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I CONDUCTION This report we. prepared, at the request of the Environmental Protection Agency {EPA), by the Remittee on Indoor Pollutants, which was appointed ~ the National ResearOb Council it, the Board on !oxicolc~gy arid - vironasutal Bealth Hazards, Assembly of Life Sciences. It is interceded to characterize the quality of the indoor environment, priority with respect to airborne pollutants, and to determine the potential adverse bealtb effects of indoor pollutants. The charge was to review, compile, and appraise the available knowledge. The Remittee has also identified the research needed for abatement of indoor pollution. .Indoor. refer e to the en~rtronments inside bones, achoole, public buildings, and similar spaces to which the public has accedes industrial working environments, however, are excluded from consideration beret It is beyond the scope of this report to list all the pollutants found indoors that are hazardous to ban health. The exiles given make it plain that humans are exposed to a variety of potentially hazardous indoor pollutants from diverse sources. It is hoped that this report will encourage researchers to broaden the list of hazardous indoor pollutants and to characterize the hazards. so that the general public and tbo~se responsible for pollution control and abatement can be informed. Throughout this report, pollutants are mentioned without discussion of their health effects. This does not constitute an o~reraight on the part of the Remittee, but rather reflects ~ decision that the discussion here be adequate to abow that there are indoor pollutants that cause adverse health effects in humane. The reader's attention is directed to Chapter ITI, which offer e come reco~send~tione for further health research with respect to t - ee pollutants, for further exposure studies, and for public education about effective ways of reducing epicure to many contaminants encountered indoors. Attention has recently been drawn to the problems of specific pollutants that originate indoors, e.g., for~ldebyde released from urea-formsidehyde foam insulation and from urea-formaldebyde resine used to bind laminated~wood products, a8be~to8 in building materials, ~6
17 and radon and its progeny. Efforts to reduce infiltration of outdoor air for energy conservation have heightened the interest in indoor pollution. It is hoped that this report wit\ ~ useful to the Administrator of EPA and other agencies and individuals in cone$dezing indoor environments as a source of exposure of members of the general public to hazardous pollutants. Some of the says pollutants, of course, are now regulated as pollutants in the outdoor There and in the workplace (see the lists of air~ualitY standards in Appendix A} . The Co~ittee's report outlines the scope of the probate regarding indoor pollutants and discus - e their sources, their effects on human health and welfare {human comfort, productivity, soiling, and corrosion}, the technologies available for their control or abatement, and concerns about the effects of energy~coneer~retion strategies on the indoor concentrations of pollutants. It approaches the subject of indoor pollution from three viewpointes a, ~ ~ ~ ~ · Physical factors, such as indoor-pollutant sources and concentrations and population exposures to those pollutants. · Biomedical evidence on the effects of several pollutants found in the indoor environment. · Engineerir~g, air-handling and Cleaning systems, and other control options for reducing indoor exposures to pollutants. The report reviews current understanding of tbese subjects, assesses the quantity and quality of available information, and offers recommendations for additional studies where appropriate. Because of the multidisciplinary and complex nature of the indoor pollution question, this document could not possibly treat all pertinent subjects. One important exclusion f roe the asees~asnt is the indoor industrial environment. It is recognized that many of the pollutants found in areas to which the public teas access are also common to industrial settings, often in higher concentrations. me Committee chose to consider only indoor environments to which the general population has acceded these include residences, public f acilities, recreational facilities, vehicles and tran~portation-related buildings, educational facilities, and many work settings. Examples of workplaces to which the public has access and in which the public Day be compromised by indoor pollution include service stations, automobile showroos's with arctic teed s - intenance areas, banks, offices, and buildings with multiple uses. This document reviews the information on the health and welfare effects of selected indoor pollutants, with emphasis on air pollutants. It includes a critical appraisal of reported measurement and exposure studies, but it does not attempt a quantitative assessment of exposure to the hazardous pollutants in the indoor environment, because in most cases current methods are inadequate for that. There is no discussion here of the legal, social, or econasic implications of regulating the indoor environment in public buildings or bomes. Sociopolitical controls of pollution are quite co - lex and beyond the scope of this document.
18 Throughout the Co~ittee's deliberations, and reflected in its conclusions and recommendations. were the following questions: · Do indoor pollution exposures adversely affect the health, welfare, productivity, or sense of well-being of the population or any portion of the population? · Does the indoor environment constitute an important component of exposure to pollutants? · Are come groups or individuals at risk by virtue of high indoor concentrations of air pollutants or by virtue of susceptibility? · What is known about the relative magnitudes of indoor and outdoor pollutant concentrations? Are the sources, ventilation rates, and reaction and removal factors that influence the indoor~outdoor relationships sufficiently well known to predict indoor concentrations and prescribe controls? · What control strategies are effective for reducing population exposures to specif ic indoor pollutants? · Will future changes in housing materials, products, ventilation codes, and activity patterns adversely affect health and welfare through changes in indoor exposures to air pollution? It is very important that health and welfare problem related to indoor pollution be clearly differentiated from perceived problems or pseudoproblema. This requires measurements that are both accurate and sufficiently representative To identify or estimate the population at risk. And it requires that health research provide reasonable assurance that current or projected exposures can cause unacceptable effects in a portion of the population. Only when these two components are present can prudent judgments on recommended concentrations and control strategies be made. Efforts to improve the public health and protect the public from hazardous airborne pollutants hay. been directed primarily toward improving the ambient and indu~t-~1 environments. Improvements in outdoor (ambient) air have been achieved fundamentally through source control or removal; dilution by tall stacks and source relocation are not considered control strategies. In the indoor industrial environment, however, ventilation or dilution with outdoor air has usually proved to be the most cost-effecti~re way of reducing worker exposure. The indoor concentrations of airborne contaminants depend on five factors: the qaneration rate (for indoor~qanerated pollutants) or the ambient concentration (for outdoor-generated pollutants), the Solve of the indoor en~rtronaent, the air-exchange rate, the mixing efficiency of the indoor space, and the decay (removal) rates of the pollutant-. Until recently, the air in most buildings has been controlled for comfort and odor considerations, not for contaminants. Depending on heating, cooling, and bu'Qidity requirements for the indoor environment, the natural or forced infiltration of outdoor air to displace ~conditioned. indoor air may entail a considerable energy penalty. Diluting ache indoor air with outdoor air reduces
19 concentrations of airborne pollutants generated by indoor sources, such as building materials, appliances, and tobaccos - oking. But outdoor air can also introduce pollutants of outdoor origin, and these pollutants may react with surfaces or other indoor contaminants. Conversely, reducing air exchange without compensating with air-cleaning will result in increased concentrations of contaminants that are generated indoor.. The current growing interest in the quality of the indoor environment is in part ~ result of efforts to reduce ventilation for energy conservation. In the United States, an estimated 20-50% of energy consumed is for space-hesting and -cooling. In many buildings, the energy used to move and condition ventilating air can be as much as 90% of the total energy demand. Buildings lose energy by conduction and radiation through windows, walls, and ceilings and by exchange of indoor conditioned air with unconditioned outdoor air. Reducing ventilation in residentis1 and commercis1 buildings can be cost-effective way to achieve energy conservation. However, it is reasonable to expect concentrations of contaminants generated by building occupants, equipment, appliances, and materials to increase when ventilation is reduced. Predicting the results of ventilation changes is limited in some cases by lack of knowledge of the nature and behavior of Contaminant sources, of the existing concentrations of pollutants, and of their chemical and physical reactions and removal rates. Wren for current situations, the significance of the potential indoor-pollution problem is undefined for many pollutants, because the populations an possible r ink have not been identif fed and the physiologic, behavioral, or welfare effects of various degrees of exposure have not been determined. Although there is considerable mass-media coverage of the quality of indoor environments, the concern for indoor pollution in the nonindustrial setting is not new. Some countries have tried to regulate pollutants in nonindustrial environments (see Appendix A). Asbestos-fiber contamination in homes and schools has been monitored and in some cases contained or removed. Ozone generation by office copying machine- has been regulated. Hinima1 acceptable ventilation rates for smoke and odor control are incorporated into municipal and state building codes. Several countries have set standards for residential or public facilities to limit exposures to formaldehyde, carbon dioxide, and radon. There have been surveys, but not systematic evaluation, of indoor pollutant concentrations in a variety of locations. The indoor environment has become an issue for the public, government, Scientific groups, and corporations because of three phenomena: energy-conservation efforts, which may exacerbate an indoor-pollution problem; the. realization that little is known on the hazards of many compounds that are commonly found indoor. and outdoors, including consumer products and fuels in common use (note, for example, the resurgence in residential wood- and coal-burning); and the evaluation of pollutant hazards by federal agencies, which have begun to recognize the need to understand the total exposure. . _ ~ ~ ~ _ For a large proportion of the population, normal activity occurs disproportionately indoors. In a consideration of integrated
20 pollutant exposures, indoor concentrations are relevant. Between 80 and 90. of an average person's day or year is spent in enclosed areas. On the average, people spend spproxi~tely 16 houre/day in their homes. And a rather consistent 1-2 hour/day is spent in transit. Thus, for at least some pollutants, the indoor concentrations are the mat important, with respect to potentis1 health effects or material damage. The time-integrated exposure is perhaps important in determining chronic effects, such as corrosion. But the ~hort-term peak or transient pollutant exposures may be more important, causing or contributing to both acute and chronic effects. Using the average amount of time ~ person is outdoors or indoors or the time-averaged concentrations may be mialead4~.g, if the concern is for peak-exposure effects. Peak exposures may occur indoors or outdoors. They may be encountered only during specific activities or in locations occupied only infreauentlv. In fact, short-term weak concentration'; mav _ , ~ ~ , contribute only a small proportion of ~ person's total time-integrated exposure. Both time-integrated concentrations and short-term, transient high concentrations must be considered, whether they occur indoors or outdoors. Although the indoor and outdoor environments have not been sufficiently assessed to characterize all pollutant constituents comprehensively, it in useful to categorize indoor pollutants into three groups. Table I-1 groups pollutants by source. Those in the first group are principally of outdoor origin; thus, their concentrations are generally higher outdoors. This group includes sulfur dioxide; ozone; many elemental, inorganic, and organic species of particles; pollen; and some organic vapors. They are encountered indoors primarily because they are carried in with infiltrating air. She may be carried indoors on surfaces. Once inside, particles can be resuspended, or organic substances may volatilize because temperatures and partial pressures are different. The higher indoor surface-to~'rolu~ ratios increase the removal rates of many of these pollutants . Pollutants in the second group have both indoor and outdoor sources. Generally considered as belonging to this class are pollutants produced during combustion, such as carbon dioxide, carbon monoxide, nitrogen oxides, and some components of suspended particulate matter (primarily fine particles--di~eter less than 3.0 - I. Because of the limited indoor mixing volume and longer residence times, concentrations of these and other combustion products often exceed outdoor concentrations. =~e group also includes organic vapors from solvents that can be used outdoors, as well as indoors. Biologic materials, such as funga1 spores, have both indoor and outdoor sources. Fibers, including asbestos f ibere, here indoor and outdoor sources . Serpentine rock, brake linings, and industrial facilities contribute asbestos fibers to the outdoor air. Insulation, fireproofing, and decorative materials used indoors may contain asbestos. Similarly, water vapor, sound, and nonion~zing radiation can be considered to belong to this group. l
21 TABLE I-1 Typical Sources of Some Pollutants Grouped by Origin Group 1--Sources predominantly outdoor: Sulfur oxides (gases, particles) Ozone Pollens Lead, manganese Calcium, chlorine, silicon, cadmium Organic Stances I=: Nitric oxide, nitrogen dioxide Carbon monoxide Carbon dioxide Particles Water vapor Organic substances Spores Group IIISources predominantly indoor: Radon Formaldehyde Asbestos, mineral, and syn- thetic fibers Organic Substances Ammonia Polycyclic hydrocarbons, arsenic, nicotine, acrolein, etc. Mercury Aerosols Viable organisms Allergens Fuel combustion, subitems Pho~cochemical reactions Trees, grass, weeds, plants Automobiles Suspension of soils or industrial emission Petrochemical solvents, natural sources, vaporization of unburned fuels Fuel-burning Fuel-burning Metabolic activity, combustion Resuspension, condensation of vapors and combustion products Biologic activity, combustion, evapora- tion Volatilization, combustion, paint, meta- bolic action, pesticides, insecticides, fungicides Fungi, molds Building construction materials (concrete, stone), weeer Part ic reboard, insul at ion, f urni shing s , tobacco smoke Fire-retardant ~ acoustic, thermal, or electric insulation Adhesives, solvents, cooking, cosmetics, solvents Metabolic activit or, cleaning products Tobacco smoke Fungicides, in paints, Spills in dental- care facilities or laboratories, thermometer breakage Consumer products Infections House dust, animal dander
\ 22 The third group of pollutants contains those whose sources are pre$:i~inantly indoor. To this third group we may add pollutants whose concentrations are high enough only indoors to warrant concern for their effects. These pollutants are either generated by the occupants or associated with building materials, appliances, machines, condor products, or art and craft materials. They include radon, formaldehyde, other organic substances from ~ variety of materials, asbestos and other f ibers, odors, molds, and the numerous compounds identified in tobacco smoke. Greater attention recently has been drawn to the third group of indoor pollutants. There have been reports of complaints about formaldehyde indoors after application of urea-formaldehyde foam insulation and particleboard and the installation of furnishings. Higher formaldehyde concentrations in European homes were reported in the early seventies. Radon and its progeny have been found in high concentrations in.hooes built on land reclaimed from phosphate mining and in other areas . Building materials, concrete, granite, and groundwater enriched in uranium are the apparent sources of radon. A plaster-resin material containing 10-308 asbestos has been used for fireproofing, acoustics, and , in some cases, decorative purposes. Asbestos Concentrations above U.S. occupational concentrations occasionally have been found indoors. The three general groups of contaminants found indoors are listed in Table I-1. Those in groups II and III are the prime focus of this report. Chapter TV discusses their sources and concentrations, and Chapter V, factors that af feet indoor concentrations and personal exposures. The current understanding is reported with an illustrative but not exhaustive review of pertinent related work. Those two chapters discuss the relationships among sources, personal activity patterns, building factors, and ventilation that influence indoor concentrations and individual pollutant exposure. Temperature, light, and especially relative humidity also help to determine concentrations, chemical activity, and effects. Measurement of these effects to the point of predicting the ramifications of altering ventilation or introducing new products is not possible for all pollutants of interest, and i"` many cases the measurements have not been made. For other pollutants, the data will not be available until instruments are developed. For still others, the sources may-be known, but their prevalence and d$atribut$on in buildings are not known. Table I-2 summarizes some typical pollutant concentrations found in the indoor environment and compares them with outdoor concentrations. An $ndoor-to~outdoor ratio greater than ~ does not imply that hazardous concentrations occur $ndoore. This table shows that high concentrations of some pollutants have been reported in a variety of buildings that are commonly used during normal daily activities. Water vapor is not reported in Table I-2 as ~ contaminant, but it is very important in the indoor environment. At low relative humidities, odors, particles, and such vapors as acrolein may be more irritating. Bigher relative humidities favor mold and mite growth.
23 TABLE I-2 Sources, Possible Concentrations, and Indoor-to-Outdoor Concentration Ratios of Some Indoor Pollutants I/O Con- Sources of Possible Indoor centration Pollutant Indoor Pollution Concentrationa Ratio Location Carbon monoxide Combustion equip 100 ppm >>1 Skating rinks, went, engines, off ices ~ homes faulty heating cars, shops SySt~ Respirable Stoves, fire- 100-5001lg/m3 >>1 Homes, offices, particles places, cigar- cars, public ettes, conden- facilities, bars g sation of restaurants volatiles, aerosol sprays, resuspens ion, cooking Organic vapors Combustion, NA >1 Homes, res tau- solvents, resin rants, public products, pesti- facilities, cides, aerosol of f ices, hospitals sprays Nitrogen dioxide Combustion, gas 200~1, 000 ug/m3 >>1 Homes, skating stoves, water rinks heaters, dryers, cigarettes, engines Sulfur dioxide Heating system 20 ug/m3 <1 Removal inside Total suspended Combustion, re- 100 Pg/m3 1 Homes, offices, particles with- suspension, transportation, out smoking heating system restaurants Sulfate Matches, gas 5 1lg/m3 a Removal inside stoves Formaldehyde Insulation, pro- 0.05~1.0 ppm >1 Homes, offices duct binders, particleboard Radon and Building 0.1-30 nCi/m3 >>1 Homes, buildings progeny materials, groundwa ter, soil
24 Table I-2 (coned) 1/0 Con- Sources of Possible Indoor centration Pollutant Indoor Polluelon Concentrationa Ratio Location Asbestos Fireproofing a fiber/cc 1 Homes, schools, offices Mineral and Products, MA - Homes, achoola, synthetic fibers cloth' rugs, offices wallboard Carbon dioxide Combnat$on, 3,000 pp. >>1 Homes, schools, humans, pets offices Viable organ- Humans, pets, NA >l Homes, hospitals isme rodents, insects, schools, offices plants, fungi, public facilitie humidifiers, air conditioners Ozone Electric arcing, 20 ppb <l Airplanes W light sources 200 ppb >l Offices aConcentrationa listed are only illustrative of those reported indoors. Both higher and lower concentrations have been measured. No averaging times are given. HA, not appropriate to list a concentration.
as greater formaldehyde release from particleboard, and deterioration of many materials. Exposure of some member. of the population to many of these pollutants may be determined by the frequency and duration of acting ities that place them in particular buildings. Hence, knowing use and activity pattern. of the population and how these patterns change with age, sex, socioeconomic status, race, and geographic region is important, if we are to assess the population exposure to pollutants. Seven classes of environmental factors with indoor sources have been identified as having substantial known or reasonably likely effects on human health: sidestream cigarette smoke, radon and radon progeny, mineral and vitreous fibers, formaldehyde, products of indoor combustion, agent. of contagion and allergy, and extremes of temperature and hu,eidi~cy. Chapter VII presents the evidence on health effects of the seven classes of indoor environmental factors. The seven classes were identif fed as particularly relevant to indoor exposures of the genere1 population. For other contaminants that may represent spects1 concerns for particular indoor locations--such as exposures to organic compound" found in pesticides, cleaning products, varnishes, or craft and hobby produc~cs--the reader is referred to the~literature developed by the National Institute of Occupational Safety and Bealth, the Environmental Protection Agency (Office of Toxic Subetances), the Consumer Product Safety Commission, the Food and Drug Administration, and the National Center for Toxicological Research. In the cane of other compounds that easy be in products found in hogans or institutional buildings, not enough is known about their concentrations or their effects to evaluate their health effects. Although this report does not recommend specif ic standards for the indoor environment, it discusses standards that have already been established for the outdoor, indoor working, and indoor public environments. It is clear that there is ~ divergence of opinion in the national and international health and regulatory communities as to what constitutes a safe exposure to contaminants and which contaminants are hazardous. Comparison with reported indoor concentrations makes it evident that - by some established ambient, occupational, or indoor standards--current exposures to some contaminants indoors could constitute a health risk to occupants. A full risk assessment of these pollutants that would identify the population exposed and assign a health-damage function aimed at determining current and projected health consequences of indoor pollution has not been attempted. In many instances, the review of health-effects literature on specific pollutants produces conclusions that are similar. At higher concentrations, these pollutants have known carcinogenic, allergenic, respiratory, or other physiologic effects. However, except for some contaminants that cause irritation, the evidence of direct or important health damage at reported concentrations is not well established. The evidence in some cases--as in passive smoking and the use of gas appliances--is ~ statistical association between a health response and the source. For
26 other indoor contaminants, such as radon and asbestos, the direct health effects have been demonstrated in experimental animals and in occupational studies. And for still others, such as formaldehyde, information is from experi~nta1 conditions and anecdotal reports of complaints. That these noncriteris pollutants do or will cause harm through current or projected exposures of the general public has not been de~onstra ted by epidemiologic studies. Indeed, direct evidence from epidemiologic studies may not be forthcoming; epidemiologic studies would be compromised from the outset by uncertainties in indoor pollution concentrations and personal exposure. Nevertheless, If there is consistency of toxicologic and occupational evidence of the harmful nature of specific pollutants at the reported indoor concentrations, then there is reason for serious concern. In the absence of ~ confirmed dose-response relationship, careful judgment is required. We should cautiously consider secondary consequences of conservation strategies to the indoor environment. Some pollutants may exert effects only at concentrations above ~ thre~bold; others may have no threshold. There may be synergism between pollutants or between pollutants and temperature, humidity, or disease organisms. Some pollutants may manifest effects subtly in behavioral changes. Others may have long latent periods between exposure and effects. In view of the uncertainty in the myriad potential outcomes, one fundamental relationship is clear: if, either deliberately or inadvertently, we systematically modify indoor environments by reducing ventilation or by increasing sources of indoor contaminants without meliorating efforts, we will be increasing the population exposure to pollutants of indoor origin. A redid of indoor pollutant concentrations and possible health significant would not be complete without a discussion of the implications of these exposures for epidemiologic studies of ambient-air pollution. Several sube~nces generated indoors are present in both indoor and outdoor air, including carbon monoxide, nitric oxide, nitrogen dioxide, and particulate otter. Recent investigations have confirmed that personal exposures to nitrogen dioxide and Despicable particles are not well represented by ambient measurement if there are substantial indoor sources. For pollutants of outdoor origin, the evidence indicates that personal and indoor exposures are lest severe than outdoor exposures. These obeervations have implications for epidemiologic studies attempting to establish ~ relationship between --hient concentrations and health responses. Air-pollution epidemiology attempts to establish a statistical relationship between the dependent health variable and the independent variable of pollution exposure. correcting for ocher influentis1 variables, such as age, sex, smoking, occupation, and socioeconomic factors. The air-pollution erasure most often chosen ts derived from ambient monitoring appropriate to the study population. Leaving aside the question of spatial representation, consider the potential misclassification of exposure that may result from indoor pollution. Depending on study design and pollutant investigated, the results could overestimate, underestimate, or simply incorrectly estimate the relationship between sir-pollution
27 exposure and health. Table I-3 illustrates by examples the potential bias imposed by indoor air pollution. The effects on the study can reflect ~ systematic bias or a random bias in exposure. Regardless of whether the pollutant is primarily outdoor or both indoor and outdoor in origin, the effects of a random misclassification of population exposure are the same. It tends to reduce the statistical power of the association. The imprecision in air-pollution health-effects cats may be due in part to indoor air-pollution concentrations. Indoor air-pollution exposures may sufficiently complicate epidemiologic investigations of the effects of outdoor pollutants so that assessments of indoor exposures, and thus larger study populations, will be needed to discern effects. In Chapter vIII, the objective is to discuss the welfare effects of contaminants in existing enclosures of all general types and the impact of energy-conservation measurer on indoor environmental quality. The effects on human comfort and productivity are presented in separate sections, and the effects of contaminants causing soiling In another section. Chapter IX discusses some of the relevant ventilation codes and standards. (Appendix A lists national primary ambient-air quality standards and occupational-safety and -health standards.) The effects of air-cleaning equipment and air diffusion control are also in separate sections, followed by a general discussion on the strategies used for control of indoor pollutants. In an effort to exemplify this complex interaction of choices, Appendix B presents some hypothetical assumptions for a residence.
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