Herbicides Diquat Research Articles

Remediation of Diquat-Contaminated Water by Electrochemical Advanced Oxidation Processes Using Boron-Doped Diamond (BDD) Anodes

The electrochemical elimination of the herbicide diquat dibromide (DQ) in an undivided electrochemical cell (Condiacell®-type cell) and an H-type cell (a divided electrochemical cell) using boron-doped diamond (BDD) electrodes is reported for the first time. The degradation of essentially 100% of the DQ present was achieved in the undivided electrochemical cell and ca. 92% in the H-type cell. Nearly 80% of the total organic carbon (TOC) and of the chemical oxygen demand (COD) were removed after 5 h of treatment at different current densities (i.e., 0.5, 1.0, and 1.5 mA/cm2 for the undivided cell, and 2.5, 5.0, and 7.5 mA/cm2 for the H-type cell) with a maximum specific energy consumption of approximately 150 kWh kg−1 of COD degraded in the undivided cell, and 300 kWh kg−1 of COD in the H-type cell. Energy consumption of about 0.30 kWh g−1 of TOC occurred in the undivided electrochemical cell and 2.0 in the H-type cell. In spite of obtaining similar percentages of DQ degradation and of COD and TOC removal, a smaller energy usage was required in the undivided cell since smaller current densities were employed. Best results were obtained with the undivided cell, since it required a smaller current density to obtain virtually the same percentage of DQ degradation and removal of COD and TOC. The results obtained herein show that the use of electrochemical advanced oxidation processes may be a good alternative for DQ degradation in polluted water.

EFFECTIVENESS OF DIQUAT, BOTH ISOLATED AND ASSOCIATED WITH COPPER SOURCES IN CONTROLLING THE Hydrilla verticillata SUBMERGED MACROPHYTES AND ANKISTRODESMUS Gracilis microphyte

ABSTRACT The goal of this study was to evaluate the effectiveness of diquat, both isolated and associated with copper sources (oxychloride and hydroxide) in controling the H. verticillata submerged macrophyte and the A. gracilis microalgae. For this purpose, 10.0 cm H. verticillata young branches and 300 mL of A. gracilis culture were used. The experiments were performed in laboratory and the tested diquat concentrations were: 0.1; 0.2; 0.4; 0.8; 1.2; and 1.8 mg L-1, either isolated or added with 1.0% copper oxychlorideand hydroxide, as well as a control sample. On day 3, 7, 11, 21 and 30 after application, phytotoxicity signs were evaluated and on day 60 after application, green and dry biomass production and plant length were measured. To obtain dry mass, plants remained in a greenhouse with forced air circulation at 65.0 oC, until constant weight. On day 1, 7, 15, 21, 30, 45 and 60 after application, the concentration of chlorophyll a in the water was assessed. The herbicide diquat used alone or in combination with sources copper oxychloride and hydroxide was effective in the control of H. verticillata and microalgae A. gracilis.

A flexible magnesium silicate coated electrospun fiber adsorbent for high-efficiency removal of a toxic cationic herbicide

A novel magnesium silicate/PAN composite electrospun fiber adsorbent was prepared and systematically investigated for the removal of the cationic herbicide diquat.

Sorption of the herbicides diquat and difenzoquat from aqueous medium by polymeric resins in the presence of sodium dodecylsulfate: Kinetic and mechanistic study

ABSTRACTThe goal of this work was to propose a novel method for the solid-phase extraction of the herbicides diquat (DQT2+) and difenzoquat (DFQT+) from aqueous medium using polymeric Amberlite XAD-2 and XAD-4 resins in the presence of sodium dodecylsulfate (SDS). The addition of SDS to the medium was of fundamental importance in order to allow the formation of a negatively charged surface able to sorb the cationic solutes. Several factors that could influence the sorption process, such as SDS concentration in the medium, sorbent mass, pH, ionic strength, and initial concentration of the solutes were investigated. Kinetic studies were also performed to model the system and to identify the mechanisms that operate the sorption process of the herbicides. SDS concentration in the medium presented remarkable influence on the extraction efficiency, achieving maximum values when the ratios [SDS]/[herbicide] were approximately 90, for XAD-2, and 22 and 11 for DQT2+ and DFQT+, respectively, for XAD-4. The sorption process followed a pseudo second-order kinetic in all cases studied. It was also found that an intraparticle diffusion process controlled exclusively the sorption of the herbicides by the Amberlite XAD-2 and XAD-4 resins in the first 15 min, becoming less active with time.

Application Volumes and Sizes of Droplets for the Application of Diquat Herbicide in the Control of Eichhornia crassipes

The objective of this study was to evaluate the efficiency of application and the efficacy of control of water hyacinth (Eichhornia crassipes) with the use of the diquat herbicide done with two application volumes associated to three droplets classes. Three experiments were conducted; in the first, the application efficiency was evaluated; in the second, the control efficiency and; in the third, the droplet spectrum. They were conducted in a completely randomized design with five, four and six replicates, respectively. The treatments were arranged in a 2 x 3 factorial design, with two application volumes (100 and 200 L ha-1) and three droplets classes (fine, extremely coarse and ultra-coarse) to the first and second experiment and the third comprised two diquat concentrations in spray solution (2 and 4 g i.a. L-1) and three droplets classes (fine, extremely coarse and ultra-coarse). The application efficiency was determined by the coverage by droplets, spray deposition and active ingredient of the herbicide (diquat). The efficacy was measured by the control and the percentage of plants with regrowth at 50 days after application. The spectrum of droplets produced per each nozzle model used to obtain the droplets classes were analyzed. According to the parameters analyzed, using the droplets classes extremely thick and ultra thick can provide greater certainty in the application of diquat in the aquatic environment associated with the deposition of the active and sufficient coverage to control Eichhornia crassipes with both application volumes

Sunlight induced photocatalytic degradation of herbicide diquat in water in presence of ZnO

Solar photocatalytic degradation of very small amounts of the pollutant herbicide diquat in water in presence of ZnO catalyst is investigated. ZnO is found to be an effective photocatalyst for the decontamination of water in presence of sunlight thus indicating its potential for achieving the twin objectives of solar energy harvesting and wastewater treatment. The influence of various parameters such as catalyst dosage, initial concentration of diquat, pH, O2 and H2O2 on the rate of degradation is investigated and optimised. The degradation follows pseudo first order kinetics. Externally added H2O2 inhibits the degradation initially though the effect becomes less significant as the reaction progresses. The degradation is slow in deaerated reaction systems and extra O2 introduced into it externally enhances the degradation. The study clearly shows that solar photocatalysis using ZnO as the catalyst can be used as an effective tool for the tertiary treatment of diquat contaminated water and the pollutant gets completely mineralised in the process.

A host–guest complexation based fluorescent probe for the detection of paraquat and diquat herbicides in aqueous solutions

A new method based on fluorescence quenching of host–guest complexation was proposed for the determination of the two herbicides in river water and cabbages. The method is rapid, direct and simple.

Chemical control of field dodder in alfalfa

Parasitic flowering plants have recently come into focus of research interests as a result of their notable expansion and increasing damage that they are causing in agricultural fields. Damage caused by field dodder in alfalfa crops mainly includes reduced yield of fresh biomass and considerable decrease in seed production. Effective control of field dodder in alfalfa crops necessarily includes a number of preventive measures and procedures, as well as chemical control. The effectiveness of glyphosate, propyzamide, imazethapyr and diquat herbicides in controlling field dodder in alfalfa crops was tested in trials conducted in 2011. Pot and field trials were set up in an experimental field of the Institute of Field and Vegetable Crops in Novi Sad (location Rimski Sancevi) and in a private field at Popovici (vicinity of Mladenovac). In pot trials, two glyphosate application rates (288 and 360 g a.i. ha) achieved the highest effectiveness of 95% and 97.5%, respectively. Both application rates of propyzamide (1500 and 2000 g a.i. ha) had weak effectiveness (85% and 87%, respectively), while imazethapyr (150 g a.i. ha) was the weakest herbicide with 80% efficacy. In field trials at both locations, diquat (450 g a.i. ha) showed the best efficacy in controlling field dodder in alfalfa. The efficacy of all other treatments was weaker at Popovici with the following survival rates of field dodder plants: 25% (glyphosate, 288 g a.i. ha), 15% (glyphosate, 360 g a.i. ha), 79% (propyzamide, 1500 g a.i. ha), 70% (propyzamide, 2000 g a.i. ha) and 72% (imazethapyr, 150 g a.i. ha). At the location Rimski Sancevi, the same treatements resulted in around 1% remaining field dodder plants in alfalfa crop.

Dense wilding conifer control with aerially applied herbicides in New Zealand

Wilding conifers are a major threat to biological conservation within New Zealand and currently cover at least 500,000 ha throughout the South Island. A range of herbicide treatments was applied to field trials established within wilding Pinus contorta (height range 1 – 15 m) and P. mugo (height range 0.5 – 5 m) infestations. Measurements of mortality taken two years post herbicide application were used to determine the efficacy of (i) the traditionally used contact herbicide diquat, applied in an application volume of 300 L ha-1, and (ii) a range of systemic herbicides applied in an application volume of 150 L ha-1. All herbicides were applied by helicopter using a coarse droplet spectra (VMD = 720 μm) to minimise spray drift. Damage assessments were made two years following application and trees were considered to have died if they had 100% dead foliage. The influence of height class and treatment on tree mortality was assessed using analysis of variance. For a treatment to be considered effective, a mortality rate of over 85% should be achieved on all trees up to 8 m in height. Under this criterion, none of the treatments used in this study provided satisfactory control of the two wilding species. Application of 7200 g ha-1 glyphosate and 120 g ha-1 metsulfuron was significantly better than any other treatment, for both species, causing 64% mortality for P. contorta and 36% for P. mugo. The traditionally used herbicide diquat was the poorest performing herbicide for P. contorta and the second poorest performing for P. mugo, inducing respective mortality rates of 2.7% and 2.4%. For all herbicides used there was a significant decline in efficacy with increases in tree height. These results suggest that control of dense wilding pine stands using low spray volumes and coarse droplet size is unlikely to be successful as foliage coverage is poor.

ZnO Photocatalysis Using Solar Energy for the Removal of Trace Amounts of Alfa-Methylstyrene, Diquat and Indigo Carmine from Water

AbstractSemiconductor photocatalysis using ZnO has been extensively investigated for the chemical and bacterial decontamination of water and air. In most of these cases, UV light is the source of energy and visible light induced photocatalytic degradation of trace pollutants in water has not received adequate attention. In the present study, ZnO is evaluated as a solar photocatalyst for the removal of trace amounts of three typical pollutants, i.e. alpha- Methylstyrene (AMS, a petrochemical), Diquat (herbicide) and Indigo carmine (IC, a dye) from water. Degradation by itself does not result in complete mineralisation and decontamination as seen from the significant Chemical Oxygen Demand even after the parent compound has disappeared. However, the intermediates also get mineralized eventually. The study indicates that solar photocatalysis can be used as a viable tool for the purification water contaminated with these chemicals. The degradation follows variable kinetics depending on the concentration of the substrates. H

Chitosan and alginate biopolymer membranes for remediation of contaminated water with herbicides

This study investigated the adsorption behavior of the herbicides diquat, difenzoquat and clomazone on biopolymer membranes prepared with alginate and chitosan (pristine and multi-layer model) for contaminated water remediation applications. Herbicides, at concentrations ranging from 5 μM to 200 μM, were adsorbed in either pure alginate, pure chitosan or a bilayer membrane composed of chitosan/alginate. No adsorption of clomazone was observed on any of the membranes, probably due to lack of electrostatic interactions between the herbicide and the membranes. Diquat and difenzoquat were only adsorbed on the alginate and chitosan/alginate membranes, indicating that this adsorption takes place in the alginate layer. At a concentration of 50 μM, diquat adsorption reaches ca. 95% after 120 min on both the alginate and chitosan/alginate membranes. The adsorption of difenzoquat, at the same concentration, reaches ca. 62% after 120 min on pure alginate membranes and ca. 12% on chitosan/alginate bilayer membranes. The adsorption isotherms for diquat and difenzoquat were further evaluated using the isotherm models proposed by Langmuir and by Freundlich, where the latter represented the best-fit model. Results indicate that adsorption occurs via coulombic interactions between the herbicides and alginate and is strongly related to the electrostatic charge, partition coefficients and dissociation constants of the herbicides. Biopolymer based membranes present novel systems for the removal of herbicides from contaminated water sources and hold great promise in the field of environmental science and engineering.

Produção e qualidade fisiológica de semente de feijão após aplicação do herbicida Diquat

The objective of this research was to evaluate the influence of Diquat herbicide application, at different periods, on production and physiological quality of bean seeds, cultivar: Perola. The experimental design used was a randomized block (RBD). The treatments were constituted of application of such herbicide with dosage of 400 g ai / ha in eight stages of application (83, 85, 87, 89, 91, 93 and 95 days after seeding (DAS) and without application with 97 days – witness .) The analyzed variables were moisture content (%), germination (%), first count of germination (%)velocity index of germination, seedling emergence (%), initial stand (%)velocity index of emergency, thousand seed weight (g) and production (kg ha-1). The moisture content of the bean seeds at the times of herbicide application declined, anticipating up to 14 days to harvest beans. For the first counting and germination no difference was observed between treatments. But for the IVG observed superior results at 83 DAS. For emergence percentage and EVI the values were lower at 87 and 89 DAS. On the other hand, the data obtained for the initial stand did not differ. For the thousand seed weight and production results were superior to 89 DAS and at 89 and 95 DAS, respectively. The application of Diquat desiccant in bean crop from 83 days after sowing did not affect the germination of the seeds, however, affect significantly the production of seeds.

Optimized liquid chromatography tandem mass spectrometry approach for the determination of diquat and paraquat herbicides

Liquid chromatography tandem mass spectrometry (LC–MS/MS) determination of quaternary ammonium herbicides diquat (DQ) and paraquat (PQ) can be very challenging due to their complicated chromatographic and mass spectrometric behaviors. Various multiple reaction monitoring (MRM) transitions from radical cations M+ and singly charged cations [M−H]+, have been reported for LC–MS/MS quantitation under different chromatographic and mass spectrometric conditions. However, interference peaks were observed for certain previously reported MRM transitions in our study. Using a Dionex Acclaim® reversed-phase and HILIC mixed-mode LC column, we evaluated the most sensitive MRM transitions from three types of quasi-molecular ions of DQ and PQ, elucidated the cross-interference phenomena, and demonstrated that the rarely mentioned MRM transitions from dications M2+ offered the best selectivity for LC–MS/MS analysis. Experimental parameters, such as IonSpray (IS) voltage, source temperature, declustering potential (DP), column oven temperature, collision energy (CE), acid and salt concentrations in the mobile phases were also optimized and an uncommon electrospray ionization (ESI) capillary voltage of 1000V achieved the highest sensitivity. Employing the proposed dication transitions 92/84.5 for DQ and 93/171 for PQ, the direct aqueous injection LC–MS/MS method developed was able to provide a method detection limit (MDL) of 0.1μg/L for the determination of these two herbicides in drinking water.

Impact of the redox-cycling herbicide diquat on transcript expression and antioxidant enzymatic activities of the freshwater snail Lymnaea stagnalis

The presence of pesticides in the environment results in potential unwanted effects on non-target species. Freshwater organisms inhabiting water bodies adjacent to agricultural areas, such as ditches, ponds and marshes, are good models to test such effects as various pesticides may reach these habitats through several ways, including aerial drift, run-off, and drainage. Diquat is a non-selective herbicide used for crop protection or for weed control in such water bodies. In this study, we investigated the effects of diquat on a widely spread aquatic invertebrate, the holarctic freshwater snail Lymnaea stagnalis. Due to the known redox-cycling properties of diquat, we studied transcript expression and enzymatic activities relative to oxidative and general stress in the haemolymph and gonado-digestive complex (GDC). As diquat is not persistent, snails were exposed for short times (5, 24, and 48h) to ecologically relevant concentrations (22.2, 44.4, and 222.2μgl−1) of diquat dibromide. RT-qPCR was used to quantify the transcription of genes encoding catalase (cat), a cytosolic superoxide dismutase (Cu/Zn-sod), a selenium-dependent glutathione peroxidase (gpx), a glutathione reductase (gred), the retinoid X receptor (rxr), two heat shock proteins (hsp40 and hsp70), cortactin (cor) and the two ribosomal genes r18S and r28s. Enzymatic activities of SOD, Gpx, Gred and glutathione S-transferase (GST) were investigated in the GDC using spectrophoto/fluorometric methods. Opposite trends were obtained in the haemolymph depending on the herbicide concentration. At the lowest concentration, effects were mainly observed after 24h of exposure, with over-transcription of cor, hsp40, rxr, and sod, whereas higher concentrations down-regulated the expression of most of the studied transcripts, especially after 48h of exposure. In the GDC, earlier responses were observed and the fold-change magnitude was generally much higher: transcription of all target genes increased significantly (or non-significantly for cat) after 5h of exposure, and went back to control levels afterwards, suggesting the onset of an early response to oxidative stress associated to the unbalance of reactive oxygen species (ROS) in hepatocytes. Although increases obtained for Gred and SOD activities were globally consistent with their respective transcript expressions, up-regulation of transcription was not always correlated with increase of enzymatic activity, indicating that diquat might affect steps downstream of transcription. However, constitutive levels of enzymatic activities were at least maintained. In conclusion, diquat was shown to affect expression of the whole set of studied transcripts, reflecting their suitability as markers of early response to oxidative stress in L. stagnalis.

Alterações anatômicas foliares em plantas de Brachiaria subquadripara submetidas à aplicação de herbicidas

O presente trabalho teve por objetivo avaliar a eficiência do controle dos herbicidas diquat, glyphosate e imazapyr e as alterações anatômicas do limbo foliar provocadas por eles em plantas de Brachiaria subquadripara. As plantas foram cultivadas em caixas-d'água sob condições de campo e, quando atingiram estádio de pleno desenvolvimento vegetativo, foram pulverizadas com soluções de diquat a 400 g ha-1, glyphosate a 4.320 g ha-1 em associação com o adjuvante Aterbane a 0,5% v v-1 e imazapyr a 750 g ha-1. Além disso, utilizou-se uma testemunha sem aplicação de herbicida. Foram realizadas avaliações de controle e das seguintes características anatômicas quantitativas das regiões da nervura central e da internervural do limbo foliar, além da região do colmo: porcentagem da epiderme adaxial e abaxial, porcentagem da endoderme, porcentagem do feixe vascular, porcentagem de lacunas do aerênquima, porcentagem de parênquima, espessura foliar, porcentagem da epiderme do colmo, porcentagem do câmbio vascular e diâmetro do colmo. Os herbicidas diquat e imazapyr promoveram o maior número de alterações nos caracteres anatômicos quantitativos das regiões da nervura central e internervural do limbo foliar e da região do colmo das plantas. Contudo, com exceção do diquat, os herbicidas foram eficientes no controle das plantas de B. subquadripara, porém todos eles permitiram a rebrota delas.

Evidence for DNA-diquat interaction and cytotoxicity in in vitro rat cells

Over 98% of sprayed insecticides and 95% of herbicides reach non-target species in air, soil, and water. Numerous studies have reported that pesticide residues can cause acute and chronic toxicity. Pesticide residues can be carcinogenic, mutagenic, and immunotoxic. There are actually too few studies that bridge the disciplines of chemobioanalysis and environmental toxicology. Here, we assessed the cytotoxicity of a bipyridilium herbicide diquat in rat adrenal pheochromocytoma cells (PC12). Our results show that diquat caused the decrease in cell viability with a lethal concentration 50 (LC50) of 1.4 × 10−5 mol/L. This cytotoxicity may result from diquat-induced apoptosis, characterized by nuclear fragmentation and chromatin condensation by Hoechst 33324 staining. To explore the possible mechanisms, the interaction between herbicide diquat and calf thymus DNA (ctDNA) was further investigated using fluorescence quenching. The detection of static quenching showed that diquat was linked with ctDNA by electrostatic interaction with a binding constant of 9.288 × 104 L/mol. This is the first study on the interaction of DNA with herbicide diquat by fluorometric method as well as on the evaluation of cytotoxicity by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and Hoechst staining. Given the widespread use of synthetic pesticides, the data would be valuable for the risk assessment of pesticide residues.

WldS Reduces Paraquat-Induced Cytotoxicity via SIRT1 in Non-Neuronal Cells by Attenuating the Depletion of NAD

WldS is a fusion protein with NAD synthesis activity, and has been reported to protect axonal and synaptic compartments of neurons from various mechanical, genetic and chemical insults. However, whether WldS can protect non-neuronal cells against toxic chemicals is largely unknown. Here we found that WldS significantly reduced the cytotoxicity of bipyridylium herbicides paraquat and diquat in mouse embryonic fibroblasts, but had no effect on the cytotoxicity induced by chromium (VI), hydrogen peroxide, etoposide, tunicamycin or brefeldin A. WldS also slowed down the death of mice induced by intraperitoneal injection of paraquat. Further studies demonstrated that WldS markedly attenuated mitochondrial injury including disruption of mitochondrial membrane potential, structural damage and decline of ATP induced by paraquat. Disruption of the NAD synthesis activity of WldS by an H112A or F116S point mutation resulted in loss of its protective function against paraquat-induced cell death. Furthermore, WldS delayed the decrease of intracellular NAD levels induced by paraquat. Similarly, treatment with NAD or its precursor nicotinamide mononucleotide attenuated paraquat-induced cytotoxicity and decline of ATP and NAD levels. In addition, we showed that SIRT1 was required for both exogenous NAD and WldS-mediated cellular protection against paraquat. These findings suggest that NAD and SIRT1 mediate the protective function of WldS against the cytotoxicity induced by paraquat, which provides new clues for the mechanisms underlying the protective function of WldS in both neuronal and non-neuronal cells, and implies that attenuation of NAD depletion may be effective to alleviate paraquat poisoning.

Alterações anatômicas do limbo foliar de plantas de Polygonum lapathifolium submetidas à aplicação de herbicidas

O presente trabalho teve por objetivo avaliar a eficiência do controle dos herbicidas 2,4-D, diquat e glyphosate e as alterações anatômicas do limbo foliar provocadas por eles em plantas de Polygonum lapathifolium. As plantas foram cultivadas em caixas-d'água sob condições de campo e, quando atingiram seu pleno desenvolvimento (antes do florescimento), pulverizadas com os herbicidas. Avaliaram-se quantitativamente as seguintes características anatômicas da nervura central e internervural das folhas: porcentagem da epiderme adaxial e abaxial, porcentagem da bainha do feixe, porcentagem do feixe vascular, porcentagem de esclerênquima e colênquima, porcentagem de parênquima paliçádico e lacunoso, bem como a espessura foliar (μm). Os tratamentos químicos foram: diquat (400 g i.a. ha-1 do produto comercial Reward), 2,4-D (1.340 g e.a. ha -1 do produto comercial DMA 806 BR) e glyphosate (4.320 g e.a. ha-1 do produto comercial Rodeo) com a adição do surfatante Silwet L-77 a 0,01% v v-1. Os principais caracteres anatômicos quantitativos da região da nervura central do limbo foliar que sofreram alterações após a aplicação dos herbicidas foram a porcentagem da epiderme adaxial, a porcentagem de feixe vascular, a porcentagem de colênquima, a porcentagem de parênquima paliçádico e lacunoso e a espessura foliar. Para a região internervural do limbo foliar, os principais caracteres anatômicos quantitativos que sofreram alterações após a aplicação dos herbicidas foram a porcentagem da epiderme adaxial, a porcentagem da bainha do feixe e a espessura foliar. Os herbicidas diquat e 2,4-D foram ineficientes no controle das plantas de P. lapathifolium; o glyphosate apresentou controle superior a 90% das plantas aos 100 dias após a aplicação. Entretanto, todos os herbicidas permitiram rebrota das plantas.

Doses e horário de aplicação do diquat no controle de Eichhornia crassipes

O aguapé (Eichhornia crassipes) é uma das mais importantes macrófitas aquáticas que colonizam reservatórios e corpos hídricos nas regiões tropicais e subtropicais do mundo, causando uma série de interferências no uso múltiplo da água e do corpo hídrico e no controle de vetores de doenças humanas. Para evitar prejuízos econômicos, sociais, estéticos e ao meio ambiente, essas plantas são controladas por vários métodos, incluindo o controle químico com o uso de herbicidas. Com o objetivo de avaliar a eficácia do herbicida diquat no controle dessa macrófita aquática, foram instalados dois ensaios em casa de vegetação. No primeiro, foram comparadas duas formulações (Reward® e Reglone®) aplicadas em dois horários (diurno e noturno) e em quatro doses (0,1, 0,2, 0,3 e 0,4 kg ha-1), num esquema fatorial 2 x 2 x 4, com seis repetições. Os resultados mostraram que a formulação Reward® foi mais eficiente no controle dessa macrófita, agindo mais rapidamente, sobretudo em menores doses, e que as aplicações realizadas no período noturno apresentavam melhor desempenho no controle em relação às realizadas no período diurno. Assim, um segundo ensaio foi realizado utilizando apenas a formulação Reward®, comparando a aplicação no período noturno e no diurno e as doses de 0,1, 0,2, 0,3 e 0,4 kg ha-1, obedecendo a um esquema fatorial 2 x 4. As plantas de aguapé foram cultivadas em caixas-d'água, e o delineamento experimental adotado foi em blocos ao acaso com quatro repetições, considerando a posição das caixas dentro da casa de vegetação. Os resultados confirmaram que o diquat é eficiente no controle do aguapé, principalmente nas doses de 0,3 e 0,4 kg ha¹ em aplicações noturnas. Doses baixas e aplicações diurnas não impediram intensas rebrotas das plantas afetadas.

Rapid fluorescence determination of diquat herbicide in food grains using quantum dots as new reducing agent

CdSe/ZnS QDs have demonstrated capacity to act as reducing agent in organic media such as acetonitrile and ethanol. By using fluorescence and Raman spectroscopy, it has been demonstrated that QDs reduce diquat herbicide to its monocation radical. The reaction is characterized to present a high reaction rate making possible to perform the reaction by simple filtration of the solution containing the herbicide through a QDs modified filter. The monocation radical presents a high fluorescence emission spectrum which was selected as the analytical signal to quantify the diquat herbicide. The method described here for the analysis of diquat herbicide in oat grains is simple and fast allowing the analysis of trace level of herbicide in only 6 min. The excellent sensitivity and reproducibility of the methods indicate that the reaction is favoured from both thermodynamic and kinetic point of view. The results presented open up the possibility to use QDs as redox agent. The sensitivity of the method expressed as detection limit was only of 0.01 mg kg −1.The lineal range was between 0.05 and 0.5 mg kg −1. The time of analysis per sample, including extraction, reaction and fluorescent measurement was only of 6 min.