Persistence of malathion residues in stored milled rice

Residues of 14C-malathion in stored milled rice were studied for 39 weeks under conditions simulating local practice. Residues from single and multiple applications were examined. For the single application total, surface, extractable and bound residues in the rice grains were determined. Only the total residues were determined after multiple applications. For the single application, 6-7% of the applied amount was found in the grains 24 weeks after treatment. After 9-11 months storage, about 10% of the total quantity of the applied malathion remained on the surface of the jute sack and about 5% was present in the grains. Data showed also that 50-60% of the total residues in the grains were present as surface residues. Washing the rice thoroughly before cooking removed the surface residues. During cooking, 57% of the extractable residues was lost. (author)