The top soil of a 14.5 km(2) region at la Chaux-de-Fonds in the Swiss
Jura is exceptionally rich in cadmium. It contains an average of 1.3 mg
per kg of soil. The spatial distribution of the metal has no simple
pattern that could be explained by atmospheric deposition or
agricultural practices.
Thin soil contained most of its Cd at the surface; in thicker soil Cd is
mainly concentrated between 60 and 80 cm depth. No specific minerals or
soil fractions could account for these accumulation, and the vertical
distribution of Cd is best explained by leaching from the topsoil and
further adsorption within layers of nearly neutral pH.
The local Jurassic sedimentary rocks contained too little Cd to account
for the Cd concentrations in the soil. Alpine gravels from glacial till
were too sparse in soils to explain such a spreading of Cd. Moreover
this origin is contradictory with the fact that Cd is concentrated in
the sand fraction of soils. The respective distributions of Fe and Cd in
soils, and soil fractions, suggested that the spreading of iron nodules
accumulated during the siderolithic period (Eocene) was not the main
source of Cd. Atmospheric deposition, and spreading of fertiliser or
waste from septic tanks seem the only plausible explanation for the Cd
concentrations, but at present few factors allow us to differentiate
between them.