Environmental Monitoring of River Basins in Vietnam Using In Vitro Bioassays

Vietnam is currently facing increasing water pollution issues alongside rapid economic development. However, due to limitations in both environmental analytical capacity and budgetary resources, the monitoring and assessment of water contamination remain insufficient. In this study, we employed in vitro bioassays using reporter gene systems for the first time in Vietnam to evaluate the toxicity of surface water samples from major urban areas. Although the majority of samples yielded low values in the pregnane X receptor (PXR, PB) assay, three samples from Hanoi and Ho Chi Minh City exhibited strong toxicity, with 1/IC50 values exceeding 1. Notably, one sample from Hanoi showed a high aryl hydrocarbon receptor (AhR) binding activity equivalent to 3,800 ng/L of β-naphthoflavone. This level is approximately 100 times higher than the average concentration (36 ng/L) measured in six typical rivers in Japan during 2011–2012, indicating severe contamination. Additionally, two sites in Ho Chi Minh City recorded AhR activity exceeding 800 ng/L. Constitutive androstane receptor (CAR) binding activity reached over 10,000 ng/L (as t-octylphenol equivalent) in two samples from Hanoi—ten times higher than values found in Japanese rivers. While most samples showed retinoic acid receptor (RAR) activity in the solid-phase fraction (SS), suggesting a possible origin from natural sources such as seaweed, samples from Hanoi exhibited high activity in the soluble fraction, indicating contamination by chemical pollutants. In the Red River (Song Hong), elevated levels of PB, CAR, AhR, and RAR activity were detected upstream from the China border, with significantly higher values observed as the river passed through Hanoi. These results suggest the presence of intense pollution in certain urban rivers in Vietnam. Ongoing chemical analyses are being conducted to identify specific contaminants. Further detailed investigations are needed to fully elucidate the sources and composition of the pollutants.