Environmentally relevant concentrations of a hexazinone-based herbicide impair zebrafish embryo-larval development by...

Hexazinone (HZN)-based herbicides are widely used in sugarcane crops and may pose risks to non-target organisms. This study evaluated the toxicity of environmentally relevant concentrations (0.05, 0.5, 5µgL^-1) of the HZN-based herbicide Nortox® and two higher concentrations across zebrafish development, assessing lethal and non-lethal endpoints, neurotoxicity, cardiotoxicity, redox imbalance, and target gene expression. All HZN treatments increased mortality and reduced spontaneous contractions, whereas only the highest concentrations affected hatching and induced bradycardia. CAT activity increased in animals exposed to 0.5µgL^-1, whereas GST activity decreased at both 0.5 and 5µgL^-1. AChE activity increased only at the lowest concentration. nrf2 and bmp4 transcripts were affected at 5µgL^-1, whereas non-monotonic responses were observed in p53, ccdn1, bax, and pax6a. These results provide the first evidence that environmentally relevant concentrations of HZN-based herbicides may affect fish development by altering signaling pathways, physiological responses, and survival rates.