Sorptive bioaccessibility extraction (SBE) of soils: combining a mobilization medium with an absorption sink

In principle, soil bioaccessibility extraction methods are simple dissolution experiments, where the fraction of compounds that is transferred to the extraction medium is measured and considered to be bioaccessible. For hydrophobic organic chemicals (HOCs) such techniques can lead to underestimation of bioaccessibility when the capacity of the extraction medium is insufficient to provide infinite sink conditions for the target compounds. A sorptive bioaccessibility extraction (SBE) method was thus developed and validated, which integrates the key processes of desorption from the matrix and subsequent consumption or depletion. Cyclodextrin was used as a diffusive carrier to enhance desorption from the matrix, while a silicone rod was used as a dominating sink that continuously absorbed the HOC molecules from the cyclodextrin solution. The silicone rod was then solvent extracted and the HOCs measured by GC-MS. For wood soot, the SBE method yielded PAH bioaccessibility estimates that were 3-24 times higher compared to a cyclodextrin extraction without a sink. The study demonstrated that the inclusion of an absorption sink into an established bioaccessibility extraction method (1) is rather simple, (2) can have a major impact on the obtained results, especially for the more hydrophobic compounds and (3) can simplify the analytics.