EFFECTS OF TRIBUTYLTIN CHLORIDE ON THE EMBRYONIC DEVELOPMENT OF THE SEA URCHIN PARACENTROTUS LIVIDUS (LMK).

Tributyltin (TBT) has been used extensively for almost 30 years in marine antifouling paints as a biocide. During this period hazardous levels of TBT and of its less toxic products of degradation, i.e. dibutyltin (DBT) and monobutyltin (MBT), were reached in estuaries and coastal water-sediment ecosystems in various parts of the world. Concern about the negative effects of low concentrations of butyltin compounds in the marine environment, recently as a lot of severe toxic effects on marine invertebrates. These effects were demonstrated mostly in molluscs, in which TBT exposure induced shell thinning, imposex and block of the embryonic development. In tunicates, immunodepression and embryotoxicity were used as indexes of butyltin pollution. Nothing is up to date known about the effects of these compounds on echinoderms. Therefore, we set up a procedure to reveal the effects and the mechanism of action of butyltin compounds on the embryonic development of the sea urchin Paracentrotus lividus. Embryos were obtained in laboratory by cross-fertilization and their development from post-fertilization to pluteus was followed in vivo after incubation with different exposure concentrations (0.1, 0.5, 1, 5, 10 µg l-1). We examined various developmental indexes, i.e. survival, frequency of developmental stages 24 and 48 hs after fertilization, embryonic growth and frequency of larval abnormalities 48 hs after fertilization. Morphological observations were also carried out under light and electron microscopies. Results show that embryotoxic effects occur in the presence of butyltin compounds in a dose-dependent manner. The exposed embryos generally suffer develpmental delay. Growth reduction of plutei, regularly increases as TBT concentration rises and becomes highly significant (p<0.001) at 1 µg l-1. At the same TBT dose plutei exhibit clear disturbance of the skeleton symmetry: the post-oral rods appear particularly short and/or folded. A very significant (p<0.001) interruption at the morula stage is observed begining from 5 µg l-1 TBT. Abnormal morula appear formed by irregular blastomeres from which many cytoplasmatic blisters jut towards a large space between the cells and the fertilization membrane. We suggest an influence of butyltin compounds with calcium homeostasis both in the microtubule polymerization during the cleavage stages and in calcification and organization of pluteus skeleton.