Organic chemicals in the environment: dissipation of polycyclic aromatic hydrocarbons in the rhizosphere
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abstract
Residual contamination of soils with polycyclic aromatic hydrocarbons (PAHs) is an environmental problem for many industrial operations, including the petroleum industry. Petroleum sludges high in PAHs are often treated through landfarming in which soil is mixed with sludge, kept bare of vegetation, tilled, and fertilized to encourage microbial degradation of the contaminants. However, recent research has demonstrated that plants can enhance the dissipation of organic pollutants in the immediate environment of the root (rhizosphere). The use of vegetation to increase the degradation of two common PAH contaminants, anthracene and pyrene, was investigated in a greenhouse experiment. Target compounds were added to a contaminated, landfarmed soil and a similar uncontaminated soil at a rate of 100 mg/ kg. Four plant species were grown in each soil; after 4, 8, 16, and 24 wk of plant growth, soil and plant material were sampled and analyzed for the target PAHs. Vegetated soils had significantly lower concentrations of the PAHs than the unvegetated soils, ranging from 30 to 44% more degradation in the vegetated soils. Enhanced biological degradation in the rhizosphere appears to be a mechanism of dissipation. Leaching, plant uptake, abiotic degradation, mineralization to CO2, and irreversible Sorption were shown to be insignificant in the overall mass balance of the target compounds. The presence of plants may enhance the clean-up of PAH-contaminated soils during in situ remediation.
