Diagnosing Sick Buildings
W
hen most people think of air pollution, they picture factory smokestacks belching black smoke and cars trailing blue exhaust. Since the federal Clean Air Act was passed by Congress in 1970, billions of dollars have been spent fighting outdoor air pollution. However, recent Environmental Protection Agency (EPA) studies reveal that most people are exposed to more harmful pollutants in their homes and offices than outdoors. Because of this, EPA is now studying ways to rid indoor air of benzene and other polycyclic aromatic compounds found in tobacco smoke; formaldehyde and polychlorinated biphenyls (PCBs) from building materials; and volatile compounds often found in paints, air fresheners, and common household cleaners. Analytical chemists are supporting these efforts by developing new methods for sampling and analyzing indoor air. The causes of indoor air pollution have been around for a long time, but it was not until the energy crisis of the early seventies, when increased emphasis was placed on energy-efficient "tight" buildings, that "sick" buildings began to attract attention. Many of these new and remodeled buildings lack windows that can be opened, resulting in poor air circulation. In fact, a
recent study by the National Institute for Occupational Safety and Health indicates that as many as half of the cases of sick building syndrome (SBS) can be blamed on poor ventilation. People living or working in a sick building may exhibit symptoms such as drowsiness, nausea, sneezing, headaches, and dizzy spells. Analytical methodology has targeted these pollutants roughly according to the volatility of the compound of interest. Volatile organic compounds Although formaldehyde has been implicated in many cases of SBS, other volatile organic compounds (VOCs) may also be contributing to the depression, lethargy, and irritability often associated with formaldehyde exposure, according to Lance Wallace, an EPA scientist who has directed studies of total exposure to both indoor and outdoor pollutants. Furthermore, exposure to other highly reactive compounds, such as SO2, ozone, acrolein, allyl alcohol, allyl acetate, or allyl ether, can have the same symptomatic effects as formaldehyde exposure. According to Linda Sheldon, a member of the team of analytical chemists at the Research Triangle Institute (Research Triangle Park, NC) that has been developing indoor air monitoring
methods for EPA, successful methods for measuring VOCs must be capable of detecting pollutants at ambient levels (i.e., ppt-ppb levels); use collection/ measurement devices that are lightweight, compact, and quiet for use in the field; provide accurate and reproducible analysis with a minimum of artifactual and contamination problems; and allow for reasonable sampling periods that are compatible with monitoring needs. These methods can be classified into two broad groups: analytical methods that detect and quantitate VOCs on site and methods in which VOCs are collected and concentrated on a sorbent for later analysis. Each group can
Focus be further divided into active methods, in which a power source is used to pull air across a sensor or collector, and passive methods, which rely on permeation or diffusion to bring the analyte in contact with the collector or detector. Although on-site analytical methods can provide concentration profiles rather than the time-integrated averages offered by collection methods,
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FOCUS they are more complex and expensive and require significant calibration and maintenance in the field. Collection methods for vapor-phase organics commonly involve collection on a solid sorbent, such as a polymeric resin (e.g., Tenax GC or XAD), activated carbon, or a carbon molecular sieve. These sorbents can be used for a wide variety of VOCs, and because they have a low affinity for water, their collection efficiency is not strongly dependent on humidity. Inorganic adsorbents (such as silica gel, alumina, and florisil) are not commonly used for collecting VOCs in air, however, because they readily adsorb water, which deactivates their surface sites. Either thermal or solvent desorption is then used to desorb collected organic compounds from the sorbent. Because polymer resins reversibly adsorb organic compounds, thermal desorption followed by GC/MS analysis, which provides positive identification of target organics as well as broad spectrum analysis, is normally used. Activated carbon, on the other hand, chemically binds organic compounds and thus requires solvent desorption for efficient recovery of collected compounds. Solvent desorption usually precludes GC/ MS analysis for low molecular weight organics because the solvent front interferes with the analysis. In these cases, solvents such as carbon disulfide or acetone are used, and GC detectors that are relatively insensitive to the eluting solvent, such as flame ionization, electron-capture, or nitrogenphosphorus detectors, are employed. Overall, the sensitivity of the solvent desorption methods is less than that for thermal desorption because only a fraction of the sample is analyzed. An alternative to sorbent methods involves collecting air samples in stainless steel canisters rather than on a sorbent cartridge. "Essentially," says Sheldon, "air is sucked into the canister in the field. Once the canister is brought back to the lab, about 200 mL of the collected air is cryofocused and analyzed using GC/MS with selected ion monitoring." This method has replaced the Tenax-desorption method for many very volatile compounds. Although real-time analytical methods can provide more information than the passive collection methods, they are not commonly used for organics because of contamination problems at the ambient levels necessary for effective indoor air monitoring. Most existing real-time methods have been developed for inorganic species (e.g., NO2 and SO2), although instruments for monitoring formaldehyde and acrylonitrile are also available. "Although
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these instruments have potential," says Sheldon, "they were primarily developed for workplace monitoring, and they just don't quite have the sensitivity necessary for detecting part-pertrillion levels of organics." Formaldehyde Because formaldehyde from insulation and building materials is among the more common indoor pollutants, specialized methods have been developed for determining formaldehyde in air. These methods involve in situ derivatization with 2,4-dinitrophenylhydrazine (DNPH) followed by reversedphase LC. Air samples are collected either on silica gel cartridges coated with acidified D N P H or in impingers containing acidified DNPH-acetonitrile solution. Back in the lab, the cartridges are eluted with acetonitrile while the impinger solutions are brought to volume with acetonitrile; the solutions are then analyzed for formaldehyde by LC. Semivolatiie and nonvolatile organic compounds Semivolatiie and nonvolatile organics include polycyclic aromatic hydrocarbons (PAHs), organochlorine and organophosphorous pesticides, PCBs, and chlorinated dibenzodioxins and furans. These compounds get into the air primarily from cigarette smoke, plasticizers in building materials, and the use of pesticides for insect and rodent control. Common methods for sampling semivolatiie and nonvolatile compounds involve the use of polyurethane foam (PUF) plugs or XAD resin. PUF has a number of advantages over other adsorbents, including low flow restriction, ease of purification and handling, and low cost. XAD, however, has better retention characteristics for the more volatile pesticides and PCBs, allowing lower detection limits for these compounds. PUF also forms mutagenic artifacts- during sampling, reducing its usefulness as a collection medium for bioassay studies. After sample collection, the analytical techniques used for both PUF and XAD are generally the same as for other media. The sorbent is extracted with a suitable solvent and the extractant analyzed using GC/MS or LC with fluorescence or ultraviolet detection for PAHs, chlorinated dioxins, and furans, and GC with electron capture detection for PCBs. Chromatographic cleanup is often needed to achieve the required sensitivity. Biological factors Indoor biological pollution is only beginning to receive the same type of at-
tention as indoor chemical pollution, according to Harriet A. Burge of the University of Michigan Medical School. This apparent lack of study stems from the difficulties of sampling biological aerosols and their variable health effects. The majority of biological pollutants comes from outdoors (e.g., pollen) and causes disease only in sensitized people. Outbreaks of Legionnaires' disease, caused by buildup of Legionella pneumophila, however, can affect a larger number of people, and have made the public more aware of indoor biological pollution. There is no single method of choice for sampling airborne microbial particles, although there are three major sampling strategies: viable particle sampling, particulate sampling with visual assessment, and immunological sampling. The most widely used type of viable sampling involves the use of a settle plate, in which a plate of culture medium is set out uncovered for a period of time to collect viable spores. Unfortunately, because the chance of impingement is directly related to a particle's mass (and thus its size), large particles are almost always overrepresented. As an alternative to settle plates, volumetric cultural sampling devices draw air through a defined orifice using a vacuum pump, accelerating the air to the point that most particles impact. Although this method ensures collection of all microbe sizes, only particles that will grow under the given culture parameters will be recovered. Particulate sampling with visual assessment is useful primarily when dealing with large particles such as pollen or fungal spores. Either impaction samplers or suction traps are used to collect microorganisms, which are then identified and counted under a microscope. For immunological sampling, samples are drawn from large volumes of air and either impinged on a filter, dissolved or suspended in a liquid, or frozen from the air on the walls of cooled containers. The samples are then used in immunoassays for antigen-specific antibodies. This method is more sensitive than either viable or visual discrimination methods, but it cannot be used for screening because it necessitates prior knowledge of a target microorganism. Control measures
What can we do to control indoor air pollution? Probably the easiest thing to do is to remove the source of the pollutants. "This can be difficult if the source is unknown or if the pollutants are in the building materials," says
Wallace, "but often getting rid of all the paint cans, aerosol spray cans, and solvents in the building will solve the problem. It's best to store such chemicals in a detached garage or in the attic rather than in the basement, so that they are out of the airflow leading into the living areas of the building." The next step is to ensure that buildings have adequate ventilation so that toxic levels of pollutants do not accumulate. There is also evidence that ordinary house plants can help to control VOCs in indoor air. A National Aeronautics and Space Administration study found that philodendrons, spider plants, and the golden pothos are most effective in absorbing formaldehyde, while flowers like the gerbera daisy and chrysanthemums can reduce levels of benzene. English ivy, peace lily, mother-in-law's tongue, and Chinese evergreen are also effective air purifiers. Biological indoor pollution can be prevented by filtering the air entering a building, eliminating standing water in which microbes can multiply, and controlling dust in the building. EPA is now getting firsthand knowledge of indoor air pollution. The Washington Post reports that workers in the Washington, DC, headquarters building have been complaining of respiratory and neurological symptoms for the past few years. Like most buildings erected 20 years ago, EPA headquarters was designed to be energy efficient, with the flow of outside air restricted and most windows sealed. Environmental monitoring revealed not only the presence of phenylcyclohexane emitted from the latex backings of newly laid carpet but also low levels of other toxic compounds as well as legionella bacteria in outdoor air conditioning cooling towers and pneumonia bacteria in a cooling system drip pan. EPA officials have promised to improve ventilation in the building to at least partially eliminate the problem. Although EPA's budget for indoor air pollution is increasing, it may be many years before all aspects of this complex issue are under control. In the meantime, it may be wise to dispose of all unnecessary paint cans, aerosol spray cans, and solvents; stop smoking; open your windows; and keep those house plants healthy. Mary Warner Suggested reading Stammer, L. B. Washington Post Health, Jan. 23, 1990, p. 17. Wallace, L. A. Proc. APCA Ann. Meet.; Air Pollution Control Association: Pittsburgh, PA, 1988; 88-110.6. Indoor Air and Human Health; Gammage, R. B.; Kaye, S. V., Eds.; Lewis Publishers: Chelsea, MI, 1985. Tejada, S. Int. J. Environ. Anal. Chem. 1986,26, 167-85.
Downstream Processing and Bioseparation Recovery and Purification of Biological Products
T
his new volume offers state-of-the-science information on the techniques and current thinking about bioseparations of large molecules such as proteins and polysaccharides. The volume contains previously unavailable data, including predictive mathematical models and new extraction techniques. In addition to an overview, three main topics are covered in 15 chapters • extraction and membrane processes • processes using biospecific interaction with proteins • novel isolation and purification processes Biphasic aqueous systems, liquid membranes, reversed-micellar systems, and membrane processes are a few of the extraction processes discussed. Information on affinity and other interaction techniques for protein purification, as well as electrophoresis and chromatography, is also included. This material can serve as a guide in the development of specific programs required by the many forms of biotechnology. The novel techniques are of interest because they are far ahead of ordinary separation methods. Jean-Francois P. Hamel, Editor. Massachusetts Institute of Technology Jean B. Hunter, Editor. Cornell University Subhas K. Sikdar, Editor, National Institute of Standards and Technology Developedfroma symposium sponsored by the Division of Industrial and Engineering Chemistry, Inc., of the American Chemical Society ACS Symposium Series No. 419 312 pages (1990) Clothbound ISBN 0-8412-1738-6 LC 89-49336 $69.95 0
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