Kegg Pathway: 1,4-Dichlorobenzene degradation

J Hazard Mater. 2008 May 29;
Gomathi Devi L, Krishnamurthy G

Gas chromatograph-mass spectroscopic identification of intermediate products in the degradation of diclofop-methyl and the kinetics of the reaction has been investigated. Formation of 4-[(2,4-dichlorophenoxy) phenoxy] ethane and (2,4-dichlorophenoxy) phenol was investigated. The other intermediate products are 2,4-dichlorophenol, 2,4-dichlorobenzene, phenol and acetic acid have been ascertained. The decrease in the concentration of the parent/intermediate compounds is followed by UV-vis spectral study and the supportive information on the functional groups in the intermediates has been obtained from IR-spectroscopy. degradation process proceeds with oxidation-reduction reaction by the attack of OH, H, O(2)(-) free radicals, which are photogenerated on the UV-light illuminated TiO(2)/BaTiO(3) photocatalysts particles in aqueous medium. In this presentation another wide band gap semiconductor BaTiO(3) is shown to have comparable photocatalytic efficiency. The oxidizing agents are added to accelerate the rate of the reaction by enhancing the formation of free radicals. Based on the intermediates formed in the process of degradation, a suitable mechanism has been proposed.

Chemosphere. 2008 Mar; 71(4): 711-6
De Coensel N, Desmet K, Sandra P, Górecki T

Moth repellent agents are considered major contributors to indoor air pollution. In this study, the chemical contamination of clothes due to their direct or indirect exposure to moth repellent agents such as p-dichlorobenzene, naphthalene and camphor were investigated. Cotton cloths were used as clothing simulant. They were analyzed using ultrasonic extraction followed by GC-MS analysis. Extrapolated results indicate that a regular cotton shirt indirectly exposed to these chemicals in a storage cabinet can contain up to 7, 3 and 7.5mg of p-dichlorobenzene, naphthalene and camphor, respectively, even after one-hour of airing. Passive sorptive sampling using polydimethylsiloxane-coated stir-bars and ultrasonic extraction followed by GC-MS analysis was used to monitor the concentration distribution in a wardrobe.

Environ Sci Technol. 2007 Nov 1; 41(21): 7523-9
Zhu BW, Lim TT

Monochlorobenzene (MCB), dichlorobenzenes (DCBs), and 1,2,4-trichlorobenzene (124TCB) dechlorination experiments in water were carried out with freshly synthesized Pd/Fe particles. The pre- and postreacted Pd/Fe samples were characterized by applying various analytical techniques (XRD, SEM, TEM, and XPS). Chlorinated benzenes could be completely reduced by the Pd/Fe to benzene and the reaction followed the pseudo-first-order kinetics. The reaction rates followed the order TCB < DCBs < MCB, while among the DCBs the order was 1,4-Dichlorobenzene >1,3-dichlorobenzene > or = 1,2-dichlorobenzene. Insignificant reactions were observed with the unpalladized iron, suggesting that Pd was the only reactive site in the Pd/Fe particles. The aged Pd/Fe particles exhibited significant decrease in its dechlorination reactivity. The loss of Pd/Fe reactivity could be due to Pd dislodgment from the aged Pd/Fe particles and Pd islets encapsulation by the iron oxides film developed over aging period. Reactivity of the aged Pd/Fe could be only partially restored after HCI treatment, while regeneration with the NaBH4 reduction method could not restore its activity, although zerovalent state of the iron was reinstated.

J Hazard Mater. 2008 May 30; 153(3): 1136-41
Selli E, Bianchi CL, Pirola C, Cappelletti G, Ragaini V

The rate of 1,4-Dichlorobenzene (1,4-DCB) degradation and mineralization in the aqueous phase was investigated either under direct photolysis or photocatalysis in the presence of commercial or sol-gel synthesized TiO2, or under sonolysis at 20 kHz with different power inputs. Two lamps, both emitting in the 340-400 nm wavelength range with different energy, were employed as irradiation sources. Photocatalysis ensured faster removal of 1,4-DCB with respect to sonolysis and direct photolysis. The highest degradation and mineralization rate was attained with the combined use of photocatalysis and sonolysis, i.e. under sonophotocatalytic conditions. The efficiency of the employed advanced oxidation techniques in 1,4-DCB degradation is discussed also in relation to their energy consumption, which might be decisive for their practical application.

J Toxicol Environ Health B Crit Rev. 2007 Oct; 10(7): 467-526
Aronson DB, Bosch S, Gray DA, Howard PH, Guiney PD

A comparison of the human health risk to consumers using one of two types of toilet rimblock products, either a p-dichlorobenzene-based rimblock or two newer fragrance/surfactant-based alternatives, was conducted. Rimblock products are designed for global use by consumers worldwide and function by releasing volatile compounds into indoor air with subsequent exposure presumed to be mainly by inhalation of indoor air. Using the THERdbASE exposure model and experimentally determined emission data, indoor air concentrations and daily intake values were determined for both types of rimblock products. Modeled exposure concentrations from a representative p-dichlorobenzene rimblock product are an order of magnitude higher than those from the alternative rimblock products due to its nearly pure composition and high sublimation rate. Lifetime exposure to p-dichlorobenzene or the subset of fragrance components with available RfD values is not expected to lead to non-cancer-based adverse health effects based on the exposure concentrations estimated using the THERdbASE model. A similar comparison of cancer-based effects was not possible as insufficient data were available for the fragrance components.

Arch Toxicol. 2007 Jul; 81(7): 505-17
Takahashi O, Oishi S, Yoneyama M, Ogata A, Kamimura H

A significant increase/decrease in uterine and ovarian weights was occasionally seen in immature mice and rats subcutaneously administered paradichlorobenzene (PDCB) at doses of 22-67 mg/kg/day, but the results were not necessarily reproducible. PDCB at a dose of 800 mg/kg/day always reduced uterine and ovarian weights. Intraperitoneal PDCB at doses more than 400 mg/kg/day significantly inhibited the uterotrophic effect of beta-estradiol (E2) in CD-1 (ICR) mice. E2-induced uterotrophy was dose-dependently prevented by 204-400 mg PDCB/kg/day in C57BL/6N (Ah responsive) mice but not DBA/2N (Ah non-responsive) mice. While PDCB did not bind to estrogen receptor (ER(alpha)) up to 10(-3) M. Hepatic ethoxyresorufin-O-deethylase in adult female C57BL/6N mice was induced by i.p. administration of PDCB. Induction activity of PDCB may be 10(5)-10(6) times lower than that of 2,3,7,8-tetrachlorodibenzo-p-dioxin. These results suggest that PDCB is a weak antiestrogenic/antiuterotrophic compound possibly due to ER modulation through arylhydrocarbon receptor.

Arch Environ Occup Health. 2006 Jan-Feb; 61(1): 17-25
Wu T, Bhanegaonkar AJ, Flowers JW

The authors analyzed data from a national sample to examine the relationships between blood concentrations of selected volatile organic compounds (VOCs) and the assessment scores of neurobehavioral evaluation tests. They calculated summary statistics to describe blood concentrations of 30 VOCs. For instance, the 95th percentiles were as follows: 1,1,1-trichloroethane, 0.799 microg/l; 1,4-Dichlorobenzene, 11.081 microg/l; benzene, 0.476 microg/l; and toluene, 0.281 microg/l. For 1,4-Dichlorobenzene, benzene, dibromochloromethane, and trichloroethene, a blood level higher than the 95th percentile was associated with a poorer neurobehavioral assessment score than was a blood level up to the 95th percentile. The authors found a linear relationship between blood toluene concentration and the Serial Digit Learning Test score. The findings suggest that exposure to certain VOCs may result in poor neurobehavioral performance. The study was exploratory and precludes a conclusive statement, so further investigation is warranted.

Chemosphere. 2007 Aug; 68(11): 2073-9
Monferran MV, Wunderlin DA, Nimptsch J, Pflugmacher S

We report the effects of 1,2- and 1,4-Dichlorobenzene (1,2-DCB and 1,4-DCB) on the aquatic macrophyte Ceratophyllum demersum. We evaluated the response of the antioxidant system through the assay of glutathione reductase (GR), guaiacol peroxidase (POD) and glutathione peroxidase (GPx). Additionally, the effect of DCBs on the detoxication system by measuring the activity of glutathione-S-transferase (GST) was evaluated. C. demersum showed elevated GST activities when exposed to 10 and 20 mg l(-1) 1,2-DCB, and at 10 mg l(-1) for 1,4-DCB. These results show that glutathione conjugation take place at relatively high concentrations of both isomers. Significantly increased activities of POD were also detected in C. demersum exposed to concentrations above 5 mg l(-1) of the corresponding isomer. The GR activity was enhanced in plants exposed to 1,2-DCB (5 mg l(-1)) and 1,4-DCB (10 mg l(-1)). GPx was also significantly increased in exposures to the corresponding isomer, each at a concentration of 10 mg l(-1). However, plants exposed to low doses of 1,4-DCB (1 mg l(-1)) showed significantly decreased activities of both enzymes GR and GPx. Consequently, it is clear that the exposure of the aquatic macrophyte C. demersum to DCBs is able to cause an activation of the antioxidant system, showing an isomer specific pattern, which suggests that the defence system of this plant is playing an important role in scavenging ROS, helping to protect the organism against adverse oxidative effects generated by the prooxidant action of the tested xenobiotics. Furthermore, increased GST activities give indirect evidence on the conjugation of either DCBs or the corresponding metabolites during phase II of detoxication, which supports the elimination process of toxic metabolites from cells of C. demersum.

Subst Abus. 2006 Dec; 27(4): 63-7
Cheong R, Wilson RK, Cortese IC, Newman-Toker DE

Paradichlorobenzene (PDB) is a common household deodorant and pesticide found in room deodorizers, toilet bowl fresheners, and some mothballs. Although human exposure to the compound is generally limited and harmless, PDB in larger doses can produce neurotoxic effects, including a chemical "high" similar to that seen with inhalants such as toluene. Although rare, frank addiction to PDB has been reported, and, in such cases, has been associated with gait ataxia, tremor, dysarthria, limb weakness, and bradyphrenia, in various combinations. In such cases, the adverse neurologic consequences have been presumed to result from a direct toxic effect of this small, organic molecule. We report a case of chronic mothball ingestion where profound encephalopathy with cognitive, pyramidal, extrapyramidal, and cerebellar features appears to have been largely the result of PDB withdrawal, rather than direct toxicity. This case raises important questions about the mechanism of PDB neurotoxicity and possible treatment options for PDB-addicted patients. We propose that in cases with clear clinical deterioration after abstinence, readministration and gradual taper of PDB might be considered a therapeutic option.

Chemosphere. 2007 Jan; 66(10): 1939-46
Adebusoye SA, Picardal FW, Ilori MO, Amund OO, Fuqua C, Grindle N

Two polychlorinated biphenyl (PCBs)-degrading bacteria were isolated by traditional enrichment technique from electrical transformer fluid (Askarel)-contaminated soils in Lagos, Nigeria. They were classified and identified as Enterobacter sp. SA-2 and Pseudomonas sp. SA-6 on the basis of 16S rRNA gene analysis, in addition to standard cultural and biochemical techniques. The strains were able to grow extensively on dichloro- and trichlorobenzenes. Although they failed to grow on tetrachlorobenzenes, monochloro- and dichlorobenzoic acids, they were able to utilize all monochlorobiphenyls, and some dichlorobiphenyls as sole sources of carbon and energy. The effect of incubation with axenic cultures on the degradation of 0.9 mM 1,4-Dichlorobenzene, 0.44 mM 1,2,3- and 0.43 mM 1,3,5-trichlorobenzene in mineral salts medium was studied. Approximately, 80-90% of these xenobiotics were degraded in 200 h, concomitant with cell increase of up to three orders of magnitude, while generation times ranged significantly (P<0.05) from 17-32 h. Catechol 1,2-dioxygenase and catechol 2,3-dioxygenase activities were detected in crude cell-free extracts of cultures pre-grown with benzoate, with the latter enzyme exhibiting a slightly higher activity (0.15-0.17 micromolmin(-1) mg of protein(-1)) with catechol, suggesting that the meta-cleavage pathway is the most readily available catabolic route in the SA strains. The wider substrate specificity of these tropical isolates may help in assessing natural detoxification processes and in designing bioremediation and bioaugmentation methods.

Nat Chem Biol. 2006 Jun; 2(6): 338-45
Kokel D, Li Y, Qin J, Xue D

Naphthalene (1) and para-dichlorobenzene (PDCB, 2), which are widely used as moth repellents and air fresheners, cause cancer in rodents and are potential human carcinogens. However, their mechanisms of action remain unclear. Here we describe a novel method for delivering and screening hydrophobic chemicals in C. elegans and apply this technique to investigate the ways in which naphthalene and PDCB may promote tumorigenesis in mammals. We show that naphthalene and PDCB inhibit apoptosis in C. elegans, a result that suggests a cellular mechanism by which these chemicals may promote the survival and proliferation of latent tumor cells. In addition, we find that a naphthalene metabolite directly inactivates caspases by oxidizing the active site cysteine residue; this suggests a molecular mechanism by which these chemicals suppress apoptosis. Naphthalene and PDCB are the first small-molecule apoptosis inhibitors identified in C. elegans. The power of C. elegans molecular genetics, in combination with the possibility of carrying out large-scale chemical screens in this organism, makes C. elegans an attractive and economic animal model for both toxicological studies and drug screens.

Environ Health Perspect. 2006 Mar; 114(3): 453-9
Sexton K, Adgate JL, Fredrickson AL, Ryan AD, Needham LL, Ashley DL

We assessed concurrent exposure to a mixture of > 50 environmental chemicals by measuring the chemicals or their metabolites in the blood of 43 ethnically diverse children (3-6 years of age) from a socioeconomically disadvantaged neighborhood in Minneapolis. Over a 2-year period, additional samples were collected every 6-12 months from as many children as possible. We analyzed blood samples for 11 volatile organic compounds (VOCs), 2 heavy metals (lead and mercury, 11 organochlorine (OC) pesticides or related compounds, and 30 polychlorinated biphenyl (PCB) congeners. The evidence suggests that numerous VOCs originated from common sources, as did many PCBs. Longitudinal measurements indicate that between-child variance was greater than within-child variance for two VOCs (benzene, toluene), for both heavy metals (Pb, Hg), for all detectable OC pesticides, and for 15 of the measured PCB congeners (74, 99, 101, 118, 138-158, 146, 153, 156, 170, 178, 180, 187, 189, 194, 195). Despite the relatively small sample size, highest measured blood levels of 1,4-Dichlorobenzene, styrene, m-/p-xylene, Pb, Hg, heptachlor epoxide, oxychlordane, dichlorodiphenyldichloroethene (p,p -DDE), trans-nonachlor, and PCB congeners 74, 99, 105, 118, 138, 146, 153, 156, 170, and 180 were comparable with or higher than 95th percentile measurements of older children and adults from national surveys. Results demonstrate that cumulative exposures to multiple environmental carcinogens and neurotoxins can be comparatively high for children from a poor inner-city neighborhood.

Chemosphere. 2005 Sep; 61(1): 98-106
Monferrán MV, Echenique JR, Wunderlin DA

A subsurface microbial community was isolated from a polluted site of Suquía River (Córdoba-Argentina), acclimated during 15 days in aerobic conditions using 1,2-dichlorobenzene (1,2-DCB) as the sole carbon source. From this acclimated community, we isolated and identified by 16S rDNA analysis a strain of Acidovorax avenae, which was able to perform the complete biodegradation of 1,2-DCB in two days affording stoichiometric amounts of chloride. This pure strain was also tested for biodegradation of chlorobenzene (CB); 1,3-DCB and 1,4-DCB, giving similar results to the experiments using 1,2-DCB. The aromatic-ring-hydroxylating dioxygenase (ARHDO) alpha-subunit gene core, encoding the catalytic site of the large subunit of chlorobenzene dioxygenase, was detected by PCR amplification and confirmed by DNA sequencing. These results suggest that the isolated strain of A. avenae could use a catabolic pathway, via ARHDO system, leading to the formation of chlorocatecols during the first steps of biodegradation, with further chloride release and subsequent paths that showed complete substrate consumption.

Chemistry. 2005 Nov 4; 11(22): 6471-7
Cai X, Sakamoto M, Fujitsuka M, Majima T

The lifetimes of benzophenone in the higher triplet excited state (BP(T(n))) and several BP derivatives in the T(n) states were measured directly to be tau(T(n))=37+/-7 ps and 20-33 ps, respectively, by using the nanosecond-picosecond (ns-ps) two-color/two-laser flash photolysis method. Based on the direct measurements of tau(T(n)) of BP(T(n)), the triplet energy transfer (TET) from BP(T(n)) to quenchers (Q), such as carbon tetrachloride (CCl4), benzene (Bz), and p-dichlorbenzene (DCB), was investigated. The fast TET from BP(T(n)) to Q can be attributed to the lifetime-dependent quenching process, according to the Ware theoretical model of the bimolecular energy transfer reaction. The contribution of the lifetime-dependent term on k(TET) was 27, 60, and 86% for CCl4, Bz, and DCB as the Q of BP(T(n)), respectively, indicating that the TET from BP(T(n)) to Q is influenced not only by tau(T(n)), but also by the size of Q.

Basic Clin Pharmacol Toxicol. 2005 May; 96(5): 361-5
Makita Y

1,4-Dichlorobenzene (DCB) is used as an air deodorant or a moth repellent and 1, 1-dichloro-2, 2-bis (p-chlorophenyl) ethylene (p,p'-DDE) is a persistent metabolite of 1, 1, 1-trichloro-2, 2-bis (p-chlorophenyl) ethane (DDT) which was used as a pesticide before. DCB concentrations of residential air and oral p,p'-DDE intake through marine products are demonstrated to be very high in Japan and consequently, foetuses and neonates may be exposed much more to DCB and/or p,p'-DDE via the maternal body. It has recently been reported that DCB is oestrogenic and that p,p'-DDE is antiandrogenic. Therefore, the combined effects of perinatal exposure to DCB and p,p'-DDE have been investigated in rat male offspring of dams ingesting these contaminants during the perinatal period from gestational day 1 to postpartum day 21 for 42 days. In this study, no obvious developmental effects on male offspring have been recognized until 6 weeks of age, following oral administration of 25 ppm DCB (approximately 2 mg/kg) and/or 125 ppm p,p'-DDE (approximately 10 mg/kg) to dams. In contrast to female offspring, the thymus weight in male offspring was not affected by DCB at 6 weeks of age, but there might be sexual differences concerning the effects of DCB on the thymus.

Huan Jing Ke Xue. 2004 Nov; 25(6): 97-101
Xu XH, Zhou HY, Wang DH

Pd/Fe bimetallic catalysts were synthesized by chemical deposition and used to dechlorination treatment of p-DCB. Batch experiments demonstrated that the Pd/Fe bimetallic particles can effectively dechlorinate p-DCB. Dechlorination efficiency accounted for more than 90% at Pd weight ratio (Pd to Fe) 0.02% and metal to solution ratio about 4g/74mL in 90min. Dechlorination ratios were affected by reaction temperature, initial pH, Pd ratio and the addition of Pd/Fe. Chlorobenzene represented stable partially dechlorinated intermediates in the generation of benzene.

Environ Health Perspect. 2005 Mar; 113(3): 342-9
Sexton K, Adgate JL, Church TR, Ashley DL, Needham LL, Ramachandran G, Fredrickson AL, Ryan AD

Blood concentrations of 11 volatile organic compounds (VOCs) were measured up to four times over 2 years in a probability sample of more than 150 children from two poor, minority neighborhoods in Minneapolis, Minnesota. Blood levels of benzene, carbon tetrachloride, trichloroethene, and m-/p-xylene were comparable with those measured in selected adults from the Third National Health and Nutrition Examination Survey (NHANES III), whereas concentrations of ethylbenzene, tetrachloroethylene, toluene, 1,1,1-trichloroethane, and o-xylene were two or more times lower in the children. Blood levels of styrene were more than twice as high, and for about 10% of the children 1,4-Dichlorobenzene levels were greater than or equal to 10 times higher compared with NHANES III subjects. We observed strong statistical associations between numerous pairwise combinations of individual VOCs in blood (e.g., benzene and m-/p-xylene, m-/p-xylene and o-xylene, 1,1,1-trichloroethane and m-/p-xylene, and 1,1,1-trichloroethane and trichloroethene). Between-child variability was higher than within-child variability for 1,4-Dichlorobenzene and tetrachloroethylene. Between- and within-child variability were approximately the same for ethylbenzene and 1,1,1-trichloroethane, and between-child was lower than within-child variability for the other seven compounds. Two-day, integrated personal air measurements explained almost 79% of the variance in blood levels for 1,4-Dichlorobenzene and approximately 20% for tetrachloroethylene, toluene, m-/p-xylene, and o-xylene. Personal air measurements explained much less of the variance (between 0.5 and 8%) for trichloroethene, styrene, benzene, and ethylbenzene. We observed no significant statistical associations between total urinary cotinine (a biomarker for exposure to environmental tobacco smoke) and blood VOC concentrations. For siblings living in the same household, we found strong statistical associations between measured blood VOC concentrations.

Drug Chem Toxicol. 2004 Nov; 27(4): 341-60
Han X, Hinderliter PM, Snow TA, Jepson GW

Perfluorooctanoic acid (PFOA) is an organic fluorochemical and is reported to have a long half-life in human blood. Its urinary elimination in rats is markedly sex-dependent, and characterized by significantly longer plasma half-life of PFOA in male rats than in females. It has been postulated that male-specific PFOA binding protein(s) is responsible for the long half-life of PFOA in male rats. In this paper, two male rat specific proteins, liver- and kidney-form alpha2u-globulins (A2U(L) and A2U(K)), were purified from male rat urine and kidney, respectively. The binding of these two nroteins to PFOA was investigated using ligand blotting, electrospray ionization mass spectrometry and fluorescence competitive binding assay. The results revealed that both A2U(L) and A2U(K) were able to bind PFOA in vitro under physiological conditions, and that PFOA and a fluorescent-labeled fatty acid shared the same binding site on both A2U(L) and A2U(K). The binding affinities, however, are relatively weak. The estimated dissociation constants are in the 10(-3) M range, indicating that bindings of PFOA to either A2U(L) or A2U(K) cannot adequately explain the sex-dependent elimination of PFOA in rats, and it is unlikely that PFOA-A2U(K) binding would induce A2U nephropathy as seen with, for example, 1,4-Dichlorobenzene.

Chemosphere. 2004 Oct; 57(2): 127-33
Qian Y, Yin D, Li Y, Wang J, Zhang M, Hu S

Four chlorobenzenes (chlorobenzene, 1,3-dichlorobenzene, 1,4-Dichlorobenzene, p-chloro-methylbenzene) were administrated to the crucian carps (Carassius auratus) by peritoneal injections in the laboratory for 30 days. Serum testosterone and 17 beta-estradiol concentrations were detected using radioimmunology assay (RIA), and the activities of two hepatic microsome enzymes, glutathione s-transferase (GST) and UDP-glucuronosyltransferase (UDPGT), were measured using the modified methods as described by Habig and Owens. Results showed that the four chlorobenzenes caused significant increases in serum testosterone concentration in the crucian carps (P < 0.05) compared to the controls, but they caused no significant effect on 17 beta-estradiol level. All test chemicals caused a change in hepatic GST activity in crucian carps, with significant increases in enzyme activity (P < 0.05). Chlorobenzene, 1,3-dichlorobenzene and p-chloro-methylbenzene resulted in a marked inhibition to UDPGT activity in crucian carp (P < 0.05) except 1,4-Dichlorobenzene. The changes in hepatic microsome enzyme activities may have resulted in the alterations of serum sex steroids levels in the crucian carps. The results indicated that these four chlorobenzenes may result in the changes of endocrine functions and may affect the reproductive success of this and other species.

Microb Ecol. 2003 Aug; 46(2): 161-76
Wenderoth DF, Rosenbrock P, Abraham WR, Pieper DH, Höfle MG

A set of microcosm experiments was performed to assess different bioremediation strategies, i.e., biostimulation and bioaugmentation, for groundwater contaminated with chlorobenzenes. The biodegradative potential was stimulated either by the supply of electron acceptors (air, (NO3-), to increase the activity of the indigenous bacterial community, or by the addition of aerobic chlorobenzene-degrading bacteria (Pseudomonas putida GJ31, Pseudomonas aeruginosa RHO1, Pseudomonas putida F1deltaCC). Experiments were performed with natural groundwater of the aquifer of Bitterfeld, which had been contaminated with 1,2-dichlorobenzene (1,2-DCB), 1,4-Dichlorobenzene (1,4-DCB), and chlorobenzene (CB). The microcosms consisted of airtight glass bottles with 800 mL of natural groundwater and were incubated under in situ temperature (13 degrees C). Behavior of the introduced strains within the indigenous bacterial community was monitored by fluorescent in situ hybridization (FISH) with species-specific oligonucleotides. Dynamics of the indigenous community and the introduced strains within the microcosms were followed by single-strand conformation polymorphism (SSCP) analysis of 16S rDNA amplicons obtained from total DNA of the microbial community. An indigenous biodegradation potential under aerobic as well as anaerobic denitrifying conditions was observed accompanied by fast and specific changes in the natural bacterial community composition. Augmentation with P. aeruginosa RHO1 did not enhance bio-degradation. In contrast, both P. putida GJ31 as well as P. putida F1deltaCC were capable of growing in groundwater, even in the presence of the natural microbial community, and thereby stimulating chlorobenzene depletion. P. putida GJ31 disappeared when the xenobiotics were depleted and P. putida F1deltaCC persisted even in the absence of CB. Detailed statistical analyses revealed that community dynamics of the groundwater microbiota were highly reproducible but specific to the introduced strain, its inoculum size, and the imposed physicochemical conditions. These findings could contribute to the design of better in situ bioremediation strategies for contaminated groundwater.