Identification of contaminants of emerging concern through temporal trend analysis of suspended particulate matter in the Rhine River catchments (2005–2022): A case study using LC-HRMS to support early-warning systems

The continuous release of synthetic chemicals into aquatic systems underscores the need for long-term assessments of contaminants of emerging concern (CECs). Archived suspended particulate matter (SPM) samples from the German Environmental Specimen Bank (ESB) (2005-2022) at two Rhine sites (Weil am Rhein and Koblenz) were analyzed using liquid chromatography-high-resolution mass spectrometry (LC-HRMS) suspect/non-target screening (SS/NTS) to evaluate temporal trends. Using retention-time indices and orthogonal MS/MS evidence (mzCloud, FISh, CFM-ID), 332 compounds were identified at varying Schymanski confidence levels (2.1: 3.0 %; 2.2: 5.7 %; 3.1: 53 %; 3.2: 38 %). Temporal analysis of LC-HRMS peak areas revealed that 25 % of contaminants increased over time, with a higher proportion at Koblenz (29 %) than Weil (18 %). Conversely, several compounds exhibited statistically significant decreasing trends at both Koblenz (14 %) and Weil sites (13 %), consistent with regulatory measures, improved wastewater treatment, and shifts in industrial practices. Aquatic toxicity prediction (ECOSAR) indicated that 47 % (154 of 332) of annotated structures were highly acutely toxic (LC₅₀/EC₅₀ ≤ 1 mg/L) to at least one test group (fish, Daphnia, or green algae). This study provides the first 18-year, site-specific non-target time series from a national archive and integrating orthogonal identification with hazard prediction to support chemical prioritization. Archived SPM enables retrospective and comparable assessment of particle-associated contaminants, complementing dissolved-phase monitoring, and supporting the identification of unmonitored emerging CECs. Crucially, long-term NTS of these SPM samples provides screening-level early-warning signals and a watch list for targeted confirmation and risk management.