Metals in gastropods—metabolism and bioreduction

Abstract

In marine gastropods, high concentrations of heavy metals can occur in the digestive gland. The metals are accumulated within intracellular mineralized granules as phosphates and within lysosomal residual bodies in association with sulphur. X-Ray microanalysis shows that in the phosphate granules, an increase in the quantity of metal is associated with a reduction in the magnesium/calcium ratio. However, analyses of the whole digestive gland by atomic absorption spectrometry show that an increase in the quantity of metal can be associated with an increase in the concentration of magnesium. To account for these changes, it is proposed that metals induce the formation of magnesium phosphate in the granules as a source of metal-binding ions. The excess magnesium is displaced from the phosphate granules by the metals and accumulated by the carbonate granules in the interstitial region of the gland. The intracellular metals are stored in a form which renders them unavailable to the general metabolic processes of the animal and also to a carnivore which eats the tissue. Thus, uptake by the first animal results in bioamplification but transfer to the second animal results in bioreduction.