Physiological, morphological, and metabolic responses of <i>Artemia franciscana</i> to 2,4-dichlorophenoxyacetic acid

Abstract The widespread use of pesticides has heightened the risk of toxic effects on nontarget species. Among these compounds, the synthetic auxin 2,4-dichlorophenoxyacetic acid (2,4-D), one of the most widely used herbicides worldwide, raises concerns about its potential environmental impacts and the exposure of nontarget organisms. This study therefore investigated the effects of the active ingredient 2,4-D on the larval physiology, morphology, and oxidative and metabolic responses of the microcrustacean Artemia franciscana. For the developmental assays, A. franciscana nauplii were exposed to different concentrations of 2,4-D (50–500 mg·L−1) for 24 and 48 hr. Based on these assays, the no observed effect concentration (100 mg·L−1), half-maximal effect concentration (EC50; 365.1 mg·L−1), and the highest tested concentration (500 mg·L−1) were selected to evaluate morphological effects after 24 hr of exposure, including body length, eye diameter, and the number of thoracopods. Apoptosis in nauplii was assessed using acridine orange staining. Enzymatic responses related to oxidative stress (catalase and glutathione peroxidase [GPx]) and energy metabolism (lactate dehydrogenase [LDH]) were also assessed after 24 hr. The four highest concentrations of 2,4-D (200, 300, 400, and 500 mg·L−1) decreased the mobility of the nauplii at both exposure times. Exposure to the EC50 and the highest tested concentration of 2,4-D resulted in decreases in body length, eye diameter, and the number of thoracopods in the nauplii. Acridine orange staining revealed apoptosis after 24 hr of exposure at the EC50 but not at sublethal concentrations. Additionally, exposure to sublethal concentrations of 2,4-D (0.1 to 100 µg·L−1) decreased LDH activity and increased GPx activity after 24 hr. This study demonstrated that only 2,4-D concentrations significantly higher than those typically found in aquatic environments adversely affected the mobility, morphology, and metabolic activity of A. franciscana nauplii. Further research is needed to assess the lethal and sublethal effects of different 2,4-D formulations on nontarget organisms.