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EHS Testing of Products Containing Nanomaterials: What is Nano Release? Jonathon A. Brame,* Aimee R. Poda, Alan J. Kennedy, and Jeffery A. Steevens U.S. Army Engineer Research and Development Center Vicksburg, Mississippi 39180-6199, United States addition to focusing on potential release of the original (or transformed) ENM included in the product, we should also be more cognizant of other nanosized particles (such as those from the matrix) that are released during use and end of life. Now that nanomaterials are being actively engineered into consumer products, regulators face the difficult task of determining when, where, how and to what extent ENMs should be controlled to protect humans and the environment.3 While the past few years have seen a significant and laudable increase in studies focusing on EHS risks of ENMs, questions surrounding how to experimentally measure the effects of ENMs released into the environment remain. For example, what is an “environmentally relevant concentration” of a nanoparticle? If an ENM is transformed (dissolved, aggregated, reacted, annealed, etc.) during manufacture, use, release or environmental exposure, should it be treated differently than pristine nanoparticles?4 And how do we determine the exposure potential of ENMs from a product containing nanomaterials? In absence of better data, an ultra-conservative risk assessment approach is to assume 100% release of the ENM from a product.1 However, this dramatically overestimates release and does not provide a clear picture of the mid the boom of scientific discoveries related to materials (nano or otherwise) to which receptors will engineered nanomaterials (ENMs) and the rapid rise of eventually be exposed. While almost all ENM toxicity testing nano-enhanced consumer products, environmental health and is performed on individual, pristine ENMs, only 15% of the safety (EHS) practitioners are struggling to define relevant nanocomposite release studies reviewed by Froggett et al.2 exposure scenarios and potential EHS risks of ENMs. The identified individual ENMs released during testing. Meanwhile, hazard portion of the risk paradigm remains an active research the majority of release testing showed release of nanosized topic, with investigations on the potential for nanounique particles of the matrix (either with or without embedded implications related to various properties of pristine ENMs ENMs), which are not exposed to any rigorous, nanospecific (reactivity, surface area, morphology, carcinogenicity). Meantoxicity testing. It is currently unclear if these non-engineered, while, much less focus has been given to ENM exposure unintentional nanoparticles will fall under the same regulatory scenarios, and even less focus to defining the potential for guidelines as any other bulk material (as released particulate relevant release of ENMs or other nanosized particles from matter), with no special nanospecific treatment, or if they will products containing nanomaterials. Establishing the exposure be included in nanospecific regulatory scrutiny. To highlight this question of “what is nano” when materials portion of ENM risk by determining what and how much are released from a product containing nanomaterials, we materials are actually released throughout the ENM lifecycle is performed aggressive release tests on a series of everyday critical to understanding the overall risk of ENMs. A greater materials in an enclosed abrasion test chamber (modified Taber focus on the structural categories of ENM-incorporated abrader concept) while measuring the particle size distribution technologies, relevant release scenarios and characterization of of the released particles. We then compared these release the released material’s size, composition and transformation is results to the particle size distribution of a direct injection of needed.1 Another rarely considered aspect of EHS for ENMs powdered TiO2 nanoparticles (NIST standard 1898, 30−50 nm and the subject of this viewpointis how to define the “nano” nominal particle size) to determine which is more “nano”, in materials released from nano-enhanced consumer products according to the size distribution of aerosolized particlesa during their use. Release testing of ENM-containing nanocommonly used ENM, or particles released during abrasion of composites shows that of all possible release types (ENM alone, everyday household items, including wood, cardboard, glass, ENM embedded in matrix, ENM dissolved into ionic form, matrix alone without ENM), the most commonly identified released material is the matrix alone, followed by ENMs Received: August 28, 2015 embedded in/protruding from the matrix.2 Therefore, in
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This article not subject to U.S. Copyright. Published XXXX by the American Chemical Society
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DOI: 10.1021/acs.est.5b04173 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Environmental Science & Technology
Viewpoint
Figure 1. Particle size distribution of particles released during abrasion of several household materials (wood, cardboard, glass, and plastic) compared to powdered nano TiO2 injected directly into the abrasion test chamber. (4) Lowry, G. V.; Gregory, K. B.; Apte, S. C.; Lead, J. R. Transformations of Nanomaterials in the Environment. Environ. Sci. Technol. 2012, 46 (13), 6893−6899. (5) Slezakova, K.; Morais, S.; Pereira, M. d. C. Atmospheric nanoparticles and their impacts on public health. In Current Topics in Public Health; Rodriguez-Morales, D. A., Ed.; InTech, 2013.
and plastic. Figure 1 shows the particle size distributions for aerosolized particles released from these materials during abrasion, divided into ultrafine particle size (100 nm).5 Surprisingly, the most clearly identifiable nanosized materials released during abrasion came from plastic and glass, and not the engineered nano-TiO2. These results should not be interpreted to imply that plastic and glass released during abrasion are more hazardous than TiO2. Instead, we present Figure 1 to ask the scientific community and regulators what aspects of nano release should be part of risk considerations and regulatory compliance decisions? If size-specific toxicity is a regulatory roadblock for products containing ENMs, should we also test for size-specific toxicity in other products that could release non-engineered nanoparticles during normal use? Or should regulation of ENM-containing products simply entail the same release and toxicity testing requirements as any other consumer product? The answers to these questions are not straightforward, but they will be essential to aid scientists and regulators alike in the search for balance between enabling distribution of novel technologies and ensuring that those new technologies do not pose significant risks to the public or the environment.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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REFERENCES
(1) Collier, Z.; Kennedy, A.; Poda, A.; Cuddy, M.; Moser, R.; MacCuspie, R.; Harmon, A.; Plourde, K.; Haines, C.; Steevens, J. Tiered guidance for risk-informed environmental health and safety testing of nanotechnologies. J. Nanopart. Res. 2015, 17 (3), 1−21. (2) Froggett, S. J.; Clancy, S. F.; Boverhof, D. R.; Canady, R. A. A review and perspective of existing research on the release of nanomaterials from solid nanocomposites. Part. Fibre Toxicol. 2014, 11, 17. (3) Wiesner, M. R.; Lowry, G. V.; Alvarez, P.; Dionysiou, D.; Biswas, P. Assessing the risks of manufactured nanomaterials. Environ. Sci. Technol. 2006, 40 (14), 4336−4345. B
DOI: 10.1021/acs.est.5b04173 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
