Reading signs from the past

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Modern mass spectrometer at Eawag (Photo: Raoul Schaffner, Eawag)
Modern mass spectrometer at Eawag (Photo: Raoul Schaffner, Eawag)

When water samples are analysed with a mass spectrometer, peaks of compounds appear that are completely unknown, or that weren’t being looked for. If these compounds prove subsequently to be of interest to environmental researchers, evidence of their presence can be retrieved from the archived measurements.

Stored measurement results from mass spectrometers are a treasure trove. Eight reference laboratories in Europe and Australia, among them Eawag, now want to make use of this via "Retrospective Suspect Screening" in order to establish a world-wide early warning network. Data can thus be made available within a short time that show how widespread the newly-appeared problematic materials are in the environment.

Identifying compounds in existing mass spectra from a variety of sources presents a number of challenges, however. It is crucial, for example, that the data were produced by high-resolution mass spectrometers combined with chromatography, and that all the parameters of quality control were observed. In a pilot project, researchers have now searched archived mass spectra from 14 countries and 3 continents for new compounds, and have developed a set of recommendations on obtaining and analysing the data, as well as on quality control. The screening has enabled them to confirm the presence of various tensides, medications and chemicals used in industry and to show that the concept functions with disparate datasets from various countries.

Mass spectrometry

Environmental analysis without mass spectrometers is no longer imaginable. The technology makes it possible to determine which compounds are contained in a sample, and in what quantities. The molecules are ionised, fragmented and separated by mass and charge. A specific pattern for each chemical compound is produced - the mass spectrum. For a compound, this is almost as unique as a person’s fingerprint. Because innumerable substances are present in environmental samples, these are first separated chromatographically. This then results in much more specific analysis.

A key challenge in the environmental and exposure sciences is to establish experimental evidence of the role of chemical exposure in human and environmental systems. High resolution and accurate tandem mass spectrometry (HRMS) is increasingly being used for the analysis of environmental samples. One lauded benefit of HRMS is the possibility to retrospectively process data for (previously omitted) compounds that has led to the archiving of HRMS data. Archived HRMS data affords the possibility of exploiting historical data to rapidly and effectively establish the temporal and spatial occurrence of newly identified contaminants through retrospective suspect screening. We propose to establish a global emerging contaminant early warning network to rapidly assess the spatial and temporal distribution of contaminants of emerging concern in environmental samples through performing retrospective analysis on HRMS data. The effectiveness of such a network is demonstrated through a pilot study, where eight reference laboratories with available archived HRMS data retrospectively screened data acquired from aqueous environmental samples collected in 14 countries on 3 different continents. The widespread spatial occurrence of several surfactants (e.g., polyethylene glycols (PEGs) and C12AEO-PEGs), transformation products of selected drugs (e.g., gabapentin-lactam, metoprolol-acid, carbamazepine-10-hydroxy, omeprazole-4-hydroxy-sulfide, and 2-benzothiazole-sulfonic-acid), and industrial chemicals (3-nitrobenzenesulfonate and bisphenol-S) was revealed. Obtaining identifications of increased reliability through retrospective suspect screening is challenging, and recommendations for dealing with issues such as broad chromatographic peaks, data acquisition, and sensitivity are provided.

Alygizakis, N. A.; Samanipour, S.; Hollender, J.; Ibáñez, M.; Kaserzon, S.; Kokkali, V.; van Leerdam, J. A.; Mueller, J. F.; Pijnappels, M.; Reid, M. J.; Schymanski, E. L.; Slobodnik, J.; Thomaidis, N. S.; Thomas, K. V. (2018) Exploring the potential of a global emerging contaminant early warning network through the use of retrospective suspect screening with high-resolution mass spectrometry, Environmental Science and Technology , 52(9), 5135-5144 , doi: 10.1021/acs.est.8b00365 , Institutional Repository