Basic Pesticides Research Articles

Guidelines to Study the Adsorption of Pesticides onto Clay Minerals Aiming at a Straightforward Evaluation of Their Removal Performance

Natural and modified clay minerals have been extensively used for the adsorption/desorption of organic substances, especially pesticides, from waters and wastewater, aiming at pollution control and more efficient use of the herbicides through controlled release. While natural clay minerals efficiently remove organic cations such as paraquat and diquat, the adsorption of anionic or neutral species demands surface chemical modification with, for instance, quaternary ammonium salts containing long alkyl chains. Basic pesticides, on the other hand, are better absorbed in clay minerals modified with polycations. Kinetic studies and adsorption/desorption isotherms provide the parameters needed to evaluate the clay mineral’s adsorptive performance towards the pollutant target. However, the direct comparison of these parameters is complicated because the experimental conditions, the analytical techniques, the kinetic and isotherm models, and the numerical fitting method differ among the various studies. The free-energy-related Langmuir constant depends on the degree of site occupation; that is, it depends on the concentration window used to construct the adsorption isotherm and, consequently, on the analytical technique used to quantify the free concentrations. This paper reviews pesticides’ adsorption on natural and modified clay minerals and proposes guidelines for designing batch adsorption/desorption studies to obtain easily comparable and meaningful adsorption parameters. Articles should clearly describe the experimental conditions such as temperature, contact time, total concentration window, the solution to adsorbent ratio, the analytical technique, and its detection and quantification limits, besides the fitting models. Research should also evaluate the competitive effects of humic substances, colloidal inorganic particles, and ionic strength to emulate real-world adsorption experiments.

Simultaneous magnetic solid phase extraction of acidic and basic pesticides using triazine-based polymeric network modified magnetic nanoparticles/graphene oxide nanocomposite in water and food samples

In this work, a triazine-based polymeric network modified magnetic nanoparticles/graphene oxide (TPN/Fe3O4 NPs/GO) nanocomposite was successfully synthesized and used as an effective nanosorbent in simultaneous magnetic solid phase extraction of basic and acidic pesticides from food and water samples by HPLC-UV. Imidacloprid (IMI) and 2,4-dichlorophenoxyacetic acid (2,4-D) were selected as model basic and acidic pesticides, respectively. The synthesized TPN/Fe3O4/GO was characterized by field emission-scanning electron microscopy (FE-SEM), Fourier transform-infrared spectroscopy (FT-IR), vibrating sample magnetometry (VSM) and thermogravimetric analysis (TGA). Some parameters that affect the extraction efficiency such as pH of solution, sorbent amount, salt amount, extraction time, desorption solvent volume and desorption time were optimized by central composite design. However, type of desorption solvent and sample volume were optimized by one variable at a time method. Under optimum conditions, the calibration curve was linear in the range of 0.5–500 μg L−1 and 5.0–500 μg L−1 for IMI and 2,4-D, respectively. The limits of detection (LODs) for IMI and 2,4-D were 0.17 and 1.7 μg L−1, respectively. Also, the limits of quantification (LOQs) for IMI and 2,4-D were 0.5 and 5.0 μg L−1, respectively. The relative standard deviations (RSDs) were <8.6% (n = 6). The proposed method was successfully applied for extraction and determination of IMI and 2,4-D in cucumber, tomato and water samples and satisfactory results (recoveries ≥90%) were obtained.

Investigation of the Soil Sorption of Neutral and Basic Pesticides

Adsorption of six neutral (chlorpyrifos, α-endosulfan, fenthion, parathion, parathion metyl, and cis permethrin) and six basic (pirimicarb, prochloraz, prometryn, pirimiphos ethyl, quinoxyfen, and triadimefon) pesticides was measured in ten natural soils in order to unravel the parameters influencing soil sorption. Linear regression confirmed that organic carbon content of soil is the determinant factor of soil sorption along with a secondary role of clay in the case of basic pesticides. Concerning pesticides themselves, their potential to be absorbed is governed by hydrophobic, electrostatic, and polar interactions. Electrostatic interactions can be expressed by considering the molecular fraction of positively charged species (F+). The combination of these parameters led to good prediction models, where the two expressions of lipophilicity, octanol-water partition (logP) and distribution coefficient (logD), showed similar performance. Finally, the role of electrostatic interactions to soil sorption and their successful expression by F+ parameter was further confirmed using artificial adjustment of the acidity of one soil at different pH values not covered by the natural acidity of the investigated soils.

Simultaneous determination of neutral, basic and acidic pesticides in aquatic environmental matrices by solid-phase extraction and liquid chromatography electrospray ionization mass spectrometry

Simultaneous determination of a wide variety of pesticides and herbicides in environmental waters by liquid chromatography electrospray-ionization mass spectrometry (LC-ESI-MS) has been a challenging task due to matrix interferences. In this study, deuterated analogues and graphitized carbon black (GCB) solid-phase extraction (SPE) were investigated to compensate for and eliminate sample matrix interferences. Significant ion suppression and enhancement were observed when deuterated pesticides were used as internal standards. GCB cartridges can well retain neutral, basic and acidic pesticides and herbicides but the complete elution requires a combination of different characteristics of the solvent. A new procedure for SPE extraction and sample preparation was developed for simultaneous determination of neutral, basic pesticides and phenoxy acid herbicides in environmental waters by LC-ESI-MS. The proposed method was validated by examining the limit of detection and range of linearity and testing river water samples. The limit of detection ranged between 0.005 and 2 μg L−1 and the correlation coefficient for 5–5000 μg L−1 calibration standards was greater than 0.995. The recoveries of 79–121% from river water samples and relative standard deviations of 2–21% were obtained at the concentrations of 0.4–500 μg L−1 for 37 pesticides and herbicides.

Extraction and stability of pesticide multiresidues from natural water on a mixed-mode admicellar sorbent

The suitability of a mixed-mode sorbent made up of admicelles of sodium dodecyl sulphate (SDS) and tetrabutylammonium (TBA) to extract and preserve pesticides from river and underground water was assessed. Pesticides belonging to different structural groups (i.e. triazines, carbamates, phenylureas, anilides, chloroacetanilides, organophosphorus and phenoxyacids), most of them well known by their instability, were selected for this purpose. Extraction of pesticides with the admicellar sorbent was optimized. Percolation of 250mL of sample through the SPE cartridge, elution with 1mL of methanol (neutral and basic pesticides) or 2mL of 0.3M NaOH:methanol (90:10, v/v) (acidic pesticides) and direct analysis of the extract by liquid chromatography/UV detection, permitted to obtain method detection limits in the range 2–60ngL−1. Their degradation on the SPE cartridges after sample percolation was investigated under a variety of experimental conditions, namely darkness, natural illumination and different temperatures (room temperature, 4°C and −20°C) for 3 months. Under darkness, most of pesticides were stable for 1 month at room temperature and 3 months at 4°C. Only atriazine and clorfenvinfos did not follow this general behaviour. No influence of matrix components on the stabilization of pesticides in the admicellar sorbent was observed. The stabilizing capability of surfactant aggregates surpassed that of C18 and black carbon and was similar to that obtained in some polymeric materials, which have the disadvantage of requiring large volumes of solvents for analyte elution. The stabilization of pesticides on the admicellar sorbent was long enough to permit easy shipping and storage of the cartridges in monitorization campaigns.

Semi-automated liquid chromatography–mass spectrometry (LC–MS/MS) method for basic pesticides in wastewater effluents

Effluent from wastewater treatment plants have been identified as an important source of micro-organic contaminants in the environment. An online high-performance liquid chromatography-heated electrospray ionization tandem mass spectrometric method was developed and validated for the determination of basic pesticides in effluent wastewaters. Most available methods for pesticide analysis of wastewater samples are time-consuming, require complex clean-up steps and are difficult to automate. The method developed used a simple solid-phase extraction clean-up for salt and lipid reduction. On-line sample pre-concentration was performed using a reversed phase (C(18)) column, and analytes were separated by back-flushing onto an analytical column (C(8)) with detection using QqQ MS. An option to increase MS resolution was exploited to minimize interference from endogenous compounds in the matrix. A better than unit mass resolution was used (Q1 full width half maximum (FWHM) = 0.2Da and Q3 FWHM = 0.7Da), which was as rugged as a unit resolution method, and improved signal/noise and better detection limits were achieved for the targeted basic pesticides. This method was applied to the determination of 11 pesticides, including methoxytriazine, chlorotriazines, chloroacetanilides, phenylurea and carbamate pesticides. The percentage recovery values for these pesticides using the online trapping column were within the range, 73-95%, with relative standard deviation (RSD) values <8.9%. The highest concentrations of these pesticides in wastewater effluents in County Cork, Ireland, were simazine (0.51μg/L), prometon (0.14μg/L), diuron (0.21μg/L) and atrazine (0.19μg/L).

QuEChERS: possibilidades e tendências no preparo de amostra para determinação multirresíduo de pesticidas em alimentos

This paper presents an updated overview of the QuEChERS multiresidue extraction method that involves initial extraction in acetonitrile, an extraction/partition step after the addition of salt, and a clean-up step utilizing dispersive solid phase extraction. QuEChERS method is nowadays the most applied extraction method for the determination of pesticide residues in food samples, providing acceptable accuracy and precision for acidic, neutral and basic pesticides.

QuEChERS: um método moderno de preparo de amostra para determinação multirresíduo de pesticidas em alimentos por métodos cromatográficos acoplados à espectrometria de massas

This review attempts to provide an updated overview of the Quick, Easy, Cheap, Effective, Ruged and Safe (QuEChERS) multiresidue extraction method, that involves initial extraction in acetonitrile, an extraction/partition step after the addition of salt, and a cleanup step utilizing dispersive solid phase extraction. QuEChERS method is nowadays the most applied extraction method for the determination of pesticide residues in food samples, providing acceptable recoveries for acidic, neutral and basic pesticides. Several applications for various food matrices (fruits, vegetables, cereals and others) in combination with chromatographic mass spectrometry analysis were presented.

Analysis of pesticide residues in fruit and vegetables with ethyl acetate extraction using gas and liquid chromatography with tandem mass spectrometric detection

A multiresidue method based on extraction with ethyl acetate has been used at the Swedish National Food Administration since 1989 to monitor pesticide residues in fruit and vegetables. The method has been continuously adjusted, resulting in simple and quick analyses of pesticide residues. To recover basic pesticides, the addition of an alkali is necessary. The addition of sodium hydrogen carbonate has been shown to recover all pesticides effectively without any degradation. The liquid chromatography (LC) with tandem mass spectrometry (MS/MS) technique has made it possible to analyse more polar pesticides and to replace many single methods. The latest development in the multiresidue method, comprising the use of gas chromatography (GC) with MS/MS, has further improved the analysis by replacing the conventional GC detectors. The need for cleanup has been reduced or eliminated entirely. Consequently, the method has been simplified in a way that makes it possible to recover all included analytes in many different matrices in one single extraction and to detect them either with GC-MS/MS or with LC-MS/MS.

Factors Influencing Degradation of Pesticides in Soil

Degradation and sorption of six acidic pesticides (2,4-D, dicamba, fluroxypyr, fluazifop-P, metsulfuron-methyl, and flupyrsulfuron-methyl) and four basic pesticides (metribuzin, terbutryn, pirimicarb, and fenpropimorph) were determined in nine temperate soils. Results were submitted to statistical analyses against a wide range of soil and pesticide properties to (i) identify any commonalities in factors influencing rate of degradation and (ii) determine whether there was any link between sorption and degradation processes for the compounds and soils studied. There were some marked differences between the soils in their ability to degrade the different pesticides. The parameters selected to explain variations in degradation rates depended on the soil-pesticide combination. The lack of consistent behavior renders a global approach to prediction of degradation unrealistic. The soil organic carbon content generally had a positive influence on degradation. The relationship between pH and degradation rates depended on the dominant mode of degradation for each pesticide. There were positive relationships between sorption and rate of degradation for metsulfuron-methyl, pirimicarb, and all acidic pesticides considered together (all P < 0.001) and for dicamba and all bases considered together (P < 0.05). No relationship between these processes was observed for the remaining seven individual pesticides.

Prediction of the Adsorption of Ionizable Pesticides in Soils

Adsorption of six acidic and four basic pesticides was measured in nine temperate soils. In general, sorption of acids was weak as compared to bases and followed the order dicamba<metsulfuron-methyl<fluazifop-P<metribuzin<2,4-D<flupyrsulfuron-methyl<fluroxypyr<terbutryn<pirimicarb<fenpropimorph. Adsorption was negatively correlated with soil pH and positively correlated with organic carbon content. Statistical analysis against a wide range of soil and pesticide descriptors was used to identify the best combination of properties that describes the variation in adsorption. A regression equation including Log D (lipophilicity corrected for pH), the soil organic carbon content, and a pesticide descriptor (related to the van der Waals volume) was selected to predict the adsorption of acids (r2=72.1% on an independent dataset). The behavior of bases was more complex, and approaches specific to each compound seem to be required.

Evaluation of Two Fast and Easy Methods for Pesticide Residue Analysis in Fatty Food Matrixes

Two rapid methods of sample preparation and analysis of fatty foods (e.g., milk, eggs, and avocado) were evaluated and compared for 32 pesticide residues representing a wide range of physicochemical properties. One method, dubbed the quick, easy, cheap, effective, rugged, and safe (QuEChERS) method for pesticide residue analysis, entailed extraction of 15 g sample with 15 mL acetonitrile (MeCN) containing 1% acetic acid followed by addition of 6 g anhydrous magnesium sulfate and 1.5 g sodium acetate. After centrifugation, 1 mL of the buffered MeCN extract underwent a cleanup step (in a technique known as dispersive solid-phase extraction) using 50 mg each of C18 and primary secondary amine sorbents plus 150 mg MgSO4. The second method incorporated a form of matrix solid-phase dispersion (MSPD), in which 0.5 g sample plus 2 g C18 and 2 g anhydrous sodium sulfate was mixed in a mortar and pestle and added above a 2 g Florisil column on a vacuum manifold. Then, 5 x 2 mL MeCN was used to elute the pesticide analytes from the sample into a collection tube, and the extract was concentrated to 0.5 mL by evaporation. Extracts in both methods were analyzed concurrently by gas chromatography/mass spectrometry and liquid chromatography/tandem mass spectrometry. The recoveries of semi-polar and polar pesticides were typically 100% in both methods (except that basic pesticides, such as thiabendazole and imazalil, were not recovered in the MSPD method), but recovery of nonpolar pesticides decreased as fat content of the sample increased. This trend was more pronounced in the QuEChERS method, in which case the most lipophilic analyte tested, hexachlorobenzene, gave 27 +/- 1% recovery (n=6) in avocado (15% fat) with a<10 ng/g limit of quantitation.

The pesticide module of the Root Zone Water Quality Model (RZWQM): testing and sensitivity analysis of selected algorithms for pesticide fate and surface runoff.

The Root Zone Water Quality Model (RZWQM) is a one-dimensional, numerical model for simulating water movement and chemical transport under a variety of management and weather scenarios at the field scale. The pesticide module of RZWQM includes detailed algorithms that describe the complex interactions between pesticides and the environment. We have simulated a range of situations with RZWQM, including foliar interception and washoff of a multiply applied insecticide (chlorpyrifos) to growing corn, and herbicides (alachlor, atrazine, flumetsulam) with pH-dependent soil sorption, to examine whether the model appears to generate reasonable results. The model was also tested using chlorpyrifos and flumetsulam for the sensitivity of its predictions of chemical fate and water and pesticide runoff to various input parameters. The model appears to generate reasonable representations of the fate and partitioning of surface- and foliar-applied chemicals, and the sorption of weakly acidic or basic pesticides, processes that are becoming increasingly important for describing adequately the environmental behavior of newer pesticides. However, the kinetic sorption algorithms for charged pesticides appear to be faulty. Of the 29 parameters and variables analyzed, chlorpyrifos half-life, the Freundlich adsorption exponent, the fraction of kinetic sorption sites, air temperature, soil bulk density, soil-water content at 33 kPa suction head and rainfall were most sensitive for predictions of chlorpyrifos residues in soil. The latter three inputs and the saturated hydraulic conductivity of the soil and surface crusts were most sensitive for predictions of surface water runoff and water-phase loss of chlorpyrifos. In addition, predictions of flumetsulam (a weak acid) runoff and dynamics in soil were sensitive to the Freundlich equilibrium adsorption constant, soil pH and its dissociation coefficient.

Multi-Residue Analysis by Liquid Chromatography-Mass Spectrometry Coupling. Application to Drinking and River Waters

The coupling between liquid chromatography and mass spectrometry with an APCI or ESI interface (in positive or negative mode) is used here for multi-residue analyses in natural waters, covering basic and neutral pesticides as well as acid pesticides. The methods developed are applied to drinking and, river waters after the samples are concentrated by liquid-liquid extraction or solid phase extraction on C18 cartridges. Comparisons are made between UV detection and mass spectrometry and between two chromatographic methods for acid substances. The quantitation limits range from 0.01 to 0.1 μg/l according to the substance.

Analysis of pesticides in water with liquid chromatography/atmospheric pressure chemical ionization mass spectrometry

LC/APCI/MS was used as a multiresidue analytical method for determining the thermolabile and/or polar pesticides in treated water and its raw water for water supply, which are not amenable to a routine GC/MS procedure. Of the 31 thermolabile and/or polar pesticides including 14 neutral or basic pesticides and 17 acidic ones used in this study, the detection limits for neutral/basic pesticides detected in positive-ion mode ranged from 10 to 50 μg/l and the limits for acidic pesticides detected in negative-ion mode ranged from 50 to 250 μg/l except for dicamba (500 μg/l) and benazolin (1000 μg/l). The structural information was significantly improved through an in-source collision-induced decomposition (CID) process. The solid-phase extraction (SPE) procedure, which used a special cartridge with its upper part filled with polystyrene/divinylbenzene and the lower part filled with carbon molecular sieve, was developed for extraction of the pesticides. The extraction recoveries of the pesticides were found to be higher than 72% in treated water and 67% in raw water except for thiophanatemethyl and sethoxydim, which were impossible to recover from treated water and raw water and were recovered at a recovery of 60 and 64%, respectively, in distilled water. When the multiresidue analytical method was applied to field analysis for Niigata public waterworks treatment plant in Japan, 8 pesticides were detected in treated water and 10 ones in its raw water.

INTERCALIBRATION OF CHROMATOGRAPHIC METHODS IN MULTIRESIDUE PESTICIDE DETERMINATION

An Ion-Interaction RP-IIR-HPLC method was developed, able to simultaneously separate neutral, basic, and acidic pesticides in a single run. The proposed method was validated by comparison of the results obtained for the same sample by conventional RP-HPLC and GC/MS methods. For this purpose parametric t-, F-, t-paired, and t- for multiple samples and non parametric Wilcoxon matched-pair signed-rank tests were employed. The accuracy of the proposed IIR-RP-HPLC method was evaluated with respect to a lab-made reference sample of spiked tap water.

Simple removal of humic and fulvic acid interferences using polymeric sorbents for the simultaneous solid-phase extraction of polar acidic, neutral and basic pesticides

A styrene-divinylbenzene (St-DVB) sorbent with a specific surface area of ca. 1000 m 2 g −1 packed in a disposable cartridge was investigated and compared with C 18 silicas and other St-DVB polymers such as those entrapped in Empore disks and the LC-grade PRP-1 or PLRP-S with specific surface areas arpund 5000 m 3g −1. A much higher retention was obtained for polar pesticides and acidic pesticides were also retained in their ionic form. The recoveries obtained on percolating 500 ml of drinking water samples at pH 7 spiked with a mixture of seventeen acidic, neutral and basic pesticides through a cartridge packed with 200 mg of SDB-1 sorbent (1060 m 2 g −1) were above 80% for each analyte. Another important result was that humic and fulvic acids were not co-extracted and co-eluted on perculating a sample adjusted to pH 7, so no clean-up was necessary. Application to the analysis of a 500-ml river Seine water sample spiked at 0.1 μg l −1 showed that detection limits in this range can be obtained without any additional clean-up step.

Systematic Determination of 6 Postharvest Pesticides in Imported Citrus Fruits

A systematic method for determination of 6 kinds of pesticides (thiabendazole, benomyl, imazalil, diphenyl, o-phenylphenol and 2, 4-D) in citrus fruits was developed. The pesticides were extracted from the citrus fruits with acetone and the extract was concentrated. After addition of ethyl acetate to the concentrated solution, 2, 4-D and the basic pesticides (thiabendazole, benomyl and imazalil) were partitioned into an alkaline aqueous layer (pH 9) and then an acid layer (0.1N HCl), respectively.The basic pesticides were re-extracted from the acid layer with ethyl acetate at pH 10, and the extract was subjected to high performance liquid chromatography (HPLC) with either UV detection or fluorescence detection. The ethyl acetate layer was concentrated for the determination of diphenyl and o-phenylphenol, and subjected to HPLC with fluorescence detection. 2, 4-D was re-extracted from the alkaline aqueous layer with ethyl ether and methylated, and the resulting derivative was determined by gas chromatography-mass spectrometry with selected ion monitoring after clean-up.The recoveries of 6 pesticides added to citrus fruits at 0.2-1.0μg/g were in the range of 80.5-97.3%. The detection limits were 0.02-0.2μg/g.