Pesticide screening of surface water and soil along the Mekong River in Cambodia

Widespread use of pesticides globally has led to serious concerns about environmental contamination, particularly with regard to aquatic and soil ecosystems. This work involved investigating concentrations of 64 pesticides in surface-water and soil samples collected in four provinces along the Mekong River in Cambodia during the dry and rainy seasons (276 samples in total), and conducting semi-structured interviews with local farmers about pesticide use. Furthermore, an ecological risk assessment of the detected pesticides was performed. In total, 56 pesticides were detected in surface water and 43 in soil, with individual pesticides reaching maximum concentrations of 1300 ng/L in the surface-water samples (tebufenozide) and 1100 ng/g dry weight in the soil samples (bromophos-ethyl). The semi-structured interviews made it quite evident that the instructions that farmers are provided regarding the use of pesticides are rudimentary, and that overuse is common. The perceived effect of pesticides was seen as an end-point, and there was a limited process of optimally matching pesticides to pests and crops. Several pesticides were used regularly on the same crop, and the period between application and harvest varied. Risk analysis showed that bromophos-ethyl, dichlorvos, and iprobenfos presented a very high risk to aquatic organisms in both the dry and rainy seasons, with risk quotient values of 850 for both seasons, and of 67 in the dry season and 78 in the rainy season for bromophos-ethyl, and 49 in the dry season and 16 in the rainy season for dichlorvos. Overall, this work highlights the occurrence of pesticide residues in surface water and soil along the Mekong River in Cambodia, and emphasizes the urgent need for monitoring and improving pesticide practices and regulations in the region.

Study on the acute toxicity of trichlorfon and its breakdown product dichlorvos to goldfish (Carassius auratus) based on 1H NMR metabonomics

Trichlorfon, one of the most widely used organophosphate insecticides, is commonly employed in aquaculture and agriculture to combat parasitic infestations. However, its inherent instability leads to rapid decomposition into dichlorvos (DDVP), increasing its toxicity by eightfold. Therefore, the environmental effects of trichlorfon in real-world scenarios involve the combined effects of trichlorfon and its degradation product, DDVP. In this study, we systematically investigated the degradation of trichlorfon in tap water over time using HPLC and LC-MS/MS analysis. Subsequently, an experiment was conducted to assess the acute toxicity of trichlorfon and DDVP on goldfish (Carassius auratus), employing a 1H NMR-based metabolic approach in conjunction with serum biochemistry, histopathological inspection, and correlation network analysis. Exposure to trichlorfon and its degradation product DDVP leads to increased lipid peroxidation, reduced antioxidant activity, and severe hepatotoxicity and nephrotoxicity in goldfish. Based on the observed pathological changes and metabolite alterations, short-term exposure to trichlorfon significantly affected the liver and kidney functions of goldfish, while exerting minimal influence on the brain, potentially due to the presence of the blood-brain barrier. The changes in the metabolic profile indicated that trichlorfon and DDVP influenced several pathways, including oxidative stress, protein synthesis, energy metabolism, and nucleic acid metabolism. This study demonstrated the applicability and potential of 1H NMR-based metabonomics in pesticide environmental risk assessment, providing a feasible method for the comprehensive study of pesticide toxicity in water environments.

Application of the QuEChERS method for the determination of pesticides, PAHs and PCBs in fish in Senegal

Pollution of water by persistent organic pollutants is well described; however, little is known about the accumulation of these pollutants by aquatic organisms. For this reason, a method based on QuEChERS extraction and gas chromatography coupled to tandem mass spectrometry (GC-MS/MS) was developed for the determination of pesticides, polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) in the muscles of five fish species from the bay of Soumbedioune (Dakar, Senegal). This method shows good recoveries of extraction (68.2-98.1% for pesticides, 83.87-98.10% for PAHs and 81.30-98.15% for PCBs), precision (% RSD ≤ 1%), sensitivity (LODs between 0.001 and 0.079 ng g^-1), linearity (R² ≥ 0.99) and repeatability and reproducibility, evaluated for three concentration levels (10 ng g^-1, 200 ng g^-1 and 500 ng g^-1), ≤ 15% for the majority of pollutants under study except for alachlor, atrazine, acetochlor, dicofol, deltamethrin and dichlorvos where a RSD ≥ 20% was determined for the 10 ng g^-1 concentration. Organic pollutants have been detected in fish from the Soumbedioune coast demonstrating the necessity of a regular survey of water and fish in order to protect the populations.

Simultaneous determination of 79 pesticides in pigeonpea grains using GC-MS/MS and LC-MS/MS

Pigeonpea grains are important sources of vegetarian proteins. It is the paramount importance to check the pesticide residues due to their frequent use during production. The LC-MS/MS and GC-MS/MS analytical method was developed and validated for the simultaneous determination of 79 pesticide residues in pigeonpea. The LOD and LOQ of the analytical method were in the range of 0.53 to 3.97 and 1.60 to 10.05 µg kg^-1, respectively, with a correlation coefficient of more than 0.997. Average recoveries were in the range of 80 to 118.8%, with the RSD of less than 15%. Measurement uncertainty (U_x) for pesticides was in the range of 3.42 to 12.76 µg kg^-1 evaluated at 50 µg kg^-1. The method was applied to analyze the sample collected from the farmer's field. This method could be useful for routine analysis of selected pesticide residue for monitoring purposes.

Smartphone-based enzyme-free fluorescence sensing of organophosphate DDVP

A novel fluorescence strategy based on the outstanding catalytic capability of CuS nanoparticles (CuS_NPs) has been developed for highly sensitive and specific determination of o,o-dimethyl-o-2,2-dichlorovinyl phosphate (DDVP) under enzyme-free and hydrogen peroxide (H₂O₂)-free conditions. In the presence of DDVP, CuS_NPs can catalyze non-fluorescence substratum of Amplex red (AR) into resorufin, which exhibits fluorescence emission at 584 nm under excitation at 540 nm. The sensing system exhibits outstanding specificity and only responds to DDVP and no other organophosphorus pesticides (OPs). A wide linear range is obtained from 0.0001 to 0.1 μg/mL, and the limit of detection (LOD) is 0.1 ng/mL. Furthermore, paper-based test strips have been constructed for visual detection of DDVP under ultraviolet light irradiation. By integrating a smartphone installed with Color Picker APP, point-of-care detection with quantitative determination is realized, demonstrating substantial potential applications of the as-developed assay for in situ detection. Graphical abstract.

Deriving water quality criteria for China for the organophosphorus pesticides dichlorvos and malathion

Organophosphorus pesticides are effective, cheap, and used extensively but can harm aquatic organism and human health. Here, water quality criteria (WQCs) for dichlorvos (DDVP) and malathion (MAL) were derived. Nine aquatic organisms native to China were used in toxicity tests. Published toxicity data for aquatic organisms native and non-native to China were also analyzed. DDVP and MAL WQCs were derived using (log-normal model) species sensitivity distributions. Species sensitivity distribution curves indicated native and non-native species have different sensitivities to DDVP. The sensitivities of native and non-native species to MAL were not different because non-native species data for fewer than eight genera were available, so further research is required. The results indicated that native species need to be considered when deriving WQCs. The criteria maximum concentration (CMC) and criteria continuous concentration (CCC) were 1.33 and 0.132 μg/L, respectively, for DDVP, and 0.100 and 0.008 μg/L, respectively, for MAL. The CMCs for DDVP and MAL derived using ETX 2.0 software and species sensitivity ranks were different from the CMCs obtained using the SSD method because of parameter uncertainties. The DDVP and MAL WQCs were significantly lower than Chinese surface water quality standard thresholds. The results provide basic data for revising these thresholds.

A liquid chromatography-tandem mass spectrometry method to simultaneously determinate dichlorvos and phoxim in tobacco

A simple pretreatment method with liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed and validated to simultaneously determine dichlorvos and phoxim in tobacco and soil matrices. Satisfactory linearity (R2  ≥ 0.9991) of the method was obtained for both analytes. The limits of detection and limits of quantification for dichlorvos and phoxim in three matrices were 0.0015-0.006 and 0.005-0.02 mg/kg, respectively. Average recoveries were 78.24-92.21% for dichlorvos and 76.62-100.51% for phoxim in soil, green tobacco leaves and cured tobacco leaves. The intra- and inter-day relative standard deviations were <6%. The established method was successfully applied for the residual analysis of dichlorvos and phoxim in real soil and tobacco samples. The results indicated that the established method could be used to detect trace amounts of dichlorvos and phoxim in tobacco. The data could also help the Chinese government establish maximum residue limits of dichlorvos and phoxim on tobacco and establish proper and safe use of dichlorvos and phoxim on tobacco plants in China.

Micropollutants removal and health risk reduction in a water reclamation and ecological reuse system

As reclaimed water use is increasing, its safety attracts growing attention, particularly with respect to the health risks associated with the wide range of micropollutants found in the reclaimed water. In this study, sophisticated analysis was conducted for water samples from a water reclamation and ecological reuse system where domestic wastewater was treated using an anaerobic-anoxic-oxic unit followed by a membrane bioreactor (A²O-MBR), and the reclaimed water was used for replenishing a landscape lake. A total of 58 organic micropollutants were detected in the system, consisting of 13 polycyclic aromatic hydrocarbons (PAHs), 16 phenols, 3 pesticides, and 26 pharmaceuticals and personal care products (PPCPs). After treatment by the A²O-MBR process, effective removal of pesticides and phenols was achieved, while when the reclaimed water entered the landscape lake, PPCPs were further removed. From the physicochemical properties of micropollutants, it could be inferred that phenols and dichlorphos (the only pesticide with considerable concentration in the influent) would have been mainly removed by biodegradation and/or volatilization in the biological treatment process. Additionally, it is probable that sludge adsorption also contributed to the removal of dichlorphos. For the predominant PPCP removal in the landscape lake, various actions, such as adsorption, biodegradation, photolysis, and ecologically mediated processes (via aquatic plants and animals), would have played significant roles. However, according to their logK_oc, logK_ow and logD (pH = 8) values, it could be concluded that adsorption by suspended solids might be an important action. Although carcinogenic and non-carcinogenic risks associated with all the detected micropollutants were at negligible levels, the hazard quotients (HQs) of PPCPs accounted for 92.03%-97.23% of the HQ_Total. With the significant removal of PPCPs through the ecological processes in the landscape lake, the safety of reclaimed water use could be improved. Therefore, the introduction of ecological unit into the water reclamation and reuse system could be an effective measure for health risk reduction posed by micropollutants.

The effect of dichlorvos on control of drosophila and its safety evaluation under different application methods

Drosophila is a common strawberry pest. In this work, toxicities of the 77.5% EC dichlorvos to 3rd instar larvae and adults of drosophila were evaluated through indoor bioassays and field bioassays, respectively. To insure the safety, dichlorvos dissipation and terminal residue in strawberry by different application methods under field conditions were determined by high-performance liquid chromatography. The decline curves of dichlorvos residues in strawberry corresponded with first-order kinetics, and dichlorvos dissipated rapidly in strawberry with half-life (t_1/2) of 7.58-13.17 h. Terminal residues below the maximum residue limit of strawberry and soil in different distance were achieved after 24 h under different application methods. This article provides guidance to the proper and safe use of dichlorvos in agriculture; it is more reasonable that dichlorvos is applied by embedding on the ground near the strawberry plants covered plastic film with holes.

Catalytic Degradation of Dichlorvos Using Biosynthesized Zero Valent Iron Nanoparticles

The removal of dichlorvos contamination from water is a challenging task because of the presence of direct carbon to phosphorous covalent bond, which makes them resistant to chemical and thermal degradation. Although there have been reports in the literature for degradation of dichlorvos using nanomaterials, those are based on photocatalysis. In this paper, we report a simple and rapid method for catalytic degradation of dichlorvos using protein-capped zero valent iron nanoparticles (FeNPs). We have developed an unprecedented reliable, clean, nontoxic, eco-friendly, and cost-effective biological method for the synthesis of uniformly distributed FeNPs. Yeast extract was used as reducing and capping agent in the synthesis of FeNPs, and synthesized particles were characterized by the UV-visible spectroscopy, X -ray diffraction, Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM). TEM micrographs reveal that the nanoparticles size is distributed in the range of 2-10 nm. Selected area electron diffraction pattern shows the polycrystalline rings of FeNPs. The mean size was found to be 5.006 nm from ImageJ. FTIR spectra depicted the presence of biomolecules, which participated in the synthesis and stabilization of nanoparticles. As synthesized, FeNPs were used for the catalytic degradation of dichlorvos in aqueous medium. The degradation activity of the FeNPs has been investigated by the means of incubation time effect, oxidant effect, and nanoparticle concentration effect. The ammonium molybdate test was used to confirm the release of phosphate ions during the interaction of dichlorvos with FeNPs.

Determination of airborne concentrations of dichlorvos over a range of temperatures when using commercially available pesticide strips in a simulated military guard post

Dichlorvos is a chemical compound which has been used for decades as a pesticide. Potential inhalational exposure to dichlorvos vapor associated with using commercially-based, dichlorvos-impregnated resin strips in a simulated military guard post was evaluated. A varying number of these pesticide strips, ranging from the manufacturer's guidelines ((3)-16 g strips) up to a full package of strips ((12)-16 g strips), were placed in a small, enclosed space (2.31 m x 2.26 m x 2.44 m, 12.7 m³), which was similar in size to a typical military guard post. Static air sampling was then conducted to simulate personal air sampling, followed by analysis using OSHA Method 62 (GC-ECD). Air sampling was conducted over a range of discrete temperatures (26-38˚C) which approximated average ambient temperatures expected in a variety of deployed environments. Air sampling in this range was conducted to determine the airborne concentration generated at each temperature setting. Airborne concentrations were then compared to established short term military exposure guidelines (MEGs) and the 8-hr OSHA permissible exposure limit (PEL) for dichlorvos (both criteria limits are 0.99 mg/m³). Results from air sampling indicated that exceeding the manufacturer-recommended number of strips for the workspace volume and environmental conditions produced airborne dichlorvos concentrations above established occupational standards (1.77-3.70 mg/m³). Such exposures may potentially lead to adverse effects, such as loss of mental and visual acuity for guard post watch standers who employ more strips within a space than recommended per the manufacturer for the size of the space. However, concentrations of airborne dichlorvos generated when adhering to manufacturer's guidelines based on workspace volume resulted in levels of 0.16-0.39 mg/m³ for 1-hr and 8-hr timeframes, which were below the established occupational health limits. While dichlorvos-impregnated strips are not currently recommended for use in manned workspaces for periods > 4 hr, findings suggest that prolonged use (8 hr) of similar pesticide strips within manned spaces to repel and/or kill disease-carrying insects may be possible without experiencing adverse health effects.

Automated high-throughput in vitro screening of the acetylcholine esterase inhibiting potential of environmental samples, mixtures and single compounds

A high-throughput and automated assay for testing the presence of acetylcholine esterase (AChE) inhibiting compounds was developed, validated and applied to screen different types of environmental samples. Automation involved using the assay in 96-well plates and adapting it for the use with an automated workstation. Validation was performed by comparing the results of the automated assay with that of a previously validated and standardised assay for two known AChE inhibitors (paraoxon and dichlorvos). The results show that the assay provides similar concentration-response curves (CRCs) when run according to the manual and automated protocol. Automation of the assay resulted in a reduction in assay run time as well as in intra- and inter-assay variations. High-quality CRCs were obtained for both of the model AChE inhibitors (dichlorvos IC50=120µM and paraoxon IC50=0.56µM) when tested alone. The effect of co-exposure of an equipotent binary mixture of the two chemicals were consistent with predictions of additivity and best described by the concentration addition model for combined toxicity. Extracts of different environmental samples (landfill leachate, wastewater treatment plant effluent, and road tunnel construction run-off) were then screened for AChE inhibiting activity using the automated bioassay, with only landfill leachate shown to contain potential AChE inhibitors. Potential uses and limitations of the assay were discussed based on the present results.

Degradation of four organophosphorous pesticides catalyzed by chitosan-metal coordination complexes

Three types of chitosan with high (3.40 × 10(6)), medium (2.11 × 10(5)), and low (5.89 × 10(4)) molecular weights were chosen as ligands to synthesize chitosan magnesium, calcium, iron(III), and zinc coordination complexes. Degradation of four organophosphorous pesticides (dichlorvos, omethoate, dimethoate, and chlorpyrifos) by the above complexes in a heterogeneous system was studied using solid-phase extraction (SPE) and gas chromatography (GC). The degradation effect is related to the different types of chitosan, metal, and organophosphorus pesticides (OPs). Complexes of transition metals and the low molecular weight chitosan showed high hydrolytic activity. The chitosan-iron(III) complex was further used to study its catalytic kinetics on the hydrolysis of OPs. At pH 7.0 and 20 °C, the half-life of dichlorvos hydrolyzed by chitosan iron(III) was 52 h, whereas that of spontaneous dichlorvos hydrolysis was 105 h. The degradation ratio of omethoate and dimethoate increased to 38 and 52 %, respectively, which were 34 and 48 % higher than the control after 6 days at pH 7.0 and 20 °C. For all tested conditions, an increase of pH and temperature resulted in a higher degradation rate.

A molecularly imprinted polymer based a lab-on-paper chemiluminescence device for the detection of dichlorvos

In this work, a new molecularly imprinted polymer (MIP) based lab-on-paper device with chemiluminescence (CL) detection of dichlorvos (DDV) was designed. With the circle-shaped device, the MIP layer with certain depth was synthesized and adsorbed on the paper surface and DDV can be selectively imprinted on it. The adsorption and washing procedures can be achieved well on the paper-based chip. The paper-based device was fabricated by a simple cutting method and many chips can be made at the same time. On the basis of DDV enhancing CL of luminol-H2O2 greatly, the proposed MIP based lab-on-paper CL device showed better selectivity to DDV and it has been applied to the determination of DDV in vegetables in the range of 3.0 ng/mL-1.0 μg/mL with the detection limit of 0.8 ng/mL. This study has made a successful attempt in the development of highly selective and sensitive monitoring of DDV in real samples and will provide a new approach for sensitive and specific assay in environmental monitoring.

Compound specific isotope analysis of organophosphorus pesticides

Compound-specific isotope analysis (CSIA) has been established as a tool to study the environmental fate of a wide range of contaminants. In this study, CSIA was developed to analyse the stable carbon isotope signatures of the widely used organophosphorus pesticides: dichlorvos, omethoate and dimethoate. The linearity of the GC-C-IRMS system was tested for target pesticides and led to an acceptable isotope composition within the uncertainty of the instrument. In order to assess the accuracy of the developed method, the effect of the evaporation procedure on measured carbon isotope composition (δ(13)C) values was studied and showed that concentration by evaporation of solvents had no significant isotope effect. The CSIA was then applied to investigate isotope fractionation of the hydrolysis and photolysis of selected pesticides. The carbon isotope fractionation of tested pesticides was quantified by the Rayleigh model, which revealed a bulk enrichment factor (ε) of -0.2±0.1‰ for hydrolysis of dichlorvos, -1.0±0.1‰ and -3.7±1.1‰ for hydrolysis and photolysis of dimethoate respectively. This study is a first step towards the application of CSIA to trace the transport and degradation of organophosphorus pesticides in the environment.

[Characterization of pesticide residual dynamics by in situ attenuated total reflection FTIR]

In-situ attenuated total reflection FTIR (in situ ATR-FTIR) was used for the dynamic research on the residual of pesticide. The in-situ characterization of dichlorvos and orthene on the tomatoes' surface shows that the dichlorvos has obvious volatility and its degradation amount is 80% 20 minutes after spraying. Meanwhile, the ATR-FTIR shows that the strong absorption peak of dichlorvos at 1 734 cm(-1) turns to negative peaks and the absorption peaks at 3 073 cm(-1) significantly abate. The absorption peaks at 1 277 cm(-1) become weak and red shift (30 cm(-1)) shows that the dichlorvos may be hydrolyzed to some extent. While the absorption peaks of orthene show no change 120 minute after spraying. It shows that the orthene is relatively stable.

[Determination of 132 pesticide residues in tobacco by gas chromatography-tandem mass spectrometry]

A simple method for the determination of 132 pesticide residues in tobacco by gas chromatography-triple quadrupole tandem mass spectrometry (GC-MS/MS) was established. The influences of different extraction solvents, different buffer systems and different purifying agents on the recoveries of pesticides were investigated. The tobacco sample was extracted with acetonitrile, then cleaned up by the mixed sorbents of primary secondary amine (PSA) and octadecylsilane (C18E). After dried by nitrogen, the extract residue was reconstituted with n-hexane-acetone (9:1, v/v). GC-MS/MS in multi-reaction monitoring (MRM) mode was used as the detection method and triphenyl phosphate (TPP) as the internal standard. All of the 132 pesticides had good linear relationships (r2 > 0.99) between 20 microg/kg and 2 000 microg/kg. At the three spiked levels of 50, 200 and 500 microg/kg in the tobacco extract, the average recoveries of all the pesticides were in the range of 68.10% to 123.15% except for mirex and hexachlorobenzene; moreover, the relative standard deviations (RSDs) of them were between 1.79% and 19.88%. We participated in the CORESTA (Cooperation Centre for Scientific Research Relative to Tobacco) 2012's co-experiment. The results of our method and the existed standard methods had good consistency. The accurate, reliable and sensitive method can be applied to the determination of the 132 pesticide residues in tobacco for rapid screening and quantitative analysis.

Pathological effects of dichlorvos and fenitrothion in mice

Seeds of faba and soybeans were treated with dichlorvos (12 mg/kg) and fenitrothion (5 mg/kg) insecticides and stored for 30 weeks. The total internal residues of dichlorvos and fenitrothion amounted to about 69%, 73% and 67%, 74% in the applied doses in faba and soybeans, respectively. The pathological potential of dichlorvos and fenitrothion residues was studied by feeding mice for 90 days with the treated seeds. Parallel studies were conducted in two control groups. Liver and kidney were taken for histological examinations. The results of blood biochemistry are supported by the histopathological changes observed in the liver and kidney of treated mice. Dichlorvos and fenitrothion insecticides caused degenerative changes in the liver and kidney of mice. Changes were more intense in mice which were given beans treated with dichlorvos than in mice fed on beans treated with fenitrothion. The livers of both treated groups showed an abnormal size and shape of hepatic cells. The kidneys of treated mice showed tubular vascular degeneration and lumen dilatation in both groups as compared with the control group.

Characterization of type "B" esterases and hepatic CYP450 isoenzimes in Senegalese sole for their further application in monitoring studies

In fish, the role that cholinesterases (ChEs) play in tissues other than those implicated in neural activity, as well as the involvement of carboxylesterases (CbEs) and cytochrome P450 isoenzymes (CYPs) in drug metabolism needs investigation. For that, Senegalese sole (Solea senegalensis) specimens were selected for characterization of several type B esterases and hepatic CYPs in order to further use this fish as sentinel. ChEs (acetylcholinesterase (AChE) and pseudocholinesterases (butyrylcholinesterase-BuChE and propionilcholinesterase-PrChE)) and CbEs were measured in brain, plasma, kidney, liver, gonad, muscle and gills. Moreover, seven fluorimetric substrates were selected to study CYP related activities in fish liver. The results showed that AChE was the dominant ChE form in brain whereas pseudocholinesterases were absent in most tissues, as demonstrated by low enzymatic activities using specific substrates and the lack of inhibition by iso-OMPA. Plasma exhibited trace activities of all the esterases assayed and no BuChE activity. CbEs were dominant in liver, but they were also present in kidney and brain. For CbE determination, α-naphtyl acetate (αNA) was seen as the most adequate substrate as it displayed higher enzymatic activities and showed more in vitro sensitivity to the carbamate eserine and the organophosphate pesticide dichlorvos. Alkoxyresorufin-O-dealkylase (EROD and BFCOD) activities, indicative in mammals of CYP1A and CYP3A subfamilies, respectively, were the highest microsomal CYP-related activities in liver. The results of this preliminary work allow us to select the most adequate esterase substrate, tissue and hepatic CYP substrate for further monitoring studies.

A screen-printed, amperometric biosensor for the determination of organophosphorus pesticides in water samples

An amperometric biosensor based on screen-printed electrodes (SPEs) was developed for the determination of organophosphorus pesticides in water samples. The extent of acetylcholinesterase (AChE) deactivation was determined and quantified for pesticide concentrations in water samples. An enzyme immobilization adsorption procedure and polyacrylamide gel matrix polymerization were used for fabrication of the biosensor, with minimal losses in enzyme activity. The optimal conditions for enzyme catalytic reaction on the SPEs surfaces were acetylthiocholine chloride (ATChCl) concentration of 5 mmol/L, pH 7 and reaction time of 4 min. The detection limits for three organophosphorus pesticides (dichlorvos, monocrotophs and parathion) were in the range of 4 to 7 microg/L when an AChE amount of 0.1 U was used for immobilization.

[Determination of 88 pesticide residues in cranberry plant extract by gas chromatography-triple quadrupole tandem mass spectrometry]

A method by using a modified QuEChERS (quick, easy, cheap, effective, rugged and safe) and gas chromatography-triple quadrupole tandem mass spectrometry (GC-MS/MS) was established to analyze 88 pesticide residues in cranberry plant extract. The sample was extracted with acetone-hexane (1: 1, v/v) containing 1% acetic acid, then cleaned-up by ethylenediamine-N-propyl silyl (PSA) and graphite carbon (GCB). The extract was determined by GC-MS/MS in multi-reaction monitoring (MRM) mode, and external standard method was applied to quantified the pesticides. All the 88 pesticides showed good linearity in the range of 0. 001 - 0. 2 mg/L, and the limits of quantification (LOQs, S/N > or = 10) were all less than 31. 5 microg/kg. The average recoveries of all the pesticides were in the range of 71. 4% to 116. 6% at three spiked levels of 5, 25 and 50 microg/kg in cranberry plant extract, with the relative standard deviations (RSDs) of 2. 4% - 16. 9%. The results demonstrated that this method is simple, rapid and suitable for the determination of 88 pesticide residues in cranberry plant extract. The analytical sensitivity and accuracy can meet the requirements of multiple pesticide residue analysis.

The dissipation rates of trichlorfon and its degradation product dichlorvos in cabbage and soil

The residual levels and dissipation rate of trichlorfon, and its degradation product, dichlorvos, in cabbage crops and the soil in which these were grown, were determined by gas chromatography at two geographically distant experimental sites, one in Kunming and one in Beijing, China. Trichlorfon was applied at two dosages (900 g ai ha(-1) and 1350 g ai ha(-1)). Maximum final residues of trichlorfon in soil and cabbage were 1.23 mg kg(-1) and 1.81 mg kg(-1) respectively at Kunming, and 0.35 mg kg(-1) and 0.70 mg kg(-1) respectively at Beijing. However, the final residues of dichlorvos in both cabbage and soil was only 0.04 mg kg(-1) at Kunming, and only 0.03 mg kg(-1), or "not detectable", at Beijing. The mean half-life of trichlorfon in cabbage was 1.80 d with a dissipation rate of 90% over 5 d, while that in soil was 3.05 d with a dissipation rate of 90% over 14 d at one experimental site. The dissipation rates of trichlorfon and its degradation product dichlorvos at the two experimental sites were different, suggesting that degradation of these pesticides was affected by local soil characteristics and climate. When applied at both the recommended dosage and at 1.5 times this, no detectable residues of either trichlorfon or dichlorvos were found in soil or cabbage at harvest. Although trichlorfon can easily degrade into dichlorvos, which is highly toxic to humans and other animals, the observed low residual levels of dichlorvos suggest that trichlorfon is safe when applied at the recommended dosage.

Disposable screen-printed electrode coupled with recombinant Drosophila melanogaster acetylcholinesterase and multiwalled carbon nanotubes for rapid detection of pesticides

Recombinant Drosophila melanogaster acetylcholinesterase (R-DmAChE), multiwalled carbon nanotubes (MWCNTs), and Prussian blue have been combined for development of a three-electrode biosensor with more rapid responses and higher stability than in our previous study. A new disposable screen-printed electrode (SPE) was developed for rapid detection of organophosphate and carbamate pesticides. After optimization, 10 microg MWCNT and 5 microL enzyme immobilization solution consisting of 0.2% glutaraldehyde, 0.1% Nafion, 0.2% bovine serum albumin, 0.1 g/L MWCNT, and 1.5 mU R-DmAChE were fixed on each of the R-DmAChE/MWCNT SPEs. The LOD of this biosensor was 0.5 microg/L for pesticide standards of dichlorvos (DDV) and carbofuran. The performance of this biosensor was tested for vegetable and water samples at various spiked levels, and good stability and sensitivity were found. The obtained recoveries were from 82.6 to 110.5% for DDV at levels of 0.5-5 microg/L and 73.4 to 118.4% for carbofuran at 1-10 microg/L in lake and sea water samples, demonstrating that the proposed approach is an alternative means for rapid detection of pesticide residues and contaminants in food safety and environmental monitoring.

[Determination of dichlorvos in water by microwave-assisted-headspace-liquid-phase microextraction coupled with high performance liquid chromatography]

A novel method for the determination of dichlorvos in environmental water samples has been developed using microwave-assisted-headspace-liquid-phase microextraction (MAE-HS-LPME) coupled with high performance liquid chromatography (HPLC). The influences of extraction parameters in the sample matrix were investigated. Under optimized experimental conditions, the detection limit (S/N = 3), the quantification limit (S/N = 10) and the enrichment factor of the proposed method for the target analyte were 0.96 microg/L, 3.20 microg/L and 54, respectively. The recoveries of target analyte spiked in real water samples were 87.4%-103%. The extraction performance of MAE-HS-LPME to the target analyte was also compared with liquid-liquid extraction (LLE). The results indicated that the developed method is simple, rapid, efficient, solvent-saving, highly selective and widely applicable.

Reduction of dichlorvos and omethoate residues by O2 plasma treatment

A practical, inexpensive, and green chemical process is greatly needed for degrading pesticides in food and environmental water. In this work, the impact of O(2) plasma treatment on reduction of dichlorvos (DDVP) and omethoate in maize was determined by gas chromatography (GC). The main plasma-induced degradation mechanisms were investigated through identification of intermediates or products during O(2) plasma treatment for DDVP and omethoate on solid surfaces by gas chromatography/mass spectrometry (GC/MS). The results clearly demonstrate that O(2) plasma treatment is significantly effective in the degradation of original DDVP and omethoate, and the degradation efficiency mainly depends upon related operating parameters and chemical structures of pesticides. Moreover, GC/MS analyses show that DDVP and omethoate molecules are degraded into less-toxic compounds, and the plasma degradation mechanisms for pesticides can be dominated by a free-radical reaction. It is concluded that O(2) plasma has the potential to reduce pesticide residues in agricultural products.

Simultaneous determination of omethoate and dichlorvos by capillary electrophoresis

A capillary electrophoresis method has been developed for the analysis of omethoate and dichlorvos. Response surface methodology (RSM) was used to optimize the separate conditions for simultaneous detection of omethoate and dichlorvos. The results indicated that the optimal conditions for omethoate and dichlorvos determination were; pH 7.64, SDS concentration 67.5 mM, separation voltage 19.0 KV. Quantitative linear ranges were 1.0-300 microg/mL for omethoate and dichlorvos with correlation of 0.9967 and 0.9965, respectively. The limits of detection were 0.046 microg/mL and 0.031 microg/mL for omethoate and dichlorvos, with relative standard deviations (R.S.D.) <3.6%. The value of recoveries for omethoate and dichlorvos were arranged from 94.1% to 106.0%.

TLC-spectrophometric separation and trace determination of monocrotophos and dichlorvos in enviromental and biological samples

Organophosphorus insecticides, monocrotophos and dichlrovos are increasingly being used in agriculture to control insects on a wide range of crops. Their ready access has resulted in misuse in many instances of homicidal and suicidal poisoning cases. This paper describes about a chromogenic spray reagent for the detection/determination of monocrophos and dichlrovos in environmental and biological samples by TLC and spectrophotometric method. Monocrotophos and dichlorvos on alkaline hydrolysis yield N-methyl acetoacetamide and dichlroacetaldehyde respectively, which in turn react with diazotized p-amino acetophenone to give red-violet and red coloured compounds. Other organophosphorus insecticides do not give this reaction. Moreover, organochlorine and synthetic pyrethroid insecticides and constituents of viscera (amino acids, peptides, proteins etc), which are generally coextracted with the insecticides, do not interfere. However, phenolic compounds and hydrolysed product of carbamate insecticides may interfere and differentiate from monocrotophos and dichlrovos by Rf values. The lower limit of detection is 0.2 mg for monocrotophos and 0.1 mg for dichlorovos. The absorption maxima of the reddish-violet and red colour formed by monocrotophos and dichlrovos, are measured at 560 nm and 540 nm respectively. Beer's Law is obeyed over the concentration range of 1.2 to 6.8 mg and 6.2 to 35 mg in the final solution volume of 25 mL. The molar absorptivity and Sandell's sensitivity of monocrotophos and dichlrovos were found to be 7.1 x 10(5) (+100) 1 mole(-1) cm(-1) and 0.008 mg cm(-2), 1.2 x 10(5) 1 mole(-1) cm(-1) and 0.003 mg cm(-2) respectively. The standard deviation and relative standard deviation were found be +/- 0.005 and 2.05% +/- 0.007 and 2.02% respectively. The developed method has been successfully applied to the detection and determination of monocrotophos and dichlrovos in environmental and biological samples.

Acute toxicity and acetylcholinesterase inhibition in grass shrimp (Palaemonetes pugio) and oysters (Crassostrea virginica) exposed to the organophosphate dichlorvos: laboratory and field studies

The use of various organophosphates to control mosquito populations is a common practice across the globe. We review the literature (LC50s) on dichlorvos, the primary breakdown product of Dibrom, and use laboratory and field experiments to determine the lethal and sublethal (bioassays) effects of dichlorvos on two widely distributed and ecologically important estuarine invertebrate species, the marsh grass shrimp, Palaemonetes pugio and the Eastern oyster, Crassostrea virginica. Laboratory results based on LC50s and sublethal acetylcholinesterase (AChE) inhibition activity bioassays indicate that adult grass shrimp are more sensitive (approximately 500 x ) to dichlorvos than juvenile oysters. Although potentially an important factor for intertidal or shallow-dwelling estuarine organisms, the toxicity of dichlorvos was not enhanced in the presence of simulated sunlight for adult P. pugio. The most notable decreases in AChE activity were for grass shrimp and oysters exposed to dichlorvos concentrations above those considered ecologically relevant. In field experiments, both species were deployed in cages in unsprayed (n = 2) and sprayed (n = 3) sites and water samples collected pre- and post-spraying. Quantifiable dichlorvos levels were measured at the two narrowest creek treatment sites following mosquito spraying, suggesting that overspray can occur and there was evidence of a sublethal AChE response at these same sites. However, experiments at the widest creek revealed no measurable dichlorvos or sublethal responses. Results from this research suggest that adult grass shrimp are more sensitive to dichlorvos than juvenile oysters. Spraying near small tidal creeks may have measurable impacts on resident species, while larger (wider) creeks appear to be capable of buffering organisms from transient fluxes of mosquito control agents that may enter the system.

Pesticide detection with a liposome-based nano-biosensor

Monitoring of the organophosphorus pesticides dichlorvos and paraoxon at very low levels has been achieved with liposome-based nano-biosensors. The enzyme acetylcholinesterase was effectively stabilized within the internal nano-environment of the liposomes. Within the liposomes, the pH sensitive fluorescent indicator pyranine was also immobilized for the optical transduction of the enzymatic activity. Increasing amounts of pesticides lead to the decrease of the enzymatic activity for the hydrolysis of the acetylcholine and thus to a decrease in the fluorescent signal of the pH indicator. The decrease of the liposome biosensors signal is relative to the concentration of dichlorvos and paraoxon down to 10(-10)M levels. This biosensor system has been applied successfully to the detection of total toxicity in drinking water samples. Also a colorimetric screening device for pesticide analysis has been evaluated.

Acute toxic tests of rainwater samples using Daphnia magna

Rainwater samples were collected at Isogo Ward of Yokohama City, Japan, from 23 June to 31 July 2003. The toxic potency of pollutants present in 13 rainwater samples was tested using Daphnia magna. Most test animals died within 48 h in five test solutions that were prepared from rainwater samples. On the other hand, when nonpolar compounds such as pesticides were removed from rainwater samples before the toxic tests, mortalities in all test solutions were less than 10%. Eight kinds of pesticides were detected in rainwater samples. The highest concentration was of dichlorvos, at 0.74 microg/L. Results indicated that insecticides in rainwater sometimes lethally affected D. magna and that toxic potency of insecticides that are present in rainwater constitutes an important problem for environmental protection.

Residue levels of captan and trichlorfon in field-treated kaki fruits, individual versus composite samples, and after household processing

The dissipation of residue levels of captan and trichlorfon in field-treated kaki crops was studied according to good laboratory practices to propose maximum residue limits (MRLs). Residue levels of captan and trichlorfon were analysed by GC/MS and LC-MS/MS, respectively. Residue levels of captan and trichlorfon permitted one to propose MRLs in kaki of 3 and 5 mg kg(-1), respectively. The behaviour of these residues was also studied after peeling and cooking, and in individual fruits versus composite samples. Residue levels of these compounds for individual fruits suggested that a variability factor up to three could be set for the acute risk assessment. Levels of captan decreased by more than 90% after peeling and completely after cooking. Trichlorfon penetrates into the flesh in a proportion of 70% of the residue at the pre-harvest interval. Cooking resulted in a decrease of 27% of residue levels of trichlorfon.

An electrochemical bioassay for dichlorvos analysis in durum wheat samples

The use of an acetylcholinesterase inhibition assay for the detection of dichlorvos in durum wheat samples by a simplified extraction procedure is reported. After an incubation step, the residual activity was determined with an amperometric biosensor using a portable potentiostat. The use of electric eel and recombinant acetylcholinesterase was compared. The effect of the matrix extract was evaluated by using various sample:solvent ratios, 1:2.5, 1:5, 1:10, and 1:20. The optimal extraction ratio, considering the electrochemical interferences and the effect on enzyme activity and bioavailability of the pesticide, was 1:10. Calibrations were performed in buffer and durum wheat extract. The calculated detection limits in buffer solution were 10 ng/ ml and 0.045 ng/ml for electric eel and recombinant acetylcholinesterase, respectively, whereas operating in the matrix extract they increased up to 45 ng/ml and 0.07 ng/ml, corresponding to 0.45 mg/kg (extraction ratio 1:10) and 0.07 mg/kg in samples. These characteristics allowed the detection of contaminated samples at the maximum residue limit, which is 2 mg/kg and well below. Fortified samples of durum wheat were obtained with both dichlorvos and the commercial product Didivane, which contains dichlorvos as an active molecule. At all the tested levels, the occurrence of contaminant was detected with an average recovery of 75%. The total assay time, including the extraction step, was 30 min. Because several extractions as well as most of the assay steps can be run simultaneously, the throughput for one operator is 12 determinations per hour.

Dissipation of endosulfan and dichlorvos residues in/on cauliflower curds

Dissipation behaviour of endosulfan and dichlorvos in/on cauliflower, variety Snowball-16, was studied during rabi season (Sep.-March) 2003-2004. Endosulfan and dichlorvos were sprayed @ 350 and 110g a.i. with 115 g a.i., respectively, 80 days after transplanting. Samples were taken at the interval of 0 (1h after spray), 3, 5, 7, and 10 days after spray (DAS) in triplicate and residues were estimated on GC-ECD system equipped with capillary column. The initial deposits of 3.452 and 0.295microg g(-1) of endosulfan and dichlorvos dissipated to 0.084 (97.56%) and 0.009 (96.95%), respectively after 10 DAS. Residues of endosulfan reached below maximum residue limit of 2microg g(-1) one day after spray and of dichlorvos were below MRL value of 0.5microg g(-1) even on 0 day. Dissipation pattern followed first order kinetics for both the insecticides with half life periods of 1.81 and 2.08 days for endosulfan and dichlorvos, respectively.

Degradation of naled and dichlorvos promoted by reduced sulfur species in well-defined anoxic aqueous solutions

This work examines the reaction of reduced sulfur species (e.g., bisulfide, thiosulfate, thiophenolate) with naled, a registered insecticide, in well-defined anoxic aqueous solutions at 5 degrees C. High concentrations of reduced sulfur species can occur in the porewater of sediments and in anoxic subregions of estuaries. The dominanttransformation product from the reaction of naled with reduced sulfur species is dichlorvos, which indicates that debromination is the major reaction pathway. Dichlorvos is also a registered insecticide which is more toxic than naled. The second-order rate constants for reaction of naled with bisulfide and thiophenolate at 5 degrees C are 10.2 +/- 0.4 M(-1) s(-1) and 27.3 +/- 0.9 M(-1) s(-1), respectively, while the second-order rate constant for the reaction of naled with hydrogen sulfide and thiophenol are not significantly different from zero. The second-order rate constant of the reaction of naled with thiosulfate at 5 degrees C is 5.0 +/- 0.3 M(-1) s(-1). In contrast, the second-order rate constant of the reaction of dichlorvos with bisulfide at 25 degrees C is (3.3 +/- 0.1) x 10(-3) M(-1) s(-1). The activation parameters of the reaction of naled with bisulfide were also determined from the measured second-order rate constants over a temperature range. The results indicate that reduced sulfur species can play a very important role in the transformation of naled and dichlorvos in the coastal marine environment. It can be expected that in the presence of reduced sulfur species, naled is almost immediately transformed into the more toxic dichlorvos, which has an expected half-life of 4 days to weeks.

Atmospheric fate of dichlorvos: photolysis and OH-initiated oxidation studies

The OH-initiated oxidation of dichlorvos (a widely used insecticide) has been investigated under atmospheric conditions at the large outdoor European photoreactor (EUPHORE) in Valencia, Spain. The rate constant of OH reaction with dichlorvos, k, was measured by using a conventional relative rate technique where 1,3,5-trimethylbenzene (TMB) and cyclohexane were taken as references. With the use of the rate constants of 5.67 x 10(-11) and of 6.97 x 10(-12) cm3 molecule(-1) s(-1) for the reactions OH + TMB and OH + cyclohexane, respectively, the resulting value of the OH reaction rate constant with dichlorvos was derived to be k = (2.6 +/- 0.3) x 10(-11) cm3 molecule(-1) s(-1). The tropospheric lifetime of dichlorvos with respect to reaction with OH radical has been estimated to be around 11 h. The major carbon-containing products observed for the OH reaction with dichlorvos in air under sunlight condition were phosgene and carbon monoxide. The formation of a very stable toxic primary product such as phosgene associated with the relatively short lifetime of dichlorvos may make the use of this pesticide even more toxic for humans when released into the atmosphere.

Analysis of organophosphorus pesticides in whole milk by solid phase microextraction gas chromatography method

Solid phase microextraction (SPME) was used for the extraction of residual coumaphos and dichlorvos in whole milk. The residues were analyzed by capillary gas chromatography equipped with nitrogen phosphorus detector (GC-NPD). A manual SPME holder with a 100-microm polyacrylate fiber was used. The optimized conditions for extraction by SPME method were: sample agitation, absorption temperature of 30 degrees C, absorption time of 40 min, desorption time of 10 min, and sample volume was 16.0 mL in the vial. Under these conditions, the calibration graphs were linear in the range of 0.17 microgL-1 to 1.75 microgL-1 for coumaphos and 0.69 microgL-1 to 6.90 microgL-1 for dichlorvos. Precision was good with RSD values of 13% for coumaphos and 14% for dichlorvos. The detection limits (LOD) were 0.060 microgL-1 for dichlorvos and 0.052 for coumaphos. The quantification limits (LOQ) were 0.086 microgL-1 for dichlorvos and 0.066 microgL-1 for coumaphos. The results obtained in this study suggest that SPME is a suitable technique for residual pesticide analysis of milk. The data demonstrate that particular OP pesticides used in dairy farming in the region of Minas Gerais were found to contaminate cow whole milk, and the residues are not removed by treating the milk by boiling.

Determination of organophosphorus pesticide residues in the roots of Platycodon grandiflorum by solid-phase extraction and gas chromatography with flame photometric detection

A simple and rapid sample preparation method using accelerated solvent extraction and solid-phase extraction (SPE) cleanup for determining organophosphorus (OP) pesticides in the roots of Platycodon grandiflorum was developed. The OP pesticides were concentrated by use of an SPE cartridge (ENVI-Carb) and quantitatively analyzed and confirmed by capillary gas chromatography with flame photometric detection. The pesticides were eluted from the cartridges with 20 mL acetonitrile-toluene (3 + 1, v/v). The average recovery from 10 g PF grandiflorum roots, fortified at 3 levels ranging from 0.04 to 1.00 mg/kg, was 91.9% with a relative standard deviation of 4.3%. The limits of detection ranged from 1.16 x 10(-3) mg/kg (dimethoate) to 4.64 x 10(-3) mg/kg (dichlorvos). The proposed method showed acceptable accuracy and precision while minimizing environmental concerns, time, and labor.

Use of electrochemical biosensor and gas chromatography for determination of dichlorvos in wheat

Two methods for the determination of dichlorvos in durum wheat by electrochemical assay and gas chromatography, respectively, have been developed. Dichlorvos, an organophosphorus anticholinesterase pesticide, was extracted from wheat with hexane, and the filtered extract was directly analyzed by gas chromatography with nitrogen-phosphorus flame detection (NPD). Recoveries of dichlorvos from milled wheat spiked at 0.25-1.5 microg/g ranged from 96.5 to 100.9%, and the limit of detection was 0.02 microg/g. The electrochemical assay was based on the detection of choline, the acetylcholinesterase product, via a choline oxidase biosensor. An aliquot of the filtered hexane extract was partitioned with phosphate buffer solution, and the organic layer was evaporated prior to electrochemical analysis. A limit of detection of 0.05 microg/g of dichlorvos was obtained with mean recoveries of 97-103% at spiking levels of 0.25-1.5 microg/g. A good correlation (r = 0.9919) was found between the results obtained with the electrochemical and those obtained with the gas chromatographic methods. The electrochemical method was peer-validated in two laboratories that analyzed 10 blind samples (5 duplicates), including a blank and 4 spiked samples with dichlorvos at levels of 0.25, 0.60, 1.00, and 1.50 microg/g. Within-laboratory repeatability (RSDr) and between-laboratory reproducibility (RSDR) ranged from 5.5 to 7.8% and from 9.9 to 17.6%, respectively.

Genetically engineered acetylcholinesterase-based biosensor for attomolar detection of dichlorvos

The design of a biosensor for the detection of dichlorvos at attomolar levels is described based on a highly sensitive double mutant (E69Y Y71D) of the Drosophila melanogaster acetylcholinesterase (Dm. AChE). This enzyme has a k(i) for dichlorvos equal to 487 microM(-1)min(-1), which is 300 and 20,000 times higher than that of the wild type Dm. AChE and the Electrophorus electricus AChE (E.el. AChE), respectively. The enzyme is immobilized into microporous-activated conductive carbon, and is used as such for the development of an inhibitor electrochemical biosensor. This E69Y Y71D mutant enables the decrease in the detection limit of the biosensor down to 10(-17) M, which is five orders of magnitude lower compared to the Electropharus electricus-based biosensor and eight orders of magnitude lower than the biosensors described so far.

Electroanalytical method for determination of the pesticide dichlorvos using gold-disk microelectrodes

This paper reports the use of laboratory-prepared gold microelectrodes and square-wave voltammetry for analytical determination of low concentrations of the pesticide dichlorvos in pure and natural water samples. After optimization of the experimental and voltammetric conditions, the best voltammetric responses-current intensity and voltammetric profile-were obtained in 0.1 mol L(-1) NaClO4 with f=100 s(-1), a=50 mV, and DeltaE(s)=2 mV. The observed detection and quantification limits in pure water were 7.8 and 26.0 microg L(-1), respectively. The reproducibility and repeatability of the method were also determined; the results were 1.4% (n=5) and 1.2% (n=10), respectively. Possible interfering effects were evaluated in natural water samples collected at different points with different levels of contamination from agricultural, domestic, or industrial waste from an urban stream. Results showed that the detection and quantification limits increased as a function of the quantity of organic matter present in the samples. Nonetheless, the values observed for these method characteristics were below the maximum value allowed by the Brazilian code for organophosphorus pesticides in water samples. Recovery curves constructed using the standard addition method were shown to be satisfactory compared with those obtained from high-performance liquid chromatography, confirming the suitability of the method for analysis of natural water samples. Finally, when the method was used to determine dichlorvos in spiked cows' milk samples, satisfactory recovery and relative standard deviations were obtained.

Aerial and tidal transport of mosquito control pesticides into the Florida Keys National Marine Sanctuary

This project was undertaken as the initial monitoring program to determine if mosquito adulticides applied along the Florida Keys cause adverse ecological effects in the Florida Keys National Marine Sanctuary (FKNMS). The study monitored the distribution and persistence of two mosquito adulticides, permethrin and dibrom (naled), during three separate routine applications by the Florida Keys Mosquito Control District. The approach was to determine if toxic concentrations of the pesticides entered the FKNMS by aerial drift or tidal transport. The amount of pesticide entering the FKNMS by way of aerial drift was monitored by collection on glass fiber filter pads, set on floats in a grid pattern on either side of the FKNMS. Permethrin was recovered from filter pads on the leeward side for each of the three applications, ranging from 0.5 to 50.1 microg/m(2) throughout the study. Tidal current transport was monitored by collection of surface and subsurface water samples at each grid site. Tidal transport of naled and dichlorvos (naled degradation product) was apparent in the adjacent waters of the FKNMS. These compounds were detected in subsurface, offshore water at 0.1 to 0.6 microg/1, 14 hr after application. Permethrin was not detected in offshore water samples; however, concentrations ranging from 5.1 to 9.4 microg/l were found in surface water from the canal system adjacent to the application route. Comparison of the observed environmental concentrations with toxicity data (permethrin LC-50, 96 hr for Mysidopsis bahia = 0.02 microg/l) indicated a potential hazard to marine invertebrates in the canals with possible tidal transport to other areas.

Multiresidue determination of organophosphorus pesticides in ginkgo leaves by accelerated solvent extraction and gas chromatography with flame photometric detection

A rapid and simple method using accelerated solvent extraction and solid-phase extraction cleanup was developed and validated for the determination of 15 organophosphorus pesticides in ginkgo leaves by capillary gas chromatography with flame photometric detection. The pesticides were extracted at 100 degrees C under 1500 psi pressure in <20 min. The average recovery from 10 g ginkgo leaves, fortified at 3 levels ranging from 0.05 to 1.00 mg/kg, was 95.2% with a relative standard deviation of 4.6%. The limits of detection ranged from 1.11 x 10(-3) mg/kg (dimethoate) to 4.44 x 10(-3) mg/kg (dichlorvos). The proposed method showed acceptable accuracy and precision while minimizing environmental concerns, time, and labor. Furthermore, the method could be easily applied to the monitoring of these 15 organophosphorus pesticides in ginkgo leaves.

Characteristics of Trapping Various Organophosphorus Pesticides with a Ferritin Reactor of Shark Liver (Sphyrna zygaena)

A reactor is composed of liver ferritin of Sphyrna zygaena (SZLF) and an oscillating bag. A reactive procedure for trapping various organphosphorus pesticides (OPs) with the SZLF reactor in the flowing water is described in detail, showing the maximal trapping numbers of 28 +/-1.0 dichlorovos/SZLF, 42 +/- 1.0 dimethoate/SZLF, and 55 +/- 1.0 methamido-phos/SZLF determined by a improved spectrophotometric method in 12 h. In addition, it is found that the OP numbers trapped by the reactor increase along with the incubation time and its concentration increment in the flowing water (or seawater), respectively. This trapping capacity is considered to depend on the composition of amino acids on the surface of the ferritin shell interior rather than the available volume within the shell. A novel pathway for trapping various OPs with the ferritin is suggested in reference to unstable characteristics of the protein subunits. We claim that the ferritin reactor will be employed to monitor the contamination level of various OPs in the flowing water continuously.

Acetylcholinesterase-based biosensor electrodes for organophosphate pesticide detection

Screen-printed carbon electrodes modified with the dialdehydes, glutaraldehyde and terephthaldicarboxaldehyde, and then polyethyleneimine have been utilized for production of pesticide biosensors based on acetylcholinesterase. To improve the extent of dialdehyde modification, the electrodes were NH2-derivatized, initially by electrochemical reduction of 4-nitrobenzenediazonium to a nitroaryl radical permitting attachment to the carbon surface. Subsequent reduction of the 4-nitrobenzene yields a 4-aminobenzene modified carbon surface. Drosophila melanogaster acetylcholinesterase was immobilized either covalently onto dialdehyde modified electrodes or non-covalently onto polyethyleneimine modified electrodes. Internal diffusion limitations due to the dialdehyde and polyethyleneimine modifications increased the apparent Km of the immobilized enzyme. The thiocholine sensitivity was about 90% for dialdehyde modified electrodes and about 10% for polyethyleneimine modified electrodes as compared with non-modified carbon electrodes. The detection limit of the biosensors produced by non-covalent immobilization of acetylcholinesterase onto polyethyleneimine modified carbon electrodes was found to be about 10(-10) M for the organophosphate pesticide dichlorvos.

Pesticide vapours in confined atmospheres. Determination of dichlorvos by SPME-GC-MS at the microg m(-3) level

A method based on SPME is described for assessing the gaseous dichlorvos concentration in confined atmospheres like a greenhouse after a pesticide application. Sampling was made by using SPME with PDMS fibres immersed into a 250 mL sampling flask into which air samples were dynamically pumped from the analysed atmosphere. Sampling duration was 40 min and samples were then analysed by GC-MS. Calibration was performed from a vapour saturated air sample and gas phase diluted samples, and this procedure afforded a curve with a regression coefficient (R2) higher than 0.98. The repeatability of these measurements was observed with an RSD of 2.5%. This analysis procedure was then applied for the determination of gaseous dichlorvos concentrations versus time, in the atmosphere of an experimental 8 m2 and 20 m3 greenhouse. The pesticide was sprayed according to real cultivation conditions and measurements were made from 2 up to 74 h after application affording observed concentrations in the range of decades and hundreds of microg m(-3) (corresponding limits of detection and quantification were found at the level of a few microg m(-3)).

Organophosphorus pesticide residues in Mexican commercial pasteurized milk

A study was conducted to measure residues of 13 organophosphorus (OP) pesticides, widely used as dairy cattle ectoparasiticides or in crops used for animal feed, in homogenized and pasteurized Mexican milk samples. Four different milk brands with high distribution were collected biweekly during a 12 month period (n = 96) in supermarkets. OP pesticide residues were measured by gas chromatography with a flame photometric detector. Approximately 39.6% of the samples contained detectable levels of OP pesticide residues. Eight samples contained residues exceeding established maximum residue limits (MRL), and the OP pesticides present in these samples were dichlorvos (five samples), phorate, chlorpyrifos, and chlorfenvinphos (one sample, respectively). Average residues of 13 OP pesticides measured were below established MRLs ranging between 0.0051 and 0.0203 ppm.

Determination of dichlorvos by on-line microwave-assisted extraction coupled to headspace solid-phase microextraction and gas chromatography-electron-capture detection

The pretreatment technique of microwave-assisted extraction on-line headspace solid-phase microextraction (MAE-HS-SPME) was designed and studied for one-step in-situ sample preparation prior to the chromatographic analysis of a pesticide on vegetables. The pesticide on chopped vegetables was extracted into an aqueous solution with the aid of microwave irradiation and then directly onto the SPME fiber in headspace. After being collected on to the SPME fiber and desorbed in the GC injection port, the pesticide (dichlorvos) was analyzed with a GC-electron-capture detection system. The optimum conditions for obtaining extraction efficiency, such as the pH, the polarity modifier, and the salt added in sample solution, the microwave irradiation, as well as the desorption parameters were investigated. Experimental results indicated that the proposed MAE-HS-SPME technique attained the best extraction efficiency of 106% recovery under the optimized conditions, i.e. irradiation of extraction solution (10% aqueous ethylene glycol) at pH 5.0 with medium microwave power for 10 min. Desorption at 220 degrees C for 3 min offered the best detection result. The detection was linear at 5-75 microg/l with correlation coefficient of 0.9985. Detection limit was obtained at approximately 1.0 microg/l level based on S/N=3. The proposed method provided a very simple, fast, and solvent-less procedure to collect pesticides directly from vegetables for GC determination. Its application was illustrated by the analysis of trace dichlorvos in vegetables.

[Simultaneous determination of dichlorvos and trichlorfon in agricultural products by GC-FPD]

We studied a gas chromatographic method for the determination of dichlorvos (DDVP) and trichlorfon (DEP) in agricultural products. DDVP and DEP were extracted from agricultural products with acetone and re-extracted with ethyl acetate instead of dichloromethane. DDVP and DEP were eluted in one fraction on a silica gel column using n-hexane-acetone (1:1). DEP is a thermally labile compound, so it was derived to a more thermally stable compound by acylation with N-methylbis(trifluoroacetamide) and pyridine in acetone at 60 degrees C for 2 hours. DDVP and the DEP-TFA derivative were determined simultaneously by GC-FPD. The recoveries of DDVP and DEP from agricultural products spiked at levels of 0.1 microgram/g were 72.6-117.7% and 86.2-106.6%, respectively. The detection limits were 0.03 microgram/g in powdered tea and < or = 0.01 microgram/g in other samples. An interlaboratory study by 6 laboratories was conducted to validate this proposed method for 6 crops. Repeatability ranged from 3.1 to 7.8% for DDVP and from 3.4 to 8.3% for DEP, and reproducibility, from 6.9 to 15.5% for DDVP, and from 7.9 to 21.8% for DEP. Precision values were well within statistically predicted levels.

Effect of ultraviolet-absorbing vinyl film on organophosphorus insecticides dichlorvos and fenitrothion residues in spinach

Dichlorvos and fenitrothion residues found in spinach grown in greenhouse covered either by regular vinyl film or UV-absorbing vinyl film (UV-A) were analyzed by gas chromatography. After one day, dichlorvos residues in spinach covered with regular vinyl film and UV-A degraded by 97% and 80%, respectively, and degraded 100% after three days covered with regular vinyl film and six days covered with UV-A. After three days, fenitrothion residue in spinach covered with regular vinyl film degraded by 72% and then by 97% after six days; residue in spinach covered with UV-A degraded by 50% after three days and by 95% after six days. These results indicate that UV-A used to prevent the occurrence of insects and fungi in greenhouses reduced the degradation rates of dichlorvos and fenitrothion.