Grouping of nanomaterials regarding environmental risk – Are the generally discussed physical-chemical parameter suitable and sufficient?

K. Hund-Rinke, M. Herrchen, D. Kühnel, C. Kussatz, C. Nickel, K. Schwirn, D. Völker
Fraunhofer Institute for Molecular Biology and Applied Ecology,

Keywords: grouping, read-across, regulation, ecotoxicity, fate


Given the large variety of engineered nanomaterials (ENMs), the effort for the individual investigation and assessment would be enormous. Therefore, it is necessary to develop approaches that allow an adequate risk assessment of ENMs and avoiding individual testing of a large number of different forms. The identification of groups consisting of ENMs with comparable fate and ecotoxicity based on literature data is limited due to fragmented reporting of nanomaterials’ physical-chemical properties, the application of different metrics and methods to characterize the ENMs as well as a high variability in the applied test procedures. All differences in the applied characterization method and testing approach can affect the outcome, whereby the extent of the impact is often unknown. The prediction is even more difficult if several parameters with potential additive, synergistic or antagonistic effects have to be considered. In addition, it has to be taken into account that these parameters can vary under different environmental conditions. Comprehensive systematic and standardized characterization and testing are key in order to promote grouping of ENMs regarding their fate and effect. Regarding fate in the environment, transformation and mobility have to be considered for the compartments air, water and sediment/soil. Based on a literature review, it seems that the surface properties of ENMs are of major relevance for a grouping regarding environmental fate. Whether this observation still holds true in the natural environment with different types and concentrations of natural organic matter has yet to be proven. Regarding grouping with focus on environmental effects, progress is made for metals and metal oxides. The experimental results of a systematic testing of a limited number of ENMs show that mono-causal relationships do not exist. A simple grouping of ENMs (same chemical composition) or read-across considering just on one parameter does not seem to be possible. Various physical-chemical parameters and the dependence of results on the choice of test organisms and test conduct have to be considered. For instance, for ion-releasing ENMs the solubility is discussed as relevant parameter causing ecotoxicity. However, due to significant discrepancies between solubility and ecotoxicity, it has to be assumed that for ion-releasing ENMs also particle effects and the morphology of the ENMs as well as the choice of the test organism have to be taken into account. Solubility as a single basis for grouping and read-across seems to be suitable only in certain cases. Additionally it was shown that modifications of ENMs can affect the test organisms differently. This fact complicates also the development of QSARs (quantitative structure activity relationships). In the future there is a need to indicate whether a grouping regarding environmental risk will be possible based on the grouping regarding fate and effect.