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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals
to incinerate regulated chemical waste. Autoclaving or disinfection of chemical-biological waste usually does not destroy its chemically hazardous constituents, except for denaturing proteins and nucleic acids.
Conflicting laws are seldom a barrier to the safe management of chemical-biological waste. Although some states regulate the disposal of laboratory infectious waste, the federal government does not. Most laboratories using infectious agents abide by Centers for Disease Control and Prevention/National Institutes of Health (CDC/NIH) guidelines, which recommend on-site decontamination for agents in biosafety levels 3 and 4 (as defined in Chapter 5, section 5.E.1) but do not inhibit chemical waste storage or treatment (U.S. DHHS, 1993).
Although EPA is proposing to regulate transgenic plants that express insecticidal proteins, most types of chemical-biological waste are not regulated by EPA as a hazardous (RCRA) chemical waste. Waste (or spent) formalin that has been used in a process such as tissue preservation is not a discarded commercial chemical product and therefore is not regulated federally. However, its handling should be consistent with personal and environmental safety and within the limits set by local regulation. Animal tissue is regulated as chemical waste only in the unlikely circumstance that it contains a toxic chemical and the waste fails the TCLP test, or if the animal had been exposed to polychlorinated biphenyls (PCBs) in concentrations greater than 50 ppm.
Disposal is most difficult for the very small amount of chemical-biological waste that is EPA-regulated as chemically hazardous or contains a chemical, such as lead, that is inappropriate for an animal or medical waste incinerator. Disposal of tissue specimens preserved in ethanol or another flammable solvent is also difficult. In most cases, storage of this waste is limited to 90 days and must be managed at an EPA-permitted chemical waste facility. However, few chemical waste facilities are prepared to handle waste that is putrescible, infectious, or biohazardous.
7.C.2.1 Disposal of Chemically Contaminated Animal Tissue
Animal carcasses and tissues that contain a toxic chemical may be the most prominent chemical-biological laboratory waste. Such waste includes biological specimens preserved in formalin and rodents that have been fed lead, mercury, or PCBs in toxicity studies. If storage of such putrescible waste is necessary, refrigeration is usually advisable. Freezing potentially infectious animal tissue at the point of generation can add a margin of safety during waste handling, transport, and prolonged storage. Infectious waste should be stored separately in a secure area.
Incineration is the most appropriate disposal method for this putrescible waste, and it can also destroy the infectious agents that such waste may contain. As discussed above (see beginning of section 7.C), federal law allows the incineration of most chemical-biological waste in an animal or medical waste incinerator. Most modern, efficiently run animal and medical waste incinerators can adequately destroy the small quantities of toxic organic chemicals present in chemically contaminated animal tissue. Large research institutions are likely to have an on-site animal incinerator. Medical waste incineration is also available through commercial waste haulers.
Incineration does not destroy lead and other inorganic chemicals, and they will be emitted or concentrated in the ash. In addition, some organic chemicals form products of incomplete combustion (PICs), which may be more toxic than the chemical contaminant. Incineration of PCBs and some other chlorinated aromatics, for example, can form extremely toxic polychlorinated dibenzo[p]dioxins and furans. Commercial disposal may be preferred for such waste.
(If animal or commercial incineration is unavailable, methods in section 7.C.3.3 below may be adaptable to chemical-biological waste.)
7.C.2.2 Sewer Disposal of Chemical-Biological Liquids
Laboratories that manipulate infectious agents, blood, or body fluids may generate waste that is contaminated with these materials and toxic chemicals. In most cases, blood and body fluids that contain toxic chemicals can be disposed of safely in a sanitary sewer, which is designed to accept biological waste. Approval for such disposal should be requested from the local wastewater treatment works. Chemical concentrations in such waste are typically low enough to be accepted by a local treatment works. OSHA recommends that a separate sink be used exclusively for disposal of human blood, body fluids, and infectious waste. It may be prudent to treat blood and body fluids with bleach (usually a 1:10 aqueous dilution of household bleach) prior to disposal in the sanitary sewer. The worker should take care to prevent personal exposure while waste is being discharged into the sewer.
7.C.2.3 Disinfection and Autoclaving of Contaminated Labware
Contaminated labware may include cultures, stocks, petri plates, and other disposable laboratory items