Semipermeable membrane device-assisted desorption of pyrene from soils and its relationship to bioavailability

Desorption of pyrene from three different soils was studied using a semipermeable membrane device (SPMD)-assisted method to develop a new approach to predict bioavailability of hydrophobic organic compounds (HOCs) in soils. The results showed that pyrene desorption increased with reduction of soil organic matter content and elevation of pyrene concentration in unaged soils, and the 50-d desorption percentage was 52.2 +/- 3.6%, 76.3 +/- 1.5%, and 99.4 +/- 3.3% for soils 1, 2, and 3, respectively, at an initial pyrene concentration of 10 mg/kg and 73.6 +/- 4.9%, 94.1 +/- 4.1%, and 98.3 +/- 4.9%, respectively, at an initial pyrene concentration of 100 mg/kg. Aging led to a reduction in SPMD-assisted desorption because of movement of pyrene molecules from easy-desorbing to difficult-desorbing sites. The pyrene 50-d desorption percentage from 180-d-aged soils reduced to 5.8 +/- 0.6%, 18.8 +/- 0.9%, and 34.2 +/- 3.1% in soils 1, 2, and 3, respectively, at an initial pyrene concentration of 10 mg/kg and 43.9 +/- 2.9%, 54.3 +/- 4.7%, and 86.3 +/- 3.5%, respectively, at an initial pyrene concentration of 100 mg/kg. Dry and wet conditions during aging had different effects on aging-derived reduction of pyrene desorption, which was found, to our knowledge for the first time, to depend on pollutant concentration. The water to soil ratio during desorption had a significant effect on SPMD-assisted desorption dynamics. When this ratio changed from 10:1 to 1:1, desorption dynamics became more linear and slower, because when the ratio was low, the SPMD could not contact with soil particles well and the diffusion of pyrene from pore water into the SPMD might become the limiting step for SPMD accumulation of pyrene from soils. Good correlations were found between SPMD-assisted desorption and the biota-soil accumulation factor for both unaged and aged soils. The SPMD-assisted desorption is considered to be a reliable approach to predict the bioavailability of HOCs in soils.