You can't compare new pressure treated wood with 12 year old wood when making your decision. In 2002/2003 the entire industry changed the chemical compostition of the solution the wood is treated with. Newer wood does not contain arsenic which is present in all PT wood made before then.
Looking at weathered wood isn't going to tell you how much arsenic is still present in the wood. A "wet" or "dry" appearance is meaningless. A study by the Envionmental Working Group has shown that the level of arsenic in the wood can remain at fairly high levels in 15 year old wood.
You don't say if the wood you wish to recycle will be in contact with the soil. This will speed up the leaching of arsenic into the soil much faster than if the wood is to be used above the soil.
Not to say that you shouldn't use the boards safely. Here's a recommendation from the
Forest Products Lab about sealing old PT wood decks to increase safety for those concerned about exposure to the chemicals:
"To address this question, researchers at the Forest Products Lab (FPL) recently evaluated the ability of three common coatings to reduce leaching from CCA pressure treated wood. Replicate matched specimens of pressure treated 2 by 6 lumber were given one of the following coatings: (1) latex primer followed by one coat of outdoor latex paint, (2) oil-based primer followed by one coat of oil-based paint or (3) two coats of a penetrating oil semi-transparent deck stain. The specimens were then exposed to 30 inches of artificial rainfall for three weeks. The water running off the specimens was collected and analyzed for preservative components.
The results were very promising. All three coatings reduced leaching of arsenic pentoxide, chromium trioxide, and copper oxide by over 99% in comparison to uncoated specimens. None of the water collected from the specimens coated with latex or oil-based paint contained any detectable copper, chromium or arsenic. In some cases, water collected from the specimens that were coated with the penetrating oil stain did contain detectable levels, but the highest level of arsenic detected in these samples was still well below the EPAs drinking water standard. This study suggests that the application of these common coatings is an excellent recommendation for consumers who are worried about chemical exposure from CCA pressure treated wood. "
There is lots of information available on the web about the dangers of older pressure treated wood containing arsenic. You need to look at the sources though. A homeowner that tells you not to worry about it because his kids are playing on it every day and haven't died yet is not a reliable source. The EPA, I think underplayed the dangers a bit , not sure if environmental groups overstated them or not, but I think the wood industry did the correct thing in making a relatively speedy and voluntary transition. I feel a little better about including PT wood in home designs now.
Wayne
[edited for spelling]
