Effects of aging on the bioavailability and sorption/desorption behavior of biphenyl in soils.

The effects of aging (soil-chemical contact time) on bioavailability, one of the main variables for determining the persistence of organic chemicals in the environment, is poorly understood. There are few studies that have tested the effects of long-term aging on chemical dynamics in soils and have related these effects to bioavailability tests of these aged compounds. In this study, sorption/desorption behavior of biphenyl (BP) on two soil types (Capac A and Capac B) was evaluated for aging times of 24 hours and 8 months. Then bioavailability experiments of BP on the same soils were performed after aging times of 24 hours to 6 months. Sorption isotherms and desorption kinetic profiles were prepared to analyze changes in uptake and release, respectively, due to aging of BP. Mineralization kinetics of BP to 14CO2 by a strain of Pseudomonas putida was used to assess changes in bioavailability due to aging. Data indicates that there was an increase in sorption with aging time for BP on both soil types. The rate of BP desorption did not much change with increased aging time. The extent of BP mineralization was found to decrease with aging time.

Identification of an unknown beta-agonist in feed by liquid chromatography/bioassay/quadrupole time-of-flight tandem mass spectrometry with accurate mass measurement.

A new approach to the search for residues of unknown growth promoting agents such as anabolic steroids and beta-agonists in feed is presented. Following primary extraction and clean-up, samples are separated using gradient liquid chromatography (LC). The effluent is split towards two identical 96-well fraction collectors and an optional electrospray quadrupole time-of-flight mass spectrometry (QTOFMS) system for accurate mass measurement. One 96-well plate is used for a bioassay (enzyme-immuno assay, receptor assay) and will detect the bioactivity and position of the relevant peak in the chromatogram. The positive well in the second 96-well plate is used for identification by LC/QTOFMS/MS. The value of this LC/bioassay/QTOFMS/MS methodology is highlighted by the finding and structure elucidation of a new beta-agonist in a feed extract.

Spectroscopic study of dinitrophenol herbicide sorption on smectite.

Sorption of two dinitrophenolic herbicides, 4,6-dinitro-o-cresol (DNOC) and 4,6-dinitro-2-sec-butylphenol (DINOSEB) to smectite was studied using FTIR, HPLC, and quantum chemical methods. The high affinity of DNOC and DINOSEB for smectite surfaces was attributed to site-specific interactions with exchangeable cations and nonspecific van der Waals interactions with the siloxane surface. The positions of the nu(asym)(NO) and nu(sym)(NO) vibrational modes were perturbed by the exchangeable cations with similar changes occurring for both alkali and alkaline earth cations as a function of ionic potential. The cation-induced changes to the vibrational bands of the NO2 groups indicate that exchangeable metal cations are coordinated to -NO2 groups. Quantum chemical methods predicted a red-shift of the nu(asym)(NO) band and a corresponding blue-shift of the nu(sym)(NO) modes, as was observed experimentally. The nature of the smectite surface itself did not strongly influence the vibrational modes of sorbed DNOC or DINOSEB on the basis of a comparison of DNOC sorbed to three different smectites (K-SWy-2, K-SAz-1, and K-SHCa-1). FTIR spectra of DNOC and DINOSEB sorbed to a K-SWy-2 smectite were studied quantitatively using a modified form of Beers law. The FTIR-derived sorption isotherm of DNOC sorbed to K-SWy-2 was in good agreement with the isotherm derived from HPLC measurements. The molar absorptivity value of DNOC sorbed to K-SWy-2 smectite was 1.43 x 10(7) cm2/mol in good agreement with literature values for nitroaromatics (average value of 1.72 x 10(7) +/- 0.3 cm2/mol). On the basis of this value, the limit of detection using the FTIR method of approximately 5 microgDNOC g(clay) was determined. These two observations (sorption isotherms and molar absorptivity) provide a direct link between the macroscopic sorption results and the FTIR spectra.

Mechanisms for the adsorption of substituted nitrobenzenes by smectite clays.

To more fully understand the potential for transport of nitroaromatic compounds in soils and subsoils,the adsorption of a series of para- and meta-substituted nitrobenzenes (SNBs) by K-smectite clay was measured. Adsorption isotherms were fit to the Freundlich equation, and the resultant Freundlich adsorption coefficients (log(Kf) were positively correlated with the Hammett substituent constant (r2 = 0.80). This relationship and a positive reaction constant (p = 1.15) indicate that the adsorption reaction is favored by electron-withdrawing substituents. These results are consistent with an electron donor (smectite)-acceptor (substituted nitrobenzene) mechanism offered previously. However, quantum calculations did not reveal any systematic relationship between the Hammett constant and the electron density on the aromatic ring, which would explain a donor-acceptor relationship. Rather, electron density donated by a second substituent on nitrobenzene appears to be appropriated by the nitro group leaving ring electron density unchanged. Fourier transform infrared spectroscopy revealed shifts in the -NO2 vibrational modes of 1,3,5-trinitrobenzene (TNB) upon adsorption to K+-smectite that were consistent with the complexation of K+ by -NO2 groups. Such TNB vibrational shifts were not observed for SWy-1 saturated with more strongly hydrated cations (i.e., Na+, Mg2+, Ca2+, and Ba2+). The simultaneous interaction of multiple -NO2 groups with exchangeable K+ was indicated by molecular dynamic simulations. Adsorption of SNBs by smectite clays appears to result from the additive interactions of -NO2 groups and secondary substituents with interlayer K+ ions. Adsorption occurs to a greater or lesser extent depending on the abilities of substituents to complex additional interlayer cations and the water solubilities of SNBs. We conclude that the adsorption trends of SNBs on K-SAz-1 can be explained without recourse to hypothetical electron donor-acceptor complexes.

Selective inhibition of ICAM-1 and E-selectin expression in human endothelial cells. 2. Aryl modifications of 4-(aryloxy)thieno[2,3-c]pyridines with fine-tuning at C-2 carbamides.

The elevated expression of cell adhesion molecules (CAMs) on the lumenal surface of vascular endothelial cells is a critical early event in the complex inflammatory process. The adhesive interactions of these CAMs that include E-selectin, ICAM-1, and VCAM-1 with their counter-receptors on leukocytes, such as integrins of the alpha(L)beta(2) family, result in migration of the leukocytes to the site of inflammation and cause tissue injury. Pharmaceutical agents that could suppress the induced expression of one or more of these cell adhesion molecules would provide a novel mechanism to attenuate the inflammatory responses associated with chronic inflammatory diseases. A-205804 (1), a potent and selective inhibitor of the induced expression of E-selectin and ICAM-1 over VCAM-1, was further modified with emphasis at the C-4 and C-2 positions to identify a more potent drug candidate with a good pharmacokinetic profile and physical properties. Replacement of the C-4 sulfur linkage in 1 with an oxygen atom eliminated one of the two major metabolites for this lead molecule. The para-position of the 4-phenoxy group of the thieno[2,3-c]pyridine lead is found to be very critical for a higher in vitro potency and selectivity of E-selectin and ICAM-1 over VCAM-1 expression. This position is presumably close to the solvent-accessible region of the target protein-inhibitor complex. An attempt to install a water-solubilizing group at the para-position of the phenoxy group to increase the aqueous solubility of this lead series through various linkages failed to provide an ideal inhibitor. Only small substituents such as fluorine are tolerated at the meta- and ortho-positions of the 4-phenoxy to retain a good in vitro potency. Bromo, trifluoromethyl, pyrazol-1-yl, and imidazol-1-yl are among the better substituents at the para-position. With fine-tuning at the C-2 position we discovered a series of very potent (IC(50) < 5 nM for ICAM-1) and selective (>200-fold vs VCAM-1) inhibitors with a good pharmacokinetic profile. Demonstrated efficacy in a rat rheumatoid arthritis model and in a mice asthma model with selected compounds is also reported.

Kinetic modeling of bioavailability for sorbed-phase 2,4-dichlorophenoxyacetic acid.

The degradation rate of 2,4-dichlorophenoxyacetic acid (2,4-D) was studied in silica-slurry systems to evaluate the bioavailability of sorbed-phase contaminant. After the silica particles were saturated with 2,4-D, the system was inoculated with the 2,4-D-degrading microorganism Flavorbacterium sp. strain FB4. The disappearance rate of 2,4-D was found to be greater than the rate predicted based upon liquid-phase 2,4-D concentrations. A kinetic formulation, termed the enhanced bioavailability model, was developed to describe the desorption and biodegradation processes in this batch system. The approach assumes that 2,4-D resides in both the liquid and solid phases and degradation occurs via both suspended and attached biomass. All biomass can degrade liquid-phase 2,4-D at one rate, while only attached biomass can degrade sorbed 2,4-D at another rate. An enhanced transformation factor (Ef) was introduced to express the increased biodegradation rate over that expected from the liquid phase only. This approach was able to account for the increased degradation rates observed experimentally. The results provide evidence that desorption to the bulk solution is not prerequisite to degradation, and that sorbed substrate may be available for degradation.

Potential contributions of smectite clays and organic matter to pesticide retention in soils.

Soil organic matter (SOM) is often considered the dominant sorptive phase for organic contaminants and pesticides in soil-water systems. This is evidenced by the widespread use of organic-matter-normalized sorption coefficients (K(OM)) to predict soil-water distribution of pesticides, an approach that ignores the potential contribution of soil minerals to sorption. To gain additional perspective on the potential contributions of clays and SOM to pesticide retention in soils, we measured sorption of seven pesticides by a K-saturated reference smectite clay (SWy-2) and SOM (represented by a muck soil). In addition, we measured the adsorption of atrazine by five different K-saturated smectites and Ca-saturated SWy-2. On a unit mass basis, the K-SWy-2 clay was a more effective sorbent than SOM for 4,6-dinitro-o-cresol (DNOC), dichlobenil, and carbaryl of the seven pesticides evaluated, of which, DNOC was sorbed to the greatest extent. Atrazine was sorbed to a similar extent by K-SWy-2 and SOM. Parathion, diuron, and biphenyl were sorbed to a greater extent by SOM than by K-SWy-2. Atrazine was adsorbed by Ca-SWy-2 to a much lesser extent than by K-SWy-2. This appears to be related to the larger hydration sphere of Ca(2+) (compared to that of K(+)) which shrinks the effective size of the adsorption domains between exchangeable cations, and which expands the clay layers beyond the apparently optimal spacing of approximately 12.2 A for sorption of aromatic pesticide structures. Although a simple relation between atrazine adsorption by different K-smectites and charge properties of clay was not observed, the highest charge clay was the least effective sorbent; a higher charge density would result in a loss of adsorption domains. These results indicate that for certain pesticides, expandable soil clays have the potential to be an equal or dominant sorptive phase when compared to SOM for pesticide retention in soil.

Stimulation of contraction of pregnant rat uterus in vitro by non-dechlorinated and microbially dechlorinated mixtures of polychlorinated biphenyls.

A previous study of six polychlorinated biphenyl (PCB) congeners showed that PCBs with four or fewer chlorines and ortho substitution stimulate uterine contraction frequency in vitro, whereas congeners with a greater number of chlorines or non-ortho substitution are inactive in vitro. We tested the hypothesis that PCB mixtures stimulate uterine contractions in a manner inversely related to the degree of chlorination and the presence of chlorines in the ortho- position of the biphenyl constituents of the mixtures. Uterine strips from pregnant rats were suspended in standard muscle baths and analyzed for changes in isometric contractions in response to in vitro exposure to commercial PCB mixtures (Aroclors) and their dechlorinated products after microbial degradation. The PCB mixtures Aroclor 1242, 1248, and 1254 significantly stimulated uterine contraction frequency, and the least chlorinated mixture, Aroclor 1242, was the most potent stimulant. Microbes from Hudson River sediment dechlorinated Aroclor 1242 and Aroclor 1254 under reducing conditions to produce mixtures with an increased proportion of ortho-substituted congeners with one or two chlorine substitutions. The PCB mixtures that had undergone microbial reductive dechlorination stimulated uterine contraction frequency to a significantly greater extent than the parent mixtures. These results show that increased uterotonic activity was associated with decreased chlorination and increased ortho substitution of the biphenyl constituents of the mixtures.

Discovery of inhibitors of cell adhesion molecule expression in human endothelial cells. 1. Selective inhibition of ICAM-1 and E-selectin expression.

A critical early event in the inflammatory cascade is the induced expression of cell adhesion molecules on the lumenal surface of vascular endothelial cells. These adhesion molecules include E-selectin, ICAM-1, and VCAM-1, which serve to recruit circulating leukocytes to the site of the inflammation. These adhesive interactions allow the leukocytes to firmly adhere to and cross the vascular endothelium and migrate to the site of tissue injury. Pharmaceutical agents which would prevent the induced expression of one or more of the cell adhesion molecules on the endothelium might be expected to provide a novel mechanism to attenuate the inflammatory responses associated with chronic inflammatory diseases. A thieno[2,3-d]pyrimidine, A-155918, was identified from a whole-cell high-throughput assay for compounds which inhibited the tumor necrosis factor-alpha (TNFalpha)-induced expression of E-selectin, ICAM-1, or VCAM-1 on human vascular endothelial cells. Traditional medicinal chemistry methods were applied to this low-micromolar inhibitor, resulting in the 2,4-disubstituted thieno[2,3-c]pyridine A-205804, a potent and selective lead inhibitor of E-selectin and ICAM-1 expression (IC(50) = 20 and 25 nM, respectively). The relative position of the nitrogen atom in the thienopyridine isomer was shown to be critical for activity, as was a small amide 2-substituent.

Spectroscopic study of nitroaromatic-smectite sorption mechanisms.

Sorption mechanisms of 1,3- and 1,4-dinitrobenzene, 1,3,5-trinitrobenzene (TNB), dinitro-o-creasol, and 6-sec-butyl-2,4-dinitrophenol (DINOSEB) on smectite were investigated using FTIR spectroscopy and HPLC methods. A quantitative method was developed that established a direct link between the HPLC and the FTIR data. Freundlich sorption values ranged from 47 (L g(-1)) for 1,3,5-TNB to 3.7 for DINOSEB and showed that the extent of nitroaromatic compounds (NAC) sorption was strongly dependent on the number and position of the nitro substituents as well as other substituents and steric effects. The amount of 1,3,5-TNB sorbed to smectite was strongly influenced by the nature of the exchangeable cation. Furthermore, the exchangeable cation significantly influenced the positions and relative intensities of the vibrational modes of the -NO2 groups. The strongest perturbations were observed for cations with lower enthalpies of hydration (e.g., K+) and included a red shift of the v(asym)(NO) band, a concomitant blue shift of the v(sym)(NO) band. These changes were accompanied by a 2-fold increase in the relative intensity of the v(asym)(NO) band relative to the intensity of the v(sym) (NO) band. Molecular quantum mechanics calculations were used to rationalize frequency shifts in terms of nitroaromatic interactions with interlayer cations. Results indicate that the sorption of NACs to smectite surfaces is controlled largely by the hydration characteristics of the exchangeable cation, which regulates both cation-nitroaromatic complexation and swelling of the smectite.

Discovery of a series of pyrrolidine-based endothelin receptor antagonists with enhanced ET(A) receptor selectivity.

Endothelins, ET-1, ET-2, and ET-3 are potent vasoconstricting and mitogenic 21-amino acid bicyclic peptides, which exert their effects upon binding to the ET(A) and ET(B) receptors. The ET(A) receptor mediates vasoconstriction and smooth muscle cell proliferation, and the ET(B) receptor mediates different effects in different tissues, including nitric oxide release from endothelial cells, and vasoconstriction in certain vascular cell types. Selective antagonists of endothelin receptor subtypes may prove useful in determining the role of endothelin in various tissue types and disease states, and hence as therapeutic agents for such diseases. The pyrrolidine carboxylic acid A-127722 has been disclosed as a potent and ET(A)-selective antagonist, and is currently undergoing clinical trials. In our efforts to find antagonists with altered selectivity (ET(A)-selective, ET(B)-selective, or nonselective), we investigated the SAR of the 2-substituent on the pyrrolidine. Compounds with alkyl groups at the 2-position possessed ET(A) selectivity improved over A-127722 (1400-fold selective), with the best of these compounds showing nearly 19,000-fold selectivity.

Altered biologic activities of commercial polychlorinated biphenyl mixtures after microbial reductive dechlorination.

The reductive dechlorination of polychlorinated biphenyls (PCBs) by anaerobic bacteria has recently been established as an important environmental fate of these compounds. This process removes chlorines directly from the biphenyl ring with replacement by hydrogen, resulting in a product mixture in which the average number of chlorines per biphenyl is reduced. In this study, dechlorination of commercial PCB mixtures (Aroclors 1242 and 1254) by microorganisms eluted from PCB-contaminated sediments of the River Raisin (Michigan) and Silver Lake (Massachusetts) caused a depletion in the proportion of highly chlorinated PCB congeners and an accumulation of lesser-chlorinated congeners. Dechlorination occurred primarily at the meta and, to a much lesser extent, para positions of biphenyl. The concentrations of the coplanar congeners including 3,3',4,4',5-pentachlorobiphenyl, the most potent dioxinlike congener, were significantly lowered by reductive dechlorination. Microbial reductive dechlorination of commercial PCB mixtures caused a substantial reduction in biologic activities in several instances. It significantly lowered or eliminated the inhibitory effects of Aroclors on fertilization of mouse gametes in vitro. Similarly, the dechlorinated product mixtures had substantially lower ethoxyresorufin-O-deethylase induction potencies and showed less ability to induce activating protein 1 transcription factor activity as compared to the unaltered Aroclors. In other assays the same dechlorinated product mixtures demonstrated biologic activities similar to the nondechlorinated Aroclors, including the ability of PCB mixtures to stimulate insulin secretion and cause neutrophil activation. The data presented here establish that the biologic activities of commercial PCB mixtures are altered by microbial reductive dechlorination and that an assessment of their toxic potential requires an array of tests that include the different mechanisms associated with PCBs.

Pyrrolidine-3-carboxylic acids as endothelin antagonists. 3. Discovery of a potent, 2-nonaryl, highly selective ETA antagonist (A-216546).

Previously we have reported the discovery of ABT-627 (1, A-147627, active enantiomer of A-127722), a 2,4-diaryl substituted pyrrolidine-3-carboxylic acid based endothelin receptor-A antagonist. This compound binds to the ETA receptor with an affinity (Ki) of 0. 034 nM and with a 2000-fold selectivity for the ETA receptor versus the ETB receptor. We have expanded our structure-activity studies in this series, in an attempt to further increase the ETA selectivity. When the p-anisyl group of 1 was replaced by an n-pentyl group, the resultant antagonist 3 exhibited substantially increased ETB/ETA activity ratio, but a decreased ETA affinity. Structure-activity studies revealed that substitution and geometry of this alkyl group, and substitution on the benzodioxolyl ring, are important in optimizing this series of highly ETA selective antagonists. In particular, the combination of a (E)-2,2-dimethyl-3-pentenyl group and a 7-methoxy-1,3-benzodioxol-5-yl group provided hydrophobic compound 10b with subnanomolar affinity for human ETA receptor subtype and with an ETB/ETA activity ratio of over 130000. Meanwhile, synthetic efforts en route to olefinic compounds led to the discovery that 2-pyridylethyl (9o) and 2-(2-oxopyrrolidinyl)ethyl (9u) replacement of the p-anisyl group of 1yielded very hydrophilic ETA antagonists with potency and selectivity equal to those of 10b. On the basis of overall superior affinity, high selectivity for the ETA receptor (Ki, 0.46 nM for ETA and 13000 nM for ETB), and good oral bioavailability (48% in rats), A-216546 (10a) was selected as a potential clinical backup for 1.

Inhibition of L-aromatic amino acid decarboxylase by polychlorinated biphenyls.

PC12 cells were used to examine the mechanisms by which polychlorinated biphenyls (PCBs) reduce cellular levels of dopamine (DA). In cells treated 3 days with Aroclor 1254, 2,2',5,5'-tetrachlorobiphenyl (2,2',5,5'-TCB), or 2,2',3,3',4,4'-hexachlorobiphenyl (2,2',3,3',4,4'-HCB), the PCB-mediated reduction in 3H-tyrosine uptake was observed only at high PCB concentrations that produced a reduction in DNA levels. The PCB congener, 2,2',4,4',5,5'-hexachlorobiphenyl (2,2',4,4',5,5'-HCB) did not produce a reduction in 3H-tyrosine uptake at any concentration tested. Thus, there were PCB concentrations at which a reduction in DA levels did not coincide with a decrease in 3H-tyrosine uptake, suggesting that inhibition of tyrosine uptake was not the primary mechanism by which PCBs reduce DA levels. Aroclor 1254-treated cells also exhibited elevated levels of DOPA, further supporting the conclusion that tyrosine levels were not limiting. Incubation of Aroclor 1254-pretreated cells with 3H-tyrosine resulted in a dose-dependent increase in cellular levels of 3H-DOPA and decrease in cellular levels of 3H-DA, suggesting a PCB-mediated inhibition of the conversion of 3H-DOPA to 3H-DA. When the media was supplemented with DOPA, Aroclor 1254-treated cells still exhibited reduced levels of DA, compared to control cells, even though the control and PCB-treated cells had similar cellular levels of DOPA. Thus, one mechanism by which PCBs may reduce cellular levels of DA is by inhibiting L-aromatic amino acid decarboxylase-mediated conversion of DOPA to DA. The PCB congeners, 2,2',4,4'-TCB, 2,2',5,5'-TCB, and 2,2',4,4',5,5'-HCB, also produced dose-dependent increases in DOPA levels. The congener 2,2',3,3',4,4'-HCB did not produce an increase in DOPA levels, although it did mediate reductions in cellular DA levels. However, when PC12 cells were supplemented with DOPA, all four PCB congeners produced a similar reduction in DA levels, suggesting that the conversion of DOPA to DA was inhibited by the PCBs.

2,4-Diarylpyrrolidine-3-carboxylic acids--potent ETA selective endothelin receptor antagonists. 1. Discovery of A-127722.

We have discovered a novel class of endothelin (ET) receptor antagonists through pharmacophore analysis of the existing non-peptide ET antagonists. On the basis of this analysis, we determined that a pyrrolidine ring might replace the indian ring in SB 209670. The resultant compounds were readily prepared and amenable to extensive SAR studies. Thus a series of N-substituted trans,trans-2-(4-methoxyphenyl)-4-(1,3-benzodioxol-5-yl)pyrroli din e-3- carboxylic acids (8) have been synthesized and evaluated for binding at ET(A) and ET(B) receptors. Compounds with N-acyl and simple N-alkyl substituents had weak activity. Compounds with N-alkyl substituents containing ethers, sulfoxides, or sulfones showed increased activity. Much improved activity resulted from compounds where the N-substituents were acetamides. Compound 17u (A-127722) with the N,N-dibutylacetamide substituent is the best of the series. It has an IC(50)=0.36 nM for inhibition of ET-1 radioligand binding at the ET(A) receptor, with a 1000-fold selectivity for the ET(A) vs the ET(B) receptor. It is also a potent inhibitor (IC(50)=0.16 nM) of phosphoinositol hydrolysis stimulated by ET-1, and it antagonized the ET-1-induced contraction of the rabbit aorta with a pA(2)=9.20. The compound has 70% oral bioavailability in rats.

Maintenance and induction of naphthalene degradation activity in Pseudomonas putida and an Alcaligenes sp. under different culture conditions.

The expression of xenobiotic-degradative genes in indigenous bacteria or in bacteria introduced into an ecosystem is essential for the successful bioremediation of contaminated environments. The maintenance of naphthalene utilization activity is studied in Pseudomonas putida (ATCC 17484) and an Alcaligenes sp. (strain NP-Alk) under different batch culture conditions. Levels of activity decreased exponentially in stationary phase with half-lives of 43 and 13 h for strains ATCC 17484 and NP-Alk, respectively. Activity half-lives were 2.7 and 5.3 times longer, respectively, in starved cultures than in stationary-phase cultures following growth on naphthalene. The treatment of starved cultures with chloramphenicol caused a loss of activity more rapid than that measured in untreated starved cultures, suggesting a continued enzyme synthesis in starved cultures in the absence of a substrate. Following growth in nutrient medium, activity decreased to undetectable levels in the Alcaligenes sp. but remained at measurable levels in the pseudomonad even after 9 months. The induction of naphthalene degradation activities in these cultures, when followed by radiorespirometry with 14C-labeled naphthalene as the substrate, was consistent with activity maintenance data. In the pseudomonad, naphthalene degradation activity was present constitutively at low levels under all growth conditions and was rapidly (in approximately 15 min) induced to high levels upon exposure to naphthalene. Adaptation in the uninduced Alcaligenes sp. occurred after many hours of exposure to naphthalene. In vivo labeling with 35S, to monitor the extent of de novo enzyme synthesis by naphthalene-challenged cells, provided an independent confirmation of the results.

Evidence for para dechlorination of polychlorobiphenyls by methanogenic bacteria.

When microorganisms eluted from upper Hudson River sediment were cultured without any substrate except polychlorobiphenyl (PCB)-free Hudson River sediment, methane formation was the terminal step of the anaerobic food chain. In sediments containing Aroclor 1242, addition of eubacterium-inhibiting antibiotics, which should have directly inhibited fermentative bacteria and thereby should have indirectly inhibited methanogens, resulted in no dechlorination activity or methane production. However, when substrates for methanogenic bacteria were provided along with the antibiotics (to free the methanogens from dependence on eubacteria), concomitant methane production and dechlorination of PCBs were observed. The dechlorination of Aroclor 1242 was from the para positions, a pattern distinctly different from, and more limited than, the pattern observed with untreated or pasteurized inocula. Both methane production and dechlorination in cultures amended with antibiotics plus methanogenic substrates were inhibited by 2-bromoethanesulfonic acid. These results suggest that the methanogenic bacteria are among the physiological groups capable of anaerobic dechlorination of PCBs, but that the dechlorination observed with methanogenic bacteria is less extensive than the dechlorination observed with more complex anaerobic consortia.