Solutions in the “big laboratory”: Toward a model for metals at the Earth’s surface*

Numerous factors control the chemistry of metal ions in natural aqueous systems. These include the presence of a host of complexing agents, speciation among a variety of competing ligands, buffering due to precipitated solid phases, and the relative influences of kinetic versus thermodynamic phenomena. Natural aqueous systems are inevitably complicated, but simple, inorganic models can be constructed to characterize a variety of different environments. While available data sets for these models are large, it is clear that much further research is required in order to develop more sophisticated models. Some of the fields of research that need to be addressed are outlined, and some of the constraints on such research are briefly discussed.