Sharp dose- and time-dependent toxicity of mercuric chloride at the cellular level in sea urchin embryos

Abstract.

Sea urchin embryos (Sphaerechinus granularis) offer the opportunity to analyse toxicity towards cell division and stages of early development. Mercuric chloride (HgCl₂) arrested early development at the level of the first cell cycle. The toxic effect occurred in a very sharp concentration range around 7 µM HgCl₂. At sub-toxic concentrations of HgCl₂, the morphology and kinetics of early development were comparable to control embryos. The time-dependence of toxicity was short; a 5-min exposure to the toxic concentration of 10 µM HgCl₂ was sufficient to provoke developmental dysfunction whereas continuous exposure to 5 µM HgCl₂ allowed development to occur normally. The effects on early development over this range of concentrations were specific to HgCl₂ toxicity since other heavy metal chlorides had no effect at 30 µM. Thus, the sea urchin model may provide new clues to the molecular mechanisms of HgCl₂ toxicity.