Acute and Sublethal Effects of Boron on Daphnia magna: Assessment Using Behavioral, Physiological and Oxidative Stress Endpoints

Boron serves as a necessary micronutrient, but elevated concentrations may exert toxic effects, which has raised concern over its increasing presence in the environment owing to anthropogenic activities. This study assessed the sublethal effects of boron on Daphnia magna, which is a commonly employed model species in freshwater ecotoxicology. D. magna neonates were subjected to boron concentrations ranging from 0.5 to 350 mg B/L over 48 h, and acute toxicity (EC50), along with swimming velocity, heart rate, and oxidative stress responses, were evaluated as toxicological endpoints. Swimming velocity increased significantly at 80 mg B/L before declining, while heart rate significantly decreased at 250 mg B/L (p < 0.05). In addition, significant increases in oxidative stress responses were observed at sublethal concentrations of 40 and 80 mg B/L (p < 0.05), highlighting the sensitivity of oxidative stress responses to boron exposure. These findings demonstrate the previously underexplored sublethal effects of boron on D. magna, including alterations in swimming velocity, heart rate, and antioxidant defenses, emphasizing the need for integrated endpoints in ecotoxicological assessments.