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Re: building raised beds

Square Foot Gardening List - http://www.flinet.com/~gallus/sqft.html

Ann Stark writes:
> >Pressure-treated
> >lumber is not known to leach its poisons into your soil
> 
> Actually, pressure treated wood does leach arsenic into the soil.  Organic 
> Gardening magazine did an article on it in 1999, I think.  Playground 
> equipment built with the stuff was leaching arsenic onto the ground and it 
> was detected in the children's blood.

Thanks!  You're right --- I was wrong.

I found this interesting page on the web site of a company that sells
the arsenides that are used in this process:
http://www.conradwp.com/08.html

It includes some data from a study of building raised-bed gardens;
apparently, there were significantly greater amounts of arsenic in
vegetables raised in treated-wood raised-bed gardens than in vegetables
raised in untreated gardens which were presumably exactly the same in
other ways.

They claim that the levels detected (all less than three parts per
million on a dry basis) are within safe limits.  I don't know anything
about arsenic toxicity (or the toxicity of chromium and copper, two
other elements used in these preservatives, except that I know that
they are toxic), so I can't evaluate whether this is true or not.

I'm not impressed with the quality of the lab work, though; the data
look rather random, suggesting that there are significant uncontrolled
differences between experimental groups.  Also, some cells are marked
"<0.8", suggesting that 0.8 ppm is the minimum level detectable by the
testing methods used, while others are marked "0.5".  This suggests
that testing methods were inconsistent.

It includes conclusions and little tidbits of data from several other
studies, suggesting it's nothing to worry about.

Other studies come to the opposite conclusion.  One study I've seen
referenced in several places is the following:

     131. Lee, Brian C., "Dislodgeable Arsenic on Playground Equipment
     Wood and the Estimated Risk of Skin Cancer," Memorandum.
     Washington, D.C., U.S. Consumer Product Safety Commission, 1990.

Other related reports:

     D. Riedel et. al., "Residues of Arsenic, Chromium and Copper on
     and Near Playground Structures Built of Wood Pressure-Treated With
     'CCA' Type Preservatives," Health and Welfare Canada, January
     1991. Office of Environmental Health Hazard Assessment, "Report to
     the Legislature: Evaluation of Hazards Posed by the Use of Wood
     Preservatives on Playground Equipment," California Department of
     Health Services, February 1987, p. 10.

Unfortunately, most of the information I've found on the potential
hazards of treated wood is "journalism" like the following, rather than
real information:

   Are you one of the millions of unsuspecting consumers who purchased
   your patio furniture or children's playset made from pressure
   treated lumber? Although the wood may last longer, the chemicals
   used to treat them contain massive amounts of the toxic chemical,
   Arsenic.

   Soil samples taken from a playground made from pressure treated wood
   showed an astounding 500 parts per million of arsenic. These levels
   are so high that if a child ate just 2 tablespoons of contaminated
   dirt every day, it could prove fatal. . . . Treated wood
   manufacturers will insist that the wood is safe, but if you can
   obtain a product brochure from the company, you may be shocked to
   find out that this product has the potential to kill you.

(from http://www.biolifeplus.com/healnews.html)

Short on facts, long on sensationalism and loaded terms.  Are you an
"unsuspecting consumer"?  Is this playground typical?

The NIH has a page at
http://ehpnet1.niehs.nih.gov/docs/1997/105-7/forum.html that explains
that (a) the wood does leach; (b) it happens slowly; (c) the nasty
stuff binds to the soil, so it moves very slowly once it is leached
out; (d) it ends up moving only a few inches in most cases.

This makes me worry that perhaps one-year experiments are not really
representative of what happens in a permanent raised bed.

The EPA has a web page that mentions the subject at 
http://www.epa.gov/region08/info/faqs2.html; it recommends against
using pressure-treated wood where it could come in contact with food or
water or be chewed by animals.  It includes the following two precious
paragraphs:

   Although wood preservatives can kill plants, and they obviously
   should not be ingested, the hazards of using preservative-treated
   wood in garden structures are not entirely clear. Each case is
   unique because the degree with which preservatives can migrate
   through soil and be taken up by plants varies with the amount of
   preservative on the wood surface, the soil type and moisture; the
   type of plant and the distance of the plant from the treated wood.

   There is no simple test to determine if plants have taken up
   preservatives from wood. Plants near treated wood which are not
   thriving may indicate that leaching is occurring. Lining raised beds
   with plastic or painting treated wood with two coats of an oil-based
   paint or shellac may impede leaching.

On the other hand, they have a web page at
http://www.epa.gov/opp00001/citizens/1file.htm specifically on CCA,
where they say:

   EPA reviewed the use of CCA in pressure treated wood extensively
   during the 1980s and concluded that pressure treated wood did not
   pose unreasonable risks to children or adults, either from direct
   contact with the wood (e.g., as used for playgrounds and decks) or
   from contact with surrounding soil where some releases may have
   occurred. Based on scientific data that EPA has reviewed to date,
   the Agency has not identified any significant health concerns from
   short or long-term exposure to arsenic residues from
   pressure-treated wood. EPA reached this conclusion based on studies
   that evaluated dermal contact (absorption through the skin),
   inhalation, and ingestion for both children and adults. EPA also
   reviewed a study that concluded that CCA does not pose a short or
   long-term toxic hazard to children playing on playground equipment.

> I personally don't think it's all that important to have wood that has been 
> treated with nasty stuff just so it will last longer.  Who cares if it rots 
> away?  Just replace it with some other found or recycled wood.  I can see the 
> point if your building a house, but a garden?   Composting and recycling are 
> the way of natural things....

Agreed --- especially if the price of having the wood last longer might
be premature death!

-- 
<kragen@pobox.com>       Kragen Sitaker     <http://www.pobox.com/~kragen/>
The Internet stock bubble didn't burst on 1999-11-08.  Hurrah!
<URL:http://www.pobox.com/~kragen/bubble.html>
The power didn't go out on 2000-01-01 either.  :)


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