Multiresidue analysis of pesticides by gas chromatography with electron-capture in rice samples from different geographical regions of Pakistan

Abstract

Since last few years Pakistani rice exporters have become very conscious about the residual level of pesticides in rice and they prefer to have a certificate for residues free rice prior to shipment. 1000 samples of rice were collected from different containers ready to export representing different geographical regions of Pakistan and were tested at the Pakistan Council of Scientific and Industrial Research. The residue levels of 37 chlorinated hydrocarbons including major groups like hexachlorocyclohexane (·HCH) isomers (·-HCH, ·-HCH, (·-HCH and ·-HCH), Dichloro-diphenyl-trichloroethane (·DDT) congeners (p,p-DDE, o,p-DDT, p,p-DDD and p,p-DDT), heptachlor isomers and Chlordane isomers, aldrin, dieldrin and endrin and chloripyrifos in rice were determined by GC-ECD. Residues of 3DDT and 3HCH were detected in 30 and 45% of the samples and during 2005 their average values were found to be 0.001 mg/kg and 0.005 mg/kg repectively. In 2006 level of 3DDT and 3HCH was 0.071 mg/kg and 0.191 mg/kg showing increased contamination of these pesticides. Similarly residual level of 3heptachlor and 3Chloradane was 0.003 and 0.002 mg/kg in 2005 and these were at the level of 0.191 and -0.005 mg/kg during 2006 repectively. The maximum permissible limit for DDT and HCH metabolites were determined on the basis of an average factor to be 0.2-0.5 mg/kg which is just near to codex limit. Mean recoveries from three replicates ranged from 85.5- 106.0%, with coefficients of variation from 0.3-9.9%. The limit of detection was in the range of 0.02-0.01 mg/kg for all organchlorines in average of 37 compounds. © Asian Network for Scientific Information, 2011.