We are thinking about putting in a retaining wall and a fence on our property, which is near a lake. Should we avoid using pressure treated wood? If so, what are some alternatives?
There are many reasons not to use treated wood for your fences and/or retaining walls. The chemicals most used to preserve wood—creosote (on railroad ties, among other things) and penta—were banned by the EPA in 1986 for indoor use and for many outdoor uses. The chemical used to pre-treat wood (CCA, a mixture of copper, chromium, and arsenic called chromated copper arsenate) has been shown to leach into the soil and to transfer to human skin through contact.
There are safe paints and preservatives for coating wood; there are safe types of pre-treated wood; some people use stone, cement blocks, or other materials instead of wood.
Below is lots of info about treated wood and alternatives.
Start with the page on the EPA site, which is full of information on treated wood. It includes a section on alternatives and some questions and answers about studies.
If you find this too technical, try the next two links below.
The Natural Handyman website has good information.
Toxic-Free Future (formerly known as Washington Toxics Coalition) has a fact sheet about safe and unsafe paints and wood preservatives. Lots of background information on the toxicity of treated wood is included as well.