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

The effects of several bioremediation stimulants, including potentialmetabolism pathway inducers, inorganic/organic nutrients, and surfactants onthe metabolism of phenanthrene and pyrene, as well as the populationdynamics of PAH degrading microorganisms was examined in five soils withdiffering background PAH concentrations, exposure histories and physicalproperties. Most of the supplements either had no significant effect ordecreased the mineralization of ¹⁴C]-phenanthrene and¹⁴C]-pyrene in soil slurry microcosms. The effect of aparticular supplement, however, was often not uniform within or acrosssoils. Decreased mineralization of ¹⁴C]-phenanthrene and¹⁴C]-pyrene was usually due to either preferential use of thesupplement as carbon source and/or stimulation of non-PAH degradingmicroorganisms. Many of the supplements increased populations ofheterotrophic microorganisms, as measured by plate counts, but did notincrease populations of phenanthrene degrading microorganisms, as measuredby the ¹⁴C]-PAH mineralization MPN analysis or cellularincorporation of ¹⁴C]-PAH. These results suggest that the PAHdegrading community at each site may be unique in their response tomaterials added in an attempt to stimulate PAH degradation. Thecharacteristics of the site, including exposure history, soil type, andtemporal variation may all influence their response.