Persistence and metabolism of Fipronil in rice (Oryza sativa Linnaeus) field.

Rice is one of the most important food crops worldwide. However, it is also a valuable tool in assessing toxicity of organic and inorganic compounds. Fipronil insecticide has been widely used to control rice pests. The research was conducted to evaluate the fate of fipronil in rice-field. Persistence and metabolism of fipronil in rice is studied by applications of Regent 0.3G @ 45 and 180 g a.i. ha(-1) was made 7 days after transplanting of paddy. Samples of paddy plants were collected at 7, 15, 30, 45, 60, 90 and 120 days after the application of insecticide. The samples of rice grains, bran, husk and straw were collected at the time of harvest. The samples were extracted and cleaned up by following a standardized methodology. Fipronil and its metabolites were quantified by gas liquid chromatography and confirmed by gas chromatography mass spectrometer. The total residues of fipronil and its metabolites in paddy plants after 7 days of its application at recommend and four times of recommend doses were found to be 6.60 and 19.85 mg kg(-1), respectively. Among fipronil metabolites, sulfone derivative had maximum residue concentration followed by other metabolites viz. sulfide, amide and desulfinyl. The residues were reached below the detectable limit (0.01 mg kg(-1)) after 45 and 90 days at recommend and four time of recommend doses, respectively. At harvest, the samples of paddy straw, rice grains, bran and husk did not reveal the presence of fipronil and its metabolites.