COMPARATIVE FIXATION OF CALCIUM AND STRONTIUM BY SNAIL SHELL

Strontium and Ca uptake by biologically formed aragonite was investigated in the fresh water pulmonate snail Australorbis glabratus. The results show a marked discrimination against Sr relative to Ca in new shell formation which decreased as the Sr/Ca ratio oi the solution was increased. Preformed shell also discriminated against Sr but to a lesser extent. Conversely, snail-free shell took up Sr preferentially as did powdered shell in an in vitro exchange study. Aragonite and calcite precipitated from Ca solutions containing Sr/sup 89/ and Ca/sup 45/ removed equal proportions of these two isotopes. Radiochemical analysis of the snail body also showed a preferentiai uptake of Ca from solution although the discrimination against Sr was less than for shell. X-ray diffraction analyses of Sr containing shells showed this ion to be substituted isomorphously for Ca in the aragonite structure. The discrimination against Sr relative to Ca in the living snail is primarily the result of metabolic processes with the possibility of some crystallographic differentiation.