Emerging and Persistent Contaminants in a Remote Coastal Stream System: Five Priority Compounds in Southeast Asia

This study is a preliminary assessment of the emerging and persistent contaminants (EPCs) in the ecologically sensitive Kamphuan Stream in Southern Thailand. The analysis of 15 compounds revealed that EPC concentrations below the main community were significantly elevated during the rainy season, with the highest levels found for sucralose (9070 ng/L), metformin (6250 ng/L), fexofenadine (5110 ng/L), and gabapentin (3060 ng/L). These spatiotemporal patterns highlight the episodic nature of contamination driven by urban stormwater runoff, where rainfall events create temporary pathways that transport EPCs to streams draining into coastal ecosystems. Maximum concentrations of three pharmaceuticals (diclofenac, gemfibrozil, and ibuprofen), as well as sucralose, caffeine, and fenobucarb, exceeded the general predicted no-effect concentrations (PNECs) for marine or fresh waters; however, these concentrations were not persistent. Limited sampling across three campaigns constrained the ability to fully characterize the dynamics of this issue through statistical inference. Furthermore, risk assessments were constrained by the absence of locally derived PNECs for tropical ecosystems and organisms, along with limited standardization in PNEC determination methodologies, making definitive conclusions challenging. A comparative analysis of five priority compounds (diclofenac, gemfibrozil, metformin, naproxen, and fluoxetine) against existing data from East and Southeast Asia underscores the need for further research in Southeast Asia to evaluate the ecological risks posed by EPCs across diverse rivers and streams. Future studies should focus on the contaminants of greatest ecological importance, investigate their transformation products, identify sources and transport pathways, and assess their environmental risks to aquatic ecosystems.