Cypermethrin is a synthetic, pyrethroid insecticide and used for agricultural practices. The leaching of this pesticide through soil is of great concern because of the possibility of contaminating ground and surface water. The mobility of pesticide in soil being the main environmental reservoir varies among soil orders and the concept is still under investigation. Hence, this study was aimed at investigating the sorption capability of Alfisol and Inceptisol at different soil depth when leached with simulated rainwater of different pH values. The leachates were determined for cypermethrin concentration using a new UV/Visible spectrometry method. The CEC, organic matter content of Alfisol were 4.05±0.03 cmol/kg and 1.74±0.02%, while the corresponding characteristics of Inceptisol were 4.45±0.05 cmol/kg and 1.03±0.01%, respectively. pH of Alfisol and Inceptisol soil orders were 5.92 and 6.25, respectively. Simulated rainwater (pH 4) of 50, 100 and 150 mL leached out 37.0±0.1, 43.1±0.1 and 59.4±0.2% of cypermethrin, respectively from Alfisol at soil depth of 10 cm. At pH 6.8, the corresponding volumes of simulated rainwater leached out 31.8±0.1, 35.4±0.1 and 37.4±0.1% of cypermethrin, respectively. For each soil order, these proportions of sorbed cypermethrin decreased progressively as soil depth increased from 10-30 cm. The proportions of cypermethrin sorbed by Inceptisol were more than the corresponding proportions sorbed by Afisol. Afisol has high clay and organic contents, which might be responsible for its surpassing potential to sorb cypermethrin compared to Inceptisol.
Key words: Pyrethroid insecticide, leaching, Alfisol-Inceptisol soil orders, simulated rainwater, UV/Visible spectrometry.
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