Phytoremediation Of Polycyclic Aromatic Hydrocarbons Spiked Soil With Arbuscular Mycorrhizal Plants

PAHs are among the most problematic substances as they could accumulate in the environment and threaten the development of living organisms because of their acute toxicity, mutagenicity and carcinogenity. Among remediation techniques for PAH contaminated sites, phytoremediation has been recognized as a promising method owing to its economical and ecological benefits. However, due to the recalcitrant nature of PAHs, multivariate and changeful environment factors, this technique is still limited in terms of effectiveness, especially when dealing with high molecular weight PAHs. Inoculation of plants with arbuscular mycorrhizal (AM) fungi, which are ubiquitous in natural and most anthropogenically influenced soils, is known to benefit PAH phytoremediation. However, diverging results were reported on PAH dissipation in plant rhizosphere, and the parameters affecting the AM fungi assisted PAH phytoremediation needed more investigation.Phenanthrene (PHE), pyrene (PYR) and dibenzo[a,h]anthracene (DBA) were used in our study to represent the three, four and five rings PAHs. Experiments were performed in pot cultures and in microplates, and parameters, plant species, AM fungi species, phosphorus nutrition and watering regimes, PAH molecular weight and interactions between PAHs, were considered in the present work.Effects of different plant species and AM fungi on PAH dissipation were compared. Phytoremediation efficiency of four plant species, including alfalfa, tall fescue, ryegrass and celery roots, inoculated with Glomus intraradices or not, were compared in PAHs spiked soil. Two way anova showed that Glomus intraradices not only increased the plant fitness by increasing the plant shoot biomass, root biomass and phosphorus uptake, but also inceased PHE phytoremediation. The four plant species displayed a positive effect on PHE dissipation, but only alfalfa improved PYR and DBA dissipation, indicating that alfalfa might be a potential candidate for PAH phytoremediation. Besides, a pot experiment was conducted to compare the ability of AM fungi colonized alfalfa and tall fescue and their combination in promoting the PAH bioremediation. And results showed that co-cultivation of alfalfa and tall fescue had no synergistic effect on PHE or DBA dissipation.Different AM fungi species showed different effects on promoting plant growth and PAH photoremediaiton. Two AM fungi speices, Glomus intraradices and Glomus mosseae were inoculated in co-cultured alfalfa and tall fescue, and their effects on promoting plant and microorganism growth and PAH phytoremediation were evaluated. Although both AM fungi increased the plant biomass, plants colonized with Glomus mosseae obtained higher biomass, and the concentration of the PAH-ring hydroxylating dioxygenase genes were significant higher, than with Glomus intraradices. Both Glomus mosseae and Glomus intraradices showed no effect on PHE dissipation owing to its fast biodegradation, but Glomus intraradices was more efficient in promoting DBA phytoremediation than Glomus mosseae. This indicated that the positive effect on PAH phytoremediation of AM fungi may not be attributed to plant biomass increase.The phosphorus concentration and water regime influenced the AM fungi colonization and PAH dissipation. The highest AM fungi colonization and a significant positive impact of mycorrhizal plants on the dissipation of DBA were detected in high-water and low-phosphorus treatment. The addition of high phosphorus Hewitt solution obtained significantly higher DBA dissipation in compare of the low phosphorus Hewitt solution. And the high water regime increased DBA dissipation in planted treatments.PAH molecular weight was a major parameter influencing PAH phytoremediation. With the increase of PAH molecular weight, the culturable PAH degraders decreased, so did the efficiency of phytoremediation. PHE decreased the plant biomass and AM fungi colonization, but it increased the DBA dissipation in both pot and microplate experiments. PYR showed no significant effect on DBA dissipation when co-existed in the microplates, but the addition of PYR into PHE+DBA substrate decreased both PHE and DBA dissipation.In conclusion, our study suggested that AM had potential as a bioremediation agent owing to their positive effect on plant growth, phosphorus uptake, and possiblely on PAH phytoremediation. However, the complex interactions between plants, microorganisms and soil controlled the fate on PAHs. All the studied parameters significantly affected PAH dissipation in PAH spiked soil, and should be considered for controlling and improving phytoremediation efficiency.