Comparison of QuEChERS with Traditional Sample Preparation Methods in the Determination of Multiclass Pesticides in Soil.

Background: The increased use of pesticides leads to permanent pollution of soil, and there is a need for continuous monitoring of these agrochemicals in soil. Objective: Three methods for the simultaneous determination of 12 pesticides belonging to eight chemical groups in soil samples were tested and compared based on analytical parameters. Methods: The quick, easy, cheap, effective, rugged, and safe (QuEChERS); traditional solid-liquid extraction (SLE); and Soxhlet extraction were used for soil sample preparation, while detection and quantification of pesticides were performed using gas chromatography-mass spectrometry (GC-MS). Results: The tested methods featured good sensitivity, and with the exception for carbofuran (Soxhlet method, LOD = 29 µg/kg), for the rest of the pesticides, the studied LODs were less than 12 µg/kg. Except for simazine and carbofuran, LODs obtained by Soxhlet extraction were lower than values obtained by other two methods, whereas QuEChERS gave lower LODs than the traditional SLE method for all compounds except atrazine and acetochlor. The recoveries obtained applying QuEChERS, traditional SLE, and Soxhlet methods for multiple analyses of soil samples fortified at 10, 75, and 200 µg/kg of each pesticide were in the ranges 54-103, 40-91, and 12-92%, respectively. Except for chlorothalonil, the highest recoveries were obtained by the QuEChERS method. Soxhlet was better than traditional SLE method for chlorothalonil, heptachlor, and aldrin; organophosphorus pesticides (fenitrothion and diazinon) and trifluralin, gave similar recoveries for both methods. All three methods were proven to be repeatable, with RSDs lower than 19%. Conclusions: Although all tested methods showed as satisfactory regarding most analytical parameters, QuEChERS method showed much better results in terms of confidence, indicating that traditional SLE and Soxhlet extraction still need improvements for determination of multiclass pesticides in soil samples.

Examination of the influence of phenyltrimethylammonium chloride (PTMA) concentration on acetochlor adsorption by modified montmorillonite.

The results presented in this paper show an impact of the concentration of the aromatic organic cation on the adsorption of acetochlor on the surface of the organic-modified montmorillonite. Natural montmorillonite from Bogovina (Boljevac municipality, Serbia) was used for organic modification in this experiment. Cation exchange capacity of this montmorillonite (86 mmol 100 g-1 of clay) was determined using the methylene blue method. In pretreatment, montmorillonite was modified with NaCl. For the purpose of organic modification, three different concentrations of phenyltrimethylammonium chloride (PTMA) have been selected, based on calculated CEC value: 43 mmol 100 g-1 of clay (0.5 CEC), 86 mmol 100 g-1 of clay (1 CEC) and 129 mmol 100 g-1 of clay (1.5 CEC). The changes in the properties of the inorganic and organic modified montmorillonite were examined using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and batch equilibrium method. Freundlich coefficients show higher uptake of the herbicide by montmorillonite modified with PTMA, compared to inorganic-modified montmorillonite. The results also indicate the influence of the organic cation concentration on the adsorption of the selected herbicide.

Influence of the organic complex concentration on adsorption of herbicide in organic modified montmorillonite.

This study was undertaken to determine the impact of the organic complex concentration on the adsorption of herbicide (acetochlor) at the surface of the organic modified montmorillonite. In this work, natural montmorillonite from Bogovina (Boljevac municipality, Serbia) was used for organic modification. Cation-exchange capacity of this montmorillonite was determined using a methylene blue method (86 mmol/100 g of clay). Montmorillonite has been modified first with NaCl and then with hexadecyltrimethylammonium bromide (HDTMA-bromide) organic complex. Saturation of cation exchange capacity (CEC) was 50%, 100%, and 150%. Changes in the properties of the inorganic and organic montmorillonite have been examined using the X-ray diffraction, Fourier transform infrared spectroscopy, and batch equilibrium method. Montmorillonite modified with HDTMA-bromide demonstrated higher uptake of the herbicide, compared to the inorganic montmorillonite. Comparing the values Freundlich coefficients in batch equilibrium method, it can be seen that the adsorption of acetochlor decreased in the series: 0.5 CEC HM > 1 CEC HM > 1.5 CEC HM > NaM.

Evaluation of Lactobacillus plantarum and Saccharomyces cerevisiae in the Presence of Bifenthrin.

This work describes the effect of insecticide bifenthrin on Lactobacillus plantarum and Saccharomyces cerevisiae. Growths of used microorganisms in growth media supplemented with pesticide were studied. Determination of bacterial and yeast fermentation efficiency in wheat supplemented with bifenthrin was conducted. Additionally, investigation of bifenthrin dissipation during microbiological activity was performed. Experiments applying bifenthrin in different concentrations highlighted a negligible impact of the pesticide on the growth of L. plantarum and S. cerevisiae. This insecticide overall negatively affected the yeast fermentation of wheat, while its presence in wheat had a slight negative impact on lactic acid fermentation. The results of bifenthrin dissipation during lactic acid and yeast fermentations of wheat showed that activities of L. plantarum and S. cerevisiae caused lower pesticide reductions. Average bifenthrin residue reduction within samples fermented with L. plantarum was 5.4 % (maximum ~16 %), while within samples fermented with S. cerevisiae, it was 11.6 % (maximum ~17 %).

The potency of Saccharomyces cerevisiae and Lactobacillus plantarum to dissipate organophosphorus pesticides in wheat during fermentation.

The degradation behaviour of pirimiphos methyl with Saccharomyces cerevisiae and chlorpyrifos methyl with Lactobacillus plantarum in wheat during fermentation was studied. Yeast fermentation was especially effective for reduction of pirimiphos methyl applied at 5 mg kg-1 (maximum residue limit-MRL) causing dissipation for max 48.8%. Pesticide reduction rate decreased with an increase of fortification rate. Thus in samples fortified with 25 and 75 mg kg-1 a reduction up to 27.1%, and 23.7% respectively, was observed. Activity of L. plantarum was especially effective for reduction of chlorpyrifos methyl applied at 3 mg kg-1 (MRL) causing dissipation for max 56.7%. This reduction rate decreased with an increase of fortification rate. In samples contaminated with 15 and 45 mg kg-1 dissipation reached up to 38.6% and 34.7% respectively. For both experiments, initial inoculums sizes had no statistically significant effect on pesticides dissipation level, while concerning fermentation temperatures at all fortification levels the highest degradations occurred at 30 °C. Overall, regardless fermentation parameters, the degradation rate constants of pirimiphos methyl fermented with yeast were increased comparing with control samples by 255-573, 56-116 and 119-594% in samples contaminated at MRL, 5MRL and 15MRL of pesticide, while the degradation rate constants of chlorpyrifos methyl fermented with lactobacilli were increased by 74-769, 59-237 and 46-469% respectively. These results evidenced that yeast and lactobacilli played an important role in promoting pirimiphos methyl i.e. chlorpyrifos methyl dissipation in wheat.