Phytoremediation of Heavy Metals


Mugwort (Artemisia vulgaris)

Us city slickers have fouled the sandboxes we play in. Find an open field in a big city like Los Angeles or New York and the odds are that it’s a former toxic waste dump. Here in our neighborhood we’ve got a lot of lead and zinc–lead from paint and gasoline and zinc from brake linings.

These heavy metals don’t magically go away. They are elements, and short of an alchemical transformation you have to physically remove them, cover them up, or apply phosphate so that plants don’t take them up as readily.

One promising strategy is phytoremediation, the use of plants to uptake heavy metals. City Atlas youarethecity, in New York, is experimenting with Indian mustard, mugwort, basket willow and sunflowers to remediate a contaminated garden. The results are promising with some metals down 50% in a year. Mugwort (Artimesia vulgaris) did an especially good job with a wide range of contaminants.

I should note that Garm Wallace, who runs Wallace Labs, a soil testing service, says that phytoremediation can take many years to get heavy metals down to a safe level. That being said, breeding plants specifically for heavy metal hyperaccumulation is a technology that could make up for our past transgressions.

Thanks to Michael Tortorello for the tip.

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  1. I love this idea but….what happens to the plants that are now contaminated with the heavy metals you have taken from the ground? It appears that this method is a most ‘natural’ way to extract heavy metal contaminates from the ground but then you end up with a bumper crop of plants that are basically contaminated. So you’ve successfully moved your undesired object from A to B….but now what. How do you safely destroy or contain B while it decomposes such that it doesn’t recontaminate anything else? You certainly wouldn’t want to compost anything you grew for the sole purpose of decontaminating the ground….would you? Throwing the plants in a landfill is an easy option but that just removes the problem from your back yard to a different space. And if you’ve read anything about landfill management you may understand the truth in this: just because it’s out of sight and mind at your house doesn’t mean that it’s not leaching out of the landfill and happily contaminating the ground at that new location. If you burn the plants does that release some horrible heavy metal combustion by products into the atmosphere for you to breathe later?
    I do like this idea, and yes there is a lot of value in removing bad things from the soil that you live and walk on and possibly grow in… but I’m curious as to what the full life cycle looks like for this process. Is there a good option for disposing of heavy metals once you’ve managed to extract them from your soil?
    P.S. – a yard full of sunflowers might be a lot of fun…

    • Exactly, Amy. This is what depresses me about the whole thing. Those sunflowers would technically be toxic waste. Sending them to a landfill (or god forbid the garden waste recycling center!) would not be cool. We could take them to one of those household toxic waste drop-off centers–if they’ll accept green waste–but what do they do with that stuff anyway?

      There’s no such thing as away.

      But maybe someone else knows something more encouraging about the safe handling of lead soaked sunflowers &etc?

    • This is where Paul Stamets comes in. So rather than phytoremediation by itself, throw mushrooms into the mix and you have a double whammy! Mycoremediation may hold the key to many of the problems we are facing with contaminated soils. Stamets spends alot of time on this very subject in Mycellium Running (a book everyone should read) and has also put forth a very serious plan for using plants (mainly trees) and mushrooms to remediate the area affected by the nuclear fallout from Fukushima. While there is too much info to sum up here, just google “Paul Stamets” if you don’t know who he is and prepare to have your mind blown…

  2. I think we need to bring Judas Priest out of retirement so they can re-cover the Joan Bayez song Diamonds and Rust but change it to Diamonds and Zinc, a couple of line changes and we have a new remediation anthem.

  3. stinging nettles (which i’ve recently researched cos we’re growing them this year) should also be on the list of phytremediators!

  4. Hi everyone,

    just to clarify. City Atlas is not doing this experiment, youarethecity is. They just let us blog about it. And yes, good question Amy, where should the plants go, when they did take up the heavy metals? One answer is: They don’t or at least not very fast, so the concentration in the plants we tested afterwards is very low. They can often be dumped like regular household waste (don’t compost them or else everything goes back to the soil). But you have to test them to make sure. A second answer is: If you test them and find that they contain dangerous amounts of heavy metal, you will have a hard time bringing it to your regular household toxic waste drop-off center. They are most likely not used receiving plants and will tell you to compost it. So you need to find a commercial waste hauler who works with toxic waste and that can cost a lot. Scientists have experimented with extracting the metal from the plants to use it again as metal, but this is not a backyard solution.

  5. Taking metals up is a possibility but not a sure thing. Phyto works amazingly on light metals, PHC and salt. Lead for example is difficult to remove. We are working with lead removal at the moment. But requires a very advanced scientific process. As for what you do with the plants – you can incinerate them and reclaim the metals.

    If you want to know more check our peer-reviewed papers on our site- our process has been developed from 15+ years of scientific research at one of the worlds leading science universities – University of Waterloo – Canada.

  6. I’m so happy to see this conversation going here and will be following it closely (and finally reading my copy of Mycelium Running !!). I know Kaja mentioned that extracting metals from phytoremediating plants isn’t exactly backyard scale, but I was heartened to read, several years ago, about the intentional extraction of silver and other metals from water hyacinth – solving 2 problems, a) getting the metals out of tropical waterways and b) dealing with the water hyacinth overpopulation that occurs in polluted water… sorry I don’t have a link, but I imagine the info is still out there.

    I’ll be especially interested to hear about (or find) research that addresses the ways plants change the things they uptake – let’s not forget that they’re not just straws, they do act and react on the things in their environments. Also, if you’re working on a scale of many years, using plants in this way might NOT be a case of simply shifting toxic waste around to new locations in the same concentrations at which we found them. While we can’t make things go *poof* and disappear, maybe this IS a viable option.

    Go team!

  7. I’m involved in a phytoremediation project in St. Louis, a part of the Sunflower+ Project StL team, winners of the St. Louis Land Lab Competition.

    Our goal is to remove lead and arsenic from unused city lots using a combination of sunflowers and winter wheat. My involvement is to experiment with acceleration of the process using electricity (aka electro-horticulture). Using electricity on plant life (and bacteria too) is known to increase growth, increase biomass and plant yields, reduce disease and more.

    In our 1st run we had positive preliminary results that had the electrified sunflowers (from seed) growing to a height about 1 foot taller than the rest of them. This Spring we’ll see how well the winter wheat performs. Then round 2 begins.

    If we can use electricity (or other forms of biostimulation) to accelerate the growth or biomass of hyperaccumulators (plants that are known for being tolerant of / love to grow on contaminants), then land owners can expect to realize the meeting of remediation goals faster.

    P.S. Kaja’s guide on phytoremediation is excellent!

  8. I read someplace that oyster mushrooms were used to clean up oil out of the ground, and that they digested the oil and it went away. I know you’re talking about heavy metals, but it was a really hopeful story. After the mushrooms died and began to decompose, insects moved in to feed on them, and laid eggs. Then birds moved in to eat the insects, and dropped plant seeds. So land that had been total waste was now on the path to a full-blown ecosystem.

  9. I’m soo impressed about all the contributions being made.I also want work on phytoremediation as my project topic using vetiver grass to remediate a named water in my area contaminated with heavy metals like lead and zinc.Please can you help me on how to go about it?. Thank you.

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