Reduce the Adverse Impacts of Chemicals in the Environment
Stresses on ecosystems and hence on humans have many important sources, including chemicals, mining, farming and forestry, and—perhaps even more serious—living conditions, levels of education and health care, and life-style choices. Clearly, this forum could not deal with all those sources and chose to concentrate on some that might be addressed with specific technology assessments and recommendations. Adverse impacts of chemicals in the environment constitute one source.
There is a desire in general on the part of societies to improve their standard of living. This inevitably results in greater consumption of water, food, mineral, and energy resources and of our manufacturing capability. Although wastes and products that follow such consumption result in a greater burden on the environment, it is also true that the higher the living standard, the greater the resources that can be, and generally are, devoted to protecting human health and the environment.
Thus, industrially advanced societies tend to have safer food, water, and air than do less advanced societies. Nevertheless, there remains a conflict between the desire of a growing population for more goods and services and the desire for a healthy environment. One of the many land-use and economic changes resulting from human expansion that generally cause impacts on ecosystems is the introduction of new products. New products that foster new desires or satisfy old needs are sometimes discovered to have environmental impacts that are unacceptable or become unacceptable relative to a continually raised environmental standard.
The last 50 years have seen the introduction of many new chemicals. Many have stood the test of time and shown their benefits to outweigh their environmental
We desperately need better tools to predict human risk from exposure to toxic chemicals. The information that will be useful will eventually arise from the development of a conceptual toxicity-evaluation scheme resulting from the recent advances in molecular genetics and biochemistry. This will enable scientists to target chemicals and substances of potential concern much more easily without needing a complex (and time-consuming) series of traditional toxicity tests.
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risks. For some, however, important adverse environmental effects emerged. The search to replace those without further environmental effects has become a strong driving force in industry, in the scientific community, and in the general public. The focus has been mostly on testing for acute human toxicity with surrogates and on estimating long-term chronic effects in humans, primarily emphasizing cancer, again with surrogates. Increasingly, researchers will strive to include effects on entire ecosystems, and long-term, multigenerational effects on fertility, reproductive quality, and hormonal functions. Of major interest will be chemicals with the potential to be persistent, toxic, and bioaccumulative (PTB). However, chemicals that are persistent but not toxic or bioaccumulative, such as CFCs, have also led to environmental problems, as have chemicals that are persistent and toxic but not bioaccumulative. Evaluations of such chemicals are also needed.
Some of the surprise effects of chemicals have been due to a failure to predict the scale on which technologies might be used once they were shown to be beneficial when used on a limited scale. For example, DDT has side effects that have increased nonlinearly with the scale of application; as a result, the incremental benefits of a seemingly benign technology reversed when it was applied on a larger scale. New technologies have to be constantly reevaluated in anticipation of scale effects.
Following are some examples of products or processes that created unforeseen environmental problems after their introduction.
Pesticides, such as DDT, endrin, dieldrin, and benzene hexachloride (BHC).
Alkylbenzene sulfonate (ABS) synthetic detergents.
Polychlorinated biphenyls (PCBs).
Lead used in gasoline and paint.
Some chlorinated solvents.
Chlorination for disinfection (in some situations).
Mercury release from chlor-alkali cells.
Older coal gasification (now replaced with modern, but expensive, technologies).
Dioxin release from incineration and some chemical reactions.
The problem of nondegradable (persistent) pesticides has been known for many years. Because of the excessive accumulation rate in higher species, a group of major pesticides used in the 1960s (DDT, endrin, dieldrin, and lindane) have been banned or greatly limited in use in the United States. Substitute pesticides that are readily degraded in the environment have been developed. New adverse environmental impacts continue to be found, even with some of the substitutes. In some cases, biodegradable substitutes proved to be much more toxic to humans and to require much more sophisticated handling than more persistent substances. At times, a parent pesticide is degraded in the environment but results in daughter products that persist. The search for alternative pesticides or other products that have less adverse environmental impact has been rewarding to society and industry. Such efforts need to be, and will be, continued and will be driven by the marketplace's responding to public and government interests.
Some persistent chemicals with a variety of uses do not bioaccumulate in birds or other higher species but instead partition readily into water and do not bind well to soils, so they migrate through the ground and cause groundwater contamination. Examples are the triazine group of herbicides, dibromo chloropropane (DBCP, a nematocide), and some industrial solvents.
PCBs were once widely used as coolants in electrical systems. Emissions from that use led to great concern over the potential for PCBs to accumulate in the environment, and cause problems similar to those caused by DDT and to accumulate in people, in whom some of the PCBs were known to be toxic.
Another problem persistent chemical was the synthetic detergent, ABS, which was widely used in the 1950s. It persisted in rivers, streams, and ground-waters, causing excessive foaming of water. It did not cause health effects, but it was aesthetically unacceptable in drinking water. Legislation outlawing its use or threats thereof led to substitution with a biodegradable alternative detergent in the early 1960s.
Major environmental problems resulted from lead in gasoline and paint, and its use in these products has been eliminated. That required the development of new formulations for gasoline, new designs for engines, and substitutes for paint pigments.
Creating safe indoor environments is emerging as an endeavor in need of much basic research, in that there appears to be very little known, atleast to a lay person like me about the cumulative effects of the many materials, products, and other environmental impacts of working in office buildings and living in homes constructed of relatively new materials.
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The presence of excessive mercury in receiving waters due to use of mercury electrodes in plants producing chlorine and alkali was a major incentive in replacing that technology with membrane cells. Chlorinated solvents have been excellent for cleaning of clothing, machine parts, engines, and electronic components, but their disposal in landfills and their leakage from storage tanks have caused extremely expensive groundwater-contamination problems that have not yet been solved. Substitutes for chlorinated solvents are now widely used, and care in their disposal is required.
Substitutes for the CFCs that cause depletion of stratospheric ozone are being developed. Those which will be used in the near future (hydrochlorofluorocarbons [HCFCs]) are of concern because a decomposition product, trifluoroacetic acid, might be very persistent and, under extreme conditions, have the potential to cause an undesirable environmental impact.
Dioxin can be formed as a byproduct in some chemical processes, including one of the old routes to production of 2,4,5-T, a widely used herbicide. 1 This example illustrates that not only pure products must be evaluated, but also the contaminants that might be present in them, even if at low concentration. Methods of producing 2,4,5-T without producing dioxin are now in use. Dioxin is now known to be produced during combustion under poorly controlled conditions and when even very small amounts of chlorine-containing compounds are present.
Another example of byproducts of concern is the trihalomethanes that are formed from humic materials in drinking water when chlorine is added as a disinfectant. The trihalomethanes are potential human carcinogens, and their concentration in drinking water is now regulated. Other chlorinated byproducts are also formed by chlorination, but their health impacts are less well known. Modifications of water-treatment operations that reduce trihalomethane formation and alternatives to chlorination are therefore being sought.
How do we determine what adverse environmental impacts the byproducts of new technologies—whatever they might be—can cause? And how do these environmental problems compare with those of the alternatives? Global transport of persistent chemicals is increasingly recognized as an issue that must be dealt with by all, or at least a combination of, nations.
The above are only a few examples of the numerous major environmental problems that were created by the introduction of new products and processes. They should serve as reminders as societies develop new products and processes to satisfy their needs and desires. The potential of any chemical for environmental damage must be assessed before its commercialization, and our capability for doing so should be expanded, although we recognize the possibility that the new
chemical might replace another substance, natural or man-made, already in use that could be even more damaging. Those cases demonstrate the need for continuous review of costs and benefits, which might not be the same for all countries and communities.
ANTHROPOGENIC CHEMICAL PRODUCTS
New chemical products intended as pharmaceuticals (and their important metabolites) are extensively tested under rules of the Food and Drug Administration (FDA). The FDA tests cover a wide variety of toxicity but concentrate on human effects. New discoveries intended for pest control or for use as agricultural insecticides, fungicides, or herbicides are subject to somewhat less rigorous testing required by EPA under the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA). The FIFRA tests concentrate on predictors of human carcinogenic effects, with increasing attention to effects on "off-target beneficial species," such as birds. Costs of testing a chemical under FIFRA can be tens of millions of dollars; costs of FDA testing can be even more.
Science and technology can contribute by helping define risks to human health and the environment and defining cost-effective solutions to prevent risks or reduce risks to acceptable levels.
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New chemical products not under the FDA or FIFRA are covered by the Toxic Substances Control Act (TSCA). If these chemicals are intended to become articles of commerce, they are subject only to submission to EPA of a request for a "Pre Marketing Notice" (PMN). EPA has 90 days to respond to such a request and often, in the absence of extensive data, relies on structure-activity relationship (SAR) predictions.
These chemicals can be subject to much more testing under the Occupational Safety and Health Act (OSHA) if they are known to be present in the workplace and a risk has been identified. In Europe, new chemicals are subject to more testing but still far less than that required for new drug or agricultural applications. International standardization of testing and international sharing of testing responsibilities and data would reduce costs and speed the availability of reliable and reproducible assessments.
ANTHROPOGENIC CHEMICAL BYPRODUCTS
Many anthropogenic chemicals end up in incinerators or wastewater treatment facilities. We need to be concerned about the reaction byproducts formed in such treatment facilities.
Chemicals that are disposed of in landfills (where they might leak from containment), are deliberately emitted (as in the case of hair spray or paint solvent),
or are merely discarded will end up in the air, in surface runoff or in groundwater, or simply reside on land.
Today, these chemicals, their degradation products, and the byproducts of their production are, for the most part, investigated only when someone suggests an environmental hazard on the basis of anecdotal environmental monitoring, local tests, or calculations. Under TSCA and OSHA, much more testing of these chemical byproducts can be required, once they are identified. This identification is unlikely to occur without better knowledge of what byproducts might be formed from anthropogenic chemical production and the use and effects such byproducts may have on the environment.
FINDINGS, CONCLUSION, AND RECOMMENDATIONS
Acute air and water pollution caused by the release of chemicals or other wastes will require continued vigilance, but 25 years of progress have already been made in reducing such pollution. Solid waste pollution by chemicals is covered under the "Industrial Ecology" section.
Although considerable advances have been made, there is still a great need to improve the ability to predict the environmental consequences of a new chemical on a variety of scales before the great expenditure of getting it into the marketplace is undertaken. Even then, unforeseen environmental questions may arise after a product is introduced. Greater proficiency in addressing such environmental questions is needed and should greatly improve our ability to develop regulations that are appropriate to the problem. Industry needs to have greater assurance that its often expensive product development and commercialization will be successful and not quickly overturned by unforeseen human health or environmental problems. Thus, both to encourage the development of desirable products and to provide adequate safeguards against potential environmental liabilities after products are introduced into the marketplace, sound procedures for evaluating potential impacts of products on human health and the environment are essential, and this need is expected to grow.
We have reasonably good testing methods for acute toxicity. The tests use surrogate animals, and the correlation to humans is the weakest element. The quality of predictive modeling for acute effects, based on SAR, is only modest. For chronic effects, testing with surrogates for humans is modestly good, particularly for cancer. Tests for chronic toxicity in animals are only fair and for cumulative effects on ecosystems are very weak. Predictive modeling for chronic effects in general is poor. The quality of toxicity testing and modeling is assessed more fully in previous National Research Council reports (NRC 1994a). Modeling to predict persistence is fair and to predict bioaccumulation potential is moderately good, at least for many common classes of chemicals (e.g., chlorinated
organics). This issue exists, not only for traditional organic chemicals, but also for organo-metallic compounds, ions, and complexes of the "heavy metals" mercury, cadmium, lead, copper, selenium, silver, beryllium, thallium, chromium, arsenic, nickel, and zinc.
There has been consideration of greater testing of chemicals covered only by premanufacturing notices, and it seems logical that a staged approach to testing similar to that required by FIFRA and based, incrementally, on exposure potential will be increasingly worthy of consideration.
For both the byproducts of various waste-treatment processes and the degradation products of intended products or processes that find their way into the environment, there will be the same need to assess potential ecological damage as there is to assess damage caused by specific intentional chemicals. "Daughter" (byproduct and degradation) chemicals pose additional complications in that their chemical formula and structure might not be known; they will be in lower concentrations than the industrial chemical products, making them and their impact harder to detect; and it will be far more difficult to obtain useful samples. They might also be in the presence of other materials that could confound tests. Small or laboratory-scale "miniecosystems" have been found highly useful for examining a wide range of conditions to sort out such variables so that the major biological processes affected by new chemicals on ecosystems can be better understood.
Ultimately, because of the sheer diversity and complexity of these potential chemical commercial products and their "daughter" products, modeling might prove to be particularly valuable. When sufficient specific industrial chemicals have been assessed for their potential for ecological damage, it should become possible to estimate this property for postulated chemicals. That would be similar to the prediction of thermodynamic properties from a combination of group contribution modeling and compound class-specific rules that have been developed and shown to be successful over the last 25 years. Similar modeling of treatment facilities and degradation processes should make it possible to estimate the potential effects of byproduct and degradation chemicals. Cross referencing those two projections ("daughter" products and ecosystem impacts) would help identify the facilities or chemicals that require more careful sampling and analysis and the need for containment or substitution.
Unexpected synergy between something already in the environment, whether anthropogenic or not and whether global or local, and a new chemical that was tested and shown safe by existing methods will remain a problem. Broader testing and testing in more "complete" simulated environments will help. However, in the long run, a better understanding of the basic biochemical process in the environment will be the strongest ally in deciding where to look and what to look for. The issue of unexpected synergy and its solution, will be similar to the problem of complex mixtures of chemicals that can be synergistic (i.e., more than additive or at least additive in their effects).
At least for the present, it seems impractical to hope that we will be able to
identify, empirically, all the environmental impacts that should be tested for or to hope that our tests could detect the most sensitive potentially affected organisms at the low end in responses to "dose-level and exposure-time" testing. Increasingly, researchers are working on collections of cells, microorganisms and entire miniecosystems, in which a broad range of subjects and surrogates are combined with mathematical models in an attempt to develop a more-accurate and holistic prediction or measurement of the effect of a chemical on an ecosystem. Again, in the long run, a better understanding of the basic biochemical processes in the environment will be the strongest ally in deciding what to measure and how to measure it.
Concerns about chemicals in the environment have focused major attention on the possible consequence for humans, animals, and whole ecosystems. Substantial progress has been made, and some contaminated bodies of water have been restored to use. However, we still lack basic knowledge and procedures for evaluating the potential impacts of chemicals, compound mixtures, or artificial concentrations of natural substances that have an adverse effect on human health and the environment. Such knowledge will be essential for developing products with adequate safeguards against unwanted side effects.
Reasonably good methods are available for testing the potential carcinogenic effects of chemicals on surrogate species for humans, particularly rodents. The correlation between these surrogates and humans is far from proved and is hotly debated. However, on the basis of experience buttressed by significant testing, use of surrogate species seems to have been most helpful in reducing exposure to many suspect carcinogens.
However, there is a need for better tests to assess ecological damage potentially caused by single compound chemicals, the byproducts of various waste-treatment processes, and the degradation products of intentional products or unintentional process emissions that find their way into the environment. Better understanding of the basic biochemical processes occurring in the environment is necessary to decide where to look, what to look for, what to measure and how to measure it.
Better test methods should be developed to evaluate, model, and monitor the potential long-term environmental impacts of single compounds emitted as a result of new products or processes. Emphasis should be placed on compounds that degrade only very slowly.
Better test methods should be developed to define and ultimately to model and predict the byproducts and degradation products associated with production and use of materials.
Basic studies of biochemical effects and of the impact of various chemicals and other adverse effects on the biochemistry of sensitive plant and animal species should be strongly supported. It is from such studies and the monitoring program that the most-effective hypotheses about items of greatest concern and about the continual development of testing will arise.
Strong support should be given to innovative ideas for modeling and tests on lower-order surrogate species that help to reduce the cost of tests for potential adverse environmental health effects on humans or shorten the response time needed to obtain that information.
International standardization of testing and international sharing of testing responsibilities should be promoted to reduce costs and speed the availability of reliable and reproducible assessments.
The emerging concept of developing experimental "miniecosystems"—focused on controlled-exposure environments for testing and for developing mathematical simulations of ecosystems impact based on limited, specific tests—should be supported.
For more information and guidance, the reader should refer to the following:
NRC (National Research Council), Opportunities in Applied Environmental Research and Development (Washington, D.C.: National Academy Press, 1991)
NRC (National Research Council), Issues in Risk Assessment (Washington, D.C.: National Academy Press, 1993).
NRC (National Research Council), Pesticides in the Diets of Infants and Children (Washington, D.C.: National Academy Press, 1993).
NRC (National Research Council), Ranking Hazardous-Waste Sites for Remedial Action (Washington, D.C.: National Academy Press, 1994).
NRC (National Research Council), Science and Judgment in Risk Assessment (Washington, D.C.: National Academy Press, 1994).
NRC (National Research Council), Carcinogens and Anticarcinogens in the Human Diet: A Comparison of Naturally Occurring and Synthetic Substances (Washington, D.C.: National Academy Press, 1996).
NRC (National Research Council), Understanding Risk: Informing Decisions in a Democratic Society Washington, D.C.: National Academy Press, 1996).