23 June 2023

Microbes give new hope for soil remediation in Alaska


Alaska, which has always struggled with cases of oil contamination, may find new solutions in phytoremediation. According to researchers at the University of Fairbanks, grasses and fertilizers shape microbial communities responsible for disposing of toxic substances

by Matteo Cavallito


A proper combination of grasses and fertilizers could enhance the ability of plants and their associated microbes to remediate oil-contaminated soils. This is supported by a research published in the journal Microbiology Spectrum.

The investigation, by a team of researchers led by University of Alaska Fairbanks professor Mary Beth Leigh, brings a new contribution to studies of phytoremediation, or the technique of using plants to restore polluted environments.

A three-decade-long study

The research follows an earlier study by the U.S. Army Corps of Engineers in a crude oil-contaminated area near Fairbanks. In 1995, scientists had divided part of the polluted soil into several micro-zones: in some of them grass had been planted, in others fertilizer had been added, and in still others both elements had been added while the remaining areas had been left untouched.

The study had lasted three years only to be abandoned. Starting in 2011, researchers at the University of Alaska, resumed monitoring noting that contamination was no longer detectable.

“By that time,” says a statement released by the U.S. university, “native species such as white spruce, fireweed, yarrow, willow, blue grass, poplar, buffalo berry, birch and clover had replaced the originally planted grasses.” Moreover, “Three years later, the team took additional samples to test for microbes in each plot. Unexpectedly, the team found that the microbes varied from plot to plot depending on the initial mix of fertilizer and grass, rather than on the types of native species that had moved in.”

Phytoremediation affected microbial communities.

What had happened? The analysis performed by sequencing the 16S rRNA gene revealed that the type of contaminated soil and the phytoremediation strategy had affected the structure of microbial communities both at the level of the rhizosphere, the part of the soil surrounding the roots, and within the plants (where endophytic microorganisms are located).

These effects were evident even many years after the application of the treatments and the subsequent disappearance of the originally planted grasses.

The results, the research explains, “demonstrate that the choice of initial phytoremediation strategy drove the succession of microorganisms associated with the colonizing vegetation.”

New hope for natural decontamination

The mechanisms behind this result are still unclear. However, scientists say, “It is possible that the plants colonizing the disturbed site generally selected microbes that alleviated the contaminant-associated stress induced by the original presence of petroleum hydrocarbons.”

In any case, future research will have to focus on the developmental factors of the microbes themselves, which, unlike plants, are the primary drivers of oil clearance. With further study, in other words, scientists should figure out how to make the natural decontamination process more effective. By identifying, then, which combinations of plants and fertilizers promote the proliferation of the microbes themselves.

Pollution in Alaska in the crosshairs

To test the most effective treatments, researchers at the University of Fairbanks have begun a project at another long-term monitoring site. Any further findings represent an opportunity for Alaska, which has always faced contamination problems. “Subarctic regions are often impacted by fuel and oil spills associated with petroleum extraction, transportation, storage, and use,” the research notes.

The release of hydrocarbons into soil and water, “can pose exposure risk to humans, impair environmental health, and disrupt diverse microbial communities and their ecological functions in the environment.”

Therefore, says Leigh, “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.” Especially in more remote areas whose ecosystems are threatened by oil pollution.