Prioritizing emerging contaminants in tropical riverine systems: An integrated approach using ecological and human health risk indices.

Emerging contaminants of concern (CECs) are increasingly detected in tropical riverine systems, yet their prioritization remains challenging due to data gaps, complex mixtures, and limited integration of ecological and human health perspectives. This study proposes an integrated framework to identify priority CECs by combining occurrence data, ecological risk quotients (RQ), human health hazard quotients (HQ), and a novel prioritization index (PI). Thirty-four (34) multiclass CECs, including pharmaceuticals, hormones, and plasticizers, were quantified in four rivers in Johor, Malaysia using optimized solid-phase extraction coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS). Caffeine (1511-6085 ng/L), paracetamol (32-7408 ng/L), and bisphenol A (344-837 ng/L) dominated the contaminant profiles. Most pharmaceuticals posed negligible ecological risk, while bisphenol A showed low ecological risk under worst-case exposure (0.01 < RQ < 0.1). In contrast, human health assessment indicated substantial risks from bisphenol A and bisphenol S, particularly for children (HQ > 1). Integration of ecological thresholds (PNEC) and reference doses (RfD) identified bisphenol analogues as highest-priority contaminants, followed by estrone, lidocaine, dexamethasone, and diphenhydramine. The framework demonstrates that concentration-based assessments may underestimate risk and supports toxicity-weighted prioritization for monitoring and regulation in tropical aquatic systems.