Marc Bourgin

Chlorination of bisphenol A: Non-targeted screening for the identification of transformation products and assessment of estrogenicity in generated water

Besides the performance of water treatments on the removal of micropollutants, concern about the generation of potential biologically active transformation products has been growing. Thus, the detection and structural elucidation of micropollutants transformation products have turned out to be major issues to evaluate comprehensively the efficiency of the processes implemented for drinking water treatment. However, most of existing water treatment studies are carried out at the bench scale with high concentrations and simplified conditions and thus do not reflect realistic conditions. Conversely, this study describes a non-targeted profiling approach borrowed from metabolomic science, using liquid chromatography coupled to high-resolution mass spectrometry, in order to reveal potential chlorination products of bisphenol A (BPA) in real water samples spiked at 50μgL(-1). Targeted measurements first evidenced a fast removal of BPA (>99%) by chlorination with sodium hypochlorite (0.8mgL(-1)) within 10min. Then, the developed differential global profiling approach enabled to reveal 21 chlorination products of BPA. Among them, 17 were brominated compounds, described for the first time, demonstrating the potential interest of this innovative methodology applied to environmental sciences. In parallel to the significant removal of BPA, the estrogenic activity of water samples, evaluated by ER-CALUX assay, was found to significantly decrease after 10min of chlorination. These results confirm that chlorination is effective at removing BPA in drinking water and they may indicate that the generated compounds have significantly lower estrogenic activity.

Differential chemical profiling to identify ozonation by-products of estrone-sulfate and first characterization of estrogenicity in generated drinking water

For a few years, the concern of water treatment companies is not only focused on the removal of target micropollutants but has been extended to the investigation of potential biologically active by-products generated during the treatment processes. Therefore, some methods dedicated to the detection and structural characterization of such by-products have emerged. However, most of these studies are usually carried out under simplified conditions (e.g. high concentration levels of micropollutants, drastic treatment conditions, use of deionized or ultrapure water) and somewhat unrealistic conditions compared to that implemented in water treatment plants. In the present study, a real field water sample was fortified at the part-per-billion level (50 μg L(-1)) with estrone-3-sulfate (E1-3S) before being ozonated (at 1 mg L(-1)) for 10 min. In a first step, targeted measurements evidenced a degradation of the parent compound (>80%) in 10 min. Secondly, a non-targeted chemical profiling approach derived from metabolomic profiling studies allowed to reveal 11 ozonation by-products, among which 4 were found predominant. The estrogenic activity of these water samples spiked with E1-3S before and after treatment was assessed by the ER-CALUX assay and was found to decrease significantly after 10 min of ozonation. Therefore, this innovative methodological strategy demonstrated its suitability and relevancy for revealing unknown compounds generated from water treatment, and permitted to generate new results regarding specifically the impact of ozonation on estrone-3-sulfate. These results confirm that ozonation is effective at removing E1-3S in drinking water and indicate that the by-products generated have significantly lower estrogenic activity.

Exploring the behaviour of emerging contaminants in the water cycle using the capabilities of high resolution mass spectrometry

To characterize a broad range of organic contaminants and their transformation products (TPs) as well as their loads, input pathways and fate in the water cycle, the Department of Environmental Chemistry (Uchem) at Eawag applies and develops high-performance liquid chromatography (LC) methods combined with high-resolution tandem mass spectrometry (HRMS/MS). In this article, the background and state-of-the-art of LC-HRMS/MS for detection of i) known targets, ii) suspected compounds like TPs, and iii) unknown emerging compounds are introduced briefly. Examples for each approach are taken from recent research projects conducted within the department. These include the detection of trace organic contaminants and their TPs in wastewater, pesticides and their TPs in surface water, identification of new TPs in laboratory degradation studies and ozonation experiments and finally the screening for unknown compounds in the catchment of the river Rhine.

Ozonation of Para-Substituted Phenolic Compounds Yields p-Benzoquinones, Other Cyclic α,β-Unsaturated Ketones, and Substituted Catechols

Phenolic moieties are common functional groups in organic micropollutants and in dissolved organic matter, and are exposed to ozone during drinking water and wastewater ozonation. Although unsubstituted phenol is known to yield potentially genotoxic p-benzoquinone during ozonation, little is known about the effects of substitution of the phenol ring on transformation product formation. With batch experiments employing differing ozone/target compound ratios, it is shown that para-substituted phenols ( p-alkyl, p-halo, p-cyano, p-methoxy, p-formyl, p-carboxy) yield p-benzoquinones, p-substituted catechols, and 4-hydroxy-4-alkyl-cyclohexadien-1-ones as common ozonation products. Only in a few cases did para-substitution prevent the formation of these potentially harmful products. Quantum chemical calculations showed that different reaction mechanisms lead to p-benzoquinone, and that cyclohexadienone can be expected to form if no such pathway is possible. These products can thus be expected from most phenolic moieties. Kinetic considerations showed that substitution of the phenolic ring results in rather small changes of the apparent second order rate constants for phenol-ozone reactions at pH 7. Thus, in mixtures, most phenolic structures can be expected to react with ozone. However, redox cross-reactions between different transformation products, as well as hydrolysis, can be expected to further alter product distributions under realistic treatment scenarios.

Non-target screening to trace ozonation transformation products in a wastewater treatment train including different post-treatments

Ozonation and subsequent post-treatments are increasingly implemented in wastewater treatment plants (WWTPs) for enhanced micropollutant abatement. While this technology is effective, micropollutant oxidation leads to the formation of ozonation transformation products (OTPs). Target and suspect screening provide information about known parent compounds and known OTPs, but for a more comprehensive picture, non-target screening is needed. Here, sampling was conducted at a full-scale WWTP to investigate OTP formation at four ozone doses (2, 3, 4, and 5 mg/L, ranging from 0.3 to 1.0 gO3/gDOC) and subsequent changes during five post-treatment steps (i.e., sand filter, fixed bed bioreactor, moving bed bioreactor, and two granular activated carbon (GAC) filters, relatively fresh and pre-loaded). Samples were measured with online solid-phase extraction coupled to liquid chromatography high-resolution tandem mass spectrometry (LC-HRMS/MS) using electrospray ionization (ESI) in positive and negative modes. Existing non-target screening workflows were adapted to (1) examine the formation of potential OTPs at four ozone doses and (2) compare the removal of OTPs among five post-treatments. In (1), data processing included principal component analysis (PCA) and chemical knowledge on possible oxidation reactions to prioritize non-target features likely to be OTPs. Between 394 and 1328 unique potential OTPs were detected in positive ESI for the four ozone doses tested; between 12 and 324 unique potential OTPs were detected in negative ESI. At a specific ozone dose of 0.5 gO3/gDOC, 27 parent compounds were identified and were related to 69 non-target features selected as potential OTPs. Two OTPs were confirmed with reference standards (venlafaxine N-oxide and chlorothiazide); 34 other potential OTPs were in agreement with literature data and/or reaction mechanisms. In (2), hierarchical cluster analysis (HCA) was applied on profiles detected in positive ESI mode across the WWTP and revealed 11 relevant trends. OTP removal was compared among the five post-treatments and 54-83% of the non-target features that appeared after ozonation were removed, with the two GAC filters performing the best. Overall, these data analysis strategies for non-target screening provide a useful tool to understand the behavior of unknown features during ozonation and post-treatment and to prioritize certain non-targets for further identification.