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Smoke from biomass and its effects on infants by Nigel Bruce
[top] [end]IntroductionA century ago, biofuels (wood, dung and crop residues) provided the great majority of household energy worldwide. With the advent of fuels such as oil and gas, and the more widespread availability of electricity, the share of household energy from bio-fuels has fallen to around 15%. However, this small percentage hides the fact that around half of the world's population (rising to three-quarters of people in developing countries) still rely on bio-mass energy. This apparent contradiction is explained by the fact that each poor household uses very much less fuel than each wealthy one. While biofuel use, especially wood, is typically associated with poor rural households, it is also extensively used -often in combination with other fuels - in the urban slums that characterise the rapidly expanding cities of many developing countries.
Most of this biomass is burnt in open fires or poorly constructed stoves, usually inside the home (Figure 1). Pollution levels inside the home and kitchen areas are therefore high. Women, with their young children, work in these heavily polluted environments for many hours each day and are thus most heavily exposed to smoke (see front cover). The effect that this pollution has on the health of mothers and their very young children is a considerable cause for concern. Growing efforts are now being made to determine just how serious this problem is, and to promote economically, socially and environmentally sustainable ways of reducing this hazard. [top] [end]Levels of exposure to biofuel pollutionIt is important to distinguish two aspects of smoke exposure:
Smoke pollution levels are most commonly described by the level of particulate matter (PM), although other components of smoke are also injurious to health. The health effects of particulates depend on their ability to get deep into the lungs, and the smaller the particles, the easier this is. Particles larger than 10 microns do not easily penetrate into the lungs, so a measurement (written as PM10), is very useful when looking at health problems. Measures of PM10 describe the weight of particles smaller than 10 microns in each cubic metre of air. A second measurement, PM2.5, describes the concentration of 2.5 micron particles, which can penetrate even more deeply and are likely to cause the most damage. A comparison between typical levels for biofuels and clean fuels is shown in Table 1. Recommendations from the most recent Environmental Protection Agency (EPA) recommendations for air quality are also shown (EPA 1997).
The key messages to be read from this table are:
The second aspect of exposure is the time spent in proximity to the fire. On average, women spend around 5-7 hours per day close to the fire, and young children (certainly up to 18 months) will usually be with their mothers or care-givers for all or most of that time. In cold and high altitude areas, which include very large numbers of biofuel-using households in Asia, Africa and the Americas, fires will often be kept alight for longer, including through the night (Figure 3). Thus millions of women and children, and especially infants, in the world's poorest communities, are exposed to extremely high levels of pollution for extended periods virtually every day of their lives. While men are also exposed, and should not be overlooked, their exposure is generally considerably lower than that of women and young children. [top] [end]Evidence for health effects of smoke on infants and young childrenSince levels of exposure are considerably in excess of standards, it would be very surprising if indoor air pollution from biofuels was not a serious hazard. Indeed, the supply and use of household energy affects the health of children, women (and men) in a range of ways, but we will focus here on the effects of smoke on young children.[top] [end]PneumoniaPneumonia, the most common type of Acute Lower Respiratory Infection (ALRI), is now the single most important cause of death worldwide among children under 5 years of age. The risk is highest in the first year of life, and especially in the first six months. A growing number of studies have reported an increased risk of ALRI associated with exposure to bio-mass smoke, although for a number of reasons to do with the methods and study design, the evidence from these studies is not reckoned to be particularly strong. (EHP 1997, Bruce 1998).Table 1: Typical particulate air pollution values and EPA standards
Few of these studies have measured exposure to smoke directly. Furthermore, people with lower exposure usually have better housing, nutrition, and less crowding etc. all of which affect ALRI. As a result, it is difficult to determine whether it is the smoke exposure itself that is responsible, or the association of smoke exposure with these other factors. Nevertheless, the results are quite compelling - especially as there is growing evidence of the effects of particulate pollution in urban settings (Pope C. 1995), and that passive smoking (another form of biomass air pollution) increases the risk of acute chest illness in young children (Strachan, 1997). [top] [end]Low birth weightAlthough there is, as yet, little in the way of research evidence for an effect of smoke exposure on birth weight, there is good reason to suspect that this may be important. The most likely mechanism is through exposure of the pregnant woman to carbon monoxide (CO) present in the smoke. Levels of this gas have been shown to be at or above recommended limits in typical biomass-burning households. Carbon monoxide reduces the ability of the blood to deliver oxygen to the fetus, and this in turn impairs growth. This is thought to be the main mechanism by which cigarette smoking during pregnancy reduces birth weight, so it is reasonable to think that exposure to biofuel pollution would have similar consequences. Low birth weight babies are at increased risk of infection, including pneumonia, and are more likely to die.[top] [end]Eye infectionsIrritation of the eyes by smoke is frequently seen, and reported by mothers. It is not certain whether this places the child at higher risk of eye disease, but it might be expected that such children would be more susceptible to eye infection, such as trachoma, which is spread by rubbing and wiping eyes with contaminated material, such as cloths.[top] [end]BurnsAlthough not a result of the smoke, burns to young children are commonly seen with open fires and simple stoves (Courtright 1993). Alternative fuels have their problems too, especially kerosene which is a common cause of fires and poisoning (children drink the kerosene, which is frequently stored in soda bottles, etc.).
[top] [end]How much benefit to health will there be from feasible reductions in smoke pollution?This is a crucial question for those working in the household energy field. Over a twenty four hour period, open fires typically yield PM10 values of at least 1000 µg/m3. Experience has shown that improved stoves which have been in operation for some months or years rarely yield twenty four hour PM10 values of less than 500 to 600 µg/m3. These values are about ten times higher than the recommended levels. The fact is, we have little or no idea whether reductions across this range of exposure levels would make any difference at all to the incidence of ALRI, or to any of the other key health problems associated with smoke.Illustrated in Figure 4 is a thatched tukul from rural Ethiopia, typical of homes in many parts of Africa and elsewhere in the world. Achieving levels at or below the current EPA standards would require substantial changes to the house, stove, and probably the fuel. This scale of change is unlikely in the short or medium term, so it is important to consider what health benefits are likely to be achieved from feasible exposure reductions. The best way to answer this question is to study directly the health benefits that result from measured reductions in exposure of children to smoke. [top] [end]Smoke is not the only problemWhen considering the effects of smoke on young children, it is important to recognise that the main health problems, principally pneumonia and possibly low birth weight, are known to be influenced by factors such as poverty, housing conditions, overcrowding, malnutrition, low birth weight (due to causes other than smoke pollution), and lack of breast feeding. These factors are mostly related to each other, as well as to many aspects of household energy and the pollution that arises from it. To address these problems in an effective way, it is necessary to take an integrated community-based approach, central to which are the needs and priorities of the household. Mothers of young children have an important part to play in this process.
In urban settings, with the additional environmental factors of transport and industrial pollution, the Healthy Cities model provides one valuable means of achieving more city-wide integration (WHO 1995). [top] [end]Conclusions - what needs to be done?Indoor air pollution is an important health hazard for young children. Given the very large numbers of children and their mothers who are exposed to high levels for many hours each day, substantial reductions in exposure should have an important public health impact. However, we do need to establish the levels of exposure at which benefits can be obtained. This has important practical implications for household energy programmes, which include the goal of reducing exposure. Health considerations can help to identify means of achieving effective and sustainable change, and the following points highlight key areas of action:
Two divisions of the World Health Organisation (WHO), Child Health and Development and the Office of Global and Integrated Environmental Health are currently collaborating on a programme of work that is designed to address these health issues. WHO is working with a wide range of development and research groups to ensure that this programme is effective and relevant, and further details of this work can be obtained from the author. [top] [end]Bibliography
[top] [end]Contents: Boiling Point 40: Household energy and health
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01 August 2007; Last edited:
04 December 2008; Version: 2 | |||||||||||||||||||||||||||||||||||
Pagename: SmokeFromBiomassAndItsEffectsOnInfants @HEDON: XDGA | |||||||||||||||||||||||||||||||||||
