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Posted: May 22, 2012
Swedish Work Environment Authority releases report on carbon nanotubes
(Nanowerk News) A new report – Carbon nanotubes: Exposure, toxicology and protective measures in the work environment – has been written on behalf of the Swedish Work Environment Authority (Arbetsmiljöverket) by researchers working at Lund University in research collaborations between Metalund and Nano-Safety.
This summary overview of current knowledge is a compilation of literature in the field of carbon nanotubes and deals with occupational exposure, toxicology and protective measures used in the work environment. Issues which in accordance with the assignment were to be investigated included - what the exposure situation was like during production, processing and handling of products containing carbon nanotubes.
A compilation of advice and guidelines on safety and protection devices and personal protective equipment is also presented. The toxicological data available for carbon nanotubes has also been summarized. The purpose of the overview is to provide Arbetsmiljöverket with information and support for different types of measures. The overview may also provide support if special hygienic limit values within the area or other regulations are being considered.
The report is based on original work and summary reviews identified in scientific databases based on systematic literature searches. For the section that deals with toxicology, a selection of relevant articles has been included. The remaining findings will be detailed in a document currently being presented to the Nordic Expert Group (NEG) for the production of criteria documents on chemical health risks.
The report was written by PhD Per Gustavsson, the Department of Biology, University of Lund, PhD Maria Hedmer, Division of Occupational and Environmental Medicine, Lund University and PhD Jenny Rissler, Department of Ergonomics and Aerosol Technology, Lund University.
A reference group of experts has been attached to this assignment and is made up of the following people: Associate Professor Maria Albin, the Department of Occupational and Environmental Medicine, Lund University; Professor Mats Bohgard, The Department of Ergonomics and Aerosol Technology, Lund University; Professor Martin Kanje, the Department of Biology, Lund University; and Professor Steffen Loft, Institut for Folkesundhedsvidenskab, University of Copenhagen.
The use of carbon nanotubes has increased substantially in recent years, and is expected to continue to increase strongly in the future. Increased production, handling and machining increase the risk of exposure in different work environments. Today, the production of carbon nanotubes takes place mainly in non-Nordic countries, but carbon nanotubes are used in the Nordic countries in research and development work. Carbon nanotubes are used mainly as a reinforcement material in various types of polymers, i.e. in composites, but there is considerable potential for use with other applications.
More recently people have become increasingly aware that the properties of nanoparticles may be substantially different than those of larger particles of the same material, parallels have also been drawn between the fibre-like shape of carbon nanotubes and asbestos.
It is therefore necessary to study the toxicity of carbon nanotubes to assess the risks associated with their handling and, if necessary, implement regulations, in the form of occupational exposure limits.
In this report, we have taken into account exposure via ingestion, inhalation and the skin. Inhalation appears to be the route of exposure that is associated with the greatest potential risk, since a carbon nanotube is a material which, in bulk form, has a very low density and produces a lot of dust during handling. Measurements also show that the highest occupational exposure takes place precisely when handling dry bulk material of carbon nanotubes.
An important issue for handling carbon nanotubes concerns their classification. Should they be classified as a separate substance or as carbon which is the main substance in the tubes, and should in that case, all tubes be classified as a substance or as single or multi-walled carbon nanotubes, with their respective functionalizations and be risk-assessed accordingly. Research indicates that the toxic properties of carbon nanotubes may be different from other types of nanoparticles that are made up of layers of graphene. It would suggest that carbon nanotubes should have a specific classification.
The risk assessment for carbon nanotubes is made more difficult by a lack of knowledge at several levels: 1) Consensus is lacking as to which dose-metric that is most relevant for health effects; 2) Carbon nanotubes can be found in a large number of variants that are likely to have different levels of toxicity; 3) The toxicological data is inadequate but indicates that there is a risk of inflammatory reaction and pulmonary fibrosis when inhaled at relatively low doses; there is also the risk of producing a DNA-damaging effect; 4) Exposure levels for the commercial handling of carbon nanotubes are incompletely characterized.
While waiting for the level of understanding to become clear, a strategy for the regulation of occupational exposure-related conditions may be to take note of the effects observed for the most toxic of carbon nanotubes. The proposed international occupational exposure limits are at very low levels. Airborne exposure arises from the manufacture, handling, and use of carbon nanotubes and in the machining of products containing carbon nanotubes. Established technical protective measures such as encapsulation and process ventilation should be applied in conjunction with personal protective equipment such as respiratory protective equipment, protective gloves and protective clothing.