Multiresidue Determination of Pesticides in Acid-Clay Soils from Thailand
Tropical and temperate soils differ with respect to their chemical conditions and mineral composition. Consequently, assessment of the contamination of tropical soils with pesticides requires methods that provide exhaustive extraction from the specific soil matrix and reliable quantification. Our objective was to optimize the simultaneous extraction and determination of 32 representative pesticides (organophosphates, organochlorines, synthetic pyrethroids, triazines, acetamides, carbamates, diphenyl ethers, acylalanines, oxadiazoles, thiadiazoles, and phenoxy compounds) frequently used in Thailand. The compounds were added to a clayey Ultisol-topsoil (45 clay) from the Yom Region in Northern Thailand. Ten different solvent mixtures were tested; the use of a shake extraction with acetoneethyl acetatewater (3 + 1 + 1, v/v/v) was most effective in providing exhaustive and reproducible extraction of pesticides both from freshly fortified soil and from fortified soil after incubation for 1428 days. The pesticides were separated and quantified by using gas chromatography with mass selective detection. Except for methamidophos, which was almost completely lost during sample workup, the recoveries of all pesticides from soil ranged from 68.6 to 104 (mean standard error, 2.8) for freshly spiked samples and from 45.9 to 107 (mean standard error, 2.3) for spiked samples incubated for 14 days. The use of internal standards compensated for the losses of most pesticides during workup and increased the mean recovery of the pesticides from freshly fortified soil to 96. The method was successfully applied to the determination of environmental concentrations of pesticides in a range of Thai agricultural soils.
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Document Type: Research Article
Affiliations: University of Bayreuth, Institute of Soil Science and Soil Geography, 95440 Bayreuth, Germany.
Publication date: November 1, 2007
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- The Journal of AOAC INTERNATIONAL publishes refereed papers and reviews in the fields of chemical, biological and toxicological analytical chemistry for the purpose of showcasing the most precise, accurate and sensitive methods for analysis of foods, food additives, supplements and contaminants, cosmetics, drugs, toxins, hazardous substances, pesticides, feeds, fertilizers and the environment available at that point in time. The scope of the Journal includes unpublished original research describing new analytical methods, techniques and applications; improved approaches to sampling, both in the field and the laboratory; better methods of preparing samples for analysis; collaborative studies substantiating the performance of a given method; statistical techniques for evaluating data. The Journal will also publish other articles of general interest to its audience, e.g., technical communications; cautionary notes; comments on techniques, apparatus, and reagents.
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