Health Effects Due to Indoor Air Pollution

John A. Hoskins

Abstract The indoor environment can be very polluted with pollution levelsindoors higher than those outdoors, particularly so when there are combustion pro-cesses associated with cooking heating or smoking and poor ventilation. About halfthe world’s population have to rely for cooking; and associated space heating onsimple household stoves using unprocessed solid fuels that have high emission fac-tors, with the consequence that they are exposed to high levels of health-damagingair pollutants. Cooking may produce very high concentrations of particulate matterparticularly when biomass is used as fuel. Tobacco smoke may add to the pol-lution and these together cause considerable human ill health world-wide. Manypollutants directly affect the respiratory and cardiovascular systems and the severityvaries according to the intensity and the duration of exposure. The health status ofthe population exposed varies with some people at greater risk than others. Severalchemicals found in the indoor environment are classed as carcinogens although atthe levels found the probability that they will cause cancer is extremely low. This isnot to lessen the problem. In a 1987 study, the US Environmental Protection Agencyranked indoor air pollution fourth in cancer risk among the 13 top environmentalproblems analysed.

Keywords Pollution · Population · Cancer · Risk

1 Introduction

We spend most of our time indoors in an environment filled with things that can pro-duce air pollution including many consumer products, gas appliances, cigarettes,and furniture, and of course ourselves. The outdoor environment, particularlythe outdoors urban environment with its vehicular traffic, adds a contribution asdo building materials [1–7]. Over most of the world cooking and heating add

J.A. Hoskins (B)Grey Cross, Haslemere, Surrey GU27 2 JH, UKe-mail: j.a.hoskins@isbe.demon.co.uk

665H. Gökçekus et al. (eds.), Survival and Sustainability, Environmental Earth Sciences,DOI 10.1007/978-3-540-95991-5_61, C© Springer-Verlag Berlin Heidelberg 2011

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a considerable contribution to the overall air pollution load in a dwelling [8].Because of this indoor spaces are important micro-environments when consideringthe impact of air pollution on health [9–11]. The problem is, in fact, compounded forthe indoor environment because pollution levels indoors are generally higher thanthose outdoors.

The World Health Organization (WHO) said that in the year 2000 3 million peo-ple were killed world-wide by outdoor air pollution annually from vehicles andindustrial emissions and 1.6 million indoors through using solid fuel add to this the2.7% of the global burden of disease (in Disability-Adjusted Life Years or DALYs)[12]. Most of the people affected were in poor countries. This makes air pollutionas a risk factor the second biggest environmental contributor to ill health, behindunsafe water and sanitation. Its importance as a public health threat varies drasti-cally according to the level of development of a country: in the poorest countriesindoor air pollution is responsible for up to 3.7% of the burden of disease it nolonger features in the top 10 risk factors in industrialised countries.

Research has shown that the indoor levels of some pollutants, such as formalde-hyde [13], chloroform [14], and styrene [15], range from 2 to 50 times higherthan outdoor levels. Overall, though, in many countries, pollutant concentrationsindoors are similar to those outdoors, with the ratio of indoor to outdoor concen-tration falling in the range 0.7–1.3. Higher levels of indoor pollution are usuallythe result of combustion processes associated with cooking or heating coupled withpoor ventilation. Exposure to some pollutants such as environmental tobacco smokeand radon occurs almost entirely indoors.

Indoor sources may lead to an accumulation of some compounds that are rarelypresent in the ambient air. Conversely the urban outdoor air is dominated by the sig-nature group of petroleum VOCs known as BTEX (benzene, toluene, ethylbenzene,xylenes). Concentrations of combustion products in indoor air can be substantiallyhigher than those outdoors when heating and cooking appliances are used. Thisis particularly true in countries where ovens and braziers are used with imperfectkitchen and stove designs [16–19]. In many countries exposure to emissions fromcooking and heating may produce the highest indoor air pollution exposures to manypollutants. Today about half the population of the world has to rely for cookingand associated space heating on simple household stoves using unprocessed solidfuels that have high emission factors for a range of health-damaging air pollutants[18, 20].

Specific health effects are often claimed for individual pollutants, particularlycauses of cancer from the presence of carcinogens in the air. Health effects fromexposure to the whole mixture of pollutants are often held responsible for vaguelydefined syndromes or conditions such as sick building syndrome (SBS) or buildingrelated illnesses (BRI) [21, 22].

SBS is the occurrence of specific symptoms with unspecified aetiology, thatare experienced by people while working or living in a particular building, butwhich disappear after they leave it. Symptoms include mucous membrane, skinand eye irritation, chest tightness, fatigue, headache, malaise, lethargy, lack ofconcentration, odour annoyance and influenza symptoms. SBS usually cannot be

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attributed to excessive exposure to any one contaminant or to a defective ventila-tion system although this is often claimed. A number of factors may be involvedand it is assumed that the interaction of these factors, involving different reac-tion mechanisms, cause the syndrome, but there is as yet no clear evidence of anyexposure-effect relationship [23, 24].

Although the definition is vague BRI is often defined as an illness related toindoor exposures to biological and/or chemical substances (e.g. fungi, bacteria,endotoxins, mycotoxins, radon, CO, HCHO). It is experienced by some peopleworking or living in a particular building and it does not disappear after leav-ing it [25]. Illnesses include respiratory tract infections and diseases, legionnaires’disease, and more controversially, cardiovascular diseases and lung cancer.

2 Factors That Affect Indoor Air Quality

The air quality inside buildings is affected by many factors. In an effort to con-serve energy, modern building design has favoured tighter structures with lowerrates of ventilation. By contrast, in some areas of the world only natural ventila-tion is used; in other areas mechanical ventilation is common [26]. In spite of themove to tighter structures there is still continuous air exchange between indoors andoutdoors such that indoor concentrations of air pollutants are influenced by outdoorlevels. The extent to which this occurs depends upon the rate of exchange betweenindoor and outdoor air; and these levels are subject to geographical, seasonal anddiurnal variations [27].

Within buildings the factors that can have a negative effect on health and comfortrange from chemical and biological pollutants, to occupant perceptions of specificstresses such as temperature, humidity, artificial light, noise and vibration [28].Important sources of chemical pollutants indoors include not only outdoor air, butalso human body and human activities, plus emissions from building materials, fur-nishings and appliances, and use of consumer products. Microbial contamination ismostly related to the presence of humidity. The heating, ventilating and air condi-tioning system can also act as a pollutant source, especially when it is not properlymaintained. For example, improper care of filters can lead to re-emission of particu-late contaminants. Biological contamination can proliferate in moist components ofthe system and be distributed throughout the building.

One of the most important causes of indoor pollution is combustion [29]. Thelevel of pollution produced depends on the fuel that is burnt and how it is burnt. Thecleanest fuel is gas, although there are several types, but at the bottom of the energyladder is biomass [9, 30]. Although part of human experience since the first con-trolled use of fire, air pollution from simple open combustion of biomass has beenscientifically characterised only in the last two decades, largely due to rising con-cerns about wood-smoke pollution in developed countries [31]. Studies have shownhigh emission factors for many important pollutants, including respirable particulatematter, carbon monoxide, polycylic aromatic hydrocarbons, such as benzo[a]pyrene,

668 J.A. Hoskins

and volatile organic compounds, such as formaldehyde and benzene. Biomass fuelsemit hundreds of chemicals during small-scale combustion, such as in householdcooking or heating stoves. It has been shown that such fuels produce 10–100 timesmore respirable particulate matter per meal as the result of low (combustion andheat-transfer) efficiencies. Although biomass makes up only 10–15% of total humanfuel use, compared to modern fuels a much larger fraction is burned indoors, sincenearly one-half of humanity cooks and/or heats with simple stoves burning tradi-tional biomass fuels and in consequence suffers chronic bronchitis and obstructiveairway disease. A recent study of women in Mexico showed that those cooking withbiomass fuels had increased respiratory symptoms and a slight average reduction inlung function compared with those cooking with gas [32].

It is not known what fraction of biomass-burning households cook indoors onun-vented stoves, although it is clear that many hundreds of millions do so duringsome or all seasons of the year. There is also little information about the ventilationrates in the many thousands of housing types in developing countries or countriesin transition although some studies have been made [19]. Monitoring such indoorenvironments is not often carried out but reports of studies are appearing in theliterature [33].

The results of these are often quite striking. Very high concentrations of particlesin indoor air can occur, sometimes for short duration, such as during cooking oversolid fuel fires in rooms with poor ventilation [33].

The active and passive inhalation of tobacco smoke can lead to reduced pul-monary function which is decreased more in females than males [34, 35] and to anincreased incidence of respiratory symptoms and infections, and to an increasedincidence of lung cancer. Tobacco smoke is a fresh biomass smoke, which hasbeen studied far more than any other pollutant mixture. Since there are similaritiesbetween ETS and biomass smoke from stoves, as hundreds of the organic com-pounds they both contain are similar it seems obvious that exposure to biomasssmoke from open stoves must causes considerable human ill-health world wide. Inthe second-hand form as ETS, it is associated with adverse health impacts in adultsand children at particle concentrations similar to those at which the epidemiolog-ical studies of health effects of outdoor particulate matter have been conducted. Itshould also be kept in mind that exposure to ETS and other air pollutants can actsynergistically to produce adverse health effects [36].

3 Health Effects

Since the early 1970s, interest in the health effects of indoor air pollution hasincreased annually. Consequently, a large body of literature is now available ondiverse aspects of indoor air pollution: sources, concentrations, health effectsand the engineering technology needed to ameliorate the problem [37–39]. Morerecently it has been realised that indoor air pollution from the use of open fires forcooking and heating is a serious problem in developing countries [12, 40].

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When it comes to health effects most indoor air pollutants directly affect therespiratory and cardiovascular systems and the severity of effect varies according toboth the intensity and the duration of exposure, and also with the health status ofthe population exposed [41–45]. The importance of this is that some members ofthe population may be greater risk than others. Many of those who are especiallysusceptible to the health effects of indoor pollutants are those who will spend nearlyall of their time indoors. These include infants and the elderly, those with heart andlung diseases and people with asthma, as well as hyper-responders and even thefitter members of society who are exercising [46].

A lot of the work on the health effects of indoor air pollution concentrates on asingle pollutant, for example, sulphur dioxide, particulate matter, carbon monoxide,or nitrogen dioxide. This specificity is particularly so when the pollutant is a knownhuman carcinogen such as benz[a]pyrene, benzene or radon.

Although carcinogenicity may be a good reason for studying individual pollu-tants as stand alone causes, the fact that all pollutants differ in the health effectsthey cause would seem to be an equally good reason for discriminating betweenthem. Thus, although we rarely breathe any one pollutant in isolation some pol-lutants, such as carbon monoxide, have such a dramatic effect on health that theyshould be considered separately [47]. Carbon monoxide causes disruption of thechemistry in several cell types, which, at low exposure levels, may be reversible.There are other pollutants that can cause cell damage and cell death, such as sulphurdioxide, nitrogen dioxide and particulate matter, and particularly mineral fibres. Celldeath removes a cell but cell damage can have more serious consequences for theorganism. On the other hand dead cells promote mitogenesis and this in its turn maylead to mutagenesis. A high level of mutagenesis may lead to inheritable changes incell DNA and eventually to cancer.

3.1 Carbon Monoxide

Acute exposure to high levels of carbon monoxide can be life-threatening but theconsequence of chronic exposure to low levels is not really known [48, 49]. Inkitchens with gas stoves, short-term values of up to 15 mg m−3 have been measured.High values have also been measured in bars and pubs, where smoking is common,with average concentrations of 10–20 mg m−3 and peak levels up to 30 mg m−3

[50].

3.2 Nitrogen Dioxide

Nitrogen dioxide is an insidious pollutant that causes lung damage and for whichthere may be no threshold of action [38, 51, 52]. In countries that cook and heatby gas (used in 20–80% of houses in some countries) indoor levels of NO2 canbe surprisingly high. In a UK study (noted with others in [53]), the average NO2

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concentrations (over a week) were in the range of 9.4–596 μg m−3 in kitchens, forhouses with gas cookers and 11.3–353.4 μg m−3 in dwellings with electric cookers.Corresponding levels outdoors were 26.3−45.1 μg m−3. These exposure levels mayhave an effect on respiratory function [54]. Peak values of up to 3800 μg m−3 for1 min have been measured in the Netherlands in kitchens with unvented gas cookingranges [50, 55].

3.3 Volatile Organic Compounds (VOCs)

All indoor environments contain a number of volatile organic compounds (VOCs)[56]. Most of these are present at very low concentrations have no measurableor, at the worst, insignificant health effects. However, high levels may have healtheffects that range from sensory irritation to behavioural, neurotoxic, hepatoxic, andgenotoxic effects [57] although these are more often associated with occupationalexposure. Several of the VOCs that cause concern do so because they are real orsuspected human carcinogens.

Environmental tobacco smoke (ETS) is another mixture of organic compoundswidely considered as an important factor in indoor air quality [58, 59]. ETS is amixture of particle and vapour phases which together make a complex mixture ofseveral thousand chemicals, including known carcinogens such as nitrosamines andbenzene. One of the most commonly used indicators of environmental pollution bytobacco smoke is the concentration of PM10. This measurement of the particulatephase is 2–3 times higher in houses with smokers than in other houses [60].

One commonly encountered volatile organic chemical that is not usually con-sidered, as a VOC is formaldehyde. In five developed European countries HCHOconcentrations in indoor air were reported to range from 9 to 70 μg m−3. Higher val-ues are occasionally encountered, especially in dwellings with urea-formaldehydefoam insulation [61] or with particle board use din their construction [62, 63].Formaldehyde has been shown to be carcinogenic in rats and more recently it hasbeen shown to be a human carcinogen [64].

A quartet of chemicals ubiquitous in the built environment is the petrol (gasoline)mixture of aromatics BTEX. For reasons known only to politicians and financiersthis excites little comment, although it may be a major part of the total VOC level.However, the minor constituent, benzene, is a known human carcinogen and is there-fore usually discussed as such. A recent study of environmental levels of benzene[65] noted that these were three orders of magnitude lower than the lowest exposuresreported to be associated with observed adverse effects.

3.4 Radon

Radon is the only radioactive pollutant found indoors. The evidence is good that itis a human carcinogen and this is its only property that causes concern. In general,

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average indoor levels of radon are 20–70 Bq m−3 [66], although they may be tentimes higher in certain areas.

So, there are reasons for studying individual pollutants in isolation and otherreasons for looking at them altogether. Leaving aside industrial and occupationalexposure, which may be to a single pollutant and may be to high doses, with thepossible exception of nitrogen dioxide the pollutants found indoors that cause con-cern with regard to their possible health effects are those which have the potentialfor such an exposure to result in cancer.

4 Cancer Causing Chemicals in Indoor Air

The causes of cancer were only discovered in comparatively recent times. One rea-son is that much cancer is a disease of the elderly and in the past conditions were sobad that few lived long enough for a tumour to develop. It was only in the twentiethcentury when life-expectancy increased considerably that it created the attention ithas today. Ascribing the cause of cancer to exposure to pollution was somethingthat probably only came about in the last 50 years or so. Studies continue clas-sifying exposure according to levels of various pollutants such as benz[a]pyrene,particulates and sulphur dioxide/sulphate levels.

4.1 The Hazard – Carcinogens in the Indoor Environment

A number of the chemicals found in the indoor environment are classed as car-cinogens, although not all of them are well documented as human carcinogens.The list of organic compounds that may be found in the indoor environment issmall and includes formaldehyde [67, 68], certain polycylic aromatic hydrocarbons(PAHs)E [69], benzene [65, 70] and 1,3-butadiene [71]. Tobacco smoke includ-ing ETS contains, among many other compounds, benzene, nitrosoamines andPAHs [72].

Several inorganic compounds are classified as carcinogens including, among oth-ers, arsenic, nickel and chromium in their elemental form or as compounds [73, 74].Arsenic is a major problem in well water in many areas of the world includingBangladesh, West Bengal [75] and Taiwan [76] where it is an undoubted cause ofcancer. In some areas of China and India, household coal use leads to high indoorconcentrations of fluorine, which causes fluorosis but not cancer, [29] and arsenic[77] with consequent health effects. Other inorganic materials that can pollute theindoor environment include the various types of asbestos and other mineral fibres.Diseases from these include lung cancer and mesothelioma but almost always asa result of occupational exposure [78–80]. The only natural radioactive element tocause concern is radon. It is a proven lung carcinogen in both animals and man butthe risks it poses, at least in the domestic rather than occupational setting, are stillunclear.

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4.2 The Risks from Carcinogens in the Indoor Environment

In a 1987 study, the US Environmental Protection Agency (EPA) ranked indoor airpollution fourth in cancer risk among the 13 top environmental problems analysed.Indoor radon ranked first in this list. The risk posed by the level of radon found indwellings is still hotly debated with the ecologists finding an inverse relationshipbetween lung cancer and radon levels [81] or that there is little correlation [82] andthe epidemiologists promoting a linear no-threshold model which contradicts thesefindings [83, 84].

However, what may be so in America, is not necessarily so in the rest of theworld. Relatively few studies, for example, have been conducted to determinethe health effects of indoor exposures to air pollutants in developing countries,although data has become available in recent years to obtain some preliminaryinformation on the type and very approximate magnitude of effects [29]. Theone major difference between rich and poor nations that are responsible for dif-ferences in observed health effects is the way in which they generate energy.When energy generation is produced remote from the areas where people live,it has little impact on personal health. If energy generation for heating, lightingand cooking is confined to the dwelling-place and is almost entirely accomplishedby direct combustion, then a greater or lesser effect on health is to be expecteddepending on the quality of the fuel that is burnt. The lower the fuel is downthe energy ladder, the greater the pollution it causes and the greater the inci-dence of cancer caused by inhaling the polluted emissions. Lung cancer is aprobable consequence of biomass burning [16] although not all studies find anassociation while coal for cooking and heating has been shown in many Chinesestudies to yield a statistically positive relationship with coal smoke and disease[85–87].

5 Conclusion

Air pollution is responsible for much morbidity and mortality in the world. Itsheterogeneous nature, though, means that few generalisations about its cause andeffects can be made. Higher levels of pollution are associated with poverty and mostpollution comes from combustion of one sort or another. For the global population asa whole, indoor pollution is more important than outdoor pollution, although highambient levels obviously adversely affect the indoor environment. Moving frompoverty to wealth does not mean an escape from pollution, but rather exchangingsome elements of it for others: radon has never been shown to be a problem in poorand draughty housing. Paradoxically, a wealthy lifestyle promotes greater concernabout pollution, but in reality it means appreciably less ill health and death fromenvironmental causes.

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