Maryland's poor, African-American communities suffer disproportionate cancer risk from air pollution

Jun 15 2005

Maryland communities that are poor and predominantly African-American incur a disproportionate cancer risk from ambient exposure to airborne toxins, according to researchers from the Johns Hopkins Bloomberg School of Public Health.

Their study revealed that among Maryland census tracts, the poorer the community and the higher the proportion of African-Americans, the greater the residents' cancer risk from air toxics. Further, the researchers were able to identify the sources underlying the inequities. Both traffic and area sources (e.g., dry cleaners and gas stations) were primarily responsible, in contrast to point sources (e.g., power plants, heavy industry) and non-road mobile sources (e.g., construction, farm vehicles and airplanes), which were more evenly distributed across Maryland's economic and racial strata. The study is published in the June 2005 issue of Environmental Health Perspectives.

“The inequity in risk from air toxins shown by this study represents yet another public health strike against that segment of Maryland's population that can least afford it,” said Benjamin Apelberg, MHS, lead author of the study and a graduate student in the Bloomberg School's Department of Epidemiology.

The researchers compared cancer risk estimates from the U.S. Environmental Protection Agency's (EPA) National Air Toxics Assessment to the racial and socioeconomic characteristics of Maryland communities found in the 2000 U.S. Census. The EPA's assessment of lifetime cancer risk, which is based on exposure to 29 toxic air pollutants, is based on a nationwide inventory of sources and emissions and accounts for atmospheric transport of the pollutants, human activity patterns and the carcinogenic potency of the air pollutants.

Apelberg and his coauthors found that census tracts in the lowest quartile of median household income were 15- to 100-fold more likely to be at high risk of cancer from air toxins. In addition, communities with higher proportions of African-American residents were three times more likely to be at a heightened risk. They also found that as the proportion of white residents increased, the level of risk decreased.

Four categories of air toxins major emissions sources; area emissions sources; on-road vehicle sources; and non-road sources were included in the EPA's cancer risk assessment. Vehicle emissions of air toxins from on-road automobiles had the highest impact on cancer risk in Maryland, followed by non-road mobile sources such as construction vehicles and farm equipment, and by area sources such as local automobile repair shops and dry cleaning facilities. Significant and consistent disparities in risk by income and race were found for on-road vehicle emissions and area sources.

The study results suggest that low-income, African-American communities are more likely to be located near busy roadways. In contrast, the researchers observed that cancer risk from large industrial point sources was more evenly distributed across economic and racial strata.

“Our study is only one piece of a larger puzzle of the factors leading to health disparities. It is widely accepted that low-income and minority communities face a disproportionate number of stressors and are more likely to have poorer health. Long-term risk from air pollution is one of the factors that can be mitigated through sound environmental policies,” said Ronald H. White, MST, coauthor of the study and deputy director of the Bloomberg School's Risk Sciences and Public Policy Institute.

The study authors suggest that low-income areas should be targeted for emissions-reduction policies, especially for on-road vehicles and area sources, to help decrease the exposure of residents to air toxins.

“Public health and environmental justice needs to be a part of zoning and transportation planning. It is time to think beyond simply building more and bigger highways as a solution to Maryland's transportations needs. Drivers need to understand that their commuting and vehicle choices impact the health of the neighborhoods they drive through,” said Timothy J. Buckley, PhD, MHS, corresponding author of the study and an associate professor in the Bloomberg School of Public Health's Department of Environmental Health Sciences.

“Socioeconomic and Racial Disparities in Cancer Risk from Air Toxics in Maryland” was supported by grants from the National Institute of Environmental Health Sciences, the Johns Hopkins Center for Urban Environmental Health and the Maryland Cigarette Restitution Fund.