Influence of pesticide-soil interactions on the recovery of pesticides using supercritical fluid extraction

The role of soil organic matter on the recovery of two classes of pesticides and two classes of herbicides using supercritical carbon dioxide has been investigated. Initial studies from spiked Celite indicated that the more polar herbicides required the addition of 10% methanol modified supercritical carbon dioxide to affect extraction. Whereas the relatively non-polar organochlorine pesticides (OCPs) could be extracted using supercritical carbon dioxide only, the moderately polar organophosphorus pesticides (OPPs) required 5% methanol-modified supercritical carbon dioxide to affect quantitative recovery. When using these supercritical conditions each class of pesticide or herbicide was extracted from a slurry-spiked soil. The effects on the recovery from soils with a range of organic matter were noticeable for both classes of pesticides, particularly when the organic matter was at its highest (35%). The role of the modifier was found to be critical in affecting recovery of the polar OPPs and herbicides. The soil-pesticide interaction from these slurry spiked soils could be negated if excess modifier (10%) was added to the supercritical carbon dioxide. Matrix interactions were most severe when no modifier was added (recoveries of OCPs from soil were approximately 50%).