Lead (Pb) and cadmium (Cd) are two of the most common toxicants found in contaminated environments. Because solubilization of these metallic elements from the solid phase can influence their fate, transport and bioavailability, the partitioning coefficient (K( sub d)) for these metals between environmental solids and natural waters is a key parameter needed for assessing the risks posed by these two elements when present in environmental solids at elevated concentrations. In common with other ionizable contaminants, theoretical models applicable to all environments for assessing the partitioning behavior of Pb and Cd do not exist. Consequently, empirical partitioning models have been developed by the international technical research community. Using large datasets of Pb and Cd partitioning obtained from 13 aquifer materials, soils and sediments, two improved, commonly applicable, empirical models of extended accuracy and applicability were developed in this work.