Impact of brown coal dust on the organic matter in particle-size fractions of a Mollisol

The influence of brown coal emissions from a briquette factory on the organic matter of a Mollisol has been investigated. Non-contaminated, heavily contaminated soils and airborne particles are compared by using chemical and spectroscopic methods (13C CPMAS-NMR, Py-GC-MS, 14C dating). Bulk soils as well as their particle-size fractions are investigated. Organic carbon content of the bulk contaminated soil (138.6 g C/kg) is higher by a factor of six than the non-contaminated soil. For particle-size fractions, the highest content of organic carbon is found in the fine sand fraction (347.2 g C/kg). Furthermore, organic matter of the contaminated site shows a trend for relatively higher abundance of aliphatic compounds in the fraction ranging from 6 to 2000 μm, whereas for particles < 6 μm no trend was observed. The A horizon of the contaminated soil is much older (15,750 yr BP0 than the non-contaminated soil, which indicates input of anthropogenic material. Py-GC-MS analyses show for the non-contaminated site a homologous series of mainly alkanes, low amounts of prist-1-ene and a high abundance of lignin- and carbohydrate-derived structures. In contrast, composition of the samples from the contaminated site are similar to a sample of brown coal analyzed and show a homologous series of n-alkane, alkene, α, ω-alkadiene triplets and a high relative abundance of prist-1-ene with few lignin derived compounds, except for the clay fraction. Reflected light microscopy shows large amounts of brown coal dust particles with typical maceral groups, huminite, liptinite, and inertinite, in the fine sand fraction from the contaminated soil. Additionally, minor amounts of thermally altered brown coal-derived particles, i.e. coke particles, are observed.