Nationwide Emergency Response:
Home » How Is Hazardous Waste Defined

How Is Hazardous Waste Defined

What is Hazardous Waste?

Hazardous waste is a waste product with traits that can 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 the by-products of manufacturing processes, discarded used substances, or discarded remaining commercial products, such as cleaning liquids (solvents) or chemicals. In regulatory terms, a hazardous waste is a waste that appears on among 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 displays among the 4 attributes of a hazardous waste– ignitability, corrosivity, reactivity, or toxicity. However, components can be hazardous wastes even if they are not specifically listed or don’t exhibit any characteristic of a hazardous waste. For example, “utilized oil,” products which consist of components on California’s M-list, components regulated according to the mixture or derived-from rules, and contaminated soil generated from a “clean up” can even be hazardous wastes. To view the hazardous waste regulations and statutes, go to the Department of Toxic Substance Control web page. See the list of California Hazardous Waste Codes for a complete list of codes.

What are the 4 Characteristics of Hazardous Waste?

A hazardous waste characteristic is a property which, when present in a waste, indicates that the waste poses a sufficient threat to merit regulation as hazardous. EPA established four hazardous waste characteristics, which are ignitability, corrosivity, reactivity and toxicity.


Liquids with flash points below 60 °C and non-liquids including compressed gases and oxidizers are considered hazardous wastes because of their ignitability characteristic. EPA assigned D001 as the waste code for ignitable hazardous wastes.


Wastes with a pH of less than or equal to 2, a pH greater than or equal to 12.5 or based on the liquids wastes ability to corrode steel are considered hazardous due to their corrosivity characteristics. The EPA assigned waste code D002 for corrosive hazardous wastes.


Hazardous wastes that are unstable under normal conditions, react with water, put off toxic gases or become capable of detonation or explosion under normal conditions or when heated have reactivity characteristics. The EPA assigned D003 as the waste code for reactive hazardous wastes.


Wastes that are harmful when ingested or absorbed are hazardous due to these toxicity characteristic. When able to leach from waste and pollute groundwater, is when toxic wastes become a concern. The the Toxicity Characteristic Leaching Procedure (TCLP) (SW-846 Test Method 1311) determines the toxicity of a waste and the EPA assigned wastes codes D004 through D043 that correspond to a contaminant and its associated TCLP concentration.

To learn more about the toxicity characteristic and regulatory levels for the for the TCLP test 40 CFR section 261.24

Toxic Waste are Divided into 8 Characteristics

  1. TCLP: Toxic as defined through application of a laboratory test procedure called the Toxicity Characteristic Leaching Procedure (TCLP – U.S. EPA Test Method 1311). The TCLP identifies wastes (as hazardous) that may leach hazardous concentrations of toxic substances into the environment. The result of the TCLP test is compared to the Regulatory Level (RL) in the table in subsection 66261.24(a)(1) of the hazardous waste regulations. This criterion does not apply to wastes that are excluded from regulation under the Resource Conservation and Recovery Act.
  2. Totals and WET: Toxic as defined through application of laboratory test procedures called the “total digestion” and the “Waste Extraction Test” (commonly called the “WET”). The results of each of these laboratory tests are compared to their respective regulatory limits, the Total Threshold Limit Concentrations (TTLCs) and the Soluble Threshold Limit Concentrations (STLCs), which appear in subsection 66261.24(a)(2) of the hazardous waste regulations.
  3. Acute Oral Toxicity: Toxic because the waste either is an acutely toxic substance or contains an acutely toxic substance, if ingested. As stated in subsection 66261.24(a)(3), a waste is identified as being toxic if it has an acute oral LD50 less than 2,500 mg/kg. A calculated oral LD50 may be used.
  4. Acute Dermal Toxicity: Toxic because the waste either is an acutely toxic substance or contains an acutely toxic substance, if dermal exposure occurs. As stated in subsection 66261.24(a)(4), a waste is identified as being toxic if it has a dermal LC50 less than 4,300 mg/kg. A calculated dermal LD50 may be used.
  5. Acute Inhalation Toxicity: Toxic because the waste either is an acutely toxic substance or contains an acutely toxic substance, if inhaled. As stated in subsection 66261.24(a)(5), a waste is identified as being toxic if it has a dermal LC50 less than 10,000 mg/kg. U.S. EPA Test Method, SW-846 Methods: 3810, Headspace (formerly Method 5020) may be used to “test out” (for volatile organic substances).
  6. Acute Aquatic Toxicity: Toxic because the waste is toxic to fish. A waste is aquatically toxic if it produces an LC50 less than 500 mg/L when tested using the “Static Acute Bioassay Procedures for Hazardous Waste Samples.” See the test procedure document for more information.
  7. Carcinogenicity: Toxic because it contains one or more carcinogenic substances. As stated in subsection 66261.24(a)(7), a waste is identified as being toxic if it contains any of the specified carcinogens at a concentration of greater than or equal to 0.001 percent by weight.
  8. Experience or Testing: Pursuant to subsection 66261.24(a)(8), a waste may be toxic (and therefore, a hazardous waste) even if it is not identified as toxic by any of the seven criteria above. At the present time, only wastes containing ethylene glycol (e.g., spent antifreeze solutions) have been identified as toxic by this subsection.

What are the Different Types of Listed Wastes?

There are four hazardous waste lists (the F, K, P and U lists) and a waste is determined as a type of waste if it’s specifically listed on one of found in title 40 of the Code of Federal Regulations (CFR) in section 261.

Search EPA Hazardous Waste Codes

What are the 7 Categories of Hazardous Wastes on the F List?

The F-list, found at 40 CFR section 261.31, identifies any waste produced from the processes common in manufacturing and industrial industries. Due to the processes in generating these wastes can occur in different sectors of industry, the F-list wastes are known referred to as as non-specific sources. Depending on the type of manufacturing or industrial operation that creates them, they can be divided into 7 different categories:

  • Dioxin-bearing Wastes
  • Spent Solvent Wastes
  • Electroplating and Other Metal Finishing Wastes
  • Multisource Leachate
  • Wood Preserving Wastes
  • Chlorinated Aliphatic Hydrocarbons Production
  • Petroleum Refinery Wastewater Treatment Sludges

What are the 13 Categories of Hazardous Wastes on the K List?

Source-specific wastes are K-list hazardous wastes identified to be produced from specific sectors of industry and manufacturing. The K-list has 13 categories and the industry waste must be listed in one of these categories to qualify K-listed hazardous waste. In addition, the waste must match one of the detailed waste descriptions in 40 CFR section 261.32. The 13 industries that generate K-list wastes are:

  • Wood Preservation
  • Petroleum Refining
  • Pesticides Manufacturing
  • Veterinary Pharmaceuticals Manufacturing
  • Inorganic Pigment Manufacturing
  • Primary Aluminum Production
  • Inorganic Chemicals Manufacturing
  • Explosives Manufacturing
  • Iron and Steel Production
  • Secondary Lead Processing
  • Ink Formulation
  • Organic Chemicals Manufacturing
  • Coking (processing of coal to produce coke)

California Waste Oil or (Used Oil)

In California, waste oil and materials that contain or are contaminated with waste oil are usually regulated as hazardous wastes if they meet the definition of “Used Oil” even if they do not exhibit any of the characteristics of hazardous waste. The term “used oil” is a legal term which means any oil that has been refined from crude oil, or any synthetic oil that has been used and, as a result of use, is contaminated with physical or chemical impurities. Other materials that contain or are contaminated with used oil may also be subject to regulation as “used oil” under Part 279 of Title 40 of the Code of Federal Regulations.

Mixed Radiological and Hazardous Waste

Hazardous wastes which also contain radioactive material are considered mixed waste. The RCRA and the Atomic Energy Act are the regulations for mixed waste. The EPA under RCRA is responsible for the regulation of mixed waste. The Department of Energy (DOE) or the Nuclear Regulatory Commission (NRC) are responsible for the regulation of the radiological component of the mixed waste. The NRC primarily regulates waste from commercial and non-DOE facilities while the waste from DOE facilities is regulated by the DOE.

If you are a generator and/or operate a facilities that manages low-level mixed waste (LLMW) and naturally occurring and/or accelerator-produced radioactive material (NARM) containing hazardous waste by exempting these wastes from RCRA storage and treatment requirements, the EPA’s Mixed Waste Rule provides increased flexibility. The exemption is conditional upon the waste is generated under a single NRC license and the waste must meet specified conditions, in which the waste is stored and treated in a tank or container. Under their NRC or NRC agreement state license, Generators may store these wastes for as long as they are permitted.

Hazardous Waste Mixture and Derived-From Rules

You should check to see if the hazardous waste mixture-rule or derived-from rule applies when evaluating materials that are mixtures or that are residuals resulting from processing other materials. The hazardous waste mixture and derived-from rules are located in 22CCR Section 66261.3. There are also additional mixture rules specifically for used oil and mining wastes. These special rules are specifically intended to ensure that hazardous waste mixtures and residuals are regulated in a manner that is protective of human health and the environment.

Contained-In Policy

Not normally considered wastes are environmental media (soil, groundwater and surface water). The environmental media may be regulated as hazardous waste if it contains hazardous waste, including both listed and characteristic hazardous wastes after being excavated (and stored or transported) for disposal at another location. For example, soil contaminated with lead is often a hazardous waste because the lead “contained-in” the soil is a hazardous waste.

Additional Hazardous Waste Information

How to Determine if Waste is Hazardous

Some wastes are specifically excluded or exempted from regulation as hazardous waste (e.g., chlorofluorocarbon refrigerants that are reclaimed for reuse) even if they may meet the definition of hazardous waste. Hazardous Waste Determination is the process of determining if a waste is a hazardous waste. Generators should always follow the Hazardous Waste Determination Procedure provided in 22CCR Section 66262.11 of the hazardous waste regulations when evaluating their wastes to ensure exclusion or exemption has not been overlooked.

Hazardous Waste Recycling

A material must be a “waste” in order to be a hazardous waste. Generally, a waste is any material that someone possesses, but does not have a use for. In regulatory terms, a waste is any discarded material that is not otherwise excluded. Waste Identification is the process of determining if something is a waste. If they are recycled in certain ways, i.e., they may be excluded from the definition of waste in 22CCR Section 66261.2 of the hazardous waste regulations, some materials may not be considered waste.