Persistence of Alachlor in Sandy loam soil

Soil was fortified with alachlor at the level of 0.5 μg g⁻¹ soil. Samples were drawn at regular intervals of 0, 5, 10, 15, 22, 29 and 40 days. For extraction of alachlor, soil was extracted with acetone. Clean-up was done by liquid-liquid partitioning with dichloromethane after diluting with brine solution. Quantification of residues was done by GC using mega bore column and ECD detector. Recovery of alachlor in soil ranged between 87–92% at 0.4 and 0.1 mg g⁻¹. The limit of detection (LOD) of alachlor was 0.005 μg ml⁻¹ and LOQ by this method was found to be 0.015 μg g⁻¹. The calibration curve was found to be linear within the range of 0.01 to 0.5 μg ml⁻¹ concentration. The DT₅₀ (disappearance time for 50% loss) of alachlor at the level of 0.5 μg g⁻¹ in sterile and non sterile soil were found to be 23.3 day and 10.03 day, respectively. The dissipations of alachlor followed first order kinetics.