Around 50% of people, almost all in developing countries, rely on coal and biomass in the form of wood, dung and crop residues for domestic energy. These materials are typically burnt in simple stoves with very incomplete combustion. Consequently, women and young children are exposed to high levels of indoor air pollution every day. There is consistent evidence that indoor air pollution increases the risk of chronic obstructive pulmonary disease and of acute respiratory infections in childhood, the most important cause of death among children under 5 years of age in developing countries. Evidence also exists of associations with low birth weight, increased infant and perinatal mortality, pulmonary tuberculosis, nasopharyngeal and laryngeal cancer, cataract, and, specifically in respect of the use of coal, with lung cancer. Conflicting evidence exists with regard to asthma. All studies are observational and very few have measured exposure directly, while a substantial proportion have not dealt with confounding. As a result, risk estimates are poorly quantified and may be biased. Exposure to indoor air pollution may be responsible for nearly 2 million excess deaths in developing countries and for some 4% of the global burden of disease. Indoor air pollution is a major global public health threat requiring greatly increased efforts in the areas of research and policy-making. Research on its health effects should be strengthened, particularly in relation to tuberculosis and acute lower respiratory infections. A more systematic approach to the development and evaluation of interventions is desirable, with clearer recognition of the interrelationships between poverty and dependence on polluting fuels.

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Indoor air pollution in developing countries: a major environmental and public health challenge

In the United States, lung cancer remains the leading cause of cancer death in both men and women even though an extensive list of risk factors has been well-characterized. Far and away the most important cause of lung cancer is exposure to tobacco smoke through active or passive smoking. The reductions in smoking prevalence in men that occurred in the late 1960s through the 1980s will continue to drive the lung cancer mortality rates downward in men during the first portion of this century. This favorable trend will not persist unless further reductions in smoking prevalence are achieved.

https://journal.chestnet.org/article/S0012-3692(15)32981-0/pdf

Epidemiology of Lung Cancer

BACKGROUND A critical review was conducted of the quantitative literature linking indoor air pollution from household use of biomass fuels with acute respiratory infections in young children, which is focused on, but not confined to, acute lower respiratory infection and pneumonia in children under two years in less developed countries. Biomass in the form of wood, crop residues, and animal dung is used in more than two fifths of the world9s households as the principal fuel. METHODS Medline and other electronic databases were used, but it was also necessary to secure literature from colleagues in less developed countries where not all publications are yet internationally indexed. RESULTS The studies of indoor air pollution from household biomass fuels are reasonably consistent and, as a group, show a strong significant increase in risk for exposed young children compared with those living in households using cleaner fuels or being otherwise less exposed. Not all studies were able to adjust for confounders, but most of those that did so found that strong and significant risks remained. CONCLUSIONS It seems that the relative risks are likely to be significant for the exposures considered here. Since acute lower respiratory infection is the chief cause of death in children in less developed countries, and exacts a larger burden of disease than any other disease category for the world population, even small additional risks due to such a ubiquitous exposure as air pollution have important public health implications. In the case of indoor air pollution in households using biomass fuels, the risks also seem to be fairly strong, presumably because of the high daily concentrations of pollutants found in such settings and the large amount of time young children spend with their mothers doing household cooking. Given the large vulnerable populations at risk, there is an urgent need to conduct randomised trials to increase confidence in the cause-effect relationship, to quantify the risk more precisely, to determine the degree of reduction in exposure required to significantly improve health, and to establish the effectiveness of interventions.

https://thorax.bmj.com/content/thoraxjnl/55/6/518.full.pdf

Indoor air pollution in developing countries and acute lower respiratory infections in children

Although some areas of China are becoming more urban, more than 60% of the population is still rural, most of which still uses biomass (mainly wood and crop residues) and coal fuels that produce substantial pollution in simple stoves. In 2003 approximately 80% of the energy consumed by rural households was in the form of biomass and almost 10% as coal. Furthermore, although most Chinese cities have plans to eliminate coal for households, many urban communities continue to rely on coal. The combustion of biomass and coal (collectively called “solid fuels”) is the dominant source of indoor air pollution (IAP) in the country and contributes significantly to the total burden of ill health.

In the most recent global analysis of the health effects of major risk factors, the World Health Organization (WHO) estimated that solid fuels used in Chinese households cause approximately 420,000 premature deaths annually; this is 40% more than the approximately 300,000 premature deaths attributed to outdoor air pollution in Chinese cities with populations of more than 100,000 (Cohen et al. 2004; Smith et al. 2004). Household use of solid fuels is thus estimated to be the largest single environmental risk factor and ranks sixth among all risk factors examined for ill-health (Figure 1; Smith et al. 2005). These risk estimates, however, were based primarily on studies in other countries because, as discussed in this review, few epidemiologic studies have been conducted in China on biomass smoke compared with those conducted on coal smoke.



Figure 1

Rough estimates of the burden of disease in China: the top 10 risk factors plus other selected risk factors [adapted from Smith et al. (2005)]. Note: Indoor smoke from solid fuels does not include smoke from other fuels or tobacco. Burden of disease is ...



In the 1980s China conducted more IAP measurements focused on household combustion than all other developing countries combined. Indeed, by the early 1990s, the results of more than 100 published studies were combined into a WHO database (Sinton et al. 1996). In contrast, the Chinese environmental health community conducted few IAP measurements in the 1990s (Saksena et al. 2003), but epidemiologic studies of coal smoke, mainly on cancer end points, continued and have resulted in a large body of evidence. In particular, over 25 years a wide-ranging set of studies has been conducted on coal smoke exposures, toxicology, and health effects in one rural area—Xuanwei in Yunnan Province—with severe impacts.

In this review we address the following questions in order to put Chinese household IAP from solid fuel use into perspective, nationally and internationally, and highlight research gaps: a) What toxic constituents have been found in the emissions of solid fuel combustion? b) What are the reported human exposure characteristics? c) What health effects have been documented? and d) What technologies exist or are possible for reducing this IAP exposure?

Household air pollution from coal and biomass fuels in China: measurements, health impacts, and interventions.

Epidemiology of Lung Cancer: ACCP Evidence-Based Clinical Practice Guidelines (2nd Edition)

Of the four principal categories of indoor pollution (combustion products, chemicals, radon and biologicals), research in developing countries has focused on combustion-generated pollutants, and principally those from solid-fuel-fired cooking and heating stoves. Such stoves are used in more than half the world's households and have been shown in many locations to produce high indoor concentrations of particulates, carbon monoxide and other combustion-related pollutants. Although the proportion of all such household stoves that are used in poorly ventilated situations is uncertain, the total population exposed to excessive concentrations is potentially high, probably several hundred million. A number of studies were carried out in the 1980s to discover the health effects of such stove exposures. The majority of such studies were done in South Asia in homes burning biomass fuels or in China with coal-burning homes, although a sprinkling of studies examining biomass-burning have been done in Oceania, Latin America and Africa. Of the health effects that might be expected from such exposures, little, if any, work seems to have been done on low birthweight and eye problems, although there are anecdotal accounts making the connection. Decreased lung function has been noted in Nepali women reporting more time spent near the stove as it has for Chinese women using coal stoves as compared to those using gas stoves. Respiratory distress symptoms have been associated with use of smoky fuels in West India, Ladakh and in several Chinese studies among different age groups, some with large population samples. Acute respiratory infection in children, one of the chief causes of infant and childhood mortality, has been associated with Nepali household-smoke exposures. Studies of chronic disease endpoints are difficult because of the need to construct exposure histories over long periods. Nevertheless, chronic obstructive lung disease has been associated with the daily time spent near the stove for Nepali women and found to be elevated among coal-stove users compared to gas-stove users in Shanghai. In contrast to early reports, there seems to be little or no risk of nasopharyngeal cancer from cookstove smoke. Several studies in China, however, have found smoke to be a strong risk factor for lung cancer among non-smoking women. In addition, severe fluorosis has been observed in several parts of China where coal fluoride levels are high.(ABSTRACT TRUNCATED AT 250 WORDS)

C J Hong

Papers

Indoor air pollution in developing countries.