Measuring bioavailability of polychlorinated biphenyls in soil to earthworms using selective supercritical fluid extraction

If the release mechanisms during selective chemical extraction of persistent organic pollutants (POP) mimic release mechanisms in natural systems during biological uptake, then a selective non-exhaustive extraction could give a quantitative measure of the bioavailable POP fraction. Supercritical fluid extraction (SFE) is suggested as a possible technique to estimate the amount of bioavailable polychlorinated biphenyls (PCBs) at contaminated sites and hence serve as a new tool in risk assessment. The uptake of PCBs by earthworm (Eisenia foetida) was investigated. PCB contaminated soil was pre-extracted with selective non-exhaustive SFE (50 degrees C, 350 bar, 1h), which removed on average 70% of the individual PCBs. Earthworms were placed in this pre-extracted soil, as well as in untreated soil. After 10 days, the PCB uptake by earthworms in the two systems was compared. The bioaccumulation factor (BAF) was 83% lower in the pre-extracted system than in the untreated system, demonstrating that SFE extracts primarily bioavailable contaminants. From the data, the bioavailable fraction could also be calculated to be 75%, which is very close to the 70% removed by SFE under the applied conditions. This suggests that the chemical methodology is capable of measuring the bioavailable fraction very accurately in this system.