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Exposure estimation

Why is it so important to define an exposure assessment methodology?

In 2016, different types of professional exposures to nanoparticles concern some 2 millions of people worldwide. The compliance to the precautionary principle and the labor regulation related to dangerous products forces the employer to maintain the personnel exposure at as low a level as possible. But how can we express exposure threshold values? What are current exposure recommendation proposals?

What is the right distribution?

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Measure unit choice characterizing dose / effects relation?

At present, there is no definition of Occupational exposure levels in the European and French regulations. In France, limit values are available for different categories of dust. For example in the case of TiO2, the limit value is 10 mg/m-3. But these values are not applicable to nanometrical substances.

The National Institute for Occupational Safety and Health (NIOSH) recommendations offered in 2011, as a function of primary particle granulometry, limit values of 2,4 mg.m-3 for thin TiO2 and 0,3 mg.m-3 for ultrafine TiO2 (weighted values for an 10 hour period per day and 40 hours a week).

The NIOSH is concluded inhalation chronic and sub-chronic rat studies provide the most reliable data regarding a quantitative assessment of the TiO2 risks. But it seems that the rat is more sensitive than human to a pro-inflammatory response of a chronique exposure. Occupational exposure levels based on rat data integrate a safety factor for human.

What is the right unit of measurement?

Distributions in number, surface and mass for each size of particle are compared for the same urban aerosol. Below 100 nm, distributions are quite different. It seems that between 1 and 100 nm, the"surface" or "number“ parameters would be more appropriate to characterize the potentially toxic effects.