In situ analysis of silver based biocides in face masks using electron microscopy and EDX, combined with total silver measurement using ICP-MS or ICP-OES demonstrated the presence of varying amounts and different types of silver-based biocides in a selection of face masks on the Belgian market and intended to be worn by the general public. Following types of silver-based biocides were demonstrated: (i) Ag+ ions, (ii) metallic Ag0 NP distributed in the matrix of the fibers, (iii) Ag NP and large silver particles at the surface of, or close to cotton fibres in face masks containing polycationic polymers binding Ag+ ions, and (iv) a coating consisting of metallic silver releasing Ag+ ions, Ag0 NP and large silver particles.

For metallic and ionic silver, an acceptable exposure level (AELmask) of 25 µg per mask was established based on occupational exposure levels and assuming an intensive exposure scenario considering subchronic exposure of the general adult population.

Comparison of the measured amount of total silver in the masks with this AELmask indicated that seven out of nine face masks, with a silver biocide based on Ag+ ions only, can be considered as safe. The two other face masks with a silver biocide based on Ag+ ions require a more refined risk evaluation.

The amount of silver in the four masks that contain Ag0 NP, Ag+ ions, and/or non-nanoparticulate silver exceeded the AELmask. Per case an in depth risk analysis needs to be undertaken to account for the different forms of silver that are potentially released from face masks treated with the applied silver-based biocides.