Identification of acrylonitrile sulfonates in the river Rhine using non-target screening and a spatially distributed sampling strategy

The aim of this study was to investigate the presence of further, as yet unknown dissolved organic contaminants with isolated point-sources (e.g. industrial origin) in river water of the Rhine by implementing a large, distributed sampling campaign stretching along a large portion of the central river course. The analysis and data processing were based on a non-target screening approach with a focus on compounds of industrial origin which often show pronounced intensity changes over time due to production cycles. Many such compounds are by-products and are not included in online databases, making their identification challenging. This study describes the process of uncovering one such chemical group utilizing a non-target screening approach. Inter-agency cooperation was essential to localize emissions and determine the inter-regional distribution of the compounds. Both spatially-distributed sampling at 17 sites along the Rhine and Danube rivers as well as daily-composite and grab samples from 2018 to 2023 at further sites across Germany were used. Analysis was accomplished by LC-QToF- and LC-Orbitrap-MS and followed by data evaluation with different non-target software solutions including open-source solutions in R. The “discovery” of the contaminants in question began with the non-target data of the spatial sampling of the Rhine, which were first processed to create feature lists, which were then prioritized based on their intensity profiles along the river course. One group of prioritized features was selected for identification, first by interpretation of MS2 fragmentation spectra followed by verification using a laboratory synthesis. This was a group of oligoacrylonitrile sulfonates originating from polymer fiber production, which to the best of our knowledge not previously detected in river water. Further spatial and time-series data showed the long-term and inter-regional occurrence of the oligoacrylonitrile sulfonates (4 to 13 acrylonitrile units) in the Rhine and Danube catchments. Consistent with the cessation of production at the measured sites in Germany, these compounds were no longer detected in the Rhine and Danube after 2021. The study highlights the need for cooperation and pooling of resources to obtain the necessary temporally and spatially distributed data for successful identification, and source localization, of unknown contaminants by non-target screening.