UNITED NATIONS	HS
	Commission on Human Settlements	Distr. GENERAL HS/C/15/INF.8 13 February 1995 ENGLISH ONLY
Fifteenth session Nairobi 25 April - 1 May 1995 Item 3 of the provisional agenda
BUILDING MATERIALS AND HEALTH
A background paper

Introduction

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1. The Commission on Human Settlements, in its decision 14/16 of 5 May 1993, requested the Executive Director of the United Nations Centre for Human Settlements (Habitat) to explore the possibility of drafting an informative document on: (a) such building materials in the housing sector that are harmful or potentially harmful to people's health and the environment, and (b) alternative building materials that could substitute for such materials. In addressing adverse environmental effects produced by construction activities in general, and building materials in particular, UNCHS (Habitat) has published a report entitled Development of National Technological Capacity for Environmentally Sound Construction (HS/293/93E). The publication, which is already widely distributed, identifies ways in which construction activities contribute to different areas of environmental stress, and considers means available for reducing adverse environmental impacts through improved technologies and through design and modified practices. The present document, therefore, focuses exclusively on ways in which a variety of building materials contribute to different aspects of health hazards, and the means available for prevention or mitigation of their adverse health impact.

2. Risks to health usually result from exposure to harmful environmental conditions in the extraction, production and use of building materials, and the disposal of related wastes. The harmful conditions include exposures to dust, fumes, gases and vapours and toxic metals. The interaction of these factors and the human organisms occurs either by absorption through the skin, or by intake into the digestive track via the mouth, or by inhalation into lungs. The results of the interactions can be harmful m human health in a variety of ways, including respiratory diseases such as asthma, heart diseases, cancer, brain damage or poisoning. The effects of the hazards may be slow, cumulative, irreversible, and complicated by non-occupational factors such as smoking.

3. The quality of the built environment too affects its inhabitants in many ways and is dependent not only on the architectural form and specification, but also on the quality and nature of materials used, the care taken in construction, the quality of building services design and components, and the timely and effective maintenance of the building fabric and support systems. The risks of diseases are also increased when the dwelling's barriers against insect and rodent vectors are inadequate or poorly maintained.

4. Some of the health hazards associated with building materials and the built-environment are well documented and programmes to reduce them are in place. Others are the subject of current and future research, consequently remedial measures are not yet in place. Furthermore, the indications, based on present knowledge, that a certain material is harmless to human health does not preclude possible discoveries of health hazards in future, bearing in mind the continuing advances in science and medicine.

5. The scope of this document is mainly limited to those hazards which are associated with the production and use, of building materials, and to some extent the disposal of wastes. The document is in three sections. Section I discusses the nature of health hazards associated with the production of building materials and their use, and the demolition and disposal effects of some of the harmful materials and wastes. Section II addresses the problems and constraints to the control of the harmful effects of building materials. Section IN outlines a strategy for the control of health hazards focusing on possible action by those principally involved in the production and use of building materials. However it should be noted that the document is still in draft form, and will be finalized after the receipt of feedbacks from all relevant bodies who have been requested to provide comments.

I. Health hazards associated with building materials

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6. This section briefly reviews the major health hazards associated with building materials according to three principal stages of the construction cycle, namely: the production of building materials; construction and maintenance; and occupancy. Furthermore, the section appraises the health hazards associated with five groups of potentially harmful and commonly used materials: asbestos; metals; solvents; insecticides and fungicides; and earthen materials. Radon emission and its effect on health has been discussed, as many of the building materials contain radium and so exhale radon which is a health hazard. An overview on the health impacts of wastes resulting from building materials has also been made. Finally, table 18 provides a summary of building materials, their areas of application, related health hazards, substitute materials and mitigation strategies.

A. Health and building materials: an overview

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1. Production of building materials

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7. The materials delivered or supplied to a site derive from a range of enterprises, operating at different scales, levels of technology and types of operation. Each type of material and production technology has its own characteristic health hazards. Many building materials industries derive their raw materials from quarrying or mining of minerals, in which workers are exposed to risks from blasting and rockfalls, and to dusts which can give rise to a variety of lung and respiratory disorders. The risks to asbestos workers were among the first identified hazards of building materials (section I.B). Fine dusts are also a problem in many other material-production industries, especially lime, cement and gypsum manufacture.⁽¹⁾ Dusts of organic origin can, likewise, create health hazards of tumours and various allergic conditions for workers in sawmills and wood-based industries.^{(1, 2)}

8. Timber treatment often takes place off-site, using a variety of toxic chemicals, insecticides and fungicides, in a concentrated form which can be exceptionally hazardous to the health of workers exposed to them, and to the health of neighbouring populations if care is not taken in the disposal of wastes.⁽²⁾

9. Handling of the solvents used in the manufacture of paints and varnishes creates health hazards for the workers in those industries (section 1.E). Workers in building-materials production plants are also exposed to a range of industrial accidents from high temperature kiln processes (in cement, lime, brick production), rotating machinery, chemical spills and toxic effluent releases, and smoke-laden atmospheres: and to hearing loss from intense noise.⁽¹⁾

10. Two factors mitigate the hazards to workers in material production plants. First, such plants are generally permanent registered factories, where health hazards to workers can be monitored and controlled by proper management, and are subject to health and safety regulations, and are liable to inspection. Secondly, although exposures are often concentrated, workers are exposed to the health hazards only during working hours. However, it should be cautioned that in many developing countries, the bulk of the small-scale production of building materials takes place in the informal sector using rudimentally and inefficient technology and ignoring legislation.⁽³⁾ Thus these mitigation measures do not have much relevance to the operation of the informal-sector producers.

2. Construction and maintenance

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11. The principal materials-related health hazards associated with the construction phase are dust, fumes, solvents and gases, and insecticides and fungicides. Many of the risks are most acute during this phase, where workers are exposed to health hazards in a concentrated form, but often without the workplace controls `of materials production. Some of the health hazards to which construction workers are particularly prone are lung diseases from inhalation of dusts (particularly mineral fibres); skin and eye irritation and allergies from volatile organic chemicals released from paints and varnishes; and poisoning from the use of insecticides. The workers most at risk are those involved in the application of finishes (e.g., painters, decorators, and flooring contractors); and in maintenance and renovation works, where the exposures are concentrated and often in confined indoor spaces. Maintenance work can also put building occupants at risk if the building continues to be inhabited. A special hazard arises from the removal of asbestos-based materials during maintenance, as it can introduce concentrations of fibres into the indoor atmosphere dangerous both to occupants and to workers. Removal of toxic metals-based paints also puts the inhabitants at risk. In both construction and maintenance, disposal of toxic or harmful wastes can create hazards to workers, occupants and the general public.

3. Occupancy

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12. The causal agents of ill-health found in the indoor environment which are associated with building materials include dusts and particulate matter, inorganic and organic chemicals, microbes, and arthropods. Table 1 shows the range of such agents. The indoor environment typically contains numerous chemicals in the form of dusts or gases, only some of which are attributable to building materials. Some building materials contribute by exhaling the chemicals of which they are made, or by contributing to the dusts as materials disintegrate. Materials can also act as a sink, storing chemicals from the surrounding atmosphere, and later releasing them.⁽⁴⁾ Such releases can be absorbed by the human body through inhalation.

13. A further range of organic chemicals is rapidly entering the indoor environment as a result of new products for the treatment of materials and furnishings. These include formaldehyde, a group of volatile organic compounds used, for example, in plastics and other polymeric materials; and pesticides which are semi-volatile and thus can remain in the environment for a long time, becoming adsorbed in dust or soft furnishings and released later. All of these chemicals are also inhaled.

14. The inhalation of dust and gases can trigger a variety of responses. The possible health effects can be classified as toxic, irritant or sensitizing.⁽⁵⁾ Toxic effects may be acute, resulting in direct damage to organs, or chronic, causing for instance cancer, genetic damage or birth defects. Irritant effects are those which affect the skin, or through inhalation, can cause discomfort or damage to the mucous membranes, the nose, lungs or eyes. Allergic effects include a variety of sensitivities, for example asthma, rhinitis or eczema.

15. Microbes tend to thrive in the indoor environment. Damp, porous building materials can contribute to the conditions needed to enable these organisms to flourish. Arthropods inhabit buildings. In tropical regions some of these are carriers of debilitating diseases such as malaria and dengue which are carried by mosquitoes, and Chagas' disease which is carried by triatomine bugs. When dead, their disintegrated remains and excreta collect in house dust, where they can cause a variety of allergic sensitivities. In northern climates, the most important arthropod is the house-dust mite whose faecal pellets are held responsible for a significant rise in asthmatic conditions.⁽⁴⁾ Other arthropods tend to inhabit small cracks and crevices in buildings; thus they are encouraged by the use of building materials which are liable to crack, such as unstabilized earth, or thatched roofs.

16. Another aspect of building materials which can impact upon human health is their radioactivity, leading to the production of radon gas. Although in most instances their contribution to indoor radioactivity is small compared with soil radon gas, building materials produced from industrial waste products can have significant emissions. Radioactivity has a variety of carcinogenic effects.

B. Asbestos

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1. Sources and health implications

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17. The term, asbestos, covers a number of naturally-occurring fibrous silicate materials in rock formations widely distributed in the Earth's crust. However, only a few of the deposits are commercially exploitable. The principal varieties of asbestos used commercially are chrysotile (hydrous magnesium silicate), a serpentine mineral, and crocidolite (iron and sodium silicate) and amosite (iron and magnesium silicate), both of which are amphiboles. Anthophyllite, tremolite, and actinolite asbestos are also amphiboles, but they are rare, and the commercial exploitation of anthophyllite asbestos has been discontinued.⁽⁶⁾

18. While the properties of asbestos have been known for thousands of years, it is only in the last century, that the manufacture of building materials incorporating asbestos has been carried out on an industrial scale.⁽⁷⁾ The main use of asbestos fibres is in the manufacture of asbestos cement products. The products are based on the addition of asbestos fibres (around 10-15 per cent by weight) to a non-combustible filler such as Portland cement. Asbestos cement is a high-compression, high-density, hard-surfaced material which is commonly employed for fire protection panels, corrugated panels for roofing and cladding, roof ales, fire surrounds, rainwater goods, water tanks and water pipework etc.⁽⁸⁾ The second largest use of asbestos fibres in the United State of America is the asphalt and vinyl floor-tile manufacturing industry. Increased use of these types of tiles in many countries is due to their durability and impermeability to water.⁽⁹⁾

19. Epidemiological studies, mainly on occupational (mining and milling, manufacturing, or product application) groups, have established that all types of asbestos fibres are associated with asbestosis, bronchial carcinoma, and mesothelioma.⁽⁹⁾ A brief account of these health problems is as follows:^{(7, 10, 11)}

• (a) Asbestosis. This is a deposition of fibrous tissues in the lung parenchyma - the region where oxygen exchange takes place. Initial coughing is followed by progressive difficulty in breathing. The patient may eventually die of cardio-respiratory failure. Severity of the disease is related to length of exposure to asbestos (a dose relationship), although it may be arrested in the early stages if contact with asbestos ceases. Asbestosis has a long latent period, rarely being seen less than 10 years after first exposure to asbestos. It seems that there is a threshold level below which the condition does not occur;
• (b) Bronchial carcinoma (lung cancer). As with asbestosis, there is a dose relationship but no threshold level below which there is no risk. There appears to be a multiplicative effect on smokers: the risk to asbestos workers who smoke is 10 times as great as to non-smokers;
• (c) Mesothelioma. A malignant tumour on the lining of the chest cavity (pleural mesothelioma) or abdomen (peritoneal mesothelioma). The latent period for the disease is very long - an average of 38 years from first exposure. Mesotheliomas have a very poor prognosis, being unresponsive to most cancer therapies;
• (d) Non-malignant conditions such as diffuse thickening or effusion (fluid in the lungs). These lung abnormalities may cause breathlessness, but are often symptomatic.

20. Health risks due to exposure to different asbestos types are dependent on the fibrous structure of the material, thus asbestos types which are liable to form fibres less than 3 microns in diameter, principally the amphiholes, are most hazardous.⁽¹⁰⁾ The fibre length is also important, with fibres longer than approximately 8 microns posing greatest risk. The principal risk is through inhalation of airborne fibres, since there is little chance that fibres will penetrate the skin or be absorbed from the digestive tract.

21. Past exposure to asbestos in industry or in the general population has not been sufficiently well documented to make an accurate assessment of the risks from future levels of exposure, which are likely to be low.⁽⁶⁾ There are two possible approaches for assessment of risks, one based on a comparative and qualitative evaluation of the literature (qualitative assessment), the other on an underlying mathematical model to link fibre exposure to the incidence of cancer (quantitative Assessment). Attempts to derive the mathematical model have had limited success.⁽⁶⁾ However, on the basis of qualitative assessment, the following conclusions have been drawn:⁽⁹⁾

• (a) Among occupational groups, exposure to asbestos poses a health hazard that may result in asbestosis, lung cancer and mesothelioma. The incidence of these diseases is related to fibre type, fibre dose, and industrial processing;
• (b) In para-occupational (neighbourhood of an asbestos industrial plant, or home of an asbestos worker) groups, the risk of mesothelioma and lung cancer is generally much lower than for the occupational groups. Risk estimation is not possible because of the lack of exposure data required for dose-response characterization. The risk of asbestosis is very low;
• (c) In the general population, the risks of mesothelioma and lung cancer attributable to asbestos cannot be quantified reliably and are probably undetectably low. The risk of asbestosis is virtually zero;
• (d) On the basis of available data, it is not possible to assess the risks associated with exposure to the majority of other natural mineral fibres in the occupational or general environment. The only exception is erionite, for which a high incidence of mesothelioma in a local population has been associated with exposure.

22. The health hazards associated with use of asbestos in the construction industry have come to a sharper focus in recent years: there has been a growing alarm about risks to dangers of breathing fine asbestos. However, there are others who believe that not enough toxicological and medical data are available to justify a ban on asbestos and asbestos products and that a lot more research is necessary before a judgement could be arrived at, and that the existence of asbestos-related diseases reflects neglect of working conditions in the factories and ignorance regarding the science of occupational diseases associated with asbestos in the past.⁽¹²⁾ Yet, due to the undisputed fact that asbestos is one of the identified carcinogens, in many countries the manufacture and use of asbestos-based products have been strictly controlled in recent years. For example:

• (a) Use of crocidolite and amosite types of asbestos is increasingly being discontinued (they are banned in the European Union countries);
• (b) The number of uses and the total consumption of asbestos and its products in the Netherlands have fallen sharply in recent years;⁽¹³⁾
• (c) The demand for asbestos was less than one third in the United State of America, in 1987 compared with its peak in 1973;⁽¹⁴⁾
• (d) Furthermore, ILO Convention No. 162 requires governments to prohibit the use of crocidolite and spraying of all forms of asbestos.⁽¹⁵⁾

23. Recently the São Paulo Declaration, an outcome of the Asbestos International Seminar: Controlled Use or Ban, held in Sao Paulo, Brazil, in March 1994, demanded the prohibition of all uses of asbestos and the promotion of substitutes which are less dangerous to the health and safety of workers.⁽¹⁶⁾

24. In spite of the opposing views about asbestos, the controlled use of asbestos appears to be favoured by agencies such as WHO, ISO, ILO, the United Nations Economic Commission for Europe, OECD, and the Commission of European Communities (EU).⁽¹²⁾ However, substitution of asbestos should be considered when safe control cannot be assured.

2. Factors influencing exposure

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25. Risk groups which may be exposed to high asbestos levels are: workers in asbestos-manufacturing and -processing industries, people who, by virtue of their professions, spend long periods of time in public buildings and offices where sprayed asbestos has been applied, and maintenance and demolition workers.⁽¹³⁾ Risks to construction and maintenance workers and building occupants occur when the material containing asbestos is cut or drilled, releasing respirable particles into the air. Installed components, for example sheet materials which may be sealed by a layer of paint, pose little risk unless degradation occurs by physical abrasion. Chemical attack is a possibility in the case of asbestos cement products in contact with water (especially if "aggressive" due to pH rating and ion content), for example roof sheets and downpipes .⁽¹⁷⁾

26. The most serious risks are likely to be associated with demolition, or programmes of removal aimed at eliminating asbestos products from a building. There are often problems in identifying components which contain asbestos, particularly since many are virtually indistinguishable from the substitute materials which have been developed incorporating MMMF. Sampling and analysis by experts in the field may be necessary for correct identification.

27. Since stripping of asbestos-containing materials often raises exposure levels for building occupants as well as the contractors for a considerable period of time, the risks involved in such activities must be carefully balanced against predicted risks if the materials remain in place. In-situ repair work and sealing may be preferable to full-scale removal, particularly if the asbestos is in a relatively inaccessible location. Heavy physical exertion increases the respiration rate and, thereby, the exposure dose. Smokers constitute a risk group with an increased susceptibility to lung cancer.

3. Acceptable exposure levels

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28. Most developed countries have regulated their asbestos industries, with specified limits to asbestos exposure. In the United Kingdom of Great Britain and Northern Ireland; for example, control limits and action levels are set out by the Control of Asbestos at Work Regulations 1987 (amended 1993). At exposures above the control limit, respirators fitted with the correct filter must be worn. In applying the exposure limit, "fibre" is defined as a particle with length less than 5 microns, average diameter less than 3 microns and ratio of length to diameter greater than 3:1. For chrysotile alone, the control limit is 0.5 fibres per millilitre (f/ml) of air averaged over 4 hours, or 1.5 f/ml averaged over any 10 minute period. For any other type of asbestos, whether or not mixed with chrysotile, the corresponding limits are 0.2 and 0.6 f/ml. If workers' exposure exceeds the action level, the employer is obliged to arrange medical examinations at a maximum of two-year intervals and to keep accessible medical records for at least 40 years. Taking into account cumulative exposure over a 12 week period, the action level is 96 fibre-hours per millilitre of air for chrysotile and 48 for other asbestos types.

29. In the case of the United States, the Environmental Protection Agency (EPA), took new regulatory action in 1988 on additional protection to state and local government employees covered by the EPA asbestos abatement worker protection.⁽⁶⁾ EPA defines "fibre" as a particulate form of asbestos 5 micrometres or longer, with a length-to-diameter ratio of at least 3:1. The permissible exposure limit to workers exposed to airbone asbestos being 0.2 f/cc of air, averaged over an eight-hour day. The action level is O.l f/cc averaged over eight hours. The action level is the level at which employers must begin activities such as air monitoring, employee training, and medical surveillance. In the case of environmental exposure, it has been estimated that fibre concentrations are unlikely to exceed one thousandth of the control level.⁽¹⁸⁾ A typical situation might give a lifetime excess risk of death from mesothelioma of 1 or 2 in 10,000.⁽¹⁸⁾ For lung cancer, the same source predicts an excess mortality of 2 per million. As noted above, there appears to be a threshold effect for asbestosis which limits its impact to workers in the asbestos industry, with little if any effect on those subject to non-occupational exposure.

4. Mitigation strategies

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30. Construction activities (including renovation, demolition and insulation) should be designed and planned to eliminate or reduce the need for mineral-fibre-based materials which have a cancer-producing potential. Stringent handling regulations in the manufacture, use, transporting, demolition, storage and disposal of asbestos and MMMFs must be established. In view of the reported carcinogenic properties of asbestos after inhalation, exposure via the respiratory route should be avoided as far as possible. To avoid eye and skin irritation, protective clothing and goggles should be used. Employers should develop a training programme for all employees who are exposed to airborne concentrations of asbestos at or above the action level. The training programme must inform employees about the methods of recognizing asbestos and the health hazards of asbestos exposure; the relationship between asbestos and smoking in producing lung cancer; operations which could result in asbestos exposure; the importance of necessary protective controls to minimize exposure including, as applicable, engineering controls, work practices, respirators, housekeeping procedures, hygiene facilities, protective clothing, decontamination procedures, emergency procedures and waste-disposal procedures; the purpose, proper use, and limitations of respirators; and the medical surveillance programme.⁽⁶⁾ Furthermore, for construction workers who may be exposed to asbestos dust, hazards will be mitigated further by following advice issued to workers in the asbestos industry:

• (a) Be aware of the materials likely to contain asbestos, and potential risks;
• (b) Follow recommended working procedures, for example, using hand tools for cutting and drilling asbestos products rather than mechanical tools;
• (c) Keep the working area clean; damp down dust before removal by vacuuming with specially-designed equipment; do not blow away debris with an air-line;
• (d) Ensure waste material is properly collected in marked dustproof containers for safe disposal;
• (e) Wear protective clothing and a respirator, where appropriate;
• (f) Wash or shower at the end of the working day;
• (g) Do not take working clothes home;
• (h) Avoid smoking.

31. Employers have a duty to protect the workforce by taking all possible steps to minimize health risks. They should ensure that workers follow the guidelines above; they should provide suitable equipment and facilities (e.g., for showering), monitor exposure and, when necessary, arrange medical checks. Measures of this type have been adopted by the Indian Government through the publication of 16 Indian Standards on Safety in the Use of Asbestos. In addition, the Indian Government has established a Development Panel and the Asbestos Products Industry and an Expert Group to examine the feasibility of substituting alternative products.⁽¹²⁾

5. Substitute materials

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32. The substitution of asbestos should be considered where safe control cannot be achieved. Many materials have been developed as substitutes for asbestos-based products, a large proportion of which use MMMFs. MMMFs, otherwise known as mineral wools, (a term used in the United States) to refer to mixtures of rock and slag wools) are amorphous glassy fibres made from molten slags, natural rocks, such as basalt, and borosilicate or calcium silicate glasses; chemically they are all amorphous silicates. Their use has increased greatly since the 1960s, partly due to a growing awareness of risks associated with asbestos. Applications of MMMFs include: reinforcement to glass-reinforced cement; glass-reinforced plastic and rubber; textiles and electrical insulation; insulating quilts, bats and boards; tiles, pipes and ductwork; acoustic insulation; high-temperature thermal insulation, e.g., lining refractory kilns; joints and gaskets; and as high-efficiency air filters.

33. Studies however indicate that all respirable size MMMFs are not biologically inert and health hazards posed by them require thorough investigation. The Intemational Agency for Research on Cancer (IARC) has indicated that:⁽¹⁹⁾

• (a) There is sufficient evidence for the carcinogenicity of glasswool and of ceramic fibres in experimental animals;
• (b) There is limited evidence for the carcinogenicity of rockwool in experimental animals;
• (c) There is inadequate evidence for the carcinogenicity of glass filaments and of slagwool in experimental animals;
• (d) There is inadequate evidence for the carcinogenicity of glasswool and of glass filaments in humans;
• (e) There is limited evidence for the carcinogenicity of rock-/slagwool in humans;
• (f) No data were available on the carcinogenicity of ceramic fibres m humans.

34. Thus IARC, in accordance with its carcinogenic evaluation criteria (see table 3), has concluded in an overall evaluation of the effects of glasswool, rockwool, slagwool and ceramic fibres that they are possibly carcinogenic to humans. On the other hand, continuous filament is not classifiable as to its carcinogenicity.

35. Other related health hazards include skin, eye and upper-respiratory tract irritation such as bronchitis.⁽²⁰⁾ Occupational health hazards are due to improper exposure to MMMFs. According to IFBWW (20), most countries in the world treat MMMFs as nuisance dust and in most cases follow a standard of 10 mg/m³ of total dust or 5 mg/m³ for respirable dust. Examples of more stringent fibre and gravimetric standards that have been introduced for MMMFs are as follows:⁽²⁰⁾

• (a) In Denmark, stationary workplaces must meet a 2.0 f/ml fibre standard, and in non-stationary workplaces a 5 mg/m³ total dust standard is in effect;
• (b) In Sweden, all work involving synthetic or inorganic fibres must meet a 1.0 f/ml standard;
• (c) In the United Kingdom, a fibre standard of if/ml applies, as well as a total inhalable dust limit of 5 mg/m³;
• (d) In Australia and in Germany, all work with MMMFs must meet a 0.5 f/ml standard as well as a 2 mg/m³ respirable dust standard;
• (e) in Canada, Alberta has adopted a limit of 1.0 f/ml for fibrous glass and mineral wool and 0.5 f/ml limit for refractory ceramic fibres, and a total dust standard of 5 mg/m³ for work with these materials also applies.

36. Other alternatives which do not contain mineral fibre, such as metallic or ceramic products, are often less available or considerably more expensive. The possible hazards posed by fibrous materials may have to be considered in relation to these other disadvantages in selecting components. For new buildings, non-fibrous alternatives to asbestos should be considered first. Whenever MMMF substitutes are considered, and as in the case of asbestos, appropriate work practices, engineering, and administrative control measures should aim at controlling the exposure of workers to airborne dust and fibres. Substitute materials and non-fibrous alternatives are suggested in table 4.

C. Metals

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1. Sources and health implications

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37. A number of metals are used in the construction industry in their metallic form, maldng use of then structural properties, their resistance to water penetration or their high thermal and electrical conductivity - or as compounds, primarily in paint and other finishes. Most of them are harmless - in fact, dietary intake of many metallic elements is essential to health. Risks may, however, result from excessive intake of certain metals. The two principal building-related sources are: soluble metallic salts in water supply, from the use of metals in pipework and joints, storage tanks and roof flashings, gutters and downpipes; and paint flakes, which may be ingested. The metals of potential concern are cadmium, chromium and lead.

38. Cadmium is highly toxic: exposure may result in bone damage and kidney damage. Again, the principal sources are dietary, but paints may also present risks. Cadmium may also be present as a contaminant of foam-rubber carpet backing.

39. Chromium is most toxic in the valence state chromium (VI). It too is a component of some paints and metallic finishes and may be a contaminant of cement. Mining waste may contaminate groundwater. Health effects observed in chromium-industry workers include: contact dermatitis on exposed skin; ulceration if the skin is penetrated through cuts and abrasions; if inhaled, inflammation of the larynx and perforation of the nasal septum; liver damage; lung cancer, and possible other types of malignant tumour.

40. Lead is perhaps the most important constructional metal with health implications. The workability of lead in its metallic form has made it an important material for roofing and associated works such as flashings, valley gutters and rainwater hoppers. It has also been used for water-supply pipes. Other uses include glazing bars for stained glass or small-paned windows, as an additive in linseed-oil putty, and as an important component of traditionally-formulated paints, in particular in primers for external use on wood and metal: red lead and calcium plumbate primers contain over 20 percent lead in their liquid state. Even paints for internal application such as eggshell finishes may contain a considerable proportion of lead. The effects of lead poisoning have been recognized for hundreds of years in lead miners and smelters. There are other health risks associated with lead, but these are of concern primarily in lead-using industries such as battery and lead-shot manufacture, and in the mining and smelting of lead, and are not of significance to the construction and building materials industries.⁽²¹⁾

2. Factors influencing exposure

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41. Concentration of soluble lead salts in water supplied through lead pipework is dependent on the characteristics of the water. Soft, acidic waters show the greatest tendency to leach lead from plumbing, but problems can also-be encountered with some types of hard water. The water temperature and the length of time that it has been in contact with lead plumbing are also important factors .⁽¹⁷⁾ Children are particularly liable to be affected by potentially toxic metallic compounds in paintwork. Small children spend a large part of their time at floor level, where they are susceptible to paint and solder flakes in household dust. Furthermore, some children develop a condition known as pica, characterized by a craving to eat non-food substances. Paint flakes can be a favourite "meal".

3. Acceptable exposure levels

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42. In the case of chromium, the WHO-recommended upper limit in drinking water is 0.05 parts per million. For lead, an upper limit of 50 microgrammes per litre for mains water has been accepted by the EU.⁽¹⁷⁾ However, many households' supply from the tap may well exceed this, because of leaching from plumbing installations. For example, a survey carried out in Scotland in the mid-1970s showed that tap water in 21 per cent of households exceeded a level of 100 microgrammes of lead per litre. An upper limit in blood level concentration of lead of 35 microgrammes per 100 millilitres has been set by the EU. The United Kingdom Government advises that environmental exposure to lead should be reduced if an individual's blood level concentration exceeds 25 microgrammes per 100 millilitres, particularly in the case of a child. Supported by scientific data from the United States,⁽²²⁾ a number of European Governments are considering lowering this level to 10-15mg/dl. However, while the medical effects of acute poisoning - including stomachache; constipation and vomiting - are clear, there is less consensus about the effects of low-level exposure. The threshold level is uncertain, and there is considerable scientific debate about appropriate action levels.⁽²¹⁾

4. Mitigation strategies

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43. If roofs have lead finishes or components such as valley gutters, the use of run-off water for cooking and drinking should be avoided. Lead-based paints, and other toxic-metal based paints too should never be used in situations accessible to children, particularly on nursery furniture or play equipment. To minimize the risks of exposure to lead compounds, paintwork should be kept in good condition: recent, lead-free paint may cover older layers of traditional paints and primers containing lead or other potentially toxic metallic compounds. It has been estimated that 60 per cent of the domestic stock in the United States contains leaded paintwork, amounting to 3 million tons.⁽²²⁾ Good maintenance of all paintwork may be preferable to removal: renovation of older timber houses in the United States has been shown to raise occupants blood lead levels two times, thus a doubling of the average load.⁽²³⁾ Where old paintwork - possibly containing lead - needs to be stripped to give a good surface for re-decoration, it is advisable to use a chemical stripper rather than mechanical methods (particularly those using exposed flame or hot air above 500°C). Good ventilation should be provided. Wet sanding is a possibility for large areas, provided that the resulting dust is carefully collected. All debris from stripping old paintwork should be meticulously cleared away for disposal. Any paints containing lead, chromium or cadmium should be clearly labelled with their content of these metals as wet film and dried paint. Unsuitable uses should also be indicated - particularly in locations accessible to children.

5. Substitute materials

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44. Substitute materials are suggested in table 5.

D. Solvents

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1. Sources and health implications

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45. Organic solvents are very widely used in construction as key ingredients of adhesives, paints, flooring materials and mastics. The most commonly used solvents include white spirit, toluene, xylene, trichloroethane, styrene and carbon tetrachloride. Paints, glues and lacquers contain toluene, methyl n-butyl ketone, n-hexane and xylene. Paint strippers and solvents contain white spirit and dichloromethane and expanded plastics contain styrene.

46. If inhaled, solvents dissolve readily in the blood stream. Sufficiently low concentrations will be metabolized quickly with no ill effects by the body. But if exposure is excessive, a variety of health effects can occur, including sedation effects ranging from slowed reaction time and decreased vigilance to anaesthesia, irritation to the eyes, nose and throat, liver damage, and damage to the nervous system.⁽²⁴⁾

47. The International Federation of Building and Wood Workers has reported major health hazards for painters which include:⁽²⁵⁾

• (a) Occupational cancer - Painters run a high risk of getting cancer from the chemicals with which they work: benzene can cause leukaemia; carbon tetrachloride can cause liver cancer; all chlorinated solvents (those with "Chloro" or "Chloride" in their names) are suspected carcinogens, for example, methylene chloride is a suspect carcinogen because it causes cancer in animals. Table 6 shows a list of known cancer agents evaluated by IARC. For the evaluation criteria refer to table 3.



Table 6. A list of some of the known cancer agents evaluated by IARC

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Cancer agent	IARC group	Likely sources
Chromates	1	Primers, paints
Coal tar pitch	1	Coal tar epoxiew
Toluene diisocyanate	2B	Some polyurethanes
Cadmium	2A	Pigments
Benzene	1	Solvents, some thinners
Methylene chloride	2B	Paint strippers
Styrene	2B	Organic solvent, e.g., in some polyesters, putties and fillers
Nickel compounds	1	Pigments
Epichlorohydrin	2A	Contaminant in some epoxy resin
Formaldehyde	2A	Phenol formaldehyde resins, urea-formaldehyde resins
3,3'-dichlorobenzidine	2B	Pigments
Lead	2B	Primers, driers, some pigments
Antimony oxide	2B	Some pigments, fire-protection coatings
2- Nitropropane	2B	Organic solvent
Tetrachloroethylene	2B	Organic solvent for degreasing
Carbon tetrachloride	2B	Contaminant in some chlorinated rubber coatings
Source: Solvents and Paint Hazards, IFBWW Series 3 (Geneva, International Federation of Building and Wood Workers, 1992).



• (b) "Painters' syndrome" - This is the name given to the effects on health which may arise from long-term exposure to organic solvents. Organic solvents get into the body and brain through the lungs or skin and slowly cause permanent changes in the brain and the central nervous system. Solvents may also damage the peripheral nervous system which is the system of nerves leading from the spinal cord to the arms and legs. The symptoms caused by this damage are numbness and angling in the hands and feet, weakness and paralysis.
• (c) Occupation skin diseases - All solvents can dissolve the skin's protective barrier of oils, causing dermatitis. There are two types of contact dermatitis: irritant contact dermatitis, and allergic contact dermatitis.
• (i) Contact dermatitis is the most common occupational skin disease, caused when the skin comes into contact with certain chemicals which can make the skin red, sore, inflamed, irritated, cracked, dry and itchy, and sometimes rashes and blisters may develop. Anyone working with paints and coatings runs a high risk of contracting irritant contact dermatitis because many paints and coatings contain chemicals which irritate the skin. This is a non-allergic skin reaction from exposure to irritating substances. Exposure to irritants accounts for 80 per cent of the cases of occupational contact dermatitis.
• (ii) Allergic contact dermatitis is a type of dermatitis caused by becoming allergic or sensitized to particular chemicals called allergens. Common allergens include epoxy adhesives, chromium and nickel compounds. Once someone has developed an allergy to a chemical (has become "sensitized"), the dermatitis will flare up again, usually within 12 hours after contact with the chemical. Some workers develop allergic contact dermatitis after many years of trouble-free working with paints/coatings. Other workers never develop it at all even though they work with the same paint ingredient that gives allergic contact dermatitis to other painters. Allergic contact dermatitis is not easy to treat. Studies show that 25 per cent of people with allergic contact dermatitis will not recover from their allergy and will have to leave their work so as to avoid all contact with the allergens.
• (d) Occupational lung diseases - occupational asthma, lung irritation from paint vapours and mists, and chronic bronchitis/emphysema Occupational asthma is the result of becoming allergic to a chemical or substance. Once the lungs become allergic to a lung allergen, the symptoms of asthma can come back with exposure to a tiny amount of the substance. This means some workers are forced to leave their jobs because the asthma is so serious. It can be very difficult to "lose" an allergy. Common symptoms are wheezing, shortness of breath and coughing but there can also be other symptoms.

2. Factors influencing exposure

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48. An important characteristic of the hazardous substances in forms of gases and vapours which strongly influences their significance as health hazards is their volatility. Highly volatile substances are those with low boiling points, which will give off gases and vapours at a very rapid rate at normal temperatures. A study on the solvent vapour hazards during painting with whitespirit-borne eggshell paints, indicated that when painting was carried out at a lower temperature (12°C instead of 24°C) the rate of solvent vapour release, and consequently the hazard, was reduced by about 25 per cent.⁽²⁶⁾ The same study concluded that the use of such paints in unventilated conditions can constitute significant health hazards: in the trials the STEL for white-spirit vapour was exceeded approximately 10 minutes from the start of painting, and concentrations approaching 700 ppm for a 10-minute time weighted average (TWA) were reached before completion of painting. The allowable long-term exposure limit for an eight hour TWA exposure is 100 ppm, and the STEL for any given 10-minute period is 125 ppm.⁽²⁶⁾ Thus, unless ventilation is good, hazardous concentrations can easily be reached shortly after use or installation; but the rate of emission will decline rapidly, and they are not likely to be a long-term problem, except where, for some reason, emissions are delayed. Substances of low volatility, or semi-volatile substances, conversely, are not emitted rapidly: but they can continue to be emitted for a long period of time; they can be absorbed by dust and furnishing materials, and then later be re-emitted to the environment; and they are metabolized only slowly in the human body, and can therefore tend to accumulate.

49. Solvents are volatile and therefore can build up, in the indoor environment during construction and maintenance work. Moreover, their emission can continue even after occupancy, and thus add to the load of other solvents and organic chemicals in the environment from dry cleaning, aerosol propellants, correction fluid, cigarette smoke and so on.

50. WHO classifies organic chemicals as very volatile (VVOC), volatile (VOC), and semi-volatile (SVOC). The VVOCs are a fairly small group of which, among building materials, formaldehyde is the most important member. The VOCs are a much larger group, of growing size; they include the binders in plastics and other polymeric materials and the large group of solvents used in the manufacture of paints and varnishes. The SVOCs consist largely of pesticides which are also very numerous. A fourth category of organic compound which has significant hazards is particulate organic matter (POM) in the form of dust. Building materials are, however, not a significant cause of POM in the indoor environment. The classes of substances, their characteristics and uses, based on WHO data, are summarized in table 7.^(5,27)

3. Acceptable exposure levels

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51. WHO and national authorities, such as American Conference of Government Industrial Hygienists (ACIGH) have set limits for industrial exposure. The Threshold Limit Values (TLV) set by ACIGH for some of the more important solvents are shown in table 6. Somewhat lower levels would be appropriate for domestic exposure, because of the increased time of exposure, and the greater susceptibility of some occupants such as small children and the elderly. Table 8 also shows some domestic air levels taken from a variety of studies.⁽²⁸⁾ It will be seen that all are far below the TLVs prescribed.

52. During occupancy, the key consideration is not the exposure or limit value of any one organic chemical but the exposure to all volatile chemicals. While exposure to individual organic chemicals in the indoor atmosphere may be acceptably low, the combination of numerous gases and vapours at low concentrations can have irritant effects. Measurements by Molhave⁽²⁴⁾ of the emissions of solvent gases and vapours from 42 building materials showed that about 80 per cent of the compounds identified in the air around the materials were known or suspected mucous membrane irritants. When combined with other gases in an indoor environment, and combined with other environmental factors such as sound, temperature and humidity, these organic chemicals are regarded as being largely responsible for the condition known as "sick building syndrome". Molhave,⁽²⁴⁾ based on experiments on people exposed to different levels of exposure, suggests that concentrations 9f total volatile organic compounds less than 0.16 mg/m³ maybe expected to cause no mucous membrane irritation, while concentrations above 5 mg/m³ are found to cause irritation. In the intermediate range, irritation may occur if promoted by other environmental exposures. Molhave⁽²⁹⁾ has subsequently proposed an approximate dose-response table for airborne VOCs (see table 9).

53. At present, there are no national or international indoor air criteria for new buildings but in some areas, they are beginning to be developed. In the state of Washington, for example, emission rates for office furniture workstations must be such that the resulting air concentrations in the building are less than those shown in table 10.⁽³⁰⁾

4. Mitigation strategies

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54. While the solvents are in use, during construction activity, levels will clearly reach much higher values over a short period of time. Where solvent-bone paints, have been specified, measures must be taken to ensure ventilation or solvent extraction sufficient to reduce solvent-vapour levels below the occupational exposure limits. Where this is not practicable the operators must be provided with suitable respiratory protection. Protective clothing should also be provided to workers. Workers too need to be provided with health and safety information about the hazards of the solvents, including the minimum requirements for safe use and exposure control to protect their health, the chemical ingredients, the short- and long-term health effects, first-aid information, .and storage and transport requirements.

5. Substitute materials

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55. There are limited options at present for the substitution of VOCs in paints and other finishes. Alternative water-based paints are available which reduce the quantity of organic chemical solvents, but although advertised as environmentally-friendly, they do contain significant quantities of organic solvents and a range of other hazardous chemicals. Solvents based purely on natural products do exist⁽³¹⁾ but are not manufactured yet in large quantities, and paints based on them are not commercially available.

E. Insecticides and fungicides

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1. Sources and health implications

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56. Pesticides are natural or chemical agents such as insecticides, used to destroy troublesome insects, herbicides for weed control, fungicides to control plant disease, rodenticides and germicides.⁽³²⁾ A range of organic chemicals are in use as insecticides and fungicides for timber treatment. They include dieldrin, lindane and benzene hexachloride, commonly used as insecticides, and pentachlorophenol, commonly used as a fungicide.⁽¹⁷⁾ There are many others in use,⁽²⁸⁾ and some, such as DDT, which have been widely banned. Table 11 shows some of the most widespread chemicals used.

57. All of these chemicals are necessarily toxic to the organisms they are intended to combat. If inhaled or ingested in sufficient quantities, they can also be hazardous to the health of those involved in applying them, particularly when used in the form of sprays. Many of them attack the nervous system, or can cause damage to internal organs such as the liver and kidney. Some can cause skin reactions. Several of them have been shown to be carcinogenic and others are suspected carcinogens.^(2,33) It has recently been estimated that as many as 3 million people annually are poisoned by pesticides, of whom perhaps 20,000 die.⁽³⁴⁾ Although most of these casualties arise from agricultural use and only a small proportion derives from the use of pesticides in buildings, the hazard from pesticides' use in buildings is significant as many of the most toxic pesticides are used for timber treatment, and exposure levels may also be particularly high in the indoor environment. Examples of some toxicity levels for some chemicals used in wood formulations are given in table 12.⁽³⁵⁾ LC50 is the statistically derived exposure concentration of a chemical that can be expected to cause death in 50 per cent of a given population of organisms under a defined set of experimental conditions (e.g., a 96 hour fish LC50), and LD50 is the dose of a toxicant that will kill 50 per cent of a given population of organisms within a designated period of time.⁽³⁵⁾

2. Factors influencing exposure

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58. As with solvents, the principal risk from insecticides and fungicides is to construction workers. A particular risk is to those involved in the remedial treatment of timber in existing degraded buildings which has to take place quite often in poorly-ventilated roof spaces, and using sprays.⁽²⁾ Those involved in the pesticide treatment of buildings to eliminate disease vectors can also be seriously at risk.⁽³⁶⁾

59. After application, the rate of emission into the indoor environment is relatively slow, since a characteristic of all pesticides is that they have low volatility. However, if used in conditions of very poor ventilation, the level of exposure to occupants after application can be significant. There is little experimental evidence available on domestic exposures, but it has been estimated that in conditions of poor ventilation exposures approaching occupational exposure limits are possible.⁽¹⁷⁾

60. Pesticides of various types are also used in timber pre-treatment, posing a potential threat to workers in those enterprises, which in some countries commonly operate under a poor state of control. Because of then persistence in the environment and damage to all forms of fife, pesticides must be treated as hazardous waste and disposed of with great care. Many of the most serious and widespread cases of pesticide poisoning occur as a result of spills and casually dumping wastes on uncontrolled sites.⁽³⁴⁾

3. Acceptable exposure levels

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61. Specific occupational exposure limits for most of the important pesticides have been proposed by national authorities. Table 11 shows those set for the United Kingdom by the Health and Safety Executive,⁽³⁷⁾ which are similar to the TLVs proposed for the United States by ACIGH (see also table 12). But it has been suggested that domestic exposure levels should be set at a level only I per cent of the occupational exposure limit to protect vulnerable occupants.

4. Mitigation strategies

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62. The number of chemicals in use as pesticides and timber preservatives is huge and growing annually, and many of their effects are as yet not clearly identified.⁽³⁸⁾ Because of their known toxicity, an international coalition of groups and individuals who oppose unnecessary use and misuse of pesticides, the Pesticides Action Network, has identified the following 13 pesticides, most commonly used as wood preservatives requiring strict control:⁽³⁸⁾ Aldicarb, Campheclor (Toxaphene), Chlordane and Heptachlor, Chlordimeform, DBCP, DDT, the "dries" -Aldrin, Endrin and Dieldrin, EDB, HCH and Lindane, Paraquat, Parathion and Methyl Parathion, Pentachlorophenol, and 245T. All of them are highly poisonous to the nervous system. Since no pesticides are free of potential health hazards if used without proper control, less poisonous wood preservative treatments, those based on synthetic pyrethroids (e.g., permethrin) and inorganic boron compounds, should be used. Protective clothing should be worn when treating or handling treated timber. If treated timber is machined or sanded an efficient dust extraction system should be used and wastes disposed of safely: if dust extraction is not available, dust masks should be used. In remedial treatment of timber, particularly in poorly-ventilated enclosures, operators should be provided with respirators.

63. There is also a growing school of thought that pesticides are not an efficient long term approach to the preservative treatment of timber, because they penetrate the timber only to a limited extent, and are gradually lost to the atmosphere. Because of this limited life, the contribution claimed by pesticide manufacturers to stemming deforestation by reducing future demand for timber has been challenged.⁽²⁾ Thus elimination of the need for pesticides by design is the recommended alternative. The alternative mitigation strategy is to eliminate by design the condition which pesticides are used to treat. Rotting of timbers can only take place under conditions of high humidity; it can be reduced or eliminated by:

• (a) Seasoning timber before use to reduce moisture content below 20 per cent;
• (b) Ensuring all timber in a building is kept at low - levels of moisture, through providing ventilation of underfloor and roof spaces;
• (c) Making use of timber species which are less susceptible to rot;
• (d) Reducing the use of the more vulnerable sapwood;

64. Likewise, where pesticides are commonly used for protection against termites, they should be replaced where possible by the use of physical barriers to entry, or by making use of naturally termite-resistant species.⁽⁴⁰⁾

F. Earthen and traditional materials

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1. Sources and health implication

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65. House design and the choice of building materials have a strong influence on the spread of a wide range of infectious human diseases. Although it is the vectors which they can harbour rather than the materials themselves which are responsible for the diseases, in many cases selection and treatment of the materials are central to the programme of control.⁽⁴¹⁾

66. The environment in and around dwellings provides an attractive habitat fora wide range of arthropods in that they provide shelter from climatic extremes, shade, stability, and an abundant source of food. A number of these arthropods are vectors of human diseases' pathogens. They include houseflies and cockroaches, triatomine bugs, and domestic ticks, bedbugs and house dust mites. Some colonize humans and animals directly, while others breed outside the house but enter it to feed.⁽⁴²⁾

67. The most important disease carried by vectors is perhaps the American form of trypanosomiasis, or Chagas' disease, which is transmitted by the bites of the triatomine bug. There are around 13 to 15 million people in Latin America infected by this debilitating disease with about 100 million at risk.⁽²⁷⁾ The disease is caused by a parasite Trypanosome Cruzi, that can be carried in the bugs' faeces. The faeces are deposited where the bug feeds, and the parasite can then get into the victim's blood stream through the bite injury. The parasite lives and reproduces inside the human body, particularly the heart. People inflicted with the Chagas' disease are often unable to work because of the damage to their cardiovascular system. Health effects of other arthropods include: plague and typhus (fleas); shigellosis, salmonellosis, and viruses - hepatitis A and poliomyelitis (cockroaches); relapsing fever (soft ticks); viral hepatitis B (bed bugs); and house dust allergy (dust mites).⁽⁴²⁾

2. Factors influencing exposure

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68. Research has indicated that the type of building materials used has an important influence on the spread of diseases. In a rural housing study carried out in Venezuela, for example, 200 traditional houses of mud and wattle were compared with the same number of newer houses made of concrete blocks. It was found that while 55 percent of the traditional houses revealed the presence of triatomine bugs, they were present in only 9 per cent of the newer houses.⁽⁴³⁾ Generally, where the dwelling is made from low-strength masonry in the form of unstabilized earth blocks, rammed earth or stone in earth mortar, or of mud and wattle, the walls are very prone to cracking as the earth dries, providing suitable dark spaces for disease vectors to hide. Plastered walls are less prone, as long as the plaster is maintained uncracked. Soil floors can also be a source of suitable cracks. Roofs made from palm thatch are also a problem as thatch provides plentiful hiding spaces. In Venezuela it has also been found that the eggs. of the Chagas' disease vector are often stuck to the palm fronds used for thatching. Traditional flat roofs of poles piled with brushwood and covered in a thick layer of mud are used in upland areas of Argentina and Bolivia where nights are cool. These also have been found to provide an ideal habitat for triatomine bugs.⁽⁴²⁾ Furthermore, the diseases associated with these arthropods are particularly prevalent in tropical areas, since higher temperatures enable the disease vectors to breed more rapidly.

3. Mitigation strategies

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69. Methods available to eliminate infestation include spraying the walls and roofs with insecticides; plastering walls with smooth materials; and replacing wall and roof materials with smooth crack-free materials. Spraying campaigns have had some success, but where the surface of the wall is absorbent, as is often the case with unstabilized mud walls, the absorbance can reduce the surface amount of the active ingredient to which the insects are exposed to the point at which it is ineffective.⁽⁴⁴⁾ Spraying also needs to be repeated frequently to be effective. This option may not be feasible to the poor population of the developing countries since the prices of insecticides are beyond their reach.

70. An alternative and effective method of eliminating infestation is through the application of a smooth, durable plaster layer. One study from Brazil reports complete elimination of triatomine bugs largely due to the use of kaolin clay to produce strong smooth walls resistant to cracking.⁽⁴⁵⁾ But the choice of materials for plastering which are compatible with earthen base materials is difficult. Cement-based plasters rarely adhere to mud walls because of the differential moisture movement.

4. Substitute materials

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71. Replacement of traditional earth and thatch materials with denser, more stable materials is often advocated as the best means of eliminating pest infestation. The least cost alternatives to earth or stone-based walls most widely available are either fired-brick or concrete-block laid in cement mortar. Thatch roofs can be replaced by corrugated galvanized-iron sheets. These materials are being very widely adopted in any case, particularly in urban areas. But using them is by itself no guarantee of protection against pest infestation, unless the building is well-built. And selection of these materials has considerable implications beyond disease control: it is much more difficult to maintain comfortable living conditions without using ceilings (which may, if used, negate all the benefits by providing new pest habitats); the cost of these materials is often prohibitive, leading to smaller built space and consequently overcrowding; and cement and fired-clay manufacture are heavy users of commercial energy contributing to urban and atmospheric pollution.⁽⁴⁶⁾

72. Alternative lower-cost and lower-energy materials are becoming available which could provide a solution - stabilized soil for floors and walling materials, and fibre concrete tiles for roofing, making use of local vegetable fibres. Extensive trials of these materials have been conducted in different countries in recent years, and low-cost equipment is now available to enable them to be produced at low cost in small-scale operations and with minimal use of commercial energy or factory-made additives.^(47,48,49) Caution should, however, be taken as substitute materials could have their own health risks. For example the substitution of traditional roofing and walling materials by cement-based and clay-fired products still exposes those involved in their production to harmful effects of dusts and gases. In the United Republic of Tanzania, for example, all the 15 dust samples which were collected in three factories (a ceramic factory, a cement factory, and a kaolin quarry) indicated that the quartz content exceeded the acceptable threshold limit value of 0.1 mg/m thus suggesting that the exposed workers had a high risk of developing silicosis.⁽⁵⁰⁾

G. Radon and its sources

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1. Sources and health implications

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73. Radon is a radioactive gas and is ubiquitous throughout the geosphere, biosphere and atmosphere⁽¹⁹⁾ and occurs in several isotopic forms; however only two of these are found in significant concentrations in human environment: radon-222, which is a member of the radioactive decay chain of uranium-238, and radon220 (thoron), which is formed in the decay chain of thorium-232. Radon-222 and its decay products provide the major contribution to the exposure of workers and of the general population. It is colourless, odourless, and inert (boiling-point, - 61.8°C), denser than air (density, 9.73 g/l at 0°C and 760 mmHg) and fairly soluble in water (51.0 cm³ radon/100 cm³ water at 0°C; 22.4 cm³/100 cm³ at 25°C; 13.0 cm³ at 50°C).⁽¹⁹⁾ Radon substances are present in all surface soils and rocks, but in concentrations which vary regionally as a function of the relative abundance of the parent uranium.

74. Among the range of radioactive substances, radon is unique in existing in a gaseous state under normal conditions. It is therefore capable of diffusing through soils, and to a lesser extent building materials, and thus entering the internal envelope of a building. The diffusion length is conditioned by its half-life of 382 days. Although radon is a gas, its decay products are not, and they occur either as unattached ions or atoms, or attached to particles.⁽¹⁹⁾ It is the decay of these less stable daughter products (Po-218, Pb-214, Bi-214 and Po-214, all with half-lives of less than 30 minutes) which is the probable cause of carcinogenic radiation associated with the gas. Risks are increased when there are high levels of particulates in indoor air, for example tobacco smoke. Smoking itself is synergistic with radon exposure in increasing lung cancer.

75. In the majority of cases, the most important source of radon in indoor air is infiltration from the ground beneath the building. Radon may also enter in the water supply, particularly if this is drawn from wells drilled in rocks such as granite. However, certain building materials may also constitute a significant source. These include natural stones, principally those of igneous or volcanic origin, and concretes which contain aggregates of similar origin. Some examples of unusually high emission rates have been found in mill tailings used as aggregates (Grand Junction, Colorado), aerocrete based on alum shale (Sweden), certain granites (Aberdeen area, Scotland), phosphate slag (Alabama) and phosphogypsum produced as a by-product of phosphoric acid generation.^(10,11) Gamma radiation is also generated by radioactive decay and in many cases may contribute more than radon to the radiation dose received by occupants.

76. Phosphogypsum, an aqueous slurry of gypsum (calcium sulphate), is produced as a by-product of the manufacture of phosphate-based fertilizers. Global