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Setting the stage for debating the roles of risk assessment and life-cycle assessment of engineered nanomaterials

Nature Nanotechnology volume 12, pages 727–733 (2017)Cite this article

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Abstract

Although technological and environmental benefits are important stimuli for nanotechnology development, these technologies have been contested from an environmental point of view. The steady growth of applications of engineered nanomaterials has heated up the debate on quantifying the environmental repercussions. The two main scientific methods to address these environmental repercussions are risk assessment and life-cycle assessment. The strengths and weaknesses of each of these methods, and the relation between them, have been a topic of debate in the world of traditional chemistry for over two decades. Here we review recent developments in this debate in general and for the emerging field of nanomaterials specifically. We discuss the pros and cons of four schools of thought for combining and integrating risk assessment and life-cycle assessment and conclude with a plea for action.

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Figure 1: The general methodological framework for RA.
Figure 2: The general methodological framework for LCA.
Figure 3: The application of silver nanoparticles in socks as a hypothetical case study illustrating the fundamental differences between RA and LCA.

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References

  1. World Nanomaterials to 2016 — Industry Market Research, Market Share, Market Size, Sales, Demand Forecast, Market Leaders, Company Profiles, Industry Trends (Freedonia, 2016); http://go.nature.com/2txlQlU

  2. Future Challenges Related to the Safety of Manufactured Nanomaterials: Report from the Special Session (OECD, 2016); http://go.nature.com/2spcMz5

  3. Meyer, D. E., Curran, M. A. & Gonzalez, M. A. An examination of silver nanoparticles in socks using screening-level life cycle assessment. J. Nanopart. Res. 13, 147–156 (2011).

    Article  CAS  Google Scholar 

  4. Toumey, C. Quick lessons on environmental nanotech. Nat. Nanotech. 10, 566–567 (2015).

    Article  CAS  Google Scholar 

  5. Meyer, D. E., Curran, M. A. & Gonzalez, M. A. An examination of existing data for the industrial manufacture and use of nanocomponents and their role in the life cycle impact of nanoproducts. Environ. Sci. Technol. 43, 1256–1263 (2009).

    Article  CAS  Google Scholar 

  6. Hicks, A. L. & Theis, T. L. A comparative life cycle assessment of commercially available household silver-enabled polyester textiles. Int. J. Life Cycle Assess. 22, 256–265 (2016).

    Article  CAS  Google Scholar 

  7. Regulation (EC) No 1907/2006 of the European Parliament and of the Council of 18 December 2006 Concerning the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) (European Parliament, Council of the European Union, 2006); http://go.nature.com/2sYN1EA

  8. Toxic Substances Control Act (US Congress, 2002); http://www.epw.senate.gov/tsca.pdf

  9. Assessing and Managing Chemicals under TSCA (EPA, 2016); http://go.nature.com/2sYKmKX

  10. Walser, T., Demou, E., Lang, D. J. & Hellweg, S. Prospective environmental life cycle assessment of nanosilver t-shirts. Environ. Sci. Technol. 45, 4570–4578 (2011).

    Article  CAS  Google Scholar 

  11. Saha, A., Saha, D. & Ranu, B. C. Copper nano-catalyst: sustainable phenyl-selenylation of aryl iodides and vinyl bromides in water under ligand free conditions. Org. Biomol. Chem. 7, 1652–1657 (2009).

    Article  CAS  Google Scholar 

  12. Polshettiwar, V. & Varma, R. S. Green chemistry by nano-catalysis. Green Chem. 12, 743–754 (2010).

    Article  CAS  Google Scholar 

  13. Wang, S. et al. Motion charged battery as sustainable flexible-power-unit. ACS Nano 7, 11263–11271 (2013).

    Article  CAS  Google Scholar 

  14. Owens, J. W. Life-cycle assessment in relation to risk assessment: An evolving perspective. Risk Anal. 17, 359–365 (1997).

    Article  Google Scholar 

  15. Olsen, S. I. et al. Life cycle impact assessment and risk assessment of chemicals — A methodological comparison. Environ. Impact Assess. 21, 385–404 (2001).

    Article  Google Scholar 

  16. Udo de Haes, H. A., Wegener Sleeswijk, A. & Heijungs, R. Similarities, differences and synergisms between HERA and LCA — An analysis at three levels. Hum. Ecol. Risk Assess. 12, 431–449 (2006).

    Article  Google Scholar 

  17. van Leeuwen, C. J. & Hermens, J. L. M. Risk Assessment of Chemicals: An Introduction (Kluwer Academic Publishers, 1995).

    Book  Google Scholar 

  18. Paustenbach, D. The practice of health risk assessment in the United States (1975–1995): How the U. S. and other countries can benefit from that experience. Hum. Ecol. Risk Assess. 1, 29–79 (1995).

    Article  Google Scholar 

  19. Boersema, J. J. & Reijnders, L. Principles of Environmental Sciences Ch. 12 (Springer 2009).

    Book  Google Scholar 

  20. Sperber, W. H. Hazard identification: From a quantitative to a qualitative approach. Food Control 12, 223–228 (2001).

    Article  Google Scholar 

  21. Ropeik, D. & Gray, G. M. Risk: A Practical Guide for Deciding What's Really Safe and What's Really Dangerous in the World Around You (Houghton Mifflin, 2002).

    Google Scholar 

  22. Savolainen, K. et al. Nanosafety 2015–2025: Towards Safe and Sustainable Nanomaterial and Nanotechnology Innovations (Finnish Institute of Occupational Health, 2013).

    Google Scholar 

  23. Mihelcic, J. R. & Zimmerman, J. B. Environmental Engineering: Fundamentals, Sustainability, Design (Wiley, 2014).

    Google Scholar 

  24. Hua, J., Vijver, M. G., Chen, G., Richardson, M. K. & Peijnenburg, W. J. G. M. Dose metrics assessment for differently shaped and sized metal-based nanoparticles. Environ. Toxicol. Chem. 35, 2466–2473 (2016).

    Article  CAS  Google Scholar 

  25. Regulatory Aspects of Nanomaterials (European Commission, 2017); http://go.nature.com/2sYEuBl

  26. Second Regulatory Review on Nanomaterials (European Commission, 2017); http://go.nature.com/2trJe3A

  27. Environmental Management — Life Cycle Assessment — Principles and Framework ISO 14040:2016 (ISO, 2006).

  28. Hauschild, M. Z. & Huijbregts, M. A. J. Selection of Impact Categories and Classification of LCI Results to Impact Categories Ch. 2 (Springer, 2014).

    Google Scholar 

  29. Environmental Management — Life Cycle Assessment — Requirements and Guidelines ISO 14040:2016 (ISO, 2006).

  30. Frankl, P. & Rubik, F. Life Cycle Assessment in Industry and Business Ch. 5 (Springer, 2000).

    Book  Google Scholar 

  31. Vink, E. T. H., Rábago, K. R., Glassner, D. A. & Gruber, P. R. Applications of life cycle assessment to NatureWorks polylactide (PLA) production. Polym. Degrad. Stabil. 80, 403–419 (2003).

    Article  CAS  Google Scholar 

  32. Clift, R. & Druckman, A. (eds) Taking Stock of Industrial Ecology Ch. 15 (Springer, 2015).

    Google Scholar 

  33. Clift, R. Life cycle assessment and ecolabelling. J. Clean. Prod. 1, 155–159 (1993).

    Article  Google Scholar 

  34. The International Environmental Product Declaration System (EPD, 2017); http://www.environdec.com/

  35. European Parliament and Council Directive 94/62/EC of 20 December 1994 on Packaging and Packaging Waste (European Parliament, Council of the European Union, 1994); http://go.nature.com/2stX2Gm

  36. Energy Independence and Security Act of 2007 (US Congress, 2016); http://go.nature.com/2txKouN

  37. Matthews, S. H., Hendrickson, C. & Weber, C. L. The importance of carbon footprint estimation boundaries. Environ. Sci. Technol. 42, 5839–5842 (2008).

    Article  CAS  Google Scholar 

  38. Sorensen, B. The role of life-cycle analysis in risk assessment. Int. J. Environ. Pollut. 6, 729–746 (1996).

    CAS  Google Scholar 

  39. Tukker, A. Risk analysis, life cycle assessment — the common challenge of dealing with the precautionary frame (based on the toxicity controversy in Sweden and the Netherlands). Risk Anal. 22, 821–831 (2002).

    Article  Google Scholar 

  40. Boize, M. et al. Relevance of life cycle analysis (LCA) for assessing health impacts: Comparison with quantitative health risk assessments (QHRA). Envir. Risques Sante 7, 265–277 (2008).

    Google Scholar 

  41. Breedveld, L. Combining LCA and RA for the integrated risk management of emerging technologies. J. Risk Res. 16, 459–468 (2013).

    Article  Google Scholar 

  42. Kobayashi, Y., Peters, G. M. & Khan, S. J. Towards more holistic environmental impact assessment: hybridisation of life cycle assessment and quantitative risk assessment. Procedia CIRP 29, 378–383 (2015).

    Article  Google Scholar 

  43. Guinée, J. B. & Heijungs, R. A proposal for the classification of toxic substances within the framework of life cycle assessment of products. Chemosphere 26, 1925–1944 (1993). This paper presents the first example of the 'knowledge integration' school of thought.

    Article  Google Scholar 

  44. Guinée, J. B. et al. USES uniform system for the evaluation of substances. Inclusion of fate in LCA characterisation of toxic releases applying USES 1.0. Int. J. Life Cycle Assess. 1, 133–138 (1996).

    Article  Google Scholar 

  45. Hauschild, M. & Wenzel, H. Environmental Assessment of Products Vol. 2 (Chapman & Hall, 1998).

    Google Scholar 

  46. Huijbregts, M. A. J. et al. Priority assessment of toxic substances in life cycle assessment. Part I: Calculation of toxicity potentials for 181 substances with the nested multi-media fate, exposure and effects model USES-LCA. Chemosphere 41, 541–573 (2000).

    Article  CAS  Google Scholar 

  47. Bennett, D. H., Margni, M. D., McKone, T. E. & Jolliet, O. Intake fraction for multimedia pollutants: a tool for life cycle analysis and comparative risk assessment. Risk Anal. 22, 905–918 (2002).

    Article  Google Scholar 

  48. Gandhi, N. et al. New method for calculating comparative toxicity potential of cationic metals in rreshwater: application to copper, nickel and zinc. Environ. Sci. Technol. 44, 5195–5201 (2010).

    Article  CAS  Google Scholar 

  49. van Zelm, R., Huijbregts, M. A. J. & van de Meent, D. Transformation products in the life cycle impact assessment of chemicals. Environ. Sci. Technol. 44, 1004–1009 (2010).

    Article  CAS  Google Scholar 

  50. Potting, J. & Hauschild, M. Spatial differentiation in life-cycle assessment via the site-dependent characterisation of environmental impact from emissions. Int. J. Life Cycle Assess. 2, 209–216 (1997).

    Article  Google Scholar 

  51. Bellekom, S., Potting, J. & Benders, R. Feasibility of applying site-dependent impact assessment of acidification in LCA. Int. J. Life Cycle Assess. 11, 417–424 (2006).

    Article  CAS  Google Scholar 

  52. Azevedo, L. B., Henderson, A. D., van Zelm, R., Jolliet, O. & Huijbregts, M. A. J. Assessing the importance of spatial variability versus model choices in life cycle impact assessment: the case of freshwater eutrophication in Europe. Environ. Sci. Technol. 47, 13565–13570 (2013).

    Article  CAS  Google Scholar 

  53. Wegener Sleeswijk, A. Regional LCA in a global perspective. A basis for spatially differentiated environmental life cycle assessment. Int. J. Life Cycle Ass. 16, 106–122 (2011).

    Article  CAS  Google Scholar 

  54. Hellweg, S. & Milài Canals, L. Emerging approaches, challenges and opportunities in life cycle assessment. Science 344, 1109–1113 (2014).

    Article  CAS  Google Scholar 

  55. Posthuma, L., Suter, G. W. II & Traas, T. P. Species Sensitivity Distributions in Ecotoxicology (CRC Press, 2002).

    Google Scholar 

  56. Harder, R., Heimersson, S., Svanström, M. & Peters, G. M. Including pathogen risk in life cycle assessment of wastewater management. 1. Estimating the burden of disease associated with pathogens. Environ. Sci. Technol. 48, 9438–9445 (2014).

    Article  CAS  Google Scholar 

  57. Heimersson, S., Harder, R., Peters, G. M. & Svanström, M. Including pathogen risk in life cycle assessment of wastewater management. 2. Quantitative comparison of pathogen risk to other impacts on human health. Environ. Sci. Technol. 48, 9446–9453 (2014).

    Article  CAS  Google Scholar 

  58. Assies, J. A. A risk-based approach to life-cycle impact assessment. J. Hazard. Mater. 61, 23–29 (1998).

    Article  CAS  Google Scholar 

  59. Sonnemann, G., Castells, F. & Schuhmacher, M. Integrated Life-Cycle and Risk Assessment for Industrial Processes Ch. 6 (CRC Press, 2004).

    Google Scholar 

  60. Harder, R., Holmquist, H., Molander, S., Svanstrom, M. & Peters, G. M. Review of environmental assessment case studies blending elements of risk assessment and life cycle assessment. Environ. Sci. Technol. 49, 13083–13093 (2015).

    Article  CAS  Google Scholar 

  61. Guinée, J. B. et al. Human and ecological life cycle tools for the integrated assessment of systems (HELIAS). Int. J. Life Cycle Assess. 11, 19–28 (2006).

    Article  Google Scholar 

  62. Bare, J. C. Risk assessment and life-cycle impact assessment (LCIA) for human health cancerous and noncancerous emissions: Integrated and complementary with consistency within the USEPA. Hum. Ecol. Risk Assess. 12, 493–509 (2006).

    Article  CAS  Google Scholar 

  63. Flemström, K., Carlson, R. & Erixon, M. Relationships Between Life Cycle Assessment and Risk Assessment — Potentials and Obstacles (Naturvardsverket, 2004).

    Google Scholar 

  64. Spina, F., Ioppolo, G., Salomone, R., Bart, J. C. J. & Milazzo, M. F. in Pathways to Environmental Sustainability (eds Salomone, R. & Saija, G.) 117–126 (Springer, 2014).

    Book  Google Scholar 

  65. Vermeire, T. G., van der Zandt, P. T. J., Roelfzema, H. & Van Leeuwen, C. J. Uniform system for the evaluation of substances I — Principles and structure. Chemosphere 29, 23–38 (1994). This paper presents the first example of the 'chain perspective' school of thought.

    Article  CAS  Google Scholar 

  66. Heijungs, R. Harmonization of methods for impact assessment. Environ. Sci. Pollut. Res. 2, 217–224 (1995).

    Article  CAS  Google Scholar 

  67. Potting, J., Schöpp, W., Blok, K. & Hauschild, M. Site-dependent life-cycle impact assessment of acidification. J. Ind. Ecol. 2, 63–87 (1998).

    Article  CAS  Google Scholar 

  68. Carpenter, A. C., Gardner, K. H., Fopiano, J., Benson, C. H. & Edil, T. B. Life cycle based risk assessment of recycled materials in roadway construction. Waste Manage. 27, 1458–1464 (2007).

    Article  CAS  Google Scholar 

  69. Wegener Sleeswijk, A. & Heijungs, R. GLOBOX: a spatially differentiated global fate, intake and effect model for toxicity assessment in LCA. Sci. Total Environ. 408, 2817–2832 (2010).

    Article  CAS  Google Scholar 

  70. Pennington, D. W., Margni, M., Payet, J. & Jolliet, O. Risk and regulatory hazard-based toxicological effect indicators in life-cycle assessment (LCA). Hum. Ecol. Risk Assess. 12, 450–475 (2006).

    Article  CAS  Google Scholar 

  71. Guinée, J. B. et al. Evaluation of risks of metal flows and accumulation in economy and environment. Ecol. Econ. 30, 47–65 (1998).

    Article  Google Scholar 

  72. Grieger, K. D. et al. Analysis of current research addressing complementary use of life-cycle assessment and risk assessment for engineered nanomaterials: Have lessons been learned from previous experience with chemicals? J. Nanopart. Res. 14, 958 (2012).

    Article  CAS  Google Scholar 

  73. Wardak, A., Gorman, M. E., Swami, N. & Deshpande, S. Identification of risks in the life-cycle of nanotechnology-based products. J. Ind. Ecol. 12, 435–448 (2008).

    Article  CAS  Google Scholar 

  74. Willis, H. H. & Florig, H. K. Potential exposures and risks from beryllium-containing products. Risk Anal. 22, 1019–1033 (2002).

    Article  Google Scholar 

  75. Shatkin, J. A. Informing environmental decision making by combining life cycle assessment and risk analysis. J. Ind. Ecol. 12, 278–281 (2008).

    Article  Google Scholar 

  76. Shatkin J. A. Nanotechnology: Health and Environmental Risks Ch. 6 (CRC Press, 2012).

    Google Scholar 

  77. Shatkin, J. A. & Kim, B. Cellulose nanomaterials: life cycle risk assessment, and environmental health and safety roadmap. Environ. Sci. Nano 2, 477–499 (2015).

    Article  CAS  Google Scholar 

  78. Shih, H. C. & Ma, H. W. Life cycle risk assessment of bottom ash reuse. J. Hazard. Mater. 190, 308–316 (2011).

    Article  CAS  Google Scholar 

  79. Sharratt, P. N. & Choong, P. M. A life-cycle framework to analyse business risk in process industry projects. J. Clean. Prod. 10, 479–493 (2002). This paper can be considered as a first example of the 'RA for LCA hotspots' school of thought.

    Article  Google Scholar 

  80. Socolof, M. L. & Geibig, J. R. Evaluating human and ecological impacts of a product life cycle: The complementary roles of life-cycle assessment and risk assessment. Hum. Ecol. Risk Assess. 12, 510–527 (2006).

    Article  CAS  Google Scholar 

  81. Sweet, L. & Strohm, B. Nanotechnology — Life-cycle risk management. Hum. Ecol. Risk Assess. 12, 528–551 (2006).

    Article  CAS  Google Scholar 

  82. Lim, S.-R., Lam, C. W. & Schoenung, J. M. Priority screening of toxic chemicals and industry sectors in the U. S. toxics release inventory: A comparison of the life cycle impact-based and risk-based assessment tools developed by U.S. EPA. J. Environ. Manage. 92, 2235–2240 (2011).

    Article  CAS  Google Scholar 

  83. Kuczenski, B., Geyer, R. & Boughton, B. Tracking toxicants: Toward a life cycle aware risk assessment. Environ. Sci. Technol. 45, 45–50 (2011).

    Article  CAS  Google Scholar 

  84. Benetto, E., Tiruta-Barna, L. & Perrodin, Y. Combining lifecycle and risk assessments of mineral waste reuse scenarios for decision making support. Environ. Impact Assess. 27, 266–285 (2007). This paper presents the first example of the 'combining results' school of thought.

    Article  Google Scholar 

  85. Linkov, I. et al. For nanotechnology decisions, use decision analysis. Nano Today 8, 5–10 (February, 2013).

  86. Tsang, M. P., Bates, M. E., Madison, M. & Linkov, I. Benefits and risks of emerging technologies: Integrating life cycle assessment and decision analysis to assess lumber treatment alternatives. Environ. Sci. Technol. 48, 11543–11550 (2014).

    Article  CAS  Google Scholar 

  87. Rotolo, D., Hicks, D. & Martin, B. R. What is an emerging technology? Res. Policy 44, 1827–1843 (2015).

    Article  Google Scholar 

  88. Hischier, R. & Walser, T. Life cycle assessment of engineered nanomaterials: state of the art and strategies to overcome existing gaps. Sci. Total Environ. 425, 271–282 (2012).

    Article  CAS  Google Scholar 

  89. Klöpffer, W. et al. Nanotechnology and Life Cycle Assessment. A Systems Approach to Nanotechnology and the Environment (Technical University of Denmark, 2007); http://orbit.dtu.dk/files/3374746/NanoLCA_3.07.pdf

    Google Scholar 

  90. Vaseashta, A. Life Cycle Analysis of Nanoparticles — Risk, Assessment, and Sustainability (Destech, 2015).

    Google Scholar 

  91. Wender, B. A. et al. Illustrating anticipatory life cycle assessment for emerging photovoltaic technologies. Environ. Sci. Technol. 48, 10531–10538 (2014).

    Article  CAS  Google Scholar 

  92. Miller, S. A. & Keoleian, G. A. Framework for analyzing transformative technologies in life cycle assessment. Environ. Sci. Technol. 49, 3067–3075 (2015).

    Article  CAS  Google Scholar 

  93. Tecchio, P., Freni, P., De Benedetti, B. & Fenouillot, F. Ex-ante life cycle assessment approach developed for a case study on bio-based polybutylene succinate. J. Clean. Prod. 112, 316–325 (2016).

    Article  CAS  Google Scholar 

  94. Villares, M., Işıldar, A., Mendoza Beltran, A. & Guinée, J. Applying an ex-ante life cycle perspective to metal recovery from e-waste using bioleaching. J. Clean. Prod. 129, 315–328 (2016).

    Article  CAS  Google Scholar 

  95. Selck, H., Handy, R. D., Fernandes, T. F., Klaine, S. J. & Petersen, E. J. Nanomaterials in the aquatic environment: A European Union–United States perspective on the status of ecotoxicity testing, research priorities, and challenges ahead. Environ. Toxicol. Chem. 35, 1055–1067 (2016).

    Article  CAS  Google Scholar 

  96. Adam, V., Loyaux-Lawniczak, S. & Quaranta, G. Characterization of engineered TiO2 nanomaterials in a life cycle and risk assessments perspective. Environ. Sci. Pollut. Res. 22, 11175–11192 (2015).

    Article  CAS  Google Scholar 

  97. Pereira, S. R. & Coelho, M. C. Can nanomaterials be a solution for application on alternative vehicles? — A review paper on life cycle assessment and risk analysis. Int. J. Hydrogen Energ. 40, 4969–4979 (2015).

    Article  CAS  Google Scholar 

  98. http://www.ecoinvent.org/database/database.html

  99. Beck, U. Risk Society: Towards a New Modernity (Sage, 1992).

    Google Scholar 

  100. Swierstra, T. & Rip, A. Nano-ethics as NEST-ethics: patterns of moral argumentation about new and emerging science and technology. Nanoethics 1, 3–20 (2007).

    Article  Google Scholar 

  101. Collingridge, D. The Social Control of Technology (St. Martin's Press, 1980).

    Google Scholar 

Download references

Acknowledgements

The authors would like to thank L. Breedveld for helpful discussions while preparing this manuscript and L. van Oers for assistance with some of the figures.

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Authors and Affiliations

  1. Institute of Environmental Sciences (CML), Leiden University, PO Box 9518, Leiden, 2300 RA, The Netherlands

    Jeroen B. Guinée, Reinout Heijungs, Martina G. Vijver & Willie J. G. M. Peijnenburg

  2. Department of Econometrics and Operations Research, Vrije Universiteit Amsterdam, De Boelelaan 1105, Amsterdam, 1081 HV, The Netherlands

    Reinout Heijungs

  3. National Institute of Public Health and the Environment, Center for Safety of Substances and Products, PO Box 1, Bilthoven, 3720 BA, The Netherlands

    Willie J. G. M. Peijnenburg

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  1. Jeroen B. Guinée
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Correspondence to Jeroen B. Guinée.

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Guinée, J., Heijungs, R., Vijver, M. et al. Setting the stage for debating the roles of risk assessment and life-cycle assessment of engineered nanomaterials. Nature Nanotech 12, 727–733 (2017). https://doi.org/10.1038/nnano.2017.135

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