Evaluation of 35S-residues in grains and grain fractions fumigated with 35S-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.