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ajpa_gw

What plants will remove arsenic from soil?

ajpa
15 years ago

There is an old pressure treated swing set that we should get rid of. I suspect that the soil beneath it may have arsenic leached into it. Since the grass is patchy there, I was thinking I might as well plant something that will absorb the arsenic, to eventually clean the soil. Does that makes sense?

So, anyone know what would be good to plant ... that won't be eaten by critters?

(I don't want to murder the bunnies or birds).

I'm doing some googling and it seems like grass or fern won't work.

Comments (15)

  • val_s
    15 years ago
    last modified: 9 years ago

    Hmmm...in my last house we had a dedicated area for the kid. We had it raised, filled with wood mulch and set one of those swing sets in there. It was a neighborhood draw for years. We added more wood mulch a couple of times as it would decay.

    A year before we moved here, we decided the kid was too old for the area anymore and so we gave away the swing set, added compost, tilled the area, planted a veggie garden and everything seemed to do fine. We had tomatoes, green peppers, beans, peas and various herbs. I never thought about the soil being possibly contaminated. The garden did great, we ate all the fresh we could, canned the rest and even gave some away. As far as I know everyone's still kicking and doing well...but what do I know? LOL

    I'm sure someone will come on and tell you to do a "good reliable soil test" but personally I wouldn't sweat it too much...but that's just me.

    Val

  • ajpa
    Original Author
    15 years ago
    last modified: 9 years ago

    Well, this area was un-mulched, and sad the say the wood was not well-maintained (not sealed regularly). Regular sealing will help prevent the chemicals from leaching. Many veggies will die if the soil has too much Arsenic, and others may tolerate it but don't absorb it.

    But I thought it would be a neat thing to figure out for 12yo's next science fair project -- test the soil now, if there is Arsenic, plant something and remove, test soil again next winter.

    (OT: This year's science fair project was lipstick chromatography -- I wish someone had warned us not to use bright red lipstick -- too stubborn. Dark red worked nicely.)

  • blutranes
    15 years ago
    last modified: 9 years ago

    Ajpa asked:

    "So, anyone know what would be good to plant ... that won't be eaten by critters?"

    Compost is used throughout the world to clean up all types of pollution including lead, arsenic, oil, gas, the list is endless. Try the link below as a start for your answer. As well, believe it or not, mustard greens or sunflowers are some of the plants used in the process as well. Weather they will be eaten or not is something you will have to figure out how to keep from happening. I trust this helps in some way...

    Blutranes

    Here is a link that might be useful: Introduction to Phytoremediation

  • digdirt2
    15 years ago
    last modified: 9 years ago

    In addition to what Blutranes said, ferns. Study done in Florida several years back used ferns to remove arsenic from both soil and water. Testing showed they store it in their leaves.

    But soil testing for arsenic first would be the only way to insure there even is a problem to begin with. ;)

    Dave

  • gardengal48 (PNW Z8/9)
    15 years ago
    last modified: 9 years ago

    Both situations appear to be more of an issue of closing the barn door after the horse has run off.....:-) By far, the primary exposure to arsenic would have been to the kids using the playsets, in which case, the damage has aready been done.

    Depending on how the playsets were designed - how much of the actual wood has come into contact with the soil - the leaching may be minimal. Most leaching of the chemical will occur from wood that is directly in contact with damp soils. If only the legs or supports are in soil contact, then I'm not sure I'd be overly concerned about excessive levels. And the only way that can be confirmed is, as Val notes, through a soil test.

    Arsenic is present in all soils, generally in concentrations that range from 1-40 ppm. Concerns arise when levels are or become excessive but that is most often due to other outside factors - industry or smelters that may emit this chemical - although public and governmental awareness in recent years in this country has pretty much reduced this type of situation to a non-issue.

    All plants absorb arsenic to some degree but typically not in any significant concentration. Plants grown in arsenic-heavy soils generally test out at relatively low levels of the chemical. And by and large, they do not remove arsenic to any signficant degree, so "cleaning' the soil is not practical. AFAIK, there is only one documented case of a plant actually remediating arsenic-contaminated soil and that is a fern, Pteris vittata, the so-called "eden fern", that is now registered for this purpose, but is used primarily on heavily contaminated industrial sites.

    Actually, planting a lawn over the area is likely the best way to go. Since you are not going to be able to cleanse the soil fully from any contamination, shielding it from a lot of contact, like with a lawn or thick groundcover, is the best plan.

    And remember that arsenic treated lumber is now considered a hazardous waste and must be disposed of under strict guidelines. Don't burn it! And it would be prudent to use gloves and a face mask when dismantling the play structure or anything else built from this product.

  • gardengal48 (PNW Z8/9)
    15 years ago
    last modified: 9 years ago

    I guess it depends on how you define 'remediation'. Compost has been shown to immobilize arsenic in the soil, reducing its uptake by plants grown in this condition and limiting its ability to leach into groundwater, but it doesn't remove or neutralize it.

  • albert_135   39.17°N 119.76°W 4695ft.
    15 years ago
    last modified: 9 years ago

    Mining engineers once asked graduate students to study which metals and other vial chemicals would be taken up by Tamarack. I don't know the results. If anything was published it might, but not necessarily, be found via Google Scholar .

  • cowgirl2
    15 years ago
    last modified: 9 years ago

    Here's a good treatment of the subject of CCA lumber. There newer ACQ is briefly mentioned.

    Here is a link that might be useful: Does Pressure-Treated Wood Belong in Your Garden?

  • dchall_san_antonio
    15 years ago
    last modified: 9 years ago

    Back in 1996, before I knew any better, I built a tree house out of treated lumber. I set up a sawhorse and did all the cutting in one place. After 12 years I still have a bare spot in my lawn where the saw dust blew to the ground. I've composted it annually since 2002. Occasionally it teases me into thinking it's all fixed, but it isn't.

    For your problem I would assume it is okay simply because you are going to remove the wood. Plus you don't currently have that much area in contact with the soil. In my case the sawdust is still there and making huge contact with the soil. I'm just saying I would not worry about whether there is going to be a problem with it.

  • joepyeweed
    15 years ago
    last modified: 9 years ago

    I wouldn't assume the soil was contaminated, but if I were planning to grow food there, I would have the soil tested.

    If I were planning to just grow grass or landscaping in the area, I wouldn't worry about a soil test. I would amend the soil with lots of organic matter... which I would do whether the soil was contaminated or not.

    Arsenic is uptaken by plants, there is lots of information out there... rice, corn, beans etc. I think most of the studies that have been done focus on grain producing food crops. It may be harder to find data on non-food crops.

  • toxcrusadr
    15 years ago
    last modified: 9 years ago

    The last post has some good advice. Taht's the way I look at it.

    dchall, it's possible the chromium and copper are impeding growth in your bare spot! Especially copper. Which isn't all that toxic to humans but is used to kill algae in ponds, for example.

    It might be interesting to do a little arsenic calculation on the back of an envelope. From Wiki:

    A study cited in Forest Products Journal found 1213 percent of the CCA leached from treated wood buried in compost during a 12-month period. On the other hand there have been many other studies in less aggressive soil types that show leaching to be as low as 0.5 ppm (red pine poles in service,) or up to 14 ppm (treated pine in garden beds). A report published in Wood and Fibre Science (Vol 36 pp 119-128, 2004) concluded that soil contamination due to the presence of CCA-treated wood after 45 years is minimal.

    Let's use 10% as a guess for the total amount leached. Other parameters: 500 lb swingset with a density similar to oak, say 40 lb/cu ft; .25 lb/cu ft. CCA treatment rate; 15 ft. square area one foot deep. Assume CCA is equal amounts of chromium arsenate and copper arsenate. What is the average arsenic content of the soil? If you're morbidly interested in the rest of the calculations I'll share, but I come up with:

    51 mg/kg or 51 parts per million average As concentration in the soil.

    My state has natural arsenic levels in the range of 10 ppm. This is also the range considered acceptable for residential use based on a disease rate of 1 in 100,000 - i.e. vanishingly small. So we're a little above that but not screaming hot. If it was 500 I would definitely not be growing a garden in it!

    This is a semi-scientific exercise and there are a lot of assumptions. In real life a site could come out higher or lower by an order of magnitude. I just did this for fun.

    Tox

  • dchall_san_antonio
    15 years ago
    last modified: 9 years ago

    theman,
    Sawdust has been discussed here and elsewhere many times. I suppose anything is possible but the general consensus is that the nitrogen robbing quality is only a problem when the sawdust is dug into the soil. As long as it is applied only on the surface, where most wood naturally decomposes, the fungi that decompose it get the nitrogen and oxygen they need from the air. I don't dig anything into the soil so the original sawdust would be on or near the top and not buried where a nitrogen deficiency would be a problem.

    The purpose of treating the lumber in the first place was to permanently prevent decomposition. Whether the sawdust is in or on the soil, it should not be decomposing and using nitrogen.

    Regarding the plant you mentioned: does it have a common name? and does it grow in the shade?

  • themanicgardener
    15 years ago
    last modified: 9 years ago

    DSchall asked: 'Regarding the plant you mentioned: does it have a common name? and does it grow in the shade?'

    I've seen it referred to most often as Chinese brake fern, Chinese ladder brake fern, or brake fern; 'edenfern,' the name mentioned by an earlier commenter, is the name adopted by Edenspace, which produces them commercially for phytoremediation.

    As for shade tolerance, that took some digging, but it appears that it is happy in full sun to partial shade. (Let me know if you want sources!)

    About the sawdust/nitrogen question: Your point about chemically treated wood resisting decomposition is well taken; I'd like to know how deep the treatment seeps into the wood, though. All the sources (some scientific, most university extension) I've looked at except the California Master Gardener Handbook say that sawdust, whether dug in or used as a surface mulch, will tie up nitrogen. Earthworms and other organisms will mix some of it into the soil, even if you didn't, and the layer at the surface will be decomposed by organisms that can't access nitrogen or oxygen from the air, esp. as sawdust creates such a dense mat.

    You obviously know a good deal about this, and I'm just speculating in a semi-informed sort of way, but I think it would be interesting to try adding nitrogen, perhaps to part of the affected area, and see what happens.
    --Kate

  • dchall_san_antonio
    15 years ago
    last modified: 9 years ago

    Thanks a lot Kate. Big help!!