What the Baltimore County Building Code says about Arsenic

This is interesting:
2. Hardware- Nails, screws and bolts aren’t very glamorous, but they
are what hold the deck together. Since the beginning of 2004, pressure
treated wood has contained a new chemical preservative mixture
called ACQ. This new mixture, formulated to eliminate the use of
arsenic, is corrosive to steel and aluminum. The old style deck nails
and galvanized bolts won’t do any more. The new preservative can
destroy the old style fasteners in just a few years. Only triple dip
galvanized, stainless steel, or other approved fasteners are safe to
use.

Also:
Pressure treated wood protects against rot, insects, and decay. For
many years, Chromated Copper Arsenate (CCA) has been the chief
chemical compound used to treat wood for outdoor use, but
environmental concerns about arsenic have led to a gradual withdrawal
of this type of treated wood. No more has been produced since December
31, 2003. Today’s copper-based preservatives are just as effective,
but environmentally safe for long term outdoor applications. The
disadvantage of using copper based preservative is its corrosiveness
to ordinary metal fasteners. This can be avoided by using high
quality corrosion resistant nails, screws, hangers, etc (See item 2).
For more information, call building inspection at 410-887-3953. Let’s
make the environment safe for future generations.