Evaluation of S-residues in grains and grain fractions fumigated with S-labelled carbonyl sulfide

³⁵S-labelled carbonyl sulfide (CO³⁵S) was used to measure the amount of sorbed ³⁵S residues and converted ³⁵S residues in grains and grain fractions after fumigation with CO³⁵S. Hard wheat, soft wheat, paddy rice, brown rice, polished rice, sorghum, maize, canola, barley, oats and peas were exposed for 4 days to 50 mg L^?1 of CO³⁵S with a total radioactivity of 20 mCi. After exposure, the samples were aired. The levels of ³⁵S residues varied with extraction solvent, e.g. 0.003–0.02 mg (COS equivalents) kg^?1 (grain) in chloroform extractions and 0.09–0.38 mg kg^?1 in water extractions. More than 90% of ³⁵S (COS equivalents) residues were in the water extractions. The total radioactivity determined by scanning radiation images (fluorescent image) of extractions and sectioned commodities ranged from 0.1 to 0.4 mg kg^?1. The radiation image shows that more than 90% of ³⁵S residues were located or distributed in the embryo, testa, pericarp and husk, and that the ³⁵S was still slowly desorbing from grains after 2 days aeration.