Chlorobenzene Congeners Research Articles

Degradation behaviors and accumulative effects of coexisting chlorobenzene congeners on the dechlorination of hexachlorobenzene in soil by nanoscale zero-valent iron.

It is well known that many chlorinated organic pollutants can be dechlorinated by nanoscale zero-valent iron. However, in the real chlorinated organic compounds contaminated soil, the congeners of high- and low-chlorinated isomer often coexist and their dechlorination behaviors are poorly known, such as hexachlorobenzene (HCB). In this work, the degradation behaviors of three coexisting chlorobenzene congeners pentachlorobenzene (PeCB), 1,2,4,5-tetrachlorobenzene (1,2,4,5-TeCB) and 1,2,4-trichlorobenzene (1,2,4-TCB) and the influence of initial pH and reaction temperature on the dechlorination of HCB in HCB-contaminated soil by nanoscale zero-valent iron were studied. The amount and extent of accumulated coexisting chlorobenzenes was analyzed under different environmental conditions. The results indicate that nanoscale zero-valent iron can improve the degradation efficiency of highly toxic chlorinated benzenes and reduce the accumulative effects of highly toxic chlorinated benzenes on dechlorination of HCB. The accumulative effects of three coexisting chlorobenzene congeners on the dechlorination of HCB were ranked as follows: 1,2,4-TCB > 1,2,4,5-TeCB > PeCB.

The kinetic reaction of anaerobic microbial chloerobenzenes degradation in contaminated soil

The kinetic reactions of hexachlorobenzene (HCB) and coexisting chlorobenzene congeners in real HCB-contaminated soil and effects of environmental factors on degradation rate, such as solid-liquid ratio, pH and incubation temperatures, were investigated. The Monod model was adopted for the kinetic study and the related kinetic parameters were evaluated. The Monod model showed good fitness for HCB degradation, not for coexisting chlorobenzene congeners. For pentachlorobenzene (PeCB), 1,2,4,5-tetrachlorobenzene(1,2,4,5-TeCB) and 1,2,4-trichlorobenzene(1,2,4-TCB), the calculated value of average degradation rate may not be “positive” or “negative” invariably, depending on production and degradation of these halogenated organic compounds. For HCB, a maximum degradation rate constant of 0.0359 d−1 and half-life time of 19.3 d were achieved, respectively. The hydrogen ion played the most important role in degradation of four chlorobenzenes. However, this role could be weakened if the solubility of compound was considered. Also, the results showed that the initial weak acid to neutral pH (5 – 7) environment with the incubation temperature of 45 °C was favorable for the rapid kinetic degradation of chlorobenzenes and the removal of chlorobenzenes was evaluated to reach 46%. This study offers direct kinetic behaviors and environmental factors analysis of the biodegradation process of HCB and coexisting chlorobenzene congeners, and is beneficial to explored the potential of optimized anaerobic microbial degradation for remediation engineering of chlorobenzenes contained soil.

Transformation of chlorobenzenes to chlorophenols by Mn(III) generated in permanganate/bisulfite process via an electrophilic substitution mechanism

Chlorobenzenes are a group of toxic compounds that have been widely used as intermediates in chemical synthesis, process solvents, pesticides, and hygiene products. In this study, we reported rapid transformation of chlorobenzenes by soluble Mn(III) generated in permanganate/bisulfite (PM/BS) process, which can be taken advantage of in practical treatment of chlorobenzenes. Chlorobenzenes with five or less chlorine atoms could be removed (10–83%) in PM/BS process within 5 s, while the fully chlorinated congener, hexachlorobenzene, could be hardly degraded. The removal efficiency of chlorobenzenes was not significantly impacted by changes in initial solution pH (4.0–8.0). Results of quenching experiments and UV–Vis spectra consistently indicated that Mn(III) was the primary reactive species responsible for the transformation of chlorobenzenes. Based on the degradation products detected for the chlorobenzene congeners, an electrophilic substitution mechanism was proposed, in which Mn(III) acted as a strong electrophile to attack the ortho/para positions on the benzene ring and subsequently transformed chlorobenzenes into more reactive chlorophenols. While most studies attributed the high reactivity of soluble Mn(III) towards organic contaminants to its strong oxidizing power, the findings of this study revealed that Mn(III) could act as a strong electrophilic reagent to initiate the degradation of chlorobenzenes. As PM was more efficient at mineralizing the phenolic products produced from degradation of chlorobenzenes compared to PM/BS and peroxymonosulfate, PM/BS coupled with PM process could be utilized as a fast and effective method for the treatment of chlorobenzenes.

Syntrophic Partners Enhance Growth and Respiratory Dehalogenation of Hexachlorobenzene by Dehalococcoides mccartyi Strain CBDB1.

This study investigated syntrophic interactions between chlorinated benzene respiring Dehalococcoides mccartyi strain CBDB1 and fermenting partners (Desulfovibrio vulgaris, Syntrophobacter fumaroxidans, and Geobacter lovleyi) during hexachlorobenzene respiration. Dechlorination rates in syntrophic co-cultures were enhanced 2-3 fold compared to H2 fed CBDB1 pure cultures (0.23 ± 0.04 μmol Cl− day−1). Syntrophic partners were also able to supply cobalamins to CBDB1, albeit with 3–10 fold lower resultant dechlorination activity compared to cultures receiving exogenous cyanocobalamin. Strain CBDB1 pure cultures accumulated ~1 μmol of carbon monoxide per 87.5 μmol Cl− released during hexachlorobenzene respiration resulting in decreases in dechlorination activity. The syntrophic partners investigated were shown to consume carbon monoxide generated by CBDB1, thus relieving carbon monoxide autotoxicity. Accumulation of lesser chlorinated chlorobenzene congeners (1,3- and 1,4-dichlorobenzene and 1,3,5-trichlorobenzene) also inhibited dechlorination activity and their removal from the headspace through adsorption to granular activated carbon was shown to restore activity. Proteomic analysis revealed co-culturing strain CBDB1 with Geobacter lovleyi upregulated CBDB1 genes associated with reductive dehalogenases, hydrogenases, formate dehydrogenase, and ribosomal proteins. These data provide insight into CBDB1 ecology and inform strategies for application of CBDB1 in ex situ hexachlorobenzene destruction technologies.

Influence of Degradation Behavior of Coexisting Chlorobenzene Congeners Pentachlorobenzene, 1,2,4,5-Tetrachlorobenzene, and 1,2,4-Trichlorobenzene on the Anaerobic Reductive Dechlorination of Hexachlorobenzene in Dye Plant Contaminated Soil

The degradation of hexachlorobenzene (HCB) is of great concern and attracts considerable scientific and regulatory interests, due to the high toxicity, great bioaccumulation, and persistence of HCB in the environment. However, in the real HCB-contaminated soil, the effect of coexisting chlorobenzene congeners on the degradation capacity of HCB is poorly known. In this work, the anaerobic degradation behaviors of three coexisting chlorobenzene congeners pentachlorobenzene (PeCB), 1,2,4,5-tetrachlorobenzene (1,2,4,5-TeCB), and 1,2,4-trichlorobenzene (1,2,4-TCB) and the influence of initial pH and reaction temperature on the dechlorination of HCB in HCB-contaminated soil from the dye plant were studied. The amount and extent of accumulated coexisting chlorobenzenes was analyzed under different environmental conditions. The results indicate that the concentrations of three coexisting chlorobenzene congeners change in the form of wave. The anaerobic degradation activity of HCB is reduced due to the feedback inhibition caused by accumulation of coexisting chlorobenzene congeners, and the feedback inhibition varies from environmental conditions.

Determination of chlorobenzenes in water samples based on fully automated microextraction by packed sorbent coupled with programmed temperature vaporization–gas chromatography–mass spectrometry

A fully automated method consisting of microextraction by packed sorbent (MEPS) coupled directly to programmed temperature vaporizer-gas chromatography-mass spectrometry (PTV-GC-MS) has been developed to determine the 12 chlorobenzene congeners (chlorobenzene; 1,2-, 1,3-, and 1,4-dichlorobenzene; 1,2,3-, 1,2,4-, and 1,3,5-trichlorobenzene; 1,2,3,4-, 1,2,3,5-, and 1,2,4,5-tetrachlorobenzene; pentachlorobenzene; and hexachlorobenzene) in water samples. The effects of the variables on MEPS extraction, using a C18 sorbent, and the instrumental PTV conditions were studied. The internal standard 1,4-dichlorobenzene d4 was used as a surrogate. The proposed method afforded good reproducibility, with relative standard deviations (RSD %) lower than 12%. The limits of detection varied between 0.0003 μg L(-1) for 1,2,3,4-tetrachlorobenzene and 0.07 μg L(-1) for 1,3- and 1,4-dichlorobenzene, while those of quantification varied between 0.001 μg L(-1) and 0.2 μg L(-1) for the same compounds. Accuracy of the proposed method was confirmed by applying it to the determination of chlorobenzenes in different spiked water samples, including river, reservoir, and effluent wastewater.

Near-Real-Time Combustion Monitoring for PCDD/PCDF Indicators by GC-REMPI-TOFMS

The boiler exit flue gas of a municipal waste combustor was sampled to evaluate an online monitoring system for chlorobenzene congeners as indicators of polychlorinated dibenzodioxin and dibenzofuran (PCDD/PCDF) concentrations. Continuous measurements of chlorobenzene congeners using gas chromatography coupled to a resonance-enhanced multiphoton ionization - time-of-flight mass spectrometry (GC-REMPI-TOFMS) system were compared over 5-min periods with conventional sampling methods for PCDD/PCDF. Three pairs of values were taken every hour over a period of three days to characterize the combustor's response to transient operating conditions (shutdowns and startups). Isolation of specific chlorobenzene congeners from other same-mass compounds was accomplished by using a GC column separator ahead of the REMPI-TOFMS. The 50-fold variation of PCDD/PCDF concentration was paralleled by similar changes in monitored compounds of 1,4-dichlorobenzene, 1,2,4-trichlorobenzene, 1,2,3-trichlorobenzene, and 1,2,4,5-tetrachlorobenzene. A correlation of R = 0.85 and 0.89 was established between 40 pairs of simultaneous 5-min GC-REMPI-TOFMS measurements of 1,2,4-trichlorobenzene and 5 min conventional sampling and analysis for the TEQ and Total measures of PCDD/PCDF, respectively. The GC-REMPI-TOFMS system can be used to provide frequent measures of correlative PCDD/PCDF concentration thereby allowing for an understanding of measures to minimize PCDD/PCDF formation and develop operational feedback to limit emissions.

Distribution of mono- through hexa-chlorobenzenes in floodplain soils and sediments of the Tittabawassee and Saginaw Rivers, Michigan

Chlorobenzenes are used as solvents or as feedstocks in the production of pesticide formulations, dyes, room deodorizers, moth-proofing agents, and de-inking solvents. Chlorobenzenes were produced by the Dow Chemical Company in Midland, Michigan, for several decades. In this study, concentrations of 12 chlorobenzene (CBz) congeners, from mono- to hexachlorobenzenes, were measured in more than 150 floodplain soil (FPS), surface sediment, and sediment core (SC) samples collected during 2002-2004 from the Pine River, Tittabawassee River, Shiawassee River, Saginaw River, and Saginaw Bay, Michigan. Five grams of wet sediment were homogenized with anhydrous sodium sulfate and extracted with 20% dichloromethane/hexane. The extracts were purified by silica gel column chromatography and analyzed by a gas chromatograph interfaced with a mass spectrometer (GC/MS). Mean concentrations of ΣCBz in FPS and surface sediment were seven to 30 times higher in the Tittabawassee River (80 and 60 ng/g dry weight (dw), respectively) than in the Saginaw River (2.4 and 8.1 ng/g dw, respectively) and Saginaw Bay (5.5 and 8.0 ng/g dw, respectively). Concentrations of ΣCBz were low in surface sediment and FPS from locations upstream of Midland, Michigan, on the Tittabawassee River. Concentrations of ΣCBz were higher in FPS than in surface sediment of the Tittabawassee River; on the contrary, surface sediment contained higher concentrations of CBz than FPS from the other rivers studied. High concentrations of hexachlorobenzene were found in FPS of the Tittabawassee River. All CBz congeners, except for dichlorobenzenes (DCBz), showed a trend of spatial decrease with downstream of the Dow Chemical Company in Midland. The CBz congener composition of the samples showed multiple patterns that reflected differences in historical emissions and environmental partitioning, arising from variations in physico-chemical properties of CBz. 1,4-Dichlorobenzene (1,4-DCBz) was found in all of the samples and accounted for a high proportion of total CBz. The relationship between concentrations of CBz and previously reported concentrations of PCDD/Fs for the same set of samples (Kannan et al. 2008) was significant, indicating similarities in sources and depositions of these two classes of compounds in the watershed.

By-Side Chlorobenzenes and Chlorophenols in Technical Chlorobiphenyl Formulations of Aroclor 1268, Chlorofen, Clophen T 64, Kanechlor 600, and Kanechlor 1000

All 19 possible chlorophenol (CPh) and 12 chlorobenzene (CBz) congeners as potential impurities or additive were quantified in a relatively highly chlorinated type of technical chlorobiphenyl (CB) mixtures of Aroclor 1268, Chlorofen, Clophen T 64, Kanechlor 600, and Kanechlor 1000 using isotope dilution technique and HRGC/HRMS. The total CBzs content of Aroclor 1268, Chlorofen and Clophen T 64, Kanechlor 600, and Kanechlor 1000 was 0.039, 0.5, 230, 0.068, and 400 mg/g, respectively, while of CPhs was < 0.007, 0.48, 10, 0.093, and 0.98 μg/g. All 12 congeners of chlorobenzene could be quantified in all the formulations examined, but their proportions varied largely. It seems that stockpiles of technical chlorobiphenyl formulations and hazardous wastes containing CBs, both with added and/or by-side CBzs are also a somehow forgotten source of environmental contamination with those environmentally relevant compounds. No CPhs were found in Aroclor 1268 (< 7 ng/g). 2-MoCPh, 2,6-DiCPh, 3,5-DiCPh, 3,4,5-TrCPh, and 2,3,4,5,6-PeCPh were absent (< 1– < 20 ng/g) in Chlorofen and Clophen T 64, while other chlorophenol congeners were found at concentration from 7.4 to 130 and from 9.9 to 8,800 ng/g, respectively. Then, 3- and 4-chlorophenol, which co-eluted, were main contributors (88%) to the total CPhs content of Clophen T 64, while 2,3,4,6-TeCPh with 27% abundance was a major congener among CPhs in Chlorofen. Then, 2,4,6-TrCPh was the most abundant congener in Kanechlor 600, while 2,4,5-TrCPh was the most abundant congener in Kanechlor 1000.

Dehalorespiration with hexachlorobenzene and pentachlorobenzene by Dehalococcoides sp. strain CBDB1.

The chlororespiring anaerobe Dehalococcoides sp. strain CBDB1 used hexachlorobenzene and pentachlorobenzene as electron acceptors in an energy-conserving process with hydrogen as electron donor. Previous attempts to grow Dehalococcoides sp. strain CBDB1 with hexachlorobenzene or pentachlorobenzene as electron acceptors failed if these compounds were provided as solutions in hexadecane. However, Dehalococcoides sp. strain CBDB1 was able to grow with hexachlorobenzene or pentachlorobenzene when added in crystalline form directly to cultures. Growth of Dehalococcoides sp. strain CBDB1 by dehalorespiration resulted in a growth yield ( Y) of 2.1+/-0.24 g protein/mol Cl(-) released with hexachlorobenzene as electron acceptor; with pentachlorobenzene, the growth yield was 2.9+/-0.15 g/mol Cl(-). Hexachlorobenzene was reductively dechlorinated to pentachlorobenzene, which was converted to a mixture of 1,2,3,5- and 1,2,4,5-tetrachlorobenzene. Formation of 1,2,3,4-tetrachlorobenzene was not detected. The final end-products of hexachlorobenzene and pentachlorobenzene dechlorination were 1,3,5-trichlorobenzene, 1,3- and 1,4-dichlorobenzene, which were formed in a ratio of about 3:2:5. As reported previously, Dehalococcoides sp. strain CBDB1 converted 1,2,3,5-tetrachlorobenzene exclusively to 1,3,5-trichlorobenzene, and 1,2,4,5-tetrachlorobenzene exclusively to 1,2,4-trichlorobenzene. The organism therefore catalyzes two different pathways to dechlorinate highly chlorinated benzenes. In the route leading to 1,3,5-trichlorobenzene, only doubly flanked chlorine substituents were removed, while in the route leading to 1,3-and 1,4-dichlorobenzene via 1,2,4-trichlorobenzene singly flanked chlorine substituents were also removed. Reductive dehalogenase activity measurements using whole cells pregrown with different chlorobenzene congeners as electron acceptors indicated that different reductive dehalogenases might be induced by the different electron acceptors. To our knowledge, this is the first report describing reductive dechlorination of hexachlorobenzene and pentachlorobenzene via dehalorespiration by a pure bacterial culture.

Reductive dehalogenation of chlorobenzene congeners in cell extracts of Dehalococcoides sp. strain CBDB1.

Enzymatic reductive dehalogenation of tri-, tetra-, penta-, and hexachlorobenzenes was demonstrated in cell extracts with low protein concentration (0.5 to 1 micro g of protein/ml) derived from the chlorobenzene-respiring anaerobe Dehalococcoides sp. strain CBDB1. 1,2,3-trichlorobenzene dehalogenase activity was associated with the membrane fraction. Light-reversible inhibition by alkyl iodides indicated the presence of a corrinoid cofactor.

Sources and distribution of chlorobenzenes and hexachlorobutadiene in surficial sediments along the coast of Southwestern Taiwan

The spatial distribution of chlorobenzenes in surficial sediments of the estuaries of major rivers along the coast of southwestern Taiwan was determined. Analytical results from sediment sampling stations indicate that the three outfall fields near Taiwan's largest industrial city, Kaohsiung, exhibit the highest concentrations of chlorobenzenes. More specifically, sediments from Tso-yin outfall field, which receives the wastewater from a very large petrochemical complex, had concentrations of 1,3,5-trichlorobenzene, pentachlorobenzene, hexachlorobenzene and hexachlorobutadiene 2–3 times higher than those from Chon-chou and Da-lin-pu outfall fields. Chlorobenzene congeners in sediments from the three outfall fields correlate closely and most of their correlation coefficients are even higher than those reported for Ise Bay, Japan. Results from undeveloped areas, estuaries of the Da-du, Tso-shui, and Chi-shui Chi, will be of value after the impact of planned industrial expansion development begins.

Application of multivariate statistical analysis to evaluate local sources of chlorobenzene congeners in soil samples

The distribution of tri- thru hexachlorobenzene congeners in the surface soil from five locations in the Niagara Falls/Erie County area of western New York State has been determined. The extract obtained by steam distillation was used directly with minimal additional clean-up steps for GC/MS analysis. Using GC/MS in the selected ion monitoring mode, a detection level of 100 pg/g (100 pptr) of the chlorobenzene congeners was achieved. Application of SIMCA pattern recognition and multiple discriminant analysis showed that the pattern of chlorobenzene congeners in soil samples collected near Love Canal is similar to the patterns found in other areas of Niagara Falls. The sources of these congeners may be nearby industrial plants and combustion sources. The soil samples from the town of Cheektowaga (comparison area) in nearby Erie County exhibit a different pattern of chlorobenzene congeners from the other soil samples.

The behavior of chlorobenzenes in Ise bay, estimated from their concentrations in various environmental media

Field survey of pollutants in various environmental media is indispensable for modeling the behavior of organic compounds discharged into the coastal environment. In this study, the concentrations of chlorobenzenes were measured in Ise Bay where industrial wastewater enters. Some chlorobenzene congeners, 1, 3-dichlorobenzene and 1, 2, 4-trichlorobenzene, were detected in seawater, suspended particulate and bottom sediment samples and their behavior was analyzed. The horizontal distributions showed that these chlorobenzene concentrations in the surface water and sediments were higher in the area near the shore of the industrial area than in the offshore area. The soluble chlorobenzene concentrations in the bottom water were low at all stations. The vertical distribution survey at each sampling site showed that the soluble concentrations were high in the surface water and low in the bottom water, but that those in the suspended particulates and the bottom sediments (dry solid base) had relatively similar concentrations. This indicated that chlorobenzenes in the bottom suspended particulates and in the bottom sediments were not equilibrated with chlorobenzenes in the bottom seawater. This could be explained by the following chlorobenzene behavior: the chlorobenzenes were adsorbed by suspended particulates in the surface water and settled to the bottom swiftly through less polluted seawater in the lower water layer with little desorption. This caused the chlorobenzene concentration gradient in the bottom sediment which reflected the chlorobenzene concentration absorbed by suspended particulates in the surface water. The behavior of chlorobenzenes suggested in this study showed that the use of chemical fate models based on the assumption that the soluble fraction and the fraction adsorbed by suspended particulates are always in equilibrium may yield misleading results.

Organic trace contaminants in St. Lawrence River water and suspended sediments, 1985–1987

The concentrations of organic trace contaminants, including chlorobenzene congeners, hexachlorocyclohexane isomers, DDT group pesticides, polychlorobiphenyls (PCB) and several other biocides, such as mirex, dieldrin and endosulfan, have been determined in water and suspended sediments of the St. Lawrence River. The data cover important areas of the river between Kingston and Quebec City for four sampling periods, i.e. May 1985, October 1985, June/July 1986 and June 1987. The results indicate: (i) low levels of suspended sediments at the head of the river (∼ 1 mgl −1) which increase towards the river mouth to ∼10 mgl −1 (up to 25 mgl −1 in October 1985); (ii) significant inputs of PCB along certain river sections; (iii) low levels of mirex in suspended sediments throughout the river; (iv) the riverine lakes in the St. Lawrence (Lakes St. Francis, St. Louis and St. Pierre) appear to be short-term contaminant sinks only.