Per- and Polyfluoroalkyl Substances in Surface Water and Fluvial Sediments of a Rural Gulf Coast Watershed: A Year-long Spatiotemporal Assessment

Abstract Per- and polyfluoroalkyl substances (PFAS) are persistent contaminants of significant health concern. This study quantified the spatiotemporal occurrence of 40 PFAS in surface water and fluvial sediments across the Lavaca Watershed and Lavaca Bay, Texas, a rural Gulf Coast system with limited potential point sources. Monthly sampling was conducted at 12 sites from January to December 2025, and samples were analyzed following U.S. Environmental Protection Agency (EPA) Method 1633A. Surface water exhibited low PFAS detection frequency, and detections were dominated by short-chain compounds. Two widely studied legacy PFAS, perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), were absent from all water samples. In contrast, sediments exhibited greater compound diversity and more frequent detection of long-chain PFAS, indicating preferential partitioning and long-term retention within benthic deposits. Spatially, upstream sites showed higher detection frequencies and analyte diversity than downstream tidal and estuarine locations, consistent with dilution and mixing along the fluvial-estuarine continuum. Temporal variability was episodic and not directly associated with instantaneous high-flow conditions, suggesting that PFAS transport is likely influenced by a variety of hydrologic factors collectively. Overall, PFAS occurrence in this rural coastal watershed varies across space and time, influenced by both hydrologic forcing and phase partitioning behavior.