Soil (1 g) was spiked with 100 μL of the surrogate and mixed with anhydrous Na2SO4. A 50:50 (V/V) mixture of hexane and acetone (10 mL) was added, and the mixture was sonicated for 6 min using an ultrasonic cleaner (Model 2510-DTH; Branson, CT, USA). Finally, the extract was filtered through 3-cm of glass wool. This procedure was repeated three times. Extracts were decreased to 2 mL by way of rotary evaporation under vacuum at 55°C. The percentage of recovery from this method was 101(±2)% for DDT, 101.6(±8)% for DDE and 101.3(±8)% for DDD. Cleanup was performed using a silica gel method (USEPA,1996). Deactivated silica gel (1.5 g) was transferred into a 1-cm ID column and a 1-cm layer of anhydrous Na2SO4 was used to cap the silica gel. The column was prewashed with 20 mL of hexane before it was used. The concentrated extract was transferred into the column, and then it was eluted with 8 mL of hexane (fraction I), 6 mL of hexane (fraction II) and 1.5 mL of dichloromethane (fraction III) at a rate of 5 mL/min.