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Plants Healing The Planet

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— October 4, 2019

Plants Healing The Planet

By Jodi Helmer
  • Planting the right vegetation can help clean up contaminated places.
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In 2009—almost three decades after BP closed a refinery in Wood River, Illinois—24 acres of the original site were planted with groves of willow, poplar, river birch and swamp oak trees.

Establishing a forest on the site was more than just an aesthetic choice. BP planted 3,500 trees as part of its efforts to clean up the once-industrial site.

The trees draw significant amounts of water through their roots, keeping water levels low and minimizing the risk that tainted groundwater will escape the site. They are also able to absorb residual petroleum and chemicals without being harmed in the process.

Green Pollution-Cleaning Power

Elizabeth Pilon-Smits, PhD, a biology professor at Colorado State University, believes phytoremediation represents a great potential for plants to heal a lot of environmental damage in not only soil but also air, surface water and groundwater as well.

“Phytoremediation is the most recent addition to the toolbox,” Pilon-Smits says. “It’s used less than chemical or mechanical remediation methods, but it is effective for removing organic pollutants from soil and water.” Such pollutants include the herbicide atrazine and an industrial solvent called trichloroethylene.

In phytoremediation, plants are used to clean up polluted soil and water. Click To Tweet

In 2019, researchers found that switchgrass helped remove trace heavy metals such as zinc, cadmium, lead and cobalt from the soil. Additional research showed that one species of floating exotic fern accumulated heavy metals in wetlands.

Thanks to these and other studies, phytoremediation has been used to decontaminate brownfield sites and toxic spills around the world.

Sunflowers were planted near Hiroshima and Fuku-shima to help remediate the soil after the nuclear disasters. Italian farmers planted hemp to absorb heavy metals released into the soil by a local steel mill. And after the Deepwater Horizon accident in 2010, BP used plants to clean up spilled oil and restore the environment along the Gulf Coast

Finding the Right Plant for the Problem

While all plants have some potential to remediate soil and water, some are better than others.

More than 400 plant species have been declared hyperaccumulators, plants capable of growing in soils with high concentrations of metals. Several species of mustard, sedum and milkvetch all excel at preventing or cleaning up eco-pollution, removing contaminants without killing the plants.

The effectiveness of phytoremediation depends on using the appropriate plants for specific applications.

Grasses and herbaceous plants like fescue, clover and alfalfa are best for surface soils, while trees with deeper roots, including poplars and willows, work best for contamination of deeper soil layers as well as groundwater. And cattails, reeds, bulrushes and other wetland species perform well for surface waters, notes Pilon-Smits.

More than 400 plant species have been found to pull toxins from polluted areas. Click To Tweet

While phytoremediation can be more cost-effective than other bioremediation techniques, the approach has a few limitations. The biggest issue, says Pilon-Smits, is that it can take longer to clean up soil than chemical or mechanical remediation.

“If time is a consideration, it might not be the best choice,”she says.

Stuart Strand, PhD, a professor at the University of Washington, has been testing the effectiveness of genetic modification to ramp up the phytoremediation potential of certain plants.

Strand created a version of a common houseplant, pothos ivy, to remove chloroform and benzene from the air; his newest research explores how adding a bacterial gene to tobacco plants could help remove formaldehyde from the atmosphere.

“Without proteins to break down these molecules, we’d have to use high-energy processes to remove them from the air,” he says. “We’re engineering plants that can be useful for phytoremediation, which is a new approach.”

Taking an organic approach to removing pollutants from the air, water and soil could have a profound impact on the environment. “We’ve created an enormous amount of pollution and there is not enough funding to clean it up,” Pilon-Smits says. “The more cost-effective we can be, the more we can clean up.”

Hemp Potential

Is hemp a potential hyperaccumulator? Studies are underway to find out.

Researchers at West Virginia University planted three acres of industrial hemp on their campus to assess whether the crop could remove metals from soil on the site of a former zinc smelter.

Research shows that hemp appears to have “stress tolerance genes” that allow it to tolerate soils contaminated with heavy metals. What’s more, this plant produces higher yields than other plants used in phytoremediation, allowing it to take up more metal from the soil.

Although hemp has the ability to accumulate toxic trace metals such as lead, copper and cobalt, the presence of the metals in the plant material does not impact the quality of the fiber, making it an ideal dual-purpose crop.

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