18    SORPTION, DESORPTION, AND BIODEGRADATION OF
PHENANTHRENE IN SOIL
Jian-Shin Chen, Research Assistant
Walter J. Maier, Professor
Dept. of Civil and Mineral Engineering
University of Minnesota
Minneapolis, Minnesota 55455
INTRODUCTION
Polynuclear aromatic hydrocarbons are omnipresent products of the combustion of carbon-based
materials. These compounds are important environmentally because many PAH individuals have
been demonstrated to be a mutagen or carcinogen.1,2
Sorption of PAHs on soil particles plays a major role in controlling the fate of these pollutants in
aquatic environments. The sorption of PAH contaminants in soils and sediment has been correlated
to the organic carbon content (foc) of sorbent.3,4 Several regression expressions relating equilibrium
partition coefficient (Kp) and organic carbon content of the soil to octonal/water distribution coefficient (Kow) or the aqueous solubility of the sorbate have been proposed.3"5 However, when the
fraction of sand changed, the sorbent organic carbon content is not a valid predictor of the partitioning of PAHs. This is the reason that the organic carbon content normalized partition coefficients (Koc)
for phenanthrene reported in the literature are 2- to 5-fold apart.3,6"8 This study employed a soil
mixture with various sand fractions and organic carbon content in order to investigate the sorption
behavior of phenanthrene.
Organic pollutants buried within pores of soil particles can be inaccessible to microorganisms.
Because microorganisms only degrade substrate that is soluble in solution, therefore, the contaminant
in solution makes up the bioavailable fraction.9 As biodegradation proceeded, solution concentrations are reduced and a gradient develops whereby sorbed material moves into solution. Thus, the rate
and extent of desorption of compounds from the sorbed to the aqueous phase will greatly affect the
overall mineralization rate of sorbed compounds.10,1'
Although researches have been conducted to understand the extent of biodegradation of phenanthrene in the presence of soil, surprisingly little information is available on the biodegradation of
sorbed phenanthrene. Researchers usually coated phenanthrene on the glass container or spiked it
onto the pre-conditioned soil right before the experiment.'
If a microorganism cannot use the sorbed form of a substrate, it may be expected that the organism
will first metabolize the substrate that is in aqueous phase but that the subsequent rate of mineralization of the substrate will be limited by the rate of desorption. This study was conducted to investigate
the desorptive behavior of phenanthrene from a soil that has been contaminated. Meanwhile, the
biodegradation study was undertaken, then, to determine the extent of mineralization of sorbed
phenanthrene.
MATERIALS AND METHODS
Chemicals
[9"'4C] Phenanthrene (specific activity, 13.1 mCi/mmol) was obtained from Sigma Chemical Co.
(St. Louis, MO), and was >95% purity as determined by liquid high-performance liquid chromatography. C-14 isotope was assayed by liquid scintillation counting (Beckman Model LS 1801). Counts
were corrected for quench. Working solutions were prepared by dissolving C-14 radiolabeled phenanthrene in methanol (HPLC grade; Fisher Scientific, Rochester, NY) and then diluted with organic-free
distilled and deionized water that was generated by a Milli-Q purifying system (Millipore). Methanol
fractions in all experiments ranged from 3.2E-5 to 1.2E-4 (by volume) and were small enough to avoid
solvophobic effects.6,15
47th Purdue Industrial Waste Conference Proceedings, 1992 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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