chromated copper arsenate

:  a chemical combination of chromium, copper, and arsenic used to protect wood against insects and decay Then, in the 1930s, scientists found a way to infuse wood with a solution that included copper (toxic to the fungi that cause rot) and arsenic (then the most common insecticide). To ensure the protection would last and builders and the environment wouldn't be hurt, they also added chromium. It triggered a chemical reaction that locked the pesticides into the wood. The formula became known as chromated copper arsenate, or just CCA. But the industry called it pressure-treated because the chemicals were injected under great pressure. — Curtis Rist —abbreviation CCA