a publication of the
Environmental Associates

Know Your Environment

PCBs: A Persistent Issue

by Roland Wall, February 2002

  1. Introduction
  2. What are PCBs and why should I care?
  3. PCBs, the environment and public health
  4. Political dimensions of PCBs
  5. Conclusion
  6. References

Introduction

Over the past century, certain classes of chemicals were manufactured which remained present in the environment long after their usefulness had ended. When first developed, many of these substances were thought to be harmless or even beneficial, but later research revealed them to have unintended consequences. Though valuable in their day, persistent pollutants—particularly those with uncertain effects on public health—have become long-term environmental problems.

One such pollutant first came to public attention in 1964. That year, Soren Jenson—a chemist at the University of Stockholm—was testing samples of human blood for the lingering presence of pesticides such as DDT. In the course of his analysis, Jenson was surprised to discover that another unidentified chemical was also present in all the blood samples he examined. Eventually, he learned that other scientists (in many locations) had found evidence of the same chemical in both human tissue samples and in specimens from the environment, such as bird feathers. In some cases these samples had been collected decades earlier, suggesting that—for many years—a variety of organisms were being exposed to an unknown and unsuspected artificial chemical.

Eventually, Jenson determined that the substance was the now-familiar class of chemicals called polychlorinated biphenyls, or—as they are now better known—PCBs. Scientists were astonished by how widespread the presence of PCBs—a common industrial product in use since the 1920s—had become. Traces of the substances could now be detected in people and animals around the world, from areas as remote as the Arctic to those as heavily populated as New York City.

This unexpected discovery led scientists, policy makers and the public to question the effects that PCBs might be having on human and environmental health. In 1979, amid suggestions that PCBs could have carcinogenic properties, the manufacture and use of the substances was banned in the U.S. Yet, despite the fact that they have not been manufactured in over 20 years, the tendency of PCBs to persist in the environment has kept the subject alive as a public concern.

Most recently, the accumulation of PCBs in river sediment, particularly the Hudson, has resulted in on-going disputes between industry, community groups and regulatory agencies. An intense controversy has emerged, with disagreements as to the level of danger presented by PCBs, and over the best way to remove them.

And while highly technical research continues on the characteristics and effects of PCBs, the questions are far from academic. Enormous sums of money, the integrity of large fisheries, and the security of the public health are all potentially at stake in this issue. It is crucial that the public have accurate information on the topic to better understand and influence decisions on PCBs now and in the future.

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What are PCBs and why should I care?

To understand why PCBs are such a complex issue, one must first understand some of the basic chemistry of the substances. Much of the dispute hinges on the chemical characteristics of PCBs.

In the first place, PCBs are synthetic, organic compounds, meaning simply they are manufactured and contain carbon. Carbon has a specific chemical property which is unusual in that each carbon atom can combine with other carbon atoms, forming long carbon chains or carbon rings. Chains and rings of carbons (and in some cases, rings attached by chains attached to rings ad infinitum) give each carbon compound unique characteristics, and form the foundation for most of the substances found in living systems. Carbon is also the basis for an enormous number (50,000+) of manufactured organic chemicals that are central to the modern economy, many of which—like PCBs—do not occur in nature.

Molecules of PCBs have several characteristics which affect how they behave in the environment. They are hydrophobic, that is, they tend not to dissolve in water or bind with water molecules. Conversely, they are lipophilic, meaning they are attracted to fats and oils. Because of this, they often become stored in both the sediments of waterways, and in the fat tissue of animals. This characteristic is important, because it allows PCBs—stored in this manner—to persist in the environment for remarkably long periods of time.

As well as attaching themselves to fat and organic tissues, PCBs are very stable chemically, meaning that they do not decompose easily. This, along with them being nonflammable and having superior qualities as an electric insulator, led to the wide use of PCBs in a variety of industrial applications. From the 1920's until being banned in the U.S. in 1979, an estimated 1.5 billion pounds of PCBs were made for purposes ranging from microscope oil to electrical capacitors.

There are actually 209 related substances which are classified as polychlorinated biphenyls. They consist of two connected phenyl molecules (rings of six carbon atoms each), with chlorine attached to one or more carbons. (See Figure 1). The exact form (known as a congener) of PCB depends on how many chlorine atoms it contains and to which carbons they are attached. This variation in form has complicated attempts by researchers to determine the extent PCBs have contaminated the environment, and the degree to which they affect human and environmental health.

PCB chemical structure
Figure 1: A Typical PCB Molecule consists of two phenyl rings (1 and 2) joined by a single bond between them, with chlorine atoms (in this case, five) attached. Note that each carbon can form four other bonds. In addition to the chlorine atoms, carbon in a PCB molecule is bonded to hydrogen atoms or forms double bonds (3) with other carbons. The molecule tends to be very stable.

Polychlorinated biphenyls were manufactured in the U.S. under the trade Aroclor. The commercial manufacturing process for Aroclors resulted in the production of various mixes of PCB congeners, each present in a variety of proportions depending on the amount of chlorine desired. Aroclors were classified by numbers that indicated their level of chlorination, (i.e. the percentage of the substance that was chlorine, by weight). Thus Aroclor 1221 was 21% chlorine, while Aroclor 1260 contained 60%. A variety of other "Aroclors" were marketed with similar designations. In general, the more chlorine present in a PCB, the longer it will take to degrade and the more potential harm it may cause organisms.

Although no longer manufactured, a sizable percentage of these chemicals remain intact, either in applications that pre-date the ban, or persisting in the environment following accidental or intentional release. It should be noted that throughout much of the time they were being manufactured experts felt that PCBs were harmless, discharging them was perfectly legal. In fact, the continuing use of PCBs in pre-existing applications is still legal if equipment is properly maintained.

The most important feature of PCBs from an environmental standpoint is not just their persistence but their tendency to bioaccumulate and biomagnify. These complementary processes can result in the percentage of PCBs in the fat of organisms (sometimes called the "body burden") being much higher than the levels in which it appears in the environment.

As the term implies, bioaccumulation is a cumulative process. Over its lifetime, an organism is exposed to environmental contaminants through sources such as food and sediments. Because PCBs bind to fat and degrade very slowly, the amount of the substance may increase in the fat of an animal. As the PCBs are stored, the amount in the animals tissues may exceed that in the environment. This is bioaccumulation. The ratio of the amount of PCBs in the animal's fat to the amount in its diet is sometimes known as the bioaccumulation factor.

Across the environment, PCBs can also biomagnify up the food chain. A simple example of this would be a songbird that eats insects that have been contaminated with PCB. While the amount in each insect may be minuscule (a tiny fraction of a gram) over its lifetime the bird will consume thousands of the insects, ultimately adding up to a significant amount. The bird will have a much larger amount of PCBs in its tissue than did the insects. If songbirds are then preyed on by a carnivore—a hawk, for example—the body burden of each songbird will be accumulated in the tissues of the hawk. Thus at each level of the food chain, the amount of PCBs will be increased. So-called "top predators" like hawks or bears (or humans) can have significantly higher percentage of PCBs than their prey.

This is of particular concern for human populations in areas where fish are a major part of the diet. Because of the amount of PCBs stored in sediment, fish—particularly bottom feeders like catfish and "top" predators like bass—can become heavily laden with the chemical. This can biomagnify into humans. In many areas of the country there are advisories and restrictions on the amount of fish people should eat from contaminated waterways, though these restrictions tend to vary from jurisdiction to jurisdiction. Also, according to Johnson et al [1], such advice is often ignored.

Because they are lipophilic and do not easily degrade, PCB molecules can attach to a variety of mediums such as dust particles or oils. The molecules can also evaporate (i.e. turn to vapor). In these forms, PCBs can be transported by a variety of natural or artificial means, ranging from wind currents to household garbage.

The ability of PCBs to turn to vapor is a particularly important factor in their global movement. Although PCBs resist bacterial degradation, in some cases they may lose some of their chlorine atoms to biological processes. While this would seem to lessen the danger from the substance, paradoxically, the congeners with lower chlorine levels are more likely to become volatile, enter the atmosphere and ultimately be deposited in distant locations.

By this process, it is possible for PCB levels to be as high (or higher) in remote areas, such as the Arctic, as they are in the industrialized regions of the world. A study in 1989 [2], for example, demonstrated that PCB levels in the breast milk of Inuit women in northern Quebec was up to 4 times higher than that of nursing mothers in the southern part of the province. As it is now believed that PCBs have a particular affinity for breast milk, this would present special dangers for transmission of PCBs to infants.

Though the risks presented by PCBs were (and still are) unclear, preliminary health studies, combined with the issues of persistence and accumulation, prompted the U.S. to opt for caution. In 1977, the Congress passed the Toxic Substances Control Act (TSCA) which, among other things, specifically banned the production and sale of PCBs. Since that time, there has been an ongoing effort to manage the levels of PCBs that remain in the environment.

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PCBs, the environment and public health

A great deal of research and debate has centered on deciding the best ways to deal with PCBs, but two points of uncertainty hamper these efforts. First, while it has long been assumed that exposure to PCBs poses some threat to human health, determining the exact nature and degree of that threat has been elusive. Secondly, there is considerable controversy over risks and benefits of specific techniques for removing or remediating the level of PCBs that are present.

In regards to the first issue, studies have suggested that PCBs are associated with a variety of possible health problems, including skin diseases, cancer, and neurological conditions, as well as with possible effects on prenatal and early childhood development. However, despite extensive research on such medical connections, science cannot yet establish clear patterns or mechanisms for how PCBs impact human heath.

Thus, the EPA can state, with all earnestness, that PCBs are a "probable human carcinogen;" at the same time, an official of a major company which produced PCBs can say, with equal earnestness, "There is no credible evidence that PCBs cause cancer." [3] In fact, contrasting scientific evidence lends some support to both claims, while leaving neither proven. Indeed, considering the difficulty of correlating any single cause with human health problems, these claims may never be resolved to the satisfaction of all concerned.

The uncertainty over the health effects of PCBs can be illustrated by considering two recent, contrasting scientific articles evaluating the current state of knowledge on the topic. "Public Health Concerns About Environmental Polychlorinated Biphenyls (PCBs)" by Flynn [4] and "Public Health Implications of Exposure to Polychlorinated Biphenyls (PCBs)" by Johnson et al [5] are similarly titled studies, both written by accredited researchers. Both present what are apparently exhaustive reviews of current literature. Yet they reach conclusions that differ in many significant areas.

Johnson's team, writing for the U.S. Agency for Toxic Substances and Disease Registry (ASTDR), make the following assertion: "The findings of elevated PCB levels in human populations, together with findings of developmental deficits and neurologic problems in children whose mothers ate PCB-contaminated fish, have compelling implications. The weight of evidence clearly indicates that populations continue to eat fish containing PCBs and that significant health consequences are associated with consumption of large amounts of some fish. Although PCBs are declining in the environment, health concerns are still warranted."

Flynn however, in an article published by the American Council on Science and Health (ACSH), makes a different interpretation: "No conclusive evidence exists that background levels [of PCBs] in the general population, or even the very high levels that occurred among some occupational groups, resulted in acute or carcinogenic effects. In humans, the only adverse health effects that are strongly associated with PCB exposures are skin and eye problems.None of these effects have been observed in populations exposed through the consumption of fish. Cancer has not been correlated with levels of PCB exposure, and therefore, cannot be attributed to PCB exposure." (Italics added in both quotes.)

How can such widely differing conclusions be explained? One clue may lie in the context of the articles. The ATSDR is part of the U.S. Department of Health and Human Services, and as such, has a mission "to prevent exposure and adverse human health effects and diminished quality of life associated with exposure to hazardous substances.." [6] The ACSH, on the other hand, is an independent, non-profit organization with a stated goal "to help Americans distinguish between real and hypothetical health risks. ACSH aims to separate the leading causes of disease and death from the leading causes of unnecessary anxiety." [7]

It is likely, given these differing missions, that publications of the two organizations would have differing priorities in presenting information. However rigorous the science of either group, the level of uncertainty allows value judgments to be made in presenting research. For example, the bibliographies of the two papers totaled 250 studies, yet only 22 of these were cited by both sets of researchers. Put another way, there were 228 studies related to PCBs that were seen as significant by one group but not by the other. However unintentional, this suggests that bias played some role in choosing evidence and reaching conclusions.

The second major point of uncertainty which plagues the search for long term solutions to PCB contamination lies in determining appropriate environmental remediation for the substances, that is, how to clean it up. Recommendations for action on PCBs have ranged from leaving them to degrade naturally to comprehensive dredging of sediments with removal to safe to disposal areas. Not surprisingly, support for different techniques tends to vary according to who would be assuming the costs for the remediation.

The Hudson River has become a major focal point in disputes over how PCBs should be handled and who should be responsible for the costs associated with cleaning them up. For over 30 years the General Electric Company (GE) operated electrical capacitor plants along the river in the New York towns of Hudson Falls and Fort Edwards. Until the practice was discontinued in 1977, over a million pounds of PCBs were released into the waters of the Hudson and some spillage went into the surrounding soil of these factories.

The result of this was PCB contamination of sediments in various locations along the river. Because of patterns in the dynamics and sediment deposits of the river, there are particular areas—the so-called "hot spots"—where PCB concentrations are highest. Ultimately a large portion of the upper Hudson was declared a federal Superfund site, marking the river for special enforcement measures and placing liability for clean-up on GE. In the past two decades, environmental regulators, GE officials, local governments, activists and communities have engaged in a prolonged dispute over how best to resolve this problem.

In essence, the dispute comes down to a single issue: would it be better to dredge the contaminated sediment and remove it from the river, or is it safer to allow the sediment to remain in place, with the PCBs becoming covered by clean sediment and ultimately biodegraded by bacteria over time? It has been the contention of the EPA—including a recent set of new recommendations that have been supported by the Bush Administration—that dredging and disposal of the sediment is imperative to restore the river. General Electric, however, asserts that dredging would release more PCBs into the river and that the best answer is to leave the sediments in place.

But while the choices may seem simple enough, reaching a final decision is quite complex. General Electric, which would end up paying the costs of dredging—possibly in the hundreds of millions of dollars—contends that science supports their argument that PCB levels in the river are steadily declining. Furthermore, they believe that the EPA has taken an unreasonable rigidity regarding dredging, ignoring evidence that natural processes degrade the molecules.

Because the discharge of PCBs was legal during the time of the disposal, GE feels they are now being penalized for actions they undertook in good faith. They also question the level of health hazard posed by PCBs. Other questions raised by dredging opponents include where and how the dredged sediments would be disposed of, and what the impact would be on the communities during the dredging itself.

Proponents of the dredging, notably the EPA and groups of environmental advocates, counter that natural remediation is not effective and that the contaminated sediments will continue to present a significant hazard for years to come. Regarding claims that dredging would be more dangerous than leaving sediments in place, advocates of dredging contend that it could be accomplished with modern suction dredges that would lead to minimal release of sediment into the waterway.

With fishing banned or restricted on much of the Hudson River, some community leaders feel the contamination has diminished important natural, cultural, and recreational values of the region. They further argue that even though the disposal of PCBs was legal, GE had a common-law responsibility to insure the safety of the substances they were discharging into the river.

To present its arguments, GE has undertaken a spirited advocacy and public relations campaign, aimed particularly at swaying the opinion of Hudson Valley residents. Some advocates have questioned the manner in which GE is trying to impact public opinion, noting that the immense resources of the corporation might overwhelm opposition regardless of the factual bases of the arguments. Officials of GE however believe that the effort is an important public education campaign, and feel they have a duty to oppose actions like dredging which they believe lack scientific foundation.

Like the health issues, the question of remediation of PCBs lies at the edge of scientific certainty, with political and economic interests tending to overwhelm the more cautious and ambiguous conclusions of scientists. While it would be expected that further research would help fill some of the gaps in the level of certainty, it seems likely that decision making on this topic will include elements of subjectivity and social attitudes for some time to come.

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Political dimensions of PCBs

Some writers have dismissed PCBs as "political pollution." While this may understate the real health and environmental risks that they could pose, there is no doubt that PCBs were among the early synthetic chemicals that provoked a public outcry. It also seems apparent that the broad ranges of uncertainty offered by experts in assessing both the risk level and the best way of remediating PCBs has led to the debate on the issue becoming far more political than it is scientific.

Determining the potential hazard of PCBs is part of the larger and equally controversial subject of risk analysis. Because risk analysis is playing an ever greater role in public policy, and because those performing risk analysis often have to deal with issues such as bias and uncertainty, it is important to understand what risk analysis is, and what it can and cannot tell us about the safety of substances in the environment.

According to one source [8], risk is "precisely what it implies-a possibility.it refers to the possibility of injury, harm, or other adverse and unwanted effects." Risk analysis is a process designed to "understand the nature of unwanted, negative consequences to human life, health, property or the environment." In looking specifically at the health effects of PCBs, risk analysis is used to evaluate the likelihood that certain levels of exposure under particular conditions will lead to certain consequences for human health.

Although there are many models and definitions for risk analysis, depending on its application "there is agreement that risk assessment, comparative risk analysis (CRA), risk communication, and risk management are the essential pillars of the field." [9] Briefly, risk assessment determines the degree of danger presented by the substance or activity, while comparative risk assessment ranks that danger relative to other hazards. Risk communication is intended to strengthen public awareness of the relative risks. Finally, risk management involves the technical and policy decision making that will reduce the risk, determine the level of acceptable risk, and balance the relative risks and benefits of using the substance or performing the activity.

Despite the attempts to systematize the study of hazard, it is important to recognize that risk assessment cannot state with complete certainty that something is safe. This is true whether the hazard is PCBs, ozone pollution, mountain climbing or any of the other endless number of ways humans might be exposed to risk. The best it can do is use probability and data regarding toxicity to guide personal decisions and public policy in regards to those activities and environmental conditions that entail possible "adverse and unwanted effects."

There are numerous factors that result in this inherent uncertainty, six of which have been summarized [10] by the Canadian Medical Association:

This uncertainty is particularly true when dealing with low doses of substances over prolonged time periods. In the case of PCBs, while the average human body burden is certainly higher than it was a century ago, the amounts remain very small relative to the human body. Because most people are exposed to many other substances over their lifetime, it is very difficult to isolate the effects of a single chemical.

As a result of these factors, "The relation of risk to dose or exposure is generally unknown and often controversial." [11] While mathematical modeling, toxicological reports and animal experiments are (hopefully) providing data that steadily decreases the level of uncertainty, it is still possible that "independent and technically competent reports on the same hazard often differ by a factor of a thousand or more."

The inherent uncertainty involved in risk assessment, and the tendency for the recommendations of risk analysis to change as more information becomes available, have led to widespread skepticism on the part of the public to accept the judgement of risk evaluators in policymaking. As Bailar and Bailar note, when scientific studies seem to go back and forth as to whether something is hazardous, "the whole process may be considered shady, and the credibility of science more generally may be damaged." [12]

In the past, notes the National Research Council [13], technical experts have believed that describing risk (or "risk characterization") is simply a matter of communicating "a summary or translation of technical analysis for use of a decision maker." In this approach, risk is defined by the expert evaluator.

However, as Borsuch [14] observes "it is clear from survey data that a sizable gap exists between risk experts and nontechnical citizens over how to appropriately define and measure risk." This is because "officials with technical training tend to focus on-and are comfortable with-the standard concept of risk as the possibility of damage or unwanted effects," while the "non-technical public often expands the concept of risk to include various nondamage attributes."

These "non-damage" attributes are an array of factors that "reflect both societal values and the play of anger and fear that hazards can readily evoke." They include such public perceptions as to whether the risk is being involuntarily imposed, the level of uncertainty, the unfamiliarity of the risk and the perceived trustworthiness of the persons making the evaluation.

When considering PCBs, many of these non-damage factors may come into play. Public responses are not likely to tolerate huge ambiguities in the potential for outcomes such as cancer and birth defects. Nor is this a case where "better educating" the public (as some technical experts advocate) is likely to make a difference. As we have seen, it is possible for very authoritative figures to differ widely in how they view the risk presented by these substances.

Yet, as Bailar and Bailer point out, "we cannot avoid making decisions about risk management: to ignore them is to make those decisions by default, covertly and without full appreciation of their implications." And as there are political pressures to avoid ambiguity, so too does the public expect some action to minimize possible risks to human and environmental health.

In 1996 the National Research Council proposed a new approach to risk management that would address some of these issues. Though not yet widely practiced, the NRC approach would "re-conceive" risk assessment as "a process in which the characterization of risk emerges from a combination of analysis and deliberation." [15] In this model, characterizing the risk would be a critical part of the risk management process, with a process that considers the interests and concerns of the affected parties.

More recently, in 2001, the NRC released a report on risk management specifically as it relates to PCBs in river sediment. Though recognizing the uncertainties, the NRC supports the conclusion that PCBs may represent a significant risk to humans and the environment, and that PCB contamination should be remediated. They further recommend that decreasing risk, rather than preferences for particular remediation techniques, should be the emphasis of any decisions regarding PCB contamination. Recognizing that each contaminated site has different characteristics, they reiterate the participation of all affected parties, particularly as the final decision relates to local cultural, social and economic factors.

It is suggested that such a holistic process might move beyond the issues of "dueling experts" to consider the key questions of concern to the affected stakeholders. Given the level of scientific uncertainty, the decision-making process would strive towards a balanced and on-going deliberation that acknowledges scientific ambiguity and public perceptions. While this may not seem as scientifically "rigorous" as the risk experts would prefer, it acknowledges the very real, subjective—and often political—factors that influence how risk is perceived and how decisions are made.

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Conclusion: The future of PCBs

Despite the disputes over existing PCB contamination, there is a general consensus that the substances should be no longer be manufactured or utilized. This was first stated by the U.S. in the TSCA legislation but has more recently been recognized on an international level by the passage of the UN Treaty on Persistent Organic Pollutants (POPS).

Finalized late last year and signed by the U.S. in May of 2001, the POPS treaty is designed to ban the so-called "dirty dozen" of persistent manufactured chemicals. In addition to pesticides such as DDT, and industrial by-products like Dioxin, the treaty specifically s PCBs as one of the chemicals to be banned.

The treaty includes the criteria for regulating such chemicals and financial mechanisms to assist developing nations in complying with these criteria. On signing the treaty, President Bush indicated [16] that it "would safeguard the health of Americans, particularly those most at risk, such as native Alaskans, while extending a helping hand to developing countries."

In effect, then, the risk analysis regarding the future of PCBs has been decided, both in the U.S. and around the world. It is the level of risk still presented by their past uses, however, and—the actions needed to address that risk—that remain in dispute. Like the PCBs themselves, these questions will probably persist for some time to come.

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References

  1. Johnson, B., H. Hicks, W. Cibulas, O. Faroon, A. Ashizawa, C. De Rosa V. Cogliano, M. Clark, 1999. Public Health Implications of Exposure to Polychlorinated Biphenyls (PCBs). Agency for Toxic Substances and Disease Registry. [go back]
  2. Dewailly, E., A. Nantel, J-P. Weber, and F. Meyer. 1989. High levels of PCBs in breast milk of Inuit women from Arctic Quebec. Bull. Env. Contam. Toxicol. 43:641-646. [go back]
  3. Quote from General Electric source by Kolbert, E. in "Letter from Hudson Falls: The River." The New Yorker, Dec. 4, 2000. [go back]
  4. Kleiman, C. 1997. (Update of report by L. Flynn, 1991). Public Health Concerns About Environmental Polychlorinated Biphenyls (PCBs). American Council on Science and Health (Postion Paper). [go back]
  5. Johnon et al, 1999, cited above. [go back]
  6. ATSDR, Web Page, On-line: http://www.atsdr.cdc.gov/ [go back]
  7. ACSH, Web Page, On-line: http://www.acsh.org/ [go back]
  8. Boroush, M, 1998. Understanding Risk Analysis: A short guide for health, safety and environmental policy making. American Chemical Society. [go back]
  9. Boroush, M, 1998, cited above. [go back]
  10. Bailar, J.C. III and A. Bailer, 2001. Environment and health: 9. The science of risk assessment. Canadian Medical Association Journal V. 164(4) p. 503-506. [go back]
  11. Bailar and Bailar, 2001, cited above. [go back]
  12. Bailar and Bailar, 2001, cited above. [go back]
  13. Stern, P. and H. Fineberg (eds). 1996. Understanding Risk: Informing Decisions in a Democratic Society. National Academy Press: Wash. D.C. [go back]
  14. Boroush, M, 1998, cited above. [go back]
  15. Stern and Fineberg, 1996, cited above. [go back]
  16. U.S. Department of State, International Information Programs, 2001. U.S. Statement on POPs Treaty Signing. [go back]

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