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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals
which may contain levels of radioactivity below license limits for radioactive waste. The still bottom and aqueous phase must be handled as a mixed waste.
High-performance liquid chromatography (HPLC), used to purify radiolabeled proteins and lipids, can generate a waste radioactive solution of acetonitrile, water, methanol, acetic acid, and often a small amount of dimethylformamide. When the solution is distilled by rotary flash evaporation, the distillate of acetonitrile, methanol, and water is nonradioactive and can be handled as a hazardous chemical waste. The radioactive still bottom, containing 1 to 5% methanol and acetic acid, can usually be neutralized, diluted, and disposed of in the sanitary sewer.
Aqueous solutions containing uranyl or thorium compounds can be evaporated to dryness and the residues disposed of as radioactive waste. Because of their toxicity, solidification may be necessary prior to burial at a low-level radioactive waste site.
Activated carbon, Molecular Sieves®, synthetic resins, and ion-exchange resins have been used with varying success in the separation of chemical and radioactive waste constituents. Activated carbon has been used to remove low concentrations of chloroform (less than 150 ppm) from aqueous mixed waste solutions. However, activated carbon is not suitable for high concentrations of phenol-chloroform or acetonitrile-water mixed waste. Amberlite® XAD resin, a series of Amberlite® polymeric absorbent resins used in chromatography, has been shown to be effective in removing the organic constituents from aqueous phenol, chloroform, and methanol solutions, leaving an aqueous solution that can be managed as a radioactive waste. Chemical constituents can be separated from mixed waste by using supercritical fluid extraction (e.g., carbon dioxide), which is now available commercially.
Surface contamination from radioactively contaminated lead can be removed by dipping the contaminated lead into a solution of 1 M hydrochloric acid. After rinsing the lead with water, it usually can be documented as nonradioactive. The acidic wash and rinse solutions contain radionuclides and lead and must be handled accordingly. However, decontaminating the lead results in a smaller mass of mixed waste and allows the decontaminated lead to be reused or recycled. Commercial rinse products are also available for this purpose.
Incineration is advantageous as a treatment for many types of chemical-radioactive waste, especially those that contain toxic or flammable organic chemicals. Incineration can destroy oxidizable organic chemicals in the waste. To comply with radionuclide release limits, U.S. NRC licensees need to control emissions and may need to restrict the incinerator's waste feed. Radioactive ash is typically managed as a radioactive waste. It is important to keep toxic metals (e.g., lead, mercury) out of the incinerable waste so that the ash is not chemically hazardous according to the TCLP test. On-site incineration minimizes handling and transportation risks; however, incineration of chemical waste is regulated by EPA and requires a permit, which is beyond the resources of most laboratory waste generators.
Procedures for the solidification and stabilization of inorganic compounds from mixed waste (using concrete or epoxy resin) to meet federal land ban restrictions have been outlined (40 CFR 268). This method may also abate the waste's chemical hazard and render a chemical-radioactive waste a radioactive waste. For example, waste lead citrate and uranyl acetate mixtures from electron microscopy can be solidified with port-land cement, which may be accepted for burial at a low-level radioactive waste site.
7.C.1.4 Commercial Disposal Services for Mixed Waste
Because of the great variety of laboratory mixed waste, it is often difficult to find a facility that can manage both the radioactive and the chemical hazards of the waste. In general, existing commercial disposal facilities are in business to manage mixed waste from the nuclear power industry, not waste from laboratories. Several commercial disposal facilities that accept mixed waste from off-site generators do exist in the United States. These sites have the capacity to manage liquid scintillation fluid, halogenated organics, and other organic waste. Treatment capacity exists for stabilization, neutralization, decontamination/ macroencapsulation of lead, and reduction of chromium waste.
In spite of this capacity, many types of laboratory mixed waste have no commercial repository. No commercial mixed waste disposal facilities exist for waste contaminated with most toxic metals (such as mercury) or for lead-contaminated oils. Commercial disposal capacity likewise does not exist for high concentrations of halogen-containing organics and other TCLP waste, such as waste that contains chloroform.
Laboratory waste that is both chemically hazardous and exhibits a biological characteristic (depicted in Figure 7.2b) merits special disposal procedures. Animal and medical waste incinerators are usually not licensed