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The production of manufactured nanomaterials (MNMs) and their use in consumer and industrial products including aerospace, cosmetics, foods, electronics, construction and medicine among others, increased these last years. This means that workers in those industries across the globe will be among the first to be exposed to these new materials, which puts them at risk of potential adverse health effects. Even though the economic benefits of nanotechnology are fully appreciated by all stakeholders, concerns about health and safety risks are especially articulated by workers and their organizations.
The assessment of health impacts of new technologies, work processes and products is one of the activities under the WHO Global Plan of Action on Workers’ Health adopted in 2007. Among other international organizations involved in the area of nanomaterial safety, the most active and influential are the Organisation for Economic Co-operation and Development (OECD) and the International Organization for Standardization (ISO). Even though full information about nanomaterial risks is not yet available and despite some differences, the recommendations produced by ISO, OECD and WHO are in general very consistent and aim to proactively minimize workers’ exposure.
The term “nanomaterial” refers to a material that has at least one dimension (height, width or length) that is smaller than 100 nanometres (one nanometer being a millionth of a millimeter), which is about the size of a virus. This particular size dimension represents a major characteristic of both manufactured (MNMs) and natural nanomaterials. The unique properties of MNMs including size, shape (i.e. size in a particular dimension), composition, surface characteristics, charge and rate of dissolution, may provide desirable properties leading to varying applications such as better paints, better drugs and faster electronics and many others.
Among the most produced MNMs are carbon black, synthetic amorphous silica, aluminium oxide , barium titanate , titanium, cerium and zinc dioxides and,to a lower extent, carbon nanotubes, carbon nanofibres and silver nanoparticles .
| 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 |
The same physicochemical characteristics of nanomaterials, that provide useful properties in various applications make that these may also present health hazards that differ from those of the same substance in larger size (“bulk form”). Indeed, the toxicological properties may adapt to changes in their physical properties such as size and shape, since those dimensions are in the same order of magnitude as cells and cellular components, and so they could potentially interact with cells in unexpected ways. The increased production of MNMs and their use in consumer and industrial products mean that workers in particular are increasingly exposed to them. This places them at the front line when coming to the risks of potential adverse health effects.
Air quality is influenced by small particles that are usually divided into particulate matter smaller than 10 micrometers (PM10), smaller than 2.5 micrometers (PM2.5) and ultrafine nanoparticles that are smaller than 100 nanometers. The ultrafine particles are naturally occurring in air and a result of combustion processes.
While new MNMs are constantly being developed, very few existing systematic reviews were found and the ability to predict their hazardous properties is still limited. There is indeed currently a paucity of precise information about human exposure pathways for MNMs, their fate in the human body and their ability to induce unwanted biological effects such as generation of oxidative stress. The most potential adverse effects and hazard classes assigned to different MNMs are:
Data from in vitro, animal and human inhalation studies are available for only a few nanomaterials. Given their particular physicochemical properties, these may require toxicological test methods for hazard, exposure occupational health exposure and risk assessment different from those used for their bulk material counterparts, as well as methods for this type of assessment, which are not yet very well established. Therefore, systematic reviews were commissioned for all questions with the aim of locating studies that could answer the pertinent questions and the Guideline Development Group (GDG) on manufactured nanomaterials of the World Health Organization (WHO) considered that in the absence of toxicological information, a precautionary approach should be adopted and, that when there are reasonable indications to do so, workers should not be exposed despite uncertainty about the adverse health effects.
The report highlights that in Europe, the European Trade Union Confederation (ETUC) has expressed its concern about health and safety issues surrounding MNMs and criticized the failure to fund research on health and safety, ethical, social and environmental issues at the same levels as research and development work on nanotechnologies. In Canada, the Canadian Union of Public Employees recommends following a precautionary approach that prevents workers’ exposure until sufficient data can show there are no harmful effects on human health or the environment. The Australian Council of Trade Unions has expressed similar concerns.
So far however, no long-term adverse health effects have been observed in humans. This could be due to the still relatively recent development and manufacture of MNMs, to the precautionary approach adopted to avoid exposure to them but also to the ethical concerns about conducting experimental studies on MNMs on humans. There were 11 OECD dossiers containing toxicity testing information. These were used by the systematic review team to assign one or more hazard classes, according to the Globally Harmonized System (GHS) of Classification and Labelling of Chemicals (see table below).
| Source : WHO guidelines on protecting workers from
potential risks of manufactured nanomaterials *Single Walled Carbon NanoTubes **Multi Walled Carbon NanoTubes |
|||
| Type of MNMs | No hazard for: | Evidence of hazard for: | No data for: |
|---|---|---|---|
| Carbon fullerene | acute toxicity, skin-, eye- or respiratory damage, germ cell mutagenicity or specific target organ toxicity after repeated exposure | the other hazard classes, data were missing | |
| SWCNT* | acute toxicity, skin damage, respiratory/skin sensitization, or reproductive toxicity | Germ cell mutagenicity (Cat 2) and specific organ toxicity after repeated exposure (Cat 1). | no clear hazard for reproductive toxicity; no data for specific target toxicity after single exposure, for carcinogenicity; IARC classification 3, meaning not classifiable. |
| MWCNT** | acute toxicity, skin damage, respiratory/skin sensitization, or reproductive toxicity. | eye damage (Cat 2), germ cell mutagenicity (Cat 2), carcinogenicity (Cat 2, IARC 2B/3) and specific organ toxicity after repeated exposure (Cat 1). | for specific target toxicity after single exposure |
| silver | acute toxicity, skin corrosion, eye damage, germ cell mutagenicity and reproductive toxicity | respiratory/skin sensitization (Cat 1B) and specific target organ toxicity after repeated exposure (Cat 1 & 2). | carcinogenicity and specific target organ toxicity after single exposure |
| gold | specific target organ toxicity after repeated exposure (Cat 1). | for the other classes | |
| silicon dioxide | for acute toxicity, skin or eye damage, respiratory or skin sensitization, germ cell mutagenicity and reproductive toxicity | specific target organ toxicity after repeated exposure (Cat 2), | carcinogenicity and specific organ toxicity after single exposure |
| titanium dioxide | for acute toxicity, skin or eye damage, respiratory or skin sensitization or germ cell mutagenicity. | possible carcinogenicity ((IARC Cat 2B), reproductive toxicity (Cat 1), and specific organ toxicity after repeated exposure (Cat 1), | for specific organ toxicity after single exposure. |
| cerium dioxide | for acute toxicity | specific target organ toxicity after repeated exposure | the other hazard classes. |
| zinc oxide | no hazard for acute toxicity, skin or eye damage, germ cell mutagenicity and reproductive toxicity. | specific organ toxicity after repeated exposure (Cat 1) | respiratory/skin sensitization, carcinogenicity and specific organ toxicity after single exposure. |
The recommendations are intended to help policy-makers and professionals in the field of occupational health and safety in making decisions about the best protection against potential risks specific to MNMs in workplaces. These guidelines are also intended to support the workers and their employers.
As an important guiding principle in preventing the adverse health effects of MNMs, the 3 following “best practices” are recommended:
When there is a choice between control measures, those measures that are closer to the root of the problem should always be preferred over other measures that put a greater burden on workers, such as the use of personal protective equipment (PPE). This is what the Guideline Development Group (GDG) calls the "hierarchy of controls".
However, these guidelines are not intended to be a complete "manual for safe handling of MNMs in the workplace" because this requires addressing more general occupational hygiene issues which are beyond the scope of these guidelines. As considerable progress in validated measurement methods and risk assessment are expected in the future, the GDG proposes to update these guidelines in 2022.
Except for the few materials where human studies are available1, health recommendations are based on extrapolation to the possible effects in humans of the evidence from in vitro, animal or other studies from fields that involve exposure to nanoscale particles, such as air pollution.
In the workplace, health hazards can result from inhalation, ingestion or skin absorption of MNMs. The human lungs represent indeed an excellent entry portal for nanomaterials due to their high surface area, thin epithelial barriers and extensive vasculature and while dermal and oral exposure may occur, inhalation is more likely to result in a larger dose for the whole body. While acute effects from nanomaterials’ translocation to secondary organs are likely to be minimal, it is possible that chronically exposed populations may face greater risks from cumulative, low-dose translocation processes.
The GDG strongly recommends assigning hazard classes to all MNMs according to the Globally Harmonized System (GHS) of Classification and Labelling of Chemicals for use in safety data sheets. For a limited number of MNMs this information is made available in these guidelines. Forming groups of MNMs with similar properties is indeed 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. Therefore, the GDG considers best practice to class MNMs into three groups: those with specific toxicity, those that are respirable fibres and those that are granular bio-persistent particles.
A comprehensive and up-to-date list of proposed occupational exposure limit (OEL) values specifically for manufactured nanomaterials (MNMs) is available in the appendix of the report. These OELs do not imply a safe level below which adverse health effects do not occur, because they are all based on extrapolation from animal research, or other fields such as air pollution, since there are only very limited data available on long-term human health effects. If specific OELs for MNMs are not available in workplaces, the GDG suggests a stepwise approach for inhalation exposure with, first an assessment of the potential for exposure; second, conducting a basic exposure assessment, and third, conducting a comprehensive exposure assessment such as proposed by the Organisation for Economic Cooperation and Development (OECD) or the European Committee for Standardization (CEN).
Given the current high occupational exposures to MNMs documented in the exposure review, considerable efforts are needed by all stakeholders to ensure country implementation of these guidelines with a particular focus on low- and middle-income (LMI) countries.
1 There were 11 OECD dossiers containing toxicity testing information. These were used by the systematic review team to assign one or more hazard classes, according to the GHS, to the following nanomaterials: fullerene, single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT), silver, gold, silicon dioxide, titanium dioxide, cerium dioxide, dendrimer, nanoclay and zinc oxide in nanoparticle form. For the assessment of carcinogenicity, the review team also used the evidence summaries compiled by IARC on SWCNTs, MWCNTs and titanium dioxide.
The Guideline Development Group (GDG) recommends reduction of exposures to a range of MNMs that have been consistently measured in workplaces especially during cleaning and maintenance, collecting material from reaction vessels and feeding MNMs into the production process. 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 health and safety risks. They should be educated on the risks of MNMs and trained in how they can best protect themselves.
Over the reviewed period (January 2000–January 2015), 50 studies in 72 workplaces with 306 exposure situations were eligible and included in the review. Studies were mainly located in the Republic of Korea and the United States, but none in LMI countries. Most studies (62.5%) were in research laboratories or pilot plants.
To formulate recommendations and to determine the strength of the recommendations, the GDG used in a global and qualitative way the balance between harms and benefits, values and preferences, monetary costs and the quality of evidence. Five area are considered, to evaluate and manage the health risks for workers from exposure to MNMs:
For the first three areas, 11 recommendations are made:
A. Assessment of health hazards of MNMs
1. Assign hazard classes to all MNMs according to the Globally Harmonized System (GHS) of Classification and Labelling of Chemicals which are used in the safety data sheets (SDS) accompanying all chemical substances. These WHO guidelines make this information available for a limited number of MNMs. The hazard classification forms the basis for labelling products according to their hazards2. In many countries, this is legally binding. This information is also included in the SDS informing workers and employers about the safety and hazards of the products they use.
2. Update safety data sheets of the corresponding substance with the hazard information specific to MNMs- or indicating which toxicological end-points did not have adequate testing available;
3. Use the available classification of MNMs for respirable fibres provisional classification and granular bio-persistent nanomaterials particles’ groups of the same group;
B. Assessment of exposure to MNMs
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.
4. Assess workers’ MNM exposure in workplaces with methods similar to those used for to propose a specific Occupational Exposure Limit (OEL) value of the corresponding MNMs.
5. Assess whether workplace exposure exceeds a proposed OEL value for the MNMs. There are indeed no specific regulatory OEL values for MNMs in workplaces3. The chosen OEL should be at least as protective as a legally mandated OEL for the bulk form of the material.
6. Apply a stepwise approach for inhalation exposure when specific OELs for MNMs are not available in workplaces, this with:
C. Control of professional exposure to MNMs
7. Focus control of exposure on preventing inhalation exposure with the aim based on a precautionary approach of reducing it as much as possible;
8. Reduce exposures to a range of MNMs that have been consistently measured in workplaces, especially during cleaning and maintenance, when collecting material from reaction vessels and when feeding MNMs into the production process;
9. Implement the highest level of controls in the absence of toxicological information on MNMs,. When more information is available, a more tailored approach is recommended.
10. Eliminate the source of exposure should be the first control measure before implementing control measures that are more dependent on worker involvement, this according to the principle of hierarchy of controls. Engineering controls should be used when there is a high level of inhalation exposure or when there is no, or very little, toxicological information available. Personal protective equipment (PPE) should be used only as a last resort, in the absence of appropriate engineering controls, especially respiratory protection, as part of a respiratory protection programme that includes fit-testing.
11. Prevent dermal exposure by occupational hygiene measures such as surface cleaning, and the use of appropriate gloves (conditional recommendation, low quality evidence).
12. Use control banding4 for nanomaterials to select exposure control measures in the workplace when assessment and measurement by a workplace safety expert is not available. Owing to a lack of studies, the GDG cannot recommend one method of control banding over another.
For the two last areas, no recommendations could be made at this stage:
D. Health surveillance
Owing to the lack of evidence, the GDG cannot make a recommendation for worker’s health surveillance specific programmes targeted to MNMs over the other existing health surveillance programmes that are already in use.
E. Training and involvement of workers
Training of workers and worker involvement in health and safety issues has 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 Studies were classified at low risk of bias if they were in the
OECD category 1 or 2, complied with GLP, were based on test guidelines and
resulted in a peer-reviewed publication; at medium risk of bias if the above
applied but there was no compliance with GLP; and at high risk of bias if
none of the above applied.
3 A list of proposed OEL values is provided in Annex 1 of these
WHO guidelines. The chosen OEL should be at least as protective as a legally
mandated OEL for the bulk form of the material
4 For a definition of control banding, see :
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