Sources and health implications
A number of metals are used in the construction industry in their metallic form, making use of their 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.
Cadmium is highly toxic: exposure may result in bone damage, kidney damage and lung cancer. 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.
Chromium is most toxic in the valence state chromium. It too is a component of some paints and metallic finishes and may be a contaminant of cement. Mining waste may contaminate ground water. 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.
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 per cent 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 recognised 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 (23).
Factors influencing exposure
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, characterised by a craving to eat non-food substances. Paint flakes can be a favourite “meal”.
Acceptable exposure levels
In the case of chromium, the World Health Organisation (WHO) recommended upper limit in drinking water is 0.05 parts per million (50 μg/1). For lead, an upper limit of 50 microgrammes per litre for mains water has been accepted by the European Union (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-70s 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 British 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 of America (24) a number of European governments are considering lowering this level to 10-15 μg/dl. WHO has made an international risk evaluation on health effects from exposure to inorganic lead and the results will be published in Environmental Health Criteria No. 165 on Inorganic Lead in 1995 by WHO. The most substantial evidence from cross-sectional and prospective studies of populations with BPb levels generally below 25 μg/dl relates to decrements in intelligence quotient (IQ). It is important to note that such observational studies cannot provide definitive evidence of a causal relationship with lead exposure. Existing epidemiological studies do not provide definitive evidence of a threshold. Below the BPb range of 10-15 μg/dl, the effects of confounding variables and limits in the precision of analytical and psychometric measurements increase the uncertainty attached to any estimate of effect. (WHO. 1995, Environmental Health Criteria No. 165, Inorganic Lead in press). However, while the medical effects of acute poisoning - including stomach ache, 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 (23).
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 minimise 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 United States of America contains leaded paintwork, amounting to 3 million tons (24). Good maintenance of all paintwork may be preferable to removal: renovation of older timber houses in United States of America has been shown to raise occupants blood lead levels two times, thus a doubling of the average load (25). 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.
WHO recommends an immediate ban of leaded paints and progressive elimination of lead as water-pipe material. Substitute materials are suggested in table 5.
Table 5. Constructional uses of potentially toxic metals, and alternatives
Source: Spence, R. J. S., Cambridge Architectural Research Limited (UK), Building Materials and Health (Unpublished draft report prepared for the United Nations Centre for Human Settlements (Habitat), September 1994).
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