Effects of the herbicide 2,4 D active ingredient and commercial formulations on the early life stages of the amphibian Physalaemus gracilis

The herbicide 2,4-D is extensively employed and detected in surface waters, representing a risk for amphibians. Species of the genus Physalaemus , such as P. gracilis , show sensitivity to the compound even at low concentrations. This study compared the toxicity of the active ingredient (D AI ) and two of its commercial formulations of 2,4-D (DBH 1 and DBH 2 ) on survival, heart rate, swimming activity, and biochemical parameters (TBARS levels and CAT activity) of P. gracilis during its initial development stages. The tested concentrations (5, 10, 15, 20, and 25 µg/L) were selected based on the limits established for 2,4-D in Brazilian freshwater regulations. D AI decreased survival and altered swimming activity at all tested concentrations, increased TBARS levels at 5 and 10 µg/L, and reduced CAT activity at 20 and 25 µg/L. Both commercial formulations also affected survival and swimming activity at all concentrations; DBH 1 reduced heart rate at 15 and 25 µg/L, while DBH 2 increased it at all tested concentrations. Additionally, DBH 1 increased TBARS levels at 15 µg/L in exposed embryos and tadpoles, whereas DBH 2 decreased TBARS levels at 5 µg/L and reduced CAT activity at all tested concentrations. Overall, exposure to 2,4-D and its commercial formulations induced physiological and behavioral alterations in Physalaemus gracilis tadpoles, although the magnitude and direction of the effects varied among compounds.