Effects of abamectin on bullfrog tadpoles: insights on cytotoxicity

Abamectin is one of the most used pesticides worldwide. However, investigations about its effects on amphibian populations are rare. Thus, the present study sought to investigate possible cytotoxic effects on Lithobates catesbeianus tadpoles exposed to low abamectin concentrations diluted in water. Accordingly, four experimental groups were set: negative control, positive control (cyclophosphamide-40 mL L^-1), abamectin at concentrations 36 μg a.i./L (ABA36 group), and 72 μg a.i./L (ABA72 group), applied as Kraft® 36EC. The micronucleus test was conducted and other nuclear abnormalities in peripheral blood erythrocytes were checked after 24, 48, and 72 h of exposure to the treatments. The total of other nuclear abnormalities was influenced by the treatments, whereas the frequency of micronuclei was influenced by the exposure time. Such frequency was higher in the animals comprising the ABA72 group, which was assessed 72 h after the exposure had begun. The total of other nuclear abnormalities was influenced by the treatments. Animals in the positive control, ABA36, and ABA72 groups showed similar frequency of these abnormalities at 48 and 72 h. However, this frequency was statistically higher than that of animals in their respective negative control groups. Thus, the present study confirmed the hypothesis that the exposure of L. catesbeianus tadpoles to abamectin caused cytotoxic effects on them, although this exposure lasted short and the concentrations were low. It disclosed prospects for variations in the nucleus of erythrocytes circulating in amphibians, a fact that may provide an important/complementary approach for the detection of cytotoxicity caused by abamectin exposure.