Role of nanoporosity and hydrophobicity in sequestration and bioavailability: Tests with model solids

Phenanthrene was rapidly and extensively mineralized by a bacterium in the presence of glass or polystyrene beads with no pores, silica beads with 2.5-15 nm pores, 3-aminopropyl-bonded silica beads with 6-nm pores, and diatomite beads with 5.4 mu m pores. These beads sorbed 10-99% of the compound in 15 h, but 48-100% of the sorbed hydrocarbon was desorbed in 240 h. Although little phenanthrene was desorbed from octadecyl-bonded silica beads with 6-nm pores, the hydrocarbon was rapidly and extensively degraded. In contrast, the bacterium mineralized <7% of the phenanthrene sorbed to polystyrene beads with 5- or 300-400-nm pores, and little of the compound was desorbed. These findings are consistent with the hypothesis that sequestration and reduced bioavailability occur when hydrophobic compounds enter into nanopores having hydrophobic surfaces.