36 ll. Buried organic horizons contain more cst?? than adjacent soil layers. 12. Roots are generally more radioactive than the surrounding soil except at the soil surface. 13. Pumice particles in the soil adsorb radionuclides. 14, Mechanical mixing by animals in old soils and by erosion in young soils results in a redistribution of radionuclides in the surface layers. L5. cst37 and sr?° are the principal radionuclides entering a cycle within the soil-plant system. por