Pressure treatment protects wood from attacks by insects, microorganisms, and decay by fungi. The life of outdoor wood products, can be significantly extended to well over 40 years.
CCA-preserved wood has proven track record. CCA-preserved wood has been used effectively for almost 70 years. It has a safe track record when used according to industry guidelines (link) and has been reviewed in numerous scientific studies with positive results.(link)
Using pressure-treated makes environmental sense. The material comes from a renewable ressource whose service life is extended with treatment.The environmental costs of plastics and steel are greater than those of treated pine for example.
Using pressure-treated wood is economical. Substitute materials, such as steel, concrete and aluminum, can cost more partially due to greater manufacturing energy requirements, greater air/water pollution and/or environmental protection costs, and higher dependency on foreign source for imported materials. Of the preserved lumber that's sold for residential uses like decks, fences and playsets, 98% is treated with CCA. Alternatives that don't contain arsenic are available for most of those uses, but they are most expensive-currently 20%-25% more expensive for the lumber at the retail level.