February 10, 2012 by Rhiannon Smith
At the beginning of January, I attended a three-day SETAC “summer-school” entitled ‘The synthesis, characterisation, ecotoxicity, and hazard and risk assessment of engineered nanoparticles’. The workshop was run in the School of Biomedical and Biological Sciences at Plymouth University. Attendees, from across Europe and even North and South America, represented a range of academic and industrial institutions, with backgrounds both inside and outside the nanotechnology sector.
It was a busy three days, including a series of lectures by Richard Handy, Rik Brydson, Andrew Nelson, Claus Svendsen and Richard Owen and practical sessions held in the laboratory. There was even time for an impromptu tour of the aquaculture and food nutrition facilities. Topics covered in the lectures included:
- Varieties, structures, chemical classifications and ecotoxicology of nanoparticles
- Practical approaches to particle characterisation
- Colloid chemistry and particles properties of relevance to ecotoxicology
- Ecotoxicity testing with fish, invertebrates and algae
- Soils and tests with soil micro-organisms
- Environmental concentrations and the fate of nanoparticles in real ecosystems
- Risk assessment and policy issues
Practical sessions in the laboratory included:
- Synthesis of gold nanoparticles
- Light scattering for particle size determination
- Nanoparticle tracking analysis (NTA) for particle size distributions
- Critical coagulation concentrations and the Schultz-Hardy rule
- Ecotoxicity tests with nanoparticles using Daphnia
- ICP-MS and ICP-OES methods for determining metal particles
The workshop showed that research and discussions on the environmental fate and hazards of nanoparticles has been going on for several years, though currently there are few definitive answers.
A variety of techniques are used to characterise nanoparticles. However, some of these reveal characteristics of the solution/suspension system rather than the nanoparticles themselves, which is problematic. The use of suspensions at different concentrations and in different media will also affect nanoparticle properties i.e. the degree of dispersion and the form/speciation of particles.
There are knowledge gaps regarding appropriate ecotoxicity testing strategies, but there is consensus that the overall hazard assessment process is likely to be fit for purpose. Details of methodologies, including preparation and dispersion methods, are likely to need some revision for the appropriate assessment of nanoparticles. It is not yet clear whether ageing of nanoparticles is needed prior to conducting tests.
The biggest problem with predicting concentrations of nanoparticles in the environment is assessing how much the nanoparticles are actually used and lost to the environment. Sewage treatment plants are expected to be the most likely route, but nanoparticles in wastewater are very likely to aggregate/agglomorate with other nanoparticles and/or other particles before and during treatment. Likely releases to the environment are therefore very difficult to predict.
With regard to risk management, it is too late for a moratorium as nanomaterials are already in general use. Although technically REACH covers nanomaterials, there are issues facing its implementation as some nanoparticles behaviours change in different media and physico-chemical properties can change with particle size. Substance identification and sameness assessment is required, but there are concerns about nomenclature and whether current criteria can distinguish between bulk and nano, and different nano, forms of the same substance. Also it is not clear for many nanoparticles how reference materials and chemical standards apply.
The workshop was very enjoyable and informative, having covered a wide range of topics. It has been useful to develop my understanding of the practical problems with characterising and testing nanoparticles. This is a problem often mentioned in respect to their regulation, but usually without any in-depth explanation. Hopefully, the information from the workshop will be beneficial when REACH registration dossiers for nanoparticles start to be compiled.