Airborne contamination of forest soils by carbonaceous particles from industrial coal processing

In the German Ruhr-area industrial coal processing emitted large amounts of carbonaceous particles for a century until 1970. Our objectives were to de tect the presence of airborne carbonaceous particles and assess their impac t on the chemical structure of soil organic matter in two forest soils (Pod zols) with potential sources of carbonaceous particles approximately 10 to 30 km away. Contamination was not visible macroscopically. Organic matter w as characterized in bulk soils and in particle-size separates by elemental analysis, magnetic susceptibility measurement, reflected light microscopy, and C-13 solid. state nuclear magnetic resonance (NMR) spectroscopy. Organi c and mineral horizons contained carbonaceous particles including char, cok e, and bituminous coal from coal combustion, coking, coal processing, and s teel production. In the organic horizons of both soils we observed a materi al high in magnetic susceptibility (max. 10(9) x 10(-8) m(3) kg(-1)), where as in the mineral horizons only the Podzol with an intense intermixing mode r-type humus had high magnetic susceptibly. This Aeh horizon was extremely rich in organic carbon (139.4 g organic C kg(-1)), concentrated in the 20 t o 2000 pm size separates. In the second Podzol, like in many natural soils, C concentrations were largest in the <20 mu m separates. Bloch decay C-13 magic angle spinning (MAS) NMR spectroscopy revealed a highly aromatic stru cture of the carbonaceous particles. Airborne carbonaceous particles formed a macroscopically indistinguishable mixture with natural soil organic matt er and could be present in many soils neighboring industrialized areas.