Arsenic exposure from treated wood
Chromated copper arsenate (CCA) has been commonly used to preserve wood used for building materials for many years. Other preservatives containing inorganic arsenic include ACA and ACZA. Arsenic is a heavy metal which can build up in the system over time and cause several types of cancer, severe neurological damage and death in high doses. Because the effects take time to accumulate most people are unaware of any danger when working with treated wood.
Tests on various samples of CCA treated woods have shown high levels of arsenic exposure, well exceeding state limits. It is only necessary to touch treated wood to transfer the poison to your skin, from where it can be transferred to other parts of the body. The worst case is with children and in particular children's playgrounds, where a lot of contact may be made with the wood. If children put their hands in their mouth they can transfer the arsenic into their system.
Treehouse building using these treated woods presents a high risk of exposure to arsenic. Cutting, sanding and shaping this wood can produce poisonous sawdust which may be breathed in.
Since the end of 2004, CCA has not been permitted for use as a wood preservative for pre-treated lumber, but wood manufactured before this time may still contain arsenic.
Burning treated wood
Burning CCA-treated wood produces toxic fumes of arsenic and chromium and is illegal for this reason. As there are now a large range of preservatives used for pressure treating and it is not easy to determine which have been used, it is recommended that treated wood is never burned. Untreated wood, such as that used for internal studwork, can be burned without the danger of chemical exposure. All other waste wood should be disposed of to landfill (or controlled waste disposal locations depending on your location). This is particularly important when removing old wood which may have been treated with CCA, creosote, formaldehyde or have painted layers containing lead.
Alternatives to chemical preservatives
Pressure treated pine is generally the cheapest option for outdoor building work. The main alternatives to chemical treatments are the use of naturally durable timbers. These are generally hardwoods (especially oak) but also some softwoods like cedar. Softwoods can be specially heat treated but this material is not yet widely available. Although these materials cost more initially, there will be less concern about disposal or burning at the end of their life.