Study of toxins in Houston air warrants new standards

September 27, 2006

HOUSTON, Sept. 27, 2006 -- A new report recommends immediate action to reduce levels of four toxic air pollutants because exposure to them poses a high risk to community health. Released today by Rice University and funded by Houston Endowment, the study proposes a new set of air quality standards based on the underlying toxicology of the four pollutants investigated.

Baylor College of Medicine, Texas Southern University, University of Houston Law Center and The University of Texas Medical Branch (UTMB) at Galveston collaborated with Rice on the study, which focused on benzene, 1,3-butadiene, formaldehyde and diesel particulate matter.

"Based on the results of our study, we strongly recommend immediate action to lower the ambient concentrations of the four hazardous air pollutants we researched," said principal investigator Matt Fraser, associate professor in civil and environmental engineering at Rice. "The level of air toxics concentration that we're seeing in the Houston area poses a dangerously high risk of cancer and other health problems."

According to the report, the ultimate goal is the adoption of enforceable ambient air quality standards for which only one more person in a million would be expected to develop cancer from a lifetime of exposure to individual hazardous air pollutants.

The study provides the detailed toxicology and health risk assessment for four compounds and also investigates how a variety of factors leads to a greater impact from exposure to air toxics for some people. The study also compiles how other states and countries regulate air toxics.

One of the report's most alarming statistics indicates that the 2004 annual average concentration of 1,3-butadiene in Houston is 4 parts per billion (ppb) - higher than any other city referenced in the report and about 20 times higher than Los Angeles, whose 0.2 ppb was the next highest in the report. 1,3-butadiene is a product of petrochemical manufacturing and is present in motor-vehicle exhaust. The most pressing environmental health concern for exposure to 1,3-butadiene is an increased risk of cancer, but the chemical also has noncarcinogenic effects.

Benzene, also a product of petrochemical manufacturing and present in motor vehicle exhaust, averaged an annual concentration of 1.7 ppb in Houston during 2004; the amount in Los Angeles was 0.9 ppb. Benzene exposure leads to an increased risk of leukeumia as well as noncarcinogenic effects, including decreased blood cell counts.

Formaldehyde, a gas formed through atmospheric chemical reactions and also emitted directly from various sources, had an annual average concentration of 7.9 ppb in Houston in 2004; Los Angeles was close behind with 7.2 ppb. Exposure can cause irritation of the eyes and respiratory tract. Inhalation of formaldehyde causes degenerative effects in laboratory animals and nasal tumors in rats, and similar risks are anticipated in humans.

Diesel particulate matter (PM) originates from widespread sources, including vehicles, engines, and generators. Diesel particulates are not monitored routinely at local air quality monitoring sites, but recent air pollution research studies in Houston indicate concentrations of diesel PM between 1.6 and 3.7 micrograms per cubic meter. The report estimates that if one million people were exposed to this level over their lifetime, between 50 and 1,000 would contract cancer.

"Based on the toxicological information and the concentrations seen in the Houston area for the selected four pollutants, it is clear that large portions of the city have environmental air concentrations posing an unacceptably high health risk," Fraser said. "Observed concentrations of 1,3-butadiene and diesel PM approach a level indicating a risk greater than one additional cancer death per 10,000 people during a lifetime of exposure."

The researchers noted that since these risk levels are calculated for individual compounds, the cumulative risks from several pollutants that are present simultaneously are even greater and emphasize the need for action.

The full report, titled "The Control of Air Toxics: Toxicology Motivation and Houston Implications," is available online at
Houston Endowment funded the study in response to reports of Houston's poor air quality. A private philanthropic foundation established by Jesse and Mary Gibbs Jones in 1937, Houston Endowment makes contributions to charitable organizations and educational institutions to improve life for Houstonians.

Fraser and colleagues at Rice coordinated the study and compiled the final report. The University of Houston Law Center investigated the regulation of air toxics in other states and evaluated the efficacy of different regulatory strategies. Baylor College of Medicine evaluated the toxicology of diesel particulate matter and formaldehyde, determined the appropriate risk-assessment values for establishing air toxics standards for these compounds and investigated international regulations of air toxics. UTMB-Galveston evaluated the toxicology of benzene and 1,3-butadiene, determined the appropriate risk-assessment values for air toxics standards for these chemicals and wrote summaries of the toxicological and risk-assessment methods. Texas Southern University investigated factors that modify the basic risk assessment for exposure to air toxics in population groups, including socioeconomic position, age, ethnicity and genetics, disparities in access to health care, and occupational and housing patterns.

Fraser co-authored the report with Andrea Clements, Ph.D. student in civil and environmental engineering at Rice; Victor Flatt, the A.L. O'Quinn Chair in Environmental Law at the University of Houston Law Center; Winifred Hamilton, assistant professor in the Departments of Medicine and Neurosurgery at Baylor College of Medicine and director of the Environmental Health Section of Baylor's Chronic Disease Prevention and Control Research Center; Polly Ledvina, community outreach coordinator for the Environmental Health Section of Baylor's Chronic Disease Prevention and Control Research Center; Sondip Mathur, assistant professor in the College of Pharmacy and Health Sciences at Texas Southern University; Avanti Tamhane, M.S. student in the Environmental Analysis and Decision Making Program at Rice; and Jonathan Ward Jr., professor and director of the Division of Environmental Toxicology in the Department of Preventive Medicine and Community Health at UTMB-Galveston.

Rice University

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