Broad Study Suggests a Lower Tolerance for Exposure to Benzene

December 4, 2004

By ANDREW C. REVKIN

The first study of a large group of workers breathing air with very low levels of benzene suggests that the chemical may harm the bone marrow, the body's main factory for blood cells, even in amounts below the threshold deemed safe under American law.

The researchers said counts of certain protective white blood cells in 250 Chinese shoe factory workers exposed to small amounts of benzene - less than one part per million in the air - were 15 percent to 18 percent lower than counts in a similar group of 140 garment workers who were not exposed. The lower blood counts were not in a range deemed harmful, but independent experts said the findings strongly hinted that benzene was one of a small group of chemicals for which no safe threshold exists.

The study was conducted by scientists from the National Cancer Institute, China's Center for Disease Control and Prevention, the University of California, Berkeley, and several other institutions. It was published yesterday in the journal Science.

For more than a century, benzene has been one of the most heavily used solvents in the world, with applications in many products, like tires, drugs, paper and refined sugar. It makes up about 1 percent of gasoline and is also produced when coal and other fuels are burned. Benzene has long been identified as a cause of leukemia and other blood ailments in people exposed to significant amounts over many years, so regulations have steadily tightened in most industrialized countries, and increasingly in poorer nations as well.

Experts not affiliated with the new study said it should prompt a re-evaluation of the American workplace standard, which the Occupational Safety and Health Administration set at one part per million in 1987, even though the National Institute of Occupational Safety and Health recommended a standard of 0.1 parts per million.

"These results clearly indicate that the current OSHA permissible exposure limit is not sufficiently protective of worker health," said Dr. David A. Eastmond, a professor of environmental toxicology at the University of California, Riverside.

John D. Graham, the administrator of the Office of Information and Regulatory Affairs of the White House Office of Management and Budget, said the study "deserves careful consideration by scientists, physicians and regulators."

Bill Perry, director of the Office of Chemical Hazards at OSHA, said the agency had not yet reviewed the new study but that the 1987 standard "was developed after more than a decade of extensive research and a comprehensive regulatory process."

Groups representing the chemical and oil industries, which have fought the progressive tightening of benzene standards over the last three decades, said they would need to analyze the study before commenting. The American Petroleum Institute, a trade group in Washington, is financing a similar study on factory workers in China, which has become a focal point for such research because it is one of the few places where worker exposure remains commonplace.

In the United States, overall air concentrations have dropped sharply in recent decades, although many workers are still exposed. There is no good current estimate of workplace exposure in the United States, mainly because of a lack of money for surveys, officials at the National Institute for Occupational Safety and Health said. The last thorough federal survey of exposure, released in 1987, estimated that more than 200,000 workers were chronically exposed to some benzene.