Before you buy fasteners, read this article for important information on Treated Wood

ACQ Treated (Alkaline Copper Quaternary) - ACQ Treated wood is the preferred choice as a new generation of pressure-treated wood, providing the same level of reliable performance as standard pressure treated wood without the use of arsenic and chromium.

            ACQ Treated wood can be used for a wide variety of construction projects and are particularly suited for applications such as decking, playgrounds, walkways, benches, outdoor tables and chairs, fencing, gazebos and landscaping, where long-term protection against decay and termites is a priority. It is available with built-in water repellent to provide additional protection from the effects of weathering.

Copper Azole - Copper Azole is a water-based wood preservative that prevents fungal decay and insect attack; it is a fungicide and insecticide. It is used for treating a variety of softwood species including southern pine, red pine, ponderosa pine, hem-fir and Douglas fir.

            Water-based preservatives like copper azole leave wood with a clean, paintable surface after they dry. Copper Azole is registered for treatment of millwork, shingles & shakes, siding, plywood, structural lumber, fence posts, building and utility poles, land and freshwater piling, composites, and other wood products that are used in above-ground, ground contact and fresh water as well as in salt water splash (marine) decking applications.

Borate Treated - Borate treatment provides permanent protection against Formosan and other termite species, decay fungi and wood destroying insects in dry interior applications. Borate treated wood is comparable to ACQ and Copper Azole treated wood, however it is not suitable for applications exposed to the weather or in ground contact, and must be protected from exposure to liquid water to maintain its preservative properties..
 

CCA Treated (Chromated Copper Arsenate) – CCA Treated wood has been preserved by pressure-treatment with an EPA-registered pesticide containing inorganic arsenic to protect it from insect attack and fungal decay. Inorganic arsenic penetrates deeply into and remains in the pressure-treated wood for a long time. The preservative in CCA Treated wood bonds to the wood cells through a chemical reaction.

            A few years back, the EPA began a voluntary program of eliminating CCA from wood due to the health effects, especially in children and pets. The concern is children rubbing their hands on the lumber found in things such as playground equipment, and then ingesting the CCA material. If you have any concerns about your existing structure that utilizes CCA lumber, here is an informative link from the EPA.