Organophosphate pesticides (OPs), a class of acetylcholinesterase inhibitors, are used widely in agriculture to reduce insect populations. Because of the conservation of acetylcholinesterase between invertebrates and vertebrates, OPs also can adversely affect nontarget species, such as aquatic and terrestrial animals. This study used uniform conditions to analyze the morphological and physiological effects caused by developmental exposure to 3 commonly used OPs-chlorpyrifos, dichlorvos, and diazinon-on 2 aquatic vertebrate species, Danio rerio (zebrafish) and Xenopus laevis. Survival, locomotor activity, heart rate, and gross anatomical abnormalities, including kyphosis and edema, were observed over a 5-d period in response to OP concentrations ranging from 0 µM to 1000 µM. Both zebrafish and Xenopus showed decreased survival for all 3 OPs at higher concentrations. However, Xenopus showed higher mortality than zebrafish at lower chlorpyrifos and dichlorvos concentrations. Both models showed a dose-dependent decrease in heart rate and free-swimming larval activity in response to chlorpyrifos and dichlorvos. In addition, kyphosis and decreased spine length were prominent in Xenopus in response to 10 µM of chlorpyrifos and 0.1 µM dichlorvos. Although diazinon induced no effects on skeletal and cardiac motor activity in either species, it did induce cardiac edemas in zebrafish. Differences in the biological actions of OPs and their differential effects in these 2 vertebrate models demonstrate the importance of using common protocols and multiple models to evaluate the ecotoxicology of OPs.

Organophosphate pesticides are known to inhibit acetylcholine esterase, an enzyme that degrades acetylcholine at the cholinergic synapse. In this study zebrafish were used to understand the impact chlorpyrifos, dichlorvos, and diazanon on vertebrate developmental physiology. Pre‐epiboly zebrafish embryos were exposed pesticides at concentrations ranging from 1μM to 1mM. Survival, spontaneous movements, heart rate, swimming behavior, and physical abnormalities were examined. All three pesticides were found to be toxic to developing zebrafish embryos at concentrations at or above than 100 μM. However, disruption of physiological processes controlled by the cholinergic neurons was only seen in embryos exposed to chlorpyrifos and dichlorvos. Chlorpyrifos and dichlorvos exposed embryos exhibited increased spontaneous movements, decreased embryonic heart rate, and a transient decrease in larval swimming ability. Although diazanon was the most toxic, it had no effect on these physiological systems. The effects of organophosphate pesticide exposure on vertebrate development are diverse and may be mediated through pathways other than the inhibition of acetylcholine esterase.