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 lives—which is related to the amount of radioactive nuclides in the air and the amount found both in food and especially in drinking water—and, 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 sources—even though their relative influence is much less—are outside air, water and natural gas. Figure 1 shows the contribution that each source makes to the total.

Figure 1. 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 this 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.

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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 vapors 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 EnvironmentalTobacco 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 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). 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.

Table 1. Some toxic and tumorigenic agents in undiluted cigarette sidestream smoke

^a C=Carcinogenic; CoC=co-carcinogenic; T=toxic; TP=tumor promoter.
^b ND=not detected.
^c NNN=N‘-nitrosonornicotine.
^d NNK=4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone.

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 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 vapor 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 vapor 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 vapor phase of ETS (Hoffmann and Hecht 1990; Guerin et al. 1992).

Table 2. Some toxic and tumorigenic agents in indoor environments polluted by tobacco smoke

^a NNN=N‘-nitrosonornicotine.
^b ND=not detected.
^c NNK=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 3, 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 3. 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

^a Trend 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).

Lung cancer

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:

The observations on non-smokers that have been made so far, are compatible with either an increased risk from ‘passive’ smoking, or an absence of risk. Knowledge of the nature of sidestream and mainstream smoke, of the materials absorbed during ‘passive’ smoking and of the quantitative relationship between dose and effect that are commonly observed from exposure to carcinogens, however, leads to the conclusion that passive smoking gives rise to some risk of cancer (IARC 1986).

Thus, there is an apparent dichotomy between experimental data which support the concept that ETS gives rise to some risk of cancer, and epidemiological data, which are not conclusive with respect to ETS exposure and cancer. Experimental data, including biomarker studies, have further strengthened the concept that ETS is carcinogenic, as was discussed earlier. We will now discuss how far the epidemiological studies that have been completed since the cited IARC report have contributed to a clarification of the ETS lung cancer issue.

According to the earlier epidemiological studies, and in about 30 studies reported after 1985, ETS exposure of non-smokers constituted a risk factor for lung cancer of less than 2.0, relative to the risk of a non-smoker without significant ETS exposure (US Environmental Protection Agency 1992; Kabat and Wynder 1984; IARC 1986; Brownson et al. 1992; Brownson et al. 1993). Few, if any, of these epidemiological studies meet the criteria of causality in the association between an environmental or occupational factor and lung cancer. Criteria that fulfil these requirements are:

1. a well-established degree of association (risk factor≥3)
2. reproducibility of the observation by a number of studies
3. agreement between duration of exposure and effect
4. biological plausibility.

One of the major uncertainties about the epidemiological data lies in the limited reliability of the answers obtained by questioning cases and/or their next-of-kin with regard to the smoking habits of the cases. It appears that there is generally an accord between parental and spousal smoking histories provided by cases and controls; however, there are low agreement rates for duration and intensity of smoking (Brownson et al. 1993; McLaughlin et al. 1987; McLaughlin et al. 1990). Some investigators have challenged the reliability of the information derived from individuals about their smoking status. This is exemplified by a large-scale investigation carried out in southern Germany. A randomly selected study population consisted of more than 3,000 men and women, ranging in age from 25 to 64 years. These same people were questioned three times in 1984-1985, in 1987-1988 and again in 1989-1990 as to their smoking habits, while each time urine was collected from each proband and was analysed for cotinine. Those volunteers who were found to have more than 20 ng of cotinine per ml of urine were considered to be smokers. Among 800 ex-smokers who claimed to be non-smokers, 6.3%, 6.5% and 5.2% had cotinine levels above 20 ng/ml during the three time periods tested. The self-proclaimed never-smokers, who were identified as actual smokers according to cotinine analyses, constituted 0.5%, 1.0% and 0.9%, respectively (Heller et al. 1993).

The limited reliability of the data obtained by questionnaire, and the relatively limited number of non-smokers with lung cancer who were not exposed to carcinogens at their workplaces, point to the need for a prospective epidemiological study with assessment of biomarkers (e.g., cotinine, metabolites of polynuclear aromatic hydrocarbons, and/or metabolites of NNK in urine) to bring about a conclusive evaluation of the question on causality between involuntary smoking and lung cancer. While such prospective studies with biomarkers represent a major task, they are essential in order to answer the questions on exposure which have major public health implications.

Environmental Tobacco Smoke and the Occupational Environment

Although epidemiological studies have thus far not demonstrated a causal association between ETS exposure and lung cancer, it is nevertheless highly desirable to protect workers at the site of employment from exposure to environmental tobacco smoke. This concept is supported by the observation that long-term exposure of non-smokers to ETS at the workplace can lead to reduced pulmonary function. Furthermore, in occupational environments with exposure to carcinogens, involuntary smoking may increase the risk of cancer. In the United States, the Environmental Protection Agency has classified ETS as a Group A (known human) carcinogen; therefore, the law in the United States requires that employees be protected against exposure to ETS.

Several measures can be taken to protect the non-smoker from exposure to ETS: prohibiting smoking at the worksite, or at least separating smokers from non-smokers where possible, and assuring that the smokers’ rooms have a separate exhaust system. The most rewarding and by far the most promising approach is to assist employees who are cigarette smokers in cessation efforts.

The worksite can offer excellent opportunities for implementing smoking cessation programmes; in fact, numerous studies have shown that worksite programmes are more successful than clinic-based programmes, because employer-sponsored programmes are more intense in nature and they offer economic and/or other incentives (US Surgeon General 1985). It is also indicated that the elimination of occupationally related chronic lung diseases and cancer frequently cannot proceed without efforts to convert the workers into ex-smokers. Furthermore, worksite interventions, including smoking cessation programmes, can produce lasting changes in reducing some cardiovascular risk factors for the employees (Gomel et al. 1993).

We greatly appreciate the editorial assistance of Ilse Hoffmann and the preparation of this manuscript by Jennifer Johnting. These studies are supported by USPHS Grants CA-29580 and CA-32617 from the National Cancer Institute.

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In regard to taking action to reduce the use of tobacco, governments should keep in mind that while people decide on their own whether they should stop smoking, it is a government’s responsibility to take all the necessary measures to encourage them to stop. The steps taken by legislators and governments of many countries have been indecisive, because while the reduction in the use of tobacco is an undisputed improvement in public health—with attendant savings in public health expenditures—there would be a series of economic losses and dislocations in many sectors, at least of a temporary nature. The pressure that international health and environmental organizations and agencies can exert in this regard is very important, because many countries may water down measures against the use of tobacco because of economic problems—especially if tobacco is an important source of income.

This article briefly describes regulatory measures that can be adopted to reduce smoking in a country.

Warnings on Cigarette Packs

One of the first measures adopted in many countries is to require that cigarette packs prominently display the warning that smoking seriously injures the smoker’s health. This warning, whose aim is not so much to exert an immediate effect on the smoker, but rather to show that the government is concerned about the problem, is creating a psychological climate that will favour the adoption of later measures that otherwise would be considered aggressive by the smoking population.

Some experts advocate the inclusion of these warnings on cigars and pipe tobacco. But the more general opinion is that those warnings are unnecessary, because people who use that type of tobacco do not normally inhale the smoke, and extending these warnings would lead more likely to a disregard of the messages as a whole. This is why the prevalent opinion is that the warnings should be applied only to cigarette packs. A reference to second-hand smoke has not, for the moment, been considered, but it is not an option that should be discarded.

Smoking Restrictions in Public Spaces

Forbidding smoking in public spaces is one of the most effective regulatory instruments. These prohibitions can significantly reduce the number of people exposed to second-hand smoke and, in addition, can reduce smokers’ daily cigarette consumption. The common complaints by owners of public spaces, such as hotels, restaurants, recreational facilities, dance halls, theatres and so forth, are based on the argument that these measures will result in a loss of customers. However, if governments implement these measures across the board, the negative impact of a loss of clientele will occur only in the first phase, because people will eventually adapt to the new situation.

Another possibility is the design of specific spaces for smokers. The separation of smokers from non-smokers should be effective in order to obtain the desired benefits, creating barriers that prevent non-smokers from inhaling tobacco smoke. Separation must thus be physical and, if the air-conditioning system uses recycled air, the air from smoking areas should not be mixed with that from non-smoking areas. Creating spaces for smokers therefore implies construction and compartmentalization expenses, but may be a solution for those who want to serve the smoking public.

Aside from locations where smoking is obviously forbidden for security reasons because of possible explosion or fire, there should also be areas—such as health care and sports facilities, schools and day-care centres—where smoking is not permitted even though there are no safety risks of that kind.

Smoking Restrictions at Work

Smoking restrictions in the workplace may also be considered in light of the above. Governments and business owners, together with trade unions, can establish programmes to reduce the use of tobacco at work. Campaigns to curtail smoking at work are generally successful.

Whenever possible, creating non-smoking areas to establish a policy against tobacco use and to support people who defend the right not to be second-hand smokers is recommended. In case of a conflict between a smoker and a non-smoker, regulations should always allow the non-smoker to prevail, and whenever they cannot be separated, the smoker should be pressured to abstain from smoking at the workstation.

In addition to places where for health or safety reasons smoking should be forbidden, the possibility of synergism between the effects of chemical pollution in the workplace and tobacco smoke should not be ignored in other areas either. The weight of such considerations will result, without a doubt, in a broad extension of smoking restrictions, especially in industrial workplaces.

Greater Economic Pressure against Tobacco

Another regulatory tool governments rely on to curb the use of tobacco is levying higher taxes, chiefly on cigarettes. This policy is intended to lead to lower tobacco consumption, which would justify the inverse relation between the price of tobacco and its consumption and which can be measured when comparing the situation in different countries. It is considered effective where the population is forewarned of the dangers of tobacco use and advised of the need to stop consuming it. An increase in the price of tobacco can be a motivation to quit smoking. This policy, however, has many opponents, who base their criticisms on arguments briefly mentioned below.

In the first place, according to many specialists, the increase in the price of tobacco for fiscal reasons is followed by a temporary reduction in the use of tobacco, followed by a gradual return to the previous consumption levels as the smokers get used to the new price. In other words, smokers assimilate a rise in the price of tobacco much in the same way that people get used to other taxes or to the rise in the cost of living.

In the second place, a shift in the habits of smokers has also been observed. When prices go up they tend to seek out cheaper brands of lower quality that probably also pose a greater risk to their health (because they lack filters or have higher amounts of tar and nicotine). This shift may go so far as to induce smokers to adopt the practice of making home-made cigarettes, which would completely eliminate any possibility of controlling the problem.

In the third place, many experts are of the opinion that measures of this kind tend to bolster the belief that the government accepts tobacco and its consumption as yet another means to collect taxes, leading to the contradictory belief that what the government really wants is that people smoke so that it can collect more money with the special tax on tobacco.

Limiting Publicity

Another weapon used by governments to reduce tobacco consumption is to restrict or simply forbid any publicity for the product. Governments and many international organizations have a policy of forbidding publicity for tobacco in certain spheres, such as sports (at least some sports), health care, the environment, and education. This policy has unquestionable benefits, which are especially effective when it eliminates publicity in those environments that affect young people at a time when they are likely to take up the smoking habit.

Public Programmes that Encourage People to QuitSmoking

The use of anti-smoking campaigns as a normal practice, adequately funded and organized as a rule of conduct in certain spheres, such as the world of work, has been shown to be highly successful.

Campaigns to Educate Smokers

Complementing what was said above, educating smokers so that they will smoke “better” and cut down on their consumption of cigarettes is another avenue available to governments to reduce the adverse health effects of tobacco use on the population. These efforts should be directed at reducing the daily consumption of cigarettes, at inhibiting the inhalation of smoke as much as possible, at not smoking the butts of cigarettes (the toxicity of smoke increases towards the end of the cigarette), at not keeping the cigarette steadily at the lips, and at adopting preferences for brands with lower tar and nicotine.

Measures of this type evidently do not reduce the number of smokers, but they do reduce how much smokers are harmed by their habit. There are arguments against this type of remedy because it may give the impression that smoking is not intrinsically a bad habit, since smokers are told how best to smoke.

Concluding Remarks

Regulatory and legislative action by different governments is slow and not sufficiently effective, especially given what would be required due to the problems caused by tobacco use. Often this is the case because of legal hurdles against implementing such measures, arguments against unfair competition, or even the protection of the individual’s right to smoke. Progress in the use of regulations has been slow but it is nonetheless steady. On the other hand, the difference between active smokers and second-hand or passive smokers should be kept in mind. All the measures that would help someone to stop smoking, or at least to reduce daily consumption effectively, should be directed at the smoker; all the weight of regulations should be brought to bear against this habit. The passive smoker should be given every possible argument to support his or her right not to inhale tobacco smoke, and to defend the right to enjoy the use of smoke-free environments at home, at work and at play.

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From the standpoint of pollution, indoor air in non-industrial situations displays several characteristics that differentiate it from outside, or atmospheric, air and from the air in industrial workplaces. Besides contaminants found in atmospheric air, indoor air also includes contaminants generated by building materials and by the activities that take place within the building. The concentrations of contaminants in indoor air tend to be the same or less than concentrations found in outside air, depending on ventilation; contaminants generated by building materials are usually different from those found in outside air and can be found in high concentrations, while those generated by activities inside the building depend on the nature of such activities and may be the same as those found in outside air, as in the case of CO and CO₂.

For this reason, the number of contaminants found in non-industrial inside air is large and varied and the levels of concentration are low (except for instances where there is an important generating source); they vary according to atmospheric/climatologic conditions, the type or characteristics of the building, its ventilation and the activities carried out within it.

Analysis

Much of the methodology used to gauge the quality of indoor air stems from industrial hygiene and from measurements of immission of outdoor air. There are few analytic methods validated specifically for this type of testing, although some organizations, such as the World Health Organization and the Environmental Protection Agency in the United States are conducting research in this field. An additional obstacle is the paucity of information on the exposure-effect relationship when dealing with long-term exposures to low concentrations of pollutants.

The analytical methods used for industrial hygiene are designed to measure high concentrations and have not been defined for many pollutants, while the number of contaminants in indoor air can be large and varied and the levels of concentration can be low, except in certain cases. Most methods used in industrial hygiene are based on the taking of samples and their analysis; many of these methods can be applied to indoor air if several factors are taken into account: adjusting the methods to the typical concentrations; increasing their sensitivity without detriment to precision (for example, increasing the volume of air tested); and validating their specificity.

The analytical methods used to measure concentrations of pollutants in outdoor air are similar to those used for indoor air, and therefore some can be used directly for indoor air while others can be easily adapted. However, it is important to keep in mind that some methods are designed for a direct reading of one sample, while others require bulky and sometimes noisy instrumentation and use large volumes of sampled air which can distort the reading.

Planning the Readings

The traditional procedure in the field of workplace environmental control can be used to improve the quality of indoor air. It consists of identifying and quantifying a problem, proposing corrective measures, making sure that these measures are implemented, and then assessing their effectiveness after a period of time. This common procedure is not always the most adequate because often such an exhaustive evaluation, including the taking of many samples, is not necessary. Exploratory measures, which can range from a visual inspection to assaying of ambient air by direct reading methods, and which can provide an approximate concentration of pollutants, are sufficient for solving many of the existing problems. Once corrective measures have been taken, the results can be evaluated with a second measurement, and only when there is no clear evidence of an improvement a more thorough inspection (with in-depth measurements) or a complete analytical study can be undertaken (Swedish Work Environment Fund 1988).

The main advantages of such an exploratory procedure over the more traditional one are economy, speed and effectiveness. It requires competent and experienced personnel and the use of suitable equipment. Figure 1 summarizes the goals of the different stages of this procedure.

Figure 1. Planning the readings for exploratory evaluation.

Sampling Strategy

Analytical control of the quality of indoor air should be considered as a last resort only after the exploratory measurement has not given positive results, or if further evaluation or control of the initial tests is needed.

Assuming some previous knowledge of the sources of pollution and of the types of contaminants, the samples, even when limited in number, should be representative of the various spaces studied. Sampling should be planned to answer the questions What? How? Where? and When?

What

The pollutants in question must be identified in advance and, keeping in mind the different types of information that can be obtained, one should decide whether to make emission or immission measurements.

Emission measurements for indoor air quality can determine the influence of different sources of pollution, of climatic conditions, of the building’s characteristics, and of human intervention, which allow us to control or reduce the sources of emissions and improve the quality of indoor air. There are different techniques for taking this type of measurement: placing a collection system adjacent to the source of the emission, defining a limited work area and studying emissions as if they represented general working conditions, or working in simulated conditions applying monitoring systems that rely on head space measures.

Immission measurements allow us to determine the level of indoor air pollution in the different compartmentalized areas of the building, making it possible to produce a map of pollution for the entire structure. Using these measurements and identifying the different areas where people have carried out their activities and calculating the time they have spent at each task, it will be possible to determine the levels of exposure. Another way of doing this is by having individual workers wear monitoring devices while working.

It may be more practical, if the number of pollutants is large and varied, to select a few representative substances so that the reading is representative and not too expensive.

How

Selecting the type of reading to be made will depend on the available method (direct reading or sample-taking and analysis) and on the measuring technique: emission or immission.

Where

The location selected should be the most appropriate and representative for obtaining samples. This requires knowledge of the building being studied: its orientation relative to the sun, the number of hours it receives direct sunlight, the number of floors, the type of compartmentalization, if ventilation is natural or forced air, if its windows can be opened, and so on. Knowing the source of the complaints and the problems is also necessary, for example, whether they occur in the upper or the lower floors, or in the areas close to or far from the windows, or in the areas that have poor ventilation or illumination, among other locations. Selecting the best sites to draw the samples will be based on all of the available information regarding the above-mentioned criteria.

When

Deciding when to take the readings will depend on how concentrations of air pollutants change relative to time. Pollution may be detected first thing in the morning, during the workday or at the end of the day; it may be detected at the beginning or the end of the week; during the winter or the summer; when air-conditioning is on or off; as well as at other times.

To address these questions properly, the dynamics of the given indoor environment must be known. It is also necessary to know the goals of the measurements taken, which will be based on the types of pollutant that are being investigated. The dynamics of indoor environments are influenced by the diversity of the sources of pollution, the physical differences in the spaces involved, the type of compartmentalization, the type of ventilation and climate control used, outside atmospheric conditions (wind, temperature, season, etc.), and the building’s characteristics (number of windows, their orientation, etc.).

The goals of the measurements will determine if sampling will be carried out for short or long intervals. If the health effects of the given contaminants are thought to be long-term, it follows that average concentrations should be measured over long periods of time. For substances that have acute but not cumulative effects, measurements over short periods are sufficient. If intense emissions of short duration are suspected, frequent sampling over short periods is called for in order to detect the time of the emission. Not to be overlooked, however, is the fact that in many cases the possible choices in the type of sampling methods used may be determined by the analytical methods available or required.

If after considering all these questions it is not sufficiently clear what the source of the problem is, or when the problem occurs with greatest frequency, the decision as to where and when to take samples must be made at random, calculating the number of samples as a function of the expected reliability and cost.

Measuring techniques

The methods available for taking samples of indoor air and for their analysis can be grouped into two types: methods that involve a direct reading and those that involve taking samples for later analysis.

Methods based on a direct reading are those by which taking the sample and measuring the concentration of pollutants is done simultaneously; they are fast and the measurement is instantaneous, allowing for precise data at a relatively low cost. This group includes colorimetric tubes and specific monitors.

The use of colorimetric tubes is based on the change in the colour of a specific reactant when it comes in contact with a given pollutant. The most commonly used are tubes that contain a solid reactant and air is drawn through them using a manual pump. Assessing the quality of indoor air with colorimetric tubes is useful only for exploratory measurements and for measuring sporadic emissions since their sensitivity is generally low, except for some pollutants such as CO and CO₂ that can be found at high concentrations in indoor air. It is important to keep in mind that the precision of this method is low and interference from unlooked-for contaminants is often a factor.

In the case of specific monitors, detection of pollutants is based on physical, electric, thermal, electromagnetic and chemoelectromagnetic principles. Most monitors of this type can be used to make measurements of short or long duration and gain a profile of contamination at a given site. Their precision is determined by their respective manufacturers and proper use demands periodic calibrations by means of controlled atmospheres or certified gas mixtures. Monitors are becoming increasingly precise and their sensitivity more refined. Many have built-in memory to store the readings, which can then be downloaded to computers for the creation of databases and the easy organization and retrieval of the results.

Sampling methods and analyses can be classified into active (or dynamic) and passive, depending on the technique.

With active systems, this pollution can be collected by forcing air through collecting devices in which the pollutant is captured, concentrating the sample. This is accomplished with filters, adsorbent solids, and absorbent or reactive solutions which are placed in bubblers or are impregnated onto porous material. Air is then forced through and the contaminant, or the products of its reaction, are analysed. For the analysis of air sampled with active systems the requirements are a fixative, a pump to move the air and a system to measure the volume of sampled air, either directly or by using flow and duration data.

The flow and the volume of sampled air are specified in the reference manuals or should be determined by previous tests and will depend on the quantity and type of absorbent or adsorbent used, the pollutants that are being measured, the type of measurement (emission or immission) and the condition of the ambient air during the taking of the sample (humidity, temperature, pressure). The efficacy of the collection increases by reducing the rate of intake or by increasing the amount of fixative used, directly or in tandem.

Another type of active sampling is the direct capture of air in a bag or any other inert and impermeable container. This type of sample gathering is used for some gases (CO, CO₂, H₂S, O₂) and is useful as an exploratory measure when the type of pollutant is unknown. The drawback is that without concentrating the sample there may be insufficient sensitivity and further laboratory processing may be necessary to increase the concentration.

Passive systems capture pollutants by diffusion or permeation onto a base that may be a solid adsorbent, either alone or impregnated with a specific reactant. These systems are more convenient and easy to use than active systems. They do not require pumps to capture the sample nor highly trained personnel. But capturing the sample may take a long time and the results tend to furnish only medium concentration levels. This method cannot be used to measure peak concentrations; in those instances active systems should be used instead. To use passive systems correctly it is important to know the speed at which each pollutant is captured, which will depend on the diffusion coefficient of the gas or vapor and the design of the monitor.

Table 1 shows the salient characteristics of each sampling method and table 2 outlines the various methods used to gather and analyse the samples for the most significant indoor air pollutants.

Table 1. Methodology for taking samples

+ Means that the given method is suitable to the method of measurement or desired measurement criteria.

Table 2. Detection methods for gases in indoor air

— = Method unsuitable for pollutant.
^a GC = gas chromatography.
^b UV-Vis = visible ultraviolet spectrophotometry.
^c HPLC = high precision liquid chromatography.
^d CD = electron capture detector.
^e FID = flame, ionization detector.
^f NPD = nitrogen/phosphorous detector.
^g PID = photoionization detector.
^h MS = mass spectrometry.

Selecting the method

To select the best sampling method, one should first determine that validated methods for the pollutants being studied exist and see to it that the proper instruments and materials are available to gather and analyse the pollutant. One usually needs to know what their cost will be, and the sensitivity required for the job, as well as things that can interfere with the measurement, given the method chosen.

An estimate of the minimum concentrations of what one hopes to measure is very useful when evaluating the method used to analyse the sample. The minimum concentration required is directly related to the amount of pollutant that can be gathered given the conditions specified by the method used (i.e., the type of system used to capture the pollutant or the duration of sample taking and volume of air sampled). This minimum amount is what determines the sensitivity required of the method used for analysis; it can be calculated from reference data found in the literature for a particular pollutant or group of pollutants, if they were arrived at by a similar method to the one that will be used. For example, if it is found that hydrocarbon concentrations of 30 (mg/m³) are commonly found in the area under study, the analytical method used should allow the measurement of those concentrations easily. If the sample is obtained with a tube of active carbon in four hours and with a flow of 0.5 litres per minute, the amount of hydrocarbons gathered in the sample is calculated by multiplying the flow rate of the substance by the period of time monitored. In the given example this equals:

of hydrocarbons  

Any method for detecting hydrocarbons that requires the amount in the sample to be under 3.6 μg can be used for this application.

Another estimate could be calculated from the maximum limit established as the allowable limit for indoor air for the pollutant being measured. If these figures don’t exist and the usual concentrations found in indoor air are not known, nor the rate at which the pollutant is being discharged into the space, approximations can be used based on the potential levels of the pollutant that can negatively affect health. The method chosen should be capable of measuring 10% of the established limit or of the minimal concentration that could affect health. Even if the method of analysis chosen has an acceptable degree of sensitivity, it is possible to find concentrations of pollutants that are below the lower limit of detection of the chosen method. This should be kept in mind when calculating average concentrations. For example, if out of ten readings taken three are below the detection limit, two averages should be calculated, one assigning these three readings the value of zero and another giving them the lowest detection limit, which renders a minimum average and a maximum average. The true measured average will be found between the two.

Analytical Procedures

The number of indoor air pollutants is great and they are found in small concentrations. The methodology that has been available is based on adapting methods used to monitor the quality of outdoor, atmospheric, air and air found in industrial situations. Adapting these methods for the analysis of indoor air implies changing the range of the concentration sought, when the method allows, using longer sampling times and greater amounts of absorbents or adsorbents. All these changes are appropriate when they do not lead to a loss in reliability or precision. Measuring a mixture of contaminants is usually expensive and the results obtained imprecise. In many cases all that will be ascertained will be a pollution profile that will indicate the level of contamination during sampling intervals, compared to clean air, to outside air, or to other indoor spaces. Direct reading monitors are used to monitor the pollution profile and may not be suitable if they are too noisy or too large. Ever smaller and quieter monitors, that afford greater precision and sensitivity, are being designed. Table 3 shows in outline the current state of the methods used to measure the different types of contaminants.

Table 3. Methods used for the analysis of chemical pollutants

^a ++ = most commonly used; + = less commonly used; – = not applicable.

Analysis of gases

Active methods are the most common for the analysis of gases, and are carried out using absorbent solutions or adsorbent solids, or by directly taking a sample of air with a bag or some other inert and airtight container. In order to prevent loss of part of the sample and increase the accuracy of the reading, the volume of the sample must be lower and the amount of absorbent or adsorbent used should be more than for other types of pollution. Care should also be taken in transporting and storing the sample (keeping it at low temperature) and minimizing the time before the sample is tested. Direct reading methods are widely used for measuring gases because of the considerable improvement in the capabilities of modern monitors, which are more sensitive and more precise than before. Because of their ease of use and the level and type of information that they furnish, they are increasingly replacing traditional methods of analysis. Table 4 shows the minimum detection levels for the various gases studied given the method of sampling and analysis used.

Table 4. Lower detection limits for some gases by monitors used to assess indoor air quality

^a Carbon dioxide monitors that use infrared spectroscopy are always sensitive enough.
^b Passive monitors (length of exposure).

These gases are common pollutants in indoor air. They are measured by using monitors that detect them directly by electrochemical or infrared means, even though infrared detectors are not very sensitive. They can also be measured by taking air samples directly with inert bags and analysing the sample by gas chromatography with a flame ionization detector, transforming the gases into methane first by means of a catalytic reaction. Thermal conduction detectors are usually sensitive enough to measure normal concentrations of CO₂.

Nitrogen dioxide

Methods have been developed to detect nitrogen dioxide, NO₂, in indoor air by using passive monitors and taking samples for later analysis, but these methods have presented sensitivity problems that will hopefully be overcome in the future. The best known method is the Palmes tube, which has a detection limit of 300 ppb. For non-industrial situations, sampling should be for a minimum of five days in order to obtain a detection limit of 1.5 ppb, which is three times the value of the blank for a one-week exposure. Portable monitors that measure in real time have also been developed based on the chemiluminescence reaction between NO₂ and the reactant luminol, but the results obtained by this method can be affected by temperature and their linearity and sensitivity depend on the characteristics of the solution of luminol used. Monitors that have electrochemical sensors have improved sensitivity but are subject to interference from compounds that contain sulphur (Freixa 1993).

Sulphur dioxide

A spectrophotometric method is used to measure sulphur dioxide, SO₂, in an indoor environment. The air sample is bubbled through a solution of potassium tetrachloromercuriate to form a stable complex which is in turn measured spectrophotometrically after reacting with pararosaniline. Other methods are based on flame photometry and pulsating ultraviolet fluorescence, and there are also methods based on deriving the measurement before the spectroscopic analysis. This type of detection, which has been used for outside air monitors, is not suited for indoor air analysis because of a lack of specificity and because many of these monitors require a venting system to eliminate the gases that they generate. Because emissions of SO₂ have been greatly reduced and it is not considered an important pollutant of indoor air, the development of monitors for its detection have not advanced very much. However, there are portable instruments available on the market that can detect SO₂ based on the detection of pararosaniline (Freixa 1993).

Ozone

Ozone, O₃, can only be found in indoor environments in special situations in which it is generated continuously, since it decays rapidly. It is measured by direct reading methods, by colorimetric tubes and by chemiluminescence methods. It can also be detected by methods used in industrial hygiene that can be easily adapted for indoor air. The sample is obtained with an absorbent solution of potassium iodide in a neutral medium and then subjected to spectrophotometric analysis.

Formaldehyde

Formaldehyde is an important pollutant of indoor air, and because of its chemical and toxic characteristics an individualized evaluation is recommended. There are different methods for detecting formaldehyde in air, all of them based on taking samples for later analysis, with active fixing or by diffusion. The most appropriate capturing method will be determined by the type of sample (emission or immission) used and the sensitivity of the analytical method. The traditional methods are based on obtaining a sample by bubbling air through distilled water or a solution of 1% sodium bisulphate at 5°C, and then analysing it with spectrofluorometric methods. While the sample is stored, it should also be kept at 5°C. SO₂ and the components of tobacco smoke can create interference. Active systems or methods that capture pollutants by diffusion with solid adsorbents are used more and more frequently in indoor air analysis; they all consist of a base that can be a filter or a solid saturated with a reactant, such as sodium bisulphate or 2,4-diphenylhydrazine. Methods that capture the pollutant by diffusion, in addition to general advantages of that method, are more sensitive than active methods because the time required to obtain the sample is longer (Freixa 1993).

Detection of volatile organic compounds (VOCs)

The methods used to measure or monitor organic vapors in indoor air must meet a series of criteria: they should have a sensitivity in the order of parts per billion (ppb) to parts per trillion (ppt), the instruments used to take the sample or make a direct reading must be portable and easy to handle in the field, and the results obtained must be precise and capable of being duplicated. There are a great many methods that meet these criteria, but the ones most frequently used to analyse indoor air are based on sample taking and analysis. Direct detection methods exist that consist of portable gas chromatographs with different detection methods. These instruments are expensive, their handling is sophisticated and they can be operated only by trained personnel. For polar and nonpolar organic compounds that have a boiling point between 0°C and 300°C, the most widely used adsorbent both for active and passive sampling systems has been activated carbon. Porous polymers and polymer resins, such as Tenax GC, XAD-2 and Ambersorb are also used. The most widely used of these is Tenax. The samples obtained with activated carbon are extracted with carbon disulphide and they are analysed by gas chromatography with flame ionization, electron-capture, or mass spectrometry detectors, followed by qualitative and quantitative analysis. Samples obtained with Tenax are usually extracted by thermal desorption with helium and are condensed in a nitrogen cold trap before being fed to the chromatograph. Another common method consists in obtaining samples directly, using bags or inert containers, feeding the air directly to the gas chromatograph, or concentrating the sample first with an adsorbent and a cold trap. The detection limits of these methods depend on the compound analysed, the volume of the sample taken, the background pollution and the detection limits of the instrument used. Because quantifying each and every one of the compounds present is impossible, quantification is normally done by families, by using as a reference compounds that are characteristic of each family of compounds. In detecting VOCs in indoor air, the purity of the solvents used is very important. If thermal desorption is used, the purity of the gases is also important.

Detection of pesticides

To detect pesticides in indoor air, the methods commonly employed consist of taking samples with solid adsorbents, although the use of bubblers and mixed systems is not ruled out. The solid adsorbent most commonly used has been porous polymer Chromosorb 102, although polyurethane foams (PUFs) that can capture a wider number of pesticides are being used more and more. The methods of analysis vary according to the sampling method and the pesticide. Usually they are analysed by using gas chromatography with different specific detectors, from electron capture to mass spectrometry. The potential of the latter for identifying compounds is considerable. The analysis of these compounds presents certain problems, which include the contamination of glass parts in the sample-taking systems with traces of polychlorinated biphenyls (PCBs), phthalates or pesticides.

Detection of environmental dust or particles

For the capture and analysis of particles and fibres in air a great variety of techniques and equipment are available and suited for assessing indoor air quality. Monitors that permit a direct reading of the concentration of particles in the air use diffuse light detectors, and methods that employ sample taking and analysis use weighting and analysis with a microscope. This type of analysis requires a separator, such as a cyclone or an impactor, to sift out larger particles before a filter can be used. Methods that employ a cyclone can handle small volumes, which results in long sessions of sample taking. Passive monitors offer excellent precision, but they are affected by ambient temperature and tend to give readings with higher values when the particles are small.

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