From: Andy Soos, ENN
Published November 16, 2011 12:07 PM

Why Wood Smoke May not Be Good for You

Some people enjoy the scent of a wood fire. Still smoke is full of particulate matter and exotic trace chemicals. Two new studies led by University of California, Berkeley, researchers spotlight the human health effects of exposure to smoke from open fires and dirty cook stoves, the primary source of cooking and heating for 43 percent, or some 3 billion members, of the world's population. Women and young children in poverty are particularly vulnerable. In the first study, the researchers found a dramatic one-third reduction in severe pneumonia diagnoses among children in homes with smoke-reducing chimneys on their cook stoves. The second study uncovered a surprising link between prenatal maternal exposure to woodsmoke and poorer performance in markers for IQ among school-age children.


Smoke is a collection of airborne solid and liquid particulates and gases emitted when a material undergoes combustion or pyrolysis, together with the quantity of air that is entrained or otherwise mixed into the mass. It is commonly an unwanted by-product of fires (including stoves, candles, oil lamps, and fireplaces). Smoke may be used in rituals, when incense, sage, or resin is burned to produce a smell for spiritual purposes. Smoke is sometimes used as a flavoring agent, and preservative for various foodstuffs.

Many compounds of smoke from fires are highly toxic and/or irritating. The most dangerous is carbon monoxide leading to carbon monoxide poisoning, sometimes with the additive effects of hydrogen cyanide and phosgene. Smoke inhalation can therefore quickly lead to incapacitation and loss of consciousness.

The findings on wood smoke pneumonia, the chief cause of death for children 5 and under, will be published in the journal The Lancet on Thursday (Nov. 10). While previous research has linked exposure to household cooking smoke to respiratory infections, the latest results come from the first-ever randomized controlled trial on air pollution.

"This study is critically important because it provides compelling evidence that reducing household woodsmoke exposure is a public health intervention that is likely on a par with vaccinations and nutrition supplements for reducing severe pneumonia, and is worth investing in," said Kirk Smith, professor of global environmental health at UC Berkeley's School of Public Health and principal investigator of the RESPIRE (Randomized Exposure Study of Pollution Indoors and Respiratory Effects) study.

In the RESPIRE study — which includes partners from Guatemala's Universidad Del Valle, the U.S. Centers for Disease Control and Prevention, University of Liverpool, Norway's University of Bergen and the World Health Organization — researchers worked with rural communities in the Western Highlands of Guatemala. Households with a pregnant woman or young infant were randomly assigned to either receive a wood stove with a chimney or to continue cooking with traditional open wood fires.

The researchers found that using chimneys to vent cooking smoke outside homes led to a striking decrease in cases of severe pneumonia compared with total pneumonia cases, possibly because the reduction in smoke with the chimney stoves was insufficient to significantly reduce all risk.

"The amount of smoke exposure babies were getting from the open woodfire stoves is comparable to having them smoke three to five cigarettes a day," said Smith, whose research in this field began 30 years ago. "The chimney stoves reduced that smoke exposure by half, on average."

In all there were 265 children in the chimney-stove homes and 253 children in the control homes. During the study, the researchers reported 149 children in the chimney-stove homes and 180 in the open-fire homes with physician-diagnosed pneumonia. For severe pneumonia, characterized by low blood oxygenation, there were 72 cases in the chimney-stove group and 101 in the control group.

In the second study, published online Sept. 24 in the journal NeuroToxicology, Smith led the research team that followed up with some of the families in the RESPIRE trial. That trial ended in 2005 when the infants were 18 months old. In 2010, when the children were 6-7 years old, the researchers recruited 39 mother-child pairs for the study.

The results found, for the first time, a link between exposure to wood smoke — as determined by carbon monoxide levels measured individually — during the third trimester of pregnancy and lower performance on neurodevelopmental tests at ages 6 and 7. Specifically, the researchers found impairments in visuo-spatial perception and integration, visual-motor memory, and fine motor skills.

"I was surprised because woodsmoke was always considered a risk for respiratory health, but not IQ," said study lead author Linda Dix-Cooper, who conducted the study for her master's thesis in UC Berkeley's Global Health and Environment graduate program.

Finding cleaner alternatives to traditional cookstoves has been an area of active research at UC Berkeley and the Lawrence Berkeley National Laboratory for decades. Some current projects are part of the UC Berkeley-based Blum Center for Developing Economies. They include one led by Smith to replace unhealthy coal stoves in rural China through carbon offsets, and another led by Daniel Kammen, Class of 1935 Distinguished Professor of Energy at UC Berkeley, to develop cost-effective methods to disseminate improved cook stoves throughout Tanzania.

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