Genotoxic Effects in Erythrocytes of Oreochromis niloticus Exposed to Nanograms-per-Liter Concentration of 17β-Estradiol (E2): An Assessment Using Micronucleus Test and Comet Assay

Pharmacologically active substances used in the treatment of human and animal illnesses may usually enter the aquatic environment via effluents from sewage treatment plants, as they are not completely biodegraded or removed during waste water treatment. 17 beta-Estradiol genotoxicity was evaluated in Oreochromis niloticus (family Cichlidae) using micronucleus test, other nuclear abnormalities assessment, and the comet assay with erythrocytes. Fish were exposed to aqueous systems contaminated with 6 ng/L 17 beta-estradiol for three periods: 24 h, 48 h, and 10 days. The results showed that 17 beta-estradiol has genotoxic potential in different periods, since significant differences (P = 0.036) were observed in the micronucleus frequencies of the 10-day exposure groups in relation to the control group. Also, the same was observed when comparing the nuclear abnormality frequencies (P = 0.018) of the 24-h exposure group with the negative control group, and when using comet assay (P < 0.001) for 48-h evaluations. The tested concentration of the 17 beta-estradiol gave rise to mutagenic and genotoxic effects on the blood cells of O. niloticus, therefore the substance being considered a clastogenic chemical contaminant on both acute and chronic exposures. The assessment using a combination of micronucleus test, nuclear abnormalities, and comet assays proved to be suitable and useful in the genotoxicity testing of 17 beta-estradiol at nanograms per liter.