Current problems in the study of colloidal transport in soil

A review of recent literature on the transport of organic and mineral colloids in soils demonstrated the role of such factors as the extrema of water flow velocities, the anisotropy of physical properties, and the presence of preferential water flows in macropores and fissures. In unsaturated soils, the concentration of colloids at the gas-water interphace and the amphiphilicity of their surface are of great importance. The transfer of "living collids" (bacteria and viruses) is mainly due to the convection mechanism; however, of great importance are the entrapping of microorganisms in fine pores, their adsorption (adhesion), their concentration on the gas-water interphace, their sedimentation, and the affecting chemical factors, such as the ionic strength and the pH of the solution. The effect of biological factors is related to the size of cells, chemotaxic mobility, and the growth and reproduction of the microbial biomass. The focal points of recent studies on colloid transport are considered: the study of mechanisms of colloid mobilization under different conditions, the improvement of methods for the direct observation of colloid migration (micromodels, computer tomography, etc.), and the possibility of quantitative description of the entrapping of colloidal particles in soil pores.