Modified superheated water extraction of pesticides from spiked sediment and soil

In this study a laboratory-made superheated water system was applied in order to extract some pesticides from sand, sediment and soil samples. Extraction efficiencies were investigated at different time intervals with regard to temperature, type and amount of organic modifier. Pesticides were removed from the aqueous extract using dichloromethane as a trapping solvent. The optimal extraction temperature from sand specimens for malathion, heptachlor, aldrin, dieldrin, butachlor, metalaxyl and propiconazole was found to be 160 degrees C, while those for chlordane and thiobencarb were 120 degrees C and 180 degrees C, respectively. The static extraction time for heptachlor, aldrin, dieldrin, butachlor and metalaxyl was found to be 15 min, whereas for malathion and thiobencarb it was 5 min, and for chlordane and propiconazole it was 10 and 20 min, respectively. Recoveries for the extractions of the pesticides from sand under optimized extraction conditions ranged between 96 and 101%. Those obtained from sediment under such conditions were unsatisfactory, and were consequently improved by adding an organic modifier to the superheated water, and sodium chloride to the extract during liquid-liquid extraction. These procedures were optimized further for the parameters described and recoveries exceeded 91%, with the exception of butachlor. The extraction technique was also applied to soil samples at a reduced water flow rate of 0.5 mL min(-1), yielding recoveries of 82 - 105%, and 76% for dieldrin. The reproducibilities, expressed as relative standard deviations (RSDs), ranged between 2 and 13%.