Polycyclic aromatic hydrocarbons (PAHs) are examples of hydrophobic organic contaminants (HOCs) which are widely distributed in soil and sediment in areas around the world where fossil fuel combustion and related activities have been and remain important sources.
It is widely acknowledged that PAHs are associated with soil/sediment organic matter (SOM) where such substrates contain >0.1% SOM. Sorption of HOCs to SOM is a complex process and it would appear to involve a combination of partitioning and adsorption processes that result in bound and sequestered forms with different degrees of recalcitrance. Sorption-desorption processes control the release and therefore the availability of HOCs in soil and sediment which has important implications for human exposure, toxicity to indigenous organisms, bioremediation potential and defining remediation end-points.
The availability of HOCs sorbed to SOM can be examined in terms of their fugacities, since in the bound form their vapour pressures will be lower than their 'free' equilibrated values. The presentation will explore the use of thermal desorption methods for determining relative binding of PAHs. In particular, a method based on thermal programme desorption coupled to MS has been developed for determining temperature profiles and peak temperatures of desorption of PAHs directly from milligram-sized samples of spiked soil. The approach provides a basis for estimating activation energies of desorption of PAHs which can be related to their partitioning and adsorption characteristics in SOM. The results will be discussed in the wider context of PAH contamination of soil and the importance of quantifying the available fraction.Poster presented at:
3rd National Meeting on Environmental Mass Spectrometry - 2006