Life Cycle Aspects of Nanoproducts, Nanostructured Materials, and Nanomanufacturing: Problem Definitions, Data Gaps, and Research Needs

Chicago, Illinois: November 5-6, 2009

Mark R. Wiesner, Duke University
Gregory V. Lowry, Carnegie Mellon University
Center for the Environmental Implications of NanoTechnology (CEINT)

Life Cycle Considerations for Nanoproducts, Nanostructured Materials, and Nanomanufacturing

Research at CEINT is addressing the need for information on nanomaterials production, use and disposal and potential reservoirs of materials that may create the possibility for exposure throughout the nanomaterial life cycle. This information is being developed with a view to inform a series of risk assessments regarding nanomaterials.

Our risk assessment work addresses both hazard and exposure but places an accent on exposure assessment. To this end we consider exposure at consecutive stages in the value chain of nanomaterials production and incorporation into products, and the potential “leakage” from each node in the value chain and end-of useful life practices.

This approach to estimating exposure requires considerable amounts of (currently unavailable) information concerning practices over a wide range of activities and great speculation.  As an alternative, we are also developing “inventories” of nanomaterials production for key materials and predictions of nanomaterial production based on indices of commercialization and innovation.  The details of this approach have been recently published for the case of nano TiO2 [1]. The estimates presented in this work represent the best forecasts for production of that material available to date. Similar assessments are on-going for nano-Ag, fullernenes (including carbon nanotubes), and cerium oxide. Based on an estimated “reservoir” of nanomaterial production, first-order estimates of exposure (however debatable) can be obtained that employ explicit, easily understood assumptions regarding the quantities of nanomaterials that enter the environment integrated over the entire life cycle of production through disposal.

Estimates of “unconstrained” nanomaterial production based on indices of innovation and commercialization will be compared with estimated reserves of critical elements as a basis for identifying shortfalls or limitations to forecasted production levels of critical nanomaterials.

A key question we are examining concerns the potential for “collateral damage”  i.e. environmental impacts that arise from the production of nanomaterials rather than the nanomaterials themselves.  These issues may greatly outweigh direct health or environmental impacts associated with an emerging nanomaterials industry. Indeed, the first ever published work on nanomaterial risk assessment [2] dealt directly with issues of collatoral damage. An insurance industry algorithm for calculating premiums as a function of the materials used in producing nanomaterials was used to quantify risks associated with nanomaterial production independent of the risks associated with the nanomaterials themselves. One of the important findings reported in this work was that methods for manufacturing nanomaterials tend to become “greener” with time; substituting, for example, less toxic solvents or implementing more energy-efficient procedures for fabricating nanomaterials. Subsequent work by others looking at carbon nanotube production [3] showed that nanomaterial production may involve the production of non-nano wastes that pose significant hazards.  Linkov and co-workers underscore the multi-criteria dimensions of evaluating nanomaterial risk [4].

The “green chemistry” prospects for nanomaterials are promising.  Products of nanochemistry and manipulation at the nanoscale will lead to the substitution of dangerous materials by nanomaterials and processes shown to pose less risk. Nanotechnology-inspired production will likely lead to more efficient use of materials and energy and an associated lower environmental footprint. Nonetheless, the entropic penalties associated with creating order at the atomic scale set boundaries on the gains that can be achieved in applying nanomaterials to solve environmental problems.  For example, theoretical gains in adsorptive efficiency using nano-iron oxides for arsenic removal are more than outweighed by the energy investments and associated costs when compared with conventional ferric chloride salts. 

The novel properties of nanomaterials that make them useful in a specific application are often the same properties that produce the hazard. For example just as a sharp knife makes it useful for cutting but may also injure, it is the capacity for ROS generation by nanoscale TiO2 that makes it useful for degrading contaminants in water and causes concern over potential environmental impacts. The possibility of designing nanomaterials to reduce hazard has been suggested as a means to ensure that nanostructured materials pose a minimum risk. While this “safe by design” approach is not without merit, success in “designing-out” hazard from non-nanomaterials (as opposed to designing materials to limit exposure) has been limited at best.  Moreover, this approach implicitly assumes the ability to predict biological effects based on nanomaterial properties using QSAR-type relationships that may range from simple correlation to expert systems. The success in applying QSAR to systems such as drug design where considerable information is available regarding molecular properties and effects has been limited, for the most part to cases where there is relatively little variability in molecular design and extrapolation is more reasonable. In contrast, nanomaterial “taxonomy” relevant properties and potential effects are all poorly defined at the current time. Moreover, nanomaterials interact with a wide range of solutes and nanometric materials that change the fundamental properties of these materials. Therefore, the outlook for success in applying QSAR-type relationships to “design out” adverse biological effects is not promising.

Much of our work has focused on understanding processes that control exposure rather than hazard, with the goal of managing exposure to manage risk. Mitigating exposure will be necessary to obtain the maximum benefits from nanotechnology, particularly those employing nanomaterials whose benefits are derived from the same properties that impart an inherent hazard.  Important questions to be answered in evaluating nanomaterial risk are therefore related to the format that nanomaterials will be present in as commercial products, the potential for these materials to be released to the environment, and the transformations that those materials may undergo that affect their transport and potential for exposure.

References Cited
1.         Robichaud, C.O., et al., Estimates of upper bounds and trends in nano-TiO2 production as a basis for exposure assessment. Environmental Science & Technology, 2009. 43(12): p. 4227-4233.
2.         Robichaud, C.O., et al., Relative risk analysis of several manufactured nanomaterials: An insurance industry context. Envirionmental Science and Technology, 2005. 39(22): p. 8985-8994.
3.         Plata, D.L., P.M. Gschwend, and C.M. Reddy, Industrially synthesized single-walled carbon nanotubes: compositional data for users, environmental risk assessments, and source apportionment. Nanotechnology, 2008. 19(18): p. 14.
4.         Linkov, I., et al., Multi-criteria decision analysis and environmental risk assessment for nanomaterials. Journal of Nanoparticle Research 2007. 9: p. 543-554.