Magnetic properties of salt-marsh soils contaminated by iron industry emissions (southeast France)

Abstract

Detailed magnetic properties of salt-marsh soils exposed to intense atmospheric deposition of fly ashes from the iron industry (southeast France) are reported. An enhancement in the concentration of magnetic particles in topsoil through this area is observed. Low values of frequency-dependent susceptibility ( χ FD) are characteristic of coarse multidomain (MD) grains and were observed in surface samples. Concentration of ferrimagnetic minerals in different soil horizons is linked to pollution sources and the prevailing wind direction. The anhysteretic remanent magnetisation/saturation anhysteretic remanent magnetisation (ARM 40 mT/SARM) ratio versus isothermal remanent magnetisation/saturation isothermal remanent magnetisation (IRM −100 mT/SIRM) ratio and the IRM −20 mT/SIRM ratio versus IRM −200 mT/SIRM ratio can differentiate two different contamination emission sources. Magnetic methods used reflect not only the concentration of ferrimagnetic minerals but also their grain size, thus enabling discrimination of metallurgical dusts and fine pedogenic particles created in situ. Our results suggest that pollution is not the only source and that pedogenesis also plays a role.