Modeling the fate of polynuclear aromatic hydrocarbons in the rhizosphere

Polynuclear aromatic hydrocarbons (PAHs) are major contaminants associated with wastes from manufactured gas plants, wood treating operations, and petroleum refining; they are potentially carcinogenic and mutagenic. It has been known that vegetation can enhance the rate and extent of degradation of PAHs in contaminated soil. Plant roots release exudates capable of supplying carbon and energy to microflora for degrading PAHs. It has also been well established that the population of microorganisms in the rhizosphere is significantly greater than that in the non-vegetated soil; these microorganisms are apparently responsible for the enhanced biodegradation of PAHs. A model has been derived for describing the rate of disappearance of a non-aqueous phase contaminant in the rhizosphere, which takes into account dissolution, adsorption, desorption and biodegradation of the contaminant, without neglecting the size distribution of the organic-phase droplets; the rate of biodegradation is expressed in terms of the Monod kinetics. The model is validated with the available experimental data for pyrene.