Pressure Treated Wood and Arsenic in Soil

11 years ago

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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Comments (10)

nc_crn
11 years ago
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.
gardengal48 (PNW Z8/9)
11 years ago
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.
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As of January 2004 it is illegal to use CCA. The product has been replaced with ACQ (Alkaline Copper Quat) and CBA-A (Copper Azole). Neither of these have arsenic in them. They cost more though and the content in the lumber you buy is based on the likelihood of them coming in contact with the soil, i.e. 5/4 boards for decking have much less than the 4x4 posts that go in the ground. These metals can become toxic if levels become too high though, if you are putting down a deck, let it dry first and then coat it with an oil based stain. Make sure you use corrosion resistant nails or screws when you put these together. As a professional I use only pressure treated compatible screws (sometimes nails are used to temporarily fasten in place but the screws are what hold things together). Alternatively there are Borate treated lumber products disodium octaborate tetrahydrate (DOT) but these can leach out more rapidly and require re-treatment. Hope this helps a bit Al
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It's advised to not use PT wood because there are safer alternatives. That said, the stuff isn't a deal breaker for your garden. Once built the biggest real danger is putting your hands all over the stuff while harvesting...contact stuff. There isn't much to leach into the fruits even in the most toxic of PT lumbers. Plants generally don't pass on much soil toxins because they have no use for their uptake and very little makes it to the actual fruits. Like the above poster said...if you bought your PT lumber recently there's an even larger chance that it's the safer stuff. A lot of the issues with old PT lumber involved people putting their hands all over the stuff or laying produce on it to rest. Even then, a good washing takes care of most all of that. It's the arsenic in the wood that was a huge issue with the last generation PT wood and how you could accumulate arsenic levels on skins just by rubbing your hands across it. A lot of the "panic" came from how much PT lumber is used in kid's playground equipment.
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The pressure treating was probably CCA, copper-chromium-arsenic. Unless the shed was extraordinarily leaky it is likely the only place that any leaching of arsenic from wood took place was at the edges where the footing got rained on, or especially at any footing or posts on or into the ground, but only where the ground could get wet. Thus the interior area may be fine. It might be worth your while just to dig up where soil was in contact with, say, a post, or just beneath the exposed (rained on) outer edge of the flooring/footing. However, arsenic is a lot worse than we often credit to be (arsenic in food and drinking water has triggered the research). The foods are mostly animal though, I believe, or marine plants. There is a lot of interest in this now: I'll bet a fair amout of information is posted on the Net. In city gardening where lead is a big problem it is said that an superabundance of organic matter helps inhibit uptake, but I haven't seen a scientific study.
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Comments (1)
CCA was phased out in 2004 so if the deck is at least 12 years old, then it likely contains CCA. In any case, you really don't want to burn any kind of pressure treated wood.
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wayne_5 zone 6a Central Indiana
11 years ago
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.
dirtguy50 SW MO z6a
11 years ago
Have it tested and then you will know. Then there isn't an issue. JMO
dirtguy50 SW MO z6a
11 years ago
Have it tested and then you will know. Then there isn't an issue. JMO
dirtguy50 SW MO z6a
11 years ago
oops, sorry for the double post.
toxcrusadr
11 years ago
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.
plaidbird
11 years ago
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 ? ;)
wayne_5 zone 6a Central Indiana
11 years ago
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.
toxcrusadr
11 years ago
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.

Pressure Treated Wood and Arsenic in Soil

Comments (10)

nc_crn

gardengal48 (PNW Z8/9)

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