Our Vision #4: Bioremediation

Bioremediation Research Center

Phyto- or green remediation looks to nature to help clean up contaminated soils. It is cheaper and of lower impact than more traditional remediation methods. In particular, phytoremediation uses plants to draw heavy metals out of the soil.  Although this process has not been scientifically proven to treat lead contamination, there are scientists who think it might be possible.  A cheap and quick-to-construct hoop house on top of a small area of lead-heavy tailings could serve as a research center for phytoremediation techniques.

Pennycress

Alpine pennycress (Thlaspi caerulescens) is a plant that is usually thought of as a wild flower or a weed. It’s a member of the brassica family that grows in western Colorado, Wyoming and up to Montana. It’s often found at high elevations in the Rockies as well as in the Alps and the Pyrenees, among other places.

In an earlier post about phyto or green remediation, I wrote about the possibility of using plants to draw heavy metals out of contaminated soil. Alpine pennycress is a particularly promising plant for remediation because it can tolerate high amounts of cadmium, lead, and zinc. It has also been shown to draw cadmium and zinc out of the soil and can be used to mitigate erosion on lead contaminated soil.

We’ve found alpine pennycress growing on the site of the Ute Ulay. It’s small and scrubby but it’s there. This seems to be a promising sign, both for the soil and for the possibility of phytoremediation.

And there’s more: alpine pennycress’s cousin field pennycress is being developed in the US as a source of biodiesel. Pennycress is not useful as livestock feed, though its leaves and seeds are a good source of oil, and it’s production would not compete with land for food production because it is used as a winter cover crop.

As far as we can tell, alpine pennycress is not being tested for bio-fuel possibilities, perhaps because it has fewer leaves and smaller seeds and doesn’t grow in the mid-west, where most of the field pennycress research is going on. But what if it was useful for bio-fuel on a small scale? We could use the plants for soil remediation and then process them as bio-diesel to run the Buckeye Engine.* An almost perfect loop!

*This plan is not scientifically verifiable.

Phytoremediation

Phytoremediation or green remediation refers to the use of plants to treat environmental problems. It does not require excavation or removal of contaminated soil and is very low impact environmentally.

Phytoremediation is based around the use of hyperaccumulators. These plants draw heavy metals and other toxic materials out of the soil through their roots and into their leaves. The plants are then harvested and removed from the site, taking the metals with them. In some cases, valuable materials which are toxic in soil at high concentrations, like zinc, can be extracted from the plants and sold at the going rate. This process is called phytomining.

In addition to its environmental benefits, phytoremediation is extremely cost effective. In other words, it's cheap. For each acre of contaminated soil, it’s estimated phytoremediation will cost $250 to $1000. Traditional remediation runs around $1 million dollars an acre.

So why is this not a more common practice? For one thing, not all metals can be treated through phytoremediation. Lead, for example, which is a problem on the town site of the Ute Ulay, cannot be treated this way as far as science knows (although plants can be used as a sort of barrier to trap lead in by preventing erosion). Another reason may be that phytoremediation is an ongoing process and can take several growing seasons to bring soil toxins down to an acceptable level. Traditional remediation is generally a once and done deal that involves a combination of capping and relocating contaminated soil. But to compare, the tailings piles from the Ute Ulay (adjacent to the site on public land) remediated by the Bureau of Land Management a few years ago cost about $1 million dollars. It took ten years and a lot of work to raise that much money. If it had taken ten years to remediate the land using plants, the results might have been similar for a markedly smaller amount of money.

There are other considerations with phytoremediation including making sure that the metal-laden plants are not going to be problematic for wildlife (fences can do wonders in this department) and that respiration doesn't turn a ground problem into an air problem. Additionally, amendments of some kind must generally be added to disturbed soil to make it suitable for new plant life. At least one promising experiment done using pulp from paper plants has shown that what is normally an industrial waste can become a food source for bioremediating plants.

Artist Mel Chin, working with scientists like Rufus Chaney currently of the USDA, brought broader attention to this process through his piece Revival Field (1990-present) and while scientists continue to experiment with it, phytoremediation is a nascent technology in many ways.

Stay tuned for another blog post about alpine pennycress, a Rocky Mountain weed and hyperaccumulator extraordinaire.