what the U.S. NRC specifies for an unrestricted area.) As a result, some chemical-radioactive waste with a U.S. NRC-approved level of radioactivity can be managed as chemical waste. Likewise, laboratory personnel can specify which biological wastes require no special handling and should not be mixed with infectious or biohazardous waste. Laboratory personnel may also determine if their waste meets the definition of a chemically hazardous waste. If the waste component is not regulated within this category, then it may be possible to manage it as only a radioactive or biological waste.
Minimize the waste's hazards. Waste minimization methods specific to chemical, radioactive, or biological waste can be applied to multihazardous waste to mitigate or eliminate one hazard, which will then allow it to be managed as a single-hazard waste. For example, the substitution of nonignitable liquid scintillation fluid (LSF) for toluene-based LSF reduces a chemical-radioactive waste to a radioactive waste.
Determine options for managing the waste's hazards. Waste management options include laboratory methods, management at institutional waste facilities, and treatment and disposal at commercial sites. Options can vary considerably between laboratories owing to institutional capabilities and state and local laws. It may be appropriate to manage the waste in order of risk priority, from high to low risk. Options must be compatible with all hazards, and combinations of waste management methods may be limited by their order of application. Reject any combination or sequence of methods that may create an unreasonable risk to waste handlers or the environment, or that might increase the overall risk. If an option has a clear advantage in efficiency and safety, it should have highest priority. For example, if safe facilities are available on site, hold short-half-life radioactive waste for decay before managing it as a chemical or biological waste. However, remember that in most cases a waste that has chemically hazardous characteristics may not be held beyond 90 days.
When possible, select a single management option. Some waste management methods are appropriate for more than one waste hazard. Low-level radioactive animal tissue (a radioactive-biological waste) can often be incinerated on-site, which may be a satisfactory disposal option for both the radioactive and the biological characteristics of the waste. Some multihazardous waste can be disposed of safely in the sanitary sewer when allowed by the local publicly owned treatment works (POTW).
(See also Chapter 4 on chemical and waste management.)
''Mixed waste" is the regulatory term for multihazardous waste that contains chemical and radioactive hazards (see Figure 7.2a). Mixed waste is defined by EPA as "wastes that contain a chemically hazardous waste component regulated under Subtitle C of the Resource Conservation and Recovery Act of 1978 (RCRA) and a radioactive component consisting of source, special nuclear, or byproduct material regulated under the Atomic Energy Act of 1946 (AEA)" (U.S. EPA, 1986). The U.S. NRC defines mixed waste slightly differently. According to the U.S. NRC, mixed waste is a waste "that contains a chemically hazardous waste as defined in RCRA, and source, special nuclear, by-product material, low-level radioactive waste" (as defined in the Low-level Radioactive Waste Policy Act of 1980 (42 USC 2021(b) to 2021(j)), or "some types of naturally-occurring or accelerator-produced radioactive material (NARM), such as uranium and thorium." Regardless of the precise definition, well-informed laboratory workers should be prepared to deal with mixed waste in a prudent manner.
Examples of laboratory mixed waste include the following:
Used flammable (e.g., toluene) liquid scintillation cocktails.
Phenol-chloroform mixtures from extraction of nucleic acids from radiolabeled cell components.
Aqueous solutions containing more than 6 ppm chloroform (which exceeds the limit set by the Toxicity Characteristic Leaching Procedure (TCLP) test) and radioactive material (typically found in solutions generated by the neutralization of radioactive trichloroacetic acid solutions).
Certain gel electrophoresis waste (e.g., methanol or acetic acid containing radionuclides).
Lead contaminated with radioactivity.
Mixed waste produced at university, hospital, and medical research laboratories is typically a mixture of a low-level radioactive waste and chemically hazardous waste. Mixed waste from nuclear and energy research laboratories can include both low- and high-level (e.g., spent nuclear fuels) radioactive materials combined with chemically hazardous waste. Disposal options for mixed waste are usually very expensive. For many types of mixed waste, there are no management options other than indefinite storage on site, or at an approved facility, in the hope that treatment or disposal options will be created in the near future.
An example of the mixed waste problem and the importance of keeping waste separate is illustrated by