How They Found the Vinyl-Cancer Link
Chemical Week  17jul74
Research on animals in Italy and U.S. uncovered hazard, may be used to predict other chemical-cancer links

 

And there could be widespread repercussions because similar research mold be applied to other chemicals that are suspected of being carcinogenic The big question is: How much stake can be placed is the predictive research effort?
The emergency standard of 50 ppm. or vinyl chloride monomer as an air contaminant, set in April by OSHA, has already been challenged by data from the two laboratories. Angiosarcoma, a rare form of liver cancer, has been reported in test animals subjected to inhalation studies at the 50-ppm. level.

In the Beginning: The trigger was pulled on vinyl chloride in the fall of 1972 by Cesare Maltoni (see also p. 56), whose work at the Institute of Oncology was sponsored by Montedison, SCI. Solvay and Rhone-Progil. Maltoni came to suspect vinyl chloride is 1979 as a result of work by Pier Luigi Viola of the Regina Elena Institute for Cancer Research in Rome and pilot checks Maltoni made of sputum cytology in Italian chemical workers who had been exposed to materials such as chromium, chlorine, caustic nitric acid and VCM.

Viola had found evidence of a VCM-cancer link in research for the Solvay plant in Rosignano, Italy and reported on it at the 10th International Cancer Congress in Houston, Tex., in 1970. But evidence was largely discounted--even by Viola--as having no correlation to humans because of the high dosages Viola used is his research and impurities is the gas.

Maltoni's s sputum pilot checks were made at the request of Montedison with a view toward longer-range studies. On the basis of his findings, Maltoni decided on a project of integrated experiments is vinyl chloride carcinogenicity. The work was encouraged sad supported by Montedison, whose health service supplied the Bologna institute with technical data on occupational exposure. This. Maltoni ex plains, made possible the reproduction of occupational conditions among lab animals. Later, the three other European chemical companies joined in sponsoring the project

Different Design: A three-may committee from the Manufacturing Chemists Assn. that visited Bologna, in January 1973 came away with praise for Maltoni's work and methods. But some changes in design, which they thought could affect the results, were instituted for MCA's own studies at Bio-Test's Decatur labs.

One basic change was the animals that were used. Maltoni experimented only with rats, but Bio-Test uses mice and hamsters, in addition to rats. M.L. Keplinger, Bio-Test's s manager of toxicology, says the lab has had extensive experience with the strain of mice it uses and knows that tumors do not occur spontaneously in the animals.

Another basic change was is the length of exposure. Maltoni's s rats went exposed to VCM gas for four hours a day, five days a week. Ac Bio-Test, the animals are exposed for seven hours a day, five days a week.

In addition, the cage sizes are different. Bio-Test uses four inhalation chambers, about 8 ft. high and 6 ft. wide--said to be about the largest sash test chambers available. Maltoni used much smaller cages.

Keplinger feels that large chambers are an advantage because all the animals exposed to a certain level of VCM can be kept together. Mallow had to maintain careful controls of VCM levels in several cages to make sure the animals got the same exposure

There has been some criticism of Maltoni for feeding the animals in the exposure cages. Except for an "ancillary" control, test feeding is not carried out during the Bio-Test exposures.
Maltoni calls this criticism "sheer sophistry." He says that. food does not absorb VCM and that even animals that regularly slept during treatment and did not eat also contracted angiosarcoma. He explains that the food was administered to keep the rats from fighting and causing lesions. In fact, many of the Bio-Test animals died from cannibalism.

Test Methods: Maltoni's project involved a series of 15 experiments to determine the effects of VCM administered by inhalation, ingestion and peritoneal and subcutaneous injection. Doses were administered fur varying periods of time at different concentrations and included continuous and intermittent treatment of animals of different species and strains, sex and age.
For example, in one experiment 481 Sprague-Dawley rats in seven groups were tested. Doses of inhalation ranged from 10,000 ppm. to 50 ppm, for one year. One control group received no exposure. Vinyl chloride was regularly checked for purity. Doses were checked by gas chromatography and recorded hourly.

After a year in the exposure chambers, the rats were removed to live out their lives. All the animals were kept under observation until they died. Each underwent autopsy, which included histological studies of zymbal and saliva glands, tongue, lungs, liver, kidneys, spleen, stomach, parts of the intestine, bladder. brain, paws. and fat between the shoulders. All animals exhibiting tumors were X-rayed regularly.

Each of Bio-Test's large test chambers holds 200 animals--Charles River CD-1 outbred albino mice, Charles River CD outbred albino rats, or Golden Syrian hamsters. Each series of the newly weaned animals is equally divided by sex.

VCM mixed with air is fed through the chamber at a rate that assures a steady VCM concentration--50 ppm., 200 ppm., or 2,500 ppm. A gas chromatograph checks for stable concentrations.
Tumor Surprise: Seven months into the year-long study at Bio-Test, the development of tumors in mice exposed to 50-ppm. VCM came as a "surprise." "We felt obligated to report this immediately to MCA" instead of waiting for the monthly report, says Keplinger. MCA, in turn. reported immediately to the Environmental Protection Agency, National Institute of Occupational Safety and Health and the Occupational Safety and Health Administration and also issued a public report.

The quick response to test animals to VCM exposure had also surprised Maltoni. When his studies began in late 1970, it was thought the work would be completed in time to report to the 11th International Cancer Congress in Florence in October. But it became clear in the fall of 1972 that VCM inhalation at 250 Ppm. was producing three kinds of tumors in rats: zymbal gland carcinoma, nephroblastoma (cancer of the kidney) and angiosarcoma. The information was immediately transmitted m Maltoni's sponsors, who, he says, informed MCA.

At Bio-Test, after seven months of testing, none of the control mice shows any cancer signs. Of those exposed to 2,500-ppm. VCM, 19 had visible tumors; to 200 ppm, six had visible tumors: to 50 ppm., four had rumors. Only mice have developed tumor so far because they are smaller, have higher metabolism and breathing rates. Keplinger believes.

Bio-Test has a contract with MCA to do further VCM testing to determine a "no effect" level, or to "prove a negative find the level at which no deleterious effect occurs. "You can say all chemicals are toxic, or none is toxic, depending on the dose;" Keplinger explains.

Maltoni also is involved in further inhalation studies, at doses ranging from 25 ppm. to 1 ppm.
No-Man's-Land: What does all this evidence mean for humans? "We're in A no-man's-land as far as extrapolation to humans is concerned," Keplinger Observes.

Says Maltoni, referring to the death of a PVC worker from angiosarcoma reported in January: "Do you think that without the death at the B.F. Goodrich plant much attention would have been paid to my work.'"

The general procedure with food additives is to find the "no effect" level for an animal that is sensitive. One hundredth of that level is considered safe for humans. In occupational situations, the safety level is usually one-tenth the highest "no effect" level.

Maltoni says there have been questions about extrapolating animal carcinogenicity tests to humans. But he claims, the correct occupational conditions and sophistication of equipment: used in his tests "actually prove the validity of using animals in laboratory experiments. Under carefully controlled conditions, we have provoked a rare cancer in rats never spontaneously seen before, and then, suddenly we detect the same cancer in humans linked m the same cause."
He feels that the impact of the success of his predictive testing goes far beyond vinyl chloride. "Vinyl chloride is probably only one tree in a large forest. I am very suspicious of all compounds of the carbon-chloride group." Maltoni says.

The Institute of Oncology is now engaged is several projects to assess the carcinogenic risk of other chemicals, including chromium compounds, asbestos. various plastic resins and alloys.
At this point. Maltoni is unwilling to be more precise, preferring to maintain. a professional silence until definitive results are obtained. He points out, however, that there seems in be a high risk in vitalium implants

Maltoni says his work so far "should serve as an example of the need to test other industrially produced substances before they are released into the human environment This is my mission as a Scientist."