Chemosphere (v.58, #3)

Concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) and polychlorinated biphenyls (PCB) were determined in 23 soil samples collected at reference sites of the Swiss national soil monitoring network (NABO). Total PCDD/F and PCB concentrations are well correlated and proportional (R 2  = 0.720). The total PCDD/F levels were between 72 and 703 ng/kg corresponding to 1.1–11 ng I-TEQ/kg, total PCB concentrations (sum of seven congeners IUPAC no. 28, 52, 101, 118, 138, 153, and 180) were from 1.1 to 12 μg/kg. In all samples, the PCDD/F and PCB concentrations were in the range of background levels for these contaminants in Central Europe. Ninteen samples revealed PCDD/F levels below the guide value of 5 ng I-TEQ/kg set by the Swiss ordinance relating to impacts on the soil (OIS); concentrations for the remaining four samples were below the trigger value (20 ng I-TEQ/kg). All PCB concentrations were below the guide value of 100 μg/kg. The elevated PCDD/F and PCB levels in some of the samples originating from forested sites could be attributed to the scavenging effect of forest canopies for semivolatile organic compounds. This interpretation could be substantiated by the observed distortion of the congener and homolog patterns of PCDD/F and PCB which is characteristic for forested sites.
Keywords: PCB; PCDD; PCDF; Soil; Switzerland;

Congener-specific concentrations and carbon stable isotope ratios (δ13C) of two technical toxaphene products (Toxaphene® and Melipax®) by Walter Vetter; Gerd Gleixner; Wolfgang Armbruster; Steffen Ruppe; Gary A. Stern; Eric Braekevelt (235-241).
In this study we compared the contribution of individual congeners and the ratios of stable carbon isotopes of two technical toxaphene products. The former US-American product Toxaphene® was from 1978 and the East-German product Melipax® from 1979. Both technical products showed the known complexity in GC/ECD measurements. Contributions of 24 peaks to each of the technical products were determined by gas chromatography in combination high resolution electron capture negative ion mass spectrometry (GC/ECNI-HRMS). The percentages of the compounds studied in the technical mixtures ranged from ∼0.05% to ∼2.5% but showed some individual differences. 2,2,5,5,8,9,9,10,10-nonachlorobornane (B9-1025 or P-62) was identified as a major congener in both mixtures. 2-Endo,3-exo,5-endo,6-exo,8,8,10,10-octachlorobornane (B8-1413 or P26) and 2-endo,3-exo,5-endo,6-exo,8,8,9,10,10-nonachlorobornane (B9-1679 or P-50) were found at similar concentration in both technical products.Identical amounts of Melipax or Toxaphene were combusted to CO2 in an element analyzer and their δ13C values were determined relative to the international standard Vienna PeeDee belemnite (VPDB). The mean δ13C values of both products varied by 2.8% (determined at two different locations) which is roughly one order of magnitude more than the precision obtained in repetitive analyses of the individual products. Thus, both investigated products could be unequivocally distinguished by stable isotope ratio mass spectrometry (IRMS). IRMS analyses may thus be a suitable tool for tracing back toxaphene residues in environmental and food samples to the one or both of the products.
Keywords: Toxaphene; Melipax; Isotope ratio mass spectrometry; Stable isotopes; δ13C values; GC/ECNI-HRMS;

The pulsed laser photolysis/pulsed laser-induced fluorescence (PLP/PLIF) technique has been applied to obtain rate coefficients for OH + dioxin (DD) (k 1), OH + 2-chlorodibenzo-p-dioxin (2-CDD) (k 2), OH + 2,3-dichlorodibenzo-p-dioxin (2,3-DCDD) (k 3), OH + 2,7-dichlorodibenzo-p-dioxin (2,7-DCDD) (k 4), OH + 2,8-dichlorodibenzo-p-dioxin (2,8-DCDD) (k 5), OH + 1,2,3,4-tetrachlorodibenzo-p-dioxin (1,2,3,4-TCDD) (k 6), and OH + octachlorodibenzo-p-dioxin (OCDD) (k 7) over an extended range of temperature. The atmospheric pressure (740 ± 10 Torr) rate measurements are characterized by the following Arrhenius parameters (in units of cm3  molecule−1  s−1, error limits are 1σ): k 1 ( 326 – 907 K ) = ( 1.70 ± 0.22 ) × 10 - 12 exp ( 979 ± 55 ) / T , k 2 ( 346 – 905 K ) = ( 2.79 ± 0.27 ) × 10 - 12 exp ( 784 ± 54 ) / T , k 3 ( 400 – 927 K ) = ( 1.83 ± 0.19 ) × 10 - 12 exp ( 742 ± 67 ) / T , k 4 ( 390 – 769 K ) = ( 1.10 ± 0.10 ) × 10 - 12 exp ( 569 ± 53 ) / T , k 5 ( 379 – 931 K ) = ( 1.02 ± 0.10 ) × 10 - 12 exp ( 580 ± 68 ) / T , k 6 ( 409 – 936 K ) = ( 1.66 ± 0.38 ) × 10 - 12 exp ( 713 ± 114 ) / T , k 7 ( 514 – 928 K ) = ( 3.18 ± 0.54 ) × 10 - 11 exp ( - 667 ± 115 ) / T . The overall uncertainty in the measurements, taking into account systematic errors dominated by uncertainty in the substrate reactor concentration, range from a factor of 2 for DD, 2-CDD, 2,3-DCDD, 2,7-DCDD, and 2,8-DCDD to ± a factor of 4 for 1,2,3,4-TCDD and OCDD. Negative activation energies characteristic of an OH addition mechanism were observed for k 1k 6. k 7 exhibited a positive activation energy. Cl substitution was found to reduce OH reactivity, as observed in prior studies at lower temperatures. At elevated temperatures (500 K <  T  < 500 K), there was no experimental evidence for a change in reaction mechanism from OH addition to H abstraction. Theoretical calculations suggest that H abstraction will dominate OH reactivity for most if not all dioxins (excluding OCDD) at combustion temperatures (>1000 K). For OCDD, the dominant reaction mechanism at all temperatures is OH addition followed by Cl elimination.
Keywords: Arrhenius parameters; Atmospheric reactivity; Air emissions; Combustion; Thermal treatment;

Analysis of short chain chlorinated paraffins in sediment samples from the Czech Republic by short-column GC/ECNI-MS by Petra Štejnarová; Mehmet Coelhan; Romana Kostrhounová; Harun Parlar; Ivan Holoubek (253-262).
Top layer sediment samples from the Czech Republic were analyzed to obtain the preliminary information about contamination of the region by chlorinated paraffins. Sediment samples from three locations with different industrial discharges were taken over the period of 2 years. The analysis was performed by short-column gas chromatography-electron capture negative ion mass spectrometry (SCGC/ECNI-MS). Short chain chlorinated paraffin sediment concentrations varied between 24.00 and 45.78 ng g−1 (dry weight, d.w.) in the Košetice area, 16.30–180.75 ng g−1 (dry weight) in the Zlı́n area and 4.58–21.57 ng g−1 dry weight in the Beroun area. Highly chlorinated undecanes prevailed in the samples.On the basis of these results, more detailed studies should be conducted to determine the magnitude and extent of chlorinated paraffin contamination in these regions.
Keywords: Chlorinated paraffins; Polychlorinated n-alkanes; SCCPs; SCGC/ECNI-MS; Sediment; Czech Republic;

Large quantities of trinitrotoluene (TNT) have been associated with past and present military activities worldwide. Because this contaminant is highly toxic and strongly sorbs to soil particles, bacteria that are able to transform it have had very little success, if any. This study was conducted to evaluate the bioavailability of 14C-labeled TNT in soil for microbial mineralization. Sorption–desorption experiments indicated that a Kendaia loam soil effectively adsorbs this explosive compound, with approximately 30–45% of the added TNT remaining sorbed to the soil after a total of 10 washings. A bacterial consortium isolated from explosive-contaminated sites was prepared in liquid medium and then tested in a TNT-spiked Kendaia loam soil. The concentration of TNT in the soil that was inoculated with the bacterial consortium was reduced by more than 30% of the initial concentration compared to the soil that did not contain the bacterial consortium within a period of 20 weeks. Nearly half of the TNT was mineralized as determined by the percentage of 14CO2 produced. Only one member of the consortium (i.e., Enterobacter sp.) significantly mineralized 25% of TNT although the extent of mineralization was significantly enhanced to 35% in the presence of the other two members of the consortium. The data suggest that some of the strongly adsorbed TNT may be accessible for metabolism if conditions for the right combination of microorganisms with specialized capabilities are optimized. The remaining sorbed fraction of substrate is presumably sequestered and thus unavailable to the microorganisms.
Keywords: Microbial consortium; Biodegradation; Adsorbed TNT; Inoculum;

Organochlorine pollutants in soils and mosses from Victoria Land (Antarctica) by Francesca Borghini; Joan O. Grimalt; Juan C. Sanchez-Hernandez; Roberto Bargagli (271-278).
The major organochlorine (OC) pollutants, i.e. pentachlorobenzene (PCBz), hexachlorobenzene (HCB), hexachlorocyclohexanes (HCHs), polychlorobiphenyls (PCBs) and DDTs have been analyzed in soils and mosses from coastal areas of Victoria Land (70–80°S, 160–170°E). PCBs (23–34 ng g−1  dry wt.) and PCBz (0.38–1.3 ng g−1  dry wt.) were the dominant OCs in mosses and soils, respectively. In general, the concentrations of OC in soils, i.e. HCB (0.034–0.17 ng g−1  dry wt.), PCBs (0.36–0.59 ng g−1  dry wt.) and 4,4′-DDE (0.053–0.086 ng g−1  dry wt.), range among the lowest reported in remote regions. These concentrations exhibited high correlation coefficients when represented vs. total organic carbon (TOC) which is consistent with the general correlation between OC and TOC in soils from remote areas recently observed (Meijer, S.N., Ockenden, W.A., Seetman, A., Breivik, K., Grimalt, J.O., Jones, K.C., 2003. Global distribution and budget of PCBs and HCB in background surface soils: implications for sources and environmental processes. Environ. Sci. Technol. 37, 667–672). Statistically significant dependences between reciprocal of temperature and log-transformed concentrations of HCB and 4,4′-DDE in mosses and α-HCH in soils have been found. These observations provide further data illustrating that temperature is a major factor determining the planetary scale distribution and accumulation of OCs giving additional ground to the general validity of the global distillation effect for description of planetary OC distribution.
Keywords: Organochlorine compounds; Mosses; Soils; Antarctica; Long-range pollutant transport;

The changing state of contamination in the Lagoon of Venice. Part 1: organic pollutants by Tommaso Secco; Francesca Pellizzato; Adriano Sfriso; Bruno Pavoni (279-290).
The Lagoon of Venice is a transitional environment suffering from industrial, urban and agricultural impact. Recently the mechanical clam fishing, preventing a regular deposition of sediments has made sampling of cores suitable for radiodating very problematic. Therefore, in this study, in order to assess temporal and spatial trends of contamination, the same sampling scheme was repeated three times over a 12-year period. The concentrations of PCBs, PAHs and organochlorine pesticides were measured in the uppermost 5 cm of sediments collected in 25 sites in the central portion of the lagoon during three campaigns conducted in 1987, 1993 and 1998. Analytical results, validated statistically, indicated that, while PCB and pesticide concentrations tend to decrease during the considered period of time, PAH do not, showing that the input rate of these compounds to the lagoon environment is still important. A spatial trend of pollution was also found in the lagoon for PCBs and pesticides, which decrease from the sources, namely the industrial zone and the mouths of rivers, to areas closer to the sea: a reduction up to 80% and 90%, respectively, was monitored. PAH contamination, originating chiefly from incomplete combustion of fossil fuels, as inferred from ratios of congeners, was mainly located around the historical center of Venice, where most of the boat traffic is concentrated and has an increasing trend.
Keywords: PAHs; PCBs; Pesticides; Sediments; Venice Lagoon;

Dissolution and removal of PAHs from a contaminated soil using sunflower oil by Zongqiang Gong; Kassem Alef; B.-M. Wilke; Peijun Li (291-298).
This study reports on the feasibility of remediation of polycyclic aromatic hydrocarbon (PAH) contaminated soils using sunflower oil, an environmentally-friendly solvent. Batch experiments were performed to test the influence of oil/soil ratio on the remediation of PAH contaminated soil, and to test the mass transfer behaviors of PAHs from soil to oil. An empirical model was employed to describe the kinetics of PAH dissolution and to predict equilibrium concentrations of PAHs in oil. PAH containing oil was regenerated using active carbon. Results show that dissolution of PAHs from a Manufactured Gas Plant (MGP) soil at oil/soil ratios of one or two were almost the same. Nearly all PAHs (81–100%) could be removed by sunflower oil dissolution. Mass transfer coefficients for low molecular PAHs namely fluoranthene, phenanthrene and anthracene were one or two orders of magnitude higher than those for high molecular PAHs with 4–6 rings. Ninety milliliters of PAH containing oil could be regenerated by 10 g active carbon in a batch reactor. Such a remediation procedure indicates that sunflower oil is a promising agent for the removal of PAHs from MGP soils. However, further research is required before the method can be used for in situ remediation of contaminated sites.
Keywords: Polycyclic aromatic hydrocarbons; Soil remediation; Vegetable oil; Mass transfer; Equilibrium partitioning;

Carbon/electron source dependence of polychlorinated biphenyl dechlorination pathways for anaerobic granules by Hendrik Nollet; Iris Van de Putte; Lutgarde Raskin; Willy Verstraete (299-310).
The effect of acclimating anaerobic granules from commercial bioreactors with different carbon/electron sources on their ability to reductively dechlorinate a tri-(2,3,4-CB) and heptachlorobiphenyl (2,2′,3,3′,4,5,6-CB) was studied. The anaerobic granules were first grown in upflow anaerobic sludge blanket (UASB) reactors fed with two different mixtures of carbon/electron sources, i.e., propionate/butyrate/methanol and formate/methanol. Differences in dechlorination patterns for 2,2′,3,3′,4,5,6-CB were observed in batch experiments inoculated with granules from these two sets of UASB reactors. Variation of the carbon/electron source, during the dechlorination process, had no effect on the dechlorination pathway, but the extents and rates of dechlorination were highest for ethanol and formate and lowest for pyruvate fed batches. Pre-acclimation of different anaerobic sludges to polychlorinated biphenyls (PCBs) shortened the lag period, but did not influence the PCB dechlorination pathway. This is the first time that similar acclimation conditions for several anaerobic microbial communities prior to inoculation were reported to yield similar substrate specificities for the reductive dechlorination of specific PCB congeners. This research demonstrates a successful strategy for the development of biocatalysts to serve as the inoculum of partially decontaminated sites in order to provide microorganisms with specificities complementary to those of naturally occurring dechlorinators.
Keywords: Polychlorinated biphenyl; Anaerobic granules; Carbon/electron source; Reductive dechlorination pathway; Unadapted;

This work compares two lipid extraction methods for determining 24 polychlorinated biphenyls (PCBs), seven dibenzo-p-dioxins (PCDDs) and ten dibenzofurans (PCDFs) in human blood plasma. The first method was based on conventional liquid–liquid partitioning with chloroform–methanol and the other made use of a sorbent (Chem-Elut) to facilitate the partitioning of lipids into a mixture of hexane and 2-propanol. A multi-layer-silica column including acid- and base-impregnated silica gel was used to reduce the amounts of lipid present in the samples before a basic alumina clean-up step and activated carbon fractionation of planar analytes (PCDD/Fs and non-ortho-PCBs) and non-planar analytes (including ortho-chlorinated PCBs). Gas chromatography coupled to high resolution mass spectrometry was used to identify and quantify the analytes in the two fractions. The wet weight based concentrations obtained by the two methods were in agreement but both methods suffer from large organic solvent consumption. The toxic equivalencies derived for PCBs and PCDD/Fs using the two methods were also in agreement. However, the chloroform–methanol method gave slightly higher lipid recoveries, although with greater variation, than the sorbent-assisted method. Nevertheless, despite giving lower lipid recoveries, the sorbent-assisted method has advantages in ease of use and applicability to whole blood samples. The formation of emulsions was avoided with the Chem-Elut method, which probably explains the lower variability in the lipid determinations.
Keywords: Analysis; Lipid determination; PCB; PCDD; PCDF; Bligh and Dyer; Hydromatrix;

Influence of pre-treatment step on PAHs analyses in contaminated soils by Laurence Belkessam; Paul Lecomte; Véronique Milon; Agnès Laboudigue (321-328).
There is no specific standardization for the pre-treatment of a soil sample for PAHs analyses. The ISO/FDIS 14507 method for soil quality gives a guidance for sample pre-treatment before measurement of organic contaminants in soil. It refers to cryogenic crushing which is not so easy to carry out. So, analysts lead to develop in house methods which can be very different from a laboratory to another and can involve deviations in the pollution quantification.This study has explored different ways of drying, grinding and sieving in order to determine the influence of the soil sample handling on the measured pollutant concentration. It appears that the influence of pre-treatment depends on the soil nature and on the PAHs distribution. As a conclusion, it is advised “light” drying ways like air drying or drying at 40 °C in a drying oven instead of more “drastic” ways (freeze-drying, cryogenic crushing) which can induce some losses. Crushing and sieving are also recommended for more reproducible measures.
Keywords: Polycyclic aromatic hydrocarbons; Contaminated soils; Soil preparation; Drying; Measure; Reproducibility;

Concentrations of dioxins and related compounds in the blood of Fukuoka residents by Yoshito Masuda; Koichi Haraguchi; Suminori Kono; Hiroshi Tsuji; Olaf Päpke (329-344).
Blood samples of 152 residents (male 75 and female 77) aged 20–60 years in Fukuoka, Japan, were analyzed for dioxin toxic compounds of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), non-ortho polychlorinated biphenyls (non-ortho PCBs) and mono-ortho polychlorinated biphenyls (mono-ortho PCBs) as well as 35 PCB congeners and 12 chlorinated pesticides by high-resolution gas chromatography/high-resolution mass spectrometry. Average concentrations of dioxin toxic equivalents (TEQ) from PCDDs, PCDFs, non-ortho PCBs, mono-ortho PCBs and their total in the blood of 152 residents were 10.28, 5.56, 7.75, 4.57 and 28.15 ppt in lipid, respectively. These total TEQ levels were comparable to the blood TEQ levels of normal Japanese (n  = 735). Lipid basis total TEQ levels progressively increased in the males from 17.1 ppt at age 20s to 47.5 ppt at age 50s and in the females from 19.5 ppt at age 20s to 54.5 ppt at age 50s. Dioxin toxic contribution of PCBs to total TEQ was increased from 31% at age 20s to 55% at age 50s. Average concentrations of total 35 PCBs and total 12 pesticides in the blood of 151 residents were 386 and 1079 ppb in lipid, respectively. Average concentrations (ppb in lipid) of total PCBs and total pesticides also progressively increased in the males from 213 and 444 at age 20s to 868 and 2140 at age 50s, respectively, and in the females from 199 and 588 at age 20s to 550 and 1977 at age 50s, respectively. The levels of TEQ, PCBs, hexachlorobenzene, beta-hexachlorocyclohexane, dieldrin, p,p′-dichlorodiphenyldichloroethylene, p,p′-dichlorodiphenyltrichloroethane, trans-nonachlor and cis-nonachlor were positively correlated with each other in most of the combinations, and the highest correlations (r  > 0.8) were observed between total TEQ and PCBs in both sexes.
Keywords: Human blood; Polychlorinated dibenzo-p-dioxins; Polychlorinated dibenzofurans; Polychlorinated biphenyls; Organochlorine pesticides; Concentrations and age;

Blubber samples from grey seal (Halichoerus grypus) pups were collected in 1998 through to 2000. Twenty four newly weaned pups were sampled in November 1998, 13 of which were re-sampled during their first year of life, between March and December 1999, and an additional 48 and 25 samples (new cohorts) were obtained in 1999 (November–December) and 2000 (May–September) respectively. ∑PBDE concentrations (sum of Di-HxBDEs) ranged from 45 to 1500 ng/g lipid, with a geometric mean of 290 ng/g lipid. BDE 47 dominated the congener profile, followed by BDEs 100, 99, 153 and 154. ∑PCB concentrations (sum of 41 congeners) ranged from 100 to 93 000 ng/g lipid, with a geometric mean of 4600 ng/g lipid, with CB congeners 153, 138 and 180 making up 84% of the total PCB concentrations. The predominant OC pesticides were p,p′-DDE (geometric mean = 860 ng/g lipid, range = 160–3800 ng/g lipid) and p,p′-DDT (geometric mean = 120 ng/g lipid, range = 30–670 ng/g lipid). No significant differences were found between males and females, probably due to the young age of the animals. Significant decreases (P  < 0.01 for PBDEs and P  < 0.05 for PCBs/OCs) were observed between newly weaned seals in 1998 and 1999, but not for the majority of juveniles in 1999 and 2000. Significant differences (P  < 0.01) were also found between the different seasons in 1999 newly weaned and juvenile seals, reflecting changes in blubber mass.
Keywords: PBDEs; PCBs; Organochlorine pesticides; United Kingdom; Pinnipeds;

Airborne PCB as a contamination risk on freeze-drying of sediment by Maria Söderström; Kerstin Nylund; Ulf Järnberg; Tomas Alsberg; Lillemor Asplund (355-366).
In a study of polychlorinated biphenyls (PCB) in freeze-dried sediments from Swedish lakes, the samples were found to contain unexpectedly high concentrations of PCBs. In one of the lakes (Björken), e.g. the concentration of PCB-28 was found to be 189 ng/g dw after freeze-drying compared to 7 ng/g dw after air-drying of the sediment and therefore our hypothesis was that the contamination had occurred during the freeze-drying procedure. Hence, a dry reference sediment (RS) was used in order to identify potential sources of PCB contamination. The investigation included freeze-drying of the dry RS in five different laboratories, exposure to the air in the freeze-drying room, storage at room temperature and air-drying in a certain fume hood and in a laminar flow clean bench. The pattern and concentrations of PCBs detected in the exposed RS were strongly influenced by low chlorinated PCB congeners under all of these conditions with exception for air-drying in the fume hood. Storage in the laboratory air resulted in a slight elevation in the concentrations of low chlorinated PCB congeners, whereas higher concentrations of all PCB congeners were observed after freeze-drying. In all experiments the contamination appeared to be due to adsorption of PCB from the laboratory air. On the basis of these findings we recommend that reference material be subjected to the entire procedure, including sample preparation, in order to monitor contamination and that a procedure involving solvent extraction of wet sediment samples is used, whenever possible, instead of procedures involving dry samples.
Keywords: Airborne contamination; α-HCH; PCB-28; PCB-52; PCB-101; Storage;

Within this project the emissions into the atmosphere of polychlorinated dibenzo-p-dioxins and -furans (PCDD/F) of 30 domestic heating appliances in Austrian households were tested. The appliances were single stoves (kitchen stove, continuous burning stove and tiled stove) and central heating boilers for solid fuels up to a nominal heat input of 50 kW.A main objective of this survey was to determine the PCDD/F emissions of domestic heating units under routine conditions. Therefore, the habitual combustion conditions used by the operators were not influenced. The original fuels and lightning supports were used and the operation of the units was carried out by the householders according to their usual practice. The data obtained were used to calculate in-field PCDD/F-emission factors.Most of the appliances have shown PCDD/F emissions within a concentration range of 0.01–0.3 ng TEQ/MJ. Modern fan-assisted wood heating boilers with afterburning and units for continuously burning of wood chips and wood pellets had the lowest emissions. High emissions were caused by unsuitable heating habits such as combustion of wastes and inappropriate operation of the appliances. There were only small differences between single stoves and central heating boilers or between wood and coal-fired appliances. The emission factors calculated are higher than those cited in literature, which are mainly derived from trials on test stands under laboratory conditions.
Keywords: PCDD/F; Solid fuel; Emission factor; Single stove; Heating boiler; Domestic heating appliances;

Groundwater, used in this study, contaminated predominantly with aromatic compounds, was biologically treated in a fluidized-bed reactor (FBR) with immobilized cells. The aromatics were completely decomposed, while cis-1,2-dichloroethylene (cis-DCE) and trichloroethylene (TCE) were decomposed only approximately 20% and 5%, respectively. In these studies a significant improvement of the decomposition efficiency for chlorinated ethylenes was achieved by utilizing cometabolism. Methanol (MeOH) and toluene were used as the substrate in the case of one-stage reactor (Single Reactor). MeOH (187 mg l−1) increased the decomposition efficiency up to 40% and 60% for cis-DCE and TCE, respectively, while toluene (20 mg l−1) increased the decomposition efficiency of cis-DCE to 92% and the decomposition efficiency of TCE to 76%. In the case of two-stage reactor system (Reactor 1 and Reactor 2), MeOH and methane (CH4) were used as the substrate. In this system, cells grown on MeOH or CH4 in the Reactor 1 were continuously fed into Reactor 2 and groundwater was fed into Reactor 2 only. When MeOH (384 mg l−1  d−1) was used as substrate the decomposition efficiency of cis-DCE and TCE were 60% and 70%, respectively. Similar decomposition efficiency was observed for a small amount of CH4 (19.3 mg l−1  d−1).
Keywords: Cometabolic degradation; Contaminated groundwater; Dichloroethylene; Trichloroethylene; Two-stage bioreactor;