Degradação fotocatalítica do inseticida Fipronil: otimização multivariada, identificação dos produtos de degradação e avaliação da toxicidade

Abstract

In this work it was evaluated the degradation of the insecticide fipronil (FIP) by heterogeneous photocatalysis induced by TiO2-P25. Using chemometric methods (Fatorial Design and Response Surface methodology), it was possible to evaluate the role of interaction between pH of the reaction medium, the reaction time and concentration of TiO2, optimizing the conditions for degradation of FIP using artificial radiation. At optimized conditions (79.4 mg L–1 TiO2 and 66.3 min of reaction time for 1.1 mg L–1 of FIP, at pH 5.6-5.8 (natural pH of the irradiated suspension)), 90.9% of FIP degradation was achieved at a degradation rate of 1.54 x 10–2 m2 kJ–1 in terms of accumulated UVA radiation, corresponding to a first order rate constant of 1.34 x 10–2 min–1 and a half-life of 51.7 min. Under the same conditions, these assays were extended to the use of solar radiation, when the degradation rate was 14% higher, with half-life of 44.7 min, suggesting that in both cases FIP degradation was successful. Four by-products of FIP photocatalytic degradation could be separated, identified, and their formation and consumption followed by UHPLC-ESI-Q-TOF. Although the same intermediates have been obtained using both irradiation sources, a faster degradation of the degradation products (DPs) was observed under solar irradiation due to its expressive photonic flux covering the UVA and UVB. It is noteworthy that both the untreated solution and the identified compounds have low toxicity with respect to the Vibrio fischeri bacteria, suggesting that the heterogeneous photocatalysis may be a good alternative for treatment of wastewaters containing FIP and its DPs, mainly when solar radiation is the source of radiation, since under this condition the power consumption during the treatment can be significantly reduced.