2,4,6-tris(2,4,6-tribromophenoxy)-1,3,5-triazine (TTBP-TAZ) exposure can cause cardiac toxicity in zebrafish larvae

2,4,6-tris(2,4,6-tribromophenoxy)-1,3,5-triazine (TTBP-TAZ) is a widely used novel brominated flame retardant with environmental persistence, yet its developmental toxicity remains poorly characterized. In this study, we investigated the developmental and cardiotoxic effects of TTBP-TAZ in zebrafish embryos/larvae. Embryos (4 hpf) were exposed to 0-20 μM TTBP-TAZ for 120 hpf. Assessments included survival, hatching kinetics, burst activity (24 hpf), heart rate (48 hpf), caudal venous blood-flow velocity (72 hpf), locomotor behavior under alternating light/dark conditions (120 hpf), cardiac morphology in Tg(myl7:EGFP), and transcription of key cardiac genes. Results indicated low mortality of embryos/ larvae across all concentrations. However, TTBP-TAZ accelerated hatching rate in a concentration-dependent manner (significant by 60 hpf) and increased burst activity. Elevated heart rate (48 hpf) and enhanced tail-vein blood flow (72 hpf) suggested tachycardia and stimulated circulation. Transgenic larvae exhibited reduced ventricular/atrial fluorescence intensity, along with enlarged cardiac size and indistinct contours, indicating structural abnormalities. qPCR analysis revealed up-regulation of nkx2.5, tbx20, and vmhc, and down-regulation of gata4, mef2, and myh7, suggesting disruption of core cardiogenic transcription and chamber-specific contractile programming. Locomotor assays demonstrated hyperactivity at higher concentrations under both light and dark conditions. These findings indicate sub-lethal TTBP-TAZ exposure induces significant developmental and cardiotoxic disturbances in zebrafish, associated with altered cardiac gene expression and functional hyperactivation. This study supports the need for further mechanistic investigation and exposure-relevant risk assessment of TTBP-TAZ.