Assessing the transformation of chlorinated ethenes in aquifers with limited potential for natural attenuation: added values of compound-specific carbon isotope analysis and groundwater dating

The evaluation of biotransformation of chlorinated ethenes (CEs) in contaminated aquifers is challenging when variable redox conditions and groundwater flow regime are limiting factors. By using compound-specific stable carbon isotope analysis (C-CSIA) and ³H-³He based groundwater dating, we assessed three CE-contaminated field sites that differed in groundwater flow velocities, redox conditions, and level of contamination. CE isotopic signatures and carbon isotopic mass balances were applied to quantify CE transformation, whereas groundwater dating allowed determining degradation timescales and assessing hydrodynamic regimes. The combination of these techniques enabled at all field sites to indicate zones within the aquifers where CE dechlorination preferably occurred, sometimes even to metabolites of no toxic concern. However, the natural transformation processes were insufficient to mitigate the entire CE contamination at the studied sites. Such situations of limited transformation are worldwide far more common than sites where optimal natural (mainly redox) conditions are enabling complete CEs degradation. Despite such constraints for natural transformation, this study showed that even under non-favorable biogeochemical CEs degradation, the combination of CSIA and groundwater dating provide valuable information to the understanding of the fate of the CEs, thus, being an important contribution in the definition of efficient remediation measures at any given biogeochemical conditions.     

Development and validation of a new fluorescence-based bioassay for aquatic macrophyte species

Bioassays with unicellular algae are frequently used as ecotoxicological test systems to evaluate the toxicity of contaminated environmental samples or chemicals. In contrast, aquatic macrophyte test systems are still rarely used as they are laborious to handle because species exhibit distinct ecological requirements. The aim of this study was to establish a fast and reproducible measuring system for aquatic macrophyte species to overcome those limitations for use. Thus, a newly developed pulse-amplitude modulated chlorophyll fluorometer (Imaging-PAM) was applied as an effect detection in short-term bioassays with aquatic macrophyte species. This multiwell-plate-based measuring device enables the incubation and measurement of up to 24 samples in parallel. The Imaging-PAM was used (i) to establish and validate the sensitivity of the test systems to three Photosystem II (PSII) inhibitors (atrazine, prometryn, isoproturon), (ii) to compare the test systems with established biotests for macrophytes and (iii) to define necessary time scales in aquatic macrophyte testing. The results showed that fluorescence-based measurements with the Imaging-PAM allow rapid and parallel analysis of large amounts of aquatic macrophyte samples and of toxicants effects of the PSII inhibitors tested on aquatic macrophytes. Measurements revealed a good correlation between obtained median effective concentrations (EC50s) for the new and the established biotest systems. Hence, the Imaging-PAM measuring device is a promising tool to allow fast chemical effect screening for high amounts of samples with little time and material and thus offers scope for high-throughput biotesting using aquatic macrophyte species.     

Prevention or cure? Optimal abatement mix

Environmental Economics and Policy Studies - We develop a model for pollution abatement that distinguishes between prevention and treatment technologies, in order to better understand the optimal...