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 galloprovincialis were exposed to elevated concentrations of sea water cadmium, zinc and mercury, 48 hr post-fertilization, 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 larval 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 metal content as well as according to their chromatographic and spectral 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 zinc and cadmium simultaneously, resulted in an antagonistic effect, showing a larger proportion of normally formed veliger larvae and a smaller growth inhibition in comparison with the sum of single metal effects. The induction of MT in larvae subjected to cadmium and zinc mixture was markedly larger than the addition of individual metal effects.