The behavior of elemental mercury in aqueous systems containing organics has been examined thermodynamically in terms of the complexing effect of a natural organic ligand species on aqueous electrochemical equilibria in the Hg-H2O system, and supplemented by tests on liquid mercury exposed to solutions containing natural organics. The implications of the study are serious in relation to the likely effect of organic-containing aquatic systems on mercury solubility in the mercury contaminated regions of the world.