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Smart Nanotoxicity Testing for Biodiversity Conservation Lan Song* Leiden University, The Netherlands
Martina G. Vijver Leiden University, The Netherlands
Willie J. G. M. Peijnenburg Leiden University, The Netherlands National Institute for Public Health and the Environment, Bilthoven, The Netherlands
Geert R. De Snoo Leiden University, The Netherlands
R
isk assessment of nanoparticles (NPs) currently focuses on NP-specific properties and metrics affecting the environmental fate and effects of the particles, with little attention given to extrapolating potentially adverse effects with a view to protecting biodiversity. Given the huge diversity of species in ecosystems, evaluating these effects on the basis of current research directions is problematic. After all, it is unrealistic to either test the diversity of NPs across all taxonomic groups and species under various environmental conditions, or extrapolate the current set of NP toxicity data to other (nontested) species in ecosystems. Indeed, the potential adverse effects of NPs in nature are still largely unknown, and NP risk assessment faces major challenges when it comes to investigating nanotoxicological implications for biodiversity conservation. r 2011 American Chemical Society
We suggest that an approach based on ecological traits could be extremely helpful for interpreting NP toxicity test results and efficiently extrapolating them to living ecosystems. “Ecological traits” usually refer to measurable morphological and physiological characteristics and ecological attributes of species that are comparable within and across species. Examples include the following: organism surface area, target site distribution, dispersal mode, respiratory mode, and reproduction mode, etc.1 Traits are taxa-independent, since the same trait modality can be found across a range of taxa. Baird et al.2 were the first to propose that such traits would help link the potential toxicity of contaminants to wide arrays of organisms and thus allow for better interpretation of the vulnerability of species to toxicants in terms of the ecological functions of the organisms in question. Quantitative, mechanistic links between such traits and the toxicokinetic end points of organisms have been identified experimentally by exposure of organisms to pesticides.3 However, as far as we are aware ecological traits have never been related to risk assessment of NPs. A trait approach is even more meaningful for extrapolating the toxicity profiles of NPs than it is for pesticides and other chemicals. Due to the unique properties of NPs, such as their shape and highly specific reactivity, interactions between NPs and organisms are far more target-oriented and determined by organism morphology and physiology than in the case of “regular” chemicals. Given the specific interactions between NPs and organisms in ecosystems, a trait-based framework can be established that comprises environmental characteristics, particle properties, and ecological traits (Figure 1). Normally, external exposure concentrations and internal reaction mechanisms are responsible for the actual damage of toxicants to organisms. On the one hand, environmental characteristics and the particle properties of NPs are the main factors determining the stability (zeta potential), fate, and distribution of NPs in the environment. Subsequently, these parameters
Published: July 05, 2011 6229
dx.doi.org/10.1021/es202094w | Environ. Sci. Technol. 2011, 45, 6229–6230
Environmental Science & Technology
Figure 1. Trait-based framework. Environmental characteristics: determining the fate of NPs; particle properties: including parameters that could be used to describe the properties of NPs; ecological traits: representing any physiological or morphological property and the evolutionary life history of organisms, as long as these are comparable across different species.
influence the effective external exposure concentration of NPs and the potential damage to the species in the different compartments. On the other hand, the internal reaction mechanisms of NPs depend largely on the morphological and physiological characteristics and the life pattern of organisms. By establishing relationships among environmental characteristics, NP particle properties, and ecological traits, the external exposure and internal reaction mechanism of NPs can be systematically described. Many research studies provide concrete evidence of how to adopt the trait-based framework for assessing nanotoxicity. For instance, it has been found that the interaction between nanoparticles and algae is mainly at the algal surface because of the highly reactive surface of algae and the high surface/volume ratio of both NPs and algae.4 Hence, trait modalities such as surface type, total surface area, and the intrinsic membrane mechanisms that protect algae from excess nutrients could be important factors that affect the potential toxicity of NPs. These trait modalities can be applied across species and therefore permit extrapolation of toxicity patterns of NPs across algae, higher plants, and cells. In addition, it has been demonstrated that NPs cause inhibition of exchange processes across fish gills, while no histological or biochemical evidence for damage to other organs could be observed.5 The gill is therefore the most likely primary target of NP exposure. In the context of the trait approach discussed here, it is critical to evaluate the role of gill morphology and physiological processes in determining the toxicity of NPs to fishes before toxicity data can be extrapolated from one fish species to another. The traits approach provides a third research direction and improves testing systems of NPs by regarding characteristics of species in ecosystems. Moreover, it creates a basis for extrapolating the toxicity of NPs within and across species, because NPs are anticipated to act according to similar toxicity mechanisms and cause similar damage to organisms having the same trait modalities under similar exposure conditions. Another advantage of the trait approach is that it permits distinct treatment of the sensitivities of the same type of organisms to NPs in different life stages and under different sexualities. The drawback of the trait approach lies in the increased complexity of NP risk assessment
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and the requirement to document species traits during experiments. However, once the system is established and suitable traits are defined, the extrapolation of experimental toxicity data can be easily carried out because initial trait data sets have already been created within the discipline of ecology.3 Consequently, fewer species and less time will be needed for determining the toxicity of NPs experimentally. A major gap in knowledge that presently hampers application of such a framework is the lack of a basis for relating ecological traits and toxicity results, since little experimental data on the individual morphology and physiology of organisms are reported in NP toxicity testing, thus constraining extrapolation of NP toxic effects within and across species. To implement the trait-based framework and protect all species at different life stages under diverse environmental conditions, we suggest that research priority be given to establishing databases that systematically document the trait modalities of individual experimental species, types and properties of NPs, and exposure conditions, as well as the corresponding toxicity of NPs. Given the rapid growth of nanotechnology and the wide diversity of species in living ecosystems, the trait-based framework deserves priority in the risk assessment of NPs.
’ AUTHOR INFORMATION Corresponding Author
*Mail: Institute of Environmental Sciences (CML), Leiden University, Einsteinweg 2, PO Box 9518, 2333 CC Leiden, The Netherlands; e-mail:
[email protected].
’ ACKNOWLEDGMENT L.S. is sponsored by the Environmental ChemoInformatics (ECO), Marie Curie Initial Training Network within the seventh research framework programme of the European Union (238701). M.G.V. is supported via VENI grant (863.08.023) awarded by The Netherlands Organization for Scientific Research (NWO). Part of the work was performed within the framework of the RIVMsponsored project “IRAN”. We thank Nigel Harle for his editing of the English. ’ REFERENCES (1) Webb, C. T.; Hoeting, J. A.; Ames, G. M.; Pyne, M. I.; Poff, L. N. A structured and dynamic framework to advance traits-based theory and prediction in ecology. Ecol. Lett. 2010, 13, 267–283. (2) Baird, D. J.; Rubach, M. N.; Van den Brink, P. J. Letter to the Editor: Trait-based ecological risk assessment (TERA): The new frontier? Integr. Environ. Assess. Manage. 2008, 4, 2–3. (3) Rubach, M. N. Predicting the response of aquatic invertebrates to stress using species traits and stressor mode of action. PhD dissertation, Wageningen University, Wageningen, NL, 2010. (4) Van Hoecke, K.; Quik, T. K.; Mankiewicz-Boczek, J.; De Schamphelaere, K. A.C.; Elsaesser, A.; Van der Meeren, P.; Barnes, C.; McKerr, G.; Howard, V. C.; Van De Meent, D.; Rydzynski, K.; Dawson, K. A.; Salvati, A.; Lesniak, A.; Lynch, I.; Silversmit, G.; De Samber, B.; Vincze, L.; Janssen, C. R. Fate and effects of CeO2 nanoparticles in aquatic ecotoxicity tests. Environ. Sci. Technol. 2009, 43, 4537–4546. (5) Griffitt, R. J.; Weil, R.; Hyndman, K. A.; Denslow, N. D.; Powers, K.; Taylor, D.; Barber, D. S. Exposure to copper nanoparticles causes gill injury and acute lethality in zebrafish (Danio rerio). Environ. Sci. Technol. 2007, 41, 8178–8186. 6230
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