Radiotracer study on pesticide residues of chlorpyrifos during soybean oil processing
1993
Ratana Sitayoung
C-14 chlorpyrifos (specific activity 4.56 micro ci/mg) was applied to soybean S.J. 2 with 10.60 % moisture content. Two experiments were carried out : (i) to study the persistence of C-14 chlorpyrifos on the surface, extractable and bound stored soybean for 90 days, (ii) to determine the degradation of C-14 chlorpyrifos during laboratory refining technique, i.e., degumming, neutralizing, bleaching and deodorizing. A total of 17.75 ppm of the applied dose (20 ppm) was recovered at 24 hr and decreased to 7.34 ppm after 90 days of storage. The decay constant was 0.0099 ppm/day. The major part of the residue was concentrated on the surface. There was a gradual increase in the methanol extractable residues. At the end of the storage, the total extractable residue was 11.23 % of the applied dose. Bound residues increased gradually from 0.82 % in 60 days and to the maximum of 0.97 % in 90 days.The residues of C-14 chlorpyrifos in refining process decreased from 7.24 to 1.32 ppm which was 81.77 % of the initial residues. The reduction of radioactivity during processing was 4.70 %, 2.17 % 53.19 % and 58.23 % for degumming, bleaching, neutralizing and deodorizing, respectively.The major metabolite of chlorpyrifos (3, 5, 6-trichloro-2-pyridinol) was only 2 % of the parent material in the unprocessed soybean oil. At the end of the process, the total metabolite was 5 % of the C-14 chlorpyrifos residues.
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