CADMIUM AND MANGANESE SORPTION BY SOIL MACROPORE LININGS AND FILLINGS

Trace element sorptivity of materials partially filling or coating the walls of soil macropores was compared with that of homogenized whole soil samples from the same soil profile. Contrasting profiles, a cherty silt loam and a silt loam, were selected. Sorptivity was determined as batch distribution coefficients using radiotracers. The organic macropore fillings exhibited higher cadmium and manganese sorptivities than did whole soils or micropore clays, which showed similar values. Sorptivity increased with increasing pH but, owing to the higher density of pH-dependent sorption sites on organic matter, did so faster for organic fillings than for whole soils or macropore clays. Results suggested that migration of cadmium and manganese would probably be more highly retarded in root-derived macropores than in other types of macropores. Factors other than sorptivity, eg hydrology, might also be important in determining migrations rates of cadmium and manganese.