Photo by NCI/DCEG
Studies of Chinese factory workers contributed to action in the U.S.
and China to reduce exposure to benzene, a known carcinogen
used in manufacturing and contained in gasoline.
by Shana Potash
Studies in China have advanced the understanding of benzene's relationship to cancer and other effects on the body. The research contributed to the U.S. decision limiting benzene in gasoline and Chinese regulations reducing workplace exposure to the cancer-causing chemical.
Benzene is used in the production of shoes, leather, rubber goods, paint and pesticides, for example, and in the shipping and refinement of crude oil. It's estimated that more than two million workers worldwide are exposed to the chemical every year. Benzene also is contained in gasoline, so vehicle exhaust and fumes at gas pumps can reach anyone, although the amounts are substantially lower than in occupational exposure.
Scientists with NIH's National Cancer Institute (NCI) and China's Center for Disease Control have been studying benzene's effects on Chinese factory workers for nearly 30 years. The toxin already had been linked to leukemia when the research project started. Over the years, their studies found that workers exposed to benzene had a greater risk of most blood malignancies; that the risk of non-Hodgkin lymphoma and lung cancer rose as exposure increased; and that benzene can have a toxic effect on blood even at or below levels generally considered acceptable in workplaces in Western countries.
The findings played a role in China's decision in 2002 to lower the permitted occupational exposure level for benzene. The studies also influenced the U.S. Environmental Protection Agency's (EPA) regulations that reduced the permitted benzene in gasoline and tailpipe emissions to improve outdoor air quality. When the EPA issued the rule in 2007, it estimated the health benefits would total $6 billion by 2030.
"This has been extremely important for both countries, the net effect in terms of benefiting public health by reducing levels of exposure to this known carcinogen," says Dr. Martha Linet. She is co-principal investigator of the benzene collaboration, which has followed more than 110,000 Chinese workers in hundreds of factories in a dozen cities.
Linet says the benzene research conducted in China produced findings that couldn't have been achieved in the West because of the uniqueness and size of the population, and the access to information the government provided.
While China's occupational benzene levels have decreased in recent years, the environment was quite different in the 1980s. "When we first began the study, the factories used older processes and had higher levels of exposures," Linet explains. Also, because China has so many factories, the workforce was large enough to provide the statistical power to show whether benzene increased the risk of cancer overall and for specific malignancies.
Another benefit was that the Chinese scientists identified government-run factories that had been measuring benzene for a long time, which allowed the researchers to study dose-response. Epidemiologists assigned an estimated exposure risk to each worker for each year they were on the job, and then calculated cancer risk based on level of exposure. Finally, Linet notes, China was eager to learn state-of-the-art epidemiological methods to measure worker health, so scientists were given access to factory information and to worker medical records kept at the factories.
"We have shown a number of different cancers appear to be related to benzene exposure," Linet says. "Our ongoing work will try to uncover in more depth what that relationship is all about."
Other studies of Chinese factory workers by different research teams have shown a link between occupational exposure to benzene and abnormalities in sperm, even at levels near what's allowed in the U.S. And small studies have found links between benzene exposure and sperm with abnormal chromosomes and genetic mutations that can cause intellectual disability. That research was funded by NIH's National Institute of Environmental Health Sciences (NIEHS).
- A retrospective cohort study of cause-specific mortality and incidence of hematopoietic malignancies in Chinese benzene-exposed workers
International Journal of Cancer, November 2015 (published online June 16, 2015)
- Occupational Exposure to Benzene and Chromosomal Structural Aberrations in the Sperm of Chinese Men
Environmental Health Perspectives, November 15, 2011
- Benzene Exposure Near the U.S. Permissible Limit Is Associated with Sperm Aneuploidy
Environmental Health Perspectives, June 2010
- EPA Rule Slashes Toxics from Gasoline, Vehicles, and Portable Fuel Containers
EPA news, February 9, 2007
- Hematoxicity in workers exposed to low levels of benzene
Science, December 3, 2004
- Benzene and the dose-related incidence of hematologic neoplasms in China
Journal of the National Cancer Institute, July 16, 1997