Quantitative criteria for selection of tracers for assessment of mixing of wastewater and pristine water are proposed and evaluated for leakage from a wastewater effluent recharge system to nearby pristine water wells and the dilution of the effluents in a reclamation well by pristine water from the surrounding aquifer. Two molecular tracers were compared: carbamazepine, an organic drug whose refractory behavior was evaluated on-site, and chloride, a widely used conservative tracer. The mixing ratios and the corresponding uncertainty levels in their calculation were evaluated using actual field data. Uncertainty level analysis illuminates the effects of the analytical errors in the determination of trace micropollutants on one hand and the high level of chloride in the background on the other. Uncertainty level calculations revealed that chloride is a somewhat better tracer for the estimation of the dilution of wastewater by flow from a pristine aquifer, whereas carbamazepine is a much better tracer for the calculation of wastewater contamination of nearby drinking water wells. Surprisingly, we show that even when carbamazepine degrades to a large and unknown extent, it can still be used to estimate accurately the probability that a site is contaminated by a wastewater stream.

The Rayleigh equation is frequently used to describe isotope fractionation as a function of conversion. In this article we propose to draw a parallel between isotope and enantiomeric enrichments and derive a set of conditions that allow the use of the Rayleigh approach to describe the enantiomeric enrichment-conversion dependencies. We demonstrate an implementation of the Rayleigh equation for the enantioselective enzymatic hydrolysis of Mecoprop-methyl, Dichlorprop-methyl, and dimethyl-methylsuccinate by lipases from Pseudomonas fluorescens, Pseudomonas cepacia, and Candida rugosa. The data obtained for all the studied reactions gave good fits to the Rayleigh equation, with a linear regression R(2) > 0.96. In addition to that, our analysis of four microcosm studies on the hydrolysis of the individual enantiomers of Dichloroprop methyl, Lactofen, Fenoxaprop-ethyl, and Metalaxyl reported in the literature by other research groups revealed a suitability of the Rayleigh dependence. Two dimensional plots describing the isotope fractionation versus enantiomeric enrichment are demonstrated for all studied cases. Processes not accompanied by enantiomeric enrichment (acid and base hydrolysis) and by isotope enrichment (transesterification) are demonstrated, their 2-D plots are either horizontal or vertical which can illuminate concealed degradation pathways.

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Probing electrochemical processes by mass spectrometry (EC/MS) is a developing field that benefits from the unmatched identification power of mass spectrometry and from the rapid transfer of electrochemical cell products to the mass spectrometer. Most of the current EC/MS efforts are directed towards the development of differential electrochemical mass spectrometry (DEMS) using the electro‐ionization source for identification of volatile compounds, and towards the application of electrospray mass spectrometers for determination of semivolatile and nonvolatile products. The challenges in coupling mass spectrometry and electrochemistry are described, and different approaches to using the coupled system for diverse applications are reviewed, with emphasis on electrospray mass spectrometry. Reaction mechanism studies, diagnostic applications, and activity imaging of electrodes are demonstrated based on approaches that were devised in our laboratory.

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