Phytochemical characterisation and biosafety profiling of Elsholtzia communis (Collett & Hemsl.) Diels essential oil using zebrafish embryos

Elsholtzia communis (Collett & Hemsl.) Diels is traditionally used in herbal medicine, yet the phytochemical composition and developmental safety of its flower-derived essential oil remain insufficiently explored. This study aimed to characterise the essential oil of E. communis flowers (EOEC), evaluate its antioxidant and antibacterial activities and assess its developmental toxicity using zebrafish (Danio rerio) embryos. The EOEC was extracted by hydro-distillation and characterised using gas chromatography-mass spectrometry (GC-MS) and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. Antioxidant potential was evaluated through DPPH and ABTS radical scavenging assays, while antibacterial activity against selected Gram-positive and Gram-negative bacteria was determined using agar well diffusion and minimum inhibitory concentration (MIC) assays. Developmental toxicity was assessed in zebrafish embryos by monitoring mortality and morphological abnormalities to calculate LC₅₀ values. The GC-MS analysis revealed citral-A (geranial, 45.5 %) and citral-B (neral, 37.8 %) as the major constituents of EOEC, while FTIR spectra confirmed the presence of characteristic OH, C=O and CH functional groups. EOEC exhibited moderate antioxidant activity with EC₅₀ values of 45.12 µg/mL (DPPH) and 43.15 µg/mL (ABTS) and demonstrated significant antibacterial effects against both Gram-positive and Gram-negative strains. Zebrafish embryo assays showed clear dose-dependent lethality and developmental abnormalities, with LC₅₀ values of 123 µg/mL for EOEC and 145 µg/mL for citral. Notably, adverse developmental effects occurred at concentrations close to those producing biological activity. In conclusion, EOEC possesses promising antioxidant and antibacterial properties but exhibits concentration-dependent embryotoxicity, emphasising the need for careful dose optimisation and biosafety evaluation prior to therapeutic or nutraceutical applications.