Triclopyr, an auxin-like herbicide that is widely employed for managing weeds in food crops and pastures, has been identified in various environmental settings, particularly aquatic ecosystems. Limited understanding of the environmental fate of this herbicide, its potential repercussions for both the environment and human health, and its insufficient monitoring in diverse environmental compartments has caused it to be recognized as an emerging contaminant of concern. In this study, we have investigated how triclopyr affects zebrafish, considering a new alternative methodology. We focused on the endpoints of developmental toxicity, neurotoxicity, and behavior of zebrafish embryos and larvae. We determined that triclopyr has a 96 h median lethal concentration of 87.46 mg/L (341.01 µM). When we exposed zebrafish embryos to sublethal triclopyr concentrations (0.5, 1, 5, 10, and 50 μM) for up to 144 h, we found that 50 µM triclopyr delayed zebrafish egg hatchability. Yolk sac malabsorption was significant at 0.5, 1, 5, and 10 µM triclopyr. In zebrafish larvae, uninflated swim bladder was significant only at 50 µM triclopyr. Furthermore, zebrafish larvae had altered swimming activity after exposure to 10 µM triclopyr for 144 h. In summary, these comprehensive results indicate that even low triclopyr concentrations can elicit adverse effects during early zebrafish development.

Triclopyr is an auxin-like herbicide extensively employed to manage weeds in food crops and pastures. Triclopyr has been detected in environmental matrices, with a notable presence within aquatic ecosystems. Given the limited understanding of its fate in the environment, potential implications for environmental and human health, and the lack of adequate monitoring in various environmental compartments, triclopyr is now considered a contaminant of emerging concern (CEC). The present study was undertaken to investigate the impact of triclopyr on zebrafish development, with a specific focus on assessing its embryotoxic, behavioral, and neurotoxic effects at environmentally realistic concentrations ranging from 0.5 to 50 µM on zebrafish embryos. Our results revealed that triclopyr caused sublethal effects on zebrafish embryos, such as delayed hatchability at 50 µM, yolk sac retention at 0.5, 1, 5, and 10 µM, and uninflated swim bladder at 50 µM concentration of triclopyr. Moreover, a subtle alteration in the swimming activity of larvae was observed in the 10 µM triclopyr after 144 hours of exposure. However, the activity of acetylcholinesterase, remained unchanged after triclopyr exposure. Taken together, these comprehensive findings suggest that triclopyr can induce adverse effects on the early development of zebrafish, even at concentrations detected in aquatic environments.