Avaliação da degradação do pesticida Malation comercial por processo UV/H2O2

Abstract

The indiscriminate use of pesticides can lead to several health problems in the population, due to the neurological action that most of these compounds present. Malathion is an organophosphorus pesticide classified as highly toxic. In Brazil, malation is also the pesticide used to combat the Aedes aegypti mosquito, where it is nebulized in areas of interest, usually urban. In this sense, the frequent occurrence of this type of substance in the environmental matrices has generated concern. Due to the need for efficient treatment of these substances, the advanced oxidation processes (AOP) have presented promising results for the degradation of micropollutants, especially the UV/H2O2 process. The objective of this work was to evaluate the degradation of the pesticide Malation® 500 CE by UV/H2O2 processes and photolysis, following the determination of the concentration of the active principle malation by HPLC-DAD. The degradation experiments were carried out by a bench scale reactor using a high-pressure mercury vapor lamp of 125 W at a time of 15, 30, 60 and 90 minutes as the radiation source. The nominal initial concentration of Malation® 500 CE for the degradations was 500 μg L-1. For the study of the UV/H2O2 process, the H2O2 concentration was 100 mg L-1, with every 10 minutes reinjections of 100 mg L-1. Bioassays with larvae of the Aedes aegypti mosquito were carried out in order to evaluate the larvicidal activity of the compound before and after the degradations. Analyzes of dissolved organic carbon were also performed in order to observe the degradation of the compound. The quantification of the active principle malation was made from the use of solid phase extraction, with recovery percentage of 80%. Within 90 minutes of photolysis, degradation levels above 95% were achieved. For the UV/H2O2 process, within 30 minutes the chromatographic signal of the pesticide malation was no longer observed. The organic carbon had a significant increase in 30 minutes of photolysis, but the value decreased until the end of the reaction. In the UV/H2O2 process, the dissolved organic carbon content was 99% in 60 minutes of reaction. In relation to the bioassays, toxic effect was observed only in 90 minutes for the UV/H2O2 process, attributed to the formation of by-products of the degradation. From the results obtained, it is concluded that the UV/H2O2 process is the most suitable for the degradation of the commercial pesticide.