The effect of hybrid zinc oxide/graphene oxide (ZnO/GO) nano-catalysts on the photocatalytic degradation of simazine.

The photocatalytic degradation of simazine (SIM) was investigated using zinc oxide/graphene oxide (ZnO/GO) composite materials under visible light irradiation. The reaction kinetics was studied to optimize the reaction parameters for efficient degradation of SIM. Batch studies were performed to investigate the effects of initial reaction pH, the loading of the ZnO onto GO, and mass of catalyst on the removal of SIM from aqueous solution. A pH of 2 was determined to be the optimal reaction pH for the different ZnO-loaded GO catalysts. In addition, a mass of 40 mg of catalyst in the reaction was observed to be the most effective for the catalysts synthesized using 20 and 30 mmol of Zn2+ ions; whereas a mass of 10 mg was most effective for the ZnO/GO composite material synthesized using 10 mmol Zn2+ ions. The reaction was observed to follow a second-order kinetics for the degradation process. Furthermore, the synthesized ZnO/GO composite catalysts resulted in higher reaction rates than those observed for pure ZnO. The 30 mmol ZnO/GO composite expressed a rate of SIM degradation ten times greater than the rate observed for pure ZnO, and sixty-two times greater than the rate of photolysis. In addition, the catalyst cycling exhibited a constant photocatalytic activity for the ZnO/GO composite over three reaction cycles without the need of a conditioning cycle.

A non-edible waste as a potential sorptive media for removal of herbicide from the watershed.

A non-edible waste, from biodiesel processing industry is being turned to carbonaceous material (biochar) using slow pyrolysis. The material was found to be amorphous with hydroxyl, methyl, carbonyl and carboxyl functional groups onto the surface. The influencing parameters, namely adsorbate concentration (0.05-5 mg/l), biochar loading (0.02-0.4 g), pH(3-12) and particle sizes (0.03-0.13 mm) were studied to observe the effect on the sorption of simazine using biochar. A multivariate optimization using central composite design in response surface methodology was performed employing desirability function. The optimized biosorption efficiency (B%) and capacity qe was found to be 91.98 % and 0.83 mg/g respectively with the optimized parameters as 3.76 mg/l of adsorbate concentration, 0.12 g of biochar loading, pH of 5.26 and 0.0535 mm of particle size. The simazine adsorption phenomena were found to be multilayer heterogeneous sorption based on Langmuir and Freundlich models. The kinetics investigation shows that chemisorption was involved for the transfer of simazaine to the surface of biochar with three distinct intra particulate diffusional zones. An adsorption process requires activation energy of 11.27 kJ/mol and the negative magnitude of ΔH* indicates the exothermicity involved in the process.

Towards Simazine Monitoring in Agro-Zootechnical Productions: A Yeast Cell Bioprobe for Real Samples Screening.

Simazine is an herbicide that is able to contaminate surface waters, ground waters, and milk/dairy products, thus posing concerns in both environmental health and food safety. A yeast-based bioprobe was utilized to detect simazine in spiked real samples of livestock drinking water and raw cow's milk. Yeast aerobic respiration was taken as short-term toxicological endpoint. We carried out comparative measures of yeast oxygen consumption between simazine-spiked samples and blank samples. Percentage interference (%ρ) on yeast aerobic respiration was calculated through the comparison of aerobic respiration of simazine-exposed and non-exposed yeast cells. The method was optimized for raw cow's milk samples by using boric acid as fungistatic agent in order to avoid cellular proliferation. Overall, the results have shown that simazine can be detected up to concentrations five times below the EU legal concentration limits for drinking water (0.02 ppb) and cow's milk (2 ppb) (%ρ values of 18.53% and 20.43% respectively; %RSD ≤ 15%). Dose-effect relationships of simazine were assessed. The findings of the bioassays match reasonably well with known mechanisms of toxicity and intracellular detoxification in yeast. A correlation between fat content in milk samples and analytical performance of the bioprobe was established. Results suggest the involvement of a matrix effect, presumably due to lipid sequestration of simazine. The yeast-based bioprobe has proved to be sensitive and suitable for the detection of simazine in real samples in concentrations of interest.

Study on Mobility, Distribution and Rapid Ion Mobility Spectrometry Detection of Seven Pesticide Residues in Cucumber, Apple, and Cherry Tomato.

This research explores the mobility and distribution rules of simazine, acetamiprid, hexazinone, paclobutrazol, amitraz, clofentezine, and boscalid in the pulp and peel of apple, cucumber, and cherry tomato. A laboratory test was carried out by treating the matrices with standard solution for different periods of time. The percentage sorption of pesticides ranged from 0.02 to 89.3% for the three matrices. The pesticides' distribution was also determined, and all pesticides showed ratio values (Q) between pulp and peel concentrations in the three matrices of <0.8, which proved that the highest pesticides' content was found in the peel. In addition, a rapid and simple process combining a surface swab capture method and pulse glow discharge-ion mobility spectrometry (PGD-IMS) detection was established for the detection of pesticides on matrix surfaces. In the swab method, the whole matrix surface was swabbed manually by swab sticks, and swab sticks were agitated in acetonitrile to release the pesticides. The releasing factors of pesticides in the three matrices were calculated. The linearity, LOD, LOQ, and matrix effect were investigated to assess the applicability of the swab-IMS process in practical analysis. The swab-IMS method is rapid, sensitive, and quantitative and can be achieved in the field.

Application of highly porous materials for simazine removal from aqueous solutions.

The removal of simazine from both pure water and solute-bearing well water was studied by adsorption on two solids: zeolite H-Y from the commercial Na form and porous silica tailored by the sol-gel technique. The pH dependence of the amount adsorbed in a closed system at constant total simazine content as well as the apparent isotherms of adsorption was measured in all four cases. The low ion content of natural water suffices to alter the adsorption features in the case of silica, but not with zeolite H-Y. Iteration of the adsorption process onto constant amounts of solid allowed bringing the residual simazine concentration below 0.05 mg/L, the value allowed by Italian laws in wastewaters.

The role of outer surface/inner bulk Brønsted acidic sites in the adsorption of a large basic molecule (simazine) on H-Y zeolite.

The simple means adopted for investigating H-Y zeolite acidity in water is the pH-dependence of the amount of a basic molecule adsorbed under isochoric conditions, a technique capable of yielding, under equilibrium conditions, an estimate of the pKa value of the involved acidic centres: the behaviour with temperature of adsorbed amounts yields instead some information on thermodynamics. Simazine (Sim, 2-chloro-4,6-bis(ethylamino)-s-triazine) was chosen as an adsorbate because its transverse dimension (7.5 Å) is close to the opening of the supercage in the faujasite structure of H-Y (7.4 Å). In short term measurements, Sim adsorption at 25 °C occurs only at the outer surface of H-Y particles. Two types of mildly acidic centres are present (with pKaca. 7 and ca. 8, respectively) and no strong one is observed. Previous adsorption of ammonia from the gas phase discriminates between the two. The former survives, and shows features common with the silanols of amorphous silica. The latter is suppressed: because of this and other features distinguishing this site from silanol species (e.g. the formation of dimeric Sim2H(+) species, favoured by coverage and unfavoured by temperatures of adsorption higher than ambient temperature) a candidate is an Al based site. We propose a Lewis centre coordinating a water molecule, exhibiting acidic properties. This acidic water molecule can be replaced by the stronger base ammonia, also depleting inner strong Brønsted sites. A mechanism for the generation of the two sites from surface Brønsted species is proposed. Long term adsorption measurements at 25 °C already show the onset of the interaction with inner strongly acidic Brønsted sites: because of its size, activation is required for Sim to pass the supercage openings and reach inner acidic sites. When adsorption is run at 40-50 °C, uptake is much larger and increases with temperature. Isochoric measurements suggest a pKa value of ca. 3 compatible with its marked acidic nature, although attainment of equilibrium conditions is questionable. Measurements at 60 °C (both isochors and DRIFT) show the onset of changes at the outer surface brought about by the presence of hot water. Control experiments run with USY (Ultra Stabilized zeolite Y), featuring wormholes and cavities rendering accessible internal sites, show the extensive involvement of internal Brønsted sites already at 25 °C.

Adsorption of simazine on zeolite H-Y and sol-gel technique manufactured porous silica: A comparative study in model and natural waters.

In this work, we studied the removal of simazine from both a model and well water by adsorption on two different adsorbents: zeolite H-Y and a porous silica made in the laboratory by using the sol-gel technique. The pH dependence of the adsorption process and the isotherms and pseudo-isotherms of adsorption were studied. Moreover, an iterative process of simazine removal from both the model and well water, which allowed us to bring the residual simazine concentration below the maximum concentration (0.05 mg L(-1)) of agrochemicals in wastewater to be released in surface waters or in sink allowed by Italian laws, was proposed. The results obtained were very interesting and the conclusions drawn from them partly differed from what could reasonably be expected.

Microchip capillary electrophoresis based electroanalysis of triazine herbicides.

The number of pesticides used in agriculture is increasing steadily, leading to contamination of soil and drinking water. Herein, we present a microfluidic platform to detect the extent of contamination in soil samples. A microchip capillary electrophoresis system with in-channel electrodes was fabricated for label-free electroanalytical detection of triazine herbicides. The sample mixture contained three representative triazines: simazine, atrazine and ametryn. The electropherogram for each individual injection of simazine, atrazine and ametryn showed peaks at 58, 66 and 72 s whereas a mixture of them showed distinct peaks at 59, 67 and 71 s respectively. The technique as such may prove to be a useful qualitative and quantitative tool for the similar environmental pollutants.

Solid lipid nanoparticles co-loaded with simazine and atrazine: preparation, characterization, and evaluation of herbicidal activity.

Solid lipid nanoparticles (SLN) containing the herbicides atrazine and simazine were prepared and characterized, and in vitro evaluation was made of the release kinetics, herbicidal activity, and cytotoxicity. The stability of the nanoparticles was investigated over a period of 120 days, via analyses of particle size, ζ potential, polydispersion, pH, and encapsulation efficiency. SLN showed good physicochemical stability and high encapsulation efficiencies. Release kinetics tests showed that use of SLN modified the release profiles of the herbicides in water. Herbicidal activity assays performed with pre- and postemergence treatment of the target species Raphanus raphanistrum showed the effectiveness of the formulations of nanoparticles containing herbicides. Assays with nontarget organisms (Zea mays) showed that the formulations did not affect plant growth. The results of cytotoxicity assays indicated that the presence of SLN acted to reduce the toxicity of the herbicides. The new nanoparticle formulations enable the use of smaller quantities of herbicide and therefore offer a more environmentally friendly method of controlling weeds in agriculture.

Modelling the biphasic sorption of simazine, imidacloprid, and boscalid in water/soil systems.

The sorption kinetics of simazine (6-chloro-N,N'-diethyl-1,3,5-triazine-2,4-diamine), imidacloprid (1-(6-chloro-3-pyridylmethyl)-N-nitroimidazolidin-2-ylideneamine), and boscalid (2-chloro-N-(4'-chlorobiphenyl-2-yl)nicotinamide), three pesticides of wide use in agriculture, was determined in five different water/soil systems over a time interval from the initial few seconds to about 1 month. In all the experiments, sorption kinetics showed a biphasic pattern characterized by an initial, relatively short phase with a high sorption rate and a later phase with much a lower sorption rate. Initial sorption capacity increased with soil organic carbon content and with sorbate hydrophobicity. We postulate that the first phase of the process involves a fast second-order sorption reaction on superficial sites of soil particles, whereas the second phase depends on diffusion-controlled migration to internal binding sites. A kinetic equation based on this hybrid model accurately fitted all data sets. Less satisfactory results were obtained employing the pseudo-first order, pseudo-second order, Elovich, two site non-equilibrium, or Weber-Morris equation. The superior performance of the hybrid model for describing boscalid sorption probably reflects the high hydrophobic character and consequent low diffusion rates of this compound. The accuracy of modelling was in any case strongly dependent on the time interval considered.

Degradation of simazine from aqueous solutions by diatomite-supported nanosized zero-valent iron composite materials.

A novel composite material based on deposition of nanosized zero-valent iron (nZVI) particles on acid-leached diatomite was synthesised for the removal of a chlorinated contaminant in water. The nZVI/diatomite composites were characterised by X-ray diffraction, scanning electron microscopy, elemental analysis, transmission electron microscopy and X-ray photoelectron spectroscopy. Compared with the pure nZVI particles, better dispersion of nZVI particles on the surface or inside the pores of diatom shells was observed. The herbicide simazine was selected as the model chlorinated contaminant and the removal efficiency by nZVI/diatomite composite was compared with that of the pristine nZVI and commercial iron powder. It was found that the diatomite supported nZVI composite material prepared by centrifugation exhibits relatively better efficient activity in decomposition of simazine than commercial Fe, lab synthesised nZVI and composite material prepared via rotary evaporation, and the optimum experimental conditions were obtained based on a series of batch experiments. This study on immobilising nZVI particles onto diatomite opens a new avenue for the practical application of nZVI and the diatomite-supported nanosized zero-valent iron composite materials have potential applications in environmental remediation.

Online sequential-injection chromatography with stepwise gradient elution: a tool for studying the simultaneous adsorption of herbicides on soil and soil components.

The adsorption of triazine herbicides simazine (SIM), atrazine (ATR), and propazine (PRO) as well as the metabolites deisopropylatrazine (DIA), deethylatrazine (DEA), and 2-hydroxyatrazine (HAT) on soil, humic acid, and soil modified with humic acidic was studied by sequential-injection chromatography with UV detection at 223 nm. An online monitoring system was assembled, which was composed of a tangential filter and a peristaltic pump for the circulation of the soil (25 g L(-1)) or humic acid (2.5 g L(-1)) suspensions. A stepwise gradient elution separated the compounds using three mobile phases whose compositions were 28, 40, and 50% (v v(-1)) methanol in 1.25 mmol L(-1) ammonium acetate buffer, pH 4.7. The sampling throughput was about six analyses per hour; the linear dynamic range was between 100 and 1000 µg L(-1) for all of the studied compounds. The detection limits varied from 9 µg L(-1) for ATR to 36 µg L(-1) for DEA. At contact times <2 h, humic acid was the material with a higher adsorptive capacity (from 1470 ± 43 µg g(-1) for DIA to 2380 ± 51 µg g(-1) for PRO). In soil, HAT exhibited the highest adsorption (23.8 ± 0.2 µg g(-1)). The presence of humic acid in the soil increased the adsorption of ATR (14 ± 1 to 23 ± 2 µg g(-1)) and PRO (21.5 ± 0.5 to 24.0 ± 0.2 µg g(-1)), decreased the adsorption of HAT (23.8 ± 0.2 to 18 ± 2 µg g(-1)), and did not affect DIA and DEA. The adsorption of SIM was negligible in all of the sorbents studied. Simazine is the herbicide with the greatest potential for leaching to water bodies followed by DEA and DIA.

Grafting of molecularly imprinted polymer to porous polyethylene filtration membranes by plasma polymerization.

An application of plasma-induced grafting of polyethylene membranes with a thin layer of molecularly imprinted polymer (MIP) was presented. High-density polyethylene (HDPE) membranes, "Vyon," were used as a substrate for plasma grafting modification. The herbicide atrazine, one of the most popular targets of the molecular imprinting, was chosen as a template. The parameters of the plasma treatment were optimized in order to achieve a good balance between polymerization and ablation processes. Modified HDPE membranes were characterized, and the presence of the grafted polymeric layer was confirmed based on the observed weight gain, pore size measurements, and infrared spectrometry. Since there was no significant change in the porosity of the modified membranes, it was assumed that only a thin layer of the polymer was introduced on the surface. The experiments on the re-binding of the template atrazine to the membranes modified with MIP and blank polymers were performed. HDPE membranes which were grafted with polymer using continuous plasma polymerization demonstrated the best result which was expressed in an imprinted factor equal to 3, suggesting that molecular imprinting was successfully achieved.

The interaction between natural organic matter in raw waters and pesticide residues: a three dimensional excitation-emission matrix (3DEEM) fluorescence investigation.

This paper examines the interaction between dissolved natural organic matter and pesticide residues, both of which are found in raw water sources, using three dimensional excitation-emission matrix (3DEEM) fluorescence spectroscopy. It was observed that pesticide residue at 0.1 mg L(-1) formed a complex with humic-like fluorophores that are commonly found in raw water samples. Applying 3DEEM fluorescence to investigate the humic fractions, it was found that identification of changes in water sources was possible, and, importantly, the presence of a number of pesticides was able to be determined. In addition, the formation of this complex, and the influence of soluble cations and anions upon it, was shown to impact the efficiency of analytical extraction procedures for pesticides; however, 3DEEM fluorescence could be an approach to account for such losses.

Simazine transport in undisturbed soils from a vineyard at the Casablanca valley, Chile.

Simazine is a soil-active herbicide that has been applied worldwide in agricultural soils, being the second most commonly detected herbicide in groundwater and surface waters. Although its use has been restricted in many countries of Europe, it is still applied in many locations around the world in orchards, vineyards and forestry. Therefore, it is important to study its fate and transport in the environment. This paper investigates simazine transport in undisturbed bare soils from a vineyard at the Casablanca valley, Chile. In the study site, shallow groundwater tables (<1.0 m depth) and high simazine levels (>15 µg L(-1)) in the groundwater were observed and thus, there is potential for simazine to be transported further away through the saturated zone. The soils from the study site were characterized and the hydrodynamic transport parameters were determined. Column leaching experiments showed that the two-site chemical non-equilibrium model correctly represented simazine transport. It was found that 36.3% of the adsorption sites achieve instantaneous equilibrium and that the first-order kinetic rate of the non-equilibrium sites was 6.2 × 10(-3) h(-1). Hydrus 2D was used to predict the transport of simazine in the study site under natural field conditions. Simulation results showed that simazine concentrations at depths shallower than 2.1 m are above the maximum contaminant level of 4 µg L(-1) (defined by the U.S. Environmental Protection Agency). The timing of herbicide application was found to be important on simazine leaching and the main processes involved in simazine transport were degradation and adsorption, which accounted for 95.78 and 4.19% of the simulated mass of pesticide, respectively. A qualitative agreement in the timing and magnitude of simazine concentration was obtained between the simulations and the field data. Therefore, the model utilized in this investigation can be used to predict simazine transport and is a valuable tool to assess agricultural practices to minimize environmental impacts of simazine.

Effect of ammonium on liquid- and gas-phase protonation and deprotonation in electrospray ionization mass spectrometry.

The electrospray ionization (ESI) is a complex process and there has been a long debate regarding the gas-phase effect on ion generation in the process. In this paper we investigated the effect of liquid chromatographic mobile phase additives (formic acid, aqueous ammonia and their combination) on the ESI signal intensities for a wide variety of compounds. The addition of a trace amount of aqueous ammonia to the common formic acid-methanol mobile phase significantly enhances the ESI signals of protonated molecules and suppresses the formation of sodium adduct ions. This effect is well observed for the compounds containing the -N-C=O group but not for those without N or O atoms. The ESI signal intensity of deprotonated molecules increases with increase in pH of the mobile phase for neutral compounds, such as substituted urea, whereas this trend is not observed for acidic compounds such as phenoxy acids. The mechanistic analysis regarding liquid- and gas-phase protonation and deprotonation is discussed.

Cyclic process of simazine removal from waters by adsorption on zeolite H-Y and its regeneration by thermal treatment.

Removal of the agrochemical simazine from polluted waters through adsorption by zeolite Y in its protonic form was studied. The investigated parameters were: pH, time, initial simazine concentration and solid/liquid ratio. An iterative process of simazine removal from waters is proposed, featuring: (i) final agrochemical concentration well below 0.05 mg/dm(3), the maximum concentration allowed by Italian laws in wastewaters; (ii) regeneration of the adsorbent by a few minutes thermal treatment in air at about 500°C, which results in the combustion of simazine without damage of the adsorbent; (iii) destruction of the agrochemical compound by combustion.

Sorption of simazine to corn straw biochars prepared at different pyrolytic temperatures.

Simazine sorption to corn straw biochars prepared at various temperatures (100-600 °C) was examined to understand its sorption behavior as influenced by characteristics of biochars. Biochars were characterized via elemental analysis, BET-N(2) surface area (SA), FTIR and (13)C NMR. Freundlich and dual-mode models described sorption isotherms well. Positive correlation between log K(oc) values and aromatic C contents and negative correlation between log K(oc) values and (O + N)/C ratios indicate aromatic-rich biochars have high binding affinity to simazine (charge transfer (π-π*) interactions) and hydrophobic binding may overwhelm H-bonding, respectively. Dual-mode model results suggest adsorption contribution to total sorption increases with carbonization degree. Positive correlation between amounts of adsorption (Q(ad)) and SA indicates pore-filling mechanism. Comparison between our results and those obtained with other sorbents indicates corn straw biochars produced at higher temperature can effectively retain simazine. These observations will be helpful for designing biochars as engineered sorbents to remove triazine herbicides.

Biological degradation of simazine by mixed-microbial cultures immobilized on sepiolite and tepojal beads.

Simazine degradation by mixed microbial cultures was carried out in biological reactors with tepojal and sepiolite beads. The inoculum used is derived from a biotechnological product applied to plant roots, which contains mixed microbial cultures. This inoculum presented a stable adherence to the microorganism support throughout the experiment. In this research, the supports were evaluated in relation to both biofilm formation and simazine removal. For this study, hydraulic and mass starting-up parameters were established for simazine degradation and for the use of these reactors in the two types of supports. Tepojal had never been used before as a microbial support in any previous research paper. Tepojal demonstrated to be more efficient than sepiolite. Statistical analysis was done for the relationship among the parameters of chemical oxygen demand, colony formation units, total suspended solids, and volatile suspended solids.

Removal of simazine in a UV/TiO2 heterogeneous system.

The degradation of simazine by photocatalytic oxidation in a TiO2 suspension was studied. The influence of various parameters such as wavelength sources, light intensity, TiO2 dosage, and initial pH has been investigated, and the optimum conditions for the degradation of simazine have been identified. The photocatalytic degradation of simazine was observed to follow a pseudo-first-order reaction. The overdose of light intensity and photocatalyst does not always guarantee a beneficial effect on the photocatalytic reaction, and the optimum TiO2 dosage was found to be 0.1 g/L in this study. The optimum pH value is 9.0 for the photocatalytic degradation of simazine, whereas extremely acidic and alkaline conditions inhibit photocatalytic efficiency. Simazine can be fully destroyed, but ring-opening and mineralization are not observed in this system. In addition, seven simazine derivatives (CEAT, OEET, CAAT, ODET, OEAT, OAAT, OOOT) were detected by LC-ESI/MS. It is suggested that dealkylation is the major pathway of simazine photodecay in UV/TiO2 systems. The final product was found to be cyanuric acid.