Letter to the Editor pubs.acs.org/est
Cite This: Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Response to Comment on “Risk Assessments Show Engineered Nanomaterials To Be of Low Environmental Concern”
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most accurate estimate of production volumes seems difficult to tell in general and may depend on specific details in the respective estimations. In the best of worlds, the two approaches should provide results within the same order of magnitude, although that does not seem to be the case for ENMs at the moment.9
n a Viewpoint, I reviewed risk characterization factors (RCRs) for engineered nanomaterials (ENMs) from bestestimate scenarios in seven environmental risk assessment studies.1 The result was that ENMs seem to be of low environmental concern since the RCRs were mostly well below 1. In a comment, Musee raises concerns about the validity of the reviewed RCRs and questions whether such conclusions can be drawn from them.2 He further writes that the material flow-based approaches in the reviewed studies are only suitable as first-tier screening tools. I agree that the seven studies reviewed are to be seen as first-tier assessments, and it is as such they were reviewed. As stated in the Viewpoint, “[t]here still remain a number of data gaps and challenges related to the production of ENMs, the release of ENMs from products, the measurement of ENMs in environmental media, the assessment of ENMs exposure to different organisms and the ecotoxicity testing of ENMs”.1 Still, a review of RCRs from first-tier assessments may provide some preliminary insights, and I maintain that a main insight from the studies conducted so far is that ENMs seem to be of low environmental concern. Musee also raises some more detailed concerns related to the calculation of the RCRs. I understand the most important to be (1) measured environmental concentrations (MECs) of ENMs often exceed the predicted environmental concentrations (PECs) used to calculate the RCRs, (2) sublethal toxic effects were not considered, (3) no observable effect concentrations (NOECs) were used, (4) RCRs between 0.1 and 1 can also imply risk, and (5) top-down approaches were used to derive global production data.2 Regarding point 1, the review study cited by Musee does not seem to fully support this concern: there were some cases (fullerenes and nanosized zinc oxide in wastewater, nanosized titanium dioxide in biosolids, and fullerenes in the atmosphere) in which the highest MEC was higher than the highest PEC.3 However, for nanosized titanium dioxide and silver in surface and waste waters, as well as for nanosized silver in biosolids, the opposite was true. Regarding point 2, ecotoxicity data reflecting sublethal effects of ENMs were considered in most of the reviewed studies, for example from a study of algal growth inhibition4 (considered by Gottschalk et al.5), as well as from a study of egg hatching times and morphological alterations for zebrafish6 (considered by Wang et al.7). Regarding point 3, most of the reviewed studies indeed employed NOECs to calculate RCRs, which may be seen as a drawback that future studies can improve on. Regarding point 4, I maintain that 1 is a relevant threshold level for RCRs in accordance with the mainstream literature on risk assessment of chemicals,8 even though specific studies applying other threshold levels can be found. Regarding point 5, the production volumes employed in the reviewed studies are indeed based on top-down global and regional (e.g., European Union and United States) estimations. Whether a top-down down-scaling of global production volumes or a bottom-up summing of ENMs in different products used in the geographic area of interest provide the © XXXX American Chemical Society
Rickard Arvidsson*
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Environmental Systems Analysis, Chalmers University of Technology, Vera Sandbergs Allé 8, SE 412 96 Gothenburg, Sweden
AUTHOR INFORMATION
Corresponding Author
*Phone: +46 (0) 31 772 2161. E-mail: rickard.arvidsson@ chalmers.se. ORCID
Rickard Arvidsson: 0000-0002-9258-0641 Notes
Environmental Science & Technology edits all Letters for length, punctuation, and clarification of references. Authors approve of changes prior to publication. The author declares no competing financial interest.
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ACKNOWLEDGMENTS The financial support from the Swedish Research Council Formas is gratefully acknowledged. I furthermore thank Anna Furberg and Sverker Molander for comments on a draft of this response.
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REFERENCES
(1) Arvidsson, R. Risk Assessments Show Engineered Nanomaterials To Be of Low Environmental Concern. Environ. Sci. Technol. 2018, 52 (5), 2436−2437. (2) Musee, N. Comment on “Risk Assessments Show Engineered Nanomaterials to Be of Low Environmental Concern”. Environ. Sci. Technol. 2018, DOI: 10.1021/acs.est.8b02070. (3) Gottschalk, F.; Sun, T.; Nowack, B. Environmental concentrations of engineered nanomaterials: Review of modeling and analytical studies. Environ. Pollut. 2013, 181 (0), 287−300. (4) Aruoja, V.; Dubourguier, H.-C.; Kasemets, K.; Kahru, A. Toxicity of nanoparticles of CuO, ZnO and TiO2 to microalgae Pseudokirchneriella subcapitata. Sci. Total Environ. 2009, 407 (4), 1461−1468. (5) Gottschalk, F.; Sonderer, T.; Scholz, R. W.; Nowack, B. Modeled Environmental Concentrations of Engineered Nanomaterials (TiO2, ZnO, Ag, CNT, Fullerenes) for Different Regions. Environ. Sci. Technol. 2009, 43 (24), 9216−9222. (6) Fent, K.; Weisbrod, C. J.; Wirth-Heller, A.; Pieles, U. Assessment of uptake and toxicity of fluorescent silica nanoparticles in zebrafish (Danio rerio) early life stages. Aquat. Toxicol. 2010, 100 (2), 218−228. (7) Wang, Y.; Kalinina, A.; Sun, T.; Nowack, B. Probabilistic modeling of the flows and environmental risks of nano-silica. Sci. Total Environ. 2016, 545−546, 67−76.
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DOI: 10.1021/acs.est.8b02738 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Environmental Science & Technology
Letter to the Editor
(8) van Leeuwen, C. J. General introduction. In Risk Assessment of Chemicals: An Introduction, 2nd ed.; van Leeuwen, C. J., Vermeire, T. G., Eds.; Springer: Dordrecht, 2007. (9) Wigger, H.; Wohlleben, W.; Nowack, B. Redefining environmental nanomaterial flows: consequences of the regulatory nanomaterial definition on the results of environmental exposure models. Environ. Sci.: Nano 2018, DOI: 10.1039/C8EN00137E.
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DOI: 10.1021/acs.est.8b02738 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
