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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals
of, the disposal cost per container is less for smaller containers.
Later in this chapter (section 4.D.2), the exchange or transfer of chemicals to other laboratory workers is discussed. The use of smaller containers increases the chance that chemicals to be transferred will still be in sealed containers, which increases the receiver's confidence that the chemicals are pure.
4.B.2Strategies to Minimize Hazardous Waste Generation
Experimental design and execution are central in strategies to minimize the generation of hazardous waste, just as they were in the section above. The design should evaluate all potential sources of hazardous waste expected from the proposed experiment and incorporate strategies to minimize those sources. Examples of such strategies include
carrying out chemical reactions and other laboratory procedures on a smaller scale;
considering the use to which a reaction product will be put and then making only the amount needed for that use;
appreciating the price that may be paid for making and storing an unneeded material;
thinking about minimization of material used in each step of an experiment;
using less solvent to rinse equipment, for example, by carrying out several rinses with small volumes of solvent, rather than using only one or two rinses with larger volumes;
using more sensitive analytical equipment;
substituting nonhazardous, or less hazardous, chemicals where possible by considering alternate synthetic routes and alternate procedures for working up reaction mixtures;
recycling and reusing materials where possible, and coordinating laboratory work with co-workers who may be using some of the same chemicals (section 4.D.2);
isolating nonhazardous waste from hazardous waste; and
including in the experiment plan the reaction work-up steps that deactivate hazardous materials or reduce toxicity (see Chapter 7-examples include oxidation of carcinogens in situ or treating excess potassium metal with t-butyl alcohol).
Clearly, some of these steps have become important only recently as a result of the changing requirements and economics of laboratory management. Three of these critical strategies are elaborated on below.
4.B.2.1 Microscale Work
In microscale chemistry the amounts of materials used are reduced to 25 to 100 milligrams (mg) for solids and 100 to 200 microliters (µL) for liquids, compared to the usual 10 to 50 g for solids or 100 to 500 milliliters (mL) for liquids. Carrying out synthetic and analytical work on a small scale requires that smaller amounts of materials be ordered. Working with smaller amounts of materials can promote more attention to detail, which improves the quality of the science being done. The smaller scale also means that there will be less to recycle or dispose of from reaction work-up. Smaller quantities of items such as used filter papers, used filter cakes and filtrate from washings of the cakes, residues from distillation, and solvents to be redistilled will be produced. The glassware used in smaller-scale procedures is also generally not as easily broken as that required by procedures on a larger scale. Broken glassware contaminated with hazardous materials is itself a waste that must be disposed of. Microscale work also reduces the likelihood and severity of accidents resulting in personal exposure to hazardous chemicals. Fire hazards are also likely to be reduced.
As an example of the benefits of microscale work, consider the typical Kjeldahl reaction, which uses mercury as a catalyst. The mercury waste produced by this procedure creates a difficult disposal problem. Converting to micro-Kjeldahl equipment and quantities reduces the waste by 90%, which could result in a reduction of several liters of waste per day in laboratories that routinely run Kjeldahl reactions.
If 30,000 educational institutions that currently generate more than 4,000 metric tons of hazardous waste per year in the United States were to convert to microscale chemistry, 3,960 metric tons of that waste would be eliminated, at a savings of hundreds of millions of dollars per year. Many industrial research and development laboratories could achieve comparable financial and environmental savings.
The committee recognizes that enormous quantities of hazardous waste can be minimized by converting to microscale chemistry with proportionate environmental and financial savings. Many tons of waste and millions of dollars would be saved by going to the microscale level. At the same time it must be recognized that multi-gram laboratory preparation is often required to provide sufficient material for further work. Precaution appropriate to the scale, as well as the inherent hazard, of a laboratory operation must be exercised.