Where to begin?
March [?] 1986
This is the opening piece in the five-part series “Toxics.” In it, we laid out how toxics pollution touches upon technology and testing, biology and politics, economic activity, government regulations and public health. The article introduction read in part, “Just determining where to begin is almost overwhelming.” It sure was.
This article is one of a five-part series. For more, see "Toxics and risk" on the "Nature & environment" page.
There is a machine called a gas chromatograph/mass spectrometer which can detect the presence in the atmosphere of such gases as benzene in concentrations as rarefied as a few parts per trillion. Such machines may be understood not just as mechanical marvels but as symbols of the attempt to see and control the flow of toxic chemicals through the environment. They are expensive to buy and complex to run. They are sophisticated, and a little slow. And with them regulators can grab answers about toxics out of thin air.
Toxics are not an "environmental problem" in the 1970s style. They are a public health problem, and that poses awkward challenges to regulators who less than a decade ago measured the fatal effects of pollution in terms of dead fish. Regulators face not only the need to collect more information but more kinds of information.
The official national register of chemical substances bulges with more than nine million names. Of these, human ingenuity has contrived ways to make money from the manufacture and use of roughly 70,000, and another thousand or so new ones are introduced each year. Not all of these chemicals are toxic, although those that are not cannot reliably be identified at the moment, since only a handful have been exhaustively analyzed for possible effects on human health.
Illinois industry may be in decline, but there are still more than 10,000 smokestacks in the state, each capable of adding its own peculiar part to the state's toxic burden. Its exact rank is disputable, but Illinois is among the nation's top producers of toxic industrial wastes. Officially designated hazardous wastes comprise only one galaxy in the universe of toxics, but the volume of such leftovers suggests the magnitude of that universe. Any precise accounting is difficult; Illinois is home to tens of thousands of chemical plants, and foundries and pesticide plants and plating shops and paint manufacturers and electronics assemblers.
Estimates of the amount of officially defined hazardous wastes generated each year in Illinois vary from roughly 400 million gallons to 2.7 billion gallons. The smaller amount is derived from Illinois Environmental Protection Agency (IEPA) records, which are acknowledged to be incomplete; the larger is extrapolated from national data by methods acknowledged to be crude. In 1982 Senate President Philip J. Rock and Illinois Atty. Gen. Neil F. Hartigan formed a task force to study aspects of the hazardous wastes problem in Illinois. Concluded one task force committee, helplessly, "There is no basis on which to choose one estimate as better than another." Their conclusion might serve as a motto for toxics policymakers.
Condition, not event
What we face in toxics is not the familiar possibility that we don't know enough to act, but that we cannot know enough. The blind men touching the proverbial elephant had it easy. They had only to describe the large and ungainly beast they could not see, not regulate it. Regulation—including the regulation by the marketplace, which in theory is exercised inexorably if unconsciously by consumers making informed choices—depends utterly on knowledge. The world's ignorance about conventional pollutants has been ameliorated by decades of sustained scientific investigation; except for the heavy metals, toxics have been a topic of scientific inquiry since only about World War II. Partly as a result, practically nothing is "known" about the health effects of toxics in the way that it is known that typhoid fever is caused by the Salmonella typhosa bacillus.
Early research into toxics' health effects suggests disquieting questions but no real answers. Regulations about the use and disposal of toxics thus are based on provisional scientific truths, with the result that both are especially subject to revision, even contradiction. The regulation of conventional pollutants proceeded from a consensus about cause and effect, and disputes typically were over means more than ends. In the case of toxics there is no consensus, and everything is in dispute.
Unlike conventional pollution, toxic pollution is less an event than a condition. The laws, the administrative structures, the sampling protocols, even the language of environmental regulation that evolved during the hopeful campaigns against conventional pollutants in the 1970s are biased toward pollution that is discrete, episodic and comprehensible in both its causes and its effects. Toxics, on the other hand, tend to be pervasive, persistent, mobile and mysterious.
Eliminating conventional pollutants was never as simple as plugging up a pipe, but it is simpler than plugging up the many leaks by which toxics enter the water, soil and air. Hazardous wastes, we have learned, don't stay dead even after they've been buried, but can return to haunt the living. Certain organic solvents such as carbon tetrachloride can eat through clay landfill linings; the landfilling of liquid wastes was banned in Illinois as of 1985 as a result. Heavy metals are so armored against biological or chemical assault that they are practically immortal; unfortunately, the steel drums they are stored in are not. Flares installed to burn off the gas methane produced by decomposition of garbage in landfills may also be releasing buried PCBs (polychlorinated biphenyls) back into the atmosphere. Even securely lined landfills can, perversely, fill up with rainwater and overflow, a phenomenon known as the bathtub effect. Volatile organic compounds evaporate from sewage treatment plants where they arrive after having been flushed down sewer drains. Waste oils are often contaminated by heavy metals such as cadmium, arsenic or lead; when they are burned as boiler fuel they release unknown quantities of those toxics into the air.
Similarly, emissions of particulates and hydrocarbon intermediates (the latter the large class of petroleum fractions that includes solvents and plastics) have been dropping in Illinois to "just" (the Illinois EPA's word) 377,000 tons in 1982. But as Roger Kanerva, the IEPA's manager of environmental programs, put it in testimony to a U.S. Senate subcommittee in 1984, "available data is inadequate to define the extent of toxic chemical substances" in those emissions.
The unhappy lesson of the 1970s was that most of the accepted methods of disposing of toxics in fact merely moved them. Indeed, the then-cures often proved more confounding than the diseases. Factory wastes were no longer dumped into rivers, which could be cleaned up, but into landfills where they risked spoiling groundwater formations, which can't. Common household plastics could be burned instead of buried, in low-temperature municipal incinerators that transform those plastic molecules into dioxins. For those inclined to such conclusions, the 1970s offer a cautionary tale about the risks of regulating in advance of the facts.
It was not only the nature of toxic pollution that was misconstrued in the 1970s but its scale. Cleaning up hazardous waste is itself such a daunting task that it is easy to forget that industrial waste is what is left over from something else. To an inattentive public, toxics are things that are dumped. Toxics, however, are also manufactured, transported, burned in boilers and used in factories, put into cans and bottles and sold in supermarkets. "Once generated or transported into the state," reads the IEPA's major policy statement on toxics, issued in 1984, "chemical substances may become toxic problems in a number of ways." Exposure of workers who use them is one such way. So are spills, "air releases" and other emergencies, and the home use of commercial products containing toxic ingredients.
In one form or another, toxics flow through an advanced industrial economy like blood through a body. For example:
• Illinois' chemical industry makes, or imports for use, roughly 3,600 different substances, many of which remain untested for toxic effects; total chemical production in the state has been more than 60 million tons annually in recent years, according to USEPA estimates.
• Nearly 75 million pounds of chemicals designed to kill insects, weeds and fungi are sprayed and spread on Illinois each year. Fewer than a quarter of the state's farmers have received specific training in the safe use of such chemicals, nor is there a feasible way to monitor the disposal of leftovers.
• The quantity of pesticides used for such tasks as mosquito abatement or lawn care off the farm in Illinois is not known. There are probably as many cockroaches as corn rootworms in Illinois, and the attempts to exterminate them may also pose grave risks to humans; a study by the Chicago-based Citizens for a Better Environment (CBE) suggested that city dwellers are exposed to from two to six times more pesticides than rural residents are.
• Illinois hasn't had a Bhopal-type accident at one of its dozens of chemical plants, but it isn't because one can't happen. Mini-Bhopals are in fact quite common. Typical is the leak of chlorine gas in January from a Downers Grove electronics plant, which left 11 workers needing hospital treatment. During the five-year period, 1978-1982, roughly 4,000 such emergencies involving leaks or spills occurred in the state and affected several thousand people, ranging from death to the inconvenience of temporary evacuation. A more recent audit by the IEPA suggested that chemical plant safety plans and procedures were "poor" in 8 percent of the plants that make and handle toxic chemicals in the state.
• Nearly 4,000 Chicago children were treated for lead-related conditions in 1982, a number which may safely be assumed not to include all such cases. Much of the lead that appears in the blood of inner-city children is thought to come from the combustion (much of it illegal) of leaded gasolines. The soils near major auto thoroughfares in some cities is so laden with lead that, in the words of a CBE researcher, "If the soils were in a barrel, they would be considered hazardous wastes."
The risks to health posed by an oil refinery and a neighborhood dry cleaners differ largely in degree, not kind, in other words. IEPA director Richard J. Carlson elaborates. There is "too much emphasis" on the regulation of toxics in the form of hazardous wastes in the federal programs, he complains. "Nobody is concerned about hazardous wastes in common household products," he says, "or in sanitary landfills." The average Illinoisan generates nearly 1,800 pounds of municipal solid waste—garbage—each year. Garbage is objectionable to neighbors principally because of its smell, and to city halls because of its bulk. But while it is not regulated as hazardous under IEPA regulations, even ordinary garbage contains its share of poisons—empty spray paint cans, old batteries, unrinsed pesticide containers.
What can't be tossed out often is flushed out: Contaminated motor oil, solvents such as paint thinners and other materials identical to their industrial counterparts in everything except quantity are washed into municipal sewage plants. Depending on their chemical personality, they there evaporate or are flushed out with effluent, collect in sludges (which in turn pose their own disposal problems) or wreak havoc on the bacterial populations on which advanced sewage treatment depends. To some sewage plant operators, Mr. Clean, the popular household cleaner whose active ingredient is toxic to bacteria, is a dirty name.
Evidence is accumulating that the typical U.S. home may pose far graver risks to its inhabitants than does the world at large. Drain and oven cleaners, paint removers and thinners, aerosol propellants, glues, spray insecticides, lawn weed killers, used motor oil—all are, or harbor, toxic substances. Foods, both fresh and processed, contain pesticide residues, as well as dyes and other contaminants. Nor is toxic pollution in the home always the result of chronic, low-dose exposures. For example, recent federal studies confidently assert that people using commercial paint removers in poorly ventilated basement and garage workshops are thus exposed to concentrations of methylene chloride—a halogenated hydrocarbon that causes lung and liver tumors in mice—that reach 3,000 parts per million. The maximum safe exposure level recommended by the federal Occupational Safety and Health Administration is 75 parts per million.
Regulating the uncharted
The IEPA, on whose back most of the regulatory responsibility for toxics lies, may be likened to the mapmakers of an earlier century who sat poised on the edge of an unknown continent, armed against ignorance with only the crudest surveying tools. Examples:
• Toxic pollution tends to be specific to this waste stream, that industry or this dump site. Participants at a 1981 symposium at Rockefeller University admitted that they didn't know much, but they did know that generalizations about the health effects of toxics from one dump site to another "should always be considered unreliable."
• The reporting categories set up under the various toxic control statutes are often vague or incongruous, reflecting variously either political fudging or scientific uncertainty. In the latter case, for instance, PCBs are not defined as hazardous under the regulations of the federal Resource Conservation and Recovery Act, although they are under the Toxic Substances Control Act.
• Under-reporting of waste, accidents, etc. may be assumed to be chronic due to ignorance, criminal evasion or plain confusion. The CBE, for instance, estimates that only about a third of the estimated cases of misuse of commercial pesticides in Illinois is reported each year.
Measuring toxics by the millions of gallons is scarcely harder than measuring them by the molecule. The technology exists to measure molecules in concentrations as scarce as a few parts per trillion. This is a necessary achievement: Some toxics, like dioxins, are thought to cause harm in doses that slight. The ability to track toxics so assiduously also pushes regulators' grasp past their reach. Only a few years ago, a substance present in the air or water in even a parts-per-billion concentration could be said not to be present at all when measured by instruments capable only of detecting it in the parts-per-million range. That air or water might still be poisoned, but from a regulatory point of view it was immaculate. Such helpful ignorance is no longer so easy to maintain.
Regulation is commonly misunderstood as the means by which government controls what is "out there." Just as often it is the means by which government finds out what is out there. While Illinois' system of monitor wells, ambient air samplers, emergency dump site analyses, waste shipment manifests, and so on, is widely held to be inadequate to the scope of the toxics problem, the system is providing regulators with a swelling stream of facts. IEPA's data files, for example, contain the results of 160,000 analyses of sewage effluent and surface water for toxic metals done between 1978 and 1984; that's 160,000 tests for one class of toxics in one "receiving medium."
Indeed, such is the size of that data stream that regulators risk being drowned in it. Toxics have made clear the differences between mere data and information. "I'm appalled," says William Frerichs, assistant chief of the Illinois attorney general's environmental control division. "We have accumulated a lot of information, but it isn't put to its best use." Toxics are regulated under 17 major acts, many of which require different definitions and different methods of gathering and storing data. In fact, data sometimes isn't even comparable within agencies like the IEPA.
Programs designed to supply information often end up confusing it. The Illinois auditor general recently followed the paper trail left by the manifest system set up to track the movements of certain designated hazardous wastes from dock to dump in Illinois. The auditor general found that the data thus collected were inaccurate, incomplete, underverified and out of date. The response to the audit by Robert Kuykendall, manager of the IEPA land pollution control division, revealed the pride of a wounded bureaucrat and inadvertently revealed some of what is wrong with the system: "The manifest system does not, and cannot, track every shipment of . . . waste from cradle to grave . . . . it does accurately track all hazardous waste manifests." It is interesting to note that one of the first pieces of information published by the fledgling Hazardous Waste Research and Information Center of the Illinois Department of Energy and Natural Resources concluded with a complaint about how little usable information there is on the topic of hazardous wastes. The report cited "lack of consistency" and "major anomalies" in available information. Efforts are underway by all involved agencies to reduce this babble to a common tongue understandable by all, but progress is predictably slow.
In addition to the obvious technological limits, data collection has bureaucratic limits as well. In the simplified world described in EPA regulations, individuals are assumed to be exposed to toxics in one medium at a time, and the effects of toxics on vulnerable organisms are assumed to be isolated and independent. People endure multiple exposures, however, from air, water and (less directly) soil. Concentrations of arsenic in the air, for instance, properly concern the air pollution control administrator, but it is the concentrations of arsenic in human blood and flesh by whatever means they entered the body that must concern the physician.
Current regulations also tend not to take into account the sinister synergy of toxics. They assume that people are exposed to one toxic at a time, not the dozens revealed by the busy monitors. As Jacob Dumelle, long-time chairman of the Illinois Pollution Control Board, once put it, "The Illinoisan is the integrator of all these insults to health." Some toxics known to be damaging to certain organs have their virulence magnified by the presence of certain other toxics. A recent example in the news: Smoking is bad for you, says the U.S. surgeon general. Inhaling asbestos fibers is bad for you, too. Inhaling asbestos and smoking—as roughly half the workers in asbestos-related industries are thought to do—leaves you five to ten times more likely to develop lung cancer than people doing either alone.
Tracking toxics in what has been called the "inner environment" of a single human body is bewilderingly complex. Tracking them in groups of bodies has proven, so far at least, to be practically impossible. Public health risk assessments, especially those based on chronic exposures of disparate populations to minute doses of many different toxics, are seldom more than estimates based on extrapolations based on assumptions. However shaky the numbers may be about toxic concentrations in the environment at large, the inferences drawn from them about disease often are far shakier—what a learned critic once described, with the minimum respect consistent with professional politeness, as "toxicological guestimation" and "epidemiological number-crunching."
It remains true in both regulation and science that the quality of the answers one gets depends on the quality of the questions one asks. And research into toxic effects, especially in chronic doses, remains in its infancy. "Conclusive information is very difficult to find," explains Gilbert Zemansky, head of the Illinois Pollution Control Board's science section. "Answers are several years down the road, even if the country devotes the resources necessary for research."
State information initiatives
The recent uncertainty of the federal commitment to environmentalism has made state funding for research all the more important. Information was the key component of Gov. James R. Thompson's chemical safety initiative unveiled in the spring of 1984. "Current available information does not provide sufficient data for . . . policy development," Thompson told the General Assembly in announcing the plan. The ungenerous might translate his words to mean that the state doesn't know that it's doing.
Says Dumelle on the Illinois situation, "General environmental research sort of got lost." Administrative reorganizations left the responsibility for such research in the hands of the Department of Energy and Natural Resources (DENR) beginning in 1978, a time when energy and not the environment preoccupied state and federal budget-makers.
As a result of Thompson's chemical safety plan, Illinois is hurrying to catch up. The IEPA has expanded its monitoring and analysis capacities, including a new emphasis on testing of toxics for biological effects, in pursuit of the ambition to take IEPA's testing programs "to the next level of scientific sophistication." Another direct result of Thompson's plan is the new Champaign-based Hazardous Waste Research and Information Center, which operates under DENR to coordinate "problem assessment" research for both state agencies and industry. DENR researchers have recently linked toxic waste hot spots with vulnerable aquifers, and the IEPA as a result plans expansion of its groundwater monitoring system.
One can't do more until one knows more has become the general precept in many agencies. The Illinois Pollution Control Board has added a science section to keep its members abreast of developments in the field. The Department of Public Health has expanded its staff to include a toxicologist and an epidemiologist, in part a response to the widening of that agency's historical realm of concern about bacterial and inorganic pollutants to the more exotic organic toxics. The new staff will also study correlations between public health risks and hazardous waste sites in accordance with the state's new Environment Toxicology Act, which might be called one of the General Assembly's own chemical safety initiatives. The Department of Public Health has also opened the Illinois Health and Hazardous Substances Registry, a data repository where the incidences around the state of cancers, "adverse pregnancy outcomes" such as miscarriages, and occupational diseases will be recorded; it is a disease atlas that will help future researchers draw crucial connections between toxic cause and health effect.
The Hartigan-Rock task force, which met in 1983, included a committee on public health. That committee concluded: "There is presently no comprehensive method available for predicting health effects associated with existing hazardous waste sites. Predictions are based on a variety of assumptions and a relatively small amount of data with unknown accuracy."
What is true of hazardous waste disposal sites is also generally considered true for toxics in other environments.
The IEPA has its own phrase for the condition, warning that the public will have to learn to live with "a residual of uncertainty" when it comes to toxics.
But does our present ignorance preclude action? It would be easy to conclude that regulation would be imprudent. The risks of not regulating are real, if undefinable, but there are also risks in regulating the wrong things, or in regulating the right things in the wrong ways. After all, the landfills that today are threatening groundwater supplies were touted 20 years ago as ways to protect rivers and streams.
The public health experts assembled for the 1983 task force created by Rock and Hartigan concluded that on balance action was justified. Cochaired by Dr. Samuel Epstein of the University of Illinois Medical Center, who is the author of the widely regarded books, The Politics of Cancer and Hazardous Waste in America, the task force's public health committee stated that the available data justified regulation "to reduce the potential for future adverse health effects." That ambition falls far short of the optimism expressed by the Congress in the 1970s; then, the ambition was not limited to reducing pollution's potential for harm but was determined to eliminate the harm.
Not for the first time, it is politicians who must rush in where scientists fear to tread. Writing 20 years ago in the Yale Review, government professor Lynton Caldwell pointed out that biological facts (we don't know enough) in conflict with popular truths (the government should protect us) can be reconciled only politically. Conflicts not resolvable in the labs, in other words, must be resolved in law. As biology comes to play a bigger and bigger part in our politics, Caldwell warned in 1964, politics will almost inevitably become a bigger part of biology. ●
Toxics monitoring: The Lake Calumet experience
No single study better illustrates the cost and contrariness of monitoring techniques, or the difficulties of analyzing phenomena that cross bureaucratic boundaries than the soon-to-be-released Southeast Chicago study. Undertaken by the Illinois Environmental Protection Agency (IEPA) in 1982, initially at the urging of a local neighborhood association and later expanded, the study resulted in what the Citizens for a Better Environment (CBE) somewhat grudgingly calls the "most exhaustive" look yet at total toxic pollution at a single Illinois site. That site was the Lake Calumet district of Chicago.
Since 1869, those 30 square miles have been home to one of the densest concentrations of heavy industry in the country—steel mills, paint and pesticide factories, food handlers, metal fabricators. Used in part as a municipal landfill since the 1940s, the land around Lake Calumet is itself largely industrial waste, having been built up from the original marshes with boiler slag and mud dredged from nearby waterways that had been the district's sewers for decades.
Roughly 100,000 people live near the site. Chronic emissions from both old landfills and present businesses are an immediate concern; so, too, is the prospect that talked-about redevelopment of the now-blighted district might disturb long-interred toxics and expose workers and residents alike to risks thought buried in the past. Sampling teams found 20 recognized toxic substances in soils taken from study sites, another 13 in surface waters and 28 in the air.
Still, the study may have been only a beginning. The CBE, for example, later complained that the more than 30 landfills in the area had not been specifically monitored as possible sources of airborne toxics, nor were the city's sewage sludge drying operations. The IEPA samplers had looked for toxic "hot spots" where concentrations might reach acute-dose levels rather than the much lower concentrations that might be expected from a volatilizing landfill. "I wouldn't be surprised if a lot of things come from landfills," concedes Dan D'Auben of IEPA's air pollution staff. "I can't say that the science is there to measure it though."
Tracing a toxic present in the ambient environment back to its source is like sorting out a can filled with a quadrillion worms. The air around Lake Calumet is already polluted with benzene, for example, most of which comes from automobiles. Presumably as a result, the levels of benzene recorded near landfills did not differ significantly from levels commonly found in Illinois cities. D'Auben's crew traversed the area in a mobile sampling lab and found only two benzene hot spots—one at a traffic light where the lab pulled up next to a truck and another when the lab was driven through a fast food pickup lane and its monitor began reading the exhaust from the hamburger grill. "Whoosh, the needle went right off the scale," D'Auben recalls.
The CBE also criticized the study for the failure to test fish for the presence of such likely posions as polynuclear aromatic hydrocarbons or dioxins. Here the problem was system, not science. Fish tests were done not by the IEPA but by the Illinois Department of Public Health, which routinely tests only for PCBs and pesticides; more exhaustive tests are technically feasible but were prohibitively expensive.
Meanwhile, monitoring continues. ●
Discovering the link between toxics and health
The world has always been an unfriendly place for people. Among the most potent of the known causes of cancer in humans are anatoxins, which are fungal agents that grow on spoiled crops and which have afflicted the race since humans began farming. Some of the heavy metals also have a toxic legacy that dates back centuries. As Dr. Samuel Epstein, public health expert with the University of Illinois Medical Center notes in his 1982 book, Hazardous Waste in America, "Lead leached by wine from lead-lined storage jugs is thought to have poisoned the bibulous Roman aristocracy."
Indeed, toxic substances occur naturally. It is assumed—perhaps "hoped" is a more accurate word—that the majestic symmetries in the chemistry of life and the chemistry of the world in which it took root have been exploited by the human immune system over millions of years, equipping the body with a complex armor against natural organic toxics. Unhappily the genius of modern industrial economies for concentrating asbestos or uranium or lead into economically valuable quantities also concentrates their potential for environmental havoc.
Man-made toxics differ from their natural cousins in kind as well as concentration. Man-made organic chemicals typically differ in structure from natural ones. The molecular complexity of the immense family of synthetic hydrocarbons derived from petroleum enables them to combine into such helpful miracles as plastics or high-temperature lubricants. But it leaves them unhelpfully long-lived; bacteria seem to be baffled by them, although new varieties may be able to digest them. The appalling deaths and injuries that followed the leak of methyl isocyanate in Bhopal, India, were reminders that hundreds of chemicals in common use can have immediate and horrific health effects in even low doses. Late in 1985, the U.S. Environmental Protection Agency (USEPA) released a list of 402 such "acutely toxic" chemicals. A few ounces of many of them released into the air can cause vomiting, muscle paralysis, even death, to anyone standing as far as 200 feet away. Many such toxics are produced in Illinois plants, often in quantities measurable in tons per year. The specific toxic effect varies with the chemical character of each. Some are powerfully corrosive, others volatile and thus prone to explode. Others can paralyze nerves or scar the lungs or poison the kidneys. For example, phosgene may have been outlawed as a weapon after World War I, when it was used as a poison gas against troops in the trenches, but it is still used as a dye and as a component in pesticide manufacture.
The regulations promulgated under the federal Resource Conservation and Recovery Act, or RCRA, state that waste containing more than prescribed concentrations of substances known to be corrosive, flammable or chemically reactive are automatically defined as hazardous, and these wastes must be regulated as such. The RCRA rules allow further additions to its list of hazardous materials if substances can be shown to cause less dramatic but still grave damage to human health at lower, so-called "chronic" exposures. These other toxic effects include:
• carcinogenicity, or ability to cause cancer;
• teratogenicity, or ability to cause abnormal fetal development;
• mutagenicity, or ability to cause genetic mutation.
It should be noted that many toxics show an unwelcome versatility, being capable of producing tumors, mutations and birth defects. Toxicity in many cases is subtle and diverse; the same substance can produce different health effects, depending on the size of the dose or the route of exposure. Benzene, for instance, is highly flammable at high concentrations, while in lower concentrations it can cause skin irritation to those who touch it and drowsiness to those who breathe it; it can also cause leukemia and aplastic anemia.
The mechanisms by which different toxics interfere with the normal function of human cells vary with their chemical structure. For example, genetic instructions to the cells can be blocked or jumbled by certain toxics. Linking a specific substance to a specific health effect, however, remains difficult. Unable to penetrate to the core mysteries at the cellular level, researchers must resort to less conclusive proofs of harm. They include:
• Epidemiological studies. If a given population—workers in a particular plant, residents of a particular town, drinkers from a certain well, users of a certain product—show signs of distinctive ailments in common, one may reasonably posit a common cause.
Such epidemiological studies are widely regarded as offering the most conclusive evidence of toxic harm, but they are far from perfect. They are the public health equivalent of slamming barn doors: People must get sick, even die, before an incriminating pattern of disease shows itself. Diseases caused by exposure to chronic, low-dose toxics typically have very long latency periods before symptoms develop, often as long as 20 years; victims move or fall prey to other ailments; or they forget what they ate or drank and when.
• Follow-up studies. This is a sort of epidemiological study in reverse. A population known to have been exposed to a suspected toxic substance is studied after the fact for confirming signs of the onset of disease. Such studies are useful to confirm the health effects of a suspected toxic, or to measure their incidence more precisely. The fallout victims at Hiroshima and Nagasaki comprise one well-known study population, as do the residents of New York's Love Canal; in Illinois, people who eat quantities of contaminated Lake Michigan fish comprise a third. Unlike the case of epidemiological studies, the victims are known in advance; like epidemiological studies, follow-up studies demand years of careful and expensive attention. After nearly 40 years, for instance, the Japanese fallout studies, whose aims include charting the effects of radiation exposure on reproduction, have achieved only preliminary results.
"People studies" can be misleading, however. By choosing which population to study, which health effects to look for, and when to look for them, one can prove almost any number of hypotheses. Industry groups in particular have offered such studies as proof that there is no evidence of harm, even though the study subjects were tested before signs of disease might reasonably be expected to have appeared.
• Animal studies. Unable to test the effects of toxics on humans under laboratory conditions, researchers must resort to the next best thing and test animals, usually choosing mice or rats, partly because they're cheap. Animal studies are the source of much suggestive evidence about toxics, especially their carcinogenic potentials. They also are the source, inadvertently, of much of the public skepticism and confusion about toxics.
The problem lies in animal test methodology. If a suspect substance causes tumors in one victim out of 100,000 at real-world doses, and if a researcher must induce not just one but many tumors in order to establish a conclusive link between toxic and tumor, he or she would need to test a sample of mice numbering in the hundreds of thousands. To avoid this dreadful necessity, the research exploits one of the fundamental truths about cancer, the fact that the likelihood of tumor in a victim is proportional to the dose of carcinogen the victim is exposed to. Thus the super-doses used in cancer tests: If a given dose produces one tumor per 100,000 mice, a dose 100 times as strong should produce the same incidence of tumor in only 1,000 mice. During the saccharin controversy of the last decade such tests became a point of popular comment, although much of it was uniformed. Many people dismissed laboratory evidence linking the artificial sweetener with mouse tumors by asking, "Who drinks 100 cans of diet soda a day?"
Scientists have their own doubts about the validity of testing animals for human carcinogenicity. Extrapolating data from large doses to small ones, from small animals to big ones, from one species to another requires mathematical and methodological assumptions, virtually all of which are subject to criticism.
• Ames bioassay. Given the cost and complexity of "whole animal" tests, and given the enormous numbers of substances that bear testing, the need for a quick test to screen substances for their toxic potential quickly became obvious. One such test was developed in 1975 by Bruce Ames in California. The Ames test proceeds from the fact that most carcinogens are also mutagenic. In its simplest form, the test requires exposing bacteria to a suspect substance, then examining that bacteria for evidence of DNA damage.
Use of the Ames bioassay has become widespread, but its early promise as a cancer screener has faded. It remains fairly crude, and it is of little use in identifying the many potential carcinogens that are not mutagenic. The search continues for reliable and inexpensive ways to screen substances for toxic effects.
Had Shakespeare been a toxicologist, he might have written that all the world's a laboratory, and the men and women merely mice. The heedless creation of toxics and concentration of them by man has in effect converted much of the country and other parts of the world into a laboratory. When it comes to toxics, we are the rats. ●