Hazardous waste is a waste with properties that make it potentially dangerous or harmful to human health or the environment. The universe of hazardous wastes is large and diverse. Hazardous wastes can be liquids, solids, or contained gases. They can be discrete chemical compounds, mixtures of compounds, or simply have some property that makes them hazardous. In regulatory terms, a hazardous waste is a waste that appears on one of the four RCRA (Resource Conservation and Recovery Act) hazardous wastes lists (the F-list, K-list, P-list, or U-list) or that exhibits one of the four characteristics of a hazardous waste - ignitability, corrosivity, reactivity, or toxicity.
Most creosote mixtures that are used today are byproducts of the petroleum industry or coal gasification processes. They are mixtures of several hundreds of chemicals mostly polynuclear aromatic hydrocarbons (PAHs) but contain a host of other chemicals including complex heterocyclic compounds