Soil column experiments used as a means to assess transport,sorption, and biodegradation of pesticides in groundwater

Soil column experiments are used to investigate the fate of three pesticides of high, intermediate, and low solubility in groundwater: N- phosphonomethyl glycine (glyphosate); O,O-diethyl-S-[(ethylthio)methyl]phosphorodithioate (phorate); (2,4-dichlorophenoxy)acetic acid (2,4-D). Feed solutions are prepared by adding each pesticide (100 mg/L glyphosate, 50 μ g/L phorate, 50 mg/L 2,4-D) along with conservative tracer, KBr, in synthetic groundwater. The concentration of the pesticides in effluents is detected by ion chromatography (glyphosate, 2,4-D) and GC-FID (phorate). The Br^? breakthrough curves are employed to estimate the dispersion coefficient and mean pore velocity in each column. Solute transport and reactive models accounting for equilibrium/non-equilibrium sorption and biodegradation are coupled with inverse modeling numerical codes to estimate the kinetic parameters for all pesticides.     

Biodegradation of mixed pesticides by mixed pesticide enriched cultures

This paper discusses the degradation kinetics of mixed (lindane, methyl parathion and carbofuran) pesticides by mixed pesticide enriched cultures (MEC) under various environmental conditions. The bacterial strains isolated from the mixed microbial consortium were identified as Pseudomonas aeruginosa (MTCC 9236), Bacillus sp. (MTCC 9235) and Chryseobacterium joostei (MTCC 9237). Batch studies were conducted to estimate the biokinetic parameters like the maximum specific growth rate (μ_max), Yield Coefficient (Y_T), half saturation concentration (K_s) and inhibition concentration (Ki) for individual and mixed pesticide enriched cultures. The cultures enriched in a particular pollutant always showed high growth rate and low inhibition in that particular pollutant compared to MEC. After seven weeks of incubation, mixed pesticide enriched cultures were able to degrade 72% lindane, 95% carbofuran and 100% of methyl parathion in facultative co-metabolic conditions. In aerobic systems, degradation efficiencies of lindane methyl parathion and carbofuran were increased by the addition of 2g L^{? 1} of dextrose. Though many metabolic compounds of mixed pesticides were observed at different time intervals, none of the metabolites were persistent. Based on the observed metabolites, a degradation pathway was postulated for different pesticides under various environmental conditions.     

Comparative study of accessibility of distinctive pesticides

Interactions of micro-contaminants with soil may play a crucial role in their environmental fate and possible harmful effects. Major goals of our investigations were to model the availability of widely used pesticides and characterize adsorption capabilities of distinctive soil types by the accomplishment of extensive comparative studies and application of several extraction methods. Environmental and biological relevance of these examinations is enhanced by the fact that intrinsic features and specific details of pesticide accessibility have not been revealed so far by a comparative approach. Five different experimental methods were assessed for modelling accessibility of five selected pesticides. The applied models for regaining the pesticides showed diverse efficiency in extraction capability in cases of the different soil types (sandy, brown forest and alluvial soils). The amounts of the obtained pesticides were determined by using gas-chromatography coupled to mass spectrometry (GC-MS) and high pressure liquid chromatography coupled to mass spectrometry (HPLC-MS). Accessibility of pesticides was also compared in cases of sterilized and real soil samples in order to estimate the extent of the influence of microflora. Aqueous extraction solvents proved to be suitable for accurate assessment of the accessible amounts of pesticides, as their effectivity was at least as high as that of the applied organic solvents. In our studies pesticide-soil interactions have comprehensively been characterized, and possible influences of environmental factors on the accessibility have also been revealed. Our study might be regarded as a tentative approach to model some significant circumstances playing key roles in pesticides' possible bioavailability.     

Biodegradation of insecticide carbofuran by Paracoccus sp. YM3

A bacterium (Paracoccus sp. YM3) capable of degrading carbofuran was isolated from carbofuran-contaminated sludge. The strain was shown to metabolize carbofuran (50 mg L^?1) to carbofuran-7-phenol in minimal salt medium within 6 days in which the pesticide was the only source of carbon. Carbofuran and its main metabolite were analyzed by high performance liquid chromatography (HPLC). The addition of an other carbon source led to accelerated biodegradation. The relevant degrading-enzyme was intracellular and inducible. A tobacco hypersensitivity experiment showed that YM3 could eliminate carbofuran in soils effectively and safely. This is the first report of a Paracoccus sp. that could degrade carbofuran. The present study may provide a basis for biotreatment of wastewaters and bioremediation of carbofuran-contaminated soils.     

Evaluation of pressurized liquid extraction for the analysis of four pesticides in unpolished rice

The aim of to evaluate efficiency of this study was extraction pressurized liquid extraction (PLE) for the analysis of four pesticides, fthalide, etofenprox, fenitrothion, and isoprothiolane, in unpolished rice by comparing with homogenization as a reference technique. The concentrations of four selected pesticides obtained by PLE with acetonitrile at 130°C for 10 min × 2 cycles were comparable to those by homogenization with water-soaking. The repeatability of the analysis, represented as relative standard deviations (RSDs), were 1.4–3.6% (n = 3) for PLE at 130°C and 1.2–3.8% (n = 3) for homogenization with water-soaking. Recovery yields of surrogates were 75–88% and 87–109% for PLE at 130°C and homogenization with water-soaking, respectively, and these were satisfactory according to the method of positive list. This study suggested that PLE can be applied for the analysis of selected four pesticides in unpolished rice as well as homogenization with water-soaking.     

Effect of triazophos,fipronil and their mixture on miRNA expression in adult zebrafish

MicroRNA (miRNA) plays a crucial role in gene expression regulation. However, no data are available on change of miRNA expression of zebrafish (Danio rerio) after treatment with pesticides. We evaluated the effect of fipronil (5-amino-1-[2, 6-dichloro-4-(trifluoromethyl) phenyl]-4-[(trifluoromethyl) sulfinyl]-1H-pyrazole-3-carbonitrile) and triazophos (3-(O, O-diethyl)-1-phenyl thiophosphoryl-1, 2, 4-triazol) and their mixture on miRNA expression in zebrafish. MiRNA expression profiles in zebrafish were altered after treatment with these chemicals. An association between these chemicals and the expression of 21 miRNAs was found 96 h after treatment. Among them, 14 miRNAs were differentially expressed due to the treatments with fipronil, triazophos and their mixture; 5 miRNAs showed altered expression level after treatment with formulations of these chemicals; miR-29b and miR-738 were differentially expressed after treatment with adjuvants. MiRNAs might present a novel toxicological response that could be used as a toxicological biomarker and have a different direction for future investigations of their association with miRNAs involved in chemical related diseases.     

High-performance liquid chromatography (HPLC) as a tool for monitoring the fate of fluazinam in soil

Fluazinam is a widely used pesticide employed against the fungal disease late blight in potato cultivation. A specific, repeatable, and rapid high-performance liquid chromatography (HPLC) method utilizing a diode array detector (DAD) was developed to determine the presence of fluazinam in soil. The method consists of acetonitrile (ACN) extraction, clean-up with solid-phase extraction (SPE), and separation using a mobile phase consisting of 70% ACN and 30% water (v/v), including 0.02% acetic acid. HPLC was performed with a C18 column and the detection wavelength was 240 nm. The method was successfully applied to an incubation experiment and to soil samples taken from potato fields where fluazinam had been applied two to three times during the on-going growing season. In the 90-day incubation experiment, analytical standard fluazinam and the commercial fungicide Shirlan^® were added to soil samples that had never been treated with fluazinam, and were then extracted with ACN and 0.01 M calcium chloride (CaCl₂). Fluazinam was not extractable with CaCl₂, indicating that it does not leach to watercourses in the dissolved form. Recovery with ACN extraction for sandy soils was 72–95% immediately after application and 53–73% after 90 days of incubation. Out of the eight potato field soil samples, fluazinam was found in two samples at concentrations of 2.1 mg kg^?1 and 1.9 mg kg^?1, well above the limit of quantification (0.1 mg kg^?1).     

Secretory expression of organophosphorus hydrolase OPHC2 in Yarrowia lipolytica Polg

In the present study, recombinant organophosphorus hydrolase OPHC2 was successfully produced by Yarrowia lipolytica and purified. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and western blot analyses showed a major polypeptide band of 36 kDa. The purified enzyme was optimally active at 65°C and pH 8.5 and also displayed good thermal and pH stability using methyl parathion (O,O-dimethyl-O-4-p-nitrophenyl phosphorothioate) as a substrate. Moreover, as Y. lipolytica is a non-pathogenic, generally regarded as safe (GRAS) yeast, the cell culture supernatant can be used directly on vegetables and fruits that are contaminated by organophosphorus pesticides.     

Review of advances in the thin layer chromatography of pesticides: 2012–2014

Publications reporting techniques and applications of thin layer chromatography (planar chromatography) for the separation, detection, qualitative, and quantitative determination, and preparative isolation of pesticides and their metabolites are reviewed for the period from November 1, 2012 to November 1, 2014. Analyses are described for a variety of sample types and pesticide classes. In addition to references on residue analysis, studies such as pesticide structure – retention relationships, identification and characterization of natural and synthesized pesticides, metabolism, bioactivity, degradation, soil mobility, and lipophilicity are covered.     

Residues of five pesticides in field‐treated alfalfa seeds and alfalfa sprouts

Abstract

Residues of five different pesticides applied to alfalfa seed crops were determined in the harvested seeds and in sprouts grown from these seeds. Although seeds are usually used for future production of alfalfa plants, some of these seeds may be sprouted for human food consumption. The pesticides studied — aldicarb (Temik®), chlorothalonil (Bravo®), chlorpyrifos (Lorsban®), methamidophos (Monitor®) and propargite (Comite®) — were applied at a normal usage rate and at two to three times that rate. Residues on the seeds and sprouts, if any, were insignificant at rates of application.