Association between occupational lead exposure and the risk of brain cancer mortality

The epidemiological literature regarding the association between brain cancer risk and lead exposure is inconsistent despite some evidence from experimental studies to support such an association. We evaluated the relationship between potential occupational lead exposure and death from brain tumors in the National Longitudinal Mortality Study (NLMS), which is a prospective census-based cohort study of mortality among the United States population (1979-1989). Estimates of probability and intensity of lead exposure were assigned based on a job-exposure matrix (JEM) to 317,986 individuals with self-reported occupation and industry at baseline. About 19 percent of individuals were considered potentially exposed to lead at the workplace, which is similar to the exposure prevalence reported in previous studies. Those who were employed in a job possibly involving lead exposure were about 50 percent more likely to die of brain tumors as compared with those who were not considered exposed at the job. The risk of brain tumor mortality increased with increasing likelihood and intensity of exposure. There are several caveats that need to be considered when interpreting these results. First, exposure assessment based on linking occupation and industry reported by the subjects with a JEM can only be considered a crude surrogate of exposure. Second, different classes of brain tumor subtypes may have different etiologies. Finally, we cannot confidently rule out potential confounding by other exposures in the workplace because the jobs assigned the highest exposures to lead also involve exposure to other metals, aromatic hydrocarbons, or electromagnetic fields. Nevertheless, these findings provide further support for an association between occupational lead exposure and brain tumor mortality. Future studies should improve upon the methodological limitations found in this literature by focusing on biological markers of lead exposure (e.g., bone lead levels) and different brain tumor subtypes (e.g., glioblastoma multiforme, meningioma).

Bibliographic reference:

"Brain cancer mortality and potential occupational exposure to lead: findings from the National Longitudinal Mortality Study, 1979-1989", Int J Cancer. 2006 Sep 1;119(5):1136-44

Edwin van Wijngaarden

Division of Epidemiology, Department of Community and Preventive Medicine, University of Rochester School of Medicine and Dentistry, NY, USA