From a article:
Pressure-treated wood is commonly used in the construction of patios, decks, and fences because it lasts longer than untreated wood. Until recently, arsenic was used as a preservative in the most common type of pressure-treated wood available, CCA (chromated copper arsenate). Because of the health risks associated with this chemical, the EPA banned the use of CCA lumber in home construction in January 2004.
ACQ (alkaline copper quat) lumber is one of the varieties that replaced CCA lumber. ACQ uses copper instead of the harmful arsenic, making it environmentally safer. Unfortunately, when the copper in the wood makes contact with metal, such as common aluminum building nails, a chemical process called "galvanic corrosion" occurs.
Galvanic corrosion is a process where one metal, in this case the copper in ACQ, steals the integrity or strength of another metal it is in contact with, like the aluminum nails or fasteners. In a relatively short period of time, sometimes less than a year, these nails can be completely corroded, causing structural instability to the home and creating possible safety
