Synergistic effects between hydroxyl radicals and hydrated electrons on strengthening decomposition of an s-triazine compound: A combined experimental and theoretical study.

The decomposition of an environmentally recalcitrant s-triazine compound, prometry (PMT), was carried out by experimental and theoretical approaches to study the combined effects of hydroxyl radicals (OH) and hydrated electrons (eaq-). With the participation of strongly oxidative radicals OH and reductive radicals eaq- induced by electron beam (EB), PMT obtained a good decomposition performance, which was obviously better than those methods simply using OH as the single active species. The evolution of cyanuric acid (CA) during the EB and UV irradiation processes elucidate that former method could efficiently decompose such chemically stable intermediate. The experiments of radical scavengers further suggest that OH was the predominant radical during PMT degradation, while eaq- was beneficial to further decomposition and mineralization. Combined with the results of density functional theory (DFT) calculations, the strengthened synergistic effects between OH and eaq- were proven. The calculations illustrated OH could attack the carbon-branch-chains of s-trazine ring and form OH-adducts rather than nitrogen oxides. Moreover, the presence of eaq- could not only greatly change the geometry of the s-triazine ring, but also help cleaving alkyl chain on ring, thus facilitate the complete mineralization.

Determination triazine pesticides in cereal samples based on single-hole hollow molecularly imprinted microspheres.

Single-hole hollow molecularly imprinted microspheres (h-MIMs) were prepared by hard template method and applied to extract six triazine pesticides in cereal samples, followed by HPLC-MS/MS detection. The synthesis mechanism of the h-MIMs has been studied. The h-MIMs exhibited bigger specific surface area and much higher binding capacity than the molecularly imprinted polymers prepared by precipitation polymerization (p-MIPs) and surface polymerization (s-MIPs). Besides, the adsorption rate of h-MIMs to prometryn was significantly higher than that of p-MIPs and s-MIPs. Owing to the hollow structure of the h-MIMs, more binding cavities were located on the inner and outer surfaces of the h-MIMs, which could facilitate the removal of template molecules from the polymers and the rebinding of the target molecules to the polymers. Under the optimal conditions, the detection limits of triazines are in the range of 0.08-0.16ngg(-1). At the spiked level (5ngg(-1)), the recoveries of triazines are in the range of 81±4% to 96±4%. The proposed method was successfully applied to determine six triazines in five cereal samples. Atrazine was found in two rice samples and a wheat sample with the contents of 5.1, 6.7 and 5.6ngg(-1), respectively. Ametryn and prometryn were found in a maize sample with the contents of 7.6 and 7.3ngg(-1), respectively.

[Determination of prometryne residue in shellfish by gas chromatography].

OBJECTIVE: To develop a method of gas chromatography (GC) for determining residues of promtryne in shellfish. METHODS: The sample was extracted with ethyl acetate, and cleaned-up with Envi-Carb SPE cartridge, alumina-N SPE cartridge, and determined by GC-FPD with DB - 1701 capillary chromatographic column (30 m x0.53 .mm x 0.5µm). RESULTS: Good linear was obtained in the concentration range of 0.10-0.96µg/ml with a correlation coefficient of 0. 999. The limit of detection (LOD) was 0.0037 mg/kg and limit of quantity (LOQ) was 0.010 mg/kg. The average recoveries was 83. 7% - 102. 0% and relative standard deviations (RSD) was 0. 54% - 8.14% CONCLUSION: The method is simple, fast and credible, so it can be applied to determination of prometryne in shellfish.

Interaction of prometryn to human serum albumin: insights from spectroscopic and molecular docking studies.

Prometryn possesses much potential hazard to environment because of its chemical stability and biological toxicity. Here, the binding properties of prometryn with human serum albumin (HSA) and the protein structural changes were determined under simulative physiological conditions (pH 7.4) by multispectroscopic methods including fluorescence, UV-vis absorption, Fourier transform infrared (FT-IR) and circular dichroism (CD) spectroscopy, coupled with molecular modeling technique. The result of fluorescence titration suggested that the fluorescence quenching of HSA by prometryn was considered as a static quenching procedure. The negative enthalpy change (ΔH(○)) and positive entropy change (ΔS(○)) values indicated that the binding process was governed mainly by hydrophobic interactions and hydrogen bonds. The site marker displacement experiments suggested the location of prometryn binding to HSA was Sudlow's site I in subdomain IIA. Furthermore, molecular docking studies revealed prometryn can bind in the large hydrophobic activity of subdomain IIA. Analysis of UV-vis absorption, synchronous fluorescence, CD and FT-IR spectra demonstrated that the addition of prometryn resulted in rearrangement and conformational alteration of HSA with reduction in α-helix and increases in ß-sheet, ß-turn and random coil structures. This work provided reasonable model helping us further understand the transportation, distribution and toxicity effect of prometryn when it spreads into human blood serum.

A novel luminescent terbium-3-carboxycoumarin probe for time-resolved fluorescence sensing of pesticides methomyl, aldicarb and prometryne.

The luminescence arising from lanthanide cations offers several advantages over organic fluorescent molecules: sharp, distinctive emission bands allow for easy resolution between multiple lanthanide signals; long emission lifetimes (µs-ms) make them excellent candidates for time-resolved measurements; and high resistance to photo bleaching allow for long or repeated experiments. A time-resolved (gated) luminescence-based method for determination of pesticides methomyl, aldicarb and prometryne in microtiterplate format using the long-lived terbium-3-carboxycoumarin in 1:3 metal:ligand ratio has been developed. The limit of detection is 1.20×10(6), 5.19×10(5) and 2.74×10(6)ng L(-1) for methomyl, prometryne and aldicarb, respectively. The quantum yield (QY=0.08) of Tb(III)-3-carboxycoumarin was determined using 3-(2-benzothiazolyl)-7-diethylamino-coumarin (coumarin 6). Stern-volmer studies at different temperatures indicate that collisional quenching dominates for methomyl, aldicarb and prometryne. Binding constants were determined at 303, 308 and 313 K by using Lineweaver-Burk equation. A thermodynamic analysis showed that the reaction is spontaneous with negative ΔG. Effect of some relevant interferents on the detection of pesticides has been investigated.

Fluorescence and electrochemical sensing of pesticides methomyl, aldicarb and prometryne by the luminescent europium-3-carboxycoumarin probe.

This work describes the application of time resolved fluorescence in microtiterplates and electrochemical methods on glassy carbon electrode for investigating the interactions of europium-3-carboxycoumarin with pesticides aldicarb, methomyl and prometryne. Stern-volmer studies at different temperatures indicate that static quenching dominates for methomyl, aldicarb and prometryne. By using Lineweaver-Burk equation binding constants were determined at 303 K, 308 K and 313 K. A thermodynamic analysis showed that the reaction is spontaneous with ΔG being negative. The enthalpy ΔH and the entropy ΔS of reactions were all determined. A time-resolved (gated) luminescence-based method for determination of pesticides in microtiterplate format using the long-lived europium-3-carboxycoumarin has been developed. The limit of detection is 4.80, 5.06 and 8.01 µmol L(-1) for methomyl, prometryne and aldicarb, respectively. This is the lowest limit of detection achieved so far for luminescent lanthanide-based probes for pesticides. The interaction of the probe with the pesticides has been investigated using cyclic voltammetry (CV), differential pulse polarography (DPP), square wave voltammetry (SWV) and linear sweep voltammetry (LSV) on a glassy carbon electrode in I = 0.1 mol L(-1) p-toluenesulfonate at 25 °C. The diffusion coefficients of the reduced species are calculated. The main properties of the electrode reaction occurring in a finite diffusion space are the quasireversible maximum and the splitting of the net SWV peak for Eu(III) ions in the ternary complex formed . It was observed that the increase of the cathodic peak currents using LSV is linear with the increase of pesticides concentration in the range 5 × 10(-7) to 1 × 10(-5) mol L(-1). The detection limit (DL) were about 1.01, 2.23 and 1.89 µmol L(-1) for aldicarb, methomyl and prometryne, respectively. In order to assess the analytical applicability of the method, the influence of various potentially interfering species was examined. Influence of interfering species on the recovery of 10 µmol L(-1) pesticides has been investigated.

Effect of size-fractionation dissolved organic matter on the mobility of prometryne in soil.

Import of organic materials in the form of compost, sludge or plant residues introduces large amounts of dissolved organic matter (DOM) into soils. DOM as a dynamic soil component affects the behaviors of organic pollutants. Different DOM constituents may affect herbicide action in a different way. However, the process of interaction between the distinct DOM-fractions and herbicides is largely unknown. In this study, DOM was separated by size-fractionation into three molecular size groups: MW<3500 Da, 3500 Da14000 Da. Effects of DOM-fractions on prometryne sorption/desorption and mobility were analyzed using approaches of batch experiments, soil column and soil thin-layer chromatography. Application of varied DOM-fractions at 50mg DOCL(-1) to the soil reduced the sorption and increased desorption of prometryne. DOM-fraction with MW>14000 Da appeared most effective in prometryne mobilization in the soil than any other fractions. Finally, DOM-fractions were characterized by chemical analyses, fourier transformed infrared spectroscopy (FT-IR) and excitation-emission matrices (EEMs) fluorescence spectroscopy. Our studies revealed that the high-molecular weight fraction contained more aromatic framework and unsaturated structure that was most likely the dominant factor modulating the behavior of prometryne in soils.

Prometryne-induced oxidative stress and impact on antioxidant enzymes in wheat.

Prometryne is one of the herbicides widely used for controlling weed/grass in agricultural practice. However, whether it has an adverse effect on crops is unknown. In this study, we investigated prometryne-induced oxidative stress in wheat (Triticum aestivum). Wheat plants were grown in soils with prometryne at 0-24 mgkg(-1) soil. The growth of wheat treated with prometryne was inhibited. Chlorophyll content significantly decreased even at the low level of prometryne (4 mgkg(-1) soil). Accumulation of thiobarbituric acid reactive substances (TBARS), an indicator of cellular peroxidation, increased, suggesting oxidative damage to the plants. The prometryne-induced oxidative stress triggered significant changes in activities of a variety of antioxidant enzymes including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX) and glutathione S-transferase (GST). Activities of the enzymes showed a general increase at low prometryne concentrations but a decrease at high levels. Analysis of non-denaturing polyacrylamide gel electrophoresis (PAGE) confirmed the results. To get an insight into the molecular response, a qRT-PCR-based assay was performed to analyze the transcript abundance of Cu/Zn-SOD and GST with prometryne exposure. Our analysis revealed that both genes displayed up-regulated expression patterns similar to the activities of the two enzymes. These data imply that prometryne-induced oxidative stress was responsible for the disturbance of the growth and antioxidant defensive systems in wheat plants.

Mobility of prometryne in soil as affected by dissolved organic matter.

Incorporation of organic fertilizers/amendments in soils has been, and will continue to be, a popular strategy for improving the quality of arable soils. However, the mechanism by which the dissolved organic matters (DOMs) affect soil properties or interact with other substances in soils is largely unknown. In this study, a batch equilibrium experiment was performed to evaluate the effect of two types of DOMs on the behavior of prometryne (a herbicide) in soils. Two sorts of DOMs were derived from lakebed sludge (SL) and rice straw (ST), respectively. The results show that sorption capacity in one soil for prometryne was significantly reduced by application of DOMs, whereas desorption of prometryne was promoted by DOM treatments. To understand the mobility behavior of prometryne in soils with DOMs, a column leaching experiment was carried out. It is shown that both DOMs enhanced the solubility and migration of prometryne in soils. To confirm the role of DOMs in regulating the mobility of prometryne in soils, a soil thin-layer chromatography was performed. The migration of prometryne was promoted by DOMs, which were used as a developing solvent or directly incorporated in the soil thin layer. The data indicate that DOM extracts can modify the mobility of prometryne in soil.

Effects of SOM, surfactant and pH on the sorption-desorption and mobility of prometryne in soils.

Sorption and desorption of the herbicide prometryne in two types of soil subjected to the changes of pH and soil organic matter and surfactant were investigated. The sorption and desorption isotherms were expressed by the Freundlich equation. Freundlich K(f) and n values indicate that soil organic matter was the major factor affecting prometryne behavior in the test soils. We also quantified the prometryne sorption and desorption behavior in soils, which arose from the application of Triton X-100 (TX100), a nonionic surfactant and change in pH. Application of TX100 led to a general decrease in prometryne sorption to the soils and an increase in desorption from the soils when applied in dosages of the critical micella concentration (CMC) 0.5, 1 and 2. At the concentration below the CMC, the non-ionic surfactant showed a tendency to decrease prometryne sorption and desorption. It appeared that TX100 dosages above CMC were required to effectively mobilize prometryne. Results indicate that the maximum prometryne sorption and minimum prometryne desorption in soils were achieved when the solution pH was near its pK(a). Finally, the influence of TX100 on the mobility of prometryne in soils using soil thin-layer chromatography was examined.

Heterogeneous photocatalytic degradation of prometryn in aqueous solutions under UV-Vis irradiation.

In this study, the heterogeneous photocatalytic degradation of prometryn using TiO(2) as photocatalyst was investigated. The main objectives of the study were: (I) to evaluate the kinetics of the pesticide disappearance, (II) to compare the photocatalytic efficiency of two different types of TiO(2), (III) to examine the influence of various parameters such as initial concentration of pesticide or catalyst and presence of oxidants (H(2)O(2) and K(2)S(2)O(8)), (IV) to evaluate the degree of mineralization and (V) to assess the detoxification efficiency of the studied processes. The experiments were carried out in a 500 ml pyrex UV reactor equipped with a 125 W high-pressure mercury lamp surrounded by a pyrex filter blocking wavelengths below 290 nm. Prometryn concentration was determined using HPLC. It was found that the degradation of the pesticide follows the first order kinetics according to the Langmuir-Hinshelwood model. Parameters like the type and concentration of the catalyst affect the degradation rate. A synergistic effect was observed when an oxidant was added in the TiO(2) suspensions increasing the reaction rate of photodegradation. In order to examine the extent of pesticide mineralization, DOC measurements were carried out. After 6h of illumination, mineralization was achieved up to almost 70%. The toxicity of the treated solution was evaluated using the Microtox test based on the luminescent bacteria Vibrio fisheri, in order to compare the acute toxicity of prometryn and its photoproducts. The detoxification efficiency was found to be dependent on the studied system and it did not follow the rate of pesticide disappearance.

Biodegradation of methylthio-s-triazines by Rhodococcus sp. strain FJ1117YT, and production of the corresponding methylsulfinyl, methylsulfonyl and hydroxy analogues.

A novel bacterial strain FJ1117YT was isolated from an enrichment culture with the herbicide simetryn. The isolate was capable of degrading the herbicide supplied as the sole sulfur source in an aquatic batch culture. The strain FJ1117YT was identified as that belonging to Rhodococcus sp. on the basis of comparative morphology, physiological characteristics and comparison of the 16S rRNA gene sequence. The biodegradation pathway of simetryn was established by isolating the methylsulfinyl analogue as the first metabolite and by identification of the methylsulfonyl intermediate and the hydroxy analogue by liquid chromatography-mass spectrometry (LC-MS) and/or nuclear magnetic resonance (NMR) analysis. The results indicate that the methylthio group was progressively oxidised and hydrolysed by the strain FJ1117YT. The same strain is also able to metabolise other methylthio-s-triazines such as ametryn, desmetryn, dimethametryn and prometryn through similar pathways.

Effect of temperature on the disappearance of four triazine herbicides in environmental waters.

The influence of temperature on the disappearance of four s-triazine herbicides, terbuthylazine, simazine, atrazine and prometryn was studied in sea, river and groundwaters spiked with approx. 5 mg l(-1) of each during long-term laboratory incubation. Residues were analyzed by GC-NPD and confirmed by GC-MSD. No clean-up was necessary and a micro on-line method for the determination of herbicide residues was used. The results showed that temperature had little effect on the behaviour of the four herbicides in river and seawaters but strongly affected their behaviour in groundwater. Simazine was the most readily affected compound in sea, river and groundwaters, while terbuthylazine and atrazine were the most persistent in all cases, especially in riverwater. Half-lives ranged from 41 days (constant rate = 0.017 days(-1)) to 196 days (constant rate = 0.003 days(-1)) for simazine (40 degrees C) and terbuthylazine (20 degrees C), respectively, in riverwater. Only for terbuthylazine in riverwater was the remaining percentage at the end of the experiment higher than 50% (58%, 3.21 mg l(-1)). In the other cases, the remaining percentage varied from 4% (0.20 mg l(-1), 40 degrees C) to 43% (2.25 mg l(-1), 20 degrees C) for simazine and terbuthylazine, respectively, in groundwater.

Adsorption and correlation with their thermodynamic properties of triazine herbicides on soils.

Adsorption of atrazine, prometryne and prometon was determined on six soils with different physical and chemical properties. The adsorption isotherms of three herbicides could well fit Freundlich equation. On all of six soils, adsorption of herbicides increased in the order: atrazine approximately = prometon < prometryne. This order is quite the same to the calculation result of by means of excess thermodynamic properties of triazine. The Freundlich adsorption constants, Kf, showed to have good correlation with organic matter (OM%) of soils for each of these herbicides, suggesting that OM is the main factor, which dominates in the adsorption process of these triazine herbicides.

Photodegradation of triazine herbicides in aqueous solutions and natural waters.

The photodegradation of three triazines, atrazine, simazine, and prometryn, in aqueous solutions and natural waters using UV radiation (lambda > 290 nm) has been studied. Experimental results showed that the dark reactions were negligible. The rate of photodecomposition in aqueous solutions depends on the nature of the triazines and follows first-order kinetics. In the case of the use of hydrogen peroxide and UV radiation, a synergistic effect was observed. The number of photodegradation products detected, using FIA/MS and FIA/MS/MS techniques, suggests the existence of various degradation routes resulting in complex and interconnected pathways.

Coupled effects of treated effluent irrigation and wetting-drying cycles on transport of triazines through unsaturated soil columns.

The physical and chemical parameters controlling the movement of atrazine (6-chloro-N2-ethyl-N4-isopropyl-l,3,5-triazine-2,4-diamine; 98.8%) and prometryn [N,N'-bis(1-methylethyl)-6-(methylthio)-l,3,5triazine-2,4-diamine; 99.5%] were investigated in columns infiltrated with treated effluent under unsaturated transient conditions and subjected to drying events at 22 or 60 degrees C followed by rewetting. Three soils varying in soil pH and texture and three solutions were used. The infiltrating solutions consisted of either a CaCl2 matrix (CC), a swine waste-derived lagoon effluent (SW), or a simulated buffer solution (SB) representative of the element composition and pH of the SW but with no dissolved organic matter. Several parameters were monitored including leachate triazine concentrations, pH, dissolved organic carbon (DOC), inorganic carbon, and flow rates. Compared with CC, application of SW and SB increased column leachate pH, enhanced dissolution of organic carbon and particle dispersion, and decreased average flow rates, which allowed for increased desorption time. The coupled effect of these processes enhanced movement of triazines in some cases, with SW generally having the greatest effect. The individual effect of increased pH was more pronounced for prometryn (pKa=4.05) versus atrazine (pKa=1.66), and most dramatic for the soil with the lowest initial pH. High-temperature drying, which simulated intensive evaporation, further enhanced the dissolution of soil organic matter and the reduction in leachate flow rates with SW and SB applications; however, the net effect under the experimental conditions employed varied with soil type. Relative to low-temperature drying, high-temperature drying in the silty clay loam-packed columns reduced pesticide migration.

Sorption and desorption kinetics of diuron, fluometuron, prometryn and pyrithiobac sodium in soils.

The sorption and desorption characteristics of four herbicides (diuron, fluometuron, prometryn and pyrithiobac-sodium) in three different cotton growing soils of Australia was investigated. Kinetics and equilibrium sorption and desorption isotherms were determined using the batch equilibrium technique. Sorption was rapid (> 80% in 2 h) and sorption equilibrium was achieved within a short period of time (ca 4 h) for all herbicides. Sorption isotherms of the four herbicides were described by Freundlich equation with an r2 value > 0.98. The herbicide sorption as measured by the distribution coefficient (Kd) values ranged from 3.24 to 5.71 L/kg for diuron, 0.44 to 1.13 L/kg for fluometuron, 1.78 to 6.04 L/kg for prometryn and 0.22 to 0.59 L/kg for pyrithiobac-sodium. Sorption of herbicides was higher in the Moree soil than in Narrabri and Wee Waa soils. When the Kd values were normalised to organic carbon content of the soils (Koc), it suggested that the affinity of the herbicides to the organic carbon increased in the order: pyrithiobac-sodium < fluometuron < prometryn < or = diuron. The desorption isotherms were also adequately described by the Freundlich equation. For desorption, all herbicides exhibited hysteresis and the hysteresis was stronger for highly sorbed herbicides (diuron and prometryn) than the weakly sorbed herbicides (fluometuron and pyrithiobac-sodium). Hysteresis was also quantified as the percentage of sorbed herbicides which is not released during the desorption step (omega = [nad/nde - 1] x 100). Soil type and initial concentration had significant effect on omega. The effect of sorption and desorption properties of these four herbicides on the off-site transport to contaminate surface and groundwater are also discussed in this paper.