Bioremediation of PAH-contaminated shooting range soil using integrated approaches.

Serious contamination of polycyclic aromatic hydrocarbons (PAHs) occurs at outdoor shooting ranges due to the accumulation of clay target fragments containing coal tar or petroleum pitch. These contaminated sites are characterized with high-molecular-weight PAHs that are low in bioavailability and recalcitrant to bioremediation. We evaluated the effectiveness of different remediation strategies, used individually or in combinations, to decontaminate PAHs in a shooting range soil. The treatments included vegetation with bermudagrass [Cynodon dactylon (L.) Pers] or switchgrass [Panicum virgatum]), bioaugmentation of Mycobacterium vanbaalenii PYR-1, and addition of surfactants (Brij-35, rhamnolipid biosurfactant, or Brij-35/sodium dodecyl sulfate mixture). The initial total PAH concentration in the shooting range soil was 373 mg/kg and consisted of primarily high-molecular-weight PAHs (84%). Planting of bermudagrass and switchgrass resulted in 36% and 27% ∑16PAH reduction compared to the non-vegetated control, respectively. Bermudagrass enhanced soil dehydrogenase activity and both vegetation treatments also increased polyphenol oxidase activity. Bioaugmentation of M. vanbaalenii PYR-1 had a significant effect only on the dissipation of high-molecular-weight PAHs, leading to a 15% decrease (∑10PAH) compared to the control. In the non-vegetated soil, Brij-35/sodium dodecyl sulfate mixture increased PAH degradation compared to the no surfactant control. The increased PAH biodegradation in the vegetated and bioaugmented treatments improved lettuce [Lactuca sativa] seed germination, suggesting reduced toxicity in the treated soils. Phytoremediation using bermudagrass or switchgrass with bioaugmentation of M. vanbaalenii PYR-1 was an effective in situ remediation option for shooting range soils with heavy PAH contamination.

Soil bacterial community dynamics following surfactant addition and bioaugmentation in pyrene-contaminated soils.

Because of their toxic properties, polycyclic aromatic hydrocarbons (PAHs) are designated as priority pollutants. The low solubility and strong sorption of PAHs in soil often limits bioremediation. To increase PAH bioavailability and enhance microbial degradation, surfactants are often added to contaminated soils. However, the effects of surfactants on the PAH degradation capacities of soil microbes are generally neglected. In this study, 16S rRNA gene high-throughput sequencing was used to evaluate changes in the soil microbial community after the application of rhamnolipid biosurfactant or Brij-35 surfactant and Mycobacterium vanbaalenii PYR-1 bioaugmentation over a 50-d mineralization study in two soils contaminated with pyrene at 10 mg kg-1. The introduction of pyrene in both soils resulted in an increase in Firmicutes and a decrease in microbial richness and Shannon diversity index. Amendment of rhamnolipid at 1,400 µg g-1 to the native clay soil resulted in a decrease in Bacillus from 48% to 2%, which was accompanied with an increase in Mycoplana that accounted for 67% of the total genera relative abundance. Phylogenetic investigation of communities by reconstruction of unobserved states was used to predict the activity of functional genes involved in the PAH degradation KEGG pathway and determined that M. vanbaalenii PYR-1 bioaugmentation resulted in an increased number of functional genes utilized in PAH biodegradation. Results of this study provide a better understanding of the soil microbial dynamics in response to surfactant amendments in addition to bioaugmentation of a PAH-degrading microbe. This knowledge contributes to successful and efficient surfactant-enhanced bioremediation of PAH-contaminated soils.