By Tara Failey

University of Washington researcher Anjum Hajat, Ph.D.

(Photo courtesy of Anjum Hajat)

Exposure to air pollution can vary greatly by socioeconomic status (SES), according to a new NIEHS-funded review of existing literature. Socioeconomic Disparities and Air Pollution Exposures: A Global Review provides insight on what is known about air pollution inequities by SES worldwide. Overall, the review found that poorer communities tend to be exposed to higher concentrations of air pollution, compared to richer communities.

“In the United States, we often focus on race when looking at air pollution inequities,” said lead author Anjum Hajat, Ph.D., an epidemiologist at the University of Washington. “On a global level, our research underscores the importance of social class when considering the unequal distribution of air pollution.”

The research team, which also included Charlene Hsia and Marie O’Neill, Ph.D., conducted a systematic review to identify published studies on SES and ambient air pollution exposures. Using a rigorous methodology, 37 studies met their inclusion criteria and were included in the review. Studies were organized by geographic location, with 22 North American studies, 10 European studies, and five studies from New Zealand, Asia, and Africa.

Air Pollution Inequality Varies Globally

While the review generally showed that air pollution is higher in poorer communities, 8 of 10 studies illustrated this relationship, the researchers noted that results varied in different regions of the world. Most North American studies consistently indicated that low-SES communities experience higher concentrations of criteria air pollutants, while European research was mixed.

“In Europe, the results were all over the place — often wealthy people see higher exposures, but that does not necessarily translate into the same negative health effects,” said Hajat. The researchers note that the trend in poorer air quality among higher SES groups may be related to the popularity of large cities, like Rome, where people with higher incomes are living in more desirable areas with more amenities and higher levels of air pollution due to traffic.

In contrast, research from Asia, Africa, and other parts of the world revealed trends similar to that of North America, but research in these parts of the world is extremely limited. In Africa, for example, the only study, that met their inclusion criteria was an examination of particulate matter in four communities in Ghana. “So while the trends we noted were consistent, we can’t even begin to summarize what’s happening on an entire continent based on one study,” said Hajat.

Further Studies to Improve Global Public Health

A recent infographic from the WHO Global Assessment of the Burden of Disease from Environmental Risks emphasizes the burden on low- and middle-income countries. WHO: Environmental Impacts on Health

(Photo courtesy of WHO)

While noting limitations in available data, Hajat sees a booming interest in studying inequality in developing countries, comparing this interest to the 1980s birth of the environmental justice movement in the U.S. “Since I began working in this field, I’ve seen a surge in interest on environmental justice across the globe. If you look at research from the past, you find that much of it is U.S.-based, but that is not the case anymore,” she said. “People across the globe recognize the importance of identifying the health effects of air pollution to improve the health of communities. Whether domestically or internationally, research is important because it informs policies — and policymakers often won’t enact policies unless you show them the data.”

A recent World Health Organization (WHO) assessment on the global burden of disease illustrates the growing interest in studying environmental health disparities according to SES. This assessment found that environmental impacts on health are uneven across different social groups, and the greatest health burdens fall on low- and middle-income countries. Further, 23 percent of all global deaths are linked to the environment, which translates to 12.6 million deaths per year due to environmental causes.

Next Steps

Moving forward, Hajat and her research team seek to advance their research in several key ways. First, they aim to continue looking at the health outcomes associated with air pollution, which were not examined in this review. Air pollution is commonly linked to asthma, cardiovascular disease, and chronic obstructive pulmonary disease. Next, the research team seeks to examine how other social factors, such as stress, education level, and neighborhood factors, interact with air pollution to influence health outcomes.

Hajat’s research examining the intersection of social factors and air pollution is funded by NIEHS. The agency has had a long-standing interest in this area, as seen in its strategic plan.

Ultimately, this research could help decrease environmental health disparities and air pollution exposure. “My goal is to deepen our understanding of how social and environmental factors work together to impact the health of vulnerable populations,” Hajat said.