Extrapolation of biodegradation results to groundwater aquifers: reductive dehalogenation of aromatic compounds

Niche-specification of aerobic 2,4-dichlorophenoxyacetic acid biodegradation by tfd-carrying bacteria in the rice paddy ecosystem

This study aimed for a better understanding of the niche specification of bacteria carrying the tfd-genes for aerobic 2,4-dichlorphenoxyacetic acid (2,4-D) degradation in the rice paddy ecosystem. To achieve this, a dedicated microcosm experiment was set up to mimic the rice paddy system, with and without 2,4-D addition, allowing spatial sampling of the different rice paddy compartments and niches, i.e., the main anaerobic bulk soil and the aerobic surface water, surface soil, root surface and rhizosphere compartments. No effect of 2,4-D on the growth and morphology of the rice plant was noted. 2,4-D removal was faster in the upper soil layers compared to the deeper layers and was more rapid after the second 2,4-D addition compared to the first. Moreover, higher relative abundances of the 2,4-D catabolic gene tfdA and of the mobile genetic elements IncP-1 and IS1071 reported to carry the tfd-genes, were observed in surface water and surface soil when 2,4-D was added. tfdA was also detected in the root surface and rhizosphere compartment but without response to 2,4-D addition. While analysis of the bacterial community composition using high-throughput 16S rRNA gene amplicon sequencing did not reveal expected tfd-carrying taxa, subtle community changes linked with 2,4-D treatment and the presence of the plant were observed. These findings suggest (i) that the surface soil and surface water are the primary and most favorable compartements/niches for tfd-mediated aerobic 2,4-D biodegradation and (ii) that the community structure in the 2,4-D treated rice paddy ecosystem is determined by a niche-dependent complex interplay between the effects of the plant and of 2,4-D.

2,4-Dichlorophenoxyacetic acid degradation in methanogenic mixed cultures obtained from Brazilian Amazonian soil samples

2,4-Dichlorophenoxyacetic acid (2,4-D) is the third most applied pesticide in Brazil to control broadleaf weeds in crop cultivation and pastures. Due to 2,4-D's high mobility and long half-life under anoxic conditions, this herbicide has high probability for groundwater contamination. Bioremediation is an attractive solution for 2,4-D contaminated anoxic environments, but there is limited understanding of anaerobic 2,4-D biodegradation. In this study, methanogenic enrichment cultures were obtained from Amazonian top soil (0-40 cm) and deep soil (50 -80 cm below ground) that biotransform 2,4-D (5 µM) to 4-chlorophenol and phenol. When these cultures were transferred (10% v/v) to fresh medium containing 40 µM or 160 µM 2,4-D, the rate of 2,4-D degradation decreased, and biotransformation did not proceed beyond 4-chlorophenol and 2,4-dichlorophenol in the top and deep soil cultures, respectively. 16S rRNA gene sequencing and qPCR of a selection of microbes revealed no significant enrichment of known organohalide-respiring bacteria. Furthermore, a member of the genus Cryptanaerobacter was identified as possibly responsible for phenol conversion to benzoate in the top soil inoculated culture. Overall, these results demonstrate the effect of 2,4-D concentration on biodegradation and microbial community composition, which are both important factors when developing pesticide bioremediation technologies.

Anaerobic degradation of 2,4,5-trichlorophenoxyacetic acid by enrichment cultures from freshwater sediments

The anaerobic biodegradation of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) was investigated using enrichment cultures from freshwater sediments at two different sites in the region of Halle, central Germany. 2,4,5-T and different organic acids or hydrogen were added as possible electron acceptor and electron donors, respectively. The primary enrichment cultures from Saale river sediment completely degraded 2,4,5-T to 3-chlorophenol (3-CP) (major product) and 3,4-dichlorophenol (3,4-DCP) during a 28-day incubation period. Subcultures showed ether cleavage of 2,4,5-T to 2,4,5-trichlorophenol and its stoichiometric dechlorination to 3-CP only in the presence of butyrate. In contrast, the primary enrichment culture from sediment of Posthorn pond dechlorinated 2,4,5-T to 2,5-dichlorophenoxyacetic acid (2,5-D), which, in the presence of butyrate, was degraded further to products such as 3,4-DCP, 2,5-DCP, and 3CP, indicating ether cleaving activities and subsequent dechlorination steps. Experiments with pure cultures of Dehalococcoides mccartyi and Desulfitobacterium hafniense demonstrated their specific dechlorination steps within the overall 2,4,5-T degradation pathways. The results indicate that the route and efficiency of anaerobic 2,4,5-T degradation in the environment depend heavily on the microorganisms present and the availability of slowly fermentable organic compounds.

Desulfitobacterium contributes to the microbial transformation of 2,4,5-T by methanogenic enrichment cultures from a Vietnamese active landfill

The herbicide 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) was a major component of Agent Orange, which was used as a defoliant in the Vietnam War. Little is known about its degradation under anoxic conditions. Established enrichment cultures using soil from an Agent Orange bioremediation plant in southern Vietnam with pyruvate as potential electron donor and carbon source were shown to degrade 2,4,5-T via ether cleavage to 2,4,5-trichlorophenol (2,4,5-TCP), which was further dechlorinated to 3,4-dichlorophenol. Pyruvate was initially fermented to hydrogen, acetate and propionate. Hydrogen was then used as the direct electron donor for ether cleavage of 2,4,5-T and subsequent dechlorination of 2,4,5-TCP. 16S rRNA gene amplicon sequencing indicated the presence of bacteria and archaea mainly belonging to the Firmicutes, Bacteroidetes, Spirochaetes, Chloroflexi and Euryarchaeota. Desulfitobacterium hafniense was identified as the dechlorinating bacterium. Metaproteomics of the enrichment culture indicated higher protein abundances of 60 protein groups in the presence of 2,4,5-T. A reductive dehalogenase related to RdhA3 of D. hafniense showed the highest fold change, supporting its function in reductive dehalogenation of 2,4,5-TCP. Despite an ether-cleaving enzyme not being detected, the inhibition of ether cleavage but not of dechlorination, by 2-bromoethane sulphonate, suggested that the two reactions are catalysed by different organisms.

Deep urban groundwater vulnerability in India revealed through the use of emerging organic contaminants and residence time tracers

Demand for groundwater in urban centres across Asia continues to rise with ever deeper wells being drilled to avoid shallow contamination. The vulnerability of deep alluvial aquifers to contaminant migration is assessed in the ancient city of Varanasi, India, using a novel combination of emerging organic contaminants (EOCs) and groundwater residence time tracers (CFC and SF₆). Both shallow and intermediate depth private sources (<100 m) and deep (>100 m) municipal groundwater supplies were found to be contaminated with a range of EOCs including pharmaceuticals (e.g. sulfamethoxazole, 77% detection frequency, range <0.0001-0.034 μg L^-1), perfluoroalkyl substances (e.g. PFOS, range <0.0001-0.033 μg L^-1) as well as a number of pesticides (e.g. phenoxyacetic acid, range <0.02-0.21 μg L^-1). The profile of EOCs found in groundwater mirror those found in surface waters, albeit at lower concentrations, and reflect common waste water sources with attenuation in the subsurface. Mean groundwater residence times were found to be comparable between some deep groundwater and shallow groundwater sources with residence times ranging from >70 to 30 years. Local variations in aquifer geology influence the extent of modern recharge at depth. Both tracers provide compelling evidence of significant inputs of younger groundwater to depth >100 m within the aquifer system.

Rapid degradation of 2,4-dichlorophenoxyacetic acid facilitated by acetate under methanogenic condition

Acetate can be used as an electron donor to stimulate 2,4-dichlorophenoxyacetic acid (2,4-D), which has not been determined under methanogenic condition. This study applied high-throughput sequencing and methanogenic inhibition approaches to investigate the 2,4-D degradation process using the enrichments obtained from paddy soil. Acetate addition significantly promoted 2,4-D degradation, which was 5-fold higher than in the acetate-unsupplemented enrichments in terms of the 2,4-D degradation rate constant. Dechloromonas and Pseudomonas were the dominant 2,4-D degraders. Methanogenic inhibition experiments indicated that the 2,4-D degradation was independent of methanogenesis. It was proposed that the accelerated 2,4-D degradation in the acetate-supplemented enrichment involved an unusual interaction, where members of the acetate oxidizers primarily oxidized acetate and produced H₂. H₂ was utilized by the 2,4-D degraders to degrade 2,4-D, but also partially consumed by the hydrogenotrophic methanogens to produce methane. The findings presented here provide a new strategy for the remediation of 2,4-D-polluted soils.

Reductive dehalogenation activity of indigenous microorganism in sediments of the Hackensack River, New Jersey

Organohalogen pollutants are of concern in many river and estuarine environments, such as the New York-New Jersey Harbor estuary and its tributaries. The Hackensack River is contaminated with various metals, hydrocarbons and halogenated organics, including polychlorinated biphenyls (PCBs) and polychlorinated dibenzo-p-dioxins. In order to examine the potential for microbial reductive dechlorination by indigenous microorganisms, sediment samples were collected from five different estuarine locations along the Hackensack River. Hexachlorobenzene (HCB), hexabromobenzene (HBB), and pentachloroaniline (PCA) were selected as model organohalogen pollutants to assess anaerobic dehalogenating potential. Dechlorinating activity of HCB and PCA was observed in sediment microcosms for all sampling sites. HCB was dechlorinated via pentachlorobenzene (PeCB) and trichlorobenzene (TriCB) to dichlorobenzene (DCB). PCA was dechlorinated via tetrachloroaniline (TeCA), trichloroanilines (TriCA), and dichloroanilines (DCA) to monochloroaniline (MCA). No HBB debromination was observed over 12 months of incubation. However, with HCB as a co-substrate slow HBB debromination was observed with production of tetrabromobenzene (TeBB) and tribromobenzene (TriBB). Chloroflexi specific 16S rRNA gene PCR-DGGE followed by sequence analysis detected Dehalococcoides species in sediments of the freshwater location, but not in the estuarine site. Analysis targeting 12 putative reductive dehalogenase (rdh) genes showed that these were enriched concomitant with HCB or PCA dechlorination in freshwater sediment microcosms.

Biodegradation of three selected benzotriazoles in aquifer materials under aerobic and anaerobic conditions

We investigated the biodegradation of three selected benzotriazoles (BTs), namely benzotriazole (BT), 5-methyl-benzotriazole (5-TTri) and 5-chloro-benzotriazole (CBT), in aquifer materials. Biodegradation experiments were conducted in microcosms with fresh groundwater and aquifer sediment materials under aerobic and anaerobic (nitrate, sulfate, and Fe (III) reducing) conditions. All three BTs were degraded by microorganisms in aquifer materials under aerobic and anaerobic conditions. Under aerobic conditions, BT and 5-TTri were found to be degraded fastest with their half-lives of 43 days and 31 days, respectively, among the redox conditions used. Under anaerobic conditions, CBT was found to be degraded better with its half-life of 21 days under nitrate reducing conditions than under aerobic conditions with its half-life of 47 days. The two BT derivatives 5-TTri and CBT could be biotransformed into BT via demethylation and dechlorination reactions, respectively.

Effect of phenol and acetate addition on 2-chlorophenol consumption by a denitrifying sludge

Chlorophenols are widely distributed in the environment. Various strategies have been used to improve their biological elimination under anaerobic conditions; however, such information is still scarce. The aim of this study was to evaluate in batch assays the consumption of 2-chlorophenol (2-CP) by a denitrifying sludge and the influence of acetate or phenol as co-substrates in the 2-CP consumption. It was observed that phenol (69 and 92 mg phenol-C L(-1)) and acetate (60 and 108 mg acetate-C L(-1)) enhanced 2-CP consumption by the denitrifying sludge, increasing both the efficiency (up to 100%) and specific rate of 2-CP consumption. When phenol was added at 92 mg C L(-1), the specific consumption rate of 2-CP increased 2.6 times with respect to the control lacking co-substrates, whereas with acetate (108 mgC L(-1)) the increase was 9.0 times. Acetate appeared to be a better co-substrate for 2-CP consumption, obtaining a specific consumption rate of 2.48 +/- 0.14 mg 2-CP-C g(-1) VSS d(-1) at 108 mg acetate-C L(-1). The mass balance analysis indicated that the denitrifying sludge was able to simultaneously mineralize 2-CP, phenol or acetate (E2-CP, E(Phenol), and E(Acetate) close to 100% [E = consumption efficiency], Y(HCO3-) of 0.90 +/- 0.10 [Y = yield]) and reduce nitrate to nitrogen gas (E(NO3-) of 100% and Y(N2) of 0.96 +/- 0.02). It was shown that the addition of co-substrates as phenol or acetate could be a good alternative for improving the elimination of chlorophenols from wastewaters by denitrifying sludges.

Biodegradation of the ultraviolet filter benzophenone-3 under different redox conditions

Biodegradation of the ultraviolet (UV) filter benzophenone-3 (BP-3) was investigated in the laboratory to understand its behavior and fate under oxic and anoxic (nitrate, sulfate, and Fe [III]-reducing) conditions. Biodegradation experiments were conducted in microcosms with 10% of activated sludge and digested sludge under oxic and anoxic conditions, respectively. Benzophenone-3 was well degraded by microorganisms under each redox condition. Under the redox conditions studied, the biodegradation half-life for BP-3 had the following order: oxic (10.7 d) > nitrate-reducing (8.7 d) > Fe (III)-reducing (5.1 d) > sulfate-reducing (4.3 d) ≥ anoxic unamended (4.2 d). The results suggest that anaerobic biodegradation is a more favorable attenuation mechanism for BP-3. Biodegradation of BP-3 produced two products, 4-cresol and 2,4-dihydroxybenzophenone, under oxic and anoxic conditions. Biotransformation of BP-3 to 2,4-dihydroxybenzophenone by way of demethylation of the methoxy substituent (O-demethylation) occurred in cultures under each redox condition. The further biotransformation of 2,4-dihydroxybenzophenone to 4-cresol was inhibited under oxic, nitrate-reducing, and sulfate-reducing conditions.

Biodegradation of three selected benzotriazoles under aerobic and anaerobic conditions

We examined the biodegradability of three benzotriazoles (benzotriazole: BT, 5-methylbenzotriazole: 5-TTri and 5-chlorobenzotriazole: CBT) under aerobic and anaerobic (nitrate, sulfate, and Fe (III) reducing) conditions. All three benzotriazoles were degraded by microorganisms under aerobic and anaerobic conditions. Both the biodegradation efficiency and biodegradation products were dependent on the predominant terminal electron-accepting condition. Among the redox conditions studied, the shortest biodegradation half lives for BT and 5-TTri were 114 days and 14 days, respectively, under aerobic condition. The shortest half-life for CBT was 26 days under Fe (III) reducing condition. The longest biodegradation half lives for BT and CBT were 315 days and 96 days, respectively, under sulfate reducing condition, while that of 5-TTri was 128 days under nitrate reducing condition. These results suggest that aerobic biodegradation is the dominant natural attenuation mechanism for BT and 5-TTri, while the most favorable process for CBT was anaerobic biodegradation. This study demonstrated that different predominant terminal electron-acceptors present in natural environment play a key role on the biodegradation of BT, 5-TTri and CBT, leading to specific biodegradability. This could have significant implications on in-situ biodegradation of the selected benzotriazoles in aerobic and anaerobic waters, soils and sediments.

Reductive dechlorination of chlorophenols in estuarine sediments of Lake Shinji and Lake Nakaumi

Dechlorination of all mono- and dichlorophenol isomers in anaerobic sediment samples of estuarine Lake Shinji and Lake Nakaumi was examined to characterize the chlorophenol-dechlorinating microbial communities in the environments with different salinity levels. Dechlorination was observed only in 2-chlorophenol (2-CP), 3-chlorophenol (3-CP) and 2,6-dichlorophenol (2,6-DCP), and in 2-CP and 2,6-DCP in the Lake Shinji and Nakaumi sediment, respectively. In the sediment of Lake Shinji, the highest activity was observed without adding sodium chloride and sulfate, whereas in the Lake Nakaumi sediment, the highest activity was at 0.7 % of sodium chloride and 6.0 mM of sodium sulfate. The chlorophenols were degraded to benzoate via phenol in both sediments under methanogenic conditions. Benzoate then disappeared from the cultures. All microbial consortia enriched with each monochlorophenol dechlorinated 2-CP, but showed different substrate specificities for dichlorophenols as follows: 2-CP-enriched consortium dechlorinated 2,3-dichlorophenol and 2,6-DCP, 3-CP-enriched consortium dechlorinated all dichlorophenol isomers, and 4-chlorophenol-enriched consortium dechlorinated 2,4-dichlorophenol and 2,6-DCP. Maintenance of the population by halorespiration was suggested in the dechlorination of 2-CP.

Reductive dehalogenation of a nitrogen heterocyclic herbicide in anoxic aquifer slurries

We studied the metabolic fate of bromacil in anaerobic aquifer slurries held under denitrifying, sulfate-reducing, or methanogenic conditions. Liquid chromatograhy-mass spectrometry of the slurries confirmed that bromacil was debrominated under methanogenic conditions but was not degraded under the other incubation conditions. This finding extends the range of aryl reductive dehalogenation reactions to include nitrogen heterocyclic compounds.

Characterization of anaerobic dechlorinating consortia derived from aquatic sediments

Four methanogenic consortia which degraded 2-chlorophenol, 3-chlorophenol, 2-chlorobenzoate, and 3-chlorobenzoate, respectively, and one nitrate-reducing consortium which degraded 3-chlorobenzoate were characterized. Degradative activity in these consortia was maintained by laboratory transfer for over 2 years. In the methanogenic consortia, the aromatic ring was dechlorinated before mineralization to methane and carbon dioxide. After dechlorination, the chlorophenol consortia converted phenol to benzoate before mineralization. All methanogenic consortia degraded both phenol and benzoate. The 3-chlorophenol and 3-chlorobenzoate consortia also degraded 2-chlorophenol. No other cross-acclimation to monochlorophenols or monochlorobenzoates was detected in the methanogenic consortia. The consortium which required nitrate for the degradation of 3-chlorobenzoate degraded benzoate and 4-chlorobenzoate anaerobically in the presence of KNO(3), but not in its absence. This consortium also degraded benzoate, but not 3-chlorobenzoate, aerobically.

Anaerobic Aryl Reductive Dehalogenation of Halobenzoates by Cell Extracts of "Desulfomonile tiedjei"

We studied the transformation of halogenated benzoates by cell extracts of a dehalogenating anaerobe, "Desulfomonile tiedjei." We found that cell extracts possessed aryl reductive dehalogenation activity. The activity was heat labile and dependent on the addition of reduced methyl viologen, but not on that of reduced NAD, NADP, flavin mononucleotide, flavin adenine dinucleotide, desulfoviridin, cytochrome c(3), or benzyl viologen. Dehalogenation activity in extracts was stimulated by formate, CO, or H(2), but not by pyruvate plus coenzyme A or by dithionite. The pH and temperature optima for aryl dehalogenation were 8.2 and 35 degrees C, respectively. The rate of dehalogenation was proportional to the amount of protein in the assay mixture. The substrate specificity of aryl dehalogenation activity for various aromatic compounds in "D. tiedjei" cell extracts was identical to that of whole cells, except differences were observed in the relative rates of halobenzoate transformation. Dehalogenation was 10-fold greater in "D. tiedjei" extracts prepared from cells cultured in the presence of 3-chlorobenzoate, suggesting that the activity was inducible. Aryl reductive dehalogenation in extracts was inhibited by sulfite, sulfide, and thiosulfate, but not sulfate. Experiments with combinations of substrates suggested that cell extracts dehalogenated 3-iodobenzoate more readily than either 3,5-dichlorobenzoate or 3-chlorobenzoate. Dehalogenation activity was found to be membrane associated. This is the first report characterizing aryl dehalogenation activity in cell extracts of an obligate anaerobe.

Dechlorination of chlorocatechols by stable enrichment cultures of anaerobic bacteria

Metabolically stable anaerobic cultures obtained by enrichment with 5-bromovanillin, 5-chlorovanillin, catechin, and phloroglucinol were used to study dechlorination of chlorocatechols. A high degree of specificity in dechlorination was observed, and some chlorocatechols were appreciably more resistant to dechlorination than others: only 3,5-dichlorocatechol, 4,5-dichlorocatechol, 3,4,5-trichlorocatechol, and tetrachlorocatechol were dechlorinated, and not all of them were dechlorinated by the same consortium. 3,5-Dichlorocatechol produced 3-chlorocatechol, 4,5-dichlorocatechol produced 4-chlorocatechol, and 3,4,5-trichlorocatechol produced either 3,5-dichlorocatechol or 3,4-dichlorocatechol; tetrachlorocatechol produced only 3,4,6-trichlorocatechol. Incubation of uncontaminated sediments without additional carbon sources brought about dechlorination of 3,4,5-trichlorocatechol to 3,5-dichlorocatechol. O-demethylation of chloroguaiacols was generally accomplished by enrichment cultures, except that catechin enrichment was unable to O-demethylate tetrachloroguaiacol. None of the enrichments dechlorinated any of the polychlorinated phenols examined. The results suggested that dechlorination was not dependent on enrichment with or growth at the expense of chlorinated compounds and that it would be premature to formulate general rules for the structural dependence of the dechlorination reaction.

Effects of sulfuroxy anions on degradation of pentachlorophenol by a methanogenic enrichment culture

We studied the degradation of pentachlorophenol (PCP) under methanogenic and sulfate-reducing conditions with an anaerobic mixed culture derived from sewage sludge. The consortium degraded PCP via 2,3,4,5-tetrachlorophenol, 3,4,5-trichlorophenol, and 3,5-dichlorophenol and eventually accumulated 3-chlorophenol. Dechlorination of PCP and metabolites was inhibited in the presence of sulfate, thiosulfate, and sulfite. A decrease in the rate of PCP transformation was noted when the endogenous dissolved H(2) was depleted below 0.11 muM in sulfate-reducing cultures. The effect on dechlorination observed with sulfate could be relieved by addition of molybdate, a competitive inhibitor of sulfate reduction. Addition of H(2) reduced the inhibition observed with sulfuroxy anions. The inhibitory effect of sulfuroxy anions may be due to a competition for H(2) between sulfate reduction and dechlorination. When cultured under methanogenic conditions, the consortium degraded several chlorinated and brominated phenols.

Anaerobic Degradation of Chloroaromatic Compounds in Aquatic Sediments under a Variety of Enrichment Conditions

Anaerobic degradation of monochlorophenols and monochlorobenzoates in a variety of aquatic sediments was compared under four enrichment conditions. A broader range of compounds was degraded in enrichments inoculated with sediment exposed to industrial effluents. Degradation of chloroaromatic compounds was observed most often in methanogenic enrichments and in enrichments amended with 1 mM bromoethane sulfonic acid. Degradation was observed least often in enrichments with added nitrate or sulfate. The presence of 10 mM bromoethane sulfonic acid prevented or inhibited degradation of most compounds tested. Primary enrichments in which KNO(3) was periodically replenished to maintain enrichment characteristics degraded chlorobenzoates, but not chlorophenols. In contrast, primary enrichments in which Na(2)SO(4) was periodically replenished failed to degrade any chloroaromatic compounds. Upon transfer to fresh medium, none of the sulfate enrichments required the presence of Na(2)SO(4) for degradation, while only two nitrate enrichments required the presence of KNO(3) for degradation. As a class of compounds, chlorophenols were degraded more readily than chlorobenzoates. However, as individual compounds 3-chlorobenzoate, 2-chlorophenol, and 3-chlorophenol degradation was observed most often and with an equal frequency. Within the chlorophenol class, the relative order of degradability was ortho > meta > para, while that of chlorobenzoates was meta > ortho > para, In laboratory transfers, 2-chlorobenzoate, 3-chlorobenzoate, and 2-chlorophenol degradation was most easily maintained, while degradation of para-chlorinated compounds was very difficult to maintain.

Anaerobic degradation of brominated flame retardants in sewage sludge

Tetrabromobisphenol A (TBBPA), hexabromocyclododecane (HBCD), and decabromodiphenyl ether (DecaBDE) are high production volume chemicals used as flame retardants in plastics for products such as electronic equipment, insulation panels, and textiles. The environmental safety of brominated flame retardants, especially their persistence, bioaccumulation, and toxicity is a controversial topic. Here, we studied and compared the degradation of TBBPA, HBCD, and DecaBDE under anaerobic conditions in digested sewage sludge. The half-lives of TBBPA and a technical HBCD mixture were 0.59 and 0.66 d, respectively. The fact that (+/-)-alpha-HBCD exhibited an almost doubled half-life compared to (+/-)-beta-HBCD and (+/-)-gamma-HBCD is an important finding with respect to the discussion on the persistence of individual HBCD stereoisomers and the recent reports on strong relative enrichment of alpha-HBCD in biota. We found no statistically significant enantioselective degradation of alpha-, beta-, or gamma-HBCD. Half-lives of TBBPA and a technical HBCD mixture were not dependent on the presence of additional nutrients or primers. Concentrations of TBBPA and a technical HBCD mixture decreased also in sterile control samples, however, at a rate that was more than a factor of 50 smaller than in incubations under non-sterile conditions. Compared to TBBPA and a technical HBCD mixture, DecaBDE exhibited a much longer half-life of 7 x 10(2)d in the same system. Pseudo-first-order degradation rate constants decreased according to the following sequence: TBBPA congruent with(+/-)-gamma-HBCD congruent with(+/-)-beta-HBCD>(+/-)-alpha-HBCD>>DecaBDE. Preliminary investigations suggest that degradation of TBBPA, HBCD, and DecaBDE occurs in full-scale anaerobic digesters, as well.

Anaerobic degradation of decabromodiphenyl ether

The environmental safety of decabromodiphenyl ether (BDE-209), a widely used flame retardant, has been the topic of controversial discussions during the past several years. Degradation of BDE-209 into lower brominated diphenyl ether congeners, exhibiting a higher bioaccumulation potential, has been a critical issue. Here, we report on the degradation of BDE-209 and the formation of octa- and nonabromodiphenyl ether congeners under anaerobic conditions. Sewage sludge collected from a mesophilic digester was used as the inoculum and incubated up to 238 days with and without a set of five primers. Following Soxhlet extraction and a liquid chromatography cleanup procedure, parent compounds and debromination products were analyzed by GC/HRMS. In experiments with primers, concentrations of BDE-209 decreased by 30% within 238 days. This corresponds to a pseudo-first-order degradation rate constant of 1 x 10(-3) d(-1). Without primers, the degradation rate constant was 50% lower. Formation of two nonabromodiphenyl ether and six octabromodiphenyl ether congeners proved that BDE-209 underwent reductive debromination in these experiments. Debromination occurred at the para and the meta positions, whereas debromination at the ortho position was not statistically significant. All three nonabromodiphenyl ether congeners (BDE-206, BDE-207, and BDE-208) were found to undergo reductive debromination as well. No significant change of the BDE-209 concentration and no formation of lower brominated congeners was observed in sterile control experiments. To our knowledge, this is the first report demonstrating microbially mediated reductive debromination of BDE-209 under anaerobic conditions.

Developmental effects of ambient UV-B light and landfill leachate in Rana blairi and Hyla chrysoscelis

This study assessed the effects of ambient UV light on the development of two native species of anurans, Rana blairi and Hyla chrysoscelis, during their normal breeding season in Oklahoma. Additionally, the effects of ambient UV light and water contaminated with landfill leachate in Rana blairi were examined. Embryos were collected from the field and distributed equally among replicates of four filter treatments of ambient UV light in experimental tubs filled with either FETAX solution or landfill leachate diluted to 25, 10, and 5% concentrations. Three endpoints (mortality, teratogenesis, and growth) were compared between filter treatments. By itself, UV-B caused no significant effects. Leachate at 10 and 25% concentrations caused 100% mortality across all filter treatments. There was a significant interaction between filter treatment and water toxicity at leachate concentrations of 5% for both malformation and growth. Increased UV-B exposure decreased the malformation rate and increased growth in the leachate treatments.

Dissipation of the herbicide [14C]dimethenamid under anaerobic conditions in flooded soil microcosms

The objective of this research was to investigate the dissipation of the herbicide dimethenamid under anaerobic redox conditions that may develop in the soil environment. Soil-water biometers were prepared with a saturated soil and made anaerobic by either glucose pretreatment (according to the Environmental Protection Agency registration study for anaerobic fate) or N2 sparging. Treatments included glucose pretreatment, NO3- + SO42- amendment, unamended, and autoclaved. Volatile, aqueous, extractable, and bound (unextractable) 14C-residues were quantified and characterized. The redox potential decreased over time, and evidence of denitrifying, iron-reducing, sulfate-reducing, and methanogenic conditions was observed, depending on the amendments. Anaerobic degradation of 14C-dimethenamid occurred in all treatments, and the time observed for 50% disappearance (DT50) was 13-14 days for nonautoclaved treatments. 14C-metabolites accumulated to up to 20% of applied 14C. At least two major metabolites were observed in nonautoclaved treatments, whereas only one was observed in autoclaved microcosms. More than 50% of the applied 14C was eventually incorporated into soil-bound residue.

Evidence for degradation of 2-chlorophenol by enrichment cultures under denitrifying conditions

Although chlorophenol (CP) degradation has been studied, no bacterium responsible for degradation of CP under denitrifying conditions has been isolated. Moreover, little substantial evidence for anaerobic degradation of CPs coupled with denitrification is available even for mixed cultures. Degradation of CP [2-CP, 3-CP, 4-CP, 2,4-dichlorophenol (DCP) or 2,6-DCP] under denitrifying conditions was examined in anaerobic batch culture inoculated with activated sludge. Although 3-CP, 4-CP, 2,4-DCP and 2,6-DCP were not stably degraded, 2-CP was degraded and its degradation capability was sustained in a subculture. However, the rate of 2-CP degradation was not significantly enhanced by subculturing. In 2-CP-degrading cultures, nitrate was consumed stoichiometrically and concomitantly during 2-CP degradation, and a dechlorination intermediate was not detected, suggesting that 2-CP degradation was coupled with nitrate reduction. A 2-CP-degrading enrichment culture degraded 2-CP in the presence of nitrate, but did not in the absence of nitrate or the presence of sulfate. This suggests that the enrichment culture strictly requires nitrate for degradation of 2-CP. The apparent specific growth rate of the 2-CP degrading species was 0.0139 d(-1). Thus the apparent doubling time of the 2-CP-degrading population in the enrichment culture was greater than 50 d, which may explain difficulty in enrichment and isolation of micro-organisms responsible for CP degradation under denitrifying conditions.

Fate of the herbicides 2,4,5-T, atrazine, and DNOC in a shallow, anaerobic aquifer investigated by in situ passive diffusive emitters and laboratory batch experiments

The fate of the three herbicides 2,4,5-T (2,4,5-trichlorophenoxyacetic acid), atrazine (6-chloro-N-ethyl-N'-[1-methyl-ethyl]-1,3,5-triazine-2,4-diamine), and DNOC (4,6-dinitro-2-methylphenol) in an anaerobic sandy aquifer was investigated. In the field, each of the herbicides was released simultaneously with tritiated water (HTO) as tracer in the depth interval 3 to 4 mbs (meters below surface) by use of passive diffusive emitters. Atrazine and 2,4,5-T were persistent during the approximately 18 days residence time in the aquifer. In contrast, DNOC was rapidly removed from the water phase following first-order kinetics. The removal mechanism was likely an abiotic reduction. At day 25, the first-order rate constant was 1.47 d(-1), but it decreased with time and seemed to stabilize at 0.35 d(-1) after 150 to 200 days. In the laboratory, batch experiments were conducted with sediments from 3 to 4 mbs and from 8 to 9 mbs. In these incubations, formation of Fe2+ and depletion of sulfate showed iron and sulfate reduction in sediment from 3 to 3.5 mbs and sulfate reduction in 3.5 to 4 mbs sediment. In sediment from 8 to 9 mbs, the dominant redox process was methane formation. In sediment from 3 to 3.5 mbs, only 27% to 52% of the 2,4,5-T remained after 196 days. 2,4,5-trichlorophenol was identified as the major metabolite. A lag period of at least 50 days was observed, and no degradation occurred in HgCl2 amended controls, verifying that the process was microbially mediated. In the other 2,4,5-T incubations and all the atrazine incubations, concentrations decreased linearly, but less than 25% was removed within 200 to 250 days. No degradation products could be detected, and slow sorption was the likely explanation. In all the laboratory incubations DNOC was degraded, following first-order kinetics, and when normalized to the sediment/water-ratio, the field and laboratory derived rate constants compared well. The DNOC degradation in the methanogenic incubations (8 to 9 mbs) was up to 50 times faster than in the sediments from 3 to 4 mbs, likely due to the low redox potential.

The effect of redox potential changes on reductive dechlorination of pentachlorophenol and the degradation of acetate by a mixed, methanogenic culture

The effect of changes in redox potential on methanogenesis from acetate, and on the reductive dechlorination of pentachlorophenol (PCP), was evaluated using a computer-monitored and feedback-controlled bioreactor. PCP was transformed via 2,3,4, 5-tetrachlorophenol (2,3,4,5-TeCP) to 3,4,5-trichlorophenol (3,4, 5-TCP). In 6- to 12-d experiments, pH, acetate concentration, and temperature were held constant; the redox potential, defined here as the potential measured at a platinum electrode (EPt), was maintained at different set points, while transformation of multiple PCP additions was monitored. Without redox potential control, the value of EPt for the culture was approximately -0.26 V (vs. SHE). The value of EPt was elevated from -0.26 V for periods up to 10 h by computer-controlled addition of H2O2 or K3Fe(CN)6. Methanogenesis continued during a relatively mild shift of EPt to -0.2 V with H2O2, but was halted when EPt was raised to -0.1 V with either H2O2 or K3Fe(CN)6. Methanogenesis resumed when EPt returned to -0.26 V. During periods in which EPt was elevated significantly and methanogenesis stopped, transformation of PCP and 2,3,4,5-TeCP continued at progressively slower rates, but the rate of 2,3,4, 5-TeCP transformation was diminished to a greater extent. When a small volume of pure H2 was added to the reactor headspace, while EPt was maintained at -0.1 V, reductive dechlorination rates increased dramatically. Lower H2 concentrations during periods of oxidant addition, perhaps due to the effect of the oxidant on H2-producing bacteria, may contribute to decreased reductive dechlorination rates. Copyright 1999 John Wiley & Sons, Inc.

Ground and surface water developmental toxicity at a municipal landfill: description and weather-related variation

Contaminated groundwater poses a significant health hazard and may also impact wildlife such as amphibians when it surfaces. Using FETAX (Frog Embryo Teratogenesis Assay-Xenopus), the developmental toxicity of ground and surface water samples near a closed municipal landfill at Norman, OK, were evaluated. The groundwater samples were taken from a network of wells in a shallow, unconfined aquifer downgradient from the landfill. Surface water samples were obtained from a pond and small stream adjacent to the landfill. Surface water samples from a reference site in similar habitat were also analyzed. Groundwater samples were highly toxic in the area near the landfill, indicating a plume of toxicants. Surface water samples from the landfill site demonstrated elevated developmental toxicity. This toxicity was temporally variable and was significantly correlated with weather conditions during the 3 days prior to sampling. Mortality was negatively correlated with cumulative rain and relative humidity. Mortality was positively correlated with solar radiation and net radiation. No significant correlations were observed between mortality and weather parameters for days 4-7 preceding sampling.

Dehalogenation and biodegradation of brominated phenols and benzoic acids under iron-reducing, sulfidogenic, and methanogenic conditions

The anaerobic biodegradation of monobrominated phenols and benzoic acids by microorganisms enriched from marine and estuarine sediments was determined in the presence of different electron acceptors [i.e., Fe(III), SO4(2-), or HCO3-]. Under all conditions tested, the bromophenol isomers were utilized without a lengthy lag period whereas the bromobenzoate isomers were utilized only after a lag period of 23 to 64 days. 2-Bromophenol was debrominated to phenol, with the subsequent utilization of phenol under all three reducing conditions. Debromination of 3-bromophenol and 4-bromophenol was also observed under sulfidogenic and methanogenic conditions but not under iron-reducing conditions. In the bromobenzoate-degrading cultures, no intermediates were observed under any of the conditions tested. Debromination rates were higher under methanogenic conditions than under sulfate-reducing or iron-reducing conditions. The stoichiometric reduction of sulfate or Fe(III) and the utilization of bromophenols and phenol indicated that biodegradation was coupled to sulfate or iron reduction, respectively. The production of phenol as a transient intermediate demonstrates that reductive dehalogenation is the initial step in the biodegradation of bromophenols under iron- and sulfate-reducing conditions.

Influence of sulfur oxyanions on reductive dehalogenation activities in Desulfomonile tiedjei

The inhibition of aryl reductive dehalogenation reactions by sulfur oxyanions has been demonstrated in environmental samples, dehalogenating enrichments, and the sulfate-reducing bacterium Desulfomonile tiedjei; however, this phenomenon is not well understood. We examined the effects of sulfate, sulfite, and thiosulfate on reductive dehalogenation in the model microorganism D. tiedjei and found separate mechanisms of inhibition due to these oxyanions under growth versus nongrowth conditions. Dehalogenation activity was greatly reduced in extracts of cells grown in the presence of both 3-chlorobenzoate, the substrate or inducer for the aryl dehalogenation activity, and either sulfate, sulfite, or thiosulfate, indicating that sulfur oxyanions repress the requisite enzymes. In extracts of fully induced cells, thiosulfate and sulfite, but not sulfate, were potent inhibitors of aryl dehalogenation activity even in membrane fractions lacking the cytoplasmically located sulfur oxyanion reductase. These results suggest that under growth conditions, sulfur oxyanions serve as preferred electron acceptors and negatively influence dehalogenation activity in D. tiedjei by regulating the amount of active aryl dehalogenase in cells. Additionally, in vitro inhibition by sulfur oxyanions is due to the interaction of the reactive species with enzymes involved in dehalogenation and need not involve competition between two respiratory processes for reducing equivalents. Sulfur oxyanions also inhibited tetrachloroethylene dehalogenation by the same mechanisms, further indicating that chloroethylenes are fortuitously dehalogenated by the aryl dehalogenase. The commonly observed inhibition of reductive dehalogenation reactions under sulfate-reducing conditions may be due to similar regulation mechanisms in other dehalogenating microorganisms that contain multiple respiratory activities.

Reductive dehalogenation and mineralization of 3-chlorobenzoate in the presence of sulfate by microorganisms from a methanogenic aquifer

We investigated the anaerobic biodegradation of 3-chlorobenzoate (3CBz) by microorganisms from an aquifer where chloroaromatic compounds were previously found to resist decay in the presence of sulfate. After a lengthy lag period, 3CBz was degraded in the presence of sulfate and concurrently with sulfate reduction. Chlorine removal from 2,5- or 3,5-dichlorobenzoates and the transient appearance of benzoate from 3CBz confirmed that reductive dehalogenation was the initial fate process for these substrates. Sulfate did not influence 3CBz degradation rates in acclimated enrichment cultures but accelerated the development of 3CBz degradation activity in fresh transfers. Benzoate degradation was more rapid in the presence of sulfate regardless of the enrichment history. Nitrate, sulfite, and a headspace of air inhibited 3CBz dehalogenation, while thiosulfate had no effect. Mass balance determinations revealed that 71 to 107% of the theoretically expected amount of methane was produced from 3CBz and benzoate oxidation in the absence of sulfate. In parallel cultures containing 15 mM sulfate, methanogenesis was reduced to 48 to 71% of that theoretically expected, while sulfate reduction accounted for 12 to 50% of the reducing equivalents. In either the presence or absence of sulfate, steady-state dissolved hydrogen concentrations were similar to those reported for sulfate-reducing or methanogenic environments, respectively. Molybdate inhibited sulfate reduction and 3CBz dehalogenation to a similar extent but did not affect benzoate biodegradation. Sulfate-dependent 3CBz biodegradation was not observed. We conclude that reductive dehalogenation and sulfate reduction occur concurrently in these enrichments and that the sulfate-dependent stimulation in fresh transfers was likely due to the acceleration of benzoate oxidation.

Characterization of Desulfitobacterium chlororespirans sp. nov., which grows by coupling the oxidation of lactate to the reductive dechlorination of 3-chloro-4-hydroxybenzoate

Strain Co23, an anaerobic spore-forming microorganism, was enriched and isolated from a compost soil on the basis of its ability to grow with 2,3-dichlorophenol (DCP) as its electron acceptor, ortho chlorines were removed from polysubstituted phenols but not from monohalophenols. Growth by chlororespiration was indicated by a growth yield of 3.24 g of cells per mol of reducing equivalents (as 2[H]) from lactate oxidation to acetate in the presence of 3-chloro-4-hydroxybenzoate but no growth in the absence of the halogenated electron acceptor. Other indicators of chlororespiration were the fraction of electrons from the electron donor used for dechlorination (0.67) and the H2 threshold concentration of < 1.0 ppm. Additional electron donors utilized for reductive dehalogenation were pyruvate, formate, butyrate, crotonate, and H2. Pyruvate supported homoacetogenic growth in the absence of an electron acceptor. Strain Co23 also used sulfite, thiosulfate, and sulfur as electron acceptors for growth, but it did not use sulfate, nitrate or fumarate. The temperature optimum for growth was 37 degrees C; however, the rates of dechlorination were optimum at 45 degrees C and activity persisted to temperatures as high as 55 degrees C. The 16S rRNA sequence was determined, and strain Co23 was found to be related to Desulfitobacterium dehalogenans JW/IU DC1 and Desulfitobacterium strain PCE1, with sequence similarities of 97.2 and 96.8%, respectively. The phylogenetic and physiological properties exhibited by strain Co23 place it into a new species designated Desulfitobacterium chlororespirans.

Anaerobic dechlorination and mineralization of pentachlorophenol and 2,4,6-trichlorophenol by methanogenic pentachlorophenol-degrading granules

Anaerobic granules developed for the treatment of pentachlorophenol (PCP) completely mineralized 14C-labeled PCP to 14CH4 and 14CO2. Release of chloride ions from PCP was performed by live cells in the granules under anaerobic conditions. No chloride ions were released under aerobic conditions or by autoclaved cells. Addition of sulfate enhanced the initial chloride release rate and accelerated the process of mineralization of 14C-labeled PCP. Addition of molybdate (10 mM) inhibited the chloride release rate and severely inhibited PCP mineralization. This suggests involvement of sulfate-reducing bacteria in PCP dechlorination and mineralization. Addition of 2-bromoethane sulfonate slightly decreased the chloride release rate and completely stopped production of 14CH4 and 14CO2 from [14C]PCP. 2,4,6-trichlorophenol was observed as an intermediate during PCP dechlorination. On the basis of experimental results, dechlorination of 2,4,6-trichlorophanol by the granules was conducted through 2,4-dichlorophenol, 4-chlorophenol or 2-chlorophenol to phenol at pH 7.0-7.2.

Biodegradation of chlorinated phenolic compounds

Chlorophenolic compounds are generated from a number of industrial manufacturing processes including pulp and paper manufacture. These compounds are found to be toxic and recalcitrant and hence their discharge into the environment must be regulated. Slow and partial degradation of chlorophenols under aerobic and anaerobic natural environment has been observed. Aerobic biodegradation of chlorophenols proceeds through the formation of catechols while under anaerobic conditions, reductive dehalogenation is the preferred metabolic pathway. Number and position of chlorine substituents on the phenolic ring has influence on the rate and extent of biodegradation of chlorophenols. In engineered systems, acclimatization of biomass to chlorophenols markedly enhances the biodegradation ability by reducing the initial lag phase and by countering inhibition. Partial removal of chlorophenols between 40-60% is usually observed in aerobic and anaerobic processes. Removal can be enhanced by a combination of aerobic and anaerobic operations.

Diversity of anaerobic microbial processes in chlorobenzoate degradation: nitrate, iron, sulfate and carbonate as electron acceptors

The utilization of monochlorobenzoate isomers (2-, 3- and 4-chlorobenzoate) by anaerobic microbial consortia in River Nile sediments was systematically evaluated under denitrifying, Fe-reducing, sulfidogenic and methanogenic conditions. Loss of all three chlorobenzoates was noted in denitrifying cultures; furthermore, the initial utilization of chlorobenzoates was fastest under denitrifying conditions. Loss of 3-chlorobenzoate was seen under all four reducing conditions and the degradation of chlorobenzoates was coupled stoichiometrically to NO3- loss, Fe2+ production, SO4(2-) loss or CH4 production, indicating that the chlorobenzoates were oxidized to CO2. To our knowledge, this is the first observation of halogenated aromatic degradation coupled to Fe reduction.

Biotransformation of dichloroaromatic compounds in nonadapted and adapted freshwater sediment slurries

Nonadapted freshwater sediment slurries and sediment slurries adapted to dechlorinate 2,3-dichloropyridine (2,3-Cl2Pyd), 2,3-dichloroaniline (2,3-Cl2Anl), 2,3-dichlorophenol (2,3-Cl2PhOH), 3,5-dichloropyridine (3,5-Cl2Pyd), 3,5-dichloroaniline (3,5-Cl2Anl) and 3,5-dichlorophenol (3,5-Cl2PhOH) were studied to determine the rate, range and extent of biotransformation of structurally related compounds under anaerobic conditions. 2,3-dichloroanisole (2,3-Cl2Ans) and 3,5-dichloroanisole (3,5-Cl2Ans) were initially demethylated, producing 2,3-Cl2PhOH and 3,5-Cl2PhOH as intermediate transformation products. All other dichloroaromatic compounds examined were initially dechlorinated. The rates of dechlorination of 2,3-Cl2PhOH, 2,3-Cl2Anl, and 2,3-Cl2Pyd were significantly lower (5-15 times) in nonadapted sediment slurries compared to sediment slurries adapted to 2,3-Cl2Anl or 2,3-Cl2Pyd. In 2,3-Cl2PhOH adapted sediment, the rate of dechlorination of 2,3-Cl2PhOH was 15 times greater than in nonadapted sediment; however, the rates of dechlorination of 2,3-Cl2Anl and 2,3-Cl2Pyd were similar for 2,3-Cl2PhOH-adapted and nonadapted sediment slurries. In adapted and nonadapted sediment slurries, 2,3-Cl2PhOH, 2,3-Cl2Anl, and 2,3-Cl2Pyd were preferentially dechlorinated at the ortho, meta, and meta positions, respectively. Additionally, 2,3-Cl2Pyd adapted sediment slurries dechlorinated 2,3-Cl2PhOH and 2,3-Cl2Pyd at both ortho and meta positions. Rates of dechlorination of 3,5-Cl2PhOH, 3,5-Cl2Anl, and 3,5-Cl2Pyd were lower (2-4 times) in nonadapted sediment slurries compared to sediment slurries adapted to 3,5-Cl2Anl or 3,5-Cl2Pyd. In 3,5-Cl2PhOH adapted sediment, the rate of dechlorination of 3,5-Cl2PhOH was approximately 10 times greater than in nonadapted sediment.(ABSTRACT TRUNCATED AT 250 WORDS)

Anaerobic degradation of halogenated phenols by sulfate-reducing consortia

Sulfidogenic consortia enriched from an estuarine sediment were maintained on either 2-, 3-, or 4-chlorophenol as the only source of carbon and energy for over 5 years. The enrichment culture on 4-chlorophenol was the most active and this consortium was selected for further characterization. Utilization of chlorophenol resulted in sulfate depletion corresponding to the values expected for complete mineralization to CO2. Degradation of 4-chlorophenol was coupled to sulfate reduction, since substrate utilization was dependent on sulfidogenesis and chlorophenol loss did not proceed in the absence of sulfate. Other sulfur oxyanions, sulfite or thiosulfate, also served as electron acceptors for chlorophenol utilization, while carbonate, nitrate, and fumarate did not. The sulfidogenic consortium utilized phenol, 4-bromophenol, and 4-iodophenol in addition to 4-chlorophenol. 4-Fluorophenol, however, did not serve as a substrate. 4-Bromo- and 4-iodophenol were degraded with stoichiometric release of halide, and 4-[14C]bromophenol was mineralized, with 90% of the radiolabel recovered as CO2.

Specificity of reductive dehalogenation of substituted ortho-chlorophenols by Desulfitobacterium dehalogenans JW/IU-DC1

Resting cells of Desulfitobacterium dehalogenans JW/IU-DC1 growth with pyruvate and 3-chloro-4-hydroxyphenylacetate (3-Cl-4-OHPA) as the electron acceptor and inducer of dehalogenation reductively ortho-dehalogenate pentachlorophenol (PCP); tetrachlorophenols (TeCPs); the trichlorophenols 2,3,4-TCP, 2,3,6-TCP, and 2,4,6-TCP; the dichlorophenols 2,3-DCP, 2,4-DCP, and 2,6-DCP; 2,6-dichloro-4-R-phenols (2,6-DCl-4-RPs, where R is -H, -F, -Cl, -NO2, -CO2, or -COOCH3; 2-chloro-4-R-phenols (2-Cl-4-RPs, where R is -H, -F, -Cl, -Br, -NO2, -CO2-, -CH2CO2, or -COOCH3); and the bromophenols 2-BrP, 2,6-DBrP, and 2-Br-4ClP [corrected]. Monochlorophenols, the dichlorophenols 2,5-DCP, 3,4-DCP, and 3,5-DCP, the trichlorophenols 2,3,5-TCP, 2,4,5-TCP, and 3,4,5-TCP, and the fluorinated analog of 3-Cl-4-OHPA, 3-F-4-OHPA ("2-F-4-CH2CO2- P"), are not dehalogenated. A chlorine substituent in position 3 (meta), 4 (para), or 6 (second ortho) of the phenolic moiety facilitates ortho dehalogenation in position 2. Chlorine in the 5 (second meta) position has a negative effect on the dehalogenation rate or even prevents dechlorination in the 2 position. In general, 2,6-DCl-4-RPs are dechlorinated faster than the corresponding 2-Cl-4-RPs with the same substituent R in the 4 position. The highest dechlorination rate, however, was found for dechlorination of 2,3-DCP, with a maximal observed first-order rate constant of 19.4 h-1 g (dry weight) of biomass-1.(ABSTRACT TRUNCATED AT 250 WORDS)