Genotoxic and Biochemical Responses of the Amphibian Rhinella arenarum Under Exposure to the Herbicide 2,4-Dichlorophenoxyacetic Acid (2,4-D).

Abstract

The widespread use of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D), an analogue to the hormone auxin, raises concerns regarding its potential impact on aquatic organisms, particularly amphibians. Thus, this study aimed to evaluate the genotoxic and oxidative effects of an environmentally relevant concentration of 2,4-D on Rhinella arenarum tadpoles. To this end, tadpoles were acutely exposed to 5 μg/L of 2,4-D under laboratory conditions using the microformulation Dedalo Elite (30% a.i.). Genotoxicity was assessed via the alkaline comet assay, measuring DNA single- and double-strand breaks. Oxidative balance was evaluated by determining catalase (CAT) and glutathione S-transferase (GST) activities, along with reduced glutathione (GSH) levels. The results demonstrated that, after exposure, tadpoles showed significant increases in DNA damage, with 3.32- and 2.92-fold increases at 48 and 96 h, respectively. The 48-h exposure increased DNA damage, but extended exposure (96 h) had a lesser effect. In addition, after 96 h of exposure, CAT activity was significantly reduced (43.8%), and GSH levels decreased by 29.8%, indicating the induction of oxidative stress. These findings highlight the sensitivity of R. arenarum tadpoles to sublethal 2,4-D concentrations and emphasise the ecological relevance of assessing early life stage responses in amphibians. Our results add to the growing evidence on the risks posed by widely used auxinic herbicides, with detrimental effects on cellular integrity that may compromise the early life stages of freshwater species in their natural environments.