Data from the new study, which was based on information from the U.S. Census Bureau and the National Death Index and could be the largest study to find a lead-cancer link, according to researchers, provides evidence that widespread environmental risk factors must be explored, said Edwin van Wijingaarden, Ph.D., lead author of the study.
"If we are able to help explain the cause of even 1 or 2 percent of the total number of cases, that's important," he said.
Published in the Sept. 1 issue of the International Journal of Cancer, the study calculated the risk estimates for lead exposure and brain cancer from a census sample of 317,968 people who reported their occupations between 1979 and 1981. Van Wijngaarden was looking for evidence of an exposure-response trend or a rise in cancer incidence or mortality associated with an exposure to a toxic substance.
Firefighters at Risk
Gas station attendants from the 1970s and early 1980s were estimated to have a high probability of exposure, but only medium intensity of exposure because their direct contact with leaded gasoline was not as great as the potential for contact. The jobs with the highest probability and intensity of lead exposure were painters and automobile mechanics. But firefighters, engineers, automobile assemblers, truck drivers, plumbers, welders and printers or typesetters were all among those individuals with some likelihood of lead exposure, according to the study.
Van Wijngaarden followed the cancer rates of the people from the census sample for 9 years, finding 119 brain cancer deaths. The death rate among people with jobs that potentially exposed them to lead was 50 percent higher than unexposed people, and the number of deaths was larger than in many previous studies, van Wijngaarden said. Other trends that emerged were slightly higher death rates among less educated and married individuals.
Scientists have suspected for years that lead is a carcinogen that passes through the blood-brain barrier, making the brain especially sensitive to the toxic effects of lead. Van Wijngaarden said he is continuing his research with a pilot study to measure the actual bone-lead levels in people who have been diagnosed with brain tumors.
More than 18,000 brain and spinal cord tumors will be diagnosed in the United States this year, yet little is known about what causes brain cancer. The only established risk factor is radiation, according to the American Cancer Society.