We investigated the biochemical weathering of unaltered lava and scoria samples from Tolbachik volcanic field (Kamchatka). An experimental study on leaching of main (Si, Fe, Mg, Al, and Ca) and trace element constituents (Li, Sr, Ba, V, Mn, Co, Ni, Cu, Ti, and other trace metals) was conducted. We used 0.01 M (pH 2) solutions of oxalic and acetic acids as analogs of natural bioorganic solvents. Meanwhile, a constant mass ratio of solid and liquid phases was maintained. The results suggested that the mobilization of trace elements occurs mainly as a result of the destruction of the crystalline structures of rock-forming minerals. In the case of oxalic acid solution, Fe(III) and Mn(IV) oxyhydroxides are reduced to soluble Fe(II) and Mn(II) compounds. The formation of organic complexes increases the stability of metals in solution and makes it possible to achieve significantly higher concentrations of dissolved forms than in the absence of organic ligands. For example, water that has passed through an old lava field covered with lichen may contain 2.5 times more Co than the maximum permissible concentration for fish reproduction. This study demonstrated that the spikes in concentrations of heavy metals in the Kamchatka River, observed during the 2015 – 2016 period, can be explained by the leaching of fresh products from the Tolbachik Fissure Eruption (2012 – 2013).