5.1. Classification of MNMs

The specific toxicity group consists of (i) MNMs with high dissolution rates through the release of ions or amenable to biodegradation and, (ii) MNMs with low dissolution rates but with high specific toxicity. The latter are MNMs with specific toxicity, which is mediated by the specific chemical properties of their components (19).

The respirable fibres group consists of MNMs that are rigid, biopersistent or biodurable and respirable, which have dimensions agreed upon by a WHO working group for man-made mineral fibres in the past. These dimensions are a fibre length (FL)>5 µm, fibre diameter (FD)<3 µm and an aspect ratio (FL/FD)>3 (20). Although this group of fibres is characterized as being rigid, it should be kept in mind that there is no consensus on specific criteria for rigidity even though some have proposed crystallinity as a measure of rigidity for MNMs (21).

The granular biopersistent particles (GBP) group consists of respirable granular biodurable particles that are characterized by both low dissolution rates and lack of high specific toxicity. GBP are respirable granular and biopersistent but not fibrous (as defined above) and these particles are also known as poorly soluble particles or poorly soluble, low-toxicity particles (19).

Forming groups of MNMs with similar properties is important in the absence of information on the hazards of many new materials. This enables the transfer of hazard information, also called bridging or read across, from one material to another. Because there is no general accepted approach on how to do this, the GDG commissioned a systematic review of possibilities to group MNMs based on toxicological considerations. The systematic review was undertaken by Zienolddiny & Skaug (2017) (22). The systematic review team located 22 reviews of grouping MNMs, or approaches to transfer hazard information from one MNM to another. To be included in the overview the authors of the reviews had to have considered which mechanisms of action could lead to toxicity of nanomaterials. The systematic review team authors concluded that there is evidence that there are three main mechanisms of toxicity of nanomaterials: specific toxicity of the material, inhalation and biopersistence in the lungs, and one mediated specifically by the fibre structure. For other potentially hazardous properties, such as genotoxicity, there was no consistency in the included reviews that this is inherent to the nanoscale size of the MNMs.

Given that the grouping of MNMs is based on expert opinion, the GDG considered that changes are likely when more research becomes available.

5.2. Worker Involvement

The GDG considers it best practice that workers should be involved in health and safety issues and that this will lead to more optimal control of health and safety risks.

In most countries, worker involvement in health and safety issues is mandatory. Article 19 of the International Labour Organization (ILO)’s C155 Occupational Safety and Health Convention, 1981, stipulates that representatives of workers in the undertaking cooperate with the employer in the field of occupational safety and health. In many other ILO conventions and European Union (EU) directives, the term “worker participation” is frequently used.

5.3. Additional Training and Education of Workers

The GDG considers it best practice that workers potentially exposed to MNMs should be educated on the risks of MNMs and trained in how they can best protect themselves.

MNMs have risk aspects that are specific to being a nanomaterial and that are not self-evident. For proper control measures to be well implemented, workers need information about these risks. Safety data sheets (SDS) do not always provide reliable information on MNMs and users should be aware of this. In addition, MNMs require specific control measures that can be different from those for the bulk material. This is also recognized by the EU, which has provided specific guidance for workers (23).

There are good training materials available, for instance from the National Institute of Environmental Health Sciences in the United States of America (USA) and from the Health and Safety Executive in the United Kingdom of Great Britain and Northern Ireland, which can easily be adapted to local circumstances (24,25).

Education and training should focus on those aspects of MNMs that are dealt with in these guidelines and that are additional to, or different from, education and training in the safe handling of bulk material chemicals. Topics should include which hazards are specific to MNMs and different from the bulk material; which hazard classes are assigned to MNMs; which routes of exposure are important; which workplace exposures have been measured and which tasks put workers most at risk; how proposed OELs can be interpreted; when and how control banding, specific controls and PPE for MNMs can be used.

ILO Convention 155 concerning Occupational Safety and Health and the Working Environment also states that there should be a national policy to provide information and education and implement training for workers, including necessary further training, qualification and motivation of persons involved, in one capacity or another, in the achievement of adequate levels of safety and health. This also holds for workers exposed to MNMs.