Researchers at Washington University in St. Louis published a paper late last year that found carcinogens present in the air of the St. Louis metropolitan area to be highly concentrated in Black and poor neighborhoods. They found that approximately 14% of the census tracks in the city had elevated cancer risk due to exposure to toxic chemicals in the air and that these air toxic hots spots were independently associated with neighborhoods with high levels of poverty and unemployment, and low levels of education. Census tracks with the highest levels of both racial isolation of Blacks and economic isolation of poverty were more likely to be located in air toxic hot spots than those with low combined racial and economic isolation.

This paper is important because the authors used an innovative geospatial approach developed by other researchers to identify spatial patterns of residential segregation in their study area. This approach captures the degree of segregation at the neighborhood level and identifies patterns of isolation of different metrics, which in this study was black isolation and poverty isolation. This approach differs from tradition methods that looked at the percentage of blacks or poverty in a neighborhood.

The authors used these two segregation measures – Black isolation and poverty isolation – to identify neighborhoods segregated by race and income in the St. Louis metropolitan area and evaluated the risks of exposure to carcinogens in the air in these areas. The cancer risk data came from the Environmental Protection Agency’s National Air Toxics Assessment and the census track sociodemographic data came from the American Community Survey. All spatial analyses were conducted using Arc GIS software.

These researchers found that census track levels of poverty, undereducation and unemployment were associated with toxic hot spots, while factors such as per capita income and median household income were inversely associated with toxic hot spots. These findings support other studies that identified disparities in exposures to ambient air emissions of toxic chemicals and that raised questions about whether residential segregation leads to differential exposure to air pollutants.

While the authors discuss a number of possible pathways connecting segregation and health, the relationship between segregation and exposure to air toxics is unclear. They discuss various factors that result in segregation leading to the “cycle of segregation” that includes neighborhoods with low social capital, few community resources and low property values which tends to attract more low income and minority residents and exposures to unhealthy air toxics.

The authors concluded that this study provides strong evidence of the unequal distribution of carcinogenic air toxics in the St Louis metropolitan area and that residential segregation leads to differential exposure to chemicals in the air that cause cancer.