Nature, Causes, and Burden of Condition
About 3 billion people still rely on solid fuels, 2.4 billion on biomass, and the rest on coal, mostly in China (IEA 2002; Smith, Mehta, and Feuz 2004). There is marked regional variation in solid fuel use, from less than 20 percent in Europe and Central Asia to 80 percent and more in Sub-Saharan Africa and South Asia.
This issue is inextricably linked to poverty. It is the poor who have to make do with solid fuels and inefficient stoves, and many are trapped in this situation: the health and economic consequences contribute to keeping them in poverty, and their poverty stands as a barrier to change. Where socioeconomic circumstances improve, households generally move up the energy ladder, carrying out more activities with fuels and appliances that are increasingly efficient, clean, convenient, and more expensive. The pace of progress, however, is extremely slow, and for the poorest people in Sub-Saharan Africa and South Asia, there is little prospect of change.
Illustrated in figures 42.1 and 42.2 are findings for Malawi and Peru, respectively from Demographic and Health Surveys (ORC Macro 2004). The examples are selected from available national studies with data on main cooking fuel use to represent the situation in poor African and South American countries. The main rural and urban cooking fuels are illustrated in figures 42.1a and 42.2a; the findings are then broken down nationally by level of education of the principal respondent (woman of childbearing age) in figures 42.1b and 42.2b, and in urban areas by her level of education in figures 42.1c and 42.2c.
[Figure
42.1]
[Figure
42.2]
Biomass is predominantly, though not exclusively, a rural fuel: indeed, in many poor African countries, biomass is the main fuel for close to 100 percent of rural homes. Marked socioeconomic differences (indicated by women's education) exist in both urban and rural areas. During the 1990s, use of traditional fuels (biomass) in Sub-Saharan Africa increased as a percentage of total energy use, although in most other parts of the world the trend has generally been the reverse (World Bank 2002).
In many poorer countries, the increase in total energy use accompanying economic development has occurred mainly through increased consumption of modern fuels by better-off minorities. In Sub-Saharan Africa, however, the relative increase in biomass use probably reflects population growth in rural and poor urban areas against a background of weak (or negative) national economic growth. Reliable data on trends in household energy use are not available for most countries. Information is available from India, where the percentage of rural homes using firewood fell from 80 percent in 1993-94 to 75 percent in 1999-2000 (D'Sa and Narasimha Murthy 2004). Nationally, liquid petroleum gas (LPG) use increased from 9 to 16 percent over the same period, with a change from 2 percent to 5 percent in rural areas, and it is expected to reach 36 percent nationally and 12 percent for rural homes by 2016. International Energy Agency projections to 2030 show that, although a reduction in residential biomass use is expected in most developing countries, in Africa and South Asia the decline will be small, and the population relying on biomass will increase from 2.4 billion to 2.6 billion, with more than 50 percent of residential energy consumption still derived from this source(OECD and IEA 2004). The number of people without access to electricity is expected to fall from 1.6 billion to 1.4 billion. Because electricity is used by poor households for lighting and not as a cleaner substitute for cooking, electrification will not, at least in the short to medium term, bring about substantial reductions in IAP.
Levels of Pollution and Exposure
Biomass and coal smoke emit many health-damaging pollutants, including particulate matter (PM),1 carbon monoxide (CO), sulfur oxides, nitrogen oxides, aldehydes, benzene, and polyaromatic compounds (Smith 1987). These pollutants mainly affect the lungs by causing inflammation, reduced ciliary clearance, and impaired immune response (Bruce, Perez-Padilla, and Albalak 2000). Systemic effects also result, for example, in reduced oxygen-carrying capacity of the blood because of carbon monoxide, which may be a cause of intrauterine growth retardation (Boy, Bruce, and Delgado 2002). Evidence is emerging, thus far only from developed countries, of the effects of particulates on cardiovascular disease (Pope and others 2002, 2004).
Saksena, Thompson, and Smith (2004) have recently compiled data on several of the main pollutants associated with various household fuels from studies of homes in a wide range of developing countries. Concentrations of PM10, averaged over 24-hour periods, were in the range 300 to 3,000 (or more) micrograms per cubic meter (Mug/m3). Annual averages have not been measured, but because these levels are experienced almost every day of the year, the 24-hour concentrations can be taken as a reasonable estimate. By comparison, the U.S. Environmental Protection Agency's annual air pollution standard for PM10 is 50 Mug/m3, one to two orders of magnitude lower than levels seen in many homes in developing countries. During cooking, when women and very young children spend most time in the kitchen and near the fire, much higher levels of PM10 have been recorded—up to 30,000 Mug/m3 or more. With use of biomass, CO levels are generally not as high in comparison, typically with 24-hour averages of up to 10 parts per million (ppm), somewhat below the World Health Organization (WHO) guideline level of 10 ppm for an eight-hour period of exposure. Much higher levels of CO have been recorded, however. For example, a 24-hour average of around 50 ppm was found in Kenyan Masai homes (Bruce and others 2002), and one Indian study reported carboxyhemoglobin levels similar to those for active cigarette smokers (Behera, Dash, and Malik 1988). The health effects of chronic exposure of young children and pregnant women to levels of CO just below current WHO guidelines have yet to be studied. For additional information on levels of other pollutants in biomass and coal smoke, see Saksena, Thompson, and Smith (2004).
Fewer studies of personal exposure have been done than of area pollution, mainly because measurement of personal PM typically requires wearing a pump, a cumbersome procedure. CO can be measured more easily and has been used as a proxy: time-weighted (for example, 24-hour average) CO correlates well with PM if a single main biomass stove is used (Naeher and others 2001). Time-activity and area pollution information can also be combined to estimate personal exposure (Ezzati and Kammen 2001). These various methods indicate that personal 24-hour PM10 exposures for cooks range from several hundred Mug/m3 to more than 1,000 Mug/m3 (Ezzati and Kammen 2001), with even higher exposures during cooking (Smith 1989). Few studies have measured personal PM exposures of very young children: one study in Guatemala found levels a little lower than those of their mothers (Naeher, Leaderer, and Smith 2000).
Health Impacts of IAP
A systematic review of the evidence for the impact of IAP on a wide range of health outcomes has recently been carried out (Smith, Mehta, and Feuz 2004; see table 42.1). This review identified three main outcomes with sufficient evidence to include in the burden-of-disease calculations and a range of other outcomes with as yet insufficient evidence.
[Table .]
Studies for the key outcomes used in the burden-of-disease calculations—acute lower respiratory infection (ALRI), chronic obstructive pulmonary disease (COPD), and lung cancer—had to be primary studies (not reviews or reanalyses), written or abstracted in English (and for lung cancer, Chinese), that reported an odds ratio and variance (or sufficient data to estimate them) and provided some proxy for exposure to indoor smoke from the use of solid fuels for cooking and heating purposes.
A limitation of almost all studies has been the lack of measurement of pollution or exposure: instead, proxy measures have been used, including the type of fuel or stove used, time spent near the fire, and whether the child is carried on the mother's back during cooking. The studies do not, therefore, provide data on the exposure-response relationship, although a recent study from Kenya has gone some way to addressing this omission (Ezzati and Kammen 2001).
In some countries, household fuels carry locally specific risks. It has been estimated that more than 2 million people in China suffer from skeletal fluorosis, in part resulting from use of fluoride-rich coal (Ando and others 1998). Arsenic, another contaminant of coal, is associated with an increased risk of lung cancer in China (Finkelman, Belkin, and Zheng 1999). There has been concern, however, that reducing smoke could increase risk of vectorborne disease, including malaria. Some studies have shown that biomass smoke can repel mosquitoes and reduce biting rates (Palsson and Jaenson 1999; Paru and others 1995; Vernede, van Meer, and Alpers 1994). Few studies have examined the impact of smoke on malaria transmission: one from southern Mexico found no protective effect of smoke (adjusted odds ratio 1.06 [0.72-1.58]; Danis-Lozano and others 1999), and another from The Gambia found that wood smoke did not protect children in areas of moderate transmission (Snow and others 1987).
Method Used for Determining Attributable Disease Burden
Smith, Mehta, and Feuz (2004) have provided a full explanation of the calculation of the disease burden associated with IAP. Summarized here are the methods they used to estimate the two most critical components of these calculations: the number of people exposed and the relative risks.
Exposure
The absence of pollution or exposure measurement in health studies required use of a binary classification: the use or nonuse of solid fuels. The authors obtained estimates of solid fuel use for 52 countries from a range of sources, mostly household surveys, and statistical modeling was used for countries with no data (the majority) (Smith, Mehta, and Feuz 2004). They assumed, conservatively, that all countries with a 1999 per capita gross national product (GNP) greater than US$5,000 had made a complete transition either to electricity or cleaner liquid and gaseous fuels or to fully ventilated solid fuel devices. To account for differences in exposure caused by variation in the quality of stoves, they applied a ventilation factor (VF), set from 1 for no ventilation to 0 for complete ventilation. In China, a VF of 0.25 was used for child health outcomes and 0.5 for adult outcomes, reflecting a period of higher exposure (to open fires) before the widespread introduction of chimney stoves. Countries with a 1999 GNP per capita greater than US$5,000 were assigned a VF of 0, and all other countries a value of 1, reflecting the very low rates of use of clean fuels or effective ventilation technologies. The authors obtained the final point estimate for exposure by multiplying the percentage of solid fuel use by the VF. They arbitrarily assigned an uncertainty range of 5 percent to the estimates.
Risk
Smith, Mehta, and Feuz (2004) carried out meta-analyses for the three health outcomes with sufficient evidence (table 42.2). They used fixed-effects models and sensitivity analysis that took account of potential sources of heterogeneity, including the way in which exposure was defined and whether adjustment had been made for confounders (Smith, Mehta, and Feuz 2004).
[Table .]
The Burden of Disease from Solid Fuel Use
Information on the proportions exposed and risk of key disease outcomes was combined with total burden-of-disease data to obtain the population attributable fractions associated with IAP (WHO 2002b). Globally, solid fuels were estimated to account for 1.6 million excess deaths annually and 2.7 percent of disability-adjusted life years (DALYs) lost, making them the second most important environmental cause of disease, after contaminated water, lack of sanitation, and poor hygiene (table 42.3). Approximately 32 percent of this burden (DALYs) occurs in Sub-Saharan Africa, 37 percent in South Asia, and 18 percent in East Asia and the Pacific. In developing countries with high child and adult mortality, solid fuel use is the fourth most important risk factor behind malnutrition, unsafe sex, and lack of water and sanitation, and it is estimated to account for 3.7 percent of DALYs lost (WHO 2002b).
[Table .]
Overall, there are more female deaths but similar numbers of male and female DALYs (table 42.3b). The reason can be found by looking further at the health outcomes. Deaths and DALYs from ALRI in children under five years of age are slightly greater for males (table 42.3c). Women experience twice the DALYs and three times the deaths from COPD (male smoking-attributable COPD deaths excluded). Far fewer cases of lung cancer are attributable to IAP, but women experience about three times the burden of men.
Table 42.3 also shows how the poorest regions of the world carry by far the greatest burden, particularly for ALRI. More than half of all the deaths and 83 percent of DALYs lost attributable to solid fuel use occur as a result of ALRI in children under five years of age. In high-mortality areas, such as Sub-Saharan Africa, these estimates indicate that approximately 30 percent of mortality and 40 percent of morbidity caused by ALRI can be attributed to solid fuel use, as can well over half of the deaths from COPD among women. Because they derive from WHO risk assessments, these estimates include age weights, such that years of life lost at very young or advanced ages count less than years lost in the prime of adult life. Age weighting makes little difference to the DALYs lost per death up to age five; how much it affects the DALY cost of adult deaths depends on the age distribution of deaths from COPD. Because these are likely to occur at age 45 or beyond, the DALY losses are underestimated compared with estimates without age weighting that follow the usual practice in this volume.
Other Effects of Household Energy Use in Developing Countries
A number of other health impacts—for example, burns from open fires—were not assessed because the burden-of-disease assessment process allowed inclusion of only those health effects resulting directly from pollution. Children are at risk of burns and scalds, resulting from falling into open fires and knocking over pots of hot liquid (Courtright, Haile, and Kohls 1993; Onuba and Udoidiok 1987). Modern fuels are not always safe either, because children are also at risk of drinking kerosene, which is often stored in soft drink bottles (Gupta and others 1998; Reed and Conradie 1997; Yach 1994).
Families—mainly the women and children—can spend many hours each week collecting biomass fuels, particularly where environmental damage and overpopulation have made them scarce. This time could be spent more productively on child care and household or income-generating tasks. There are also risks to health from carrying heavy loads and dangers from mines, snake bites, and violence (Wickramasinghe 2001). Inefficient stoves waste fuel, draining disposable income if fuel is bought. Although women carry out most of the household activities requiring fuels, they often have limited control over how resources can be spent to change the situation (Clancy, Skutsch, and Batchelor 2003). These conditions can combine to restrict income generation from home-based activities that require fuel energy (for example, processing and preparing food for sale).
Homes that are heavily polluted and dark can hinder productivity of householders, including children doing homework and others engaged in home-based income-generating activities such as handicrafts. In many poor homes, lighting is obtained from the open fire and simple kerosene wick lamps, which provide poor light and add to pollution.
Solid fuel use has important environmental consequences. Domestic use of solid fuels in high-density rural and urban environments contributes to outdoor air pollution. Many low-income urban populations rely on charcoal, the production of which can place severe stress on forests. The use of wood as fuel can contribute to deforestation, particularly where it is combined with population pressure, poor forest management, and clearance of land for agriculture and building timber. Damage to forest cover can increase the distance traveled to obtain wood and can result in the use of freshly cut (green) wood, dung, and twigs, which are more polluting and less efficient. In some urban communities, poverty and supply problems are resulting in the use of plastic and other wastes for household fuel (IEA 2002).
Stoves with inefficient combustion produce relatively more products of incomplete combustion, such as methane, which have a markedly higher global-warming potential than carbon dioxide (Smith, Uma, and others 2000). It has, therefore, been argued that, although the energy use and greenhouse gas emissions from homes in developing countries are small relative to the emissions generated in industrial countries, cleaner and more efficient energy systems could provide the double benefit of reduced greenhouse gas emissions (with opportunities for carbon trading) and improved health through reduced IAP (Wang and Smith 1999).
The evidence available for assessing these effects, which together could have a substantial influence on health and economic development, is patchy at best. This area is important for research (Larson and Rosen 2002).
