Analytical Methodology for Trace Determination of Propoxur and Fenitrothion Pesticide Residues by Decanoic Acid Modified Magnetic Nanoparticles.

A sensitive, rapid, reliable, and easily applicable method based on magnetic solid phase extraction (MSPE) combined with HPLC-PDA was developed for monitoring propoxur (PRO) and fenitrothion (FEN) pesticides in environmental water samples. The effect of major experimental variables on the extraction efficiency of both the pesticides was investigated and optimized systematically. For this purpose, a new magnetic material containing decanoic acid on the surface of particles was synthesized and characterized by XRD, FT-IR, SEM, EDX, and TGA analysis in detail. The simultaneous determination of pesticide molecules was carried out by using a Luna Omega C18 column, isocratic elution of acetonitrile (ACN): Water (70:30 v/v) with a flow rate of 1.2 mL min-1. After MSPE, the linear range for pesticide molecules (r2 > 0.9982) was obtained in the range of 5-800 and 10-800 ng mL-1, respectively. The limit of detections (LOD) are 1.43 and 4.71 ng mL-1 for PRO and FEN, respectively while RSDs % are below 3.5%. The applicability of the proposed method in four different environmental samples were also investigated using a standard addition-recovery procedure. Average recoveries at two spiking levels were over the range of 91.3-102.5% with RSD < 5.0% (n = 3). The obtained results show that decanoic acid grafted magnetic particles in MSPE combined with HPLC-PDA is a fast and simple method for the determination of PRO and FEN in environmental water samples.

High-throughput analysis of pesticides in minor tropical fruits from Colombia.

In this work, a method has been applied and validated for the determination of a group of 35 multiclass pesticides in the minor tropical fruits rose apple/pomarrosa (Syzygium malaccense), starfruit/carambola (Averrhoa carambola), yoyomo (Spondias purpurea) and papayuela (Vasconcellea pubescens) cultivated and exported in Colombia. The AOAC 2007.1 QuEChERS method, that uses an acetic acid/acetate buffer, was applied together with gas chromatography coupled to a triple quadrupole mass spectrometer. The method was validated in terms of calibration, recovery at three levels of concentration and matrix effects (MEs). A mixture of analyte protectants was also used. A good linearity was obtained in all cases, while the study of the ME revealed the need of developing matrix-matched calibration for many pesticides. Recovery values were in the range 70-120% with relative standard deviation values less than 20% for most of the pesticides studied. The lowest calibration level was 5 µg/kg. Several samples of each type were analysed.

N-methylcarbamate pesticides and their phenolic degradation products: hydrolytic decay, sequestration and metal complexation studies.

We report on the rates of decomposition of a group of N-methylcarbamate (NMC) pesticides (carbaryl, carbofuran and propoxur) under pre-determined tropical field conditions. Rates of decomposition for three NMCs were determined at pH 7.08 and T = 20 °C and pH 7.70 and T = 33 °C respectively, as follows: carbaryl (78 days and 69 days); carbofuran (143 days and 83 days) and propoxur (116 days and 79 days). Investigation on methods for removal of NMCs and their phenolic decomposition products shows that activated charcoal outperforms zeolite, alumina, diatomaceous earth, cellulose and montmorillonite clay in the removal of both NMCs and phenols from aqueous solution. Furthermore, metal complexation studies on the NMCs and phenols showed that Fe (III) forms a complex with isopropoxyphenol (IPP) within which the Fe:IPP ratio is 1:3, indicative of the formation of a metal chelate complex with the formula Fe(IPP)3.

Tropical surface water quality studies: Implications for the aquatic fate of N-methyl carbamate pesticides.

Water quality assessment was conducted on the Ruiru River, a tributary of an important tropical river system in Kenya, to determine baseline river conditions for studies on the aquatic fate of N-methyl carbamate (NMC) pesticides. Measurements were taken at the end of the long rainy season in early June 2013. Concentrations of copper (0.21-1.51 ppm), nitrates (2.28-4.89 ppm) and phosphates (0.01-0.50 ppm) were detected at higher values than in uncontaminated waters, and attributed to surface runoff from agricultural activity in the surrounding area. Concentrations of dissolved oxygen (8-10 ppm), ammonia (0.02-0.22 ppm) and phenols (0.19-0.83 ppm) were found to lie within normal ranges. The Ruiru River was found to be slightly basic (pH 7.08-7.70) with a temperature of 17.8-21.2°C. The half-life values for hydrolysis of three NMC pesticides (carbofuran, carbaryl and propoxur) used in the area were measured under laboratory conditions, revealing that rates of decay were influenced by the electronic nature of the NMCs. The hydrolysis half-lives at pH 9 and 18°C decreased in the order carbofuran (57.8 h) > propoxur (38.5 h) > carbaryl (19.3 h). In general, a decrease in the electron density of the NMC aromatic ring increases the acidity of the N-bound proton removed in the rate-limiting step of the hydrolysis mechanism. Our results are consistent with this prediction, and the most electron-poor NMC (carbaryl) hydrolyzed fastest, while the most electron-rich NMC (carbofuran) hydrolyzed slowest. Results from this study should provide baseline data for future studies on NMC pesticide chemical fate in the Ruiru River and similar tropical water systems.

Degradation of the insecticide propoxur by electrochemical advanced oxidation processes using a boron-doped diamond/air-diffusion cell.

A solution with 0.38 mM of the pesticide propoxur (PX) at pH 3.0 has been comparatively treated by electrochemical oxidation with electrogenerated H2O2 (EO-H2O2), electro-Fenton (EF), and photoelectro-Fenton (PEF). The trials were carried out with a 100-mL boron-doped diamond (BDD)/air-diffusion cell. The EO-H2O2 process had the lowest oxidation ability due to the slow reaction of intermediates with •OH produced from water discharge at the BDD anode. The EF treatment yielded quicker mineralization due to the additional •OH formed between added Fe2+ and electrogenerated H2O2. The PEF process was the most powerful since it led to total mineralization by the combined oxidative action of hydroxyl radicals and UVA irradiation. The PX decay agreed with a pseudo-first-order kinetics in EO-H2O2, whereas in EF and PEF, it obeyed a much faster pseudo-first-order kinetics followed by a much slower one, which are related to the oxidation of its Fe(II) and Fe(III) complexes, respectively. EO-H2O2 showed similar oxidation ability within the pH range 3.0-9.0. The effect of current density and Fe2+ and substrate contents on the performance of the EF process was examined. Two primary aromatic products were identified by LC-MS during PX degradation.

Short persistence of bendiocarb sprayed on pervious walls and its implication for the indoor residual spray program in Ethiopia.

BACKGROUND: With the emergence and spread of vector resistance to pyrethroids and DDT in Africa, several countries have recently switched or are considering switching to carbamates and/or organophosphates for indoor residual spraying (IRS). However, data collected on the residual life of bendiocarb used for IRS in some areas indicate shorter than expected bio-efficacy. This study evaluated the effect of pH and wall type on the residual life of the carbamates bendiocarb and propoxur as measured by the standard World Health Organization (WHO) cone bioassay test. METHODS: In phase I of this study, bendiocarb and propoxur were mixed with buffered low pH (pH 4.3) local water and non-buffered high pH (pH 8.0) local water and sprayed on two types of wall surface, mud and dung, in experimental huts. In the six month phase II study, the two insecticides were mixed with high pH local water and sprayed on four different surfaces: painted, dung, mud and mud pre-wetted with water. The residual bio-efficacy of the insecticides was assessed monthly using standard WHO cone bioassay tests. RESULTS: In phase I, bendiocarb mixed with high pH water killed more than 80% of susceptible Anopheles arabiensis mosquitoes for two months on both dung and mud surfaces. On dung surfaces, the 80% mortality threshold was achieved for three months when the bendiocarb was mixed with low pH water and four months when it was mixed with high pH water. Propoxur lasted longer than bendiocarb on dung surfaces, staying above the 80% mortality threshold for four and five months when mixed with high and low pH water, respectively. Phase II results also showed that the type of surface sprayed has a significant impact on the bio-efficacy of bendiocarb. Keeping the spray water constant at the same high pH of 8.0, bendiocarb killed 100% of exposed mosquitoes on impervious painted surfaces for the six months of the study period compared with less than one month on mud surfaces. CONCLUSIONS: Mixing the insecticides in alkaline water did not reduce the residual bio-efficacy of bendiocarb. However, bendiocarb performed much better on impervious (painted) surfaces than on porous dung or mud ones. Propoxur was less affected by wall type than was bendiocarb. Studies on the interaction between wall materials, soil, humidity, temperature and pH and the residual bio-efficacy of new and existing insecticides are recommended prior to their wide use in IRS.

A four-step approach to evaluate mixtures for consistency with dose addition.

Mixture risk assessment is often hampered by the lack of dose-response information on the mixture being assessed, forcing reliance on component formulas such as dose addition. We present a four-step approach for evaluating chemical mixture data for consistency with dose addition for use in supporting a component based mixture risk assessment. Following the concepts in the U.S. EPA mixture risk guidance (U.S. EPA, 2000a,b), toxicological interaction for a defined mixture (all components known) is departure from a clearly articulated definition of component additivity. For the common approach of dose additivity, the EPA guidance identifies three desirable characteristics, foremost of which is that the component chemicals are toxicologically similar. The other two characteristics are empirical: the mixture components have toxic potencies that are fixed proportions of each other (throughout the dose range of interest), and the mixture dose term in the dose additive prediction formula, which we call the combined prediction model (CPM), can be represented by a linear combination of the component doses. A consequent property of the proportional toxic potencies is that the component chemicals must share a common dose-response model, where only the dose coefficients depend on the chemical components. A further consequence is that the mixture data must be described by the same mathematical function ("mixture model") as the components, but with a distinct coefficient for the total mixture dose. The mixture response is predicted from the component dose-response curves by using the dose additive CPM and the prediction is then compared with the observed mixture results. The four steps are to evaluate: (1) toxic proportionality by determining how well the CPM matches the single chemical models regarding mean and variance; (2) fit of the mixture model to the mixture data; (3) agreement between the mixture data and the CPM prediction; and (4) consistency between the CPM and the mixture model. Because there are four evaluations instead of one, some involving many parameters or dose groups, there are more opportunities to reject statistical hypotheses about dose addition, thus statistical adjustment for multiple comparisons is necessary. These four steps contribute different pieces of information about the consistency of the component and mixture data with the two empirical characteristics of dose additivity. We examine this four-step approach in how it can show empirical support for dose addition as a predictor for an untested mixture in a screening level risk assessment. The decision whether to apply dose addition should be based on all four of those evidentiary pieces as well as toxicological understanding of these chemicals and should include interpretations of the numerical and toxicological issues that arise during the evaluation. This approach is demonstrated with neurotoxicity data on carbamate mixtures.

Propoxur: a novel mechanism for insecticidal action and toxicity.

Propoxur is a carbamate insecticide that has recently attracted considerable attention as a possible treatment option for addressing the bedbug epidemic. The generally accepted mechanism of toxicity for propoxur involves the inhibition of ChE, as is the case for many agents in the category. Considerable research supports the concept that most physiologically active substances induce their effects through multi-faceted action. In this review, we provide evidence that ET--ROS--OS participate mechanistically in both the action and in human toxicity of pesticides, including propoxur. Propoxur is a catechol derivative that contains carbamate and isopropyl groups on the oxygens in its moiety. Metabolic studies with propoxur reveal hydrolysis of the carbamate and dealkylation of the isopropyl group to yield the parent catechol. In addition, nuclear hydroxylation produces a hydroquinone derivative. Both the catechol and this hydroquinone derivative are potentially able to undergo redox cycling with the corresponding quinone to produce ROS. It is primarily for these reasons that we believe propoxur may be similar to other classes of physiologically active compounds in producing effects through ET-ROS-OS. Generally, reactive ROS are generated by metabolic processes that yield ET entities, and this occurs with propoxur as well. Although ROS are commonly associated with toxicity, there is little recognition in the literature that they can also play a role in therapeutic action.

Evaluation of the fate of the active ingredients of insecticide sprays used indoors.

The fate of the active ingredients of insecticide sprays after use in indoor environments was investigated. Indoor air sampling was performed through two types of adsorbents, namely, TENAX TA and XAD-2 (10 L). After sampling, both adsorbents were ultrasonically extracted and analyzed by Gas Chromatography coupled to Mass Spectroscopy. The separation and analysis of the selected compounds were satisfactory and fast (duration of the chromatographic run: 40 min). The method was linear for all examined chemicals over the tested range (2 to 50 ng of absolute compound); limits of detection ranged from 0.42 to 1.32 ng of absolute compound. The method was then applied in the determination of the active ingredients of three commercially available insecticide sprays that were separately used in a full-scale environmental chamber (30 m(3)). After spraying, the fate of the active ingredients [propoxur, piperonyl butoxide (PBO) and pyrethrin insecticides] was monitored over 40 minutes, with and without ventilation. Both adsorbent materials were proven to be efficient and the differences in the concentrations deriving from sampling with both materials were in almost all cases less than 10%. All chemicals were removed in rates that exceeded 80%, after the 40 minutes of monitoring, exhibiting different decay rates. The removal of insecticides was not significantly affected by the ventilation of the chamber. The correlation analysis of propoxur, PBO and pyrethrins with the aerosols of various sizes (15 fractions, from 0.3 to > 20 microm) showed that propoxur and PBO mainly associated with the medium size aerosols (3-7.5 microm) while pyrethrins seem to link more with heavier particles (> 10 microm).

Photocatalytic degradation of aqueous propoxur solution using TiO2 and Hbeta zeolite-supported TiO2.

Photocatalytic activity of TiO2 and zeolites supported TiO2 were investigated using propoxur as a model pollutant. Hbeta, HY and H-ZSM-5 zeolites were examined as supports for TiO2. Hbeta was chosen as the TiO2 support based on the adsorption capacity of propoxur on these zeolites (Hbeta>HY=H-ZSM-5). TiO2/Hbeta photocatalysts with different wt.% were prepared and characterized by XRD, FT-IR and BET surface area. The progress of photocatalytic degradation of aqueous propoxur solution using TiO2 (Degussa P-25) and TiO2 supported on Hbeta zeolite was monitored using TOC analyzer, HPLC and UV-vis spectrophotometer. The degradation of propoxur was systematically studied by varying the experimental parameters in order to achieve maximum degradation efficiency. The initial rate of degradation with TiO2/Hbeta was higher than with bare TiO2. TOC results revealed that TiO2 requires 600min for complete mineralization of propoxur whereas TiO2/Hbeta requires only 480min. TiO2/Hbeta showed enhanced photodegradation due to its high adsorption capacity on which the pollutant molecules are pooled closely and hence degraded effectively.

Preparation, characterization, and photocatalytic activity of Gd3+ doped TiO2 nanoparticles.

TiO2 and Gd3+ doped TiO2 nanoparticles were prepared by sol-gel method and the materials were characterized by XRD, TEM, SEM-EDX, BET, FT-IR, UV-Vis absorption, and Raman spectral analysis. The photocatalytic activity of nano TiO2 and Gd/TiO2 nanoparticles was evaluated using a model pollutant propoxur, a carbamate pesticide, in a batch type UV photoreactor. The results revealed higher photocatalytic activity for Gd/TiO2 nanoparticles than both TiO2 nanoparticles and commercial TiO2 (Degussa P-25). The enhanced photocatalytic activity of Gd/TiO2 relative to TiO2 is attributed to its increased band gap energy as evidenced from the blue shift to shorter wavelength observed in the UV-Vis abso4ption spectra. The recombination rate of photogenerated electron-hole pair decreased due to increase in the band gap, which enhanced the charge transfer efficiency of Gd/TiO2 nanoparticles. Gd3+ with its half filled 7 f subshell facilitated rapid electron transfer at solid-liquid interface by shallowly trapping the electrons. Among the various dopant level of gadolinium, 0.3 wt% Gd/TiO2 nanoparticles showed higher activity than others due to its higher surface area.

Stability study of propoxur (Baygon) in whole blood and urine stored at varying temperature conditions.

A stability study has been initiated for propoxur (Baygon) in whole blood and urine samples stored over a period of 60 days at four different temperature conditions (room temperature, 4 degrees C, -20 degrees C, and -80 degrees C). Stability data was established on day 0, 1, 7, 14, 28, 42, and 60. Sample purification was done by solid-phase extraction using a weak cation exchange cartridge (Isolute CBA), and quantitation was carried out by a validated high-performance liquid chromatographic method with a photodiode-array UV detector. Propoxur was spiked at two different concentration levels in both blood and urine samples [low concentration (10 microg/L) and high concentration (100 microg/L)]. Isopropoxy phenol was observed as the major degradation product in blood and urine samples and confirmed by liquid chromatography-electrospray ionization-mass spectrometry. At room temperature, a substantial decrease in concentration of about 95% was observed at the end of the stability study in both blood and urine samples. However, at 4 degrees C, the concentration of propoxur observed after 60 days was around 60% in both samples. A decrease in temperature reduced the degradation, and finally propoxur was found to be stable at -80 degrees C and -20 degrees C for the whole observation period (60 days). The data collected suggests that knowledge about time-dependent decrease of propoxur in urine and blood samples is of considerable significance in forensic toxicology, and, therefore, forensic cases should be interpreted with caution.

Soil photolysis in a moisture- and temperature-controlled environment. 2. Insecticides.

The photolytic degradations of imidacloprid, carbofuran, diazinon, chlorpyrifos, pyridaben, propoxur, and esfenvalerate were independently compared in both moist (75% field moisture capacity at 0.33 bar) and air-dry microbially viable soils at 5 microg/g. All compounds were applied to sandy soil except for propoxur, which was applied to sandy loam soil. Diazinon was applied to both sandy soil and sandy loam soil. The samples were exposed for up to 360 h, depending on the half-life of the compound. Moisture and temperature were maintained through the use of a specially designed soil photolysis apparatus. Corresponding dark control studies were performed concurrently. With the exception of esfenvalerate, the other compounds exhibited significantly shorter half-lives in moist soils, attributed to the increased hydrolysis and microbial activity of the moist soil. The esfenvalerate metabolism was not first order due to limited mobility in the soil because of its very low water solubility. The overall half-life for esfenvalerate was 740 h, as the percent remaining did not drop below 60%. The imidacloprid half-life in irradiated moist soil was 1.8 times shorter than in air-dry soils. However, on dry soil the photodegradation showed poor first-order kinetics after 24 h of exposure. The metabolism of carbofuran and diazinon was highly dependent on soil moisture. Carbofuran exhibited 2.2 times longer half-lives when less moisture was available in the soil. Diazinon in moist sandy soil degraded rapidly, but slowed significantly in irradiated and dark control air-dry sandy soil. Diazinon photolysis on sandy loam soil was not first order, as it attained a constant concentration of 54.9%, attributed to decreased mobility in this soil. Chlorpyrifos photolysis was 30% shorter on moist sand than on air-dry sand. Pyridaben photolyzed rapidly throughout the first 72 h of irradiation but maintained 48% through 168 h. Propoxur metabolism in moist sandy loam soil was not first order and did not degrade below 50% after 360 h of exposure, but the overall half-life was still nearly half of that on irradiated air-dry soil. Three of the compounds showed differences in metabolism patterns during exposure on moist or air-dry soil. Typically, the moist soils produced a more linear decline than that seen in the dry soils, corresponding to the susceptibility of the particular chemical to hydrolysis and/or biodegradation. Four of the eight experiments had shorter half-lives in dark control moist soils than in irradiated dry soils.

Stability studies of propoxur herbicide in environmental water samples by liquid chromatography-atmospheric pressure chemical ionization ion-trap mass spectrometry.

Liquid chromatography-atmospheric pressure ionization ion-trap mass spectrometry has been investigated for the analysis of polar pesticides in water. The degradation behavior of propoxur, selected as a model pesticide belonging to the N-methylcarbamate group, in various aqueous matrices (Milli-Q water, drinking water, rain water, seawater and river water) was investigated. Two interfaces of atmospheric pressure ionization, atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI), were compared during the study. Propoxur and its transformation product (N-methylformamide) were best ionized as positive ions with both APCI and ESI, while another transformation product (2-isopropoxyphenol) yielded stronger signals as negative ions only with APCI. In addition, the effects of various pH, matrix type and irradiation sources (sunlight, darkness, indoor lighting and artificial UV lamp) on the chemical degradation (hydrolysis) were also assessed. From the kinetic studies of degradation, it was found that the half-life of propoxur was reduced from 327 to 161 h in Milli-Q water with variation of irradiation conditions from dark to sunlight exposure. Degradation rates largely increased with increasing pH. The half-life of the target compound dissolved in Milli-Q water under darkness decreased from 407 to 3 h when the pH of Milli-Q water was increased from 5 to 8.5. These suggest that hydrolysis of propoxur is light-intensity and pH-dependent. In order to mimic contaminated natural environmental waters, propoxur was spiked into real water samples at 30 microg/l. The degradation of propoxur in such water samples under various conditions were studied in detail and compared. With the ion trap run in a time-scheduled single ion monitoring mode, typical limits of detection of the instrument were in the range of 1-10 microg/l.

Volatility of propoxur from different surface materials commonly found in homes.

The purpose of this study was to determine the volatilization rates of propoxur from different surface materials commonly found in homes, and to conduct field measurements under ventilated and non-ventilated conditions. Since it is known that temperature, humidity and constant air flow most significantly affect volatility, various surface materials were sprayed using a constant amount of propoxur under the controlled conditions of an exposure chamber. Acetonitrile was used to desorb both XAD-2 resin that collected airborne propoxur and surface materials containing propoxur residue. HPLC was used to analyze propoxur concentrations. Based on multiple regression models, temperature most significantly affected volatility, followed by humidity. Volatilization rates of propoxur were highest from quartz surfaces and lowest from glass. Interaction was most readily found on glass surfaces based on humidity-air flow and humidity-temperature factors. In field applications, propoxur was sprayed in a room under two conditions with ventilation and without in order to measure the concentrations of propoxur in the air and on a quartz surface. Findings showed both airborne and settled concentrations peaked after a half hour then decreased under both conditions, both more sharply in the ventilated room. Under both conditions, no propoxur was detected on the quartz surface after three and a half hours but airborne concentrations remained detectable after thirty-three and one half hours. We conclude that to maintain good air quality, ventilation is important and special care must be taken when spraying insecticides on different surfaces.

Solid-phase extraction of polar pesticides from environmental water samples on graphitized carbon and Empore-activated carbon disks and on-line coupling to octadecyl-bonded silica analytical columns.

The suitability of Empore-activated carbon disks (EACD), Envi-Carb graphitized carbon black (GCB) and CPP-50 graphitized carbon for the trace enrichment of polar pesticides from water samples was studied by means of off-line and on-line solid-phase extraction (SPE). In the off-line procedure, 0.5-2 l samples spiked with a test mixture of oxamyl, methomyl and aldicarb sulfoxide were enriched on EnviCarb SPE cartridges or 47 mm diameter EACD and eluted with dichloromethane-methanol. After evaporation, a sample was injected onto a C18-bonded silica column and analysed by liquid chromatography with ultraviolet (LC-UV) detection. EACD performed better than EnviCarb cartridges in terms of breakthrough volumes (> 2 l for all test analytes), reproducibility (R.S.D. of recoveries, 4-8%, n = 3) and sampling speed (100 ml/min); detection limits in drinking water were 0.05-0.16 microgram/l. In the on-line experiments, 4.6 mm diameter pieces cut from original EACD and stacked onto each other in a 9 mm long precolumn, and EnviCarb and CPP-50 packed in 10 x 2.0 mm I.D. precolumn, were tested, and 50-200 ml spiked water samples were preconcentrated. Because of the peak broadening caused by the strong sorption of the analytes on carbon, the carbon-packed precolumns were eluted by a separate stream of 0.1 ml/min acetonitrile which was mixed with the gradient LC eluent in front of the C18 analytical column. The final on-line procedure was also applied for the less polar propoxur, carbaryl and methiocarb. EnviCarb could not be used due to its poor pressure resistance. CPP-50 provided less peak broadening than EACD: peak widths were 0.1-0.3 min and R.S.D. of peak heights 4-14% (n = 3). In terms of analyte trapping efficiency on-line SPE-LC-UV with a CPP-50 precolumn also showed better performance than when Bondesil C18/OH or polymeric PLRP-S was used, but chromatographic resolution was similar. With the CPP-50-based system, detection limits of the test compounds were 0.05-1 microgram/l in surface water.