PARENT SESSION

1B+C Abiotic Transformations + Biodegradation
Poster Hall
8:30 AM - Monday, 28 April 2003
Chair: Peijnenburg, W.¹, ¹
Co-chair: Jafvert, C.T.², Gombar, V.K.³, ^{2 3}

(MOP/38) Soil microbial response during the phytoremediation of PAH contaminated soil.

Johnson, David¹, Paton, Graham², Dawson, Julian², McGrath, Steve¹, ¹ Rothamsted Research, Harpenden, Hertfordshire, UK² Aberdeen University, Aberdeen, Scotland, UK

ABSTRACT- The use of plants for soil bioremediation may be an economically and environmentally feasible way of remediating large areas of surface-contamination, or of residual contamination after pre-treatment. Enhanced bioremediation in planted soils is possibly a function of increased microbial activity in the rhizosphere, but few studies have monitored rhizosphere microbiology during rhizoremediation. PAHs (polycyclic aromatic hydrocarbons) are ubiquitous environmental pollutants originating mainly from inefficient combustion of fossil fuels. Many contaminated sites contain high levels of PAHs and soils may account for up to 90% of the total environmental burden. The aim of this trial was to quantify and compare the responses of soil microbial populations during the phytoremediation of PAHs in a laboratory trial. A previously uncontaminated soil was spiked with PAHs and subjected to the following conditions and planting regime. The PAHs were incorporated in the soil using a solvent (DCM) flooding technique, developed at Rothamsted and proven to give a homogeneous mix of soil and PAHs. The resulting soil was re-inoculated with a slurry of an untreated soil. All soils were contained in 1-kg pots and planted treatments consisted of a mixed ryegrass (Lolium perenne) and white clover (Trifolium repens) sward together with a rhizobial inoculum. Throughout the 180-day experimental period soil microbial biomass, rhizobial populations and populations of PAH degraders were monitored. Survival of the inoculated rhizobia was excellent throughout the trial, suggesting this inoculum is resistant to soil PAHs and may be used as a growth enhancing inoculum. Trends in soil microbial parameters will be discussed in an attempt to elucidate the processes involved in the enhanced dissipation of PAHs in the rhizosphere. Once the microbial factors that enhance PAH dissipation in soils are identified it will allow the rhizosphere to be engineered to optimise the efficiency of phytoremediation of PAHs in the field.

Key words: rhizosphere, phytoremediation, PAHs, microbiology