In what they term the largest and most comprehensive U.S. study to date, researchers from UCLA and Southern California Edison report today that they have found no link between increased cancer rates and exposure to electric fields among the company's employees.
Several studies in the United States and Europe have shown that exposure to electric and magnetic fields, commonly known as EMFs, increase the risk of certain types of cancer, such as leukemia, lymphoma and brain cancer, particularly among children. But those studies have been highly controversial and researchers are constantly looking for better evidence on both sides of the argument.
The UCLA-Edison team examined health records of 36,221 employees who worked for Edison for at least a year between 1960 and 1988 and correlated them with the employee's on-the-job exposure to EMFs.
They report in the journal Epidemiology that an excessive number of cancers was not observed in any group, no matter how high the exposure to EMFs.
"The method we were able to use was better than that in previous studies--not because we were a better research team, but because we had access to information that others did not," said epidemiologist Jack D. Sahl, a senior research scientist at Edison. "This gives me more confidence that there isn't a large problem with EMF and it provides support for the idea that there is no problem with EMF in the workplace."
The new results come from "a well-designed and well-conducted study . . . that certainly weighs in on the negative side, but it doesn't negate the evidence that precedes it," said epidemiologist David Savitz of the University of North Carolina. "It isn't the final word on the issue, but it is an important study in the sense that it is more sophisticated . . . than previous studies."
But the results will be suspect among many researchers because the authors work for an electric utility, said physicist Louis Slesin, editor of Microwave News, who has followed the EMFs issue closely. Edison officials "would have been better served if they had given the money and the data to an independent epidemiologist," he said.
The results are also suspect because the population studied is not large enough to detect subtle risks, Slesin and others argued.
Both deficiencies will be avoided by two new studies, one Canadian and one American, which pool data from several electric utilities and are being overseen by independent scientists. Data from the Canadian study is expected this summer and from the American study by the end of the year.
EMFs are all around us, from the motors in refrigerators to the radiation from a computer or television screen to the slight emissions from electric blankets. They arise whenever an electric current is passed through a wire. The greater the current, the higher the fields. Such fields are the driving force for electric motors and electromagnets.
Such a field can produce subtle changes in living cells and many researchers believe that these changes can lead to cancer. No one has demonstrated that an electric field can cause cancer in cells or animals grown in the laboratory. Researchers have thus turned to epidemiology to study the suspected link.
Two large Swedish studies published in September have provided the strongest evidence to date. Those studies showed a fourfold increase in the risk of leukemia among children who live near power lines and a doubling of the risk among adults.
The chief deficiency of the Swedish and earlier studies is that researchers have had to estimate exposures to EMFs. In studies of job-related risk, epidemiologists would often use the job description listed on death certificates, which may not have reflected the individual's total employment experience, and which gave no clear indication of exposure.
By using Edison's personnel records, Stahl and UCLA epidemiologist Sander Greenland were able to determine how long each employee spent in a particular type of job. They also were able to equip employees in each type of work site with recording devices that measured their EMF exposure over a period of days. Therefore, they had a much better understanding of exposures than was present in previous studies.
Greenland rejects the idea that the study was biased because Edison funded it.
The company "was astonishingly open to any possibilities" that might be uncovered by the study and company officials and scientists were surprised by the negative results, Greenland said. He said Edison's role could not be compared to that of tobacco companies sponsoring research on smoking because Edison is a public utility and "doesn't have a strong financial interest in the outcome. . . . It's not the sort of company that would go bankrupt" if the results were positive.