Chemical assays of availability to earthworms of polycyclic aromatic hydrocarbons in soil

The bioavailable concentration of an organic pollutant is less than the concentration determined by vigorous extraction of soil. Because bioavailability varies with the particular compound, soil, and aging time, an assay for bioavailability is needed. Three methods were tested: extraction with a 25% aqueous solution of tetrahydrofuran (THF), 95% ethanol, and C18 membranes. Evaluations were conducted with a mixture of four polycyclic aromatic hydrocarbons (PAHs) added to five dissimilar soils and with pyrene as sole PAH added to six soils, and the availability of aged and freshly added compounds was determined. Assimilation by earthworms (Eisenia fetida) was used to assess bioavailability. For extraction with THF and earthworm uptake, the correlation coefficients of determination (R2) for anthracene, chrysene, pyrene, and benzo(a)pyrene added as a mixture exceeded 0.85. The R2 values for assays with the C18 membrane were 0.77 or higher. The values for pyrene added alone were 0.710 and 0.823, respectively. R2 values for assays with ethanol often exceeded 0.87, but lower values were sometimes obtained. We suggest that such solvent or solid-phase extractions may be useful in assessing PAH bioavailability.