Toxicity of mixtures of dimethoate and tebuconazole on the embryo-larval development of Rhinella arenarum

MERCEDES ACQUARONI; GABRIELA SVARTZ; CRISTINA PÉREZ-COLL

Valdivia

Congreso; SETAC Latin America 14th Biennial Meeting; 2021

Society of Environmental Toxicology and Chemistry (SETAC) Latin America

Frequently two or more pesticides are simultaneously or sequentially applied expecting a better crop yield. Amphibians are one of the most widely group exposed to these multiple pesticides scenarios in the agroecosystems, and the impact of pesticide mixtures represents a challenge for risk assessment and conservation purposes. The aim of this study was to evaluate the toxicity of individual and binary equitoxic mixtures of the insecticide dimethoate (DIM) and the fungicide tebuconazole (TEB) on the embryo-larval development of Rhinella arenarum. For this purpose, embryos from blastula (Stage 4) and larvae from complete operculum (Stage 25) were exposed for acute (96 h), sub-chronic (168 h) and chronic (336 and 504 h) periods to different concentrations of DIM and TEB, and dilutions of a DIM-TEB mixture. The lethal and sublethal effects of the individual pesticides and the mixture were evaluated and the interaction was analyzed at the different exposure times. The obtained results showed that embryos and larvae were more sensitive to TEB (LC50-504 h = 2.63 and 7.49 mg/L, respectively) than DIM (LC50-504 h = 50.31 and 26.48 mg/L, respectively) at all exposure times. The mixture of these pesticides was more toxic to larvae (LC50-96 and 168 h = 41.38 and 37.61 mg/L) than embryos (LC50-96 and 168 h = 112.52 and 79.16 mg/L) at acute and sub-chronic exposure periods, but expanding the exposure time there were no significant differences obtaining LC50-504 h values of 20.48 and 24.00 mg/L for embryos and larvae respectively. Respect to sublethal effects, embryos exposed to individual pesticides and the mixture showed cellular dissociation, general underdevelopment, edema and axial flexure. As for larvae, when embryos developed movements, swimming behavior, they presented mainly ethological alterations such as spasmodic contractions, erratic movements, weakness and finally complete immobility. The joint effects of the pesticide mixture showed antagonistic interactions in both embryo and larval stages. This study highlights the importance to evaluate the joint actions of pesticides, to simulate the real exposure conditions in agronomic scenarios. Moreover, complexity of toxicological interactions can lead to unpredictable effects of the mixtures putting in risk non target species.