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Plants are cleaning machines

June 10, 2017
Diane Lynch

If plants weren’t amazing enough in all their variety and glory, starting with the most awesome thing on earth — a little brown speck called a seed — they can also fix contaminated soil and water. Who knew?

Known as phytoremediation, phyto is from the Greek word for plant, derived from the verb to grow. Remediation means to remedy, especially in an environmental sense.

The ability of plants to take up toxins, mostly heavy metals, can be pretty dramatic. A decade after the 1986 Chernobyl nuclear plant meltdown, sunflowers planted in a contaminated pond took up enough cesium in 12 days to contain 8,000 times the concentration of the water and the strontium concentration was 2,000 times.

Environmental pollution is a significant threat and industries that we rely on, such as electricity generation, oil refining and manufacturing, cast off billions of gallons of contaminated wastewater every year. Agriculture alone results in massive groundwater pollution through the use of chemical fertilizers that percolate down toward the water table.

Some minerals such as selenium can concentrate after irrigation and represent a risk to humans and wildlife. Interestingly, selenium is a necessary trace mineral, but having more than a trace makes it toxic, as we remember from the wildlife catastrophe at Kesterson Reservoir in the early 1980s. The reservoir was a manmade wetland designed to hold agricultural runoff, and selenium, both in the water and draining off the Coast Range, caused the salinity to rise to unnatural levels resulting in selenium accumulation in waterfowl and wildlife.

Brassicas such as Indian mustard and canola, tall fescue (Festuca arundinacea), birdsfoot trefoil (Lotus corniculatus), Asian rice (Oryza sativa), hybrid poplars (Populus tremula) and kenaf (Hibiscus cannabinus) have shown promise in taking up selenium. It’s interesting that the plants can then be accurately blended into animal feed to supply the trace selenium needed in their diets. Talk about recycling!

There are several plant families that have potential for cleaning up heavy metals such as lead, chromium, copper and nickel used in making the things we consider necessary for our comfortable lives. Corn is good at taking up lead, for instance. Some mustards in the Brassica family are effective at removing several contaminants. The Chinese brake fern (Pteris vittata) had been used to remove arsenic.

Certain strains of tobacco could be used to sequester explosives. Bacteria can be used to promote plant growth to speed the process along.

Researcher Hai-Hong Gu in Norman Terry’s lab at the University of California at Berkeley presented her findings on remediating mine tailings using rice plants at a phytoremediation conference in 2015. Researchers in the lab are working on a degraded pond site in Pittsburg that had industrial use as a wastewater retention pond for Shell Oil until purchased by PG&E in the ’70s. They are studying the use of marsh plants to break down waste and will be submitting a remediation plan to the California Department of Toxic Substances Control, which oversees work at the site.

The EPA has estimated that there are about 30,000 sites in the US alone that require hazardous waste remediation. The website lists 1,470 relevant articles for your reading pleasure, including links to RTDF, which is an EPA collaborative arm that seeks to partner with universities, government agencies and private industry to develop cleanup technologies.

Plants work for free. Possibly not as fast as chemical or mechanical means of remediation, but in the case of nuclear accidents we’re talking decades and much longer before sites are safe for human habitation so why not let plants do some of the work over time?

Plants have so many obvious capabilities such as contributing oxygen to the atmosphere, feeding us, beautifying our existence, making life on earth possible … and the ability to help clean up some of the messes we make. It doesn’t get much better than that.

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