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National Research Council (US) Committee on Hazardous Biological Substances in the Laboratory. Biosafety In The Laboratory: Prudent Practices for the Handling and Disposal of Infectious Materials. Washington (DC): National Academies Press (US); 1989.

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Biosafety In The Laboratory: Prudent Practices for the Handling and Disposal of Infectious Materials.

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4Safe Disposal of Infectious Laboratory Waste

A. INTRODUCTION

Human activities produce biological waste in the form of human excreta or other discarded materials, much of which may contain infectious microorganisms. Such waste, if untreated, has varying degrees of potential to cause disease. Existing methods of sanitation have served effectively to protect the public's health from any disease associated with biological waste. Our understanding of the conditions required to prevent the transmission of disease has allowed the development of simple, yet highly effective management techniques for handling biologically contaminated waste. A brief review of some of the conventional measures used to protect the public's health follows.

Historically, human excreta have been linked to outbreaks of disease such as dysentery, poliomyelitis, typhoid, and cholera. Such waste may contain high concentrations of pathogens that can contaminate food and water supplies. To minimize the opportunity for such cross-contamination, several fundamental principles of sanitation are applied. The first principle consists of providing a physical barrier. Sanitary sewer systems, which consist of pipes and pumps to convey pathogen-laden sewage to a treatment plant, effectively provide such a barrier. Once the waste reaches the sewage treatment plant, other mechanisms help to reduce the disease-causing potential of the material.

The treatment of sewage usually consists of biological degradation of the organic material. The physical and biochemical conditions that are optimal for such degradation are often hostile to the survival of many human pathogens. The end result is a significant reduction in the numbers of viable pathogenic microorganisms remaining in the treated waste.

After the organic load in the sewage has been degraded to the desired level, the effluent from the sewage treatment plant is usually subjected to a final disinfection step before being released into the environment. This step is accomplished by chlorination/dechlorination, exposure to ultraviolet light, ozonation, or some other procedure. The process ensures that the concentration of pathogens in the effluent is reduced to an acceptable level.

Like sewage, much solid waste or refuse produced by man is contaminated with biological agents capable of causing infection in man[39 ], and many of the same control mechanisms apply. For both storage and transport for disposal, the barrier system is again particularly important for the protection of individuals who must handle the waste. The plastic refuse storage bag, the dumpster, and the enclosed refuse-handling vehicle all provide barriers to minimize the potential of the waste to contaminate the environment.

Most solid waste is either disposed of directly in sanitary landfills or treated first by incineration to reduce its volume. Sanitary landfilling is a controlled disposal method designed largely to protect the public's health and the environment and consequently has largely replaced the open dump. Besides producing smoke and odors, open dumps provide ideal habitats for the propagation of disease-carrying vectors of concern to man, such as rats, flies, and mosquitoes. The sanitary landfill eliminates this habitat by compacting the waste and providing a daily earth cover, also compacted, to seal off the waste from the general environment. The earth above and below is the barrier. Because the conditions of biodegradation within the landfill are hostile to many human pathogens, their numbers decrease with time[39 ][116 ].

It is recognized that sanitary landfills may produce liquid leachate that can carry viable microorganisms to the earth underlying the landfill. As a leachate percolates through the earth, remaining pathogenic microorganisms are reduced further in concentration by hostile environmental factors and by soil filtration. This principle is used to advantage in the leach fields of home septic systems[87 ].

Incineration of municipal waste is done primarily to reduce the volume of the waste. Because municipal waste is generated by both healthy and sick individuals, it contains the same array of human pathogens as those associated with hospital waste. Although it is not their primary goal, well-designed and well-operated municipal incinerators can provide effective destruction of pathogens in the same way that a hospital incinerator does. Municipal incinerators often operate at higher temperatures and with longer gas retention times, thereby enhancing their effectiveness for the destruction of pathogens.

In summary, the application of long-standing principles of sanitation is effective in controlling the threat to the general public's health associated with biological waste. In general, extraordinary pathogen control measures have not been shown to be necessary except where the physical nature of the waste (e.g., contaminated "sharps" that penetrate barriers) presents problems directly to the waste handlers, or the waste itself has an exceptional bioload in a mobile form such as a liquid culture of a pathogenic agent. In such cases special waste packaging may be needed, or on-site decontamination applied, to reduce the concentration of pathogens to acceptable levels.

B. INFECTIOUS POTENTIAL OF LABORATORY WASTE

For laboratory waste to cause infection, six essential factors must be present. These factors are as follows:

1.

The presence of an infectious agent that is capable of invading and multiplying within a human host.

2.

An environment for the infectious agent that functions as a reservoir, allowing it to survive and, perhaps, to multiply.

3.

A mechanism for the agent to escape from the reservoir.

4.

A mode of transmission from the reservoir to a human host.

5.

A means for the agent to invade, penetrate, or enter a human host.

6.

A human host that is susceptible to infection by the agent.

The absence of any one of these factors will interrupt the infectious process and human disease will not ensue.

An understanding of these factors is necessary for assessing public health risks and the risk of occupationally acquired illness that may be associated with the management of infectious waste. Infectious waste implies the presence of viable pathogenic microorganisms in sufficient concentration to infect a susceptible human host. There is no risk of disease when the concentration of pathogenic organisms is below that which is capable of invading the host and multiplying within it. The source of the infectious waste may be a patient in a health care facility, an experimental animal in an infectious disease vivarium, or the culture medium used for the propagation of an infectious agent. The processes that generate the waste provide the means by which the infectious agent escapes from the reservoir. Thus the agent, reservoir, and means of escape will always be present in institutions that generate infectious waste. Treatment and disposal strategies that protect the public's health and prevent occupationally associated infection will therefore be necessary to block transmission of the agent and exposure of a susceptible host.

1. Risks to the General Public's Health

Risks to the general public's health can be associated only with indirect modes of transmission, because the public is not directly exposed to the institutional reservoirs or the infectious waste generated by them. For indirect transmission to occur, the infectious agent must be capable of survival outside of the reservoir for an extended period of time. There also must be an opportunity for a susceptible host to be exposed to the agent. Modern sanitation practice, as discussed in the introduction, minimizes the occurrence of such events. A properly functioning community sanitary landfill, solid waste incinerator, or municipal sewage treatment facility provides adequate containment and treatment for infectious waste, even when the waste is introduced without prior treatment.

2. Occupational Risks

Unlike the general public, workers who generate, handle, and process infectious waste have the potential for direct exposure to infectious agents. Exposures can occur through direct inoculation, such as when a worker is cut accidentally by a piece of contaminated glass, or through inhalation when the handling process generates aerosols. Occupationally acquired illness associated with the handling of infectious waste has been reported[59 ]. Protection against occupationally acquired illness is achieved through appropriate waste handling and treatment methods, which either contain the waste or inactivate the infectious agent. This chapter provides guidance to assist institutions and generators in establishing prudent practices for the management of infectious waste.

C. CHARACTERISTICS OF INFECTIOUS LABORATORY WASTE

Infectious laboratory waste is characterized principally as waste that contains microorganisms capable of causing infection in a healthy, susceptible host. Hospitals, health care facilities, medical research institutions, and industrial facilities can generate infectious laboratory waste. Categories of operation that produce infectious waste include the following:

  • operations that involve the processing and analysis of specimens for diagnosis, separation or purification of cells or substances from human blood and body fluids, and in vitro and in vivo methods for the propagation of pathogenic microorganisms;
  • medical operations in which invasive procedures are likely to result in waste contaminated with blood and body fluids from an individual who harbors an infectious agent;
  • veterinary operations involving the study of zoonotic disease in which infected animal carcasses and tissues, contaminated fomites such as disposable instruments and supplies, and contaminated bedding materials are produced;
  • anatomical pathology services where workers process specimens from individuals either known to harbor, or who are at an increased risk of harboring, an infectious agent;
  • diagnostic, research, and industrial operations that involve the collection and processing of bulk quantities of human blood, blood derivatives, or body fluids; and
  • the production of biological products in which pathogenic microorganisms are used, such as vaccines.

Biological waste with objectionable or putrescent characteristics, containing viable microorganisms that are either not known to be hazardous to humans or are minimally potentially hazardous, is not considered infectious laboratory waste. Examples include tissues or medical waste generated from the care of individuals who have not contracted an infectious disease; solid waste including such items as soiled diapers, animal bedding materials or pet litter, animal carcasses, and garbage from food processing plants and eating establishments. Objectionable nonhazardous medical waste is typically generated in extended care facilities and ambulatory health care services. Adherence to good personal hygiene and prudent sanitation practice affords adequate protection to individuals involved in the handling and disposal of this type of waste.

D. RESPONSIBILITY FOR THE SAFE HANDLING AND DISPOSAL OF INFECTIOUS WASTE

The primary responsibility for the safe handling and disposal of infectious waste resides with the generator of the waste. This responsibility extends to the ultimate point of disposal even when there are other parties involved in handling the waste. The generator should conduct inspections or take other measures to ensure that the waste is being handled and disposed of properly, even though management of infectious waste is also the concern of waste haulers and treatment facility operators. In addition, there may be federal, state, or local regulations controlling medical waste disposal and recordkeeping that must be observed.

The major problem associated with infectious waste is the potential for occupational exposure. The disposal of infectious waste should, therefore, be performed in an effective manner that minimizes the potential for exposure of those who, by virtue of their employment, must handle the material.

It is incumbent upon the scientific community to educate the general public about the effectiveness of current sanitation practices in protecting the public's health, and to direct legislators' attention to the problems of the occupational hazards associated with the handling of infectious waste.

1. Generators of Infectious Waste

The initial recognition of a potential hazard should set in motion all of the mechanisms from source to final disposal. Recognition is made most effectively by the generator of the waste. The responsibility for proper handling, treatment, and disposal of infectious waste materials resides with all those who knowingly come in contact with these materials. However, the major responsibility for proper handling belongs to the initial generator of potentially hazardous materials, because such waste material should be identified and segregated according to its degree of potential hazard. Once the material has been identified as infectious waste, proper packaging and containment should be ensured until decontamination or inactivation can be accomplished.

The most senior official of the facility generating the waste has the responsibility for the development of a waste management program. Such a program should ensure proper containment of infectious waste and the development and implementation of appropriate methods for the efficacious decontamination of this waste. It is incumbent upon management to ensure that proper operational controls of selected treatment methods are maintained.

No waste management program is functional unless all appropriate personnel are cognizant of the aims of the program and trained in the procedures for handling the waste. Management should provide resources and ensure that training programs are developed and implemented. Training should be a continuing process.

2. Haulers and Waste Treatment Facilities

Infectious waste is often decontaminated at the generating facility prior to its transport to a disposal site. Decontamination protects the waste hauler from the risk of infection.

In those instances where the waste hauling company transports untreated infectious waste to a treatment and disposal site, adequate physical containment measures should be provided to minimize occupational exposure. The processing of infectious waste by a treatment facility requires the same stringent attention to detail that is required of the generator treating its own waste. The treatment company has the responsibility for ensuring that all procedures are adequate and that all systems are functioning correctly. Both hauling and treatment companies should ensure that all of their personnel are made aware of the potential hazards of exposure. Personnel should be properly trained in all of the pertinent aspects of the containment, the handling, and the treatment of infectious waste. Contingency plans should be developed to handle accidents that may occur.

E. WASTE HANDLING AND TREATMENT METHODS

The prudent management of infectious laboratory waste requires the development of site-specific plans. Procedures developed by personnel within a facility will be appropriate for the specific needs of that facility and may gain a higher level of acceptance than will procedures imposed from outside sources. The process of developing a waste management plan is, in itself, acknowledgment of the need to accept responsibility for laboratory waste.

1. Basic Principles

Persons who generate infectious laboratory waste are responsible for preparing the waste so that potential occupational exposures and environmental contamination are minimized. Infectious waste needs to be segregated by the generator from other waste streams. This process will obviate the need for decision-making by support services personnel. The waste can then be treated on-site to reduce the concentration of the pathogen to an acceptable level (decontamination), or packaged in a way to prevent subsequent exposure of other persons having to handle the waste prior to terminal treatment. Packages of infectious waste need to be identified so that the potential hazard clearly can be recognized and understood by others. The universal biohazard symbol is used for this purpose.

2. Containment

A variety of packaging items for containment and transport of infectious waste are available. Infectious waste containers serve as primary barriers to protect the worker and to minimize the chance of environmental contamination (Figure 4.1). Typically, these containers are made from leak-resistant paper or cardboard, stainless steel, or temperature-resistant polymers. The nature and volume of the waste, the terminal treatment method, and their costs are principal factors to consider in the selection of the mode of packaging.

FIGURE 4.1. Biohazardous waste should be segregated from other types of waste prior to its disposal.

FIGURE 4.1

Biohazardous waste should be segregated from other types of waste prior to its disposal. Courtesy, National Institutes of Health.

Solid waste can be packaged safely in sturdy bags or boxes. Flat trays with sealable lids are suitable for containing pipettes and other laboratory supplies during decontamination. Bulk liquids may be collected in leak-proof containers, decontaminated, and then safely discharged into the sewer system. Rigid, puncture-resistant, sealable containers are necessary for packaging "sharps," e.g., broken glass, brittle plasticware, needles, and scalpel blades. Wet waste should be packaged with sufficient absorbent materials to contain residual liquids and to minimize leakage. In packaging wet materials for transport, it is prudent to double-bag the waste, sealing each bag independently. Heavy waste such as anatomical specimens, animal bedding, and laboratory specimens need to be placed in rigid containers. Care must be taken that the weight of the waste load does not exceed the burst strength of the container.

The physical properties of the container should be compatible with the treatment process. Waste placed in stainless steel pans, waxed-lined paper bags, tempered glass, and heat-resistant plastics can all be safely processed in an autoclave. Metal containers have been shown to enhance the transfer of heat to the waste load during autoclaving, whereas containers made of plastic retard steam penetration. Processing smaller waste loads and extending the treatment period can compensate for this feature of plastic containers.

Most chemical disinfectants have no appreciable effect on high-strength plastics at room temperature, but may be corrosive to metals. Liquid infectious waste often is stored in plastic carboys designed for chemical disinfection. Metal receptacles can be autoclaved and recycled but are not suitable for incineration. Ideally, waste should be packaged in disposable receptacles that minimize handling of the waste and are suitable for the waste stream treatment method. Cleaning containers that are to be reused is labor intensive and increases the risk of occupational injuries and exposures to biohazards.

3. Personal Protection

The most important precautions for all personnel handling infectious waste are the wearing of protective gloves and frequent handwashing. Gloves and a laboratory coat are recommended for all activities involving manipulations of contaminated items. Gloves and clothing should be changed when soiled or damaged. Thorough handwashing is recommended after working with infectious materials. Scavenging through waste, as well as eating, drinking, and smoking while working with waste, must be prohibited.

The type of laboratory activity will determine if there is a need for additional protective measures. Laboratory activities with a high probability of contamination caused by spills of infectious fluids, or the production of droplets, should be performed on plastic-backed absorbent bench paper. Workers who process infectious waste in an autoclave should wear a rubber apron, sturdy shoes, asbestos-free heat-resistant gloves, and a face shield, to protect against accidents that may occur while loading or unloading the autoclave.

4. Chemical Decontamination

Liquid and gaseous chemicals are used routinely for decontaminating infectious waste. Table 4.1 summarizes use parameters and applications for chemical decontamination of specific types of frequently generated infectious waste from laboratories[140 ]. Some examples of these applications are as follows:

TABLE 4.1. Decontaminants and Their Use in Infectious Waste Management.

TABLE 4.1

Decontaminants and Their Use in Infectious Waste Management.

  • Use of an intermediate decontamination step during the storage or transport of waste, e.g., the addition of liquid chlorine bleach, iodophors, or phenolic disinfectants to pipette discard pans at work stations. The concentration of decontaminant for this use should be such that the addition of liquid waste will not interfere with its effectiveness.
  • Gaseous decontamination of HEPA filters in biological safety cabinets. This procedure should be carried out prior to removal of the filter for replacement or prior to repairing the cabinet. Decontamination is usually carried out with formaldehyde sublimed by heat from paraformaldehyde flakes in the presence of high humidity. The cabinet must be sealed with plastic sheets and tape prior to initiating decontamination. Human contact with the formaldehyde should be prevented because of the highly irritating, toxic, and possibly carcinogenic properties of the gas (the OSHA limit for permissible exposure is 2 ppm). A detailed description of the method is available[95 ].
  • Decontamination of large items of equipment that are to be removed from the laboratory for repair or discard. Care should be taken to avoid corrosion of sensitive parts if the equipment is to be reused rather than discarded. A disinfectant that has low corrosive properties and has been proven to be effective against the specific microorganism should be used for this purpose.
  • Treatment of mixed hazardous waste such as combinations of infectious agents and radioisotopes. After an appropriate assessment of the waste, it may be prudent to use chemically compatible decontaminants to avoid the release of potentially hazardous emissions. See the section on mixed waste (Chapter 4, Section F, Part 1) for a more detailed discussion of such problems.

5. Steam Autoclaving

Steam autoclaving usually is considered to be the method of choice for decontaminating cultures, laboratory glassware, pipettes, syringes, or other small items known to be contaminated with infectious agents. Location of the autoclave within the laboratory minimizes storage and transport problems. It provides a technically proved treatment method for rendering infectious material safe. Autoclaved waste can be disposed of as general waste.

Certain waste materials are difficult to decontaminate in the autoclave because they insulate and protect the contaminating organisms from heat and steam penetration. Examples include animal carcasses, human body parts, and large volumes of contaminated clothing. The preferred method for decontamination of animal remains and human body parts is incineration. Routine laundering is appropriate for clothing contaminated with all but the most hazardous infectious agents. Autoclaving is not the recommended method for decontaminating very large volumes of waste because the time required for processing is too long, and the chamber size is usually too small. The lack of volume reduction and the failure of the autoclave process to render body parts unrecognizable are also limitations to this process.

Operational considerations based on specific load conditions are very important to ensure adequate decontamination in autoclaves. Most laboratories have gravity displacement autoclaves, which operate at 121°C (15 lbs/in2 of pressure). Because of the high levels of organic matter normally associated with infectious waste, these types of autoclaves should be operated for a minimum of 60 minutes. Some laboratories may have vacuum-type autoclaves, which operate at 132°C (27 lbs/in2 of pressure). It is recommended that these autoclaves be operated for a minimum of 10 minutes. The shorter time period for this type of autoclave is due to the higher temperatures and pressures attainable with the vacuum cycle and the more effective penetration of steam.

It may be desirable to add water to a load of waste to be decontaminated in an autoclave to facilitate steam formation and penetration, as well as to avoid the collection of residues on reusable items that may be difficult to remove in subsequent cleaning processes. Caution is essential while adding water to a load, to minimize the potential for aerosolizing infectious agents in the waste. Drain lines from steam autoclaves can be connected to the sanitary sewer except for those installed in maximum containment laboratories (Biosafety Level 4).

When loads contain both reusable and disposable items, the material should be separated to prevent melted plastic from encapsulating items to be reused.

6. Incineration

Incineration is the method of choice for treating large volumes of infectious waste, animal carcasses, and contaminated bedding materials. Because incinerators usually are located some distance from the laboratory, additional precautions for handling and packaging of infectious waste are necessary.

Incinerators require approval and permits from local and state pollution control authorities. Although the initial capital costs and maintenance costs are high, incineration offers many advantages as a method for the treatment of infectious waste[16 ][49 ]. Incineration significantly reduces waste volume and produces an unobjectionable end-product, ash. Proper design and operation can provide for energy (heat) recovery, making the operation more economical[25 ].

Although specific operating standards have not been set for the incineration of infectious or pathological waste, the principles of effective combustion are well understood. Waste and the hot gaseous products of its volatilization should be retained in the combustion chamber(s) for a long enough time and at a high enough temperature to allow for mixing (turbulence) with excess oxygen, so that the combustion reactions can go to completion. A deficiency in any one or more of these critical combustion parameters can result in smoke or odor production, excessive emissions of harmful gaseous by products, and the discharge of incompletely burned waste residue.

Many modern incinerators achieve the proper conditions for complete and effective combustion by providing secondary combustion chambers or zones with burners to ensure that adequate conditions for time, temperature, and mixing are achieved. Primary combustion temperatures of at least 1600°F with good mixing and a gaseous retention time of about 2 seconds should provide for good burnout for the waste described in this chapter. All pathogens and proteinaceous materials are denatured at temperatures well below that just cited[49 ].

Complete combustion also is dependent on correct operation of the equipment. The operator of the incinerator should be careful to avoid overfeeding with waste materials. Too much raw waste in the primary combustion chamber can overwhelm the combustion zones with more volatile products than the equipment is designed to handle within a fixed gas retention time. The result of overfeeding will be smoke and odors. Overfeeding an incinerator also can result in the bottom ash being moved though the primary chamber too quickly, and consequently being discharged before complete burnout takes place.

Another condition that can result in incomplete burnout of the bottom ash (uncombusted feed material) is the lack of tumbling of the solid waste feed pile in the primary chamber. This is a common condition developing in top-fed incinerators where waste continually is fed directly on top of the existing pile of previously loaded waste materials. In this situation an outer layer of insulating ash can form that retards combustion of the contents in the center of the pile. To achieve complete residue burnout, provisions should be made to agitate or break up the pile periodically. This can be done mechanically with an oxygen pulse or manually with a rake.

In selecting a new incinerator for a facility, it is critical that the actual waste stream to be treated be characterized. Too often in the past the term ''pathological waste" has been used to determine the size of an incinerator. True pathological waste consists of animal tissue that is quite wet and has an approximate heat content of 1000 BTU/lb (555.6 kcal/kg). Infectious waste incinerators should burn a wide variety of materials including significant amounts of paper and plastics as well as pathological waste. The effective heat content of the actual waste mix usually will be well above 1000 BTU/lb. Only by knowing the specific composition of the facility's waste stream can a vendor properly size the unit.

In summary, safe, effective incineration can be achieved by (1) proper equipment design; (2) provision for the time, temperature, turbulence, and air required for complete oxidation; and (3) careful feeding of the unit. To assist the laboratory manager in the selection of equipment, a consultant knowledgeable in the field of incineration should be retained to help develop a site-specific procurement specification[49 ].

7. Validation of Decontamination Methods

Sterility testing or testing for survival of an indicator microorganism is neither applicable nor practical to verify the adequacy of the treatment of infectious waste, since sterility is not an objective of decontamination methods, and indicator microorganisms do not simulate typical waste load composition. Rather, precise reproduction of each of the conditions (operational parameters) prescribed for the different treatment methods should be relied upon to ensure adequate treatment each time waste is processed. This reliance, however, is justifiable only if all of the measuring devices used to monitor the treatment process (e.g., thermometers, pressure gauges, and timing mechanisms) are functioning properly. It is imperative that the accuracy of these measuring devices be certified independently by the user, after the equipment is first installed and before any waste is treated, and again thereafter at regularly scheduled intervals (at least annually). This process should be repeated after maintenance work or repairs are carried out, and if the equipment is relocated.

Each of the different treatment methods for infectious laboratory waste requires a different set of conditions to be effective. Effective autoclaving is dependent upon time, temperature, and steam penetration, whereas effective incineration is dependent upon time, temperature, and turbulence. Chemical decontamination is dependent upon several parameters, including selection of an effective chemical, contact time, concentration, and the presence of organic materials or other interfering substances. Operator controls include such matters as procedures for packaging the waste, placement of the load, feed rate, and—perhaps most important—the keeping of an accurate record of the operational parameters achieved for each load processed. Detailed information regarding the principles of efficacious treatment is available[48 ][49 ][52 ][75 ][111 ][140 ].

Chemical indicators are of limited value in verifying the decontamination of infectious waste. Chemical indicator inks printed on waste packaging materials intended for autoclaving provide a color change that serves only to distinguish treated waste from waste requiring treatment: i.e., failure of an indicator to change to its signal color after the process demonstrates immediately that the equipment has malfunctioned.

F. INFECTIOUS WASTE REQUIRING SPECIAL CONSIDERATION

1. Mixed Waste

Mixed waste consists of materials that exhibit multiple hazardous properties, such as infectivity, radioactivity, and chemical toxicity. Frequently, some of the components are strictly regulated by environmental protection and transportation agencies of the local, state, and federal governments. However, treatment and disposal strategies for mixed waste generally are not addressed by most regulatory agencies. One difficulty, in part due to conflicting regulations, is that mixed waste frequently is not accepted at disposal facilities operating under permits issued by the Environmental Protection Agency (EPA) or licensed by the Nuclear Regulatory Commission (NRC). Waste managers should anticipate that disposal problems will occur. Also, the concern of the public regarding hazardous waste disposal, in general, is likely to influence the development of more restrictive mandates for handling mixed waste. The uncertainty that exists with regard to the treatment and disposal of mixed waste emphasizes the importance of the prudent practice of implementing waste minimization and separation strategies for the types of operations that generate mixed waste.

Waste minimization should be attempted at several levels to address effectively the problem of mixed waste. Researchers should be encouraged to plan experiments and select reagents that minimize the production of mixed waste. Experimental design may be modified such that the wastes are generated separately and in minimal volumes. Microscale techniques are now available for most experimental procedures. When feasible, substitution of less hazardous materials should be considered. Appropriate waste containers should be made available at the work site to ensure convenient and correct segregation and labeling of the waste.

Waste managers commonly have to make a decision about the method to be used for the treatment and disposal of mixed waste. If unusual disposal problems are anticipated by the generator of mixed waste, the waste manager for the institution should be informed prior to generation of the waste. Routinely, the regulated hazardous waste component takes precedence in any treatment and disposal strategy. It is important to recognize, however, that the most serious hazard associated with the waste may not be the regulated component. Placing emphasis on the regulated component therefore may not be the safest approach; in fact, the risks involved in the handling of mixed waste could be exacerbated. A careful assessment of the waste composition is required in order to select the appropriate strategy for treating the mixture. Thermal or chemical inactivation of the infectious component of mixed waste is commonly recommended by waste managers after assessing the potential for toxic emission and chemical incompatibility. Once a strategy for handling the mixed waste is decided upon, it is important that the infectious component be decontaminated along with, or prior to, final treatment and disposal.

Several factors in addition to those associated with the infectious nature of the waste should be considered in selecting an appropriate method of treatment. Some of the more important factors are the type and volume of waste generated; other hazardous properties of the waste (e.g., radioactivity, volatility, flammability, chemical toxicity, and temperature sensitivity[22 ][91 ]); the availability of validated treatment methods and recommended safety precautions; the permit and license status of the generator to treat hazardous waste; the quantity and characteristics of the end products after treatment; and the relevant regulations, permits, and packaging requirements for the disposal of the regulated hazardous materials in the mixed waste.

When autoclaving mixed waste, precautions should be taken to avoid the release of volatile radionuclides (e.g., radioiodine) and toxic chemicals (e.g., mercury, solvents, and carcinogens). The potential volatility of the mixture when subjected to the elevated temperatures necessary to achieve thermal biological inactivation is therefore an important factor in the assessment of these types of mixed waste. Mixed waste containing conjugated tritium, technetium-99, carbon-14, and other radionuclides has been autoclaved safely at various institutions, but this method should be approved by the radiation safety officer of the institution. Waste containing flammable or reactive chemicals should not be autoclaved. Care should be taken to avoid contamination of the equipment. Autoclaves used for processing radioactive waste should be labeled with the universal radiation symbol.

Excreta that contain radionuclides from patients undergoing diagnostic nuclear medicine procedures may be discharged into the sanitary sewer if the activity levels in the sewage do not exceed license limitations. Excreta from patients receiving chemotherapeutic drugs may be discharged into the sanitary sewer, if this practice is in compliance with local regulations. Specimens of blood and body fluids obtained from these classes of patients often are submitted for laboratory analysis. These diagnostic specimens can be discharged into the sanitary sewer untreated, or autoclaved and disposed of as general waste.

The incineration of mixed waste is dependent upon the regulatory requirements and permits for the hazardous chemical or radioactive components. Volatile metals (mercury) should not be incinerated but may easily be treated by other methods. Waste management strategies are hindered when the mixture contains volatile metals in addition to other hazardous waste components that dictate incineration as the treatment of choice.

Treatment of all regulated waste and regulated components of mixed waste is restricted to facilities holding the necessary permits. At the time of this writing, none of these facilities accepts waste containing the "dioxin group" compounds (chlorinated phenols and phenoxy acetic acids, chlorinated dibenzo-p-dioxins, or chlorinated dibenzofurans) for treatment or disposal. Thus, mixed waste containing any of the dioxin group compounds is difficult to manage. Due to the lack of permitted facilities and the resulting requirement for long-term storage at the producing institution, stringent waste minimization strategies should be implemented to minimize the generation of this type of mixed waste.

Chemical decontamination of mixed waste requires an assessment prior to treatment to avoid potential occupational hazards or difficult disposal problems. For example, decontamination of mixed waste containing radioiodine with sodium hypochlorite could result in the release of the radionuclide.

2. Human Cadavers and Other Anatomical Waste

All anatomical waste requires special handling and packaging due in part to its putrescent properties at ambient temperatures. Cold storage is necessary for nonpreserved anatomical waste to minimize odors and leakage problems. Human body parts, bodies, and cadavers should be disposed of by cremation, burial, or incineration as stipulated in regulations promulgated by the state anatomy board.

Biomedical laboratory and veterinary research operations also generate anatomical waste such as pathological specimens and animal carcasses. Studies of animal and human infections may generate infectious anatomical waste. This waste may be packaged in a durable, preferably opaque, plastic liner that is placed in a sturdy paper fiber box or drum. As a precaution, absorbent material can be added to contain any fluids that might be present. Incineration is the treatment of choice for anatomical waste derived from infected hosts. A facility with a properly designed and operated medical waste incinerator can effectively treat infectious anatomical laboratory and veterinary waste for disposal.

3. Animal Bedding materials

Soiled animal bedding material also becomes malodorous when stored at ambient temperatures for extended periods of time. Adherence to good sanitation practices can minimize potential problems. Bedding materials obtained from healthy laboratory animals are managed as solid waste and disposed in a sanitary landfill. Institutional or local requirements may apply to the management and disposal of animal waste containing excreta. Decontamination of soiled bedding materials from healthy animals is not indicated, although containment precautions should be instituted to minimize the production of allergenic aerosols.

Contaminated bedding materials and disposable fomites associated with infected animals are also examples of infectious waste. Incineration is the decontamination treatment recommended for combustible, high-density waste. Incinerable small-animal cages are often used in Biosafety Level 3 facilities. This practice avoids the formation of infectious aerosols during the handling and disposal of bedding and related waste. Autoclaves may be available on site or in close proximity to the animal holding areas to decontaminate bedding materials or excreta contained in metal or heat-resistant plastic cages. Decontaminated solid waste then may be managed as general waste.

4. "Sharps"

Needles and other penetrating items such as surgical blades, pipettes, broken glass, and laboratory instrument sampling probes pose a physical hazard to laboratory and support service personnel and, if used to process infectious materials, may transmit infection. All disposable "sharps" should be placed in a prominently labeled, leak- and puncture-resistant container that is consistent with the institution's waste management plan. Sturdy corrugated fiber boxes are used routinely for packaging broken glass and brittle plastic ware such as pipettes. The addition of an absorbent material such as crushed corn cob to the package will retain residual fluids and enhance the incineration of waste containing large quantities of plastic and glass. Hypodermic needles and surgical blades often are packaged in disposable buckets made from a high-strength, temperature-resistant plastic. Used disposable needles and syringes should be placed, intact, directly into the waste receptacle without recapping. Other safety design features may include a sturdy handle to transport the waste safely, a restricted opening with a self-activating flap to keep the waste covered while in use, and sealable lids to contain the waste during treatment and disposal. Placing the waste receptacle in a location convenient to the activity generating the waste (e.g., in animal procedure rooms, at patient's bedside, and on the laboratory workbench) is one strategy to ensure proper segregation and packaging of the waste and to minimize the risk of injury to housekeeping personnel.

Copyright © 1989 by the National Academy of Sciences.
Bookshelf ID: NBK218626

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