Benzene Exposure May Negatively Affect Health

Ask chemistry students on campus about the chemical benzene and they will tell you that it is a fundamental building block in organic chemistry synthesis. What they probably will not be able to tell you is that this same chemical, used widely in industries such as oil and shoe manufacturing-and also present in second hand smoke-causes leukemia and decreases white blood cells, the cells of the immune system.

US governmental agencies, on the other hand, have known about the detriments of benzene exposure for years and regulated the level that industry workers can be exposed to at 1 ppm (one benzene molecule per million air molecules). A recent study by UC Berkeley researchers, however, may cause a reevaluation of this safety level standard because they show that exposure below 1 ppm can still impact blood cells counts. Benzene is thought to interfere with developmental processes in white blood cell precursor cells found in the bone marrow.

"Previous studies, conducted in China, have shown the detrimental effects of high benzene exposure," said Lupiong Zhang, UC Berkeley researcher and primary co-author of the study. "Our current study, though, breaks ground because it focuses on lower levels, below generally accepted health standards. We are hoping that other studies can reproduce these same results."

The study, published in last December's edition of the journal Science, was conducted in conjunction with the Chinese Center for Disease Control and Prevention and the National Cancer Institute. Researchers tracked and monitored 250 Chinese shoe workers exposed to varying levels of benzene in the workplace in addition to 140 unexposed workers at another factory over a 16-month period.

The results showed that workers exposed to high levels of benzene had lower white blood cell counts than non-exposed workers, as was expected. Unexpectedly, however, workers exposed to benzene below the 1 ppm US health standard still had reduced white blood cell counts, although not as drastic as the decrease seen with high exposure. In addition, the ability of white blood cell precursor cells to grow in laboratory cultures was also reduced.

"While we cannot determine if low levels of exposure to benzene can lead to disease, our results show that there is still hematoxicity (toxicity to blood cells)," Zhang said.

The American Petroleum Institute, a trade group in Washington, is also conducting a similar study on Chinese factory workers in order to see if the findings hold up. Oil and chemical companies have a personal stake in the regulation of benzene standards because as occupational health standards become stricter, their cost of meeting those health standards also increases.

"Clearly there may be some risk here. But any move to reduce it through more stringent regulation would have to balance the incremental costs of improved benzene control against the incremental benefits-apparently still uncalibrated-of improvements in workers' health due to lower exposures," said Eugene Bardach, professor of public policy at UC Berkeley.

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