Uncovering Hidden Pollution: Diffuse Contaminant Sources in a Sparsely Industrialized Estuarine System

Understanding sediment contamination in low-industrial activity areas remains a critical but understudied issue, particularly in estuarine ecosystems subject to diffuse pollution sources. This study employed nontarget screening with high-resolution mass spectrometry to analyze sediment samples from Ganggu Estuary, South Korea, to evaluate the composition and distribution of sediment contaminants in a region lacking heavy industry but influenced by agriculture, fisheries, and tributary discharges. The investigation revealed that contamination stems from multiple sources, including streams, agricultural runoff, and fish market discharges. A total of 678 chemicals were identified, including human and veterinary drugs (8.7%), food additives (6.5%), pesticides (2.8%), and PFAS (1.9%), with spatial variability confirmed by total organic carbon (TOC) analysis. Notably, this study is the first to report the detection of dinoseb, a banned herbicide in estuarine sediments, identified with high confidence alongside key pollutants such as 6:2 fluorotelomer sulfonic acid and 2,4-di-tert-butylphenol. We linked contamination hotspots to U-shaped river bends, streamwater and sediment inputs, and agricultural runoffs, and highlight the role of natural processes in pollutant deposition in a region where heavy industry is absent, yet diffuse sources still drive significant contamination.