Ultrafine particles in the environment

Yesterday I logged into a webinar run by the instrument manufacturer, TSI, on “Exposure to Ultrafine Particles- Indoor, Outdoor and In-Vehicle Concentrations: Sources, and Particle Dynamics”, presented by Dr Lance Wallace a leading researcher in the measurement of ultrafine particles.

The potential risks to health from sub-micron ultrafine particles has been a high profile occupational health issue for a number of years due to the increasing use of “engineered” nanoparticles (over 1000 consumer products already contain them). The risks aren’t properly understood and their measurement presents a number of difficulties.

The normal method for assessing the risk from airborne particulates involves determining their mass concentration. However, with nanoparticles it’s their surface area of nanoparticles which affects their toxicological properties so a different approach is needed. Another problem is that sub-micron ultra-fine particles are generated by natural and other sources, so results are confused by the background concentration of nanoparticles from natural and other sources making interpretation difficult.

The webinar concentrated on environmental concentrations, rather than occupational exposures, and was based on studies carried out in the USA by the Environmental Protection Agency (EPA), the National Institute of Standards and Testing (NIST) and Stanford University, and a major study undertaken by Health Canada.

Major outdoor sources of ultrafine particles are traffic emissions and atmospheric processes leading to “nucleation bursts” (atmospheric reactions involving sulphuric acid, ammonia, and water vapour).

Indoor sources in domestic premises included

  • cooking
  • gas heaters
  • electric cookers
  • electric motors (including power tools and kitchen appliances)
  • Smoking

Of these, the main contributor to indoor concentrations (other than smoking) was cooking.

Unfortunately we are unable to provide accessible alternative text for this. If you require assistance to access this image, please contact help@nature.com or the author

Source: Wallace and Ott (2011)

I was surprised that electric cookers generated ultrafines. This is due to metal vapourising from the cooking element and then condensing. Ultrafines are generated by electric motors by vapourisation of carbon and metal from the brushes. Given the wide use of electric motors in industry this is likely to be a significant background source in the workplace.

Particles from outdoors also infiltrate into buildings, the proportion entering depends on a number of factors including particle size, building design, air change rate and occupant behaviour (e.g. opening windows and doors).

90% of the particles detected in the studies were smaller than 10 nm. The particle size distribution changing over time due to settlement and coagulation (small particles “clumping” together).

Results from studies reported in Wallace and Ott (2011) indicated that the median background (indoor) number concentration was 2,700 particles/cm3 (5th percentile 900 particles/cm3, 95th percentile 9000 particles/cm3).

One interesting fact that came out of the talk was that relatively high numbers of ultrafine particles can be found in restaurants (see chart below). These are generated due to cooking in the kitchen. The measurements were taken in the dining rooms so the levels in the kitchens, to which the restaurant staff would be exposed, would probably be higher. Also, diners would only be exposed to a couple of hours on occasions whereas restaurant employees would be exposed for considerably longer periods on a regular basis.

Unfortunately we are unable to provide accessible alternative text for this. If you require assistance to access this image, please contact help@nature.com or the author

Particle concentrations measured in a restaurant. Source: Wallace and Ott (2011)

So what are the implications from an occupational hygiene perspective? The key points for me are

  • Although the studies discussed during the webinar were concerned with domestic exposures, many of the sources, including gas burners, electric heaters and electric motors, are used in industry and so would also emit ultrafines that would contribute to the background levels in the workplace environment
  • Infiltration of ultrafine particles generated by outdoor sources will also occur with industrial buildings
  • Workers in restaurants are likely to be exposed to ultrafine particles generated in kitchens. It’s difficult to say whether the risks are significant and, perhaps, it is something worth investigating – if funding was available.



Lance Wallace and Wayne Ott Personal exposure to ultrafine particles Journal of Exposure Science and Environmental Epidemiology (2011) 21, 20–30;  published online 20 January 2010

Photo credit

J Grigg  The health effects of fossil fuel derived particles  Arch Dis Child 2002;86:79-83


BOHS Conference workshop on nanotechnology

Titanium dioxide nanoparticles

In her Keynote address to the 2011 BOHS Conference, the Chair of the HSE, Judith Hackitt, mentioned nanotechnology as one of the “emerging issues” that HSE will continue to give priority to despite the cutbacks in its budget. Nanotechnology has been a high profile issue for HSE for a number of years as the production of “engineered” nanoparticles has increased. Their toxicology isn’t fully understood and measurement presents a number of problems, so it is difficult to properly evaluate the risks to health.

At last year’s conference, a plenary session was devoted to nanotechnology and this year it was the theme for one of the workshops. It was a good session, with three speakers covering health effects, assessment and control. However, the content of their talks was very similar to those given during the plenary sessions last year, suggesting that there haven’t been any major advances in the science over the past 12 months.

Rosemary Gibson form HSL made a very good presentation summarising the health implications of engineered nanoparticles. The key points she made included

  • Nanoparticles have a very large surface area to volume ratio and this has implications for their effects on health. Some researchers have identified a relationship between surface area and inflammation and this suggests that surface area is the best metric to use to assess the risk, rather than mass concentration (which is normally used with particulates).
  • Research has mainly focused on their effects on the respiratory system with some work on skin effects. Less work has been carried out on systemic effects. However, the main concern identified from experience with ultrafine particulate air pollutants (from non-engineered sources such as diesel exhaust emissions) is effects on the cardiovascular system, and some research has suggested that this is also relevant with engineered particles, so more work is needed on this aspect.
  • There are continuing concerns about the effects of carbon nanotubes and whether these fine, fibre like particles may behave like asbestos. Work by Poland et al, the results of which were published n 2008, certainly suggest that this may be the case with long multiwalled carbon nanotubes, where there was evidence of inflammation and granulomas. However their research also suggested that short multiwalled carbon nanotubes were non-harmful. (For further details, see the commentary by Ken Donnaldson, here).

The other two speakers, James Wheeler of the HSE and John Hulme of Cambridge University (who gave a Keynote on Nanoparticles at last year’s conference) both concentrated on practical implications in the workplace.

James emphasised the need for a sensible approach to risk management. Precaution was needed, as nanotechnology was a “step into the unknown”, but he emphasised that the risks could be managed and controlled in the same way as high hazard materials, using the principles of good practice embodied in the COSHH Regulations. HSE has a website on nanotechnology and has also issued guidance on carbon nanotubes. Further guidance, produced in conjunction with relevant partners, should be available in March 2012

John, who has considerable experience of managing the risks from nanoparticles in research laboratories at Cambridge University, concentrated on the practical assessment and control of the risks. He pointed out that the hazard information provided by some suppliers of nano-materials was inadequate, treating them as if they were no different from macro forms of the substance when there were clear differences in toxicology. He re-emphasised one of the points Rosemary made about the importance of surface area and discussed the practical difficulties of measurement.  Methods are available to measure particles on the basis of their surface area, but as these techniques can’t identify what the particles are it isn’t possible to tell where they have originated. There can be high background levels of fine particles from natural and man-made sources, which confuse the results from any surveys. So the problem with nanoparticles is that we aren’t sure of the hazards and can’t properly quantify the risk!

John’s answer was that we need to take a precautionary approach and control all potential exposures to a high standard. He provided some good examples from his experience of controls that can be applied in practice including:

  • preventing particles becoming airborne by using slurries rather than powders
  • working in glove boxes and microbiological safety cabinets
  • applying well designed local exhaust ventilation, pointing out that nanoparticles behave like gases and so are easy to capture
  • using HEPA filters to minimise emissions to the environment and workplace

For further information on nanotechnology hazards and control see

HSE nanotechnology website

HSE guidance on carbon nanotubes

Safenano website

Image credit : http://newsroom.ucla.edu/portal/ucla/srp-view.aspx?id=85846

BOHS Conference – Nanotechnology

I’ve allocated this week for catching up on reports, but I’ve also spent a bit of time reading through the notes I made at BOHS Conference in Harrogate a few weeks ago.

One of the sessions I attended was devoted to nanotechnology.  This is a fast developing area, although as it is generally still very much in the R & D phase, I guess most occupational hygienists haven’t had much involvement with it yet – I certainly haven’t – but as we’re likely to see more production processes coming on line in the not too distant future its important to keep abreast of developments.

The first presentation was a keynote address from John Hulme, a safety adviser at Cambridge University. A lot of research work on nanotechnology takes place at the University so he has had to work with the research scientists to ensure the risk are assessed and controlled. This isn’t easy when we’re not certain about the hazards and risks associated with nanoparticles. John gave a good overview of the state of knowledge. Some of the key points I noted were:

  • over 1000 consumer products already contain nanoparticles
  • nano-particles are not new – they’ve been around for a long time – there are natural sources (e.g. forest fires, wood stoves, volcanoes) and some “old” technology creates them (e.g. carbon black, traffic exhaust fume, welding fume, plastic fume)
  • the small size of nanoparticles means that they can interact with DNA
  • nanoparticles have a very high surface area to volume ratio and have highly reactive surfaces which can increase their toxicity
  • nano-particles can pass through biological barriers (including the blood brain barrier) much easier than larger particles
  • the chemical (and toxicological) properties of materials change when they are nano-sized
  • as the surface area of nanoparticles is the main parameter which affects their toxicological properties, measuring their mass concentration is unlikely to be the most relevant way of evaluating he degree of risk

Professor Ken Donaldson of Edinburgh University, a leading authority on the health effects of nanoparticles provided an update on research into their effects.  Up to now much of the work has focused on pulmonary effects, but there are concerns about the effects on the cardiovascular system which need to be investigated.  Other key areas of research include potential effects on the brain and the foetus, the risk of chronic pulmonary obstructive disease (COPD) and asthma, and the effects caused by exposure to nano-fibres

Gary Burnett of HSL talked about the difficulties involved in measuring nanoparticles. His key points were

  • what metric should be used? – mass concentration, the number of particles or the surface area
  • results are confused by the background concentration of nanoparticles from natural and other sources
  • even when measuring the same parameter, different instruments can give different results

Rachel Smith and Colin Webb of the Health Protection Agency presented a practical case study on the introductions of exposure controls for nanoparticles during the design and commissioning of a new research facility. They talked about some of the difficulties involved in deciding on controls when the hazards and risks are not fully understood and described the very comprehensive measures that were introduced.

UK Nanotechnology Strategy

The UK Nanotechnologies Strategy was published on 18th March 2010.  It outlines the strategy of the current government, so things may change after May 6th – we’ll have to wait and see!

The potential health risks from nanoparticles are one of the “emerging issues” that occupational hygienists and health and safety professionals in general need to keep abreast of. Nanotechnology is a fast developing field and the toxicological implications are not fully understood.  Governments see nanotechnology as an important emerging technology that can lead to economic benefits and is encouraging its development. It’s important that sufficient emphasis is given to research into the health implications.

One of the strategic aims set out in the strategy document is a commitment to

“Better understanding of the risks associated with the use of, and exposure to, nanomaterials, and enough people with the right skills to assess them. “
In respect to this aim the document sets out the following actions
  • Approaches to Government EHS research on nanotechnologies will be explored by the Chief Scientific Adviser network, with the aim of improving co-ordination. A meeting will be chaired by the Government Chief Scientific Adviser, John Beddington.
  • There will be an ongoing portfolio of Government and publically funded research into a wide range of crucial EHS nanotechnologies issues including the behaviour of key nanomaterials in the gut when eaten and when inhaled into the lungs.
  • Contributions will be made to international work programmes on nanotechnologies including the Organisation for Economic Co-operation and Development’s (OECD) Nanotechnology Working Parties and the EU’s Framework Programme. The UK will work to influence the future scope of these projects.
All commendable, but rather vague
One of the problems is that its only possible to see an effect once exposure has occurred so there is a dilemma – how can we detect effects in humans without exposing them to possible dangers? Animal experiments present difficulties both in terms of transferability of the findings to humans and the ethical implications.

Until stronger evidence is available the only sensible approach is to be cautious and apply a high degree of control. Nano-particles may or may not have serious health effects – we don’t know – but if we treat them as if they do and design our control strategies similar to those for carcinogens and sensitisers, then we should ensure that worker health risks are minimised.

See also https://diamondenv.wordpress.com/2010/01/13/nanoparticles/


I came across the following video slideshow by Andrew Maynard (2020science.org), a researcher in nanotechnology. It’s a nice, gentle introduction to nanoparticles and their properties.

The key points he makes about these new materials are

* the particles are small
* they are “strange” – they don’t behave how you might expect and the properties of a substance manufactured or created as a nanoparticle can be different from the same substance in the form of larger particles
* they are “sophisticated” – in that they can be used to manufacture complex products with advanced uses

There are inevitable concerns about the toxicity of nanoparticles and the risks from exposure, both from an occupational and environmental context.

* the small size of the particles means that they can, potentially, be absorbed easily into the body by inhalation AND skin contact (there is evidence that some particles can be absorbed through intact skin)
* nanoparticles are much more likely to be absorbed into the blood via the lungs than their larger cousins. Once absorbed they can make their to other organs where they may be able to exert toxic effects.
* their small size also means that they can be potentially absorbed into cells where larger particles of the same substance would not
* the “strangeness” of nanoparticles means that it can be difficult to predict what their toxicological properties will be, even where there is a good understanding of the toxicity of larger particles of the same substance
* In some cases, effects such as cancer are due to the physical form of particles and their Small size (aka asbestos fibres) rather than their chemical nature

It is too early to now whether any of these concerns will be borne out in practice. However, it’s an area where a lot of research is taking place.