Effect-Directed Toxicity Assessment of the Surface Water of Chao Phraya River by Integrating a Panel of Bioluminescent E. coli with ICP-OES and HPLC-DAD

Abstract This study presents an effect-directed analysis (EDA) combining Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES), High-Performance Liquid Chromatography-Diode Array Detection (HPLC-DAD), and five bioluminescent Escherichia coli bioreporters to map surface water toxicity along a 372-km gradient of the Chao Phraya River, Thailand. Evaluating cytotoxicity, genotoxicity, metabolic disturbance, oxidative stress, and quorum sensing via a new Toxic Index (TI) and Dynamic Time Warping (DTW) kinetic alignment, the panel unmasked complex cellular stress gradients. Although ICP-OES revealed localized mercury spikes (119 μg/L), metals contributed minimally to overall toxicity. Instead, upstream freshwater exhibited severe, multi-pathway stress (Total Toxicity Index, TTI ∼ 2.48) statistically associated with trace bioactive organic fractions isolated via solid-phase extraction. In complex urban matrices, DTW effectively exposed non-monotonic toxicity masking. Conversely, the downstream estuarine TTI peak (3.06) was identified as an isolated, non-chemical osmotic shock response driven by extreme salinity (18,710 ppm total dissolved solids). This integrated framework demonstrates that relying on bulk chemical quantification inherently underestimates latent ecotoxicological hazards, proving the necessity of mechanistic biological diagnostics to accurately evaluate and protect complex aquatic ecosystems.