Most of the inorganic materials designated as pollutants in soil are trace elements that occur naturally in all soils in a wide range of concentrations. They are considered harmful only where their concentrations exceed certain threshold values. In most cases there is no method that specifically characterizes these elements according to their origin. An assessment of inorganic pollution, based on total element concentrations of top-soil samples only, is therefore almost impossible. More promising results can be obtained using radio isotope techniques or from chemical analysis of entire soil profiles. The latter approach is demonstrated in a case study with lead, extracted with nitric acid and NH₄-acetate-EDTA from soil samples collected by horizons in 100 profiles from Switzerland. The total (extracted by nitric acid) and the extractable (extracted by NH₄-acetate-EDTA) amounts of lead varied significantly among the different parent materials.
Using at least two different extraction procedures, varying in their ability to affect the lithogenic fraction of the soil, will strongly improve the assessment of soil pollution.