Toxicity of Organotin Compounds on Embryos of a Marine Invertebrate (Styela plicata;Tunicata)

In order to clarify the interaction mechanism between organotin compounds and organisms, the effects of these compounds on the development of a benthonic filter-feeding invertebrate were studied. Embryos of the ascidianStyela plicatawere obtained in laboratory by cross-fertilization and their development was followedin vivoafter incubation with 0.1, 1, and 10 μMorganotin compounds for various exposure times. Moreover, embryos selected at opportune stages after incubation with 10 μMtributyltin (TBT) or triphenyltin (TPT) for 1 hr were observed at the electron microscope to recognize cell alterations. Results indicate that organotins significantly affect all stages of ascidian development in a dose- and time-dependent manner and the most sensitive stages are gastrula and neurula. These compounds are able to block development, giving rise to anomalous embryos with irreversible effects. The order of inhibition appears to be strongly dependent on the organotin liposolubility: TBT > dibutyltin (DBT) > monobutyltin (MBT) and TPT gt; tricyclohexyltin (TCHT). The mitosis block of blastomeres in the early stages may be related to an inhibition of the microtubule polymerization. Observations with light and electron microscopes reveal globe-shaped blastomeres with large intercellular spaces in the morula and gastrula stages, suggesting a toxic damage with alteration of the cytoskeleton. Moreover, the occurence of electron-dense precipitates of organotins in the inner membrane of mitochondria and morphological changes of their cristae suggest an inhibitory effect on oxidative phosphorylation which is conspicuous in the gastrula stage. In this stage, the size of the electron-dense aggregates grow from 50–70 to 110–170 nm, while at the same time the alteration of the cristae increases.