We reported previously that Gts1p regulates oscillations of heat resistance in concert with those of energy metabolism in continuous cultures of the yeast Saccharomyces cerevisiae by inducing fluctuations in the levels of trehalose, but not in those of Hsp104 (heat shock protein 104). Further, the expression of TPS1, encoding trehalose-6-phosphate synthase 1, and HSP104 was activated by Gts1p in combination with Snf1 kinase, a transcriptional activator of glucose-repressible genes, in batch cultures under derepressed conditions. Here we show that, in continuous cultures, the mRNA level of TPS1 increased 6-fold in the early respiro–fermentative phase, while that of HSP104 did not change. The expression of SUC2, a representative glucose-repressible gene encoding invertase, also fluctuated, suggesting the involvement of the Snf1 kinase in the periodic activation of these genes. However, this possibility was proven to be unlikely, since the oscillations in both TPS1 and SUC2 mRNA expression were reduced by approx. 3-fold during the transient oscillation in gts1Δ (GTS1-deleted) cells, in which the energy state determined by extracellular glucose and intracellular adenine nucleotide levels was comparable with that in wild-type cells. Furthermore, neither the mRNA level nor the phosphorylation status of Snf1p changed significantly during the oscillation. Thus we suggest that Gts1p plays a major role in the oscillatory expression of TPS1 and SUC2 in continuous cultures of Saccharomyces cerevisiae, and hypothesized that Gts1p stabilizes oscillations in energy metabolism by activating trehalose synthesis to facilitate glycolysis at the shift from the respiratory to the respiro–fermentative phase.
- Snf1 kinase
- transcriptional activator
- ultradian oscillation
Abbreviations: AMPK, AMP-activated protein kinase; DR, dilution rate; DO, dissolved oxygen; Hsp104, heat shock protein 104
- The Biochemical Society, London
INDOOR AIR QUALITY: INTRODUCTION
The connection between the use of a building either as a workplace or as a dwelling and the appearance, in certain cases, of discomfort and symptoms that may be the very definition of an illness is a fact that can no longer be disputed. The main culprit is contamination of various kinds within the building, and this contamination is usually referred to as �poor quality of indoor air�. The adverse effects due to poor air quality in closed spaces affect a considerable number of people, since it has been shown that urban dwellers spend between 58 and 78% of their time in an indoor environment which is contaminated to a greater or lesser degree. These problems have increased with the construction of buildings that are designed to be more airtight and that recycle air with a smaller proportion of new air from the outside in order to be more energy efficient. The fact that buildings that do not offer natural ventilation present risks of exposure to contaminants is now generally accepted.
The term indoor air is usually applied to nonindustrial indoor environments: office buildings, public buildings (schools, hospitals, theatres, restaurants, etc.) and private dwellings. Concentrations of contaminants in the indoor air of these structures are usually of the same order as those commonly found in outdoor air, and are much lower than those found in air in industrial premises, where relatively well-known standards are applied in order to assess air quality. Even so, many building occupants complain of the quality of the air they breathe and there is therefore a need to investigate the situation. Indoor air quality began to be referred to as a problem at the end of the 1960s, although the first studies did not appear until some ten years later.
Although it would seem logical to think that good air quality is based on the presence in the air of the necessary components in suitable proportions, in reality it is the user, through respiration, who is the best judge of its quality. This is because inhaled air is perceived perfectly through the senses, as human beings are sensitive to the olfactory and irritant effects of about half a million chemical compounds. Consequently, if the occupants of a building are as a whole satisfied with the air, it is said to be of high quality; if they are unsatisfied, it is of poor quality. Does this mean that it is possible to predict on the basis of its composition how the air will be perceived? Yes, but only in part. This method works well in industrial environments, where specific chemical compounds related to production are known, and their concentrations in the air are measured and compared with threshold limit values. But in nonindustrial buildings where there may be thousands of chemical substances in the air but in such low concentrations that they are, perhaps, thousands of times less than the limits set for industrial environments, the situation is different. In most of these cases information about the chemical composition of indoor air does not allow us to predict how the air will be perceived, since the combined effect of thousands of these contaminants, together with temperature and humidity, can produce air that is perceived as irritating, foul, or stalethat is, of poor quality. The situation is comparable to what happens with the detailed composition of an item of food and its taste: chemical analysis is inadequate to predict whether the food will taste good or bad. For this reason, when a ventilation system and its regular maintenance are being planned, an exhaustive chemical analysis of indoor air is rarely called for.
Another point of view is that people are considered the only sources of contamination in indoor air. This would certainly be true if we were dealing with building materials, furniture and ventilation systems as they were used 50 years ago, when bricks, wood and steel predominated. But with modern materials the situation has changed. All materials contaminate, some a little and others much, and together they contribute to a deterioration in the quality of indoor air.
The changes in a person�s health due to poor indoor air quality can show up as a wide array of acute and chronic symptoms and in the form of a number of specific illnesses. These are illustrated in figure 44.1 . Although poor indoor air quality results in fully developed illness in only a few cases, it can give rise to malaise, stress, absenteeism and loss of productivity (with concomitant increases in production costs); and allegations about problems related to the building can develop rapidly into conflict between the occupants, their employers and the owners of the buildings.
Figure 44.1 Symptoms and illnesses related to the quality of indoor air
Normally it is difficult to establish precisely to what extent poor indoor air quality can harm health, since not enough information is available concerning the relationship between exposure and effect at the concentrations in which the contaminants are usually found. Hence, there is a need to take information obtained at high dosesas with exposures in industrial settingsand extrapolate to much lower doses with a corresponding margin of error. In addition, for many contaminants present in the air, the effects of acute exposure are well known, whereas there are considerable gaps in the data regarding both long-term exposures at low concentrations and mixtures of different contaminants. The concepts of no-effect-level (NOEL), harmful effect and tolerable effect, already confusing even in the sphere of industrial toxicology, are here even more difficult to define. There are few conclusive studies on the subject, whether relating to public buildings and offices or private dwellings.
Series of standards for outdoor air quality exist and are relied on to protect the general population. They have been obtained by measuring adverse effects on health resulting from exposure to contaminants in the environment. These standards are therefore useful as general guidelines for an acceptable quality of indoor air, as is the case with those proposed by the World Health Organization. Technical criteria such as the threshold limit value of the American Conference of Governmental Industrial Hygienists (ACGIH) in the United States and the limit values legally established for industrial environments in different countries have been set for the working, adult population and for specific lengths of exposure, and cannot therefore be applied directly to the general population. The American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) in the United States has developed a series of standards and recommendations that are widely used in assessing indoor air quality.
Another aspect that should be considered as part of the quality of indoor air is its smell, because smell is often the parameter that ends up being the defining factor. The combination of a certain smell with the slight irritating effect of a compound in indoor air can lead us to define its quality as �fresh� and �clean� or as �stale� and �polluted�. Smell is therefore very important when defining the quality of indoor air. While odours objectively depend on the presence of compounds in quantities above their olfactory thresholds, they are very often evaluated from a strictly subjective point of view. It should also be kept in mind that the perception of an odour may result from the smells of many different compounds and that temperature and humidity may also affect its characteristics. From the standpoint of perception there are four characteristics that allow us to define and measure odours: intensity, quality, tolerability and threshold. When considering indoor air, however, it is very difficult to �measure� odours from a chemical standpoint. For that reason the tendency is to eliminate odours that are �bad� and to use, in their place, those considered good in order to give air a pleasant quality. The attempt to mask bad odours with good ones usually ends in failure, because odours of very different qualities can be recognized separately and lead to unforeseeable results.
A phenomenon known as sick building syndrome occurs when more than 20% of the occupants of a building complain about air quality or have definite symptoms. It is evidenced by a variety of physical and environmental problems associated with non-industrial indoor environments. The most common features seen in cases of sick building syndrome are the following: those affected complain of non-specific symptoms similar to the common cold or respiratory illnesses; the buildings are efficient as regards energy conservation and are of modern design and construction or recently remodelled with new materials; and the occupants cannot control the temperature, humidity and illumination of the workplace.
The estimated percentage distribution of the most common causes of sick building syndrome are inadequate ventilation due to lack of maintenance; poor distribution and insufficient intake of fresh air (50 to 52%); contamination generated indoors, including from office machines, tobacco smoke and cleaning products (17 to 19%); contamination from the outside of the building due to inadequate placement of air intake and exhaust vents (11%); microbiological contamination from stagnant water in the ducts of the ventilation system, humidifiers and refrigeration towers (5%); and formaldehyde and other organic compounds emitted by building and decoration materials (3 to 4%). Thus, ventilation is cited as an important contributory factor in the majority of cases.
Another question of a different nature is that of building-related illnesses, which are less frequent, but often more serious, and are accompanied by very definite clinical signs and clear laboratory findings. Examples of building-related illnesses are hypersensitivity pneumonitis, humidifier fever, legionellosis and Pontiac fever. A fairly general opinion among investigators is that these conditions should be considered separately from sick building syndrome.
Studies have been done to ascertain both the causes of air quality problems and their possible solutions. In recent years, knowledge of the contaminants present in indoor air and the factors contributing to a decline in indoor air quality has increased considerably, although there is a long way to go. Studies carried out in the last 20 years have shown that the presence of contaminants in many indoor environments is higher than anticipated, and moreover, different contaminants have been identified from those that exist in outside air. This contradicts the assumption that indoor environments without industrial activity are relatively free of contaminants and that in the worst of cases they may reflect the composition of outside air. Contaminants such as radon and formaldehyde are identified almost exclusively in the indoor environment.
Indoor air quality, including that of dwellings, has become a question of environmental health in the same way as has happened with control of outdoor air quality and exposure at work. Although, as already mentioned, an urban person spends 58 to 78% of his or her time indoors, it should be remembered that the most susceptible persons, namely the elderly, small children and the sick, are the ones who spend most of their time indoors. This subject began to be particularly topical from around 1973 onwards, when, because of the energy crisis, efforts directed at energy conservation concentrated on reducing the entry of outside air into indoor spaces as much as possible in order to minimize the cost of heating and cooling buildings. Although not all the problems relating to indoor air quality are the result of actions aimed at saving energy, it is a fact that as this policy spread, complaints about indoor air quality began to increase, and all the problems appeared.
Another item requiring attention is the presence of micro-organisms in indoor air which can cause problems of both an infectious and an allergic nature. It should not be forgotten that micro-organisms are a normal and essential component of ecosystems. For example, saprophytic bacteria and fungi, which obtain their nutrition from dead organic material in the environment, are found normally in the soil and atmosphere, and their presence can also be detected indoors. In recent years problems of biological contamination in indoor environments have received considerable attention.
The outbreak of Legionnaire�s disease in 1976 is the most discussed case of an illness caused by a micro-organism in the indoor environment. Other infectious agents, such as viruses that can cause acute respiratory illness, are detectable in indoor environments, especially if the occupation density is high and much recirculation of air is taking place. In fact, the extent to which micro-organisms or their components are implicated in the outbreak of building-associated conditions is not known. Protocols for demonstrating and analysing many types of microbial agents have been developed only to a limited degree, and in those cases where they are available, the interpretation of the results is sometimes inconsistent.
Aspects of the Ventilation System
Indoor air quality in a building is a function of a series of variables which include the quality of the outdoor air, the design of the ventilation and air-conditioning system, the conditions in which this system operates and is serviced, the compartmentalization of the building and the presence of indoor sources of contaminants and their magnitude. (See figure 44.2.) By way of summary it may be noted that the most common defects are the result of inadequate ventilation, contamination generated indoors and contamination coming from outside.
Figure 44.2 Diagram of building showing sources of indoor and outdoor pollution
Regarding the first of these problems, causes of inadequate ventilation can include: an insufficient supply of fresh air due to a high level of recirculation of the air or a low volume of intake; incorrect placement and orientation in the building of intake points for outside air; poor distribution and consequently incomplete mixing with the air of the premises, which can produce stratification, unventilated zones, unforeseen pressure differences giving rise to unwanted air currents and continuous changes in the thermohygrometric characteristics noticeable as one moves about the buildingand incorrect filtration of the air because of lack of maintenance or inadequate design of the filtering systema deficiency which is particularly serious where the outdoor air is of poor quality or where there is a high level of recirculation.
Origins of Contaminants
Indoor contamination has different origins: the occupants themselves; inadequate materials or materials with technical defects used in the construction of the building; the work performed within; excessive or improper use of normal products (pesticides, disinfectants, products used for cleaning and polishing); combustion gases (from smoking, kitchens, cafeterias and laboratories); and cross-contamination coming from other poorly ventilated zones which then diffuses towards neighbouring areas and affects them. It should be borne in mind that substances emitted in indoor air have much less opportunity of being diluted than those emitted in outdoor air, given the difference in the volumes of air available. As regards biological contamination, its origin is most frequently due to the presence of stagnant water, materials impregnated with water, exhausts and so on, and to defective maintenance of humidifiers and refrigeration towers.
Finally, contamination coming from outside must also be considered. As regards human activity, three main sources may be mentioned: combustion in stationary sources (power stations); combustion in moving sources (vehicles); and industrial processes. The five main contaminants emitted by these sources are carbon monoxide, oxides of sulphur, oxides of nitrogen, volatile organic compounds (including hydrocarbons), polycyclic aromatic hydrocarbons and particles. Internal combustion in vehicles is the principal source of carbon monoxide and hydrocarbons and is an important source of oxides of nitrogen. Combustion in stationary sources is the main origin of oxides of sulphur. Industrial processes and stationary sources of combustion generate more than half of the particles emitted into the air by human activity, and industrial processes can be a source of volatile organic compounds. There are also contaminants generated naturally that are propelled through the air, such as particles of volcanic dust, soil and sea salt, and spores and micro-organisms. The composition of outdoor air varies from place to place, depending both on the presence and the nature of the sources of contamination in the vicinity and on the direction of the prevailing wind. If there are no sources generating contaminants, the concentration of certain contaminants that will typically be found in �clean� outdoor air are as follows: carbon dioxide, 320 ppm; ozone, 0.02 ppm: carbon monoxide, 0.12 ppm; nitric oxide, 0.003 ppm; and nitrogen dioxide, 0.001 ppm. However, urban air always contains much higher concentrations of these contaminants.
Apart from the presence of the contaminants originating from outside, it sometimes happens that contaminated air from the building itself is expelled to the exterior and then returns inside again through the intakes of the air-conditioning system. Another possible way by which contaminants may enter from the exterior is by infiltration through the foundations of the building (e.g., radon, fuel vapours, sewer effluvia, fertilizers, insecticides and disinfectants). It has been shown that when the concentration of a contaminant in the outdoor air increases, its concentration in the air inside the building also increases, although more slowly (a corresponding relationship obtains when the concentration decreases); it is therefore said that buildings exert a shielding effect against external contaminants. However, the indoor environment is not, of course, an exact reflection of the conditions outside.
Contaminants present in indoor air are diluted in the outdoor air that enters the building and they accompany it when it leaves. When the concentration of a contaminant is less in the outdoor air than the indoor air, the interchange of indoor and outdoor air will result in a reduction in the concentration of the contaminant in the air inside the building. If a contaminant originates from outside and not inside, this interchange will result in a rise in its indoor concentration, as mentioned above.
Models for the balance of amounts of contaminants in indoor air are based on the calculation of their accumulation, in units of mass versus time, from the difference between the quantity that enters plus what is generated indoors, and what leaves with the air plus what is eliminated by other means. If appropriate values are available for each of the factors in the equation, the indoor concentration can be estimated for a wide range of conditions. Use of this technique makes possible the comparison of different alternatives for controlling an indoor contamination problem.
Buildings with low interchange rates with outdoor air are classified as sealed or energy-efficient. They are energy-efficient because less cold air enters in winter, reducing the energy required to heat the air to the ambient temperature, thus cutting the cost of heating. When the weather is hot, less energy is also used to cool the air. If the building does not have this property, it is ventilated through open doors and windows by a process of natural ventilation. Although they may be closed, differences of pressure, resulting both from the wind and from the thermal gradient existing between the interior and the exterior, force the air to enter through crevices and cracks, window and door joints, chimneys and other apertures, giving rise to what is called ventilation by infiltration.
The ventilation of a building is measured in renewals per hour. One renewal per hour means that a volume of air equal to the volume of the building enters from outside every hour; in the same way, an equal volume of indoor air is expelled to the exterior every hour. If there is no forced ventilation (with a ventilator) this value is difficult to determine, although it is considered to vary between 0.2 and 2.0 renewals per hour. If the other parameters are assumed to be unchanged, the concentration of contaminants generated indoors will be less in buildings with high renewal values, although a high renewal value is not a complete guarantee of indoor air quality. Except in areas with marked atmospheric pollution, buildings that are more open will have a lower concentration of contaminants in the indoor air than those constructed in a more closed manner. However, buildings that are more open are less energy-efficient. The conflict between energy efficiency and air quality is of great importance.
Much action undertaken to reduce energy costs affects indoor air quality to a greater or lesser extent. In addition to reducing the speed with which the air circulates within the building, efforts to increase the insulation and waterproofing of the building involve the installation of materials that may be sources of indoor contamination. Other action, such as supplementing old and frequently inefficient central heating systems with secondary sources that heat or consume the indoor air can also raise contaminant levels in indoor air.
Contaminants whose presence in indoor air is most frequently mentioned, apart from those coming from outside, include metals, asbestos and other fibrous materials, formaldehyde, ozone, pesticides and organic compounds in general, radon, house dust and biological aerosols. Together with these, a wide variety of types of micro-organisms can be found, such as fungi, bacteria, viruses and protozoa. Of these, the saprophytic fungi and bacteria are relatively well known, probably because a technology is available for measuring them in air. The same is not true of agents such as viruses, rickettsiae, chlamydias, protozoa and many pathogenic fungi and bacteria, for the demonstration and counting of which no methodology is as yet available. Among the infectious agents, special mention should be made of: Legionella pneumophila, Mycobacterium avium, viruses, Coxiella burnetii and Histoplasma capsulatum; and among the allergens: Cladosporium, Penicillium and Cytophaga.
Investigating Indoor Air Quality
Experience so far suggests that the traditional techniques used in industrial hygiene and heating, ventilation and air-conditioning do not always provide satisfactory results at present for solving the ever more common problems of indoor air quality, although basic knowledge of these techniques permits good approximations for dealing with or reducing problems rapidly and inexpensively. The solution to problems of indoor air quality often requires, in addition to one or more experts in heating, ventilation and air-conditioning and industrial hygiene, specialists in indoor air quality control, analytical chemistry, toxicology, environmental medicine, microbiology, and also epidemiology and psychology.
When a study is carried out on indoor air quality, the objectives set for it will profoundly affect its design and the activities directed at sampling and evaluation, since in some cases procedures giving a rapid response will be required, while in others overall values will be of interest. The duration of the programme will be dictated by the time required to obtain representative samples, and will also depend on the season and on meteorological conditions. If the aim is to carry out an exposure-effect study, in addition to long-term and short-term samples for evaluating peaks, personal samples will be required for ascertaining the direct exposure of individuals.
For some contaminants, well-validated and widely used methods are available, but for the majority this is not the case. Techniques for measuring levels of many contaminants found indoors are normally derived from applications in industrial hygiene but, given that the concentrations of interest in indoor air are usually much lower than those occurring in industrial environments, these methods are frequently inappropriate. As for the measurement methods used in atmospheric contamination, they operate with margins of similar concentrations, but are available for relatively few contaminants and present difficulties in indoor use, such as would arise, for example, with a high-volume sampler for determining particulate matter, which on the one hand would be too noisy and on the other could modify the quality of the indoor air itself.
The determination of contaminants in indoor air is usually carried out by using different procedures: with continuous monitors, whole-time active samplers, whole-time passive samplers, direct sampling and personal samplers. Adequate procedures exist at present for measuring levels of formaldehyde, oxides of carbon and nitrogen, volatile organic compounds and radon, among others. Biological contaminants are measured using techniques of sedimentation on open culture plates or, more frequently nowadays, by using active systems that cause the air to impact on plates containing nutrient, which are subsequently cultured, the quantity of micro-organisms present being expressed in colony-forming units per cubic metre.
When a problem of indoor air quality is being investigated, it is usual to design beforehand a practical strategy consisting of an approximation in phases. This approximation begins with a first phase, the initial investigation, which can be carried out using industrial hygiene techniques. It must be structured so that the investigator does not need to be a specialist in the field of indoor air quality in order to carry out his work. A general inspection of the building is undertaken and its installations are checked, particularly as regards the regulation and adequate functioning of the heating, ventilation and air-conditioning system, according to the standards set at the time of its installation. It is important in this respect to consider whether the persons affected are able to modify the conditions of their surroundings. If the building does not have systems of forced ventilation, the degree of effectiveness of the existing natural ventilation must be studied. If after revisionand adjustment if necessarythe operational conditions of the ventilation systems are adequate for the standards, and if despite this the complaints continue, a technical investigation of a general kind will have to ensue to determine the degree and nature of the problem. This initial investigation should also allow an assessment to be made as to whether the problems can be considered solely from the functional point of view of the building, or whether the intervention of specialists in hygiene, psychology or other disciplines will be necessary.
If the problem is not identified and resolved in this first phase, other phases can follow involving more specialized investigations concentrating on potential problems identified in the first phase. The subsequent investigations may include a more detailed analysis of the heating, ventilation and air-conditioning system of the building, a more extensive evaluation of the presence of materials suspected of emitting gases and particles, a detailed chemical analysis of the ambient air in the building and medical or epidemiological assessments to detect signs of disease.
As regards the heating, ventilation and air-conditioning system, the refrigeration equipment should be checked in order to ensure that there is no microbial growth in them or accumulation of water in their drip trays, the ventilation units must be checked to see that they are functioning correctly, the air intake and return systems must be examined at various points to see that they are watertight, and the interior of a representative number of ducts must be checked to confirm the absence of micro-organisms. This last consideration is particularly important when humidifiers are used. These units require particularly careful programmes of maintenance, operation and inspection in order to prevent the growth of micro-organisms, which can propagate themselves throughout the air-conditioning system.
The options generally considered for improving indoor air quality in a building are the elimination of the source; its insulation or independent ventilation; separating the source from those who may be affected; general cleaning of the building; and increased checking and improvement of the heating, ventilation and air-conditioning system. This may require anything from modifications at particular points to a new design. The process is frequently of a repetitive nature, so that the study has to be started again several times, using more sophisticated techniques on each occasion. A more detailed description of control techniques will be found elsewhere in this Encyclopaedia.
Finally, it should be emphasized that, even with the most complete investigations of indoor air quality, it may be impossible to establish a clear relationship between the characteristics and composition of the indoor air and the health and comfort of the occupants of the building under study. Only the accumulation of experience on the one hand, and the rational design of ventilation, occupation and compartmentalization of buildings on the other, are possible guarantees from the outset of obtaining indoor air quality that is adequate for the majority of the occupants of a building.
NATURE AND SOURCES OF INDOOR CHEMICAL CONTAMINANTS
Characteristic Chemical Pollutants
Chemical contaminants of the indoor air can occur as gases and vapours (inorganic and organic) and particulates. Their presence in the indoor environment is the result of entry into the building from the outdoor environment or their generation within the building. The relative importance of these indoor and outdoor origins differs for different pollutants and may vary over time.
The major chemical pollutants commonly found in the indoor air are the following:
1. carbon dioxide (CO2), which is a metabolic product and often used as an indicator of the general level of air pollution related to the presence of humans indoors
2. carbon monoxide (CO), nitrogen oxides (NOx) and sulphur dioxide (SO2), which are inorganic combustion gases formed predominantly during the combustion of fuels and ozone (O3), which is a product of photochemical reactions in polluted atmospheres but may also be released by some indoor sources
3. organic compounds that originate from a variety of indoor sources and outdoors. Hundreds of organic chemicals occur in indoor air although most are present at very low concentrations. These can be grouped according to their boiling points and one widely used classification, shown in table 44.1 , identifies four groups of organic compounds: (1) very volatile organic compounds (VVOC); (2) volatile (VOC); (3) semi-volatile (SVOC); and (4) organic compounds associated with particulate matter (POM). Particle-phase organics are dissolved in or adsorbed on particulate matter. They may occur in both the vapour and particle phase depending on their volatility. For example, polyaromatic hydrocarbons (PAHs) consisting of two fused benzene rings (e.g., naphthalene) are found principally in the vapour phase and those consisting of five rings (e.g., benz(a)pyrene) are found predominantly in the particle phase.
Table 44.1 Classification of indoor organic pollutants
Boiling range (ºC)
Sampling methods typically used in field studies
Very volatile(gaseous) organic compounds
<0 to 50-100
Batch sampling; adsorption on charcoal
Volatile organic compounds
50-100 to 240-260
Adsorption on Tenax, carbon molecular black or charcoal
Semivolatile organic compounds
240-260 to 380-400
Adsorption on polyurethane foam or XAD-2
Organic compounds associated with particulate matter or particulate organic matter
An important characteristic of indoor air contaminants is that their concentrations vary both spatially and temporally to a greater extent than is common outdoors. This is due to the large variety of sources, the intermittent operation of some of the sources and the various sinks present.
Concentrations of contaminants that arise principally from combustion sources are subject to very large temporal variation and are intermittent. Episodic releases of volatile organic compounds due to human activities such as painting also lead to large variations in emission with time. Other emissions, such as formaldehyde release from wood-based products may vary with temperature and humidity fluctuations in the building, but the emission is continuous. The emission of organic chemicals from other materials may be less dependent upon temperature and humidity conditions but their concentrations in indoor air will be greatly influenced by ventilation conditions.
Spatial variations within a room tend to be less pronounced than temporal variations. Within a building there may be large differences in the case of localized sources, for example, photocopiers in a central office, gas cookers in the restaurant kitchen and tobacco smoking restricted to a designated area.
Sources within the Building
Elevated levels of pollutants generated by combustion, particularly nitrogen dioxide and carbon monoxide in indoor spaces, usually result from unvented, improperly vented or poorly maintained combustion appliances and the smoking of tobacco products. Unvented kerosene and gas space heaters emit significant quantities of CO, CO2, NOx, SO2, particulates and formaldehyde. Gas cooking stoves and ovens also release these products directly into the indoor air. Under normal operating conditions, vented gas-fired forced air heaters and water heaters should not release combustion products into the indoor air. However flue gas spillage and backdrafting can occur with faulty appliances when the room is depressurized by competing exhaust systems and under certain meteorological conditions.
Environmental tobacco smoke
Indoor air contamination from tobacco smoke results from sidestream and exhaled mainstream smoke, usually referred to as environmental tobacco smoke (ETS). Several thousand different constituents have been identified in tobacco smoke and the total quantities of individual components varies depending upon the type of cigarette and the conditions of smoke generation. The main chemicals associated with ETS are nicotine, nitrosamines, PAHs, CO, CO2, NOx, acrolein, formaldehyde and hydrogen cyanide.
Building materials and furnishings
The materials which have received greatest attention as sources of indoor air pollution have been wood-based boards containing urea formaldehyde (UF) resin and UF cavity wall insulation (UFFI). Emission of formaldehyde from these products results in elevated levels of formaldehyde in buildings and this has been associated with many complaints of poor indoor air quality in developed countries, particularly during the late 1970s and early 1980s. Table 44.2 gives examples of materials that release formaldehyde in buildings. These show that the highest emission rates may be associated with the wood-based products and UFFI which are products often used extensively in buildings. Particleboard is manufactured from fine (about 1 mm) wood particles which are mixed with UF resins (6 to 8 weight%) and pressed into wood panels. It is widely used for flooring, wall panelling, shelving and components of cabinets and furniture. The plies of hardwood are bonded with UF resin and are commonly used for decorative wall panelling and components of furniture. Medium-density fibreboard (MDF) contains finer wood particles than those used in particleboard and these are also bound with UF resin. MDF is most often used for furniture. The primary source of formaldehyde in all these products is the residual formaldehyde trapped in the resin as a result of its presence in excess needed for the reaction with urea during the manufacture of the resin. Release is therefore highest when the product is new, and declines at a rate dependent upon product thickness, initial emission strength, presence of other formaldehyde sources, local climate and occupant behaviour. The initial decline rate of emissions may be 50% over the first eight to nine months, followed by a much slower rate of decline. Secondary emission can occur due to hydrolysis of the UF resin and hence emission rates increase during periods of elevated temperature and humidity. Considerable efforts by manufacturers have led to the development of lower-emitting materials by use of lower ratios (i.e. closer to 1:1) of urea to formaldehyde for resin production and the use of formaldehyde scavengers. Regulation and consumer demand have resulted in widespread use of these products in some countries.
Table 44.2 Formaldehyde emission rates from a variety of construction material furnishings and consumer products
Range of formaldehyde emission rates (µg/m2/day)
Hardwood plywood panelling
Urea-formaldehyde foam insulation
Building materials and furnishings release a wide range of other VOCs which have been the subject of increasing concern during the 1980s and 1990s. The emission can be a complex mixture of individual compounds, though a few may be dominant. A study of 42 building materials identified 62 different chemical species. These VOCs were primarily aliphatic and aromatic hydrocarbons, their oxygen derivatives and terpenes. The compounds with the highest steady-state emission concentrations, in decreasing order, were toluene, m-xylene, terpene, n-butylacetate, n-butanol, n-hexane, p-xylene, ethoxyethylacetate, n-heptane and o-xylene. The complexity of emission has resulted in emissions and concentrations in air often being reported as the total volatile organic compound (TVOC) concentration or release. Table 44.3 gives examples of rates of TVOC emission for a range of building products. These show that significant differences in emissions exist between products, which means that if adequate data were available materials could be selected at the planning stage to minimize the VOC release in newly constructed buildings.
Table 44.3 Total volatile organic compound (TVOC) concentrations and emission rates associated with various floor and wall coverings and coatings
Type of material
Emission rate (mg/m2hr)
Vinyl and paper
Vinyl and glass fibres
Varnish, clear epoxy
Varnish, polyurethane, two-component
aPVC, polyvinyl chloride.
Wood preservatives have been shown to be a source of pentachlorophenol and lindane in the air and in dust within buildings. They are used primarily for timber protection for outdoor exposure and are also used in biocides applied for treatment of dry rot and insect control.
Consumer products and other indoor sources
The variety and number of consumer and household products change constantly, and their chemical emissions depend on use patterns. Products that may contribute to indoor VOC levels include aerosol products, personal hygiene products, solvents, adhesives and paints. Table 44.4 illustrates major chemical components in a range of consumer products.
Table 44.4 Components and emissions from consumer products and other sources of volatile organic compounds (VOC)
Cleaning agents and pesticides
Liquid floor wax
TVOC (trimethylpentene and dodecane isomers)
Paste leather wax
TVOC (pinene and 2-methyl- 1-propanol)
TVOC (limonene, pinene and myrcene)
Wet copy machine
Toluene, ethyl benzene
Dichloromethane, toluene, propane
1,1,1-Trichloroethane, pro- pane, petroleum distillates
2-Propanol, butanone, ethyl- benzene, toluene
Nonane, decane, ethyl- heptane, limonene
Other VOCs have been associated with other sources. Chloroform is introduced into the indoor air chiefly as a result of dispensing or heating tap water. Liquid process copiers release isodecanes into the air. Insecticides used to control cockroaches, termites, fleas, flies, ants and mites are widely used as sprays, fogging devices, powders, impregnated strips, bait and pet collars. Compounds include diazinon, paradichlorobenzene, pentachlorophenol, chlordane, malathion, naphthalene and aldrin.
Other sources include occupants (carbon dioxide and odours), office equipment (VOCs and ozone), mould growth (VOCs, ammonia, carbon dioxide), contaminated land (methane, VOCs) and electronic air cleaners and negative ion generators (ozone).
Contribution from the external environment
Table 44.5 shows typical indoor-outdoor ratios for the major types of pollutant that occur in indoor air and average concentrations measured in outdoor air of urban areas in the United Kingdom. Sulphur dioxide in the indoor air is normally of outdoor origin and results from both natural and anthropogenic sources. Combustion of fossil fuels containing sulphur and smelting of sulphide ores are major sources of sulphur dioxide in the troposphere. Background levels are very low (1 ppb) but in urban areas maximum hourly concentrations may be 0.1 to 0.5 ppm. Sulphur dioxide can enter a building in air used for ventilation and can infiltrate through small gaps in the building structure. This depends upon the airtightness of the building, meteorological conditions and internal temperatures. Once inside, the incoming air will mix and be diluted by the indoor air. Sulphur dioxide that comes into contact with building and furnishing materials is adsorbed and this can significantly reduce the indoor concentration with respect to the outdoors, particularly when outdoor sulphur dioxide levels are high.
Table 44.5 Major types of chemical indoor air contaminant and their concentrations in the urban United Kingdom
Substance/group of substances
Ratio of concentrations indoors/outdoors
Typical urban con- centrations
≤5-12 (indoor sources)
≤5-11 (indoor source)
Other organic compounds
0.5-1 (excluding ETSa) 2-10 (including ETS)
a ETS, environmental tobacco smoke.
Nitrogen oxides are a product of combustion, and major sources include automobile exhaust, fossil fuel-fired electric generating stations and home space heaters. Nitric oxide (NO) is relatively non-toxic but can be oxidized to nitrogen dioxide (NO2), particularly during episodes of photochemical pollution. Background concentrations of nitrogen dioxide are about 1 ppb but may reach 0.5 ppm in urban areas. The outdoors is the major source of nitrogen dioxide in buildings without unvented fuel appliances. As with sulphur dioxide, adsorption by internal surfaces reduces the concentration indoors compared with that outdoors.
Ozone is produced in the troposphere by photochemical reactions in polluted atmospheres, and its generation is a function of intensity of sunlight and concentration of nitrogen oxides, reactive hydrocarbons and carbon monoxide. At remote sites, background ozone concentrations are 10 to 20 ppb and can exceed 120 ppb in urban areas in summer months. Indoor concentrations are significantly lower due to reaction with indoor surfaces and the lack of strong sources.
Carbon monoxide release as a result of anthropogenic activities is estimated to account for 30% of that present in the atmosphere of the northern hemisphere. Background levels are approximately 0.19 ppm and in urban areas a diurnal pattern of concentrations is related to use of the motor vehicle with peak hourly levels ranging from 3 ppm to 50 to 60 ppm. It is a relatively unreactive substance and so is not depleted by reaction or adsorption on indoor surfaces. Indoor sources such as unvented fuel appliances therefore add to the background level otherwise due to the outdoor air.
The indoor-outdoor relationship of organic compounds is compound-specific and may vary over time. For compounds with strong indoor sources such as formaldehyde, indoor concentrations are usually dominant. For formaldehyde outdoor concentrations are typically below 0.005 mg/m3 and indoor concentrations are ten times higher than outdoor values. Other compounds such as benzene have strong outdoor sources, petrol-driven vehicles being of particular importance. Indoor sources of benzene include ETS and these result in mean concentrations in buildings in the United Kingdom being 1.3 times higher than those outdoors. The indoor environment appears not to be a significant sink for this compound and it is therefore not protective against benzene from outdoors.
Typical Concentrations in Buildings
Carbon monoxide concentrations in indoor environments commonly range from 1 to 5 ppm. Table 44.6 summarizes results reported in 25 studies. Concentrations are higher in the presence of environmental tobacco smoke, though it is exceptional for concentrations to exceed 15 ppm.
Table 44.6 Summary of field measurements of nitrogen oxides (NOx) and carbon monoxide (CO)
NOx values (ppb)
CO mean values (ppm)
Restaurants and cafeterias
Bars and taverns
aND = not detected.
Nitrogen dioxide concentrations indoors are typically 29 to 46 ppb. If particular sources such as gas stoves are present, concentrations may be significantly higher, and smoking can have a measurable effect (see table 44.6).
Many VOCs are present in the indoor environment at concentrations ranging from approximately 2 to 20 mg/m3. A US database containing 52,000 records on 71 chemicals in homes, public buildings and offices is summarized in figure 44.3 . Environments where heavy smoking and/or poor ventilation create high concentrations of ETS can produce VOC concentrations of 50 to 200 mg/m3. Building materials make a significant contribution to indoor concentrations and new homes are likely to have a greater number of compounds exceeding 100 mg/m3. Renovation and painting contribute to significantly higher VOC levels. Concentrations of compounds such as ethyl acetate, 1,1,1-trichloroethane and limonene can exceed 20 mg/m3 during occupant activities, and during residents� absence the concentration of a range of VOCs may decrease by about 50%. Specific cases of elevated concentrations of contaminants due to materials and furnishings being associated with occupant complaints have been described. These include white spirit from injected damp-proof courses, naphthalene from products containing coal tar, ethylhexanol from vinyl flooring and formaldehyde from wood-based products.
Figure 44.3 Daily indoor concentrations of selected compounds for indoor sites
The large number of individual VOCs occurring in buildings makes it difficult to detail concentrations for more than selected compounds. The concept of TVOC has been used as a measure of the mixture of compounds present. There is no widely used definition as to the range of compounds that the TVOC represents, but some investigators have proposed that limiting concentrations to below 300 mg/m3 should minimize complaints by occupants about indoor air quality.
Pesticides used indoors are of relatively low volatility and concentrations occur in the low microgram-per-cubic-metre range. The volatilized compounds can contaminate dust and all indoor surfaces because of their low vapour pressures and tendency to be adsorbed by indoor materials. PAH concentrations in air are also strongly influenced by their distribution between the gas and aerosol phases. Smoking by occupants can have a strong effect on indoor air concentrations. Concentrations of PAHs range typically range from 0.1 to 99 ng/m3.
Most of the radiation that a human being will be exposed to during a lifetime comes from natural sources in outer space or from materials present in the earth�s crust. Radioactive materials may affect the organism from without or, if inhaled or ingested with food, from within. The dose received may be very variable because it depends, on the one hand, on the amount of radioactive minerals present in the area of the world where the person liveswhich is related to the amount of radioactive nuclides in the air and the amount found both in food and especially in drinking waterand, on the other, on the use of certain construction materials and the use of gas or coal for fuel, as well as the type of construction employed and the traditional habits of people in the given locality.
Today, radon is considered the most prevalent source of natural radiation. Together with its �daughters�, or radionuclides formed by its disintegration, radon constitutes approximately three fourths of the effective equivalent dose to which humans are exposed due to natural terrestrial sources. The presence of radon is associated with an increase in the occurrence of lung cancer due to the deposition of radioactive substances in the bronchial region.
Radon is a colourless, odourless and tasteless gas seven times as heavy as air. Two isotopes occur most frequently. One is radon-222, a radionuclide present in the radioactive series from the disintegration of uranium-238; its main source in the environment is the rocks and the soil in which its predecessor, radium-226, occurs. The other is radon-220 from the thorium radioactive series, which has a lower incidence than radon-222.
Uranium occurs extensively in the earth�s crust. The median concentration of radium in soil is in the order of 25 Bq/kg. A Becquerel (Bq) is the unit of the international system and it represents a unit of radionuclide activity equivalent to one disintegration per second. The average concentration of radon gas in the atmosphere at the surface of the earth is 3 Bq/m3, with a range of 0.1 (over the oceans) to 10 Bq/m3. The level depends on the porousness of the soil, the local concentration of radium-226 and the atmospheric pressure. Given that the half-life of radon-222 is 3.823 days, most of the dosage is not caused by the gas but by radon daughters.
Radon is found in existing materials and flows from the earth everywhere. Because of its characteristics it disperses easily outdoors, but it has a tendency to become concentrated in enclosed spaces, notably in caves and buildings, and especially in lower spaces where its elimination is difficult without proper ventilation. In temperate regions, the concentrations of radon indoors are estimated to be in the order of eight times higher than the concentrations outdoors.
Exposure to radon by most of the population, therefore, occurs for the most part within buildings. The median concentrations of radon depend, basically, on the geological characteristics of the soil, on the construction materials used for the building and on the amount of ventilation it receives.
The main source of radon in indoor spaces is the radium present in the soil on which the building rests or the materials employed in its construction. Other significant sourceseven though their relative influence is much lessare outside air, water and natural gas. Figure 44.4 shows the contribution that each source makes to the total.
Figure 44.4 Sources of radon in the indoor environment
The most common construction materials, such as wood, bricks and cinder blocks, emit relatively little radon, in contrast to granite and pumice-stone. However, the main problems are caused by the use of natural materials such as alum slate in the production of construction materials. Another source of problems has been the use of by-products from the treatment of phosphate minerals, the use of by-products from the production of aluminium, the use of dross or slag from the treatment of iron ore in blast furnaces, and the use of ashes from the combustion of coal. In addition, in some instances, residues derived from uranium mining were also used in construction.
Radon can enter water and natural gas in the subsoil. The water used to supply a building, especially if it is from deep wells, may contain significant amounts of radon. If this water is used for cooking, boiling can free a large part of the radon it contains. If the water is consumed cold, the body eliminates the gas readily, so that drinking this water does not generally pose a significant risk. Burning natural gas in stoves without chimneys, in heaters and in other home appliances can also lead to an increase of radon in indoor spaces, especially dwellings. Sometimes the problem is more acute in bathrooms, because radon in water and in the natural gas used for the water heater accumulates if there is not enough ventilation.
Given that the possible effects of radon on the population at large were unknown just a few years ago, the data available on concentrations found in indoor spaces are limited to those countries which, because of their characteristics or special circumstances, are more sensitized to this problem. What is known for a fact is that it is possible to find concentrations in indoor spaces that are far above the concentrations found outdoors in the same region. In Helsinki (Finland), for instance, concentrations of radon in indoor air have been found that are five thousand times higher than the concentrations normally found outdoors. This may be due in large part to energy-saving measures that can noticeably favour the concentration of radon in indoor spaces, especially if they are heavily insulated. Buildings studied so far in different countries and regions show that the concentrations of radon found within them present a distribution that approximates the normal log. It is worth noting that a small number of the buildings in each region show concentrations ten times above the median. The reference values for radon in indoor spaces, and the remedial recommendations of various organizations are given in �Regulations, recommendations, guidelines and standards� in the chapter.
In conclusion, the main way to prevent exposures to radon is based on avoiding construction in areas that by their nature emit a greater amount of radon into the air. Where that is not possible, floors and walls should be properly sealed, and construction materials should not be used if they contain radioactive matter. Interior spaces, especially basements, should have an adequate amount of ventilation.
In 1985 the Surgeon General of the US Public Health Service reviewed the health consequences of smoking with regard to cancer and chronic lung disease in the workplace. It was concluded that for most US workers, cigarette smoking represents a greater cause of death and disability than their workplace environment. However, the control of smoking and a reduction of the exposure to hazardous agents at the workplace are essential, since these factors often act synergistically with smoking in the induction and development of respiratory diseases. Several occupational exposures are known to induce chronic bronchitis in workers. These include exposures to dust from coal, cement and grain, to silica aerosols, to vapours generated during welding, and to sulphur dioxide. Chronic bronchitis among workers in these occupations is often aggravated by cigarette smoking (US Surgeon General 1985).
Epidemiological data have clearly documented that uranium miners and asbestos workers who smoke cigarettes carry significantly higher risks of cancer of the respiratory tract than non-smokers in these occupations. The carcinogenic effect of uranium and asbestos and cigarette smoking is not merely additive, but synergistic in inducing squamous cell carcinoma of the lung (US Surgeon General 1985; Hoffmann and Wynder 1976; Saccomanno, Huth and Auerbach 1988; Hilt et al. 1985). The carcinogenic effects of exposure to nickel, arsenicals, chromate, chloromethyl ethers, and those of cigarette smoking are at least additive (US Surgeon General 1985; Hoffmann and Wynder 1976; IARC 1987a, Pershagen et al. 1981). One would assume that coke-oven workers who smoke have a higher risk of lung and kidney cancer than non-smoking coke-oven workers; however, we lack epidemiological data that substantiate this concept (IARC 1987c).
It is the aim of this overview to evaluate the toxic effects of the exposure of men and women to environmental tobacco smoke (ETS) at the workplace. Certainly, curtailing smoking at the workplace will benefit active smokers by reducing their consumption of cigarettes during the workday, thereby increasing the possibility that they become ex-smokers; but smoking cessation will also be of benefit to those non-smokers who are allergic to tobacco smoke or who have pre-existing lung or heart ailments.
Physico-Chemical Nature of Environmental Tobacco Smoke
Mainstream and sidestream smoke
ETS is defined as the material in indoor air that originates from tobacco smoke. Although pipe and cigar smoking contribute to ETS, cigarette smoke is generally the major source. ETS is a composite aerosol that is emitted primarily from the burning cone of a tobacco product between puffs. This emission is called sidestream smoke (SS). To a minor extent, ETS consists also of mainstream smoke (MS) constituents, that is, those that are exhaled by the smoker. Table 44.7 lists the ratios of major toxic and carcinogenic agents in the smoke that is inhaled, the mainstream smoke, and in the sidestream smoke (Hoffmann and Hecht 1990; Brunnemann and Hoffmann 1991; Guerin et al. 1992; Luceri et al. 1993). Under �Type of toxicity�, smoke components marked �C� represent animal carcinogens that are recognized by the International Agency for Research on Cancer (IARC). Among these are benzene, β-naphthylamine, 4-aminobiphenyl and polonium-210, which are also established human carcinogens (IARC 1987a; IARC 1988).
Table 44.7 Some toxic and tumorigenic agents in undiluted cigarette sidestream smoke
Type of toxicitya
Amount in sidestream smoke per cigarette
Ratio of side- stream to main- stream smoke
Nitrogen oxides (NOx)
aC=Carcinogenic; CoC=co-carcinogenic; T=toxic; TP=tumour promoter. bND=not detected. cNNN=N�-nitrosonornicotine. dNNK=4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone.
When filter cigarettes are being smoked, certain volatile and semi-volatile components are selectively removed from the MS by filter tips (Hoffmann and Hecht 1990). However, these compounds occur in far higher amounts in undiluted SS than in MS. Furthermore, those smoke components that are favoured to be formed during smouldering in the reducing atmosphere of the burning cone, are released into SS to a far greater extent than into MS. This includes groups of carcinogens like the volatile nitrosamines, tobacco-specific nitrosamines (TSNA) and aromatic amines.
ETS in indoor air
Although undiluted SS contains higher amounts of toxic and carcinogenic components than MS, the SS inhaled by non-smokers is highly diluted by air and its properties are altered because of the decay of certain reactive species. Table 44.8 lists reported data for toxic and carcinogenic agents in indoor air samples of various degrees of tobacco smoke pollution (Hoffmann and Hecht 1990; Brunnemann and Hoffmann 1991; Luceri et al. 1993). The air dilution of SS has a significant impact on the physical characteristics of this aerosol. In general, the distribution of various agents between vapour phase and particulate phase is changed in favour of the former. The particles in ETS are smaller (<0.2 µ) than those in MS (~0.3 µ) and the pH levels of SS (pH 6.8 - 8.0) and of ETS are higher than the pH of MS (5.8 - 6.2; Brunnemann and Hoffmann 1974). Consequently, 90 to 95% of nicotine is present in the vapour phase of ETS (Eudy et al. 1986). Similarly, other basic components such as the minor Nicotiana alkaloids, as well as amines and ammonia, are present mostly in the vapour phase of ETS (Hoffmann and Hecht 1990; Guerin et al. 1992).
Table 44.8 Some toxic and tumorigenic agents in indoor environments polluted by tobacco smoke
Bars, restaurants, offices
Cardroom with smokers
Cardroom with smokers
Cardroom with smokers
Cars with smokers
aNNN=N�-nitrosonornicotine. bND=not detected. cNNK=4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone.
Biomarkers of the Uptake of ETS by Non-Smokers
Although a significant number of non-smoking workers are exposed to ETS at the workplace, in restaurants, in their own homes or in other indoor places, it is hardly possible to estimate the actual uptake of ETS by an individual. ETS exposure can be more precisely determined by measuring specific smoke constituents or their metabolites in physiological fluids or in exhaled air. Although several parameters have been explored, such as CO in exhaled air, carboxyhaemoglobin in blood, thiocyanate (a metabolite of hydrogen cyanide) in saliva or urine, or hydroxyproline and N-nitrosoproline in urine, only three measures are actually helpful for estimating the uptake of ETS by non-smokers. They allow us to distinguish passive smoke exposure from that of active smokers and from non-smokers who have absolutely no exposure to tobacco smoke.
The most widely used biomarker for ETS exposure of non-smokers is cotinine, a major nicotine metabolite. It is determined by gas chromatography, or by radioimmunoassay in blood or preferably urine, and reflects the absorption of nicotine through the lung and oral cavity. A few millilitres of urine from passive smokers is sufficient to determine cotinine by either of the two methods. In general, a passive smoker has cotinine levels of 5 to 10 ng/ml of urine; however, higher values have occasionally been measured for non-smokers who were exposed to heavy ETS over a longer period. A dose response has been established between duration of ETS exposure and urinary cotinine excretion (table 44.9 , Wald et al. 1984). In most field studies, cotinine in the urine of passive smokers amounted to between 0.1 and 0.3% of the mean concentrations found in the urine of smokers; however, upon prolonged exposure to high concentrations of ETS, cotinine levels have corresponded to as much as 1% of the levels measured in the urine of active smokers (US National Research Council 1986; IARC 1987b; US Environmental Protection Agency 1992).
Table 44.9 Urinary cotinine in non-smokers according to the number of reported hours of exposure to other people�s tobacco smoke within the previous seven days
Duration of exposure
Urinary cotinine (mean ± SD) (ng/ml)a
aTrend with increasing exposure was significant (p<0.001).
Source: Based on Wald et al. 1984.
The human bladder carcinogen 4-aminobiphenyl, which transfers from tobacco smoke into ETS, has been detected as a haemoglobin adduct in passive smokers in concentrations up to 10% of the mean adduct level found in smokers (Hammond et al. 1993). Up to 1% of the mean levels of a metabolite of the nicotine-derived carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), which occurs in the urine of cigarette smokers, has been measured in the urine of non-smokers who had been exposed to high concentrations of SS in a test laboratory (Hecht et al. 1993). Although the latter biomarker method has not as yet been applied in field studies, it holds promise as a suitable indicator of the exposure of non-smokers to a tobacco-specific lung carcinogen.
Environmental Tobacco Smoke and Human Health
Disorders other than cancer
Prenatal exposure to MS and/or ETS and early postnatal exposure to ETS increase the probability of complications during viral respiratory infections in children during the first year of life.
The scientific literature contains several dozens of clinical reports from various countries, reporting that children of parents who smoke, especially children under the age of two years, show an excess of acute respiratory illness (US Environmental Protection Agency 1992; US Surgeon General 1986; Medina et al. 1988; Riedel et al. 1989). Several studies also described an increase of middle ear infections in children who had exposure to parental cigarette smoke. The increased prevalence of middle ear effusion attributable to ETS led to increased hospitalization of young children for surgical intervention (US Environmental Protection Agency 1992; US Surgeon General 1986).
In recent years, sufficient clinical evidence has led to the conclusion that passive smoking is associated with increased severity of asthma in those children who already have the disease, and that it most likely leads to new cases of asthma in children (US Environmental Protection Agency 1992).
In 1992, the US Environmental Protection Agency (1992) critically reviewed the studies on respiratory symptoms and lung functions in adult non-smokers exposed to ETS, concluding that passive smoking has subtle but statistically significant effects on the respiratory health of non-smoking adults.
A search of the literature on the effect of passive smoking on respiratory or coronary diseases in workers revealed only a few studies. Men and women who were exposed to ETS at the workplace (offices, banks, academic institutions, etc.) for ten or more years had impaired pulmonary function (White and Froeb 1980; Masi et al. 1988).
In 1985, the International Agency for Research on Cancer (IARC) reviewed the association of passive tobacco smoke exposure with lung cancer in non-smokers. Although in some studies, each non-smoker with lung cancer who had reported ETS exposure was personally interviewed and had supplied detailed information on exposure (US National Research Council 1986; US EPA 1992; US Surgeon General 1986; Kabat and Wynder 1984), the IARC concluded: