“Nanoparticles, even from the same material, can be synthesized utilizing a variety of methods. Different methods are used in order to optimize specific properties of the materials. These properties include, but are not limited, to size (diameter, length, volume), size distribution, symmetry, surface properties, surface coating, purity, ease of manipulation, yield and suitability for scaling up. Methods used for the commercial or deliberate manufacture of nanoparticles may be divided into four main groups:

• Gas Phase Processes including flame pyrolysis, high temperature evaporation and plasma synthesis.
• Vapor Phase Processes.
• Colloidal, or liquid phase methods in which chemical reactions in solvents lead to the formation of colloids.
• Mechanical processes including grinding, milling and alloying.

For all of these processes the recovery stage may be quite similar and is likely to comprise of mainly powder or slurry handling techniques.”¹

Gas Phase Processes

Particle formation

Potential risks of exposure arise from leakage of product from the reactor vessel in which nanoparticles are formed.¹

Product recovery

Potential risks of exposure differ depending on the process used for product recovery. “Ineffective filter systems could result in escape of product into the working environment, particularly where recirculation into the workplace air occurs.”¹

Potential exposure routes

Since nanopartiles are formed as an aerosol inside a reactor vessel, greatest risk is of inhalation exposure. “There are potential risks of dermal (and ingestion) exposure by touching surfaces contaminated by airborne releases, handling of product during recovery and processing or packing and during maintenance or cleaning of the plant and workplace.”¹

Vapor Phase Processes

Particle formation

Potential risks of exposure unlikely given that particle formation is on a substrate.¹

Product recovery

Potential risks of exposure differ depending on the process involved in mechanical removal of particles from substrate. “Depending on the level of energy used, this could result in re-suspension of product into the air. It is very unlikely that this would be in the form of discrete nanoparticles but could be agglomerated particles.”¹

Potential exposure routes

Similar to gas-phase processes, potential risks of dermal and ingestion exposure occur by touching surfaces contaminated by airborne releases, handling of product during recovery and processing or packing, and during maintenance or cleaning of the plant and workplace.¹

Colloidal Phase Processes

Particle formation

Potential risks of exposure unlikely given that particle formation is in liquid suspension.¹

Product recovery

Potential risks of exposure again differ depending on the process involved in mechanical removal of particles from substrate. In situations where product recovery is by spray drying, “airborne exposure is possible in the event of leakage although it is unlikely to be to primary single nanoparticles but rather to agglomerates of nanoparticles. Spillage of liquid product in the workplace, followed by evaporation and cleaning could result in airborne dispersion and inhalation exposure. Again this is more likely to be to agglomerated materials.”¹

Potential exposure routes

“In these processes, dermal (and ingestion) exposure could occur as a result of spillage in the workplace. Exposure could be directly to the suspension or to dried material. Handling of the product during recovery/packing and maintenance and cleaning could also result in dermal exposure. The risks of inhalation, dermal and ingestion exposures would be similar in attrition processes to colloidal processes but would differ in detail.”¹

1. R. Aitken, K.Creely, C. Tran, An occupational hygiene review,” Prepared by the Institute of Occupational Medicine for the Health and Safety Executive 2004, Research Report 274, at 34 (2004).