Chlorine isotope fractionation during catalytic reductive dechlorination of Trichloromethane (CHCl₃) over palladium-on-alumina in hydrogen-saturated water: implication to managed aquifer recharge as sustainable storage solution for desalinated water (MAR-DSW) in Menashe recharge basin, Israel

During the storage of excess desalinated water in a managed coastal aquifer in Israel, chlorine in desalinated water may react with natural organic matter, forming toxic disinfection by-products (DBPs), like trihalomethanes (THMs). In order to facilitate managed aquifer recharge as storage solution for desalinated water (MAR-DSW), it is important to understand the mechanisms of the formation and degradation of such DBPs. In this work, degradation of chloroform (CHCl₃), a main pollutant of interest at the Menashe recharge basin in Israel, was investigated to derive chlorine isotope enrichment factors for the educt and degradation products as a part of the Israel-German joint research “aquifer recharge as sustainable storage solution for desalinated water (MAR-DSW)”. 100ml of deionized water spiked with 30mg/l chloroform was saturated with hydrogen, which serves as an electron donor. Then, 0.25g/l palladium was added as palladium-on-alumina (10% wt.) to catalyze the reaction. Samples were taken at specified intervals from a sampling port designed at the bottom of the reactor, which is closed with a plunger from the top so that no headspace was created as samples were taken out or during the entire experimental period. During degradation of chloroform, the change in chlorine isotope ratios of CHCl₃ as well as its chlorinated degradation products was determined using a gas-chromatograph-mass spectrometer online connected to a purge and trap system (P&T-GC/MS). This simple online method was developed and optimized at TU Darmstadt. In addition to the reaction kinetics, isotope fractionation of CHCl₃ and its degradation products dichloromethane (CH₂Cl₂) as well as methyl chloride (CH₃Cl) were investigated. A chlorine isotope enrichment factor (ε) of -2.7‰ was derived for chloroform using the Rayleigh equation. The investigation of isotope fractionation during the reductive dechlorination of chloroform i.e the Cl-CSIA can potentially be used as a tool to discriminate the source, pathway and fate of these compounds so as to foresee the feasibility of medium and long term use of managed aquifer recharge as a storage solution

Evaluation of a quick one‐step sample preparation method for the determination of the isotopic fingerprint of rapeseed (Brassica napus): Investigation of the influence of the use of 2,2‐dimethoxypropane on compound‐specific stable carbon and hydrogen isotope analyses by gas chromatography combustion/pyrolysis isotope ratio mass spectrometry

Rationale Gas chromatographic analyses for vegetable oils require transesterification, which generally involves multiple steps, mainly to generate fatty acid methyl esters (FAMEs). A quick method based on acid-catalyzed transesterification using 2,2-dimethoxypropane (DMP) enables the conversion in one step, in a single reactor. For compound-specific stable carbon and hydrogen isotope analyses (C- and H-CSIA) of individual fatty acids (FAs) in oil, the verification of this one-step method has not yet been reported. Methods In this study, we evaluated the feasibility of the one-step method for C- and H-CSIA of individual FAMEs in rapeseed samples. The focus was on the investigation of the influence of methanol, which was produced from the reactions of DMP with glycerol and water during transesterification, on the accuracy of isotope composition of FAMEs, consequently of the FAs. The reproducibility of the one-step method was assessed by the measurement of the FAMEs from rapeseed and rapeseed oil. For the C- and H-CSIA of individual FAMEs, a gas chromatography combustion/pyrolysis isotope ratio mass spectrometry system was used. Results Our results showed that no significant differences arise in the carbon and hydrogen isotope compositions of the selected main FAMEs produced with and without DMP except for the H-CSIA value of C18:3. The reproducibility of the one-step method for rapeseed was in the range of ±0.1 mUr to ± 0.3 mUr for C-CSIA and ±1 mUr to ±3 mUr for H-CSIA of the main FAMEs

Optimization of compound‐specific chlorine stable isotope analysis of chloroform using the Taguchi design of experiments

Rationale Chloroform, a probable human carcinogen, is commonly detected in various concentration levels in many surface water and groundwater sources. Compound-specific chlorine stable isotope analysis (Cl-CSIA) is significant in investigating the fate of chlorinated contaminants in the environment. Analytical conditions should, however, be thoroughly examined for any isotopic fractionation. In this study, we simultaneously optimize three analytical parameters for a robust online Cl-CSIA of chloroform using the Taguchi design of experiments. Methods For Cl-CSIA, a purge-and-trap autosampler coupled to a gas chromatograph in tandem with a quadrupole mass spectrometer, with electron ionization in selected ion monitoring (SIM) mode, was used. Using the Taguchi method, the dominant parameter affecting the results of Cl-CSIA for chloroform was identified through concurrent investigation of the signal-to-noise ratios (S/N) of three parameters, each at three levels: purging time (5, 10, 15 min), transfer time (80, 120, 160 s), and dwell time (20, 60, 100 ms). Moreover, the optimum combination of the levels was identified. Results The purging time, with a maximum S/N, resulted in the highest influence on the isotope ratios determined. It was further refined through additional experiments to sufficiently extract chloroform from the aqueous phase. Accordingly, 8 min of purging time, 120 s transfer time and 100 ms dwell time were the optimum conditions for Cl-CSIA of chloroform. Post-optimization, a precision of ±0.28 ‰ was achieved for 8.4 nmol of chloroform (equivalent to 0.89 μg or approx. 25 nmol Cl-mass on column). Conclusions A simple online method for Cl-CSIA of chloroform was optimized with the Taguchi design of experiments. The Taguchi method was very useful for the optimization of the analytical conditions. However, the purging conditions should be fine-tuned and selected so that sufficient extraction of a target compound is confirmed to acquire a stable and higher precision of the method

Low Trihalomethane Formation during Managed Aquifer Recharge with Chlorinated Desalinated Water

Trihalomethanes (THMs) are toxic disinfection by-products, formed in the reaction of chlorine with organic matter. This work aimed to study THM formation during a unique case study of managed aquifer recharge (MAR) with chlorinated desalinated seawater. THM formation was tested in the field, along a 3.0 m deep vadose zone gallery. Two small-scale experiments were conducted in the site, with untreated and with bromide spiked desalinated seawater. These were accompanied by a large-scale, ~1-month long operational MAR event. In the small-scale experiments, THM concentrations were shown to increase with bromide concentrations, with increasing dominance of the brominated species. Nevertheless, concentrations remained within the single µg/L range, which is an order of magnitude lower than drinking water regulations. Such low THM concentrations were also determined in the large-scale event. In both cases, THM formation occurred in the ponding water, without significant formation or degradation in the upper 3.0 m of the vadose zone. This study shows that MAR with chlorinated (<0.5 mg/L) desalinated seawater through sandy infiltration basins does not pose a threat to drinking water quality at this site

Lösungsstrategien zur Verminderung von Einträgen von urbanem Plastik in limnische Systeme - PLASTRAT - Synthesebericht

Der Einsatz von Plastik gehört zu den großen Errungenschaften unserer Zeit. Die Nutzung von Plastik in unseren verschiedenen Lebensbereichen ermöglicht uns heute Vieles. Dabei setzen wir Plastik oft ein, ohne dass uns dies bewusst ist. Wieviel „virtuelles Plastik“ war allein notwendig, um diesen Synthesebericht zu erstellen? Wieviel Plastik benötigen Sie gerade, um diesen Synthesebericht zu lesen? Wie so oft, so hat auch der Einsatz von Plastik zwei Seiten: den positiven Errungenschaften stehen negative Auswirkungen gegenüber, vor allem nach der Nutzung von Plastik. Im Fokus stehen hierbei Fragestellungen der Toxikologie sowie der Abfallverwertung. Im Gegensatz zu vielen anderen Stoffen, mit denen wir täglich in Berührung sind, hat Plastik die Eigenschaft, dass sich kleinste Partikel bilden. So ist es nicht verwunderlich, dass sich mittlerweile in allen Umweltmedien Mikroplastikpartikel finden lassen. Die Idee von PLASTRAT war es, in einem interdisziplinären Team Ansätze für die Verminderung von Einträgen von Plastik in Gewässer zu untersuchen. Dabei standen über den Ansatz der systemischen Risikoanalyse die unterschiedlichen Sektoren im Fokus, angefangen von der Erzeugung, über die Nutzung bis hin zu den Eintragspfaden und die toxikologische Bewertung. Der Synthesebericht fasst die Ergebnisse von PLASTRAT zusammen. Vor allem zeigt der Synthesebericht die großen Herausforderungen sowie Lösungsansätze zum Thema Mikroplastik auf. Dabei wird auch deutlich, dass wir bei vielen Fragestellungen zum Umgang mit Plastik erst am Anfang stehen. Die ersten Ideen zu PLASTRAT entstanden 2016. In den vergangenen fünf Jahren stand das Thema Plastik im Fokus von Öffentlichkeit und Presse. In dieser Zeit gab es bereits wichtige Veränderungen beim Einsatz von Plastik bei diversen Produkten, beispielsweise durch die Substitution durch alternative Materialien. Dies zeigt deutlich, dass eine Bewusstseinsveränderung stattgefunden hat, die sich sicherlich in der Zukunft fortsetzten wird. Die Arbeiten und Diskussionen im Projektteam von PLASTRAT waren spannend. In vielen Projektbesprechungen wurde an den Forschungsfragestellungen gearbeitet und nach Lösungen gesucht. Es gab einen intensiven persönlichen Austausch mit allen am Projekt beteiligten Personen, so dass uns die seit 2020 geltenden Einschränkungen durch die Corona-Pandemie nicht immer leichtgefallen sind. Wir möchten uns bei allen bedanken, die bei PLASTRAT mitgewirkt haben. Allen Lesern des Syntheseberichts wünschen wir viele Freude beim Lesen und hoffen, dass wir Ihnen einen Impuls für den zukünftigen Umgang mit (Mikro-)Plastik geben können