Degradation of γ-Cyhalothrin and Deltamethrin in Rice due to Storage and Processing

The persistence of γ-cyhalothrin and deltamethrin on rice grains was studied under laboratory conditions. The grains were treated with γ-cyhalothrin (5 mg kg⁻¹) and deltamethrin (10 mg kg⁻¹) and stored for 120 days. The residues of γ-cyhalothrin and deltamethrin were reduced by 69.9 and 68.4%, respectively, within 120 days after storage. The half-life value for both the pyrethroids during storage was 71.7 days. The over-all result revealed marginal reduction of the pesticides due to flour preparation. Cooking of rice grains using pressure cooker, microwave oven and in open vessel resulted in reduction of γ-cyhalothrin residues by 10.6–49.2% and deltamethrin by 11.3–71.5%. Dosa preparation resulted in 81.8 and 73.2% loss of γ-cyhalothrin and deltamethrin, respectively. The processing factors obtained for flour and dosa were 0.94 and 0..8 for γ-cyhalothrin nnd 0.96 and 0.27 for deltamethrin, respectively. The corresponding factors for cooked rice in pressure cooker, microwave and open vessel cooking were 0.89, 0.73 and 0.51 for γ-cyhalothrin and 0.89, 0.46 and 0.29 for deltamethrin, respectively.