Pharmaceuticals and Their Main Metabolites in Treated Sewage Sludge and Sludge-Amended Soil: Availability and Sorption Behaviour

This work evaluated the availability and sorption behaviour of four pharmaceuticals and eight of their metabolites in sewage sludge and sludge-amended soil. Digested sludge and compost were evaluated. The highest levels found in digested sludge corresponded to caffeine (up to 115 ng g−1 dm), ibuprofen (45 ng g−1 dm) and carbamazepine (9.3 ng g−1 dm). The concentrations measured in compost were even lower than in digested sludge. No compound was detected in sludge-amended soils. This fact could be due to the dilution effect after sludge application to soil. Different adsorption capacities in sludge–soil mixtures were measured for the studied compounds at the same spike concentration. In general, except for paraxanthine and 3-hydroxycarbamazepine, the metabolite concentrations measured in the mixtures were almost two-fold lower than those of their parent compounds, which can be explained by their mobility and lixiviation tendency. The log Kd ranged from −1.55 to 1.71 in sludge samples and from −0.29 to 1.18 in soil–sludge mixtures. The log Kd values calculated for compost were higher than those calculated for digested sludge. The obtained results implied that the higher organic carbon content of compost could influence soil contamination when it is applied to soil.