An assessment of environmental and solution parameter impact on trace-metal sorption by soils

When studying metal sorption by soils, the potential influence of environmental and solution parameters on the experimental systems cannot be ignored, Characteristics of the soil mineral surfaces are the final determinative factors in whether a metal ion will be sorbed, but soil-solution composition affects both mineral surface properties and whether the metal ions will be in forms that can react with the surfaces. Examples of factors affecting sorption of metals by soil surfaces include ionic strength, cations, anions, and/or organic ligands present in solution, solution pH, and solution metal concentration. In addition, sorption will be affected by external factors such as pressure, temperature, soil/solution ratio, and the manner in which soils to be studied are sampled and stored before investigation. To date, there has been little attempt to standardize experimental protocol, so results obtained using varied systems in different laboratories cannot be readily compared. An initial suggestion that all sorption studies include at least one treatment meeting minimal standards of ionic strength (0.01), background electrolyte (NaNO3), pH (between 5.5 and 6.0), and temperature (25 +/- 3 degreesC) is presented as a first step toward enabling improved ability to make interlaboratory comparisons.