• 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.

Future work

• 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