Cadmium has considerably less affinity for the absorbents tested than do copper, zinc, and lead and might be expected to be more mobile in the environment than these materials. Studies have indicated that cadmium concentrations in bed sediments are generally at least an order of magnitude higher than in the overlying water. Addition of anions, such as humate or tartrate, to dissolved cadmium cause an increase in adsorption. The mode by which cadmium is sorbed to the sediments is important in determining its disposition towards remobilization. Cadmium found in association with carbonate minerals, precipitated as stale solid compounds, or co-precipitated with hydrous iron oxides would be less likely to be mobilized by resuspension of sediments or biological activity.
Copper has high toxicity to aquatic organisms.
Lead tends to accumulate in the soil surface, usually within 3 to 5 centimeters of the surface. Concentrations decrease with depth. Insoluble lead sulfide is typically immobile in soil as long as reducing conditions are maintained. Lead can also be biomethylated, forming tetramethyl and tetraethyl lead. These compounds may enter the atmosphere by volatilization.