Indoor Air Pollution from Household Fuel Combustion in China: a Review

Nearly all China’s rural residents and a shrinking fraction of urban residents use solid fuels (biomass and coal) for household cooking and heating. As a result, by use of global metaanalyses of epidemiological studies, it is estimated that indoor air pollution from solid fuel use in China is responsible for ~ 420,000 premature deaths annually, more than the ~300,000 attributed to urban outdoor air pollution in the country. To help elucidate more fully the extent of this hazard, we reviewed nearly 200 publications reporting health effects, emission characteristics, and/or indoor air concentrations associated with the use of solid fuels, mainly coals, in both rural and urban areas of China. Health effects include cancer (mainly lung cancer), chronic obstructive pulmonary diseases, respiratory illnesses, immune system weakening, and lung function reductions. Arsenic poisoning and fluorosis, resulting from coal combustion, have also been observed. Although attempts have been made in a few studies to identify specific coal smoke constituents responsible for specific adverse health effects, the majority of indoor air measurements include only particulate matter, carbon monoxide, sulfur dioxide, and/or oxides of nitrogen. Based on the measurements made in 122 individual studies, we summarize the distributions across residences from 29 provinces, showing indoor concentrations exceeding health-based standards in many of the measured households. Finally, we review various past and potential intervention options including the National Improved Stove Program and several emerging fuel technologies. INDEX TERMS Biomass fuels, coal, household stoves, cancer, respiratory disease, burden of disease INTRODUCTION More than 60% of China’s population is still rural and nearly all the rural population still uses highly polluting biomass (e.g., wood, crop residue, animal dung) and coal fuels, which produce substantial pollution in simple stoves, to meet most of their household needs (NBS 2005a,b). In 2003, about 80% of the energy consumed by rural households was in the form of solid biomass, and nearly 10% as coal. Although most Chinese cities have plans to eliminate * Corresponding author email: [email protected] 2 coal for households, there are still many urban communities all over the country – even in the wealthiest citiesthat rely on coal. The combustion of biomass and coal (collectively called solid fuels) are the dominant source of indoor air pollution and may contribute significantly to total burden of the ill health. China has done more indoor air pollution studies on household combustion pollutants than any other developing countries; more than 100 studies by the early 1990s, for example, have been summarized in the World Health Organization (WHO) database (Sinton et al. 1996). As a result, the most recent WHO global analysis of the health effects of major risk factors found that indoor air pollution from solid fuel use in China is responsible for about 420,000 premature deaths annually, some 50% more than the 300,000 attributed to all urban outdoor air pollution in the country (WHO 2002, Cohen et al. 2004). As such it is the largest single environmental risk factor in all China for ill-health and second largest globally, after poor water/sanitation/hygiene. To help better understand why exposure to solid fuel smoke contribute so significantly to ill health, we conduct a critical review of indoor air pollution resulting from household solid fuel combustion. Specifically, we attempt to address the following questions: (1) What are the observed or suspected health effects of household solid fuel combustion? (2) What are the major constituents of the smoke released from solid fuel combustion? (3) What are the concentrations typically measured in various rooms (e.g., kitchen, bedroom, and living room) for several common pollutants? (4) What are the current and emerging technologies for reducing smoke exposures? HEALTH EFFECTS More than 100 peer-reviewed papers reporting health effects of household solid fuel combustion in China have been published in Englishor Chinese-language journals. Almost all these papers, however, focus on the coal smoke health effects both in urban and rural populations. In contrast, the studies conducted in other developing countries have focused on biomass-using households. The relative large research effort on household coal smoke in China reflects the unique status of China as a “Coal Kingdom” where the use of household coal is widely spread throughout the country and that some of the coals contain toxic contaminants with unique health effects. Household biomass use, however, is more prevalent and, as in the rest of the developing world, undoubtedly affects health as well, even though few studies of health effects seem to have been done to date in China itself. 1 Health effects of indoor coal combustion Lung Cancer. Associations between lung cancer and coal smoke exposure have been found in numerous epidemiologic studies conducted in urban and rural households in China (Smith and Liu 1994, Smith et al. 2004, Smith and Tian 2005). Among these studies include the decades-long investigations in Xuanwei County, Yunnan Province, which has been the site of numerous studies of the relationship of coal smoke and lung cancer due to its unusually high lung cancer rates in non-smoking women exposed to emissions of so-called “smoky” (bituminous) coal when burned without venting (e.g., Mumford et al. 1987, Liu et al. 1991, Chapman et al. 1989). The odds ratios (ORs) for lung cancer due to indoor coal use, were summarized in a recent meta-analysis by Smith et al. (2004). For comparison, the ORs were estimated with and without adjusting two important confounding factors. Tobacco smoking status was either adjusted or analyses were done solely in non-smokers. Since chronic respiratory diseases, such as chronic bronchitis, tuberculosis, asthma, and emphysema, may 1 Although not directly related to solid fuel combustion, cooking fume from “Chinese style cooking”, usually ascribed to wok-frying with certain cooking oils (e.g., rape seed oil), has received attention due to some evidence showing its adverse health effects including lung cancer (Smith and Tian 2005) and immune system weakening (Zhang et al. 2001, Shen et al. 2004). 3 increase the probability of developing lung cancer later in life (Luo et al. 1996), adjustment was made for these diseases. This may result in underestimating the OR of lung cancer, as some previous lung diseases may be on the intermediate path from exposure to lung cancer – in this case, they are not confounders and should not be adjusted. The overall OR estimate for women was 1.17 with 95% confidence interval (95% CI) of 1.02–1.35. However, when the analysis was restricted to studies that adjusted for smoking and chronic respiratory disease, the estimated OR for women was substantially increased to 1.94 (95% CI: 1.09–3.47). The estimated OR for men was 1.79 (95% CI: 1.18–2.72), and slightly lower when taking into account confounding by smoking and chronic airway disease (OR=1.51 with 95% CI: 0.97– 2.46). The combined overall risk estimate for men and women was expressed as an OR estimate of 1.86 (95% CI: 1.48–2.35), and a substantially increased OR of 2.55 (95% CI: 1.58–4.10) when adjusted for smoking and chronic respiratory disease. The meta-analysis by Smith et al. (2004) presents strong epidemiologic evidence that exposure to indoor coal smoke significantly increases lung cancer risk. The role of certain genotypes and proteins in the development of lung cancer has been examined in the Xuanwei County residents exposed to “smoky” coal smoke, suggesting that individual’s susceptibility to lung cancer may be increased by the GST1 null genotype (Mumford et al. 1999, Lan et al. 2000, 2001, Lan and He 2004). There is also limited evidence of other cancers from household coal smoke exposures, including esophageal (Pan et al. 1999) and cancers of the head and neck (Dietz et al. 1995). This may be due not only to direct respiration of airborne pollutants, but also to the contamination of food by coal smoke (Roth et al. 1998). Respiratory illnesses. Indoor coal smoke exposure has been linked to various respiratory symptoms and diseases. A study conducted in Anhui Province shows that the prevalence rates of chest illness, cough, phlegm, and shortness of breath were significantly elevated from non-smoking women living in homes with both smokers and coal heating (Pope and Xu 1993). A survey of 10892 Xuanwei residents found that the ORs for “smoky” coal users, compared to “smokeless” (anthracite) coal users, were 1.73 for shortness of breath, 3.30 for cough, and 4.23 for phlegm, and that the ORs for “smokeless” coal users, compared to wood users, were 1.35 for cough and 1.67 for phlegm (Zhou et al. 1995). A recent study of 5051 seventh-grade students from 22 randomly selected schools in the greater metropolitan area of Wuhan, Hubei Province, found that coal burning for cooking and/or heating increased odds of wheezing with colds (OR = 1.57 with 95% CI: 1.07-2.29) and without colds (OR = 1.44, 95% CI: 1.05-1.97) (Salo et al 2004). In a population-based case-control study of childhood asthma, conducted in Shunyi County located in suburban Beijing, an increased risk was observed for use of coal for heating (OR =1.5, 95% CI: 1.1-1.9) and for use of coal for cooking without ventilation (OR = 2.3, 95% CI: 1.5-3.5) (Zheng et al. 2002). Indoor coal combustion was associated with increased incidence of rhinitis, faucitis, and tonsillitis in children (6-13 years old) living in Taiyan City, Shanxi Province (Cheng et al. 2002). The effects of household coal use were also observed in 624 infants and young children (1-3 years old) in Nantong, Jiangsu Province, as the prevalence of cough and that of pneumonia were significantly higher in coal-use households (Zhou et al. 1994). Exposure-response relationships have been examined in a study of 7058 elementary school children living in the four Chinese cities of Chongqing, Guangzhou, Lanzhou, and Wuhan. When lifetime exposure to heating coal smoke was classified into four ordinal levels (no reported exposure, light exposure, moderate exposure, and heavy exposure, monotonic and positive exposure-response relationships were observed for ORs of phlegm, cough with