Developmental Toxicity of C10 Massoia Lactone, the Main Constituent of Cryptocarya massoia, on Zebrafish (Danio rerio) Embryos

C10 massoia lactone (C10) is the main component of massoia essential oil derived from Cryptocarya massoia plant bark, which is used as natural flavoring agent of “generally recognized as safe” status. In this study, the developmental toxicity of C10 was evaluated on zebrafish (Danio rerio) embryos at an exposure level of 0–2000 µg·L−1, and acute toxicity was determined with respect to lethal effects, hatching rates, and morphological changes. Additionally, morphological changes were determined for the endpoints as the occurrence of yolk edema, pericardial edema, spine curvature, and shortened body length after treatment until 96 h post-fertilization (hpf). The complete lethality of C10 was achieved with embryos treated at 2000 µg·L−1, and most embryos treated at 1000 µg·L−1 developed pericardial edemas with some spine curvature. Some embryos exhibited delayed development with shortened body length when compared with the control. Hatchability was completely accomplished at the tested dose of 1000 µg·L−1, and cardiac malformation was observed using a transgenic zebrafish line Tg(cmlc:EGFP), with a lower heartbeat rate in embryos treated with C10 for 72 hpf. After 96 hpf, heartbeat rates were normalized when compared with the control group, and two cardiac development-related genes such as nppa and canca1 were differently expressed in C10-treated embryos by 2.3-fold and 0.4-fold, respectively. Therefore, C10 must be studied further in other higher organisms for its risk.