The concept and the derivation of a distribution coefficient are developed. Ion exchange and the nature of competition among cations are given. Distribution coefficients for carrier-free cesium, strontium, and iodine were determined on 17 samples collected during July, 1961, in the vicinity of Cape Thompson, northwestern Alaska. High percentage uptake of these ions was measured under the test conditions. Cesium adsorption, at 1 day, was found to be represented by the mass-action equation. The distribution coefficients for cesium adsorption were so large that, in all but a few cases, very little of this nuclide would remain long in solution in the natural waters of the area. Strontium adsorption was found to be a function of the calcium-plus-magnesium concentration and to be independent of the sodium concentration. In most samples, its equilibrium is reached in less than 1 day. Iodine sorption varied with percent organic matter in the samples. If the iodine were in contact with organic matter for several days, a substantial part of it probably would be removed from solution in the natural waters.
