It is relative, it depends of physical and chemical properties of the soil. I did a study about pesticide residues in soil in Colombia with a methodology made by Ahumada and Zamudio (2011), for andian soils, using ultra performance liquid chromatograph coupled to mass spectrometry
It is relative, it depends of physical and chemical properties of the soil. I did a study about pesticide residues in soil in Colombia with a methodology made by Ahumada and Zamudio (2011), for andian soils, using ultra performance liquid chromatograph coupled to mass spectrometry
It may be useful
Conference Paper COMPARISON AMONG PESTICIDE RESIDUES IN SOIL FROM GREENHOUSES...
Pestic. Phytomed. (Belgrade), 27(3), 2012, 239–244 DOI: 10.2298/PIF1203239D
Trends in Analytical Chemistry, Vol. 23, No. 10–11, 2004
Mostly important: J Sep Sci. 2013 Jan;36(2):376-82. doi: 10.1002/jssc.201200673.
Alejandra's answer is close, as the soil properties are important, but I think more important are the properties of the pesticide. You need to find an extraction procedure that is suitable for the pesticide of interest. Non-ionic pesticides can be extracted many ways - critical solvents, soxhlet, or even simple solvent extraction. I have found that for extremely hydrophobic pesticides (i.e., DDT), is it useful to add about 20% ethanol to water (with about 10% soil), and then extract overnight on a shaker (end-over-end is the best), with about 10% non-miscible solvent (like hexane). The ethanol reduces the soil-water partition coefficient so that more pesticide resides in the water phase, so that it can partition to the hexane phase. Without it, the mass transfer to the hexane is very slow. For organic anions (like 2,4-D), it is best to remove most of the water (i.e., moist soil), and extract directly with methanol or ethanol. with mild sonication, or end-over-end mixing. Adding some water actually may help, as the anions are extracted generally as ion-pairs with cations in the soil, and water allows for them to exist as free ions in the ethanol. You may be tempted to lower the pH below the pKa value of the pesticide, but this only increased the partition coefficient to the soil. Pesticides that are cationic (i.e., diaquat), are difficult to remove, with removal efficiencies quite low. With these, you need ion-pairing reagents, and you need to load the soil with other cations, is the sorption mechanism is basically ion-exchange.
Concerning the determination of residues, the conducted extraction procedure is one of the most important steps. In this context, we did really good experiences with accelerated solvent extractions (case) using different organic solvents (depending on the pesticides). I attached a link to a good paper exactly dealing with this topic. If you have further questions, feel free to ask or contact the author of the paper (they are quite experienced with that research question)
http://pubs.acs.org/doi/abs/10.1021/es990145%2B
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