Assessing the chronic toxicity of the organic UV filter 2-ethylhexyl-4-methoxycinnamate (EHMC) on Daphnia magna.

2-ethylhexyl-4-methoxycinnamate (EHMC), as one of the most prevalent and mass-produced organic UV filters (OUVFs), has emerged as a globally significant pollutant. The continuous release of EHMC into surface waters presents significant hazards to aquatic biota, but its toxicological effects on aquatic invertebrates remain largely unknown. In the present study, Daphnia magna neonates were exposed to 0, 0.14, 1.65, and 15.71 μg/L EHMC for 21 days to investigate potential chronic adverse impacts on the growth, reproduction, antioxidant defense, and swimming behavior, and to explore the underlying toxicological mechanisms. The results indicated that EHMC significantly inhibited D. magna growth and reproduction, reducing body length, delaying first brood, lowering offspring count, and causing severe locomotor inhibition with decreased swimming speed and distance. qPCR analysis demonstrated that EHMC interfered with the expression patterns of core genes (e75, hr3) involved in the ecdysone signaling pathway and affected the transcriptional levels of reproductive-related genes (vtg1, vtg2). Furthermore, based on elevated juvenile hormone (JH) levels and upregulated jhe expression, we speculated that disruption of JH metabolism might contribute to reproductive suppression. Additionally, high concentrations of EHMC collapsed the antioxidant defense and triggered oxidative damage. Principal component analysis (PCA) revealed a marked negative correlation between ROS level, GPx activity and growth-reproduction indicators, suggesting a potential trade-off strategy that D. magna redistributed energy against oxidative damage under EHMC stress, thereby impairing physiological functions. Collectively, these findings deepen our understanding of EHMC's toxicity to aquatic invertebrates, and provide essential scientific basis for organic UV filters pollution control in aquatic environments.