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 those from specific and nonspecific sources and those which are acutely hazardous and generally hazardous. There are four characteristic tests: ignitability, reactivity, corrosivity, and extraction-procedure toxicity.
A waste fails the ignitable test if it is a liquid with flash point below 140°F (60°C); or a solid that, under standard temperature and pressure, causes fire through friction, absorbing moisture, or spontaneous changes and burns vigorously and persistently; or a compressed gas defined by the Department of Transportation (DOT) as an oxidizer or as being ignitable. Spent solvents, paint removers, epoxy resins, and waste inks are often classified as hazardous under this definition.
A waste fails the corrosivity test if it is aqueous and has a pH of either 2 or less or 12.5 or more, or if it is a liquid that corrodes steel at a rate equal to or more than 0.25 in (6.35 mm) per year. Examples of corrosive wastes include various acids and bases such as nitric acid , ammonium hydroxide, perchloric acid, sulfuric acid, and sodium hydroxide, though a waste will not be classified as hazardous in this test if these acids and bases are neutralized or present at low levels.
Reactivity is related to one of the following criteria: If the material is unstable, with the potential for violent reactions with water, or generates toxic fumes; if it has cyanide and sulfide content; if it can be easily detonated; or is defined by DOT as a Class A or B explosive. Compounds commonly causing wastes to fall into this category are chromic acid, hypochlorites, picric acid, nitroglycerin, dinitrophenol, and organic peroxides.
Extraction-Procedure toxicity is determined through the extraction of solid waste , in a procedure referred to as the Toxicity Characteristic Leaching Procedure (TCLP). Liquid waste can also fail this test, although a liquid containing less than 0.5% solids after filtration does not need to undergo it. Such a liquid can be directly analyzed for contaminants. In the TCLP, solids are extracted in a mildly acidic medium (pH 5.0) for 18 hours using a tumbling apparatus, and the resulting liquid extract is then analyzed for contaminants. The waste is deemed to be hazardous if the level of a contaminant detected in this extraction procedure exceeds a given level. If liquid extracts contain arsenic at a concentration greater than 5.0 mg/l, for example, the waste is classified as hazardous. Different methods are recommended by the Environmental Protection Agency (EPA) for measuring the contaminants in each class.
The Resource Conservation and Recovery Act (1976) and the Hazardous and Solid Waste Amendments added to it in 1984 were intended to protect groundwater , surface water, and land from improper management of solid wastes. The act and the amendments defined the responsibilities of industries and others who generate and transport hazardous waste . They also set standards for land disposal facilities and underground storage tanks, as well as standards for proper management of hazardous materials from "cradle to grave."
The Toxic Substances Control Act (1976) is another important piece of legislation concerning hazardous materials. It was intended to regulate the introduction and use of new, potentially hazardous substances. The bill requires industry to test extensively chemicals that may be harmful, and it requires industries to provide the EPA with information about the production, use, and health effects of any new substances or mixtures before they are manufactured.
The Comprehensive Environmental Response, Compensation and Liabilities Act (CERCLA) (1980) and the Superfund Amendments and Reauthorization Act (SARA) (1986) set policy for situations in which hazardous materials have been mismanaged in the past. These legislations have established a system for ranking sites that need remediation , called the Hazard Ranking System , as well as a procedure for raising funds to support these efforts. The bills also impose schedules for site investigations, feasibility studies, and remedial action.
The definition of hazardous materials remains a difficult and complex issue. There are changes in public perceptions about certain materials, such as asbestos or lead , and there are scientific contributions which result in the addition or deletion of various chemicals or compounds from lists of hazardous materials. The definition is therefore dynamic, but changes are made within a regulatory framework designed to protect both life and the environment.
[Gregory D. Boardman ]
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