Letter pubs.acs.org/est
Footprints and Safe Operation Space: Walk the Line?
P
osthuma et al.1 suggest and discuss the concept of a “chemical footprint”. It follows a trend toward footprinting in life-cycle based environmental assessments in general,2 and in particular of footprints revolving around toxicity impacts.3,4 There are two major concerns regarding their proposal: (1) the suggestion of the dilution approach, and (2) the lack of a time dimension. (1) The dilution approach to set thresholds is not only problematic concerning the setting of safe limits and their regional variation, as the authors point out, but it implies that there is a line between “good” and “bad” behavior and that a certain amount of pollution is acceptable. Different emissions have different impacts and hence LCA-based assessments might be more appropriate.4 Moreover, dealing with the combined effect of chemicals in mixtures becomes troublesome in distance-to-target approaches, since it is unclear whether the required dilution space would be additive or simply the highest calculated one. The benefits of such footprints compared to suggested LCA-based footprints2,4 are not evident. Consequent to the dilution approach with respect to a global carrying capacity is that it becomes more difficult to present uncertainties transparently, making the planetary boundary not a thin but a very broad line, as pointed out for the case of water consumption.5 As a result, we might appear to always be walking the line, almost independently of the level of pollution. In fact, given that the impacts of chemical emissions to water/ air/soil are so dependent on the highly variable local conditionsan issue LCA-based approaches are still trying to tackleone might argue that it makes little sense to set any planetary boundary at all.6 (2) The second, major concern has to do with the dynamics of the emissions and the persistence of chemicals. One of the strengths of LCA models is that concentration is integrated over time and therefore a distinction can be made between persistent and short-lived chemicals. One of the best known human-produced chemical (besides alcohol) is carbon dioxide (CO2). The carbon footprint and its related global warming potential might not be part of a chemical footprint (although CO2 constitutes a massively emitted chemical), but it serves as a nice example of how important time-integrals are for assessing impacts: the effects of methane (CH4) are much more relevant for carbon footprints if we consider a short time horizon, while CO2 is much more persistent in the atmosphere. For aggregation of the global warming effects, the integral is typically cut off after 100 years in LCA-based assessments. Likewise, when toxicity impacts are addressed, such assessments involve calculating the average residence time of emitted chemicals in an environmental compartment, meaning that substances with low effects occurring over a very long time might have a higher impact than those with high effects but a shorter lifetime. Such time-related impacts are lost when it comes to the chemical footprint. While a footprint might be more easily comprehended by citizens and policy-makers, it is crucial to take into © 2014 American Chemical Society
consideration the aforementioned drawbacks compared to LCA-based assessment methods.
Stephan Pfister* Catherine Raptis
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ETH Zurich, Institute of Environmental Engineering, 8093 Zurich, Switzerland
AUTHOR INFORMATION
Corresponding Author
*Phone: +41-44-633-75-71; fax: +41-44-633-10-61; e-mail: pfi
[email protected]. Notes
The authors declare no competing financial interest.
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REFERENCES
(1) Posthuma, L.; Bjørn, A.; Zijp, M. C.; Birkved, M.; Diamond, M. L.; et al. Beyond safe operating space: finding chemical footprinting feasible. Environ. Sci. Technol. 2014, 48, 6057−6059, DOI: 10.1021/ es501961k. (2) Ridoutt, B. G.; Pfister, S. Towards an integrated family of footprint indicators. J. Ind. Ecol. 2013, 17, 337−339, DOI: 10.1111/ jiec.12026. (3) Hitchcock, K.; Panko, J.; Scott, P. Incorporating chemical footprint reporting into social responsibility reporting. Integr. Environ. Assess. Manage. 2012, 8, 386−388, DOI: 10.1002/ieam.1288. (4) Sala, S.; Goralczyk, M. Chemical footprint: A methodological framework for bridging life cycle assessment and planetary boundaries for chemical pollution. Integr. Environ. Assess. Manage. 2013, 9, 623− 632, DOI: 10.1002/ieam.1471. (5) Gerten, D.; Hoff, H.; Rockström, J.; Jägermeyr, J.; Kummu, M.; Pastor, A. V. Towards a revised planetary boundary for consumptive freshwater use: role of environmental flow requirements. Curr. Opin. Environ. Sustain. 2013, 5, 551−558, DOI: 10.1016/j.cosust.2013.11.001. (6) Ridoutt, B. G.; Pfister, S. Reducing humanity’s water footprint. Environ. Sci. Technol. 2010, 44, 6019−6021, DOI: doi:10.1021/ es101907z.
Received: July 16, 2014 Accepted: July 18, 2014 Published: August 4, 2014 8935
dx.doi.org/10.1021/es503441s | Environ. Sci. Technol. 2014, 48, 8935−8935
