News Release

Benzene responsible for high percentage of leukemia deaths induced by smoking

Peer-Reviewed Publication

University of North Carolina at Chapel Hill

Benzene, a potent chemical found in cigarette smoke and automobile emissions, appears responsible for between 8 percent and 48 percent of all smoking-induced leukemia deaths, a new University of North Carolina at Chapel Hill study indicates. The chemical also causes between 12 percent and 58 percent of smoking-related deaths from acute myeloid leukemia.

How likely smokers are to develop the life-threatening illness depends largely on how much they smoke, scientists say.

Dr. Irva Hertz-Picciotto, professor of epidemiology at the UNC-CH School of Public Health, conducted the study with Dr. Jeffrey E. Korte of the International Agency for Research on Cancer in Lyon, France; graduate student Mark R. Schultz and Dr. Louise M. Ball, professor of environmental sciences and engineering, both at UNC-CH; and Dr. Eric J. Duell of Harvard University.

A report on their findings appears in the current (April) issue of the journal Environmental Health Perspectives. They originally intended to help explain why smokers were one-and-a-half to two times more likely to develop the blood-borne cancer than non-smokers and the possible influence of benzene.

"We extrapolated down from different studies that have been done on leukemia and people exposed to benzene in the workplace and established what's called a dose-response curve," Hertz-Picciotto said. "We found that linear mathematical models provided more plausible estimates of benzene's influence than a quadratric model."

Some scientists and industry officials argue that linear models over-estimate the risks at low doses. They say that only at high doses when it overwhelms the body's ability to detoxify the chemical can it cause cancer.

The shape of the dose-response curve is important for the Occupational Safety and Health Administration and Environmental Protection Agency when they attempt to set standards to protect workers and the public. If cancer increases linearly with increases in benzene levels, permissible levels will need to be set lower than if other suggested models are used.

"We think our work establishes that there are significant risks of leukemia from low to moderate doses of benzene," Hertz-Picciotto said.

Perhaps surprisingly, the risk of death from acute myeloid leukemia over a lifetime was slightly higher in light smokers than in heavy smokers, the scientists found. That result likely reflects the increased risk to heavy smokers of death from competing causes, such as other cancers and heart disease.

"Other known or suspected leukemogens (substances causing leukemia) are present in cigarette smoke, including urethane, 1,3-butadiene, radioactive elements, N-nitrosodi-n-butylamine and styrene," the authors wrote. "Benzine is therefore unlikely to be independently responsible for all smoking-induced leukemia. However, based on current knowledge ... of these compounds and their relative concentrations in cigarette smoke, it seems likely that benzene's contribution is substantial."

The EPA and the National Institute of Environmental Health Sciences supported the study, which is part of a larger effort to understand the risks of mixtures of different pollutants. Hazards from such common mixtures as automobile exhaust or the pollutants in air at some work sites may exceed the total risk from individual chemicals when added together.

This is important, Hertz-Picciotto said, because agencies that regulate environmental or occupational pollutants estimate risks by adding up risks from individual chemicals. Simply adding the risks may not provide an adequate level of safety if interactions among the chemicals occur.

"We need to understand better what we are putting into the environment and what we're putting into our bodies," Hertz-Picciotto said. "That way, we can better protect ourselves from the carcinogens and other toxins out there. Benzene is clearly one of them."

Other pollutants in cigarette smoke believed to cause cancer include polycyclic aromatic hydrocarbons, cadmium, arsenic, nickel, chromium, aromatic amines and nitrosamine. Benzene is used by industry in making film developer, nylon and solvents, and workers are exposed to concentrations 10 to 100 times higher than those smokers encounter.

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Note: Hertz-Picciotto can be reached at 919-966-7445.
School of Public Health contact: Lisa Katz, 966-7467.
News Services contact: David Williamson, 966-8596.


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