Adsorption-Desorption and Leaching of Bifenthrin in Soil

Wide spread concern over the adverse effect of pesticides on aquatic environment especially ground water makes it pertinent to study the leaching behaviour of pesticides. Adsorption-desorption and leaching of bifenthrin, a highly effective synthetic pyrethroid, was studied under laboratory conditions in an alluvial soil. Adsorption-desorption studies were carried out using batch equilibration technique with aqueous bifenthrin solutions prepared in 0.01 M CaCl₂. Adsorption isotherm was observed to be ’S’ type. K_d (7.5–23.1), K_F (222.4) and n (0.67) values show high and strong adsorption of bifenthrin in soil. Strong adsorption resulted in hysteresis effect (hysteresis coefficient 8.9–20.8) and only up to 15% of the adsorbed compound was desorbed in four desorption cycles. Leaching study was performed under saturated flow conditions with soil packed in polythene tubes. Leaching study clearly revealed low mobility of bifenthrin in soil. Even with 240 mL water addition, bifenthrin residues remained within top 15 cm with more than 99% of residues was recovered from top 0–10 cm. The high immobility of bifenthrin in soil column could be attributed to its high adsorption. Thus, the potential of bifenthrin to leach down to ground water under natural conditions is negligible.