What is pressure treatment?

Pressure treatment is a process in which chemical preservatives are forced into wood using a combination of pressure and vacuum(5). These chemicals defend the wood from insects, microbes, and fungi.

These chemicals are typically:

Where are waterborne preservatives used?

Widespread use: decks, gazebos, trellises, railings, playground equipment, utility poles, marinas.

Here is a formulation for the most commonly used pressure treatment mixture(CCA):

 

 

Wolmanac Solution (CCA) in a treated "2x4" board.
(Assuming a typical 0.4 lbs solution/cubic foot of wood)

 

* This is the amount, by weight, of elemental arsenic from the arsenic pentoxide in solution. According to the American Wood Preservers Institute, the water soluble arsenic pentoxide "undergoes a chemical reaction to convert it into an insoluble form that is highly leach-resistant(3)". What if it turns out that these chemicals do leak out of the wood?

 

Keep in mind that the LD50(death) ratings are much higher than amounts for toxic effects. Clinically significant illness may result after doses of one-tenth the lethal dose(1). Furthermore, 'safe' doses for children are very difficult to predict (they're not just small adults).

 

Recent findings about CCA

significant amounts of Cu, Cr, and As leaches from deck wood and manifests itself in the soil. Acidic rain could contribute.
Arsenic, chromium, and copper readily leach in acidic environments.
Arsenic measured over limits from some deck wipes.
Excerpts from EPA and OSHA.