Ocorrência e degradação dos fármacos amoxicilina e cafeína em esgoto doméstico e águas superficiais

Abstract

The presence of pharmaceuticals in surface waters has been an issue of big concern, due to the fact that these compounds have low biodegradability, they generally persist in conventional treatment processes and the chronic effects of the exposure in aquatic organisms and humans are unknown. Sewage Treatment Plants (STPs) are indicated as the main sources of discharge of these substances into the environment. In this context, the degradation of caffeine and the antibiotic amoxicillin through direct photolysis using ultraviolet radiation in water and sewage was studied. Degradation tests were carried out using a bench reactor with artificial radiation source composed of a high-pressure mercury vapor lamp (254 nm), the analysis of the degradation of these compounds by natural insolation was also studied, in order to evaluate the rate of persistence in the environment. The pH and initial concentration variables were optimized by experimental design in order to find the optimum degradation condition, which occurred at a concentration of 6 mg.L-1 and pH 4. Degradation kinetics was also evaluated; in which the data were adjusted in kinetics models and the reaction rates and the half-life time in the conditions studied were obtained. There was degradation of both pharmaceuticals and the direct photolysis was considered promising, however it is suggested to combine it with oxidant catalysis for better results. Further degradation was observed in complex matrices such as sewage and surface waters and natural photolysis indicated persistence of these drugs in the environment. A methodology for the determination of caffeine and amoxicillin was also developed using High Performance Liquid Chromatography with Ultraviolet Detection (HPLC-UV). The proposed method was validated in the parameters linearity, precision, accuracy, limit of detection and limit of quantification, according to INMETRO and ANVISA standards. The method was then applied for the determination of these compounds in samples of river water and sewage, in the municipality of Medianeira-PR. The results indicated the presence of both substances in the analyzed samples, suggesting the low treatment efficiency of the STP analyzed against these micropollutants. The concentrations found for caffeine ranged from undetected to 0.1187 mg.L-1, with a detection limit of 0.08 mg.L-1 and a limit of quantification of 0.27 mg.L-1. For amoxicillin, the concentrations ranged from 0.0029 to 0.026 mg.L-1 for a limit of detection of 0.05 mg.L-1 and a limit of quantification of 0.18 mg.L-1. Thus, the methodology showed to be proper and can be used in other studies of the same nature.