Encapsulation of water soluble pesticides for extended delivery of pesticides without contaminating water bodies

The main objective of this study is to develop polymeric encapsulated formulation for the water soluble broad-spectrum pesticides. Pesticides contaminate the environment in different ways but foremost hazards are linked with the contamination of water bodies. Water soluble pesticides are the major deleterious agents and go off into ground water and different water bodies through leaching or surface runoff from the applied places. Besides this some of the water soluble pesticides are broad-spectrum, but proper methods and techniques are not available for their effective and safe usage, all broad-spectrum pesticide are disappearing from the pesticide lists every year. Hence, the present study is based on development of encapsulated formulation for water soluble broad-spectrum pesticide i.e. Monocrotophos. In this study, water soluble pesticide was encapsulated in polyvinyl alcohol (PVA) polymer along with surfactants and cross linker. The developed microspheres were analyzed in HPLC for calculating loading capacity and encapsulation efficacy, these were calculated 0.75 and 90% respectively. The FT-IR data results confirmed that the monocrotophos successfully encapsulated in the PVA polymer with respective bands. The degradation studies show that in encapsulated formulation monocrotophos degradation was found only 10% after 94 hrs. Optical micrographs in aqeous solution indicate spherical shapes with size in the rage of 7-8 µm of encapsulated formulation. XRD data further crystalline nature of polymeric encapsulated formulation. The study may provide a new corridor to save the broad-spectrum water soluble pesticides which are on the verge to be banned.

Establishment of resveratrol and its derivatives as neuroprotectant against monocrotophos-induced alteration in NIPBL and POU4F1 protein through molecular docking studies

Monocrotophos (MCP) is a broad spectrum organophosphorus insecticide, which is widely used as foliar spray to the different important crops. MCP may reach the soil and the aquatic environment directly or indirectly during and after the application, which leads to the different environmental issues. MCP is found to be associated with neurotoxicity and its toxic effects have been monitored during different stages of neuronal development. Identification of gene expression in MCP-induced neurotoxicity during neuronal developmental stage is a major area of genomic research interest. In accordance with this identification, screening of potential neuroprotective, natural resources are also required as a preventive aspects by targeting the impaired genes. In this current course of work, microarray experiment has been used to identify genes that were expressed in monocrotophos (MCP)-induced mesenchymal stem cells (MSC) and also the neuroprotectant activity of RV on MCP-exposed MSCs. Microarray experiment data have been deposited in NCBI's Gene Expression Omnibus database and are accessible through GEO Series accession number GSE121261. In this paper, we have discussed two important genes NIPBL (nipped-B-like protein) and POU4F1 (POU domain, class 4, transcription factor 1). These genes were found to be significantly expressed in MCP-exposed MSC and show minimum expression in presence of RV. Homology modelling and docking study was done to identify the interaction and binding affinity of resveratrol and its derivatives with NIPBL and POU4F1 protein. Docking analysis shows that RV and its derivatives have strong interaction with NIPBL and POU4F1 protein hence proves the significance of resveratrol as potential neuroprotectant. This paper highlights the hazardous impact of MCP on neuronal development disorders and repairing potentiality of RV and its derivatives on altered genes involved in neuronal diseases. Graphical Abstract.

Molecular characterization of monocrotophos and chlorpyrifos tolerant bacterial strain for enhancing seed germination of vegetable crops

The main aim of this study is to investigate the toxicity of organophosphate (OPs) insecticides monocrotophos (MCP) and chlorpyrifos (CLS) on plant growth promoting (PGP) properties and seed germination of brinjal, tomato and okra vegetables inoculated by Microbacterium hydrocarbonoxydans (BHUJP-P1), Stenotrophomonas rhizophila (BHUJP-P2), Bacillus licheniformis (BHUJP-P3) and Bacillus cereus (BHUJP-P4). Maximum increase in microbial growth (52.6% & 47.9%) with enhanced EPS production (447.67 mg/ml & 75.00 mg/ml) was showed by BHUJP-P4 and BHUJP-P3 at 10× dose of MCP and CLS over control, BHUJP-2 and BHUJP-P1 respectively. Simultaneously, both strains recorded minimum reduction in PGP activities and seed germination at 3× dose of both insecticides as compared to BHUJP-2 and BHUJP-P1, respectively. Strains BHUJP-P3 and BHUJP-P4 showed 83 and 81% of monocrotophos degradation at 50 mg/kg concentration; 81 and 80% at 150 mg/kg concentration within 5days respectively. Concurrently, these strains BHUJP-P3 and BHUJP-P4 were recorded 53 and 90% of chlorpyrifos degradation at 50 mg/kg concentration; 49% and 87% at 100 mg/kg concentration within 72 h, respectively. The OPs insecticide degrading gene opdA and opd was found in strain BHUJP-P3 and BHUJP-P4, respectively. The multifarious biological activities of strain BHUJP-P3 and BHUJP-P4 showed maximum tolerance against insecticide, and minimum reduction in P-solubilisation, IAA, siderophore and HCN production for plant growth promotion and biological control under insecticide stress. Thus, these novel isolates may be used as biodegradation of organophosphate insecticide and plant growth promoting bacterial (PGPB) inoculum for enhancing seed germination of vegetables under stress insecticide. These novel strains will be environment friendly, socially acceptable and economically viable.

Degradation of monocrotophos by Starkeya novella YW6 isolated from paddy soil

A bacteria strain, YW6, capable of utilizing monocrotophos (MCP) as the sole carbon and nitrogen sources for growth was isolated from paddy soil and identified as Starkeya novella. Strain YW6 completely degraded 0.2 mM MCP within 36 h without any lag period. Addition of carbon source resulted in slowing down of the initial rate of degradation of MCP, while the presence of a more favorable source of nitrogen enhanced the degradation of MCP. In addition to the degradation of MCP, strain YW6 was also able to degrade a wide range of organophosphorus pesticides (OPs) containing P-O-C bond, but not dimethoate, which has P-S-C bond. A MCP degradation pathway was proposed on the basis of metabolite production patterns and identification of the metabolites. MCP is hydrolyzed at the P-O-C bond to form N-methylacetoacetamide and dimethyl phosphate; N-methylacetoacetamide is transformed to N-methyl-4-oxo-pentanamide, which was subsequently converted to 5-(methylamino)-5-oxo-pentanoic acid, and 5-(methylamino)-5-oxo-pentanoic acid is cleaved to glutaric acid and methylamine. These findings provide new insights into the microbial metabolism of MCP. To the best of our knowledge, this is the first report on the degradation of MCP by Starkeya bacteria.

Cytogenotoxicity assessment of monocrotophos and butachlor at single and combined chronic exposures in the fish Catla catla (Hamilton)

Cytogenotoxic effects in the form of micronuclei and deformed nucleus, nuclear buds, binucleated cells, vacuolated nucleus, vacuolated cytoplasm, echinocytes, and enucleus induced by two compounds belonging to two different chemical classes of agrochemicals (monocrotophos and butachlor) at sublethal concentrations (0.625, 1.3, and 2.3 ppm and 0.016, 0.032, and 0.064 ppm) in single and combined chronic exposures were studied under laboratory conditions for a period of 35 days in the economically important Indian fish Catla catla. Statistically significant duration-dependent increases in the frequencies of micronucleus (MN) and other cytological anomalies were observed. Compared to single exposures, a twofold increase in micronuclei frequency was noted at combined exposures indicating the synergistic phenomenon. Binucleated and enucleated cells appeared only in fishes exposed to sublethal concentrations of butachlor. The present study is the first of its kind in exploring a significant positive correlation between micronuclei and other nuclear anomalies suggesting them as new possible biomarkers of genotoxicity after agrochemical exposures. The study highlights the sensitivity of the assay in exploring various predictive biomarkers of genotoxic and cytotoxic events and also elicits the synergistic effects of agrochemicals in apparently healthy fishes. C. catla can be considered as a suitable aquatic biomonitoring sentinel species of contaminated water bodies.

Dispersive microextraction based on "magnetic water" coupled to gas chromatography/mass spectrometry for the fast determination of organophosphorus pesticides in cold-pressed vegetable oils

This article presents a novel application of dispersive microextraction based on "magnetic water" (m-water) for the purification of organophosphorus pesticides (methamidophos, omethoate, monocrotophos) from cold-pressed vegetable oils. In the present study, a trace amount of water (extractant) was adsorbed on bare Fe₃O₄ by hydrophilic interaction to form m-water. Rapid extraction can be achieved while the m-water is dispersed in the sample solution with the aid of a vigorous vortex. After extraction, the analyte-adsorbed m-water can be readily isolated from the sample solution by a magnet, which could greatly simplify the operation and reduce the whole pretreatment time. Several parameters affecting the extraction efficiency were investigated, and under the optimized conditions, a simple and effective method for pesticide analysis was established by coupling with gas chromatography/mass spectrometry (GC/MS). The linearity range of the proposed method was 2-100 ng/g with satisfactory correlation coefficients (R) of 0.9997-0.9998, and the limits of quantification (LOQ) for the target compounds were in the range of 0.70-1.27 ng/g. In addition, the reproducibility was obtained by evaluating the intra- and interday precisions with relative standard deviations (RSDs) less than 7.2% and 6.5%, respectively. Finally, the established "magnetic water" microextraction method was successfully applied for the determination of pesticide residues in several kinds of cold-pressed vegetable oils.

The interaction between natural organic matter in raw waters and pesticide residues: a three dimensional excitation-emission matrix (3DEEM) fluorescence investigation

This paper examines the interaction between dissolved natural organic matter and pesticide residues, both of which are found in raw water sources, using three dimensional excitation-emission matrix (3DEEM) fluorescence spectroscopy. It was observed that pesticide residue at 0.1 mg L(-1) formed a complex with humic-like fluorophores that are commonly found in raw water samples. Applying 3DEEM fluorescence to investigate the humic fractions, it was found that identification of changes in water sources was possible, and, importantly, the presence of a number of pesticides was able to be determined. In addition, the formation of this complex, and the influence of soluble cations and anions upon it, was shown to impact the efficiency of analytical extraction procedures for pesticides; however, 3DEEM fluorescence could be an approach to account for such losses.

Photocatalytic degradation of monocrotophos pesticide--an endocrine disruptor by magnesium doped titania

Mg-doped TiO(2) with different Mg concentrations were prepared using sol-gel method and characterized by XRD, UV-visible, XPS, SEM and FT-IR. The XRD results revealed that Mg(2+) goes into the TiO(2) lattice. SEM images of the doped and pure TiO(2) indicated that there is a smaller particle size for the doped catalyst compared to that of the pure TiO(2). UV-visible absorption spectra indicated that upon doping with Mg(2+) ion, the catalyst exhibits absorption in visible region. FT-IR and XPS spectra demonstrated that the presence of Mg(2+) ion in the TiO(2) lattice as substitutional dopant. Photocatalytic activity of doped TiO(2) has been evaluated by degradation of the monocrotophos (MCP) pesticide. The effect of solution pH, catalyst dosage and initial concentration of MCP on the photocatalytic activity of Mg-doped TiO(2) with different loadings was studied. It was observed that the rate of degradation of MCP over Mg-doped TiO(2) is better than Pure TiO(2) and Degussa P-25.

Sonophotocatalytic degradation of monocrotophos using TiO2 and Fe3+

Monocrotophos (MCP) is an organophosphate insecticide that has been found as a pollutant in aqueous environments. The sonolytic, photocatalytic and sonophotocatalytic degradation of MCP in the presence of homogeneous (Fe(3+)) and heterogeneous photocatalysts (TiO(2)) were studied. The photocatalytic degradation rate using TiO(2) was found to be lower than that of sonolysis alone due to the interference of phosphate ions formed as an intermediate product. On the other hand, a 15 fold enhancement in the degradation rate was found when photolysis was carried out in the presence of Fe(3+) compared to the rate observed with photolysis alone. The combination of sonolysis and photocatalysis (using either TiO(2) or Fe(3+)) showed a detrimental effect. Synergy indices of 0.62 and 0.87 were found for the sonophotocatalytic degradation of MCP in the presence of TiO(2) and Fe(3+), respectively. Total organic carbon (TOC) analysis was carried out to study the extent of mineralization of MCP. It was found that the mineralization process was additive for both TiO(2) and Fe(3+) sonophotocatalysis. HPLC and electrospray mass spectrometry (ESMS) techniques were employed for the identification of the degradation intermediates. The sonication of MCP led to the formation of dimethyl phosphate, dimethylphosphonate, 3-hydroxy 2-buteneamide and N-methyl 3-oxobutanamide as the intermediate products.

Impact of repeated pesticide applications on the binding and release of methyl 14C-monocrotophos and U-ring labelled 14C-carbaryl to soil matrices under field conditions

The dissipation of (O-methyl-14C) monocrotophos and U-ring labelled 14C-carbaryl was monitored for over two years in absence and presence of other insecticides using in situ soil columns. The dissipation of 14C-monocrotophos from soil treated with methomyl and carbaryl showed a faster rate of downward movement than in a control column tagged with the labelled insecticide alone. The same trend was observed in experiments with 14C-carbaryl that dissipated more readily in soil treated with non-labelled monocrotophos and methomyl. In the presence of other insecticides the percentage of bound residues was generally lower than in control experiments. The bound residues at the top of the column are released at a low rate under conditions prevailing in the field. The overall time required for dissipation of 50% of monocrotophos and carbaryl (t50) as estimated from control experiment was approximately 20 and 24 weeks, respectively. The data indicate that repeated applications of pesticides might enhance the release of 14C-bound residues.

Determination of polar organophosphorus pesticides in water samples by hydrophilic interaction liquid chromatography with tandem mass spectrometry

A method combining hydrophilic interaction liquid chromatography (HILIC) with tandem mass spectrometry (MS/MS) was developed for the determination of polar organophosphorus pesticides (OPPs; acephate, methamidophos, monocrotophos, omethoate, oxydemeton-methyl, and vamidothion) in water samples. To extract the polar OPPs and minimize matrix effects from the water sample, an activated carbon cartridge was used for pretreatment. After pretreatment of the water sample, the eluate from the activated carbon cartridge was directly injected into the HILIC/MS/MS system. The OPPs were separated on an Atlantis HILIC silica column by isocratic elution with a mixture of acetonitrile, isopropanol, and ammonium formate buffer as a mobile phase, and they were detected by positive electrospray ionization MS/MS in the selected reaction monitoring mode. The method was validated at 0.05, 0.5, and 5 microg/L levels in water samples, and the recoveries of polar OPPs were between 76.4 and 98.6%. The limits of detection were between 0.13 and 1.0 pg on-column, and the limits of quantification were between 0.43 and 3.4 pg on-column. The method can be applied to the determination of trace amounts of OPPs in environmental water samples.

Films coated with molecular imprinted polymers for the selective stir bar sorption extraction of monocrotophos

The flexibility and simplicity of stir bar sorption extraction (SBSE) have been combined with the selectivity of molecularly imprinted polymers (MIP). Stir bars were coated reproducible with a 180 microm film formed from a formic acid solution of nylon-6 polymer either nonimprinted or imprinted with monocrotophos. Time sorption profiles were measured for the extraction of monocrotophos from dichloromethane at the concentration of 10-200 micromol/L levels with both types of films in order to compare extraction characteristics. The results indicated that the MIP coated layer showed remarkable high affinity toward monocrotophos and equilibrium adsorption was attained rapidly (60 min) in contrast to free standing molecularly imprinted polymer in which equilibrium adsorption was normally attained after several hours. The stir bars coated with MIP films were capable of extracting four structural analogues of monocrotophos from dichloromethane solution, which suggests that both the amino group and PO part of these molecules is responsible for interaction with the imprinted polymer. Evidence was also presented by FT-IR analysis that the amide-hydrogen-bonding interaction between the MIP-coated films and monocrotophos was originated for monocrotophos recognition. To achieve selective extraction of monocrotophos from sample, stir bars coated with MIP films were washed with 10% (v/v) acetic acid/methanol and methanol. Clean extracts and yields of 95% were obtained, demonstrating the suitability of stir bar coated with MIP films for the analysis of environmental and biological samples. Compared with traditional MIP and SBSE, the MIP-coated film showed not only the high selectivity but also the rapid equilibrium adsorption.

Dissipation and leaching of (14)C-monocrotophos in Soil Columns under subtropical climate

Dissipation and leaching behavior of 14C-monocrotophos was studied for 365 days under field conditions using PVC cylinders. The first set (24 cylinders) was spiked with 1.0 microCi 14C-labeled monocrotophos along with 1.06 mg unlabeled monocrotophos to give a concentration of 2 mg kg -1 in the soil up to 15 cm depth. The second set (24 cylinders) received 14C-labeled monocrotophos along with other non-labeled insecticides viz., dimethoate @ 300 g a.i ha-1, deltamethrin @ 12.5 g a.i ha-1, endosulfan @ 750 g a.i ha-1, cypermethrin @ 60 g a.i ha-1, and triazophos @ 600 g a.i ha-1 at an interval of 15 days each as recommended for the cotton crop. 14C-monocrotophos dissipated faster, up to 45% in first 90 days in columns treated with only monocrotophos compared to 25% in columns that received monocrotophos along with other insecticides. However, both the columns showed similar residues 180 days onward. After 180 days of treatment, 46% radiolabeled residues were observed, which reduced up to 39.6% after 365 days. Leaching of 14C-monocrotophos to 15-30 cm soil layer was observed in both the experimental setups. In the 15-30 cm soil layer of both soil columns, up to 0.19 mg 14C-monocrotophos kg-1d. wt. soil was detected after 270 days.

Molecularly Imprinted Polymer for Monocrotophos and its Binding Characteristics for Organophosphorus Pesticides

In this study, molecular imprinting was used to develop a method based on noncovalent interaction for the synthesis of a monocrotophos-specific polymer. The selective binding characteristics of the template polymer were evaluated by 1H NMR study. The result was consistent with the existence of multi-molecular complexes formed by hydrogen-bonding interactions. Batch rebinding studies in acetonitrile were undertaken to quantitatively evaluate the affinity of the polymer for monocrotophos. The experimental binding isotherms were fitted to the Freundlich isotherm and the total number of binding sites of the polymer can be calculated to be 4.046 micromol g(-1). The induced affinity and selectivity by imprinting were examined chromatographically. The polymer gave more than 15 times longer retention for monocrotophos than the nonimprinted polymer with the same chemical composition. Other organophosphorus pesticides under study were eluted close to the void volume on the polymer column.

Effects of monocrotophos and its analogs in acetylcholinesterase activity's inhibition and its pattern of recovery on euryhaline fish, Oreochromis mossambicus

Acute toxicity of monocrotophos (MCP) and its newly synthesized thiol analogs 2-butenoic acid-3-(diethoxyphosphinothionyl) methyl ester (RPR II) and 2-butenoic acid-3-(diethoxyphosphinothionyl) ethyl ester (RPR-V) was studied on euryhaline fish, Oreochromis mossambicus. The median lethal concentrations of MCP, RPR-II, and RPR-V are 11.506, 0.167, and 0.174 mgL(-1), respectively. Both the analogs were found to be 65-fold more toxic than MCP. Inhibitory and recovery patterns of brain, gill, and muscle acetylcholinesterase (AChE) was studied in vivo after exposure to LC(50) (96 h) concentrations. Recovery study was performed of regular intervals of day-1, -7, -14, -21, and -28 to establish the time course of 50% and 100% recovery in neurotransmitter enzyme of brain, gill, and muscle tissues. The sensitivity of the tissue AChE was in the order gill>brain>muscle. The relative toxicity of these compounds with regard to AChE was RPR-II>RPR-V>MCP. The MCP-treated fishes recovered at a faster rate than for RPR-V, followed by RPR-II.

Enhanced photocatalytic degradation of monocrotophos in aqueous solution over titania hybridised with beta-zeolite

Photocatalytic degradation of monocrotophos has been carried out in a slurry type batch reactor. The reaction variables were optimised to obtain maximum degradation efficiency. The degradation rate of monocrotophos is significantly higher for acidic solutions than for alkaline solutions. It is also observed that the high concentration environment of the pollutant formed around the hybridised TiO2, enhances the mineralisation rate of monocrotophos. Hence an increase in relative photonic efficiency is obtained.

Biomineralization of an organophosphorus pesticide, Monocrotophos, by soil bacteria

AIMS

To study biomineralization of Monocrotophos (MCP) and identify the metabolites formed during biodegradation.

METHODS AND RESULTS

Two cultures, namely Arthrobacter atrocyaneus MCM B-425 and Bacillus megaterium MCM B-423, were isolated by enrichment and adaptation culture technique from soil exposed to MCP. The isolates were able to degrade MCP to the extent of 93% and 83%, respectively, from synthetic medium containing MCP at the concentration of 1000 mg x l(-1), within 8 d, under shake culture condition at 30 degrees C. The cultures degraded MCP to carbon dioxide, ammonia and phosphates through formation of one unknown compound--Metabolite I, valeric or acetic acid and methylamine, as intermediate metabolites. The enzymes phosphatase and esterase, reported to be involved in biodegradation of organophosphorus compounds, were detected in both the organisms.

CONCLUSIONS

Arthrobacter atrocyaneus MCM B-425 and B. megaterium MCM B-423 isolated from soil exposed to MCP were able to mineralize MCP to carbon dioxide, ammonia and phosphates.

SIGNIFICANCE AND IMPACT OF THE STUDY

Pathway for biodegradation of MCP in plants and animals has been reported. A microbial metabolic pathway of degradation involving phosphatase and esterase enzymes has been proposed. The microbial cultures could be used for bioremediation of wastewater or soil contaminated with Monocrotophos.

Fate of (14)C-labeled soybean and corn pesticides in tropical soils of Brazil under laboratory conditions

The dissipation rate of seven currently used soybean and corn pesticides in two tropical soils (Ustox and Psamments) of Brazil was studied in a laboratory incubation experiment. Dissipation half-lives of pesticides ranged between 2 (monocrotofos) and 90 days (endosulfan-beta). The contrasting clay contents of the studied tropical soils (130 versus 470 g of clay kg(-1) of soil) did not influence the dissipation dynamics of pesticides substantially. Mineralization to CO(2) was high [up to 78% of the applied radioactivity (AR)] for the studied organophosphorus compounds and deltamethrin, which also formed considerable amounts of bound residues (>20% of AR) during the 80 days of incubation. The highest portion of nonextractable residues was found for alachlor and simazine (55-60% of AR). In contrast, the nonpolar trifluralin and endosulfan formed only small amounts of bound residues (mostly <20% of AR) but showed the highest dissipation half-lives (>14 days) in the studied soils, also due to a low mineralization rate. When endosulfan-sulfate, as the main metabolite of endosulfan, was considered, the half-life time of endosulfan compounds (sum of -alpha, -beta, and -sulfate) was enhanced to >160 days in both soils. In comparison with the laboratory experiments, dissipation half-life times of chlorpyrifos, endosulfan-alpha, and trifluralin were shortened by a factor of 10-30 in field trials with the same soils, which was related to the volatilization potential of pesticides from soils.

Preparation and characterization of microcapsules of water-soluble pesticide monocrotophos using polyurethane as carrier material

Microencapsulation of the water soluble pesticide monocrotophos (MCR), using polyurethane (PU) as the carrier polymer, has been developed using two types of steric stabilizers, namely PLMA macrodiol and PLMA-g-PEO graft copolymer. The microencapsulation process is carried out in non-aqueous medium and at a moderate temperature to avoid any chemical degradation of monocrotophos during the encapsulation process. Microcapsules were characterized by optical microscopy and SEM for particle size and morphology, respectively. The effects of loading of MCR, crosslinking density of PU, and nature of steric stabilizer on the release of MCR from PU microcapsules have been studied.

Genotoxic effect of monocrotophos to sentinel species using comet assay

Monocrotophos is the single largest selling agrochemical in India. Sensitive biomarkers to study the genotoxic effects caused by monocrotophos in aquatic organisms, especially fish, are lacking. The fish used in this study are Tilapia mossambica, which are edible, commercially valuable and distributed all over India. The objective of this study was to study DNA strand breaks induced by monocrotophos in T. mossambica in vivo using single-cell micro gel electrophoresis/comet assay. Tilapia were treated orally with 0.313, 0.625, 1.25, 1.875, 2.5, 3.125, 3.75 and 4.375 ppm of monocrotophos and the assay was performed on nucleated erythrocytes after 24, 48, 72 and 96 h. A significant increase in mean comet tail-length (5.21-7.46 microM), indicating DNA damage, was observed at all the doses with monocrotophos when compared to controls (3.36 microM). The mean tail-length showed a dose-related increase and time-dependent decrease. The maximum increase in mean comet tail-length was observed at 24 h. Relative to these effects, reductions in mean comet tail-length were seen at 48 and 72 h. By 96 h, values had returned to control levels at all doses, indicating repair of the damaged DNA and/or loss of heavily damaged cells. The study reveals that the comet assay is a sensitive and rapid method to detect genotoxicity of monocrotophos and other environmental pollutants in sentinel species.

Leaching and degradation of corn and soybean pesticides in an Oxisol of the Brazilian Cerrados

Pesticide pollution of ground and surface water is of growing concern in tropical countries. The objective of this pilot study was to evaluate the leaching potential of eight pesticides in a Brazilian Oxisol. In a field experiment near Cuiabá, Mato Grosso, atrazine, chlorpyrifos, lambda-cyhalothrin, endosulfane alpha, metolachlor, monocrotofos, simazine, and trifluraline were applied onto a Typic Haplustox. Dissipation in the topsoil, mobility within the soil profile and leaching of pesticides were studied for a period of 28 days after application. The dissipation half-life of pesticides in the topsoil ranged from 0.9 to 14 d for trifluraline and metolachlor, respectively. Dissipation curves were described by exponential functions for polar pesticides (atrazine, metolachlor, monocrotofos, simazine) and bi-exponential ones for apolar substances (chlorpyrifos, lambda-cyhalothrin, endosulfane alpha, trifluraline). Atrazine, simazine and metolachlor were moderately leached beyond 15 cm soil depth, whereas all other compounds remained within the top 15 cm of the soil. In lysimeter percolates (at 35 cm soil depth), 0.8-2.0% of the applied amounts of atrazine, simazine, and metolachlor were measured within 28 days after application. Of the other compounds less than 0.03% of the applied amounts was detected in the soil water percolates. The relative contamination potentials of pesticides, according to the lysimeter study, were ranked as follows: metolachlor > atrazine = simazine >> monocrotofos > endsulfane alpha > chlorpyrifos > trifluraline > lambda-cyhalothrin. This order of the pesticides was also achieved by ranking them according to their effective sorption coefficient Ke, which is the ratio of Koc to field-dissipation half-life.

Reaction behaviors of decomposition of monocrotophos in aqueous solution by UV and UV/O processes

The decomposition of monocrotophos (cis-3-dimethoxyphosphinyloxy-N-methyl-crotonamide) in aqueous solution by UV and UV/O(3) processes was studied. The experiments were carried out under various solution pH values to investigate the decomposition efficiencies of the reactant and organic intermediates in order to determine the completeness of decomposition. The photolytic decomposition rate of monocrotophos was increased with increasing solution pH because the solution pH affects the distribution and light absorbance of monocrotophos species. The combination of O(3) with UV light apparently promoted the decomposition and mineralization of monocrotophos in aqueous solution. For the UV/O(3) process, the breakage of the >C=C< bond of monocrotophos by ozone molecules was found to occur first, followed by mineralization by hydroxyl radicals to generate CO(3)(2-), PO4(3-), and NO(3)(-) anions in sequence. The quasi-global kinetics based on a simplified consecutive-parallel reaction scheme was developed to describe the temporal behavior of monocrotophos decomposition in aqueous solution by the UV/O(3) process.

Decomposition of monocrotophos in aqueous solution by UV irradiation in the presence of titanium dioxide

The decomposition of monocrotophos in aqueous solution by UV/TiO2 reduction process was studied under various pH values, TiO2 dosages, light intensities, dissolved oxygen levels and other operating conditions. The presence of dissolved oxygen inhibits the recombination of electrons and holes, and enhance the decomposition of monocrotophos by UV/TiO2 process, but excessive dissolved oxygen posed no further effect on the decomposition of monocrotophos. The decomposition rates of monocrotophos were significantly higher for acidic solutions than those for alkaline solutions. Increasing the light intensity would drastically increase the decomposition rate of monocrotophos, but was ultimately influenced by the amount of TiO2 present in solutions. The quasi-global kinetics based on a simplified consecutive reaction scheme was developed to describe the temporal behavior of monocrotophos decomposition in aqueous solution by UV/TiO2 process.

Formulation of monocrotophos

Monocrotophos is an old product that is still very much appreciated as a low-cost and efficient insecticide. Due to its water solubility, formulation recipes are rather simple and no sophisticated equipment is required in a formulation plant. Formulations can easily be manufactured locally where they are going to be used. Formulants and the formulation process do not add much to the total product cost. Monocrotophos is chemically not very stable. A consequence of this property is the marginal shelf life of formulations when stored under tropical conditions. On the other hand, the limited stability of monocrotophos is a most favorable feature in the environment that outweighs the marginal shelf life. By strictly using the "first in-first out" system in stock management, no major problems relating to storage stability will be encountered. An unfavorable characteristic of monocrotophos is its high mammalian toxicity. The objective of future projects will be to develop less toxic formulations.

Residue analytical methods for monocrotophos

This paper summarizes and reviews a variety of methods that have been and are being used for the determination of residues of monocrotophos. Of the different techniques, gas-liquid chromatography was recommended as the technique of choice because it is sensitive as well as selective. The other techniques reviewed may still be useful in cases where gas chromatography is not available. The recommended methods were described in detail to allow their direct use by experienced residue analysts. Some multiresidue methods that include monocrotophos and may be used for surveillance purposes were briefly discussed.