Sorption and desorption behavior of residual antidepressants and caffeine in freshwater sediment and sewage sludge

Abstract The use of antidepressants is widespread in modern times. Thus, they present a potential risk for ecosystems due to occurrence in domestic sewage containing unaltered metabolites and structures, even after the treatment plants have processed the sewage. The current research investigated the sorption and desorption of antidepressants (citalopram, venlafaxine, fluoxetine, sertraline, and amitriptyline) and caffeine from freshwater sediment and sewage sludge. The samples of freshwater sediment were collected in a river spring in an area with few anthropogenic sources of pollution and samples of sewage sludge were taken from stabilization ponds of a sewage treatment. The matrices were mainly composed of organic fractions, sediment of humic nature, and aliphatic biomolecules in sludges. The presence of silt and clay in the sediment proved to be important for the sorption process when compared to the flocs and colloidal structure of the sludge. The kinetic study indicated pseudo-first order behavior. The Freundlich isotherm was satisfactorily used in the interpretation of sorption and desorption for all analytes and matrices. The high percentages obtained for desorption suggest analyte mobility, which is more intense in the sludge than in the sediment since each matrix has a different composition. It can be considered that the information obtained here reinforces the ecotoxicological concern with respect to pharmacological residues in the environment, as processes of retention by sorption in the sludge and the sediment have been confirmed, as well as the preferential partition of some analytes by the aqueous phase.