The environmental and health risks associated with ‘non-extractable’ residues (NERs) of polycyclic aromatic hydrocarbons (PAHs) in soils and their potential for remobilisation remain largely unexplored. These represent considerable uncertainties constraining risk-based approaches to managing contaminated lands. Using sequential extraction, we investigated the time-dependent remobilisation of benzo[a]pyrene (B[a]P) NERs and associated kinetics after re-equilibration periods of 30 d in four artificially-spiked soils which had been aged for up to 200 days. Benzo[a]pyrene NERs, following exhaustive solvent extraction of soils, were remobilised after re-equilibration based on increase in cumulative B[a]P extractability after re-equilibration, as well as the decrease in the absolute amounts recovered by methanolic saponification of NER. The kinetics of remobilised B[a]P in soils throughout aging followed a first-order decrease, and modelled rates were similar to rates reported of slowly desorbing pools (10 <sup>-3</sup>). Soils with larger clay contents exhibited more delayed NER remobilisation compared to sandier soils. Estimated half-lives of B[a]P in soils may span months or years. Amounts of B[a]P remobilised were significantly influenced (p &lt; 0.05) by aging and soil properties. Specifically, butanol-remobilised B[a]P in soils spiked at 10 mg/kg and 50 mg/kg B[a]P ranged from 0.15 to 0.39 mg/kg and 0.67 to 2.30 mg/kg respectively after 200 d of aging. Overall, the remobilised B[a]P concentrations were lower than the health investigation levels (3 mg/kg) for residential land uses in Australia, implying that health risks associated with B[a]P NERs in the aged soils may be minimal and acceptable. To the best of our knowledge, this is the first report of the time-dependent remobilisation of B[a]P NERs in aged soils with associated aging kinetics and may be useful for risk-based contaminated land management.

Remobilisation of ‘non-extractable’ Benzo[a]pyrene residues in contrasting Australian soils

256th National Meeting (2018)

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