Influence of Combustion Temperature and Composition of Organic Soil Horizons on the PAH Content (Laboratory Experiment)

The change in the content and composition of polycyclic aromatic hydrocarbons (PAHs) was studied in organic horizons of soils of the boreal zone subjected to combustion under oxygen deficiency conditions. Organic soil horizons from the oligotrophic bog and two types of forest ecosystems (lichen pine and green moss spruce forest) were analyzed. It was found that combustion conditions, the composition of burned organic material, and its flammability influence significantly the content and composition of PAHs. Polyarenes are formed, for the most part, at 300°C. As compared to original samples, their content increases from 2.7 to 9.7 times. The maximum content of PAHs in the samples is reached at 300°C, whereas it falls by 5.8–33.0 times at 500°C. An abrupt decrease in the PAHs content is probably due to the decomposition to simpler substances. The experimentally obtained ratio of low-molecular weight to high-molecular weight polyarenes, which exceeds one, may indicate the pyrogenic origin of PAHs.