The art and science of OELs for nanomaterials
By Jos Verbeek and Raluca Mihalache
This guest blog post from our Finnish colleagues summarizes the challenges of identifying OELs for new nanomaterials as part of the development of a WHO guideline for working safely with nanomaterials.
Engineered nanomaterials are fascinating. Just by making stuff smaller researchers have discovered forms of materials and even completely new materials that can be applied as diversely as better drugs, better paints or faster electronics. Using chemicals in a nanoscale version can completely alter their nature. We find nano-gold one of the most striking examples. The ‘big’ gold in its normal state is the yellow colored metal that does not interact with the body but nano-sized gold is purple or red, depending on its nanosize, and binds proteins very easily1. Therefore, nano-gold is interesting both as a potential cancer drug and as a potential toxic substance. For society, the question is how to find the right balance between the benefits of new products and the potential harms to health and the environment as new products are developed. One way of preventing harm to workers is to set and adhere to occupational exposure limits (OEL), concentrations of a chemical below which adverse health effects are not likely to occur. Therefore, we systematically searched for proposals for OELs for new nanomaterials as part of the development of a WHO guideline for working safely with nanomaterials2.
Occupational exposure limits fascinate us as well. They have been in use for over 100 years to protect the health of workers who are exposed to potential toxic chemicals during work. For many chemicals there is a concentration below which exposure to the chemical is considered safe and unlikely to have a negative impact on health. Other chemicals, especially those that cause cancer, are considered not to have a safe threshold. For those chemicals, concentrations can be estimated below which the risks are considered negligible. Some chemicals have been considered so potentially harmful that countries such as Finland, the UK and Korea have restricted or forbidden their use. Regulation using OELs to require employers to lower exposures has worked well. In the past 50 years workplace exposures to chemicals like solvents have decreased substantially in the US and part of Europe most probably due to regulated OELs3. Also as part of a risk management strategy OELs are helpful. They help employers and workers to decrease exposure levels as a clear benchmark value that should not be exceeded. However, there are also many issues around OELs that are good for heated debates. Because there is no generally accepted way of deriving OELs, this has led to differences between OEL values. These variations are also reflected in the names of the OELs such as Threshold Limit Values (TLV®) in use by the occupational hygienists, Permissible Exposure Levels in use by OSHA in the US, Recommended Exposure Limits in use by NIOSH and Derived No-Effect Levels in use by the EU REACH agency. Basically, these are all concentrations of chemicals that should help to achieve a safe working environment but in different regulatory and cultural contexts4.
Historically, with the introduction of then-new materials such as asbestos or PVC, a number of workers died before exposure to these chemicals in workplaces was regulated. No one wants this to happen again with nanomaterials. The European Union has explicitly stated that a precautionary approach should be taken. This means that we don’t wait with taking safety measures until we have full certainty about the adverse health effects of nanomaterials but that we act immediately. When more knowledge comes available these measures can be tightened or loosened based on the results of new research.
Even though there is so far not much evidence that simply nanosize leads to toxicological properties that are different from the bulk material or unique for the nanosize, many studies have shown that nanoscale particles can be more biologically active such as eliciting greater pulmonary inflammation at a given mass dose5,6. Thus, the mass-based OEL for the bulk material is not automatically...Click here to read the rest of the blog post.