A new study has acknowledged a long-suspected link between exposure to vinyl chloride monomer and angiosarcoma of the liver, a rare form of liver cancer.
The report also confirms industry's contention that employees at PVC resin plants no longer face an elevated risk of liver cancer.
The final phase of a 25-year study was released Jan. 26 by the Vinyl Chloride Group of the Chemical Manufacturers of America.
The study, led by Kenneth Mundt, an associate professor of the Department of Biostatistics and Epidemiology at the University of Massachusetts, is an update of a 1974 study of 10,109 men who were employed in 37 resin plants for at least one year between 1942 and 1972. That study also showed a high incidence of liver cancer among those with high exposure to VCM.
After the early study confirmed the link between VCM and liver cancer, the Occupational Safety and Health Administration in 1974 reduced the permissible exposure limit from 500 parts per million to 1 part per million.
The new study also explores the link between VCM exposure and other diseases, such as brain cancer and lung cancer.
Elevated occurrences of brain cancer were revealed when researchers updated the study in 1981, but Mundt said that by 1995 those occurrences tapered back down to the same numbers expected among the general population.
``There was an excess at one point, but not since,'' he said, explaining that the brain cancer could have been caused by exposure to other chemicals either at the plants or at previous jobs.
``The bad news is that there was a problem [with elevated occurrences of brain cancer],'' he said. ``The good news is whatever the problem was doesn't seem to be sustained.''
As for occurrences of cancer of connective and soft tissues, again, the men in the study who had worked in the plants for 10 or more years were most affected.
This, combined with the observation that these cancers occurred mostly among people who were hired at the plants at age 35 or older, ``seems to show that exposure may have occurred in previous jobs,'' he said.
Peter Infante, who was involved with reducing the OSHA exposure standard in 1974 and now serves as director of OSHA's Office of Standards Review, said he doesn't agree with the study's conclusion that the link to brain cancer is inconclusive.
``In my opinion, it's fairly clear that brain cancer is caused by exposure to vinyl chloride,'' based on information detailed in the final report and on results of other research.
He also believes that the link between VCM and lung cancer and cancer of soft and connective tissues should be looked at more closely. ``We need to pursue what those cancer deaths were.''
As for lung cancer, he said the study includes no data on cigarette smoking. ``It doesn't look like there's a lot of evidence'' that VCM can cause lung cancer, ``but I don't think they're out of the woods yet,'' he said.
Noting that the study found two deaths from breast cancer — twice the number as would be expected in the general population — Infante said that connection must also be studied further.
Studies of women show there is a link between breast cancer and exposure to VCM, and experimentally, mammory carcinoma has been induced in laboratory animals, he said.
Lemen said he does not question the science and methodology used in the study. ``Dr. Mundt is a good epidemiologist,'' he said.
Adam Finkel, OSHA director of health standards, said that though the study shows signs that reducing workers' exposure to VCM has reduced cancer risk, it doesn't mean that more restrictions won't be needed down the road.
He said the risk seems to be down to about one in 1,000, but OSHA wants to see the risk reduced to one in a million.
``We're not planning additional regulation, but in terms of voluntary actions by the industry, we wouldn't want them to stop [finding ways to reduce cancer risk] based on this study,'' he said. ``It does not confirm that the risks are so low that they shouldn't be dealt with. ... But it's to everyone's credit that they are keeping track, and without the threat of regulation. It's good to see these companies banding together to keep track of this issue.''
The $450,000 study was conducted by Applied Epidemiology Inc. of Amherst, Mass., and paid for by Arlington, Va.-based CMA.
The next step for Mundt's study is peer review by ``outside experts who don't have a vested interest in the plastics industry,'' said Kip Howlett, CMA vice president. Two manuscripts culled from the study have been submitted for publication in the Journal of Occupational and Enironmental Medicine.