- Not necessarily true to say nano (less than 100nm) more toxic than fine
(greater than 100nm) particles - other contributing factors are surface coatings
(or lack thereof), aggregation/disaggregation potential; and whether the particle-type
was synthesized in the gas or liquid phase (i.e., fumed vs.precipitated/colloidal).
- Toxicity depends on surface characteristics, particularly surface area and
free radical generation by interaction of particles with cells, plus the other
factors mentioned above.
- So far only 3 NP types have been studied for toxicity (TiO2, carbon black,
diesel exhaust), and most experiments with NP TiO2 use one type - Degussa
P25. There is need for a larger toxicity database.
- Aggregation and surface coatings are also important. Andrew Maynard, physicist
(now aerosol scientist) at NIOSH, USA (formerly at Cambridge) has done recent
studies of NP TiO2 in simulated lung fluid – particles aggregated and
did not fully disaggregate.into discrete, individual particles.
- Exposure assessments, not just hazard, are also very important. To his
knowledge very few exposure assessment studies have not been done. It should
be remembered that risk = hazard + exposure.
- Species-dependence - rats chosen because of high lung sensitivity, convenience,
tradition. They are more sensitive than other animals (especially larger mammals).
- Measurement – it remains to be determined whether there is knowledge
in industry of how to measure nanoparticles in the workplace.
- Advocated an international standardisation of nomenclature (eg a nanoparticle
is less than 100nm in diameter).
- Regulation - agreed that size or surface area are important metrics but
thought that this might be impractical to measure for every chemical in practice.
- May be a need to characterise 5 or 10 nanomaterials as representative and
regulate according to these catergories.
- Expressed dismay that of $2bn govt budget for nanotech only $4million to
be spent on environmental issues.
- DuPont will soon be carefully evaluating the literature on the dermal toxicity
database for TiO2 and proceeding accordingly.
- There is the possibility of collaboration with Vicki Colvin of Rice University
and the Center for
Biological and Environmental Nanotechnology at Rice University, USA, possibly
on some EPA-funded studies