Benzene: Invisible urban killer

Benzene, a carcinogen associated with leukemia and other cancers, is dangerous in even smaller amounts than was previously believed. Though both the United States and the European Union have set safety limits for exposure, a recent study by American scientists has brought those limits into doubt by showing that benzene damages the health of people exposed to levels below the legal limit in the US, causing a drop in the number of white blood cells. Benzene is released into the atmosphere by cars with catalytic converters, especially when the converters are damaged, and is used in industry and in cigarettes. A research team led by Dr Martin Smith of the University of California at Berkeley working with the Disease Prevention Center of Beijing spent 16 months examining 250 workers in a shoe factory that used benzene in the production process and comparing their findings with samples taken from workers in a neighboring factory that did not use benzene. The researchers focused their study on the effects of benzene on the blood. According to the results of their work, which were published in Science magazine, workers exposed to benzene had lower levels of white blood cells and blood platelets. The researchers also recorded significant indications of long-term harm to health – changes in the blood and early signs associated with leukemia. They found that the higher the level of benzene, the lower the levels of white blood cells in the workers’ blood. For instance, workers who had been exposed to benzene at a concentration of more than 10 parts per million (ppm) had around 24 percent fewer white blood cells than workers in the benzene-free factory. Workers exposed to benzene concentrations of 1ppm – which is the permitted level in the US – had 15 percent fewer white blood cells. In short, the study revealed that even concentrations below the US legal limit can have significant negative effects on human health. A noteworthy finding of the study was that benzene caused a reduction of white blood cells in a wide range of cells, leading researchers to believe that it probably strikes forerunner cells which then split, making way for a new series of cells. It also appeared that an increased presence of two particular enzymes made matters worse. Unfortunately, these enzymes are linked to heightened physical activity, so the team noted that physical exercise in the presence of benzene creates greater problems. Commenting on the findings, Nathaniel Rothman of the National Cancer Institute in Maryland said, «Benzene pollution on American streets is much lower but we may have to re-examine the limits along stricter lines.»