Dustiness testing : a support to nanosafety by design

Abstract : Nanotechnology is often said to be the industry of the 21st century. Its growth and development may pose potential occupational health and safety issues. The “safety-by-design” approach may be a suitable solution to address these issues. It consists in taking into account the risks (exposure and hazards) and performances in the manufacturing of the future nanomaterial-based products to enhance their safety over their entire lifecycle. Synthesizing nanopowders is one of the techniques to elaborate nanoproducts. One of the major risks related to the powders is that of aerosolization. Indeed, particle release at the workplace (inhalation risk) is not to be underestimated and is therefore to be taken into account in the nanosafety-by-design approach. As a consequence, there is a need to develop experimental systems and protocols to assess dustiness of the powders. Among all the known techniques available to assess dustiness, the vortex shaker appears to be most promising for nano-dustiness [1, 2]. This system is based on the use of a “vortex” type mixer onto which a glass test tube containing the sample is mounted. The test tube is sealed with a stopper pierced with quarter-inch diameter stainless steel inlet and outlet tubes. Clean air is flowed in the glass test tube through the inlet. Air circulation within the glass tube combined with shaking makes the aerosolized fraction of the powder flow out through the outlet tube. Dustiness experiments have been carried out on ZrO2 powders produced by the PLASMACHEM company in the frame of the SANOWORK project (7th European Framework Program, GA: 280716). The studied materials included one original (unmodified) and three “modified-through-design” powders. The modified ZrO2 samples were synthesized with the aim to reduce aerosolization. The objective of these experiments was therefore to compare the dustiness of the original and modified powders. Several tests were performed on the powders and their aerosolized fractions. First, SEM observations were made to visualize the powders. The temporal evolution of the number concentration of the aerosolized fraction of the powder was monitored using particle counters whereas the aerosol composition and morphology was characterized by TEM analysis. The experimental results show significant reduction in the dustiness of some modified powders. These results make it clear that efforts made to modify powders in order to make them less emissive are worth implementing to reduce the inhalation risks. They also highlight dustiness tests as a simple and efficient tool to assist remediation strategies.