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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals
Basic principles for the management of radioactive-biological waste include the following:
Risk associated with the waste should be assessed. It may be prudent to disinfect highly biohazardous agents first to minimize handling risks and prevent growth of the waste's microbiological load. Appropriate containment, handling, and storage precautions should be taken prior to treatment.
Radioactive-biological waste containing short-half-life radionuclides can be held for decay. After decay-in-storage, most U.S. NRC licenses allow the waste to be managed as biological waste. If the waste supports the growth of an infectious agent that it contains, storage should be in a freezer to prevent the waste's infectious risk from increasing.
Refrigerated storage facilities or other preservation methods are necessary for putrescible waste.
7.C.3.1 On-site Incineration of Low-level Radioactive Waste
Laboratories that have an on-site radioactive waste incinerator have a great advantage in their ability to manage radioactive-biological waste. On-site incineration of radioactive-biological waste is practical and can be done with minimal impact to health or the environment. For waste that is putrescible or may be infectious, on-site incineration is ideal.
The institution's U.S. NRC license will identify which radionuclides can be incinerated and will set emission limits for those materials based on activity. It is usually beneficial to separate waste by radionuclide volatility and half-life. Incinerator emissions of waste containing short-half-life radionuclides can be minimized by refrigerated storage for decay prior to incineration. If the license allows, ash from the incineration of nonvolatile radionuclides that have short half-lives may be held for decay and disposed of as normal trash. Other ash must be disposed of at a radioactive waste site.
7.C.3.2 Off-site Management of Low-level Radioactive Waste
Many laboratories do not have an on-site incinerator for radioactive-biological waste. Communities tend to oppose waste incinerators, and on-site incineration is prohibitively costly for some radioactive-biological waste generators. Even institutions that have incinerators must usually rely on off-site disposal for some of their radioactive waste. For radioactive putrescible waste, off-site disposal requires special packaging, storage, and transport considerations.
Reliable access to off-site disposal will depend on the establishment of regional sites, which have been slow to develop under the Low-level Radioactive Waste Policy Act of 1980. Moreover, when established, regional low-level radioactive waste sites may not immediately accommodate laboratory radioactive-biological waste. As discussed earlier in this chapter, choice of off-site disposal must involve careful consideration of the safety record of the facility to ensure that the generator's long-term responsibility is liability-free.
7.C.3.3 Disposal of Radioactive Animal Carcasses and Tissue
Waste radioactive animal carcasses and tissue generated from biomedical research typically pose no significant infectious hazard, but they are putrescible. U.S. NRC regulations allow animal carcasses and tissue with less than 1.85 kilobecquerels per gram (kBq/g) of 3H or 14C to be disposed of without regard to radioactivity. Thus animal carcasses and tissue below this limit need not be managed as a radioactive-biological waste but only as a biological waste. Animal tissue with higher levels of activity or other radionuclides must be managed as a radioactive waste. As with all putrescible waste, waste should be either refrigerated, frozen, or otherwise preserved during accumulation, transport, and storage.
While on-site incineration is the preferred method of managing radioactive animal carcasses and tissue, several alternatives exist. Alkaline digestion of animal carcasses containing 3H, 14C, and formaldehyde, followed by neutralization, results in an aqueous radioactive stream that can usually be disposed of in the sanitary sewer. The process uses 1 M sodium hydroxide at 300 °C and pressures up to 150 psi. Commercial units are available for this process. Radioactive animal carcasses may be accepted at a low-level radioactive waste site when packed in lime.
Some institutions grind radioactive animal tissue for disposal in the sanitary sewer, although the U.S. NRC requires that all sewer-disposable waste be dispersible. Preventing contamination and exposure of waste handlers to dust or particles is an important safety measure in this operation.
Autoclaving of infectious animal carcasses is difficult because of the waste's high heat capacity and poor heat conductivity, and often unproductive because treated waste remains putrescible.
7.C.3.4 Disposal of Radioactive-Biological Contaminated Labware
Radioactive-biological contaminated labware (e.g., gloves and disposable laboratory articles) is generated