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

Detailed magnetic properties of salt-marsh soils exposed to intense atmosph eric deposition of fly ashes from the iron industry (southeast France) are reported. An enhancement in the concentration of magnetic particles in tops oil through this area is observed. Low values of frequency-dependent suscep tibility (chi (FD)) are characteristic of coarse multidomain (MD) grains an d were observed in surface samples. Concentration of ferrimagnetic minerals in different soil horizons is linked to pollution sources and the prevaili ng wind direction. The anhysteretic remanent magnetisation/saturation anhys teretic remanent magnetisation (ARM(40) (mT)/SARM) ratio versus isothermal remanent magnetisation/saturation isothermal remanent magnetisation (IRM-10 0 (mT)/SIRM) ratio and the IRM-20 (mT)/SIRM ratio versus IRM-200 (mT)/SIRM ratio can differentiate two different contamination emission sources. Magne tic methods used reflect not only the concentration of ferrimagnetic minera ls but also their grain size, thus enabling discrimination of metallurgical dusts and fine pedogenic particles created in situ. Our results suggest th at pollution is not the only source and that pedogenesis also plays a role. (C) 2001 Elsevier Science BN. All rights reserved.