We report the performance of a field-scale permeable reactive barrier (PRB) for the biological treatment of nitrate-contaminated groundwater. The reactive material of the PRB consisted of a mixture of gravel and mulch as a carbon source for denitrifying bacteria. The PRB was equipped with a delivery system that allowed injecting NO3at controlled rates from the surface directly into the up-gradient layer of the PRB. This way, NO3concentration entering the PRB

R. M. (2014) Highlighting the effects of co-eluting interferences on compound specific stable isotope analysis of polycyclic aromatic hydrocarbons using comprehensive two-dimensional gas chromatography. ChemPlusChem, 79 (6). pp. 804-812. ISSN 2192-6506 Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim A copy can be downloaded for personal non-commercial research or study, without prior permission or charge Content must not be changed in any way or reproduced in any format or medium without the formal permission of the copyright holder(s) When referring to this work, full bibliographic details must be given http://eprints.gla.ac.uk/93257/ Accuracy is the most important issue when carrying out compound specific stable isotope analysis of polycyclic aromatic hydrocarbons extracted from complex samples. It depends on two main factors: the possible isotopic fractionation of the compounds during extraction and the potential co-elution with interfering compounds with different isotopic signatures. We present here a simplified pressurised liquid extraction method for compound specific stable isotope analysis of polycyclic aromatic hydrocarbons (PAHs) in non-aqueous phase liquids of coal tar. Samples extracted using the new method and using fractionation on silica gel column were analysed using comprehensive twodimensional gas chromatography. We were able to evaluate the effect of coelution on carbon and hydrogen stable isotope signatures of the 16 US EPA priority PAHs in the coal tars with various proportions of aromatic and aliphatic content. Even in samples that presented a good baseline resolution, the PAHs of interest co-eluted with other aromatic compounds with a notable effect on their stable isotope values; it demonstrated the necessity to check the quality of all extraction and clean-up methods (either the simplified pressurized liquid extraction or more traditional labour-intensive methods) for the more complex samples prior to data interpretation. Additionally, comprehensive twodimensional gas chromatography enabled visualisation of the suspected coelutions for the first time. IntroductionPolycyclic aromatic hydrocarbons (PAHs) are a ubiquitous global contaminant, produced by a number of sources, including vehicle emissions and fuel combustion1. Many PAHs are known to have toxic, mutagenic and carcinogenic properties2, making their source, fate and remediation within the environment a highly studied topic. However, due to the great number (and similarity) of potential PAH sources it is often difficult to provide irrefutable source attribution. This is evident in the analysis of coal tars, a by-product produced by manufactured gas plants (MGPs), often found in high volumes at contaminated former MGP sites across Europe and North America3. Isotope studies have gained much popularity within environmental forensic investigations, due to their ability to differentiate between chemically identical contaminants4. Compound-specific isotope analysis (CSIA) has the additional ability to measure the isotop...

The anaerobic degradation potential at a chloroethene-contaminated site was investigated by operating two anoxic column aquifer microcosms enriched in iron(III). One column was fed with vinyl chloride (VC) only (column A) and one with VC and acetate (column B). In column A, after about 600 pore volume exchanges (PVEs), VC started to disappear and reached almost zero VC recovery in the effluent after 1000 PVEs. No formation of ethene was observed. In column B, effluent VC was almost always only a fraction of influent VC. Formation of ethene was observed after 800 PVEs and started to become an important degradation product after 1550 PVEs. However, ethene was never observed in stoichiometric amounts compared with disappeared VC. The average stable isotope enrichment factor for VC disappearance in column A was determined to be -4.3‰. In column B, the isotope enrichment factor shifted from -10.7 to -18.5‰ concurrent with an increase in ethene production. Batch microcosms inoculated with column material showed similar isotope enrichment factors as the column microcosms. These results indicated that two degradation processes occurred, one in column A and two in parallel in column B with increasing importance of reductive dechlorination with time. This study suggests that in addition to reductive dechlorination, other degradation processes such as anaerobic oxidation should be taken into account when evaluating natural attenuation of VC and that isotope analysis can help to differentiate between different pathways of VC removal.

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