From klier@cobra.uni.edu Tue Apr 18 13:23:10 EDT 1995
Article: 63733 of rec.gardens
Path: bigblue.oit.unc.edu!concert!gatech!howland.reston.ans.net!cs.utexas.edu!math.ohio-state.edu!hobbes.physics.uiowa.edu!cobra.uni.edu!klier
From: klier@cobra.uni.edu
Newsgroups: rec.gardens
Subject: PT Wood Info from Michigan Extension
Message-ID: <1995Apr13.053050.41641@cobra.uni.edu>
Date: 13 Apr 95 05:30:50 -0500
Organization: University of Northern Iowa
Lines: 54

From:	Michigan State University, Cooperative Extension Service.

          MSU COOPERATIVE EXTENSION FACT SHEETS
Number 5                                               1990

             USING TREATED WOOD AROUND THE GARDEN

     The most commonly available treated wood is impregnated with
a combination of chemicals known as CCA (chromated copper
arsenate).  This is sometimes known by its trade name, Wolmanized
wood.  The chemicals protect the wood from attack from agents,
such as fungi, which can shorten the useful lifetime of the wood.
Since these chemicals can have toxic effects at high enough
levels of exposure, there is concern about using CCA-treated wood
around gardens where these chemicals might contaminate fruits and
vegetables that are eaten by the growers.

      From what is presently known about this type of treated
wood, the risk of such contamination is low.  First, the
chemicals are forced into the wood at very high pressure and
remain effectively bound to the wood for very long periods of
time.  Only very small amounts of these chemicals leak out and
get into the soil.  Second, these elements (i.e., arsenic,
chromium, copper) do not move very rapidly through the soil so
migration is limited.  Movement from treated wood would not be
expected to cause a significant increase in the normal background
levels of these elements (commonly found in all soils) except
within 6 inches of distance from this type of wood.  Plant roots
growing within 6 inches of treated wood could be expected to take
up higher levels of copper and arsenic than would occur in
similar soil located greater than 6 inches away.  The
significance of this increased uptake depends on several factors
(e.g., plant species, volume of soil in close proximity to
treated wood, soil fertility conditions, etc.) and is difficult
to predict. Due to the general unavailability of chromium from
soils, no increase in plant uptake of this element would be
expected.

      Overall, the potential for contamination of vegetables and
fruits by CCA is very small and any residues would be at levels
far below those known to cause toxic effects.  However, if the
gardener wishes to reduce this potential even further, barriers
can be used. For example, if this wood is used for a raised bed,
the inside of the wood can be lined with heavy duty plastic.
Another possibility in this and other situations is to coat the
wood with an appropriate sealer.  In general, these steps are not
necessary but they may be used to provide an extra margin of
safety.

Author: Michael A. Kamrin
        Institute for Environmental Toxicology
        Michigan State University
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