Environ. Sci. Technol. 2011, 45, 45–50
Tracking Toxicants: Toward a Life Cycle Aware Risk Assessment† B R A N D O N K U C Z E N S K I * ,‡ ROLAND GEYER‡ BOB BOUGHTON§ Department of Environmental Science and Management, University of California, Santa Barbara, California, USA, and Department of Toxic Substances Control, California Environmental Protection Agency, Sacramento, California, USA
paper, when we refer to “toxic substances” we include chemicals that meet any of these criteria. The principles of green chemistry and the precautionary principle encourage manufacturers and regulators to minimize the generation and use of toxic substances and seek safer alternatives (3, 4). In addition, the public should have access to information about toxic substances in products so that businesses and consumers can make informed purchasing decisions. This includes evaluating the safety of chemicals whose harmful properties are unknown. We argue that these goals would be advanced if flows of toxic substances were examined using a “life cycle perspective”, from chemical manufacture to product disposal. In this paper we explain how chemical risk assessments can be made “life cycle aware” by incorporating the process flow model of life cycle assessment (LCA) into the analysis of risk.
Managing Risks
† This manuscript is part of the Environmental Policy: Past, Present, and Future Special Issue. * Corresponding author e-mail:
[email protected]; phone: +1 805 893-5058; fax: +1 805 893-7612. ‡ University of California, Santa Barbara. § California DTSC.
Society has long recognized the need to monitor the use of harmful substances to ensure the health and safety of the public and the environment. Current chemical regulatory policies in the U.S. and Europe emphasize the assessment of risks presented by chemical use. When a human or organism comes into contact with a harmful chemical, there is a chance that the chemical will have some adverse effect. The adverse effect is understood to come from an inherent property of the chemical, dubbed a “hazard trait”. Risk is a function of the severity of the hazard trait and the level of likely exposure. Risk assessment (RA) is the process of making quantitative estimates about the likelihood of adverse effects occurring under a specific exposure scenario. If the risk is too great, risk management practices may be necessary, such as the use of safety equipment by workers or the treatment of wastewater before it is released into the environment. Since each RA is performed under a specific exposure scenario, the full “risk profile” of a chemical only emerges after compiling numerous RAs from throughout its life cycle. An example can be found in the Risk Assessment Reports (RARs) in the European chemical substances Information System (ESIS), a freely accessible database of chemical information (5). These reports provide a summary of the results of individual RAs reported by industry to European chemicals authorities. Risks are characterized in terms of a risk ratio, which relates the expected level of exposure to an exposure level considered to be “safe”. When the risk ratio is greater than 1, there is cause for concern that the expected exposure may exceed this safe threshold. Figure 1 shows the results of risk characterization for dibutyl phthalate (DBP), a plasticizer, as an illustrative example (data from ref 6). ESIS represents the state of the art in compiling public information about chemical risks. However, in many cases, particularly for low-volume chemicals, there is no information publicly available about chemical risks and few regulatory requirements to provide information. RA results that are available remain highly technical, putting them out of the reach of product designers and the general public. The risk paradigm also has other shortcomings. It is costly to
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Introduction Industrial chemistry provides the foundation for virtually all modern production and manufacturing. From synthetic textiles and polymers to semiconductor fabrication to intensive agriculture, synthetic chemicals now pervade the industrial world and are dispersed throughout nature. The U.S. chemical industry produced or imported over 11.8 billion tonnes of chemicals in 2006 (1), and in so doing consumed roughly a quarter of all U.S. manufacturing energy (2). As chemicals are integral to so many aspects of modern society, involvement of the chemical industry is crucial to the success of any national-scale project to promote sustainable production and consumption. Some chemicals have properties that make them dangerous to humans or the environment. Chemicals are generally regarded as “toxic” if they are deleterious to the health of humans, animals, and/or plants. Effects in addition to acute and immediate harm may include cancer, mutations, reproductive damage, birth defects, and endocrine disruption. Chemicals are “persistent” if they remain in the environment for long periods of time, and “bioaccumulative” if they cannot be broken down by metabolic pathways or flushed from the body. Often bioaccumulative substances are taken up by small organisms and work their way up the food chain until they are ingested by top predators, such as humans. In this
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FIGURE 1. Risk characterization results for dibutyl phthalate (CAS 84-74-2), reported in ref 6. Risks are reported as a ratio of expected to threshold concentrations. A ratio of greater than 1 indicates concern. For environmental effects, the authors of 6 state the risk ratio in terms of Predicted Environmental Concentration (PEC) over Predicted No Effect Concentration (PNEC). For human health effects, the risk ratio is minimal Margin of Safety (MOS) over expected margin of safety. All risks assume a worst-case approach. For consumer exposure, no minimal MOS was reported; a value of 80 was assumed. implement, because of extensive requirements for empirical data, and subject to uncertainties in both the nature and degree of possible effects (7). Laboratory testing does not always resolve controversies regarding toxicity potentials (8). The analysis of risks is also confounded by the question of what constitutes a tolerable or “reasonable” level of risksthe answer often relies on a value judgment by analysts or regulators (9, 10). RAs based on empirical studies face difficulty in addressing nonlinear dose responses (11) and may not be designed to capture certain harmful conditions such as chronic low-level exposure or the synergistic effects of multiple stressors (12). Recent developments in mechanistic toxicology have the potential to address some of these issues through improved understanding of the molecular drivers of toxicity (13). Critics also contend that the exclusive attention to risk diverts resources that could be used to investigate possible safer alternatives to problematic designs or pursue other pollution-prevention measures (4, 14). Calls have been made for a more comprehensive mode of chemical safety evaluation which considers a broader array of threats and relies less on quantitative models of environmental damage (15, 16). Safety is typically defined as the 46
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differential between likely exposure and the amount necessary to cause adverse effects. A more integrative framework is needed to understand and monitor systemic risks to the public and to ecosystems (17, 18). Chemical safety evaluation shouldnotbelimitedtoassessingtoxicityhazard,dose-response, and exposure in order to determine whether specific risks are reasonable. Rather, RA methods should be complemented by green chemistry principles and a focus on the inherent characteristics of chemicals, their uses, and their manufacturing processes, with an aim to avoid unnecessary risks (3, 19, 20). The gaps in our understanding of uncertainties in assessing toxic risks, such as threats associated with chronic exposure or multiple independent stressors, call for a more precautionary stance than RA alone provides (7, 21, 22). While the risk paradigm is vital for determining unsafe levels of exposure to chemicals, practical difficulties in implementation combined with substantial uncertainties suggest that risk alone is not sufficient to manage the toxic effects of chemicals. In the next section we describe how product life cycle modeling can be used to place RAs in context, leading to a better understanding of the flow of toxic substances through the economy.
FIGURE 2. (a) Model of a unit process for life cycle assessment. (b) Relationship between a unit process and potential exposure scenarios to a toxic substance.
A Life Cycle Perspective The industrial world is gradually becoming concerned with the impacts it has on the natural world and on how those impacts affect human and ecological health. When considering environmental health, the adoption of a “life cycle perspective” for industrial production and consumption is increasingly prevalent. In essence, a life cycle perspective means an awareness of the material flows associated with a given product system, from the extraction of raw materials through the use of the product, to the disposal of wastes, as well as the fuels, electricity, chemicals, and infrastructure required along the way. This is formalized in LCA, a methodology for quantifying the environmental impacts of products and services (23, 24). At its core is a model of industrial production as a network of “unit processes” which take in resources, energy, and materials and put out products, emissions, and wastes. Figure 2a shows a schematic representation of a unit process. In an LCA, many such processes would be linked together to model the life cycle of a product. Use-phase assumptions and the selection of which processes to include or exclude can have a profound effect on the outcome of the analysis. LCA and RA are highly complementary (25), and numerous efforts have been made to bridge the two approaches (26-28). RA focuses on a specific scenario of exposure to a certain substance and uses detailed modeling of substance-specific uptake mechanisms (e.g., inhalation, ingestion) to evaluate the threat posed. LCA, on the other hand, combines many spatially and temporally diverse emissions into a few impact scores. Discussions of the potential role of LCA in developing chemicals policy suggest that LCA may be useful for screening or priority-setting in advance of RA (29) or as a decision support tool for risk reduction (30). Figure 2b shows how exposure scenarios which may be modeled in RA relate to the activity described by a unit process. If a process requires an input which is itself toxic or which contains a toxic substance, then that process carries the risk of exposure. Workers operating the process may be exposed to the substance, or the substance may be present in the product, industrial byproducts, or environmental releases. Any of these sources of exposure may warrant an RA. When an RA is conducted, it is necessary to make a number of assumptions about a specific exposure scenario to model the likely dose and effects. The results of an RA are thus highly dependent on the unit process with which the exposure is associated. Often the main area of interest for combining LCA and RA is in impact assessment, where the aggregated impacts of material flows are characterized. This makes sense in terms of developing technical compatibility between the two methodologies. However, it effectively narrows the scope of LCA to impact assessment alone. It thus omits the significant
aspect of LCA that distinguishes it from RA, namely its focus on a product system and its reference to a unit of service delivered to a customer (25). It also ignores the processspecific nature of RA. Risks should be regarded as a property of a specific industrial process or product use, and not as a system-wide impact metric. In other words, risk information should be integrated into the product system modeling stage of LCA as well as the impact assessment stage. We propose that RAs be made “life cycle aware” by describing them in terms of specific unit processes. Essentially, RA data could be supplemented with basic metadata about the assessment: which process led to the exposure scenario being modeled? What is the product of that process? Looking upstream in the process flow, what is the source of the toxic substance? Looking downstream, what happens to the toxic substance after use? Is it contained within the product? If so, what happens at the end of the product’s life? Similarly, LCA could be made “toxics aware” by describing explicitly the toxics content of “intermediate flows”sthe flows between processes. Current LCA practice generally involves the characterization of flows emitted into the environment, but flows used in manufacturing processes are often ignored. Substances used in manufacturing may have known hazard traits that could be included in life cycle models. Processes that take those flows as inputs (or produce them as outputs) may have RA information available that a product life cycle analyst could locate and incorporate into the analysis. The use of a toxic substance in a process indicates that the substance may be released into the environment and should be included in an emission inventory. If a product contains a substance with a hazard trait, potential consumers have a right to know. RA data such as hazard traits and exposure scenarios could easily be put into an LCA-compatible form and included in process inventory data without compromising the confidentiality of proprietary information. This could eventually lead to a “joint inventory database” as suggested by Christensen and Olsen (30). While we believe that siginificant amounts of toxicity information could be shared without competitive concerns, conflicts are likely and may have to be resolved in dialogue with industry. Organizing and sharing RA data on a process flow basis would provide support for pollution prevention, product safety regulation, and public health. Specifically, we see four potential benefits from this approach. First, it would allow for the distributed development of a database to track flows of toxic materials through the economy. Hazard traits and RA results for products in commerce could be made available to the public without divulging confidential information. Each party might report only on products (intermediate flows) for which it is responsible, and reports from different parties (i.e., a manufacturer and its suppliers) could be integrated within VOL. 45, NO. 1, 2011 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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the process flow model. This minimizes the data-collection burden on any one actor in the product chain. Second, it would introduce a framework for productoriented toxic flow modeling. While LCA has been effective at modeling resource requirements and global environmental impacts, it has been less effective at characterizing regional and local threats to human and environmental health. If toxicity information were attached to intermediate flows, LCA practitioners could incorporate toxicity data into their inventory models where appropriate. Better integration of toxicity data into process models would allow LCA practitioners to understand the dangers associated with specific product systems or manufacturing techniques, not just with specific chemicals or emissions. Risk information from multiple chemicals involved in a product could be linked together. Third, relating toxicity information to unit processes would support pollution prevention efforts, including the systematic search for safer alternatives, by establishing a relationship between the use of a toxic chemical and the function of a product system. LCA is based on modeling a functional unit of service delivered to a customer. If an intermediate flow featuring toxicity information were used in an LCA, it would link the use of that chemical (and any associated risk data) to the product’s function. It may be possible to find an alternative approach which does not require the chemical in question. This is in line with the principles of green chemistry (3). Finally, it would facilitate the dissemination of risk information to a broader range of researchers, technicians, regulators, and the public. The process flow model is a powerful metaphor, providing an easily intelligible mapping between industrial activity and individual consumption. This quality of understanding is typified by the Risk Assessment Reports available for some chemicals in ESIS (mentioned above), which already include information about risks at every life cycle stage when data are available. Making the connection between RA and process flow modeling explicit would establish a foundation on which a cross-disciplinary and distributed effort at product safety evaluation can be pursued, encompassing and integrating chemical RA, life cycle impact assessment, resource management, and public health.
Process-Specific Toxicity Information Risks to workers, consumers, and the environment are encountered at multiple points in a product life cycle, and they may be assessed in different ways by different firms. Companies operating in different jurisdictions may face different reporting requirements from environmental authorities. The process flow model of the product system provides a framework for integrating these disparate reports. Process-specific toxicity inventories from different reporters can be immediately combined with one another to build an account of the flow of toxic materials involved with a specific product. In this way the burden of identifying and evaluating toxicity is distributed broadly throughout the supply chain to the parties with knowledge of the specific processes involved. Different companies that use similar materials can pool their efforts to develop a comprehensive portfolio of hazards and risks. Public agencies, nongovernmental organizations, researchers, and consultants can collect toxicity data from different sources and use the process flow model to identify gaps in data or regulatory coverage, advocate for safer policies, or advise companies on reducing their use of toxic substances. Figure 3 presents a hypothetical life cycle toxicity inventory for a soft plastic child’s toy made of poly(vinyl chloride) (PVC) and containing DBP as a plasticizer. The manufacturer of DBP assesses the hazard characteristics of its product, as 48
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well as the risks associated with emissions of the chemical to the environment around its manufacturing facility. It also wishes to report the risks of environmental contamination regarding its product’s end-of-life. The second reporter, a toy manufacturer, may have no knowledge of the ecological risks associated with DBP manufacture; however, it does assess and report the occupational risks to its manufacturing employees and the risks to the consumers of its products. Manufacture of the toy may involve multiple toxic substances. A third reporter, a public agency overseeing toxics use, estimates the risks the product presents to consumers during use and after disposal. The aggregate information may be most useful if it were organized and maintained, perhaps by a research organization or other independent third party.
Development of Safer Alternatives One common aim of many pollution prevention strategies is the development of alternatives to the use of toxic chemicals. “Alternatives” may include substitution of the toxic chemical with something less hazardous; some change in the manufacturing process leading to reduced use, exposure, or release of the chemical; or some broader change in the process or redesign of the product which reduces or eliminates the need for the chemical in the first place (31). A variety of methodological frameworks for alternatives development have been produced, with two examples being the U.S. EPA’s Cleaner Technologies Substitutes Assessment (CTSA) (32) and the Alternatives Assessment Framework of the Lowell Center for Sustainable Production (33). CTSA, a product of the EPA’s Design for Environment (DfE) program, is predicated on a search for alternatives to a process that presents risks. The DfE program led to a number of industry collaborations with formulators and manufacturers to reduce the use of toxic substances (34). In contrast, the Lowell framework looks at the end-use function of the product system in question, emphasizing the potential for innovation, pollution prevention, and multirisk reduction by finding alternative means to fulfill an equivalent function to the product under study. The strategy underlying the Lowell center framework is embodied in the landmark “Five Chemicals” alternatives assessment study performed by the Massachusetts Toxics Use Reduction Institute (35). A life cycle perspective on toxic chemical use enables the development of safer alternatives while informing analysts of potential trade-offs and unforeseen consequences of alternative designs. The ability of process-specific RAs to lead to the development of safer alternatives is demonstrated by the CTSA case studies in electronics manufacture (36, 37). In both studies, safer alternatives to problematic processes were identified. As another example, Neto et al. (38) created an inventory of options for pollution reduction at a die casting plant. Their assessment began with a complete account of the different manufacturing processes that comprise the plant’s operations, and the pollution problems associated with each. On the other hand, Skak et al. (39) failed to identify any viable alternatives to chlorinated paraffin lubricants, which are used in certain high-pressure metal-forming operations. The results of their study suggest that in that case, use of the toxic chemicals can be avoided only by redesigning products so as not to require those particular forming operations.
Conclusion: Fostering “Hazard Literacy” We propose the incorporation of process flow information into “life cycle aware” RAs, enabling them to be situated in the broader context of industrial production and creating a facility for tracking the flow of toxic agents through the economy. The principle of process flow modeling from LCA has great potential for organizing knowledge about industrial
FIGURE 3. Modeling toxic flows in the life cycle of a child’s toy containing dibutyl phthalate (DBP) using risk and toxicity data reported by three hypothetical agents. Reporter 1 produces the chemical of concern. Reporter 2 manufactures the toy in question. Reporter 3 is a public agency which oversees the use of toxic substances. activities and for synthesizing information about the hazards inherent in products. Because hazard traits are properties of specific chemicals, it is appropriate for those properties to be tied to those chemicals in LCA, and for RA results to be tied to the processes which use them. This approach complements the risk paradigm and addresses several shortcomings. The question of whether a chemical is toxic or possesses a hazard trait is subject to far less uncertainty than the question of the maximum safe exposure to the chemical. Tracking toxicants through process flow modeling is thus more straightforward and less costly than assessing their risk, and can be done using existing knowledge. It allows both companies and individuals to seek safer alternatives and avoid unnecessary risks. In addition, it provides an integrative framework for studying toxic flows. As the public becomes more engaged with questions of environmental impact, human health, and resource sustainability, it is becoming clear that communication of risk and hazard information is vitally important in promoting toxics use reduction. Information on toxic substances is needed up and down the supply chain to send proper market signals. The approach we have outlined promises to advance this goal by spelling out the relationship between toxic substances and products in an intuitive way. As consumers become aware of the sources of toxicity and the way harmful chemicals relate to the products they buy, they will begin to develop a familiarity with their own exposure to toxics and
the opportunities to reduce exposuresa “hazard literacy” that could catalyze a widespread shift toward safer products. Brandon Kuczenski is a postdoctoral scholar at the University of California, Santa Barbara. He received his PhD in mechanical engineering from Carnegie Mellon University and now studies industrial ecology at UCSB’s Bren School of Environmental Science and Management. Roland Geyer is an Assistant Professor at the Bren School, where he uses life cycle assessment and other research methods to study pollution prevention strategies. Roland has a PhD in Engineering from the University of Surrey, UK, and a Masters in Physics from the Technical University Berlin in Germany. Bob Boughton is a Senior Engineer at the Department of Toxic Substances Control within California EPA. He leads a team developing alternatives assessment guidelines for the safer products regulations being developed under the Green Chemistry Initiative. He has an MS in Chemical Engineering and 25 years of environmental engineering experience.
Acknowledgments This work was funded by the Green Chemistry Initiative of the California Department of Toxic Substances Control, under contract 08-T3629 (http://www.dtsc.ca.gov).
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