Effect of Refining Processes on Magnitude and Nature of Fenitrothion and Pirimiphos-Methyl Residues in Maize Oil and Bioavailability of their Cake Residues on Rats*


MAIZE seeds obtained from 14C-fenitrothion or 14C-pirimiphos-methyl treated maize plants contained about 0.12 % and 0.16 % of the originally applied radioactivity, respectively. The concentration of 14C-fenitrothion residues and 14C-pirimiphos-methyl residues in crude oil (hexane extract) ranged from 2.8-3.0 ppm, methanol solubles 2.3 ppm and in seed cake 1.2-1.4 ppm. Commercial processing procedures led to a gradual decrease in the total amount of 14C-residues in oils with aged residues. The refined oil contained only about 13-19% of the radioactivity originally present. The deodorization and alkali treatment are the most effective steps as they removed over 50 % of the residues. Chromatographic analysis of refined oil revealed the presence of fenitrothion, 3-methyl-4-nitrophenol as main products beside smaller amounts of fenitrooxon and desmethyl fenitrothion. Whereas, pirimiphos-methyl and 2-diethyl-2-amino-4-hydroxy-6-methylpyrimidine were detected as principal compounds together with minor amounts of 2-ethyl-amino-4-hydroxy-6-methylpyrimidine and 2-amino-4-hydroxy-6-methyl-pyrimidine.
On feeding rats with the extracted seeds (cake) for three days, the bound residues were found to be considerably bioavailable. A substantial amount of administrated bound
14C-residues was eliminated via respiration (50%) for 14C-fenitrothion and excreted urine (47%) for 14C-pirimiphos-methyl. While feces contained only 10-12% and about 22-26% of the radioactive residues were distributed among various organs of experimental animals.