The effect of inorganic and organic supplements on the microbial degradation of phenanthrene and pyrene in soils

The effects of several bioremediation stimulants, including potential metabolism pathway inducers, inorganic/organic nutrients, and surfactants on the metabolism of phenanthrene and pyrene, as well as the population dynamics of PAH degrading microorganisms was examined in five soils with differing background PAH concentrations, exposure histories and physical properties. Most of the supplements either had no significant effect or decreased the mineralization of [C-14]-phenanthrene and [C-14]-pyrene in soil slurry microcosms. The effect of a particular supplement, however, was often not uniform within or across soils. Decreased mineralization of [C-14]-phenanthrene and [C-14]-pyrene was usually due to either preferential use of the supplement as carbon source and/or stimulation of non-PAH, degrading microorganisms. Many of the supplements increased populations of heterotrophic microorganisms, as measured by plate counts, but did not increase populations of phenanthrene degrading microorganisms, as measured by the [C-14]-PAH mineralization MPN analysis or cellular incorporation of [C-14]-PAH. These results suggest that the PAH degrading community at each site may be unique in their response to materials added in an attempt to stimulate PAH degradation. The characteristics of the site, including exposure history, soil type, and temporal variation may all influence their response.