Exposure to indoor air pollution from the combustion of solid fuels has been implicated, with varying degrees of evidence, as a causal agent of several diseases in developing countries. In a review of the epidemiological evidence for the health effects of indoor smoke from solid fuels, Bruce et al. concluded that, despite some methodological limitations, epidemiological studies provide compelling evidence of causality for acute respiratory infections (ARI) and chronic obstructive pulmonary disease (COPD). This is reinforced by experimental data, studies of pathogenesis, and indirect evidence from environmental tobacco smoke (ETS) and ambient air pollution studies.
The relationship between coal smoke (but not biomass smoke) and lung cancer has also been consistently established in a number of epidemiological studies. A relationship between biomass smoke and lung cancer may also exist, because biomass smoke contains carcinogens, although at lower concentrations compared to coal smoke. Due to smaller risks and greater difficulties in exposure quantification, epidemiological studies on biomass smoke and lung cancer have so far been inconclusive. For other diseases, including asthma, upper aerodigestive tract cancer, interstitial lung disease, low birth weight and perinatal conditions, tuberculosis, and eye diseases, Bruce et al. classified the evidence as tentative.
Conservative estimates of global mortality due to indoor air pollution from solid fuels show that, in 2000, more than 1.6 million deaths were attributed to this risk factor. This accounts for approximately 4–5% of total mortality worldwide. Approximately 1 million of the deaths were due to childhood acute respiratory infections, with the remainder due to other causes, dominated by COPD and then lung cancer among adult women (Table I). The estimated health effects, currently limited to those diseases with strong epidemiological evidence, would of course be even larger if causality and quantitative relationships were established for other diseases. At the same time, even the diseases quantified so far show that the public health effects of indoor smoke in developing countries are enormous. As a result, coupled with the attention to details of exposure, health research has shifted to the ‘‘exposure– response’’ relationship for indoor air pollution and disease. Unlike early studies that divided the population into exposed and non-exposed, the exposure–response relationship, which quantifies the health effects along a continuum of exposure levels (or a larger number of categories), allows considering the benefits of partial exposure reduction for designing new interventions.
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The main factors influencing indoor air quality include building design, construction materials, ventilation rates, and building maintenance; outdoor air quality; seepage of pollutants through the ground; occupant activities and preferences; and the occupants themselves. It shows typical sources of indoor air problems in the home. The indoor air pollutants posing the greatest hazard include carbon monoxide, which is responsible for many accidental deaths every year; and radon and environmental tobacco smoke, both of which are implicated in the incidence of cancer. Other pollutants of concern are volatile organic compounds (VOCs), nitrogen dioxide, house dust mite allergens (all of which are implicated in the incidence of respiratory disease, especially in children), fungi, bacteria, and asbestos. A summary of the key indoor pollutants, sources, and effects is shown in Table I.
