The degree of degradation of 12 organic compounds from various classes, comprising of pharmaceuticals, pesticides, and industrial chemicals, was analyzed after hydrothermal treatment at 200 °C for 4 or 16 h, or 255 °C for 16 h. The reactions were conducted in water, aqueous H₂SO₄, or sucrose solution in aqueous H₂SO₄ as a representative matrix of hydrothermal carbonization (HTC) of wet biomasses. The impact of the sucrose-matrix, which formed during the HTC reaction as a solid hydrochar material and a complex pattern of dissolved organic matter in the aqueous phase, was found to be insignificant for the degree of conversion of most compounds. On the contrary, the degree of degradation of 2,6-dinitrotoluene, 2-chloronaphthalene and 3-chlorobiphenyl was enhanced when biomass was present. At high temperatures most of the pollutants were converted except for ibuprofen and chlorinated aromatics. Hydrothermal treatment of β-hexachlorocyclohexane and 4,4′-dichlorodiphenyltrichloroethane led to the formation of stable chlorinated aromatic intermediates.