Multi-residue Determination of Synthetic Pyrethroids and Organophosphorus Pesticides in Whole Wheat Flour using Gas Chromatography

Abstract

Wheat grain in the form of flour and its processed products have become and essential part of human diet. The consumption of wheat flour and its products is increasing everyday throughout the world. As a result of increasing demand in Pakistan, cultivation and production of wheat crop has increased tremendously. However, the system still in primitive and is facing many pre and post harvest problems that requiring to be addressed. There are two principal sources of pesticides contamination in stored commodities, pesticide residues resulting from field spraying and the residues accumulated as a result of pesticides’ admixture with grain or fabric treatment during storage. Cereal grain are treated with degradable pesticides, including organophosphates, carbamates, synthetic pyrethroids and insect growth regulators in storage premises as well as prior to shipment to other countries to prevent insect infestation. In this regard, residual efficacy of some pesticides in stored wheat studied by Arthur (1992). Noble et al. (1982) studied the stability of pyrethroids. A large number of pesticides are in common use as grain protectants. This usage has been comprehensively reviewed by Snelson (1987). The identification and quantification of pesticide residues in flour as well as in its products is important because small quantity of pesticides or their metabolites may persist in flour after processing or refining even in baked or cooked products (Skerritt et al. 1996). Therefore it is necessary to monitor flour for pesticides residues. A collaborative study on method development of organophosphorus pesticide residues in wheat has been reported (Desmarchelier et al. 1977). Bottomley and Baker (1984) developed a method to screen most of the commonly used pyrethroid and organophosphorus pesticides in grain using gas chromatography. Fishwick (1985) studied a wide range of organophosphorus pesticides residues in grain. Brown et al. (1974) reported a rapid screening method using gas chromatography for the determination of resmethrin in wheat flour. A multi-residue method for N-methyl carbamates and metabolite pesticide residues at ppt level for fruits/vegetables and wheat grain was reported by Podhorniak et al. (2004). A new multi-residue method for simultaneous determination of 405 pesticide residues in grain has also been developed (Guo-Fang et al. 2006). Toteja et al. (2006) determined residues of DDT and HCH pesticides in wheat grain and flour samples. The present study was restricted to pesticides which are internationally used as grain protectants. These pesticides are also used in Pakistan, however the technical data relating to the contamination in finished products is not available. Periodical monitoring of grain and flour at various supply channels for multiple pesticide residues is therefore desirable in order to protect the consumer from the possible health hazards. In the present study samples of whole wheat flour were screened for residues of a mixture of five synthetic pyrethroids and six organophosphorus pesticides using gas chromatography with electron capture I. A. T. Khan (&) Z. Parveen Pesticide Research Institute, Southern-zone Agricultural Research Center, Pakistan Agricultural Research Council, Karachi University Campus, Old Blocks No. 09 and 10, Karachi 75270, Pakistan e-mail: iffku@yahoo.com