TY - JOUR T1 - Colloidal transport JF - Journal of Soil and Water Conservation SP - 55A LP - 56A VL - 62 IS - 3 AU - Brian K. Richards AU - John F. McCarthy AU - Tammo S. Steenhuis AU - Anthony G. Hay AU - Yuniati Zevi AU - Annette Dathe Y1 - 2007/05/01 UR - http://www.jswconline.org/content/62/3/55A.abstract N2 - The term “groundwater pollution” typically brings to mind contaminants-pesticides, solvents, and excess nutrients, among others-that are either soluble in water or are fluids themselves, percolating downward through the soil. However, another significant class of contaminants is that of colloids. Colloids are microscopic particles between 0.005 and 5 μm, similar in size to the particles in tobacco smoke (see figure 1). Colloids move by what is often referred to as colloidal transport. Often the colloidal particles themselves are contaminants of concern, such as colloid-sized pathogenic bacteria and viruses (sometimes referred to as biocolloids) or aggregations of toxic elements. In other cases, mobile colloidal mineral or organic matter particles are simply a convenient transport mechanism for contaminants that would be otherwise immobile in soils. In either case, particles this small can filter through soil with varying degrees of ease and can often reach groundwater. UNPLEASANT SURPRISES The acceleration of movement of normally immobile contaminants due to linking up with mobile colloids (figure 2) is referred to as colloid-facilitated transport. Some of the initial discoveries of facilitated contaminant transport came as an unpleasant surprise, especially because the contaminants in question happened to be radioactive. … ER -