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Confronting Unknown Planetary Boundary Threats from Chemical Pollution Linn M. Persson,*,†,‡ Magnus Breitholtz,‡ Ian T. Cousins,‡ Cynthia A. de Wit,‡ Matthew MacLeod,‡ and Michael S. McLachlan‡ †
Stockholm Environment Institute, Kräftriket 2B, Stockholm 10691, Sweden Department of Applied Environmental Sciences, Stockholm University, 10691 Stockholm, Sweden Nine planetary boundaries were identified by Rockström et al. They are climate change, ocean acidification, stratospheric ozone, global phosphorus and nitrogen cycles, atmospheric aerosol loading, freshwater use, land use change, biodiversity loss, and chemical pollution. For seven of these boundaries, quantitative measures and estimates of society’s margin of safety or exceedance with respect to the safe operating range were provided. Five of the nine planetary boundaries are governed by chemical agents: ozone depletion (halocarbons), climate change (CO2, CH4 and other climate-forcing agents), ocean acidification (CO2), the nitrogen and phosphorus cycles, and chemical pollution. Thus, it is clear that chemicals can have a variety of impacts on vital earth system processes. Rockström et al. proposed a set of planetary boundaries that The “chemical pollution” boundary is one of the two delimitate a “safe operating space for humanity”. One of the boundaries for which Rockström et al. provided no clear planetary boundaries is determined by “chemical pollution”, quantitative definition. Instead, several examples of possible however no clear definition was provided. Here, we propose parameters that might define a boundary were listed. This paper that there is no single chemical pollution planetary boundary, aims to identify the conditions that are required for chemicals but rather that many planetary boundary issues governed by to present a planetary boundary threat. We propose that chemical pollution exist. We identify three conditions that must “chemical pollution” is not a single category in the planetary be simultaneously met for chemical pollution to pose a boundary framework, but rather that many unknown planetary planetary boundary threat. We then discuss approaches to boundary issues governed by chemical agents may exist. With identify chemicals that could fulfill those conditions, and this perspective, it is clear that avoiding planetary boundary outline a proactive hazard identification strategy that considers problems caused by chemical agents requires the development long-range transport and the reversibility of chemical pollution. of a new, proactive, and global approach to identify and manage INTRODUCTION chemicals that are planetary boundary threats. 1 Rockströ m et al. introduced the concept of planetary IGNORANCE GIVES RISE TO PLANETARY boundaries that delimitate a “safe operating space for BOUNDARY THREATS humanity”. Human activities that result in exceedance of a planetary boundary disrupt the stable conditions known as the The global economy employs over 100 000 synthetic Holocene that supported human development during the past chemicals5 and introduces hundreds of new substances each 12 000 years, and threaten the viability of the Earth system. The year.6 There is thus a large potential for chemicals to impact history of human development is replete with examples of environmental quality and human well-being. In attempting to human activities causing detrimental, and in some cases confront the range of possible effects of chemicals released by catastrophic, impacts on the environment at local and regional human activities, a report from the European Environment scales.2,3 The planetary boundary concept emerged from a Agency7 provides an insightful categorization of assessment recognition that the current magnitude of human activity can challenges according to the degree of scientific certainty (Table lead to impacts at a planetary scale that threaten the vital earth 1). The distinction between assessment challenges that involve system processes that allow humanity to thrive. Rockström et characterization of risk versus confronting uncertainty or al. described these processes as the “biophysical processes of ignorance has direct implications for the type of policy the Earth System that determine the self-regulating capacity of response that is possible. When risks are unacceptably high, the planet”. A more detailed description is proposed by the measures can be taken to prevent or reduce the likelihood of International Geosphere-Biosphere Programme (IGBP): damage. When there is uncertainty, society may choose to act Earth’s interacting physical, chemical and biological processes on incomplete evidence and take actions motivated by including the land, oceans, atmosphere and poles, the planet’s natural cycles such as the carbon, water, nitrogen, phosphorus, Published: August 27, 2013 sulfur, and other cycles, deep Earth processes and life.4 ‡
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Condition 1 (C1). The Chemical or Mixture of Chemicals Has a Disruptive Effect on a Vital Earth System Process. As noted above, we presume that we are currently ignorant of this effect because in the absence of ignorance it would be managed based on risk characterization and uncertainty considerations (Table 1). The effect on an earth system process can be either direct or indirect, but it must have the potential to induce an impact of sufficient magnitude to disrupt the process. We note that recognizing such an effect can be difficult, as the nature of the effect or even the vital earth system process that it impacts may be something we have not imagined. Furthermore, drawing the line between an effect on a vital earth system process and a serious effect where the end point is not considered to be a vital earth system process may not always be straightforward. For instance, a pollutant that influences key biochemical processes resulting in an adverse impact on reproduction in a few species would probably not be considered a chemical planetary boundary concern. However, a large-scale reduction of biodiversity at the planetary level caused by chemical pollution would be considered a chemical planetary boundary crisis because biodiversity is considered a vital earth system process. In this example, it is not clear how to establish how many species can be lost or impacted before the overall biodiversity of the planet is considered threatened. Condition 2 (C2). The Disruptive Effect Is Not Discovered until It Is, Or Inevitably Will Become, A Problem at a Planetary Scale. Many currently unknown effects that have the potential to impact vital earth system processes will be discovered in the future. It is likely that many of these discoveries will be made before the effect has resulted in a significant planetary-scale impact. In this case we presume that society will take action to prevent transgression of a planetary boundary based on risk characterization or uncertainty considerations. The chemicals and associated effects of highest concern in this context are those for which the disruptive effects will not be discovered nor manifested until they occur on a planetary scale and are already impacting a vital earth system process. One can also imagine a problematic variant in which effects are manifested at the local or regional scale, but that the existing levels of pollution and the properties of the chemical already make it inevitable that the effects will also be manifested at the planetary scale. Condition 3 (C3). The Effects of the Pollutant in the Environment Cannot Be Readily Reversed. If a chemical pollution problem satisfies the first two conditions, that is, if a disruptive planetary-scale chemical impact on a vital earth system process is discovered, then society can still readily deal with the problem if it is possible to rapidly reduce the impact on the vital earth system. Generally, we anticipate that the impact could be mitigated by reducing the concentrations of the pollutant in the environment. The inability to readily reduce a pollutant’s levels in the environment thus greatly increases the possibility of a chemical or mixture of chemicals posing a planetary boundary threat. The reversibility of the pollution is a function both of the properties of the pollutant13 and of the spatial pattern of use and emissions. However, if the disruption of the earth system process has resulted in a regime shift, that is, a change to a new, stable state,12 then reducing pollutant levels will not be an effective strategy to mitigate the impact. In summary, chemical pollution planetary boundary threats that we must identify and avoid are characterized by currently unknown effects on vital earth system processes, likelihood that
Table 1. Risk, Uncertainty and Ignorance in the Assessment of Effects of Human Activities (Adapted From EEA7) scientific certainty
assessment challenge
high
characterizing risk uncertainty
medium low to zero
ignorance
characteristics of the assessment challenge the effects of an activity are associated with known impacts with known probabilities the effects of an activity have known impacts, but the probabilities of effects are unknown an activity has unknown effects and therefore unknown impacts with unknown probabilities
precaution. The case of ignorance is the most critical and problematic because finding the appropriate response is by far the most challenging.8 Most of the nine planetary boundary issues identified by Rockström et al. can be classified as problems that are currently governed by characterized risk or uncertainty as defined in Table 1. It is the knowledge of risk or uncertainty that allowed boundaries, albeit uncertain, to be defined. One virtue of the planetary boundary concept is that it provides a framework for highlighting important international environmental issues that can be confronted by management strategies tailored for risk or uncertainty, and it has proven useful in structuring the sociopolitical discourse required to address these issues.9,10 However, the planetary boundary concept has a second important virtue; it points society toward the need to confront the problem of planetary boundary issues that are governed by ignorance. The depletion of stratospheric ozone as a result of the production and release of halocarbons provides a clear, planetary-scale case study of an environmental impact that was initially characterized by ignorance.11 Nobody foresaw that the large-scale production, use and emission of the halocarbons would result in detrimental loss of the ozone layer in the stratosphere, and there was already a significant impact on this vital earth system before the effect was discovered. The planetary boundary concept demands that we strive to ensure that human activities do not result in interference with vital earth system processes that threaten the stable Holocenelike conditions on the planet. At the same time, logic and experience tell us that unknown planetary boundary issues likely exist. The poorly defined “chemical pollution” planetary boundary can therefore be viewed as a placeholder for all chemical pollution-related planetary boundary problems that we are currently ignorant about. We refer to such problems as planetary boundary threats. Below, we confront the challenge posed by chemical-related planetary boundary threats by providing an outline for the development of a global chemical management strategy that would allow society to better avoid them. Our strategy is not intended to replace existing hazard and risk assessment schemes for managing chemicals, but rather to supplement them. Our outline for a management strategy depends on understanding the conditions required for a chemical to pose a planetary boundary threat, developing criteria to identify chemicals that may fulfill those conditions, and acting proactively to mitigate potential threats.
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CONDITIONS FOR CHEMICAL POLLUTION TO POSE A PLANETARY BOUNDARY THREAT We propose that three conditions must be met simultaneously for a chemical or mixture of chemicals to pose a planetary boundary threat. 12620
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not effective warning flags, and including them could even lead to false negative assessments. Persistence and long-range transport hazard criteria are relevant to identify planetary boundary threats since they address parts of C2 (problem not discovered until it is a planetary scale issue) and C3 (difficult to reduce contaminant levels). The importance of persistence and long-range transport potential as hazard indicators for chemicals when effects are highly uncertain or unknown has already been discussed by Scheringer and Berg.14,18 However, in the planetary boundary context a nuanced application of these indicators is required. Chemicals that are not transported over long distances in the environment may nevertheless be planetary boundary threats if they are emitted on a planetary scale. For example, the pesticide DDT became a planetary scale problem primarily because emissions occurred all over the globe,19 and many modern chemicals of commerce such as phthalate esters used in plastics have emissions on the planetary scale due to the globalization of trade in chemicals and consumer products. On the other hand, chemicals that are subject to long-range transport may manifest their adverse effects at the local or regional scale well before a planetary scale problem develops, and thus not satisfy C2. Sulfur dioxide (SO2) as an agent of acid rain is an example of such a case.7 As for persistence, it addresses the reversibility of pollution for a chemical that is already in the natural environment (one aspect of C3), but does not address the reversibility of the emissions of chemicals, nor the case of a regime shift where impacts are irreversible even when concentrations of the chemical are reduced. Clearly there are situations in which the application of the P and LRT criteria to screen for chemical planetary boundary threats could lead to false positives or false negatives. The risk of false positives or negatives when using solely P and LRT as screening criteria for planetary boundary threats calls for additional criteria to be developed and considered in hazard identification. Gee8 proposed a set of precautionary actions that would help to avoid unacceptable chemical risks of which we are ignorant: 1. Screen for problematic intrinsic properties including persistence (P), bioaccumulation (B), and long-range transport (LRT) 2. Reduce exposure on the basis of credible early warnings 3. Limit technological monopolies such as those seen for asbestos, halocarbons and polychlorinated biphenyls in order to reduce risks 4. Use scenarios, long-term research and monitoring of surprise-sensitive sentinels. This list provides a point of departure for developing additional hazard assessment criteria and precautionary management strategies that are applicable to vital earth system processes and thus help to avoid planetary boundary problems. One of the precautionary actions suggested by Gee8 that complements P to partially address C3 is to limit the existence of technological monopolies for the economic services provided by the use of a certain chemical. When there are no ready substitutes for a chemical (or for the processes that emit a chemical into the environment) it will be more difficult to respond quickly to a planetary boundary problem by reducing the use of the chemical or eliminating emissions. The case of carbon dioxide emissions is a clear example of a neartechnological monopoly on many forms of energy generation leading to a slow and ineffective response to two planetary boundary problems where there are high degrees of scientific certainty. If the existence of the technological monopoly held by fossil fuel combustion had been recognized as a planetary boundary hazard, then management policies aimed at
these effects will not be discovered until the impacts are manifested at the planetary scale, and poor reversibility of the impact, which may be due to difficulty in reducing pollutant levels once the impacts are discovered (Figure 1). Chemicals
Figure 1. Conditions for chemical pollution to pose a planetary boundary threat.
that combine these characteristics will threaten the earth systems that allow humanity to thrive. Therefore, if we identify chemicals that may fulfill the three conditions, precautionary management should be employed.
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IDENTIFYING AND AVOIDING PLANETARY BOUNDARY THREATS The central challenge in identifying chemical-related planetary boundary threats is confronting and overcoming ignorance about the effects of chemical pollution. Given that the effects associated with a planetary boundary threat are per definition unknown (C1), such a threat cannot be identified using toxicity assessment or risk-based strategies. Instead, we can only assess whether a chemical or mixture of chemicals fulfills the other conditions for being a planetary boundary threat (C2 and C3), whereby the evaluation of C2 in particular is challenging in the face of ignorance about effects. A regulatory approach that confronts ignorance is to regulate chemicals based on hazard rather than risk, where hazard is the potential to cause harm, and risk is the probability of harm occurring.14−16 Forms of hazard assessment that are currently used in some chemical assessments include the PBT (persistent (P), bioaccumulative (B), and toxic (T)) and vPvB (very persistent, very bioaccumulative) classifications in the European REACH regulation17 and the definition of a persistent organic pollutant (POP) in the Stockholm Convention (persistent, bioaccumulative, toxic, and subject to long-range transport (LRT)). In all cases these hazard definitions require that a chemical exceeds a persistence threshold and at least one of the thresholds defined for B and T before it is considered for regulation. However, while persistence is related to C3 in Table 1, neither B nor T is relevant in the planetary boundary threat context. As noted above, since the effects are, per definition, unknown (C1) we cannot assume they are related to T. Clearly, toxicity only encompasses effects on a subset of vital earth system processes, since none of the four chemical planetary boundaries that were quantitatively defined by Rockström involve toxicity. Although the reversibility of bioaccumulation can be a factor affecting the reversibility of pollution (C3), the magnitude of bioaccumulation (i.e., the hazard criterion B) is not a factor that influences either C2 or C3. When end points are known and risk assessment is possible, both bioaccumulation and toxicity are important properties. However, in the specific context of defining screening criteria for chemicals posing a threat to earth system processes, these properties are 12621
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ACKNOWLEDGMENTS This work was financed by faculty funding from the Department of Applied Environmental Science, Stockholm University.
stimulating the development of alternative energy sources could have been pursued much earlier, and a more rapid transition away from fossil fuels would be possible in the face of the dual planetary boundary problems of climate change and ocean acidification. Indicators that address C1 (unwanted effect on a vital earth system process of which we are ignorant) are difficult to conceive, and may be impossible to develop. In the absence of indicators that can compensate for our ignorance, we concur with Gee8 that it is prudent to have continuous close monitoring of vital earth system processes and to attempt to identify relevant sentinels. Research is needed to understand how vital earth system processes function, how they might be disturbed by chemicals and what appropriate sentinels might be. The findings of this research should be an important component in a preventative management strategy. Based on these points of depature, we propose that there is a need to develop and implement a new hazard identification strategy that is linked to proactive policies designed to specifically address the challenge posed by unknown chemical-related planetary boundary issues. The system should be built to address the three conditions for chemical pollution to pose a planetary boundary threat that we defined above. There is existing scientific knowledge and regulatory experience to serve as a foundation for addressing many aspects of C2 and C3 using a weight-of-evidence approach that includes case-specific consideration of persistence, long-range transport, the geographical extent of emissions and the existence of technological monopolies. However, an improved scientific basis for developing effective hazard screening, monitoring and management options that will avoid transgressing planetary boundaries of which we are currently unaware is also needed. Confronting planetary boundary threats from chemical pollution is an important task; the costs of failure could be tremendous. Current chemical management practices do not address this issue and must therefore be complemented with new approaches. Meeting the challenge will require society’s willingness to take proactive and preventative actions to address planetary boundary threats, and then to react with decisive measures when a planetary boundary problem is discovered. We call for all stakeholders to actively engage and shoulder their responsibility. Industry has a particularly important role to play, for instance in evaluating the relevant intrinsic properties of the substances that they produce. The implementation of good management practice holds great challenges for all countries, but especially so for developing countries with weak institutions. Finally, scientists should seize upon the multidisciplinary challenges associated with confronting ignorance about the threats posed by chemicals to vital earth system processes and lead a dialogue on how these can be met in the soundest possible manner.
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REFERENCES
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AUTHOR INFORMATION
Corresponding Author
*(L.M.P.) Phone: +46-8-6747257; e-mail:
[email protected]. Notes
The authors declare no competing financial interest. 12622
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