A mixture of substances is designated for introduction into a liquid aqueous system and comprises at least one extremely finely divided active substance component that is designated for subsequent dissolution or dispersion in the liquid aqueous system. The mixture of substances comprises a proportion of cellulose-containing plant fibers and is present in finely particulate form. The cellulose-containing plant fibers improve both the transformation of the extremely finely divided active substance component into the finely particulate form and also its subsequent redissolution in the liquid aqueous system.