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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
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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.
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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
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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
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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
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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 III—Sources 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
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\
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.
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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
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Representative terms from entire chapter:
indoor pollutants
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
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.
28
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