RESUMO
This paper presents experimental results on the effect of temperature on the rate of Imidacloprid removal from waste water using homogeneous photo-Fenton processes. Experiments were conducted in a 2 L photo reactor set at 15-42 degrees C, initial concentrations in the range of 10 to 40 mg L(-1) Fe(II) and 100-450 mg L(-1) H(2)O(2); 30 150 min processing times. Initial H(2)O(2) concentration determined the extent of the oxidation process, whereas iron concentration played a key role in the process kinetics. Homogeneous photo-Fenton showed a fast initial reaction leading to 50% Imidacloprid degradation after less than 1 min of treatment, followed by a slower process until full removal was achieved. Rapid Fe(II) oxidation to Fe(III) seems responsible for the initial Imidacloprid removal. Imidacloprid removal fitted well a pseudo-first order kinetic scheme, with apparent activation energy of approximately 31.6 kJ/mole. Untreated Imidacloprid samples showed significant acute toxicity to Daphnia magna and genotoxic effects on Bacillus subtilis. Acute toxicity and genotoxicity remained detectable even after complete pesticide removal, showing that toxic by-products were present. The design and operation of photo Fenton processes should focus on toxicity removal rather than on specific target pollutants.
Assuntos
Peróxido de Hidrogênio/análise , Imidazóis/isolamento & purificação , Inseticidas/isolamento & purificação , Nitrocompostos/isolamento & purificação , Animais , Bacillus subtilis/efeitos dos fármacos , Daphnia/efeitos dos fármacos , Imidazóis/química , Imidazóis/efeitos da radiação , Imidazóis/toxicidade , Inseticidas/efeitos da radiação , Inseticidas/toxicidade , Ferro , Cinética , Luz , Neonicotinoides , Nitrocompostos/química , Nitrocompostos/efeitos da radiação , Nitrocompostos/toxicidade , Oxirredução , Tempo de Reação , Temperatura , TermodinâmicaRESUMO
Kinetic studies of endosulfan photochemical degradation in controlled aqueous systems were carried out by ultraviolet light irradiation at lambda = 254 nm. The photolysis of (alpha + beta: 2 + 1) endosulfan, alpha-endosulfan and beta-endosulfan were first-order kinetics. The observed rate constants obtained from linear least-squares analysis of the data were 1 x 10(-4) s(-1); 1 x 10(-4) s(-1); and 2 x 10(-5) s(-1), respectively, and the calculated quantum yields (phi) were 1, 1 and 1.6, respectively. Preliminary differential pulse polarographic (DPP) analysis allowed to observe the possible endosulfan photochemical degradation pathway. This degradation route involves the formation of the endosulfan diol, its transformation to endosulfan ether and finally the ether's complete degradation by observing the potential shifts.
Assuntos
Endossulfano/efeitos da radiação , Inseticidas/efeitos da radiação , Fotoquímica/métodos , Raios Ultravioleta , Endossulfano/análise , Endossulfano/química , Inseticidas/análise , Inseticidas/química , Cinética , Oxirredução , Fotólise , Espectrofotometria Ultravioleta , ÁguaRESUMO
This paper presents experimental results on the imidacloprid removal from wastewater using homogeneous photo-Fenton reactions illuminated with black light lamps. Multivariate experimental design was used to identify the effect of initial Fe(II) and H(2)O(2) concentrations on process performance. The initial iron concentration played a key role in the process kinetics, whereas hydrogen peroxide concentration directly affected the extent of the oxidation process. Imidacloprid degradation proceeded via two distinctive kinetics regimes, an initial stage of rapid imidacloprid reduction, followed by a slower oxidation process until complete removal. Under optimal conditions, more than 50% imidacloprid degradation was observed after less than 1 min treatment, and TOC and COD removal up to 65% and 80%, respectively, were measured after all hydrogen peroxide was consumed. Raw imidacloprid samples presented significant acute toxicity to Daphnia magna and genotoxic effects on Bacillus subtilis sp. Such toxic effects remained detectable even after significant pesticide removal had been achieved, due to the presence of toxic by-products. Both acute toxicity and genotoxicity disappeared after considerable mineralization resulting in final low molecular weight by-products. Results obtained here confirm that design and operation of photo-Fenton processes should focus on toxicity removal rather than on specific target pollutants.
Assuntos
Imidazóis/química , Imidazóis/efeitos da radiação , Inseticidas/química , Inseticidas/efeitos da radiação , Nitrocompostos/química , Nitrocompostos/efeitos da radiação , Raios Ultravioleta , Poluentes Químicos da Água/química , Poluentes Químicos da Água/efeitos da radiação , Purificação da Água/métodos , Animais , Bacillus subtilis/efeitos dos fármacos , Bacillus subtilis/genética , Dano ao DNA , Daphnia/efeitos dos fármacos , Peróxido de Hidrogênio/química , Imidazóis/toxicidade , Inseticidas/toxicidade , Ferro/química , Dose Letal Mediana , Neonicotinoides , Nitrocompostos/toxicidade , Oxirredução , Fotoquímica , Poluentes Químicos da Água/toxicidadeRESUMO
Photodegradation of the insecticide thiamethoxam (1), 3-[(2-chloro-5-thiazolyl)methyl]tetrahydro-5-methyl-N-nitro-4H-1,3,5-oxadiazin-4-imine, in an aqueous medium was monitored by electrospray ionization mass spectrometry in the positive ion mode, ESI(+)-MS. An aqueous solution of (1) was incessantly exposed to a UV radiation source and aliquots were taken after reaction times of 1, 2, 3, and 4 h. Analysis by GC/NCI-MS revealed that (1) was continuously degraded under these experimental conditions. However, the total organic carbon (TOC) content remained practically constant during the exposition period, thereby indicating that 1 was not mineralized but continuously converted into other compounds. ESI(+)-MS monitoring revealed that whereas the intensity of the ions of m/z 292/294 ([1 + H](+)) constantly decreased, there was the emergence of other ions of m/z 247/249, 197, 168, and 116 whose intensities simultaneously increased. Their structures were proposed on the basis of: (1) the data of their ESI(+)-MS/MS; (2) their high resolution m/z values; and (3) a plausible reactivity of the thiamethoxam molecule exposed to UV radiation in aqueous solution. Finally, these data allowed us to suggest a reaction route for the photodegradation of 1 in an aqueous medium.