Letter to the Editor pubs.acs.org/est
Cite This: Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Comment on “Risk Assessments Show Engineered Nanomaterials To Be of Low Environmental Concern”
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rvidsson’s1 opinion on environmental risks of engineered nanomaterials (ENMs) raises concerns since drawn conclusions have implications for future management of ENMs risks. The materials flow analysis (MFA) approach used in estimating risk quotient (RQ) relies on several assumptions; hence yields findings with uncertainties too high to support the categorical conclusions drawn.1 This is particularly problematic for emerging contaminants like ENMs that are characterized by many unknowns concerning their environmental exposure and toxicity. Herein, reasons why such conclusions1 remain inconceivable based on current science are outlined. Studies cited in Arvidsson1 used MFA to estimate ENMs risks in the environment by calculating predicted environmental concentrations (PECs) in the absence of measured environmental concentrations (MECs). A recent review2 demonstrated that MECs for several ENMs in certain environmental compartments were higher than PECs, implying higher RQs than those derived using PECs. As low concentrations of ENMs are incorporated in nanoproducts (w/w ≤ 5%),3 their likely emitted concentrations into the environment are expected to remain low.4 ENMs at low concentrations (μg) can induce effects at sublethal levels following coexposure with micropollutants5 to aquatic organisms, for example, DNA damage. Yet, while sublethal effects are known to be deleterious to organisms, they are excluded from the hazard data used in MFA models including for ENMs. Therefore, inferences that ENMs are of low concern to the environment raise concerns because ENMs studies suggest otherwise.5 Predicted no-effect concentrations (PNECs) used in MFA models to estimate RQ rely on no observable effect concentrations (NOECs). However, NOECs cannot describe the exposure−response (or dose−response) curve needed to establish the link between exposure and effect in environmental toxicology.6 Since NOECs (with their limitations) are used in MFA, hence the reliability of risk results derived becomes questionable. ECB categorizes risk using a binary system where RQ ≥ 1 (risk exists) or RQ < 1 (no risk),7 while other systems rank RQs between 0.1 and 1 as medium risk.8 Furthermore, MFA model mass inputs based on global production statistics for given ENMs, introduce high uncertainty to the results. Thus, top-down approaches cannot justify absence of ENMs risks simply because bottom-up approaches that are more reliable for estimating mass input9 remain largely unexplored for ENMs. A different system would likely emerge if MFA were to be developed for the first time using current scientific understanding on distinctive ENMs attributes. Furthermore, OECD is revising technical guidelines to improve accuracy in measuring ENMs toxicity and exposure in aquatic systems. The above reasons, plus the Arvidsson1 caveats, for example, “...few realistic modeling results...”, do not support the conclusion that ENMs are of low environmental concern. Such a conclusion is unconvincing because an in-depth data © XXXX American Chemical Society
critique yields a different outcome. In addition, the use of a logarithmic scale masks vital data insights and reported RQs > 1 remain inadequately explained. Unsurprisingly, the few active ENMs MFA studies in this field is perhaps an acknowledgment of these limitations. While MFA is useful as a first-tier rapid screening tool for high-volume chemicals, its suitability as a tool for ENMs remains questionable.
Ndeke Musee*
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Emerging Contaminants Ecological Risk Assessment (ECERA) Group, Department of Chemical Engineering, University of Pretoria, Hatfield 0028, Pretoria South Africa
AUTHOR INFORMATION
Corresponding Author
*Phone: +27 12 420 2048. E-mail:
[email protected]. ORCID
Ndeke Musee: 0000-0002-5096-492X 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 Water Research Commission (WRC) (K5/2509/1), South Africa, and University of Pretoria (AOY229), South Africa, are greatly acknowledged. Dr. Peter Ashton’s willingness to edit the letter is graciously appreciated.
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REFERENCES
(1) Arvidsson, R. Risk assessments show engineered nanomaterials to be of low environmental concern. Environ. Sci. Technol. 2018, 52, 2436−2437. (2) Gottschalk, F.; Sun, T. Y.; Nowack, B. Environmental concentrations of engineered nanomaterials: review of modelling and analytical studies. Environ. Pollut. 2013, 181, 287−300. (3) Musee, N. A model for screening and prioritizing consumer nanoproduct risks: A case study from South Africa. Environ. Int. 2017, 100, 121−131. (4) Sun, T. Y.; Conroy, G.; Donner, E.; Hungerbuhler, K.; Lombi, E.; Nowack, B. Probabilistic modelling of engineered nanomaterial emissions to the environment: a spatiotemporal approach. Environ. Sci.: Nano 2015, 2, 340−351. (5) Mahaye, N.; Thwala, M.; Cowan, D. A.; Musee, N. Genotoxicity of metal based engineered nanoparticles in aquatic organisms: a review. Mutat. Res., Rev. Mutat. Res. 2017, 773, 134−160. (6) Landis, W. D.; Chapman, P. M. Well past time to stop using NOELs and LOELs. Integr. Environ. Assess. Manage. 2011, 7 (4), vi− viii. (7) Technical Guidance Document on Risk Assessment: Part 1; European Chemicals Bureau, Institute for Health and Consumer Protection, European Commission: Dublin, Ireland, 2003.
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DOI: 10.1021/acs.est.8b02070 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Environmental Science & Technology
Letter to the Editor
(8) Al Aukidy, M.; Verlicchi, P.; Voulvoulis, N. A framework for the assessment of the environmental risk posed by pharmaceuticals originating from hospital effluents. Sci. Total Environ. 2014, 493, 54− 64. (9) Domercq, P.; Praetorius, A.; Boxall, A. B. A. Emission and fate modelling framework for engineered nanoparticles in urban aquatic systems at high spatial and temporal resolution. Environ. Sci.: Nano 2018, 5, 533−543.
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DOI: 10.1021/acs.est.8b02070 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
