Biomass Fuels and Health: The Gap between Global Relevance and Research Activity

The greatest burden on health related to biomass fuels affects the world's poorest and most vulnerable populations. Approximately half of the world's population, and up to 90% of households in rural areas of developing countries, still depend on unprocessed biomass fuels, mainly wood, dung, and crop residues, for cooking and heating (1, 2). These are burned indoors in open fires and stoves that often are not vented. Combustion is incomplete and leads to high indoor concentrations of substances harmful to health, such as respirable particles (PM), carbon monoxide, nitrogen oxides, polycyclic organic hydrocarbons, and other toxic compounds (3). In developing countries, women are traditionally responsible for cooking, and consequently the exposures are highest for them and for their infants and young children, who are often carried on their mother's back. Typically, exposure to high levels of pollutants lasts for 3 to 7 hours daily over many years (2). In global perspective, the magnitude of the health consequences of indoor air pollution, biomass fuels being the major source, is comparable to that of tobacco use, exceeded only by malnutrition, poor water/sanitation, and unsafe sex (4).

What do we know about the health effects of biomass fuels? The known or suggested adverse effects include common respiratory diseases, along with low birth weight and increased infant mortality (2, 3), and even DNA damage (5). Considering the extent of biomass fuel exposure, it is surprising how little research there is to date on its health consequences. At present, the strongest evidence exists for a relation between biomass fuel exposure and acute respiratory infections in children, with effect estimates for incidence and mortality ranging from two- to three-fold (6). Other major respiratory effects that have been linked to biomass fuels more or less consistently include chronic obstructive pulmonary disease, asthma, nasopharyngeal and laryngeal cancer, and susceptibility to pulmonary tuberculosis (2, 3).

In this issue of the Journal (pp. 901-905), a study of more than 800 women from a rural community in Mexico investigated the relations between biomass fuel cooking and respiratory symptoms and lung function (7). The study demonstrates that it is feasible to carry out studies applying high-quality research methods in the often-difficult conditions of developing countries. This is important for getting reliable effect estimates and also for being able to assess adequately the benefits from any interventions aiming at solving these problems.

Earlier studies have shown an increase in respiratory symptoms and lung function impairment related to biomass fuel burning in children and in adults (2, 8-13), but there have been some methodologic issues, such as compromised validity of exposure assessment and limited control for confounding. To address these problems, the Mexican study (7) measured particle concentrations while cooking was in progress with the usual fuel, thus also capturing peak concentrations. In addition, it estimated a cumulative exposure index combining reported daily exposure in hours with years of exposure (hour-years) to assess lifetime biomass fuel exposure. The results showed high PM^sub 10^ peak concentrations of the order of 2,600

A limitation of the study is its small reference group of women with exposure to gas only, which reduces the power of this otherwise rather large study. Even more important is the fact that practically all women had previous exposure to biomass fuels, most of them in their childhood. This means that current biomass fuel exposure could not be contrasted to "never exposure," but instead to "no recent exposure," so the effect estimates are underestimated. The strongest effects on lung function were detected in relation to high current concentrations of PM^sub 10^, so how much of the effect is acute and perhaps reversible and how much of it is long-term reduction that cannot be recovered remains somewhat unclear. Distinguishing these two types of effects is important from a preventive point of view and, in the future, development of better assessment methods for long-term exposures and longitudinal assessment of the change in lung function over time are needed. In many developing countries, smoking by men indoors is also common, and the interactions between tobacco smoke and biomass fuel exposures may add to the health problems, but this has not been studied.

From the global preventive perspective, the key question is the strong link between poverty and use of biomass fuels. Sustainable development calls for interventions that replace biomass fuels with more processed and cleaner fuels, that improve stoves, ventilation, and housing conditions in general, and that educate women about behavioral possibilities to reduce the exposure to themselves and their children. Sustainable development also requires that these interventions should be affordable and easy to implement. Research on biomass fuels and evidence-based interventions should be a high global priority, since reducing indoor biomass fuel exposures locally in developing countries would contribute to simultaneous reduction of harmful outdoor pollutants (3). Indeed, giving more emphasis to such interventions could be a cost-effective way to reduce globally the harmful pollutants leading to the greenhouse phenomenon.

Conflict of Interest Statement: Neither author has a financial relationship with a commercial entity that has an interest in the subject of this manuscript.

Acknowledgment: The authors thank Professor Margaret R. Becklake for her valuable comments on the editorial.

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