Analytical method validation to evaluate dithiocarbamates degradation in biobeds in South of Brazil

Abstract

In order to evaluate the efficiency of biobeds on DTC degradation, the aim of this study was to apply, optimize and validate a method to determine dithiocarbamate (mancozeb) in biobeds using gas chromatography-tandem mass spectrometry (GC-MS). The DTC pesticide mancozeb was hydrolysed in a tin (II) chloride solution at 1.5% in HCl (4 mol L), during 1 h in a water bath at 80 °C, and the CS formed was extracted in isooctane. After cooling, 1 mL of the organic layer was transferred to an auto sampler vial and analyzed by GC-MS. A complete validation study was performed and the following parameters were assessed: linearity of the analytical curve (r), estimated method and instrument limits of detection and limits of quantification (LODm, LODi, LOQm and LOQi, respectively), accuracy (recovery%), precision (RSD%) and matrix effects. Recovery experiments were carried out with a standard spiking solution of the DTC pesticide thiram. Blank biobed (biomixture) samples were spiked at the three levels corresponding to the CS concentrations of 1, 3 and 5 mg kg, with seven replicates each (n = 7). The method presented satisfactory accuracy, with recoveries within the range of 89-96% and RSD ≤ 11%. The analytical curves were linear in the concentration range of 0.05-10 µg CS mL (r > 0.9946). LODm and LOQm were 0.1 and 0.5 mg CS kg, respectively, and the calculated matrix effects were not significant (≤ 20%). The validated method was applied to 80 samples (biomixture), from sixteen different biobeds (collected at five sampling times) during fourteen months. Ten percent of samples presented CS concentration below the LOD (0.1 mg CS kg) and 49% of them showed results below the LOQ (0.5 mg CS kg), which demonstrates the biobeds capability to degrade DTC.

Microbial growth in biobeds for treatment of residual pesticide in banana plantations

“…(2017) , the pesticide oxamyl is rapidly hydrolyzed in soils with neutral pH, whereas it is slowly degraded in alkaline soils and with difficulty in acidic soils. According to Vareli et al. (2018) , the pH influences the sorption and mobility of pesticides.…”

“…The mobility of pesticides in biobeds will depend on the soil’s sorption capacity, water solubility, and pH. Highly soluble pesticides with low sorption capacity tend to move through the soil, which decreases the residence time and the chances of being degraded by microorganisms ( Vareli et al., 2018 ).…”

“…Therefore, research evaluating the relationship of physicochemical and biological parameters in different biomixtures, and climates is of interest. The microbiological studies would identify the effectiveness or depletion of the biomixture, the accumulation or mineralization of toxic compounds, and the mobility of pesticides in the biobed ( Vareli et al., 2018 ). In this sense, previous research has not considered microbial colony and cell counts.…”

Dithiocarbamate Residues in Fruits and Leaves of Passion Fruit (Passiflora edulis) from Different Brazilian Regions

“…The origin of CS 2 determined in the sample could not be identified, which is a limitation of the indirect methods to quantify dithiocarbamates, regardless of the detection method used. [11][12][13][14][15] Another limitation of the indirect methods is the possibility of false positive results in crops containing sulfur compounds, such as brassica (e.g., broccoli and cabbage), allium species (e.g., leek and onion) 27 and papaya, 13 a limitation that does not affect the analysis of passion fruit. Although there are specific methods for the determination of some dithiocarbamates in foods, mainly by high performance liquid cromatography (HPLC) using UV or mass spectrometric detectors, [28][29][30][31][32] none can discriminate all the dithiocarbamate compounds, including mancozeb from metiram.…”

“…11 The classic method for the determination of dithiocarbamates quantifies the CS 2 generated by the acid degradation of the compound present in the sample, which can be spectrophotometrically determined after complexation, 7,[12][13][14] or by gas chromatography using different detectors. 11,[12][13][14][15] However, since all DTCs produce CS 2 , none of these methods allow the identification of the compound applied to the crop, and the results are expressed in mg kg -1 CS 2 .…”