Number Of Chlorine Substituents Research Articles

Dioxin-like compounds in paired maternal serum and breast milk under long sampling intervals.

Serum and breast milk are both important biological samples to evaluate body burden of dioxin-like compounds which include polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (dl-PCBs). We collected maternal serum at early pregnancy, and breast milk at 3-8 weeks after delivery from 55 mothers living in Beijing, China, and measured 29 dioxin-like compounds in these samples. The sampling intervals in this study were extended up to 10 months to analyze differences of contents between serum and breast milk under long sampling intervals. The results showed that mean TEq level of PCDD/Fs in serum (9.8pg TEq g-1 lipid) was 1.7 times higher than that in milk (4.5pg TEq g-1 lipid), while the TEq concentrations of dl-PCBs in serum (1.2pg TEq g-1 lipid) was significantly lower than that in milk (2.0pg TEq g-1 lipid). There were only two congeners, OCDD (r=0.32) and PCB105 (r=0.33), the correlations of which between serum and milk were significant. The differences in distributions of congeners in serum and milk might be influenced by number of chlorine substituents and structures of congeners. In addition, maternal age and BMI were positively and negatively correlated with mass concentrations of dioxin-like compounds in milk and serum respectively. These results suggest that, compared with serum, it is limited to use breast milk to assess long-term exposure for the wider population.

Tunable electron transfer rate in a CdSe/ZnS-based complex with different anthraquinone chloride substitutes

We use femtosecond transient absorption spectroscopy to study ultrafast electron transfer (ET) dynamics in a model donor and acceptor system using CdSe/ZnS core/shell structure quantum dots (QDs) as donors and anthraquinone (AQ) molecules as acceptors. The ET rate can be enhanced by decreasing the number of chlorine substituents in the AQ molecules because that increases the driving force, which is the energy level offset between the conduction band energy of CdSe/ZnS and the lowest upper molecular orbital potential of AQ derivatives, as confirmed by cyclic voltammetry measurements. However, the electronic coupling between the QDs and AQ derivatives, and the sum of reorganization energy of AQ molecules and solvent calculated by density functional theory are not the main reasons for the change in ET rate in three systems. Our findings provide new insights into selecting an acceptor molecule and will be useful in tuning ET processes for advanced QD-based applications.

Ascorbic Acid Assisted High Performance Liquid Chromatography Mass Spectrometry Differentiation of Isomeric C-Chloro- and N-Chloro-Tyrosyl Peptides in Water.

We report a new method of ascorbic acid assisted high performance liquid chromatography (HPLC) with high resolution tandem mass spectrometry (HRMS/MS) for the differentiation of isomeric N-chloro (N-Cl) from phenol ring C-chloro (C-Cl) peptides produced during chlorination of water. Using the specific reductive nature of ascorbic acid, we successfully identified the N-Cl isomers and C-Cl isomer, overcoming the difficulty that, due to lack of standards, these isomers cannot be separated by HPLC-HRMS. Using the new approach, we identified 36 new chlorinated products including mono-, di-, tri-, and tetra-Cl-tyrosyl dipeptides in the reaction mixture based on retention time, accurate mass, 35Cl/37Cl isotopic pattern, and characteristic MS/MS fragments. The method was further applied to investigate competitive reactions when mixed tyrosyl dipeptides were chlorinated. Tyrosyl histidine was the most reactive tyrosyl dipeptide in the mixture. The chlorinated products formed are identical when the dipeptides are chlorinated separately or as a mixture. The formation conditions and stability of the chlorinated products were also examined. With increasing chlorine dose, the number of chlorine substituents on the tyrosyl dipeptides increased from products with one/two to three/four Cl atoms. Most of the chlorinated products are stable for up to 9 days. By chlorination of tyrosyl dipeptides spiked into raw water, we projected that chlorinated tyrosyl dipeptides can form during treatment of raw water containing tyrosyl dipeptides even at low μg/L levels. This new method can be utilized for the discovery of a wide range of chlorinated peptide DBPs and the study of their formation and occurrence in water.

Allocyclinones, hyperchlorinated angucyclinones from Actinoallomurus.

A screening program on a limited number of strains belonging to the Actinoallomurus genus yielded a series of new angucyclinones. NMR and MS analyses established that these compounds are characterized by an unusual lactone ring and present up to four halogens per molecule, with one congener representing the first natural product containing a trichloromethyl substitution on an aromatic system. Remarkably, this family of metabolites seems to be produced by phylogenetically distinct Actinoallomurus isolates. Because of the unique structural features and wide distribution among Actinoallomurus, we have designated these angucyclinones as allocyclinones. Allocyclinones possess interesting activity against different Gram-positive bacteria, including antibiotic-resistant strains, with antibacterial potency increasing with the number of chlorine substituents. The tetrachlorinated compound is the most abundant congener in the allocyclinone complex.

Features of polychlorinated biphenyls nitration

Nitration of mono-, di-, and trichlorobiphenyls has been studied. The nitration degree depends on the number of chlorine substituents; one to four nitro groups can be introduced. The conclusions have been confirmed by results of nitration of the “Trikhlorbifenil” technical mixture of polychlorinated biphenyls.

Prediction of Vapor–Liquid Coexistence Properties and Critical Points of Polychlorinated Biphenyls from Monte Carlo Simulations with the TraPPE–EH Force Field

Gibbs ensemble Monte Carlo simulations using the explicit-hydrogen version of the transferable potentials for phase equilibria (TraPPE–EH) force field were carried out to predict the vapor–liquid coexistence and critical properties of biphenyl, monochlorinated biphenyls, and of 16 polychlorinated biphenyls. The predictions are in very good agreement with the limited experimental data. Transferring the TraPPE–EH Lennard-Jones parameters from benzene to construct biphenyl yields predicted critical properties and normal boiling temperature with an average deviation of less than 1 %. The saturated vapor pressures for biphenyl, 2-chorobiphenyl, and 4-chlorobiphenyl fall within 10 % of the experimental data. Overall, the critical temperatures increase nearly linearly with the number of chlorine substituents and are correlated with the dipole moment for the monochlorinated isomers. In contrast, 4,4′-dichlorobiphenyl, the most elongated compound, exhibits the highest critical temperature among the disubstituted biphenyls.

Theoretical Study of the Molecular Geometries, Electronic and Thermodynamic Properties of Chlorinated Dipyrido-(3,2-a:,-c)-Phenazine

Theoretical study of the molecular geometries, electronic and thermodynamic properties of dipyrido-(3,2-a:,-c)-phenazine (dppz) was carried out in the gas phase under standard conditions using PM6 Hamiltonian in semiempirical model. Effects of chlorine substituents on these properties were also investigated. The results showed that all the electronic and thermodynamic properties investigated were affected by the number and relative position of chlorine substituents. Variations in some properties are not significant for some isomeric congeners, having the same number of chlorine substituents, while a number of properties showed general variation with both the number and position of chlorine substituents. Successive addition of one chlorine atom after the other at adjacent position to the last chlorine substituent increases the total energy by 241 eV and decreases the LUMO-HOMO gap by an average value of 0.124 eV. Geometry and energy optimization show that all the molecules considered are planar.

Carbon 1s photoelectron spectroscopy of the chlorinated methanes: Lifetimes and accurate vibrational lineshape models

Construction of accurate lineshape models for chlorosubstituted hydrocarbons is challenging. In this account the problem has been investigated thoroughly for the chloromethane series, CH4−nCln, n=1–4, using high-resolution experimental data and extensive theoretical calculations. The CCl bond contraction following ionization is a key parameter for a quantitative description of the vibrational excitation for all four molecules. We determine this quantity accurately for the title molecules and also propose approximate approaches that may applied to larger molecules. Having developed accurate vibrational lineshape models as well as reliable estimates of the instrumental broadening in each case, the carbon 1s hole lifetime broadening is determined from a fit to the experimental spectrum for each molecule. The resulting values for the lifetime broadening are 88±5meV for CH3Cl, 80±5meV for CH2Cl2, 74±5meV for CHCl3 and 62±5meV for CCl4. The lifetime widths decrease systematically with the number of chlorine substituents and correlate excellently with the valence occupancy of the core-ionized carbon. This indicates that the one-center model for Auger decay of the core hole is valid for the present series of molecules.

Analysis of PCBs degradation abilities of biphenyl dioxygenase derived from Enterobacter sp. LY402 by molecular simulation

Enterobacter sp. LY402 is a bacterium isolated from polluted soil. It can efficiently degrade polychlorinated biphenyls (PCBs) under aerobic conditions. However, the degradation was limited when it comes to high chlorine or double para-substituted PCBs. Biphenyl dioxygenase (BDO) is the key enzyme in the PCBs biodegradation process. It has been confirmed that the α-subunit of the iron-sulfur protein of biphenyl 2,3-dioxygenase (BphA1) directly influenced catalytic activities and substrate specificity. To know the degradation characteristics of BDO to PCBs, we analyzed PCBs degradation abilities of BphA1 from Enterobacter sp. LY402 by experiment and molecular simulation. Firstly, the degradation experiment of PCBs was performed, and the degradation rate constants (k) were calculated. Then the three-dimensional model of LY402-BphA1 was constructed. Through further docking studies with 209 PCB congeners, the PCBs binding abilities of LY402-BphA1 were measured and some crucial active site residues were identified. Moreover, the molecular descriptors of PCBs were calculated and analyzed to determine the correlation of molecular properties and degradation. The results showed that the affinity energy of PCBs was well matched with the k values of the different number of chlorine substituents. The binding ability of BphA1 greatly affected the PCBs degradation abilities of BDO. Hydrophobic contact was the main interaction between the residues of active site and PCB substrates. The number and subposition of chlorine substituents would influence the PCBs binding ability of BphA1 significantly. Ser283, Val287, Gly321 and Tyr384 residues in the active site of LY402-BphA1 showed high variability, and the space limitation of the active site of BphA1 had negative influence on the PCBs binding affinity of BDO. The changes of physical, electronic and geometrical properties could influence degradation and binding affinity of PCBs. Analysis of structural information, binding affinity and influences of molecular properties could be used to direct further modification of BDO to enhance biodegradation of PCBs and other toxic compounds.

Congener Selectivity During Polychlorinated Biphenyls Degradation by Enterobacter sp. LY402

The relationship between the selectivity of a particular polychlorinated biphenyls (PCBs) congener and its biodegradability under the same concentration, especially by Enterobacter sp. LY402, is less well studied. To measure congener selectivity of Enterobacter sp. LY402, several influencing factors were studied. The results showed LY402 effectively degraded coplanar 3,4,3',4'-chlorobiphenyl (CB) at a concentration of 0.05 μM, but not 0.5 μM. The degradation rates of 2,4,5,2',3'-CB and 2,4,5,2',4',5'-CB were increased significantly when the sample constituents were changed from 12 to 5 congeners or to one congener. This indicated that bioremediation of individual congener was affected by other congeners present in the mixture. Moreover, for PCBs containing one chlorine on each phenyl ring, the reactivity preference of LY402 was 2,2'-CB ≥ 3,3'-CB ≫ 4,4'-CB. For two ortho chlorines congeners of PCBs, 2,2'-CB was degraded faster than 2,6-CB. Although 2,6-CB and 4,4'-CB were poorly degraded, the addition of one (i.e., 2,4,4'-CB and 2,6,3'-CB) or two more chlorines (i.e., 2,4,2',4'-CB) on the phenyl ring significantly increased their biodegradability. In addition, comparing the two congeners of ortho-meta-chlorinated biphenyl, 2,3,2',3'-CB with neighbor meta chlorines was degraded slower than 2,5,2',5'-CB with interval meta chlorines. All these indicated that the transformation rates of PCBs were not consistent with the number of chlorines, and PCBs containing the same numbers of chlorines but at different positions also resulted in different conversions. In principle, the extents of effect caused by the position of chlorine substituents on the degradation of PCBs by LY402 were ortho- > meta- > para-CB. In conclusion, the congener selectivity of LY402 was determined by many factors, including the composition of the congeners, their concentrations in the mixture and location and number of chlorine substituents on the phenyl rings.

Si–C coupling reaction of polychloromethanes with HSiCl 3 in the presence of Bu 4PCl: Convenient synthetic method for bis(chlorosilyl)methanes

Coupling reaction of polychloromethanes CH 4− n Cl n ( n = 2–4) with HSiCl 3 in the presence of tetrabutylphosphonium chloride (Bu 4PCl) as a catalyst occurred at temperatures ranging from 30 °C to 150 °C. The reactivity of polychloromethanes increases as the number of chlorine-substituents on the carbon increases. In the reactions of CCl 4 with HSiCl 3, a variety of coupling products such as bis(chlorosilyl)methanes CH 2(SiCl 3)(SiXCl 2) [X = Cl ( 1a), H ( 1b)], (chlorosilyl)trichloromthanes Cl 3CSiXCl 2 [X = Cl ( 2a), H ( 2b)], and (chlorosilyl)dichloromthanes Cl 2HCSiXCl 2 [X = Cl ( 3a), H ( 3b)] were obtained along with reductive dechlorination products such as CHCl 3 and CH 2Cl 2 depending on the reaction temperature. In the reaction of CCl 4, 2a is formed at the initial stage of the coupling reaction and converted to give CHCl 3 at low temperature of 30 °C, to give 1a, 3a, and CHCl 3 at 60 °C, and to afford 1a as major product and CH 2Cl 2 in competition above 100 °C. Si–H bond containing silylmethanes can be formed by the H–Cl exchange reaction with HSiCl 3. Reaction of CHCl 3 with HSiCl 3 took placed at 80 °C to give three compounds 1a, 3a, and CH 2Cl 2, and finally 3a was converted to give 1a and CH 2Cl 2 at longer reaction time. While the condition for the reaction of CH 2Cl 2 with HSiCl 3 required a much higher temperature of 150 °C. Under the optimized conditions for synthesizing bis(chlorosilyl)methanes 1a, b, a mixture of 1a and 1b were obtained as major products in 65% ( 1a: 1b = 64:1) and 47% (42:5) yields from the reaction of CCl 4 and CHCl 3 at 100 °C for 8 h, respectively, and in 41% (34:7) yield from that of CH 2Cl 2 at 170 °C for 12 h. In the Si–C coupling reaction of polychloromethanes with HSiCl 3, it seems likely that a trichlorosilyl anion generated from the reaction of HSiCl 3 with Bu 4PCl is an important key intermediate.

Using QSPR Models to Predict the Enthalpy of Vaporization of 209 Polychlorinated Biphenyl Congeners

AbstractQuantitative Structure–Property Relationship (QSPR) models to correlate the vaporization enthalpies (ΔvapHm) of a set containing biphenyl and 16/26 Polychlorinated Biphenyls (PCBs) with their conceptual Density Functional Theory (DFT)‐based global reactivity parameter such as electrophilicity index (ω) along with the energy of lowest unoccupied molecular orbital (ELUMO) and the number of chlorine substituents (NCl) as descriptors are presented. A good coefficient of determination (r2=0.976/0.858) and internal predictive ability ($\rm{ r_{{\rm{cv}}}^2 }$=0.948/0.758) values are obtained indicating the significance of the considered descriptors in the property analysis. The developed model is used to predict ΔvapHm of the remaining 193/183 PCB congeners.

Simultaneous determination of gaseous and particulate chlorinated polycyclic aromatic hydrocarbons in emissions from the scorching of polyvinylidene chloride film

An analytical method for the determination of gaseous and particulate chlorinated polycyclic aromatic hydrocarbons (ClPAHs) was investigated. By means of this method, concentrations and isomer profiles of the 27 target ClPAHs could be analyzed. To evaluate the usefulness of the method for analyzing ClPAH emissions, laboratory-scale scorching tests were performed on polyvinylidene chloride (PVDC) plastic wrap over a flame of the gas burner. Only seven of the target ClPAHs were detected, and all compounds detected had 2, 3, or 4 rings. The detected ClPAHs were present in both the particulate phase and the gaseous phase, but they were present at higher concentrations in the gaseous phase than in the particulate phase. Relationships between the number of chlorine substituents on the naphthalene/phenanthrene rings and the overall concentration and the percentage in the particulate phase were also investigated.

QSPR models for polychlorinated biphenyls: n-Octanol/water partition coefficient

The logarithmic n-octanol/water partition coefficient (log K ow) is an important property for pharmacology, toxicology and medicinal chemistry. Quantitative structure–property relationship (QSPR) model for the lipophilic behaviour (log K ow) of the data set containing 133 polychlorinated biphenyl (PCB) congeners is analyzed using the conceptual density functional theory based global reactivity parameter such as electrophilicity index ( ω) along with energy of lowest unoccupied molecular orbital ( E LUMO) and number of chlorine substituents ( N Cl) as descriptors. A reasonably good coefficient of determination ( r 2 = 0.914) and the internal predictive ability ( r cv 2 = 0.909 ) values are obtained indicating the significance of the considered descriptors in the property analysis of PCBs. Further, the developed method has widespread applicability from chemical reactivity to toxicity analysis and in studies related to various physicochemical properties in the series of dioxins and other polyaromatic hydrocarbons.

Hydroxyl free radical reactivity toward aqueous chlorinated phenols

Second-order kinetic constants (k(OH,S)) for the hydroxyl free radical attack on a series of nine chlorophenols (2-chlorophenol, 2,4-dichlorophenol, 2,5-dichlorophenol, 2,4,5-trichlorophenol, 2,4,6-trichlorophenol, 2,3,5,6-tetrachlorophenol, 2,3,4,5-tetrachlorophenol, 2,3,4,6-tetrachlorophenol, and pentachlorophenol) in aqueous solution were determined by means of the competitive kinetics method. Experimental values ranged from 3.5 x 10(09)M(-1)s(-1) for pentachlorophenol to 8.2 x 10(09)M(-1)s(-1) for 2-chlorophenol. A general trend of lower kinetic constant values with higher degree of chlorination was observed and tested with four different correlations using Hammett's sigma values, the number of chlorine substituents on the aromatic ring, and estimated diffusion coefficients. These correlations were statistically significant (alpha=0.01), although the regression coefficients were moderate (R(2)<0.6). Statistical analysis indicated that all correlations were equally valid. This report includes second-order kinetic constants not previously reported for six chlorophenols, and also provides the means to estimate constants for other chlorophenols for which no experimental data are available.

Quadrupole mass spectrometer operating in the electron-capture negative ion mode as detector for comprehensive two-dimensional gas chromatography

A recently introduced rapid-scanning quadrupole mass spectrometer (qMS) with an electron-capture negative ion (ECNI) option, the Perkin-Elmer Clarus 500, was tested as a detector for comprehensive two-dimensional gas chromatography (GC × GC). The parameters influencing the data acquisition rate in the scan mode, such as scan time and inter-scan delay, and in the selected ion monitoring mode, such as dwell time and inter-channel delay, were evaluated. In the scan mode, good-quality mass spectra covering a range of 300 Da can be obtained at an acquisition rate of 23 Hz; in selected ion monitoring, an acquisition rate of 90 Hz can be achieved when monitoring a single ion. Compared with electron ionisation, the use of electron-capture negative ionisation causes no extra peak broadening. As applications, mixtures of polychlorinated n-alkanes (PCAs), polybrominated diphenyl ethers (PBDEs) and polychlorinated dibenzo- p-dioxins (PCDDs) and dibenzofurans (PCDFs) were analysed. The separation of PCAs based on their number of chlorine substituents was confirmed for the first time by using GC × GC–ECNI qMS in the scan mode and a significantly improved limit of detection was achieved for BDEs (10–150 fg injected) and CDD/Fs (10–700 fg injected) in the selected ion monitoring mode.

Reductive dechlorination of weathered Aroclor 1260 during anaerobic biotreatment of Arctic soils.

We investigated the microbial reductive dechlorination of both weathered (aged) and nonweathered (freshly added) Aroclor 1260 in aerobic soil from Resolution Island, Nunavut, Canada. Initial polychlorinated biphenyl (PCB) concentrations were 106 and 100 ppm, respectively. The aerobic soil samples were inoculated with anaerobic sediment, incubated at 30 degrees C until methanogenic, inoculated with a dechlorinating enrichment culture, and incubated a further 8 weeks. The average number of chlorine substituents per biphenyl molecule was biologically reduced from 6.6 to 5.1 and from 6.2 to 4.5 for weathered and nonweathered Aroclor 1260, respectively. Removal of hexa- and heptachlorobiphenyls (CBs), the major homolog groups present, was significantly greater for nonweathered than for weathered Aroclor 1260. Formation of dechlorination products, primarily 2,2',4,4'- and 2,2',4,6'-tetraCBs, was also significantly greater for nonweathered than for weathered Aroclor 1260. We additionally compared the dechlorination at 21 degrees C of weathered Aroclor 1260 in soils from Resolution Island and Saglek, Labrador, Canada. The average number of chlorine substituents per biphenyl molecule was biologically reduced from 6.7 to 5.1 and from 6.5 to 4.6, respectively. This study demonstrated the potential for bioremediation of aerobic soil contaminated with Aroclor 1260 and showed that weathering may limit such treatment to an extent variable among different soils.

High-resolution separation of polychlorinated biphenyls by comprehensive two-dimensional gas chromatography

Comprehensive two-dimensional gas chromatography (GC×GC) with micro electron-capture detection (μECD) has been optimised for the separation of polychlorinated biphenyl congeners with emphasis on the separation of 12 toxic non- and mono- ortho chlorinated biphenyls (CBs), viz. CBs 77, 81, 105, 114, 118, 123, 126, 156, 157, 167, 169 and 189. The selection of the first- and second-dimension columns and the temperature programme optimisation were carried out with a mixture of 90 CBs and the results are compared with those of one-dimensional GC. A complete separation of all 12 priority CBs was obtained with two column combinations, HP-1–HT-8 and HP-1–SupelcoWax-10. With the HP-1–HT-8 column set, ordered structures show up in the two-dimensional plane, with the number of chlorine substituents and their position ( ortho vs. non- ortho) being the main parameters of interest. This can help with congener identification. Estimated detection limits are excellent, i.e. about 10 fg. To illustrate the potential and the versatility of GC×GC–μECD, a cod liver extract and a standard mixture of the 17 most toxic polychlorinated dibenzo- p-dioxins and polychlorinated dibenzofurans together with 90 CBs were analysed as an application.

Purification and Characterization of Glutathione Conjugate Reductase: A Component of the Tetrachlorohydroquinone Reductive Dehalogenase System from Phanerochaete chrysosporium

A membrane-bound glutathione S-transferase and a soluble glutathione conjugate reductase constitute the reductive dehalogenase system of P. chrysosporium. This enzyme system reductively removes chlorine substituents from tetrachlorohydroquinone, a metabolite of pentachlorophenol. The membrane-bound glutathione S-transferase converts tetrachlorohydroquinone to S-glutathionyltrichloro-1,4-hydroquinone, which is subsequently reduced to 3,5,6-trichlorohydroquinone by the soluble glutathione conjugate reductase (GCR). This GCR can accept glutathione, dithiothreitol, cysteine, or β-mercaptoethanol as cosubstrates. GCR was purified to apparent homogeneity by ion-exchange and covalent chromatography. The enzyme exhibits optimum activity at pH 6.0 and 55°C and appears to be a homodimer with a Mr of ∼60 kDa. Activity increases as the number of chlorine substituents on the hydroquinone ring is increased. GCR has an apparent Km of ∼33 μM and an apparent kcat of ∼3.43 s−1 for 2-S-glutathionyl-3,5,6-trichloro-1,4-hydroquinone. Inhibitors of GCR include Cd2+, Fe2+, Mn2+, iodoacetic acid, and p-chloromercuribenzoic acid, suggesting the presence of a catalytic cysteine thiol(s) at the active site. When glutathione is used as a cosubstrate, reduction of S-glutathionyltrichloro-1,4-hydroquinone is accompanied by the production of trichlorohydroquinone and oxidized glutathione in a 1:1 ratio. A mechanism for this novel enzyme is proposed.

Influence of chlorine substituents on rates of oxidation of chlorinated biphenyls by the biphenyl dioxygenase of Burkholderia sp. strain LB400.

Biphenyl dioxygenase from Burkholderia (Pseudomonas) sp. strain LB400 catalyzes the first reaction of a pathway for the degradation of biphenyl and a broad range of chlorinated biphenyls (CBs). The effect of chlorine substituents on catalysis was determined by measuring the specific activity of the enzyme with biphenyl and 18 congeners. The catalytic oxygenase component was purified and incubated with individual CBs in the presence of electron transport proteins and cofactors that were required for enzyme activity. The rate of depletion of biphenyl from the assay mixture and the rate of formation of cis-biphenyl 2,3-dihydrodiol, the oxidation product, were almost equal, indicating that the assay accurately measured enzyme-specific activity. Four classes of CBs were defined based on their oxidation rates. Class I contained 3-CB and 2,5-CB, which gave rates that were approximately twice that of biphenyl. Class II contained 2,5,3',4'-CB, 2,3,2',5'-CB, 2,3,4,5-CB, 2,3,2',3'-CB, 2,4, 5,2',5'-CB, 2,5,3'-CB, 2,5,4'-CB, 2-CB, and 3,4,5-CB, which gave rates that ranged from 97 to 35% of the biphenyl rate. Class III contained only 2,3,4,2',5'-CB, which gave a rate that was 4% of the biphenyl rate. Class IV contained 2,4,4'-CB, 2,4,2',4'-CB, 3,4,5, 2'-CB, 3,4,5,3'-CB, 3,5,3',5'-CB, and 3,4,5,2',5'-CB, which showed no detectable depletion. Rates were not significantly correlated with the aqueous solubilities of the CBs or the number of chlorine substituents on the rings. Oxidation products were detected for all class I, II, and III congeners and were identified as chlorinated cis-dihydrodiols for classes I and II. The specificity of biphenyl dioxygenase for the CBs examined in this study was determined by the relative positions of the chlorine substituents on the aromatic rings rather than the number of chlorine substituents on the rings.