Dissipação e monitoramento dos inseticidas clorpirifós e thiamethoxam em tubérculos e solo cultivado com batata (Solanum tuberosum L.) / Dissipation and monitoring of chlorpyrifos and thiamethoxam in potato (Solanum tuberosum L.) tubers and soil

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

The objectives of this study were to evaluate dissipation of insecticides chlorpyrifos and thiamethoxam in potato plants during development and monitor pesticide residues in tubers grown in southern Minas Gerais and in samples collected from retail markets in Viçosa-MG. First, the solid-liquid extraction at partition at low temperature (SLE-PLT) was optimized and validated. At this stage, a preliminary test was performed on soil and potato samples fortified with known amounts of chlorpyrifos and thiamethoxam to test pesticide extraction efficiency using the methanol and acetonitrile mixture. Afterward, a 23 factorial experiment was carried out to quantitatively assess the effects of the factors (1) proportion of extraction solvent acetonitrile:ethyl acetate, (2) ionic force and (3) time of sample shaking on the extraction efficiency of chlorpyrifos in the soil and thiamethoxam in potato and soil samples. The optimized method consists of adding a specific amount of sample (10000 g of soil and 30000 g of potato), small volume of 0.2 mol L-1 of Na2HPO4 aqueous solution or distilled water and 8 mL of an extraction mixture (6.5 mL of acetonitrile + 1.5 mL of ethyl acetate). The mixture is agitated and kept in a freezer at -20C for 8 hours. The organic extract in the liquid phase is analyzed by gas chromatography. The optimized method was validated by determining selectivity, linearity limits of detection and quantification, precision and accuracy. The results showed that the SLE-PLT optimized method is efficient for testing chlorpyrifos and thiamethoxam residues in potato and soil, with recuperation percentages over 80% and detection limits below maximum residue limits (MRL) established for these pesticides in these matrices. The optimized and validated method was applied to assess the dissipation of the insecticides in potato and soil samples collected from containers. This method was also used to monitor residues in field crop samples. The study of chlorpyrifos dissipation showed larger residue quantities in both soil and tubers with dose 2 (twice the dose recommended by the manufacturer). Soil receiving dose 2 had, during each analysis, chlorpyrifos concentration approximately 2 times larger than the concentration obtained with dose 1. The final concentration (91st day) of chlorpyrifos found in the soil for dose 1 was approximately 24 times larger than in tuber samples. The analysis of thiamethoxam dissipation found that the amount of residues in potato tubers was lower than in the soil, regardless the dose, showing that dose 2 led to a larger amount of residues in tubers. It was also found that, at the end of the period (on the 91st day), the thiamethoxam concentration in the soil was almost the same regardless the applied dose. No thiamethoxam residues were detected in potatoes grown in southern Minas Gerais (field crops), however, presence of chlorpyrifos residues was confirmed. Chlorpyrifos was also detected in potato samples obtained at retail markets in Viçosa - MG. In all cases, the levels found were below the limit established by law.

ASSUNTO(S)

residues thiamethoxam resíduo solo soil cromatografia gasosa thiamethoxam dissipation batata clorpirifós chlorpyrifos potato quimica analitica dissipação gas chromatography

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