Chemical and physical factors affecting the extractability of methidathion from soil samples.

Determination of methidathion in soil samples using Soxhlet extraction has been studied. Several factors were investigated for their effect on methidathion recovery. Some were related to the extraction procedure, for example solvent type used for the extraction (acetone or hexane/toluene), extraction time, soil humidity, and type of sterilisation system employed. Other factors tested included the addition of organic matter to the soil, for example urban sewage sludge and the cationic surfactant TDTMA. Experimental designs were used to determine the effects of the different factors. Acetone resulted in higher recoveries and was less affected by the presence of water. Autoclaving was the most appropriate sterilisation method. Thimerosal resulted in a decrease in insecticide recovery. Methidathion recovery increased as the amount of cationic surfactant was increased, but decreased as the amount of sewage sludge added to the soil was increased. In general, because the factors studied were not always independent of each other, a clear description of the methodology used is needed when analysing pollutants in environmental samples.