Melanophryniscus admirabilis tadpoles' responses to sulfentrazone and glyphosate-based herbicides: an approach on metabolism and antioxidant defenses

Melanophryniscus admirabilisis a frog endemic to the southern Atlantic Forest (Brazil), with restricted distribution and considered as critically endangered. The aim of this study was to evaluate possible alterations in biomarkers of metabolism (glycogen, proteins, and uric acid) and oxidative balance (superoxide dismutase, catalase, glutathione S-transferase, and lipoperoxidation) of tadpoles ofMelanophryniscus admirabilisexposed to commercial herbicide formulations containing sulfentrazone (Boral (R) 500 SC: 130 and 980 mu g a.i./L) and glyphosate (Roundup (R) Original: 234 and 2340 mu g a.i./L). Mortality was not observed in any of the groups studied. Our results show that a 96-h exposure to the herbicides decreased glycogen levels, indicating increased energy demand for xenobiotic metabolism. Protein levels increased in the Boral group but decreased in the higher concentration of Roundup, and uric acid levels did not change significantly between the experimental groups. Lipoperoxidation decreased in the Boral group and in the higher concentration of Roundup. Decreased levels of superoxide dismutase in both treatments and of catalase in the lowest concentration of the herbicides were observed. Glutathione S-transferase activity increased in the Roundup group; this enzyme seems to be crucial in the metabolization of the herbicides and in the survival of the tadpoles. Our results suggest thatM. admirabilishas a high antioxidant capacity, which guaranteed the survival of tadpoles. Nevertheless, exposure to pesticides could impose a serious risk to this species, especially considering its restricted distribution, habitat specificity, and high physiological demand to metabolize xenobiotics.

Automated summary

The study evaluated the impact of herbicide exposure on biomarkers and oxidative balance in Melanophryniscus admirabilis tadpoles. Results showed decreased glycogen levels, reduced lipoperoxidation, and lower levels of superoxide dismutase and catalase. Glutathione S-transferase activity increased in response to herbicide exposure.