About Nano

Nanomaterials and nanoparticles.
 
Definition
 
Most particulate materials consist of particles of with variable sizes, but the majority of particles are between a certain minimal and maximal size range. The variation in size is called ‘particle size distribution’. Most particulate materials are thus characterized by their particle size distribution and this also applies to nanomaterials. In 2011 the European Commission published the ‘Recommendation on the definition of a nanomaterial’. Herein it is recommended to define a nanomaterial as a material containing particles, of which 50 % or more of the particles are in the size range of 1 - 100 nanometres. Thus, while nanomaterials can also contain larger particles, the definition aims to distinguish nanomaterials from non-nanomaterials.
 
Nanoparticles are between 1 and 100 nanometres. To put this into perspective, the diameter of a hair is 80.000 times larger than 1 nanometer. Nanoparticles are nanosized (1 – 100 nanometres) in one or more external dimensions. Thus flakes (for example clay), tubes (like carbon nanotubes) as well as rounded nanoparticles (TiO2) can be nanomaterials.
 
Particles between 1 and 100 nanometres tend to cluster. This clustering is known as agglomeration or aggregation. Loosely clustered particles are called agglomerates; fused or almost fused particles are called aggregates.
 
Agglomerates and aggregates are within the definition of nanomaterials, because the starting material is nanoparticles and they are thus not identical to solid particles of similar size. Larger particles may behave differently than nanoparticles; agglomerates and aggregates may behave like larger particles or like nanoparticles, depending on the situation.
 
Nanomaterials may be classified roughly into three categories:
• Naturally occurring materials like (vulcanic) ash, minerals etc.
• By-products of processes with high temperature like combustion, some industrial processes, welding etc.
• Synthetic nanomaterials.
 
Synthetic nanomaterials are produced intentionally, because of their special properties.
 
The discussion on nanomaterial safety is the focus of this particular section. Nanoparticles are known to be associated with health issues, especially the single nanoparticles (un-agglomerated, un-aggregated). Therefore, implementation of the definition of nanomaterials in regulations and guidelines to restrict health risks is necessary (see Bleeker et al. 2013).
 
Materials within the definition clearly contain nanomaterials, but materials outside the definition might also contain free nanoparticles (with potentially related health issues).
 
Why are nanomaterials used?
 
Chemical substances may acquire new mechanical, optical, electrical or magnetic properties when nano-sized. Existing products can have new innovative applications through the incorporation of nanomaterials, thereby offering financial opportunities for companies to innovate with nanomaterials.
 
The use of nanomaterials is part of nanotechnology. Nanotechnology is the manipulation of materials on very small (atomic, molecular, supramolecular) scale. This applies to the production of nanomaterials (e.g. stacking of nanostructures like graphene layers) as well as to the processing on nanoscale (e.g. in nano-electronics where grooves at nanoscale level are used in the manufacturing of printed circuits or chips). Nanoproducts and -processes are used already in many sectors of industry.
 
Besides the advantages of nanotechnology and nanomaterials, there are also worries relating to the safety of man and the environment. Especially single (un-agglomerated, un-aggregated), poorly degradable synthetic nanoparticles are cause for concern.
 
Widely used nanomaterials
 
A broad range of nanomaterials is available and their functionalities are diverse. Nanomaterial-containing products may be for example ultra-strong, extremely economical, or dirt-repellent.
 
Widely-used nanomaterials are metal oxides like TiO2, SiO2, ZnO, CeO2, metals like silver and aluminum, and carbon compounds like carbon nanotubes (CNT). Nanomaterials may be used for their antibacterial properties (silver and TiO2), ‘easy-to-clean’ surfaces (TiO2), UV-protection (TiO2, ZnO, CeO2), increased corrosion resistance (SiO2), flame retardant nature (TiO2, SiO2, clay), improved conduction (CNT), purification of water (aluminum, silver, TiO2) and stronger and lighter materials (CNT). These frequent applications are only few of many.
 
Potential safety concerns of nanomaterials
 
Much is already known about potential health effects related to exposure to nanomaterials, but insight comprehensive view of all nanomaterials is missing. At present, poorly soluble nanoparticles are our main concern. Their extremely small size increases the risk that they enter the body via the airways, the gastrointestinal tract and the skin. Little is known about the health issues directly related to bodily uptake but knowledge has shown that the amount of particles taken up, the frequency of exposure, the properties of the particles and the targeted organs and tissues are important. Smaller particles have a bigger surface area to mass ratio than larger-sized particles, which can increase the reactivity and the potential to release ions. The increased reactivity may induce cells to produce large quantities of molecules such as oxygen radicals and inflammation messengers, leading to tissue damage and disturbance of the normal functioning of the body. At present it is unknown which nanomaterials can induce what kind of negative impact on health.
 
Lists with safe and non-safe nanomaterials do not exist. Health risks may be related especially to insoluble, long and stiff fibre- and sheet-shaped materials and nanoparticles of which the bulk material is classified as carcinogenic, mutagenic, sensitizing and/or reprotoxic (Cornelissen et al., 2011). However, experimental data on safety and epidemiological studies into the health risks are lacking. The behaviour and toxicity of nanomaterials depend on their characteristics, including chemical composition, particle size, particle morphology, electrical charge, surface properties, and functional groups (if present). The particle diversity is such that it is impossible to fully test each and every particle type, thus research focuses on relationships between characteristics and toxicity in general, rather than on actually testing each individual type of particles.
 
What about legislation?
 
Nanomaterials are chemical substances to which the following legislation applies with respect to occupational health and safety:
• The Nationale Arbeidsomstandighedenwet (Arboportaal) is the Dutch translation of the European Chemical Agent Directive (CAD). The CAD captures the most important workplace regulations and directs that the employer maintains a healthy and safe environment at work. Risks and (intended) control measures must be described in the inventory and evaluation of risks (RI&E) and in an implementation plan (PVA). The requirements of the CAD are fulfilled automatically when the requirements of the Arbowet have been met.
• A number of Dutch laws are applicable to hazardous substances, in addition to the Arbowet/Arboportaal. For example, these laws relate to storage, labelling of packages and transport. You can find more information on ‘Arboportaal’.
• The European regulation CLP relates to grouping, labelling and packaging of chemical substances and preparations.
• The European regulation REACH relates to registration, evaluation, authorisation and restriction of chemical substances. Producers and importers of large quantities of substances (>1 ton annually) must perform risk evaluations and propose how to limit risks. The manufacturer/importer needs to demonstrate that all registered applications of a substance are safe for man and the environment.
 
Nano-specific adaptations in legislation are already implemented with regard to cosmetics and food. The new European Cosmetics Directive obliges the notification of nano-ingredients in cosmetics. In addition, the presence of nanomaterials must be mentioned on the labels of cosmetics. From Decembre 13 2014 onwards, the new European legislation on food obliges to record on labels ‘nano’ behind those ingredients which contain nanomaterials.
 
The Arbobesluit is an elaboration of the Arbowet. It describes the rules to which employer and employee must conform in order to counteract occupational risks. The following obligations are applicable to all substances including nanomaterials. The employer must:
• Record synthetic nanomaterials in the inventory and evaluation of risks (RI&E).
• Prepare an implementation plan with measures to control, as much as possible, exposure to synthetic nanomaterials. The ALARA-principle is leading herein: As Low As Reasonably Achievable, meaning that exposure of man and the environment must be as low as reasonably achievable. According to the occupational hygiene strategy, exposure needs to be reduced first at the source, followed by personal protection as a last resort.
• Carry out measures as described in the implementation plan.
• Train and educate employees, working with nanomaterials, in risks and control measures.
 
How to implement legislation?
 
In 2009 a SER-advice on "veilig omgaan met nanodeeltjes op de werkplek" (safe handling of nanomaterials at the workplace) was written. The advice focuses on safety and health of employees working with nanomaterials. The advice assumes that nanomaterials or nanoproducts with unknown or uncertain risks have to be regarded as (very) hazardous, as long as little is known of health effects related to the nanomaterials. This means that exposure to nanomaterials should be prevented or minimalized (precautionary principle).
 
Most attention is paid at present to workplace exposure via inhalation. Certain occupational activities deserve special interest due to possible inhalation during these activities. For instance, production of nanomaterials, processing of nanopowders and nebulization of fluids containing nanomaterials in particular require special attention for control of exposure to nanomaterials. Opportunities to control exposure exist in process engineering as well as in customized complementary control measures for use under specific circumstances.
 
The SER-advice "veilig omgaan met nanodeeltjes op de werkplek" also recommended to ask the Dutch Health Council to prioritize the derivation of health limit values of a number of widely-used nanomaterials. However, The Dutch Health Council currently has insufficient scientific knowledge to establish health-based limit values. The lack of limit values in combination with the precautionary principle means that industries must do the most possible to prevent exposure to nanomaterials. One alternative option is to use Nano Reference Values (NRVs) when information is absent. The NRVs can indicate to what level exposure should be restricted. However, these reference values are not based on health data and, therefore, contain no guarantee that health effects are avoided. Thus the NRV’s will expire as soon as health-based limit values are available for specific nanoparticles or for a group of comparable nanoparticles. HBR-OEL’s (Health-Based Recommended Occupational Exposure Limits) or DNEL’s (Derived No-Effect Levels) are health-based limit values, which are established in the framework of REACH.
 
A few models to support risk assessment and instructions to work safely with nanomaterials are developed already or under construction.
 
Preliminary nanoreference values
 
The table below contains the agreed preliminary nanoreference values (NRV) applicable to the four classes of  ‘engineered nanoparticles (ENP’s)’. The NRV’s are meant only to serve as  pragmatic guidance values and do not guarantee that exposures lower than the NRV are safe.

 Class

 Description

 Density

 NRV (8-hours time-weighed average)

 Example

1

Rigid, biopersistent nanofibres which may have asbestos-like effects 

-

 0,01 fibres/cm³
(= 10.000 fibres/m³)

 

Single- or multiwalled carbon nanotubes or fibrous metal oxides which may have asbestos-like effects according to the manufacturer    

2

Biopersistent, granular nanomaterials within the range of 1 - 100 nm

 > 6000 kg/m³

 20.000 particles/cm³

 Ag, Au, CeO2, CoO, Fe, FexOy, La, Pb, Sb2O5, SnO2,

3

Biopersistent, granular and fibrous nanomaterials within the range of 1 - 100 nm

 < 6000 kg/m³

 40.000 particles/cm³

Al2O3, SiO2, TiN, TiO2, ZnO, nanoclay, Carbon Black, C60, dendrimers, polystyrene nanofibres, without asbestos-like effects as stated explicitly

4

Non-biopersistent

granular
nanomaterials within the range of 1 - 100 nm 

-

Conventional  limit

Fats, salt (=NaCl)

 
It is recommended to take precautionary measures, within applicable reason, even when the nano reference values (NRV) are met. Within reason means that the measures are technically, organizationally and financially feasible. Also, it is important to keep exposure to small-sized particles as low and as short as possible. 
 
In case the NRVs are not met, it is recommended to take all measures that are technically and organizationally possible in order to reduce exposure levels below the NRV. 
 
Alternatively, the air can be analysed with respect to synthetic nanomaterials and process-generated nanoparticles (PGNP’s). It is strongly recommended to reduce exposure by all measures, which are technically and organizationally possible, if the concentration of nanomaterials in the air is above the NRV. Additionally, it is advised to take measures to reduce exposure even if the concentration is below the NRV.   
 
Models and instructions to work safely
 
Various methods have been developed to gain insight into the risks related to working and handling nanomaterials. These qualitative methods provide ways to prioritize methods and are necessary due to the absence of safety data and the difficulties in determining exposure. 
 
The following are models and instructions that are already developed, or under construction, and provide information on how to work safely:
 
• Stoffenmanager Nano: This module enables estimation of health risks associated with exposure to synthetic nanomaterials. Control measures can be selected and included in the implementation plan.
• Control Banding Nanotool: A tool to establish exposure while working with nanomaterials, for research purposes and, less so, to estimate health risks run by end-users.
• Handleiding Veilig werken met nanomaterialen en -producten (2010): This instruction aims to create a safe working place with nanomaterials and products containing nanomaterials. 
• Control Banding Nanotool: A tool to establish exposure while working with nanomaterials for research purposes and, less so, to estimate health risks run by-end-users. 


 
 
 
 
 

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