September 13, 2010 by Peter Simpson
Last week I went to a technical workshop organised by NanoImpactNet on the hazard assessment of nanomaterials in Biota. NanoImpactNet is a coordination action funded by the EC’s 7th Framework Programme. The workshop was hosted by University College Dublin. It rained!
The objective of the workshop was to identify problems and potential solutions when studying the biological effects of nanomaterials. It was hoped that some agreement could be reached in terms of modifications required to ecotoxicity methods for fundamental research and more applied regulatory testing.
I started out by giving a presentation on ‘standard’ methods for assessing chemicals and a broad overview of current regulatory requirements for ecotox test data. Jukka Ahtiainen from the Finnish Environmental Institute/OECD then gave an update on OECD coordinated efforts to characterise the toxicity of nanomaterials and, whilst doing this, aid the further development of standardised testing protocols for nanomaterials.
There were then specific workshop sessions on soils/sediments, aquatic invertebrates, algae, fish and in vitro methods.
Hopefully the output of the workshop will be a paper (tentatively targeted at ecotoxicology) produced before Christmas. I’m scheduled to write the section on current tests with Jukka and contribute to the conclusions:
Some specific points of interest from the workshop, at least from my perspective, as follow:
- Many of the difficulties associated with testing nanomaterials is not because they are small it is rather, compared to conventional ‘chemicals’, because they are large! This was a bit of an epiphany!;
- Despite this, testing the ecotoxicity nanomaterials is not fundamentally different from testing conventional chemicals. However there are some areas that need further understanding:
- Conventional solvents are not suitable for aiding the dissolution of nanomaterials because they can damage the surface of structures (nanotubes, C60). Sonication can also damage materials;
- ‘Dispersants’ may be a better term for substances added to tests with nanomaterials to help them from falling out of suspension (e.g. dissolved organic carbon, bovine serum albumin, protein solution), but their use is not well understood at the moment (e.g. use of DOC could reduce to toxicity of free ions released from materials for instance and BSA causes an immune response in fish). Stirring solutions is effective in some cases, but length of time reported (~3 months) is extremely long;
- Many nanomaterials are photoactive and produce reactive oxygen free radicals. As this may be their principal mode of action is might be important to conduct tests under lighting that simulates sunlight;
- ‘Characterisation’ of nanomaterials (mass, particle size distribution, surface area, zeta potential) is fundamental to comparing results between labs and different nanomaterials. Characterisation is currently very difficult in sediments/soils and in biota. However, this might be an issue for fundamental research rather than regulatory testing and risk assessment. However, there is always the problem of false negatives (were these test organisms actually exposed?);
- Nanomaterials can be ‘functionalised’ by the media in which they are tested. This is no different to changes in metal speciation that could occur at different pH levels for instance, but could drive stricter definitions from test media for nanomaterials testing (e.g. more artificial media potentially);
- Concept of equilibrium in conventioanl bioaccumulation testing is fundamentally flawed in relation to nanomaterials. Uptake via diet likely to be more important than from aqueous phase (endocytosis);
- Ames test for genotoxicity assessment may not be fit for purpose (nanomaterials cannot pass through agar matrix and cell wall);
- Sediment and soil testing may be more appropriate then aqueous phases at early tiers of nanomaterial hazard and risk assessment because of their partitioning behaviour.
Other groups e.g. OECD are also working on guidance for conducting tests with nanomaterials and it is hoped that anything we produce will feed into this ongoing work.