Analysis of the adsorption kinetics of pyrene to soil using laser-induced fluorescence spectroscopy (LIF)

The main objective of this work was to contribute to the development of an in-situ analytical method for polycyclic aromatic hydrocarbons (PAH´s) in soils. Beside natural sources like forest fires, PAH´s result from any incomplete combustion of organic material. Man-made sources come from heating systems, industrial power generators, diesel engines or gaswork sites (Dabestani and Ivanov 1999). For that reason, the US Environmental Protection Agency (EPA) indicates 16 PAH´s as priority pollutants (see appendix 1). The background level for PAH´s in soils of Europe and North-America varies between 50 μg/kg and 500 μg/kg soil (Maxin and Kögel-Knabner 1995). Because pyrene is widely prevalent as a soil contaminant and only little information is available about its sorption kinetics to soils (Hwang et al. 2003), pyrene was chosen as a model compound for PAH´s in this work. The classic way to analyse the adsorption characteristics of compounds to soil are batch experiments. They are easy to handle and useful for sorption equilibrium studies. One aim of this work was to follow the adsorption kinetics of pyrene to soil components. In this case batch studies are not the ideal instrument. Maxin and Kögel-Knabner (1995) reported, that the adsorption of PAH´s to water soluble soil components is completed within 15 min and therefore it is difficult to analyse it by batch experiments due to the time-consuming phase separation. Additionally many authors emphasise the advantages of procedures without a separation step for the adsorption analysis (Belardi, Pawliszyn 1989, Ohlenbusch et al. 2000). Aiken and Leenheer (1993) point out, that centrifugation and filtration processes lead to a concentration of the sample and therefore the quantity and quality of the interactions between the components and the sample might be changed. In this context, we intended to show the potentials and limitations of the laser-induced fluorescence spectroscopy (LIF) as an in-situ, real-time method for the analysis of adsorption kinetics in soil. Until now, laser applications in the pedosphere and in aquifer systems are scarce. Recent investigations of petroleum products in soils have shown that a quantitative determination of oil contaminations on soil surfaces is possible with LIF spectroscopy (Schade and Bublitz 1996, Löhmannsröben and Roch 1997). These measurements were carried out on the soil surface or through the glass wall of soil columns. In combination with measurements in a flow-through cell at the column outlet, the breakthrough of free pyrene can be observed (Baumann et al. 2000).[...