Analysis of Synthetic Pyrethroid Insecticide Residuesin Chinese Cabbage to Determine Harvesting Time for of Consumers Safety

Abstract

Analysis of synthetic pyrethroid insecticides i.e. cyhalothrin, permethrin, fenvalerate, cypermethrin and deltamethrin was carried out in Chinese cabbage with GC. The vegetable was planted at Huai Luek Royal Project Development Center. The experiment was composed of 3 parts. Expt. 1: Cyhalothrin, permethrin and fenvalerate were sprayed to the plant at recommended rates successively for 2 and 4 times at 5 day intervals. The samples were collected and analyzed for the insecticide residues after the last spray of each set at 0 day (1 hr after spray), 1, 3, 5, 7 and 10 days. Expt. 2: Cyhalothrin, permethrin and fenvalerate were sprayed successively for 6 times at 5 day intervals, and Expt. 3: Cypermethrin and deltamethrin were sprayed successively for 6 times at 5 day intervals. The samples from both experiments were collected and analyzed after the last spray at 0 day (1 hr after spray), 1, 5, 10, 15, 20, 25 and 30 days. The analysis results were compared with MRL to set harvesting time for safety of consumers. Only permethrin had low quantity of its residues and the chinese cabbage can be harvested in 1 day after spray. Other tested insecticides had high accumulation of residues followed the number of sprays e.g. cyhalothrin and fenvalerate with 4 and 6 successive sprays at 5 day intervals, the safe harvesting time were at 10 and 20 days respectively.