Degradation of aged creosote and diesel contaminated soils by phytoremediation or biostimulation (nutrients)

Abstract: Aged creosote and diesel fuel polluted soil was collected from Resecentrum, Uppsala (deposited at Hovgården). The aims of this study were: 1) to compare the growth and degradation of PAHs and diesel by five Salix clones and 2) to study the effect of nutrients on biodegradation of PAHs and diesel. Three kinds of soil were included in this study: creosote and diesel contaminated soil (undiluted); mixed soil 1:1 (diluted with not contaminated soil) and control soil (not contaminated). The initial total concentration of PAHs in the creosote soil (undiluted) was 10 mg/kg and 1,150 mg/kg of aliphatic and aromatic hydrocarbons (diesel components). The Salix clones used were Tora, Björn, Orm, 78138 and 78112 and Blomstra was used as nutrients. During four months, no obvious difference was found between the five willow clones regarding shoot growth except that Orm grew less well in creosote and diesel contaminated soils. Root biomass increased and the Shoot/Root ratio (S/R) decreased for most clones at higher concentrations of creosote and diesel contaminants. Between clones, 78112 and Orm had lower PAH degradation capacities as compared to others. The presence of plants in the creosote and diesel contaminated soil retarded the degradation of most PAHs as compared to the treatment without plants. It was probably due to the interaction between root exudates and diesel in our study since the latter hydrocarbons could act both as carbon sources and co-substrates that are needed in the co-metabolic degradation of PAHs whereas many microbes preferred the former more easily metabolisable compounds. High degradation of PAHs in the creosote soil occurred in treatments without plants, but even more so in treatment with nutrients especially for high molecular weight (HMW) PAHs, such as benzo(b)fluoranthene (94.7%) and benzo(a)pyrene (100%) as compared to the initial values. The bacterial counts were significantly higher in both the treatment with plants and the unplanted treatment with nutrients, as compared to the initial soil and the control treatment. Eight bacterial strains with the ability to degrade phenanthrene were isolated from the undiluted creosote and diesel contaminated soil.