Recommendations for measurement

Conclusion:
The exposure of employees to nanoparticles should be determined. Besides the use of traditional gravimetric methods, the particle number concentration and, if possible, their size distribution should be measured. Simple instruments which deliver only a subset of the information may be used effectively to check the efficacy of protective measures.

Convention for measurement

In response to the discussion of the possible effects of ultrafine particles, the IFA launched a measurement campaign as early as 1998 in order to obtain a preliminary overview of the exposure of employees to ultrafine particles. The existing scientific findings suggest that the mass is of only subordinate relevance to the impact of nanoparticles and ultrafine particles. The mass concentration is therefore measured only as a secondary parameter, in order to permit reference to older, conventional measurements if necessary. Concurrent with the launch of the measurement programme, a convention [1] for the measurement of ultrafine particles was drawn up in co-operation with the DFG (the German Research Foundation) and European OSH institutes in order to permit comparison between the results of measurements. The core points of this convention are:

• An ultrafine aerosol particle is a particle with a mobility equivalent diameter of < 0.1 µm.
• The particle number concentration should be measured in the range from approx. 10 to approx. 600 nm.
• The entire particle size distribution should be measured if possible.
• A concentration range of up to approximately 108 particles/cm³ should be covered.
• The mobility equivalent diameter should be used for the particle size analysis.

This convention has since been taken up by international standardization activity (ISO/TR 27628:2007, Workplace atmospheres – Ultrafine, nanoparticle and nano-structured aerosols – Inhalation exposure characterization and assessment).

The IFA and other institutions and research groups employ scanning mobility particle sizers in order to measure the particle number concentration of nanoparticles and ultrafine particles and their size distribution in the workplace atmosphere. In recent years, the use of instruments of this type has become standard procedure for the measurement of nanoparticles. Owing to their size, however, these instruments are not suitable for mobile personal measurements. Particular expertise is also required for their operation and for interpretation of the measurement results. These instruments also fail to provide any information on the chemical properties of the measured nanoobjects or on their geometry. This necessitates methods for collection and subsequent imaging analysis. Such methods are however still largely at the experimental stage and do not yet constitute routine analysis methods. An overview of instruments for measurement of the particle number concentration is provided by Pelzer et al. [2].

Measurement results

The results of the measurement programme conducted by the accident insurance institutions are available and have been published for a range of working areas and tasks, such as welding, soldering, smelting/casting, grinding, stripping, coating, and textile manufacture [3-5]. An overview of the international measurements of nanomaterials at workplaces is provided by Brouwer et al. [6] and Kuhlbusch et al. [7].

Simple instruments

Overall, simple, portable instruments continue to be lacking for the measurement of and clear distinction between nanoparticles and ultrafine particles at the workplace. The EU "NanoDevice" project launched on 1 April 2009 is intended to correct this deficit.

The first simple instruments appeared on the market in recent years. They do not enable nanoparticles to be distinguished from ubiquitous particles. They can however be used to advantage on a limited scale, for example for examining the effectiveness of protective measures.

Further recommendations

In its guidelines for risk assessment of tasks involving nanomaterials at the workplace [8], the VCI (the association of the German chemical industry), together with the BAuA (Federal Institute for Occupational Safety and Health), recommends that employees' exposure be measured during checks of the effectiveness of the measures taken.

The NanoCommission's report also states in Annex IV that checks of the measures' effectiveness should include measurement of the exposure. In addition, exposure measurements should be documented in such a way that they can also serve as a basis for personal exposure dossiers for employees.

Altogether however, a need exists for a harmonized measurement strategy which takes account of the limitations of the existing measurement methods [9]. A number of institutions in Germany (BAuA, BG RCI, IFA, IUTA, TUD, VCI) have agreed upon a procedure for workplace measurements [10]. At international level, too, concrete efforts are being made to harmonize the procedure [11].