Influence of temperature on biomarker responses of bullfrog tadpoles (Lithobates catesbeianus) exposed to the herbicide ametryn.

The S-triazine herbicide ametryn (AMT) is relatively low adsorbed in soils and has high solubility in water, thus believed to affect non-target aquatic organisms such as amphibians. Temperature increases can intensify the effects of herbicides, possibly increasing the susceptibility of amphibians to these compounds. The aim of this study was to evaluate the influence of temperature (25 and 32 °C) on the responses of biochemical biomarkers in bullfrog tadpoles (Lithobates catesbeianus) exposed to different concentrations of AMT (0, 10, 50 and 200 ng.L) for a period of 16 days. The antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD) and the biotransformation enzyme glutathione S-transferase (GST) had their activity decreased at the highest temperature (32 °C). SOD activity was reduced at 200 ng.L and 32 °C compared to the control at the same temperature. AMT exposure also decreased the activities of alanine aminotransferase and gamma glutamyl transferase. On the other hand, the activities of acetylcholinesterase, carboxylesterase, alkaline phosphatase, levels of lipid peroxidation and protein carbonyl, as well genotoxic markers (micronucleus and nuclear abnormalities frequencies) were unchanged. The evaluation of integrated biomarker response index (IBR) indicated highest variations at the concentration of 200 ng.L at 32 °C, suggesting that the combination of high AMT concentrations and temperatures generate more pronounced negative effects to tadpoles.