Kinetic and Mechanistic Modelling of Pyrimethanil Fungicide Adsorption onto Soils of Varying Physico-chemical Properties.

Pesticide transport in the environment is impacted by the kinetics of its adsorption onto soil. The adsorption kinetics of pyrimethanil was investigated in ten soil samples of varying physicochemical properties. The highest adsorption was in the soil having the maximum silt and CaCO3 contents, pH and electrical conductance but the lowest amorphous Fe oxides and CaCl2 extractable Mn. Pseudo-second order kinetics and intra-particle diffusion model best accounted the adsorption kinetics of pyrimethanil. The equilibrium adsorption estimated by pseudo-second order kinetics (q02) was significantly and positively correlated with CaCl2 extractable Cu content (r = 0.709) while rate coefficient (k02) had a negative correlation with crystalline iron oxides content (r = -0.675). The intra-particle diffusion coefficient (ki.d.) had inverse relationship with CaCl2 extractable Mn content in soils (r = -0.689). FTIR spectra showed a significant interaction of pyrimethanil with micronutrient cations. Adsorption kinetic parameters of pyrimethanil could be successfully predicted by soil properties. The findings may help to evolve fungicide management decisions.

Simple adsorptive removal of crystal violet, a triarylmethane dye, from synthetic wastewater using Fe (III)-treated pine needle biochar.

Untreated and Fe (III)-treated pine needle biochar (PNB) were evaluated at different pH for the removal of toxic crystal violet (CV) dye from synthetic wastewaters. Adsorption kinetics followed the pseudo-first-order kinetics involving intra-particle diffusion process. The adsorption rate constant increased with Fe treatment of PNB especially at pH 7.0. Adsorption data of CV conformed well to Freundlich adsorption isotherms and both adsorption capacity (ln K) and order of adsorption (1/n) of CV were nearly doubled with Fe (III) treatment of PNB at pH 7.0. Desorption of adsorbed CV from both untreated and Fe (III)-treated PNB could be accounted satisfactorily by third-degree polynomial equations. An increase in ionic strength and temperature enhanced dye adsorption onto untreated and Fe (III)-treated PNB. Adsorption of CV was an endothermic and spontaneous reaction with an increase in entropy of the system. FTIR spectra revealed that C = O of carboxylic acid aryls and C = O and C-O-C in lignin residues of PNB reacted with Fe (III) besides the formation of some iron oxyhydroxide minerals. The changes in FTIR confirmed the possible bonding of positively charged moiety of CV with the untreated and Fe-treated PNB. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) revealed the porous surfaces of PNB with clear accumulation of Fe (III) after treatment and deposition of CV dye on surfaces and pores of PNB. Iron (III)-treated PNB at pH 7.0 can serve as an ecofriendly and cost-effective adsorbent for the efficient removal of CV dye from wastewaters.

An insight into the sorption kinetics of boscalid onto soils: Effect of general soil properties.

Boscalid is a carboxamide fungicide widely used for crop protection, however owing to its high persistence, it is detected in high concentrations in various environments. Since the fate of such xenobiotics is strongly influenced by its interaction with soil components a better understanding of its adsorption onto soils of varying properties could allow the adjustment of its application in a given agro-ecological region to limit the consequent environmental burden. The present investigation was carried out to examine the kinetics of boscalid adsorption onto ten Indian soils of varying physico-chemical properties. Kinetic data of boscalid for all soils under investigation fitted well to both pseudo-first-order and pseudo-second-order kinetic models. However, based on the standard error of estimate (S.E.est.) values pseudo-first-order model was better for all soil samples, except one soil which had the lowest readily oxidizable organic carbon. Adsorption of boscalid by soils appeared to be controlled by the diffusion-chemisorption process while for soils especially rich in readily oxidizable organic carbon or clay + silt content the intra-particle diffusion process seemed to be more important. Stepwise regression of kinetic parameters on soil properties revealed that the inclusion of a set of some soil properties could help better prediction of adsorbed amounts of boscalid and kinetic constants. These findings may help assess the fate and possible transport of boscalid fungicide in different soils.

Evaluation of three novel soil bacterial strains for efficient biodegradation of persistent boscalid fungicide: Kinetics and identification of microbial biodegradation intermediates.

Boscalid, a new fungicide of anilide group, is intended to prevent and treat grey mould (Botrytis cinerea), primarily in vines and other fruit plants. In many regions, its long half-life in soil and water poses a serious environmental threat. Boscalid is reported to be toxic to a variety of aquatic organisms. One of the best ways to lessen the amount of boscalid that gets into surface and ground waters is to reduce its concentration in soil. Soil microbes are crucial for the degradation of organic pollutants including pesticides. The present study reports the assessment of three novel soil bacterial strains isolated from pesticide-contaminated soil of Crop research centre, Pantnagar, Uttarakhand, India, which possess boscalid degradation ability. Two of these bacterial isolates could degrade boscalid up to 85-95% within 36 h of incubation period under shaking conditions in the minimal medium. The growth pattern of degrading bacterial isolates was monitored by recording the optical density (OD) of bacterial suspension using an ultra violet (UV)-visible spectrophotometer, whereas the concentration of primary boscalid was recorded by High-Performance Liquid Chromatography (HPLC-UV). A linear relationship was observed between the bacterial growth and the decrease in the residual concentration of boscalid. The concentration of boscalid during incubation with different bacterial strains could be best predicted by a second-order polynomial relationship with time and OD of the suspension as independent variables. Three degradation intermediates of boscalid namely, N-(1,1'-biphenyl-2-yl)pyridine-3-carboxamide (C18H14N2O, N-{[1,1'-biphenyl]-2-yl}-2-chloropyridine-3-carboxamide (C18H13N2OCl), and N-{[4'-chloro-1,1'-biphenyl]-2-yl}-2-chloropyridine ({C17H11NCl2}OH) were identified by the liquid chromatography-mass spectrometry (LC-MS) analysis of biodegraded samples. The biodegradation of boscalid through bacterial isolates seemed to be an economical and eco-friendly method for degrading a highly persistent boscalid fungicide.

Method validation for simultaneous determination of four neonicotinoids in vegetables by liquid chromatography.

Pesticides are widely employed to boost the production of vegetable crops, but their indiscriminate application leaves residue in the crops for long, even after harvesting. Among pesticides, neonicotinoids are the most commonly applied group of insecticides which are used on vegetables to defend against a variety of sucking pests. The purpose of this study was to validate an analytical approach focused on QuEChERS extraction for the validation and simultaneous determination of residues of four neonicotinoids (imidacloprid, clothianidin, acetamiprid and thiamethoxam) in six diverse crops such as cucumber, brinjal, tomato, beans, cabbage, and cauliflower. Insecticides were quantified using high-performance liquid chromatography (HPLC) fitted with a UV-Vis detector. Specificity, linearity, precision, accuracy, limit of detection, and the limit of quantification were all considered for validation. The fortification of the vegetables was done at three different levels (0.2, 0.3 and 0.5 µg mL-1), for confirming the validity of the method adopted. The results demonstrated adequate recoveries ranging from 77.5 to 96.4% and good accuracy (RSDs between 0.3 and 8.9%). For all the insecticides, the approach had good linearity with R2 ≥ 0.99. The limit of detection (LOD) and the limit quantification (LOQ) levels of all the four analytes were 0.05 µg mL-1 and 0.2 µg mL-1, respectively. The validation characteristics of the devised method are satisfactory in terms of specificity, linearity, precision, accuracy, limit of detection and limit of quantification and thus can be successfully employed for simultaneous determination of the neonicotinoids.

Method validation for determination of nine pesticides in okra and their mitigation using different solutions.

In this paper we optimized QuEChERS method for extraction of nine pesticides viz. acephate, acetamiprid, chlorpyrifos, cypermethrin, imidacloprid, thiamethoxam, profenofos (insecticides), carbendazim and tebuconazole (fungicides) and performed their quantitative estimation in okra crop by HPLC-UV and GC-ECD. Decontamination treatments namely washing with running tap water, soaking in lukewarm water (50-60°C), soaking in solutions of 1% NaCl, 5% NaHCO3, 2% CH3COOH, 0.01% KMnO4 and three commercial formulations were also done for ten minutes every time, to calculate the extent of pesticide removal from okra. Results revealed that the proposed extraction method was efficient, inexpensive, accurate, rapid and precise and can suitably be used for the simultaneous quantitative determination of the above pesticides. The standard curve was linear over the concentration range of 0.05-5µg g-1 with R2 close to one (0.999). Soaking of okra in 2% acetic acid and then washing proved as the best decontamination treatments for all the pesticides. It showed the highest relative decontaminating capacity in comparison to the other solutions tested. Since the pesticide residues are usually present in higher amount in vegetables being consumed, it is of utmost importance to keep an eye over the use of pesticides to protect the crops.

Efficacy of Different Decontamination Processes in Mitigation of Pesticide Residues from Chili Crop.

ABSTRACT: This study was conducted to evaluate the efficacy of seven decontamination processes in reducing the pesticide mixture load of six insecticides (quinalphos, profenophos, ethion, lambda-cyhalothrin, imidacloprid, and acetamiprid) from chili (Capsicum annuum L.). In the control treatment, the pesticide residues were extracted without following any decontamination procedure. The extraction of the insecticides from chili was initiated after 48 h of pesticide mixture spray and was done using the QuEChERS (quick, easy, cheap, effective, rugged, and safe) method. The quantitative analysis of four insecticides, namely quinalphos, profenophos, ethion, and lambda-cyhalothrin, was done by coupled gas chromatography-electron capture detection and that of imidacloprid and acetamiprid by high-performance liquid chromatography-UV detection. The results depicted reduction of pesticide residues in all the decontamination treatments compared with the control, although it varied for different insecticides. Solutions of 1 and 5% NaCl and 5% CH3COOH served as efficient decontaminants in removal of quinalphos, profenophos, ethion, and lambda-cyhalothrin residues from chili to ca. 90%, whereas for imidacloprid and acetamiprid there was a mild decontamination only (33.33 to 52.44%). The solutions of 5% NaHCO3 and 0.01% KMnO4 were effective only in removing lambda-cyhalothrin residues from the chili crop, but for all other pesticides the decontamination was not much pronounced.

Effect of iron treatment and equilibrium pH on the kinetics of removal of some substituted phenols from synthetic wastewater onto Nostoc sp. biomass.

Substituted phenols, such as 4-Nitrophenol (4-NP) and 2,4-Dichlorophenol (2,4-DCP), that are present in industrial wastewaters are considered as priority pollutants due to their toxic effects. Their removal by biosorption presents an eco-friendly, cost-effective method. The kinetics of removal of 4-NP and 2,4-DCP by untreated Nostoc sp. (UNB) and Fe-treated Nostoc sp. biomass (FNB) were studied at three different pH (4.0, 7.0 and 9.0). The highest sorption of both phenols (2.28 mg 4-NP and 1.51 mg 2,4-DCP g-1) coupled with the lowest cumulative percentage desorption was recorded with FNB at pH 7.0. The sorption of both phenols by UNB and FNB was best accounted for by pseudo-second-order kinetics. Compared to UNB, FNB had significantly higher equilibrium sorption capacities for both phenols at all the three pH values and also higher sorption rate constants of 4-NP at pH 4 and 9 and of 2,4-DCP at pH 4 and 7. The Fourier transform infrared spectroscopy (FTIR) analysis showed that -OH and COO- groups of UNB interacted with Fe+3. The sorption of 4-NP and 2,4-DCP on UNB was likely through H-bonding/structural cation bridging with the phenolic group, while their sorption onto FNB appeared to be a complexation reaction with very low reversibility.

Persistence Behavior of Penoxsulam Herbicide in Two Different Soils.

Penoxsulam, a new post emergence herbicide is suspected to be toxic to aquatic organisms, crop plants and also to soil microbial community even at low concentrations. Laboratory studies were therefore performed to examine the persistence of, penoxsulam in two different soils at two application rates (0.5 and 1.0 µg g-1). The study revealed that the dissipation followed the first order kinetics with a half life of 3.48 and 3.57 days at 0.5 µg g-1 and 4.1 and 4.17 days at 1.0 µg g-1 fortification rate. Both microbial- and photo-degradation seemed to play a vital role in the dissipation of penoxsulam. The results of LC MS/MS revealed that one minor and five major metabolites were formed during the degradation process of the herbicide and the cleavage of sulfonamide bridge served as the major metabolic pathway.

Immobilization of ß-glucosidase onto silicon oxide nanoparticles and augment of phenolics in sugarcane juice.

Purified ß-glucosidase was immobilized on SiO2 nanoparticles with 52 % efficiency and 14.1 % yield. It had a temperature optima at 60 °C and pH optima of 5.0. Immobilized enzyme was fairly stable at 60-70 °C. After immobilization, the Km value of ß-glucosidase for p-nitrophenyl-ß-d-glucopyranoside (pNPG) increased from 0.9 to 1.074 mM and Vmax decreased from 3.5 to 1.513 U/mg. The immobilized enzyme showed improved storage stability at temperature 4 and 25 °C and was reusable for up to ten cycles with 70 % residual activity in pNPG and 60 % residual activity in sugarcane juice treatment. Sugarcane juice density, viscosity; surface tension etc. changed after treatment with immobilized ß-glucosidase. ß-Glucosidase treated sugarcane juice showed higher phenolics than untreated sugarcane juice. Caffeic acid which was absent in juice, was detected in ß-glucosidase treated juice at a concentration of about 1 mg/L.

Novel pathway of cypermethrin biodegradation in a Bacillus sp. strain SG2 isolated from cypermethrin-contaminated agriculture field.

Pesticides belonging to pyrethroid group are widely used in agricultural fields to check pest infestation in different crops for enhanced food production. In spite of beneficial effects, non-judicious use of pesticides imposes harmful effect on human health as their residues reach different food materials and ground water via leaching, percolation and bioaccumulation. Looking into the potential of microbial degradation of toxic compounds under natural environment, a cypermethrin-degrading Bacillus sp. was isolated from pesticide-contaminated soil of a rice field of Distt. Udham Singh Nagar, Uttarakhand, India. The bacteria degraded the compound up to 81.6 % within 15 days under standard growth conditions (temperature 32 °C pH 7 and shaking at 116 rpm) in minimal medium. Analysis of intermediate compounds of biodegraded cypermethrin revealed that the bacteria opted a new pathway for cypermethrin degradation. GC-MS analysis of biodegraded cypermethrin showed the presence of 4-propylbenzoate, 4-propylbenzaldehyde, phenol M-tert-butyl and 1-dodecanol, etc. which was not reported earlier in cypermethrin metabolism; hence a novel biodegradation pathway of cypermethrin with Bacillus sp. strain SG2 is proposed in this study.

Differential expression and characterization of cypermethrin-degrading potential proteins in Bacillus thuringiensis strain, SG4.

A cypermethrin-degrading bacterium (SG4) was isolated from the pesticide-contaminated soil in the agricultural field of the crop research centre of the University, and characterized as Bacillus thuringiensis strain, SG4. The bacterium degraded 78.9 % of cypermethrin (50 ppm) in 15 days when grown in a minimal medium. To understand the functional proteins of cypermethrin degradation in Bacillus thuringiensis strain SG4, a comparative proteomic analysis was performed in the presence/absence of cypermethrin after 5 days of incubation in minimal medium. More than 450 spots corresponding to different proteins were recorded by 2D electrophoresis. We report expression of 223 and 250 unique proteins under normal and induced conditions (cypermethrin stress), respectively. Identified proteins were categorized into different functional groups on the basis of their biological functions, viz., catabolic enzymes, translational and stress proteins, etc. Characterization of cypermethrin-specific proteins in a bacterial strain will help in biodegradation practices in situ.

Sorption-desorption of fipronil in some soils, as influenced by ionic strength, pH and temperature.

BACKGROUND: The sorption-desorpion of fipronil insecticide is influenced by soil properties and variables such as pH, ionic strength, temperature, etc. A better understanding of soil properties and these variables in sorption-desorption processes by quantification of fipronil using liquid chromatography may help to optimise suitable soil management to reduce contamination of surface and groundwaters. In the present investigation, the sorption-desorption of fipronil was studied in some soils at varying concentrations, ionic strengths, temperatures and pH values, and IR specta of fipronil sorbed onto soils were studied. RESULT: The sorption of fipronil onto soils conformed to the Freundlich isotherm model. The sorption-desorption of fipronil varied with ionic strength in each of the soils. Sorption decreased but desorption increased with temperature. Sorption did not change with increasing pH, but for desorption there was no correlation. The cumulative desorption of fipronil from soil was significantly and inversely related to soil organic carbon content. IR spectra of sorbed fipronil showed the involvement of amino, nitrile, sulfone, chloro and fluoro groups and the pyrazole nucleus of the fipronil molecule. CONCLUSION: The sorption of fipronil onto soils appeared to be a physical process with the involvement of hydrogen bonding. An increase in soil organic carbon may help to reduce desorption of fipronil. High-temperature regimes are more conducive to the desorption. © 2015 Society of Chemical Industry.

Sorption kinetics of fipronil on soils.

Sorption kinetics of fipronil was studied on five soils of varying physico-chemical properties by batch equilibration method. Fipronil sorption on soils conformed to pseudo-second order kinetics and both the initial uptake rate and rate constant had a significant and positive correlation with clay content. The sorption kinetics of fipronil onto soils could be explained by intraparticle diffusion model consisting of an initial faster step followed by later slower step. The intraparticle diffusion rate constants for the initial faster and later slower step showed a significant and positive correlation with clay content (r = 0.978, significant at p ≤ 0.01) and soil electrical conductance (r = 0.901, significant at p ≤ 0.05), respectively.

Kinetics of sorption-desorption of benfuracarb insecticide in mollisols.

BACKGROUND: Sorption-desorption processes govern the movement of pesticides in soil. These processes determine the potential hazard of the pesticide in a given environment for groundwater contamination and need to be investigated. RESULTS: In the present study, sorption-desorption processes of benfuracarb were investigated using a batch method in two mollisols. The kinetics of benfuracarb sorption in mollisols conformed to two-compartment (1 + 1) first-order kinetics. The fast sorption rate constant was about 3 times higher for silt loam than for loam soil. However, the slow sorption rate constants were statistically similar for both soils. The concentration-dependent sorption-desorption isotherms of benfuracarb could not closely conform to the Freundlich isotherm in mollisols of high organic C content. The computed values of both the sorption (log K) and desorption (log K') capacities were higher for silt loam than for loam soil. The desorption index (n'/n) values in the range 30.0-41.3 indicated poor reversibility of sorbed benfuracarb in mollisols. CONCLUSION: In view of the strong sorption of benfuracarb in mollisols with only partial desorption, the possibility of the leaching of soil-applied benfuracarb to contaminate groundwaters appears to be low.

Fate of benfuracarb insecticide in mollisols and brinjal crop.

The fate of benfuracarb was studied under field conditions in brinjal fruits and soil following foliar spray application at 0.25 and 0.50 microg g(-1) by HPLC. At 0.25 microg g(-1), benfuracarb persisted up to 7 days both in soil and brinjal but at 0.50 microg g(-1), benfuracarb residues persisted up to 10 and 12 days in soil and brinjal fruits, respectively. The persistence of benfuracarb residues, both in soil and brinjal, followed first-order kinetics. The half-life values of benfuracarb in soil and brinjal fruit were found to be 3.54 and 3.90 days at 0.25 microg g(-1) and 3.75 and 4.73 days at 0.50 microg g(-1), respectively.

Persistence behavior of Fantac biostimulant in chili and soil under subtropical conditions.

The persistence of the biostimulant Fantac (N-ATCA) in chili and soil was evaluated at two application rates (0.25 and 0.50 microg g(-1)) by high-performance liquid chromatography. At 0.25 microg g(-1) Fantac persisted up to 3 days in soil and 5 days in chili. However, at 0.50 microg g(-1) Fantac residues persisted up to 5 days both in soil and chili. The dissipation of the biostimulant from soil and chili appeared to occur in a single phase and conformed to first-order kinetics. Half-lives of Fantac in soil and chili were calculated.

Dissipation behaviour of spinosad insecticide in soil, cabbage and cauliflower under subtropical conditions.

BACKGROUND: Pesticides used on cauliflower and cabbage, which are important vegetable crops for India, must be investigated for the persistence and magnitude of their residues in the crops and soil to ensure human and environmental safety. The behaviour of spinosad, an effective insecticide with a favourable environmental profile, was investigated in field trials under subhumid and subtropical conditions. RESULTS: The persistence of spinosad in soil, cabbage and cauliflower was evaluated at two application rates (17.5 and 35.0 g ha(-1)) by high-performance liquid chromatography (HPLC). At 17.5 g ha(-1), spinosad persisted up to 7 days in soil, cabbage and cauliflower. However, at 35.0 g ha(-1), spinosad residues persisted up to 7 days in soil and 10 days in cabbage and cauliflower. CONCLUSION: The dissipation of the insecticide from soil, cabbage and cauliflower appeared to occur in a single phase and conformed to first-order kinetics. The half-lives of spinosad residues in cabbage, cauliflower and soil were calculated as 1.5, 2.8 and 2.8 days respectively for the 17.5 g ha(-1) treatment, and as 2.6, 2.0 and 2.0 days for the 35 g ha(-1) treatment.