Probiotics – or natural microbes – are believed to provide boost the human immune system and provide other health benefits. New research involving a Missouri University of Science and Technology professor indicates that microbes can also help remove pollutants from groundwater.

Researchers from the University of Washington, working with Dr. Joel Burken, Curators’ Distinguished Professor and chair of civil, architectural and environmental engineering at Missouri S&T, conducted the first large-scale experiment on a Superfund site using poplar trees fortified with a probiotic to clean up groundwater with trichloroethylene (TCE). TCE is a common pollutant found in industrial areas that is harmful to humans when ingested through water or inhaled from the air. The results were published recently in the journal Environmental Science & Technology.

Trees growing on the Silicon Valley test site at the start of their third season. The second and fourth trees (from left) have been given microbes and are growing faster than the poplars with no microbes (first and third trees, from left). Michael Blaylock/Edenspace Systems Corporation

The successful field trial could lead to faster and more effective cleanup of Superfund sites around the country and polluted sites abroad that have high levels of TCE, the authors say.

Less expensive clean up

Contaminated sites containing TCE and other pollutants can be expensive to clean up when using engineering methods such as excavating or pumping toxins from underground, says Burken, who is a leading expert in the field of phytoremediation, or the use of plants to remove toxins from the environment. This new method allows contaminated sites to be dealt with more effectively, often at lower costs, he says.

University of Washington researchers studied poplar wood from a site in the Midwest where trees were already growing in TCE-contaminated soil. After grinding down small samples of the trees and isolating over a hundred different microbes, each strain was then placed in a flask containing high levels of TCE. The researchers worked to find the best microbe strain that could effectively break down TCE and boost tree growth.

The microbe that ultimately was selected eliminated nearly all of the TCE in its flask. The researchers had a clear winner.

“The poplar at the older site in the Midwest selected for the best microbes to help it do its job,” says Dr. Sharon Doty of the University of Washington. “We took advantage of that natural selection process. We just had to find the best ones that the plant already chose.”

For the experiment, Burken and Missouri S&T analyzed the pollutant concentrations in the trees planted by University of Washington to clean the TCE-contaminated soil. That chemical analysis of the tree tissues, also termed phytoforensic analysis, “provided the evidence that the pollutants were degraded to less toxic compounds,” Burken says. The research involved molecular scientists, foresters, environmental engineers and practitioners working to find the best microbe strain that could effectively break down TCE and boost tree growth, and then to integrate the approach into full-scale site remediation.

“The success of this project may open new doors to protecting human health and the environment,” Burken says.

The pollutant TCE has been used widely as a degreaser and a solvent in industrial manufacturing sites across the country. The U.S. Environmental Protection Agency cites TCE as one of the most common pollutants in soil or water, and it is present in more than 1,000 sites the agency lists as priorities for cleanup. TCE is a known carcinogen to humans, affecting the liver and even transferring the toxin to nursing babies through mothers’ breastmilk.

Given the prevalence and toxicity of TCE, the researchers used the chemical to test the ability of poplar trees infused with microbes to clean up groundwater in the Middlefield-Ellis-Whisman Superfund research area in California’s Silicon Valley after it had subsequently flowed into the NASA Research Park at NASA’s Ames Research Center. At NASA Ames, in coordination with NASA Ames’ Environmental Division, the researchers planted rows of young poplar trees — some inoculated with the specific microbe, and others without — on a field above a known groundwater plume contaminated with TCE.

Bigger and healthier

After only a year, the trees given the microbe were bigger and healthier than the poplars with no special treatment. After three years, the inoculated trees were still more robust, and a sample of tree trunks revealed greatly reduced levels of TCE inside the trees.

When trees take up and degrade chemicals, called phytoremediation, it often comes at the expense of their own health. This manifests as stunted growth, yellow leaves, withering brown leaves and branches, and sometimes death as the pollutant hampers the tree’s ability to survive. But when the microbe selected specifically to deal with this toxin is introduced, the trees destroyed the TCE — and experienced more robust growth and increased survival rates, clear benefits of the probiotic.

Additionally, the researchers found that groundwater samples taken directly downstream from the test site showed much lower levels of the toxin, compared with higher levels up-gradient from the testing area. They also found evidence of increased chloride in the soil around the poplar roots, a harmless, naturally occurring element and byproduct of TCE as it is degraded by the bacteria inside trees.

The work was funded by the National Institutes of Health through a Small Business Innovation Research grant.