Ozone and hydrogen peroxyacetic acid treatment to reduce or remove EBDCs and ETU residues in a solution

Degradation of malathion and carbosulfan by ozone water and analysis of their by-products

BACKGROUND

Treatment by ozone water is an emerging technology for the degradation of pesticide residues in vegetables. The ozone dissolved in water generates hydroxyl radicals (^· OH), which are highly effective in decomposing organic substances, such as malathion and carbosulfan.

RESULTS

We found that washing pak choi with 2.0 mg L^-1 ozone water for 30 min resulted in 58.3% and 38.2% degradation of the malathion and carbosulfan contents respectively, and the degradation rates of these pure pesticides were 83.0% and 66.3% respectively. In addition, the 'first + first'-order reaction kinetic model was found to predict the trend in the pesticide content during ozone water treatment. Based on investigations by gas chromatography-mass spectrometry combined with the structures of the pesticides, the by-products generated were identified. More specifically, the ozonation-based degradation of carbosulfan generated carbofuran and benzofuranol, whereas malathion produced succinic acid and phosphoric acid. Although some new harmful compounds were formed during degradation of the parent pesticides, these were only present in trace quantities and were transient intermediates that eventually disappeared during the reaction.

CONCLUSION

Our results, therefore, indicate that ozone water treatment technology for pesticide residue degradation is worthy of popularization and application. © 2022 Society of Chemical Industry.

Oxidation of ethylenethiourea in water via ozone enhanced by UV-C: identification of transformation products

Ethylenethiourea (ETU) is a toxic degradation product of one class of fungicide which is largely employed in the world, the ethylenebisdithiocarbamates. In this study, ETU was degraded by ozonation enhanced by UV-C light irradiation (O₃/UV-C) in aqueous medium. Degradation experiments were conducted at natural pH (6.8) and neutral pH (7.0, buffered). ETU was promptly eliminated from the reactive medium during ozonation in the presence and absence of light. Within the first few minutes of reaction conducted in natural pH, the pH decreased quickly from 6.8 to 3.0. Results show that ETU mineralization occurs only in the reaction conducted in neutral pH and that it takes place in a higher rate when enhanced by UV-C irradiation. Main intermediates formed during the O3/UV-C experiments in different conditions tested were also investigated and three different degradation mechanisms were proposed considering the occurrence of direct and indirect ozone reactions. At pH 7, ethylene urea (EU) was quickly generated and degraded. Meanwhile, at natural pH, besides EU, other compounds originated from the electrophilic attack of ozone to the sulfur atom present in the contaminant molecule were also identified during reaction and EU was detected within 60 min of reaction. Results showed that ozonation enhanced by UV-C promotes a faster reaction than the same system in the absence of light, and investigation of the toxicity is recommended.

Innovative technologies to manage aflatoxins in foods and feeds and the profitability of application - A review

Aflatoxins are mainly produced by certain strains of Aspergillus flavus, which are found in diverse agricultural crops. In many lower-income countries, aflatoxins pose serious public health issues since the occurrence of these toxins can be considerably common and even extreme. Aflatoxins can negatively affect health of livestock and poultry due to contaminated feeds. Additionally, they significantly limit the development of international trade as a result of strict regulation in high-value markets. Due to their high stability, aflatoxins are not only a problem during cropping, but also during storage, transport, processing, and handling steps. Consequently, innovative evidence-based technologies are urgently required to minimize aflatoxin exposure. Thus far, biological control has been developed as the most innovative potential technology of controlling aflatoxin contamination in crops, which uses competitive exclusion of toxigenic strains by non-toxigenic ones. This technology is commercially applied in groundnuts maize, cottonseed, and pistachios during pre-harvest stages. Some other effective technologies such as irradiation, ozone fumigation, chemical and biological control agents, and improved packaging materials can also minimize post-harvest aflatoxins contamination in agricultural products. However, integrated adoption of these pre- and post-harvest technologies is still required for sustainable solutions to reduce aflatoxins contamination, which enhances food security, alleviates malnutrition, and strengthens economic sustainability.

Effects of hydrochemistry variables on the half-life of mancozeb and on the hazard index associated to the sum of mancozeb and ethylenethiourea

Mancozeb is a dithiocarbamate non-systemic agricultural fungicide with multi-site, protective action. It helps to control many fungal diseases in a wide range of field crops, fruits, nuts, vegetables, and ornamental plants. We have investigated the stability profiles of mancozeb in aqueous solutions to determine the effect of pH, temperature and light on the degradation process of mancozeb. In addition, the toxicological risk for humans associated with the joint intake of mancoze7b and its final degradation product, ethylenethiourea (ETU), was calculated and modelled as a function of the experimental conditions. Stability study results showed a very low stability profile of mancozeb in all the aqueous solutions with rapid degradation that varied with experimental conditions. The process followed first order kinetics. The study of the degradation kinetics showed a significant effect of pH*temperature interaction on the degradation process. The results also expressed that light has a greater impact on the stability of mancozeb and the formation of ETU. The current study concludes that mancozeb is unstable in aqueous solutions, particularly at an acid pH, in addition to presenting both severe light and lower temperature sensitivity. The toxicological risk associated with mancozeb degradation increases with time and temperature, being higher at basic pH and in absence of light.

Kinetic modelling of mancozeb hydrolysis and photolysis to ethylenethiourea and other by-products in water

The aim of this study was to propose kinetic models suitable for reproducing and predicting mancozeb (Mz) conversion to by-products as a function of the operational conditions. The main factors (pH, temperature and light) potentially affecting the mancozeb degradation in aqueous models were studied by a multifactorial screening design. In addition, the response surface methodology (RSM) was applied to evaluate the interactive effects of these factors on ethylenethiourea (ETU) formation. The response surface revealed that the best degradation conditions to minimize mancozeb conversion to ETU were low pH (2), low temperature (25 °C) and darkness. Under these conditions, the percentage of mancozeb remained in the solution at 72 h was approximately 10% of the initial concentration and the percentage of ETU conversion was 5.4%. However, according to the model, in surface waters under typical environmental conditions (pH 8, 25 °C and light) the percentage of mancozeb conversion to ETU would be about 17.5%. The proposed model provides a satisfactory interpretation of the experimental data obtained during the hydrolysis of mancozeb.

Formaldehyde vapor produced from hexamethylenetetramine and pesticide: Simultaneous monitoring of formaldehyde and ozone in chamber experiments by flow-based hybrid micro-gas analyzer

Simultaneous analysis of HCHO and O3 was performed by the developed flow analysis system to prove that HCHO vapor is produced from solid pesticide in the presence of O3. HCHO is produced in many ways, including as primary emissions from fuel combustion and in secondary production from anthropogenic and biogenic volatile organic compounds by photochemical reactions. In this work, HCHO production from pesticides was investigated for the first time. Commonly pesticide contains surfactant such as hexamethylenetetramine (HMT), which is a heterocyclic compound formed from six molecules of HCHO and four molecules of NH3. HMT can react with gaseous oxidants such as ozone (O3) to produce HCHO. In the present study, a flow analysis system was developed for simultaneous analysis of HCHO and O3, and this system was used to determine if solid pesticides produced HCHO vapor in the presence of O3. HMT or the pesticide jimandaisen, which contains mancozeb as the active ingradient and HMT as a stabilizer was placed at the bottom of a 20-L stainless steel chamber. Air in the chamber was monitored using the developed flow system. Analyte gases were collected into an absorbing solution by a honeycomb-patterned microchannel scrubber that was previously developed for a micro gas analysis system (μGAS). Subsequently, indigotrisulfonate, a blue dye, was added to the absorbing solution to detect O3, which discolored the solution. HCHO was detected after mixing with the Hantzsch reaction reagent. Both gases could be detected at concentrations ranging from parts per billion by volume (ppbv) to 1000 ppbv with good linearity. Both HMT and jimandaisen emitted large amount of HCHO in the presence of O3.

A novel pre-oxidation method for elemental mercury removal utilizing a complex vaporized absorbent

A novel semi-dry integrative method for elemental mercury (Hg(0)) removal has been proposed in this paper, in which Hg(0) was initially pre-oxidized by a vaporized liquid-phase complex absorbent (LCA) composed of a Fenton reagent, peracetic acid (CH3COOOH) and sodium chloride (NaCl), after which Hg(2+) was absorbed by the resultant Ca(OH)2. The experimental results indicated that CH3COOOH and NaCl were the best additives for Hg(0) oxidation. Among the influencing factors, the pH of the LCA and the adding rate of the LCA significantly affected the Hg(0) removal. The coexisting gases, SO2 and NO, were characterized as either increasing or inhibiting in the removal process, depending on their concentrations. Under optimal reaction conditions, the efficiency for the single removal of Hg(0) was 91%. Under identical conditions, the efficiencies of the simultaneous removal of SO2, NO and Hg(0) were 100%, 79.5% and 80.4%, respectively. Finally, the reaction mechanism for the simultaneous removal of SO2, NO and Hg(0) was proposed based on the characteristics of the removal products as determined by X-ray diffraction (XRD), atomic fluorescence spectrometry (AFS), the analysis of the electrode potentials, and through data from related research references.

Denitrification utilizing a vaporized enhanced-Fenton reagent: kinetics and feasibility

Macrokinetics and feasibility of denitrification using a vaporized enhanced-Fenton reagent were determined.

Ozone microbubble treatment at various water temperatures for the removal of residual pesticides with negligible effects on the physical properties of lettuce and cherry tomatoes

In this study, the effects of ozone microbubbles (OMCB) treatment at various water temperatures on the removal of residual fenitrothion (FT) pesticides and on the physical properties of lettuce and cherry tomatoes was examined. The residual FT percentage in lettuce and cherry tomatoes was shown decreased by using higher water temperatures, particularly at 30 °C, resulting in a decrease within the range of 32% to 52%, after the 20-min treatment. In addition, bubbling OMCB treatment did not alter the color and pulling strength of lettuce and cherry tomatoes. These results indicate that bubbling OMCB treatment at 30 °C is a highly effective method for the removal of FT residues in lettuce and cherry tomatoes, with relatively little effect on crop quality.

PRACTICAL APPLICATION

The bubbling OMCB has a potential of reducing the FT reduces on vegetables with no adverse effect on the sensory quality of vegetables.

Removal of residual pesticides in vegetables using ozone microbubbles

The removal of fenitrothion (FT) pesticide residues from vegetables by immersion in ozone-microbubbled solution was demonstrated. FT-treated lettuce, cherry tomatoes, and strawberries were immersed in ozone-microbubbled, ozone-millibubbled, and dechlorinated water. After that the percentage of residual FT in the vegetables was determined. Residual FT was efficiently removed from lettuce by immersing it in ozone-microbubbled solution containing more than 1.0 ppm dissolved ozone, or continuously generated ozone-microbubbled solution containing 2.0 ppm dissolved ozone. Similarly, for cherry tomatoes and strawberries, the continuously generated ozone-microbubbled solution containing 2.0 ppm dissolved ozone was highly effective. These results showed that ozone microbubbles effectively removed residual pesticides not only from leafy vegetables but also from fruity vegetables.

Use of a low-cost biosorbent to remove pesticides from wastewater

A lignocellulosic substrate (LS) obtained from our local agroindustry was used as a low-cost and effective adsorbent for the removal of pesticides from wastewaters. The studied pesticides were terbumeton (N-(1,1-dimethyl)-Nethyl-6-methoxy-1,3,5-triazine-2,4-diamine), desethyl terbumeton (N-(1,1-dimethylethyl)-6-methoxy-1,3,5-triazine-2,4-diamine), dimetomorph (4-[3-(4-chlorophenyl)-3-(3,4-dimethoxyphenyl)acryloyl]morpholine), and isoproturon (3-(4-isopropylphenyl)-1,1-dimethylurea). Batch and column experiments were conducted as a function of pH and pesticide concentration under laboratory and industrial conditions. The concentration range studied for the pesticides varied from 2 x 10(-7) to 3 x 10(-4) mol L(-1). The influence of organic and inorganic pollutants was assessed by studying the retention of pesticide in the presence of copper(II) and a surfactant. These experiments indicated that LS is an efficient adsorbent toward the investigated pesticides and has little influence of the other pollutants. The kinetic adsorptions are fast, and the amounts of adsorbed pesticide varied from 1 to 8 g kg(-1) of LS. These retention capacities show that LS can provide a simple, effective, and cheap method for removing pesticides from contaminated waters. Thus, this biomaterial may be useful for cleaning up polluted waters.