Study On The Sorption, Leaching And Degradation Of Fipronil In Soil

Fipronil [IUPAC name as (±)5-amino-l-[2, 6-dichloro-4-(trifluoromethyl) phenyl]-4- (trifluoro methylsulphinylpyrazole-3-carbonitrile] is a new soil and foliar broad-spectrum insecticide developed by Rhone-Poulenc (now Bayer). Its principal tradenames are "Regent"and "Termidor". It is active against a wide range of soil and foliar insects such as rice grasshoppers, rice skippers, vine weevil, termites, and black ants in agricultural, forestry and pastoral zones. It acts on gamma amino butyric acid (GABA) receptors, the principal nerve transmitter of insects, preventing the inhibition of GABA. It is high toxic to aquatic organisms, such as Mysid Shrimp, etc. In this paper, the sorption, leaching and degradation behaviors of fipronil in four typical Chinese soils were studied, which can supply the scientific evidence of the environmental and ecological safety evaluation.Adsorption/desorption dynamics and isotherm of fipronil in four typical Chinese soils were studied. Batch equilibration method was used in this experiment. The distribution coefficient (Kd) values for fipronil on the soils ranged from 3.28 to 36.47 and the adsorption rate ranged from 39.64% to 87.94%, which obtained from the adsorption dynamics experiment results. The sorption ability of fipronil was weak in northeast black soil and JiangXi paddy soil, and it had less risk to pollute groundwater, but the half life of fipronil is long comparatively, and strong absorption may reduce efficacy, or do harm to microbe in soil potentially; While the transfer ability of fipronil was strong in Beijing soil and Jiaxing soil relatively, which had more risk to pollute groundwater; The Freundlich adsorption coefficient (Kf) values for fipronil on the soils ranged from 1.99 to 10.32 using a 0.01M CaCl₂ redistilled water solution as the soil solution. The adsorption coefficients were found to be better related to the content of organic carbon/matter (OC% or OM%) and cation exchange capacity (CEC) than clay content and pH value.Several environmental substances including anionic surfactant sodium dodecylbenzene sulfonate (SDBS), cationic hexadecyltrimethyl-ammonium bromide (HDAB), humic acid (HA), NH4NO3 as a chemical fertilizer and CaCl₂ as a background electrolyte were selected to see the their influence on the adsorption dynamics of fipronil in Jiaxing paddy soil. The results showed that fipronil adsorption capacity could be enhanced greatly by solid HA. The presence of NH4NO3 can slightly decrease the adsorption of fipronil in soil by comparison with that measured in NH₄NO₃-free solution. The role of CaCl₂ as an electrolyte may be similar to NH₄NO₃. In soil-water system, surfactant-fipronil interaction is very complex, and the adsorption of surfactant may also need to be considered. When fipronil-soil suspensions contained SDBS, Kf for fipronil adsorption was decreased compared with that measured in SDBS-free solution; on the contrary, the...