EMBRYO-LARVAL TOLERANCE OF MYTILUS-GALLOPROVINCIALIS, EXPOSED TO THE ELEVATED SEA-WATER METAL CONCENTRATIONS .1. TOXIC EFFECTS OF CD, ZN AND HG IN RELATION TO THE METALLOTHIONEIN LEVEL

Developing eggs of Mytilus galloprovincalis were exposed to elevated c oncentrations of sea water cadmium, zinc and mercury, 48 hr post-ferti lization, in order to study the toxic effects at the morphological and biochemical level comparatively. Decreasing order of metal toxicity ( Hg > Zn > Cd) was based on the proportion of normally formed straight- hinge veliger larvae and upon the growth inhibition of the primary lar val shell. Metal-induced proteins isolated from homogenate extract of the straight-hinge veliger larvae by Sephadex G-75 chromatography were considered to belong to the metallothionein class due to their high m etal content as well as according to their chromatographic and spectra l properties. The inverse relationship between relative toxicity level and amounts of total and induced metal bound to MT has been found to be described by the function of a potency type. Combined exposure to z inc and cadmium simultaneously, resulted in an antagonistic effect, sh owing a larger proportion of normally formed veliger larvae and a smal ler growth inhibition in comparison with the sum of single metal effec ts. The induction of MT in larvae subjected to cadmium and zinc mixtur e was markedly larger than the addition of individual metal effects.