Any agent that presents a risk to life-forms or the environment can be considered a hazardous material. This is a very broad term which encompasses pure compounds and mixtures, raw materials, and other naturally occurring substances, as well as industrial products and wastes. Depending on the nature and the length of exposure, virtually all substances can have toxic effects, ranging from headaches and dizziness to cancer. The challenge facing any legislation is not only to devise regulations for the safe handling of hazardous materials but also to define the term itself.

The legislation that offers the most detailed and comprehensive definition of hazardous materials is the Resource Conservation and Recovery Act (RCRA), enacted in 1976. RCRA classifies a waste mixture or compound as hazardous if it fails what is called a characteristic test or appears on one of a few lists. The lists of hazardous wastes include...