In celebration of the 2019 National Nanotechnology Day, we are taking a look at a list we compiled for the 15th anniversary of The National Nanotechnology Initiative which highlights 15 (or so) key things that we have learned from an academic, regulatory, industry, and public perspective, about nanomaterial environmental health and safety.
1. There has been an exponential rise in nanosafety-related publications.
In 2003 there were hundreds of published papers on nanotoxicity, but since then, there have been over 250,000 papers published. Journals were created to cover topics related to nanosafety, such as Nanomedicine: Nanotechnology, Biology and Medicine (2005), Nature Nanotechnology (2006), Nanotoxicology (2007), and NanoImpact (2016), among others. There is significantly more work reported on inhalation related toxicity than on oral, dermal or exposure related investigations.
2. Early publications generally did not contribute reliable data to the field of risk assessment.
Risk assessment requires both hazard and exposure data from reproducible studies. Prior to 2010, most published studies did not report enough physical chemical information on their nanomaterials, or enough study details to provide relevant information for risk assessment. This resulted in conflicting results and an inability to compare studies but has led to improved study design and reporting. Around 2009, there was an effort to engage journal editors to adopt minimum characterization standards for manuscripts.
Fernández-Cruz, M.L., Hernández-Moreno, D., Catalán, J., Cross, R.K., Stockmann-Juvala, H., Cabellos, J., Lopes, V.R., Matzke, M., Ferraz, M., Izquierdo, J.J., and Navas, J.M., 2018. Quality evaluation of human and environmental toxicity studies performed with nanomaterials – the GUIDEnano approach. Environmental Science: Nano, 2, pp.381-397.
Hartmann, N.B., Agerstrand, M., Lutzhoft, H.C.H. and Baun A., 2017. NanoCRED: A transparent framework to assess the regulatory adequacy of ecotoxicity data for nanomaterials – Relevance and reliability revisited. NanoImpact, 6, pp.81-89.
Krug, H.F. and Wick, P., 2011. Nanotoxicology: an interdisciplinary challenge. Angewandte Chemie International Edition, 50(6), pp1260-1278.
Card J.W. and Magnuson B.A., 2010. A method to assess the quality of studies that examine the toxicity of engineered nanomaterials. International Journal of Toxicology, 4(29), pp.402-410.
Minimum Information for Nanomaterial Characterization (MINChar) Initiative, 2008. About the initiative.
3. There is no single physical chemical property of nanomaterials that is predictive of biological activity, including size.
One of the primary objectives of nanotoxicology research is to link physical and chemical properties to biological activity and develop predictive models. This would help us predict which nanomaterials may be toxic and under what conditions. Improving study design and reporting (point #2) and understanding how nanomaterials change in different conditions (point #4) will go a long way toward helping us make these connections. There have been substantive efforts over the last 15 years, but no silver bullet has emerged. The methods and equipment available to measure nanomaterial characteristics are slowly improving, though methods like dynamic light scattering, the standard for measuring hydrodynamic size and distribution, are still part of standard reporting, despite common knowledge of its flaws.
Godwin, H., Nameth, C., Avery, D., Bergeson, L.L., Bernard, D., Beryt, E., Boyes, W., Brown, S., Clippinger, A.J., Cohen, Y., and Doa, M., 2015. Nanomaterial categorization for assessing risk potential to facilitate regulatory decision-making. ACS Nano, 9(4), pp.3409-3417.
Tantra, R., Oksel, C., Puzyn, T., Wang, J., Robinson, K.N., Wang, X.Z., Ma, C.Y. and Wilkins, T., 2015. Nano (Q)SAR: Challenges, pitfalls and perspectives. Nanotoxicology, 9(5), pp.636-642.
Stone, V., Pozzi-Mucelli, S., Tran, L., Aschberger, K., Sabella, S., Vogel, U., Poland, C., Balharry, D., Fernandes, T., Gottardo, S. and Hankin, S., 2014. ITS-NANO-Prioritising nanosafety research to develop a stakeholder driven intelligent testing strategy. Particle and Fibre Toxicology, 11(1), p.9.
4. Interactions between nanomaterials and environmental and biological systems are complex.
We have learned that a ‘pristine’ nanomaterial in its original form changes quickly once it enters different biological and environmental media. Nanomaterials quickly form ‘coronas’ which change material properties (e.g. size, surface charge, shape, ability to stick to each other (i.e. agglomeration/aggregation) and other molecules, etc.) and behavior. Therefore, a nanomaterial may have different health/environmental risk potential at different life-cycle stages due to the changes in its properties.
Lead, J.R., Batley, G.E., Alvarez, P.J., Croteau, M.N., Handy, R.D., McLaughlin, M.J., Judy, J.D. and Schirmer, K., 2018. Nanomaterials in the environment: Behavior, fate, bioavailability, and effects—An updated review. Environmental Toxicology and Chemistry, 37(8), pp.2029-2063.
Lynch, I. and Dawson, K.A., 2008. Protein-nanoparticle interactions. Nano Today, 3(1-2), pp.40-47.
Cedervall, T., Lynch, I., Lindman, S., Berggård, T., Thulin, E., Nilsson, H., Dawson, K.A. and Linse, S., 2007. Understanding the nanoparticle–protein corona using methods to quantify exchange rates and affinities of proteins for nanoparticles. Proceedings of the National Academy of Sciences, 104(7), pp.2050-2055.
5. Only a small proportion of academic studies are relevant for risk assessment.
The field of nanotoxicology is generally focused on testing the limits of toxicity, and hownanomaterials may affect health, rather than assessing effects under realistic conditions. This means studies are usually performed at high concentrations, using unrealistic dosing methods (e.g. a lifetime dose in a single delivery) that will definitively result in a negative outcome, so that scientists can determine the mechanism of how an effect may occur. Unfortunately, these concentrations and routes of exposure are not representative of what happens in real-life and don’t allow extrapolation to current exposure scenarios. Gradually, as scientists are increasingly testing under realistic scenarios (e.g. using real lake water instead of pure water), and lower doses, we are advancing our understanding of nanomaterial toxicity. In particular, there is a great need to fill data gaps in risks from nano-enabled products, versus ingredients to composite products.
Shatkin, J.A. and Oberdörster, G., 2016. Comment on Shvedova et al.(2016),“Gender differences in murine pulmonary responses elicited by cellulose nanocrystals”. Particle and Fibre Toxicology, 13(1), p.59.
Warheit, D.B. and Donner, E.M., 2015. How meaningful are risk determinations in the absence of a complete dataset? Making the case for publishing standardized test guideline and ‘no effect’ studies for evaluating the safety of nanoparticulates versus spurious ‘high effect’ results from single investigative studies. Science and Technology of Advanced Materials, 16(3), p.034603.
Krug, H.F., 2014. Nanosafety research—Are we on the right track? Angewandte Chemie International Edition, 53(46), pp.12304-12319.
6. Many nanomaterials are no more hazardous than their bulk counterparts.
Despite our concerns about nano-specific effects, a relatively small number of studies have found effects that are ‘nano-specific’, such as certain carbon nanotubes with characteristics that meet the fiber paradigm. Many nanomaterials may have similar hazardous properties as the larger forms of the material. For example, nanomaterials that dissolve quickly (e.g.silver, zinc, cadmium) can have similar toxicity to their conventional materials in that both forms release dissolved ions. Similarly, some nanomaterials may simply be more reactive than their bulk counterparts due to a relatively larger surface area to volume ratio, increasing the available surface area for reactions. In particular, poorly soluble, low toxicity (PSLT) nanomaterials, such as polystyrene, carbonaceous materials, and titanium dioxide, may fall under this paradigm. That said, we have learned that it is not possible to generalize about the safety of nanomaterials as a class. Like chemicals, some pose a low risk in the products they are used in, while others may bring greater concern due to certain characteristics.
This isn’t to say that we shouldn’t continue to study nanomaterial toxicity – there are still unique nanomaterial properties to consider (e.g. ability to cross some membranes) but study designs should continue to compare nanomaterials to their bulk counterparts, where applicable. One caveat about this finding is that most of the literature is studies of single materials, not more complex assemblies.
Kane, A.B., Hurt, R.H. and Gao, H., 2018. The asbestos-carbon nanotube analogy: An update. Toxicology and Applied Pharmacology. In press. https://doi.org/10.1016/j.taap.2018.06.027
Schmid, O. and Stoeger, T., 2016. Surface area is the biologically most effective dose metric for acute nanoparticle toxicity in the lung. Journal of Aerosol Science, 99, pp.133-143.
Clift, M.J. and Rothen-Rutishauser, B., 2013. Studying the oxidative stress paradigm in vitro: A theoretical and practical perspective. In Oxidative Stress and Nanotechnology (pp. 115-133). Humana Press, Totowa, NJ.
Donaldson, K. and Poland, C.A., 2013. Nanotoxicity: Challenging the myth of nano-specific toxicity. Current Opinion in Biotechnology, 24(4), pp.724-734.
Donaldson, K., Murphy, F.A., Duffin, R. and Poland, C.A., 2010. Asbestos, carbon nanotubes and the pleural mesothelium: A review of the hypothesis regarding the role of long fibre retention in the parietal pleura, inflammation and mesothelioma. Particle and Fibre Toxicology, 7(1), p.5.
7. Detection and measurement of nanomaterials in complex matrices is a major challenge.
To understand how much of a nanomaterial ends up in the environment, in consumer products, or in different parts of the body, we need to be able to detect and measure it. Measurement methods that are adequately accurate, sensitive and selective remain an issue. Some nanomaterials have intrinsic properties that are easy to detect (e.g. metals). However, carbon-based materials such as cellulose or carbon nanotubes present significant challenges. Researchers have been improving methods to separate nanomaterials based on size, attach fluorescent or other labels to nanomaterials so that they are more easily detectable, and develop more complex (and often more expensive) approaches to measure them. Despite these efforts, this field is generally underdeveloped, and it is expected that it will continue to grow rapidly as more nanomaterials are commercialized and there is a need for detection in complex matrices.
Montano, M., Ranville. J., Lowry, G., Blue, J., Hiremath, N., Koenig S. and Tuccillo, M., 2014. Detection and characterization of engineered nanomaterials in the environment: Current state-of-the-art and future directions report, annotated bibliography, and image library. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-14/244.
Von der Kammer, F., Ferguson, P.L., Holden, P.A., Masion, A., Rogers, K.R., Klaine, S.J., Koelmans, A.A., Horne, N. and Unrine, J.M., 2012. Analysis of engineered nanomaterials in complex matrices (environment and biota): General considerations and conceptual case studies. Environmental Toxicology and Chemistry, 31(1), pp.32-49.
8. Risk assessment, nanotoxicology and nanomaterial exposure assessment are built on already existing paradigms.
While some modification is needed, particularly to address different metrics and to include physical and chemical characterization, the risk assessment paradigm is appropriate for analyzing potential health and environmental risks of nanomaterials. Despite the fact that many engineered nanomaterials are ‘new’, much of our nanotoxicity knowledge can rely on existing paradigms. For example, the existing oxidative stress, genotoxicity paradigm, and fiber paradigms apply to many nanomaterials. Similarly, categorization approaches are based on substance properties such as solubility, poorly soluble particles, biopersistence, and high aspect ratio materials. Not only can we learn from such paradigms, the study of nanomaterials is improving our understanding of such paradigms (e.g. the importance of ‘stiffness’ in the fiber paradigm). Similarly, occupational exposure assessment and management approaches for conventional substances are generally applicable for nanomaterials.
Magdolenova, Z., Collins, A., Kumar, A., Dhawan, A., Stone, V. and Dusinska, M., 2014. Mechanisms of genotoxicity. A review of in vitro and in vivo studies with engineered nanoparticles. Nanotoxicology, 8(3), pp.233-278.
Shatkin, J.A., Abbott, L.C., Bradley, A.E., Canady, R.A., Guidotti, T., Kulinowski, K.M., Löfstedt, R.E., Louis, G., MacDonell, M., Maynard, A.D. and Paoli, G., 2010. Nano risk analysis: Advancing the science for nanomaterials risk management. Risk Analysis: An International Journal, 30(11), pp.1680-1687.
Xia, T., Kovochich, M., Brant, J., Hotze, M., Sempf, J., Oberley, T., Sioutas, C., Yeh, J.I., Wiesner, M.R. and Nel, A.E., 2006. Comparison of the abilities of ambient and manufactured nanoparticles to induce cellular toxicity according to an oxidative stress paradigm. Nano letters, 6(8), pp.1794-1807.
9. Defining the key attributes of ‘nano’ is still an issue because “nanomaterials” are not all the same.
Regulatory agencies all over the world do not present a harmonized definition of ‘nano’. This is not surprising, given that not all nanomaterials behave in the same way.
Most still define a ‘nanomaterial’ as an engineered material with at least one dimension less than 100 nm, and/or present properties unique to the nano-form. There is still much debate as to whether this definition is appropriate and is generally considered a ‘working definition’. Definitions that include some “unique or novel” attribute, are poorly defined and lack specificity.
U.S. Environmental Protection Agency (EPA), 2017. Chemical substances when manufactured or processed as nanoscale materials: TSCA reporting and recordkeeping requirements.
Boverhof, D.R., Bramante, C.M., Butala, J.H., Clancy, S.F., Lafranconi, M., West, J. and Gordon, S.C., 2015. Comparative assessment of nanomaterial definitions and safety evaluation considerations. Regulatory Toxicology and Pharmacology, 73(1), pp.137-150.
European Commission (EC), 2011. Commission recommendation of 18 October 2011 on the definition of nanomaterial.
Health Canada, 2011. Policy statement on Health Canada’s working definition for nanomaterial.
10. Regulatory frameworks are increasingly modified to include nanomaterials, rather than develop new frameworks.
While there are currently few regulatory frameworks that have been developed specifically for nanomaterials, modifications to existing frameworks are common. Additional testing, such as physical chemical measurements, additional safety testing, and even labeling may be required. Some agencies treat nano-forms with the same chemical and molecular structure as their bulk form under existing frameworks, whereas others require a new evaluation for nano-forms.
European Food Safety Authority (EFSA), 2018. Guidance on risk assessment of the application of nanoscience and nanotechnologies in the food and feed chain: Part 1, human and animal health.
U.S. Environmental Protection Agency (EPA), 2017. Control of nanoscale materials under the Toxic Substances Control Act (TSCA).
U.S. Food and Drug Administration (FDA), 2014. Guidance for Industry: Safety of nanomaterials in cosmetic products.
European Chemicals Agency (ECHA), 2012-2017. Guidance on information requirements and chemical safety assessment – Appendices to Chapters R.6, R.7a, R.7b, R.7c, R8, R.10, R.14: Recommendations for nanomaterials.
11. The ability to ‘group’ nanomaterials is important.
It is impossible to test all nanomaterials for toxicity (there are just too many!), so the current practice of evaluating nanomaterials on a case-by-case basis remains an impossible task. To deal with the large number of emerging nanomaterials, grouping and read-across strategies are being developed to allow for extrapolation between nanomaterials. Large consortia, such as the ECETOC DF4nanoGrouping scheme, and Horizon 2020’s NanoReg2 and GRACIOUS Projects are working on strategies to group nanomaterials based on properties (e.g. shape, biopersistence, dissolution rate, biological effects, etc.) to support streamlined risk assessment and reduce the resources needed to test each nanomaterial.
Arts, J.H., Hadi, M., Irfan, M.A., Keene, A.M., Kreiling, R., Lyon, D., Maier, M., Michel, K., Petry, T., Sauer, U.G. and Warheit, D., 2015. A decision-making framework for the grouping and testing of nanomaterials (DF4nanoGrouping). Regulatory Toxicology and Pharmacology, 71(2), pp.S1-S27.
12. Many standardized toxicity tests are valid for nanomaterial testing – with some modifications.
Most regulatory guidance documents endorse the continued use of existing standardized tests for nanomaterials; notable exceptions include the genotoxicity Ames assay (nanomaterials can’t get through the cell wall, and therefore don’t interact with the DNA) and making sure nanomaterials don’t interfere with the components of biochemical assays. Efforts on harmonization of data requirements are ongoing. There is increasing effort to develop alternative testing strategies for nanomaterials, recognizing the impossibility of animal testing for evaluating the effects of the diversity of nanomaterials forms.
Organisation for Economic Co-Operation and Development (OECD), 2018. Report on considerations from case studies on integrated approaches for testing and assessment (IATA).
Organisation for Economic Co-Operation and Development (OECD), 2017. Alternative testing strategies in risk assessment of engineered nanomaterials: Current state of knowledge and research needs to advance their use.
Stone, V., Johnston, H.J., Balharry, D., Gernand, J.M. and Gulumian, M., 2016. Approaches to develop alternative testing strategies to inform human health risk assessment of nanomaterials. Risk Analysis, 36(8), pp.1538-1550.
Ong, K.J., MacCormack, T.J., Clark, R.J., Ede, J.D., Ortega, V.A., Felix, L.C., Dang, M.K., Ma, G., Fenniri, H., Veinot, J.G. and Goss, G.G., 2014. Widespread nanoparticle-assay interference: implications for nanotoxicity testing. PLoS One, 9(3), p.e90650.
Organisation for Economic Co-Operation and Development (OECD), 2014. Report of the expert meeting on the physical chemical properties of manufactured nanomaterials and test guidelines.
13. Inhalation of powdered materials is a high priority for nanomaterial testing.
One of the highest exposure risks is likely inhalation of dry nanomaterials during manufacturing and handling. Few nano-specific Occupational Exposure Limits (reasonable levels to which a worker may be repeatedly exposed without negative effects) have been developed, and proposed exposure limits are generally lower than those of the bulk material. Until more is understood about the effects of inhaling nanomaterials, precautionary measures are recommended.
Nakanishi, J., Morimoto, Y., Ogura, I., Kobayashi, N., Naya, M., Ema, M., Endoh, S., Shimada, M., Ogami, A., Myojyo, T. and Oyabu, T., 2015. Risk assessment of the carbon nanotube group. Risk Analysis, 35(10), pp.1940-1956.
National Institute for Occupational Safety and Health (NIOSH), 2013. Current Intelligence Bulletin 65: Occupational Exposure to Carbon Nanotubes and Nanofibers.
National Institute for Occupational Safety and Health (NIOSH), 2011. Current Intelligence Bulletin 63: Occupational Exposure to Titanium Dioxide.
British Standards Institution (BSI Group), 2007. Nanotechnologies – part 2: Guide to safe handling and disposal of manufactured nanomaterials.
14. Traditional safety measures are a good foundation for nanomaterials.
Approaches relying on existing exposure controls have generally been found to be adequate, including engineering controls (e.g. using proper ventilation, filters, and working with nanomaterials in wet form, where possible), and personal protective equipment (e.g. gloves and respirators). A number of guidance documents on the safe handling of nanomaterials have been published, relying on a solid body of toxicology and exposure research, including from the U.S. National Institute for Occupational Safety and Health (NIOSH), and other occupational research organizations.
ASTM International, 2018. Standard guide for handling unbound engineered nanoscale particles in occupational settings.
National Institute for Occupational Safety and Health (NIOSH), 2018. Workplace design solutions: Protecting workers during the handling of nanomaterials.
World Health Organization (WHO), 2017. WHO guidelines on protecting workers from potential risks of manufactured nanomaterials.
15. Consumers are not likely to be exposed to high concentrations of nano-sized materials.
Even when nanomaterials are incorporated into composites for consumer use, ‘pristine nanomaterials’ are generally not released from these products. Nanomaterials usually quickly stick together, or bind to other particles, and so do not come into contact with organisms as nano-sized materials. The intensity of exposure from sprayed, aerosolized, and high temperature products (e.g. tires, home use conventional and 3-D printers) remains uncertain.
Predicted environmental concentrations are by and large extremely low for nanomaterials – much lower than levels deemed ‘unsafe’. Despite this, determining potential effects is still important as nanomaterial concentrations at ‘point source’ exposures (e.g. in case of an accidental spill, or at an outfall of a production plant) will be higher. There are some indicators that global releases may be significant, but there is much uncertainty as to the amount of nanomaterial production and emission rates.
Giese, B., Klaessig, F., Park, B., Kaegi, R., Steinfeldt, M., Wigger, H., Gleich, A. and Gottschalk, F., 2018. Risks, release and concentrations of engineered nanomaterial in the environment. Scientific Reports, 8(1), p.1565.
Koivisto, A.J., Jensen, A.C.Ø., Kling, K.I., Nørgaard, A., Brinch, A., Christensen, F. and Jensen, K.A., 2017. Quantitative material releases from products and articles containing manufactured nanomaterials: Towards a release library. NanoImpact, 5, pp.119-132.
Froggett, S.J., Clancy, S.F., Boverhof, D.R. and Canady, R.A., 2014. A review and perspective of existing research on the release of nanomaterials from solid nanocomposites. Particle and Fibre Toxicology, 11(1), p.17.
Gottschalk, F., Sun, T. and Nowack, B., 2013. Environmental concentrations of engineered nanomaterials: review of modeling and analytical studies. Environmental Pollution, 181, pp.287-300.
Keller, A.A., McFerran, S., Lazareva, A. and Suh, S., 2013. Global life cycle releases of engineered nanomaterials. Journal of Nanoparticle Research, 15(6), p.1692.
Wohlleben, W., Brill, S., Meier, M.W., Mertler, M., Cox, G., Hirth, S., von Vacano, B., Strauss, V., Treumann, S., Wiench, K. and Ma‐Hock, L., 2011. On the lifecycle of nanocomposites: Comparing released fragments and their in‐vivo hazards from three release mechanisms and four nanocomposites. Small, 7(16), pp.2384-2395.
16. Public awareness of nanomaterials has increased, but there is still uncertainty regarding safety.
A lot of information has been developed and made available to the public regarding nanomaterial safety. However, due to different perspectives regarding risk amongst experts, the message to the public has not been clear. Labeling schemes, for example, inform users of the presence, but do not indicate concern levels or hazard information about nanoscale substances. We can see why it would be confusing for the public; especially given that ‘nanomaterials’ represent a large group of materials, with a myriad of different properties and applications, and therefore risk potential. Hopefully continuing advances in the field of nanosafety, and continued transparency by regulatory agencies, academia, and industry, will continue to support public acceptance of these materials.
van Giesen, R.I., Fischer, A.R. and van Trijp, H.C., 2018. Changes in the influence of affect and cognition over time on consumer attitude formation toward nanotechnology: A longitudinal survey study. Public Understanding of Science, 27(2), pp.168-184.
Johansson, M. and Boholm, Å., 2017. Scientists’ understandings of risk of nanomaterials: Disciplinary culture through the ethnographic lens. Nanoethics, 11(3), pp.229-242.
Grieger, K.D., Hansen, S.F., Mortensen, N.P., Cates, S. and Kowalcyk, B., 2016. International implications of labeling foods containing engineered nanomaterials. Journal of Food Protection, 79(5), pp.830-842.
Brown, J., Fatehi, L. and Kuzma, J., 2015. Altruism and skepticism in public attitudes toward food nanotechnologies. Journal of Nanoparticle Research, 17(3), p.122.
17. Collaboration is key to advancing the environmental health and safety knowledge base and practices.
Nanotoxicology, as well as exposure, environmental and risk analysis are interdisciplinary sciences – due to the complex challenges outlined here, it is clear that collaboration between biologists, chemists, computational scientists, physicists, engineers, ethicists, and more, as well as between stakeholders in academia, industry, government and the public is essential. This is well reflected in the make-up of large projects, such as the Nano Health and Safety Consortium, the Graphene Flagship, the HSPH-NIEHS Nanosafety Center, and in meetings and workshops such as the “Quantifying Exposure to Engineered Nanomaterials from Manufactured Products” (QEEN/QEEN II) where the combined expertise of many fields work together to advance nanomaterial science.
Geraci, C.L., Tinkle, S.S., Brenner, S.A., Hodson, L.L., Pomeroy-Carter, C.A. and Neu-Baker, N., 2018. Launching the dialogue: Safety and innovation as partners for success in advanced manufacturing. Journal of Occupational and Environmental Hygiene, 15(6), pp.D45-D50.