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 surface and subsurface sediments from a coal tar waste-contaminated: field site. C-14-labeled phenanthrene was aged in both subsurface sand and organic matter-rich seep sediments that had previously been sterilized by gamma irradiation. After aging periods ranging from 0 to 28 d, the sediments were dispensed to replicate vials and inoculated with site-derived phenanthrene-degrading, microorganisms (with and without previous enrichment on phenanthrene), and cumulative (CO2)-C-14 production was measured. When pure culture and mixed inocula originated from the seep sediments, phenanthrene mineralization from sand sediment samples was retarded with longer aging periods. However, when a mixed inoculum originating from the sand sediments was tested, aging of the phenanthrene had only a slight or no effect on its rate or extent of mineralization. Thus, the susceptibility of phenanthrene to biodegradation varied with the source of the microbial inocula. When gamma-irradiated seep sediments were the sorbent, all mineralization of C-14 phenanthrene was eliminated. Several hypotheses were tested for explaining this sorbent-dependent inhibition of phenanthrene metabolism. Gamma radiation-induced changes in the sorptive properties of the seep sediment seemed to be the cause.