326 Acta Chim. Slov. 2011, 58, 326–332 @abar et al.: Stability of Pesticides’ Residues Under Ultraviolet Germicidal Irradiation Scientific paper Stability of Pesticides’ Residues Under Ultraviolet Germicidal Irradiation Romina @abar,1 Mohamed Sarakha,2 Pascal Wong Wah Chung2 and Polonca Treb{e1,* 1 Laboratory for Environmental Research, University of Nova Gorica, Vipavska 13, P.O. Box 301, 5000 Nova Gorica, Slovenia 2 Clermont Université, Université Blaise Pascal, Laboratoire de Photochimie Moléculaire et Macromoléculaire, UMR CNRS 6505, F-63006, Clermont Ferrand Cedex, France * Corresponding author: E-mail: polonca.trebse@ung.si Tel: +386 5 331 5238, Fax: +386 5 331 5295 Received: 13-01-2011 Abstract Legislation for food safety is limited mostly to pesticides monitoring and no attention is paid to the presence and toxic- ity of by-products formed after pesticide application. Stability studies of three selected transformation products: IMP – 2-isopropyl-6-methyl-4-pyrimidinol (diazinon hydrolysis product), TCP – 3,5,6-trichloro-2-pyridinol (chlorpyrifos transformation product), and 6CNA – 6-chloronicotinic acid (imidacloprid and acetamiprid transformation product) were performed under exposure to sunlight at room temperature (22 °C) and in the dark at 4 °C over 90 days. The results showed slight change in concentration with samples under refrigeration in darkness.Alternatively, an aqueous solution of TCP exposed to sunlight resulted in a high decrease of initial concentration within time. The toxicity assessment was performed using luminescent bacteria Vibrio fischeri and the results expressed low toxicity in the case of IMP and 6CNA. However, for TCP the calculated EC50 value after 30 minutes of exposure equated to roughly 15.1 mg L –1. Stability of the selected transformation products upon 245 nm irradiation indicated little decrease in concentration for IMP and 6CNA in deoxygenated and oxygenated aqueous solutions. In the case of TCP, the photochemical behaviour appeared to depend on oxygen concentration in the medium. For more detailed comparison, the degradation quantum yields were calculated. Keywords: Pesticides transformation products, quantum yield, toxicity, Vibrio fischeri 1. Introduction One of the most important goals of the food scien- tists is to make food as safe as possible whether it is con- sumed fresh or processed. Several techniques are applied for food preservation, mostly heating, preservation by low water activity, low pH and organic acid, and by the addi- tion of specific chemicals such as carbon dioxide, sul- phite, nitrite and nitrate.1 Recently, ultraviolet irradiation as a food preservation tool has gained application inter- est.2–3 The most effective and widely used is an UVC ger- micidal lamp with emission at wavelengths around 254 nm. The wavelength of 253.7 nm is most efficient in terms of germicidal effect since photons are mostly absorbed by the micro-organisms’ DNA.4 Through food processing and consumption, it is possible to ingest pesticides as well as their transforma- tion products (TP) in the food chain. According to food safety legislation only residues of insecticides in vegeta- bles and fruits are required to be monitored.Alternatively, there is no control for the presence of transformation products which can be formed after the application of in- secticides. In the literature there is a wealth of publica- tions regarding the identification of transformation prod- ucts of different insecticides in different food matrices,5–6 as well as in water samples.7 In addition, metabolic path- ways of some insecticides were studied and major degra- dation products were identified.6,8,9 Much information is available on the adverse effects of parent chemicals (pesti- cides) and almost none about the possible adverse effects 327Acta Chim. Slov. 2011, 58, 326–332 @abar et al.: Stability of Pesticides’ Residues Under Ultraviolet Germicidal Irradiation of transformation products. However, transformation products may possess greater toxicity as in case of organophosphorus insecticides; they can be more persist- ent and more mobile than their parent compounds.10 Toxicity tests of selected pesticides and their transforma- tion products on aquatic organisms (daphnids) were per- formed as well as on terrestrial organisms (earthworms)11 and it has been clearly demonstrated that on the basis of earthworms ecotoxicologocal data, the transformation product 3,5,6-trichloropyridinol can be classified in a high- er risk category than its parental compound chlorpyrifos. In general, we may say with assurance that few stud- ies have been published on transformation products re- garding their chemical properties, stability and toxicity. For this reason we decided to explore the properties of three selected transformation products, studing their per- sistence, toxicity and stability under various conditions: presence and absence of oxygen, temperature and sunlight with the emphasis on their degradation under UV irradia- tion as a tool for food preservation, since all those condi- tional changes might occur during food processing. This research focused on three transformation prod- ucts from two different groups of insecticides. From the group of organophosphorous pesticides, the transforma- tion product of diazinon: 2-isopropyl-6-methyl-4-pyrim- idinol (IMP) and the transformation product of chlorpyri- fos: 3,5,6-trichloro-2-pyridinol (TCP) were chosen.5,12 From the group of neonicotinoid insecticides the common transformation product of acetamiprid and imidacloprid: 6-chloronicotinic acid (6CNA) were chosen.13 The chemi- cal structures of selected chemicals are shown on Figure 1. It has been reported that 2-isopropyl-6-methyl-4- pyrimidinol (IMP) can be formed by diazinon hydrolysis within a few days.6 Possible toxic effects of IMP on cultivat- ed human blood cells and skin fibroblasts were investigated and the results showed that IMP possesses stronger genotox- ic potential than diazinon alone.14 As mentioned above, the primary transformation product of chlorpyrifos, by both hy- drolysis and photolysis, is 3,5,6-trichloro-2-pyridinol (TCP).14–15 Investigations on selected food were performed and the results indicated the presence of TCP in several agri- cultural crops such as spinach, cauliflower and potato.5 Moreover, TCP has been found also in human urine in the United States.16 The acute toxicity of TCP was studied on Daphnia carinata and it has been suggested that it is more toxic to D. carinata than its parent chemical compound chlorpyrifos.17 Since neonicotinoid insecticides are a quite new group of insecticides, little data on their environmental fate is available in comparison with organophosphorous in- secticides. The presence of 6-chloronicotinic acid was con- firmed in soil and toxicity was tested on the honeybee Apis mellifera, however, no adverse effects were observed.18–19 2. Experimental 2. 1. Materials The transformation product IMP (2-isopropyl-6- methyl-4-pyrimidinol), 99% pure was provided by the Aldrich Chemical Company Inc., TCP (3,5,6-trichloro-2- pyridinol) analytical standard was provided by Fluka and 6CNA (6-chloronicotinic acid), 97.0% pure was also pro- vided by Fluka. Solvents for the HPLC mobile phase were obtained from different suppliers: acetic acid glacial 100% p.a. from Merck and acetonitrile, CHROMASOLV for HPLC grade from Sigma Aldrich Company Ltd. Che- micals used in toxicity tests were supplied from different producers, sodium hydroxide p.a. from AppliChem, sodi- um chloride from Carlo Erba Reagenti and hydrochloric acid 37% puriss. p.a. from Sigma Aldrich Company Ltd. Deionised water (< 18 MΩ/cm) was prepared through the NANOpure water system (Barnstead, USA). 2. 2. Analytical Procedures HPLC-DAD: Aqueous solution of 2-isopropyl-6- methyl-4-pyrimidinol, 3,5,6-trichloro-2-pyridinol and 6-chloronicotinic acid were analyzed by HPLC-DAD (UV-Vis) consisting of a Hewlett Packard 1100 Series chromatograph, coupled with DAD detector. The separa- tion was achieved using C8 column with stationary phase Chromasil 100 (5 μm) produced by BIA Separations d.o.o., kept at 25 °C. The injection volume was 75 μL. The eluents consisted of acetonitrile (A) and acetic acid 1.5 vol. % (B); flow rate was 1 mL min–1 and the wavelength 242 nm. The gradient elution was as follows: 0 min to 16 min 15% A; 16 min to 20 min 70% A. The retention time for 2-isopropyl-6-methyl-4-pyrimidinol was 6.6 min, for 6-chloronicotinic acid 12.5 min and for 3,5,6-trichloro-2- pyridinol 18.4 min. For quantification purposes calibra- tion curves for all three transformation products from 0.1 ppm to 100 ppm were prepared. The r2 value of the regres- Figure 1: The chemical structures of the studied compounds. 328 Acta Chim. Slov. 2011, 58, 326–332 @abar et al.: Stability of Pesticides’ Residues Under Ultraviolet Germicidal Irradiation sion line for 2-isopropyl-6-methyl-4-pyrimidinol was 0.9998, for 6-chloronicotinic acid was 0.9985 and for 3,5,6-trichloro-2-pyridinol was 0.9998. UV-Vis spectra were recorded on a Cary 300 scan spectrophotometer produced by Varian. 2. 3. Stability Tests Stability of 2-isopropyl-6-methyl-4-pyrimidinol, 3,5,6-trichloro-2-pyridinol and 6-chloronicotinic acid was assessed by exposing water samples to different tempera- tures, different pHs (4,7,10), presence of sunlight and ab- sence of oxygen. Samples containing selected transforma- tion products were dissolved in double deionised water and stored under different laboratory conditions in 100 mL SCHOTT DURAN flasks. One set of flasks was kept on the laboratory desktop at direct sunlight at room tem- perature 22 °C and the second set of flasks was kept in a refrigerator in the dark, at 4 °C. The selected pH was achieved by adding hydrochloric acid or sodium hydrox- ide. During the period of 90 days, the concentration of so- lutions were monitored with the HPLC-DAD system and the pH was monitored with a pH meter, Hanna Instru- ments HI 8417. 2. 4. Ultraviolet Irradiation of Samples Quartz cells (10 × 10 × 40 mm) were filled with aqueous solution of each chemical and placed in front of the monochromatic low pressure mercury germicidal lamp emitting at 254 nm. The photon flux was evaluated by actionometry using potassium ferrioxalate and the val- ue obtained was 4.86 × 1014 photons s–1 cm–2. The solu- tions were stirred and irradiated for a given period of time (0, 5, 10, 20 and 30 min) then analysed by the HPLC- DAD (UV-Vis) as well as by an UV-Vis spectrophotome- ter. After each sample collection, a fresh sample was irra- diated in order to retain the same sample volume. All the samples were irradiated in deaerated oxygen free solu- tions. In the latter case, prior to irradiation, the samples were purged for 10 minutes with argon. In order to obtain a better insight into possible degradation behaviour, the additional experiments were performed in order to esti- mate the degradation quantum yields under various condi- tions. Adequate values were calculated by employing the following expression; (1) dC/dt: the slope of the initial linear part of the kinetic curve (con- centration as a function of irradiation time) [mol L–1 s–1] N: Avogadro number [molecules mol–1] l: optical path length [cm] Io: photonic flux evaluated to 4.68 × 10 14 [photons s–1 cm–2] A0: the initial absorbance of the studied solution at the excitation wavelength 254 nm. 2. 5. Toxicity Experiments Toxicity of 2-isopropyl-6-methyl-4-pyrimidinol, 3,5,6-trichloro-2-pyridinol and 6-chloronicotinic acid was assessed using luminescence bacteria Vibrio fischeri with system LUMIStox, Dr.LANGE. The toxicity endpoint was determined as reduced luminescence emittion after incubating with presence of the selected chemical or mix- ture. The crucial experimental step was sample prepara- tion in order to avoid possible adverse effects due to an in- correct pH value or inappropriate sodium chloride con- centration. Before analyzing the samples, adjusting the pH to 7 ± 0.2 with hydrochloric acid or sodium hydroxide was performed as well as adding the correct amount of sodium chloride salt i.e. 2% w/v. Bacteria were incubated for 15 min in reactivation solution, meanwhile the sam- ples were mixed with 2% sodium chloride solution (1:1 v/v) and temperature controlled at 15 °C in a thermob- lock. Luminescence of each cuvette with bacteria was measured; afterwards the sample was added and ther- mostated to 15 °C for 30 minutes. After 30 minutes the lu- minescence of bacteria with sample was measured again and the inhibition of luminescence according to ISO 11348-2 was calculated. Luminescence was measured with a photomultiplier also temperature controlled at 15 °C. The blank test was performed with 2% sodium chlo- ride. All the measurements were carried out in two aliquots. As an appropriate endpoint for toxicity assess- ment, the EC50 value was calculated. 3. Results and Discussion The results of stability tests for 2-isopropyl-6- methyl-4-pyrimidinol (IMP), 3,5,6-trichloro-2-pyridinol (TCP) and 6-chloronicotinic acid (6CNA) in double deionised water was performed at room temperature (22 °C) under exposure to sunlight and in the dark (in the re- frigerator at 4 °C) are shown in Table 1. The experiments performed at 4 °C in the darkness clearly indicate that the thermal degradation or transforma- tion is very low in case of all three substances over the 90 days of experiment. Moreover, the concentration of IMP and 6 CNA samples exposed to sunlight decreased for 2% and 9% and can be compared with the samples kept in the refrigerator, where the observed decrease was very similar, i.e. 3% and 8%. However, experiments with TCP per- formed at room temperature (22 °C) with exposure to sun- light led to an important transformation. Within 90 days of experiment, 70% conversion was observed, compared to the sample kept in the dark which resulted in only 2% con- version. It should be noted, that this result clearly shows the transformation of TCP into another compound(s), which were not recorded and monitored at that time. Toxicity assessment of aqueous solutions for all three substances were performed and the results revealed 329Acta Chim. Slov. 2011, 58, 326–332 @abar et al.: Stability of Pesticides’ Residues Under Ultraviolet Germicidal Irradiation relatively high toxicity in case of 3,5,6-trichloro-2-pyridi- nol (TCP), while for 2-isopropyl-6-methyl-4-pyrimidinol (IMP) and 6-chloronicotinic acid (6CNA) solutions did not cause significant inhibition in luminescence of Vibrio fischeri bacteria. The results are presented in Table 2. Table 2: Inhibition of luminescence in Vibrio fischeri bacteria for IMP, 6CNA and TCP aqueous solution. concentration inhibition of the luminescence [%] [mg L–1] IMP 6CNA TCP 54 7.6 ± 0.7 21.4 ± 1.1 80.1 ± 0.1 27 6.6 ± 0.0 14.8 ± 1.3 65.6 ± 0.4 13.5 7.3 ± 0.1 8.3 ± 0.9 45.3 ± 1.1 6.8 3.6 ± 2.2 8.7 ± 2.7 25.1 ± 1.9 3.4 3.2 ± 0.5 5.0 ± 1.6 10.0 ± 0.2 On the basis of results listed above, the dose re- sponse curve for TCP was derived and the 30 min EC50 value of 15.1 mg L–1 was calculated. The dose response curves for 6CNA and IMP could not be derived due to the very low toxicity of samples and consequently, the 30 min EC50 values for these solutions were not calculated. Nevertheless, the used concentrations were still very high from the environmental point of view. The influence of the germicidal lamp emitting at 254 nm on the stability of 2-isopropyl-6-methyl-4-pyrim- idinol (IMP), 3,5,6-trichloro-2-pyridinol (TCP) and 6- chloronicotinic acid (6CNA) was assessed as possible change in concentration within irradiation time. Experi- ments were performed in aerated as well as in deaerated by bubbling with argon for roughly 10 minutes. Under both experimental conditions, similar results were ob- tained. In Table 3, the percentages of initial concentrations still remained in the solution for each sample after given times of irradiation are presented. Within 30 minutes of ir- radiation, the highest disappearance rate was achieved by the TCP aqueous solution – it retained just 54% of its ini- tial concentration, but for the 6CNA and IMP the remain- ing concentrations in the solution were still relatively high (around 84%). The disappearance of all three studied products in aqueous solutions was also monitored by UV-Vis spec- troscopy within 200–400 nm. On Figures 2, 3 and 4 the Table 1: Concentration of IMP, TCP and 6CNA within time in refrigerator and exposed to sunlight. time refrigerator T = 4 °C sunlight T = 22 °C [days] C/C0 [%] C/C0 [%] IMP TCP 6CNA IMP TCP 6CNA 0 100 100 100 100 100 100 7 99.6 99.6 96.8 99.8 81.8 97.2 17 100 99.6 96.8 99.8 68.7 98.9 28 100 98.3 100 100 59.5 96.9 45 99.1 97.8 93.8 99.2 51.2 93.9 62 99.0 96.7 95.0 98.3 40.0 94.7 90 97.8 98.2 91.6 98.1 28.9 91.1 Table 3: Concentration of IMP, TCP and 6CNA within irradiation time with low pressure mercu- ry lamp (254 nm) in the presence and in the absence of oxygen. oxygenated aqueous solutions time IMP TCP 6CNA [min] C/C0 C C/C0 C C/C0 C [%] [mol L–1] [%] [mol L–1] [%] [mol L–1] 5 96.2 1.13 × 10–4 83.9 9.15 × 10–5 98.2 1.33 × 10–4 10 93.7 1.11 × 10–4 74.0 8.06 × 10–5 96.6 1.30 × 10–4 15 89.7 1.06 × 10–4 61.7 6.73 × 10–5 98.5 1.25 × 10–4 20 84.6 9.98 × 10–5 54.4 5.93 × 10–5 89.8 1.21 × 10–4 deoxygenated aqueous solutions time IMP TCP 6CNA [min] C/C0 C C/C0 C C/C0 C [%] [mol L–1] [%] [mol L–1] [%] [mol L–1] 5 97.1 1.15 × 10–4 84.7 9.23 × 10–5 95.2 1.28 × 10–4 10 95.2 1.12 × 10–4 73.5 8.01 × 10–5 90.6 1.22 × 10–4 15 90.2 1.06 × 10–4 62.2 6.78 × 10–5 84.5 1.14 × 10–5 20 / / / / / / 330 Acta Chim. Slov. 2011, 58, 326–332 @abar et al.: Stability of Pesticides’ Residues Under Ultraviolet Germicidal Irradiation absorption spectra of IMP, TCP and 6CNA are given as a function of irradiation time. Figure 2: Absorption spectra for the oxygenated solution of IMP upon excitation at 254 nm for 30 minutes. Note: The (↑) indicates increase of absorbance in comparison to stationary spectra and (↓) indicates decrease of absorbance. As shown in Figure 2, the 254 nm irradiation of an oxygenated solution of IMP, led to important changes in the absorption spectrum. The absorbance decreased with- in the wavelength range 225–375 nm which clearly re- flects the photodegradation of IMP, whereas the ab- sorbance significantly increased at wavelength range 275–340 owing to the formation of by-product(s). The presence of an isobestic points are observed at 275 nm and 220 nm, that lead to the conclusion that a clean photo- chemical reaction was occurring. Figure 3: Absorption spectra for the oxygenated solution of TCP upon excitation at 254 nm for 30 minutes. Note: The (↑) indicates increase of absorbance in comparison to stationary spectra and (↓) indicates decrease of absorbance. A similar trend has been observed in case of TCP ir- radiation at 254 nm. The absorbance decreased within the wavelength range 225–255 nm and 290–340 nm which again demonstrates the transformation of TCP. However, the absorbance slightly increased within the wavelength range 255–290 nm and this was again attributed to no newly formed by-product occurring. Figure 4: Absorption spectra for the oxygenated solution of 6CNA upon excitation at 254 nm for 30 minutes. Note: The (↑) indicates increase of absorbance in comparison to stationary spectra and (↓) indicates decrease of absorbance. The smallest change in evolution absorbance spectra upon excitation at 254 nm was recorded in the case of 6CNA aqueous solution. There a decrease in absorbance at wavelength range 210–235 nm was indicated and an in- crease at wavelength ranges 235–270 nm and 275–325 nm. The presences of at least three isobestic points are demonstrating a clean photochemical process. It is worth nothing that no change in the absorption spectra occurred with deoxygenated conditions in comparison with oxy- genated conditions; therefore the figures are not present- ed. All the results are in compliance with HPLC-DAD da- ta, where the highest photo degradation was recorded for the TCP aqueous solution and the lowest in the case of 6CNA aqueous solution. In order to better estimate the effect of aerated or de- oxygenated conditions to transformation products pho- todegradation, the quantum yields were calculated for each compound within specific conditions. The calculated parameters for degradation quantum yields are detailed and presented in the Table 4. In case of the IMP aqueous solution, the quantum yields, as calculated from data obtained from both condi- tions, are very similar and low. However, the results are in compliance with degradation quantum yields for pesti- cides, calculated in similar research recently published.20 The quantum yield is the number of destroyed molecules divided by the number of photons absorbed by the system. This, therefore, means that only small part of molecules for IMP were actually degraded by absorbed photons. A slightly different situation appears with the quantum yields 331Acta Chim. Slov. 2011, 58, 326–332 @abar et al.: Stability of Pesticides’ Residues Under Ultraviolet Germicidal Irradiation calculated from the experiment with the aqueous solution of TCP. Degradation quantum yield was slightly higher in the case of deoxygenated conditions. We can thus propose that oxygen could have an inhibitory impact on the photo degradation of TCP. Obvious changes in degradation quan- tum yields for oxygenated and deoxygenated conditions were observed for the aqueous solution of 6CNA. When performing irradiation experiments in presence of argon, the degradation quantum yield increased. 4. Conclusions This work constitutes the first attempt to understand pesticides’ residues behaviour under an ultraviolet germi- cidal lamp (254 nm). Our investigations involved analysis of three selected pesticides’ transformation products un- der diverse conditions, such as presence of natural sun light, as well as UVC light radiation. Samples of 6- chloronicotinic acid and 2-isopropyl-6-methyl-4-pyrim- idinol exposed to the natural sun light showed persistency, in the same conditions the 3,5,6-trichloro-2-pyridinol showed high susceptibility to natural sunlight, therefore, within 90 days of our experiment the concentration de- creased by 70%. Exposure of three transformation prod- ucts to the 254 nm germicidal light resulted in degradation of just 3,5,6-trichloro-2-pyridinol. Quantum yields have been determined for all three compounds within oxy- genated and deoxygenated conditions. The obtained val- ues were in the range 0.088 to 0.15. As it was demonstrat- ed through the research, the application of an ultraviolet germicidal lamp does not degrade transformation prod- ucts completely, so it is critical and necessary to extend the quality of toxicity testing for food and water. The tox- icity testing clearly pointed out the fact, that 3,5,6- trichloro-2-pyridinol posses toxicity towards bacteria Vibrio fischeri, while the other two transformation prod- ucts showed negative effects. In this work it was demon- strated that additional attention needs to be paid to the chemicals formed after pesticide application. The persist- ence under various natural conditions within the environ- ment as well in the different food matrices should be thor- oughly investigated and monitored. However, additional analyses of possible by-products formation with GC-MS or LC-MS techniques will be part of our future research. It needs to be stressed that attention must be paid also to fur- ther investigations of possible adverse effects to several organisms or even biomarkers. 5. Acknowledgements This work was supported by the Slovenian Research Agency. The work was partially performed at the Cler- mont Université, Université Blaise Pascal, Laboratoire de Photochimie Moléculaire et Macromoléculaire, Clermont Ferrand, France. 6. References 1. T. Prokopov, S.Tanchev, in A. McElhatton, R. Marshall (eds): Food Safety, A Practical and Case Study Approach, Springer, New York, 2007, pp. 3–25. 2. A. Allende, F. Artés, Food Research International 2003, 36, 739–746. 3. D. J. Geveke, Food Bioprocess Technol, 2008, 1, 201–206. 4. T. Koutchma, Food Bioprocess Technol, 2009, 2, 138–155. 5. M. A. Randhawa, F. M. Anjum, A. Ahmed, M. S. Randhawa, Food. Chem. 2007, 103, 1016–1023 6. M. Bavcon, P. Treb{e, L. Zupancic-Kralj, Chemosphere 2003, 50, 595–601. 7. H. Shemer, C.M. Sharpless, K.G. Linden, Water Air Soil Pollut. 2005, 168, 145–155. 8. S. P. Kale, F. P. Carvalho, K. Raghu, P. D. Sherkhane, G. G. Pandit, A. Mohan Rao, P. K. Mukherjee, N. B. K. Murthy, Chemosphere 1999, 39, 969–976. 9. P. N. Moza, K. Hustert, E. Feicht, A. Kettrup, Chemosphere 1998, 36, 497–502. 10. M. Bavcon Kralj, U. ^ernigoj, M. Franko, P. Treb{e, Water Research, 2007, 41, 4504–4514. 11. C. J. Sinclair, The Handbook of Environmental Chemistry, 2009, Vol 2, Part P, 177–204. 12. M. S. Diaz-Cruz, D. Barcelo, J. Chromatogr. A. 2006, 1132, 21–27. 13. M. Martinez Galera, G. A. Frenich, J. L. M. Vidal, P. P. Vazq- uez, J. Chromatogr. A. 1998, 799, 149–154. 14. M. ^olovi}, D. Krsti}, S. Petrovi}, A. Leskovac, G. Joksi}, J. Savi}, M. Franko, P. Treb{e, V. Vasi}, Toxicology Letters 2010, 193, 9–18. 15. B. Liu, L. L. McConnell, A. Torrents, Chemosphere 2001, 44, 1315–1323. Table 4: Parameters for photodegradation quantum yields for oxy- genated and deoxygenated samples of IMP, TCP and 6CNA. oxygenated aqueous solutions IMP TCP 6CNA A 0.725 0.291 0.372 [254 nm] –dC/dt 9.662 × 10–9 2.620 × 10–8 8.476 × 10–9 [mol L–1 s–1] Φ [molecules 0.015 0.069 0.019 photons–1] deoxygenated aqueous solutions IMP TCP 6CNA A 0.725 0.291 0.372 [254 nm] –dC/dt 1.000 × 10–8 3.330 × 10–8 1.724 × 10–8 [mol L–1 s–1] Φ [molecules 0.016 0.088 0.039 photons–1] 332 Acta Chim. Slov. 2011, 58, 326–332 @abar et al.: Stability of Pesticides’ Residues Under Ultraviolet Germicidal Irradiation 16. D. B. Barr, R. Allen, A. O. Olsson, R. Bravo, L. M. Caltabia- no, A. Montesano, J. Nguyen, S. Udunka, D. Walden, R. D. Walker, G. Weerasekera, R. D. Whitehead Jr., S. E. Schober, L. L. Needham, Environ. Res. 2005, 99, 314–326. 17. T. Cáceres, W. He, R. Naidu, M. Megharaj, Water Research 2007, 41, 4497–4503. 18. N. Ruiz de Erenchun, Z. G. de Balugera, M. A. Goicolea, R. J. Barrio, Anal. Chim. Acta. 1997, 349, 199–206. 19. T. Iwasa, N. Motoyama, J. T. Ambrose, R. M. R. M. Roe, Crop Protection 2004, 23, 371–378. 20. M. Menger, X. Pan, P. Wong-Wah-Chung, M. Sarakha, J. Photochem. Photobiol. A: Chem. 2007, 192, 41–48. Povzetek Zakonodaja glede varnosti hrane je prete`no omejena na sledenje pesticidov, zelo malo pozornosti pa je namenjeno ugo- tavljanju prisotnosti in ocenjevanju strupenosti razgradnih produktov, ki nastanejo pri razgradnji pesticidov. [tudije sta- bilnosti treh izbranih razgradnih produktov pesticidov: IMP – 2-izopropil-6-metil-4-pirimidinol (hidrolizni produkt dia- zinona ), TCP – 3,5,6-trikloro-2-piridinol (razgradni produkt klorpirifosa), in 6CNA – 6-kloronikotinska kislina (raz- gradni produkt imidakloprida in acetamiprida), so bile izvedene na podlagi izpostavljenosti s pesticidi onesna`enih vod- nih vzorcev son~ni svetlobi pri sobni temperaturi (22 °C) in v temnem prostoru pri 4 °C tekom 90 dni. Rezultati so po- kazali majhno spremembo koncentracije vzorcev, hranjenih v hladilniku v temi, kar nam nakazuje da so IMP, TCP in 6CNA v vodi dokaj stabilne spojine. Po drugi strani, je bilo v vodni raztopini TCP, ki je bila izpostavljena soncu, zazna- ti veliko zni`anje za~etne koncentracije v izbranem ~asu. Oceno strupenosti izbranih razgradnih produktov smo izvedli z luminiscen~nimi bakterijami Vibrio fischeri in rezultati so pokazali majhno strupenost za IMP in 6CNA. V primeru TCP pa smo EC50 po 30 minutni izpostavljenosti ocenili na pribli`no 15,1 mg L–1. Stabilnost izbranih razgradnih pro- duktov smo raziskali tudi med obsevanjem z germicidno sijalko z valovno dol`ino 245 nm in rezultati so pokazali majh- no zmanj{anje koncentracije za IMP in 6CNA tako v prisotnosti kisika kot tudi v prisotnosti argona. Nasprotno pa se je koncentracija TCP pod vplivom svetlobe in v prisotnosti kisika spreminjala skladno s spreminjanjem koncentracije ki- sika. Za podrobnej{o primerjavo stabilnosti in razumevanje procesov vseh izbranih razgradnih produktov pri razli~nih pogojih smo izra~unali tudi kvantne izkoristke pri procesu razgradnje.