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Phenolic compounds in industrial wastewaters are toxic pollutants and pose a threat to public health and ecosystems. More recently, focus is being directed towards combining the treatment of these compounds with a cost-effective and environmentally sound technology. The removal efficiency of dimethylphenol and ammonium nitrogen was studied, for the first time, in three different laboratory-scale horizontal subsurface flow constructed wetlands planted with Juncus effusus. Two of the wetlands used were filled with gravel. One of these was planted and the second left without vegetation. The third wetland was a hydroponic system. It was found that the removal efficiencies of dimethylphenol was dependent on the inflow loading of the contaminant and was higher in the planted systems. Both planted systems yielded 99% removal efficiency up to loads of 240 mg/d, compared to only 73% for the unplanted constructed wetland. Factors and processes such as redox dynamics, methanogenesis, reduction of ammonium and low nitrate and nitrite concentrations imply simultaneous aerobic and anaerobic dimethylphenol transformations. A significant surplus of organic carbon was detected in the planted wetlands, which may originate from intermediates of the dimethylphenol transformation processes and/or organic plant root exudates. The present study demonstrates that horizontal subsurface flow constructed wetlands are a promising alternative system for the treatment of effluents contaminated with dimethylphenol isomers.

The modification of DNA by adduct formation is a potential molecular initiating event of genotoxicity. A chemoassay was established to study adduct formation of electrophiles with deoxynucleosides. Liquid chromatography-mass spectrometry was used to determine the reactivity of the model electrophiles para-benzoquinone, hydroquinone, and 1,4-naphthoquinone with deoxynucleoside (deoxyadenosine (dA), deoxyguanosine (dG), deoxycytidine (dC) and thymidine (dT)) to detect formation of adducts via constant neutral loss scan of deoxyribose (116 Da), and to elucidate adduct structures using high resolution mass spectrometry. Of the four deoxynucleosides dG was most susceptible, followed by dC and para-benzoquinone was the most reactive electrophile. With this approach five dG and four dC adducts were detected, formed by Michael addition and subsequent condensation. Also oxidation occurred with reactive oxygen species (ROS). Three of the adducts formed by benzoquinone have not been reported before. This chemoassay combined with mass spectrometry offers a way (a) to screen a large number of chemicals for their genotoxic potential, (b) to determine novel adducts that may be searched for in in vitro and in vivo studies and thus (c) to better understand the reaction of electrophiles with nucleobases.

A rarely used hydroponic plant root mat filter (PRMF, of 6 m2) and a horizontal subsurface flow constructed wetland (HSSF CW, of 6 m2), operating in continuous flow and discontinuous outflow flushing modes, were investigated for treating sulfate-rich and organic carbon-lean groundwater contaminated with monochlorobenzene (MCB); 1,2-dichlorobenzene (1,2-DCB); 1,4-dichlorobenzene (1,4-DCB); and 2-chlorotoluene. Whereas the mean inflow loads ranged from 1 to 247 mg m−2 days−1, the range of mean inflow concentrations of the chlorobenzenes recorded over a period of 7 months was within 0.04 and 8 mg L−1. A hydraulic surface loading rate of 30 L m−2 days−1 was obtained in both systems. The mean load removal efficiencies were found to vary between 87 and 93 % in the PRMF after a flow path of 4 m, while the removal efficiencies were found to range between 46 and 70 % and 71 to 73 % in the HSSF CW operating in a continuous flow mode and a discontinuous outflow flushing mode, respectively. Seasonal variations in the removal efficiencies were observed for all low-chlorinated hydrocarbons both in the PRMF and the HSSF CW, whereby the highest removal efficiencies were reached during the summer months. Sulfide formation occurred in the organic carbon-lean groundwater particularly in summer, which is probably due to the plant-derived organic carbon that fostered the microbial dissimilatory sulfate reduction. Higher redox potential in water was observed in the PRMF. In conclusion, the PRMF could be an option for the treatment of water contaminated with compounds which in particular need oxic conditions for their microbial degradation, such as in the case of low-chlorinated benzenes.

A laboratory-scale planted fixed bed reactor planted with the helophyte Juncus effusus was utilized for long-term experiments in the treatment of an artificial industrial wastewater using a mixture of 2,6-, 3,4-, and 3,5-dimethylphenol (DMP) in equimolar ratios (total DMPs of 20, 40 and 100 mg L−1), and only adding the isomer 2,6-DMP. The permanent circulation flow of the process water in the reactor enabled the simulation of the rooted zone of a constructed wetland (CW). Removal performance of the DMP isomers varied, and was determined to be in the order of 3,4- > 3,5- > 2,6. A stepwise increase in the inflow concentration of the total DMPs from 20 to 100 mg L−1 caused a decrease in the removal of total DMPs by more than 90%, and ultimately led to nearly complete removal inhibition. The results showed that DMP removal performance was dependent on concentration and specific isomer. At a DMP inflow concentration of 100 mg L−1, methane appeared in the pore water with a concentration of approximately 1.5 mg L−1 using a DMP mixture and 0.7 mg L−1 by only 2,6-DMP addition. Whether the carbon source for methanogenesis come either from the rhizodeposition products or/and the DMPs, has yet to be discovered. These experimental results, and further studies with higher effluent complexity, will assist in developing new treatment strategies for industrial effluents from the petro-chemical and, in particular, the carbo-chemical industry using CWs.

Fish embryos are widely used as an alternative model to study toxicity in vertebrates. Due to their complexity, embryos are believed to more resemble an adult organism than in vitro cellular models. However, concerns have been raised with respect to the embryo's metabolic capacity. We recently identified allyl alcohol, an industrial chemical, to be several orders of magnitude less toxic to zebrafish embryo than to adult zebrafish (embryo LC50 = 478 mg/L vs. fish LC50 = 0.28 mg/L). Reports on mammals have indicated that allyl alcohol requires activation by alcohol dehydrogenases (Adh) to form the highly reactive and toxic metabolite acrolein, which shows similar toxicity in zebrafish embryos and adults. To identify if a limited metabolic capacity of embryos indeed can explain the low allyl alcohol sensitivity of zebrafish embryos, we compared the mRNA expression levels of Adh isoenzymes (adh5, adh8a, adh8b and adhfe1) during embryo development to that in adult fish. The greatest difference between embryo and adult fish was found for adh8a and adh8b expression. Therefore, we hypothesized that these genes might be required for allyl alcohol activation. Microinjection of adh8a, but not adh8b mRNA led to a significant increase of allyl alcohol toxicity in embryos similar to levels reported for adults (LC50 = 0.42 mg/L in adh8a mRNA-injected embryos). Furthermore, GC/MS analysis of adh8a-injected embryos indicated a significant decline of internal allyl alcohol concentrations from 0.23-58 ng/embryo to levels below the limit of detection (< 4.6 µg/L). Injection of neither adh8b nor gfp mRNA had an impact on internal allyl alcohol levels supporting that the increased allyl alcohol toxicity was mediated by an increase in its metabolization. These results underline the necessity to critically consider metabolic activation in the zebrafish embryo. As demonstrated here, mRNA injection is one useful approach to study the role of candidate enzymes involved in metabolizatio

A hydroponic plant root mat filter (HPRMF) was compared over 7 months with a horizontal subsurface flow constructed wetland (HSSF CW) regarding the removal of perchloroethene (PCE) (about 2 mg L−1) from a sulfate- (850 mg L−1) and ammonia-rich (50 mg L−1) groundwater with a low TOC content. At a mean area specific inflow PCE load of 56 mg m−2 d−1, after 4 m from inlet, the mean PCE removal during summer time reached 97% in the HPRMF and almost 100% in the HSSF CW. Within the first 2 m in the HSSF CW metabolites like dichloroethenes, vinyl chloride and ethene accumulated, their concentrations decreased further along the flow path. Moreover, the tidal operation (a 7-d cycle) in the HSSF CW decreased the accumulation of PCE metabolites within the first 1 m of the bed. The carcinogenic degradation metabolite vinyl chloride was not detected in the HPRMF. The smaller accumulation of the degradation metabolites in the HPRMF correlated with its higher redox potential. It can be concluded from this study that HPRMF appears an interesting alternative for special water treatment tasks and that tidal operation will show some positive effects on the removal of the accumulated PCE metabolites in HSSF CW.

Natural wetlands are transition zones between anoxic ground and oxic surface water which may enhance the (bio)transformation potential for recalcitrant chloro-organic contaminants due to the unique geochemical conditions and gradients. Monochlorobenzene (MCB) is a frequently detected groundwater contaminant which is toxic and was thought to be persistent under anoxic conditions. Furthermore, to date, no degradation pathways for anoxic MCB removal have been proven in the field. Hence, it is important to investigate MCB biodegradation in the environment, as groundwater is an important drinking water source in many European countries. Therefore, two pilot-scale horizontal subsurface-flow constructed wetlands, planted and unplanted, were used to investigate the processes in situ contributing to the biotransformation of MCB in these gradient systems. The wetlands were fed with anoxic MCB-contaminated groundwater from a nearby aquifer in Bitterfeld, Germany. An overall MCB removal was observed in both wetlands, whereas just 10% of the original MCB inflow concentration was detected in the ponds. In particular in the gravel bed of the planted wetland, MCB removal was highest in summer season with 73 ± 9% compared to the unplanted one with 40 ± 5%. Whereas the MCB concentrations rapidly decreased in the transition zone of unplanted gravel to the pond, a significant MCB removal was already determined in the anoxic gravel bed of the planted system. The investigation of hydro-geochemical parameters revealed that iron and sulphate reduction were relevant redox processes in both wetlands. In parallel, the addition of ferric iron or nitrate stimulated the mineralisation of MCB in laboratory microcosms with anoxic groundwater from the same source, indicating that the potential for anaerobic microbial degradation of MCB is present at the field site.

In order to characterize the effect of vegetation on performance of constructed wetlands (CWs) treating low and high chlorinated hydrocarbon, two pilot-scale horizontal subsurface flow (HSSF) CWs (planted with Phragmites australis and unplanted) treating sulphate rich groundwater contaminated with MCB (monochlorobenzene, as a low chlorinated hydrocarbon), (about 10 mg L−1), and PCE (perchloroethylene, as a high chlorinated hydrocarbon), (about 2 mg L−1), were examined. With mean MCB inflow load of 299 mg m−2 d−1, the removal rate was 58 and 208 mg m−2 d−1 in the unplanted and planted wetland, respectively, after 4 m from the inlet. PCE was almost completely removed in both wetlands with mean inflow load of 49 mg m−2 d−1. However, toxic metabolites cis-1,2-DCE (dichloroethene) and VC (vinyl chloride) accumulated in the unplanted wetland; up to 70% and 25% of PCE was dechlorinated to cis-1,2-DCE and VC after 4 m from the inlet, respectively. Because of high sulphate concentration (around 850 mg L−1) in the groundwater, the plant derived organic carbon caused sulphide formation (up to 15 mg L−1) in the planted wetland, which impaired the MCB removal but not statistically significant. The results showed significant enhancement of vegetation on the removal of the low chlorinated hydrocarbon MCB, which is probably due to the fact that aerobic MCB degraders are benefited from the oxygen released by plant roots. Vegetation also stimulated completely dechlorination of PCE due to plant derived organic carbon, which is potentially to provide electron donor for dechlorination process. The plant derived organic carbon also stimulated dissimilatory sulphate reduction, which subsequently have negative effect on MCB

Long-term investigations were carried out in two pilot-scale horizontal subsurface flow constructed wetlands (planted and unplanted) with an iron-rich soil matrix for treating sulphate-rich groundwater which was contaminated with low concentrations of chlorinated hydrocarbons. The temporal and spatial dynamics of pore-water sulphide, Fe(II) and phosphate concentrations in the wetland beds were characterized and the seasonal effects on sulphide production and nitrification inhibition were evaluated. The results demonstrated that the pore-water sulphide concentrations gradually increased from less than 0.2 mg/L in 2005 to annual average concentrations of 15 mg/L in 2010, while the pore-water Fe(II) concentrations decreased from 35.4 mg/L to 0.3 mg/L. From 2005 to 2010, the phosphate removal efficiency declined from 91% to 10% under a relatively constant inflow concentration of 5 mg/L. The pronounced effect of plants was accompanied by a higher sulphate reduction and ammonium oxidation in the planted bed, as compared to the unplanted control. A high tolerance of plants towards sulphide toxicity was observed, which might be due to the detoxification of sulphide by oxygen released by the roots. However, during the period of 2009–2010, the nitrification was negatively impacted by the sulphide production as the reduction in the removal of ammonium from 75% to 42% (with inflow concentration of 55 mg/L) correlated with the increasing mean annual sulphide concentrations. The effect of the detoxification of sulphide and the immobilization of phosphate by the application of the iron-rich soil matrix in the initial years was proven; however, the life-span of this effect should not only be taken into consideration in further design but also in scientific studies.

Mixed groundwater contaminations by chlorinated volatile organic compounds (VOC) cause environmental hazards if contaminated groundwater discharges into surface waters and river floodplains. Constructed wetlands (CW) or engineered natural wetlands provide a promising technology for the protection of sensitive water bodies. We adapted a constructed wetland able to treat monochlorobenzene (MCB) contaminated groundwater to a mixture of MCB and tetrachloroethene (PCE), representing low and high chlorinated model VOC. Simultaneous treatment of both compounds was efficient after an adaptation time of 2 years. Removal of MCB was temporarily impaired by PCE addition, but after adaptation a MCB concentration decrease of up to 64% (55.3 µmol L-1) was observed. Oxygen availability in the rhizosphere was relatively low, leading to sub-optimal MCB elimination but providing also appropriate conditions for PCE dechlorination. PCE and metabolites concentration patterns indicated a very slow system adaptation. However, under steady state conditions complete removal of PCE inflow concentrations of 10-15 µmol L-1 was achieved with negligible concentrations of chlorinated metabolites in the outflow. Recovery of total dechlorination metabolite loads corresponding to 100%, and ethene loads corresponding to 30% of the PCE inflow load provided evidence for complete reductive dechlorination, corroborated by the detection of Dehalococcoides sp.

Low-chlorinated benzenes (CBs) are widespread groundwater contaminants and often threaten to contaminate surface waters. Constructed wetlands (CWs) in river floodplains are a promising technology for protecting sensitive surface water bodies from the impact of CBs. The efficiency and seasonal variability of monochlorobenzene (MCB), 1,4-dichlorobenzene (1,4-DCB) and 1,2-dichlorobenzene (1,2-DCB) removal, the impact of planting, and gaseous MCB emissions from the filter surface were investigated over the course of 1 year in both a vegetated pilot-scale CW and an unplanted reference plot (UR). Annual mean concentration decreases of MCB and 1,4-DCB were observed; however, annual mean 1,2-DCB removal was seen only in the upper filter layer. Planting (Phragmites australis) had a statistically significant beneficial effect on removal. The CB removal efficiency in the CW generally decreased with depth, and seasonal variations of removal were evident, with less concentration decrease during summer. Load removal efficiencies of 59-65% (262-358 mg m-2 d-1) for MCB, 59-69% (4.0-5.1 mg m-2 d-1) for 1,4-DCB and 29-42% (0.6-2.1 mg m-2 d-1) for 1,2-DCB were observed in June and July. Volatilization of MCB from the filter surface accounted for 2-4% of the total amount removed. Simple cover layers of organic materials on the filter surface were suitable for MCB emission reduction. Model calculations were carried out to estimate the MCB removal potential attributable to microbial degradation, volatilisation, and plant uptake in the CW and UR. Microbial degradation was the dominating process. The observed positive impact of plants on MCB removal was caused by improved oxygen supply (due to root oxygen release into the rhizosphere and enhanced water table fluctuations), and direct plant uptake.

Chlorobenzene-contaminated groundwater was used to assess pulsed gas sparging as a minimum effort aeration strategy to enhance intrinsic natural attenuation. In contrast to existing biosparging operations, oxygen was supplied at minimum rate by reducing the gas injection frequency to 0.33 day-1. Field tests in a model aquifer were conducted in a 12 m long reactor, filled with indigenous aquifer material and continuously recharged with polluted groundwater over 3 years. The closed arrangement allowed yield balances, cost accounting as well as the investigation of spatial distributions of parameters which are sensitive to the biodegradation process. Depending on the injection frequency and on the gas chosen for injection (pure oxygen or air) oxygen-deficient conditions prevailed in the aquifer. Despite the limiting availability of dissolved oxygen in the groundwater, chlorobenzene degradation under oxygen-deficient conditions proved to be more effective than under conditions with dissolved oxygen being available in high concentrations.Minimum rate gas sparging resulted in sustained biodegradation of chlorobenzene in a polluted groundwater aquifer.

A new approach for headspace sorptive extraction is presented and demonstrated for the determination of 12 chlorobenzenes in water samples. It consists of a silicone tube (15-mm length) arranged around a stainless steel rod. This device is fixed on a septum cap and exposed to the headspace of 50 mL of a salt-saturated water sample. After extraction (60-min optimized extraction time), thermodesorption is carried out by direct insertion of the silicone tube into the thermodesorption-gas chromatography-mass spectrometry system. Desorption of the analytes is performed at 250 °C for 5 min with a gas flow of 50 mL/min. Repeatability (relative standard deviation 5-10%), extraction yields (9-46%), enrichment factors (129-657), and detection limits (0.002-0.012 µg/L) were determined and four real water samples were analyzed with the headspace tube extraction. The results were verified by standard addition. A comparison of headspace tube extraction with other headspace enrichment techniques underlined the high extraction capacity of the proposed method. A big advantage of tube extraction is the low cost of the silicone material. The tubes can be discarded after single use, avoiding carryover problems and cross-contamination.

MESCO ist die Abkürzung für Membrane-Enclosed Sorptive Coating oder Membrane-Enclosed Silicone Collector. Dabei handelt es sich um Passivsammler zur membrankontrollierten Extraktion gelöster organischer Verbindungen im Wasser, die in den letzten Jahren am Helmholtz-Zentrum für Umweltforschung - UFZ (Leipzig) entwickelt und erprobt wurden. Der MESCO besteht aus einem Sorbenskörper, eingebettet in einer fluidgefüllten Extraktionskammer, deren Wandung mindestens teilweise von einer Membran gebildet wird. Mit solchen Vorrichtungen können im Wasser gelöste, das heißt bioverfügbare organische Spurenstoffe (z. ß. PAK, CKW) über zwei bis sechs Wochen angereichert und nach Thermodesorption oder Lösemittelextraktion analysiert werden. Schon die pro Sammler absolut bestimmten Substanzmengen ermöglichen Standortvergleiche analog zum Biomonitoring (z. B. mit Muscheln oder Fischen). Mithilfe bekannter Aufnahmeraten kann man aus den akkumulierten Stoffmengen zeitgemittelte Konzentrationen im Gewässer berechnen. Damit sind die MESCO-Sammler preiswerte und multifunktionelle Alternativen zu konventionellen Beprobungsverfahren im Gewässermonitoring.

The spatial and temporal biogeochemical development of a model wetland loaded with cis- and trans-1,2-dichloroethene contaminated groundwater was characterized over 430 days by hydrogeochemical and compound-specific isotope analyses (CSIA). The hydrogeochemistry dramatically changed over time from oxic to strongly reducing conditions as emphasized by increasing concentrations of ferrous iron, sulfide, and methane since day 225. d13C values for trans- and cis-DCE substantially changed over the flow path and correlated over time with DCE removal. The carbon enrichment factor values (?) retrieved from the wetland became progressively larger over the investigation period, ranging from -1.7 ± 0.3‰ to -32.6 ± 2.2‰. This indicated that less fractionating DCE oxidation was progressively replaced by reductive dechlorination, associated with a more pronounced isotopic effect and further confirmed by the detection of vinyl chloride and ethene since day 250. This study demonstrates the linkage between hydrogeochemical variability and intrinsic degradation processes and highlights the potential of CSIA to trace the temporal and spatial changes of the dominant degradation mechanism of DCE in natural or engineered systems.

At industrial megasites worldwide, the natural seepage of contaminated groundwater from surface-near layers into rivers and river floodplains may give rise to serious environmental hazards. To prevent adverse effects on the environment, affordable and energy-efficient treatment methods for these sites are required. Large-scale constructed wetlands (CW) may represent a promising approach to protect river catchment areas. A pilot-scale horizontal subsurface flow CW planted with Phragmites australis and an unplanted reference plot were investigated for the removal of monochlorobenzene (MCB), 1,4-dichlorobenzene (1,4-DBC) and 1,2-dichlorobenzene (1,2-DCB) from polluted groundwater in Bitterfeld (Germany). At inflow concentrations of 20 mg L-1 MCB, 0.19 mg L-1 1,2-DCB and 0.25 mg L-1 1,4-DCB, the planted system showed high removals of MCB and 1,4-DCB already after 2 m of the flow path with averages of 48% MCB and 38% 1,4-DCB over all depths (71% MCB and 62% 1,4-DCB in the upper layer of the wetland). The unplanted wetland showed its highest mean removals only after 4 m of the flow path with 35% MCB and 32% 1,4-DCB. 1,2-DCB was not removed in either system. Oxygen limitation prevailed in both systems but concentrations were higher in the planted wetland with redox potentials of 65-90 mV (0-65 mV in the unplanted wetland). The presence and activity of aerobic MCB degraders in the wetland was shown via most probable number (MPN) determination and aerobic microcosm experiments. Since plants have a significant effect on chlorobenzene removal, constructed wetlands provide a high potential for the treatment of chlorobenzene-contaminated groundwater.

The degradation of monochlorobenzene (MCB) was assessed in a constructed wetland treating MCB contaminated groundwater using a detailed geochemical characterisation, stable isotope composition analysis and in situ microcosm experiments. A correlation between ferrous iron mobilisation, decreasing MCB concentration and enrichment in carbon isotope composition was visible at increasing distance from the inflow point, indicating biodegradation of MCB in the wetland. Additionally, in situ microcosm systems loaded with 13C-labelled MCB were deployed for the first time in sediments to investigate the biotransformation of MCB. Incorporation of 13C-labelled carbon derived from the MCB into bacterial fatty acids substantiated in situ degradation of MCB. The detection of 13C-labelled benzene indicated reductive dehalogenation of MCB. This integrated approach indicated the natural attenuation of the MCB in a wetland system. Further investigations are required to document and optimise the in situ biodegradation of MCB in constructed and natural wetland systems treating contaminated groundwater. An integrated approach including isotope composition analysis and in situ microcosm experiments provided evidences for in situ biodegradation of MCB in a wetland system.

Selected polycyclic musk compounds and drugs were extracted from water samples by membrane-assisted micro liquid-liquid extraction. The two-phase extraction system consisted of polyethylene membrane bags filled with an organic solvent. Chloroform proved to be most suited as acceptor phase to extract caffeine, Galaxolide, Tonalide, phenazone and carbamazepine from aqueous samples. The compounds were enriched from 50 mL sample into a volume of 500 mu L of chloroform. Gas chromatography-mass spectrometry (GC-MS) was applied for analysis. The extraction procedure was optimised in regard to membrane material, extraction time and temperature. The evaluation of the entire analysis protocol found limits of detection that ranged from 20 to 200 ng/L. The linear range of calibration covered one magnitude with standard deviations between 4 and 12%. Method comparison with standard analysis techniques such as solid-phase extraction (SPE) combined with GC-MS as well as LC-MS-MS confirmed this method as an easy and reliable protocol, even for the monitoring of matrix-loaded wastewater. The analysis of real samples established the feasibility of the technique.

Lipid-filled semipermeable membrane devices (SPMDs) are receiving increasing attention as passive, in situ samplers for the assessment of environmental pollutant exposure. Although SPMDs have been successfully used in a variety of field studies in surface waters, only a few studies have addressed their characteristics as groundwater samplers. In this study, the performance of the SPMDs for monitoring organic contaminants in groundwater was evaluated in a pilot field application in an area severely contaminated by chemical waste, especially by chlorinated hydrocarbons. The spatial distribution of hydrophobic groundwater contaminants was assessed using a combination of passive sampling with SPMDs and non-target semiquantitative GC-MS analysis. More than 100 contaminants were identified and semiquantitatively determined in SPMD samples. Along the 6 field sites under investigation, a large concentration gradient was observed, which confirms a very limited mobility of hydrophobic substances in dissolved form in the aquifer. The in situ extraction potential of the SPMD is limited by groundwater flow, when the exchange volume of well water during an exposure is lower than the SPMD clearance volume for the analytes. This study demonstrates that SPMDs present a useful tool for sampling and analyzing of groundwater polluted with complex mixtures of hydrophobic chemicals and provides guidance for further development of passive sampling technology for groundwater.