The Lumber Industry has many different ways of treating wood so that the wood will not rot / be eaten by insects / fall apart. Some of the different ways that wood is treated are:
2) CCA (Chromated copper arsenate)
3) ACZA (Ammoniacal copper zinc arsenate)
4) Borate Preservatives
5) Copper naphthenate
6) ACQ (Ammoniacal Copper Quat)
7) CC (Ammoniacal copper citrate)
8) CDDC (Copper dimethyldithiocarbamate)
9) CBA (Copper Boron Azole)
See http://www.fpl.fs.fed.us/documnts/techline/III-1.pdf for a full description.
There are some fact sheets about CCA on the Internet but you have to critically read each to make sure that the authors perspective (or monetary interests) doesn't taint the article.
While some of these treatments of wood were thought to be safe in the past for use in residential areas and playgrounds, it has recently been found that some of the chemicals leach out of the wood and may pose a hazard to humans. Children are especially susceptible because of their size.
While CCA is being phased out, it is still in many residential structures. When working with this wood, BE SURE to follow standard safety precautions as described in the web site http://www.preservedwood.com/ and specifically in the FAQ:
Q. What additional safety equipment do I need while working with CCA-treated wood?
A. Use standard safety equipment and common sense when working with all types of building materials. Eye protection and dust masks should be used when sawing or machining any wood product, treated or untreated. Inhalation of sawdust can cause nose and throat irritation. Protecting your eyes from any foreign matter while sawing or machining is good safety practice. Wearing gloves provides extra protection against splinters. Practicing good housekeeping hygiene at the completion of any construction project is always advisable. This includes washing hands and cleaning up sawdust in the work area. Any other recommendations by the EPA are based on OSHA requirements for all wood products.
Here is some additional information that I found while looking around the Internet for more information on this kind of wood. Please read the material on this page with a skeptical eye as some of the sites have their own bias.
Search for leaching of CCA and Creosote:
Leach rate of CCA:
Can Garden Plants Take Up Enough Arsenic to be a Concern?
There is very little need to test soils for leached arsenic. Rather, the key precaution is that soils beneath and directly adjacent to CCA-treated wood structures not be used for play or gardening activities.
Should Soils be Tested for Arsenic Contamination?
Is Treated Lumber a Risk in the Home Garden?
Safety working with CCA wood:
However, according to news reports, essentially all documented human health impacts have been to individuals who have been working with CCA wood; primarily sawing and sanding. These activities resulted in exposure to CCA wood dust with subsequently identified health effects.
Unlike children on playgrounds, workers can adequately protect themselves from these impacts through being informed about the potential hazards (material safety data sheets and similar information sources), the proper use of personal protective equipment (dust masks, gloves, etc.), and sensible work practices (ventilation, washing hands and clothing after work, and not eating or drinking in the work area). The key issue that has been lacking for workers (including do-it-yourselfers) on a nation-wide basis is the lack of available information about the health hazards of CCA wood.
Does Pressure-Treated Wood Belong in Your Garden?
Intensive Vegetable Gardening:
Remove arsenic from your soil:
Web site: http://www.altpest.org
Page on the history:
Copper, chromium and arsenic leaching from new and weathered wood were found at all pH levels, with higher metal concentrations in acidic conditions. At pH 5.5, for instance, 92% of the copper, 12% of the chromium and 32% of the arsenic leached out. This raises concern for the amount of leaching caused by acid rainfall along eastern areas of Canada and the U.S. It also means that the rate of leaching is accelerated in acid environments such as bogs, silage and compost.
Leaching of Chromated copper arsenate (CCA):
Creosote is a distillate of coal tar produced by high temperature carbonization of bituminous coal.
And why Creosote doesn't get into plants ( but is carcinogenic), however it does retard the plant growth:
Creosote can volatilize into the air, especially during hot weather, and plant foliage in the vicinity of the ties may be damage by the vapors. It can also leach into the soil near the ties, but it will not be absorbed by the roots and will therefore not get into the plants' tissues.
My raised garden bed consists of creosote-treated railway sleepers. Should I be digging these up?
No. Wood treated with creosote prior to the coming into force date of the Creosote Directive, may be used in gardens, providing there is no risk of frequent skin contact. Furthermore, the prohibition on the use of treated wood does not apply where the treated wood was in such use before 30 June 2003, the date these Regulations came into force.