Chemical Residues of some Pyrethroid Insecticides in Egg plant and Okra Fruits: Effect of Processing and Chemical Solutions

We investigated residual levels of cypermethrin [(RS)-alpha-cyano-3-phenoxybenzyl (1RS,3RS;1RS,3SR)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropanecarboxylate], deltamethrin [(S)-alpha-cyano-3-phenoxybenzyl(1R,3R)-3-(2,2-dibromovinyl)-2,2-dimethylcyclopropane car-boxylate] and lambda cyhalothrin [(RS)-alpha-cyano-3-phenoxybenzyl (Z)-(1RS,3RS)-3-(2-chloro-3,3,3-trifluoroprop-1-enyl)-2,2-dimethylcyclopropanecarboxylate] in eggplant and okra fruit and their dissipation patterns during different processing operations viz washing, peeling, cooking and blanching, and dipping in acidic and alkaline solutions. The samples were extracted in ethyl acetate and cleaned up with activated charcoal. After concentration on rotary evaporator the samples were analysed on High Performance Liquid Chromatograph (HPLC). Mobile phase was methanol: water (85: 15) and separation of insecticides was achieved on C-18 cloumn at 202 nm with UV-VIS detector. The samples of eggplant and okra fruit were collected from supervised fields as well as from farmer's field. In the supervised field trials, the higher levels of residues of each of the three insecticides were found in the raw samples of eggplant and okra fruit. In raw eggplant fruit the residues were in the order of cyhalothrin (1.40 +/- 0.15 mg kg(-1)) > cypermethrin (1.13 +/- 0.01 mg kg(-1)) > deltamethrin (0.65 +/- 0.1 mg kg(-1)), whereas in raw okra fruit these were in the order of cypermethrin (1.17 +/- 0.1 mg kg(-1)) > deltamethrin (1.08 +/- 0.12 mg kg(-1)) > cyhalothrin (0.48 +/- 0.03 mg kg(-1)). Among all the processing operations, cooking was found the most effective for reduction of the insecticide residues followed by blanching, peeling, washing and dipping in the tap water in both vegetables. Treatments with acidic solutions were more effective than with alkaline solutions for reduction of residues of insecticides in these vegetables. These results have implications for assessing dietary exposure limits of these insecticides.