permaculture

[Jack Rowe <jackrowe@compuserve.com>]

CCA-treated 2x4's retain 2.5 pounds CCA per cubic foot of lumber, 4x4's
retain 4#/cu ft (pressure is used, and penetration is pretty complete.)
There're 2.5 pounds of CCA in 27 feet of 2x4, and 4# in 11.8 feet of 4x4.
The Ag Extension study of treated wood found that up to 16% of the CCA
could be leached from new wood in the first season when used to construct
compost bins. They concluded that 16% of 2.5#/cu ft was a safe level for
compost, though no medical evidence was cited. In too-telling a summary
statement, they assured the public that treated wood was safe to purchase
and that no 'economic disruption' need occur. Geez.

A fair number of people develop small allergic blisters when they handle
CCA-treated wood, though the reaction is much milder and less universal
than the reaction to Penta-treated wood (Sodium pentachlorophenol) or
creosoted wood. 

Arsenic accumulates in bone tissue if ingested faster than bone tissue is
replaced. I'd think the entire issue would be much more critical where
children are involved, as Kevin points out. An amazing, frightening variety
of chemicals are found in semen, breast milk, fatty tissues, etc worldwide
(breakdown products of DDT are still found in a large percentage of North
Americans). 

An average pc design should probably include a good number of post trees.
Perhaps Black Locust is one of the fastest/most adaptable/straightest (var.
rectissima--sp?). Cypress is good, fast-growing if water is available.
Juniper is rampant in many degraded areas and good for fence posts up to 12
feet or so. Bois d'Arc is good, too hard to cut easily but splits readily
and straight. 

The US Forest Service tested a variety of natural products, one of the
50-year ground-contact mixtures was of 1:1:1 beeswax, turpentine and
linseed oil, applied by completely immersing the wood in boiling solution
(fire!!) and then allowing the whole mix of solution and posts to cool
before removing posts (a reverse 'pressure' treatment, the solution is
pulled into the cooling wood... a very old procedure described by
old-timers in the Foxfire books, for instance). 

Removal of heavy metals (arsenic, mercury, lead, yadda yadda) from rocks
and distributing them throughout our soil environment is an ominous,
popular modern pastime.

Jack