JBL, Yes, it is our opinion that there would be a danger using pressure treated wood to surround a garden. Pressure treated lumber is injected with chemicals that resist damage by moisture and pests. In the past, the most common chemical used was copper chrome arsenate, which many consider unsafe. Visit the EPA's copper chrome arsenate page for more information. Some similar but safer chemicals used now are copper azole and amoniacal copper quat. There are several degrees of concentration of the chemical depending on the intended use of the wood. For example: fence posts that will be underground contain a higher concentration of the poison than fence boards that will not be used underground. However, the degree of concentration is academic when it comes to any possibility of ingesting the chemical. The companies that make pressure treated wood will tell you that it is safe for deck surfaces and furniture. We disagree. Anywhere that a "chewing/chomping" toddler can easily access pressure treated wood, we feel, is cause for concern. We think that pressure treated lumber is superior to any other kind for use outside (deck framing ? not the finished decking) or in contact with the earth or other regularly wet surfaces (retaining walls, foundation mudsill, etc.). If it were our garden we would use plain wood. Cedar and redwood are good choices. And, good luck!