Communicating the health effects of indoor exposure to particulate matter

While the health effects of outdoor exposure to particulate matter (PM) have long been the subject of both research efforts and regulatory action, indoor exposure to PM has only recently started getting attention as a potential source of adverse health effects. Studies have yielded evidence linking such exposure to outcomes including cardiovascular disease,1 adverse birth outcomes,2 and neurological and cognitive disorders.3 These developments led the U.S. Environmental Protection Agency's Indoor Environments Division to request the National Academies of Sciences, Engineering, and Medicine to conduct a workshop on the topic. The National Academies have been offering advice to the U.S. federal government on indoor air issues since the 1980s, examining the state of the scientific evidence on indoor pollutants,4 allergens,5 asthmagens,6 dampness,7 the influence of “green” practices in schools,8 and climate change.9 A forthcoming report will examine how microbial communities in built environments are affected by occupants and influence human health.10 An international workshop held in February 2016 at the National Academies brought together researchers, practitioners, and other stakeholders to discuss the potential health risks of indoor exposure to PM and the state of scientific understanding regarding them, focusing on exposure to PM2.5 and ultrafine particles. The workshop examined a range of issues relating to indoor PM and public health: sources, particulate matter dynamics and chemistry, exposure levels and characterization, exposure mitigation, identified and emerging health concerns, and interventions and risk communication. A synthesis of these discussions appears in a recent National Academies report.11 Since the publication of the report, we have had the opportunity to present and discuss the results of the workshop at several international meetings, including Indoor Air 2016 in Ghent, Belgium; ISES 2016 in Utrecht, the Netherlands; and IAQ 2016 in Alexandria, VA. A core theme emerging from these symposia was the high degree of practitioner and scholarly interest in how best to communicate information about indoor exposures and their health consequences—not just to occupants but to all those involved in the design, construction, maintenance, operation, and renovation of buildings. This attention is understandable: occupant behavior and building management and maintenance practices have a great influence on indoor particulate matter levels. Effective messaging on risks and interventions thus represent a primary means of limiting adverse exposures. However, those with the greatest knowledge regarding these scientific issues are generally not so well informed about the science and art of good communication. Three workshop speakers discussed the opportunities and challenges concerning indoor PM risk communication. George Gray of the Milken Institute School of Public Health at the George Washington University identified two fundamental questions regarding indoor PM: what to tell people about the associated risks and how to tell them. In general, the public's attitude about environmental risks is shaped by many factors, including the magnitude of the risk, whether the risk outcome is fatal or not fatal, whether the risk arises from voluntary or involuntary behavior, whether it is controllable or uncontrollable, whether it is manmade or natural, whether it is observable or not, and whether there is any benefit associated with incurring the risk. Within this framework, though, he noted that it is not enough to know how the public thinks about the indoor exposure risks; one must also understand how they feel about them. Getting the public to grasp the risk of indoor PM exposure will be difficult, Gray observed, because many of the most important sources are familiar, voluntary, and linked to benefits. Cooking, for example, is something that people do every day and it produces food they enjoy eating. Using candles or incense is voluntary and makes the house smell good or may be part of a cultural or religious experience that is important to some people. From the standpoint of the indoor air scientific community, the challenges in conveying the risk of indoor PM exposure to the public will include the need to understand the magnitude of the risk before deciding how much to communicate about it. Gray said that it will also be important to provide information on the relative contributions of different sources—including the relative contributions of indoor versus outdoor contaminants—how much of the exposure to these sources is under the individual's control, and what trade-offs are involved in achieving exposure reduction if people are to take effective actions. The good news in all of this is that there are other exposure circumstances from which the indoor PM field can borrow and adapt. Indoor radon, secondhand smoke, and pesticides share commonalities with PM and each topic has been the subject of research on public perceptions and interventions. Information gained from such work, he concluded, may provide insight on what will and will not work in risk communication. William Hallman of Rutgers University built upon Gray's talk, extending lessons learned from communicating about other health risks to communicating about indoor PM. He began by listing the basic goals of risk communication: education, advocacy or persuasion, and fostering partnerships for decision-making. Education aims to supply information and context so that people can choose what they believe is the right action to take in the face of risk. Advocacy or persuasion starts with the premise that experts can objectively determine the best course of action to deal with a risk and that getting people to take these actions are in their own best interests, and then proceeds with efforts to change beliefs, attitudes, and behaviors to convince people to take those actions. The aim of fostering partnerships is to collect and discuss information with stakeholders in a way that leads to better collective decisions about what the right course of action should be. These goals differ in terms of who is considered to have information worth sharing and who gets to decide what action should be taken. Each requires a different strategy to be effective. Hallman cautioned that simply alarming people about a hazard without also giving them the means to address it is both ethically problematic and does not always lead to actions that make people safer. In contrast, helping people understand the nature of the hazard, what they can do to reduce their exposures, and helping them do it can motivate people to take action. However, convincing people that they need to take action can be particularly difficult. When individuals are responsible for their own exposures, it is easy to ignore them, particularly when the hazard is invisible, because the absence of situational indicators can give people a false sense that they are not at risk. Thus, making invisible hazards perceptible—as smoke and carbon monoxide detectors do, for example—may be essential to getting people to reduce their exposures. More generally, Hallman noted that while it is important to understand what people know and want to know about an issue, it is more important to understand how they think about an issue. Researchers know that when people are faced with trying to make sense of risks that are unfamiliar to them they will use whatever information is available—including advertising claims—to fill in gaps in their understanding. In doing so, they are vulnerable to incorporating information into their mental models that is plausible, but not scientifically valid. Given these conditions, Hallman said that people need practical, effective, and affordable advice on what actions they should be undertaking, that this advice must be consistent to be credible, and that they should be provided with help to take appropriate actions. He underscored that the uncertainties in present-day indoor PM science cannot be ignored. His prescription is to acknowledge these uncertainties and tell people, “This is what we know and do not know now. This is why it matters, this is what we are doing to become more certain, and this is what you can do while we continue to work on this particular problem.” Lee Ann Kahlor of the University of Texas at Austin described what might be learned from research to gauge public understanding and information seeking related to indoor PM risk. Baseline information is needed, she said, because little is known about how the public perceives indoor environmental issues broadly and the issues of indoor PM in particular. Kahlor noted that each of the many audiences for information on PM may need to be approached differently, in ways that account for individuals’ values and resources and that take into account the many competing factors that influence peoples’ health, safety, and quality of life. She suggested a preliminary set of questions that could be part of a baseline study from the presentations made at the workshop: Data from a survey of public knowledge and attitudes would provide information on the social norms that would help or hinder conveying information to audiences. It would also reveal patterns in perceived risk and related worry and existing knowledge versus how much knowledge individuals think they need. These data would help researchers understand beliefs about the information available and attitudes toward that information, the ability to obtain and process information, and whether such information will be accessible. The data would also identify trusted sources for conveying information and the preferred modalities for receiving information. This last point is important because people do not simply absorb the information that the scientific community generates, but rather need to be engaged in such a way that they process the information and make it meaningful personally. Kahlor thought that it would be desirable for such a survey not only to look at the general population but also to make a special effort to sample parents of children up to age 12, residents of disadvantaged communities, and the elderly. The results of a baseline survey would help to illuminate the target audiences for information on indoor PM and what information they need. Once this information is in-hand, Kahlor said, the challenge in putting it into practice would become identifying meaningful, relatable narratives for the lay public. Partnerships between and among indoor air professionals and those affected by indoor PM, she said, will be critical to delivering those stories in ways that resonate with place, time, and most critically, their personal lives. As these speakers and our extensive interactions with international indoor air professionals demonstrate, there is still much to learn about how best to inform the public about indoor PM risks and how best to manage them in the face of competing priorities, limited resources, and gaps in the information concerning the scope and magnitude of the problem. It does appear, though, that we know enough to begin asking the right questions. That is a start. Funding for the Workshop on the Health Risks of Indoor Exposure to Particulate Matter was provided by the U.S. Environmental Protection Agency, Indoor Environments Division. The authors wish to express their thanks to the members of the workshop planning committee—William Nazaroff (chair), Richard Corsi, Howard Kipen, Tiina Reponen, and Terry Brennan—co-rapporteur Joe Alper, the workshop presenters, and the participants. The views expressed in this article are those of the authors and do not necessarily reflect the positions or statements of the National Academies of Sciences, Engineering, and Medicine.