Investigators have determined that 8 million of Michigan's 9.1 million residents are carrying in their bodies toxic chemicals that have caused deaths in cattle and liver cancer in rats.

The chemicals, polybrominated biphenyis, or PBBs, are flame retardants used until recently by the plastics industry. They accidentally were put in cattle feed in 1973 and 1974, resulting in contamined meat and milk. What at first appeared to be local health hazard for farm workers and plant production workers now is recognized as a statewide disaster.

The study PBBs are widely disseminated throughout the state's population and are likely to be retained in their bodies forever. These conclusions are based on tests of mothers' milk in 1976 that showed PBB residues, and on those findings, extrapolations, for the entire state population were made.

Earlier this year, Dr. Irving Selikoff of the Mount Sinai School of Medicine tested blood and fat tissue samples from men and women. He found 98 percent of the samples contained PBBs, at a lower detectable level than was technologically possible at the time of the mothers' milk study. Selikoff said his findings corroborate the conclusions drawn on the breast milk study evidence.

Although no level of toxicity or safety for humans is known in terms of containation, PBBs had a devastating effect on the cattle herds that ingested the chemical. Physicians are concerned about how contaimination of the food chain may injure people's health in the future.

"If the women are representative of the population, and there is no reason to believe that PBBs are sex discriminatory in their dissemination process, then most of Michigan's population is carrying PBBs," says Dr. Lawrence B. Brilliant, professor of epidemiology at the University of Michigan and lead author of the study reported in the current issue of The Lancet.

"The chemical has gotten all through the food chain," says Dr. Philip J. Landrigan, of the bureau of epidemiology at the Center for Disease Control in Atlanta, "and although it went through like a comet with a long tail, meaning little recontamination will occur, these people will probably carry PBBs with them the rest of their lives."

Human exposures to PBBs initially were thought to be PBBs initially were thought to be limited to workers in the production process of the chemicals and to farm workers who consumed contaminated produce. An estimated 10,000 to 12,500 persons lived on the contaminated farms.

This belief was based on the manner in which the stock became contaminated. In 1973 and 1974, as the result of a packaging and shipping error, several hundred pounds of PBB's were substituted for magnesium oxide, a dairy-cattle nutritional supplement, and distributed in cattle feed throughout Michigan. In exposed cattle, it caused an often fatal syndrome - anorexia, weight loss, decreased milk production and increased miscarriages.

In June 1976, during an unrelated survey for pesticide residues, the laboratory of the Michigan Department of Public Health discovered that milk from four mothers who weren't from the affected farms contained PBBs. As a result, the health department decided to further document the extent of breast milk contamination. Breast milk was chosen over other tissues for study because it is 4 percent fat, and PBBs are fat soluble.

Samples from 53 mothers who gave birth in August 1976 showed that 51, or 96 percent, contained detectable PBBs, ranging between 0.05 parts of the chemical in a million parts of milk to one part PBB per million parts of milk. Because there isn't any conclusive data on toxicity in humans, scientists can't knowledgeably advise mothers about the relative risk and benefits of breast-feeding at various PBB levels.

"Ad a pediatrician, I'm concerned about the implications of these findings for children," Dr. Landrigan said. "Breast-feeding is considered a good psychological factor for children. So we want to be careful not to (declare a ban on breast-feeding Michigan)." He observes that concomitantly there is a potential risk to the children who receive this milk depending on what is discovered about the chemical's human toxicity in the future.

The only way that these affected women can execrete the chemical is through lactation, the secretion of milk. There is no know way of execreting the substance from the male body.

Dr. Brilliant said the University of Michigan's School of Public Health is investigating ways to remove PBBs from humans. Furthermore, the U.S. Public Health Service has initiated a 20-year follow-up study using a 4,500-case sample of the affected Michigan population as well as control population of 2,000 from Iowa to track these people's health. Landrigan said they have found symptons of fatigue, decreased muscle strength and sleep problems that don't seem to relate to body levels of PBBs and aren't being corroborated by phsical examinations.

Dr. Landrigan said it originally was assumed that farm people were only affected as a result of consuming their own produce. What's devastating is the finding that some milk, contaminated with small amounts of PBBs, mixed with milk from uncontaminated dairy cows and marketed at grocery stores across of the state, still contained high levels of PBBs.