COMMENTARY

Health Effects of Indoor Air Pollution From Biomass Cooking Stoves

Martin Donohoe, MD, FACP; Emily P. Garner

Disclosures

May 19, 2008

Introduction

On a typical day in Tezo, Kenya, the sun blazes at nearly 100o F in a cloudless blue sky. It is late in the afternoon by the time the women and young girls return with water, dusty and tired from the trip. After pausing for a moment to play with the children, they begin preparations for dinner.

The firewood they collected earlier that morning is transferred into the cooking hut. Within the hut lies a stove which consists of a circle of stones, piled with carefully assembled wood, beneath a metal potholder. The fire is lit and several women gather around to help stir the prepared cornmeal and to feed logs into the fire. The younger girls are eager to help, and many women have infants slung over their backs as they squat low over the fire.

Every few minutes, the fire emits a waft of smoke or the wind changes direction, causing some of the women to laugh and run out of the hut to avoid inhaling the fumes. This nightly cooking ritual brings these women closer together and allows them to exchange stories with one another, complain about their spouses, tease the younger girls about their adolescent worries, and prepare the only substantial meal that their families will eat all day.

This scene is typical for a large portion of the human population, especially those living in the developing world. Close to 3 billion people, or nearly half of the world's population, use biomass such as wood, dried leaves, dung, or hay as their main source of fuel for cooking and heating.[1] The majority of these people live in rural areas of developing nations.[2] In the poorest countries of the world, the number of people using biomass to heat cooking stoves amounts to over 80% of the population.[1]

Adverse Consequences of Indoor Air Pollution From Biomass Cooking Stoves

Typical indoor stoves do not burn biomass smoothly, making them low-efficiency sources of heat.[3] Additionally, the use of biomass as a source of heat for cooking has several harmful consequences. First, the demand for firewood for cooking contributes to deforestation, often in areas of developing countries suffering from other ecological stressors.[4]

Second, significant pollutants released by biomass combustion include greenhouse gasses that contribute to global warming, such as carbon dioxide, carbon monoxide, and methane.[5] Additional pollutants include sulfur dioxide (a major component of acid rain), nitrogen oxides, dioxins, polycyclic aromatic hydrocarbons (PAHs) and other volatile organic compounds (VOCs), and fine particulate matter.[6] Nearly 50% of the polynuclear organic material in our air is from residential wood burning.[7] VOCs are precursors of ground-level ozone, a major contributor to air pollution and asthma exacerbations. Dioxins and PAHs are known carcinogens.

There are over 200 different chemicals and organic compounds in wood smoke alone, nearly all of which are pollutants small enough to be inhaled by humans and other animals.[8] Levels of harmful pollutants released by indoor biomass burning are often 10-20 times higher than the recommended upper limits of exposure established by the World Health Organization (WHO).[4] The WHO has shown that patterns of exposure to indoor air pollution from biomass smoke make it a more significant threat to human health than outdoor air pollution.[4]

Biomass cooking stoves are typically found in areas with low ceilings, making it necessary to squat so that a person's face is in close proximity to smoke. Cooking huts are often poorly ventilated, filled with smoke, and crowded with several women at once. Under these conditions, it would be easy for a person's hair, clothing, or the surrounding structure (often also made of wood) to catch fire.

Young children are usually eager to help their mothers cook, and women often have their babies and infants secured to their backs.[4] This exposes the children, whose lungs and immune systems are still developing (and therefore more susceptible to damage),[5] to similar levels of smoke as their mothers. Typical exposures last from 3-7 hours each day.[4] Indoor air pollution contributes to 36% of all acute respiratory infections in children. Such infections are the leading worldwide cause of death in children under age 5.[9] Deaths linked to biomass smoke exposure compete with malaria as the leading cause of death in adults in developing nations every year.[10]

High concentrations of indoor air pollutants lead to a number of adverse health consequences, which disproportionately burden women and young girls.[11] These consequences include acute lower respiratory tract infections, including sinusitis, otitis media, and pneumonia.[4] Prolonged exposures can cause chronic bronchitis, chronic obstructive pulmonary disease, asthma, upper airway cancers (including nasopharyngeal and laryngeal cancers), cardiovascular disease, pulmonary arterial hypertension, cataracts, low birth weight, and perinatal mortality (stillbirths and deaths during the first week of life).[4]

Exposure to indoor air pollution from biomass smoke interferes with macrophage activity, obstructs cellular membranes, and destroys epithelial cells lining the respiratory tract,[5] all of which increase the risk for pulmonary infections. Smoke can exacerbate symptoms of tuberculosis, and confined cooking quarters facilitate transmission of this deadly and increasingly multidrug-resistant infection.

Due to high concentrations of PAHs, the risk of developing lung cancer from indoor biomass smoke can be 12 times greater than the risk from exposure to similar amounts of environmental tobacco smoke.[12] In total, biomass smoke exposure causes nearly 2 million deaths annually, the equivalent of 1 life lost every 20 seconds,[11] or nearly 3% of the global disease burden each year.[4]

Solutions

Feasible, low-cost measures that could reduce the devastating health outcomes of exposure to indoor biomass smoke include: cooking outdoors; cooking in rotations and for shorter time periods; keeping children, especially infants, away from cooking areas as much as possible; having women or older children who are not involved in cooking assume temporary childcare duties; improving ventilation by adding more windows around cooking areas or by building chimneys over stoves; improving stove construction and technology, including through the use of fumes or hoods to divert smoke[13]; using cleaner burning, low-smoke fuels such as liquid petroleum gas, kerosene, ethanol, or biogas[14]; or, ideally, switching to solar-powered stoves.

Educating women regarding the health risks of biomass smoke inhalation,[15] providing access to quality healthcare (including the full-spectrum of reproductive options), and improving the overall status of women by enhancing their access to capital, political, and legal representation would also contribute to a lessening of biomass cooking practices which place women and children in harm's way.[16,17]

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