environmental stressors such as combat exposure, job-related stress, and other environmental pollutants such as dust storms. The committee focused on health effects related to combustion products as related to burn pits and did not attempt to assess health effects from these other exposures.
The committee did not consider studies of health effects reported for first responders to the World Trade Center attacks in 2001 because the composition of the smoke and emissions from this event are substantially different from combustion emissions, particularly those expected from burn pits.
Extensive searches of the scientific literature published after 1980 were conducted using two major biomedical databases: MEDLINE and EMBASE. The literature search for long-term health effects among firefighters retrieved over 400 studies, including studies of structural fires, wildland or forest fires, and chemical fires. The titles and abstracts of those studies were reviewed and studies that did not appear to be immediately relevant were deleted from the database. Deleted studies included those not linked to inhalation exposure (such as studies of job-related stress); studies that had fewer than 10 participants; studies of acute or short-term health effects only (unless considered relevant to long-term effects); studies of exposures to uranium and other types of radiation; studies reporting behavioral or psychiatric outcomes; or studies that assessed DNA or other cellular damage. The literature search for incineration workers and residents of nearby communities also returned over 400 studies. In this case, rejected studies included those that were not linked to inhalation exposures; studies that reported acute or short-term health effects only; studies that were modeling studies of emissions or that focused on children, genetics, or DNA damage; and studies of ambient air pollution. Studies that characterized emissions from incinerators but not their health effects, or that focused on waste management, were also rejected.
The committee adopted a policy of using only published papers that had undergone peer review as the basis of its conclusions. An exception was made for the epidemiologic studies conducted by the DoD to assess health effects in military personnel exposed to burn pits; theses studies are summarized below and discussed after the peer reviewed epidemiologic studies for each health outcome. Since epidemiologic studies of Gulf War veterans have been described previously by other Institute of Medicine (IOM) committees, most recently in Volume 8 of the Gulf War and Health series (IOM 2010), this committee relied on those assessments supplemented with a review of more recent publications.
Key and Supporting Studies
After the removal of the extraneous studies, the full text of the remaining articles and reports were retrieved. For each health outcome, committee members reviewed the studies most closely related to their area of expertise, to determine whether the criteria for a key or supporting study were met. Consistent with previous IOM reports (IOM 2010), to be designated as key, a study had to be published in a peer-reviewed journal, present information about the putative exposure and specific health outcomes, demonstrate rigorous methods, include methodological details adequate to allow a thorough assessment, and use an appropriate control or reference group. A supporting study typically had methodological limitations, such as lack of a rigorous or well-defined diagnostic method or a lack of an appropriate control group. The committee as a group reviewed the key and supporting studies identified by the committee members responsible for each health outcome. The strengths and limitations of each study and its categorization as key or supporting were discussed in plenary session and a consensus reached on its contribution to the evidence base for each category of association for each health outcome. After having reviewed all the studies in detail, the committee based its conclusions primarily on key studies. Supporting studies are included as part of the committee’s analysis because they provide information that might modify confidence in the conclusions based on key studies, but they carry less weight than key studies. The committee considered the DoD epidemiologic studies as supporting literature when making conclusions about associations between exposure to combustion products and health outcomes.