Airborne carbon nanotube (CNT) size distributions measured at an industrial manufacturing facility.

Engineered nanoparticles (ENPs) at work places and in residential areas are mixed with background atmospheric particles such as sulphates, nitrates, organic compounds and others. Therefore it is important to consider the atmospheric aerosol background during evaluation of the various metrics for nanoparticle characterisation. The total mass of airborne particles can vary substantially with time and location. This interferes with engineered particles and creates considerable difficulties in identifying ENPs characteristics. The chemical composition of engineered nanoparticles is of high importance for any industrial health risk evaluation. Therefore, the first requirement of an appropriate technique for health risk evaluation is to provide data that is not influenced or corrupted by the atmospheric background aerosol.

Airborne aerosol particles were fractionated in the size range from 2nm to 30μm and sampled using a Nano-ID Select, a novel size fractioning aerosol sampler, at a European industrial plant where carbon nanotubes are manufactured. Samples collected at the plant were analysed for certain elements or markers (traces of catalytic compounds) that are known indicators of the presence of CNT particles. ICP analysis was employed to quantify these CNT markers.

Figure 1.1: A CNT aerosol particle mass size distribution (dm/dLogD in units of ng/m3) obtained at a European production plant. The white bars represent aerosol in the air, grey bars represent the size distribution corresponding to particles deposited in the entire respiratory system, and the dark bars represent the size distribution corresponding to particles deposited in the alveolar and trachea bronchial ranges.

The Nano-ID Select and its user-friendly software enable size distributions of CNTs to be obtained over a large size range. The total mass concentration of CNT particles in the air was 3.2μg/m3, which is much lower than the typical mass concentration of an atmospheric background aerosol (20-60μg/m3).  

The CNT distribution was used to calculate deposition of airborne particles in the respiratory system as well as in the alveolar and trachea bronchial regions. This knowledge is very important for assessing the potential health damage that can be caused by nanoparticles. It has been shown that conventional metrics used for quantifying exposure (for example PM10) overestimate the actual mass of deposited material that can lead to health problems.