Getting On Our Nerves

When applying linear models to these steps, the researchers calculated that benzene is responsible for 8-48% of all smoking-induced leukemia deaths and 12-58% of smoking-induced AML deaths. These results, the researchers say, are reasonable, compared to published data on the numbers of such deaths. The quadratic model yielded far less plausible results, suggesting that less than 1% of smokinginduced leukemia deaths are benzene related. Some studies have found benzene to be most strongly associated with AML, but the chemical's link to other forms of the disease has not been ruled out. The study not only provides information on the quantitative contribution of benzene to cancer deaths from cigarette smoking, it also helps demonstrate the validity of linear models in extrapolating to low doses of benzene. Benzene is an important industrial chemical used in making nylon, film developer, and solvents. Industrial workers are exposed to benzene concentrations that are 10-100 times greater than those encountered by smokers. For the past decade, the Occupational Safety and Health Administration and the U.S. Environmental Protection Agency have used linear models to set workplace benzene standards and evaluate environmental risks, respectively; both are reviewing that approach. The researchers point out that their results, being plausible predictions, contradict the theoretical argument that linear models may overestimate the low-dose risk from benzene. The results also show that if there is a threshold dose below which benzene does not cause leukemia, it is considerably lower than that received by smokers. The researchers caution, however, that benzene is not the only leukemia-causing chemical in cigarette smoke. They note t;4. 1,3-butadiene, styrene, N-nitrosodi-n-butylamine, urethane, and radioactive elements are also suspected of being leukemogenic. Benzene, however, appears to cause a substantial proportion of the leukemia deaths induced by smoking. -Harvey Black