Analysis of non-native fluorescent pesticides by thermo-induced and photo-induced fluorescence, a comparative study.

This paper compares the performance of three analytical methods for the determination of pesticides in natural waters. As many pesticides are non-fluorescent, they are transformed into highly fluorescent by-products in two ways: elevated temperature in an alkaline medium (thermo-induced fluorescence - TIF); or UV irradiation in water (photo-induced fluorescence - PIF). The first method studied uses TIF, the second one uses PIF and the third one uses an automatic sampling and analysing PIF system. Analytical applications were carried out using the three methods for the determination of deltamethrin and cyhalothrin, pesticides widely used in Senegal. In both cases, the calibration curves obtained are linear without matrix effects, and the detection limits are good in the ng mL-1 range. It appears that the analytical performances of the automatic PIF method are better than the two others. The advantages and disadvantages of the three methods are then compared and discussed in term of analytical performance and usability.

High sensitivity on-site early warning system monitoring of pesticides by photo-induced fluorescence.

This paper describes the prototype of an on-site High Sensitivity Early Warning Monitoring System, using Photo-Induced Fluorescence, for pesticide monitoring in natural waters (HSEWPIF). To obtain a high sensitivity, the prototype was designed with four main features. Four UV LEDs are used to excite the photoproducts at different wavelengths and select the most efficient one. Two UV LEDs are used simultaneously at each wavelength to increase the excitation power and then the fluorescence emission of the photoproducts. High-pass filters are used to avoid the saturation of the spectrophotometer and to increase the signal-to-noise ratio. The HSEWPIF prototype also employs UV absorption to detect any occasional increase of suspended and dissolved organic matter, which could disrupt the fluorescence measurement. The conception of this new experimental set-up is explained and described, then analytical applications are carried out online for the determination of fipronil and monolinuron. We obtained a linear calibration range from 0 to 3 µg mL-1 with limits of detection of 1.24 ng mL-1 for fipronil and 0.32 ng mL-1 for monolinuron. A mean recovery of 99.2% for fipronil and 100.9% for monolinuron show that the method is accurate, moreover a standard deviation of 1.96% for fipronil and 2.49% for monolinuron show that the method is repeatable. Compared to other methods for the determination of pesticides by photo-induced fluorescence, the HSEWPIF prototype has good sensitivity with better limits of detection, and good analytical performances. These results show that HSEWPIF can be used for monitoring pesticide in natural waters to protect industrial facilities against accidental contamination.

Micellar enhanced photo-induced fluorescence and absorbance for the development of an on-site early warning water quality monitoring system for pesticides.

This paper describes two prototypes of an on-site Early Warning Water Quality Monitoring System (EWWQMS) for pesticide quantification in natural waters. As many pesticides are non-fluorescent, the EWWQMS setup uses UV photoconversion to form highly fluorescent photoproducts. To enhance sensitivity, the two prototypes use micellar-enhanced fluorescence with surfactant (cetyl trimethyl ammonium chloride) in aqueous solution. To improve specificity, four UV LEDs at different wavelengths then excite the fluorescent photoproducts. The EWWQMS prototypes also employ UV absorption for quantification of non-photosensitive pesticides. The first prototype detects the pesticides via a diode array spectrometer. The second system is developed with higher resolution spectrometer and an intensified CCD camera detection to improve the sensitivity of the method. These experimental set-ups are described, explained and tested. Analytical applications were carried out online in CTAC aqueous solution, for the determination of isoproturon, flufenoxuron and profenofos. The calibration curves obtained are linear over one order of magnitude, and the detection limits are in the ng mL-1 range. The analytical performances of these new methods are good compared with other published classical micellar enhanced photo-induced fluorescence methods for the determination of pesticides in aqueous solutions. Our results show that these EWWQMS prototypes can be used as a warning system to protect against pesticide contamination exceeding the threshold of treatment capabilities at industrial facilities using natural waters.

Development of an on-site early warning water quality monitoring system for pesticide detection by absorption and photo-induced fluorescence.

This paper describes prototypes of an on-site early warning water quality monitoring system (EWWQMS) for pesticide quantification in natural waters by fluorescence and absorbance. As many pesticides are not naturally fluorescent, this EWWQMS uses UV irradiation to transform these compounds into highly fluorescent photoproducts and obtain sufficient sensitivity. To obtain a better specificity, the system uses four UV LEDs at different wavelengths to excite the fluorescent photoproducts. For pesticides that are not sensitive to photoconversion, the EWWQMS prototypes also use UV absorption for their quantification, thus offering a wider application range. A first system uses a diode array spectrometer for detection. A second system uses a higher resolution spectrometer and an intensified CCD camera detection to increase sensitivity. Analytical applications were conducted for the determination of fipronil, acetamipride, cyprodinil, trifluraline and pendimethaline in water using both the EWWQMS prototypes. The analytical performances of these new systems are good compared with other photo-induced fluorescence methods already published. Limits of detection without pre-concentration are in the range of 0.2 to 3 ng mL-1 and the recovery values range from 95 to 108%. These results show that the EWWQMS prototypes can be used as an alert system to protect industrial plants from pesticide contaminations that exceed the capabilities of their cleaning processes.

Combination of photoinduced fluorescence and GC-MS for elucidating the photodegradation mechanisms of diflubenzuron and fenuron pesticides.

Diflubenzuron (DFB) and fenuron (FEN) are benzoylurea and phenylurea pesticides, widely used in Senegal, that do not exhibit any natural fluorescence, but can be determined by means of photoinduced fluorescence (PIF) methods. Photodegradation of DFB and FEN yielded a number of fluorescent and non-fluorescent photoproducts. For both pesticides, at least 10 photoproducts were detected and identified by gas chromatography-mass spectrometry (GC/MS). To identify the formed fluorescent DFB and FEN photoproducts, their fluorescence spectra were compared with those of standard compounds, including phenol and p-hydroxyaniline.

Monitoring survey of the use patterns and pesticide residues on vegetables in the Niayes zone, Senegal.

The main objective of this work was to determine the impact of pesticide use practices on vegetables contamination in the Niayes zone of Dakar. A preliminary survey involving 200 farmers, showed the application of pesticides belonging to different groups on vegetable crops. Use practices in terms of application intervals and methods, measuring tools and dosage were not in compliance with good agricultural practices. In view of survey results, investigations on vegetable contamination were conducted. Therefore, 175 vegetable samples including cabbage (31 samples), lettuce (88 samples), tomato (57 samples) collected from four sites of the Niayes zone during four campaigns, were analyzed for residues of 21 pesticides, eighteen of which (18) were cited to be used by farmers. The results indicated that 65% of tomato samples, 71% of lettuce and 93% of cabbage contained one or more detectable residues. Among the monitored pesticides dicofol, chlorpyrifos, DDTs, dimethoate, and λ-cyhalothrin were the most predominant, found in at least 35% of samples for each vegetable. The frequencies of pesticide detection were, generally in agreement with the citation frequencies. The results provided important information on vegetable contamination status and pointed an urgent need to control pesticide use.