Supplementary Information: Temporal Trends of Environmental Contaminants in Durham, NC, Creek Using Non-targeted Analysis

Third Fork Creek is an urban tributary in Durham, North Carolina, USA that drains to Jordan Lake, a regional drinking‑water supply. Because the last comprehensive chemical survey of this creek was conducted in 2014 and demonstrated poor water quality, we used a combined targeted and non‑targeted analysis (NTA) approach to establish an updated baseline of organic contamination and to prioritize analytes for future monitoring. We sampled three sites monthly from July–December 2022. Water samples were filtered, extracted by solid‑phase extraction, and analyzed by UHPLC–Orbitrap HRMS. In total, 1,346 features were detected (1,043 in positive mode; 303 in negative mode). Spectral library matching returned 43 candidate identifications (29 positive, 14 negative), and mass‑list screening provided additional tentative IDs. Principal component analysis showed that temporal (monthly) variation explained more of the compositional differences than spatial location across the three sites. Detected compound classes included pharmaceuticals, PFAS, plasticizers, biocides, and personal‑care residues. Compounds confirmed with analytical standards included atrazine, deisopropyl‑atrazine, metolachlor, imidacloprid, sucralose, dibutyl phthalate, caffeine, 6:2 fluorotelomer sulfonate, PFOS, and 4‑methylbenzotriazole. Sucralose, a wastewater tracer, ranged from 1.2 to 53.5 ng L−1 and was highest at the South Alston site in August and October. Suspect screening highlighted several additional priority contaminants for follow‑up—8‑hydroxyquinoline, sildenafil, and oxymetazoline among them. These results demonstrate that seasonal NTA campaigns can (1) provide a broad, up‑to‑date contaminant baseline in urban surface waters, (2) reveal temporal pulses and hotspots that routine targeted networks may miss, and (3) generate prioritized target lists to make subsequent routine monitoring and remediation efforts more efficient and cost‑effective. The following Supplementary Information for this abstract includes an excel file with associated NTA data and Word Document with associated supplementary information.