KINETICS OF METALS IN MOLLUSCAN FECAL PELLETS AND MINERALIZED GRANULES, INCUBATED IN MARINE-SEDIMENTS

Marine snails excrete metals via the gut. The sediment-feeding, tower shell Cerithium vulgatum, from a polluted environment, accumulates Cr and Ni to 3500 ppm dry weight in the faecal pellets. Pellets from C. v ulgatum acid the grazing, top shell Monodonta mutabilis were incubated in surface and deeper anoxic layers of clean and metal-polluted sedim ent. Pellets retained the original load of metals and in some cases ga ined Ti, Cr, Mn, Fe and Ni. Effects were modified by sediment properti es. Pellets of C. vulgatum are durable, membrane-bound structures and they reduce metal bioavailability to food chains by compartmentalizati on. Intracellular, phosphate granules bind metals in digestive glands of snails and they are excreted via the gut and faecal pellets. These granules were extracted from digestive glands of both species of snail and incubated in the same sediments. Magnesium phosphate granules fro m M. mutabilis dissolved but calcium/metal phosphate granules from C. vulgatum remained; they had differentially retained or lost Mn, Fe, Co , Ni acid Zn according to the type of sediment.