REGULATION OF MICROBIAL PHENANTHRENE MINERALIZATION IN SEDIMENT SAMPLES BY SORBENT-SORBATE CONTACT TIME, INOCULA AND GAMMA-IRRADIATION-INDUCED STERILIZATION ARTIFACTS

Time-dependent diffusion and/or sorption reactions were proposed as a mechanism for protecting polycyclic aromatic hydrocarbons (PAHs) in su rface and subsurface sediments from a coal tar waste-contaminated: fie ld site. C-14-labeled phenanthrene was aged in both subsurface sand an d organic matter-rich seep sediments that had previously been steriliz ed by gamma irradiation. After aging periods ranging from 0 to 28 d, t he sediments were dispensed to replicate vials and inoculated with sit e-derived phenanthrene-degrading, microorganisms (with and without pre vious enrichment on phenanthrene), and cumulative (CO2)-C-14 productio n was measured. When pure culture and mixed inocula originated from th e seep sediments, phenanthrene mineralization from sand sediment sampl es was retarded with longer aging periods. However, when a mixed inocu lum originating from the sand sediments was tested, aging of the phena nthrene had only a slight or no effect on its rate or extent of minera lization. Thus, the susceptibility of phenanthrene to biodegradation v aried with the source of the microbial inocula. When gamma-irradiated seep sediments were the sorbent, all mineralization of C-14 phenanthre ne was eliminated. Several hypotheses were tested for explaining this sorbent-dependent inhibition of phenanthrene metabolism. Gamma radiati on-induced changes in the sorptive properties of the seep sediment see med to be the cause.