AbstractThe sorption of iodide by several soil component materials was examined over a range of pH values and compared with sorption by a surface soil. A compost, prepared from grass roots which had been allowed to decompose for 24 weeks, sorbed substantial amounts of iodide from solution and showed changes in sorption, due to pH and drying, similar to those shown by the soil. Freshly precipitated hydrated ferric oxide also sorbed substantial amounts of iodide from solutions of pH<5.5 but the amount decreased to zero as the pH approached 7. Sorption by freshly precipitated hydrated aluminium oxide was impossible to assess at pH<5 owing to its solubility but at pH 5.5 to 7.5 its sorption was similar to that of ferric oxide. No sorption of iodide was detected by kaolinite, montmorillonite, chalk or limestone.Drying markedly reduced the capacity for iodide sorption of the compost and soil and had a smaller effect on the ferric and aluminium oxides.