Soxhlet and Microwave Extrac- Tion in Determining the Bioaccessibility of Pesticides from Soil and Model Solids

The inadvertent ingestion of contaminated soil can be an important source of pesticide exposure, especially in young children. The actual level of a pesticide that is available for absorption into a biological system may be much lower than the overall contamination level due to the interaction of each chemical with the solid matrix. This bioaccessibility is dependent on characteristics of the chemical species as well as the soil type and residence time of the compound in the soil. In an effort to improve understanding of this phenomenon, we report a comparison of the recoveries of pesticides spiked into soil and two model solids using different analytical extraction techniques: Soxhlet extraction, microwave-assisted extraction with an organic solvent (MAE), and microwave extraction using water as a solvent (WME). The efficiency of each technique is compared to the maximum bioaccessible fraction determined by a physiologically based extraction test (PBET). Recoveries by Soxhlet and MAE are shown to be in good agreement with each other, but do not predict the bioaccessible fraction. Recoveries by WME, however, are in agreement with bioaccessible fractions of all pesticides and soil types studied. WME has the potential to be useful in bioavailability studies.