Chronic Toxicity of the Synthetic Pyrethroid Tau Fluvalinate to Aquatic Invertebrates: Life History, Oxidative Stress, and Molecular Responses of Daphnia magna

Tau fluvalinate, a broad-spectrum pyrethroid insecticide/acaricide, can affect not only target pests but also nontarget aquatic organisms. In this study, the chronic toxicity of tau fluvalinate on Daphnia magna was evaluated at three different concentrations (0.001, 0.002, and 0.004 μg/L) for 21 days, and its effects on life history traits, physiological parameters, biochemical markers, and gene expression profiles were comprehensively assessed. Tau-fluvalinate exposure exhibited a clear concentration-dependent toxicity pattern, with a 48-h EC50 value of 0.016 μg/L. Chronic exposure significantly reduced body length, offspring number per female, molt frequency, heart rate, and survival probability, while increasing the time to first offspring. Biochemical analyses revealed oxidative damage and impaired antioxidant defense mechanisms. Furthermore, transcriptional changes were observed in genes related to detoxification (CYP4, CYP360A8, CYP314, and HR96, P-GP), oxidative stress regulation (SOD, CAT, MDA, and GST), nuclear receptor signaling (Nrf2), and endocrine/developmental pathways (CUT, DMRT, and VTG). These findings demonstrate that even low doses of tau fluvalinate can induce severe physiological and molecular disruptions in D. magna, highlighting its potential ecological risk from the molecular level to population dynamics. The life history results further suggest that delayed first reproduction may reduce population growth, indicating that toxic effects observed at the individual level could extend to the population level.