Cumulative Environmental Hazards Article Wins Editor's Choice Award

The Los Angeles study area, covering central and southern Los Angeles County, with major roads and ports shown.

Scientists from UC Berkeley won an Editor's Choice Award from the leading journal, Environmental Science and Technology (EST). Out of nearly 1,500 articles published yearly, EST editors chose theirs as one of the best in 2009 from among 80 nominated. Lead author Jason Su is a post-doctoral scientist in the Health and Exposure Analysis Laboratory within the School of Public Health. Co-authors include Rachel Morello-Frosch, Bill Jesdale, Amy Kyle, Bhavna Shamasunder and Michael Jerrett, also from the School of Public Health. 

In their study, Su and colleagues propose an index for summarizing racial-ethnic and socioeconomic inequalities in cumulative environmental hazards, then apply the method in Los Angeles County, one of the most ethnically diverse and polluted metropolitan areas in the United States.1

Researchers show the interplay between individual and cumulative hazards using multiplicative and additive statistical approaches. To summarize social inequality, they measure poverty and racial-ethnic composition at the census tract-level. To illustrate unequal levels of pollution in the region, they use measurements of nitrogen dioxide (NO2), particulate matter less than or equal to 2.5 micrometers in diameter (PM2.5) and estimates of cancer risk associated with diesel exhaust from the Environmental Protection Agency's National-Scale Air Toxics Assessment (NATA) model.

The greatest environmental inequities were seen for diesel particulate matter cancer risk, followed by NO2 then PM2.5. Importantly, the inequalities in cumulative hazards were more pronounced than for any single pollutant when assuming existence of synergistic impacts. The highest levels of cumulative impacts cluster in downtown Los Angeles followed by the Los Angeles/Long Beach port area. “A key question,” says Jerrett, “is whether the health risks also magnify, similar to exposures.”

Su says scientists can integrate other environmental risk factors in the model based on their research objectives, such as proximity to industrial or agricultural land uses--even positive attributes that are thought to benefit health, like access to green space or grocery stores. Scientists can further test assumptions by age or gender.

"The reason for using NO2 and PM2.5 is that they are criteria pollutants with ambient air quality standards set by the US Environmental Protection Agency, which enables us to compare our data to national standards," said Su. A widely accepted regulatory benchmark for cancer risk associated with diesel exhaust was also used.

Looking ahead, researchers will apply the index in two additional regions--San Diego and the San Francisco Bay area--and then compare cumulative impacts in all three regions to identify communities of concern in California.

"Quantitative indicators are extremely important for environmental and economic decision-making," notes Michael Jerrett. "Two indices--the Air Quality Index and Gross Domestic Product--have had tremendous impact, but until now, we haven't had a quantitative index to summarize the cumulative hazards suffered by disadvantaged groups. Once social disparities in exposure can be summarized quantitatively, the imperative for policymakers to act increases."


1 US Census Bureau

2 Su JG, Morello-Frosch R, Jesdale BM, Kyle AD, Shamasunder B, Jerrett M. An index for assessing demographic inequalities in cumulative environmental hazards with application to Los Angeles, California. Environ Sci Technol. 2009;43(20):7626-34.

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