UAF-led team uncovers plant remediation effects on petroleum contamination

Two people kneeling in front of grass and shrubs.
Courtesy of Mary-Cathrine Leewis
Chris Kasanke, left, and Mary-Cathrine Leewis were part of the UAF research team led by microbiology professor Mary Beth Leigh that studied plant remediation of a site contaminated by petrochemicals. Their recently published study of the Fairbanks site revealed that initial choices about fertilization and seeding affected which plants and soil microbes were present two decades later.

Initial choices about fertilization and grass seeding on petroleum contaminated soils could have a long-lasting effect on how plants and their associated microbes break down the pollution, a research team led by a University of Alaska Fairbanks professor recently reported.

Microbiology professor Mary Beth Leigh and the team found that planting grasses and-or adding fertilizer to a contaminated site had surprisingly persistent effects on the microbes associated with local vegetation.

The team studied microbes in the soils surrounding the roots and inside root and leaf tissue of native plant species on a contaminated site near Fairbanks, Alaska. The native plants emerged during the 20 years after initial planting with grasses and-or fertilization. 

The study indicates that an even greater importance should be placed on initial phytoremediation — the use of plants to restore environments contaminated by pollutants. 

Phytoremediation strategies have lasting effects on the microbes that are thought to be responsible for breaking down contaminants. Understanding these legacy effects may help researchers strategize ways to make phytoremediation more effective by encouraging petroleum-biodegrading microbes to thrive. 

The results of the study were recently published in Microbiology Spectrum, a journal of the American Society of Microbiology.

Crude oil and diesel pollution often threaten ecosystems in rural sub-Arctic areas, Leigh noted.

“Phytoremediation could be an important tool in the toolbox of rural communities that experience soil contamination with diesel fuel,” said Leigh, who is with the UAF Institute of Arctic Biology. “Giving communities the best advice on how to mitigate contamination in an affordable way, such as by using local plants and their associated microbes, has the potential to significantly empower Alaska Native communities in remote areas whose ecosystems are threatened by petroleum pollution.” 

The current study is based on previous long-term research at a petroleum-contaminated area begun in 1995 by the U.S. Army Corps of Engineers. 

The original study determined that the introduction of different grass species, fertilization or their combination improved the remediation of contaminated soils within the first two years. 

The site was no longer monitored after the initial three-year study but was later revisited by the UAF team to examine long-term progress. In 2011, the contamination concentrations at the research plots were below detection limits in all tested soils. 

One surprising finding was that the originally planted grasses had been replaced by volunteer plant species. The mixture of volunteer species differed depending on the original grass or fertilization treatments, indicating that the initial phytoremediation strategy of each plot drove which plants moved in later. 

The colonizing plants were white spruce, fireweed, yarrow, willow, blue grass, poplar, buffalo berry, birch and clover. 

Unexpectedly, the team found that the microbial communities associated with the colonizing vegetation also depended on the initial treatment rather than the identity of the new plants, indicating that the treatments had long-term effects on the microbes. 

Since microbes, rather than plants, are responsible for breaking down petroleum, these differences could be important to improving the phytoremediation process. 

Rodney Guritz, a former student of Leigh’s and the owner and principal chemist of Arctic Data Services, compiled the chemical analysis for the study.

Guritz sees the potential for practical applications of the new findings in industry.

“In light of climate change, we urgently need to shift from dig, haul and burn, and I see phytoremediation as an important part of this needed shift,” he said. 

The study has implications for phytoremediation strategies worldwide, according to collaborator Ondrej Uhlik, of the University of Chemistry and Technology, Prague, in the Czech Republic.  

“The implications for reviving previously contaminated areas for agricultural purposes are huge in the Czech Republic, and also for Alaska Native communities that depend on fragile ecosystems,” Uhlik said. “Moving forward, it’s exciting to think about reclaiming land to be able not just to live on but also grow food there.”

Additional contact: Mary Beth Leigh, mbleigh@alaska.edu, 907-474-6656.