CarboSafe - Characterising the environmental behaviour and ecotoxicological potential of carbon nanotubes (UBC)

Projektlaufzeit: 2008-2012 

Leitung:

Prof. Dr. rer. nat. Andreas Schäffer
Dr. rer. nat., ir. Hanna Maes


Bearbeitung:

Dipl.-Biol. Helga von Lochow


 Auftraggeber:

Förderung durch Bundesministerium für Bildung und Forschung (BMBF)
Projekt Carbosafe, Teilprojekt der Innovationsallianz CNT: Inno.CNT www.inno-cnt.de

Project partners:

- BAM Bundesanstalt für Materialforschung und -prüfung
- BAUA Bundesanstalt für Arbeitsschutz und Arbeitsmedizin
- Bayer MaterialScience AG
- Bayer Technology Services GmbH
- IUTA Institut für Energie- und Umwelttechnik e. V.


Cooperation:

- Prof. Dr. W. Baumgartner, RWTH Aachen University, Institute for Biology II, Mies-van-der-Rohe-Strasse 15, 52056 Aachen, Germany
- Dr. Priv.-Doz. E. Klumpp, Forschungszentrum Jülich GmbH, Institute of chemistry and dynamics of the geosphere, ICG-4, 52425 Jülich, Germany
- Prof. Dr. K. Jones & Dr. K. Semple, The Lancaster Environmental Centre, University of Lancaster, Centre for Chemicals Management, Lancaster LA1 4YQ, Great Britain

 

Hintergrund:

Carbon nanotubes (CNTs) are considered one of the most promising materials in nanotechnology. Due to its unique properties, i.e. nanoscale size, high electrical conductivity, very lightweight, flexibility and extremely high tensile strength, this material has a lot of commercial expectations in different manufacturing sectors, e.g. electronic industries, medical applications, composite material development, aerospace technology, military purposes and energy storage. Investment in nanotechnology research and development is increasing rapidly worldwide. However, the expected widespread use of CNTs raises concern regarding potential risks to environmental and human health.

An important objective of the project Carbosafe is to perform an environmental risk assessment of carbon nanotubes (CNT). Therefore, the fate of CNT in and their effects on ecosystems are studied in order to understand the environmental behaviour and to evaluate the ecotoxicological potential of CNT.

Fate studies:

There is a distinct lack of data concerning the bioavailability of CNT to aquatic organisms. Due to the hydrophobic character of CNT surfaces, CNT are poorly dispersed in aquatic media and therefore, affinity of CNT for other particles, organisms and adsorption to sediment is likely. In organisms, the absorption, distribution, metabolism, excretion and toxicity of CNT depends on the nature of the CNT. The chemical and physical characteristics of CNT such as functionalisation, coating, length, and agglomeration state might vary and are influenced by external environmental conditions during CNT production, use, and disposal stages.    

There is a distinct lack of data concerning the bioavailability of CNT to aquatic organisms. Due to the hydrophobic character of CNT surfaces, CNT are poorly dispersed in aquatic media and therefore, affinity of CNT for other particles, organisms and adsorption to sediment is likely. In organisms, the absorption, distribution, metabolism, excretion and toxicity of CNT depends on the nature of the CNT. The chemical and physical characteristics of CNT such as functionalisation, coating, length, and agglomeration state might vary and are influenced by external environmental conditions during CNT production, use, and disposal stages.      

Radiolabelled CNT (14C-CNT) were synthesized in cooperation with Bayer Technology Services by chemical vapour deposition of 14C-benzene, resulting in nanotubes labelled at the carbon framework. This enables quantification of biological uptake and evaluation of the fate of the nanomaterial at concentrations that cannot be detected by other methods.      

Laboratory experiments are performed to

- determine the partitioning of CNT between water and sediment
- quantify uptake of CNT by both sediment-dwelling organisms (the worm Lumbriculus variegatus and larvae of the midge Chironomus riparius) and organisms of the water phase (the alga Desmodesmus subspicatus, waterflea Daphnia magna and a fish Danio rerio)
- study food chain transfer of CNT
- evaluate the influence of dissolved organic carbon (DOC) on CNT partitioning, bioavailabily and agglomeration in water-sediment systems
- investigate the distribution of CNT within organisms, e.g. to different fish organs
- assess the role of CNT as adsorbents for other organic compounds, like pharmaceuticals or plant protection products, and thus, as possible carriers of toxicants towards organisms.

The objectives are to identify the major sink of CNT in the environment, to balance the fate of CNT in water, sediment and biota, to derive uptake and elimination kinetics of CNT material and to assess its bioaccumulation potential after water and sediment exposure (bioconcentration) and dietary exposure (biomagnification). Spotting target tissues in organisms, using radiolabelled CNT, may be an aid to predict possible mechanisms of action, and thus, to allow for an effective selection of ecotoxicological tests for the effect studies (next §). Combining bioaccumulation and effect data, the critical body burden (CBB) can be calculated. This is an important parameter for the causal interpretation of toxicity and to compare the risks of a compound to different organisms.      

Ecosystem effect studies

Acute and chronic ecotoxicity tests are performed according to OECD Guidelines with both water and sediment dwelling organisms. If necessary, these guidelines are adapted for the testing of CNT. It is for example required to add a solubilising agent, stabilising CNT dispersions, due to the formation of CNT agglomerates in the water phase. The use of DOC in biotests for this purpose is investigated. Next to the standard tests, further tests are selected and designed considering indications to mode of actions extracted from the fate studies described above.      

The tests to be performed are:

- acute tests with Daphnia magna (OECD 202), Danio rerio (OECD 203) and Chironomus riparius (analogue to OECD 202, 203) (mortality)
- algae tests with Desmodesmus subspicatus (OECD 201; algae growth rate)
- chronic tests with Daphnia magna (OECD 211) and Chironomus riparius (OECD 218 & 219) (reproduction)
- chronic fish tests with Danio rerio (OECD 215; growth, mortality)
- sediment contact tests with Arthrobacter globiformis (DIN Draft)
- Ames assays for assessing the mutagenic action of CNT
- assays for assessing the possible endocrine effects of CNT (e.g. MVLN reporter gene assay, YES, ER-Calux)
The objectives are to provide toxicity data (LC/EC50 and NOEC) for an environmental risk assessment, to give indications of possible mode of toxic actions, to discuss whether the available standard tests are suitable for ecotoxicological evaluation of CNTs and to suggest possible adaptations of the existing guidelines in order to appropriately test CNT material.

Characterisation of CNT in different media

Another challenge in this project is to characterise and visualise CNT in the different compartments of an aquatic system in order to differentiate between agglomerates and single nanotubes. Environmental samples that show a high affinity for CNT, as quantitatively determined by means of the experiments with 14C-labelled CNT, are subjected to transmission electron microscopy (TEM), scanning electron microscopy (SEM) and two-photon excitation microscopy (TPEM).