Increase in bioavailability of aged phenanthrene in soils by competitive displacement with pyrene

Competitive sorption to natural solids among mixtures of organic compounds has been documented in the literature. This study was conducted to determin e co-solute competitive effects on the biological and physical availability of polycyclic aromatic hydrocarbons. in soils after long contact periods ( aging). Sterile suspensions of Mount Pleasant silt loam (Mt. Pleasant, NY, USA) and Pahokee pear soils were spiked with phenanthrene and allowed to ag e for 3 or 123 d before inoculation with a phenanthrene-degrading bacterium in the presence or absence of the nonbiodegradable co-solute pyrene. As ex pected, mineralization decreased with aging in the samples not amended with pyrene. However, addition of pyrene just prior to inoculation at 123 d sig nificantly mitigated this decrease; that is, the extent of mineralization w as greater in the 123-d pyrene-amended samples than in the 123-d nonamended samples. Parallel experiments on sterile soils showed that pyrene increase d the physical availability of phenanthrene by competitive displacement of phenanthrene from sorption sites. First, the addition of pyrene increased r ecovery of 123-d-aged phenanthrene by mild solvent extraction. Second, addi tion of pyrene (at three concentrations) dramatically reduced the apparent distribution coefficient (K-d(app)) of several concentrations of 60-, 95-, and 111-d-aged phenanthrene. At the lowest phenanthrene and highest pyrene concentrations, reductions in the K-d(app) of phenanthrene in the peat soil reached 83%. The competitive displacement effect observed in this study ad ds further support to the dual mode model of sorption to soil organic matte r. The displacement of an aged contaminant by a nonaged co-solute might als o prove useful in the development of novel remediation strategies.