Residue levels of malathion and its metabolites and fenitrothion in post-harvest treated wheat during storage, milling and baking

In order to investigate residue levels of malathion and its metabolites (malaoxon and isomalathion) and fenitrothion during storage, milling and baking, pesticide-free wheat was treated with the insecticides. Wheat was placed in a sealed plastic container and treated with dust malathion (2%). Fenitrothion emulsion (41.6% wettable powder) was applied onto the wall of a small-scale storage vessels. Residues were determined in wheat, bran, flour, white and bran bread at about one-month intervals during storage. The analysis of the residues was carried out by GC equipped with a NPD. The highest amounts of insecticides and metabolites were present in bran and the least in white bread. Reduction of malathion residues was about 95% in wheat through milling to flour and about 82% in flour through white bread baking. For fenitrothion, the residue levels were also lower in white breads than in bran breads. They generally did not exceed the maximum residue limits, except for the fenitrothion level of bran breads.