Regulation of microbial phenanthrene mineralization in sediment samples by sorbent‐sorbate contact time, inocula and gamma irradiation‐induced sterilization artifacts

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Abstract
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. 14C‐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 14CO2 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 14C 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.