Managing the potential health risks and protection for workers from occupational exposure to manufactured nanomaterials

1. What is defined as a nanomaterial?

The term nanomaterials refers to materials whose size (length, width or diameter) is less than 100 nanometers (a nanometer is one millionth of a millimeter), or about the size of a virus. The interest for nanomaterials stems from the fact that they have unique physical properties that may result in desirable behaviour leading to such varying applications as better paints, better drugs and faster electronics because of their size, shape, composition, characteristics of their surface, their charge or their dissolution rate.

Manufactured nanomaterials (MNMs) are distinguished from natural nanomaterials by the fact that they are not naturally present but deliberately manufactured for certain applications.

Amount produced and uses of the most produced manufactured nanomaterials (MNMs)

MNM	Amount produced	Exemples of Uses
Carbon black	9.6 million t	Tires, black pigment for plastics
Synthetic amorphous silica	1.5 million t	Additive in many products including foods and cosmetics
Aluminium oxide	200 000 t	Pigment
Barium titanate	15 000 t	Electronic components
Titanium and zinc dioxide	About 10 000 t each	Pigments
Cerium dioxide	About 10 000 t	Polishing compounds
Cerium dioxide	Less than 20 t	Energy storage, supercapacitors, field emission transistors, high-performance catalysis, photovoltaics, and biomedical devices and implants.
Silver nanoparticles	Less than 20 t	Antibacterial agent in fabrics

2. What makes a nanomaterial potentially hazardous?

The same physico-chemical characteristics of nanomaterials that provide useful properties in various applications make that these may also present unexpected health hazards that differ from those of the same substance in larger size (“bulk form”). Since their dimensions are in the same order of magnitude as living cells and cellular components, they could potentially interact with cells in unwanted ways.

3. What do we know about human health effects of nanomaterials?

While new nanomaterials are constantly being developed, very few existing systematic reviews were found and thus the ability to predict their hazardous properties is still limited. There is currently a lack of precise information about how nanomaterials -manufactured or not - enter the human body, their fate once they have entered, and their ability to induce unwanted biological effects.

The main potential adverse health effects and hazard classes that could be assigned to different nanomaterials are:

• Respiratory or skin sensitization; 
• Serious eye damage; 
• Specific target organ toxicity after repeated exposure; 
• Germ cell mutagenicity, carcinogenicity. 

For the identification of hazardous properties of nanomaterials and the assessment of the risks linked to an exposure to such hazards and given their particular physico-chemical properties, nanomaterials may require toxicological test methods different from their bulk material counterparts. Methods for such types of hazard identifications are not currently well established.

So far however, no long-term adverse health effects in humans have been observed. This could be due to the recent introduction of MNMs, to the precautionary approaches adopted to avoid exposure to them but also to the ethical concerns about conducting studies on the potential effects MNMs could have on humans.

In the absence of sufficient toxicological information, the World Health Organization (WHO) recommends that the precautionary approaches are adopted and, when there are reasonable indications to do so, workers should not be exposed given this uncertainty about the possibility of adverse health effects.

4. What are the recommendations of the WHO when it comes to managing the health risks for workers of manufactured nanomaterials?

The Guideline Development Group (GDG) of the WHO strongly recommends assigning hazard classes to all MNMs according to the Globally Harmonized System (GHS) of Classification and Labelling of Chemicals of the United Nations for use in Product Safety Data Sheets provided to the professional users of a product. It also recommends reduction of exposures to MNMs that have been consistently measured in workplaces, especially during cleaning and maintenance, collecting material from reaction vessels and feeding MNMs into the production processes. To this end, 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 the associated risks.

In this context, the WHO considers five area to evaluate and manage the health risks for workers from exposure to MNMs, and makes recommendations for three of these areas:

A. Assessment of health hazards of MNMs

1. Assign hazard classes to all manufactured nanomaterials;
2. Update safety data sheets of the corresponding substance with the hazard information specific to nanomaterials;
3. For the respirable fibres and granular bio-persistent particles’ groups, use the available OECD classification of MNMs applied for provisional classification of nanomaterials of the same group. 

B. Assessment of exposure to MNMs

1. Assess workers’ MNMs exposure in workplaces;
2. Assess whether workplace exposure exceeds a proposed occupational exposure level;
3. Apply a stepwise approach for inhalation exposure when specific Occupational Exposure Limits (OELs) for MNMs are not available in workplaces.

There is moderate-quality evidence that basic and comprehensive inhalation exposure assessment methods are feasible in practice. There was only very low-quality evidence about feasibility of measurements for dermal exposure assessment.

C. Control of professional exposure to MNMs

1. Focus control of exposure on preventing inhalation exposure as much as possible; 
2. Reduce exposures to a range of MNMs that have been consistently measured in workplaces; 
3. Eliminate the source of exposure should be the first control measure;  
4. Prevent dermal exposure by occupational hygiene measures such as surface cleaning, and the use of appropriate gloves (conditional recommendation, low quality evidence); 
5. Use control banding² for nanomaterials to select exposure control measures in the workplace. 

Owing to the lack of sufficient evidence, the GDG cannot make recommendations for the two other areas (worker’s Health surveillance and Training and involvement of workers). In particular for worker’s health surveillance specific programmes targeted to MNMs over the other existing health surveillance programmes that are already in use. Training of workers and worker involvement in health and safety issues have to be best practice but, owing to the lack of studies available, no form of training of workers over another can be recommend, nor one form of worker involvement over another.

² For a definition of control banding, see :  www.anses.fr/fr/system/files/AP2008sa0407RaEN.pdf