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Crop models use mathematical equations to simulate the physical and chemical processes that generally control the uptake, translocation, and sorption of xenobiotics in all part of plants. Each compartment is anatomically characterized and described by a series of mathematical equations. Sample preparation, such as liquid extraction methods and solid-phase-based methods are presented. Analysis of xenobiotics are generally carried out by gas chromatography (GC) or liquid chromatography (LC) coupled to different detectors, especially to mass spectrometers (MSs) and hyphenated techniques that have become extremely developed in recent years. As an example the wheat plant, as a model to describe xenobiotic uptake by roots and sorption of xenobiotic in grain, is applied.
Method for determination of carbendazim residues in fruits, vegetables and cereals was described. The compound was extracted with methanol-hydrochloric acid mixture, and after liquid-liquid partition step with dichloromethane, was determined by high performance liquid chromatography (HPLC) with column switching and ultraviolet (UV) detection. The average recoveries of carbendazim from fortified sample were from 68.7% ± 4.3% to 92.6% ± 4.5%, the coefficients of variation were from 2.9% to 6.3%, and the limits of quantification at λ = 279 nm were from 0.02 mg/kg to 0.2 mg/kg.
Fenoxycarb residues are analyzed by column switching and reversed-phase high performance liquid chromatography (RP-HPLC). The active ingredient is extracted from apples on a silica gel column using a n-hexane - diethyl ether mixture. The eluate is evaporated, dry residue dissolved in acetonitrile-deionized water, and injected into the liquid chromatograph with a column switching system (C8 columns), and a UV-photodiode array detector (UV - PDA). The analyte is quantified by the external standard method. The average recoveries of the active ingredient from the spiked sample are 81.3 +/- 3.2% and 80.3 +/- 5.8%, the coefficients of variation are 3.9% and 7.2% for fortification levels 0.1 mg/kg and 0.05 mg/kg, respectively, and the limit of quantification at lambda = 228 nm is 0.05 mg/kg. Labor and organic solvent uses are greatly reduced in comparison to the existing methods. The overall procedure allows a sample throughput of up to 30 samples per day. The method was applied to the determination of fenoxycarb residue in apples from treated orchards.
In 2011, a total of 977 samples of domestic crops were tested in the official control of pesticide residues carried out by the Institute of Plant Protection – National Research Institute. The samples were taken randomly by the staff of Plant Health and Seed Inspection at production sites in the whole country. The monitoring programme covered 230 compounds and 38 products. 126 samples of fruit, 484 samples of vegetables, 346 samples of cereals and 21 samples belonging to other products groups were analysed. Residues of 43 compounds were detected in 21.7% of the samples. Violations of MRLs were found in 0.6% of analysed samples, while the unauthorised plant protection product use in 2.5% of samples tested. Pesticide residues were detected in 58.7% of fruit samples, 23.8% of vegetable samples and 4.9% of cereal samples and in 28.6% of other samples. They were found most often in samples of apples (60.5%), tomatoes (52.6%), sweet peppers (50.0%) and carrots (42.1%). Most of the residues detected in twenty five commodities were fungicides and insecticides, and their percentages from 335 findings were equal respectively to 63.9% and 32.5%. The most commonly found were residues of chlorothalonil in tomatoes (31.6%), chlorpyrifos in carrots (28.9%), prochloraz in mushrooms (26.1%), and dithiocarbamates in apples (25.4%), potatoes (24.2%) and tomatoes (21.1%).
In total, 1351 samples of fresh fruit, vegetables and agricultural crops of Polish origin were analysed in 2010 in five laboratories of the Institute of Plant Protection – National Research Institute. The monitoring programme covered 52 commodities and 143 pesticides including some isomers and breakdown products. Residues of 48 compounds, mainly fungicides (26), were detected. The percentage of samples with residues at or below the MRL was 24.2%. In 74.8% of the samples no residues were found. Violations of MRLs were stated in 1.0% of the samples, while the use of non-approved pesticides in 2.7% of the samples tested. Pesticide residues were detected most often in samples of fruit (41.7%), especially in samples of gooseberries (70.0%), cherries (61.3%) and apples (52.4%). Samples of vegetables, as well as agricultural crops were less contaminated with pesticide residues. However, a high sample percentage of tomatoes grown under cover (43.1%) or in the field (60.3%) contained pesticide residues.
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