An investigation was undertaken to develop a standardized batch adsorption procedure that uses the initial and 24-h solution concentrations to calculate a distribution ratio Rd between solutes and soil materials. In developing these procedures, it was found that the method of mixing the solute-soil mixtures influenced the amounts of solute adsorbed. To ensure reproducibility, a National Bureau of Standards rotating tumbler was adopted as the mixing system. An interval of 24 h was established as a valid operational definition of reaction time for determining Rd values.
Interlaboratory testing was conducted with arsenic and cadmium using soil materials having a range in physiochemical properties. The interlaboratory coefficients of variation (CV) were generally less than 10%. The precision of an Rd measurement for a species that meets the criteria of being stable and nonvolatile should yield percent CV within the range established. The method has not been tested for organic solutes and is not considered viable for volatile chemical species. The method is considered a reliable and useful technique for comparing the adsorption properties of various soil materials under a given set of conditions.