Influence of Sorption Processes on Bioavailability and Risk Assessment of PAHs in a Contaminated Soil. A. Abu and S. Smith, King’s College London, UK.
Assessment of risks from Polyaromatic hydrocarbon (PAH) pollutants in soils commonly use partitioning models to estimate exposure and bioavailability. This study compares differences in organic carbon-normalized sorption coefficients (Koc), time-dependent slow aqueous desorption, and contaminant release by GC-MS thermal desorption and pyrolysis techniques in two soils. The influence of these on bioavailability and the effectiveness of remediation strategies and risk assessment measures are also considered. One soil (SBS; 0.24% organic matter) was taken from a former coal-gas production facility, and the other (LHS; 1.5%) an uncontaminated pristine soil. At the same phenanthrene or pyrene aqueous concentration level, SBS had Koc values 2 - 30 times greater than those of LHS. 1% - 3% of initially added PAHs was desorbed in 21 days after an initial 60 or 270 days of sorption.The amount of phenanthrene evolved during thermal desorption at 300°C for 10 mins. was ~ 25% - 40% for SBS and 46%-65% for LHS,comparable to amounts extracted by a mild solvent. No significant structural fragments were evolved when samples were further pyrolysed in the GC at 600°C for 10 mins. GC-MS pyrolysis also failed to reveal any significant structural differences in organic matter profile of both soils. Preliminary application of diffusion weighted NMR spectroscopy to study a saturated sample of SBS identified (1) a domain of free diffusion, and (2) a diffusion restricted environment. These findings suggest that partitioning/diffusion patterns into other SBS soil compartments besides organic matter perhaps contribute more significantly to the desorption-resisitant "irreversibly bound" PAH fractions, with real implications for contaminant bioavailability and the success of any remediation and/or risk assessment measures. This work also highlights the usefulness of GC-MS thermal desorption/pyrolysis and NMR techniques in risk and exposure assessment processes for PAHs in contaminated soils.
This work was part of a PhD research at King’s College London (UK) funded by the Joint Japan/World Bank Graduate Scholarship Program.
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