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.

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.

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. Conclusions: DMP improves the transesterification efficiency without influencing the accuracy of the C‐ and H‐CSIA of FAMEs. The performance of the one‐step method for rapeseed samples for the determination of C‐ and H‐CSIA values of FAMEs is satisfactory. Thus, the applicability of the one‐step method for isotopic fingerprint analyses of FAs in oilseeds is reported for the first time.