimethylsiloxane (PDMS) as stationary phase, in splitless and split injection modes, respectively, and a direct SPME method using 100-μm PDMS fibre were studied. For headspace SPME, 7-μm and 100-μm PDMS fibres were used and good sensitivity was obtained by adding 200 μl of water to the soil, at a sampling temperature of 30°C and absorption times of 40 and 60 min, respectively. For direct SPME, which involves extraction of chlorobenzenes from stirred soil solutions using a 100-μm PDMS fibre, the effect of the addition of different organic solvents, such as methanol or acetone, on the sensitivity and the extraction time was evaluated. The shortest time to reach equilibrium (50 min) was achieved when a mixture acetone–water (30:70) was added to the sample. Repeatabilities lower than 8% were obtained for headspace and direct SPME with 100-μm PDMS fibre, whereas for 7-μm PDMS fibre, repeatabilities were slightly higher (between 7 and 11%). The SPME methods were applied to the analysis of chlorobenzenes in an industrially contaminated clay soil, CRM-530, which is a candidate reference material. Chlorobenzenes in this soil were quantified by standard addition, which led to good reproducibility (R.S.D. between 2 and 10%) for headspace and direct SPME with the 100-μm PDMS fibre and acceptable detection limits (30 to 100 pg g −1 of soil). The results were consistent with those obtained in a European intercomparison exercise.

Determination of chlorobenzenes in environmental samples using solid phase microextraction, thermal desorption and analysis by gas chromatography coupled to FID, ECD, MSD, IRD detectors

A complex method was developed for the determination of chlorobenzenes in soil and groundwater samples. Samples were taken at two sites in Baranya county, where a mixture of chlorobenzene waste was deposited, causing severe contamination in the environment. Clean-up of these sites demands modern and reliable analytical methods. Several sample preparation techniques were used, such as solid phase microextraction (SPME), supercritical fluid extraction (SFE), and a recently developed thermal desorption method. The applicability of various sample preparation methods was compared by measuring recovery percentages, relative standard deviations and by investigating the matrix dependency of these values. Gas chromatography was used for quantitative determination of chlorobenzenes, using MS, IR, FID and ECD detection techniques. Detection levels were as low as 1 ppt in water, and 10 ppt in soil samples. Chlorobenzene concentration was in the range 1 ppt-1 ppm in water and 100 ppb-100 ppm in soil samples. Identification and calibration of these compounds were performed by quantitative standards. This complex analytical method can be used for rapid and precise quantitative and qualitative determination of chlorobenzenes.

Analysis of chlorobenzenes in soils by headspace solid-phase microextraction and gas chromatography-ion trap mass spectrometry

Headspace solid-phase microextraction (SPME) with gas chromatography-ion trap mass spectrometry (GC-IT-MS) was investigated as a possible alternative to Soxhlet extraction in the analysis of chlorobenzenes in soils. A 100 μm polydimethylsiloxane fibre was used for the optimization studies. Maximum sensitivity was obtained at a sampling temperature of 30°C and with an absorption time of 25 min. The effect of the addition of solvents of different polarity was evaluated. Better repeatability (R.S.D. between 5 and 7%) and higher responses were obtained when water was added to the soil. The headspace SPME method was applied to the analysis of the chlorobenzenes, 1,2,3-trichlorobenzene, 1,2,3,4-tetrachlorobenze and pentachlorobenzene, in an industrially contaminated sandy soil, CRM-529 (Candidate Reference Material). The chlorobenzenes in this soil were quantified by standard addition, which led to good reproducibility (R.S.D. between 3 and 5%) and adequate detection limits (0.03 to 0.1 ng g − of soil). The method was validated by comparing the results with those obtained in a European intercomparison exercise.

Uptake of Chlorobenzenes by Carrots from Spiked and Sewage Sludge-Amended Soil

Download Hi-Res ImageDownload to MS-PowerPointCite This:Environ. Sci. Technol. 1994, 28, 7, 1260-1267

Behaviour and fate of chlorobenzenes (CBs) introduced into soil-plant systems by sewage sludge application: A review

Sewage sludges are routinely applied to agricultural soils in many countries. There are potential benefits to agriculture in terms of improved soil structure and nutrient additions, but there is a need to safeguard against possible unwanted environmental effects from heavy metals and trace organic contaminants added to soil in this form. Regulations have been enforced to restrict the additions of metals in sludge, but much less information exists to support scientifically-based restrictions for trace organics. Chlorobenzenes (CBs) are always present in sludges and possess a range of properties which suggests that soil-borne CBs may be susceptible to transfer to crops, grazing livestock and groundwater. In the absence of data specific to sludge amended soils and prior to a detailed case study of these compounds in sludge treated soils, this paper presents a review of the potential behaviour and fate of CBs in soil-plant systems. Volatilisation is identified as an important fate of CBs in soil, while degradation is thought to be minor. Plant uptake is deemed likely to occur, with the potential for transfer to root and shoots. This group of compounds provide a useful insight into the likely behaviour of other non-polar trace organics which may be present in sewage sludges.

Formation and fate of bound residues of [ 14C]benzene and [ 14C]chlorobenzenes in soil and plants

Outdoor experiments with [ 14C]hexachlorobenzene, [ 14C]pentachlorobenzene, [ 14C]1,2,4-trichlorobenzene, and [ 14C]benzene in soil-crop systems indicate that the formation rate of bound residues in soil and plants, expressed as bound residues in percentage of total residue in the sample, decreases with increasing number of chlorine in the molecule and, thus, with increasing chemical stability. The time course of formation and fate of bound residues in soil and plants is characterized by a very slow decrease of residue levels in soil, indicating that biodegradation of bound residues hardly exceeds their reformation from the parent compound during one vegetation period, and by a decrease of residue levels in plants. The portion of bound residues as compared to the total residue increases with time, indicating that bound residues are more persistent than the parent compounds and their soluble metabolites; benzene is an exception. Cress plants, in general, contain less bound residues than do barley plants. Again, benzene is an exception. In deeper soil layers, soil-bound residues occur also. The ratio between bound and extractable residues does not differ to a larger extent between the soil layers.