Direct electrochemical detection of glyphosate at carbon paste electrode and its determination in samples of milk,orange juice,and agricultural formulation

Abstract

This paper describes a simple, inexpensive, highly sensitive, selective, and efficient electrochemical method to determine glyphosate (GLY) in samples of milk, orange juice, and agricultural formulation. The oxidation reaction on the electrode surface was electrochemically characterised by cyclic voltammetry (CV) and square wave voltammetry (SWV). The investigation of GLY at carbon paste electrode revealed a non-reversible oxidation peak at +0.95 V versus Ag/AgCl, which was used for electrochemical detection of GLY. The operating parameters (pH, frequency, step potential, and amplitude) were optimised in relation to the peak current intensity, and a calibration curve was set up in a concentration range of 4.40?×?10^?8–2.80?×?10^?6 mol L^?1, with a detection limit of 2?×?10^?9 mol L^?1. After calibration curve was plotted, the developed procedure was applied to determine GLY in previously contaminated samples: milk and orange juice, and in a commercial formulation, obtaining recovery values between 98.31% and 103.75%. These results show that the proposed method can be used for GLY quantification in different samples with high sensitivity, specificity, stability, and reproducibility.     

Nylon 6,6 modified screen printed carbon electrodes as electrochemical sensors for rapid chlorothalonil determination in water samples using differential pulse cathodic stripping voltammetry

A newly developed electrochemical sensor for chlorothalonil based on nylon 6,6 film deposited onto screen printed electrode (SPE) with electrochemical modulation of pH at the electrode/solution interface was studied for the first time. Differential pulse cathodic stripping voltammetry (DPCSV) was used to carry out the electrochemical and analytical studies. Experimental parameters such as accumulation potential, initial potential, accumulation time and pH of Britton-Robinson buffer have been optimized. Chlorothalonil gave optimum analytical signal in a medium of 0.04?M Britton-Robinson buffer at pH 6.0. A well-defined reduction peak was observed, at E_p= ?0.851 and ?0.938?V vs. Ag/AgCl (3.0?M KCl) for both bare SPE and modified SPE, respectively. The peak currents of modified SPE were significantly increased as compared to bare SPE. At the modified SPE, a linear relationship between the peak current and chlorothalonil concentration was obtained in the range from 0.1 to 2.8?×?10^?6?M with a detection limit of 1.53?×?10^?8?M (S/N=?3). The practical applicability of the newly developed method has been demonstrated on analyses of real water samples. The newly developed sensor shows good reproducibility with RSD of 3.92%. The nylon 6,6 modified SPE showed itself as promising sensor with good selectivity for chlorothalonil determination.     

A voltammetric screening method to determine ronidazole in bovine meat

Abstract

An original voltammetric screening method, employing glassy carbon electrode (GCE) with the differential-pulse voltammetry technique (DPV), has been developed to determine residues of the anti-parasitic agent Ronidazole (RNZ) in bovine meat. By using cyclic voltammetry (CV), it has been demonstrated that an irreversible cathodic process occurs at approximately ?0.740?V (vs. Ag|AgCl, KCl 3?mol L^?1) in a 0.100?mol L^?1 phosphate buffer at pH 6.5 as supporting electrolyte. Furthermore, the behavior of RNZ in CV indicates the occurrence of a diffusion mass transfer process to the working electrode surface. The RNZ reduction mechanism was proposed as a 6-electron transfer, similar to Metronidazole under the same pH range. Quantification of RNZ and method validation were then carried out by DPV. The relative standard deviation (RSD) were 3.21% for intraday precision of 10 consecutive repetitions and 6.78% for interday precision after five analysis. Limits of detection and quantification were also obtained, and the values were 0.107 and 0.358?mg kg^?1, respectively. The recovery percentage for three different concentrations of RNZ in the bovine meat matrix ranged between 98.1% and 100.3%. The method proved to be efficient for screening RNZ in bovine meat.     

A new strategy for determination of hydroxylamine and phenol in water and waste water samples using modified nanosensor

A carbon paste electrode modified with p-chloranil and carbon nanotubes was used for the sensitive and selective voltammetric determination of hydroxylamine (HX) and phenol (PL). The oxidation of HX at the modified electrode was investigated by cyclic voltammetry (CV), chronoamperommetry, and electrochemical impedance spectroscopy. The values of the catalytic rate constant (k), and diffusion coefficient (D) for HX were calculated. Square wave voltammetric peaks current of HX and PL increased linearly with their concentrations at the ranges of 0.1–172.0 and 5.0–512.0 μmol L^?1, respectively. The detection limits for HX and PL were 0.08 and 2.0 μmol L^?1, respectively. The separation of the anodic peak potentials of HX and PL reached to 0.65 V, using square wave voltammetry. The proposed sensor was successfully applied for the determination of HX and PL in water and wastewater samples.     

Nanocellulosic fiber-modified carbon paste electrode for ultra trace determination of Cd (II) and Pb (II) in aqueous solution

In recent years, increasing awareness of the environmental impact of heavy metals has prompted a demand for monitoring and decontaminating industrial wastes prior to discharging into natural water bodies. This paper describes the preparation and electrochemical application of carbon paste electrode modified with nanocellulosic fibers for the determination of cadmium and lead in water samples using anodic stripping voltammetry. First, cadmium and lead were adsorbed on the carbon paste electrode surface at open circuit potential, followed by anodic stripping voltammetric scan from -1 to 0 V. Different factors affecting sensitivity and precision of the electrode, including accumulating solvent, pH of the accumulating solvent, accumulation time, supporting electrolyte, and scan rate were investigated. The proposed method was also applied to the determination of Cd (II) and Pb (II) in the presence of other interfering metal ions and cetyl trimethyl ammonium bromide, sodium dodecyl sulfate, and Triton X-100 as a representative of cationic, anionic, and neutral surfactants. Linear calibration curves were obtained in the concentration ranges of 150–650 μg?L^?1 and 80–300 μg?L^?1, respectively, for cadmium and lead at an accumulated time of 10 min with limits of detection 88 and 33 μg?L^?1. Optimized working conditions are defined as acetate buffer of pH?5 as accumulating solvent, hydrochloric acid as supporting electrolyte, and scan rate 50 mV/s. This technique does not use mercury and therefore has a positive environmental benefit. The method is reasonably sensitive and selective and has been successfully applied to the determination of trace amounts of Cd (II) and Pb (II) in water samples.     

Selective sensing of mercury(II) using PVC-based membranes incorporating recently synthesized 1,3-alternate thiacalix[4]crown ionophore

The construction and electrodes characteristics of poly(vinylchloride) (PVC)-based polymeric membrane electrode (PME) and coated graphite electrode (CGE), incorporating 1,3-alternate thiacalix[4]crown as ionophore for estimation of Hg(II) ions, are reported here. The best potential response was observed for PME-1 having membrane composition of: ionophore (6.2 mg), PVC (100.0 mg), 2-nitrophenyl octyl ether (2-NPOE; 200.0 mg), and sodium tetraphenyl borate (NaTPB; 2.0 mg); for CGE-1 with the membrane composition: ionophore (3.5 mg), PVC (40.0 mg), 2-NPOE (80.0 mg), and NaTPB (2.0 mg). The electrodes exhibits Nernstian slope of 29.16 mV/decade with PME-1 and 30.39 mV/decade with CGE-1 for Hg(II) ions over wide concentration range, i.e., 1.0?×?10^?1 to 5.0?×?10^?6?M with PME-1 and 1.0?×?10^?1 to 5.0?×?10^?7?M with CGE-1. Lower detection limits were found to be 9.77?×?10^?6?M for PME-1 and 7.76?×?10^?7?M for CGE-1 with response time varying from 10 to 20 s. Also, these electrodes work within pH range of 2.0–6.0 for PME-1 and 1.5–6.5 for CGE-1. Overall, CGE-1 has been found to be better than PME-1. CGE-1 has been used as indicator electrode for the potentiometric titration of Hg(II) ions with EDTA as well as successfully applied for determination of Hg(II) content in wastewater, insecticide, dental amalgam, and ayurvedic medicines samples with very good performance (0.9974 correlation coefficient in the comparison against volumetric method).     

In vitro assessment of corticosteroid effects of eight chiral herbicides

Abstract

Information regarding the enantioselective endocrine disruption of chiral herbicides is scarce. This study assessed the disrupting effects of eight typical chiral herbicides on corticosteroids (including glucocorticoids and mineralocorticoids). Enantioselectivity of eight chiral herbicides were evaluated for their agonistic/antagonistic effects on glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) with CHOK1 cell line using reporter gene assay. Their influence on the production of corticosteroids were further investigated in H295R cell line using enzyme-linked immunosorbent assay (ELISA). None of the racemates or enantiomers of eight chiral herbicides exhibited GR or MR agonistic activity at non-cytotoxic concentrations. However, rac-propisochlor and S-imazamox antagonized cortisol-induced transactivation of GR by 21.79% and 38.73% at the concentration of 1.0?×?10^?7 M and 1.0?×?10^?6 M, respectively, and R-napropamide remarkably attenuated aldosterone-induced MR transactivation by 68.78% at 1.0?×?10^?6 M. The secretion of cortisol was significantly restrained after treated with 1.0?×?10^?6 M rac-propisochlor and rac-/R-napropamide at the concentration of 1.0?×?10^?6 M by 26.49%, 30.10% and 35.27%, respectively, while this glucocorticoid was remarkably induced by 1.0?×?10^?5 M rac-diclofop-methyl and its two enantiomers at the concentration of 1.0?×?10^?5 M by 75.60%, 100.1% and 68.78%, respectively. Exposure to rac-propisochlor (1.0?×?10^?6 M), S-diclofop-methyl (1.0?×?10^?5 M) or rac-/S-/R- acetochlor (1.0?×?10^?6 M) and rac-/S-/R-lactofen (1.0?×?10^?6 M) inhibited the secretion of aldosterone by approximately 40%. Our findings suggested that chiral herbicides disrupted corticosteroid homeostasis in an enantioselective way. Therefore, more comprehensive screening is required to better understand the ecological and health risks of chiral pesticides.     

Biopesticide and formulation processes based on starch industrial wastewater fortified with soybean medium

Abstract

The aim of this study was to produce Bacillus thuringiensis-based biopesticide using starch-producing industry wastewater (SIW) fortified with soybean medium and optimize the formulated product using different adjuvants. This study was necessary as low endotoxin concentration is obtained in formulated biopesticide when SIW alone is used as fermentation medium. The fermentation runs were conducted using SIW alone and SIW fortified with 25% soybean (w/v) medium in 2000?L and 150?L bioreactor, respectively. SIW supplemented with soybean medium showed an increase in cell count (from 1.95?×?10⁸ to 1.65?×?10⁹ CFU mL^–1), spore synthesis (from 1.5?×?10⁸ to 1.35?×?10⁹ CFU mL^–1) and endotoxin concentration (from 436 to 1170?μg mL^–1) when compared to SIW medium alone. The fermented broth was concentrated using continuous centrifugation and adjuvants were added for biopesticide formulation in order to enhance its resistance against UV rays and rainfastness. Entomotoxicity of the formulation produced using fermented broth of SIW fortified with soybean (38,000?IU μL^–1) was higher than that obtained by SIW medium alone (21,000?IU μL^–1), commercial biopesticide Foray 76B (20,000?IU μL^–1) and Btk sander’s (12,500?IU μL^–1).     

Influence of tetracycline exposure on the growth of wheat seedlings and the rhizosphere microbial community structure in hydroponic culture

In this study, the effects of tetracycline exposure on wheat growth and the microbial community structure in the rhizosphere were investigated under hydroponic culture conditions. Exposure to various concentrations of tetracycline resulted in significant suppression of the growth of wheat roots and shoots, with minimum doses of 0.8 mg L^?1 and 4 mg L^?1 resulting in inhibition rates of 32% and 15.4%, respectively. Complete inhibition of the growth of these two parts of wheat plants was observed in response to treatment with tetracycline at 20 mg L^?1 and 100 mg L^?1, respectively. However, the germination of wheat seeds was not sensitive to exposure to tetracycline. The effects of tetracycline exposure on the microbial community in the wheat rhizosphere were evaluated through traditional cultivation and molecular biological analyses. The cultivation results indicated that bacteria were the dominant population, being present in concentrations of 1× 10⁸–2.45× 10⁹CFUs mL^?1, although 39% to 87% inhibition occurred in response to tetracycline. The concentration of fungi increased in all tetracycline treated samples to 2.5 to 15.8 times that of the control. The highest concentration of fungi (4.27× 10⁸ CFU mL^?1) was observed in response to 60 mg L^?1 tetracycline after 15 days of cultivation. In this stage, a large amount of fungal colonies was observed on the surface of the culture solution, the wheat roots became rotted and the plants became atrophic or even died. Molecular biological analysis indicated that the bacterial community structure was significantly different in samples that were exposed to high levels of tetracycline (over 20 mg L^?1) than in samples that were exposed to lower concentrations. As the concentration of tetracycline increased, the diversity of the bacteria decreased. Additionally, several dominant sensitive species such as Sphingobacterium multivorum were suppressed by tetracycline, while some resistant species such as Acinetobacter sp. appeared or were conserved. The bacteria population tended to stabilize when the drug concentration exceeded 40 mg L^?1.     

Impact of pH buffer capacity of sediment on dechlorination of atrazine using zero valent iron

This research investigated the role of the pH buffer capacity of sediment on the dechlorination of atrazine using zero valent iron (ZVI). The buffer capacity of the sediment was quantified by batch experiments and estimated to be 5.0 cmol OH^? · pH^?1. The sediments were spiked with atrazine at 7.25-36.23 mg kg^?1 (6.21 × 10^?7–3.09 × 10^?6 mol atrazine · g^?1 sediment) for the batch experiments. The buffer capacity of the sediment maintained the sediment suspension at neutral pH, thereby enabling continuous dechlorination until the buffer capacity of the sediment was depleted. The pseudo-first order dechlorination constants were estimated to be in the range of 1.19 × 10^?2?7.04 × 10^?2 d^?1 for the atrazine-spiked sediments.     

Remediation of alachlor and atrazine contaminated water with zero-valent iron nanoparticles

Zero-valent iron nanoparticles (nZVI, diameter < 90 nm, specific surface area = 25 m² g^?1) have been used under anoxic conditions for the remediation of pesticides alachlor and atrazine in water. While alachlor (10, 20, 40 mg L^?1) was reduced by 92–96% within 72 h, no degradation of atrazine was observed. The alachlor degradation reaction was found to obey first-order kinetics very closely. The reaction rate (35.5 × 10^?3–43.0 × 10^?3 h^?1) increased with increasing alachlor concentration. The results are in conformity with other researchers who worked on these pesticides but mostly with micro ZVI and iron filings. This is for the first time that alachlor has been degraded under reductive environment using nZVI. The authors contend that nZVI may prove to be a simple method for on-site treatment of high concentration pesticide rinse water (100 mg L^?1) and for use in flooring materials in pesticide filling and storage stations.     

Ultrasensitive determination of carbendazim in water and orange juice using a carbon paste electrode

A carbon paste electrode was used for the electrochemical quantification of carbendazim in water and orange juice samples. Carbendazim oxidation on the electrode surface was found to be controlled by adsorption. The novel electrochemical procedure for carbendazim quantification employed differential pulse voltammetry using a carbon paste electrode under optimal conditions. Carbendazim oxidation currents were linear at concentrations of 2.84 to 45.44 µg L^?1, with a limit of detection of 0.96 µg L^?1. The proposed method was applied to carbendazim quantification in ultrapurified water, river water, and orange juice. Recovery rates in water and orange juice samples were in the 97%–101% range, indicating that the method can be employed to determine carbendazim in these matrices, with advantages including shorter analysis time and lower cost than routine methods such as chromatography or spectroscopy. The electrode showed good reproducibility, remarkable stability, and especially good surface renewability by simple mechanical polishing. The recovery rates observed were highly concordant with those obtained for high-performance liquid chromatography, having a relative standard deviation of less than 1.3%.     

Degradation of ethylenethiourea pesticide metabolite from water by photocatalytic processes

In this study, photocatalytic (photo-Fenton and H₂O₂/UV) and dark Fenton processes were used to remove ethylenethiourea (ETU) from water. The experiments were conducted in a photo-reactor with an 80 W mercury vapor lamp. The mineralization of ETU was determined by total organic carbon analysis, and ETU degradation was qualitatively monitored by the reduction of UV absorbance at 232 nm. A higher mineralization efficiency was obtained by using the photo-peroxidation process (UV/H₂O₂). Approximately 77% of ETU was mineralized within 120 min of the reaction using [H₂O₂]₀ = 400 mg L^?1. The photo-Fenton process mineralized 70% of the ETU with [H₂O₂]₀ = 800 mg L^?1 and [Fe²⁺] = 400 mg L^?1, and there is evidence that hydrogen peroxide was the limiting reagent in the reaction because it was rapidly consumed. Moreover, increasing the concentration of H₂O₂ from 800 mg L^?1 to 1200 mg L^?1 did not enhance the degradation of ETU. Kinetics studies revealed that the pseudo-second-order model best fit the experimental conditions. The k values for the UV/H₂O₂ and photo-Fenton processes were determined to be 6.2 × 10^?4 mg L^?1 min^?1 and 7.7 × 10^?4 mg L^?1 min^?1, respectively. The mineralization of ETU in the absence of hydrogen peroxide has led to the conclusion that ETU transformation products are susceptible to photolysis by UV light. These are promising results for further research. The processes that were investigated can be used to remove pesticide metabolites from drinking water sources and wastewater in developing countries.     

Infrared Measurement of Fluorocarbons,Carbon Tetrachloride,Carbonyl Sulfide,And Other Atmospheric Trace Gases

A cryogenic procedure for concentrating trace gases in the atmosphere has been developed and applied to the ambient air at Research Triangle Park, NC, Atlantic Beach, NC, and New York City. The concentrated gases have been analyzed by long path infrared absorption spectroscopy, with a detectability down to partial pressures of 10^?11 atmospheres. Carbonyl sulfide has been detected at partial pressures in the range 1 × 10^?10 atm. to 3 × 10^?10 atm. Carbon tetrachloride was always detected with a rather narrow partial pressure range of 0.7 × 10^?10 atm. to 1.1 × 10^?10 atm. Fluorocarbon-11 values ranged from about 1.3 × 10^?10 atm. at Research Triangle Park to 8 × 10^?10 atm. at New York City. Fluo-rocarbon-12 covered the range 1.8 × 10^?10 atm. to 1.0 × 10^?9 atm. Hydrocarbon pollutants varied widely in concentration, but were always detected, even in the clean rural air.     

Micronucleus frequency in sheep lymphocytes after in vitro exposure to fungicide tolylfluanid

The fungicide tolylfluanid (N - dichlorofluoromethylthio-N′, N - dimethyl - N - p - tolylsulfamide), was investigated by cytokinesis-block micronucleus assay. Tolylfluanid at the lowest concentration (1 × 10^{? 6}mol L^{? 1})did not influence significantly the frequency of micronuclei in sheep lymphocyte cultures in comparison with control (32.33 ± 3.51/1000 binucleated cells versus 30.33 ± 2.82/1000 binucleated cells in dimethylsulfoxide (DMSO) control, P = 0.44). Higher tolylfluanid concentrations (1 × 10^{? 4} and, 1 × 10^{? 5} mol L^{? 1}) resulted in a significant dose-dependent increase in the number of micronuclei in comparison with control (74.00 ± 13.00/1000 binucleated cells and 52.67 ± 10.12/1000 binucleated cells versus 30.33 ± 2. 82/1000 binucleated cells in DMSO control, P = 0.005 and 0.02, respectively, ANOVA followed by Tukey test P < 0.05). Many of the treated cells also possessed multiple micronuclei. Tolylfluanid did not affect the nuclear division index at all treatment concentrations. Our in vitro results thus demonstrate that tolylfluanid had a significant genotoxic effect at only the highest concentration tested.     

Kinetics and equilibrium properties of the biosorption of Cu2+ by algae

The purpose of this study was to examine the kinetics and equilibrium properties of freshwater algae with Cu²⁺. This was a model system to explore using algae as biosensors for water quality. Methods included making luminescence measurements (fluorescence) and copper ion-selective electrode (CuISE) measurements vs. time to obtain kinetic data. Results were analyzed using a pseudo-first-order model to calculate the rate constants of Cu²⁺ uptake by algae: k _p(Cu?Calgae)?=?0.0025?±?0.0006?s^?1 by CuISE and k _p(Cu?Calgae)?=?0.0034?±?0.0011?s^?1 by luminescence. The binding constant of Cu?Calgae, K _Cu?Calgae, was 1.62?±?0.07?×?10⁷?M^?1. Fluorescence results analyzed using the Stern?CVolmer relationship indicate that algae have two types of binding sites of which only one appears to affect quenching. The fluorescence-based method was found to be able to detect the reaction of algae with Cu²⁺ quickly and at a detection limit of 0.1?mg?L^?1.     

Hg<Superscript>2+</Superscript> detection using a disposable and miniaturized screen-printed electrode modified with nanocomposite carbon black and gold nanoparticles

A miniaturized screen-printed electrode (SPE) modified with a carbon black-gold nanoparticle (CBNP-AuNP) nanocomposite has been developed as an electrochemical sensor for the detection of inorganic mercury ions (Hg²⁺). The working electrode surface has been modified with nanocomposite constituted of CBNPs and AuNPs by an easy drop casting procedure that makes this approach extendible to an automatable mass production of modified SPEs. Square wave anodic stripping voltammetry (SWASV) was adopted to perform Hg²⁺ detection, revealing satisfactory sensitivity and detection limit, equal to 14 μA ppb^?1 cm^?2 and 3 ppb, respectively. The applicability of the CBNP-AuNP-SPE for the determination of inorganic mercury has been assessed in river water by a simple filtration and acidification of the sample as well as in soil by means of a facile acidic extraction procedure assisted by ultrasound.     

Neutral poly- and perfluoroalkyl substances in air and seawater of the North Sea

Concentrations of neutral poly- and perfluoroalkyl substances (PFASs), such as fluorotelomer alcohols (FTOHs), perfluoroalkane sulfonamides (FASAs), perfluoroalkane sufonamidoethanols (FASEs), and fluorotelomer acrylates (FTACs), have been simultaneously determined in surface seawater and the atmosphere of the North Sea. Seawater and air samples were taken aboard the German research vessel Heincke on the cruise 303 from 15 to 24 May 2009. The concentrations of FTOHs, FASAs, FASEs, and FTACs in the dissolved phase were 2.6–74, <0.1–19, <0.1–63, and <1.0–9.0 pg L^?1, respectively. The highest concentrations were determined in the estuary of the Weser and Elbe rivers and a decreasing concentration profile appeared with increasing distance from the coast toward the central part of the North Sea. Gaseous FTOHs, FASAs, FASEs, and FTACs were in the range of 36–126, 3.1–26, 3.7–19, and 0.8–5.6 pg m^?3, which were consistent with the concentrations determined in 2007 in the North Sea, and approximately five times lower than those reported for an urban area of Northern Germany. These results suggested continuous continental emissions of neutral PFASs followed by transport toward the marine environment. Air–seawater gas exchanges of neutral PFASs were estimated using fugacity ratios and the two-film resistance model based upon paired air–seawater concentrations and estimated Henry's law constant values. Volatilization dominated for all neutral PFASs in the North Sea. The air–seawater gas exchange fluxes were in the range of 2.5?×?10³–3.6?×?10⁵ pg m^?2 for FTOHs, 1.8?×?10²–1.0?×?10⁵ pg m^?2 for FASAs, 1.1?×?10²–3.0?×?10⁵ pg m^?2 for FASEs and 6.3?×?10²–2.0?×?10⁴ pg m^?2 for FTACs, respectively. These results suggest that the air–seawater gas exchange is an important process that intervenes in the transport and fate for neutral PFASs in the marine environment.     

Tea bag filter paper as a novel protective membrane for micro-solid phase extraction of butachlor in aqueous samples

An innovative, cost-effective, simple, and environmental friendly tea bag filter paper protected micro-solid phase extraction (μ-SPE) technique was developed for the first time with the aim to miniaturize and minimize the use of organic solvents for the extraction and determination of butachlor in aqueous samples. The μ-SPE device was produced by packing 3.0 mg of an easily synthesized new sorbent, hydroxyl-functionalized polypyrrole (OH-PPY), inside a small tea bag filter paper sachet (1.0 cm × 0.5 cm) that served as a protective envelope. Both the extraction and desorption procedures were facilitated by sonication. Due to the high porosity and the fast water absorption of the tea bag filter paper, the analyte could easily diffuse through and enhance the interaction with the sorbent. Under the optimized conditions for the GC-ECD and the μ-SPE, the limit of detection (S/N ≥ 3) was 2.0 μg L^?1 while the limit of quantitation (S/N ≥ 10) was 10.0 μg L^?1. The recoveries of the butachlor spiked at 0.050, 0.10, and 0.50 μg mL^?1 ranged from 77.9 ± 3.0 to 112.5 ± 2.9%. The proposed method was successfully applied for the determination of butachlor in water samples from paddy cultivation sites. The levels found were from non-detectable to 24.71 ± 0.37 μg L^?1.     

Environmental photochemical fate of pesticides ametryn and imidacloprid in surface water (Paranapanema River,São Paulo,Brazil)

In addition to direct photolysis studies, in this work the second-order reaction rate constants of pesticides imidacloprid (IMD) and ametryn (AMT) with hydroxyl radicals (HO^●), singlet oxygen (¹O₂), and triplet excited states of chromophoric dissolved organic matter (³CDOM^*) were determined by kinetic competition under sunlight. IMD and AMT exhibited low photolysis quantum yields: (1.23?±?0.07)?×?10^–2 and (7.99?±?1.61)?×?10^–3 mol Einstein^?1, respectively. In contrast, reactions with HO^● radicals and ³CDOM* dominate their degradation, with ¹O₂ exhibiting rates three to five orders of magnitude lower. The values of k_IMD,HO● and k_AMT,HO● were (3.51?±?0.06)?×?10⁹ and (4.97?±?0.37)?×?10⁹ L mol^?1 s^?1, respectively, while different rate constants were obtained using anthraquinone-2-sulfonate (AQ2S) or 4-carboxybenzophenone (CBBP) as CDOM proxies. For IMD this difference was significant, with k_IMD,3AQ2S*?=?(1.02?±?0.08)?×?10⁹ L mol^?1 s^?1 and k_IMD,3CBBP*?=?(3.17?±?0.14)?×?10⁸ L mol^?1 s^?1; on the contrary, the values found for AMT are close, k_AMT,3AQ2S*?=?(8.13?±?0.35)?×?10⁸ L mol^?1 s^?1 and k_AMT,3CBBP*?=?(7.75?±?0.80)?×?10⁸ L mol^?1 s^?1. Based on these results, mathematical simulations performed with the APEX model for typical levels of water constituents (NO₃^?, NO₂^?, CO₃^2?, TOC, pH) indicate that the half-lives of these pesticides should vary between 24.1 and 18.8 days in the waters of the Paranapanema River (São Paulo, Brazil), which can therefore be impacted by intensive agricultural activity in the region.