The use of biosolids as a source of organic matter improves the physical and chemical properties of agricultural soils, resulting in an increase in crop yields. In previous studies, between 29-45% of sludge-borne carbon was recalcitrant a year after land application of biosolids from Buenos Aires City. Although high concentrations of some persistent organic pollutants have been worldwide reported to be present in this waste, this study has not been addressed in Argentina until now. Therefore, our aim was to characterize the organic compounds in Buenos Aires City's biosolids. Different extracting solvents were evaluated for ultrasound-assisted extraction (UAE). Results indicated that the combination of hexane: acetone (3:2, v/v) showed the highest extractability, allowing the identification of a wide range of organic compounds, without a clean-up or a pre-concentration step. The organic compounds mainly consisted of fatty acids, n-alkanes and steroids, with concentrations of persistent organic pollutants below detection limits. We conclude that the recalcitrant organic fraction reported in previous research is mainly due to the presence of stable sterols.