Assessment of pyrene bioavailability in soil by mild hydroxypropyl-β-cyclodextrin extraction

Bioavailability of organic pollutants in soil is currently a much-debated issue in risk assessment of contaminated sites. Ecorisk of an organic pollutant in soil is strongly influenced by the properties of the soil and its contamination history. To evaluate the effect of aging on the availability of pyrene, earthworm (Eisenia fetida) accumulation and chemical extraction by exhaustive and nonexhaustive techniques in soil spiked with a range of pyrene levels (1.07, 9.72, 88.4, 152, and 429 μg g⁻¹ dry soil) were measured in this study using both unaged (i.e., 0 days) and aged (i.e., 69, 150, and 222 days) soil samples. The results showed that the amount of pyrene accumulated by earthworms did not change greatly with aging time under different high-dose contamination levels, but changed significantly at lower concentrations. Moreover, aging (after 222 days) significantly decreased biological and chemical availability of pyrene. Furthermore, the relationship between earthworm bioaccumulation, hydroxypropyl-β-cyclodextrin (HPCD), and organic solvent extraction was investigated in order to find a suitable and rapid method to predict pyrene bioavailability. Results showed that, at different levels of pyrene, the mean values of earthworm uptake and HPCD extractability were 10-40% and 10-65%, respectively. Correlation (r² = 0.985) and extraction results for pyrene suggested that mild HPCD extraction was a better method to predict bioavailability of pyrene in soil compared with organic solvent extraction.