| An investigation was conducted to determine possible treatments to increase the biodegradability of residual pyrene by microorganisms in two loam soils after biodegradation and of polycyclic aromatic hydrocarbons (PAHs) in bioremediated soil collected from a former manufactured-gas plant.; In the loams, slurrying, repeated inoculation, heating at 75°C for 18 d or 121°C for 18 h, freezing and thawing for one cycle, drying and wetting, methylene chloride soaking, and the addition of 2,2,4,4,6,8,8-heptamethylnonane (HMN), naphthalene, phenanthrene, anthracene, benzoic acid, palmitic acid, ethylenediaminetetraacetic acid disodium salt, and surfactants (Triton X-100 and Alfonic 810-60 ethoxylate) enhanced further biodegradation of residual pyrene remaining after biodegradation. The pyrene concentrations in treated soils were 18 to 81% lower than those in untreated soils. When the final biodegradation was performed using slurried soil, adding nonaqueous-phase liquids inhibited the further biodegradation of pyrene, and the concentrations in treated soil were 14 and 29% higher than those in untreated soil.; In the bioremediated soil collected from a former manufactured-gas plant site, inoculation of a soil suspension, heating at 75°C for 9 to 21 d, and adding 2,2,4,4,6,8,8-heptamethylnonane enhanced the biodegradation of some PAHs. The residual concentrations of those PAHs in treated soils were 11 to 70% lower than those in untreated soils. Adding surfactants did not significantly enhance further biodegradation.; The data show that several treatments increased the biodegradability of PAHs remaining after an initial biodegradation. These treatments may thus be useful in bioremediation technologies. Some naturally occurring processes, e.g., freezing-and-thawing and drying-and-wetting, also increased the biodegradability of the pyrene remaining in soil. The risk of increased bioavailability of aged and bioremediated toxicants in soil by naturally occurring processes should be further assessed. |
