Exposure Guidelines for Residential Indoor Air Quality

4.0 Guidelines and Recommendations (continued)

Part C. Substances with Recommendations for Controlling Exposure

In examining the need for guidelines for pollutants listed in this part of the document, the scientific literature was reviewed for pollutants listed in Parts A and B of this section. The development of quantitative exposure guidelines was, however, considered inappropriate for a number of reasons:

• for some groups of substances the individual components may have widely differing toxicological properties; the complexity of the mixtures precluded establishing a guideline for each constituent or for the group as a whole;
• establishment of air quality guidelines may not be the appropriate strategy for control, especially where inhalation is not the most significant route of exposure;
• there are deficiencies in the scientific data base.

For these substances or groups, information on potential adverse health effects and possible sources has been provided, and recom-mendations that should help to eliminate or reduce exposure to them have been developed.

4.C.1 Biological Agents

In order to prevent many of the common indoor problems due to biological agents, measures should be taken to ensure that:

• excess humidity and condensation are not present;
• surfaces are kept free of dust;
• stagnant water sources, such as humidifier tanks, are kept clean and occasionally disinfected;
• a high standard of appropriate personal hygiene is maintained.

The indoor environment can present the potential for illness due to exposure to biological agents. These agents may include microorganisms from humans, pets or insects within the home, or from growth on surfaces or in stagnant water. Dust from outside and inside the home includes pollens, spores, cells, cell debris and insects. Such materials in the air may cause infectious diseases or allergic illnesses in sensitized persons in the home. Illnesses must be systematically investigated in order to reveal the cause and to determine possible means of control. Control measures include disinfection and physical removal of the agent where possible and various means of controlling particulate matter and excess humidity. Due to varying individual sensitivity, however, extraordinary measures may sometimes be required to prevent symptoms.

The variety of biological agents that may occur in air is immense, and their potential for effects on susceptible individuals is unpredictable. Because of the complexity of the problem and the lack of data from which contamination levels can be related to disease incidence, it is not possible to recommend limits for biological agents in general.

4.C.2 Consumer Products

It is recommended that exposures resulting from the use of consumer products be kept to a minimum by ensuring adequate ventilation and observing any other precautionary measures described on the product label and in any accompanying information.

Pest control products should be used only when absolutely necessary.

4.C.2.1 Chlorinated Hydrocarbons

Large quantities of chlorinated hydrocarbons are produced and used annually worldwide. They are present in the home environment principally as solvents, cleansers and aerosol propellants, and some individuals may be exposed to relatively high levels of them in the pursuit of hobbies. In some cases, chlorinated hydrocarbons may be released continuously from household products; they have also been detected in drinking water.

Chlorinated hydrocarbons are absorbed into the body principally by inhalation, but also through the skin and gastro-intestinal tract; they tend to accumulate in fatty tissues such as the brain, bone marrow and body fat. Recovery from the acute effects of exposure to the volatile chlorinated hydrocarbons is usually complete, but, after repeated exposures, adverse health effects can include depression of, or permanent damage to, the central nervous system, irritation of the eyes and lungs, and damage to the skin, liver and kidneys. In the case of dichloro-methane, a metabolite is carbon monoxide, which can cause cardiovascular stress (see Section 4.A.3).

In the home, exposures occur primarily through the use of consumer products and can be of short duration, but levels may be sufficiently high to have the potential for adverse health effects.

4.C.2.2 Pest Control Products

Pest control products comprise a very large number of diverse chemicals. They are widely used in and around the home environment, both by residents and by professional pest control applicators. These products are employed to control insects in the home, to prevent insect damage to fabrics, to treat house plants against both insects and fungi, to treat pets, and to disinfect the air, water and surfaces around the home. Occasional inadvertent exposure may occur because of impregnation of building products or household articles with pesticidal preservatives and subsequent release of these into the air. Surfaces in the home may be coated with pesticides after normal use, and food prepared or stored in the room during or after pesticide use can also be contaminated. Pesticides may also infiltrate homes after outdoor application. Many pest control products contain, in addition to the active ingredients, non-active ingredients such as solvents, wetting agents and stabilizers. Such ingredients may have much higher vapour pressures, and hence be present at higher airborne levels, than the active ingredients, and a few have biological activity of their own.

Exposure to pest control products in the home can occur both by inhalation and by absorption through the skin, for example, following contact with pesticide-treated surfaces. Pesticides may also be ingested following injudicious use in the vicinity of foods.

Available data on exposure levels in the home indicate that airborne levels of most pesticides are very low if products are used as directed. Misuse of pesticides, whether through failure to follow the instructions provided, heavy use in areas where food is stored, prepared or eaten, use in poorly ventilated spaces or misapplication of products designed for outdoor use, provides the greatest potential for exposure in the home, and levels can then be high enough to create a health hazard.

Adverse human health effects from exposure to low levels in the home tend to be non-specific, similar to ailments caused by many other chemical agents: respiratory effects, coughing, burning of eyes and nose, rhinitis, headache, dizziness, fatigue and general malaise. Two major groups of pesticides are anticholinesterase agents, causing augmentation of secretory activity in bronchial, lachrymal, salivary and other glands, and contraction of smooth muscles of the bronchioles. Allergic reactions to a few pesticides occur very occasionally. Most pesticides used in Canada today break down quickly in body tissues. No pesticides available for domestic use in Canada have been assessed as human carcinogens.

Pest control products are subject to extensive review and regulation by several federal and provincial departments before they are released to the market. This ensures that the consumer is provided only with products that, although potentially toxic, are safe if used as directed and that adequate instructions and warnings regarding the use of these products are also provided. Thus, the consumer is ultimately responsible for the proper use of pesticides in the home.

4.C.2.3 Product Aerosols

An aerosol can be a suspension of fine liquid or solid particles in air or other gases; in these guidelines, product aerosols are considered to be consumer products that are dispersed under pressure from disposable containers.

An aerosol product has three main components: the active ingredient or ingredients, the propellant, and miscellaneous additives used to improve the product, such as plasticizers, synthetic resins, surfactants and emulsifiers. Some products consist of gaseous components only and therefore do not result in the production of an aerosol.

Aerosol propellants used currently in Canada include hydrocarbons, such as propane, butane and isobutane; nitrous oxide; dichloromethane (commonly called methylene chloride); carbon dioxide; dimethyl ether; and nitrogen. Nitrous oxide may also be used as the propellant for food products.

Product aerosols are formulated from a wide variety of chemicals, some of which are potentially toxic at high concentrations. Certain components may be subjected to review, and hence control, under federal legislation such as the Hazardous Products Act and the Environmental Contaminants Act. For example, prior to 1980, fluorochlorohydrocarbons were used as propellants for most aerosol sprays. Fluorochlorohydrocarbons are still used as aerosol propellants in many products, including aerosol cooking sprays, but trichlorofluoromethane and dichloro-difluoromethane have been banned, under the Environmental Contaminants Act, for use as propellants in hair sprays, deodorants and antiperspirants.

Generally the use of product aerosols in the home is of short duration and intermittent, ranging from about once or twice a day for deodorant sprays to four times a year for oven cleaners.

4.C.3 Fibrous Materials

Precautions should be taken to minimize inhalation of, and skin contact with, mineral fibres during home renovations and installation operations. Materials and products containing fibres should also be examined periodically for signs of deterioration. Advice should be sought before removing or damaging any materials thought to contain asbestos.

Asbestos is the general term for six fibrous silicate minerals that are useful because of their high tensile strength, durability, flexibility and resistance to heat and chemicals. A large proportion of total asbestos production is used in the construction industry in materials such as asbestos-cement sheeting and pipes. Under normal conditions of use, asbestos fibres are not expected to be released from such materials. Fibres may, however, be released from friable surfaces (such as sprayed asbestos-containing insulation or low-density insulation blocks), or from other construction materials in the course of renovation or maintenance. Available data indicate that, in general, asbestos levels in homes are not significantly greater than those in ambient air. Concentrations as much as three orders of magnitude higher have been measured during such operations as sanding of drywall taping compounds. Under the Hazardous Products Act, asbestos is now prohibited in most consumer products where respirable dusts are generated during normal use.

Prolonged exposure to elevated levels of asbestos fibres causes asbestosis, lung cancer, mesothelioma and possibly laryngeal cancer and malignancies of the gastrointestinal tract. The risk of developing asbestosis as a result of exposure to levels of asbestos in indoor or ambient air is probably negligible. It is difficult to quantify the risks of lung cancers and mesothelioma associated with exposure to indoor (and outdoor) levels, owing, in part, to problems inherent in using data from historical epidemiological studies for extrapolation, but mainly owing to the complexity of asbestos itself (i.e., variations in risk associated with different sizes and properties of the fibres). Nevertheless, it is likely that these risks are small.

Man-made mineral fibres (MMMF) include fibrous glass, mineral wool and ceramic fibres. Fibrous glass accounts for approximately 80% of all MMMF produced and is used mainly as thermal or acoustical insulation. There are few data on levels of fibrous glass in residences; mean levels measured during the installation of glass-fibre insulation have ranged from 0 to 8 fibres/mL. Levels in homes are probably not significantly above ambient levels except during such installations or modifications. Levels in public buildings have been found to range from 0 to 0.008 fibres/mL.

Glass fibres cause transient irritation of skin and eyes in workers occupationally exposed to them. Long-term studies have provided only equivocal evidence of respiratory disease as a result of exposure to glass fibres; however, an excess of lung cancer deaths (not consistently related to dose or duration) has been found in mineral wool workers 20 or more years after first exposure. The available data indicate that man-made mineral fibres are less pathogenic than asbestos, possibly because of their size distribution and greater solubility in the lung.

4.C.4 Lead

In order to minimize the exposure of people, and especially children, to lead of airborne origin, it is recommended that surfaces that may be contaminated be cleaned frequently and that a high standard of overall cleanliness be maintained.

Airborne lead is present mainly as inorganic lead compounds in dust particles. More than 90% of the global emissions of airborne lead are from man-made sources, principally the combustion of leaded gasoline, followed by mining and smelting. Atmospheric levels of lead in remote areas are in the range 0.05 to 8 ng/m³. Levels in urban areas depend upon proximity to roadways and industrial sources, and upon such factors as traffic density, wind speed and height above the ground. Annual geometric mean lead concentrations measured in Canada declined steadily from 0.74 µg/m³ in 1973 to 0.27 µg/m³ in 1982.

The major indoor source of airborne lead is the outside air, and indoor levels tend to be lower than outdoor levels.

People are exposed to airborne lead both directly by inhalation and indirectly by ingestion of lead that has settled as dust. In adults, approximately 10% of the ingested lead is absorbed; for young children, the figure may be as high as 53%. The amount of lead absorbed from the lungs is believed to range from 30% to 50% of the total inhaled lead.

Once lead is absorbed, it is distributed to the soft tissues and the skeleton. Lead in blood reflects current exposure to lead and has a biological half-life of about 16 days. Lead in the skeleton represents long-term accumulation and its half-life is several decades.

Lead can produce many toxic effects in the body. The main symptoms of lead poisoning include anaemia, abdominal cramps, constipation, renal damage and encephalopathy. Children are more sensitive than adults to the harmful effects of lead and may also experience irritability and loss of appetite. Learning impairment and alterations in neurobehavioural responses may occur at low exposure levels.

There is uncertainty in determining total exposure to airborne lead because of indirect exposure to lead of airborne origin that has settled as dust. Therefore, it is not possible to derive an acceptable air lead level for the indoor environment.

Although lead is introduced into the domestic environment mainly as an airborne pollutant, the major pathway for exposure is through ingestion of dust once it has settled. Exposure to lead can be controlled to some extent in homes by frequent cleaning of surfaces, including food preparation areas.

4.C.5 Polycyclic Aromatic Hydrocarbons (PAHs)

Exposure to polycyclic aromatic hydrocarbons indoors should be kept to a minimum by:

• ensuring that any combustion systems, for example wood - and coal-burning stoves, are properly installed and maintained and operated under conditions of satisfactory ventilation;
• adhering to the guidelines and recommendations given in this document for particulate matter and tobacco smoke.

Polycyclic aromatic hydrocarbons (PAHs) are a large class of organic compounds, most of which are non-volatile solids that are very insoluble in water. They are frequently adsorbed onto the surfaces of particulates, and over 100 PAHs have been detected in airborne particulate matter.

Polycyclic aromatic hydrocarbons are produced when materials containing carbon and hydrogen are burned. Coal burning and the use of internal combustion engines are reported to be major sources, although it has also been claimed that residential wood burning is the major source of PAHs in the USA. Outdoor levels have been measured in the range 0.1 to 60 ng/m³ in urban areas and 0.001 to 2 ng/m³ in rural areas. Indoor levels are often dominated by levels in the outdoor air, but cooking (where charring of food occurs), improperly operating wood stoves and open fireplaces and tobacco smoking can add significantly to indoor exposures. There are few quantitative data on levels of airborne PAHs in houses, and limitations in the available methods for collecting and measuring PAHs may mean that the available data are unreliable.

Exposure to PAHs is possible through skin contact, inhalation and ingestion. Although it has been estimated that ingestion of foods accounts for most of the exposure to PAHs, exposures through the dermal and inhalation routes appear to have more significant effects on human health. In particular, in some instances elevated concentrations of PAHs have been found in air, and the concern over exposure to airborne PAHs centres on the potential of these compounds to cause lung cancer.

There is a paucity of toxicological data (especially inhalation data) for most individual PAHs and almost no data for PAH mixtures. Epidemiological studies of humans are limited by the fact that exposures are usually to low levels of PAH mixtures, and often in the presence of other pollutants. As a result, it is impos-sible to identify the effects of any particular PAH and to reliably quantify the risks to human health.

The lack of reliable data on which to base dose-response relationships and the difficulty of distinguishing the effects of PAHs in the environment from those of other pollutants prevent the assignment of a guideline for exposure to PAHs in indoor air. Since some PAHs are known to be carcinogenic, exposure to these substances should be minimized.

4.C.6 Tobacco Smoke

In view of the carcinogenic properties of tobacco smoke, it is recommended that any exposure to tobacco smoke in indoor environments be avoided.

Tobacco smoke is a complex mixture of substances, including carbon dioxide, carbon monoxide, oxides of nitrogen and a large number of organic vapours and solids. Over 50 of the components are known to cause adverse health effects; 12 (including vinyl chloride, 2-naphthylamine, benzo(a)pyrene and formaldehyde) are known or suspected carcinogens. Carbon dioxide, carbon monoxide, oxides of nitrogen, formaldehyde and particulate matter are among the components of tobacco smoke for which individual air quality guidelines are recommended elsewhere in this document.

The largest amounts of most components are found in the smoke emitted into the environment directly from the burning end of the cigarette. Symptoms reported by non-smokers exposed to such "sidestream" smoke include eye, nose and throat irritation, headache, nausea, dizziness and loss of appetite. Furthermore, the lingering odour and reduced visibility from tobacco smoke are aesthetically unpleasant to many people.

Increased risks of lung cancer have been observed in non-smoking populations exposed to sidestream smoke. Other suspected health effects of tobacco smoke on non-smokers include the aggravation of such conditions as asthma and angina pectoris, increased risks of spontaneous abortion, congenital malformation or sudden infant death syndrome in the children of smoking mothers, and retarded development of children whose mothers were exposed to tobacco smoke during pregnancy. Increased risks of respiratory diseases have been observed among children whose parents were smokers, and non-smoking wives of smokers have been found to have increased risks of death from nasal sinus cancer and ischaemic heart disease.

Estimates indicate that non-smokers repeatedly exposed to tobacco smoke are at a significantly higher risk of contracting tobacco-smoke-induced lung cancer. While these calculations involve a number of assumptions that lead to uncertainty in the actual magnitude of the hazard, it is widely believed that there is no level of exposure to carcinogenic substances below which a risk does not exist.