Abstract
BackgroundCurrent compound prioritisation and monitoring approaches within Europe focus mainly on widely occurring priority and river basin specific pollutants but may overlook site-specific contamination from local emission sources. Thus, we propose a robust and semiautomated approach for the identification of site-specific chemicals and a prioritisation of water bodies with specific contamination based on non-target screening data from liquid chromatography coupled to high-resolution mass spectrometry.ResultsFor prioritisation of site-specific contaminants, we calculated rarity scores for all peaks occurring in a set of 31 surface water samples, which combine the maximum signal intensity of a peak in a dataset with its frequency of occurrence in that dataset in one single number. These were a robust measure without the need to address the problems of missing data in more sophisticated multivariate statistical methods. For our dataset, site-specific compounds were defined for rarity scores > 1000, and the studied 31 sites showed a huge difference in the number of such peaks (0–91 in positive and 0–48 in negative ion mode). Together with isotopologue detection, the evaluation of mass defects and the occurrence of homologue series, which all could be obtained from automated data processing, a more detailed characterisation of these site-specific contaminations was possible. For three selected sites with a high number of site-specific peaks, novel or unexpected compounds could be identified, which stem from specific usage or (former) industrial production upstream of these sites.Conclusions and outlookThe proposed approach allows for a rapid screening of large non-target screening datasets for site-specific contaminants, the prioritisation of sites with such a specific contamination and the subsequent identification of these compounds. Thus, the risk of overlooking possibly hazardous chemicals (including unknowns) which are not covered in conventional monitoring and prioritisation schemes is reduced.
Highlights
Current compound prioritisation and monitoring approaches within Europe focus mainly on widely occurring priority and river basin specific pollutants but may overlook site-specific contamination from local emission sources
Prioritisation of site‐specific contamination based on rarity scores The distribution of rarity scores was similar for electrospray ionisation (ESI)+ and ESI− mode, with about 80% of the detected peaks showing values between 10 and 100
At this rarity scores (RS) level, peaks down to a signal intensity of 106 might become classified as rare peaks if they occur in a low number of samples
Summary
Current compound prioritisation and monitoring approaches within Europe focus mainly on widely occurring priority and river basin specific pollutants but may overlook site-specific contamination from local emission sources. The European Water Framework Directive (WFD; European Union 2000) is currently the main basis for surface water monitoring activities in European countries. It has a specific focus on European scale Priority Substances, which are used to define the Chemical Status of a water body, together with varying lists of river basin specific pollutants (RBSPs). Water pollution due to household effluents treated in and emitted via municipal wastewater treatment plants (WWTPs) is expected to be composed of a more or less consistent, typical set of substances from major human activities including laundry care, home care, health care, personal care and food [10]. These inputs might contain highly specific substances or substances in much higher concentrations as compared to municipal wastewater (e.g. [14, 41, 43])
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