Fate of febantel in the aquatic environment—the role of abiotic elimination processes

Abstract

Febantel is widely used anthelmintic drug active against a range of gastrointestinal parasites in animals. Despite the fact that it has been detected in the aquatic environment, there is no information on its environmental fate. Therefore, abiotic elimination processes of febantel in the aquatic environment have been studied. The results of direct and indirect photodegradation experiments showed that febantel was persistent against solar radiation. Kinetics of hydrolytic elimination was pH and temperature dependent with half-lives in the range from 210 min to 99 days. Febantel metabolites, fenbendazole and fenbendazole sulfone, were found as major degradation products using high-resolution mass spectrometry. The proposed hydrolytic degradation pathway consisted of the base catalyzed hydrolysis followed by consecutive oxidative cyclization to the five-membered ring of the benzo-imidazole derivative. Aquatic toxicity of febantel and its hydrolytic mixture were evaluated toward the luminescence bacteria Vibrio fischeri. Investigation of febantel sorption onto river sediments showed that the best agreement was obtained with the linear model (R² > 0.99), while the rate of sorption is the best described with the kinetic model of pseudo-second order. The organic carbon-normalized sorption coefficient, K_OC, ranged from 1490 to 3894 L kg⁻¹ for five sediment samples. The results of this research demonstrate that febantel persist in the natural waters and potentially could travel far from the source.