Necrophytoremediation of phenanthrene and pyrene in contaminated soil

In this study, the effect of necrophytoremediation, using pea and wheat straws on the remediation soil contaminated with two common polycyclic aromatic hydrocarbons (PAHs), phenanthrene and pyrene alone or in combination was investigated. In addition, monitoring of the population of PAH-utilising microorganisms together with PCR-Denaturing Gradient Gel Electrophoresis (DGGE)-sequencing methods were used to further elucidate the effect of straw addition on the bacterial, fungal and nidA gene (a functional gene involved in the degradation of PAHs) communities. The addition of pea straw had a positive effect on the degradation of PAHs, especially for pyrene. For example, the addition of pea straw to pyrene-contaminated soil resulted in an increase in the degradation of pyrene from 15% (66mgkg^-1) in the corresponding control to 70% (301mgkg^-1). The results from the most probable number (MPN) of PAH-utilising microorganisms and PCR-DGGE-sequencing methods indicated that the addition of straw led to an increase in microbial hydrocarbonoclastic biomass rather than changes in microbial diversity. For example, in pyrene-contaminated soil, the number of PAH-utilising microorganisms in the soil amended with pea straw reached 5.6log₁₀CFUg^-1 dry soil, ~13-fold increase when compared with the numbers present in the control soil (4.5log₁₀CFUg^-1 dry soils); however, the Shannon diversity index did not increase significantly. The sequencing of bands of interest from DGGE profiles revealed the presence of Actinobacteria, Firmicutes and Proteobacteria in the bacterial community. For fungi, sequenced bands belonged to Ascomycota, Basidiomycota and Mucoromycotina. In summary, this study has shown that necrophytoremediation using pea straw represents a promising biostimulation and cost effective agent which can be used for the bioremediation of PAH-contaminated soils.