Scientists: Health Risks for Children Uncertain
Medical science--to which policymakers at all levels of society are turning for information about the nature of the asbestos hazard--has not arrived at a clearcut assessment of the degree of danger posed by asbestos in school buildings.
Scientists agree that asbestos is one of the most carcinogenic substances known to mankind. But the cancers it produces develop many years after the exposure. And like the effects of many other substances that man has introduced widely into the environment in this century, the diseases induced by asbestos fibers are just beginning to be understood.
It is too soon for cancer to have appeared in schoolchildren who may have been exposed to airborne asbestos fibers, so no studies exist of asbestos-related-cancer rates among them as a group. Medical scientists can only speculate, based on studies of cancer rates among groups of adults who have worked with or been exposed to asbestos, about the degree of probability that some children who have been exposed to the fibers in schools will eventually contract asbestos-related diseases.
"There is some evidence that people who are in minimally exposed occupational settings--let's say, who worked in an asbestos factory for a week--have increased risks for developing lung cancer," said Dr. Lawrence Garfinkel, vice president for epidemiology and statistics for the American Cancer Society. "But as far as the very low type of exposure that one would presumably get in schools, there just is no evidence for it. Most authorities would agree that any exposure to asbestos is too much exposure ... but other than that, we don't know."
Dr. Richard A. Lemen, director of the division of standards development and technology transfer for the National Institute for Occupational Safety and Health, has stated that "asbestos, as far as our institute is concerned, is one of the most hazardous compounds that we have ever studied. It's a very potent carcinogen, and we have not seen any levels below which there's not some health risk associated."
Scientists interviewed for this report concurred that there is no known "safe" level of exposure.
"From a public-health standpoint, and in the absence of final clarification of the uncertainties, it is prudent to behave as if asbestos fibers may be carcinogenic at low exposure levels and at small particle sizes," concludes the Chronic Hazard Advisory Panel's July 1983 report on asbestos for the U.S. Consumer Product Safety Commission.
Virtually all experts agree that asbestos is one of the most hazardous substances in the environment. When airborne, its microscopic, needle-like fibers can be inhaled into the lower reaches of the respiratory tract, where they may remain throughout a person's lifetime.
Studies have strongly linked these minute fibers--whose length may equal the diameter of a red blood cell, and whose width may be 1/16 to 1/32 that size--to lung cancer; mesothelioma (a rare but fatal cancer of the tissues lining the chest and abdominal cavities); asbestosis (a progressive scarring of the lungs that can result in severe disability and death); and cancers of the esophagus, stomach, colon, rectum, and upper respiratory tract. (See accompanying story on this page.)
Researchers also think that the fibrous material, which in its natural state may look like hair or cotton, may cause changes of unknown significance in the body's immunological system.
The length and diameter of asbestos fibers are usually expressed in mi-crons. One micron is equal to one-millionth of a meter. Research indicates that once such tiny fibers are in place in the lungs, it is the long, thin asbestos fibers, which are less than half a micron in diameter, that may be the most active in producing tumors.
Alarm over asbestos-related diseases swept the nation during the 1960's and 70's, as men who had worked with asbestos or asbestos-containing materials 20 to 40 years earlier began dying of cancer and asbestosis in significant numbers. The Occupational Safety and Health Administration, for example, estimates that lung cancer causes 20 percent of all deaths among asbestos workers.
Since 1979, the World Health Organization has listed asbestos as one of 18 substances known to cause cancerous growth in human tissues.
About 2 to 3 percent of cancer deaths in the United States each year are associated with past exposure to asbestos, according to Dr. Irving J. Selikoff, director of the Environmental Sciences Laboratory at the Mount Sinai School of Medicine of the City University of New York. This is approximately 10,000 deaths annually, or 200 deaths each week. This death rate is expected to continue well into the 21st century.
In the past few years, the concern over asbestos-related deaths has spread to the nation's schools, where the Environmental Protection Agency has estimated that as many as 15 million children and 1.4 million school employees may be exposed to asbestos-containing materials in ceiling and floor tiles, wallboards, pipe and ceiling insulation and soundproofing, and spackling.
Although such materials are dangerous only when the asbestos fibers contained in them break lose and become airborne, the epa does not know how many of the schools surveyed contain potentially airborne asbestos.
Because asbestos-related diseases generally do not appear until 20 to 40 years after a person's first exposure, medical experts are particularly worried that children who are exposed to the fibers in schools, and who have long lives ahead of them, will live to develop these diseases.
Once asbestos is in the lungs or in any other tissue to which the fibers migrate, Dr. Selikoff writes, "We know of no way to remove or neutralize the fibers." Each newly inhaled fiber, he points out, adds to the danger that is already present.
Because children are in school buildings for hundreds of hours each year, year after year, doctors worry that even low levels of exposure will prove harmful, as more and more fibers accumulate in the lungs.
Most medical warnings about the danger of asbestos in schools are based on the incidence of death and disease among industrial workers, whose exposure to asbestos fibers may be at levels 200 times higher than those found in most schools.
To establish a comparision between what happens at high levels of exposure with what might happen at low levels of exposure, research-Continued on Page 13 Continued from Page 11
ers use what they call a "dose-response" relationship, which is used for many carcinogens. This means "less asbestos, less disease; more asbestos, more disease," according to Dr. Selikoff, who is one of the foremost authorities on asbestos-related diseases. Researchers have found that the risk of disease varies proportionately with the level of exposure, which has led them to predict disease at very low exposure levels.
Studies have found, for instance, that relatively low levels of exposure to asbestos can cause cancer. In 1965, Dr. Muriel Newhouse of the London School of Hygienic Medicine, identified nine cases of mesothelioma in the wives and children of asbestos workers, and 11 cases among people who simply lived within a half mile of an asbestos plant.
Dr. Newhouse's findings indicated that far lower levels of asbestos exposure than previously anticipated could cause disease. According to Dr. Selikoff, the cases of cancer among asbestos workers' families "presumably were due to the fibers brought home on the shoes, hair, and clothes of the men."
"So far," he told members of Congress in a March 4, 1982, hearing on the Occupational Hazards Compensation Act of 1982, "limited studies indicate that about 1 percent of the deaths among the wives and the children of the asbestos-factory workers studied, more than 20 years from the outset of the men's work, will be of mesothelioma. The lung cancer rates appear to be about double [the already existing risk for lung cancer]."
Lung abnormalities have been seen in 38 percent of some asbestos workers' family members, according to the Occupational Safety and Health Administration.
Estimates such as these regarding environmental exposure to asbestos fibers have led almost all researchers to conclude that there is no "safe threshold" below which airborne asbestos does not carry some health risk, although the level of risk decreases with the amount of exposure.
Writes Dr. Selikoff: "What will happen at the lowest levels of exposure is still not known. There are other uncertainties. Brief exposure, if fairly intense, produces disease. Long-term exposure, at relatively low levels, produces disease. It is not known whether brief exposure to low levels will produce detectable disease. Complicating such analyses is the cumulative nature of even low-level exposure."
All of these factors make it difficult to predict the health risks in schools. Moreover, no one knows what the level of exposure to asbestos is in schools around the country. Nor do they know how many maintenance workers, teachers, and students have been exposed to asbestos in the past.
A further complicating factor is that asbestos is present in the indoor and outdoor air that everyone breathes. A recent report published by the National Academy of Sciences, Asbestiform Fibers: Nonoccupational Health Risks, estimates that people breathing low levels of asbestos in the air (5,000 times lower than the federal limit currently set on asbestos exposure in the workplace) throughout a 73-year lifetime would have approximately a 9-in-one-million lifetime median risk of contracting mesothelioma. The corresponding lifetime risk for lung cancer would be about 64 in a million for male smokers and 23 in a million for female smokers; and 6 and 3 in a million, respectively, for male and female nonsmokers.
Risk for Schoolchildren
Studies show that the airborne asbestos levels in some buildings may be more than 25 times higher than those used for the nas's estimate.
The corresponding "worst" estimated risk of mesothelioma for a 5-year-old child who spends one year in a school building with asbestos levels approximately 25 times higher than the nas level (and 200 times lower than the industrial limit) would be approximately 100 in one million, according to Dr. William J. Nicholson, associate director of Mount Sinai's Environmental Sciences Laboratory.
According to Dr. Nicholson, this is the upper limit of risk for each year of exposure the children receive. (The lower limit is 10 deaths per million.) The deaths from this level of exposure would not occur immediately, however, but over the lifetimes of the children. The risk of death would also decrease fairly rapidly, the older the person was at the time of first exposure.
Dr. Nicholson also cautioned that his estimate cannot be applied across the board. First, he noted, although the epa has identified exposure levels that are high in some large-city schools, they are probably uncommon in most schools. Second, the estimate is based on findings of disease from even higher levels of exposure to asbestos in the workplace, and many of these estimates disagree with one another. Third, the estimate is a "worst" case scenario, or the upper range of possible risk.
Dr. Nicholson said that even though his "worst" case estimate of risk is "very low," it is comparable to the risk of death from motor vehicle accidents for the very young. He added that motor vehicle accidents are the leading cause of death for elementary-school children. Moreover, the health risk from asbestos is one that he believes can be eliminated.
Special Risks for Children
Medical researchers also warn that even though the statistical probability--based on comparisons with asbestos in the workplace--that any one child will become ill from asbestos exposure is small, the nature of asbestos-related diseases may make asbestos exposure especially dangerous for children.
The risk of mesothelioma, for example, increases over time, even after exposure to asbestos has ended. "For every doubling in time," Dr. Nicholson said, "there is a 30-fold increase in the risk of death from mesothelioma." After 30 or 50 years, he stated, the risk can become enormously large, even if the initial exposure was low.
Because of the way the risk increases, "a child of 5 has five times the risk of death from mesothelioma [over time] from the same exposure as a teacher of 30," Dr. Nicholson said.
Moreover, children may be more susceptible to cancer because their cells are dividing more rapidly, he said. Studies have found that young children may be more susceptible to cancers associated with radiation for this reason.
Dr. Nicholson did not include the possible, additional susceptibility of children to cancer in his calculations of risk. Therefore, he stated, the upper range of estimated risk may, in fact, be most realistic.
However, other medical experts point out that there is no empirical evidence for the theory that children are more susceptible to cancer due to their rate of cellular reproduction. It remains speculation.
Some medical specialists also argue that the risk of children developing lung cancer and other cancers later in life from exposure to asbestos in schools will not exceed that for mesothelioma unless they smoke. If they do smoke, the risk of lung cancer becomes greater.
Risk for Workers
Among teachers and maintenance workers, however, the risk of lung cancer is "overwhelmingly the biggest concern" for two reasons, according to Dr. Mark Cullen, assistant professor of medicine and epidemiology at the Yale University School of Medicine and director of the Yale-New Haven Occupational Medicine Program.
First, he said, teachers and maintenance workers are more likely to smoke. And second, they are closer to the age at which lung cancer begins to appear within the population as a whole.
In the case of lung cancer, asbestos appears to act as a promoter of disease, rather than an initiator, according to Dr. Selikoff. This means that the background risk of lung cancer at any particular age must be multiplied by the total amount of asbestos that a person has inhaled. Since the risk for lung cancer is much greater at age 50 than at age 20, for example, a 50-year-old teacher would have a greater risk of lung cancer from asbestos exposure than an 20-year-old teacher, if both had inhaled the same amount of fibers.
Unlike mesothelioma, the risk of lung cancer from exposure to asbestos does not increase with each successive year, but only with additional exposure, according to experts. The risk increases dramatically with cigarette smoking.
"Asbestos workers who smoke regularly have a 92-times greater risk of dying from lung cancer than nonsmokers who do not work with asbes-tos," according to the Occupational Safety and Health Administration. ''When compared with the general smoking population, asbestos workers who smoke show an eight-times greater risk of lung cancer."
The first, isolated cases of mesothelioma and lung cancer are beginning to appear in teachers and maintenance workers, according to doctors across the country. In addition, they are beginning to see a few school maintenance workers with asbestosis of varying severity. Most doctors say that asbestosis is not a risk for other school groups besides maintenance workers, because it is usually associated with large amounts of asbestos exposure.
In one of the first studies to document actual physical injury among a group of people exposed to asbestos in schools, a doctor with the School of Medicine at the University of Southern California has diagnosed asbestosis in 40 maintenance workers employed by the Los Angeles Unified School District.
Dr. Kaye H. Kilburn, Edgington Professor of Medicine at the university's Barlow Occupational Health Center, in the past year has found lung scars appearing in the X-rays of maintenance workers that he has diagnosed as asbestosis.
None of the lung scarring observed in the workers is debilitating at present, Dr. Kilburn said, but he added that "there is no way to predict" whether any of the workers will develop more advanced asbestosis or cancers of the lungs and digestive tract that have been associated with exposure to asbestos.
Medical examinations of the workers were initiated following the discovery that three Los Angeles school maintenance workers had developed mesothelioma, Dr. Kilburn said.
He found that among the 500 workers he examined, the flow of air through the lungs of nonsmokers was about 18 percent below what would have been predicted as normal. Among smokers, the flow of air through the lungs was 35 percent below what would have been predicted as normal.
Dr. Kilburn said that because all 500 workers were drawn from schools with the greatest identified exposure to asbestos, there is no way to predict what the chances are for similar exposure among the rest of Los Angeles's 10,000 school maintenance workers.
The study provides some of the first documentation that levels of airborne-asbestos exposure in schools may, under conditions of routine custodial activity, not only approach the levels found in asbestos workers' homes, and even in their workplaces, but also eventually could cause similar damage.
"The potential [for disease] for the janitor or the maintenance worker is very similar to what you see in construction workers who inspect and remove and deal with asbestos materials," said Dr. Lemen of the National Institute for Occupational Safety and Health.
"Generalizations on this wholeinued on Page X Continued from Page 13
thing are hard to make, but for the maintenance worker or the janitor who has to go up into the rafters and tear insulation [containing asbestos] off of a pipe and replace it with something else, they have a great deal of potential for heavy exposure to asbestos," he said. "And in most cases, they have no awareness: one, that they are dealing with asbestos; two, what the health hazard is; and, three, how to protect themselves."
Question of Effect
It is difficult to find members of the scientific or medical worlds who argue that the dangers of environmental asbestos have been overstated.
Malcolm Ross, a research mineralogist with the U.S. Geological Survey, is virtually alone in contending, after reviewing the medical literature, that some types of asbestos--particularly the "chrysotile" or "white" asbestos that is most commonly used in the United States--are not dangerous in nonoccupational settings.
"There is little evidence that the very frequent nonoccupational exposures to this form of asbestos have caused any harm," he contends. And he believes that regulatory responses and remedial actions should differ for different kinds of asbestos.
However, officials from other federal agencies and medical experts have universally condemned Mr. Ross's work. While some agree that chrysotile may be less pathogenic in terms of mesothelioma, they say that it presents a high risk in terms of lung cancer, and that all kinds of asbestos are dangerous.
Dr. Ross "is a very dangerous man, as a geologist trying to play a medical game," said Dr. Kilburn of the University of Southern California. "There's no question in my mind that chrysotile is a cause of cancerous and noncancerous diseases."
Medical experts argue, in fact, that even if all asbestos were re6moved from schools today, asbestos-related diseases from school exposure would continue to appear 40 years down the road, because of the diseases' long latency period.
Effects Will Emerge
"It's sort of like the person who jumps out of the Empire State Building," said Dr. David M. Ozonoff, chief of the environmental health section at Boston University's school of public health. "He passes the 14th floor, and he says, 'So far, so good.' What we're concerned about is what's going to happen when he hits ground level."
He and others say that society probably will not see as many deaths from asbestos in schools as from exposure in industrial settings.
But he adds: "I think it's really impossible to say. From a public policy point of view, I don't think anybody wants to take a chance. One thing about long-latency diseases is that once they become manifest, it's really too late to do something about it."
Vol. 04, Issue 04