Genotoxic evaluation of different delta-endotoxins from Bacillus thuringiensis on zebrafish adults and development in early life stages.

The use of toxins from Bacillus thuringiensis as biopesticides in the biological control of insects and in transgenic plants has increased their availability in the environment. Ecotoxicological evaluations of four delta-endotoxins cry 1Aa, cry 1Ab, cry 1Ac, and cry 2A from B. thuringiensis were carried out on zebrafish Danio rerio to explore the adverse effects on their genome and embryos. Cry 1Aa increased the micronucleus (MN) frequency in peripheral erythrocytes of adult D. rerio, while cry 1Ab, cry 1Ac and cry 2A did not show genotoxicity, after 96-h of exposure at concentration of 100mg/L. Exposures to binary mixtures (cry 1Aa+cry 1Ac, 50:50mg/L) and (cry 1 Aa+cry 2A, 50:50mg/L) for 96-h showed also significant increased MN frequency. Other evaluated binary mixtures did not show genotoxicity. Activity of glutathione S-transferase measured in the gills did not seem to be altered after exposure to all tested toxins as well as to the six combinations of binary mixtures. In the embryo-larval study, all tested delta-endotoxins showed embryo toxicity and developmental delay after exposure to the concentrations of 25, 50, 100 and 150mg/L for 96-h. However, each toxin presented a different pattern of toxic response suggesting that a specific approach should be taken into account to its toxicological evaluations.