DENANA – Design criteria for sustainable nanomaterials
One of the major objectives of DENANA was to derive design criteria and to test the usability of data generated in the project for hazard and risk assessment of nanomaterials. The nanomaterials silicon dioxide, (SiO2), cerium dioxide (CeO2) and silver (Ag) were chosen due to their market relevance as they are added, among other things, to lubricants, catalytic convertors, medical products and abrasives and a potential environmental exposure of these nanomaterials. In order to differentiate between the potential of certain nanomaterial properties to influence a specific environmental behaviour or an environmental effect and thus to function as possible design criteria, variations of these nanomaterials were prepared and tested in different behavioural and effect investigations.
Europium- and Palladium-doped CeO2-NMs and functionalized SiO2-NMs were prepared in the frame of the DENANA project and extensively studied for their toxic potential in water and soil. Goal of the developmental work on the SiO2-NM was to optimise lubricants. In addition to the ecotoxicological effects of nanomaterials, questions on the behaviour of nanomaterials in soils and sediments, especially mobility and transport, were considered.
Only very limited statements on the relevance of the tested differences in the physico-chemical properties of the nanomaterials with regard to the ecotoxicological effects can be made since no clear effects or clear differences of effects and behaviour between the various nanomaterials occurred. Therefore, it is hard to assess the relevance of the individual physicochemical properties as design criteria for environmentally sound nanotechnology applications. Based on the data generated in DENANA, however, qualitative statements on the suitability of the various physicochemical properties as relevant design criteria for applications using the three nanomaterials are possible. The following relevant parameters were identified: core material, ion toxicity, solubility and zeta potential. The suitability of primary particle size and ROS formation potential as design criteria for nanomaterials cannot be determined based on the DENANA data. In addition, the agglomeration behaviour under environmental conditions should be considered for the respective application scenarios.
Furthermore, the ecotoxicological behaviour of the nanomaterials affected other properties, which are critical for an environment-friendly, harmless design. Throughout the investigation period of 3 years, the Ag-NM continuously caused negative effects in the investigated soil microorganisms (ammonium-oxidizing microorganisms with substrate-induced respiration) under field conditions, which could not be reversed by sulphidation of the Ag-NM. For sewage sludge applications it is therefore necessary to assume an accumulation of the respective substance and, in the case of silver, a significant increase in the toxicity to the soil microorganisms. This impairment can also be demonstrated in advance in short-term laboratory tests, which can thus serve as early warning indicators for toxic, soluble nanomaterials such as Ag-NM.
Aquatic test systems showed the crucial importance of chronic test systems (algae growth, daphnia reproduction) in the investigation of nanomaterials. An important finding is that the aquatic toxicity observed in chronic tests is caused by agglomeration of the nanomaterials, which causes mechanical / physical effects such as clouding or attachment to the test species, but also malnutrition. An uptake of nanomaterials into plant roots could be demonstrated for Ag-NM and CeO2-NM.
Work on the behaviour of nanomaterials in soil showed that different stabilisation mechanisms of Ag-NM and soil properties lead to variations in the nanomaterials’ mobility in environmental media. Furthermore, the results showed that formulations and dispersion aids can also influence the toxicity of the nanomaterials or, in the case of non-toxic SiO2-NMs, even cause it.
