If you’re thinking of building a deck or repairing outdoor structures, bear in mind that the EPA has recently banned wood treated with chromated copper arsenate — long the industry’s standard — in residential construction.
Why? Apparently, the usual concern about children:

The EPA conducted risk assessment, and evaluation of public comments and input from an external scientific review panel on methodologies to perform a risk assessment for residential settings and potential exposure to children from CCA.
On February 12, 2002, the EPA announced a voluntary decision by the lumber industry to move consumer use of treated lumber products away CCA-treated wood by Dec. 31, 2003, in favor of new alternative wood preservatives. This transition affects virtually all residential uses of wood treated with CCA, including wood used in play-structures, decks, picnic tables, landscaping timbers, residential fencing, patios and walkways/boardwalks. According to this announcement, by January 2004, EPA will not allow CCA products for any of these residential uses.

I’d love to know what “public comments” we’re talking about here. In practice, “democracies” like ours allow small organized minorities to dictate terms to ordinary taxpayers, while making us all pay for their hordes of consultants and government-funded Ph.D. candidates.
Large businesses — and (of course) government — may continue to use CCA:

The use of CCA-treated wood will be limited to certain industrial and commercial applications. Residential applications affected by the change include play structures, decks, picnic tables, landscaping timbers, residential fencing, patios, and walkways/boardwalks. Some applications not affected by the settlement include highway construction, marine (saltwater) applications, utility poles, pilings, and selected engineered wood products.
Despite this shift away from CCA, the EPA asserts that no reason exists to remove or replace CCA-treated structures, including decks or playground equipment.

(No wonder they had no problem pushing this through, what with govermnment and big business exempt.)
But if there’s no reason to remove it from existing structures, why ban it? And why would anyone care? Because, as I just learned, CCA’s replacement, (ACQ) wreaks havoc with construction materials:

With environmental and health concerns growing over the use of arsenic, the wood-preservative industry surrendered the right to use arsenic in wood for residential uses at the beginning of 2004.
The most common replacement preservatives are ammoniacal copper quat, or ACQ, followed by copper azole and borate. Borate is sometimes used in home foundation sill plates, but experts say borate-treated wood isn’t appropriate for outdoor uses.
The higher metal corrosion rates associated with ACQ-treated wood have raised concerns with the federal Consumer Product Safety Commission and a San Francisco Bay Area district attorney who recently issued a consumer alert.
“CPSC is recommending consumers use stainless-steel brackets and fasteners in conjunction with ACQ-treated lumber,” said commission spokesman Scott Wolfson. The CPSC is considering whether it needs to study the corrosion issue further, based on information from the connector industry and Contra Costa County.
That county’s district attorney, Bob Kochly, warned in a recent consumer alert that wood treated with ACQ and copper azole “may result in serious and premature corrosion . . . especially in wet or moist conditions” unless stainless-steel connectors are used.

This all makes prices go up, of course, and forces suppliers to order new, “improved” materials.
Are environmentalists and big business working in collusion?
And is the concern really about children eating arsenic-treated wood?
What happens if they eat ammoniacal copper quat, followed by copper azole and borate?
(I’m not an expert, but I suspect there might be another corrosive effect.)