Agricultural Fires and Health at Birth

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While industrialization, forest fires, and traditional cookstoves are often considered primary contributors to air pollution, the traditional use of fires in agricultural practices is still widespread, and there is limited research on the health impacts of exposure to those fires. In the sugar-growing region of São Paulo, Brazil, farmers produce one-fifth of global sugar cane tonnage annually and conduct widespread field burns during harvest. Land devoted to sugarcane agriculture in Brazil doubled from 2000 to 2014, and it is expected to continue rising, given the increased global demand for sugar and biofuels. Particulate matter (PM) concentration from agricultural burns does not reach levels deemed dangerous by international regulations, so research into the health impacts of repeated exposure to moderate-scale pollution is limited. In this study, researchers assessed the impact of upwind fires in São Paulo to determine if in utero exposure to smoke from sugarcane fires reduces birthweight and gestational age at birth.

Findings indicate a significant negative relationship between increased pollution from upwind sugarcane fires and impacts on birth outcomes. In this study, upwind fires between 5 and 50 km from a municipality’s population centroid lead to a significant increase in both particulate matter 10 (PM10) and ozone (O3). When a pregnant woman is exposed to pollution from these fires during the last gestational period of pregnancy, there is a reduction in average birthweight by 98 grams; rates of very preterm births rise significantly, by 23 per 1,000; the average stillbirth rate increases by 17 per 1000 births; and the number of live births decreases by 12%. Similar effects are not seen when a pregnant woman is exposed to this pollution during earlier gestational periods, and researchers did not find a significant effect on postnatal mortality. There is, however, a positive relationship between upwind fires and hospitalization of reproductive-age women.

Interestingly, researchers found that non-upwind fires during the final gestation period can have a positive impact on birth outcomes. This finding reflects the known child health benefits associated with the increased economic activity that comes during sugarcane harvests. When agricultural fire activity does not expose mothers to increased levels of pollution, the economic benefits of fires likely lead to an improved in utero environment. Global trends in sugarcane harvesting involve increased mechanization of the process, which reduces fires and associated pollution but has been shown to have negative economic impacts on GDP per capita and job creation. While mechanization would decrease exposure to upwind fires, it is important to consider the economic consequences that could ultimately produce a net negative impact on child health outcomes.


Researchers used data from thirteen air monitoring stations operated by São Paulo’s environmental agency from 2009 to 2014 to measure ozone, particulate matter, wind direction, and temperature in areas affected by agricultural fires. To assess birth outcomes and gestational length, researchers used 287,506 vital and hospitalization records of live births from mothers residing in sugar-growing municipalities with air pollution sensors. Researchers then used two estimations to link fires to air pollution and health outcomes. An important aspect of these estimations is comparing outcomes for upwind and non-upwind fires in the same geographic area to estimate the differential impact on birth outcomes.

For related research on birth outcomes, read "Brazil’s Missing Infants: Zika Risk Changes Reproductive Behavior."



Marcos Rangel (Duke University), Tom Vogl (University of California San Diego)


  • National Institutes of Health
  • Health Grand Challenge at Princeton University

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Human Development, Climate & Sustainability, Environment, Health, Economic Development, South America