The kinetics of accumulation and excretion of ferric hydroxide in Mytilus edulis (I.) and its distribution in the tissues

Iron, which occurs in sea water as particulate ferric hydroxide, is accumulated to high concentrations by the common mussel, Mytilus edulis (L.). The kinetics of the accumulation and excretion of iron in Mytilus has been studied using ⁵⁹Fe-labelled ferric hydroxide and the tissue distribution and identification at the sub-cellular level determined by analytical electron microscopy. Iron-59 accumulates in linear proportion to the sea-water concentration and is found in all tissues; the concentration factors for viscera, kidneys, gills, muscle = mantle is 25: 6: 4: 1, respectively. The particulate iron is taken up by pinocytosis by special epithelial cells in the gills, gut, kidney and possibly labial palps and held in membrane-bound vesicles, unaccompanied by mucus in the case of gills and kidney, but with mucus present in the digestive diverticulum and mid-gut cells. There is no free iron within the cytoplasm. Approximately 30 % of the iron presented to the gut is not absorbed being voided with the faeces. The absorbed iron is exocytosed and then passed on to amoebocytes in the haemolymph for transport to other tissues, a major portion being excreted by transfer to the byssal threads.