Impacts of microbial activity on trace metal behavior during the bioremediation of phenanthrene-contaminated soils

Abstract

A novel method for the bioremediation of phenanthrene using the fungus Penicillium frequentans was utilised to remove phenanthrene (200 mg kg\(^{-1}\)) from soil containing both metals and phenanthrene, over 29 days. Bioremediation of phenanthrene and its effects on trace metal behaviour has been investigated. Metal behaviour studied includes metal speciation and the kinetics of exchange between solution and solid phase and plant uptake of the more labile and mobile, and potentially more bioavailable metal species. Phenanthrene removal by P. frequentans was optimised in terms of both soil water and nutrient composition. Slightly lower removal rates were obtained using P. frequentans alone (73%) and plants alone (67%). However, the highest phenanthrene removal (77%) was obtained using both fungus and plant. Assessment of the metal behaviour before and after phenanthrene biodegradation showed that the removal of phenanthrene by either fungal or mixed fungal and native microflora resulted in an increased flux of metal from solid to solution, an increased pool of potentially bioavailable and toxic metal species and increased plant uptake to both Echinochloa polystachia and Triticum aestivum, by factors of 4-13. In the presence of plants alone, metal mobilisation and uptake increased by smaller factors. In some cases, there was no increase in metal mobilisation and a maximal increase of 2 was found in Ni and Pb. These results highlight the impact of bioremediation process on metal behaviour. In addition, it is suggested that phytoremediation and not bioaugmentation using P. frequentans is the best overall option to obtain a considerable phenanthrene removal, reducing the increased pool of potentially bioavailable and toxic metal species