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Natural pollution

Pollution is understood to mean the natural or anthropogenic pollution of the living environment by polluting nature with harmful substances such as toxins, microorganisms and radioactive material.

In-situ gamma spectrometry
Field measurement: in-situ gamma spectrometry
© Expert Group for Aerial Radiometry



Naturally unstable elements – examples include uranium, thorium and potassium – occur in soils and rocks and emit radiation during their decomposition. The top 30 to 40 cm of the soil provides the bulk of the radiation measured at the surface. The portion from greater depth is shielded by the overlying soil layers. The terrestrial radiation level is recorded one meter above the ground in the unit of measure nanosievert per hour (nSv/h).

The actual radiation level is as variable as the composition of the rocks. In Switzerland one finds, especially in the Alps, rocks with high concentrations of uranium, thorium and potassium. The highest values are measured over granitic rocks which have a high proportion of potassium (alkali feldspar). 


Arsenic is a chemical element naturally present in the earth's crust. The concentration of arsenic in soils varies and depends on the geological characteristics of the subsurface in question. Human activities such as mining and industry also release arsenic into the environment. Since the substance is considered carcinogenic, it should be present in food in the smallest possible quantities.


The map of the terrestrial radiation level is based on different measurement methods: firstly, the activity is determined by gamma spectrometry measurements of soil samples in the laboratory. The activities are also carried out with the aid of aero-radiometric and in situ gamma spectrometric measurements on site. From the results, the radiation levels are calculated assuming a homogeneous distribution in the soil. The measurement procedures have a different spatial resolution. Since the data points are heterogeneously distributed across Switzerland, values were interpolated into a grid of 2 x 2 km from the existing data.

Geologische Gefahren

Terrestrial radiation (ENSI)