The sorption-desorption balance of barium at the interaction of muddy-sandy terrigenous material with seawater was experimentally determined. The average value of barium desorption in the mixing zone of river and sea waters is 13 μg/g, which leads to additional input of 80 thousand t/year of barium into the ocean, or 8,6% of its entry into the ocean without taking into account the transformation of runoff at the river-sea geochemical barrier. The assessment of the role of desorption processes in the transformation of dissolved barium runoff is in order of magnitude consistent with the data of field observations for most of the mouth areas of the world’s rivers.