ABSTRACT
In this study, 14 antibiotics and one metabolite were determined in sewages and size-dependent sewer sediments at three sampling sites in the city of Dresden, Germany. Adsorption and desorption experiments were conducted with fractionated sediments. All antibiotics and the metabolite investigated were determined in the sewages; 9 of 14 antibiotics and the metabolite were adsorbed to sewer sediments. The adsorbed antibiotic loads in ng of antibiotic per g of sediment correlated with antibiotic concentrations in ng of antibiotic per litre of sewage. The size fractions <63⯵m, 63-100⯵m and 100-200⯵m had significantly higher loads of adsorbed antibiotics than bigger size fractions. In general, the adsorbed load decreased with an increasing size fraction, but size fractions >200⯵m had similar levels of adsorbed antibiotic loads. An antibiotic-specific adsorption coefficient, normalized to organic content, was calculated: four antibiotics exceeded 10.0â¯Lâ¯g-1, three antibiotics fell below 1.0â¯Lâ¯g-1 and all residual antibiotics and the metabolite were in the range of 1.0-10.0â¯Lâ¯g-1. The adsorbed antibiotic load and the organic matter increased with time, generally. The mineral composition had a minor effect on the adsorption coefficients. Desorption dynamics of five antibiotics and the metabolite were quantified. Regardless of the size fraction, the predominant part of the equilibrium antibiotic concentration was desorbed after 10â¯min. The calculated desorption distribution coefficient indicated adsorption as irreversible at the pH investigated (7.5⯱â¯0.5).