Abstract
The systems of natural waters are too complicated to investigate low concentrations of strong ligands in their media. It is important to establish experimental conditions where un-biased measurements of intrinsic complexing properties of strong ligands can be performed, in due consideration of the aspects of both thermodynamics and kinetics on the nature peculiar to strong ligands. The accumulation of information on properties and characteristics of strong ligands in the simpler systems should be very helpful in developing the model and estimating metal speciation in more complex systems of natural waters. Our methodology involves the processes of concentration and desalting of natural ligands in sample waters, and of the removal of metals bound to natural ligands. These processes are especially effective in detecting the low levels of strong ligands in sample waters which contain the high levels of trace metals. The application of this approach to the actual natural waters allows us to compare the complexing properties of natural ligands between samples from various sources with each other and well-known synthetic complexing reagents on the same basis without serious influence of the enormous complexity of the equilibrium systems in natural waters. The results obtained by our method from different marine environments indicated that three classes of natural ligands were commonly detected and the sources of these ligands would be of marine origin. The horizontal and vertical characteristics of these ligands suggested their refractory nature in the marine environments.
