September
1, 2005: I was working on my grape arbor the other
day and noticed that some of the posts need to be replaced.
We use the grapes to make jelly, juice, and homemade wine.
We don’t sell any of the grapes or grape products, but
we still follow organic standards and we have the grapes listed
on our Organic System Plan.
So I need to use rot-resistant posts, but according to organic
regulations I can’t use posts treated with copper chromium
arsenate or creosote. This is a common dilemma faced by many
organic vegetable, fruit and livestock producers.
The National Organic Standards, in section 205.206(f) state,
“The producer must not use lumber treated with arsenate
or other prohibited materials for new installations or
replacement purposes in contact with soil or livestock.”
My posts will be used for replacement purposes, and they
will contact the soil, so I must not use lumber treated with
arsenate or other prohibited substances. How do I know which
types of posts on the market are treated with prohibited substances?
Pennsylvania Certified Organic (PCO) reported in their Spring
2005 newsletter, Organic Matters, that they reviewed four
wood treatments and found that all contained prohibited substances.
They were:
- Natural Select® Wolmanized Wood
- Copper Azole Wood Treatment (CBA)
- Preserve® and Preserve Plus® (AQC)
- Akaline Copper Quaternary Ammonium
So now I know what I can't use—what can I use?
ATTRA (Appropriate Technology Transfer to Rural Areas) also
has an informative booklet, titled Organic Alternatives to
Treated Lumber, posted at http://www.attra.org/attra-pub/lumber.html.
According to the ATTRA publication, chromated copper arsenate
(CCA), often referred to as “pressure-treated lumber,”
is most commonly available in retail outlets. The CCA mixture,
which contains copper, arsenic, and chromium compounds, is
dissolved in ammonia and then forced, under high pressure,
deep into the wood.
Arsenic, chromium, and copper do leach from treated wood.
Arsenic can collect in the soil under most CCA-treated wood
applications. Burning CCA-treated wood volatilizes some of
the arsenic, but the ash remaining is technically a hazardous
waste. Disposal of CCA-treated wood to landfills may be potentially
dangerous because as the wood rots in the landfills, the metals
are released and may pose a threat to groundwater.
Recent studies have shown that arsenic can be absorbed through
the skin from contact with treated wood. The results of prolonged
exposure to arsenic can include vomiting, diarrhea, nerve
damage, blood vessel damage, and heart rhythm dysfunction
(Rodale, 2000). Arsenic is also an extremely potent carcinogen,
and chromium is a suspected carcinogen.
Because of the health concerns surrounding CCA-treated wood,
the U.S. Environmental Protection Agency implemented a ban
on its manufacture and sale for residential applications effective
January 1, 2004. Many of the "alternative" treated
wood products (such as those listed above that were tested
by PCO) also contain substances prohibited in organic systems,
however.
Cooperative Extension of the University of Nebraska-Lincoln
has a publication, Native Wood Fence Posts (Schmidt and Kuhns,
1990), that lists the expected lifespan of many untreated
wood species used for fence posts, along with information
on some of the advantages of seasoning posts before use. See
http://ianrpubs.unl.edu/forestry/g314.htm.
According to the Nebraska publication, the best species for
use as fence posts without treatment are osage orange, also
known as hedge (>35 years), black locust (>20 years),
and eastern red cedar (>20 years).
Besides untreated wood fence posts, other options include
plastic, plastic/wood composites, steel T–posts, steel
pipe, concrete, fiberglass, or even concrete–filled
plastic pipe. These fence posts will vary in cost, availability,
and practicality for each specific fencing need.
Many plastic fence posts are made from recycled plastic containers.
They come in various lengths, dimensions, and colors; can
be stapled, drilled, or cut like wood; and are self-insulating
for electric fencing.
If you already have treated wood posts in your field, garden,
arbor, or orchard, you are “grandfathered in.”
However, if the treated wood comes in direct contact with
crops or livestock, it may present a contamination risk, and
you might need to remove or replace it. As always, check with
your certifying agent.
When it's time to replace wood treated with prohibited substances
or put in new posts, you must use approved materials in order
to follow the organic standards.
Osage orange doesn’t grow in my area, but we have plenty
of eastern red cedar. We have been clearing a savannah prairie
of red cedar and buckthorn, so I’ll use the red cedars
for posts in my vineyard.
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