Pressure Treated Wood and Arsenic in Soil

anise_hyssop(8)March 26, 2013

I have recently moved into a home and am anxious to create garden spaces, especially for food. There are several beds along the foundation that are contained by well-crafted borders of 6x6 lumber. It's pressure treated, and most likely from the day before arsenic was outlawed in lumber.
I would appreciate any advice on how to proceed. I have limited funds to spend on this. I've been researching but have yet to find any definitive answers.
Should I spring for soil tests? Should I replace the wood? Should I line it with something? Do I need to replace the soil? Is the amount of arsenic minimal from this kind of wood given overall environmental contamination? I'm interested in edible landscaping and food gardening. Thank you in advance for sharing your experience and knowledge.

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nc_crn

Most danger from the "bad" arsenic treated lumber would be it's effect on handling it...be it direct contact or it degraded parts coming in contact with the soil.

As far as plants go...it's a non-issue. It's more of a human health issue.

If you're afraid of it...wear gloves, minimize direct contact with the wood, itself...wash harvested produce. Almost all of the danger of it is going to be found on residues outside of the plant, not within the plant.

Most people don't bother with replacing it unless it's so old it's degrading/flaking away. If it's intact the biggest risk is going to be surface residues on the wood, itself.

You could always put a layer of waterproof coating or some other type of paint/coating/covering (like tiles) over the wood, but it too will degrade over time.

    Bookmark   March 26, 2013 at 5:12PM
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gardengal48

Is the amount of arsenic minimal from this kind of wood given overall environmental contamination?

Yes. Arsenic is a naturally occurring element. It is present in all soils. The leaching from CCA treated lumber is minimal but occurs in higher concentrations the newer the material is. Old, weathered wood really poses no problems.

If you have concerns, you can line the sides of the beds but plastic lining materials likely give off as many toxins as the treated wood can. I'd look to some sort of preservative or sealant first.

FWIW, CCA treated lumber has been banned from sale for almost 10 years. Even with treated wood, I doubt a raised bed would hold up that long here in the very winter damp PNW. Your beds are most likely harmless.

    Bookmark   March 26, 2013 at 5:28PM
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wayne_5 zone 6a Central Indiana

Concern about arsenic is understandable. Along a related line..... If you have an older treated picnic table or children's play fixtures, you can seal them with an oil base sealer stain. It is the touching and rubbing that is rather a problem.

    Bookmark   March 26, 2013 at 10:25PM
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dirtguy50 SW MO z6a(6a)

Have it tested and then you will know. Then there isn't an issue. JMO

    Bookmark   March 26, 2013 at 11:23PM
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dirtguy50 SW MO z6a(6a)

Have it tested and then you will know. Then there isn't an issue. JMO

    Bookmark   March 26, 2013 at 11:24PM
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dirtguy50 SW MO z6a(6a)

oops, sorry for the double post.

    Bookmark   March 26, 2013 at 11:26PM
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toxcrusadr

Good advice here. Although there is a safe limit for arsenic in soil in a yard, the biggest risk and what led to its removal from the market was kids touching and even chewing on it.

To be a danger in the garden, the arsenic has to move from the wood to the soil to the vegetables and then be absorbed (and not excreted) by your body. There are a lot more steps it has to go through compared to Billy chewing on the jungle gym.

Arsenic (and chromium) affects soil within a couple of inches of the wood, not the entire garden. If you were to mix up all the soil in the garden and then have it tested, it would likely not be a very big difference from background.

    Bookmark   March 27, 2013 at 10:27AM
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plaidbird

Quote:

There are several beds along the foundation

My concern would be if this is an older home, the old paints had lead, which then contaminates the soil next to the house. As a young, beginning gardener many years ago, that's exactly where I always planted my peas. Easy place to hook a trellis you know, plus in the earliest springtime, the side of the house reflected some heat to speed things along.

All those lead enhanced peas I ate. Maybe that's what's wrong with me ? ;)

    Bookmark   March 28, 2013 at 5:37PM
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wayne_5 zone 6a Central Indiana

The advice about lead paints usually gives a date when lead in paints was banned. ...1972. Perhaps a lot of people might assume that about all paints were lead based until that date. i hardly think so. I remember the oil exterior paint I bought in 1958 was titanium pigmented. So I suspect that leads were on the way out by the early 1950s.

    Bookmark   March 28, 2013 at 6:05PM
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toxcrusadr

It's true that not all paint was leaded, but lead was not just used as a white pigment either. Red paint was colored with 'red lead' (lead oxide) as well as white lead (lead carbonate) and lead chromate (which was yellow).

In addition to pigment (according to Wiki), "Lead is added to paint to speed up drying, increase durability, maintain a fresh appearance, and resist moisture that causes corrosion."

All of which is to say that you can't assume anything when looking at an old house with layers of different colored paints on it.

Lead paint was actually banned for most uses in the US in 1978 (not '72). It was (and is) still used for very limited applications.

    Bookmark   March 29, 2013 at 11:11AM
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