Developmental toxicity from exposure to various forms of mercury compounds in medaka fish ( Oryzias latipes ) embryos

This study examined developmental toxicity of different mercury compounds, including some used in traditional medicines. Medaka ( Oryzias latipes ) embryos were exposed to 0.001-10 μM concentrations of MeHg, HgCl2, α-HgS ( Zhu Sha ), and β-HgS ( Zuotai ) from stage 10 (6-7 hpf) to 10 days post fertilization (dpf). Of the forms of mercury in this study, the organic form (MeHg) proved the most toxic followed by inorganic mercury (HgCl 2 ), both producing embryo developmental toxicity. Altered phenotypes included pericardial edema with elongated or tube heart, reduction of eye pigmentation, and failure of swim bladder inflation. Both α-HgS and β-HgS were less toxic than MeHg and HgCl 2 . Total RNA was extracted from survivors 3 days after exposure to MeHg (0.1 μM), HgCl 2 (1 μM), α-HgS (10 μM), or β-HgS (10 μM) to examine toxicity-related gene expression. MeHg and HgCl 2 markedly induced metallothionein ( MT ) and heme oxygenase-1 ( Ho-1 ), while α-HgS and β-HgS failed to induce either gene. Chemical forms of mercury compounds proved to be a major determinant in their developmental toxicity.