André F. Oliveira

Effects of ozone fumigation treatment on the removal of residual difenoconazole from strawberries and on their quality

The effect of ozone fumigation on the reduction of difenoconazole residue on strawberries was studied. Strawberries were immersed in 1.0 L of aqueous solution containing 400 μL of the commercial product (250 g L−1 of difenoconazole) for 1 min. Then, they were dried and exposed to ozone gas (O3) at concentrations of 0.3, 0.6 and 0.8 mg L−1 for 1 h. The ozone fumigation treatments reduced the difenoconazole residue on strawberries to concentrations below 0.5 mg kg−1, which corresponds to a 95% reduction. The strawberries treated with ozone and the control group, which was not treated with ozone, were stored at 4°C for 10 days. Some characteristics of the fruit were monitored throughout this period. Among these, pH, weight loss and total color difference did not change significantly (P > 0.05). The fumigation with ozone significantly affected the soluble solids, titratable acidity and ascorbic acid content (vitamin C) of the strawberries preventing a sharp reduction of these parameters during storage.

Aqueous ozone solutions for pesticide removal from potatoes

The presence of pesticide residues in potatoes is of concern because of the potential impact to human health due to the high consumption of this vegetable. In this study, aqueous solutions with and without ozone saturation as postharvest wash treatment at pH 4.0, 7.0, and 9.0 were tested to remove chlorothalonil from potatoes. The method used for pesticide analysis has been validated, presenting recovery values of 94–103%, with variations in the repeatability coefficients of ≤10.6%, and a quantification limit of 0.05 mg kg−1. Regardless of pH, treatment with aqueous ozone solutions removed 70–76% of the pesticide present in the potato. In the no-ozone treatments, the percentage average removal of chlorothalonil residues in potatoes was only 36%. Over 24 days of storage, the quality of potatoes washed with aqueous ozone solutions was not significantly different from those washed with pure water.

Evaluation of the Effects of Hofmeister Series on Salting Out in the Determination of Organophosphorous Pesticides and Pyrethroids by LDS/DLLME

Various greener microextraction procedures have been proposed with low limits of detection to control of pesticides present in the environment, including the low-density solvent dispersive liquid‑liquid microextraction (LDS/DLLME) technique. The addition of electrolytes is important in order to induce the salting-out effect. Thus, it is possible to use the Hofmeister series and the Voet lyotropic number to study the effect of different ions on pesticide extraction in LDS/DLLME technique. Different anions were tested and a strong correlation was observed between the lyotropic number of the anion and the recovered volume of extraction solvent. The lyotropic numbers of the anions were successfully compared with the chromatographic peak areas normalized by the recovered solvent volumes, and similar empirical cubic relationships were obtained for all the pyrethroids evaluated. In the extraction of the organophosphorous pesticides, chlorpyrifos presented similarity with the pyrethroids, while correlation was observed between methyl parathion and profenofos.

OTIMIZAÇÃO, VALIDAÇÃO E APLICAÇÃO DE MÉTODO PARA DETERMINAÇÃO DA CONCENTRAÇÃO RESIDUAL DE DIFENOCONAZOL EM MORANGOS APÓS MÚLTIPLAS APLICAÇÕES

Difenoconazole residues in strawberry fruit cultivated in pots were estimated using the solid-liquid extraction with low temperature partition (SLE/LTP) method for sample preparation and gas chromatography with electron capture detection (GC/ECD) for analysis. The optimized method presented excellent recovery values from fortified samples and reproducibility (average recovery values ≥ 98%; CV values < 15%). Linearity of response was demonstrated (r = 0.995) with a detection limit of 9 µg kg-1. The method was successfully applied for the determination of difenoconazole residues in strawberries. Based on these results, the fungicide dissipates quickly, but the residual concentration increases after multiple applications.

Single drop microextraction: a sensitive multiresidue method for determination of pesticides in water using GC/ECD

The monitoring of pesticides in environmental samples at low concentrations is needed due to the risks that these compounds can pose to human health and the environment. In this work, a single drop microextraction (SDME) method was optimized and validated for the determination of trace concentrations of eight pesticides in water, using gas chromatography with electron capture detector (GC/ECD). The kinetics of the transfer of material from the aqueous phase to the organic phase during the extraction process was also evaluated. The method showed recoveries between 89.5 and 122.7%, with coefficients of variation smaller than 22.9%, and detection limits between 5.9 and 58.9 ng L-1. The method was applied to spiked samples at different concentration levels, and recoveries between 50.5 and 148% were obtained. The extraction process could be described by the Noyes-Whitney diffusion model, and methyl parathion showed the highest rate of transfer between the two phases.

Degradation of the Reactive Blue 4 Dye in Aqueous Solution Using Zero-Valent Copper Nanoparticles

The degradation of the Reactive Blue 4 (RB4) dye by zero-valent copper nanoparticles (nZVC) was investigated. Degradation rates of approximately 90% were reached within 10 minutes of reaction. Total Organic Carbon (TOC) analysis shows that the dye molecules undergo mineralization, therefore indicating the degradation process is oxidative. Experimental tests, held in the presence of tertiary butyl alcohol, acting as a hydroxyl radicals ) captor, and copper (I) oxide, demonstrated that the reaction mechanism is governed by the concentration of Cu (I) instead of . The second-order kinetics model was the most appropriate one to explain the experimental data. Higher values of the reaction rate constant were obtained in higher temperatures and higher nZVC doses and in lower RB4 initial concentrations. The initial pH in more acidic conditions (3 and 4) was kinetically more favorable to the degradation reaction; the activation energy was estimated to be 42 kJ mol−1 based on calculations using the experimental data. Finally, the recovered nanoparticles were utilized on a new reaction cycle, showing a small loss of their efficiency and catalytic activity.

Pesticide residue removal in classic domestic processing of tomato and its effects on product quality

ABSTRACT This study was undertaken to evaluate the effectiveness of several household practices (washing with water or acidic, alkaline, and oxidizing solutions, and peeling) in minimizing pesticide residue contamination of tomatoes, as well as the impact on the quality of the treated fruit. Tests were performed using two systemic fungicides (azoxystrobin and difenoconazole) and one contact fungicide (chlorothalonil). Solid-liquid extraction with low temperature partition (SLE/LTP) and liquid-liquid extraction with low temperature partition (LLE/LTP) were used to prepare the samples for pesticides determination by gas chromatography. Washing the tomatoes with water removed approximately 44% of chlorothalonil, 26% of difenoconazole, and 17% of azoxystrobin. Sodium bicarbonate (5%) and acetic acid (5%) solutions were more efficient, removing between 32 and 83% of the residues, while peeling removed from 68 to 88% of the pesticides. The washing solutions altered some fruit quality parameters, including acidity and chroma, and also caused weight loss. Acetic acid (0.15 and 5%) and hypochlorite (1%) solutions had the greatest effect on these parameters.

Determination of Pesticides in Soil Using a Hyphenated Extraction Technique

A new method for the extraction of pesticide residues from soil was developed, optimized, validated and applied to real samples. The technique consisted of combining single-drop microextraction and solid-liquid extraction with low temperature partitioning (SLE/LTP-SDME) followed by analysis using gas chromatography with electron capture detection (GC/ECD). This method was used to determine the presence of alachlor, methyl parathion, trifluralin, endrin, lindane, dieldrin and dichloro-diphenyl-trichloroethane (4,4’-DDT) in soil samples. Recoveries ranging from 67.2 to 122.5% were achieved, coefficients of variation (repeatability) were lower than 22.4% and limits of detection ranged from 0.18 to 0.59 µg kg-1. Recovery from soils fortified with different concentrations of the pesticides ranged from 61.5 to 123.5%. The new method combines the primary advantages of the two techniques: purification of the sample using SLE/LTP and preconcentration using SDME. The new method also enables the determination of low volatility compounds without requiring the sample to be heated.

A new spectrophotometric method for determination of EDTA in water using its complex with Mn(III)

EDTA is an important ligand used in many industrial products as well as in agriculture, where it is employed to assist in phytoextraction procedures and the absorption of nutrients by plants. Due to its intensive use and recalcitrance, it is now considered an emerging pollutant in water, so there is great interest in techniques suitable for its monitoring. This work proposes a method based on formation of the Mn(III)-EDTA complex after oxidation of the Mn(II)-EDTA complex by PbO2 immobilized on cyanoacrylate spheres. A design of experiments (DOE) based on the Doehlert matrix was used to determine the optimum conditions of the method, and the influence of the variables was evaluated using a multiple linear regression (MLR) model. The optimized method presented a linear response in the range from 0.77 to 100.0μmolL(-1), with analytical sensitivity of 7.7×10(3)Lmol(-1), a coefficient of determination of 0.999, and a limit of detection of 0.23μmolL(-1). The method was applied using samples fortified at different concentration levels, and the recoveries achieved were between 97.0 and 104.9%.

Modelling of Lead Migration from Electronic Waste to Mixtures of Kaolinite, Iron Oxides and Organic Matter

Improper disposal of electronic waste in the environment facilitates migration of heavy metals, especially lead, into the soil and can contribute to the bioavailability of this species. Based on a simplex-centroid mixture experimental design, small-scale tests were performed for incubation of printed circuit boards (PCBs) in mixtures containing organic matter (OM), kaolinite (KA) and iron oxides (IO) to verify lead migration. Regression equations were acquired and were adjusted to the obtained responses. Results showed high total content of Pb, ranging from 400 to 4000 mg kg-1, depending on the mixture and incubation time. Mobility and/or bioavailability of lead in the mixtures were evaluated by a three-step sequential extraction. The bioavailability factor (BF) was obtained from the ratio of the sum of exchangeable fraction (F1) and the organically bound fraction (F2) by F1, F2 and the residual fraction (F3) and the values of bioavailability factor for Pb, the heavy metal considered of greatest environmental concern in this study, ranged between 0.16 and 0.52.