Toxic effects of two pesticides, Imazalil and Triadimefon, on the early development of the ascidian Phallusia mamillata (Chordata, Ascidiacea)

Azole compds. are fungicides used in agriculture and in the clin. area and are suspected to produce craniofacial malformations in vertebrates. Toxicity tests on sperm viability, fertilization, and embryogenesis of the solitary ascidian P. mamillata were performed to evaluate the effects of 2 azole derivs., Imazalil and Triadimefon. Ascidian (Chordata, Ascidiacea) embryos and larvae could provide biol. criteria for seawater quality stds. because the larvae are lecitotrophic and have a short pelagic period, allowing to run the larval toxicity tests over a short period of time. Imazalil and Triadimefon proved to have strong consequences on P. mamillata. They could influence the reproductive rate of the animal exerting their effects at different levels: acting as spermiotoxic agents, inhibiting fertilization, and impairing embryol. development. The fertilization rate significantly decreased after 30-min exposure of sperm to 25 mM Imazalil (P < 0.0001) and after exposure of both gametes to 50 mM Imazalil (P < 0.05) and 1 mM Triadimefon (P < 0.0001) as compared to controls. Malformations caused by exposure of embryos to both substances were dose-dependent. Imazalil median teratogenic concn. (TC50 concn., the concn. that resulted in 50% malformed larvae) value was 0.67 mM and median lethal concn. (LC50, the concn. that resulted in 50% embryos dead before completing the development) value was 10.23 mM while for Triadimefon TC50 value was 29.56 and LC50 value was 173.7 mM. Larvae developed from embryos treated with Imazalil and Triadimefon showed alterations of the anterior structures of the trunk: papillary nerves and the anterior central nervous system failed to correctly differentiate, as shown by immunostaining with anti-b-tubulin antibody. Comparing the anomalies caused by retinoic acid, reported in a previous study, it was possible to hypothesize that malformations induced by Imazalil and Triadimefon could be due to a perturbation of the endogenous retinoid content, as it has been proposed for mammals. Ascidians proved to be good models to study the toxic effects of pesticides since they offered both the convenience of working with an invertebrate species and the tissue sensitivity to chem. compd. comparable to vertebrates. [on SciFinder (R)]