The Effect on Ecological Systems of Remediation to Protect Human Health

Abstract

Environmental remediation of contaminated eco-sytems reduces stresses to these ecosystems, including stresses caused by the production, use, and storage of weapons of mass destruction. The effects of these various stressors on humans can be reduced by remediation or by blocking the exposure of humans, but blocking the exposure of resident biota is almost impossible.

Remediation may involve trade-offs between reducing a minor risk to public health and increasing risks to workers and ecosystems. Remediation practices such as soil removal disrupt ecosystems, which take decades to recover. Without further human disturbances, and with low levels of exposure to stress-ors, ecosystems can recover from physical disruptions and spills.

Remediation to remove negligible risk to humans can destroy delicate ecosystems for very little gain in public health.

SOCIETY MUST INCREASINGLY deal with the effects of chemical, radiological, biological, and physical stresses (in the form of a destructive event or occurrence)—both natural and human influenced—on ecosystems, and the public, scientists, managers, and policymakers are required to determine how to manage, remediate, or restore damaged ecosystems. These stresses have increased in magnitude and frequency since the Industrial Revolution. Some nations developed weapons of mass destruction, such as chemical and nuclear weapons, which has led to extensive contamination of the land and water around the factories that produced such weapons. However, sufficient time since the contamination occurred has now passed so that adjustments in species assemblages or community structure and the persistence of organisms in the face of contamination have resulted in the maintenance of a substantial portion of these degraded ecosystems.

In more recent times, the threat of potential stressors has increased, particularly those involving nonmilitary terrorism, which could be directed at nuclear or chemical facilities. For example, nuclear weapons plants and chemical factories could be bombed, unleashing radiation and toxic chemicals into surrounding communities, or chemicals could be deliberately released during transport.

Decisions on what methods to use and how much of the damaged ecosystem to remediate or restore and to what condition involve trade-offs in several domains, including public health, worker health, and ecological health. In recent years, remediation, restoration, and management of ecosystems have evolved as methods of dealing with the risks from stressors,1^–4 and examples from the US Department of Energy’s (DOE’s) nuclear weapons sites can help define the issues.

I provide conceptual models for the relations between stressor events, natural ecosystem recovery, and remediation and restoration; examine the possible tradeoffs between ecological and human health risks; and use examples from the DOE’s nuclear weapons complex to explore what could happen to ecological health when we remediate contaminated sites solely on the basis of human health. I argue that (1) ecosystems can undergo natural recovery (resiliency) from degradation caused by stressors, such as physical disruptions or waste from producing weapons of mass destruction, but remediation itself provides an additional stressor for functioning ecosystems; (2) physical remediation itself can cause lasting and irreversible damage to natural ecosystems; (3) remediation, when the human health risk is relatively low, can cause more damage to ecological systems than is warranted by any incremental reduction in the public health risk; and (4) lessons from the DOE complex indicate that valuable, rare, and unique ecosystems can be present in regions with some exposure to chemicals or radionuclides, and remediation to remove pollutants can stress valuable ecosystems more than leaving minor contamination in place.

Remediation of contaminated sites is a national priority in the United States and elsewhere, within a framework of protecting humans and the environment, now and in the future.5 There are many different ethical dimensions of sustainable and long-term management of contaminated areas, including public trust and the trade-offs between human health and the environment.6^–8

VULNERABILITIES TO STRESSORS AND REMEDIATION

Ecosystems are composed of the physical environment and a wide range of species, including plants, animals, and microorganisms. All levels of biological organization (organisms, populations, communities, ecosystems, landscapes) are vulnerable to chemical, radiological, biological, and physical stressors. Species and species assemblages, however, evolved with stressors and have mechanisms for adapting, although not necessarily to rapid or massive human-induced stressors. Nonetheless, the adaptive mechanisms that allow species to cope with natural stressors (for example, intrinsic genetic variability) allow many species to recover eventually from anthropogenic stressors. There are 3 types of adaptation to disturbances: adaptations of species to disturbances through natural selection (a long process), adaptation to disturbances because of the plastic behavior of individuals, and adaptations involving adjustments of assemblage structure and function. An example of the latter would be a switch in prey type because the preferred prey was eliminated or decreased because of a disturbance (such as a storm or chemical). The latter 2 responses may preserve ecosystem health in the face of disturbances. Thus, some natural recovery is possible following the occurrence of any stressor or disaster. For example, the devastation of a natural fire is similar to that of a fire following bombings, and ecosystems can usually recover in both cases.

A distinction should be made between ecosystem health and ecosystem integrity. Although ecologists can argue about the meanings of each, ecosystem health generally refers to the services that an ecosystem provides to humans (e.g., clean air and water, species diversity), and ecosystem integrity refers to the possession of structure and function approximating an undisturbed ecosystem. Both can be endpoints of remediation and restoration. Remediation normally refers to removing contamination, and restoration involves the enhancement or reconstruction of functioning ecosystems, possibly including creating wetlands, adding plantings, and reintroducing wildlife.

Conceptually and simplistically, ecosystems (and the species and populations within them) experience some degradation in response to a wide range of stressors, both natural and anthropogenic (Figure 1 ▶). Remediation of contaminated soil may entail the removal of large amounts of soil and the replacement with a soil type not necessarily suited to the original ecosystem. Full recovery after soil removal is severely hampered because of the removal of the seed bank that would germinate and restore the original ecosystem. The degree of degradation depends on the vulnerability of the species composing that ecosystem; deleterious effects in some organisms have a greater effect on overall ecosystem integrity than do others. For example, in the northeastern United States, gypsy moths, which devastate hardwood trees, can have a greater effect on forest health than would an insect that affects a ground cover species, because the hardwoods are the dominant species.

FIGURE 1—

Schematic of degradation caused by any stressor, natural recovery that occurs in the absence of additional stressors, and the degradation that can follow physical remediation. …Note. The trajectory of recovery depends on the degree of physical degradation, the amount and kind of remediation, and the amount and kind of restoration.

With time, ecosystems and individual species begin to recover; given enough time, the same or a similar ecosystem can develop. The time to recover depends partly on the strength of the stressor, whether there are multiple stressors, and individual species effects. Physical remediation, however, has the potential to cause additional degradation, particularly if soil is removed, habitat is destroyed (e.g., “capping,” or the placement of an impermeable covering over the contamination), and roads are built into the habitat (Figure 1 ▶). Roads allow nuisance, exotic, and introduced species to move into intact habitats. Many neotropical migrants breed only in interior forests, and roads through these forests eliminate these species.

Whether species can recover from remediation depends on the type of remediation as well as on the species. Many environmental engineers and planners consider remediation to be the removal of the contaminant, which then destroys the physical and biological components of an ecosystem. Some forms of remediation can preclude natural recovery, e.g., the deep removal of surface soil that eliminates the seed bank, capping to prevent invasion of native plants, and the destruction of the surrounding environment, which could otherwise provide seeds or other propagules from which new plants would grow and thereby allow animals to move into the remediated region. With some forms of remediation, such as soil removal or capping, the native ecosystem may not recover or recovery may require decades or centuries.

Natural recovery following remediation occurs when the physical and biological environments provide sufficient structure for normal ecosystem functioning. If soil and seed banks remain, natural recovery will be quicker (Figure 2 ▶). Likewise, restoration of the physical environment (e.g., when ponds, marshes, and streams are constructed) will accelerate recovery. Biological restoration, the reintroduction of plants and animals, is emerging as a relatively new science that can both enhance the environment and reduce recovery time dramatically.2^,3

FIGURE 2—

Schematic of recovery following physical remediation (e.g., soil removal, capping), which depends on the kinds and type of physical and biological restoration.

Restoration is often beyond the scope of remediation that is aimed at the removal of a chemical or radionuclide to reduce risk to humans. However, the public, managers, and policymakers need to consider that restoration is to ecological health what building houses, schools, roads, and businesses is to community health. In New Orleans after the hurricane, for example, the public and politicians would not consider the city rebuilt if the physical environment was clean but devoid of human habitation. Similarly, ecosystems are not rebuilt simply by removing contamination from the soil. Finally, humans and other organisms (i.e., the “receptors”) differ in that a risk to humans can be eliminated by physical blocks to the exposure pathway, but this is not true for nonhuman biota that reside permanently in the area (Figure 3 ▶).

FIGURE 3—

Differences between risk reduction that is possible for humans and ecological receptors following chemical, radiological, physical, or biological stresses.

RISK BALANCING

Although there is general agreement among the public, scientists, public health officials, and policymakers that some remediation should follow ecosystem degradation and contamination, there is less agreement about the strategy for such cleanup with respect to the role of risk to humans and the environment and the effect of planned future land uses on cleanup decisions.9 The stressor event, remediation, and the aftermath of the event present health risks for humans and the ecosystem. The magnitude of that risk, however, varies considerably with the type, magnitude, and severity of the stressor.

The stressor event itself can initially cause an increase in risk to ecosystem health and to public health (Figure 4 ▶). Ecological health initially declines because of the physical disruption and then increases when disruption ceases and plants can grow. The stress may initially be greater to the ecosystem than to human health because it sustains damage from both physical disruption and chemical, radiological, or biological contamination. Although people can be similarly affected by the latter factors, physical disruption may cause people to leave but does not usually eliminate their populations, although atomic bomb blasts and chemical disasters such as the one in Bhopal, India, have devastating direct human impacts. People do not usually die when there is a ground-level chemical spill, although toxic fumes can result in devastation (e.g., as in the spill at Bhopal). Animals, however, may remain in the area and experience continued exposure to the chemicals or radionuclides. Oil spills are a prime example; people simply evacuate an area, but plants and animals become oiled and die or suffer chronic exposure and sublethal effects.

FIGURE 4—

Health risk to workers, the public, and ecosystems following a stressor event and remediation, which is usually undertaken to reduce the risk to public health but may greatly increase the risk to ecosystems. …Note. The dashed vertical line indicates the end of remediation.

Remediation of hazardous chemical and radioactive waste sites poses an ongoing risk to remediation and support workers.10 The risk to workers may also increase with time, because some environmentally caused diseases (e.g., cancers) have a long latency. Ecological systems may also show long-lasting and irreversible effects (Figure 4 ▶) from ecosystem disruptions or elimination caused by road building, soil removal, capping, human disturbance, and the introduction of disease and invasive species. Because the goal of remediation is usually to reduce the risk to human health, such measures do not usually adversely affect public health during or after the process. Instead, remediated lands can then be used for a variety of industrial or residential purposes or for ecological preserves.11^,12

In many cases, the small reduction in risk to public health may not be reasonable given the greatly increased risk to workers and the ecosystem. The issue of remediation following disturbances, such as nuclear accidents, is of considerable importance in both Europe and the United States,13^–16 and such evaluations usually involve assessment of environmental impacts.17^–18 When managers consider the value of unique and functioning ecosystems, it may be more prudent, more cost effective, and a wiser use of the environment to make such lands nature reserves.18 This may be particularly true where the contaminant (e.g., many complex organic compounds and some radionuclides) degrades or decays over time, reducing the risk to humans and the environment within the time frame of a human generation.

REMEDIATION, COMANAGEMENT, AND RESTORATION

At the end of the Cold War, when nuclear weapons production in the United States ended (1989), the DOE redefined its mission to include environmental remediation and restoration and the protection of ecological resources (including the plants and animals composing ecosystems).4^,12^,19 Nonetheless, protecting ecological resources was not part of the remediation process, even though many DOE lands were ecologically valuable.12^,20^–22 The nature of physical disruption and human disturbance on many DOE sites is similar to that of other degraded ecosystems, but the extent, severity, and type of chemical and radiological contamination on DOE sites are distinctive. DOE sites have highly toxic and long-lived radiological wastes in storage facilities and as surface and groundwater contamination. This limits the types of remediation that are possible and involves high remediation costs, with long-term care of wastes in cases in which remediation costs are prohibitive, transportation is difficult, or remediation technology does not exist.5

Difficult issues resulting from the DOE cold war legacy include determining levels, methods, and time frames for remediation and restoration and determining future land uses within the framework of what is legally, logistically, and economically feasible while incorporating the diverse views and values of stakeholders. Some of these same issues will follow any large-scale assaults with weapons of mass destruction. Seminal questions will include how much land to remediate, what risk level to remediate it to (whether all or only some contamination should be removed), and how much risk workers should be exposed to during remediation to reduce the risk (sometimes very minor) to the general public. Clearly, significant risks to human health and the environment must be dealt with.

The DOE established large buffer areas around its industrial facilities primarily for security reasons to protect the secrecy of the nuclear programs. These buffer lands have been left undisturbed for more than 50 years. The levels of radioactivity within intact ecosystems on the buffer lands are generally low; the risk is mainly from nuclear waste storage facilities, such as tanks, pits, and buildings. Because humans have been protected from risk by barriers to exposure, removal of the radionuclides from buffer lands would serve mainly to destroy intact ecosystems.

The DOE deals with the questions of remediation effects in part by developing long-term stewardship programs,23 with the goal of achieving sustainable development through ecosystem management of valuable national resources.22 The policy required the integration of economic, ecological, social, and cultural factors into land use decisions. Cost estimates for cleanup to residential standards were astronomical,15^,24 worker health and safety risks were great, and suitable technologies for safe, permanent, and cost-effective remediation were not available. This led the DOE to develop a risk-based approach to cleanup and future land use.25^,26 Not all land should be used for residential purposes, and some land at the large DOE sites may be best used as ecological reserves.11^,12^,20^,21 As Whicker et al. note, the DOE should avoid remediation that destroys functioning ecosystems.15

Even though some DOE lands are contaminated, the 2.54 million acres of DOE land are of considerable ecological value.21 Approximately 79% of this land served as security buffers for the nuclear production facilities, and much of it has little or no contamination.24 The buffer areas now hold some of the finest and least-disturbed plant and animal habitats in the United States.11^,12^,20^,21^,27 The ecological importance of 7 of the largest DOE sites has been recognized through their designation as National Environmental Research Parks.18^,19

The DOE has several options for dealing with risk at contaminated sites: (1) to remediate to some predetermined human health risk (e.g., to residential standards), regardless of ecological risk; (2) to remediate to reduce human health risk while minimizing ecological health risk; and (3) to remediate or act to reduce and minimize both ecological and human health risk. Although the third option may seem similar to the second, the emphasis differs substantially. The third choice may be preferred, especially when the risk to humans is low or can be eliminated by barriers to exposure. At many DOE sites, reducing the risk to human health was accomplished with exposure barriers or education because physical remediation would destroy valuable ecosystems.

At the Savannah River Site (SRS) in South Carolina, mercury contamination in the Savannah River posed a risk to people who consumed a large amount of fish.28 Although some mercury contamination of rivers and streams is caused by atmospheric deposition, DOE operations resulted in much higher levels on SRS lands than in nearby habitats. Levels in Steel Creek on SRS, in the surrounding habitats, and in the fish are much higher than in upstream waters. Although the mercury contamination could have been dealt with by sediment removal from Steel Creek or from the Savannah River itself, the cost would have been high. Steel Creek and its associated wetlands are not unduly impaired ecologically; they function appropriately and provide valuable habitat for fish and wildlife, and species diversity is high.

Large-scale removal of sediment from Steel Creek would have severely damaged the intact and valuable ecosystem, and educational efforts to limit the consumption of fish caught from the Savannah River near SRS was deemed a more reasonable strategy for reduction of human health risk, protection of the ecosystem, and cost effectiveness.28 A targeted effort to provide fishermen and their families with the necessary information for high-risk individuals (e.g., pregnant women or women of childbearing age) to limit consumption of fish with high levels of mercury was deemed a more appropriate action than ecosystem destruction by soil removal. This effort entailed collecting information on contaminants in fish and fish consumption patterns, computing risk from fish consumption, and designing a fish fact sheet for fishermen and their families.29^–31 This intervention was preferable to sediment removal and the destruction of the Steel Creek ecosystem by remediation that might not have reduced the risk from mercury in fish.

Similarly, at Brookhaven National Laboratory, the corrective action to reduce mercury exposure from fish consumption included educational and outreach efforts.32 Dealing with mercury in aquatic environments is also partly a matter of evaluating whether the reduction in mercury in fish caused by soil removal or other remediation is offset by continued atmospheric deposition. Achieving further reductions in mercury in lakes and other bodies of water in some geographical regions may require reducing the sources that contribute to mercury in the atmosphere.

Par Pond, an old nuclear reactor cooling pond on SRS, is maintained with a dam. The sediment of Par Pond is contaminated with ¹³⁷Cs. Exposure by draining would entail risk to humans and to wildlife that might migrate from the pond, and the exposed soil would require remediation.26 Drainage and remediation would destroy valuable fish and wildlife populations, which are flourishing. The only risk Par Pond could pose to humans would be from fish consumption, but because Par Pond is within a restricted region of SRS, human exposure is blocked. Further, the local people all know that the fish in Par Pond are “hot,” and they avoid eating them.

At some DOE sites, remediation itself might cause damage not only to the places being remediated but also to surrounding intact ecosystems. For example, much of the wind-dispersed plutonium contamination of soil at Rocky Flats resulted from soil disturbance during previous remediation and not from contaminated soil left in place.26 Animals displaced from remediated sites can move into nearby habitats, carrying contamination with them. For example, demolition of a nuclear reactor at the Idaho National Laboratory was halted because displaced rattlesnakes entered the buildings and became contaminated.

The choice of whether to remediate or maintain these contaminated habitats as ecological preserves may be similar following terrorist actions, whether they are of a physical, biological, chemical, or radiological nature. Where the risks to human health are small or can be contained by barriers (physical or educational; Figure 3 ▶), it may be prudent to protect and maintain intact and valuable ecosystems without physical remediation that could destroy rather than protect them.

LESSONS FOR PUBLIC HEALTH

Public health officials will increasingly be faced with intentional assaults on society’s health and well-being, whether from chemical, radiological, or biological weapons of mass destruction or the legacy of our chemical and nuclear weapons plants. Although the immediate threat to human health will be the greatest concern, eventually society must make decisions about the cleanup and disposition of contaminated land. It is at this point that risk-balancing decisions are required, such as whether the risk to public health is worth the risk to the welfare of workers and to ecological integrity caused by remediation; what level of remediation is optimal for lowering the risk to workers, ecosystems, and public health; when the value of a functioning (but slightly impaired) ecosystem is greater than the resulting lessening of risk to public health; when physical and biological restoration is essential; and how much and what type of physical and biological restoration society can support and sustain.

The answers to these questions depend in part on the severity of the risk, our ability to contain or isolate the risk, the potential natural attenuation (e.g., the risks from cesium will be largely gone in 300 years because of natural decay), and the value of the land for human development or as ecological reserves. Public health officials, as well as the public and managers of the land, are faced with these challenges following weapons production, accidental releases (e.g., Chernobyl, Bhopal), and militaristic or terrorist events.