Supercritical fluid extraction of planar and mono-ortho PCB in selected tropical soils

Supercritical carbon dioxide was used to extract three planar (PCB-77, PCB-169, PCB-126) and three mono-ortho (PCB-105, PCB-156, PCB-189) PCBs from three different tropical soil types. At constant temperature of 40°C, elevating the fluid density from 0.25 to 0.8 g/mL. resulted in enhancing the extraction efficiency of compounds in all soils. Clay minerals played a major role for the extraction of the selected PCBs from all soils. In addition the selected planar congeners were extracted less than the selected mono-ortho congeners. The PCB properties were found to have greater effect on the extraction yield than soil properties. Addition of 3 to 5% methanol could increase the extraction yield up to 28%. Increased the temperature from 40°C to 100°C at constant pressure (167 bar) was found to have negligible effect on the recoveries of all congeners. At 5% soil moisture the yield of PCB-105, PCB-156 and PCB-189 had been increased but had no effect on the extraction yield of PCB-77 and PCB-169. However the PCB-126 started to decrease its yield at 5% moisture. Adding up soil moisture from 15–25% reduced a yield of all congeners. Fourty minutes is the optimum dynamic time for extraction of all congeners from all soils studied at 40°C temperature, 0.8 g/mL density and 3% methanol modifier.