Sources and health implications
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.
If inhaled, solvents dissolve readily in the blood stream. Sufficiently low concentrations will be metabolised 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 (26).
The International Federation of Building and Wood Workers has reported major health hazards for painters which include (27):
• 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. See also table 6. A complete list of known cancer agents evaluated by IARC is given in the Annex. For the evaluation criteria refer to table 3.
Table 6. A list of some of the known cancer agents related to painting as evaluated by IARC (27,28).
Source: IFBWW Series 3 (1992). Solvents and Paint Hazards, International Federation of Building and Wood Workers, Geneva, and IARC (1995). IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Lists of IARC Evaluations, Lyon, France.
Factors influencing exposure
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 white - spirit - 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 (29). The same study concluded that the use of such paints in unventilated conditions can constitute significant health hazards: in the trials the short-term exposure limit (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 time weighted average (TWA) exposure is 100 parts per million (ppm), and the short-term exposure limit (STEL) for any given 10-minute period is 125 ppm (29). 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 metabolised only slowly in the human body, and can therefore tend to accumulate.
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.
The World Health Organization 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 which is a gas 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 semi-volatile materials, 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 the World Health Organisation (WHO) data, are summarised in table 7 (5, 30).
Table 7. Classification of organic compounds in the indoor atmosphere and their sources.
Source: Crowther, D. (1994). Buildings and Health, Ph.D. Thesis, University of Cambridge, UK, and WHO (1990). Indoor Environment: Health Aspects of Air Quality, Thermal Environment, Light and Noise, UNCHS/UNEP/WHO
Acceptable exposure levels
WHO and national authorities, such as American Conference of Government Industrial Hygienists (ACGIH) have set limits for industrial exposure. The Threshold Limit Values (TLV) set by ACGIH for some of the more important solvents are shown in table 8. Guidelines recommended by WHO regarding ambient and indoor air 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 (31,32). It will be seen that all are far below the Threshold Limit Values prescribed.
Table 8. Threshold Limit Values (ACGIH) and recorded domestic air levels for some solvents used in construction.
Source: Ray, D.E, (1992). Hazards from Solvents, Pesticides and PCBs in Leslie, C.B. and Lunau, F.W., Indoor Air Pollution: Problems and Priorities, Cambridge University Press, Cambridge, UK, and ACGIH (1994). 1994-1995 Threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices.
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 (26) 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, humidity, these organic chemicals are regarded as being largely responsible for the condition known as sick building syndrome. Molhave (26), based on experiments on people exposed to different levels of exposure, suggests that concentrations of total volatile organic compounds less than 0.16 mg/m3 may be 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 (24) has subsequently proposed an approximate dose-response table for airborne VOCs (Table 9).
Table 9. Draft dose response table for airborne VOCs.
Source: Molhave, L. (1990). Volatile Organic Compounds - Indoor Air Quality and Health, Indoor Air ‘90, Vol. 5, pp. 447-452
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, United States of America, 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 (34).
Table 10. Emission limits for office furniture workstations set by the State of Washington, United States of America.
Source: Tucker, W. (1990). Building with Law-emitting Materials and Products: Where Do We Stand?”, Indoor Air ‘90, Vol. 3, pp. 251-256.
While the solvents are in use, during construction activity, levels will clearly reach much higher values over a short period of time. Where solvent - borne 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.
There are limited options at present for the substitution of volatile organic chemicals 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 (35) but are not manufactured yet in large quantities and paints based on them are not commercially available.
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