Treated Wood Q&A

This is a question I was asked today and thought it was interesting. My answer is below.

Chris,
I am wondering why the companies that treat timbers with CCA don't treat them for just the first four to six feet of the timber? Of course, some would proabably have to be fully treated depending on the use of the timber but...

Since the arsenic is so very poisonous even in the ash form it seems much wiser to make timbers available that were treated only for the area that will be beneath the soil. I would like your input on this.
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Answer:

Good questions. 1st, against intuition, the part of the pole that rots is not always what is below the ground but what is right AT the ground line. With pilings, it is the part of the pole right at the water line - where the air meets the environment where the harmful organisms live.

The reason timbers are not partially treated is because of the WAY they are pressure treated. The entire timber is put into a cylinder into which the treatment chemicals are poured. That cylinder is sealed air-tight and pressure is put into it to drive the chemicals deep into the cells of the wood. It is not currently possible to partially pressure treat wood.

The arsenic is actually arsenate, which is a naturally occurring form of the element. I have yet to see proof that arsenate is actually harmful. Rather, it sounds a lot like arsenic, so rules were made against it.