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Risks Seen in Low Exposure to Benzene

Study: Blood cells harmed even below U.S. worker standards

THURSDAY, Dec. 2, 2004 (HealthDayNews) -- Exposure to the commonly used chemical benzene, even at levels below current guidelines deemed to be safe, could still have harmful health effects, a new study says.

Researchers have found that workers in China who were exposed to benzene at concentrations below the current U.S. occupational standard experienced damage to their blood cells.

Whether those biological changes actually translate into health problems down the line remains to be seen. "We do not know the health consequences," said Dr. Nat Rothman, co-author of the study and a senior investigator in the division of cancer epidemiology and genetics at the National Cancer Institute (NCI). "These findings need to be independently confirmed. This is not a done deal, but it does raise a question about whether there are more serious effects occurring in the bone marrow."

The paper, which appears in the Dec. 3 issue of Science, represented a collaboration between the NCI, the University of California at Berkeley, and the Chinese Center for Disease Control and Prevention.

Above certain levels, benzene, a hydrocarbon used in the manufacture of many common products -- including household items from plastics to pesticides to detergents -- is known to harm the blood system and to cause leukemia. As a result, the U.S. Occupational Safety and Health Administration (OSHA) has set exposure limits in the workplace at one part per million of air. It hasn't been clear what effect the chemical has below that level.

Exposure to benzene is mostly an issue for workers in the oil, shipping, automobile repair, shoe manufacture and other industries. The general public can be exposed through cigarette smoke, gas and automobile emissions. There has been concern that people in urban areas are exposed to benzene via air pollution.

For this study, researchers looked at factory workers in Tianjin, China. Specifically, they compared 250 workers in a shoe factory who had been exposed to various levels of benzene to 140 controls who worked in clothing manufacturing and thus had not had any exposure.

Although other studies had looked at some of these questions before, Rothman said this paper was especially meticulous in carrying out measurements. Researchers also assessed the volunteers' out-of-work exposure to benzene and other chemicals.

Significant blood defects were found only in the workers who had been exposed to benzene, including some who were exposed to levels under the U.S. standard of one part per million. White blood cell and platelet counts were lower in the exposed workers, even if that exposure was below the standard.

Much of the damage was to the progenitor cells that give rise to different types of blood cells.

"These cells seemed to be a bit more sensitive to benzene's effect than mature cells," Rothman said. "We could only show for more highly exposed people, but even though statistical significance was only reached at higher levels, it showed that these cells are more sensitive -- and that means that perhaps monitoring people with a standard approach [i.e., monitoring mature cells] might underestimate effects."

What all of this means for health is a subject for future studies to address. "We need to understand what the long-term effects are of exposure to benzene in this particular range, what kinds of real disease. That's the bottom line," Rothman said. "We looked at people who were healthy, but we did see these biological changes. We want to confirm and understand what it means for the long term."

The U.S. government plans to investigate whether the findings will warrant any changes.

"OSHA's current standard for benzene, in effect since 1987, was developed after more than a decade of extensive research and a comprehensive regulatory process," Bill Perry, director of OSHA's Office of Chemical Hazards, said in a statement. "We have not yet reviewed the study in Science magazine; evaluation will take some time. However, we look forward to reviewing it."

Meanwhile, the U.S. Environmental Protection Agency (EPA) said that the study should not be alarming to consumers, who don't come in heavy contact with benzene.

Efforts to control the pollutant "have dramatically reduced benzene in the environment and will continue to protect public health," the agency said in a statement. "Workers in the study were exposed to 100 times more benzene than the level established by EPA as safe. The agency would expect to find adverse health reactions in people exposed to that magnitude of benzene."

More information

Learn about exposure to benzene from the U.S. Occupational Safety and Health Administration.

SOURCES: Nat Rothman, M.D., senior investigator, division of cancer epidemiology and genetics, National Cancer Institute, Bethesda, Md.; U.S. Occupational Safety and Health Administration, U.S. Environmental Protection Agency statements; Dec. 3, 2004, Science
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