Biological impacts of organophosphates chlorpyrifos and diazinon on development, mitochondrial bioenergetics, and locomotor activity in zebrafish (Danio rerio).

The objectives of this study were to compare the biological responses in developing zebrafish to two organophosphate insecticides, chlorpyrifos (CPF) and diazinon (DZN). Zebrafish embryos were exposed to either solvent control (0.1% DMSO, v/v), or one dose of 0.1, 1.0, 10.0 and 25.0 µM CPF, as well as one dose of 0.1, 1.0, 10.0 and 100.0 µM DZN for 96 h. CPF at 10.0 and 25.0 µM caused 70-80% and 100% mortality in embryos after 96 h exposure, whereas embryos treated with 10.0 and 100.0 µM DZN showed 30-40% and 70-80% lethality. CPF at 10.0 µM significantly decreased cumulative hatching rate, whereas hatching rate was significantly reduced in embryos treated with 100.0 µM DZN. Spinal lordosis was primarily observed in larvae exposed to 1.0 and 10.0 µM CPF, whereas pericardial edema was mainly detected with 10.0 and 100.0 µM DZN exposure. Embryo exposed to 1.0, 10.0 and 25.0 µM CPF exhibited no mitochondrial dysfunction; exposure to 100.0 µM DZN significantly inhibited mitochondrial bioenergetics. To determine if CPF and DZN affected larval activity, dark photokinesis response was assessed in larvae following 7 days exposure to 0.1 and 1.0 µM CPF, as well as to 0.1 1.0, and 10.0 µM DZN. Larvae exposed to 1.0 µM CPF showed hypoactivity, whereas the activity in the dark was not overtly changed in larvae exposed to DZN. In summary, CPF showed higher developmental toxicity compared to DZN. Moreover, based on the types of morphological deformities noted, as well as differences in locomotor activity, we conclude that OPs have unique chemical-specific modes of action that can result in varied biological responses during early development.