Number Of Chlorine Atoms Research Articles

Reductive removal of chloroacetic acids by catalytic hydrodechlorination over Pd/ZrO2 catalysts

Chloroacetic acids are common disinfection byproducts in drinking water and are of significant concern due to their strong carcinogenic, mutagenic and hepatotoxic effects. In the present study, the catalytic hydrodechlorination of chloroacetic acids (monochloroacetic acid, dichloroacetic acid and trichloroacetic acid) was investigated over supported Pd catalysts on SiO2, ZrO2, and activated carbon (AC) prepared by the impregnation method (denoted as im-Pd/support) and/or the deposition-precipitation method (denoted as dp-Pd/support). The catalysts were characterized by X-ray diffraction, transmission electron microscopy, measurement of point of zero charge, N2 adsorption–desorption isotherm, H2 chemisorption, and X-ray photoelectron spectroscopy. Characterization results showed that the points of zero charge of the supports varied. In contrast to im-Pd/ZrO2, strong metal–support interaction was identified in dp-Pd/ZrO2. Accordingly, im-Pd/ZrO2 was found to be more active than im-Pd/AC and im-Pd/SiO2, and dp-Pd/ZrO2 exhibited higher catalytic activity than im-Pd/ZrO2. Complete dechlorination of chloroacetic acids to acetic acid could be achieved on dp-Pd/ZrO2 within 120min of hydrodechlorination. The hydrodechlorination rate constants of trichloroacetic acid, dichloroacetic acid, and monochloroacetic acid over dp-Pd(1.74)/ZrO2 were 0.22, 0.16, and 0.044min−1, respectively, reflecting an increase in dechlorination activity with increasing number of chlorine atoms in chloroacetic acids. It was further demonstrated that the catalytic hydrodechlorination was accomplished via a combined stepwise and concerted pathway for both trichloroacetic acid and dichloroacetic acid.

Statistical properties of spectra of chloronaphthalenes

We introduce spectral density distribution moments as molecular descriptors. We demonstrate that these descriptors correctly represent the molecular structure. To prove the correctness of the new descriptors, we consider the IR spectra of 76 chloronaphthalenes. We show that the consecutive substitutions of the hydrogen atoms by the chlorine atoms are reflected by a regular behavior of the descriptors and, consequently, that the descriptors may be used to construct classification diagrams. The diagrams allow for a clear distinction between the compounds containing different numbers of the substituents. In the diagrams, symbols corresponding to the isomers with a given number of chlorine atoms nearly overlap and form clusters. The clusters corresponding to different numbers of chlorine atoms are well separated and distributed in a regular way. The same kind of analysis we also use as a tool for checking the correctness of the calculated spectra.

Sulfate radical-induced degradation of 2,4,6-trichlorophenol: A de novo formation of chlorinated compounds

The degradation of 2,4,6-trichlorophenol (TCP) by sulfate radical generated via Co(II)-mediated activation of peroxymonosulfate (PMS) was examined. The influencing factors, such as substrate concentration and pH were investigated. The initial pH and its adjustment orders significantly affected the TCP degradation and mineralization. Several chlorinated products were detected, as well as some carboxylic acids, such as glycolic acid and oxalic acid. Many polychlorinated (chlorine atom number ⩾3) aromatics (e.g. 2,4,5-trichlorophenol, 2,3,4,6-tetrachlorophenol, 2,3,5,6-tetrachloro-1,4-benzenediol) and even their ring-opening products (e.g. 2,4-dichloro-5-oxo-2-hexenedioic acid, 1,1,3,3-tetrachloro-2-propanone) were identified, indicating a de novo formation mechanism of organohalogens may be involved in TCP degradation. The released chlorine atoms from TCP and/or dichloride radicals activated by sulfate radicals played an important role. This finding may have significant scientific and technical implications for utilizing Co/PMS reagent to detoxify chlorinated pollutants.

Identification of Sulfated Metabolites of 4-Chlorobiphenyl (PCB3) in the Serum and Urine of Male Rats

Polychlorinated biphenyls (PCBs) are legacy pollutants that exert toxicities through various mechanisms. In recent years exposure to PCBs via inhalation has been recognized as a hazard. Those PCBs with lower numbers of chlorine atoms (LC-PCBs) are semivolatile and have been reported in urban air, as well as in the indoor air of older buildings. LC-PCBs are bioactivated to phenols and further to quinone electrophiles with genotoxic/carcinogenic potential. We hypothesized that phenolic LC-PCBs are subject to conjugation and excretion in the urine. PCB3, often present in high concentrations in air, is a prototypical congener for the study of the metabolism and toxicity of LC-PCBs. Our objective was to identify metabolites of PCB3 in urine that could be potentially employed in the estimation of exposure to LC-PCBs. Male Sprague-Dawley rats (150-175 g) were housed in metabolism cages and received a single intraperitoneal injection of 600 μmol/kg body weight of PCB3. Urine was collected every 4 h; rats were euthanized at 36 h; and serum was collected. LC/MS analysis of urine before and after incubation with β-glucuronidase and sulfatase showed that sulfate conjugates were in higher concentrations than glucuronide conjugates and free phenolic forms. At least two major metabolites and two minor metabolites were identified in urine that could be attributed to mercapturic acid metabolites of PCB3. Quantitation by authentic standards confirmed that approximately 3% of the dose was excreted in the urine as sulfates over 36 h, with peak excretion occurring at 10-20 h after exposure. The major metabolites were 4'PCB3sulfate, 3'PCB3 sulfate, 2'PCB3 sulfate, and presumably a catechol sulfate. The serum concentration of 4'PCB3 sulfate was 6.18 ± 2.16 μg/mL. This is the first report that sulfated metabolites of PCBs are formed in vivo. These findings suggest a prospective approach for exposure assessment of LC-PCBs by analysis of phase II metabolites in urine.

Improvement of aquatic pollutant partition coefficient correlations using 1D molecular descriptors — chlorobenzene case study

AbstractPartition coefficients between environmental compartments are essential parameters in any predictive models on pollutants’ fate in various emission scenarios. When sufficient experimental data are not available, empirical algebraic models are capable of predicting the pollutant partitioning characteristics based on bulk physico-chemical properties or various molecular structural features. When the use of sophisticated rules based on detailed 2D–3D molecular descriptors is not available as a quick option, inexpensive, simple correlations based solely on octanol-1-ol (octanol)-water partition coefficients (K ow) are extensively employed. The present study investigates enhancing the adequacy of such hydrophobicity-based models by adding simple 1D descriptors, readily identifiable by inspecting the substance structure (i.e. the number of chlorine atoms bound to aromatic rings, or the number of aromatic 5- or 6-atom rings, etc.), in addition to the pollutant’s solubility in water. Exemplification is made for predicting the water-biota (fish)-sediment partition coefficients for chlorobenzenes (CBz).

Polychlorinated biphenyl quinone metabolites lead to oxidative stress in HepG2 cells and the protective role of dihydrolipoic acid

Parent polychlorinated biphenyls (PCBs) have been shown to induce cellular oxidative stress. However, the effects of PCB active metabolites have not been extensively investigated. Parent PCBs are first converted to hydroquinone metabolites via cytochrome P-450-catalyzed hydroxylation, and the hydroquinone metabolites are then further oxidized into the corresponding quinone metabolites. Quinones are responsible for a wide range of toxic effects because of their high reactivity. Previous studies have suggested that reactive oxygen species (ROS) play important roles in multiple toxic mechanisms. In this context, the present study was undertaken to investigate oxidative stress resulting from treatment with PCB quinones in HepG2 cells. The protective effects resulting from co-administration of dihydrolipoic acid (DH-LA) were also investigated. We have found that exposure to PCB quinones leads to: (1) a decrease in cell viability; (2) an increase in both the total ROS production and superoxide production; (3) only 3Cl-PCBQ caused significant increase in the thiobarbituric acid reactive substances (TBARS) level; (4) an increase in SOD activity and a decrease in catalase activity; and (5) a decrease in GST activity and GSH level. We have also found that quinones possessing a higher number of chlorine atoms on the quinone ring display a greater activity and that DH-LA is an effective protective agent as it diminishes PCB quinone-induced cellular oxidative stress.

Abstract P047: Circulating Levels of the DDT Metabolite p,p'-DDE are Related to Prevalent Hypertension in the Elderly

Background: Exposure to PCBs and dioxin to experimental animals increase blood pressure. We therefore investigated if circulating levels of persistent organic pollutants (POPs) were related to hypertension in a population-based sample. Methods: 1016 subjects aged 70 years were investigated in the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study. Hypertension was defined as either use of antihypertensive treatment or blood pressure > 140/90 mmHg. Twenty-one different POPs, including 16 PCBs, three pesticides (HCB, DDE and TNK), one dioxin (OCDD) and one brominated compound (BDE47) were analyzed by high-resolution chromatography coupled to high-resolution mass spectrometry (HRGC/ HRMS) at age 70. Results: 732 subjects (72%) showed hypertension. When the POPs were treated as continuous variables and adjusted for gender only, several of the PCBs with a low number of chlorine atoms (PCB74, 99, 105, 118 and 138) were related to prevalent hypertension. Also the OC pesticides, HCB, TNK, pp-DDE, and the brominated compound BDE47 were related to hypertension. The strongest of these associations were seen for pp-DDE (OR 1.35 for a SD change, 95%CI 1.17-1.56, p<0.0001). Following further adjustment for serum cholesterol and triglycerides, BMI, smoking, education and exercise habits, only pp-DDE was still significant (OR 1.23 for a SD change, 95%CI 1.06- 1.43, p=0.006). Conclusion: In this cross-sectional analysis of an elderly population, high levels of circulating levels of pp-DDE were associated with prevalent hypertension, further strengthening the experimental findings that POPs might influence blood pressure.

Determination of Half-wave Potentials of Selected Chlorophenols

Cyclic voltammetry was used in cetyltrimethylammonium bromide (CTAB) micellar solution to determine the half-wave potentials of selected chlorophenols, CPs. It is observed that all the electrochemical parameters of the studied CPs decrease with an increase in the number of chlorine atom(s) attached to the parent compound. The mathematical relationship between the obtained E 1/2 and the number of chlorine atoms in the parent compound is given. The formal potentials, E 0' , of the CPs are approximated

New route to 1,1-difluoro-5-methylquasisilatrane

A new route to 1,1-difluoro-5-methylquasisilatrane (N→Si) F2Si(OCH2CH2)2NMe is elaborated: the reaction of chlorinated methyltrifluorosilanes F3SiCH3−nCln (n = 1–3) as well as trifluoro(3-chloropropyl) silane and trifluoro(propenyl)silane with N-methyl-bis(2-hydroxyethyl)amine. The reactivity of the silanes F3SiCH3−nCln increases with the number of chlorine atoms, that is, with the electronegativity of the CH3−nCln group.

Quantification of the adsorption of phenolic compounds on the geotextile and bentonite components of four geosynthetic clay liners

ABSTRACT: The aim of this paper is to present the experimental results obtained regarding the adsorption on various constitutive geotextiles and bentonites of geosynthetic clay liners of phenol, o-cresol, p-cresol, 2-chlorophenol, 4-chlorophenol, 2,4-dimethylphenol, 3,4-dimethylphenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol, 2,3,5,6-tetrachlorophenol, pentachlorophenol, and bisphenol A. These contaminants, including certain derivatives of halogenated phenols, are known to be toxic even at very low concentrations. Geotextiles and bentonites were sampled from four geosynthetic clay liners (GCLs) representative of the GCLs commonly used in bottom liner systems in France. Adsorption was studied through batch adsorption tests. The effect of the nature of the bentonite (sodium versus calcium activated) was studied. Results obtained in this study show that, contrary to what has been observed for volatile organic compounds (VOCs), the adsorption isotherms are non-linear. For VOCs, linear adsorption isotherms are obtained both for geotextiles and for bentonites. The contrast between the adsorption on geotextiles and bentonites is smaller than for VOCs. Up to two orders of magnitude difference can be obtained between the low adsorption coefficient for bentonite as compared with the large adsorption coefficient for geotextiles when adsorption of VOCs is considered. For phenolic compounds, the adsorption coefficients are of the same order of magnitude for bentonite and geotextiles. Two different trends were observed for woven and nonwoven needle-punched geotextiles as regards the adsorption parameters measured. For chlorophenols, polarity appears to affect adsorption: the adsorption coefficients increased with increasing number of chlorine atoms.

Biological responses of maize (Zea mays) plants exposed to chlorobenzenes. Case study of monochloro-, 1,4-dichloro- and 1,2,4-trichloro-benzenes

A 7-day-exposure time experiment was designed to investigate the phytotoxicity of chlorobenzenes (CBs) on Zea mays seedlings, focusing on the growth and generation of oxidative stress. Significant growth inhibition (based on biomass gain) was observed for exposure to monochlorobenzene (MCB), dichlorobenzene (DCB) and trichlorobenzene (TCB) concentrations higher than 10 mg l(-1). It would seem that CBs inhibit cell division, since the mitotic index decreased for roots exposed to DCB at 80 mg l(-1) dose (8%) and to all the TCB concentrations tested (20% inhibition). CBs exposure resulting in an increase in the oxidative stress response in maize seedlings [reactive oxygen species like H(2)O(2), antioxidant enzymes (POD, GR), lipid peroxidation] correlated to the compound's degree of chlorination, where damage increasing with the number of chlorine atoms (MCB < DCB < TCB). This biological response was also dependent on the dose-exposure. Z. mays exposed to CBs at concentrations <10 mg l(-1) did not induce sufficient oxidative damage to cause root cell death. Therefore, CBs at current environmental concentrations are unlikely to produce evident phytotoxic effects on Z. mays seedlings.

Electrochemical Behaviors of Chlorophenol Aqueous Solutions at Boron-Doped Diamond Electrode

The electrochemical behaviors of different chlorophenols at boron-doped diamond thin film electrode were investigated. Four chlorophenols, the 2-chlorophenol (2-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6- TCP) and pentachlorophenol (PCP), with various number of chlorine atoms in the benzene rings, were studied by using cyclic voltammetry at different scan rates over the potential range of -1 V to 2.5 V (vs MSE). The results indicated that the reactions of the 2-CP, 2,4-DCP and 2,4,6-TCP at the diamond electrode are irreversible and controlled by diffusion, and the irreversible trend increases with the decrease of the chlorine atom number in the benzene ring. However, the activity of the boron-doped diamond film electrode does not depend on the number of the chlorine atom. Different from the three chlorophenols, fouling of the electrode occurs in PCP solutions. The possible electro-oxidation mechanisms are discussed for different chlorophenols.

Correlations of fish intake and plasma docosahexaenoic acid levels with each congener of PCDDs/PCDFs/dioxin-like PCBs in blood from the Japanese population

The purpose of the present study was to investigate the factors associated with blood levels of each congener of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and dioxin-like polychlorinated biphenyls (DL-PCBs) in the Japanese population. A cross-sectional study was performed on 1,656 subjects (755 men and 901 women) aged 15-73years, who were living in 90 different areas of 30 prefectures in Japan. Blood levels of 29 PCDD, PCDF, and DL-PCB congeners were determined by high-resolution gas chromatography/mass spectrometry. In addition, a questionnaire survey on life style, including dietary habit, was carried out. The median total toxicity equivalent (TEQ) was 17 pgTEQ/g lipid. After adjustment for age, sex, body mass index, smoking habit, and consumption of other food groups, six PCDDs/PCDFs with 4-6 substituted chlorine atoms and 10 DL-PCBs, but not HeptaCDD/F or OctaCDD, showed significant positive correlations with the frequency of intake of fish and shellfish. Furthermore, significant positive relationships were also found between plasma levels of docosahexaenoic acid (DHA), a biomarker of fish intake, and 10 PCDDs/PCDFs with 4-6 chlorine atoms and 10 DL-PCBs. The partial correlation coefficients with plasma DHA were significantly higher for DL-PCBs than for PCDDs/PCDFs, and partial correlation coefficients for PCDDs/PCDFs significantly decreased with increasing number of chlorine atoms (Spearman r=-0.80, P=0.001). Blood levels of PCDDs/PCDFs with 4-6 chlorine atoms and DL-PCBs were positively associated with fish intake in the Japanese population. These results may be explained by the higher degree of bioaccumulation of these congeners in fish and shellfish in the ecosystem, and the high consumption of fish among the Japanese population.

Comparison of experimental methods for determination of toxicity and biodegradability of xenobiotic compounds

Different methods for determining the toxicity and biodegradability of hazardous compounds evaluating their susceptibility to biological treatment were studied. Several compounds including chlorophenols and herbicides have been evaluated. Toxicity was analyzed in terms of EC50 and by a simple respirometric procedure based on the OECD Method 209 and by the Microtox® bioassay. The values of EC50 obtained from respirometry were in all the cases higher than those from the Microtox® test. The respirometric inhibition values of chlorophenols were related well with the number of chlorine atoms and their position in the aromatic ring. In general, herbicides showed lower inhibition, being alachlor the less toxic from this criterion. For determination of biodegradability an easier and faster alternative to the OECD Method 301, with a higher biomass to substrate ratio is proposed. When this test was negative, the Zahn-Wellens one was performed in order to evaluate the inherent biodegradability. In the fast test of biodegradability, 4-chlorocatechol and 4-chlorophenol showed a complete biodegradation by an unacclimated sludge upon 48 h. These results together with their low respirometric inhibition, allow concluding that these compounds could be conveniently removed in a WWTP. Alachlor, 2,4-dichlorophenol, 2,4,6-trichlorophenol and MCPA showed a partial biodegradation upon 28 days by the Zahn-Wellens inherent biodegradability test.

Sampling device optimization for organochlorine pesticides

In this study, miniature sampling devices consisting of a polymeric bag filled with organic solvent were exposed to an aqueous solution containing organochlorine pesticides in environmental relevant concentration. The relative amount of contaminant accumulated from the water column was compared with respect to the following chemical and physical properties of the contaminant: the relative molecular length, the degree of chlorination, and the Henry’s law constant. The solvent/membrane systems accumulated contaminants to high levels and readily approached equilibrium fast. The polypropylene system was more universal in contaminant uptake. The membrane concentration factors (MCFs) calculated ranged from null to 1446 and were less than the biological concentration factors (BCFs) reported in literature due to the complex nature of biological systems. Dieldrin, the only oxygenated compound in the study did not follow a linear regression when the log MCF was plotted against the physical properties of the contaminant. The study showed a linear relationship of at least 4 orders of magnitude between the concentration of the contaminants accumulated by the devices and the original concentrations in the aqueous phase. The number of chlorine atoms, the molecules’ relative molecular length, and Henry’s law constant affect the equilibrium concentrations of the contaminant in the sampling device. © 2010 International Formulae Group. All rights reserved. Keywords: Sampling, membrane, polymeric, uptake, contaminants, equilibrium

Luminescence of meso-pyrimidinylcorroles: relationship with substitution pattern and heavy atom effects

The luminescence properties of a series of corroles containing multiple meso-pyrimidinyl groups have been studied. In particular, nine corroles containing two pyrimidinyl moieties, four corroles containing three pyrimidinyl groups and one corrole carrying a single pyrimidinyl substituent have been investigated, and their properties have been compared with some model species. The results indicate that the energy of the emissive π-π* corrole-core-based state is not significantly perturbed by the various substituents, whereas the emission lifetimes and quantum yields depend on the number of appended meso-dichloropyrimidinyl substituents. In particular, both emission lifetime and quantum yield decrease with increasing the number of meso-dichloropyrimidinyl substituents, whereas pyrimidinyl substituents which do not carry further electron withdrawing groups such as the chlorine atoms do not affect the corrole emission properties. Two hypotheses are taken into consideration to rationalize the results: (i) the presence of meso-dichloropyrimidinyl substituents could introduce low-lying CT states which mix with the corrole π-π* emissive level, so reducing emission efficiency; (ii) the ortho,ortho'-chlorine groups of the meso-pyrimidinyl substituents, which lie in the proximity of the corrole macrocycle, can increase the intersystem crossing rate constant of the corrole-based fluorescent state via the heavy-atom effect. A comparison of the results of the studied corrole compounds with formerly investigated species and the linear dependence of the radiationless decay rate constants and emission quantum yields on the squared spin-orbit coupling constants, calculated considering the number of chlorine atoms in ortho-position of the corrole meso-substituents, suggest that hypothesis (ii) is most likely the valid one. These results are of particular interest for the design of (a) corrole compounds featuring highly efficient triplet formation and (b) multicomponent systems containing photo-active corrole subunits and pyrimidinyl spacers.

Cyclic Voltammograms of Chlorophenol Oxidation on Boron-Doped Diamond Electrode

The electrochemical behaviors of several chlorophenols were investigated on boron-doped diamond thin film electrode. 2-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol and pentachlorophenol solutions were prepared as the electrolyte. Such four chlorophenols with various number of chlorine atoms in the benzene ring were studied by cyclic voltammetry at different scan rates between –1V to 2.5V (vs. MSE). The results indicated that the reactions of the 2-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol at the diamond electrode are irreversible and under diffusion control. The irreversible trend increases as the number of the chlorine atoms decreases. However, the activity of the boron-doped diamond film electrode is not affected by the number of the chlorine atom. Different from the three chlorophenols, fouling of the electrode appears in pentachlorophenol solutions.

The stability of the 105[Rh(16S4diol)Cl2]+ radiopharmaceutical precursor in solutions containing human plasma thiols

105Rh[1,5,9,13-tetrathiacyclohexadecane-3,11-diol] is a promising drug precursor for targeted radiotherapy. Nevertheless, the axial position of chloride ions in the complex structure and their weak binding to rhodium centre, due to HSAB concept, make such a complex subject to modifying action of certain sulphuric ligands, like human plasma thiol antioxidants: glutathione and cysteine. Experiments were performed with both radioactive 105Rh and inactive rhodium. The complexation of rhodium with 1,5,9,13-tetrathiacyclohexadecane-3,11-diol (16S4diol) resulted in three distinct peaks seen on UV, radiometric and MS chromatograms. The substitution of chlorides was noted in over 80% of 105[Rh(16S4diol)Cl2]+ units after incubation with glutathione, and less than 10% of complex units after incubation with cysteine (24 h, 37 °C). Reaction of 105[Rh(16S4diol)Cl2]+ with 1,8-octandithiol and 1,9-nonandithiol resulted in disappearance of the complex peak and occurrence of two new peaks. Product of RhCl3 and 16S4diol reaction is a mixture of three distinct forms having different number of chlorine atoms. Our in vitro experiments suggest that the substitution of axial chlorides with glutathione and cysteine might also occur in vivo in human plasma. Glutathione shows higher reactivity than cysteine in replacement reaction. Axial positions in precursor might be effectively blocked by 1,8-octandithiol and 1,9-nonandithiol.

Comparison of Different Extraction Techniques of Polychlorinated Biphenyls from Sediments Samples

In this work, problems that may occur during determination of trace levels of polychlorinated biphenyls in sediment samples are described. Main error sources are connected with extraction of analytes prior to final determination. During model studies, polychlorinated biphenyls have been extracted from sediment reference material (METRANAL 2) with the use of different solvents (dichloromethane, hexsane, and toluene); the process has been enhanced by mechanical shaking or ultrasounds. Seven selected PCBs (PCB 28, 52, 101, 118, 138, 153, and 180 – according to IUPAC) were determined in extracts samples by GC–MS technique. During the studies, two calculation methods were applied to determine the amount of analytes introduced to the chromatographic column. The first approach assumes that the recovery of PCBs that contained a small amount of chlorine atoms in the molecule is similar to the recovery of 13C12PCB28 standard, whereas compounds with greater number of chlorine atoms in the molecule will be recovered from the sediment similarly to the recovery of 13C12PCB180 standard. The second approach assumes that the recovery of PCB 138 and PCB 153 is similar to the average value of 13C12PCB28 and 13C12PCB180 standards. In the case of shaking assisted extraction, 55–90% PCB recoveries were achieved when toluene was used as a solvent, while 71–86% recovery was achieved when dichloromethane was used. When hexsane was used as solvent, recovery ranged 43–107%. In the case of ultrasounds assisted extraction, PCB recoveries of 50–108% were achieved when toluene was used as solvent, while 44–101% recovery was achieved when dichloromethane was applied. When hexsane was used as solvent, recovery reached 57–95%. Studies have also shown that, when applying different isolation techniques and different solvents, the recovery of applied 13C12PCB28 and 13C12PCB180 standards is different. Recovery of 13C12PCB28 standard was from 5% (for hexane tenfold extraction assisted by shaking) to 57% (for toluene tenfold extraction assisted by shaking). However, recovery of 13C12PCB180 standard was from 9% (for hexane tenfold extraction assisted by shaking) to 82% (for toluene tenfold extraction assisted by shaking). This is due to the differences of their binding to the sludge matrix. Standard with a greater number of chlorine atoms in the molecule (13C12PCB180) is more weakly associated with sediment than 13C12PCB28 standard. In order to improve the accuracy of the results obtained, it is necessary to use labeled PCB compounds.

Behavior of PCDDs/PCDFs in remediation of PCBs-contaminated sediments by thermal desorption

Thermal desorption is an effective method for removing volatile and semivolatile organic matter in contaminated solid remediation. Formation of polychlorinated dibenzo- p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in many polychlorinated biphenyls (PCBs) destruction processes has been reported, but the removal pathways are poorly understood. We therefore investigated the behaviors of PCBs and PCDDs/PCDFs in thermal desorption of PCBs-contaminated sediment and predicted the reaction pathways. Four thermal desorption experiments using PCB-contaminated sediments containing different doses of PCBs were carried out. In all the experiments, decomposition of 48–70% of PCBs was achieved, resulting in formation of PCDFs. Despite the PCBs decomposition levels, toxic equivalencies (TEQs) in the treated and volatilized samples were 2.8–6.3 times and 8.0–10.5 times as high as the TEQs in the initial samples, respectively, indicating increased toxicity after treatment. Further analysis revealed that PCDFs with higher numbers of chlorine atoms are likely to remain in the sediments than those of volatilized PCDFs; this is supported by the positive correlation between the vapor pressures of PCDFs and the ratios of volatilized PCDFs.