A Harvard University review of whether styrene can harm people largely has given the industry a clean bill of health, but is raising concerns about some workers in the composites industry.
The review - done by the Harvard Center for Risk Analysis in Boston and funded by about $500,000 from the styrene industry - said most people, including most industry workers, are not exposed to styrene at levels that warrant concern. But it said that composites industry workers face the most risks and it urged monitoring and exposure mitigation for them.
While the report presents a detailed, 263-page assessment of the scientific evidence surrounding styrene, the issue also has some contentious political overtones.
A group of California state legislators, for example, wrote to Sen. Barbara Boxer, D-Calif., in February suggesting that the styrene industry has had too much influence in the Environmental Protection Agency's ongoing review of styrene. They wrote partly because California regulators are conducting their own review, which is on hold while EPA finishes its work.
Whatever the political debate, the latest study probably will be used by both EPA and California in their work.
The Harvard analysis said evidence is ``suggestive'' that styrene can cause cancer in people, although it said it could find no conclusive evidence. Styrene exposure can come from chemicals, cigarettes, car emissions and natural sources such as strawberries.
A styrene industry spokesman said in a written statement to Plastics News that scientific evidence is pointing in the direction of human safety.
``Evolving research is showing that possible carcinogenic effects seen in mouse studies involving styrene do not seem to be biologically relevant to humans,'' wrote Jack Snyder, executive director of the Styrene Information and Research Center in Arlington, Va.
The mice studies, which are among the key pieces of evidence raising concern, found that styrene causes lung tumors in mice at exposures of 20-160 parts per million.
But SIRC said humans are at much less risk of developing cancer because they do not process styrene in quite the same way and do not generate enough toxic styrene metabolite to cause tumors. ``The industry is sponsoring additional research to validate this conclusion,'' Snyder wrote.
The Harvard study, which reviewed existing literature but was not new research, estimates that workers in the reinforced-plastics business could get about 37 ppm exposure in an eight-hour workday. Joshua Cohen, one of the authors of the Harvard report, said that if that workplace exposure is adjusted for time away from work, it is equivalent to a lifetime exposure of about 1 ppm.
Some studies have found elevated risks of respiratory-tract cancer in workers in reinforced plastics, but that does not seem to be linked to styrene, the Harvard review said.
The study also calculated the lowest exposure that caused a 10 percent elevated risk of lung tumors in mice, and then calculated the human equivalent dose to be a lifetime average concentration of 2-20 ppm. It said action could be needed for some industry workers.
``Because there may be some workers in the reinforced plastics industry whose exposures may substantially exceed typical levels and whose [margin of exposure] values may be unacceptably small for more-severe effects, monitoring and concerted mitigation efforts are still warranted,'' the study said.
Cohen said the study does not specify what mitigation efforts might be needed.
The composites fabrication industry and the Occupational Safety and Health Administration reached an agreement in 1996 to limit styrene exposure in the workplace to less than 50 ppm, averaged over an eight-hour workday.
An official with the Composites Fabricators Association said that if every company met that voluntary 50-ppm standard, the Harvard panel would not have raised its concerns.
``The panel determined that there are some people who are not at the 50-ppm limit, and it was those folks who triggered their concerns about possible health effects,'' said John Schweitzer, senior director of government affairs for Arlington, Va.-based CFA. ``We're going to redouble our efforts to communicate to everyone in the industry that 50 ppm is the proper occupational exposure level.''
Harvard's Cohen, however, said the study is raising concerns about some worker exposure below the 50-ppm standard.
``It is reasonable to say that that margin of exposure does not give an adequate level of comfort if we assume the mice data are relevant to humans,'' Cohen said. ``The mice data being relevant is not something we can rule out at this time.''
EPA's review of styrene is just getting under way, and it will result in the agency ruling on whether it is carcinogenic. The International Agency on Cancer Research considers styrene a possible carcinogen.
Gary Foureman, chemical manager for the EPA's styrene assessment, said he did not know when the agency's review would be finished.
``This is a highly controversial chemical,'' he said. ``It can be held up at any level for any number of reasons.''
The February letter from the California legislators, including the chair of the Assembly's Committee on Environmental Safety and Toxic Materials, Hannah-Beth Jackson, questioned EPA's heavy reliance on styrene industry information.
``We are concerned that the federal process provides a dubious basis for conducting an independent scientific review of scientific findings that is sufficiently protective of public health,'' the letter said.
But Foureman said EPA has an obligation to consider peer-reviewed information from all sources, including the styrene industry. He said he questioned the premise of the California letter.
``I don't understand how [SIRC] can have influence on something that isn't done yet,'' he said.
SIRC said that its contributions to EPA's review have been ``transparent, cooperative and supportive'' and that other scientists can address any perceived inaccuracies in SIRC documents.
The Harvard center, which is part of the Harvard University School of Public Health, has been criticized by environmentalists for its close financial ties to industry.
The center's former director, John Graham, is the Bush administration's top official for reviewing new federal regulations.