Mechanism Directed Toxicity Testing and Instrumental Analysis Make Key Toxicant Identification More Targeted and Efficient: A Case in the Yangtze River

Current toxicant identification mainly relies on subjective and blind toxicity testing and compound screening. This could overlook the sensitive toxicity end point and key toxicants due to the random experiment selection, or it might incur high expenditures due to toxicity testing of multiple end points. In this context, a key toxicity-mechanism-based new effect-directed analysis strategy was established. The strategy is based on the key toxicity mechanisms from the transcriptome to determine subsequent toxicity tests and chemical analyses to achieve the efficient, rational, and focused identification of key toxicants in mixtures. Then, this strategy was applied to the Yangtze River samples. By transcriptome testing, the nerve growth factor and neurotrophin binding pathways showed the highest detection rate, indicating that the key toxicity mechanism is neurotoxicity. Zebrafish behavior tests were further chosen for neurotoxicity effect evaluation, and they showed significant inhibition in 64% of the samples. On the other hand, 38 and 94 neurotoxicants in samples were identified via targeted and pseudotargeted screening from 3363 potential toxicants. Further combining mechanism-based biological testing and chemical analysis for toxicant verification, this study ultimately identified seven key toxicants, such as atrazine, hexazinone, and niclosamide. The mechanism-directed EDA will open a new horizon for accurate identification and prioritization of key toxicants in the environment.