Because the case is under litigation, EPA declined to comment. The biotechnology industry stands by its products, however. Bt so far has been successfully engineered into corn, soybean, cotton, canola, and potato plants, eliminating the need for topical pesticide applications, some of which pose health and environmental risks if mishandled, said Val Giddings, vice president for food and agriculture with the Biotechnology Industry Organization. "Over the last three years, this
biological insect control technique has enabled cotton farmers to avoid spraying, by conservative estimates, 850,000 gallons of pesticide compounds that would've otherwise required extremely careful handling," Giddings said. "Similar numbers are in play for other crops like soybeans or corn." While the most widely planted GM crops have been developed for insect and herbicide tolerance, Giddings touted other benefits such as improved food processing traits and nutritional content; resis-
tance to adverse soil and weather conditions; and improved fruit ripening, texture, and flavor. Because of questions being raised in the scientific community, however, as to whether EPA, FDA, and the U.S. Department of Agriculture are adequately examining the potential risks and socioeconomic impacts of modifying crops for pesticide resistance, the National Research Council has begun an internal eightmonth study of the issue. —KRIS CHRISTEN
Researchers question statistical power of PCB cancer study The largest study to date of occupational exposure to polychlorinated biphenyls (PCBs) has found no significant increase in cancer deaths among exposed workers. But several experts said mat the study is still too small to be conclusive. The study's principal author, epidemiologist Renate Kimbrough contends that the results of mis and other human studies indicate no association between PCB exposure and cancer. But other experts familiar with the work say that because cancers linked to PCB exposure are rare, tiiis study is too small to reveal the carcinogenic effects of PCB exposure. "It lacks the statistical power to detect real increases," said Howard Frumkin, Chair of the Department of Environmental and Occupational Health, Rollins School of Public Health at Emory University. The study, published in the March Journal of Occupational and Environmental Medicine, was funded by General Electric (GE) Co. GE faces potential liabilities of hundreds of millions of dollars for cleaning up several rivers, including the Hudson River in New York {ES&T, Aug. 1998, p. 360A363A). For many years, company officials have contended that PCBs are not linked to cancer or other adverse human health effects. PCBs are listed as a probable human carcinogen by EPA, the National Institute for Occupational Safety and Health, and the International Agency for Research
Epidemiologist Renate Kimbrough reports that no significant increase in cancer deaths was found among workers exposed to PCBs at two General Electric capacitor factories. (Courtesy Renate Kimbrough, IEHR, Washington, DC)
on Cancer. The "probable" designation stems from the fact that numerous animal studies have shown mat PCB causes cancer in laboratory animals. But studies of humans have yielded inconsistent results, according to reviews conducted by the Agency for Toxic Substances and Disease Registry in 1992 and EPA in 1996. The new study focused on just over 7000 men and women who worked for more than 90 days in two GE capacitor factories in upstate New York from 1946 to 1977. They were divided into groups on the basis of estimates of their PCB exposure; meir medical histories were followed for more than 30 years. For the 1233 who died, causes of death were compared to national and regional averages. The study found that
353 workers died of cancer, which was less than the national and regional averages. In addition, highly exposed workers did not have higher rates of cancer. The study has two main problems, according to Frumkin—size and exposure assessment. Many of the people studied either worked for GE for a short time or had low exposure, so few cases of cancer were expected, Frumkin said. In addition, workers were classified as "highly exposed" on the basis of their jobs, not their PCB blood levels. If this classification is wrong, then the study could be biased, he said. The study was conducted by the Institute for Evaluating Health Risks (IEHR), an independent research group. In addition to the GE study, the IEHR reviewed all of the previous studies of capacitor plant workers, according to Kimbrough. "Taken together, the results of these studies could be due to chance because there is no consistent pattern," she said. Former EPA Assistant Administrator for Prevention, Pesticides, and Toxic Substances Lynn Goldman, who is now at the Johns Hopkins School of Public Health, said it is too early to determine the study's impact. "This study is a valuable part of the literature. But it is only that—one piece." Before it can be included as part of the body of evidence, it needs to be subjected to a scientific examination that is much more thorough than peer review, she said. —REBECCA RENNER
MAY 1, 1999 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS • 1 8 7 A
